TY - JOUR TI - Combination of flavor enhancement and chemosensory education improves nutritional status in older cancer patients AU - Schiffman, S.S. AU - Sattely-Miller, E.A. AU - Taylor, E.L. AU - Graham, B.G. AU - Landerman, L.R. AU - Zervakis, J. AU - Campagna, L.K. AU - Cohen, H.J. AU - Blackwell, S. AU - Garst, J.L. T2 - Journal of Nutrition, Health, and Aging DA - 2007/// PY - 2007/// VL - 11 IS - 5 SP - 439–454 ER - TY - CONF TI - Advanced Power Packaging for High Reliability and Higher Temperatures AU - Hopkins, Douglas C. T2 - 40th International Symposium on Microelectronics C2 - 2007/11/10/ C3 - 40th International Symposium on Microelectronics CY - San Jose, CA DA - 2007/11/10/ PY - 2007/11/10/ ER - TY - CONF TI - Introduction to Power Packaging Techniques AU - Hopkins, Douglas C. T2 - 22nd Annual IEEE Conference on Applied Power Electronics Conference and Exposition (APEC) C2 - 2007/2/25/ C3 - 22nd Annual IEEE Conference on Applied Power Electronics Conference and Exposition (APEC) CY - Anaheim, CA DA - 2007/2/25/ PY - 2007/2/25/ ER - TY - JOUR TI - Critical illness and changes in sensory perception AU - Schiffman, Susan S. T2 - Proceedings of the Nutrition Society AB - Impairments of sensory perception that occur during a period of critical care can seriously impact on health and nutritional status, activities of daily living, independence, quality of life and the possibility of recovery. It is emphasized from the outset that sensory losses in critically-ill patients may or may not be related to their current medical condition. The present paper provides an overview of all five senses (vision, hearing, taste, smell and touch) and describes the factors that contribute to sensory losses in critically-ill patients, including medications, medical conditions and treatments and the process of aging itself. Cancer and stroke are two critical illnesses in which profound sensory decrements often occur. Many sensory complaints in patients with cancer are related to alteration in sensory signals caused by damage to the sensory receptors. However, some complaints, such as taste aversions in patients with cancer, are not related to altered sensory physiology per se but to learned aversions that arise during the noxious effects of radiotherapy and chemotherapy. The paper also reviews a study in which the sensory performance (of all five senses) was compared in three groups of elderly subjects: (1) patients who had undergone coronary artery bypass surgery; (2) patients with cardiovascular conditions but with no history of surgery; (3) healthy non-medicated age-matched controls. Performance of patients who had undergone coronary artery bypass surgery was worse than that for the other two groups, with taste and smell losses greater than for the other senses. The study demonstrates that critical illness (e.g. coronary artery bypass surgery) can exacerbate sensory losses in an older cohort. DA - 2007/7/16/ PY - 2007/7/16/ DO - 10.1017/s0029665107005599 VL - 66 IS - 3 SP - 331-345 J2 - Proc. Nutr. Soc. LA - en OP - SN - 0029-6651 1475-2719 UR - http://dx.doi.org/10.1017/s0029665107005599 DB - Crossref ER - TY - ER - TY - JOUR TI - Time to maximum sweetness intensity of binary and ternary blends of sweeteners AU - Schiffman, Susan S. AU - Sattely-Miller, Elizabeth A. AU - Bishay, Ihab E. T2 - Food Quality and Preference AB - The purpose of the current study was to determine what effect, if any, the blending of sweeteners has on the time to maximum sweetness intensity of sweeteners. In this study that is comprised of three separate experiments, trained panelists evaluated the time to maximum sweetness intensity of sweeteners tested in both binary and ternary combinations. Sixteen sweeteners that varied widely in chemical structure were evaluated. Sweetener blends containing the protein thaumatin had the latest time to maximum sweetness intensity. As a group, blends containing neohesperidin dihydrochalcone, alitame, stevioside, rebauadioside-A, or neotame had later times to maximum sweetness intensity than blends with sugars and sugar alcohols. Many sweetener blends exhibited times to maximum sweetness intensity that fell intermediate between the earliest and latest of its constituent self-mixtures. These data indicate that the time to maximum sweetness intensity of “late” sweeteners can be shortened by blending with earlier onset sweeteners. DA - 2007/3// PY - 2007/3// DO - 10.1016/j.foodqual.2006.04.007 VL - 18 IS - 2 SP - 405-415 J2 - Food Quality and Preference LA - en OP - SN - 0950-3293 UR - http://dx.doi.org/10.1016/j.foodqual.2006.04.007 DB - Crossref ER - TY - CONF TI - Modeling and Optimization Analysis of Single Flagellum Bacterial Motion AU - Lobaton, Edgar AU - Bayen, Alexandre AB - Bacteria such as Rhodobacter sphaeroides use a single flagellum for propulsion and change of orientation. Simple organisms such as this have inspired nanorobotic designs with potential applications in medicine which motivates the present work. In this article, an elastic model for a single flagellum bacterium is presented and followed by an analysis of the system based on optimization. The model is based on the method of Regularized Stokeslet which allows for a discretization of the system into particles which are connected by spring forces. An optimal elasticity distribution that maximizes the mean forward speed is obtained. These elasticity coefficients are obtained through the use of an adjoint-based optimization scheme. The results are illustrated through a simulation showing improvement on the swimming patter of the bacteria. C2 - 2007/7// C3 - 2007 American Control Conference DA - 2007/7// DO - 10.1109/acc.2007.4282439 PB - IEEE UR - http://dx.doi.org/10.1109/acc.2007.4282439 ER - TY - CONF TI - An Architecture for Energy Efficient Sphere Decoding AU - Jenkal, R.S. AU - Davis, W.R. T2 - International Symposium on Low Power Electronics and Design (ISLPED AB - Sphere Decoding has become a popular implementation of MIMO decoding due to its improved performance at lower hardware complexity. Present ASIC implementations fail to consider sources of pipelinability and parallelism in the algorithm to achieve reduced power. In this work, we provide a proposal and initial results for an improved architecture which aims to increase overall energy efficiency (b/s/mW) of the decoder. This improvement is based on a novel implementation which combines the use of a deeply pipelined data-path and "multi symbol vector" based approach to exploit the pipeline. Implementation in 0.18μ 1.8V CMOS technology provides an operational frequency of 128/230(retimed)MHz at 409 mW(DFF memory)/ 360 mW(realistic memory) and 3.44 sq.mm (DFF memory). C2 - 2007/// C3 - ISLPED '07: Proceedings of the 2007 international symposium on Low power electronics and design DA - 2007/// PY - 2007/8/27/ DO - 10.1145/1283780.1283833 SP - 244–249 ER - TY - CONF TI - Designing FIFO Buffers using 3DIC Technology AU - Sule, A.M. AU - Davis, W.R. T2 - VLSI Multilevel Interconnection (VMIC) Conference C2 - 2007/// C3 - VLSI Multilevel Interconnection (VMIC) Conference DA - 2007/// PY - 2007/9/25/ SP - 267–272 ER - TY - CONF TI - FreePDK: An Open Source, OpenAccess Design Kit AU - Davis, W.R. T2 - OpenAccess Conference C2 - 2007/11/5/ DA - 2007/11/5/ PY - 2007/11/5/ ER - TY - SOUND TI - Energy-Efficient Sphere Decoding (and other research efforts AU - Davis, W.R. DA - 2007/9/13/ PY - 2007/9/13/ ER - TY - SOUND TI - 3D-IC Design: Theory vs. Reality AU - Davis, W.R. DA - 2007/6/21/ PY - 2007/6/21/ ER - TY - JOUR TI - 3D Interconnect Device Design: Theory vs. Reality AU - Davis, W.R. AU - Sule, A.M. AU - Schoenfliess, K.M. T2 - Future Fab International DA - 2007/// PY - 2007/// IS - 23 SP - 38–40 ER - TY - CONF TI - Information security with real-time operation: performance assessment for next generation wireless distributed networked-control-systems AU - Gupta, Rachana A AU - Chow, Mo-Yuen AU - Agarwal, Avesh Kumar AU - Wang, Wenye AB - Distributed network-control-systems (D-NCS) are a multidisciplinary effort whose aim is to produce a network structure and components that are capable of integrating sensors, actuators, communication, and control algorithms in a manner to suit real-time applications. They have been gaining popularity due to their high potential in widespread applications and becoming more realizable due to the rapid advancements in wireless communication and data transfer technologies. This paper addresses the issue of D-NCS information security as well its real-time performance with respect to network security protocols and encryption schemes. We use a wireless network based, robot navigation path tracking system called intelligent space (iSpace) as a D-NCS test bed in this paper. The paper classifies the data from every NCS module (sensors, actuators and controllers) according to bandwidth requirement, time and information sensitivity. We define performance parameters for this NCS test bed. Various system factors affecting these performance parameters are recognized. Network security algorithms DES and 3DES are integrated with the application to encrypt the sensitive information flow. These wireless security features are considered as an added factor to the NCS. Standard statistical approach (2 k factorial experiment design) is used to study and estimate the effect of each factor on the system performance especially security additions. Thorough experimental results, tables of detailed characterization and effect estimate analysis is presented followed by the discussion on the performance comparison of NCS with and without wireless security. C2 - 2007/// C3 - IECON 2007 - 33rd Annual Conference of the IEEE Industrial Electronics Society DA - 2007/// DO - 10.1109/iecon.2007.4460391 PB - IEEE UR - http://dx.doi.org/10.1109/iecon.2007.4460391 KW - distributed networked-control system KW - iSpace KW - data-sensitive wireless network KW - data security ER - TY - JOUR TI - Characterization of data-sensitive wireless distributed networked-control-systems AU - Gupta, Rachana Ashok AU - Agarwal, Avesh Kumar AU - Chow, Mo-Yuen AU - Wang, Wenye T2 - 2007 IEEE/ASME international conference on advanced intelligent mechatronics AB - Distributed networked-controlled-systems (NCS) are a multidisciplinary effort whose aim is to produce a network structure and components that are capable of integrating sensors, actuators, communication, and control algorithms in a manner to suit real-time applications. They have been very popular and widely applied for many years now due to the rapid advancements in data and communication wireless technologies. There are many challenges to be overcome in order to put such a heterogeneous system together. Key issues to be considered are network delay, data sensitivity and information security. This paper characterizes a wireless distributed NCS, a testbed called iSpace based on these key factors. We integrated static network security algorithms DES and 3DES with the NCS testbed iSpace - a multidisciplinary network based robot navigation system - and characterized it on the basis of bandwidth requirement, data classification and data sensitivity, network delay effect on the system performance. The paper demonstrates through results that a dynamic optimization is required between network security for reliability and time-sensitivity of the NCS. Future work in dynamic optimization in security is suggested. DA - 2007/// PY - 2007/// DO - 10.1109/aim.2007.4412569 ER - TY - JOUR TI - Silicon germanium based millimetre-wave ICs for Gbps wireless communications and radar systems AU - Gaucher, B. AU - Floyd, B. AU - Reynolds, S. AU - Pfeiffer, U. AU - Grzyb, J. AU - Joseph, A. AU - Mina, E. AU - Orner, B. AU - Ding, H. AU - Wachnik, R. AU - Walter, K. T2 - Semiconductor Science and Technology AB - This paper establishes the viability and suitability of silicon germanium (SiGe8HP) technology, enablement tools and circuits to millimetre-wave applications today and a roadmap to the future. Key elements discussed include SiGe technology and design enablement advancements leading to the world's most highly integrated, lowest power 60 GHz transmitter/receiver ICs. DA - 2007/// PY - 2007/// DO - 10.1088/0268-1242/22/1/S55 VL - 22 IS - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34247273093&partnerID=MN8TOARS ER - TY - CONF TI - The effect of layer thickness variation on the thermo-mechanical properties of direct aluminum bonded substrates on AlSiC AU - McKay, T. AU - Hopkins, D.C. AU - Basaran, C. T2 - 40th International Microelectronics and Packaging Society (IMAPS) International Symposium on Microelectronics C2 - 2007/// C3 - Proceedings of the 2007 International Symposium on Microelectronics : November 11-15, 2007, San Jose Convention Center, san Jose, California, USA CY - San Jose, CA DA - 2007/// PY - 2007/11/11/ PB - IMAPS ER - TY - CONF TI - Solder Interconnect Electromigration Due to Time Varying Current Stressing AU - Enser, K.E. AU - Hopkins, D.C. AU - Basaran, C. T2 - 40th International Microelectronics and Packaging Society (IMAPS) International Symposium on Microelectronics C2 - 2007/// C3 - Proceedings of the 2007 International Symposium on Microelectronics : November 11-15, 2007, San Jose Convention Center, San Jose, California, USA CY - San Jose, CA DA - 2007/// PY - 2007/11/11/ VL - 10 PB - IMAPS ER - TY - CONF TI - A Review of Electromigration Under Time Varying Current Stressing AU - Enser, Kevin E. AU - Hopkins, Douglas C. AU - Basaran, Cernal T2 - Society of Automotive Engineers (SAE) International Symposium C2 - 2007/4/19/ CY - Toronto, Canada DA - 2007/4/19/ PY - 2007/4/19/ ER - TY - CONF TI - IMC Effects in Solder from High Thermal Gradients Management AU - Abdulhamid, M.F. AU - Hopkins, D.C. AU - Basaran, C. T2 - International Electronics Packaging Symposium C2 - 2007/// CY - Niskayuna, NY DA - 2007/// PY - 2007/7/31/ ER - TY - CONF TI - Harsh Environment Thermal Management Using Aluminum-Based Packaging AU - McKay, T. AU - Hopkins, D.C. AU - Basaran, C. AU - Abdulhamid, M.F. T2 - International Electronics Packaging Symposium C2 - 2007/// CY - Niskayuna, NY DA - 2007/// PY - 2007/7/31/ ER - TY - CHAP TI - Packaging and Smart Power Systems AU - Hopkins, Douglas C. T2 - Power Electronics Handbook A2 - Rashid, Muhammad H. PY - 2007/// DO - 10.1016/b978-012088479-7/50060-2 ET - 2nd SP - 1147–1158 PB - Academic Press/Elsevier SN - 9780120884797 UR - http://dx.doi.org/10.1016/b978-012088479-7/50060-2 ER - TY - RPRT TI - Efficient support for speculative tasking AU - Tuck, James M DA - 2007/// PY - 2007/// ER - TY - JOUR TI - A review on multiple access interference cancellation and avoidance for IR-UWB AU - Güvenç, İsmail AU - Arslan, Hüseyin T2 - Signal Processing AB - In this article, a comprehensive review of multiple access interference (MAI) avoidance/cancellation for impulse radio (IR) ultrawideband (UWB) systems is presented. First, interference avoidance through transmitter-side techniques for both synchronous and asynchronous communications are discussed. Later, interference cancellation schemes at the receiver are classified and analyzed under following categories: maximum likelihood methods, linear receivers, iterative/Turbo interference cancellation methods, blind/adaptive techniques, and other algorithms. More emphasis is given on MAI cancellation for time-hopping (TH) and direct-sequence (DS) IR-UWB. On the other hand, various algorithms that are already considered for DS code division multiple access (CDMA) systems are also discussed. The goal of the article is to have a compact reference on the current state-of-the-art in MAI avoidance/cancellation techniques for IR-UWB systems, to outline analogies and differences between IR-UWB and DS-CDMA approaches to handle the MAI, and to identify possible research directions. DA - 2007/4// PY - 2007/4// DO - 10.1016/j.sigpro.2006.06.019 VL - 87 IS - 4 SP - 623-653 J2 - Signal Processing LA - en OP - SN - 0165-1684 UR - http://dx.doi.org/10.1016/j.sigpro.2006.06.019 DB - Crossref KW - multiuser interference cancellation KW - ML KW - MMSE KW - review KW - tutorial KW - ultrawideband ER - TY - JOUR TI - P4M-7 Front-End IC Design for 2D cMUT Arrays: Modeling and Experimental Verification AU - Yamaner, F. Y. AU - Bozkurt, A. T2 - 2007 IEEE Ultrasonics Symposium Proceedings AB - In this paper, we present the modeling, design and test of a front-end IC for 2D cMUT arrays. In the modeling phase, present simulation results for a front-end circuit integrated with an array transducer element, and compare these with the experimental result for a front-end IC for 2D cMUT array. The pulse-echo model for the transducer is a modified version of the Mason Equivalent Circuit where the radiation impedance term has been replaced by an RLC network to include the effects of finite transducer size and diffraction loss. The model has been verified by running transient simulations using ANSYS. The circuit was composed of a high voltage (50 Volt) pulse driver, a NMOS protection switch and a trans impedance amplifier. The IC was manufactured by AustriaMicroSystems AG, Graz, Austria, in 0.35 μm high-voltage CMOS technology. We wire bonded the IC to a cMUT element to test the overall circuit performance. The cMUT elements that we used in the experiments had an operating frequency of 10 MHz and consisted of 49 CMUT cells with an overall transducer area of 200×200 µm2. The applied DC bias was 70 Volts. The cMUTs were driven by a 40 Volts unipolar pulse. We first performed hydrophone measurements to verify the functionality of the driver circuit. A droplet of vegetable oil was used as the propagation medium for pulse-echo measurements. The echo was observed from the air-oil interface. The results show that the performance of the circuit was consistent with the simulations. We were able to receive an echo from the surface of an oil layer of thickness less than 0.5 mm. (approximately 1 μs round-trip flight time.) The overall layout size of the manufactured circuit is 170×170 µm2 and it is suitable for integration to 3-5 MHz cMUT elements. DA - 2007/10// PY - 2007/10// DO - 10.1109/ultsym.2007.540 ER - TY - JOUR TI - P4M-6 A Low Noise Capacitive Feedback Analog Front-End for CMUTs in Intra Vascular Ultrasound Imaging AU - Cenkeramaddi, L. R. AU - Bozkurt, A. AU - Yamaner, F. Y. AU - Ytterdal, T. T2 - 2007 IEEE Ultrasonics Symposium Proceedings AB - In this paper, we present the capacitive feedback analog front-end for intra vascular ultrasound (IVUS) imaging as opposed to the conventional resistive feedback analog front-ends. In our proposed capacitive feedback architecture, floating input node of the amplifier is dynamically biased during the transmit mode of the CMUTs (capacitive micromachined ultrasound transducers). During the reception mode, the biased voltage at the floating input node of the amplifier is stored on the gate of input transistor of the amplifier. A high voltage pulser circuit with small output capacitance is integrated on-chip with the proposed low-noise capacitive feedback receiver. The proposed capacitive feedback analog front-end circuit is designed using the 0.35 mum high-voltage CMOS technology library of Austria Microsystems Corporation. Based on post- layout simulation results, we were able to achieve an overall noise figure of less than 2 dB with the proposed capacitive feedback analog front end for the amplification of signals generated by a 100times200 mum 2 CMUT array element. DA - 2007/10// PY - 2007/10// DO - 10.1109/ultsym.2007.539 KW - CMUT KW - CMUT sensing circuit KW - CMUT analog front-end KW - CMUT-CMOS KW - low-noise KW - ultrasound front end KW - high voltage ultrasound pulser KW - IVUS imaging KW - capacitive feedback analog front-end ER - TY - CONF TI - Welcome message from the technical program co-chairs AU - Heath, R. AU - Bottomley, G. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECF.2007.5 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47649108327&partnerID=MN8TOARS ER - TY - JOUR TI - Uplink power control in multi-cell spatial multiplexing wireless systems T2 - IEEE Transactions on Wireless Communications AB - This paper proposes a power control strategy for the uplink of cellular MIMO spatial multiplexing systems, with a linear MMSE receiver applied at the base station and a single active user per time instant. A fixed per-stream SINR target is employed that allows guaranteed QoS for delay-sensitive applications. A straightforward application of single antenna power control is not possible in the MIMO context due to coordination between receive antennas and nonlinear dependence between interference and eigenspaces of the channel matrices. Two schemes are proposed to solve the problem. The first equally allocates power to all transmit antennas. Deriving an SINR lower bound based on an eigenvalue approximation of the composite interference, allows application of the conventional single antenna power control framework to solve this problem. To improve the feasibility performance, a second scheme is proposed that adaptively allocates power on the transmit antennas, where an iterative algorithm based on game theory is used to sequentially update each user's power distribution. The optimal solution with full channel knowledge, and a practical near-optimal solution requiring only partial channel knowledge, are both derived. Numerical results show that power control, compared to supposedly optimal waterfilling strategies, actually achieves higher throughput at the low SINRs typical in cellular systems, with significantly lower overhead and complexity. Due to its better exploitation of spatial diversity and reduced transmit power (and hence reduced interference), adaptive power allocation increases the achievable SINR by an order of magnitude over equal power allocation, resulting in far better coverage. DA - 2007/// PY - 2007/// DO - 10.1109/TWC.2007.051007 VL - 6 IS - 7 SP - 2700-2711 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547396826&partnerID=MN8TOARS KW - MIMO systems KW - power control ER - TY - JOUR TI - Transmit selection diversity for unitary precoded multiuser spatial multiplexing systems with linear receivers T2 - IEEE Transactions on Signal Processing AB - Multiuser spatial multiplexing is a downlink transmission technique that uses linear transmit precoding to multiplex multiple users and precancel interuser interference. In such a system, the spatial degrees of freedom are used for interference mitigation and generally come at the expense of diversity gain. This paper proposes two precoding methods that use extra transmit antennas, beyond the minimum required, to provide additional degrees of diversity. The approach taken is to solve for a unitary transmit precoder, under a zero interuser interference constraint, that minimizes an upper bound on the symbol error rate (SER) for each user. Solutions where all transmit antennas are employed, as well as subsets of antennas (to reduce analog components), are described. Numerical results confirm a dramatic improvement in terms of SER and mutual information over single-user multiple-input multiple-output (MIMO) methods and static allocation methods. For example, the proposed techniques achieve a signal-to-noise ratio (SNR) improvement of 6-10 dB at an uncoded SER of 10 -3 , with only one extra transmit antenna DA - 2007/// PY - 2007/// DO - 10.1109/TSP.2006.887147 VL - 55 IS - 3 SP - 1159-1171 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33947380186&partnerID=MN8TOARS KW - diversity methods KW - multiple-input multiple-output (MIMO) systems KW - precoding ER - TY - JOUR TI - Sum capacity of multiuser MIMO broadcast channels with block diagonalization T2 - IEEE Transactions on Wireless Communications AB - The sum capacity of a Gaussian broadcast MIMO channel can be achieved with dirty paper coding (DPC). However, algorithms that approach the DPC sum capacity do not appear viable in the forseeable future, which motivates lower complexity interference suppression techniques. Block diagonalization (BD) is a linear preceding technique for downlink multiuser MIMO systems. With perfect channel knowledge at the transmitter, BD can eliminate other users' interference at each receiver. In this paper, we study the sum capacity of BD with and without receive antenna selection. We analytically compare BD without receive antenna selection to DPC for a set of given channels. It is shown that (1) if the user channels are orthogonal to each other, then BD achieves the same sum capacity as DPC; (2) if the user channels lie in the same subspace, then the gain of DPC over BD can be upper bounded by the minimum of the number of transmit and receive antennas. These observations also hold for BD with receive antenna selection. Further, we study the ergodic sum capacity of BD with and without receive antenna selection in a Rayleigh fading channel. Simulations show that BD can achieve a significant part of the total throughput of DPC. An upper bound on the ergodic sum capacity gain of DPC over BD is proposed for easy estimation of the gap between the sum capacity of DPC and BD without receive antenna selection. DA - 2007/// PY - 2007/// DO - 10.1109/TWC.2007.05831 VL - 6 IS - 6 SP - 2040-2045 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547772139&partnerID=MN8TOARS KW - MIMO KW - capacity KW - multiuser KW - broadcast channels KW - precoding KW - dirty paper coding ER - TY - JOUR TI - Space division multiple access with a sum feedback rate constraint T2 - IEEE Transactions on Signal Processing AB - On a multiantenna broadcast channel, simultaneous transmission to multiple users by joint beamforming and scheduling is capable of achieving high throughput, which grows double logarithmically with the number of users. The sum rate for channel state information (CSI) feedback, however, increases linearly with the number of users, reducing the effective uplink capacity. To address this problem, a novel space division multiple access (SDMA) design is proposed, where the sum feedback rate is upper bounded by a constant. This design consists of algorithms for CSI quantization, threshold-based CSI feedback, and joint beamforming and scheduling. The key feature of the proposed approach is the use of feedback thresholds to select feedback users with large channel gains and small CSI quantization errors such that the sum feedback rate constraint is satisfied. Despite this constraint, the proposed SDMA design is shown to achieve a sum capacity growth rate close to the optimal one. Moreover, the feedback overflow probability for this design is found to decrease exponentially with the difference between the allowable and the average sum feedback rates. Numerical results show that the proposed SDMA design is capable of attaining higher sum capacities than existing ones, even though the sum feedback rate is bounded. DA - 2007/// PY - 2007/// DO - 10.1109/TSP.2007.894245 VL - 55 IS - 7 II SP - 3879-3891 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34347372828&partnerID=MN8TOARS KW - broadcast channels KW - feedback communication KW - multiuser channels KW - space division multiplexing ER - TY - JOUR TI - Systematic codebook designs for quantized beamforming in correlated MIMO channels T2 - IEEE Journal on Selected Areas in Communications AB - The full diversity gain provided by a multi-antenna channel can be achieved by transmit beamforming and receive combining. This requires the knowledge of channel state information (CSI) at the transmitter which is difficult to obtain in practice. Quantized beamforming where fixed codebooks known at both the transmitter and the receiver are used to quantize the CSI has been proposed to solve this problem. Most recent works focus attention on limited feedback codebook design for the uncorrelated Rayleigh fading channel. Such designs are sub-optimal when used in correlated channels. In this paper, we propose systematic codebook design for correlated channels when channel statistical information is known at the transmitter. This design is motivated by studying the performance of pure statistical beamforming in correlated channels and is implemented by maps that can rotate and scale spherical caps on the Grassmannian manifold. Based on this study, we show that even statistical beamforming is near-optimal if the transmitter covariance matrix is ill-conditioned and receiver covariance matrix is well-conditioned. This leads to a partitioning of the transmit and receive covariance spaces based on their conditioning with variable feedback requirements to achieve an operational performance level in the different partitions. When channel statistics are difficult to obtain at the transmitter, we propose a universal codebook design (also implemented by the rotation-scaling maps) that is robust to channel statistics. Numerical studies show that even few bits of feedback, when applied with our designs, lead to near perfect CSI performance in a variety of correlated channel conditions. DA - 2007/// PY - 2007/// DO - 10.1109/JSAC.2007.070804 VL - 25 IS - 7 SP - 1298-1310 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34548557559&partnerID=MN8TOARS KW - diversity methods KW - fading channels KW - Grassmannian line packing KW - limited feedback KW - MIMO systems KW - quantization ER - TY - JOUR TI - Simplified spatial correlation models for clustered MIMO channels with different array configurations T2 - IEEE Transactions on Vehicular Technology AB - An approximate spatial correlation model for clustered multiple-input multiple-output (MIMO) channels is proposed in this paper. The two ingredients for the model are an approximation for uniform linear and circular arrays to avoid numerical integrals and a closed-form expression for the correlation coefficients that is derived for the Laplacian azimuth angle distribution. A new performance metric to compare parametric and nonparametric channel models is proposed and used to show that the proposed model is a good fit to the existing parametric models for low angle spreads (i.e., smaller than 10deg). A computational-complexity analysis shows that the proposed method is a numerically efficient way of generating the spatially correlated MIMO channels. DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2007.897212 VL - 56 IS - 4 II SP - 1924-1934 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547879584&partnerID=MN8TOARS KW - channel capacity KW - circular arrays KW - correlation KW - linear arrays KW - multipath channels KW - multiple-input multiple-output (MIMO) systems ER - TY - CONF TI - SDMA with a sum feedback rate constraint AB - Space division multiple access (SDMA) is capable of achieving sum capacity that grows double logarithmically with the number of users. The sum rate for channel state information (CSI) feedback, however, increases linearly with the number of users, reducing the effective uplink capacity. To address this problem, a novel SDMA design is proposed, where the sum feedback rate is upper-bounded by a constant. This design consists of algorithms for CSI quantization, threshold based CSI feedback, and joint beamforming and scheduling. The key feature of the proposed approach is the use of feedback thresholds to select feedback users with large channel gains and small CSI quantization errors such that the sum feedback rate constraint is satisfied. Despite this constraint, the proposed SDMA design is shown to achieve a sum capacity growth rate close to the optimal one. Numerical results show that the proposed SDMA design is capable of attaining higher sum capacities than existing ones, even though the sum feedback rate is bounded. C2 - 2007/// C3 - ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings DA - 2007/// DO - 10.1109/ICASSP.2007.366482 VL - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547525655&partnerID=MN8TOARS ER - TY - JOUR TI - Smart antennas for next generation wireless systems T2 - Eurasip Journal on Wireless Communications and Networking DA - 2007/// PY - 2007/// DO - 10.1155/2007/20427 VL - 2007 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-43949115154&partnerID=MN8TOARS ER - TY - JOUR TI - Shifting the MIMO Paradigm T2 - IEEE Signal Processing Magazine AB - Multi-user MIMO (MU-MIMO) networks reveal the unique opportunities arising from a joint optimization of antenna combining techniques with resource allocation protocols. Furthermore, it brings robustness with respect to multipath richness, allowing for compact antenna spacing at the BS and, crucially, yielding the diversity and multiplexing gains without the need for multiple antenna user terminals. To realize these gains, however, the BS should be informed with the user's channel coefficients, which may limit practical application to TDD or low-mobility settings. To circumvent this problem and reduce feedback load, combining MU-MIMO with opportunistic scheduling seems a promising direction. The success for this type of scheduler is strongly traffic and QoS-dependent, however. DA - 2007/// PY - 2007/// DO - 10.1109/MSP.2007.904815 VL - 24 IS - 5 SP - 36-46 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-36249021932&partnerID=MN8TOARS ER - TY - CONF TI - Reduced rank signaling in spatially correlated MIMO channels AB - The optimal input covariance matrix Q that achieves the ergodic capacity under the coherent assumption in a point-to-point, multi-antenna setting is a function of the spatial correlation and the transmit SNR. While the eigenvectors of Q can be characterized in closed-form for many realistic correlation models, the eigenvalues have to be determined numerically. However, it is well-known that the rank of Q is a non-decreasing function of SNR. Motivated by this fact, in this work, we study communication with a low-complexity family of input covariance matrices that are characterized by their rank, assuming uniform power allocation over the smaller-dimensional eigen-space. We quantify the impact of spatial correlation on the M-th transition-SNR which is defined as the smallest SNR at which rank-M transmission becomes optimal. C2 - 2007/// C3 - IEEE International Symposium on Information Theory - Proceedings DA - 2007/// DO - 10.1109/ISIT.2007.4557367 SP - 1081-1085 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51649105163&partnerID=MN8TOARS ER - TY - CONF TI - Throughput scaling of uplink SDMA with limited feedback AB - In a multi-antenna system with a large number of users, combining space division multiple access (SDMA) and scheduling achieves high throughput. The implementation of joint SDMA and scheduling requires limited feedback of channel sate information (CSI) from users to a base station. In this paper, an uplink SDMA system with limited feedback and a large number of users is considered. The scaling of uplink throughput with different system parameters is analyzed. These parameters include the numbers of users, feedback bits and antennas. Our results provide guidelines for designing uplink SDMA to achieve optimum throughput scaling. For instance, in the high SNR regime, scheduling should select users with small CSI quantization error. C2 - 2007/// C3 - Conference Record - Asilomar Conference on Signals, Systems and Computers DA - 2007/// DO - 10.1109/ACSSC.2007.4487216 SP - 292-296 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-50249109554&partnerID=MN8TOARS ER - TY - JOUR TI - Reduced complexity signal detection for OFDM systems with transmit diversity T2 - Journal of Communications and Networks DA - 2007/// PY - 2007/// VL - 9 IS - 1 SP - 75-82 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34247103991&partnerID=MN8TOARS ER - TY - JOUR TI - Quantization on the Grassmann manifold T2 - IEEE Transactions on Signal Processing AB - The problem of quantization in an Euclidean space with unitary constraints can be formulated as an unconstrained problem on a Grassmann manifold. Such constraints arise in areas such as wireless communication with multiple antennas at the transmitter and at the receiver. Due to the constraints, the distortion rate analysis developed for Euclidean spaces cannot be applied directly. This paper extends Gersho's asymptotic (large rate, small distortion) distortion bounds to the case when the source is distributed on the complex Grassmann manifold. The special structure of the Grassmann manifold and the distortion measures defined on it differentiate this problem from the traditional vector quantization in Euclidean spaces. DA - 2007/// PY - 2007/// DO - 10.1109/TSP.2007.896112 VL - 55 IS - 8 SP - 4208-4216 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547894696&partnerID=MN8TOARS KW - array signal processing KW - MIMO systems KW - quantization KW - rate distortion theory ER - TY - JOUR TI - Opportunistic feedback for multiuser MIMO systems with linear receivers T2 - IEEE Transactions on Communications AB - A novel multiuser scheduling and feedback strategy for the multiple-input multiple-output (MIMO) downlink is proposed in this paper. It achieves multiuser diversity gain without substantial feedback requirements. The proposed strategy uses per-antenna scheduling at the base station, which maps each transmit antenna at the base station (equivalently, a spatial channel) to a user. Each user has a number of receive antennas that is greater than or equal to the number of transmit antennas at the base station. Zero-forcing receivers are deployed by each user to decode the transmitted data streams. In this system, the base station requires users' channel quality on each spatial channel for scheduling. An opportunistic feedback protocol is proposed to reduce the feedback requirements. The proposed protocol uses a contention channel that consists of a fixed number of feedback minislots to convey channel state information. Feedback control parameters including the channel quality threshold and the random access feedback probability are jointly adjusted to maximize the average throughput performance of this system. Multiple receive antennas at the base station are used on the feedback channel to allow decoding multiple feedback messages sent simultaneously by different users. This further reduces the bandwidth of the feedback channel. Iterative search algorithms are proposed to solve the optimization for selection of these parameters under both scenarios that the cumulative distribution functions of users are known or unknown to the base station DA - 2007/// PY - 2007/// DO - 10.1109/TCOMM.2007.896013 VL - 55 IS - 5 SP - 1020-1032 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34249075993&partnerID=MN8TOARS KW - diversity methods KW - feedback KW - multiple-input multiple-output (MIMO) systems KW - multiuser channels KW - scheduling ER - TY - CONF TI - Orthogonal beamforming for SDMA downlink with limited feedback AB - On a multi-antenna downlink channel, separation of multiple users by transmit beamforming enables simultaneous transmission from the base station to the users, resulting in high sum throughput. This paper proposes and analyzes a practical algorithm for joint scheduling and orthogonal beamforming, which is enabled by feedback of quantized channel state information (CSI). In this approach, each user quantizes CSI using a codebook comprised of multiple orthonormal vector sets and sends back quantized CSI. Using feedback CSI, the base station jointly selects a set of orthogonal beamforming vectors and schedules a subset of feedback users for downlink transmission such that the throughput is maximized. For moderate to large numbers of users, the proposed algorithm achieves higher sum capacities than the conventional ones. C2 - 2007/// C3 - ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings DA - 2007/// DO - 10.1109/ICASSP.2007.366481 VL - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547540872&partnerID=MN8TOARS ER - TY - CONF TI - Optimizing MIMO antenna placement and array configurations for multimedia delivery in aircraft AB - In this paper, the feasibility of multiple-input multiple-output (MIMO) systems in aircraft is examined for the specific application of seatback entertainment, using an approach built around a site-specific capacity analysis methodology. The average capacity is evaluated as a function of the seat location, using the proposed methodology that relies on inputs from measurement results or ray-tracing simulations. The extension of the methodology to optimize the access point and client antenna placement locations and array configurations is also described in the paper. While the specific results are for the deployment of MIMO communication in aircraft for seatback entertainment, the same methodology can be applied to other deployment scenarios as well. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECS.2007.99 SP - 425-429 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547325984&partnerID=MN8TOARS ER - TY - CONF TI - Opportunistic relay selection with limited feedback AB - It has been shown that a decentralized relay selection protocol based on opportunistic feedback from the relays yields good throughput performance in dense wireless networks. This selection strategy supports a hybrid-ARQ transmission approach where relays forward parity information to the destination in the event of a decoding error. Such an approach, however, suffers a loss compared to centralized strategies that select relays with the best channel gain to the destination. This paper closes the performance gap by adding another level of channel feedback to the decentralized relay selection problem. It is demonstrated that only one additional bit of feedback is necessary for good throughput performance. The performance impact of varying key parameters such as the number of relays and the channel feedback threshold is discussed. An accompanying bit error rate analysis demonstrates the importance of relay selection C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECS.2007.40 SP - 135-139 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547348290&partnerID=MN8TOARS ER - TY - CONF TI - Physical concerns for cross-layer prototyping and wireless network experimentation C2 - 2007/// C3 - Proceedings of the 2nd ACM International Workshop on Wireless Network Testbeds, Experimental Evaluation and Characterization, WiNTECH '07, Co-located with the ACM MobiCom 2007 Conference DA - 2007/// SP - 11-18 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70450225415&partnerID=MN8TOARS ER - TY - CONF TI - Physical concerns for cross-layer prototyping and wireless network experimentation AB - The performance of a wireless network protocol is inseparably linked to the physical layer algorithms on which it is built, the hardware used to implement the radio, and the wireless environment in which it operates. This paper identifies three features of wireless networking protocols impacted by these lower-level characteristics that are often overlooked or misunderstood by many researchers developing wireless protocols or using testbed-based evaluation methods. These features are temporal scaling, measurement reciprocity, and cross-layer adaptation. Temporal scaling refers to the time resolution with which events, such as broadcast or feedback, occur in the wireless network. This feature is tightly coupled with processing time at the physical layer and time selectivity in the wireless channel. Measurement reciprocity is an assumption used to estimate parameters of the forward link of a bidirectional communication channel, based on observations from the reverse link. This assumption directly depends on the interference properties and hardware symmetry of nodes in a wireless network. System adaptation, based on reciprocity or feedback, inevitably requires careful scrutiny of power and rate control applied to physical wireless devices. This paper also provides recommendations to guide researchers in setting up interesting and useful wireless experiments. Three concerns for wireless experimentation are addressed, namely: ambient interference, RF hardware profiling, and fading properties of the wireless channel. The motivation for this paper stems from experience prototyping and experimenting with Hydra, a wireless cross-layer testbed developed at the University of Texas at Austin. C2 - 2007/// C3 - International Conference on Mobile Computing and Networking, MobiCom'07 Co-Located Workshops -Proceedings of the the Second ACM International Workshop on Wireless Network Testbeds, Experimental Evalua DA - 2007/// DO - 10.1145/1287767.1287771 SP - 11-18 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-37849027235&partnerID=MN8TOARS ER - TY - JOUR TI - Overcoming interference in spatial multiplexing mimo cellular networks T2 - IEEE Wireless Communications AB - Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But spatial multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future spatial multiplexing cellular systems. DA - 2007/// PY - 2007/// DO - 10.1109/MWC.2007.4407232 VL - 14 IS - 6 SP - 95-104 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-37249050361&partnerID=MN8TOARS ER - TY - JOUR TI - Opportunistic space-division multiple access with beam selection T2 - IEEE Transactions on Communications AB - In this paper, a novel transmission technique for the multiple-input multiple-output (MIMO) broadcast channel is proposed that allows simultaneous transmission to multiple users with limited feedback from each user. During a training phase, the base station modulates a training sequence on multiple sets of randomly chosen orthogonal beamforming vectors. Each user sends the index of the best beamforming vector and the corresponding signal-to-interference-plus-noise ratio for that set of orthogonal vectors back to the base station. The base station opportunistically determines the users and corresponding orthogonal vectors that maximize the sum capacity. Based on the capacity expressions, the optimal amount of training to maximize the sum capacity is derived as a function of the system parameters. The main advantage of the proposed system is that it provides throughput gains for the MIMO broadcast channel with a small feedback overhead, and provides these gains even with a small number of active users. Numerical simulations show that a 20% gain in sum capacity is achieved (for a small number of users) over conventional opportunistic space division multiple access, and a 100% gain (for a large number of users) over conventional opportunistic beamforming when the number of transmit antennas is four. DA - 2007/// PY - 2007/// DO - 10.1109/TCOMM.2007.910702 VL - 55 IS - 12 SP - 2371-2380 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-41249083578&partnerID=MN8TOARS KW - beamforming KW - multiple-input multiple-output (MIMO) KW - space-division multiple access (SDMA) ER - TY - JOUR TI - On the existence of equiangular tight frames T2 - Linear Algebra and Its Applications AB - An equiangular tight frame (ETF) is a d×N matrix that has unit-norm columns and orthogonal rows of norm N/d. Its key property is that the absolute inner products between pairs of columns are (i) identical and (ii) as small as possible. ETFs have applications in communications, coding theory, and sparse approximation. Numerical experiments indicate that ETFs arise for very few pairs (d, N), and it is an important challenge to develop restrictions on the pairs for which they can exist. This article uses field theory to provide detailed conditions on real and complex ETFs. In particular, it describes restrictions on harmonic ETFs, a specific type of complex ETF that appears in applications. Finally, the article offers empirical evidence that these conditions are sharp or nearly sharp, especially in the real case. DA - 2007/// PY - 2007/// DO - 10.1016/j.laa.2007.05.043 VL - 426 IS - 2-3 SP - 619-635 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547906516&partnerID=MN8TOARS KW - equiangular lines KW - tight frame KW - harmonic frame KW - orthogonal vectors KW - eigenvalues KW - integer matrix KW - roots of unity KW - strongly regular graph ER - TY - CONF TI - Low-complexity user and antenna selection for multiuser MIMO systems with block diagonalization AB - Block diagonalization is a downlink preceding technique that pre-cancels inter-user interference in multiuser MIMO systems. When there are a large number of users, the system throughput can be significantly increased by selecting a subset of users and a subset of receive antennas for each user. The optimal user and antenna subset can be obtained by exhaustively searching over all possible user and antenna combinations to find the one with the highest sum throughput. This brute-force solution, however, is prohibitively complicated. To reduce the complexity, in this paper we propose a low-complexity suboptimal user and antenna selection algorithm. For most system configurations, we show that our proposed algorithm achieves up to 98% of the optimal sum throughput of the exhaustive search, where the complexity is orders of magnitude lower than the exhaustive search method. C2 - 2007/// C3 - ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings DA - 2007/// DO - 10.1109/ICASSP.2007.366754 VL - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547534112&partnerID=MN8TOARS ER - TY - JOUR TI - Joint interference cancellation and channel shortening in multiuser-MIMO systems T2 - IEEE Transactions on Vehicular Technology AB - In this paper, a two-stage receiver structure for interference cancellation in multiuser spatially multiplexed multiple-antenna systems is presented. A space-time equalizer is used in the first stage for joint coantenna/cochannel-interference suppression and shortening of the effective channel for each transmit stream of the desired user. The channel shortening, combined with independent detection, helps reduce the complexity of the second stage Viterbi equalizer, which is used for separate intersymbol-interference equalization for each of the streams. Three objective functions are proposed for determining the coefficients of the space-time equalizer using a direct training data-based approach, which does not require estimation of the interferer's channel. Simulation results show good symbol error performance as compared to existing algorithms with asynchronous multiple-input multiple-output interferers DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2006.889572 VL - 56 IS - 2 SP - 652-660 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34147111699&partnerID=MN8TOARS KW - equalizers KW - interference suppression KW - MIMO systems KW - multiuser channels ER - TY - CONF TI - Multiuser limited feedback for wireless multi-antenna communication AB - For a wireless multi-antenna network with a large number of users, the sum capacity scales at most linearly with the number of antennas and double logarithmically the number of users. Achieving this optimal capacity scaling potentially requires feedback of channel state information (CSI) from all users, leading to overflow of the feedback channel. This paper proposes a limited feedback strategy that provides feedback control such that a sum CSI feedback rate constraint is satisfied. It is proved that a wireless multi-antenna network using the proposed limited feedback strategy achieves the optimal capacity scaling for the broadcast channel. C2 - 2007/// C3 - IEEE International Symposium on Information Theory - Proceedings DA - 2007/// DO - 10.1109/ISIT.2007.4557520 SP - 2036-2040 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51649091653&partnerID=MN8TOARS ER - TY - JOUR TI - Multiuser antenna partitioning for cellular MIMO-CDMA systems T2 - IEEE Transactions on Vehicular Technology AB - Improving the capacity of code-division-multiple-access (CDMA) systems through advanced signal processing has been an area of intensive research for many years, with limited success. Multiantenna technologies called multiple-input multiple-output (MIMO) are an obvious candidate to increase, particularly, downlink capacity. Nearly all research on MIMO-CDMA, however, has focused on increasing the throughput achieved per user, rather than increasing the number of supportable users, which is still the most important design goal in QoS-constrained voice systems. In this paper, we consider the downlink of a heavily loaded multicell CDMA system with multiple transmit and receive antennas. Straightforward application of the known MIMO techniques to such a system does not substantially increase the number of supportable users. To overcome this, a novel MIMO-CDMA system design based on user partitioning is developed, in which each user is assigned to a single transmit antenna either without regard to channel knowledge (static) or based on antenna-selection feedback bits (dynamic). These proposed multiuser-antenna-partitioning techniques have a minimal increase in complexity and would require only small changes to existing CDMA standards. The outage probability and capacity of the proposed systems are derived, and it is shown that, particularly, the dynamic partitioning scheme has a large gain over both the conventional CDMA and the static MIMO-CDMA scheme. This gain can be credited to multiuser antenna selection diversity. Unlike prior research, the multiuser antenna selection diversity gain is achieved without the typical expense of a loss in spatial multiplexing gain.Improving the capacity of code-division-multiple-access (CDMA) systems through advanced signal processing has been an area of intensive research for many years, with limited success. Multiantenna technologies called multiple-input multiple-output (MIMO) are an obvious candidate to increase, particularly, downlink capacity. Nearly all research on MIMO-CDMA, however, has focused on increasing the throughput achieved per user, rather than increasing the number of supportable users, which is still the most important design goal in QoS-constrained voice systems. In this paper, we consider the downlink of a heavily loaded multicell CDMA system with multiple transmit and receive antennas. Straightforward application of the known MIMO techniques to such a system does not substantially increase the number of supportable users. To overcome this, a novel MIMO-CDMA system design based on user partitioning is developed, in which each user is assigned to a single transmit antenna either without regard to channel knowledge (static) or based on antenna-selection feedback bits (dynamic). These proposed multiuser-antenna-partitioning techniques have a minimal increase in complexity and would require only small changes to existing CDMA standards. The outage probability and capacity of the proposed systems are derived, and it is shown that, particularly, the dynamic partitioning scheme has a large gain over both the conventional CDMA and the static MIMO-CDMA scheme. This gain can be credited to multiuser antenna selection diversity. Unlike prior research, the multiuser antenna selection diversity gain is achieved without the typical expense of a loss in spatial multiplexing gain. DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2007.898396 VL - 56 IS - 5 I SP - 2448-2456 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-37249089377&partnerID=MN8TOARS KW - antenna partitioning KW - code division multiple access (CDMA) KW - multiple-input multiple-output (MIMO) systems KW - outage capacity ER - TY - JOUR TI - Multiplexing/beamforming switching for coded mimo in spatially correlated channels based on closed-form ber approximations T2 - IEEE Transactions on Vehicular Technology AB - This paper considers low-complexity coded multiple-input-multiple-output transmission in Rayleigh channels with correlation between antennas at both the transmitter and receiver. We consider statistical beamforming (SB) and spatial multiplexing (SM) with a zero-forcing receiver. We calculate the link-level capacity of both schemes with bit-interleaved coded modulation and derive accurate closed-form approximations to the bit error rate. We then show how the resulting expressions can be used in an adaptive algorithm to select the best combination of code rate, modulation format, and transmission scheme (SB or SM) in order to maximize throughput. Unlike other mode-switching schemes that require empirical lookup tables, this approach applies to any correlation scenario. Numerical studies are used to demonstrate the performance as a function of signal-to-noise ratio and correlation parameters. DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2007.900353 VL - 56 IS - 5 I SP - 2555-2567 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-54949131046&partnerID=MN8TOARS KW - adaptive coding KW - modulation KW - multiple-input-multiple-output (MIMO) communications KW - spatially correlated channels ER - TY - CONF TI - Jointly optimized multiuser beamforming for the MIMO broadcast channel with limited feedback AB - This paper considers the joint optimization of the transmitter beamforming filters and receiver combining filters for the multiple-input multiple-output (MIMO) broadcast channel. A low-complexity iterative algorithm to compute the filters is proposed and then a closed-form expression of the filters for the downlink with two transmit antennas is derived, avoiding the need for iterative computation in this case. To enable practical implementation, a new limited feedback algorithm is proposed that exploits the channel structure in the closed form solution, and is independent of the number of receive antennas. Performance is evaluated by Monte Carlo simulations as a function of the amount of feedback. With two receive antennas, the proposed method performs close to the sum capacity of the MIMO broadcast channel, without the need for multiuser diversity and with only limited feedback. C2 - 2007/// C3 - IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC DA - 2007/// DO - 10.1109/PIMRC.2007.4394188 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-44349103076&partnerID=MN8TOARS ER - TY - JOUR TI - Interpolation-Based Multi-Mode Precoding for MIMO-OFDM Systems with Limited Feedback AU - Khaled, N. AU - Mondal, B. AU - Leus, G. AU - Heath, R.W. AU - Petré, F. T2 - IEEE Transactions on Wireless Communications AB - Spatial multiplexing with multi-mode precoding provides a means to achieve both high capacity and high reliability in multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. Multi-mode precoding uses linear transmit precoding that adapts the number of spatial multiplexing data streams or modes, according to the transmit channel state information (CSI). As such, it typically requires complete knowledge of the multi-mode precoding matrices for each subcarrier at the transmitter. In practical scenarios where the CSI is acquired at the receiver and fed back to the transmitter through a low-rate feedback link, this requirement may entail a prohibitive feedback overhead. In this paper, we propose to reduce the feedback requirement by combining codebook-based precoder quantization, to efficiently quantize and represent the optimal precoder on each subcarrier, and multi-mode precoder frequency down-sampling and interpolation, to efficiently reconstruct the precoding matrices on all subcarriers based on the feedback of the indexes of the quantized precoders only on a fraction of the subcarriers. To enable this efficient interpolation-based quantized multimode precoding solution, we introduce (1) a novel precoder codebook design that lends itself to precoder interpolation, across subcarriers, followed by mode selection, (2) a new precoder interpolator and, finally, (3) a clustered mode selection approach that significantly reduces the feedback overhead related to the mode information on each subcarrier. Monte-Carlo bit-error rate (BER) performance simulations demonstrate the effectiveness of the proposed quantized multi-mode precoding solution, at reasonable feedback overhead DA - 2007/// PY - 2007/// DO - 10.1109/TWC.2007.05334 VL - 6 IS - 3 SP - 1003-1013 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-85008055165&partnerID=MN8TOARS KW - multiple-input multiple-output (MIMO) KW - OFDM KW - limited feedback KW - vector quantization KW - mode selection KW - linear precoding KW - matrix interpolation under a unitary constraint ER - TY - CONF TI - Hybrid-arq in multihop networks with opportunistic relay selection AB - This paper develops a contention-based opportunistic feedback technique towards relay selection in a dense wireless network. This technique enables the forwarding of additional parity information from the selected relay to the destination. For a given network, the effects of varying key parameters such as the feedback probability are presented and discussed. A primary advantage of the proposed technique is that relay selection can be performed in a distributed way. Simulation results find its performance to closely match that of centralized schemes that utilize GPS information, unlike the proposed method. The proposed relay selection method is also found to achieve throughput gains over a point-to-point transmission strategy. C2 - 2007/// C3 - ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings DA - 2007/// DO - 10.1109/ICASSP.2007.366755 VL - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547513223&partnerID=MN8TOARS ER - TY - CONF TI - Early results on hydra: A flexible MAC/PHY multihop testbed AB - Hydra is a flexible wireless network testbed being developed at UT Austin. Our focus is networks that support multiple wireless hops and where the network, especially the MAC, takes advantage of sophisticated PHY techniques, such as OFDM and MIMO. We argue that for this domain simulation alone is not adequate and that working prototypes are needed to validate algorithms and protocols. Hydra nodes consist of a flexible RF front-end and a general purpose machine with a software based MAC and PHY. Using the frameworks of the Click modular router and GNU radio and coding in C++ makes it relatively easy to implement working prototypes of cross-layer designs that require custom MACs and PHYs. We present the architecture and implementation of Hydra, as well as a preliminary cross-layer design experiment for a rate-adaptive MAC. These early results show Hydra is a capable prototyping tool for wireless network research. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECS.2007.393 SP - 1896-1900 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547325148&partnerID=MN8TOARS KW - wireless testbed KW - prototype KW - cross-layer design ER - TY - CONF TI - Impact of mutual coupling and antenna efficiencies on adaptive switching between MIMO transmission strategies AB - Previous research has shown that adaptive switching between multiple-input multiple-output (MIMO) transmission strategies like spatial multiplexing and beamforming increases link reliability and capacity gains, as compared to fixed transmission strategies. To get the full benefit of adaptive switching it is necessary to obtain accurate estimates of the SNR values when we switch between the transmission strategies. In this paper, it is shown that (relatively more) accurate switching point estimates can be obtained by taking into account real-life effects like mutual coupling and antenna efficiencies, for switching between statistical beamforming and spatial multiplexing. Using simulations, it is shown that accounting for these effects can make the switching point estimate more accurate by as much as 12 dB, compared to the case when the practical effects are not considered. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECF.2007.166 SP - 749-753 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47649132725&partnerID=MN8TOARS ER - TY - CONF TI - Ergodic capacity of spatial multiplexing MIMO systems with ZF receivers for log-normal shadowing and rayleigh fading channels AB - This paper presents a derivation of an expression for the ergodic capacity of spatial multiplexing multiple-input-multiple-output (MIMO) systems with zero-forcing (ZF) receivers and independent substream detection. Assuming that the channel is unknown at the transmitter but known at the receiver, the ergodic capacity is formulated as a function of log-normal shadowing and Rayleigh fading. Gauss-Hermite quadrature integration is used to approximate the ergodic capacity expression in a concise form. The proposed analytical approach allows investigation of the effects of the shadowing standard deviation and the transmit correlation. Numerical and simulation results confirm that under various composite channel scenarios, the analytical results match well with the simulation results. C2 - 2007/// C3 - IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC DA - 2007/// DO - 10.1109/PIMRC.2007.4394313 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-44349087569&partnerID=MN8TOARS ER - TY - CONF TI - Efficient transmit antenna selection for multiuser MIMO systems with block diagonalization AB - Block diagonalization is a preceding technique for multiuser MIMO systems that pre-cancels inter-user interference at the transmitter side. When there are a large number of base station antennas but a limited number of RF amplifiers, the system performance can be significantly improved by switching a subset of antennas to the RF chains and exploiting antenna selection diversity. The optimal antenna subset can be obtained by exhaustively searching over all possible antenna combinations. This brute-force search, however, is prohibitively complicated and impractical. To reduce the complexity, in this paper we propose several low-complexity suboptimal transmit selection algorithms that minimize a symbol error rate (SER) upper bound or maximize a capacity lower bound. Simulation results show that our proposed algorithms perform very close to the optimal exhaustive search, while the complexity is much lower. C2 - 2007/// C3 - GLOBECOM - IEEE Global Telecommunications Conference DA - 2007/// DO - 10.1109/GLOCOM.2007.664 SP - 3499-3503 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-39349115145&partnerID=MN8TOARS ER - TY - CONF TI - Coordinated multi-cell MIMO systems with cellular block diagonalization AB - A clustered base transceiver station (BTS) coordination strategy is proposed to realize the gains of multiuser MIMO communication in interference-limited cellular systems. In the proposed coordination strategy, users are divided into two groups: a full intra-cluster coordination group to enhance the sum rate gain and a limited inter-cluster coordination group to reduce interference for the cluster edge users. Multi-cell block diagonalization is used to coordinate the transmissions across multiple BTSs in the same cluster. Because of the per-BTS power constraints, three combined precoder and power allocation algorithms are considered in this paper with different performance complexity tradeoffs. Simulations show that the proposed coordination strategy improves the sum rate over conventional systems and reduces the impact of interference for the cluster-edge users. C2 - 2007/// C3 - Conference Record - Asilomar Conference on Signals, Systems and Computers DA - 2007/// DO - 10.1109/ACSSC.2007.4487516 SP - 1669-1673 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-50249093779&partnerID=MN8TOARS ER - TY - CONF TI - Downlink MIMO block diagonalization in the presence of other-cell interference AB - Block diagonalization is one approach for linear preceding in the multiple-input multiple-output broadcast channel that sends multiple interference free data streams to different users in the same cell. Unfortunately, block diagonalization neglects other cell interference, which limits the performance of users at the edge of the cell. This paper presents an OCI-aware enhancement to block diagonalization that uses a whitening filter for interference suppression at the receiver and a novel precoder using the interference-plus-noise covariance matrix for each user at the transmitter. For complex Gaussian matrix channels, the asymptotic sum rate of the proposed system is analyzed under a large antenna assumption for isotropic inputs and compared to conventional block diagonalization. C2 - 2007/// C3 - GLOBECOM - IEEE Global Telecommunications Conference DA - 2007/// DO - 10.1109/GLOCOM.2007.828 SP - 4354-4358 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-39349091848&partnerID=MN8TOARS ER - TY - JOUR TI - Blind channel estimation for MIMO-OFDM systems T2 - IEEE Transactions on Vehicular Technology AB - By combining multiple-input multiple-output (MIMO) communication with the orthogonal frequency division multiplexing (OFDM) modulation scheme, MIMO-OFDM systems can achieve high data rates over broadband wireless channels. In this paper, to provide a bandwidth-efficient solution for MIMO-OFDM channel estimation, we establish conditions for channel identifiability and present a blind channel estimation technique based on a subspace approach. The proposed method unifies and generalizes the existing subspace-based methods for blind channel estimation in single-input single-output OFDM systems to blind channel estimation for two different MIMO-OFDM systems distinguished according to the number of transmit and receive antennas. In particular, the proposed method obtains accurate channel estimation and fast convergence with insensitivity to overestimates of the true channel order. If virtual carriers (VCs) are available, the proposed method can work with no or insufficient cyclic prefix (CP), thereby potentially increasing channel utilization. Furthermore, it is shown under specific system conditions that the proposed method can be applied to MIMO-OFDM systems without CPs, regardless of the presence of VCs, and obtains an accurate channel estimate with a small number of OFDM symbols. Thus, this method improves the transmission bandwidth efficiency. Simulation results illustrate the mean-square error performance of the proposed method via numerical experiments. DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2007.891429 VL - 56 IS - 2 SP - 670-685 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34147190010&partnerID=MN8TOARS KW - blind channel estimation KW - cyclic prefix KW - multiple-input multiple-output (MIMO) system KW - orthogonal frequency division multiplexing (OFDM) KW - subspace method KW - virtual carrier ER - TY - JOUR TI - Adaptive MIMO transmission for exploiting the capacity of spatially correlated channels T2 - IEEE Transactions on Vehicular Technology AB - We consider a novel low-complexity adaptive multiple-input multiple-output (MIMO) transmission technique. The approach is based on switching between low-complexity transmission schemes, including statistical beamforming, double space-time transmit diversity, and spatial multiplexing, depending on the changing channel statistics, as a practical means of approaching the spatially correlated MIMO channel capacity. We first derive new ergodic capacity expressions for each MIMO transmission scheme in spatially correlated channels. Based on these results, we demonstrate that adaptive switching between MIMO schemes yields significant capacity gains over fixed transmission schemes. We also derive accurate analytical approximations for the optimal signal-to-noise-ratio switching thresholds, which correspond to the crossing-points of the capacity curves. These thresholds are shown to vary, depending on the spatial correlation, and are used to identify key switching parameters. Finally, we propose a practical switching algorithm that is shown to yield significant spectral efficiency improvements over nonadaptive schemes for typical channel scenarios DA - 2007/// PY - 2007/// DO - 10.1109/TVT.2007.891427 VL - 56 IS - 2 SP - 619-630 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34147175447&partnerID=MN8TOARS KW - adaptive modulation KW - channel capacity KW - channel coding KW - fading channels KW - MIMO systems ER - TY - JOUR TI - Congruent Voronoi tessellations from equiangular lines T2 - Applied and Computational Harmonic Analysis AB - It is proven that the Voronoi tessellations of the real projective space generated by equiangular lines are congruent. Two implications of this result are mentioned—an equiangular set of lines forms the best N -point representation of an isotropically distributed one-dimensional subspace in terms of mutual information and a subspace quantizer defined by equiangular lines provides equal partial distortion. DA - 2007/// PY - 2007/// DO - 10.1016/j.acha.2007.03.005 VL - 23 IS - 2 SP - 254-258 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547579650&partnerID=MN8TOARS ER - TY - CONF TI - Capacity scaling for MIMO two-way relaying AB - This paper considers capacity scaling in the recently proposed two-way MIMO (multiple input multiple output) relay channel. In the two-way relay channel, two nodes use a relay for exchanging data with each other. Under the assumption that each node has perfect receive channel state information and all nodes work only in half duplex mode, this paper shows that the sum capacity scales linearly with the number of transmit antennas and logarithmically with the number of relays, as the number of relays grows large. This result shows that with two- way relay channels it is possible to asymptotically (in the number of relays) obtain full-duplex performance while using only half-duplex nodes. C2 - 2007/// C3 - IEEE International Symposium on Information Theory - Proceedings DA - 2007/// DO - 10.1109/ISIT.2007.4557134 SP - 1451-1455 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51649103066&partnerID=MN8TOARS ER - TY - JOUR TI - 60 GHz wireless communications: Emerging requirements and design recommendations T2 - IEEE Vehicular Technology Magazine AB - Multiple GHz of internationally available, unlicensed spectrum surrounding the 60 GHz carrier frequency has the ability to accommodate high-throughput wireless communications. While the size and availability of this free spectrum make it very attractive for wireless applications, 60 GHz implementations must overcome many challenges. For example, the high attenuation and directional nature of the 60 GHz wireless channel as well as limited gain amplifiers and excessive phase noise in 60 GHz transceivers are explicit implementation difficulties. The challenges associated with this channel motivate commercial deployment of short-range wireless local area networks, wireless personal area networks, and vehicular networks. In this paper we detail design tradeoffs for algorithms in the 60 GHz physical layer including modulation, equalization, and space-time processing. The discussion is enhanced by considering the limitations in circuit design, characteristics of the effective wireless channel (including antennas), and performance requirements to support current and next generation 60 GHz wireless communication applications. DA - 2007/// PY - 2007/// DO - 10.1109/MVT.2008.915320 VL - 2 IS - 3 SP - 41-50 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-40349094869&partnerID=MN8TOARS ER - TY - JOUR TI - Coordinate interleaved orthogonal design with two transmit antennas in spatially correlated Rayleigh fading channels: Symbol-error rate and diversity order T2 - IEICE Transactions on Communications AB - Full-diversity transmission for space-time block codes (STBCs) with multiple transmit antennas can be achieved by using coordinate interleaved orthogonal designs (CIODs). To effectively evaluate the performance of CIODs, we derive union upper and lower bounds on the symbol-error rate (SER) and a corresponding asymptotic diversity order of symmetric structured CIOD, in particular, with two transmit antennas over quasi-static spatially uncorrelated/correlated frequency-nonselective Rayleigh fading channels. Some numerical results are provided to verify our analysis. DA - 2007/// PY - 2007/// DO - 10.1093/ietcom/e90-b.11.3294 VL - E90-B IS - 11 SP - 3294-3297 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67651052062&partnerID=MN8TOARS KW - space-time block codes (STBCs) KW - coordinate interleaved orthogonal designs (CIODs) KW - symbol-error rate (SER) KW - asymptotic diversity order ER - TY - CONF TI - Conference Record - Asilomar Conference on Signals, Systems and Computers: Foreword C2 - 2007/// C3 - Conference Record - Asilomar Conference on Signals, Systems and Computers DA - 2007/// DO - 10.1109/ACSSC.2007.4487150 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-50249186426&partnerID=MN8TOARS ER - TY - CONF TI - A MIMO demonstration of Hydra AB - The evaluation of cross-layer protocols for wireless networking requires analysis, simulation, and experimentation. The final step in this process is often overlooked, but is equally important. Prototyping and experimentation with testbeds not only provides a mechanism for evaluating the performance of wireless networks, but also provide keen insight into the design of new wireless protocols. Hydra, a flexible wireless network testbed developed at UT Austin, was designed to investigate cross-layer issues in wireless protocol design. In this paper, we propose a demonstration of the multiple-input multiple-output (MIMO) functionality of Hydra. We will investigate rate and spatial mode adaptation using this MIMO system. C2 - 2007/// C3 - International Conference on Mobile Computing and Networking, MobiCom'07 Co-Located Workshops -Proceedings of the the Second ACM International Workshop on Wireless Network Testbeds, Experimental Evalua DA - 2007/// DO - 10.1145/1287767.1287790 SP - 101-102 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-37849023156&partnerID=MN8TOARS ER - TY - CONF TI - A MIMO demonstration of hydra C2 - 2007/// C3 - Proceedings of the 2nd ACM International Workshop on Wireless Network Testbeds, Experimental Evaluation and Characterization, WiNTECH '07, Co-located with the ACM MobiCom 2007 Conference DA - 2007/// SP - 101-102 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70450228536&partnerID=MN8TOARS ER - TY - JOUR TI - Adaptation of two types of processing gains for UWB impulse radio wireless sensor networks AU - Güvenç, İ. AU - Arslan, H. AU - Gezici, S. AU - Kobayashi, H. T2 - IET Communications AB - Ultrawideband impulse radio systems offer two kinds of processing gains that can be adapted based on the interference level in the system so that quality of service requirements are fulfilled. An adaptive assignment scheme for two types of multiple-access parameters in cluster-based wireless sensor networks is investigated. A mathematical framework is developed for asynchronous communications using a Gaussian approximation method to model the multiple-access interference in two cases: one with fixed frame duration, where the goal is to increase the average throughput, and the other with fixed symbol duration, where the goal is to increase the network lifetime. Extension of the analysis to multipath channels is carried out, and the validity of the Gaussian approximation is investigated using the Kullback-Leibler distance. DA - 2007/// PY - 2007/// DO - 10.1049/iet-com:20045255 VL - 1 IS - 6 SP - 1280 J2 - IET Commun. LA - en OP - SN - 1751-8628 UR - http://dx.doi.org/10.1049/iet-com:20045255 DB - Crossref ER - TY - JOUR TI - Computation of constant mean curvature surfaces: Application to the gas–liquid interface of a pressurized fluid on a superhydrophobic surface AU - Lobaton, E.J. AU - Salamon, T.R. T2 - Journal of Colloid and Interface Science AB - The interface shape separating a gas layer within a superhydrophobic surface consisting of a square lattice of posts from a pressurized liquid above the surface is computed numerically. The interface shape is described by a constant mean curvature surface that satisfies the Young-Laplace equation with the three-phase gas-liquid-solid contact line assumed pinned at the post outer edge. The numerical method predicts the existence of constant mean curvature solutions from the planar, zero curvature solution up to a maximum curvature that is dependent on the post shape, size and pitch. An overall force balance between surface tension and pressure forces acting on the interface yields predictions for the maximum curvature that agree with the numerical simulations to within one percent for convex shapes such as circular and square posts, but significantly over predicts the maximum curvature for non-convex shapes such as a circular post with a sinusoidal surface perturbation. Changing the post shape to increase the contact line length, while maintaining constant post area, results in increases of 2 to 12% in the maximum computable curvature for contact line length increases of 11 to 77%. Comparisons are made to several experimental studies for interface shape and pressure stability. DA - 2007/10// PY - 2007/10// DO - 10.1016/j.jcis.2007.05.059 VL - 314 IS - 1 SP - 184-198 J2 - Journal of Colloid and Interface Science LA - en OP - SN - 0021-9797 UR - http://dx.doi.org/10.1016/j.jcis.2007.05.059 DB - Crossref KW - superhydrophobic surface KW - pressure stability KW - interfacial shape KW - constant mean curvature surface KW - Lagrangian evolution equation KW - static contact line KW - overall force balance ER - TY - JOUR TI - Effect of sapphire-substrate thickness on the curvature of thick GaN films grown by hydride vapor phase epitaxy AU - Paskova, T. AU - Becker, L. AU - Böttcher, T. AU - Hommel, D. AU - Paskov, P. P. AU - Monemar, B. T2 - Journal of Applied Physics AB - The effect of sapphire-substrate thickness on the curvature and stress in thick hydride vapor phase epitaxial GaN films was studied by high-resolution x-ray diffraction at variable temperatures. The curvature was found to have the maximum value for comparable thicknesses of the film and the substrate, while the stress at the film surface decreases with increasing film thickness and increases with increasing substrate thickness, which is in very good agreement with the simulation results. The curvature at the growth temperature was found to be strongly influenced by the value of the intrinsic tensile strain, which is determined by the film/substrate thickness ratio. DA - 2007/12/15/ PY - 2007/12/15/ DO - 10.1063/1.2817955 VL - 102 IS - 12 SP - 123507 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2817955 DB - Crossref ER - TY - JOUR TI - Defect distribution in a-plane GaN on Al2O3 AU - Tuomisto, F. AU - Paskova, T. AU - Kröger, R. AU - Figge, S. AU - Hommel, D. AU - Monemar, B. AU - Kersting, R. T2 - Applied Physics Letters AB - The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11−20] a direction on (1−102) r-plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation. DA - 2007/3/19/ PY - 2007/3/19/ DO - 10.1063/1.2715128 VL - 90 IS - 12 SP - 121915 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2715128 DB - Crossref ER - TY - JOUR TI - Interfacial structure of a-plane GaN grown on r-plane sapphire AU - Kröger, R. AU - Paskova, T. AU - Figge, S. AU - Hommel, D. AU - Rosenauer, A. AU - Monemar, B. T2 - Applied Physics Letters AB - The interface between a-plane GaN, grown by metal organic vapor phase epitaxy and hydride vapor phase epitaxy, and r-plane sapphire was investigated by transmission electron microscopy in [1−100] and [0001] zone axis orientations. The interfacial structure was well defined allowing a direct observation of the misfit dislocations in both orientations. An analysis of these dislocations revealed for the respective Burgers vectors a 1∕3⟨2−1−10⟩ component in the {0002} planes and a 1∕2⟨0001⟩ component in the {1−100} planes. In addition, the relative atomic column configurations in the GaN and sapphire were determined based on Bloch-wave simulations in comparison with the experimental images. DA - 2007/2/19/ PY - 2007/2/19/ DO - 10.1063/1.2696309 VL - 90 IS - 8 SP - 081918 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2696309 DB - Crossref ER - TY - JOUR TI - Metastability of the UV luminescence in Mg-doped GaN layers grown by MOVPE on quasi-bulk GaN templates AU - Pozina, G. AU - Monemar, B. AU - Paskov, P.P. AU - Hemmingsson, C. AU - Hultman, L. AU - Amano, H. AU - Akasaki, I. AU - Paskova, T. AU - Figge, S. AU - Hommel, D. AU - Usui, A. T2 - Physica B: Condensed Matter AB - Optical metastability in Mg-doped GaN layers grown by metal–organic vapor phase epitaxy on thick GaN templates grown by halide vapor phase epitaxy has been studied by photoluminescence (PL) and cathodoluminescence (CL). The total Mg concentration varies from 1×1019 to 1×1020 cm−3. Both PL and CL spectra change the initial shape within a few minutes exposure to the excitation source. The effect is permanent at low temperatures but the emission spectrum can be recovered to its initial shape after heating to room temperature. The difference in PL and CL spectra is explained by activation of different regions in the sample by laser and electrons, respectively. In CL the increase of the defect-related luminescence seems to be connected with an enhanced structural defect reaction under electron irradiation, which competes with the regular radiative recombination, while in PL the main effect is related to dissociation of Mg–H complexes with consequent passivation of the residual shallow acceptors. DA - 2007/12// PY - 2007/12// DO - 10.1016/j.physb.2007.08.173 VL - 401-402 SP - 302-306 J2 - Physica B: Condensed Matter LA - en OP - SN - 0921-4526 UR - http://dx.doi.org/10.1016/j.physb.2007.08.173 DB - Crossref KW - III-nitrides KW - Mg-doped KW - metastability KW - luminescence ER - TY - JOUR TI - Vacancy defect distribution in heteroepitaxial -plane GaN grown by hydride vapor phase epitaxy AU - Tuomisto, F. AU - Paskova, T. AU - Figge, S. AU - Hommel, D. AU - Monemar, B. T2 - Journal of Crystal Growth AB - We have used positron annihilation spectroscopy to study the native vacancy distribution in a-plane heteroepitaxial GaN. We show that the Ga vacancy concentration is independent of the layer thickness in the range from 5 to 25μm. This is strikingly different from the behavior in c-plane GaN, where the Ga vacancy concentration decreases dramatically with the distance from the GaN/sapphire interface. This difference in the native vacancy profiles is tentatively correlated with the differences in the O impurity and dislocation density profiles in the polar and non-polar materials. DA - 2007/3// PY - 2007/3// DO - 10.1016/j.jcrysgro.2006.11.040 VL - 300 IS - 1 SP - 251-253 J2 - Journal of Crystal Growth LA - en OP - SN - 0022-0248 UR - http://dx.doi.org/10.1016/j.jcrysgro.2006.11.040 DB - Crossref KW - characterization KW - point defects KW - hydride vapor phase epitaxy KW - metalorganic chemical vapor deposition KW - nitrides KW - semiconducting gallium compounds ER - TY - JOUR TI - Effect of anisotropic strain on phonons in a-plane and c-plane GaN layers AU - Darakchieva, V. AU - Paskova, T. AU - Schubert, M. AU - Paskov, P.P. AU - Arwin, H. AU - Monemar, B. AU - Hommel, D. AU - Heuken, M. AU - Off, J. AU - Haskell, B.A. AU - Fini, P.T. AU - Speck, J.S. AU - Nakamura, S. T2 - Journal of Crystal Growth AB - We have studied phonons in two types of anisotropically strained GaN films: c-plane GaN films grown on a-plane sapphire and a-plane GaN films grown on r-plane sapphire. The anisotropic strain in the films is determined by high-resolution X-ray diffraction (HRXRD) in different measuring geometries and the phonon parameters have been assessed by generalized infrared spectroscopic ellipsometry (GIRSE). The effect of strain anisotropy on GaN phonon frequencies is presented and the phonon deformation potentials aA1(TO), bA1(TO), cE1(TO) and cE1(LO) are determined. DA - 2007/3// PY - 2007/3// DO - 10.1016/j.jcrysgro.2006.11.023 VL - 300 IS - 1 SP - 233-238 J2 - Journal of Crystal Growth LA - en OP - SN - 0022-0248 UR - http://dx.doi.org/10.1016/j.jcrysgro.2006.11.023 DB - Crossref KW - high-resolution X-ray diffraction KW - infrared spectroscopic ellipsometry KW - phonons KW - GaN ER - TY - JOUR TI - Defect structure ofa-plane GaN grown by hydride and metal-organic vapor phase epitaxy onr-plane sapphire AU - Kröger, R. AU - Paskova, T. AU - Monemar, B. AU - Figge, S. AU - Hommel, D. AU - Rosenauer, A. T2 - physica status solidi (c) AB - Abstract To obtain a deeper insight into the mechanism of defect formation in a ‐plane GaN the defect nature in such films grown by metal‐organic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) was investigated by means of transmission electron microscopy. The films showed, beside the frequently found basal plane stacking faults and threading dislocations, prismatic stacking faults originating at the film/substrate interface and facetted voids. The density of basal plane stacking fault was about 10 5 cm –1 and the density of partial dislocations was in the range of 10 10 cm –2 , accordingly. Using selected area diffraction the epitaxial relationship between film and layer was determined. Based on these findings the impact of lattice mismatch on the observed defect characteristic is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2007/6// PY - 2007/6// DO - 10.1002/pssc.200674909 VL - 4 IS - 7 SP - 2564-2567 J2 - phys. stat. sol. (c) LA - en OP - SN - 1610-1634 1610-1642 UR - http://dx.doi.org/10.1002/pssc.200674909 DB - Crossref ER - TY - JOUR TI - Bending in HVPE grown GaN films: origin and reduction possibilities AU - Paskova, T. AU - Becker, L. AU - Böttcher, T. AU - Hommel, D. AU - Paskov, P. P. AU - Monemar, B. T2 - physica status solidi (c) AB - Abstract We have studied the effects of film and substrate thicknesses on the bending and strain of thick GaN films grown by HVPE. Both experimental and simulation data, being in a very good agreement, show the highest bending at a critical film thickness slightly smaller than the substrate thickness, while the strain remains decreasing with only a small increase at much higher film thicknesses. Temperature dependent measurements allows a separation of the thermally induced component and an extrapolation of the bending to the growth temperature. The latter was found to be dependent on both the film and substrate thickness and to have a strong effect on the remaining bending of freestanding films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2007/6// PY - 2007/6// DO - 10.1002/pssc.200674819 VL - 4 IS - 7 SP - 2256-2259 J2 - phys. stat. sol. (c) LA - en OP - SN - 1610-1634 1610-1642 UR - http://dx.doi.org/10.1002/pssc.200674819 DB - Crossref ER - TY - JOUR TI - Nonpolara- andm-plane bulk GaN sliced from boules: structural and optical characteristics AU - Paskova, T. AU - Kroeger, R. AU - Hommel, D. AU - Paskov, P. P. AU - Monemar, B. AU - Preble, E. AU - Hanser, A. AU - Williams, N. M. AU - Tutor, M. T2 - physica status solidi (c) AB - Abstract Bulk GaN substrates grown by HVPE in the [0001] direction and sliced along the (11‐20) a ‐plane and the (1‐100) m ‐plane have been studied by SEM, TEM, HRXRD, CL and PL. Smooth morphology, low defect density, and narrow linewidths of the main XRD reflections and PL peaks are revealed and thus all the results demonstrate superior structural and optical quality of both a ‐ and m ‐plane bulk GaN material achieved by HVPE growth of boules in the conventional [0001] direction and subsequently sliced along nonpolar planes, implying the approach as the most promising to produce nonpolar GaN substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2007/6// PY - 2007/6// DO - 10.1002/pssc.200674818 VL - 4 IS - 7 SP - 2536-2539 J2 - phys. stat. sol. (c) LA - en OP - SN - 1610-1634 1610-1642 UR - http://dx.doi.org/10.1002/pssc.200674818 DB - Crossref ER - TY - JOUR TI - Phonons in strained AlGaN/GaN superlattices AU - Darakchieva, V. AU - Monemar, B. AU - Paskova, T. AU - Einfeldt, S. AU - Hommel, D. AU - Lourdudoss, S. T2 - physica status solidi (c) AB - Abstract Phonons in strained AlGaN/GaN superlattices (SLs) with constant periods but different Al composition have been studied using a combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The following SL modes were identified: i) AlGaN localized E 1 (TO) modes identified for the first time and AlGaN localized A 1 (LO) phonons; ii) GaN localized E 2 , E 1 (TO) and A 1 (LO) phonons; iii) delocalized E 1 (LO) phonons; iv) A 1 (TO) phonon; v) two modes around 660 cm –1 and 594‐625 cm –1 , respectively, not predicted by theory. The effects of strain and composition on the phonon frequencies were established and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2007/1// PY - 2007/1// DO - 10.1002/pssc.200673582 VL - 4 IS - 1 SP - 170-174 J2 - phys. stat. sol. (c) LA - en OP - SN - 1610-1634 1610-1642 UR - http://dx.doi.org/10.1002/pssc.200673582 DB - Crossref ER - TY - CONF TI - STATCOM operation strategy under power system faults AB - The STATCOM (synchronous static compensator) operation can be adversely affected due to voltage source converter (VSC) over-currents and trips, during power system faults when its dynamic VAR support functionality is most required strict requirements of STATCOM losses and total system loss penalty preclude the use of PWM (pulse-width modulation) for VSC based STATCOM applications. This constraint of implementing VSC without PWM functionality, results in over- currents and trips of the STATCOM during and after system faults. In this paper, we propose an "emergency PWM" strategy to prevent over-currents (and trips) in the VSC during and after system faults, with slightly different B-H characteristics (due to manufacturing tolerances) for series connected transformers. Simulation results are presented for a 48-pulse VSC based plusmn100 MVAr STATCOM connected to a 2-bus power system. Simulation results validate the "emergency PWM" strategy to prevent VSC over-currents and to supply reactive power under all power system faults - single-line to ground, line-line and three-phase system faults. C2 - 2007/// C3 - 2007 IEEE Power Engineering Society General Meeting, PES DA - 2007/// DO - 10.1109/PES.2007.386184 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42549150053&partnerID=MN8TOARS ER - TY - CONF TI - STATCOM operation strategy with saturable transformer under three-phase power system faults AB - The STATCOM (synchronous static compensator) based on voltage source converter (VSC) is used for voltage regulation in transmission and distribution systems. The STATCOM can rapidly supply dynamic VARs required during system faults for voltage support. The "emergency PWM" strategy developed in this paper can prevent over- current and transformer saturation in the VSC during and after three-phase power system faults, and also meet the strict requirements of STATCOM losses and total system loss penalty. Simulation results are presented for a 48-pulse VSC based plusmn100 MVAR STATCOM connected to a 2-bus power system to validate the "emergency PWM" strategy to prevent VSC over-current and transformer saturation and to supply required reactive power under a three-phase system faults. The proposed "emergency PWM" strategy is explained in terms of positive and negative sequence voltage for the system bus and STATCOM voltage. C2 - 2007/// C3 - IECON Proceedings (Industrial Electronics Conference) DA - 2007/// DO - 10.1109/IECON.2007.4460311 SP - 1720-1725 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-49949091002&partnerID=MN8TOARS KW - STATCOM KW - VSC KW - 3 phi fault KW - emergency PWM ER - TY - CONF TI - STATCOM operation with saturable transformer under single line to ground power system faults AB - The STATCOM (synchronous static compensator) based on voltage source converter (VSC) is used for voltage regulation in transmission and distribution systems. The STATCOM can rapidly supply dynamic VARs required during system faults for voltage support. The "emergency PWM" strategy developed in this paper can prevent over-current and transformer saturation in the VSC during and after single line to ground system faults, and also meet the strict requirements of STATCOM losses and total system loss penalty. Simulation results are presented for a 48-pulse VSC based plusmn140 MVAR STATCOM connected to a 2-bus power system to validate the "emergency PWM" strategy to prevent VSC over-current and transformer saturation and to supply required reactive power under a single-line to ground (SLG) system faults. The proposed "emergency PWM" strategy is explained in terms of positive and negative sequence voltage for the system bus voltage and STATCOM generated voltage. C2 - 2007/// C3 - Fourth Power Conversion Conference-NAGOYA, PCC-NAGOYA 2007 - Conference Proceedings DA - 2007/// DO - 10.1109/PCCON.2007.373085 SP - 975-982 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34748857348&partnerID=MN8TOARS ER - TY - CONF TI - STATCOM operation under single line-ground system faults with magnetic saturation in series connected transformers based 48-pulse voltage-source converter AB - In this paper, we investigate an "emergency PWM" method to prevent over-currents in VSC based STATCOM and control transformer magnetic saturation under single line-ground (SLG) power system faults. The 100 MVA 48-pulse VSC topology is based on four series connected transformers on the primary side and each transformer secondary is connected to a 3 Phi, 3-level Neutral Point Connected (NPC) VSC, with a common dc bus. A practical issue of impact of slightly different saturation (B-H) characteristics of series connected transformers, on VSC performance is investigated for SLG faults in the power system. The detailed simulation results for a 48-pulse GTO thyristor based VSC +100 MVA STATCOM connected to a 2-bus power system under SLG system faults validate that the proposed "emergency PWM" enables STATCOM operation under transformer saturation without over-currents in the GTO devices. The proposed "emergency PWM" strategy prevents STATCOM tripping under SLG power system faults. C2 - 2007/// C3 - 2007 European Conference on Power Electronics and Applications, EPE DA - 2007/// DO - 10.1109/EPE.2007.4417687 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51049083112&partnerID=MN8TOARS ER - TY - CONF TI - Active power management of electric power system using emerging power electronics technology AU - Huang, A.Q. AU - Bhattacharya, S. AU - Baran, M. AU - Chen, B. AU - Han, C. AB - Operation of today's very large scale and interconnected electric power systems depends critically on the devices that facilitate management of power flow on the grid. These devices can be based on passive components such as capacitor and inductor, or rely on the solid state power electronics technology to achieve much faster control bandwidth. Widely known as FACTS (Flexible AC Transmission system) devices, these power electronics controllers can regulate voltage and improve stability, hence increasing power flow capability, or they can be used to directly control the power flow, or they can be used to separate regional grid from each other to reduce the interactions between these grids. More advanced applications include the incorporation of energy storage to shape the peak power requirement and to smooth the power output of large wind farms. While the benefit of an actively managed power grid is well understood, widespread use of power electronics controllers in electric power grid is still limited. The main reason behind this is the higher cost and perceived lower reliability. In this paper, the authors will discuss emerging power electronics controllers that are under development at Semiconductor Power Electronics Center of NC State University, and explain how these developments will facilitate wider and broader applications. C2 - 2007/// C3 - 2007 IEEE Power Engineering Society General Meeting, PES DA - 2007/// DO - 10.1109/PES.2007.386146 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42549152727&partnerID=MN8TOARS ER - TY - CONF TI - Overcurrent protection in DC zonal shipboard power systems using solid state protection devices AU - Baran, M.E. AU - Teleke, S. AU - Bhattacharya, S. AB - In this paper, potential solutions to address the protection challenges in DC Shipboard Power Systems (SPSs) have been investigated. Two different options have been considered. The first option involves the use of Solid-State Circuit Breakers (SSCBs) for fault current limiting and interruption. Simulations on a prototype DC SPS have been performed to assess the performance of a SSCB. It is shown that the SSCB can interrupt the fault current very fast, within 20 milliseconds. The second option considered involves the use of Voltage Source Converter (VSC) themselves to act like crowbars. The simulations on the prototype system have been performed to assess the feasibility and effectiveness of this approach. It is shown that this is an effective method provided that VSC switches are properly chosen for it. C2 - 2007/// C3 - IEEE Electric Ship Technologies Symposium, ESTS 2007 DA - 2007/// DO - 10.1109/ESTS.2007.372089 SP - 221-224 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34548848247&partnerID=MN8TOARS KW - protection KW - power electronic converters KW - solid state circuit breakers ER - TY - CONF TI - STATCOM control and operation with series connected transformer based 48-pulse VSC AB - Static synchronous compensator (STATCOM) is a static compensator used to regulate voltage by reactive power injection, and to improve dynamic stability of power system. In this paper, the STATCOM control and operation for a 48-pulse VSC topology implemented with series connected transformers is reported. Two different control modes - voltage control and VAR control - for the STATCOM are investigated for a single STATCOM and dual STATCOM connected to a transmission bus. The two +100 MVAR (STATCOM) based on a full model comprising 48-pulse Gate Turn-off (GTO) thyristor based VSC is modeled. The control scheme for the STATCOM is fully validated by detailed simulations for a 2-bus power system. The VSC topology issues on the STATCOM control and performance are presented C2 - 2007/// C3 - IECON Proceedings (Industrial Electronics Conference) DA - 2007/// DO - 10.1109/IECON.2007.4460359 SP - 1714-1719 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-49949112136&partnerID=MN8TOARS KW - STATCOM KW - VSC KW - voltage regulation KW - VAR control ER - TY - CONF TI - Current control of angle controlled STATCOM AB - Voltage source converter (VSC) based STATCOM (synchronous static compensator) is used for voltage regulation in transmission and distribution systems. Over-currents and trips of the STATCOM during and after system faults or harmonic distortions may occur in STATCOM without PWM control. Selecting proper DC capacitor (Cdc) may keep negative-sequence current and harmonics low, and as a result, prevent over-currents within the STATCOM. However, the capacitor value depends on the type of distortion. In this paper, we propose and develop a current control strategy based on angle control, to prevent over-currents (and trips) in the VSC during and after system faults and harmonic distortions, and to ensure the STATCOM with small Cdc to supply required reactive power. Simulation results are presented for a 48-pulse VSC based plusmn100 MVAR STATCOM connected to a 2-bus power system. Simulation results validate the current control strategy to prevent VSC over-currents and to supply required reactive power under system fault and harmonic distortions. C2 - 2007/// C3 - 2007 39th North American Power Symposium, NAPS DA - 2007/// DO - 10.1109/NAPS.2007.4402329 SP - 322-328 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-50249158114&partnerID=MN8TOARS KW - angle control KW - current control KW - harmonic distortion KW - negative sequence KW - single line- ground fault (SLG) KW - STATCOM KW - voltage source converter (VSC) ER - TY - CONF TI - STATCOM ETO failure analysis AU - Du, Z. AU - Chen, B. AU - Han, C. AU - Yang, Z. AU - Song, W. AU - Bhattacharya, S. AU - Huang, A.Q. C2 - 2007/// C3 - Conference Proceedings - IPEMC 2006: CES/IEEE 5th International Power Electronics and Motion Control Conference DA - 2007/// DO - 10.1109/IPEMC.2006.297316 VL - 3 SP - 1455-1458 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-45149086060&partnerID=MN8TOARS ER - TY - CONF TI - Magnetic saturation in transformers used for a 48-pulse voltage-source converter based STATCOM under line to a line system faults AB - The STATCOM (Synchronous Static Compensator) based on voltage source converter (VSC) is used to supply dynamic VARs required during power system faults for voltage support. However, magnetic saturation of transformers used in VSC topology result in over-current and trips of the STATCOM during system faults, when dynamic VARs and voltage support are required the most. In this paper, we propose and develop an "emergency PWM" strategy to prevent over-currents in VSC and transformer magnetic saturation for line-to-line system faults. A plusmn 100 MVAR STATCOM with a 48-pulse VSC based on 3-level Neutral Point Clamped (NPC) topology and four series connected transformers with realistic saturation (B-H) characteristics are considered. Simulation results are presented for a 48-pulse VSC based plusmn 100 MVAR STATCOM connected to a 2-bus power system to validate the "emergency PWM" strategy to prevent VSC over-current and transformer saturation and supply reactive power under line-to-line system faults. A practical issue of impact of slightly different saturation (B-H) characteristics of the four series transformers, on VSC performance is shown by simulation results for line-to-line fault. C2 - 2007/// C3 - PESC Record - IEEE Annual Power Electronics Specialists Conference DA - 2007/// DO - 10.1109/PESC.2007.4342397 SP - 2450-2456 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-48349092461&partnerID=MN8TOARS KW - STATCOM KW - Voltage Source Converter (VSC) KW - line to line fault KW - saturable transformer ER - TY - CONF TI - STATCOM impact study on the integration of a large wind farm into a weak loop power system AU - Han, C. AU - Huang, A. AU - Baran, M. AU - Bhattacharya, S. AU - Litzenberger, W. AU - Anderson, L. AU - Johnson, A. AU - Edris, A.-A. AB - Summary form only given. Recently, renewable wind energy is enjoying a rapid growth globally to become an important green electricity source to replace polluting and exhausting fossil fuel. However, with wind being an uncontrollable resource and the nature of distributed wind induction generators, integrating a large-scale wind-farm into a power system poses challenges, particularly in a weak power system. In the paper, the impact of STATCOM to facilitate the integration of a large wind farm into a weak power system is studied. First, an actual weak power system with two nearby large wind farms is introduced. Based on the field SCADA data analysis, the power quality issues are highlighted and a centralized STATCOM is proposed to solve them, particularly the short-term (seconds to minutes) voltage fluctuations. Second, a model of the system, wind farm and STATCOM for steady-state and dynamic impact study is presented, and the model is validated by comparing with the actual field data. Using simulated PV and QV curves, voltage control and stability issues are analyzed, and the size and location of STATCOM are assessed. Finally, a STATCOM control strategy for voltage fluctuation suppression is presented and dynamic simulations verify the performance of proposed STATCOM and its control strategy. C2 - 2007/// C3 - 2007 IEEE Power Engineering Society General Meeting, PES DA - 2007/// DO - 10.1109/PES.2007.385765 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42549122030&partnerID=MN8TOARS ER - TY - CONF TI - Modeling and control of three-pliase active front-end converters AU - Hon, C.-C. AU - Cheng, P.-T. AU - Bhattacharya, S. AU - Lin, J. AB - Insulated Gate Bipolar Transistor based active front-end converters are widely utilized by industries thanks to the advantages of bi-directional power flow, unity power factor, low harmonic distortion of the line current, and smaller filter size. In this paper, the model and control of the active front- end converter system are presented and the operation principles are analyzed. Detailed discussions on controller designs aiming at enhancing the disturbance rejection capability and robustness are presented, and the performance is validated by experimental results. C2 - 2007/// C3 - IECON Proceedings (Industrial Electronics Conference) DA - 2007/// DO - 10.1109/IECON.2007.4460280 SP - 1449-1454 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-49949085107&partnerID=MN8TOARS ER - TY - CONF TI - A novel PWM voltage source converter for a DC zonal Shipboard Power System AU - Teleke, S. AU - Bhattacharya, S. AU - Baran, M.E. AB - In this paper, mathematical modeling and control of a PWM VSC converter is developed for a DC zonal shipboard power system (SPS) application. After selecting suitable controller parameters, a new PWM strategy is utilized by changing the carrier frequency under non ideal operating conditions. Moreover, the effect of different design parameters such as triangular wave PWM carrier frequency and DC link capacitance are observed and using the simulation results, the DC link capacitance size and PWM carrier wave frequencies are optimized for the SPS application. Non ideal operating conditions such as sudden load change, sudden supply voltage change and unbalanced supply voltage are simulated to verify the VSC performance utilizing this new PWM strategy. From the results, it is observed that the VSC can indeed show a satisfactory performance for this specific application and it can also operate under unity power factor under these non ideal conditions. C2 - 2007/// C3 - IECON Proceedings (Industrial Electronics Conference) DA - 2007/// DO - 10.1109/IECON.2007.4460171 SP - 1536-1541 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-49949110057&partnerID=MN8TOARS KW - VSC KW - mathematical model KW - vector control KW - SPS ER - TY - CONF TI - High-contrast algorithm behavior AU - Stallmann, Matthias F. AU - Brglez, Franc T2 - the 2007 workshop AB - After extensive experiments with two algorithms, CPLEX and our implementation of all-integer dual simplex, we observed extreme differences between the two on a set of design automation benchmarks. In many cases one of the two would find an optimal solution within seconds while the other timed out at one hour. C2 - 2007/// C3 - Proceedings of the 2007 workshop on Experimental computer science - ExpCS '07 DA - 2007/// DO - 10.1145/1281700.1281712 PB - ACM Press SN - 9781595937513 UR - http://dx.doi.org/10.1145/1281700.1281712 DB - Crossref ER - TY - CHAP TI - Reliable Geographical Multicast Routing in Vehicular Ad-Hoc Networks AU - Kihl, Maria AU - Sichitiu, Mihail AU - Ekeroth, Ted AU - Rozenberg, Michael T2 - Lecture Notes in Computer Science AB - Vehicular ad-hoc networks (VANETs) offer a large number of new potential applications without relying on significant infrastructure. Many of these applications benefit from multi-hop relaying of information, thus requiring a routing protocol. Characteristics unique to VANETs (such as high mobility and the need for geographical addressing) make many conven tional ad hoc routing protocols unsuitable. Also, some envisioned applica tions have end-to-end QoS requirements. In this paper we propose a new multicast routing protocol specifically designed for VANETs. Its purpose is to provide a routing service for a future reliable transport protocol. We eval uate its performance using realistic network and traffic models. It is shown that it is possible to implement a reliable multicast routing protocol for VANETs. PY - 2007/6/23/ DO - 10.1007/978-3-540-72697-5_27 SP - 315-325 OP - PB - Springer Berlin Heidelberg SN - 9783540726944 9783540726975 UR - http://dx.doi.org/10.1007/978-3-540-72697-5_27 DB - Crossref ER - TY - CHAP TI - On the Resilient Overlay Topology Formation in Multi-hop Wireless Networks AU - Xing, Fei AU - Wang, Wenye T2 - NETWORKING 2007. Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet AB - In this paper, we study the problem of how to design overlay topologies in multi-hop wireless networks such that the overlays achieve perfect resilience, in terms of all cooperative nodes included but misbehaving nodes excluded, and preserve the k-connectivity with high probability. To address this problem, we propose a new distributed topology control protocol called PROACtive. By using PROACtive, every node pro-actively selects its cooperative adjacent nodes as neighbors by mutually exchanging neighbor request and reply messages. As a result, the union of all neighbor sets forms a resilient overlay for a given network. Our analysis finds that the PROACtive protocol is light-weighted with the message complexity of only O(m), where m is the number of links in the original network. Our simulation results validate the effectiveness of PROACtive and show that the overlays generated by our protocol preserve the k-connectivity with high probability (> 90%) and low false positive ratio (< 5%). PY - 2007/// DO - 10.1007/978-3-540-72606-7_1 SP - 1-12 OP - PB - Springer Berlin Heidelberg SN - 9783540726050 9783540726067 UR - http://dx.doi.org/10.1007/978-3-540-72606-7_1 DB - Crossref ER - TY - CONF TI - Unified Architectural Support for Soft-Error Protection or Software Bug Detection AU - Dimitrov, Martin AU - Zhou, Huiyang T2 - 16th International Conference on Parallel Architecture and Compilation Techniques (PACT 2007) AB - In this paper we propose a unified architectural support that can be used flexibly for either soft-error protection or software bug detection. Our approach is based on dynamically detecting and enforcing instruction- level invariants. A hardware table is designed to keep track of run-time invariant information. During program execution, instructions access this table and compare their produced results against the stored invariants. Any violation of the predicted invariant suggests a potential abnormal behavior, which could be a result of a soft error or a latent software bug. In case of a soft error, monitoring invariant violations provides opportunistic soft-error protection to multiple structures in processor pipelines. Our experimental results show that invariant violations detect soft errors promptly and as a result, simple pipeline squashing is able to fix most of the detected soft errors. Meanwhile, the same approach can be easily adapted for software bug detection. The proposed architectural support eliminates the substantial performance overhead associated with software-based bug-detection approaches and enables continuous monitoring of production code. C2 - 2007/9// C3 - 16th International Conference on Parallel Architecture and Compilation Techniques (PACT 2007) DA - 2007/9// DO - 10.1109/pact.2007.4336201 PB - IEEE SN - 0769529445 9780769529448 UR - http://dx.doi.org/10.1109/pact.2007.4336201 DB - Crossref ER - TY - JOUR TI - Frequency Sensitivity and Electromechanical Propagation Simulation Study in Large Power Systems AU - Tsai, Shu-Jen AU - Zhang, Li AU - Phadke, Arun G. AU - Liu, Yilu AU - Ingram, Michael R. AU - Bell, Sandra C. AU - Grant, Ian S. AU - Bradshaw, Dale T. AU - Lubkeman, David AU - Tang, Le T2 - IEEE Transactions on Circuits and Systems I: Regular Papers AB - A global view of power system's frequency behavior opens up a new window for analyzing system's dynamics. With the aid of global positioning system, measurements from different locations would have synchronous time; therefore a system-wide observation and analysis would be possible. As part of the US-wide power frequency monitoring network project this paper focus on simulation study results of power frequency dynamics of the Eastern U.S. system. The study assesses the frequency measurement accuracy needed to observe frequency dynamics from events such as remote generation drops. Electromechanical-wave propagation phenomena during system disturbances have been observed. The speeds of electromechanical-wave propagation in different areas of the U.S. systems were estimated and their characteristics were discussed. DA - 2007/8// PY - 2007/8// DO - 10.1109/tcsi.2007.902542 VL - 54 IS - 8 SP - 1819-1828 J2 - IEEE Trans. Circuits Syst. I OP - SN - 1057-7122 UR - http://dx.doi.org/10.1109/tcsi.2007.902542 DB - Crossref KW - electromechanical-wave propagation KW - power-system frequency KW - system dynamics KW - wide-area measurements (WAMs) ER - TY - JOUR TI - Some Analysis in Distributed MIMO Systems AU - Dai, Huaiyu AU - Zhang, Hongyuan AU - Zhou, Quan T2 - Journal of Communications AB - The predicted capacity gain of a traditional co- located MIMO system is often severely limited in realistic propagation scenarios, especially when the number of antennas becomes large. Recently, a generalized paradigm for multiple-antenna communications, distributed MIMO, is proposed as a remedy. In this paper, through asymptotic large-system analysis, we provide solid justifications on the advantages of distributed MIMO over co-located MIMO when communication channels are subject to spatial correlation and shadow fading. We also exploit inherent macrodiversity in distributed MIMO to devise a cost- effective link adaptation scheme that achieves significant performance gain. DA - 2007/5/1/ PY - 2007/5/1/ DO - 10.4304/jcm.2.3.43-50 VL - 2 IS - 3 J2 - JCM OP - SN - 1796-2021 UR - http://dx.doi.org/10.4304/jcm.2.3.43-50 DB - Crossref ER - TY - RPRT TI - Load Composition Data AU - Chassin, D.P. AU - Lu, N. A3 - Pacific Northwest National Laboratory DA - 2007/// PY - 2007/// M1 - PNNL-SA-57496 PB - Pacific Northwest National Laboratory SN - PNNL-SA-57496 ER - TY - RPRT TI - Composite load model evaluation AU - Lu, N. AU - Qiao, A. A3 - Pacific Northwest National Laboratory DA - 2007/// PY - 2007/// M1 - PNNL-16916 PB - Pacific Northwest National Laboratory SN - PNNL-16916 ER - TY - CONF TI - Transparent control independence (TCI) AU - Al-Zawawi, Ahmed S. AU - Reddy, Vimal K. AU - Rotenberg, Eric AU - Akkary, Haitham H. T2 - the 34th annual international symposium AB - Superscalar architectures have been proposed that exploit control independence, reducing the performance penalty of branch mispredictions by preserving the work of future misprediction-independent instructions. The essential goal of exploiting control independence is to completely decouple future misprediction-independent instructions from deferred misprediction-dependent instructions. Current implementations fall short of this goal because they explicitly maintain program order among misprediction-independent and misprediction-dependent instructions. Explicit approaches sacrifice design efficiency and ultimately performance. C2 - 2007/// C3 - Proceedings of the 34th annual international symposium on Computer architecture - ISCA '07 DA - 2007/// DO - 10.1145/1250662.1250717 PB - ACM Press SN - 9781595937063 UR - http://dx.doi.org/10.1145/1250662.1250717 DB - Crossref ER - TY - CONF TI - Inherent Time Redundancy (ITR): Using Program Repetition for Low-Overhead Fault Tolerance AU - Reddy, Vimal AU - Rotenberg, Eric T2 - 37th Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN'07) AB - A new approach is proposed that exploits repetition inherent in programs to provide low-overhead transient fault protection in a processor. Programs repeatedly execute the same instructions within close time periods. This can be viewed as a time redundant re-execution of a program, except that inputs to these inherent time redundant (ITR) instructions vary. Nevertheless, certain microarchitectural events in the processor are independent of the input and only depend on the program instructions. Such events can be recorded and confirmed when ITR instructions repeat. In this paper, we use ITR to detect transient faults in the fetch and decode units of a processor pipeline, avoiding costly approaches like structural duplication or explicit time redundant execution. C2 - 2007/6// C3 - 37th Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN'07) DA - 2007/6// DO - 10.1109/dsn.2007.59 PB - IEEE SN - 0769528554 UR - http://dx.doi.org/10.1109/dsn.2007.59 DB - Crossref ER - TY - JOUR TI - Thermionic power generation at high temperatures using SiGe∕Si superlattices AU - Vashaee, Daryoosh AU - Shakouri, Ali T2 - Journal of Applied Physics AB - Recent studies have predicted that heterostructure superlattices can enhance the effective thermoelectric power factor significantly through selective emission of hot carriers via thermionic emission. Here, we study the potential of SiGe∕Si superlattices for power generation at high temperatures. A detailed theory based on Boltzmann transport equation is developed which takes into account multiple valleys. We show that thermionic emission provides only a modest improvement in the power factor. This is due to the fact that SiGe is a multivalley semiconductor and it has a large density of states. With reasonable dopings, Fermi energy in SiGe alloy is very close to the band minimum so that the symmetry of the differential conductivity does not change very much with small barrier superlattices. Particularly at high temperatures when the thermal spread of the carriers is much larger than the Fermi energy in the band, superlattice energy filtering is not effective. DA - 2007/3// PY - 2007/3// DO - 10.1063/1.2645607 VL - 101 IS - 5 SP - 053719 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2645607 DB - Crossref ER - TY - JOUR TI - Early upregulation of iNOS mRNA expression and increase in NO metabolites in pressurized renal epithelial cells AU - Broadbelt, Nalini V. AU - Stahl, Peter J. AU - Chen, Jie AU - Mizrahi, Moshe AU - Lal, Amit AU - Bozkurt, Alper AU - Poppas, Dix P. AU - Felsen, Diane T2 - American Journal of Physiology-Renal Physiology AB - Pressure is an important physiological regulator, but under abnormal conditions it may be a critical factor in the onset and progression of disease in many organs. In vivo, proximal tubular epithelial cells are subjected to pressure as a result of ureteral obstruction, which may influence the production of nitric oxide (NO), a ubiquitous multifunctional cytokine. To directly explore the effect of pressure on the expression and activity of NO synthase (NOS) in cultured proximal tubular epithelial cells, a novel pressure apparatus was developed. Cells were subjected to pressures of 20–120 mmHg over time (5 min-72 h). RT-PCR demonstrated an increase in inducible NOS (iNOS) and sGC, while endothelial NOS remained unchanged. Real-time PCR (qPCR) confirmed an earlier induction of iNOS transcript subjected to 60 mmHg compared with cytokine mix. iNOS protein expression was significantly increased following 60 mmHg of pressure for 24 h. Use of nuclear factor-κB inhibitors was shown to prevent the increase in iNOS expression following 60 mmHg for 2 h. NO and cGMP were increased with the application of pressure. The addition of the irreversible iNOS inhibitor (1400W) was shown to prevent this increase. We demonstrate that with the use of a simply designed apparatus, pressure led to an extremely early induction of iNOS and a rapid activation of NOS activity to increase NO and cGMP in proximal tubule epithelial cells. The rapid effects of pressure on iNOS may have important implications in the obstructed kidney. DA - 2007/12// PY - 2007/12// DO - 10.1152/ajprenal.00238.2007 VL - 293 IS - 6 SP - F1877-F1888 J2 - American Journal of Physiology-Renal Physiology LA - en OP - SN - 1931-857X 1522-1466 UR - http://dx.doi.org/10.1152/ajprenal.00238.2007 DB - Crossref KW - unilateral ureteral obstruction KW - nitric oxide KW - cyclic guanosine monophosphate KW - inducible nitric oxide synthase KW - cytokine mix ER - TY - RPRT TI - Load Monitoring CEC/LMTF Load Research Program AU - Huang, Zhenyu AU - Lesieutre, B. AU - Yang, Steve AU - Ellis, A. AU - Meklin, A. AU - Wong, B. AU - Gaikwad, A. AU - Brooks, D. AU - Hammerstrom, Donald J. AU - Phillips, John AU - Kosterev, Dmitry AU - Hoffman, M. AU - Ciniglio, O. AU - Hartwell, R. AU - Pourbeik, P. AU - Maitra, A. AU - Lu, Ning A3 - Office of Scientific and Technical Information (OSTI) AB - ability of the sediments to retard the mobility of any wastes released from grout. The effects of aging on the ability of grout to retain waste must also be understood. Aging of grout can reduce or enhance the ability of the grout to contain waste. Credible predictive modeling of the fate of hazardous constituents in disposed grout for periods of up to 10,000 years would best be performed using comprehensive, coupled hydrologic and chemical reaction codes based on knowledge of the mechanisms that control waste release and mobility. It is not clear yet how soon such codes will be available or which types of waste disposal options they will apply to. In the interim we must be content with simpler and separate models that address individual reactions such as leaching and adsorption. One of these models, the Semi-Infinite Solid Diffusion Leach Model, is a popular release model used to describe the leaching of grouts and other cemented waste forms. Because others have found success in describing laboratory leach experiments with cemented waste forms using this leach model and because it appears likely to err on the conservative side for the Hanford application, we currently endorse the use of this model and its supporting experimental methodology for approximations of grout waste release rates. At the present time it is believed that the leachate from Hanford grout will not change significantly in its chemical nature once the major chemical reactions at the waste-form sediment interface are completed. Also, the range of sediments at Hanford through which the leachate will travel probably will not exhibit widely varying adsorption properties. These sediments are generally alkaline sands and silts containing little organic matter and have low-to-medium cation exchange capacities. Their interaction with the expected leachates from the Hanford grout should not appreciably affect the composition of the major constituents of the leachates. Therefore, the constant Rd adsorption model should be a useful first approximation of the adsorption processes likely to control trace concentrations of waste radionuclides and hazardous inorganic chemicals that may leach into the groundwater. Because the Rd approach is empirical, it does not lend itself to the identification of transport-controlling mechanisms, a key need for gaining credibility in longterm performance assessments. Despite its limitations, the Rd concept is believed to be a practical and useful tool for quantifying the interaction of Hanford grout leachate with Hanford sediments and assessing the mobility of waste species. Unlike waste-form leaching, the research of radionuclide adsorption does not have a programmatic focal point in which standardization of techniques and procedures is occurring. At present we recommend that sever a 1 different types of adsorption experiments be performed, including hatch and column tests. Both types of tests are needed to increase the probability that the deficiencies of each are addressed. The separation of the complex chemical interactions of grout, sediment and groundwater into simple leaching and adsorption processes for ease of experimentation and modeling is under question. Few experimenters have performed combined tests involving the waste form, sediment and leaching solution though such a combination represents the actual disposal scheme for Hanford grout. Consequently, investigations have been initiated at PNL that are intended to lead to the development of test procedures and methods of data analysis for such three-component tests. Until the controlling chemical processes are identified in the combined tests, detailed characterization of the starting materials (grout, sediment, and groundwater) and resulting products (leached grout, reacted sediment and leachate) is believed necessary. The combined tests should be used to evaluate the usefulness of the separate tests as well as to demonstrate the performance of disposed grout. Once controlling mechanisms are identified and coupled conceptual models and codes are available, many of the separate leaching and adsorption tests and detailed characterization of materials can be abandoned. Preliminary results of a combined test have been obtained and the test is continuing. In the test, a block of grout containing radioactive Hanford Facilities Waste (HFW) is supported on a layer of Hanford sediment inside a plexiglass cylinder (column). Additional sediment is packed around the grout block and fills the rema1n1ng void space at the top of the column. Hanford groundwater is pumped into the bottom of the column where it flows through the bottom layer of sediment, around the grout, and through the upper layer of sediment. The effluent is collected in a sealed container to minimize evaporation and loss or gain of CO{sub 2}. The effluent is analyzed for (a) Eh, pH, and alkalinity, (b) major cations and selected trace metals, (c) major anions, inorganic carbon and organic carbon, and (d) radionuclide content. The data collected to date show that the effluent is buffered at a pH between 8.0 and 8.8, whereas the effluent from a companion experiment (grout only, no sediment) rose quickly to the 11-12 pH range. The combined test appears to show net precipitation in the test column, whereas the grout-only test is showing net dissolution. The nitrite concentration rapidly and substantially increased in the grout-only test effluent but has not been measurable in the combined test effluent. The grout-only test effluent contained about five times the level of dissolved organic carbon that the combined test effluents showed. To date, no measurable quantities of radionuclides are present in the effluents from the combined test. The activity of {sup 137}]Ccs and {sup 85}Sr in the effluents in the grout-only test rose rapidly to steady-state values. Recause previous batch adsorption tests and a column adsorption test showed strong adsorption of these radionuclides, the radionuclide data to date are as expected. As part of the Hanford Grout Technology Program, numerous two-component leach tests have been underway since January 1qss. Two of these tests, the ANS 1n.1 test and the static test, are also showing leachates with distinctly different chemistries. A key to the differences seems to be the supply of HCO{sub 3}{sup -} or dissolved CO{sub 2} in the system. 8ifferences in pH were also observed. The pH of the ANS 16.1 system stabilized at approximately 8.5 whereas the pH of the static system rose to 12.0. At the higher pH, calcium and magnesium apparently precipitated, probably as carbonate minerals. It seems quite likely that grouts disposed in Hanford sediments will react with the carbonate-rich groundwaters to form calcite and carbonate-rich solids similar to those found in ancient artifacts from Cyprus and Greece. Whether these reactions would form protective layers on the grout that impede leaching is uncertain. Additional study is needed to explain the differences in these leach tests as well as the differences in the combined and grout-only tests. This report discusses numerous activites that will be performed in conjunction with the experiments just described. These activities include: 1) detailed mineralogic, radiochemical and total chemical characterization of the grout and sediment versus distance from the interface, 2) detailed analysis of solution data by equilibrium thermodynamic codes to identify possible solid phase solubility controls and 3) mathematical analyses of the combined test results by mass transport theory ("waste package") models deschbed in existing literature. Recommendations for future study include 1) additional development of combined tests under saturated and partially saturated conditions 2) an evaluation of whether CO{sub 2} gas will be supplied to the disposed grout monolith at a rate that maintains CO{sub 2} equilibrium conditions at the grout-sediment interface 3) development of methods to supply CO{sub 2} at an adequate rate should CO{sub 2} equilibrium prove to be a controlling factor and 4) testing of artificially aged grout for leaching properties. Until the mechanisms of leaching and the subsequent interactions with sediments are better understood, it is difficult to suggest a specific direction for the development of combined tests. It is our hope that the analyses yet to be performed on the separate leaching and adsorption tests and the combined test will provide knowledge on controlling mechanisms and shed light on what parameters should be considered as most important in designing experiments to provide the data upon which long-term performance assessments are based. In spite of the current lack of understanding of the interactions among grout, sediment, and groundwater, and considering that this effort was not started until January 1985, significant progress has been made toward the establishment of testing methodologies for assessing the long-term performance of Hanford grout. DA - 2007/11/30/ PY - 2007/11/30/ DO - 10.2172/937047 PB - Office of Scientific and Technical Information (OSTI) UR - http://dx.doi.org/10.2172/937047 DB - Crossref ER - TY - CHAP TI - Dynamic modeling in solid-oxide fuel cells controller design AU - Lu, N. AU - Li, Q. AU - Sun, X. AU - Khaleel, M. A. AU - Ieee T2 - 2007 Ieee Power Engineering Society General Meeting, Vols 1-10 PY - 2007/// SP - 234-+ PB - SE - UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000251345400048&KeyUID=WOS:000251345400048 ER - TY - CHAP TI - Controller design of power quality-improving appliances AU - Harnmerstrom, D. J. AU - Zhou, N. AU - Lu, N. AU - Ieee T2 - 2007 Ieee Power Electronics Specialists Conference, Vols 1-6 PY - 2007/// SP - 1164-1169 PB - SE - UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000252375202020&KeyUID=WOS:000252375202020 ER - TY - CONF TI - The capacitive micromachined ultrasonic transducer (CMUT) as a chem/bio sensor AU - Khuri-Yakub, B.T. AU - Park, K.K. AU - Lee, H.J. AU - Yaralioglu, G. AU - Ergun, A.S. AU - Oralkan, Ö. AU - Kupnik, M. AU - Quate, C.F. AU - Braun, T. AU - Lang, H. AU - Hegner, M. AU - Ramseyer, J. AU - Gerber, C. AU - Gimzewski, J. C2 - 2007/// C3 - Proceedings of the IEEE Ultrasonics Symposium DA - 2007/// SP - 472–475 ER - TY - CONF TI - Trench-isolated CMUT arrays with a supporting frame: characterization and imaging results AU - Zhuang, X. AU - Wygant, I. O. AU - Lin, D. S. AU - Kupnik, M. AU - Oralkan, Ö. AU - Khuri-Yakub, B. T. C2 - 2007/// C3 - Proceedings of the IEEE Ultrasonics Symposium DA - 2007/// SP - 507–510 ER - TY - CONF TI - A co-axial scanning acoustic and photoacoustic microscope AU - Vaithilingam, S. AU - Ma, T.J. AU - Furukawa, Y. AU - Zerda, A. AU - Oralkan, Ö. AU - Kamaya, A. AU - Keren, S. AU - Gambhir, S.S. AU - Jeffrey, R.B., Jr. AU - Khuri-Yakub, B.T. C2 - 2007/// C3 - Proceedings of the IEEE Ultrasonics Symposium DA - 2007/// SP - 2413–2416 ER - TY - CONF TI - Molecular Electronics AU - Franzon, P. AU - Amsinck, C. AU - DiSPigna, N.H. AU - Nackashi, D. AU - Sonkusale, S. C2 - 2007/6// C3 - 2nd IEEE International Workshop on advances in sensors and interfaces DA - 2007/6// ER - TY - CONF TI - Application and Design Exploration for 3D Integrated Circuits AU - Franzon, Paul D. AU - Davis, William Rhett AU - Steer, Michael B. AU - Hao, Hua AU - Lipa, Steven AU - Luniya, Sonali AU - Mineo, Christopher AU - Oh, Julie AU - Sule, Ambirish AU - Thorolfsson, Thor C2 - 2007/9// C3 - VLSI Multi-level Interconnect Conference DA - 2007/9// ER - TY - CONF TI - A quantum dot memory cell based on spin polaron formation AU - Enaya, Hani AU - Semenov, Yuriy G. AU - Kim, Ki Wook AU - Zavada, John M. T2 - 2007 International Semiconductor Device Research Symposium AB - A theoretical study that explores the feasibility of a new spin-based nonvolatile memory concept is presented. The active region of the memory cell is a semiconductor quantum dot (QD) sharing an interface with a dielectric ferromagnetic layer (FML). The operating principle of the device is based on the spontaneous magnetic symmetry breaking due to exchange interaction between the magnetic ions in the FML and the spins of the itinerant holes in the QD. As a result, the formation of bistable states is possible at some conditions. We find the parameters window that admits the bistability and consider its lifetime (bit retention time) as the QD is scaled down. The analysis is carried out for two different QD materials: a non-magnetic (NM) QD and a diluted magnetic semiconductor (DMS) QD. In addition, two different designs are considered: a QD sharing an interface with the FML and a QD embedded in the FML. The proposed device is ready for scalability, potentially down to a few hole level by reducing the size of the QD, and it promises high integration density since only two terminals are used for device operation. C2 - 2007/12// C3 - 2007 International Semiconductor Device Research Symposium DA - 2007/12// DO - 10.1109/isdrs.2007.4422256 PB - IEEE SN - 9781424418916 9781424418923 UR - http://dx.doi.org/10.1109/isdrs.2007.4422256 DB - Crossref ER - TY - CONF TI - SiGe vs. CMOS for 60-100 GHz: technology, circuits, packages, and systems AU - Floyd, B. AU - Gaucher, B. AU - Reynolds, S. AU - Valdes-Garcia, A. AU - Pfeiffer, U. AU - Liu, D. AU - Grzyb, J. AU - Hoivik, N. AU - Jagannathan, B. C2 - 2007/3// C3 - Government Microcircuit Applications Conference Digital Papers DA - 2007/3// SP - 31–34 ER - TY - CONF TI - Flexible Low Power Probability Density Estimation Unit For Speech Recognition AU - Pazhayaveetil, Ullas AU - Chandra, Dhruba AU - Franzon, Paul T2 - 2007 IEEE International Symposium on Circuits and Systems AB - This paper describes the hardware architecture for a flexible probability density estimation unit to be used in a large vocabulary speech recognition system, and targeted for mobile platforms. The speech recognition system is based on hidden Markov models and consists of two computationally intensive parts - the probability density estimation using Gaussian distributions, and the Viterbi decoding. The power hungry nature of these computations prevents porting the application successfully to mobile devices. We have designed a flexible probability estimation unit that is both power efficient and meets real time requirements while being flexible enough to handle emerging speech recognition techniques. The flexible nature of the design allows it to utilize emerging power and computation reduction techniques (at the algorithm level) to achieve up to an 80% power reduction as compared to conventional designs C2 - 2007/5// C3 - 2007 IEEE International Symposium on Circuits and Systems DA - 2007/5// DO - 10.1109/iscas.2007.378206 PB - IEEE SN - 1424409209 1424409217 UR - http://dx.doi.org/10.1109/iscas.2007.378206 DB - Crossref ER - TY - CONF TI - Hardware Architecture of a Parallel Pattern Matching Engine AU - Yadav, Meeta AU - Venkatachaliah, Ashwini AU - Franzon, Paul D. T2 - 2007 IEEE International Symposium on Circuits and Systems AB - Several network security and QoS applications require detecting multiple string matches in the packet payload by comparing it against predefined pattern set. This process of pattern matching at line speeds is a memory and computation intensive task. Hence, it requires dedicated hardware algorithms. This paper describes the hardware architecture of a parallel, pipelined pattern matching engine that uses trie based pattern matching algorithmic approach. The algorithm optimizes pattern matching process through two key innovations of parallel pattern matching using incoming content filter and multiple character matching using trie pruning. The hardware implementation is capable of performing at line-speeds and handle traffic rates up to OC-192, the underlying architecture allows for multiple patterns to be detected and for the system to gracefully recover from a failed partial match, the throughput of the system does not degrade with the increase in the number of patterns or the length of the patterns to be matched. The solution described outperforms most current implementations in terms of speed and memory requirement and outperforms TCAM based solutions in terms of power consumption, area, and cost while remaining competitive in terms of throughput and update times. The complete Snort rule set (2005 release) and VoIP RFC were used to validate our performance and achieve a throughput of 12Gbps with 6KBytes of content filter memory and 0.3 MBytes of total memory for Snort and 0.5KBytes of filter memory and 12KBytes of total memory for SIP. C2 - 2007/5// C3 - 2007 IEEE International Symposium on Circuits and Systems DA - 2007/5// DO - 10.1109/iscas.2007.378482 PB - IEEE SN - 1424409209 1424409217 UR - http://dx.doi.org/10.1109/iscas.2007.378482 DB - Crossref ER - TY - CONF TI - FreePDK: An Open-Source Variation-Aware Design Kit AU - Stine, James E. AU - Castellanos, Ivan AU - Wood, Michael AU - Henson, Jeff AU - Love, Fred AU - Davis, W. Rhett AU - Franzon, Paul D. AU - Bucher, Michael AU - Basavarajaiah, Sunil AU - Oh, Julie AU - Jenkal, Ravi T2 - 2007 IEEE International Conference on Microelectronic Systems Education AB - This paper discusses an open source, variation aware Process Design Kit (PDK), based on Scalable CMOS design rules, down to 45nm, for use in VLSI research, education and small businesses. This kit includes all the necessary layout design rules and extraction command decks to capture layout dependent systematic variation and perform statistical circuit analysis. The kit also includes a standard cell and pad library with the necessary support files to enable full chip place and route and verification for System on Chip designs. Test chips designed with this PDK are designed in such a way so that they can be fabricated by fabrication facilities allowing validation of the design rules so that the rules may be used in future multi-project runs and design contests. C2 - 2007/6// C3 - 2007 IEEE International Conference on Microelectronic Systems Education (MSE'07) CY - San Diego, CA DA - 2007/6// PY - 2007/6/3/ DO - 10.1109/mse.2007.44 PB - IEEE SN - 076952849X UR - http://dx.doi.org/10.1109/mse.2007.44 DB - Crossref ER - TY - CONF TI - Design for 3D Integration and Applications AU - Franzon, Paul AU - Davis, William Rhett AU - Steer, Michael B. AU - Hao, Hua AU - Lipa, Steven AU - Luniya, Sonali AU - Mineo, Christopher AU - Oh, Julie AU - Sule, Ambirish AU - Thorolfsson, Thor AU - al. T2 - 2007 International Symposium on Signals, Systems and Electronics AB - 3D stacking and integration can provide system advantages equivalent to up to two technology nodes of scaling. This paper explores application drivers and computer aided design (CAD) for 3D ICs. C2 - 2007/7// C3 - 2007 International Symposium on Signals, Systems and Electronics CY - Montreal, Quebec, Canada DA - 2007/7// PY - 2007/7/30/ DO - 10.1109/issse.2007.4294463 SP - 263–266, PB - IEEE SN - 1424414482 1424414490 UR - http://dx.doi.org/10.1109/issse.2007.4294463 DB - Crossref ER - TY - CONF TI - Design Considerations and Benefits of Three-Dimensional Ternary Content Addressable Memory AU - Oh, Eun Chu AU - Franzon, Paul D. T2 - 2007 IEEE 29th Custom Integrated Circuits Conference AB - Three dimensional (3D) ternary content addressable memory (TCAM) has been designed in a 0.18 μm fully depleted silicon on insulator (FD SOI) 3D IC process. This paper demonstrates that a 3D TCAM with three tiers can achieve 40% matchline capacitance reduction and 21% power reduction compared to a TCAM in a conventional single-tier process. This paper also discusses design considerations of 3D TCAM including partitioning methods for multiple tiers and layout methods of interconnects. C2 - 2007/9// C3 - 2007 IEEE Custom Integrated Circuits Conference DA - 2007/9// DO - 10.1109/cicc.2007.4405801 PB - IEEE SN - 9781424407866 UR - http://dx.doi.org/10.1109/cicc.2007.4405801 DB - Crossref ER - TY - CONF TI - System level Validation of Improved IO Buffer Behavioral Modeling Methodology Based on IBIS AU - Varma, Ambrish AU - Steer, Michael AU - Franzon, Paul T2 - 2007 IEEE Electrical Performance of Electronic Packaging AB - System level simulation and validation of a new macromodeling methodology based on IBIS (Input/Output Buffer Information Specification) models is presented. Enhancements of the black-box techniques discussed in [1] are discussed. The proposed macromodel is circuit based and can be customized by model makers or users. The new macromodel produces models that can be simulated accurately for Simultaneous Switching Noise (SSN). To demonstrate the solution, a CMOS voltage-mode driver circuit and a MICRON DDR2 driver are simulated using real life package models and compared with equivalent circuits created with IBIS models of the same drivers. C2 - 2007/10// C3 - 2007 IEEE Electrical Performance of Electronic Packaging DA - 2007/10// DO - 10.1109/epep.2007.4387200 PB - IEEE SN - 9781424408832 UR - http://dx.doi.org/10.1109/epep.2007.4387200 DB - Crossref ER - TY - CONF TI - System Design for 3D Multi-FPGA Packaging AU - Thorolfsson, Thorlindur AU - Franzon, Paul D. T2 - 2007 IEEE Electrical Performance of Electronic Packaging AB - 3D stacking and integration can provide tremendous advantages to electronic systems. This paper explores the system-level considerations such as layout, routing and IO in the design of 3D multi-FPGA packaging, along with their architectural implications. C2 - 2007/10// C3 - 2007 IEEE Electrical Performance of Electronic Packaging DA - 2007/10// DO - 10.1109/epep.2007.4387152 PB - IEEE SN - 9781424408832 UR - http://dx.doi.org/10.1109/epep.2007.4387152 DB - Crossref ER - TY - CONF TI - Flexible transducer arrays with through-wafer electrical interconnects based on trench refilling with PDMS AU - Zhuang, Xuefeng AU - Lin, Der-Song AU - Oralkan, Omer AU - Khuri-Yakub, Butrus T. T2 - 2007 IEEE 20th International Conference on Micro Electro Mechanical Systems (MEMS) AB - This paper reports on a method to fabricate flexible onedimensional (1D) and two-dimensional (2D) micromachined transducer arrays that are electrically connected to flip-chip bond pads on the back side of the array. In our case, the transducers are capacitive micromachined ultrasonic transducers (CMUT) intended for medical ultrasound imaging. For ultrasound imaging, flexible arrays conform to the body part being imaged. Flexible arrays are also desired for certain catheter and fixed-focus array geometries. Electrical connection to bond pads on the back side of the array is provided for flip-chip bonding to an integrated circuit or flexible PCB. The arrays are made flexible by etching through-wafer trenches and filling the trenches with polydimethylsiloxane (PDMS). The flexibility of the substrate is demonstrated by wrapping it around a needle tip with a radius of 650 μm (French catheter size of 4). C2 - 2007/1// C3 - 2007 IEEE 20th International Conference on Micro Electro Mechanical Systems (MEMS) DA - 2007/1// DO - 10.1109/memsys.2007.4433016 PB - IEEE UR - http://dx.doi.org/10.1109/memsys.2007.4433016 DB - Crossref ER - TY - CONF TI - Design of HIFU CMUT Arrays for Treatment of Liver and Renal Cancer AU - Wong, Serena H. AU - Ergun, Arif Sanli AU - Yaralioglu, Goksen G. AU - Oralkan, Omer AU - Kupnik, Mario AU - Pauly, Kim Butts AU - Khuri-Yakub, B. T. T2 - 6TH INTERNATIONAL SYMPOSIUM ON THERAPEUTIC ULTRASOUND AB - We present the development of a capacitive micromachined ultrasonic transducer (CMUT) array for noninvasive focused ultrasound ablation of lower abdominal cancers under MR‐guidance. While piezoelectric transducers have been traditionally used for HIFU, recent advances in CMUT design have made them highly competitive. Not only are CMUTs cost effective, they allow fabrication flexibility and advantages in efficiency and bandwidth. Current imaging CMUTs have shown capability of HIFU operation through high power and continuous wave operation. In this paper, we will present the development of CMUT membranes designed specifically for HIFU. These membranes are piston‐like membranes fabricated by placing a thick layer of silicon or gold at the center of the membrane. The width of the piston layer is usually 60–85% of the membrane width and allows the membrane mass and elasticity to be controlled independently. It also increases the average displacement and average output pressure of the membrane. We patterned these CMUT membranes into an 8 element, 3.5 cm concentric array. We simulated the heating patterns of this array to show it is capable of producing lesions of 5 mm in diameter within 20–30 seconds, which can be imaged using our MR detection software. C2 - 2007/// C3 - AIP Conference Proceedings DA - 2007/// DO - 10.1063/1.2744251 PB - AIP UR - http://dx.doi.org/10.1063/1.2744251 DB - Crossref ER - TY - CONF TI - 2C-3 An Integrated Circuit with Transmit Beamforming and Parallel Receive Channels for 3D Ultrasound Imaging: Testing and Characterization AU - Wygant, I. O. AU - Jamal, N. AU - Lee, H. J. AU - Nikoozadeh, A. AU - Zhuang, X. AU - Oralkan, O. AU - Ergun, A. S. AU - Karaman, M. AU - Khuri-Yakub, B. T. T2 - 2007 IEEE Ultrasonics Symposium Proceedings AB - The cost and complexity of medical ultrasound imaging systems can be reduced by integrating the transducer array with an integrated circuit (IC). By incorporating some of the system's front-end electronics into an IC, bulky cables and costly system electronics can be eliminated. Here we present an IC for 3D intracavital imaging that requires few electrical connections but uses a large fraction of a 16times16-element 2D transducer array to transmit focused ultrasound. To simplify the receive and data acquisition electronics, only the 32 elements along the array diagonals are used as receivers. The IC provides a preamplifier for each receiving element. Each of the 224 transmitting elements is provided an 8-bit shift register, a comparator, and a 25-V pulser. To transmit, a global counter is incremented from 1 to 224; each pulser fires when its stored register value is equal to the global count value. Electrical testing of the fabricated IC shows that it works as designed. The IC was flip-chip bonded to a two-dimensional capacitive micromachined ultrasonic transducer (CMUT) array. A two-dimensional image of a wire target phantom was acquired. C2 - 2007/10// C3 - 2007 IEEE Ultrasonics Symposium Proceedings DA - 2007/10// DO - 10.1109/ultsym.2007.20 PB - IEEE SN - 9781424413836 9781424413843 UR - http://dx.doi.org/10.1109/ultsym.2007.20 DB - Crossref ER - TY - CONF TI - 10C-6 Fully Integrated CMUT-Based Forward-Looking Intracardiac Imaging for Electrophysiology AU - Nikoozadeh, A. AU - Wygant, I.O. AU - Lin, Der-Song AU - Oralkan, O. AU - Ergun, A.S. AU - Thomenius, K. AU - Dentinger, A. AU - Wildes, D. AU - Akopyan, G. AU - Shivkumar, K. AU - Mahajan, A. AU - Stephens, D.N. AU - Sahn, D. AU - Khuri-Yakub, P.T. T2 - 2007 IEEE Ultrasonics Symposium AB - Minimally invasive percutaneous electrophysiological mapping of the heart chambers is becoming a standard procedure to diagnose and treat cardiac arrhythmias. Due to advances in technology that enable small feature sizes and a high level of integration, non-fluoroscopic intracardiac imaging is attracting more attention to better guide electrophysiologal (EP) interventions. In this effort, we are developing a forward-looking intracardiac ultrasound imaging catheter, which is also equipped with several EP electrode sensor bands and a metal RF ablation tip enclosure. A 24-element fine-pitch (63 mum) 1-D array, based on capacitive micromachined ultrasonic transducer (CMUT) technology, has been fabricated for high-frame-rate imaging. Through-wafer vias are incorporated in the device to connect the signal and ground electrodes to the flip-chip bond pads on the backside of the array. The total footprint of the array measures 1.73 mm x 1.27 mm. Also a custom-designed integrated circuit (IC) has been fabricated to be closely integrated with the CMUT array for improved SNR. This IC comprises some of the important front- end electronics of an ultrasound imaging system. It measures 2 mm x 2 mm and is composed of 24 individual transmit/receive blocks. The transmit circuitry is capable of delivering 25 -V unipolar pulses. The receive circuitry includes a transimpedance preamplifier followed by a line driver buffer. A CMUT array was flip-chip bonded directly on to the IC for initial testing. All of the 24 elements of the array and the IC are functional. Array uniformity was tested by measuring the resonant frequency in air. A standard deviation of 0.37 percent was measured around the mean value of 17.9 MHz. The same array operates at 9.2 MHz in immersion with a 104 percent fractional bandwidth. Imaging performance of the described front-end was tested on a commercial phantom and also in ex- vivo environment on an isolated perfused rabbit heart (Langendorfl). The final goal is to integrate the CMUT array and the front-end electronics at the tip of a 10 -F catheter. A flexible printed circuit board (PCB) has been designed and the first sub-assembly is ready for cable attachment and final catheter integration. C2 - 2007/10// C3 - 2007 IEEE Ultrasonics Symposium Proceedings DA - 2007/10// DO - 10.1109/ultsym.2007.230 PB - IEEE SN - 9781424413836 9781424413843 UR - http://dx.doi.org/10.1109/ultsym.2007.230 DB - Crossref KW - forward looking KW - electrophysiology KW - intracardiac echo KW - guidance KW - ultrasound KW - capacitive micromachined ultrasonic transducers KW - CMUT ER - TY - CONF TI - A Two-Time-Scale Redesign for Robust Stabilization and Performance Recovery of Uncertain Nonlinear Systems AU - Chakrabortty, Aranya AU - Arcak, Murat T2 - 2007 American Control Conference AB - In this paper we propose a robust redesign technique which recovers the trajectories of a nominal control design in the presence of additive input uncertainties. We design a high-gain filter and employ the fast variables arising from this filter in the feedback control law to cancel the effect of the uncertainties in the plant. Using singular perturbation theory we prove that the trajectories of the redesigned system approach those of the nominal system when the filter gain is increased. We illustrate the redesign by applying it to two physically motivated examples. C2 - 2007/7// C3 - 2007 American Control Conference DA - 2007/7// DO - 10.1109/acc.2007.4282348 PB - IEEE SN - 1424409888 1424409896 UR - http://dx.doi.org/10.1109/acc.2007.4282348 DB - Crossref ER - TY - CONF TI - Performance recovery of power systems with unknown parameters and faults AU - Chakrabortty, Aranya AU - Scholtz, Ernst AU - Arcak, Murat T2 - 2007 46th IEEE Conference on Decision and Control AB - In this paper we apply the time-scale separation design developed by Chakrabortty and Arcak (2007) for robust stabilization and performance recovery to power systems with unknown load power demands and unexpected line outages. We estimate the unknown over a fast time-scale using a high-gain filter and then employ this estimate to cancel the unknown so that over a slower time-scale the trajectories of the closed loop system approach those of the nominal system. We illustrate the effectiveness of the design in eliminating the possibilities of a Hopf bifurcation and subsequent voltage collapse in a single machine infinite bus (SMIB) power system. We then demonstrate the application of the design to fault recovery of a classical 9-bus system. C2 - 2007/// C3 - 2007 46th IEEE Conference on Decision and Control DA - 2007/// DO - 10.1109/cdc.2007.4434119 PB - IEEE SN - 9781424414970 UR - http://dx.doi.org/10.1109/cdc.2007.4434119 DB - Crossref ER - TY - CONF TI - A Three-time-scale redesign for robust stabilization and performance recovery of nonlinear systems with input uncertainties AU - Chakrabortty, Aranya AU - Arcak, Murat T2 - 2007 46th IEEE Conference on Decision and Control AB - In this paper we propose a robust redesign technique which recovers the trajectories of a nominal control design in the presence of input uncertainties. We design two sets of high gain filters - the first to estimate the input uncertainty over a fast time-scale, and the second to force this estimate to converge to the nominal input on an intermediate time- scale. Using singular perturbation theory we prove that the trajectories of the resulting three-time scale redesigned system approach those of the nominal system when the filter gains are increased. C2 - 2007/// C3 - 2007 46th IEEE Conference on Decision and Control DA - 2007/// DO - 10.1109/cdc.2007.4434118 PB - IEEE SN - 9781424414970 UR - http://dx.doi.org/10.1109/cdc.2007.4434118 DB - Crossref ER - TY - CHAP TI - Micromachined ultrasonic transducers AU - Khuri-Yakub, B.T. AU - Oralkan, Ö. AU - Kupnik, M. T2 - McGraw-Hill Yearbook of Science and Technology 2008 PY - 2007/// SP - 207–210 PB - McGraw-Hill Professional ER - TY - CONF TI - 2-Gbps Uncompressed HDTV Transmission over 60-GHz SiGe Radio Link AU - Katayama, Y. AU - Haymes, C. AU - Nakano, D. AU - Beukema, T. AU - Floyd, B. AU - Reynolds, S. AU - Pfeiffer, U. AU - Gaucher, B. AU - Schleupen, K. T2 - 2007 4th IEEE Consumer Communications and Networking Conference AB - We report a proof-of-concept demonstration of 2- Gbps uncompressed HDTV transmission using a 60-GHz SiGe radio chipset. We took a single-carrier approach with a usual DQPSK modulation scheme, assuming an LOS environment, and implemented the system with FPGAs. At the same time, in order to take care of more frequent sync/burst errors in high-data-rate single-carrier approaches, we equipped the baseband with effi- cient random/packet error recovery and symbol-timing recovery with an effective interpolation method. As a result, a clear and crisp image was obtained in the end-to-end transmission. I. INTRODUCTION C2 - 2007/1// C3 - 2007 4th IEEE Consumer Communications and Networking Conference DA - 2007/1// DO - 10.1109/ccnc.2007.10 SP - 12-16 PB - IEEE SN - 1424406676 UR - http://dx.doi.org/10.1109/ccnc.2007.10 DB - Crossref ER - TY - CONF TI - Silicon Millimeter-Wave Radio Circuits at 60-100 GHz AU - Floyd, B. AU - Pfeiffer, U. AU - Reynolds, S. AU - Valdes-Garcia, A. AU - Haymes, C. AU - Katayama, Y. AU - Nakano, D. AU - Beukema, T. AU - Gaucher, B. AU - Soyuer, M. AU - al., T2 - 2007 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems AB - This paper reviews silicon millimeter-wave radio circuits operating between 60 and 100GHz. Transmitter and receiver chips operating in the 60-GHz ISM band are highlighted, where the packaged chipset has shown data rates as high as 2 Gb/s over 5m for a wireless high-definition video link. In addition, a 60GHz PA with 23dBm output power and a class-E 60GHz PA with >20% peak PAE are reviewed. Finally, 77 and 94GHz downconverters are presented as a basis for an outlook to the performance achievable at these higher frequency bands C2 - 2007/1// C3 - 2007 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems DA - 2007/1// DO - 10.1109/smic.2007.322823 SP - 213-218 PB - IEEE SN - 0780397649 0780397657 UR - http://dx.doi.org/10.1109/smic.2007.322823 DB - Crossref KW - 60 GHz KW - millimeter wave bipolar integrated circuits KW - SiGe KW - V band ER - TY - CONF TI - A Bidirectional RF-Combining 60GHz Phased-Array Front-End AU - Natarajan, Arun AU - Floyd, Brian AU - Hajimiri, Ali T2 - 2007 IEEE International Solid-State Circuits Conference. Digest of Technical Papers AB - A 60GHz RF-combining phased-array front-end is implemented in silicon using a hybrid parallel/series phase-shift approach that reduces the requirements of the on-chip phase shifters. The 4-element array provides for simultaneous illumination of 2 angles of incidence and includes amplitude control and continuous phase adjustment. The front-end NF <6.9dB at 60GHz and the array achieves full spatial coverage with peak-to-null ratio >25dB. It consumes 265mW and occupies 4.6mm 2 . C2 - 2007/2// C3 - 2007 IEEE International Solid-State Circuits Conference. Digest of Technical Papers DA - 2007/2// DO - 10.1109/isscc.2007.373364 SP - 202-204 PB - IEEE SN - 1424408520 1424408539 UR - http://dx.doi.org/10.1109/isscc.2007.373364 DB - Crossref ER - TY - CONF TI - A 15 to 18-GHz Programmable Sub-Integer Frequency Synthesizer for a 60-GHz Transceiver AU - Floyd, Brian A. T2 - 2007 IEEE Radio Frequency Integrated Circuits (RFIC) Symposium AB - A 15 to 18-GHz frequency synthesizer is implemented in 0.13-μm SiGe BiCMOS technology as part of a 60-GHz transceiver chipset. It provides for RF channels of 56.5-64 GHz in 500-MHz steps, and features a phase-rotating multi-modulus divider capable of sub-integer division. Output frequency range from the synthesizer is 15.3 to 18 GHz. The measured RMS phase noise of the synthesizer is 0.9° (1 MHz to 1 GHz integration), while phase noise at 100-kHz and 10-MHz offsets are -90 and -124 dBc/Hz, respectively. Reference spurs are -69 dBc; sub-integer spurs are -65 dBc; and power consumption is 145 mW. C2 - 2007/6// C3 - 2007 IEEE Radio Frequency Integrated Circuits (RFIC) Symposium DA - 2007/6// DO - 10.1109/rfic.2007.380939 SP - 529-532 PB - IEEE SN - 1424405300 UR - http://dx.doi.org/10.1109/rfic.2007.380939 DB - Crossref KW - frequency conversion KW - frequency synthesizers KW - phase interpolation KW - phase-switched divider ER - TY - CONF TI - Second Generation 60-GHz Transceiver Chipset Supporting Multiple Modulations at Gb/s data rates (Invited) AU - Reynolds, Scott AU - Valdes-Garcia, Alberto AU - Floyd, Brian AU - Beukema, Troy AU - Gaucher, Brian AU - Liu, Duixian AU - Hoivik, Nils AU - Orner, Bradley T2 - 2007 IEEE Bipolar/BiCMOS Circuits and Technology Meeting AB - A feature-rich second-generation 60-GHz transceiver chipset is introduced. It integrates dual-conversion superheterodyne receiver and transmitter chains, a sub-integer frequency synthesizer, full programmability from a digital interface, modulator and demodulator circuits to support analog modulations (e.g. MSK, BPSK), as well as a universal I&Q interface for digital modulation formats (e.g. OFDM). Achieved performance includes 6-dB receiver noise figure and 12 dBm transmitter output ldB compression point. Wireless link experiments with different modulation formats for 2-Gb/s real-time uncompressed HDTV transmission are discussed. Additionally, recent millimeter-wave package and antenna developments are summarized and a 60GHz silicon micromachined antenna is presented. C2 - 2007/9// C3 - 2007 IEEE Bipolar/BiCMOS Circuits and Technology Meeting DA - 2007/9// DO - 10.1109/bipol.2007.4351867 SP - 192-197 PB - IEEE SN - 9781424410187 9781424410194 UR - http://dx.doi.org/10.1109/bipol.2007.4351867 DB - Crossref ER - TY - JOUR TI - Finite element modeling and experimental characterization of crosstalk in 1-D CMUT arrays AU - Bayram, Baris AU - Kupnik, Mario AU - Yaralioglu, Goksen AU - Oralkan, Omer AU - Ergun, Arif AU - Lin, Der-song AU - Wong, Serena AU - Khuri-yakub, Butrus T2 - IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control AB - Crosstalk is the coupling of energy between the elements of an ultrasonic transducer array. This coupling degrades the performance of transducers in applications such as medical imaging and therapeutics. In this paper, we present an experimental demonstration of guided interface waves in capacitive micromachined ultrasonic transducers (CMUTs). We compare the experimental results to finite element calculations using a commercial package (LS-DYNA) for a 1-D CMUT array operating in the conventional and collapsed modes. An element in the middle of the array was excited with a unipolar voltage pulse, and the displacements were measured using a laser interferometer along the center line of the array elements immersed in soybean oil. We repeated the measurements for an identical CMUT array covered with a 4.5-mum polydimethyl-siloxane (PDMS) layer. The main crosstalk mechanism is the dispersive guided modes propagating in the fluid-solid interface. Although the transmitter element had a center frequency of 5.8 MHz with a 130% fractional bandwidth in the conventional operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 2.1 MHz, and had a cut-off frequency of 4 MHz. In the collapsed operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 4.0 MHz, and had a cut-off frequency of 10 MHz. Crosstalk level was lower in the collapsed operation (-39 dB) than in the conventional operation (-24.4 dB). The coverage of the PDMS did not significantly affect the crosstalk level, but reduced the phase velocity for both operation modes. Lamb wave modes, A 0 and S 0 , were also observed with crosstalk levels of -40 dB and -65 dB, respectively. We observed excellent agreement between the finite element and the experimental results DA - 2007/2// PY - 2007/2// DO - 10.1109/tuffc.2007.256 VL - 54 IS - 2 SP - 418-430 J2 - IEEE Trans. Ultrason., Ferroelect., Freq. Contr. OP - SN - 0885-3010 UR - http://dx.doi.org/10.1109/tuffc.2007.256 DB - Crossref ER - TY - JOUR TI - Integration of trench-isolated through-wafer interconnects with 2d capacitive micromachined ultrasonic transducer arrays AU - Zhuang, Xuefeng AU - Ergun, Arif S. AU - Huang, Yongli AU - Wygant, Ira O. AU - Oralkan, Omer AU - Khuri-Yakub, Butrus T. T2 - Sensors and Actuators A: Physical AB - This paper presents a method to provide electrical connection to a 2D capacitive micromachined ultrasonic transducer (CMUT) array. The interconnects are processed after the CMUTs are fabricated on the front side of a silicon wafer. Connections to array elements are made from the back side of the substrate via highly conductive silicon pillars that result from a deep reactive ion etching (DRIE) process. Flip-chip bonding is used to integrate the CMUT array with an integrated circuit (IC) that comprises the front-end circuits for the transducer and provides mechanical support for the trench-isolated array elements. Design, fabrication process and characterization results are presented. The advantages when compared to other through-wafer interconnect techniques are discussed. DA - 2007/7// PY - 2007/7// DO - 10.1016/j.sna.2007.04.008 VL - 138 IS - 1 SP - 221-229 J2 - Sensors and Actuators A: Physical LA - en OP - SN - 0924-4247 UR - http://dx.doi.org/10.1016/j.sna.2007.04.008 DB - Crossref KW - capacitive micromachined ultrasonic transducer (CMUT) KW - trench isolation KW - through-wafer interconnect KW - post-processing KW - flip-chip bonding ER - TY - JOUR TI - Capacitive micromachined ultrasonic transducers for chemical detection in nitrogen AU - Park, K. K. AU - Lee, H. J. AU - Yaralioglu, G. G. AU - Ergun, A. S. AU - Oralkan, Ö. AU - Kupnik, M. AU - Quate, C. F. AU - Khuri-Yakub, B. T. AU - Braun, T. AU - Ramseyer, J.-P. AU - Lang, H. P. AU - Hegner, M. AU - Gerber, Ch. AU - Gimzewski, J. K. T2 - Applied Physics Letters AB - The authors present the prototype of a chemical sensor using a capacitive micromachined ultrasonic transducer array. Each element in the array consists of a large number of resonating membranes connected in parallel. A five-channel oscillator circuit operates at the resonant frequency around 6MHz in this prototype. The surface of the elements in the array is coated by polymers such as polyallylamine hydrochloride, polyethylene glycol, and polyvinyl alcohol to detect different chemicals. By measuring shift in oscillation frequencies due to the mass-loading effect, analytes, e.g., water and isopropanol, with concentrations around 20ppbv (parts per 109 by volume) range can be detected. DA - 2007/8/27/ PY - 2007/8/27/ DO - 10.1063/1.2776348 VL - 91 IS - 9 SP - 094102 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2776348 DB - Crossref ER - TY - JOUR TI - Synchronized Phasor Data Based Energy Function Analysis of Dominant Power Transfer Paths in Large Power Systems AU - Chow, Joe H. AU - Chakrabortty, Aranya AU - Arcak, Murat AU - Bhargava, Bharat AU - Salazar, Armando T2 - IEEE Transactions on Power Systems AB - Many large interconnected power systems such as the U.S. eastern interconnection and the U.S. western power system are characterized by many power transfer paths or interfaces with high loading. Disruptions of these transfer paths frequently lead to increased loading on neighboring transfer paths, which themselves will become less secure and could cause further disruptions. State estimators have limited performance under large system disruptions, because of low sampling rates and potentially poor solution quality due to topology errors. Furthermore, disruptions in external power systems cannot be readily seen by control room operators because most state estimators only use reduced models for external systems. A system of well-placed phasor measurement units (PMUs) that provide voltage and current magnitude and phase at a high sampling rate can provide useful system dynamic security information. In this paper we apply energy function analysis using phasor data to monitor the dynamic status of power transfer paths. The ideas will be illustrated using actual data captured by several PMUs in the U.S. western power system DA - 2007/5// PY - 2007/5// DO - 10.1109/tpwrs.2007.895162 VL - 22 IS - 2 SP - 727-734 J2 - IEEE Trans. Power Syst. OP - SN - 0885-8950 UR - http://dx.doi.org/10.1109/tpwrs.2007.895162 DB - Crossref KW - energy function KW - power system stability KW - power transfer path KW - synchronized phasor measurement unit (PMU) ER - TY - JOUR TI - Physics-Based Subsurface Visualization of Human Tissue AU - Sharp, Richard AU - Adams, Jacob AU - Machiraju, Raghu AU - Lee, Robert AU - Crane, Robert T2 - IEEE Transactions on Visualization and Computer Graphics AB - In this paper, we present a framework for simulating light transport in three-dimensional tissue with inhomogeneous scattering properties. Our approach employs a computational model to simulate light scattering in tissue through the finite element solution of the diffusion equation. Although our model handles both visible and nonvisible wavelengths, we especially focus on the interaction of near infrared (NIR) light with tissue. Since most human tissue is permeable to NIR light, tools to noninvasively image tumors, blood vasculature, and monitor blood oxygenation levels are being constructed. We apply this model to a numerical phantom to visually reproduce the images generated by these real-world tools. Therefore, in addition to enabling inverse design of detector instruments, our computational tools produce physically-accurate visualizations of subsurface structures DA - 2007/5// PY - 2007/5// DO - 10.1109/tvcg.2007.1003 VL - 13 IS - 3 SP - 620-629 J2 - IEEE Trans. Visual. Comput. Graphics OP - SN - 1077-2626 UR - http://dx.doi.org/10.1109/tvcg.2007.1003 DB - Crossref KW - volume rendering KW - near infrared KW - biological tissue KW - light scattering ER - TY - CONF TI - Usage pattern development for three-wheel auto rickshaw taxis in India AU - Lukic, Srdjan M AU - Mulhall, Priscilla AU - Choi, Gilsu AU - Naviwala, Mustafa AU - Nimmagadda, Sairam AU - Emadi, Ali T2 - IEEE C2 - 2007/// C3 - 2007 IEEE Vehicle Power and Propulsion Conference DA - 2007/// SP - 610-616 ER - TY - CONF TI - State switching digital control technique for switched reluctance motor drives AU - Lukic, Srdjan M AU - Emadi, Ali T2 - IEEE C2 - 2007/// C3 - 2007 IEEE International Electric Machines & Drives Conference DA - 2007/// VL - 2 SP - 1332-1337 ER - TY - CONF TI - Entrepreneurial projects program at Illinois Institute of Technology: solar/battery hybrid three-wheel auto rickshaw for India AU - Mulhall, Priscilla AU - Naviwala, Mustafa AU - Lukic, Srdjan M AU - Braband, James AU - Emadi, Ali T2 - IEEE C2 - 2007/// C3 - 2007 IEEE Vehicle Power and Propulsion Conference DA - 2007/// SP - 682-689 ER - TY - JOUR TI - Advanced state switching control techniques for switched reluctance motor(SRM) drives AU - Lukic, Srdjan T2 - Dissertation Abstracts International DA - 2007/// PY - 2007/// VL - 69 IS - 03 ER - TY - JOUR TI - Zone Repartitioning: A Load‐Balancing Mechanism for Data‐Centric Storage Systems AU - Chiang, Mu‐Huan AU - Byrd, Gregory T. T2 - International Journal of Pervasive Computing and Communications AB - Data‐centric storage is an efficient scheme to store and retrieve event data in sensor networks, but with the multi‐hop routing nature of sensor networks, the communication cost of the home nodes and their neighboring nodes tends to be much higher than the other nodes. These hot‐spots can adversely impact system lifetime by draining off their limited energy rapidly. In this paper, we present Zone‐Repartitioning, a load‐balancing mechanism that reduces the energy consumption of the hot‐spots by distributing their communication load while event frequency is high. The trade‐off between event storage cost and query cost makes Zone Repartitioning a competitive approach in different kinds of applications. We compare the performance of Zone Repartitioning against GHT and show that Zone Repartitioning provides better adaptability in various sensor network scenarios. DA - 2007/9// PY - 2007/9// DO - 10.1108/17427370780000161 VL - 2 IS - 4 SP - 312-320 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84893362518&partnerID=MN8TOARS KW - Sensor networks KW - data-centric storage KW - energy consumption KW - load balance ER - TY - CONF TI - Time reversal target classification from scattered radiation AU - Jin, Y. AU - Moura, J.M.F. AU - Jiang, Y. AU - Stancil, D. AU - O’Donoughue, N. AB - This paper proposed the M-ary hypothesis testing algorithm for classifying radar backscatter signals from hidden targets in a rich scattering environment using time reversal. The target recognition algorithm is to be designed to distinguish measurements of the radar backscatter from an unknown object as belonging to one of a set of M classes. The proposed time reversal target classifier is, in essence, a correlator that calculates the cross-correlation of the normalized target signature waveforms with a data dependent quantity obtained from measurements. The algorithm requires a priori empirical statistical knowledge of the scattering channel, which is dependent of configurations of the scatterers in the environment. By incorporating time reversal, the proposed algorithm provides a significant performance improvement compared with the conventional method. Proof of concept is provided using electromagnetic data collected in a laboratory environment. C2 - 2007/// C3 - IEEE Workshop on Statistical Signal Processing Proceedings DA - 2007/// DO - 10.1109/SSP.2007.4301271 SP - 317-321 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47849113912&partnerID=MN8TOARS KW - time reversal KW - target classification KW - Mary hypothesis testing KW - regularization ER - TY - CONF TI - Synthetic aperture radar ghost image cancellation using broadband time reversal averaging techniques AU - Jiang, Y. AU - Zhu, J.-G. AU - Stancil, D.D. AB - In this paper, we present a time reversal averaging scheme for removing ghost images which occur in synthetic aperture radar (SAR) target imaging in a rich scattering environment. In the highly cluttered environment, the ghost images due to secondary scattering significantly deteriorate the quality of conventional SAR image. The time reversal (TR) method enables focusing on the target, significantly enhancing signal-to-noise ratio. By averaging TR-SAR images produced using different probing angles, the target image is coherently enhanced and the ghost images due to secondary scattering are significantly reduced. The effectiveness of the scheme is demonstrated via both computer simulation analysis and experimental measurements. C2 - 2007/// C3 - IEEE MTT-S International Microwave Symposium Digest DA - 2007/// DO - 10.1109/MWSYM.2007.380532 SP - 1479-1482 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34748851324&partnerID=MN8TOARS ER - TY - CONF TI - REAL: The remote educational antenna laboratory AU - Stancil, D.D. AU - Gist, N. AU - Jiang, Y. AB - The Remote Educational Antenna Laboratory is a new facility for the purpose of providing calibrated characterization of student constructed antennas. When completely operational, it will be available for use by students and instructors around the world, providing measurement experience to enhance and deepen the practical understanding of antennas. C2 - 2007/// C3 - IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) DA - 2007/// DO - 10.1109/APS.2007.4396768 SP - 5399-5402 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-48349094871&partnerID=MN8TOARS ER - TY - CONF TI - Properties and applications of the suburban vehicle-to-vehicle propagation channel at 5.9 GHz AU - Lin, C. AU - Henty, B.E. AU - Stancil, D.D. AU - Fan, B. AU - Mudalige, P. AB - We describe a system capable of making channel measurements as a function of location while the vehicles are in motion to study the properties of the vehicle-to-vehicle wireless channel. We present results from on-road experimental tests in suburban areas of Pittsburgh. The dependence of Doppler spread on both velocity and vehicle separation is discussed. We introduce the speed-separation (S-S) diagram as a new tool for understanding and estimating Doppler spread in the vehicle-to-vehicle environment. C2 - 2007/// C3 - 2007 International Conference on Electromagnetics in Advanced Applications, ICEAA'07 DA - 2007/// DO - 10.1109/ICEAA.2007.4387252 SP - 121-124 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47349112422&partnerID=MN8TOARS ER - TY - CONF TI - Polarization sensitive time reversal SAR imaging in an environment filled with trees AU - Jiang, Y. AU - Zhu, J.-G. AU - Stancil, D.D. AU - Chabalko, M.J. AB - In this paper, we present a time reversal SAR (TR-SAR) algorithm to improve the target images and reduce the ghost images by utilizing different polarizations in an environment filled with trees. C2 - 2007/// C3 - IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) DA - 2007/// DO - 10.1109/APS.2007.4396417 SP - 4000-4003 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-48349109803&partnerID=MN8TOARS ER - TY - CONF TI - Phenomenological driving behavior model of the suburban vehicle-to-vehicle propagation cannel at 5.9 GHz AU - Cheng, L. AU - Henty, B.E. AU - Stancil, D.D. AU - Bai, F. AU - Mudalige, P. AB - Through a field implementation of vehicular ad hoc networks (VANET), we report the observation of a monotonic dependence of maximum relative velocity between two vehicles and their separation, for typical suburban driving. We introduce a hierarchical phenomenological model of driving behavior to describe this observation. As an example, we illustrate how we use this model to predict the expected Doppler shift with vehicle separation. Doppler shift computed from field measured spectra confirms the effectiveness of the model predictions. The model can be used to provide guidance in designing experiments with specific combinations of maximum velocity and separation, and to provide more accurate intelligent transportation systems (ITS) simulations. C2 - 2007/// C3 - 2007 Mobile Networking for Vehicular Environments, MOVE DA - 2007/// DO - 10.1109/MOVE.2007.4300808 SP - 79-84 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-48649095901&partnerID=MN8TOARS ER - TY - JOUR TI - Mobile vehicle-to-vehicle narrow-band channel measurement and characterization of the 5.9 GHz Dedicated Short Range Communication (DSRC) frequency band AU - Cheng, L. AU - Henty, B.E. AU - Stancil, D.D. AU - Bai, F. AU - Mudalige, P. T2 - IEEE Journal on Selected Areas in Communications AB - This study presents narrow-band measurements of the mobile vehicle-to-vehicle propagation channel at 5.9 GHz, under realistic suburban driving conditions in Pittsburgh, Pennsylvania. Our system includes differential Global Positioning System (DGPS) receivers, thereby enabling dynamic measurements of how large-scale path loss, Doppler spectrum, and coherence time depend on vehicle location and separation. A Nakagami distribution is used for describing the fading statistics. The speed-separation diagram is introduced as a new tool for analyzing and understanding the vehicle-to-vehicle propagation environment. We show that this diagram can be used to model and predict channel Doppler spread and coherence time using vehicle speed and separation. DA - 2007/// PY - 2007/// DO - 10.1109/JSAC.2007.071002 VL - 25 IS - 8 SP - 1501-1516 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-35348932792&partnerID=MN8TOARS KW - communication system KW - modeling KW - statistics KW - land vehicle KW - land mobile radio propagation factors ER - TY - JOUR TI - Long distance signaling using axionlike particles AU - Stancil, D.D. T2 - Physical Review D - Particles, Fields, Gravitation and Cosmology AB - The possible existence of axionlike particles could lead to a new type of long-distance communication. In this work, basic antenna concepts are defined and a Friis-like equation is derived to facilitate long-distance link calculations. An example calculation is presented showing that communication over distances of 1000 km or more may be possible for ${m}_{a}<3.5\text{ }\text{ }\mathrm{meV}$ and ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}>5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$. DA - 2007/// PY - 2007/// DO - 10.1103/PhysRevD.76.111701 VL - 76 IS - 11 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-37149049281&partnerID=MN8TOARS ER - TY - CONF TI - Experimental demonstration of time-reversal MISO and MIMO arrays with IEEE 802.11g devices through a ventilation duct channel AU - Henty, B.E. AU - Stancil, D.D. AB - A practical demonstration of IEEE 802.11g transmissions using time-reversal antenna arrays in MISO and MIMO configurations is presented in this work. Throughput measurements indicate significant channel improvement through the use of time-reversal array coefficients and illustrate the viability of increased access point (AP) capacity and co-channel interference reduction in multi-user scenarios. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECS.2007.439 SP - 2124-2128 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547358756&partnerID=MN8TOARS ER - TY - CONF TI - Efficient simulation of mobile-to-mobile rayleigh fading using Gaussian quadrature AU - Borries, K.C. AU - Stancil, D.D. AB - The Gaussian quadrature rules (GQRs) are used to construct a wireless fading simulator based on the popular sum of sinusoids (SoS) method. The general statistics of the proposed simulator are given. This simulator is also shown to perform well for important design parameters. An extension of the GQRs is employed to build uncorrelated simulators, which are important in frequency selective and MIMO simulators. These simulation techniques are then applied to the mobile-to-mobile (MtM) spectrum and are compared with the best known SoS techniques for the MtM spectrum. Although the proposed method is more complex, the efficiency and accuracy are significantly better than the previously proposed methods. C2 - 2007/// C3 - IEEE Vehicular Technology Conference DA - 2007/// DO - 10.1109/VETECS.2007.121 SP - 534-538 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34547292573&partnerID=MN8TOARS KW - fading channel simulator KW - sum-of-sinusoids KW - mobile-to-mobile channel ER - TY - CONF TI - Design of an overmoded-waveguide directional antenna for use in in-building ventilation duct wireless networks AU - Hess, J.C. AU - Stancil, D.D. AU - Henty, B.E. AB - We present an adaptation of a Yagi-Uda antenna design for use inside the overmoded waveguide environment of building ventilation ducts. We obtain experimentally the element size and spacing of a reflector and driven element that can be used for IEEE 802.11 b/g/n signals in a cylindrical duct to provide 3.1 dB of gain and a front-to-back ratio of 9.1 dB compared to a simple monopole antenna. We also discuss the usefulness of such an antenna in a duct network used to distribute wireless signals in a building. C2 - 2007/// C3 - IEEE MTT-S International Microwave Symposium Digest DA - 2007/// DO - 10.1109/MWSYM.2007.380387 SP - 1221-1224 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34748905415&partnerID=MN8TOARS ER - TY - CONF TI - Crossed monopole array for single mode excitation of ventilation duct communication channels AU - Henty, B.E. AU - Hess, J. AU - Stancil, D.D. AB - This work presents a novel antenna array for exciting a single mode of propagation in common ventilation ducts with a circular cross-section that are overmoded waveguides in the 2.4 GHz frequency band. By inverting the phase of one driven element with respect to the other, one of two modes can be selected for excitation, but in either case only a single mode is excited. We present the design technique and advantages of such an antenna array for use with IEEE 802.11g access points. C2 - 2007/// C3 - IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) DA - 2007/// DO - 10.1109/APS.2007.4396094 SP - 2710-2713 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-48349115383&partnerID=MN8TOARS ER - TY - CONF TI - Antenna array detection in highly cluttered environment using time reversal method AU - Jiang, Y. AU - Stancil, D.D. AU - Zhu, J.-G. AB - This paper concerns a method of target detection in a cluttered environment where a significantly large number of highly reflective scattering objects exists. With the conventional Radar detection, the detection of a target additional to this highly scattering environment would suffer greatly in their detection dynamic range. In this paper, we present a novel time reversal method that enables automatic destructive interference of the field-probing electromagnetic wave on the reflective scatters of the environment such that the cluttered environment becomes virtually transparent. The experiment in lab tree-scattering environment demonstrates that this time reversal clutter-nulling scheme substantially enhances the detection dynamic range and the signal-to-noise ratio, significantly raising target detectability. C2 - 2007/// C3 - IEEE MTT-S International Microwave Symposium Digest DA - 2007/// DO - 10.1109/MWSYM.2007.380062 SP - 1731-1734 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-34748911740&partnerID=MN8TOARS ER - TY - JOUR TI - PMPM: Prediction by combining multiple partial matches AU - Gao, H. AU - Zhou, H. T2 - Journal of Instruction-level Parallelism DA - 2007/// PY - 2007/// VL - 9 SP - 1-18 ER - TY - CONF TI - CAP: Criticality analysis for power-efficient speculative multithreading AU - Tuck, James AU - Liu, Wei AU - Torrellas, Josep T2 - IEEE AB - While speculative multithreading (SM) on a chip multiprocessor (CMP) has the ability to speed-up hard-to- parallelize applications, the power inefficiency of aggressive speculation is a concern. To improve SMs power effeciency, we note that not all the tasks that are running in a SM environment are equally critical. To leverage this insight, this paper develops a novel, widely-applicable task-criticality model for SM. It also proposes CAP, a novel architecture that builds a task-criticality graph dynamically and uses it to make scheduling decisions in a SM CMP. Experiments with SPECint, SPECfp, and Olden applications show that, in a CMP with one fast core and three slow ones, the E D 2 with CAP is, on average, 91-95% of that without. Moreover, it is only 77-91% of the E D 2 of a CMP with four fast cores and no CAP. Overall, we argue that scheduling for task criticality is beneficial. C2 - 2007/// C3 - 2007 25th International Conference on Computer Design DA - 2007/// DO - 10.1109/iccd.2007.4601932 SP - 409-416 ER - TY - CONF TI - BulkSC: Bulk enforcement of sequential consistency AU - Ceze, Luis AU - Tuck, James AU - Montesinos, Pablo AU - Torrellas, Josep AB - While Sequential Consistency (SC) is the most intuitive memory consistency model and the one most programmers likely assume, current multiprocessors do not support it. Instead, they support more relaxed models that deliver high performance. SC implementations are considered either too slow or -- when they can match the performance of relaxed models -- too difficult to implement. C2 - 2007/// C3 - Proceedings of the 34th annual international symposium on Computer architecture DA - 2007/// DO - 10.1145/1250662.1250697 SP - 278-289 ER - TY - JOUR TI - Optimizing dual-core execution for power efficiency and transient-fault recovery AU - Ma, Yi AU - Gao, Hongliang AU - Dimitrov, Martin AU - Zhou, Huiyang T2 - IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS AB - Dual-core execution (DCE) is an execution paradigm proposed to utilize chip multiprocessors to improve the performance of single-threaded applications. Previous research has shown that DCE provides a complexity-effective approach to building a highly scalable instruction window and achieves significant latency-hiding capabilities. In this paper, we propose to optimize DCE for power efficiency and/or transient-fault recovery. In DCE, a program is first processed (speculatively) in the front processor and then reexecuted by the back processor. Such reexecution is the key to eliminating the centralized structures that are normally associated with very large instruction windows. In this paper, we exploit the computational redundancy in DCE to improve its reliability and its power efficiency. The main contributions include: 1) DCE-based redundancy checking for transient-fault tolerance and a complexity-effective approach to achieving full redundancy coverage and 2) novel techniques to improve the power/energy efficiency of DCE-based execution paradigms. Our experimental results demonstrate that, with the proposed simple techniques, the optimized DCE can effectively achieve transient-fault tolerance or significant performance enhancement in a power/energy-efficient way. Compared to the original DCE, the optimized DCE has similar speedups (34 percent on average) over single-core processors while reducing the energy overhead from 93 percent to 31 percent. DA - 2007/8// PY - 2007/8// DO - 10.1109/tpds.2007.4288106 VL - 18 IS - 8 SP - 1080-1093 SN - 1558-2183 KW - multiple data stream architectures KW - fault tolerance KW - low-power design ER - TY - JOUR TI - AN EXPERIMENTAL STUDY ON SECURITY PROTOCOLS IN WLANS AU - Agarwal, Avesh Kumar AU - Wang, Wenye T2 - WIRELESS NETWORK SECURITY DA - 2007/// PY - 2007/// DO - 10.1007/978-0-387-33112-6_12 SP - 295-322 SN - 1860-4862 ER - TY - JOUR TI - Electrical and mechanical properties of carbon-black-filled, electrospun nanocomposite fiber webs AU - Hwang, Jeesang AU - Muth, John AU - Ghosh, Tushar T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - Abstract The development of flexible and compliant conductive polymer composites with textile‐like characteristics remains an important endeavor in light of the recent activity in polymer/textile‐based electronics and the need for compliant electrodes for electroactive polymer actuators. In this work, carbon black (CB) was dispersed in a polymer solution to form electrospun fiber webs consisting mainly of nanofibers. The effect of the filler content on the fiber‐web morphology, mechanical behavior, electrical conductivity, and thermal resistance was examined. The electrical conductivity percolation threshold of the fiber‐web structure was found to be around 4.6 vol %. Scanning electron micrographs of the fiber webs revealed a significant influence of the CB content on the fiber formation as well as the bond structure of the fiber web, which influenced the mechanical properties of the web. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2410–2417, 2007 DA - 2007/5/15/ PY - 2007/5/15/ DO - 10.1002/app.25914 VL - 104 IS - 4 SP - 2410-2417 SN - 1097-4628 KW - additives KW - elastomers KW - fibers KW - nanocomposites KW - polyurethanes ER - TY - CONF TI - THz detection cell for sub-wavelength bio-molecular sensing AU - Woolard, D. L. AU - Zhao, P. C2 - 2007/// C3 - 2007 7TH IEEE CONFERENCE ON NANOTECHNOLOGY DA - 2007/// SP - 320-325 PB - [Piscataway, NJ]: IEEE SN - 978-1-4244-0607-4 ER - TY - CONF TI - A Spin-Polarized interband-current source based upon staggered-bandgap heterostructures AU - Zhang, W. D. AU - Woolard, D. AU - Zhao, P. C2 - 2007/// C3 - 2007 7TH IEEE CONFERENCE ON NANOTECHNOLOGY DA - 2007/// SP - 214-219 PB - [Piscataway, NJ]: IEEE SN - 978-1-4244-0607-4 ER - TY - CONF TI - Comparisons of SiC MOSFET and Si IGBT based motor drive systems AU - Zhao, T. F. AU - Wang, J. AU - Huang, A. Q. AU - Agarwal, A. AB - With the rapid development of silicon carbide (SiC) material quality, SiC power devices are gaining tremendous attentions in power electronics. In this paper, a SiC device based motor drive system is performed to provide a quantitative estimate of the system improvement. Two 60 kW motor drive systems based on SiC MOSFET/Schottky diode and Si IGBTs are designed. The power losses of the two inverters with sinusoidal pulse width modulation (SPWM) control are calculated analytically. By comparing the efficiencies, sizes and temperatures of the two designed systems, SiC device shows the superior advantages of smaller loss, better efficiency and smaller size in the same motor drive application. C2 - 2007/// C3 - Conference record of the 2007 IEEE Industry Applications Conference forty-second IAS annual meeting DA - 2007/// DO - 10.1109/07ias.2007.51 SP - 331-335 PB - New York: IEEE SN - 9781424412600 ER - TY - CONF TI - Pricing and optimal resource allocation in next generation network services AU - Kallitsis, M. G. AU - Michailidis, G. AU - Devetsikiotis, M. C2 - 2007/// C3 - 2007 IEEE Sarnoff Symposium DA - 2007/// SP - 457-461 ER - TY - CONF TI - Pricing and measurement-based optimal resource allocation in next generation network services AU - Kallitsis, M. G. AU - Michailidis, G. AU - Devetsikiotis, M. C2 - 2007/// C3 - 2007 IEEE Globecom Workshops, Proceedings DA - 2007/// SP - 189-194 ER - TY - JOUR TI - High performance transparent thin film transistors based on indium gallium zinc oxide as the channel material AU - Suresh, Arun AU - Wellenius, Patrick AU - Muth, John F. T2 - 2007 IEEE INTERNATIONAL ELECTRON DEVICES MEETING, VOLS 1 AND 2 AB - The fabrication of high performance amorphous indium gallium zinc oxide (IGZO) transparent thin film transistors (TTFT) and their bias stress stability is presented. N-channel enhancement mode devices were fabricated with an extracted field effect mobility of ~ 11-15 cm 2 V -1 s -1 , on/off current ratios > 10 7 , subthreshold gate voltage swing of 0.20-0.25 V/decade, low off-state currents and good saturation. Low and tunable threshold voltages of 1-2 V were achieved. We conclude that a charge trapping mechanism at the semiconductor/dielectric interface is responsible for the threshold voltage shift after a gate bias stress. The threshold voltage is recovered when the bias is removed. DA - 2007/// PY - 2007/// DO - 10.1109/iedm.2007.4419007 SP - 587-590 SN - 2380-9248 ER - TY - CHAP TI - Combining cluster sampling with single pass methods for efficient sampling regimen design AU - Bryan, P. D. AU - Conte, T. M. T2 - 2007 IEEE International Conference On Computer Design PY - 2007/// SP - 472-479 PB - New York: IEEE SN - 9781424412570 ER - TY - JOUR TI - Efficient software implementation of embedded communication protocol controllers using asynchronous software thread integration with time- and space-efficient procedure calls AU - Kumar, Nagendra J. AU - Asokan, Vasanth AU - Shivshankar, Siddhartha AU - Dean, Alexander G. T2 - ACM TRANSACTIONS ON EMBEDDED COMPUTING SYSTEMS AB - The overhead of context switching limits efficient scheduling of multiple concurrent threads on a uniprocessor when real-time requirements exist. A software-implemented protocol controller may be crippled by this problem. The available idle time may be too short to recover through context switching, so only the primary thread can execute during message activity, slowing the secondary threads and potentially missing deadlines. Asynchronous software thread integration (ASTI) uses coroutine calls and integration, letting threads make independent progress efficiently, and reducing the needed context switches. We demonstrate the methods with a software implementation of an automotive communication protocol (J1850) and several secondary threads. DA - 2007/2// PY - 2007/2// DO - 10.1145/1210268.1210270 VL - 6 IS - 1 SP - SN - 1558-3465 KW - algorithms KW - design KW - experimentation KW - asynchronous software thread integration KW - hardware to software migration KW - fine-grain concurrency KW - software-implemented communication protocol controllers KW - J1850 ER - TY - JOUR TI - Tiny-sync: Tight time synchronization for wireless sensor networks AU - Yoon, Suyoung AU - Veerarittiphan, Chanchai AU - Sichitiu, Mihail L. T2 - ACM TRANSACTIONS ON SENSOR NETWORKS AB - Time synchronization is a fundamental middleware service for any distributed system. Wireless sensor networks make extensive use of synchronized time in many contexts (e.g., data fusion, TDMA schedules, synchronized sleep periods, etc.). We propose a time synchronization method relevant for wireless sensor networks. The solution features minimal complexity in network bandwidth, storage as well as processing, and can achieve good accuracy. Especially relevant for sensor networks, it also provides tight, deterministic bounds on offset and clock drift. A method for synchronizing the entire network is presented. The performance of the algorithm is analyzed theoretically and validated on a realistic testbed. The results show that the proposed algorithm outperforms existing algorithms in terms of precision and resource requirements. DA - 2007/6// PY - 2007/6// DO - 10.1145/1240226.1240228 VL - 3 IS - 2 SP - SN - 1550-4867 KW - algorithms KW - design KW - experimentation KW - performance KW - sensor networks KW - time synchronization ER - TY - JOUR TI - Comment on "Spin and cyclotron energies of electrons in GaAs/Ga1-xAlxAs quantum wells" AU - Kiselev, A. A. AU - Ivchenko, E. L. T2 - Physical Review. B, Condensed Matter and Materials Physics DA - 2007/// PY - 2007/// VL - 76 IS - 19 ER - TY - PAT TI - System and method for transferring duty cycle information in an isolated DC/DC converter or other circuit AU - Hawkes, C. E. AU - Kelley, A. W. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - PAT TI - Method for selective expression of therapeutic genes by hyperthermia AU - Li, C. Y. AU - Huang, Q. AU - Dewhirst, M. W. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - PAT TI - In situ patterning of electrolyte for molecular information storage devices AU - Misra, V. AU - Bocian, D. AU - Kuhr, W. AU - Lindsey, J. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - PAT TI - Printed circuit dielectric foil and embedded capacitors AU - Dunn, G. J. AU - Chilini, R. J. AU - Croswell, R. T. AU - Dean, T. B. AU - Gamboa, C. V. AU - Savic, J. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Reflection coefficient shaping of a 5-GHz voltage-tuned oscillator for improved tuning AU - Victor, Alan AU - Steer, Michael B. T2 - IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES AB - Negative resistance voltage-controlled oscillators (VCOs) are systematically designed to operate with loaded resonator networks that permit stable steady-state oscillation over a specified tuning bandwidth. Circuit parasitics, however, significantly affect tuning behavior and complicate straightforward design. This paper introduces a scheme that compensates for the effect of parasitics by introducing an embedding network that modifies the effective active device reflection coefficient and thus enables conventional one-port oscillator design techniques to be used. A common-base SiGe HBT VCO operating from 4.4 to 5.5 GHz demonstrates the technique. Phase noise is better than -85 dBc/Hz at 10-kHz offset from the carrier and the second harmonic is less than -20 dBc, while higher order harmonics are less than -40 dBc. The voltage-tuned oscillator demonstrates an oscillator figure-of-merit of at least -182 dBc/Hz over a 800-MHz tuning range. The phase-noise-bandwidth (in megahertz) product is -159 dBc/Hz. DA - 2007/12// PY - 2007/12// DO - 10.1109/TMTT.2007.909140 VL - 55 IS - 12 SP - 2488-2494 SN - 1557-9670 KW - negative resistance KW - oscillator KW - resonator KW - varactor tuning KW - voltage-controlled oscillator (VCO) ER - TY - CONF TI - Improving assessment efficiency and overcoming barriers: relating programmatic accreditation to institutional assessment AU - Spurlin, J. E. AU - Raubenheimer, D. AU - Nault, E. AU - Rajala, S. C2 - 2007/// C3 - NASPA International Assessment & Retention Conference DA - 2007/// M1 - June ER - TY - PAT TI - High temperature attachment of organic molecules to substrates AU - Bocian, D. F. AU - Lindsey, J. AU - Liu, Z. AU - Yesseri, A. A. AU - Misra, V. AU - Zhao, Q. AU - Li, Q. AU - Surthi, S. AU - Loewe, R. S. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Fading channel prediction for mobile radio adaptive transmission systems AU - Duel-Hallen, Alexandra T2 - PROCEEDINGS OF THE IEEE AB - Adaptive transmission methods can potentially aid the achievement of high data rates required for mobile radio multimedia services. To realize this potential, the transmitter needs accurate channel state information (CSI) for the upcoming transmission frame. In most mobile radio systems, the CSI is estimated at the receiver and fed back to the transmitter. However, unless the mobile speed is very low, the estimated CSI cannot be used directly to select the parameters of adaptive transmission systems, since it quickly becomes outdated due to the rapid channel variation caused by multipath fading. To enable adaptive transmission for mobile radio systems, prediction of future fading channel samples is required. Several fundamental issues arise in the design and testing of fading prediction algorithms for adaptive transmission systems. These include complexity, robustness, choice of an appropriate channel model for algorithm validation, channel estimation and noise reduction required for reliable prediction, and design and analysis of adaptive transmission methods aided by fading prediction algorithms. We use these criteria in the review of recent advances in the area of fading channel prediction. We also demonstrate that reliable fading prediction makes adaptive transmission feasible in diverse wireless communication systems. DA - 2007/12// PY - 2007/12// DO - 10.1109/JPROC.2007.904443 VL - 95 IS - 12 SP - 2299-2313 SN - 1558-2256 KW - adaptive modulation (AM) KW - adaptive multiple-input multiple-output (MIMO) systems KW - adaptive orthogonal frequency-division multiplexing (OFDM) KW - adaptive spread spectrum systems KW - adaptive transmission KW - fading channel prediction ER - TY - JOUR TI - Correlation between photoluminescence and magnetic properties of GaMnN films AU - Nepal, N. AU - Mahros, Amr M. AU - Bedair, S. M. AU - El-Masry, N. A. AU - Zavada, J. M. T2 - APPLIED PHYSICS LETTERS AB - GaMnN films grown by metal-organic chemical vapor deposition were studied by photoluminescence (PL) spectroscopy and hysteresis measurements. Depending on the growth conditions of these GaMnN films, hysteresis measurements along the easy axis of magnetization show a transformation from magnetic to nonmagnetic behavior. The PL spectra of both magnetic and nonmagnetic GaMnN films exhibited GaN band edge and deep-level impurity transitions at 3.4 and 1.3eV, respectively. The PL emission intensity of the 1.3eV emission peak is stronger considerably for magnetic GaMnN films and is believed to be due to the Mn3+ intraband transition. DA - 2007/12/10/ PY - 2007/12/10/ DO - 10.1063/1.2823602 VL - 91 IS - 24 SP - SN - 1077-3118 ER - TY - PAT TI - Apparatus and method for continuous conduction mode boost voltage power factor correction with an average current control mode AU - Wu, C. C. AU - Huang, Q. AU - Zhu, N. AU - Zhang, X. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Agricultural drainage management, quality and disposal issues in North America AU - Madramootoo, Chandra A. AU - Johnston, William R. AU - Ayars, James E. AU - Evans, Robert O. AU - Fausey, Norman R. T2 - IRRIGATION AND DRAINAGE AB - The North American continent, comprising Canada and the United States of America, has a wide range of climatic, soils and cropping conditions. Surface and subsurface drainage is required to remove excess soil water in the wetter regions of the continent, as well as to maintain a favorable salt and water balance in the crop root zone in the drier irrigated regions. Drainage and water table management practices are essential for the production of food and fiber. However, these practices may sometimes cause third-party impacts, which are largely of a water quality nature. Drainage practices have therefore evolved from removal of water for increased crop productivity, to a method of environmental control. Consequently, much effort over recent years has been in designing and installing drainage systems, which have multiple objectives. A very recent notable institutional development is the formation of the Agricultural Drainage Management Systems (ADMS) Coalition, comprised of farmers, drainage contractors and the drainage industry, government advisors, and water management and agricultural specialists, to promote research, education and adoption of drainage water management as a practice that can reduce the delivery of pollutants to streams. This paper describes the need, extent and status of drainage in North America, including water quality issues, drainage water management and disposal problems. Copyright © 2007 John Wiley & Sons, Ltd. L'Amérique du Nord, composée du Canada et des États-Unis d'Amérique, présente un large éventail de conditions climatiques, de sols et de cultures. Le drainage, de surface et souterrain, est nécessaire pour enlever l'excédent d'eau contenu dans le sol des régions les plus humides, de même que pour maintenir un bilan d'eau et de sels minéraux dans la zone racinaire propice aux cultures dans les régions irriguées plus sèches du continent. Le drainage et la gestion de la nappe phréatique sont, par conséquent, des pratiques essentielles à la production de nourriture et de fibres textiles. Toutefois, ces pratiques de drainage ne peuvent pas toujours être effectuées sans causer d'impacts sur une tierce partie. Les pratiques de drainage ont évolué à partir du simple prélèvement d'eau afin d'augmenter la production des cultures à une méthode de maîtrise environnementale visant à réduire les impacts sur la qualité de l'eau causés par ces pratiques. Par conséquent, au cours des dernières années, les efforts se sont concentrés sur le développement et l'installation de systèmes de drainage à objectifs multiples, prenant en considération la plante, l'hydrologie, le sol et l'environnement. La création de la Coalition sur la Gestion des Systèmes de Drainage Agricole (Agricultural Drainage Management Systems (ADMS) Coalition), composée d'agriculteurs, d'entrepreneurs de drainage, d'experts gouvernementaux, et de spécialistes de la gestion de l'eau et du monde agricole, afin de promouvoir la recherche, l'éducation, et l'adoption de la gestion de l'eau par le drainage comme une pratique innovante qui peut réduire les polluants dans les cours d'eau, constitue une avancée récente du monde institutionnel. Cet article décrit les besoins, l'étendue et la situation du drainage en Amérique du Nord, incluant les problématiques de qualité, de gestion et d'élimination de l'eau. Copyright © 2007 John Wiley & Sons, Ltd. DA - 2007/12// PY - 2007/12// DO - 10.1002/ird.343 VL - 56 SP - S35-S45 SN - 1531-0353 KW - agricultural drainage KW - management KW - quality KW - disposal KW - North America ER - TY - JOUR TI - Wavelet-based neighborhood control for self-sizing networks AU - Nalatwad, Srikant AU - Devetslkiotis, Michael T2 - SIMULATION-TRANSACTIONS OF THE SOCIETY FOR MODELING AND SIMULATION INTERNATIONAL AB - The exponential growth of the Internet has turned it into a multiservice complex network of heterogeneous elements with dynamically changing traffic conditions. To regulate such a large scale network it is necessary to place intelligence in the nodes and find simple distributed rules and strategies that can produce meaningful and consistent behavior. These control mechanisms must be adaptive to effectively respond to continually changing network conditions. A “self-sizing” network can allocate link/switch capacity automatically and adaptively using online traffic data. Such adaptive, distributed, localized mechanisms are crucial to provide a scalable solution for controlling large, complex networks. In this paper, we propose a new, distributed self-sizing framework for locally controlled networks, which can support the stringent requirements of real-time applications in the Internet. Our unified and critical study of online resource allocation algorithms of two different classical approaches, led us to the use of adaptive multi-resolution decomposition (“wavelet”) algorithms. Our results show that by performing online resource allocation at each node based on their local knowledge, we can achieve considerable bandwidth savings and also satisfy QoS at the packet level. In our novel “neighborhood control” technique, we establish that by increasing the knowledge of some nodes so that higher self-sizing gains can be attained. DA - 2007/3// PY - 2007/3// DO - 10.1177/0037549707081187 VL - 83 IS - 3 SP - 229-244 SN - 1741-3133 KW - self-sizing KW - resource allocation KW - wavelets KW - neighborhood control ER - TY - JOUR TI - Transformation-designed optical elements AU - Schurig, D. AU - Pendry, J. B. AU - Smith, D. R. T2 - OPTICS EXPRESS AB - We describe transformation design of optical elements which, in addition to image transfer, perform useful operations. For one class of operations, including translation, rotation, mirroring and inversion, an image can be generated that is ideal in the sense of the perfect lens (combining both near- and far-field components in a flat, unit transfer function, up to the limits imposed by material imperfection). We also describe elements that perform magnification, free from geometric aberrations, even while providing free-space working distance on both the input and output sides. These magnifying elements also operate in the near- and far-field, allowing them to transfer near field information into the far field, as with the hyper lens and other related devices, however in contrast to those devices, insertion loss can be much lower, due to the matching properties accessible with transformation design. The devices here described inherently require dispersive materials, thus chromatic aberration will be present, and the bandwidth limited. DA - 2007/10/29/ PY - 2007/10/29/ DO - 10.1364/OE.15.014772 VL - 15 IS - 22 SP - 14772-14782 SN - 1094-4087 ER - TY - JOUR TI - Total dose and bias temperature stress effects for HfSiON on Si MOS capacitors AU - Chen, D. K. AU - Mamouni, E. E. AU - Zhou, X. J. AU - Schrimpf, R. D. AU - Fleetwood, D. M. AU - Galloway, K. F. AU - Lee, S. AU - Seo, H. AU - Lucovsky, G. AU - Jun, B. AU - Cressler, J. D. T2 - IEEE TRANSACTIONS ON NUCLEAR SCIENCE AB - We have performed an experimental study of the effects of ionizing radiation and bias-temperature stress on Si MOS devices with HfSiON gate dielectrics. We compare the responses of homogeneous high-SiN films and low-SiN films that contain crystalline HfO. We observe that the low-SiN films are more sensitive to ionizing radiation than the high-SiN films. In particular, the low-SiN film that includes crystalline HfO is especially vulnerable to electron trapping due to substrate injection under positive irradiation bias. Both film types exhibit reduced radiation-induced charge trapping relative to previous Hf silicates. The high-SiN film exhibits less radiation-induced net oxide-trap charge density than earlier Hf silicate films processed without nitride. We also find that these devices are relatively robust against bias-temperature stress instabilities. Consistent with the radiation response, the low-SiN devices also display elevated levels of charge trapping relative to the high-SiN devices during bias-temperature stress. DA - 2007/12// PY - 2007/12// DO - 10.1109/TNS.2007.910862 VL - 54 IS - 6 SP - 1931-1937 SN - 0018-9499 KW - alternative dielectrics KW - bias-temperature instability KW - HfSiON KW - nitridation KW - total-dose irradiation ER - TY - JOUR TI - The effects of nickel germanosilicide contacts on the biaxial compressive stress in thin epitaxial silicon-germanium alloys on silicon AU - Chopra, Saurabh AU - Ozturk, Mehmet C. AU - Misra, Veena AU - Ren, Zhongqiao AU - McNeil, L. E. T2 - APPLIED PHYSICS LETTERS AB - When a thin Si1−xGex epitaxial layer is grown on Si, it is under biaxial compression. In this letter, it is shown that a nickel germanosilicide (NiSi1−xGex) layer formed on Si1−xGex can significantly reduce the in-plane compressive strain in Si1−xGex. It is proposed that the observed reduction is due to the biaxial tensile stress applied by the NiSi1−xGex layer. Because the Si1−xGex bandgap is a strong function of the strain, this is expected to have a strong impact on the metal-semiconductor barrier height and the contact resistivity of the interface if the metal Fermi level is pinned near the Si1−xGex midgap. DA - 2007/10/1/ PY - 2007/10/1/ DO - 10.1063/1.2795346 VL - 91 IS - 14 SP - SN - 1077-3118 ER - TY - JOUR TI - Studies of bonding defects, and defect state suppression in HfO2 by soft X-ray absorption and photoelectron spectroscopies AU - Lucovsky, G. AU - Seo, H. AU - Fleming, L. B. AU - Luening, J. AU - Lysaght, P. AU - Bersuker, G. T2 - SURFACE SCIENCE AB - This paper identifies two-different regimes of nano-crystallinity: (i) thin films with nano-crystallites >3 nm, that display coherent well-defined grain-boundaries, and (ii) thin films with nano-crystallites less than ∼2 nm, that display neither will-defined grain-boundaries nor lattice planes in high resolution transmission electron microscopy images, but yield an image indicative of clusters of small nano-crystallites with a length scale order of ∼2 nm. Near edge X-ray absorption spectroscopy, and soft-X-ray photoelectron spectroscopy, combined with visible and UV spectroscopic ellipsometry, provide an unambiguous way to distinguish between these two technologically important regimes of nano-crystalline order, yielding significant information on electronic structure of intrinsic band edge states and intrinsic electronically-active defects. DA - 2007/9/15/ PY - 2007/9/15/ DO - 10.1016/j.susc.2007.04.197 VL - 601 IS - 18 SP - 4236-4241 SN - 1879-2758 KW - transition metal oxides KW - crystal field and Jahn-Teller d-state splittings KW - Ab initio molecular orbital theory KW - intrinsic bonding states KW - intrinsic defect states ER - TY - JOUR TI - Spin field effect transistor with a graphene channel AU - Semenov, Y. G. AU - Kim, K. W. AU - Zavada, J. M. T2 - Applied Physics Letters AB - A spin field effect transistor (FET) is proposed by utilizing a graphene layer as the channel. Similar to the conventional spin FETs, the device involves spin injection and spin detection by ferromagnetic source and drain. Due to the negligible spin-orbit coupling in the carbon based materials, spin manipulation in the channel is achieved via electrical control of the electron exchange interaction with a ferromagnetic gate dielectric. Numerical estimates indicate the feasibility of the concept if the bias can induce a change in the exchange interaction energy of the order of meV. When nanoribbons are used for a finite channel width, those with armchair-type edges can maintain the device stability against the thermal dispersion. DA - 2007/10/8/ PY - 2007/10/8/ DO - 10.1063/1.2798596 VL - 91 IS - 15 SP - 153105 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2798596 DB - Crossref ER - TY - CONF TI - North Carolina State University faculty in technology-rich contexts: connecting teaching, learning and assessment in the classroom AU - Raubenheimer, C. D. AU - Spurlin, J. AU - North Martin, S. AU - Mehlenbacher, B. C2 - 2007/// C3 - UNC teaching and learning with technology conference proceedings DA - 2007/// ER - TY - JOUR TI - Modelling high-order filters in a transient microwave circuit simulator AU - Hart, F. P. AU - Luniya, S. R. AU - Nath, J. AU - Victor, A. AU - Walker, A. AU - Steer, M. B. T2 - IET MICROWAVES ANTENNAS & PROPAGATION AB - Transient simulation of narrowband bandpass filters used in microwave circuits is challenging because of matrix ill-conditioning. Here, such filters are modelled as the equivalent discrete-time form developed using a bilinear z-transform. The technique has been implemented in a general purpose transient circuit simulator and validated using a 1.7 GHz 5-section coaxial filter with a 0.9% bandwidth. DA - 2007/10// PY - 2007/10// DO - 10.1049/iet-map:20060231 VL - 1 IS - 5 SP - 1024-1028 SN - 1751-8733 ER - TY - JOUR TI - Impact of metal gates on remote phonon scattering in titanium nitride/hafnium dioxide n-channel metal-oxide-semiconductor field effect transistors-low temperature electron mobility study AU - Maitra, Kingsuk AU - Frank, Martin M. AU - Narayanan, Vijay AU - Misra, Veena AU - Cartier, Eduard A. T2 - JOURNAL OF APPLIED PHYSICS AB - We report low temperature (40–300 K) electron mobility measurements on aggressively scaled [equivalent oxide thickness (EOT)=1 nm] n-channel metal–oxide–semiconductor field effect transistors (nMOSFETs) with HfO2 gate dielectrics and metal gate electrodes (TiN). A comparison is made with conventional nMOSFETs containing HfO2 with polycrystalline Si (poly-Si) gate electrodes. No substantial change in the temperature acceleration factor is observed when poly-Si is replaced with a metal gate, showing that soft optical phonons are not significantly screened by metal gates. A qualitative argument based on an analogy between remote phonon scattering and high-resolution electron energy-loss spectroscopy (HREELS) is provided to explain the underlying physics of the observed phenomenon. It is also shown that soft optical phonon scattering is strongly damped by thin SiO2 interface layers, such that room temperature electron mobility values at EOT=1 nm become competitive with values measured in nMOSFETs with SiON gate dielectrics used in current high performance processors. DA - 2007/12/1/ PY - 2007/12/1/ DO - 10.1063/1.2821712 VL - 102 IS - 11 SP - SN - 1089-7550 ER - TY - JOUR TI - Estimation of co-channel nonlinear distortion and SNDR in wireless systems AU - Gharaibeh, K. M. AU - Gard, K. G. AU - Steer, M. B. T2 - IET MICROWAVES ANTENNAS & PROPAGATION AB - The effective signal-to-noise and distortion ratio (SNDR) at the output of a nonlinear amplifier is defined through the decomposition of the nonlinear output into correlated output and uncorrelated distortion. The analysis is based on the orthogonalisation of the nonlinear behavioual model that allows the accurate estimation of the effective in-band (or co-channel) distortion and hence determination of SNDR. Fundamental issues regarding the evaluation of the effective in-band distortion and its effect on digitally modulated signals are discussed. Simulations of in-band distortion and SNDR of WCDMA signals are verified experimentally using feed-forward cancelation. DA - 2007/10// PY - 2007/10// DO - 10.1049/iet-map:20070034 VL - 1 IS - 5 SP - 1078-1085 SN - 1751-8733 ER - TY - JOUR TI - Considerations for a high-performance thermionic energy conversion device based on a negative electron affinity emitter AU - Smith, Joshua Ryan AU - Bilbro, Griff L. AU - Nemanich, Robert J. T2 - PHYSICAL REVIEW B AB - A theory is developed to model the effect a negative electron affinity (NEA) emitter electrode has on the negative space charge effect of a vacuum thermionic energy conversion device (TEC). The theory is derived by treating the electrons in the interelectrode space as a collisionless gas and self-consistently solving the Boltzmann transport equation and Poisson equation. The theory determines the point on the voltage-current characteristic such that the maximum motive due to space charge is at the same level as the conduction band minimum. It is shown that emitter electrodes with an NEA significantly mitigate the negative space charge effect; therefore a TEC employing such an electrode will outperfrom a similar TEC with conventional electrodes in terms of output power. Additionally, it is shown that a TEC with an NEA emitter electrode can have a greater interelectrode spacing than a TEC with conventional electrodes operating under similar conditions where the outputs of both TEC's are comparable. DA - 2007/12// PY - 2007/12// DO - 10.1103/physrevb.76.245327 VL - 76 IS - 24 SP - SN - 1098-0121 ER - TY - JOUR TI - A molecular memory device formed by HfO2 encapsulation of redox-active molecules AU - Chen, Zhong AU - Lee, Bongmook AU - Sarkar, Smita AU - Gowda, Srivardhan AU - Misra, Veena T2 - APPLIED PHYSICS LETTERS AB - Solid state metal-insulator-molecule-metal (MIMM) devices were fabricated by encapsulating a redox-active molecular layer between a metal substrate and a dielectric thin film of atomic layer deposition (ALD) hafnium dioxide (HfO2). Redox properties of molecules are preserved after atomic layer deposition. The leakage current of devices is greatly improved by incorporating the ALD HfO2 thin layer. Capacitance measurements of these MIMM devices show a large frequency dispersion indicating the charging and discharging of the molecular layer. DA - 2007/10/22/ PY - 2007/10/22/ DO - 10.1063/1.2800824 VL - 91 IS - 17 SP - SN - 0003-6951 ER - TY - JOUR TI - Warp breaks detection in Jacquard weaving using MEMS: System development AU - Lee, J. H. AU - Seyam, A. M. AU - Hodge, G. AU - Oxenham, W. AU - Grant, E. T2 - JOURNAL OF THE TEXTILE INSTITUTE AB - Abstract Research related to warp breaks has been limited to monitoring break frequency and the reason associated with breaks in order to improve warp yarn quality. While this approach led to improvement in weaving efficiency, warp breaks still represent a major problem, especially for today's high-speed weaving machines. Researchers have been trying to develop commercial automated systems to repair warp breaks with no success. The goal of this study is to explore inexpensive methods to detect warp breaks using nontraditional technique that would pave the way to automate warp break repair. To achieve the goal, a system that can detect warp breaks using MEMS accelerometers as sensors was developed for Jacquard weaving. The MEMS accelerometers were mounted on harness cords of a Jacquard tie. MEMS output acceleration signals components in the vertical and horizontal directions were analysed using time and frequency domains. The signals were acquired while warp ends are running and at the moment of intentional breaks. The analysis led to a successful detection of warp breaks, especially using the horizontal acceleration component that is mainly due to harness cord vibration. DA - 2007/// PY - 2007/// DO - 10.1080/00405000701462559 VL - 98 IS - 3 SP - 275-280 SN - 0040-5000 KW - MEMS accelerometers KW - Jacquard weaving KW - warp breaks KW - automation of warp breaks ER - TY - JOUR TI - Uniformity analysis of wafer scale sub-25 nm wide nanowire array nanoimprint mold fabricated by PEDAL process AU - Sonkusale, Sachin R. AU - Di Spigna, Neil H. AU - Franzon, Paul D. T2 - MICROELECTRONIC ENGINEERING AB - In earlier publications [S. Sonkusale, C.J. Amsinck, D.P. Nackashi, N.H. Di Spigna, D. Barlage, M. Johnson, P.D. Franzon, E. Physica, Low Dimensional Systems and Nanostructures 28 (2005) 107–114; S. Sonkusale, C.J. Amsinck, D.P. Nackashi, N.H. Di Spigna, D. Barlage, M. Johnson, P.D. Franzon, in: Proceedings of Nano Science and Technology Institute (NSTI) conference 2005, vol. 3, pp. 255.], we proposed and successfully demonstrated an unconventional lithographic technique called PEDAL process (planar edge defined alternate layer) to define wafer scale sub 25 nm nanowires and nanoimprint template. In this publication, the uniformity results on array of sixteen line-width structures with obtained by PEDAL process are presented. The average pitch of array across the 4 in. wafer was measured to be 40.8 nm with the standard deviation of 2.3 nm where as the average pitch of the lines in an array was found to be 41.5 nm with the standard deviation of 4.6 nm. After Pd lift-off the average pitch in nanowire array was measured to be 41.9 nm with standard deviation of 1.8 nm, which is close to the values obtained for the template. DA - 2007/// PY - 2007/// DO - 10.1016/j.mee.2007.01.210 VL - 84 IS - 5-8 SP - 1523-1527 SN - 0167-9317 KW - PEDAL KW - nanoimprint KW - mold KW - nanowires ER - TY - JOUR TI - Tunable photoluminescence of polymer doped with PbSe quantum dots AU - Voitenko, Igor AU - Muth, J. F. AU - Gerhold, Michael AU - Cui, Dehu AU - Xu, Jian T2 - MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS AB - Semiconductor nanoparticle/polymer composites potentially allow the design of photonic materials for optoelectronic devices. The optical characteristics of PbSe quantum dots placed in polymer matrices are investigated for potential applications in electrically controlled absorption modulators and integrated optical circuit components. The photoluminescence yield, shape of absorption band, and effects of size variation of PbSe quantum dots on spectral features are analyzed near the absorption edge of host polymers for the different concentrations of nanocrystals in the composite. It was found that for quantum dots of nominally the same size, there is a strong dependence of position of the absorption peaks in the spectrum depending on the concentration of quantum dots. This results in the emission in the 1500–1600 nm range being tunable with quantum dot concentration. A second emission in the 1200–1300 nm range was also observed and energy transfer from the polymer matrix to the quantum dot appears to mediate the strength of this photoluminescence. DA - 2007/9// PY - 2007/9// DO - 10.1016/j.msec.2006.09.018 VL - 27 IS - 5-8 SP - 1078-1081 SN - 0928-4931 KW - polymer composite KW - semiconductor quantum dots KW - photoluminescence ER - TY - JOUR TI - Origin of the half-wavelength errors in microwave measurements using through-line calibrations AU - Buff, P. Mark AU - Nath, Jayesh AU - Steer, Michael B. T2 - IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT AB - The through–line calibration family uses measurements of a through connection and an inserted line to determine the propagation constant of the line. This is typically used with measurements of a reflect standard to characterize fixturing errors. Subsequently, the S-parameters of a device under test are de-embedded. Measurement uncertainties occur at frequencies where the length of the line standard is an odd multiple of a half-wavelength. The origin of these errors is identified as fixture inconsistencies between the through and the line measurements. Error formulations are developed, and it is shown that a small fixturing error can be accounted for as a multiplicative transmission error. An error sensitivity function is developed and highlights the importance of fixture repeatability. DA - 2007/10// PY - 2007/10// DO - 10.1109/TIM.2007.904490 VL - 56 IS - 5 SP - 1610-1615 SN - 1557-9662 KW - de-embedding KW - genetic algorithm KW - propagation constant KW - through-line (TL) calibration KW - through-reflect-line (TRL) ER - TY - JOUR TI - Numerical analysis of polarization gratings using the finite-difference time-domain method AU - Oh, Chulwoo AU - Escuti, Michael J. T2 - PHYSICAL REVIEW A AB - We report the first full numerical analysis of polarization gratings (PGs), and study their most general properties and limits by using the finite-difference time-domain (FDTD) method. In this way, we avoid limiting assumptions on material properties or grating dimensions (e.g., no paraxial approximations) and provide a more complete understanding of PG diffraction behavior. We identify the fundamental delineation between diffraction regimes (thin versus thick) for anisotropic gratings and determine the conditions for $\ensuremath{\approx}100%$ diffraction efficiency in the framework of the coupled-wave $\ensuremath{\rho}$ and $Q$ parameters. Diffraction characteristics including the efficiency, spectral response, and polarization sensitivity are investigated for the two primary types of PGs with linear and circular birefringence. The angular response and finite-grating behavior (i.e., pixelation) are also examined. Comparisons with previous analytic approximations, where applicable, show good agreement. DA - 2007/10// PY - 2007/10// DO - 10.1103/physreva.76.043815 VL - 76 IS - 4 SP - SN - 1094-1622 ER - TY - JOUR TI - Modeling the nonlinear response of multitones with uncorrelated phase AU - Hart, Frank P. AU - Steer, Michael B. T2 - IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES AB - Traditional simulation approaches for predicting the frequency-domain response of nonlinear devices to multiple tone excitation enforce correlation of the phases of the individual tones. This is the case with time-domain simulators and transform-based schemes such as Harmonic balance as the waveform must be single valued, thus enforcing correlation. Previous efforts in frequency-domain simulators using the arithmetic operator method (AOM) also produced results in good agreement with measurements for correlated-phase input signals. Here, the AOM is applied to directly determine the spectral response of nonlinear systems to excitation by multiple uncorrelated tones in a single simulation. Verification is provided using measurements of a nonlinear amplifier excited by 15 independent tones and comparison to the average of the ensemble of results from multiple correlated-phase simulations. DA - 2007/10// PY - 2007/10// DO - 10.1109/TMTT.2007.906462 VL - 55 IS - 10 SP - 2147-2156 SN - 1557-9670 KW - arithmetic operator method (AOM) KW - computer-aided KW - analysis KW - multitone signals KW - nonlinear amplifiers KW - uncorrelated phase ER - TY - JOUR TI - Increasing channel capacity of an ultrawideband MIMO system using vector antennas AU - Rajagopalan, Ajit AU - Gupta, Gaurav AU - Konanur, Anand S. AU - Hughes, Brian AU - Lazzi, Gianluca T2 - IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION AB - Recently it was shown that co-located vector antennas can provide the same capacity increase as spatial array antennas in multiple-input multiple-output (MIMO) systems. This paper describes the design of a vector antenna consisting of a loop antenna and two orthogonal bowtie antennas for a ultrawideband (UWB) MIMO system that operates in the frequency range 3.6–8.5 GHz. Channel capacity calculations performed with the antenna operating in a rich scattering environment show that spectral efficiency of the UWB vector antenna system approaches that of the traditional spatial array. This demonstrates that vector antennas can be used in place of spatial arrays where compact UWB multiantenna systems are needed. DA - 2007/10// PY - 2007/10// DO - 10.1109/TAP.2007.905938 VL - 55 IS - 10 SP - 2880-2887 SN - 0018-926X KW - multiple-input multiple-output (MIMO) antenna KW - multiple-input multiple-output (MIMO) channel capacity KW - ultrawideband (UWB) antenna KW - vector antenna ER - TY - JOUR TI - Enhancing multiple classifier system performance for machine olfaction using odor-type signatures AU - Phaisangittisagul, Ekachai AU - Nagle, H. Troy T2 - SENSORS AND ACTUATORS B-CHEMICAL AB - Traditional odor classification systems used in machine olfaction devices, which are often called electronic noses, are implemented independently for each application dataset. For different types of odor samples (dissimilar odor datasets), some researchers have proposed a multiple classifier system that combines or fuses the classification outputs of individual, independent classifiers designed specifically for each dissimilar odor. However, in this approach, the classification system has to be reconstructed when new dissimilar odors are added to the machine's operation. Moreover, the multiple classifier system's performance is likely to be degraded due to the added complexity of the combined system. In this study, an approach to assign an unknown odor sample to one specific classifier in the multiple classifier set is proposed that is based on an odor-type signature derived from the sensor array's response waveforms. This novel approach enables an independent design of the classifier for each dissimilar odor, which is very useful when new odors need to be added to an existing machine olfaction system. DA - 2007/7/16/ PY - 2007/7/16/ DO - 10.1016/j.snb.2007.02.011 VL - 125 IS - 1 SP - 246-253 SN - 0925-4005 KW - classifier selection KW - multiple classifier system KW - multilevel decomposition KW - odor-type signature ER - TY - JOUR TI - Characteristics of Ni/Gd FUSI for NMOS gate electrode applications AU - Lee, Bongmook AU - Biswas, Nivedita AU - Novak, Steven R. AU - Misra, Veena T2 - IEEE ELECTRON DEVICE LETTERS AB - This letter investigates the work function tuning of nickel/gadolinium (Ni/Gd) fully silicided (FUSI) gate electrodes on HfSiO x dielectrics. It was found that as the percentage of Gd in the Ni/Gd increased from 10% to 30%, the effective work function value after a one-step 450-degC FUSI anneal decreased from 4.75 to 4.35 eV. In addition, the presence of Gd also resulted in lowering of equivalent oxide thickness (EOT) values. The mechanism for a decreased EOT is attributed to the reduction of low-kappa interfacial layers by the presence of Gd in the gate stack. The decrease in work function is attributed to the creation of oxygen vacancies within the high-kappa layer created by the presence of Gd layer. DA - 2007/7// PY - 2007/7// DO - 10.1109/LED.2007.897889 VL - 28 IS - 7 SP - 555-557 SN - 1558-0563 KW - band edge work function KW - fully silicided (FUSI) gate KW - metal gate electrodes KW - n-MOSFET KW - nickel/gadolinium (Ni/Gd) KW - Ni-FUSI KW - work function extraction ER - TY - JOUR TI - Applications of machine learning to cognitive radio networks AU - Clancy, Charles AU - Hecker, Joe AU - Stuntebeck, Erich AU - O'Shea, Tim T2 - IEEE WIRELESS COMMUNICATIONS AB - Cognitive radio offers the promise of intelligent radios that can learn from and adapt to their environment. To date, most cognitive radio research has focused on policy-based radios that are hard-coded with a list of rules on how the radio should behave in certain scenarios. Some work has been done on radios with learning engines tailored for very specific applications. This article describes a concrete model for a generic cognitive radio to utilize a learning engine. The goal is to incorporate the results of the learning engine into a predicate calculus-based reasoning engine so that radios can remember lessons learned in the past and act quickly in the future. We also investigate the differences between reasoning and learning, and the fundamentals of when a particular application requires learning, and when simple reasoning is sufficient. The basic architecture is consistent with cognitive engines seen in AI research. The focus of this article is not to propose new machine learning algorithms, but rather to formalize their application to cognitive radio and develop a framework from within which they can be useful. We describe how our generic cognitive engine can tackle problems such as capacity maximization and dynamic spectrum access. DA - 2007/8// PY - 2007/8// DO - 10.1109/MWC.2007.4300983 VL - 14 IS - 4 SP - 47-52 SN - 1558-0687 ER - TY - JOUR TI - An ultracold neutron source at the NC state university PULSTAR reactor AU - Korobkna, E. AU - Wehring, B. W. AU - Hawari, A. I. AU - Young, A. R. AU - Huffman, P. R. AU - Golub, R. AU - Xu, Y. AU - Palmquist, G. T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT AB - Research and development is being completed for an ultracold neutron (UCN) source to be installed at the PULSTAR reactor on the campus of North Carolina State University (NCSU). The objective is to establish a university-based UCN facility with sufficient UCN intensity to allow world-class fundamental and applied research with UCN. To maximize the UCN yield, a solid ortho-D2 converter will be implemented coupled to two moderators, D2O at room temperature, to thermalize reactor neutrons, and solid CH4, to moderate the thermal neutrons to cold-neutron energies. The source assembly will be located in a tank of D2O in the space previously occupied by the thermal column of the PULSTAR reactor. Neutrons leaving a bare face of the reactor core enter the D2O tank through a 45×45 cm cross-sectional area void between the reactor core and the D2O tank. Liquid He will cool the disk-shaped UCN converter to below 5 K. Independently, He gas will cool the cup-shaped CH4 cold-neutron moderator to an optimum temperature between 20 and 40 K. The UCN will be transported from the converter to experiments by a guide with an inside diameter of 16 cm. Research areas being considered for the PULSTAR UCN source include time-reversal violation in neutron beta decay, neutron lifetime determination, support measurements for a neutron electric-dipole-moment search, and nanoscience applications. DA - 2007/8/21/ PY - 2007/8/21/ DO - 10.1016/j.nima.2007.04.116 VL - 579 IS - 1 SP - 530–533 SN - 0168-9002 KW - ultracold neutrons KW - cold neutrons KW - neutron source KW - nuclear reactor ER - TY - JOUR TI - A dynamic TCP-Aware call admission control scheme. for generic next generation packet-switched wireless networks AU - Wang, Xinbing AU - Eun, Do Young AU - Wang, Wenye T2 - IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS AB - Traditional call admission control (CAC) schemes only consider call-level performance and are mainly designed for circuit-switched wireless network. Since future wireless communications will become packet-switched systems, the packet-level features could be explored to improve the system performance. This is especially true when the TCP-type of elastic applications are running over such packet-switched wireless networks, as the elasticity of TCP applications has more tolerance toward the throughput/delay variation than non-elastic traffic does. In order to efficiently utilize the system resource from an admission control perspective, we propose a TCP-aware CAC scheme to regulate the packet-level dynamics of TCP flows. We analyze the system performance under realistic scenarios in which (i) the call holding time for non-elastic traffic like voice is independent of system states and (ii) the call holding time for TCP type of traffic depends on the system state, i.e., on the TCP flow's transmission rate. Extensive simulations are presented under different scenarios to show that the proposed scheme can effectively improve the system performance in terms of call blocking probability, call-level throughput (call/min) and link utilization, in accordance with our theoretical results. DA - 2007/9// PY - 2007/9// DO - 10.1109/TWC.2007.06064 VL - 6 IS - 9 SP - 3344-3352 SN - 1558-2248 KW - admission control KW - wireless networks KW - TCP ER - TY - PAT TI - Optoelectonic devices having arrays of quantum-dot compound semiconductor superlattices therein AU - Zhang, Z.-B. AU - Misra, V. AU - Bedair, S. M. A. AU - Ozturk, M. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - PAT TI - Methods of fabricating strained semiconductor-on-insulator field-effect transistors and related devices AU - Ozturk, M. AU - Misra, V. AU - Chopra, S. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - PAT TI - Method and circuit for cascaded pulse width modulation AU - Huang, Q. AU - Edris, A.-A. AU - Ingram, M. R. AU - Sirisukprasert, S. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Filter prototypes comprising singlet and/or in-line sections AU - Fathelbab, W. M. AU - Steer, M. B. T2 - INTERNATIONAL JOURNAL OF ELECTRONICS AB - A synthesis procedure for the design of filter prototypes comprising singlet and/or in-line sections is presented. Each singlet section realizes a finite-frequency transmission zero without requiring frequency-invariant elements at its non-resonating nodes. Prototypes comprised entirely of singlet sections realize either a lowpass or highpass response. These prototypes can also be easily transformed to in-line prototypes through the usage of simple mathematical expressions. The characteristics of an experimental bandpass filter centered at 915 MHz are reported. DA - 2007/// PY - 2007/// DO - 10.1080/00207210701682888 VL - 94 IS - 10 SP - 925-934 SN - 0020-7217 KW - singlet/in-line sections KW - lowpass/highpass filters KW - cascade synthesis ER - TY - JOUR TI - Energy-efficiency and transmission strategy selection in cooperative wireless sensor networks AU - Zhang, Yanbing AU - Dai, Huaiyu T2 - JOURNAL OF COMMUNICATIONS AND NETWORKS AB - Energy efficiency is one of the most critical concerns for wireless sensor networks. By allowing sensor nodes in close proximity to cooperate in transmission to form a virtual multiple-input multiple-output (MIMO) system, recent progress in wireless MIMO communications can be exploited to boost the system throughput, or equivalently reduce the energy consumption for the same throughput and BER target. However, these cooperative transmission strategies may incur additional energy cost and system overhead. In this paper, assuming that data collectors are equipped with antenna arrays and superior processing capability, energy efficiency of relevant traditional and cooperative transmission strategies: Single-input-multiple-output (SIMO), space-time block coding (STBC), and spatial multiplexing (SM) are studied. Analysis in the wideband regime reveals that, while receive diversity introduces significant improvement in both energy efficiency and spectral efficiency, further improvement due to the transmit diversity of STBC is limited, as opposed to the superiority of the SM scheme especially for non-trivial spectral efficiency. These observations are further confirmed in our analysis of more realistic systems with limited bandwidth, finite constellation sizes, and a target error rate. Based on this analysis, general guidelines are presented for optimal transmission strategy selection in system level and link level, aiming at minimum energy consumption while meeting different requirements. The proposed selection rules, especially those based on system-level metrics, are easy to implement for sensor applications. The framework provided here may also be readily extended to other scenarios or applications. DA - 2007/12// PY - 2007/12// DO - 10.1109/JCN.2007.6182883 VL - 9 IS - 4 SP - 473-481 SN - 1976-5541 KW - energy efficiency KW - sensor networks KW - virtual multiple-input multiple-output (MIMO) ER - TY - PAT TI - Crossbar array microelectronic electrochemical cells AU - Misra, V. AU - Damiano, J., Jr. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Correlation between compositional fluctuation and magnetic properties of Tm-doped AlGaN alloys AU - Nepal, N. AU - Bedair, S. M. AU - El-Masry, N. A. AU - Lee, D. S. AU - Steckl, A. J. AU - Zavada, J. M. T2 - APPLIED PHYSICS LETTERS AB - The magnetic properties of Tm-doped AlxGa1−xN (0⩽x⩽1) alloys grown by solid-source molecular beam epitaxy were studied by hysteresis measurements and shown to exhibit ferromagnetic behavior at room temperature. The measured magnetization was strongly dependent on the Al content and reached a maximum for x=0.62. Previously reported photoluminescence measurements on these films yielded a blue emission at 465nm with peak intensity at the same Al content. Both magnetic and optical properties are directly correlated with the alloy compositional fluctuation found in undoped AlxGa1−xN alloys. DA - 2007/11/26/ PY - 2007/11/26/ DO - 10.1063/1.2817741 VL - 91 IS - 22 SP - SN - 1077-3118 ER - TY - JOUR TI - Workload state classification with automation during simulated air traffic control AU - Kaber, David B. AU - Perry, Carlene M. AU - Segall, Noa AU - Sheik-Nainar, Mohamed A. T2 - INTERNATIONAL JOURNAL OF AVIATION PSYCHOLOGY AB - Real-time operator workload assessment and state classification may be useful for decisions about when and how to dynamically apply automation to information processing functions in aviation systems. This research examined multiple cognitive workload measures, including secondary task performance and physiological (cardiac) measures, as inputs to a neural network for operator functional state classification during a simulated air traffic control (ATC) task. Twenty-five participants performed a low-fidelity simulation under manual control or 1 of 4 different forms of automation. Traffic volume was either low (3 aircraft) or high (7 aircraft). Participants also performed a secondary (gauge) monitoring task. Results demonstrated significant effects of traffic volume (workload) on aircraft clearances (p < .01) and trajectory conflicts (p < .01), secondary task performance (p < .01), and subjective ratings of task workload (p < .01). The form of ATC automation affected the number of aircraft collisions (p < .05), secondary task performance (p < .01), and heart rate (HR; p < .01). However, heart rate and heart rate variability measures were not sensitive to the traffic manipulation. Neural network models of controller workload (defined in terms of traffic volume) were developed using the secondary task performance and simple heart rate measure as inputs. The best workload classification accuracy using a genetic algorithm (across all forms of ATC automation) was 64%, comparable to prior work. Additional neural network models of workload for each mode of ATC automation revealed substantial variability in predictive accuracy, based on the characteristics of the automation. Secondary task performance was a highly sensitive indicator of ATC workload, whereas the heart rate measure appeared to operate as a more global indicator of workload. A limited range of cardiac response might be sufficient for the demands of the brain in ATC. The results have applicability to design of future adaptive systems integrating neural-network-based workload state classifiers for multiple forms of automation. DA - 2007/// PY - 2007/// DO - 10.1080/10508410701527860 VL - 17 IS - 4 SP - 371-390 SN - 1532-7108 ER - TY - JOUR TI - Voltage-mode driver preemphasis technique for on-chip global buses AU - Zhang, Liang AU - Wilson, John M. AU - Bashirullah, Rizwan AU - Luo, Lei AU - Xu, Jian AU - Franzon, Paul D. T2 - IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS AB - This paper demonstrates that driver preemphasis technique can be used for on-chip global buses to increase signal channel bandwidth. Compared to conventional repeater insertion techniques, driver preemphasis saves repeater layout complexity and reduces power consumption by 12%-39% for data activity factors above 0.1. A driver circuit architecture using voltage-mode preemphasis technique was tested in 0.18-mum CMOS technology for 10-mm long interconnects at 2 Gb/s DA - 2007/2// PY - 2007/2// DO - 10.1109/TVLSI.2007.893588 VL - 15 IS - 2 SP - 231-236 SN - 1557-9999 KW - global buses KW - low-power KW - on-chip KW - preemphasis KW - repeater insertion ER - TY - JOUR TI - Room temperature laser action from multiple bands in photoexcited GaN grown on a silicon substrate AU - Al-Ajmi, F. S. AU - Kolbas, R. M. AU - Roberts, J. C. AU - Rajagopal, P. AU - Cook, J. W., Jr. AU - Piner, E. L. AU - Linthicum, K. J. T2 - Applied Physics Letters AB - Room temperature stimulated emission and laser action with well developed longitudinal optical modes from high-quality GaN films grown on silicon substrates by metal-organic chemical-vapor deposition are presented. Laser action with well developed Fabry-Pérot modes involving the A, B, and C bands was observed. Stimulated emission one exciton below the A band and the B band and one longitudinal optical phonon below the B band was also observed. The effective index of refraction during laser operation was measured to be 2.9. DA - 2007/4/9/ PY - 2007/4/9/ DO - 10.1063/1.2722201 VL - 90 IS - 15 SP - 151116 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2722201 DB - Crossref ER - TY - JOUR TI - Nanodiamond and onion-like carbon polymer nanocomposites (vol 16, pg 1213, 2007) AU - Shenderova, O. AU - Tyler, T. AU - Cunningham, G. AU - Ray, M. AU - Walsh, J. AU - Casulli, M. AU - Hens, S. AU - McGuire, G. AU - Kuznetsov, V. AU - Lipa, S. T2 - DIAMOND AND RELATED MATERIALS DA - 2007/9// PY - 2007/9// DO - 10.1016/s0925-9635(07)00337-8 VL - 16 IS - 9 SP - 1770-1770 SN - 0925-9635 ER - TY - PAT TI - Methods, computer program products, and devices for calibrating chronically tissue implanted sensors using chronically tissue AU - Scarantino, C. W. AU - Nagle, H. T. AU - Kim, C.-S. AU - Ufer, S. AU - Fiering, J. AU - Kermani, B. G. C2 - 2007/// DA - 2007/// PY - 2007/// ER - TY - JOUR TI - Electronic properties of molecular memory circuits on a nanoscale scaffold AU - Blum, Amy Szuchmacher AU - Soto, Carissa M. AU - Wilson, Charmaine D. AU - Amsinck, Christian AU - Franzon, Paul AU - Ratna, Banahalli R. T2 - IEEE TRANSACTIONS ON NANOBIOSCIENCE AB - Significant challenges exist in assembling and interconnecting the building blocks of a nanoscale device and being able to electronically address or measure responses at the molecular level. Here we demonstrate the usefulness of engineered proteins as scaffolds for bottom-up self-assembly for building nanoscale devices out of multiple components. Using genetically engineered cowpea mosaic virus, modified to express cysteine residues on the capsid exterior, gold nanoparticles were attached to the viral scaffold in a specific predetermined pattern to produce specific interparticle distances. The nanoparticles were then interconnected using thiol-terminated conjugated organic molecules, resulting in a three-dimensional network. Network properties were engineered by using molecular components with different I-V characteristics. Networks consisting of molecular wires alone were compared with networks containing voltage controlled molecular switches with two stable conductance states. Using such bistable molecules enabled the formation of switchable molecular networks that could be used in nanoscale memory circuits. DA - 2007/12// PY - 2007/12// DO - 10.1109/TNB.2007.908978 VL - 6 IS - 4 SP - 270-274 SN - 1558-2639 KW - biomaterials KW - molecular electronics KW - nanotechnology ER - TY - JOUR TI - Development of green, yellow, and amber light emitting diodes using InGaN multiple quantum well structures AU - Barletta, Philip T. AU - Berkman, E. Acar AU - Moody, Baxter F. AU - El-Masry, Nadia A. AU - Emara, Ahmed M. AU - Reed, Mason J. AU - Bedair, S. M. T2 - APPLIED PHYSICS LETTERS AB - The authors present optical and electrical data for long wavelength (573–601nm) InGaN∕GaN multiple quantum well light emitting diodes (LEDs) grown by metal organic chemical vapor deposition. These results are achieved by optimizing the active layer growth temperature and the quantum well width. Also, the p-GaN is grown at low temperature to avoid the disintegration of the InGaN quantum wells with high InN content. A redshift is observed for both the green and yellow LEDs upon decreasing the injection current at low current regime. In the case of the yellow LED, this shift is enough to push emission into the amber (601nm). DA - 2007/4/9/ PY - 2007/4/9/ DO - 10.1063/1.2721133 VL - 90 IS - 15 SP - SN - 0003-6951 ER - TY - JOUR TI - Transmission electron microscopy studies of regrown GaN Ohmic contacts on patterned substrates for metal oxide semiconductor field effect transistor applications AU - Saripalli, Y. N. AU - Pei, L. AU - Biggerstaff, T. AU - Ramachandran, S. AU - Duscher, G. J. AU - Johnson, M. A. L. AU - Zeng, C. AU - Dandu, K. AU - Jin, Y. AU - Barlage, D. W. T2 - APPLIED PHYSICS LETTERS AB - Contact selected area regrowth of GaN was performed by metal organic chemical vapor deposition using a silicon nitride dielectric hard mask to define plasma etched recesses and to define source-drain regions. A low temperature regrowth process at 750–850°C was adopted to limit lateral overgrowth. High resolution electron microscopy images and selected area diffraction confirmed the regrowth selectivity and revealed that the low temperature regrown GaN is epitaxial and has a wurtzite crystal structure. I-V characteristics of the fabricated metal oxidesemiconductor field effect transistor show enhancement mode operation. DA - 2007/5/14/ PY - 2007/5/14/ DO - 10.1063/1.2741123 VL - 90 IS - 20 SP - SN - 1077-3118 ER - TY - JOUR TI - Nitrogen acceptors in bulk ZnO (000(1)over-bar)) substrates and homoepitaxial ZnO films AU - Adekore, B. T. AU - Pierce, J. M. AU - Davisb, R. F. AU - Barlage, D. W. AU - Muth, J. F. T2 - JOURNAL OF APPLIED PHYSICS AB - Bulk single crystals of unintentionally doped ZnO having charge carrier concentration, ND−NA values of ∼1017 cm−3 were implanted with N+ ions at dosages of 1015 and 1016 cm−2 at 95 keV to a depth of 150 nm. The resulting p−n structure having acceptor concentrations ranging from 1017 to 1018 cm−3 was compared with nitrogen doped homoepitaxial films with ∼8×1017 cm−3 acceptors. Photoluminescence spectra acquired at 8 K showed an increase in the peak for the neutral donor-bound to acceptor-bound transition at 3.210 eV with increasing annealing temperature, thermal activation of a unique donor to acceptor transition due to nitrogen at 3.067 and 3.057 eV for implanted and epitaxial films, respectively; and an increase in the intensity of the defect-related green band at selected temperatures. Electroluminescence measurements at 300 K revealed an ultraviolet band, direct band-to-band recombination at 3.34 eV, donor-acceptor pair recombinations at 3.19 and 3.0 eV, and recombination in the green region centered at 2.49 eV. Current-voltage characteristics of implanted and homoepitaxial p−n diodes were also determined. DA - 2007/7/15/ PY - 2007/7/15/ DO - 10.1063/1.2751097 VL - 102 IS - 2 SP - SN - 1089-7550 ER - TY - JOUR TI - Management alternatives to enhance water quality and ecological function of channelized streams and drainage canals AU - Evans, R. O. AU - Bass, K. L. AU - Burchell, M. R. AU - Hinson, R. D. AU - Johnson, R. AU - Doxey, M. T2 - Journal of Soil & Water Conservation DA - 2007/// PY - 2007/// VL - 62 IS - 4 SP - 308-320 ER - TY - JOUR TI - Magnetic and magnetotransport properties of (AlGaN/GaN): Mg/(GaMnN) heterostructures at room temperature AU - Mahros, Amr M. AU - Luen, M. O. AU - Emara, A. AU - Bedair, S. M. AU - Berkman, E. A. AU - El-Masry, N. A. AU - Zavada, J. M. T2 - APPLIED PHYSICS LETTERS AB - Dilute magnetic semiconductor films (GaMnN) are highly resistive, making transport measurements difficult to achieve. However, when GaMnN films are sandwiched between p-type doped (AlGaN∕GaN) strained-layer superlattices, holes from the superlattice interact with the Mn3+∕2+ ions and transport measurements were realized. The authors have found also that the ferromagnetic properties of GaMnN critically depend on the level of p-type doping in the superlattice. They report anomalous Hall effect measurements in this (AlGaN∕GaN):Mg∕(GaMnN) multilayered structure. The current results also demonstrate the role of carriers, especially holes, in mediating the ferromagnetic properties of GaMnN dilute magnetic semiconductor films. DA - 2007/6/18/ PY - 2007/6/18/ DO - 10.1063/1.2749717 VL - 90 IS - 25 SP - SN - 0003-6951 ER - TY - JOUR TI - Fully integrated AC coupled interconnect using buried bumps AU - Wilson, John AU - Mick, Stephen AU - Xu, Jian AU - Luo, Lei AU - Bonafede, Salvatore AU - Huffman, Alan AU - LaBennett, Richard AU - Franzon, Paul D. T2 - IEEE TRANSACTIONS ON ADVANCED PACKAGING AB - Presented is the complete demonstration of an assembled system using AC coupled interconnect (ACCI) and buried solder bumps. In this system, noncontacting input/output (I/O) are created by using half-capacitor plates on both a chip and a substrate, while buried solder bumps are used to provide power/ground distribution and physical alignment of the coupling plates. ACCI using buried bumps is a technology that provides a manufacturable solution for noncontacting I/O signaling by integrating high-density, low inductance power/ground distribution with high-density, high-speed I/O. The demonstration system shows two channels operating simultaneously at 2.5 Gb/s/channel with a bit error rate less than 10$^{-12}$ , across 5.6 cm of transmission line on a multichip module (MCM). Simple transceiver circuits were designed and fabricated in a 0.35-$\mu$m complementary metal–oxide–semiconductor (CMOS) technology, and for PRBS-127 data at 2.5 Gb/s transmit and receive circuits consumed 10.3 mW and 15.0 mW, respectively. This work illustrates the increasing importance of chip and package co-design for high-performance systems. DA - 2007/5// PY - 2007/5// DO - 10.1109/TADVP.2007.896920 VL - 30 IS - 2 SP - 191-199 SN - 1521-3323 KW - AC coupled interconnect (ACCI) KW - buried bumps KW - capacitive coupling KW - MCM KW - pulse signaling KW - noncontacting I/O KW - chip and package co-design ER - TY - JOUR TI - Elastic spin-relaxation processes in semiconductor quantum dots AU - Semenov, Y. G. AU - Kim, K. W. T2 - Physical Review B AB - Electron spin decoherence caused by elastic spin-phonon processes is investigated comprehensively in a zero-dimensional environment. Specifically, a theoretical treatment is developed for the processes associated with the fluctuations in the phonon potential as well as in the electron procession frequency through the spin-orbit and hyperfine interactions in the semiconductor quantum dots. The analysis identifies the conditions (magnetic field, temperature, etc.) in which the elastic spin-phonon processes can dominate over the inelastic counterparts with the electron spin-flip transitions. Particularly, the calculation results illustrate the potential significance of an elastic decoherence mechanism originating from the intervalley transitions in semiconductor quantum dots with multiple equivalent energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity and phonon decay in spin relaxation is also examined along with that of the local effective field fluctuations caused by the stochastic electronic transitions between the orbital states. Numerical estimations are provided for typical GaAs and Si-based quantum dots. DA - 2007/5/30/ PY - 2007/5/30/ DO - 10.1103/physrevb.75.195342 VL - 75 IS - 19 SP - J2 - Phys. Rev. B LA - en OP - SN - 1098-0121 1550-235X UR - http://dx.doi.org/10.1103/PhysRevB.75.195342 DB - Crossref ER - TY - JOUR TI - Deafness alters auditory nerve fibre responses to cochlear implant stimulation AU - Sly, David J. AU - Heffer, Leon F. AU - White, Mark W. AU - Shepherd, Robert K. AU - Birch, Michael G. J. AU - Minter, Ricki L. AU - Nelson, Niles E. AU - Wise, Andrew K. AU - Stephen J. O'Leary, T2 - EUROPEAN JOURNAL OF NEUROSCIENCE AB - Here we characterized the relationship between duration of sensorineural hearing loss and the response of the auditory nerve to electrical stimulus rate. Electrophysiological recordings were made from undeafened guinea pigs and those ototoxically deafened for either 5 weeks or 6 months. Auditory neuron survival decreased significantly with the duration of deafness. Extracellular recordings were made from auditory nerve fibres responding to biphasic, charge-balanced current pulses delivered at rates of 20 and 200 pulses/s via a monopolar scala tympani stimulating electrode. The response to 20 pulses/s electrical stimulation of the deafened cochlea exhibited a decrease in spike latency, unaltered temporal jitter and unaltered dynamic range (of nerve firing rate against stimulus current), and a reduction in threshold after 6 months of deafness. The response to a 200-pulse/s stimulus was similar except that the dynamic range was greater than with 20 pulses/s and was also greater in deafened animals than in undeafened animals. Deafness and pulse rate are related; in deaf animals spike recovery appears to be complete between successive stimulus pulses at a low rate (20 pulses/s), but incomplete between pulses at a moderate pulse rate (200 pulses/s). These results suggest that changes in the function of individual auditory nerve fibres after deafness may affect clinical responses during high-rate stimulation such as that used in contemporary speech processing strategies, but not during lower rate stimulation such as that used to record evoked potentials. DA - 2007/7// PY - 2007/7// DO - 10.1111/j.1460-9568.2007.05678.x VL - 26 IS - 2 SP - 510-522 SN - 1460-9568 KW - electrical stimulation KW - guinea pig KW - hearing loss KW - neurodegeneration KW - spiral ganglion ER - TY - JOUR TI - Asymptotic analysis on the interaction between spatial diversity and multiuser diversity in wireless networks AU - Zhou, Quan AU - Dai, Huaiyu T2 - IEEE TRANSACTIONS ON SIGNAL PROCESSING AB - Spatial diversity and multiuser diversity attract much research interest recently. In this paper, through asymptotic analysis of the average system capacity and scheduling gain, we investigate the cross-layer interaction between these two forms of diversity in wireless networks. Rigorous proofs and necessarily stronger results in terms of convergence are provided for some intuitions in this area. Equally important, explicit expressions of scheduling gain and average system capacity in various circumstances that reveal interconnections and fundamental tradeoffs among key system parameters are given, which afford us some insights in system design. Our results are general enough to cover many practical scenarios of interest. DA - 2007/8// PY - 2007/8// DO - 10.1109/TSP.2007.896059 VL - 55 IS - 8 SP - 4271-4283 SN - 1941-0476 KW - average system capacity KW - multiple-input multiple-output (MIMO) KW - multiuser diversity KW - scheduling gain KW - spatial diversity ER - TY - JOUR TI - Universal behavior of the electron g factor in GaAs/AlxGa1-xAs quantum wells AU - Yugova, I. A. AU - Greilich, A. AU - Yakovlev, D. R. AU - Kiselev, A. A. AU - Bayer, M. AU - Petrov, V. V. AU - Dolgikh, Y. K. AU - Reuter, D. AU - Wieck, A. D. T2 - Physical Review. B, Condensed Matter and Materials Physics DA - 2007/// PY - 2007/// VL - 75 IS - 24 ER - TY - JOUR TI - Study of igniter in low-frequency square wave electronic ballasts for metal halide lamps AU - Guo, Rong AU - Chen, Min AU - Qian, Zhaoming T2 - IEEE TRANSACTIONS ON POWER ELECTRONICS AB - Metal halide lamps (MHLs) have serious acoustic resonance problem. The most widely used method to achieve acoustic-resonance free is to use low-frequency square wave (LFSW) electronic ballasts. There are two ignition methods commonly used in LFSW electronic ballast: high-frequency resonance ignition and additional pulse igniter. This paper analyzed the problems during ignition while using the conventional additional pulse igniter and proposed some solutions. A novel high-frequency resonance igniter is also proposed, where no extra semiconductors and feedback control circuit are needed to perform the ignition. High-voltage ignition pulses are obtained by utilizing the fast polarity inversion of the output voltage of full-bridge inverter. Theoretical analysis, simulation, and experiment results of a prototype for 70-W MHLs verified the effectiveness of both the proposed solutions and the igniter. DA - 2007/7// PY - 2007/7// DO - 10.1109/TPEL.2007.900450 VL - 22 IS - 4 SP - 1098-1106 SN - 1941-0107 KW - ballast KW - igniter KW - low-frequency square wave (LFSW) KW - metal halide lamps (MHLs) KW - start-up ER - TY - JOUR TI - Planar ZnO ultraviolet modulator AU - Zhang, X. Y. AU - Dhawan, A. AU - Wellenius, P. AU - Suresh, A. AU - Muth, J. F. T2 - APPLIED PHYSICS LETTERS AB - A planar electroabsorption modulator suitable for spatial light modulation has been constructed. The device operates near the band edge of zinc oxide at 3.3eV and is based on broadening and shifting of the unconfined exciton with an externally applied electric field. The ZnO active layer was deposited on an aluminum/titanium oxide dielectric on an indium tin oxide conducting layer on glass. A transparent conductive InGaZnO layer on a spin on glass insulator served as the top contact, allowing high electric fields to be applied transverse to the ZnO layer. The modulator operates at room temperature in transmission mode with +45% modulation at 373nm and −18% modulation at 380nm at 140V applied bias, corresponding to ∼450kV∕cm electric field across the ZnO active layer. DA - 2007/8/13/ PY - 2007/8/13/ DO - 10.1063/1.2770995 VL - 91 IS - 7 SP - SN - 0003-6951 ER - TY - JOUR TI - Monolithic/Modularized voltage regulator channel AU - Zhang, Xin AU - Huang, Alex T2 - IEEE TRANSACTIONS ON POWER ELECTRONICS AB - To achieve higher power density and design flexibility with unlimited phase number, the concept of monolithic/modularized voltage regulator channel (MVRC) is introduced to be a generic power integrated circuit (IC) solution for both central processing unit (CPU) and point-of-load (POL) power management. Novel control architecture and analog circuits are invented to implement the MVRC concept. Tolerance analysis and hardware testing verified that the MVRC approach is suitable for today's and even future's microprocessor power management. DA - 2007/7// PY - 2007/7// DO - 10.1109/TPEL.2007.900466 VL - 22 IS - 4 SP - 1162-1176 SN - 1941-0107 KW - monolithic/modularized voltage regulator channel (MVRC) KW - voltage regulator module (VRM) KW - distributed control KW - interleaving KW - adaptive voltage position (AVP) KW - current sharing (CS) KW - tolerance KW - integration ER - TY - JOUR TI - Low-power rotary clock array design AU - Yu, Zhengtao AU - Liu, Xun T2 - IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS AB - Rotary clock is a recently proposed clock distribution technique based on wave propagation in transmission lines. In this paper, we investigate the problem of power minimization of rotary clock designs. Specifically, we have developed a software tool based on the method of partial element equivalent circuit that is capable of extracting the SPICE netlist from the layout specification of a rotary clock design. Using our tool, we have performed extensive analysis that links various design parameters of a rotary clock design to its oscillation frequency and power dissipation. Based on the results of our analysis, we then propose a power minimization algorithm. Our algorithm derives a rotary clock structure that dissipates the minimal power while satisfying the clock dimension requirement and oscillating at the target frequency with the given clock load. Experimental results have demonstrated that, for target operating frequencies ranging from 0.5 to 5 GHz, rotary clock designs can achieve power savings of up to 80% in comparison with conventional clock tree implementations DA - 2007/1// PY - 2007/1// DO - 10.1109/TVLSI.2006.887804 VL - 15 IS - 1 SP - 5-12 SN - 1557-9999 KW - clocks KW - partial element equivalent circuit KW - synchronization KW - transmission line resonators KW - traveling-wave amplifiers ER - TY - JOUR TI - Length scales for coherent pi-bonding interactions in complex high-k oxide dielectrics and their interfaces AU - Seo, H. AU - Lucovsky, G. AU - Fleming, L. B. AU - Ulrich, M. D. AU - Luning, J. AU - Koster, G. AU - Geballe, T. H. T2 - MICROELECTRONIC ENGINEERING AB - This paper uses X-ray absorption and vacuum ultra-violet spectroscopic ellipsometry to distinguish between non-crystallinity, and the suppression of Jahn-Teller splittings that identify a scale of order metric, λs, of ∼3 nm for distinguishing between i) nanocrystalline-order that can be detected by x-ray diffraction for λs > 3-4 nm, and ii) reduced nanocrystalline order that can be detected by atomic-scale imaging and extended X-ray absorption spectroscopy for λs < ∼2.5 nm. This approach is first applied to elemental transition metal oxides, and then to complex oxides and complex oxide alloys. DA - 2007/// PY - 2007/// DO - 10.1016/j.mee.2007.04.069 VL - 84 IS - 9-10 SP - 2298-2301 SN - 0167-9317 KW - length scales of order KW - spectroscopic studies KW - nanocrystalline complex oxides and complex oxide alloys ER - TY - JOUR TI - Imaging properties of a metallic photonic crystal AU - Xiao, D. AU - Kim, K. W. AU - Zavada, J. M. T2 - Journal of Applied Physics AB - Imaging effects in metallic photonic crystals (PCs) are examined theoretically based on the finite difference time-domain method. The analysis shows that, in metallic PC-based systems, far-field images do form at the opposite side of the PC “lens” and more importantly, follow the rule of geometric optics with respect to the changes in the source position as a direct proof of negative refraction. However, the comparison of ideal left-handed media with a metallic PC suggests that the focusing effect in the PC based system is different from that of the ideal left-handed media in many aspects, due to the inhomogeneous nature of the PC. Particularly, strong dependence on the individual geometry as well as the frequency in the PC-based system renders the effective index sensitive to the variations and potentially limits its application as a superlens. DA - 2007/6// PY - 2007/6// DO - 10.1063/1.2737771 VL - 101 IS - 11 SP - 113105 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2737771 DB - Crossref ER - TY - JOUR TI - An independent component analysis approach for minimizing effects of recirculation in dynamic susceptibility contrast magnetic resonance imaging AU - Wu, Yang AU - An, Hongyu AU - Krim, Hamid AU - Lin, Weili T2 - JOURNAL OF CEREBRAL BLOOD FLOW AND METABOLISM AB - In dynamic susceptibility contrast (DSC) perfusion-weighted imaging, effects of recirculation are normally minimized by a gamma-variate fitting procedure of the concentration curves before estimating hemodynamic parameters. The success of this method, however, hinges largely on the extent to which magnetic resonance signal is altered in the presence of a contrast agent and a temporal separation between the first and subsequent passages of the contrast agent. Moreover, important physiologic information might be compromised by imposing an analytic equation to all measured concentration curves. This investigation proposes to exploit independent component analysis to minimize effects of recirculation in DSC. Results obtained from simulation, normal healthy volunteers, and acute stroke patients show that such a technique can greatly minimize the effects of recirculation despite a substantial overlap between the first passage and recirculation. This in turn should improve estimation of cerebral hemodynamics particularly when an overlap between the first passage and recirculation is suspected as in an ischemic lesion. DA - 2007/3// PY - 2007/3// DO - 10.1038/sj.jcbfm.9600374 VL - 27 IS - 3 SP - 632-645 SN - 1559-7016 KW - cerebral ischemia KW - dynamic susceptibility contrast KW - gamma-variate fitting KW - independent component analysis KW - perfusion-weighted imaging KW - recirculation ER - TY - JOUR TI - Spectroscopic studies of O-vacancy defects in transition metal oxides AU - Lucovsky, G. AU - Luening, J. AU - Fleming, L. B. AU - Ulrich, M. D. AU - Rowe, J. E. AU - Seo, H. AU - Lee, S. AU - Lysaght, P. AU - Bersuker, G. T2 - JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS DA - 2007/10// PY - 2007/10// DO - 10.1007/s10854-007-9192-x VL - 18 SP - S263-S266 SN - 1573-482X ER - TY - JOUR TI - Quasimonochromatic emission spectra in the near field by polar semiconductor thermal sources AU - Sokolov, V. N. AU - Kong, B. D. AU - Kim, K. W. AU - Trew, R. J. T2 - Applied Physics Letters AB - The near-field spectra of the electromagnetic field emitted from a planar surface are theoretically investigated for a number of polar semiconductor and dielectric materials that support surface phonon polaritons. All of the studied materials, InP, GaAs, GaN, SiC, and α-Al2O3 (sapphire), exhibit quasimonochromatic thermal emission symbolized by strong peaks of evanescent modes at well-defined frequencies in the near field that correspond to the appropriate peaks in the density of states for surface phonon polaritons. It is also found that the materials with lower polariton frequencies (e.g., InP and GaAs) generally demonstrate a higher peak spectral energy density compared to those with higher frequencies (e.g., SiC). This trend is maintained over the entire range of temperature (300–600K) and the distance from the surface (⩽10μm) considered in the calculation. Thus, the results clearly indicate that among the studied materials InP and GaAs are the best candidates to provide the quasicoherent thermal emission for potential use as a nanoscale thermal source. The energy density stored in the evanescent peaks, when close to the surface, is estimated to be many orders of magnitude larger than that in the blackbody radiation. DA - 2007/3/12/ PY - 2007/3/12/ DO - 10.1063/1.2713166 VL - 90 IS - 11 SP - 113106 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2713166 DB - Crossref ER - TY - JOUR TI - Prevention of warp breaks in Jacquard weaving AU - Seyam, Abdelfattah M. AU - Lee, Jin Ho AU - Hodge, George AU - Oxenham, William AU - Grant, Edward T2 - FIBERS AND POLYMERS DA - 2007/2// PY - 2007/2// DO - 10.1007/bf02908163 VL - 8 IS - 1 SP - 79-83 SN - 1229-9197 KW - MEMS accelerometers KW - Jacquard weaving KW - warp breaks detection KW - warp breaks prevention KW - automation KW - warp tension ER - TY - JOUR TI - Lead zirconate titanate thin film capacitors on electroless nickel coated copper foils for embedded passive applications AU - Kim, Taeyun AU - Kingon, Angus I. AU - Maria, Jon-Paul AU - Croswell, Robert T. T2 - THIN SOLID FILMS AB - Lead zirconate titanate (PZT, 52/48) thin film capacitors were prepared on electroless Ni coated Cu foil by chemical solution deposition for printed wiring board embedded capacitor applications. Phase development, dielectric properties, and leakage characteristics of capacitors were investigated, in particular as a function of the process temperature. Dielectric properties of the capacitors were dependent on the crystallization temperature, and capacitance densities of more than 350 nF/cm2 and loss tangent of less than 0.03 were measured for capacitors crystallized below 600 °C. Lowest leakage current densities (around 2 × 10− 7 A/cm2 at 10 V direct current (DC)) and highest breakdown fields could be obtained for capacitors crystallized at 650 °C. Capacitors with different thickness and a two-layer capacitor model were used in analyzing the interface layer between PZT and the underlying electroless Ni. From the capacitance and leakage measurements, it is suggested that the interface reaction layer has low permittivity (K around 30) and high defect concentration, which has an important effect on the electrical properties of capacitors. This interface is from the reaction of the electroless nickel layer with the adjacent PZT, and may specifically be moderated by the nickel phosphide (Ni–P) phase, transformed from amorphous Ni during the annealing step. The results have significant implications for embedded capacitors in printed wiring boards. They demonstrate that the process can be tuned to produce either voltage independent capacitors with low leakage and high breakdown fields (above 30 V DC), or the more usual hysteretic, switching, ferroelectric capacitors with higher capacitance densities. DA - 2007/6/25/ PY - 2007/6/25/ DO - 10.1016/j.tsf.2007.02.085 VL - 515 IS - 18 SP - 7331-7336 SN - 0040-6090 KW - lead zirconate titanate KW - embedded passive KW - electroless nickel KW - printed wiring board ER - TY - JOUR TI - Electrical Manipulation of Nonvolatile Spin Cell Based on Diluted Magnetic Semiconductor Quantum Dots AU - Enaya, Hani AU - Semenov, Yuriy G. AU - Kim, K. W. AU - Zavada, John M. T2 - IEEE Transactions on Electron Devices AB - In this paper, electrical manipulation of a memory cell based on a semiconductor nanostructure consisting of a diluted magnetic semiconductor (DMS) quantum dot (QD) and a reservoir of itinerant holes separated by an energy barrier is investigated theoretically. The operating principle takes advantage of the paramagnetic-ferromagnetic (PM-FM) phase transition mediated by the itinerant holes in the DMS QD that can lead to electrically controlled write/erase operations. Nonvolatility can be achieved when the structure is properly designed to reach a thermodynamic equilibrium at both the PM and FM configurations (i.e., bistability). Assuming a parabolic confining potential in the QD, the performance characteristics of the proposed nanostructure are analyzed including the scalability and the lifetime. An advantage of this memory concept is the extremely small dissipative energy for write/erase functions due to the open-circuit nature of the process. A readout scheme enabling electrical detection, with the repetition rate up to the 10-100-MHz range, is also explored by utilizing only two contacts. Finally, a potential application of the proposed memory cell is discussed as a rudimentary device for logic AND and OR operations DA - 2007/5// PY - 2007/5// DO - 10.1109/TED.2007.894377 VL - 54 IS - 5 SP - 1032-1039 J2 - IEEE Trans. Electron Devices OP - SN - 0018-9383 UR - http://dx.doi.org/10.1109/TED.2007.894377 DB - Crossref KW - magnetic logic devices KW - magnetic memories KW - semiconductor logic devices KW - semiconductor memories ER - TY - JOUR TI - Valence band tunneling model for charge transfer of redox-active molecules attached to n- and p-silicon substrates AU - Gowda, Srivardhan AU - Mathur, Guru AU - Misra, Veena T2 - APPLIED PHYSICS LETTERS AB - In this work, monolayers of the redox-active molecules, with cationic- accessible states, were incorporated on p- and n-type silicons of varying doping concentrations. The redox voltages and kinetics were found to be strongly dependent on the silicon doping concentrations, and ambient light in case of n-Si substrate, while there was no significant impact of substrate doping concentration or ambient light in case of p-Si substrate. These results suggest the redox energy states in the molecule align within the valence band of the silicon substrate. Based on this, a model for electronic coupling and charge transfer at the molecule-semiconductor interfaces is proposed. DA - 2007/4/2/ PY - 2007/4/2/ DO - 10.1063/1.2720337 VL - 90 IS - 14 SP - SN - 0003-6951 ER - TY - JOUR TI - The utility of a virtual reality locomotion interface for studying gait behavior AU - Sheik-Nainar, Mohamed A. AU - Kaber, David B. T2 - HUMAN FACTORS AB - To investigate the effect of optic flow on gait behavior during treadmill walking using an immersive virtual reality (VR) setup and compare it with conventional treadmill walking (TW) and overground walking (OW).Previous research comparing TW with OW speculated that a lack of optic flow (relative visual movement between a walker and the environment) during TW may have led to perceptual cue conflicts, resulting in differences in gait behavior, as compared with OW.Participants walked under three locomotion conditions (OW, TW, and TW with VR [TWVR]) under three walking constraint conditions (no constraint, a temporal/pacing constraint, and a spatial/path-following constraint). Presence questionnaires (PQs) were administered at the close of the TWVR trials. Trials were subjected to video analysis to determine spatiotemporal and kinematics variables used for comparison of locomotion conditions.ANOVA revealed gait behavior during TWVR to be between that of OW and TW. Speed and cadence during TWVR were significantly different from those of TW, whereas knee angle was comparable to that of OW. Correlation analysis of PQ scores with gait measures revealed a positive linear association of the distraction subfactor of the PQ with walking speed during TWVR, suggesting an increase in the sense of presence in the virtual environment led to increases in walking speed.The results demonstrate that providing optic flow during TW through VR has an impact on gait behavior.This study provides a basis for developing simple VR locomotion interface setups for gait research. DA - 2007/8// PY - 2007/8// DO - 10.1518/001872007X215773 VL - 49 IS - 4 SP - 696-709 SN - 0018-7208 ER - TY - JOUR TI - Simulation of airflow fields and microparticle deposition in realistic human lung airway models. Part II: Particle transport and deposition AU - Li, Zheng AU - Kleinstreuer, Clement AU - Zhang, Zhe T2 - EUROPEAN JOURNAL OF MECHANICS B-FLUIDS AB - In Part II, given the airflow fields discussed in Part I, microparticle deposition for a practical range of Stokes numbers, 0.025⩽St⩽0.102, has been simulated and analyzed, comparing different temporal assumptions, inlet conditions and geometric configurations. The matching steady-state assumption with equivalent Reynolds and Stokes numbers achieves basically the same deposition fraction (DF) values as under transient inhalation conditions. When comparing parabolic vs. realistic inlet velocity profiles, total DF-values are higher for the parabolic inlet flow for all Stokes numbers. Geometric features, such as out-of-plane configurations and cartilaginous rings in the trachea, further change local deposited microparticle concentrations when compared with simple airway models. Furthermore, significant differences were recorded when comparing DFs in some branches of the present realistic model and the Weibel Type A model. For practical purposes, algebraic microparticle-deposition correlations, DF=DF(Re,St), have been obtained for both the left and right upper lung airways. Based on current research results, the out-of-plane model with tracheal rings and realistic inlet condition is recommended for future work. DA - 2007/// PY - 2007/// DO - 10.1016/j.euromechflu.2007.02.004 VL - 26 IS - 5 SP - 650-668 SN - 1873-7390 KW - asymmetric upper airways KW - matching inlet Reynolds number KW - 3-D microparticle transport simulations KW - particle depositions and segmental correlations ER - TY - JOUR TI - Simulation of airflow fields and microparticle deposition in realistic human lung airway models. Part I: Airflow patterns AU - Li, Zheng AU - Kleinstreuer, Clement AU - Zhang, Zhe T2 - EUROPEAN JOURNAL OF MECHANICS B-FLUIDS AB - In Part I, transient and steady laminar airflow fields were simulated with an in-house finite volume code for realistic upper airway models subject to different inlet conditions and geometric features. Axial velocities and secondary flows were compared at key time levels during the acceleration/deceleration phase of inhaled air and for steady-state inhalation. The main results can be summarized as follows. Considering two acceleration and deceleration time levels during transient inhalation as well as steady-state inhalation generating the same inlet Reynolds number, Rein-mean=1201, the airflow patterns are quite similar. However, stronger axial and secondary velocities occur at all upper branch locations during flow deceleration because of the dynamic lingering effect. In general, the axial velocity profiles at steady state are very close to those at the point of deceleration. Variations in upper airway geometry, e.g., in-plane vs. out-of-plane configurations, have a significant effect on the airflow fields, although the primary airflow structures are similar in both idealized and more realistic airway configurations. The type of velocity inlet condition and existence of cartilaginous rings also influence the flow field; however, their impact is less important than changes in spatial angles. DA - 2007/// PY - 2007/// DO - 10.1016/j.euromechflu.2007.02.003 VL - 26 IS - 5 SP - 632-649 SN - 1873-7390 KW - asymmetric upper airways KW - transient 3-D airflow simulations KW - parabolic and realistic velocity inlet conditions KW - local velocity distributions ER - TY - JOUR TI - Queuing analysis of power management in the IEEE 802.11 based wireless LANs AU - Lei, H. Y. AU - Nilsson, A. A. T2 - IEEE Transactions on Wireless Communications DA - 2007/// PY - 2007/// DO - 10.1109/TWC.2007.04783 VL - 6 IS - 4 SP - 1286-1294 ER - TY - JOUR TI - Persistence of chirality for a weakly bound adsorbate: (R,R)- and (S,S)-tartaric acid/Ag(111) AU - Lakhani, A. M. AU - DeWitt, D. J. AU - Sant'Agata, N. M. AU - Pearl, T. P. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - The interaction of tartaric acid (C4H6O6), including both (R,R) and (S,S) enantiomers, with Ag(111) has been studied using low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM). As evidenced by both diffraction and microscopy, this molecule binds very weakly to the Ag lattice, and the interadsorbate forces strongly dictate the formation of ordered monolayers that are globally chiral. In addition to a discussion of the role that hydrogen bonding plays in the formation of monolayer domains, comparisons of this system to the growth of tartaric acid on other metallic surfaces will be made. DA - 2007/4/19/ PY - 2007/4/19/ DO - 10.1021/jp068639y VL - 111 IS - 15 SP - 5750-5755 SN - 1932-7447 ER - TY - JOUR TI - Performance analysis of TCP/AQM with generalized AIMD under intermediate buffer sizes AU - Eun, Do Young AU - Wang, Xinbing T2 - COMPUTER NETWORKS AB - For TCP/AQM systems, the issue of buffer sizing has recently received much attention. The classical rule-of-thumb suggests O(N) buffer size to ensure full link utilization when N TCP flows share a bottleneck link of capacity O(N), while recent empirical study shows the buffer of size O(N) is enough to yield high utilization (say, 95%) for large N. However, these results are all limited to the drop-tail scheme and there has been no systematic modeling framework for any buffer sizing between O(N) and O(N). In this paper, we study the limiting behavior of a TCP/AQM system for an intermediate buffer sizing of O(N^@c) (0.5=<@c<1). We develop a stochastic model in a discrete-time setting to characterize the system dynamics and then show that we can have 100% link utilization and zero packet loss probability for a large number of flows when the buffer size is chosen anywhere between O(N) and O(N). Our model is general enough to cover any queue-based AQM scheme with ECN marking (including the drop-tail) and various generalized AIMD (additive-increase-multiplicative-decrease) algorithms for each TCP flow. We also provide arguments showing that the discrete-time based modeling can effectively capture all the essential system dynamics under our choice of scaling (0.5=<@c<1) for buffer size as well as AQM parameters. DA - 2007/8/22/ PY - 2007/8/22/ DO - 10.1016/j.comnet.2007.03.005 VL - 51 IS - 12 SP - 3655-3671 SN - 1872-7069 KW - congestion control KW - buffer sizing KW - active queue management KW - discrete-time stochastic models KW - performance analysis ER - TY - JOUR TI - Particle deposition in the human tracheobronchial airways due to transient inspiratory flow patterns AU - Li, Zheng AU - Kleinstreuer, Clement AU - Zhang, Zhe T2 - JOURNAL OF AEROSOL SCIENCE AB - Considering realistic tracheobronchial airways, transient airflow structures and micro-particle deposition patterns were simulated with an in-house finite-volume code for typical inhalation waveforms and Stokes numbers, i.e., the average flow rates at the trachea inlet, Qin,av, are 15 and 60L/min and the mean Stokes number at the trachea inlet, Stmean,trachea, is in the range of 0.0229⩽Stmean,trachea⩽0.0915, respectively. While the overall airflow fields exhibit similar characteristics, the local flow patterns which influence particle deposition are largely affected by secondary flows (for both Qin,av=15 and 60L/min) as well as airflow turbulence (when Qin,av=60L/min). The particle deposition fraction is a strongly transient function according to a given inhalation waveform. In light of the importance of targeted drug-aerosol delivery, it is shown that the relation between particle-release positions at the trachea inlet and particle depositions at specific lung sites are greatly influenced by the complex airway geometry and the flow-rate magnitude. For laminar flow, the particle-release points are deterministic and unique, as required for optimal drug-aerosol targeting. DA - 2007/6// PY - 2007/6// DO - 10.1016/j.jaerosci.2007.03.010 VL - 38 IS - 6 SP - 625-644 SN - 1879-1964 KW - transient inhalation KW - laminar flow KW - turbulent flow KW - local flow pattern KW - micro-particle deposition KW - deposition fraction KW - drug-aerosol targeting ER - TY - JOUR TI - Negative small-signal impedance of nanoscale GaN diodes in the terahertz frequency regime AU - Sokolov, V. N. AU - Kim, K. W. AU - Kochelap, V. A. AU - Muntiian, P. M. T2 - Applied Physics Letters AB - A physical mechanism of electrical instability in the terahertz frequency range is explored in a nanoscale two-terminal configuration of nitride-based structures under a high-field transport regime. The investigated instability utilizes the negative differential resistance effect that is known to occur in bulk group-III nitride semiconductors. A distinctive feature of the proposed mechanism for terahertz generation is that the diode steady-state I-V characteristics maintain a positive differential resistance for a stable operation, while the small-signal response provides negative impedance within the desired frequency range. An additional advantage is that the frequency window of negative small-signal impedance can be tuned electrically. DA - 2007/4/2/ PY - 2007/4/2/ DO - 10.1063/1.2720758 VL - 90 IS - 14 SP - 142117 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2720758 DB - Crossref ER - TY - JOUR TI - Nanodiamond and onion-like carbon polymer nanocomposites AU - Shenderova, O. AU - Tyler, T. AU - Cunningham, G. AU - Ray, M. AU - Walsh, J. AU - Casulli, M. AU - Hens, S. AU - McGuire, G. AU - Kuznetsov, V. AU - Lipa, S. T2 - DIAMOND AND RELATED MATERIALS AB - The current work demonstrates that nanodiamond (ND) of detonation origin and onion-like carbon (OLC) are valuable additives in multifunctional polymer composites, particularly for polymers used in microelectronic applications. We demonstrate that addition of ND to a polyimide matrix increases the thermal degradation temperature of the composites up to 30 °C and also improves adhesion. The addition of 2 wt.% of ND increases thermal conductivity of PDMS up to 15%. Finally, we also demonstrate that the addition of OLC to polydimethylsiloxane and polyurethane matrices increases the loss tangent of the composites. DA - 2007/// PY - 2007/// DO - 10.1016/j.diamond.2006.11.086 VL - 16 IS - 4-7 SP - 1213-1217 SN - 1879-0062 KW - diamond crystal KW - nanoparticles KW - nanotechnology ER - TY - JOUR TI - Local and global stability of TCP-newReno/RED with many flows AU - Wang, Xinbing AU - Eun, Do Young T2 - COMPUTER COMMUNICATIONS AB - Stability is one of the important issues for a TCP/AQM (Active Queue Management) system. In this paper, we study the local and global stability of TCP-newReno/RED under many flows regime. The existing results of the local stability are mostly for TCP-Reno, not for newReno. These results are obtained based on a small scale model with a few number of flows and thus cannot be blindly applied to a large system with many flows. Moreover, traditional approaches for the global stability based on Lyapunov functions is not suitable for a system with a large amount of flows due to its complexity. Motivated by this, we present a normalized discrete-time model to capture the essential dynamics of TCP-newReno/RED with many flows and obtain its local stability criterion. The normalized model allows us to proceed numerical iterations to analyze the global stability in an efficient manner. Our results show that by properly choosing some 'free' parameters, we can always ensure that a locally stable TCP-newReno/RED system is in fact globally stable. Our results become more accurate as the number of flows increases. Finally, we extend our normalized model to the case of heterogeneous RTTs. DA - 2007/3/8/ PY - 2007/3/8/ DO - 10.1016/j.comcom.2006.11.007 VL - 30 IS - 5 SP - 1091-1105 SN - 1873-703X KW - TCP KW - NewReno KW - local stability KW - global stability ER - TY - JOUR TI - Evaluation of cascade-multilevel-converter-based STATCOM for arc furnace flicker mitigation AU - Han, Chong AU - Yang, Zhanoning AU - Chen, Bin AU - Huang, Alex Q. AU - Zhang, Bin AU - Ingram, Michael R. AU - Edris, Abdel-Aty T2 - IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS AB - As an industry customer of electric power, an electrical arc furnace (EAF) is a major flicker source that causes major power quality problems. For a 40-MVA EAF in Tennessee, USA, a cascade-multilevel converter (CMC)-based STATic synchronous COMpensator (STATCOM) with high bandwidth is proposed for EAF flicker mitigation. In this paper, flicker mitigation techniques by using a CMC-based STATCOM are presented and verified through a transient network analyzer (TNA) system. The required STATCOM capacity is first studied through a generalized steady-state analysis. Second, the STATCOM control strategy for flicker mitigation is introduced, and simulation results are given. Finally, a TNA system of the STATCOM and an EAF system are designed and implemented. Experimental results from the TNA test show that the proposed CMC-based STATCOM and its controller can efficiently and rapidly mitigate the EAF flicker DA - 2007/// PY - 2007/// DO - 10.1109/TIA.2006.889896 VL - 43 IS - 2 SP - 378-385 SN - 1939-9367 KW - cascade-multilevel converter (CMC) KW - electric arc furnace KW - flicker KW - STATic synchronous COMpensator (STATCOM) KW - transient network analyzer (TNA) ER - TY - JOUR TI - Electrostatic characteristics of tether atoms in connecting organic molecules to the surface of silicon AU - Zhao, P. AU - Woolard, D. L. T2 - Applied Physics Letters DA - 2007/// PY - 2007/// VL - 91 IS - 6 ER - TY - JOUR TI - Elastic continuum analysis of the liquid crystal polarization grating AU - Komanduri, Ravi K. AU - Escuti, Michael J. T2 - PHYSICAL REVIEW E AB - We apply elastic continuum theory to model critical parameters influencing the free-energy equilibrium configuration and the dynamic performance of a continuous and in-plane liquid crystal profile acting as a polarization grating. We present analytical expressions for the threshold voltage, critical thickness, and the dynamic switching times under strong anchoring conditions, negligible flow, and arbitrary splay, twist, and bend constants. We also study the influence of weak anchoring, and derive expressions describing a dramatic reduction of the critical thickness and voltage threshold, even for modest grating periods and surface anchoring strengths. Good correlation exists with previously reported experimental data, except in the dynamic response; we therefore show that flow effects (backflow and kickback) likely play an essential role in the fall times, presumably due to the prominent splay-bend deformation of the zero-field configuration. We consider the impact of surface pretilt, and validate our entire analysis with numerical simulations. The approximation technique we employ is likely broadly useful for many problems which include nano- or micropatterned surfaces. DA - 2007/8// PY - 2007/8// DO - 10.1103/physreve.76.021701 VL - 76 IS - 2 SP - SN - 1550-2376 ER - TY - JOUR TI - Dielectric elastomer based prototype fiber actuators AU - Arora, Sohil AU - Ghosh, Tushar AU - Muth, John T2 - SENSORS AND ACTUATORS A-PHYSICAL AB - Dielectric elastomer based prototype fiber actuators have been developed and evaluated. The work is motivated by the tremendous potential offered by the current multicomponent fiber forming technologies as a means to fabricate fiber actuators. To explore the potential, prototype fiber actuators have been fabricated using commercially available dielectric elastomer tubes and by applying appropriate compliant electrodes to inner cavity and outer walls of these tubes. The force and displacement generated by such actuators have been studied as a function of applied electric field under different prestrained conditions. In order to introduce anisotropy in the fiber behavior, two types of prestrains (uniaxial and uniform) were applied. Actuation strains of 7 and 18% were recorded for silicone tubes in the axial and radial directions, respectively. Polyurethane tubes produced significantly higher blocking force compared to silicone tubes. The results demonstrate significant influence of applied prestrain on actuation strains and blocking force measured under isometric condition. DA - 2007/5/1/ PY - 2007/5/1/ DO - 10.1016/j.sna.2006.10.044 VL - 136 IS - 1 SP - 321-328 SN - 0924-4247 KW - electroactive polymer actuator KW - dielectric elastorner KW - fiber actuator KW - artificial muscle ER - TY - JOUR TI - Development of a scalable power semiconductor switch (SPSS) AU - Wang, Hongfang AU - Huang, Alex Q. AU - Wang, Fei T2 - IEEE TRANSACTIONS ON POWER ELECTRONICS AB - This paper presents the design and development of a 4800-V, 300-A, 10-kHz scalable power semiconductor switch (SPSS) based on series connecting low voltage insulated gate bipolar transistors (IGBTs). The static and dynamic voltage balance among IGBTs is achieved using a hybrid approach of active clamp circuit and an active gate control that is also effective during tail current phase. The developed SPSS derives its control power directly from the main power bus. Control, packaging, and thermal characteristics are an integral part of the SPSS design. From a user's standpoint, the SPSS is a three-terminal optically controlled high-power switch. Experimental evaluation of the prototype SPSS shows it fully achieved the design objectives. In principle, the approach can be extended to building switches with higher voltages, currents, and switching frequencies, or even with other types of devices than IGBTs. DA - 2007/3// PY - 2007/3// DO - 10.1109/TPEL.2006.889892 VL - 22 IS - 2 SP - 364-373 SN - 1941-0107 KW - high frequency switch KW - high voltage switch KW - series connection KW - voltage balance ER - TY - PCOMM TI - Analytical threshold voltage model with TCAD simulation verification for design and evaluation of tri-gate MOSFETs AU - Jin, Yawei AU - Zeng, Chang AU - Ma, Lei AU - Barlage, Doug AB - Abstract The dynamics of the threshold voltage calculation is evaluated for the tri-gate architecture of device. The 3-D poisson’s equation with eight boundary conditions is solved analytically and an analytical threshold model for tri-gate Si MOSFET device is developed. TCAD simulation result of the same device structure is also presented and it agrees well with our threshold analytical model. Furthermore, this analytical threshold model is capable of doing rudimentary first order comparisons of the threshold voltage with respect to device dimensions and semiconductor material type. DA - 2007/3// PY - 2007/3// DO - 10.1016/j.sse.2007.01.023 SP - 347-353 KW - MOSFET KW - device modeling KW - analytical models KW - threshold voltage KW - double gate KW - FinFET KW - tri-gate KW - triple gate KW - undoped KW - inversion KW - TCAD simulation ER - TY - JOUR TI - Room temperature pulsed laser deposited indium gallium zinc oxide channel based transparent thin film transistors AU - Suresh, Arun AU - Wellenius, Patrick AU - Dhawan, Anuj AU - Muth, John T2 - APPLIED PHYSICS LETTERS AB - Indium gallium zinc oxide deposited by pulsed laser deposition at room temperature was used as a channel layer to fabricate transparent thin film transistors with good electrical characteristics: field effect mobility of 11cm2V−1s−1 and subthreshold voltage swing of 0.20V∕decade. By varying the oxygen partial pressure during deposition the conductivity of the channel was controlled to give a low off-current of ∼10pA and a drain current on/off ratio of ∼5×107. Changing the channel layer thickness was a viable way to vary the threshold voltage. The effect of the gate dielectric on the electrical behavior was also explored. DA - 2007/3/19/ PY - 2007/3/19/ DO - 10.1063/1.2716355 VL - 90 IS - 12 SP - SN - 0003-6951 ER - TY - JOUR TI - Quantitative nanoscale local strain profiling in embedded SiGe metal-oxide-semiconductor structures AU - Zhao, W. AU - Duscher, G. AU - Rozgonyi, G. AU - Zikry, M. A. AU - Chopra, S. AU - Ozturk, M. C. T2 - APPLIED PHYSICS LETTERS AB - Mechanical strain by strain engineering has been widely used in Si metal-oxide-semiconductor field effect transistors. Experimental convergent beam electron diffraction (CBED) strain measurements and finite element calculations to quantitatively correlate the strain in the transmission electron microscope (TEM) sample with the actual device. It was found that the magnitude of the longitudinal strain, εx, along the channel direction, is about 20% higher in the TEM sample than in the real device. This combined approach can be used to explain data from other CBED studies of strained Si devices. DA - 2007/5/7/ PY - 2007/5/7/ DO - 10.1063/1.2738188 VL - 90 IS - 19 SP - SN - 1077-3118 ER - TY - JOUR TI - Measurement-based method to characterize parasitic parameters of the integrated power electronics modules AU - Yang, Liyu AU - Odendaal, Willem G. Hardus T2 - IEEE TRANSACTIONS ON POWER ELECTRONICS AB - A measurement-based method for extracting the parasitic parameters of active power electronics modules (IPEMs) is proposed. Parasitic inductances and capacitances inside the IPEM can all be extracted using this method without destroying the structure. The linearized model is derived from impedance measurement and it is valid from low frequency to frequencies as high as 100 MHz. Extracted parameters are compared to those from commercial software and the results are in good agreement. A parallel resonance method is proposed for the characterization of common-mode capacitances DA - 2007/1// PY - 2007/1// DO - 10.1109/TPEL.2006.886615 VL - 22 IS - 1 SP - 54-62 SN - 1941-0107 KW - characterization KW - common-mode (CM) KW - differential mode (DM) KW - electromagnetic compatibility (EMC) KW - electromagnetic interference (EMI) KW - integrated power electronics modules (IPEMs) KW - measurement KW - noise KW - packaging KW - parasitic capacitance KW - parasitic inductors ER - TY - JOUR TI - Intrinsic electronically active defects in transition metal elemental oxides AU - Lucovsky, Gerald AU - Seo, Hyungtak AU - Lee, Sanghyun AU - Fleming, Leslie B. AU - Ulrich, Marc D. AU - Luning, Jan AU - Lysaght, Pat AU - Bersuker, Gennadi T2 - JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS AB - Densities of interfacial and bulk defects in high-κ dielectrics are typically about two orders of magnitude larger than those in Si–SiO2 devices. An asymmetry in electron and hole trapping kinetics, first detected in test capacitor devices with nanocrystalline ZrO2 and HfO2 dielectrics, is a significant potential limitation for Si device operation and reliability in complementary metal oxide semiconductor applications. There are two crucial issues: i) are the electron and hole traps intrinsic defects, or are they associated with processed-introduced impurities?, and ii) what are the local atomic bonding arrangements and electronic state energies of these traps? In this study, thin film nanocrystalline high-κ gate dielectrics, TiO2, ZrO2, and HfO2 (group IVB TM oxides), are investigated spectroscopically to identify the intrinsic electronic structures of valence and conduction band states, as well as those of intrinsic bonding defects. A quantitative/qualitative distinction is made between crystal field and Jahn–Teller (J–T) d-state energy differences in nanocrystralline TM elemental oxides, and noncrystalline TM silicates and Si oxynitrides. It is experimentally shown and theoretically supported that a length scale for nanocrystallite size <2–3 nm i) eliminates J–T d-state term splittings in band edge π-bonded d-states, and ii) represents a transition from the observation of discrete band edge defects to band-tail defects. Additionally, π-state bonding coherence can also be disrupted with similar effects on band edge and defect states in HfO2 films which have been annealed in NH3 at 700 °C, and display Hf–N bonds in N atom K1 edge X-ray absorption spectra. DA - 2007/4// PY - 2007/4// DO - 10.1143/JJAP.46.1899 VL - 46 IS - 4B SP - 1899-1909 SN - 0021-4922 KW - transition metal oxides KW - crystal field and Jahn-Teller d-state splittings KW - ab initio molecular orbital theory KW - valence and conduction band states KW - intrinsic defect states KW - coherent pi-bonding interactions KW - nanocrystalline length scales of order ER - TY - JOUR TI - Indirect programming of floating-gate transistors AU - Graham, David W. AU - Farquhar, Ethan AU - Degnan, Brian AU - Gordon, Christal AU - Hasler, Paul T2 - IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS AB - Floating-gate (FG) transistors are useful for precisely programming a large array of current sources. Present FG programming techniques require disconnection of the transistor from the rest of its circuit while it is being programmed. We present a new method of programming FG transistors that does not require this disconnection. In this indirect programming method, two transistors share a FG allowing one to exist directly in a circuit while the other is reserved for programming. Since the transistor does not need to be disconnected from the circuit to program it, the switch count is reduced, resulting in fewer parasitics and better overall performance. Additionally, the use of these indirectly programmed FG transistors allows a circuit to be tuned such that the effects of device mismatch are negated. Finally, the concept of run-time programming is introduced which allows a circuit to be recalibrated while it is still operating within its system DA - 2007/5// PY - 2007/5// DO - 10.1109/TCSI.2007.895521 VL - 54 IS - 5 SP - 951-963 SN - 1558-0806 KW - analog programmability KW - electron tunneling KW - floating-gate (FG) nFET KW - FG programming KW - FG transistor KW - hot-electron injection KW - indirect programming ER - TY - JOUR TI - Design of bandstop filters utilising circuit prototypes AU - Fathelbab, W. M. AU - Steer, M. B. T2 - IET MICROWAVES ANTENNAS & PROPAGATION AB - A systematic circuit-oriented approach to the design of bandstop filters with pre-defined upper passband characteristics is presented. An experimental filter is built with a fundamental stopband centred at 1.085 GHz and a first spurious stopband centred at 5.4 GHz. DA - 2007/4// PY - 2007/4// DO - 10.1049/iet-map:20060147 VL - 1 IS - 2 SP - 523-526 SN - 1751-8725 ER - TY - JOUR TI - Defect reduction by suppression of pi-bonding coupling in nano- and non-crystalline high-(medium)-kappa gate dielectrics AU - Lucovsky, G. AU - Seo, H. AU - Lee, S. AU - Fleming, L. B. AU - Ulrich, M. D. AU - Luning, J. T2 - MICROELECTRONIC ENGINEERING AB - This paper identifies two-different regimes of nanocrystallinity: i) thin films with nanocrystallites >3 nm, and ii) thin films with nanocrystallites ⩽2 nm. Near edge X-ray absorption spectroscopy, and soft-X-ray photoelectron spectroscopy, combined with visible and ultra-violet spectroscopic ellipsometry, provide an unambiguous way to distinguish between these two technologically important regimes of nanocrystalline order, yielding significant information on band edge electronic structure, and electronically-active defects. DA - 2007/// PY - 2007/// DO - 10.1016/j.mee.2007.04.062 VL - 84 IS - 9-10 SP - 2350-2353 SN - 1873-5568 KW - high-/medium-kappa dielectrics KW - spectroscopic studies KW - fundamental electronic states KW - band edge defects ER - TY - JOUR TI - ZettaRAM: A power-scalable DRAM alternative through charge-voltage decoupling AU - Venkatesan, Ravi K. AU - Al-Zawawi, Ahmed S. AU - Sivasubramanian, Krishnan AU - Rotenberg, Eric T2 - IEEE TRANSACTIONS ON COMPUTERS AB - ZettaRAMtrade is a nascent memory technology with roots in molecular electronics. It uses a conventional DRAM architecture except that the conventional capacitor is replaced with a new molecular capacitor. The molecular capacitor has a discrete threshold voltage, above which all molecules are charged and below which all molecules are discharged. Thus, while voltage still controls charging/discharging, the fixed charge deposited on the molecular capacitor is voltage-independent. Charge-voltage decoupling makes it possible to lower voltage from one memory generation to the next while still maintaining the minimum critical charge for reliable operation, whereas DRAM voltage scaling is constrained by charge. Voltage can be scaled inexpensively and reliably by engineering new, more favorable molecules. We analyze how three key molecule parameters influence voltage and then evaluate 23 molecules in the literature. Matching DRAM density and speed, the best molecule yields 61 percent energy savings. While the fixed charge is voltage-independent, speed is voltage-dependent. Thus, voltage is padded for competitive latency. We propose dynamically modulating the padding based on criticality of memory requests, further extending ZettaRAM's energy advantage with negligible system slowdown. Architectural management extends the best molecule's energy savings to 77 percent and extracts energy savings from six otherwise uncompetitive molecules DA - 2007/2// PY - 2007/2// DO - 10.1109/TC.2007.37 VL - 56 IS - 2 SP - 147-160 SN - 1557-9956 KW - DRAM KW - dynamic voltage scaling KW - low-power memory KW - molecular electronics KW - molecular memory KW - memory technology ER - TY - JOUR TI - Time-dependent transport in low-dimensional-systems - A numerical solution using the nonequilibrium Green's functions AU - He, Yuhui AU - Hou, Danqiong AU - Liu, Xiaoyan AU - Han, Ruqi AU - Chen, Jie T2 - IEEE TRANSACTIONS ON NANOTECHNOLOGY AB - In this paper, we present a novel numerical solution to analyze time-dependent transport in low-dimensional systems, such as one-dimensional (1-D) quantum dot and quasi-one-dimensional (Q1D) carbon nanotube systems, by using the nonequilibrium Green's functions (NEGF). The novelty of proposed approach is to jointly handle the NEGF in both the time-domain and the real-space-domain in a recursive fashion. The time-domain recursive approach is a straightforward approach to solve time-dependent transport problems, while the real-space recursive approach makes the calculations feasible for arbitrary-length 1-D and Q1D systems. To verify our proposed algorithm, we apply this method to explore the transient and ac transport properties of a sample 1-D quantum-dot array system. We will present in this paper the simulated electrical current curves, J (t), in response to various pulses and sinusoid waveforms. From these simulation results, we can obtain the delay and distortion information. We will then discuss how the length of a quantum-dot array and the hopping energy affect the transport behavior. The knowledge we gain from this project will help researchers to evaluate the electrical properties of 1-D and Q1D materials. The knowledge can also benefit the making of time-dependent 1-D and Q1D nanoelectronic devices DA - 2007/1// PY - 2007/1// DO - 10.1109/TNANO.2006.886780 VL - 6 IS - 1 SP - 56-62 SN - 1536-125X KW - AC transport properties of nanodevices KW - nonequilibrium Green's function KW - transient ER - TY - JOUR TI - On the limitation of fluid-based approach for Internet congestion control AU - Eun, Do Young T2 - TELECOMMUNICATION SYSTEMS DA - 2007/2// PY - 2007/2// DO - 10.1007/s11235-006-9028-7 VL - 34 IS - 1-2 SP - 3-11 SN - 1018-4864 KW - congestion control KW - fluid modeling KW - markov chains KW - stability analysis ER - TY - JOUR TI - Microcavity enhancement of spontaneous emission for Bloch oscillations AU - Sokolov, V. N. AU - Iafrate, G. J. AU - Krieger, J. B. T2 - PHYSICAL REVIEW B AB - A theory for the spontaneous emission of a Bloch electron traversing a single energy miniband of a superlattice while accelerating under the influence of a constant external electric field and radiating into a microcavity is presented. In the analysis, the quantum electromagnetic radiation field is described by the dominant microcavity ${\mathrm{TE}}_{10}$ rectangular waveguide mode in the Coulomb gauge, and the instantaneous eigenstates of the Bloch Hamiltonian are utilized as the basis states in describing the Bloch electron dynamics to all orders in the constant external electric field. The results show that the spontaneous emission amplitude, when analyzed over many integral multiple values of the Bloch period, gives rise to selection rules for photon emission in both frequency and wave number with preferred transitions at the Wannier-Stark ladder levels. From these selection rules, the total spontaneous emission probability is derived to first-order perturbation theory in the quantized radiation field. It is shown that the power radiated into the dominant ${\mathrm{TE}}_{10}$ waveguide mode can be enhanced by an order of magnitude over the free-space value by tuning the Bloch frequency to align with the waveguide spectral density peak. A general expression for the total spontaneous emission probability is obtained in terms of arbitrary superlattice single band parameters, showing multiharmonic behavior and cavity tuning properties. For $\mathrm{GaAs}$-based superlattices, described in the nearest-neighbor tight-binding approximation, the power radiated into the waveguide from spontaneous emission due to Bloch oscillations in the terahertz frequency range is estimated to be several microwatts. DA - 2007/1// PY - 2007/1// DO - 10.1103/physrevb.75.045330 VL - 75 IS - 4 SP - SN - 1098-0121 ER - TY - JOUR TI - From the editor-in-chief AU - Nagle, H. T. T2 - IEEE Sensors Journal DA - 2007/// PY - 2007/// VL - 7 IS - 1-2 SP - 3 ER - TY - JOUR TI - Electron spin relaxation in semiconducting carbon nanotubes: The role of hyperfine interaction AU - Semenov, Y. G. AU - Kim, K. W. AU - Iafrate, G. J. T2 - Physical Review B AB - A theory of electron spin relaxation in semiconducting carbon nanotubes is developed based on the hyperfine interaction with disordered nuclei spins $I=1∕2$ of $^{13}\mathrm{C}$ isotopes. It is shown that strong radial confinement of electrons enhances the electron-nuclear overlap and subsequently electron spin relaxation (via the hyperfine interaction) in the carbon nanotubes. The analysis also reveals an unusual temperature dependence of longitudinal (spin-flip) and transversal (dephasing) relaxation times: the relaxation becomes weaker with the increasing temperature as a consequence of the particularities in the electron density of states inherent in one-dimensional structures. Numerical estimations indicate relatively high efficiency of this relaxation mechanism compared to the similar processes in bulk diamond. However, the anticipated spin relaxation time of the order of $1\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in carbon nanotubes is still much longer than those found in conventional semiconductor structures. Moreover, it is found that the curvature effect and subsequent rehybridization of $s$ and $p$ orbitals in ultrathin nanotubes may significantly impact the electron spin relaxation leading to its further suppression at certain dimensions. DA - 2007/1/25/ PY - 2007/1/25/ DO - 10.1103/physrevb.75.045429 VL - 75 IS - 4 SP - J2 - Phys. Rev. B LA - en OP - SN - 1098-0121 1550-235X UR - http://dx.doi.org/10.1103/PhysRevB.75.045429 DB - Crossref ER - TY - JOUR TI - Spin-current shot noise in mesoscopic conductors AU - He, Y. H. AU - Hou, D. Q. AU - Han, R. Q. T2 - Journal of Applied Physics DA - 2007/// PY - 2007/// VL - 101 IS - 2 ER - TY - PCOMM TI - Reality thinking in 'microwave bytes' AU - Gard, K. G. DA - 2007/// PY - 2007/// SP - 14 ER - TY - JOUR TI - Power distribution outage cause identification with imbalanced data using artificial immune recognition system (AIRS) algorithm AU - Xu, Le AU - Chow, Mo-Yuen AU - Timmis, Jon AU - Taylor, Leroy S. T2 - IEEE TRANSACTIONS ON POWER SYSTEMS AB - Power distribution systems have been significantly affected by many fault causing events. Effective outage cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data often degrades the outage cause identification performance. In this paper, artificial immune recognition system (AIRS), an immune-inspired algorithm for supervised classification task is applied to the Duke Energy outage data for outage cause identification using three major causes (tree, animal, and lightning) as prototypes. The performance of AIRS on these real-world imbalanced data is compared with an artificial neural network (ANN). The results show that AIRS can greatly improve the performance by as much as 163% when the data are imbalanced and achieve comparable performance with ANN for relatively balanced data DA - 2007/2// PY - 2007/2// DO - 10.1109/TPWRS.2006.889040 VL - 22 IS - 1 SP - 198-204 SN - 1558-0679 KW - artificial immune system KW - classification KW - data imbalance KW - outage cause identification KW - neural network KW - power distribution systems ER - TY - JOUR TI - Power distribution fault cause identification with imbalanced data using the data mining-based fuzzy classification E-algorithm AU - Xu, Le AU - Chow, Mo-Yuen AU - Taylor, Leroy S. T2 - IEEE TRANSACTIONS ON POWER SYSTEMS AB - Power distribution systems have been significantly affected by many outage-causing events. Good fault cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data sets often degrades the fault cause identification performance. In this paper, the E-algorithm, which is extended from the fuzzy classification algorithm by Ishibuchi to alleviate the effect of imbalanced data constitution, is applied to Duke Energy outage data for distribution fault cause identification. Three major outage causes (tree, animal, and lightning) are used as prototypes. The performance of E-algorithm on real-world imbalanced data is compared with artificial neural network. The results show that the E-algorithm can greatly improve the performance when the data are imbalanced DA - 2007/2// PY - 2007/2// DO - 10.1109/TPWRS.2006.888990 VL - 22 IS - 1 SP - 164-171 SN - 1558-0679 KW - data imbalance KW - data mining KW - fault cause identification KW - fuzzy classification KW - g-mean KW - neural network KW - power distribution systems ER - TY - JOUR TI - Issues in recording exchange coupled composite media AU - Shen, Xiao AU - Kapoor, Manish AU - Field, Ryan AU - Victora, R. H. T2 - IEEE TRANSACTIONS ON MAGNETICS AB - Exchange coupled composite (ECC) media exhibits a lower switching field than conventional perpendicular media at the same level of thermal stability, and thus is able to achieve higher areal density. The inhomogeneity of ECC media is predicted to enhance the thermal attempt frequency: this increases both writability and adjacent track erasure (ATE). The adverse change in ATE is, however, countered by the angular dependence of the ECC media switching field. This angular dependence is further exploited with a head design featuring a larger pole width than track width and the introduction of notches in the down track direction. This reduces the effect of head skew and increases the write field. An optimized head is found to be consistent with terabit/in 2 recording DA - 2007/2// PY - 2007/2// DO - 10.1109/TMAG.2006.888231 VL - 43 IS - 2 SP - 676-681 SN - 0018-9464 KW - exchange coupled composite (ECC) media KW - pole head KW - thermal fluctuation ER - TY - JOUR TI - Heterogeneous wafer-scale circuit architectures AU - Katehi, Linda AU - Chappell, William AU - Mohammadi, Saeed AU - Margomenos, Alexandros AU - Steer, Michael T2 - IEEE MICROWAVE MAGAZINE AB - This article has presented circuit architectures that allow for the 3D integration and on-wafer packaging through the concept of an Si interposer. The presented 3D integration schemes have allowed for the design and fabrication of a fully integrated receiver that performs at 10 GHz. High-Q passives and 3D interconnects allow for the design of low-cost, high-density circuits that also exhibit very high performance DA - 2007/2// PY - 2007/2// DO - 10.1109/MMW.2007.316255 VL - 8 IS - 1 SP - 52-69 SN - 1557-9581 ER - TY - JOUR TI - Electrical and optical properties of ZnO (000(1)over-bar) wafers implanted with argon AU - Adekore, B. T. AU - Davis, R. F. AU - Barlage, D. W. T2 - Journal of Applied Physics DA - 2007/// PY - 2007/// VL - 101 IS - 2 ER - TY - JOUR TI - Beyond 3G AU - Steer, M. T2 - IEEE Microwave Magazine AB - Beyond 3G is the official IEEE designation for the next stage of wireless technology that some people call 4G or fourth-generation radio. Over the years, every conceptual shift in wireless technology has been characterized as a generational change. Third generation includes wideband mobile multimedia networks and broadband mixed wireless systems. The mobile systems support variable data rates depending on demand and the level of mobility. Typically 144 kb/s is supported for full vehicular mobility and higher bandwidths for pedestrian levels of mobility. Switched packet radio techniques and wideband CDMA-like systems (as the physical channel is) rather than assigned physical channel schemes (referred to as circuit switched) are required to support this bandwidth-on-demand environment. There are two essential concepts beyond 3G. One of these is the provision of data transmission at rates of 100 Mb/s while mobile and 1 Gb/s while stationary. The other concept is that of pervasive networks where a handset supports many access technologies (e.g., cellular, UMTS, and WiFi) perhaps simultaneously and smoothly transitions between them DA - 2007/// PY - 2007/// DO - 10.1109/MMW.2007.316254 VL - 8 IS - 1 SP - 76-82 ER - TY - JOUR TI - A multiagent-based dispatching scheme for distributed generators for voltage support on distribution feeders AU - Baran, Mesut E. AU - El-Markabi, Ismail M. T2 - IEEE TRANSACTIONS ON POWER SYSTEMS AB - This paper illustrates how a multiagent system (MAS)-based scheme can be developed for a control/optimization problem. The prototype problem considered is the dispatching of distributed generators on a distribution feeder to provide voltage support. The popular control net protocol (CNP) for MAS has been adopted to facilitate distributed control. This paper illustrates that characterization of the optimal solution is necessary in order to develop a protocol for the MAS to implement. This paper also shows that MAS facilitates a model-free control procedure, as it can monitor the local sensitivities. Test results, based on simulations on a prototype feeder, show that the proposed MAS-based control scheme is very effective in obtaining the solution for the prototype problem. The proposed method needs fast communication among the distributed generators (DGs) in order to assure fast response during emergency conditions. Communication requirements have also been identified in this paper DA - 2007/2// PY - 2007/2// DO - 10.1109/TPWRS.2006.889140 VL - 22 IS - 1 SP - 52-59 SN - 1558-0679 KW - distributed control KW - distributed generation (DG) KW - optimization KW - power distribution KW - voltage regulation ER - TY - JOUR TI - Suppression of electron-phonon scattering in double-quantum-dot based-quantum gates AU - Zhao, P. AU - Woolard, D. L. T2 - Applied Physics Letters DA - 2007/// PY - 2007/// VL - 90 IS - 9 ER - TY - JOUR TI - SOI CMOS implementation of a multirate PSK demodulator for space communications AU - Yuce, Mehmet Rasit AU - Liu, Wentai AU - Damiano, John AU - Bharath, Bhaskar AU - Franzon, Paul D. AU - Dogan, Numan S. T2 - IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS AB - A low-power phase-shift keying demodulator integrated circuit (IC) has been implemented using silicon-on-insulator CMOS technology for deep space and satellite applications. The demodulator employs double differential detection to increase its robustness to the Doppler shift caused by the movement of the space vehicle and sampling technique with 1-bit analog-to-digital converter (ADC) at the front to reduce the complexity and power dissipation. In particular, digital decimation is used after sampling to achieve a low power implementation of multirate transmission. Operating at ultra-high-frequency (435 MHz), the receiver system supports a wide range of data rates (0.1-100 Kbps). From test results, the power consumption of the demodulator circuit including the 1-bit ADC is below 1 mW for data rates up to 100 Kbps DA - 2007/2// PY - 2007/2// DO - 10.1109/TCSI.2006.885988 VL - 54 IS - 2 SP - 420-431 SN - 1558-0806 KW - differential detection KW - multirate KW - phase-shift keying (PSK) KW - sampling KW - space communications KW - symbol timing circuit ER - TY - JOUR TI - Overcurrent protection on voltage-source-converter-based multiterminal DC distribution systems AU - Baran, Mesut E. AU - Mahajan, Nikhil R. T2 - IEEE TRANSACTIONS ON POWER DELIVERY AB - This paper proposes a protection scheme which utilizes modern voltage-source converters as fast-acting current-limiting circuit breakers. This paper investigates the main challenges of detecting and localizing a fault, and interrupting it as quickly as possible in a multiterminal dc system. A system protection scheme consisting of smart relays associated with converters has been developed. The protection relays monitor local quantities to detect and isolate disturbances/faults. It is shown that overcurrent-based schemes can be adopted for these relays to meet the fast response requirements. The effectiveness of the proposed protection scheme is illustrated through simulations DA - 2007/1// PY - 2007/1// DO - 10.1109/TPWRD.2006.877086 VL - 22 IS - 1 SP - 406-412 SN - 1937-4208 KW - DC distribution KW - power-electronic converters KW - protection ER - TY - JOUR TI - On the impact of quality of protection in wireless local area networks with IP mobility AU - Agarwal, Avesh K. AU - Wang, Wenye T2 - MOBILE NETWORKS & APPLICATIONS DA - 2007/2// PY - 2007/2// DO - 10.1007/s11036-006-0009-6 VL - 12 IS - 1 SP - 93-110 SN - 1572-8153 KW - wireless local area networks KW - quality of service KW - quality of protection KW - security protocols KW - mobile IP KW - performance analysis ER - TY - JOUR TI - Distributed detection in wireless sensor networks using a multiple access channel AU - Li, Wenjun AU - Dai, Huaiyu T2 - IEEE TRANSACTIONS ON SIGNAL PROCESSING AB - Distributed detection in a one-dimensional (1-D) sensor network with correlated sensor observations, as exemplified by two problems-detection of a deterministic signal in correlated Gaussian noise and detection of a first-order autoregressive [AR(1)] signal in independent Gaussian noise, is studied in this paper. In contrast with the traditional approach where a bank of dedicated parallel access channels (PAC) is used for transmitting the sensor observations to the fusion center, we explore the possibility of employing a shared multiple access channel (MAC), which significantly reduces the bandwidth requirement or detection delay. We assume that local observations are mapped according to a certain function subject to a power constraint. Using the large deviation approach, we demonstrate that for the deterministic signal in correlated noise problem, with a specially chosen mapping rule, MAC fusion achieves the same asymptotic performance as centralized detection under the average power constraint (APC), while there is always a loss in error exponents associated with PAC fusion. Under the total power constraint (TPC), MAC fusion still results in exponential decay in error exponents with the number of sensors, while PAC fusion does not. For the AR signal problem, we propose a suboptimal MAC mapping rule which performs closely to centralized detection for weakly correlated signals at almost all signal-to-noise ratio (SNR) values, and for heavily correlated signals when SNR is either high or low. Finally, we show that although the lack of MAC synchronization always causes a degradation in error exponents, such degradation is negligible when the phase mismatch among sensors is sufficiently small DA - 2007/3// PY - 2007/3// DO - 10.1109/TSP.2006.887563 VL - 55 IS - 3 SP - 822-833 SN - 1941-0476 KW - autoregressive processes KW - distributed detection KW - error exponents KW - multiple access channel KW - sensor networks ER - TY - JOUR TI - Laser-assisted forward transfer of multi-spectral nanocrystal quantum dot emitters AU - Xu, J. AU - Liu, J. AU - Cui, D. H. AU - Gerhold, M. AU - Wang, A. Y. AU - Nagel, M. AU - Lippert, T. K. T2 - Nanotechnology DA - 2007/// PY - 2007/// VL - 18 IS - 2 ER - TY - JOUR TI - Flexible skew-symmetric shape model for shape representation, classification, and sampling AU - Baloch, Sajjad H. AU - Krim, Hamid T2 - IEEE TRANSACTIONS ON IMAGE PROCESSING AB - Skewness of shape data often arises in applications (e.g., medical image analysis) and is usually overlooked in statistical shape models. In such cases, a Gaussian assumption is unrealistic and a formulation of a general shape model which accounts for skewness is in order. In this paper, we present a novel statistical method for shape modeling, which we refer to as the flexible skew-symmetric shape model (FSSM). The model is sufficiently flexible to accommodate a departure from Gaussianity of the data and is fairly general to learn a "mean shape" (template), with a potential for classification and random generation of new realizations of a given shape. Robustness to skewness results from deriving the FSSM from an extended class of flexible skew-symmetric distributions. In addition, we demonstrate that the model allows us to extract principal curves in a point cloud. The idea is to view a shape as a realization of a spatial random process and to subsequently learn a shape distribution which captures the inherent variability of realizations, provided they remain, with high probability, within a certain neighborhood range around a mean. Specifically, given shape realizations, FSSM is formulated as a joint bimodal distribution of angle and distance from the centroid of an aggregate of random points. Mean shape is recovered from the modes of the distribution, while the maximum likelihood criterion is employed for classification. DA - 2007/2// PY - 2007/2// DO - 10.1109/TIP.2006.888348 VL - 16 IS - 2 SP - 317-328 SN - 1941-0042 KW - flexible skew-symmetric distributions (FSSM) KW - principal curves KW - sampling KW - shape classification KW - shape modeling KW - template learning ER -