TY - JOUR TI - SPECIAL ISSUE: Modeling Foreword T2 - Journal of Engineered Fibers and Fabrics DA - 2009/// PY - 2009/// UR - https://publons.com/wos-op/publon/65200210/ ER - TY - CONF TI - Shock/turbulent boundary layer interactions: Review of recent work on sources of unsteadiness AU - Clemens, N.T. AU - Narayanaswamy, V. C2 - 2009/// C3 - 39th AIAA Fluid Dynamics Conference DA - 2009/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-78349243684&partnerID=MN8TOARS ER - TY - JOUR TI - Novel Jet Impingement Cooling Geometry for Combustor Liner Backside Cooling AU - Esposito, E. I. AU - Ekkad, S. V. AU - Kim, Yong AU - Dutta, Partha T2 - Journal of Thermal Science and Engineering Applications AB - Impinging jets are commonly used to enhance heat transfer in modern gas turbine engines. Impinging jets used in turbine blade cooling typically operate at lower Reynolds numbers in the range of 10,000–20,000. In combustor liner cooling, the Reynolds numbers of the jets can be as high as 60,000. The present study is aimed at experimentally testing two different styles of jet impingement geometries to be used in backside combustor cooling. The higher jet Reynolds numbers lead to increased overall heat transfer characteristics, but also an increase in crossflow caused by spent air. The crossflow air has the effect of rapidly degrading the downstream jets at high jet Reynolds numbers. In an effort to increase the efficiency of the coolant air, configurations designed to reduce the harmful effects of crossflow are studied. Two main designs, a corrugated wall and extended port, are tested. Local heat transfer coefficients are obtained for each test section through a transient liquid crystal technique. Results show that both geometries reduce the crossflow induced degradation on downstream jets, but different geometries perform better at different Reynolds numbers. The extended port and corrugated wall configurations show similar benefits at the high Reynolds numbers, but at low Reynolds numbers, the extended port design increases the overall level of heat transfer. This is attributed to the developed jet velocity profile at the tube exit. The best possible explanation is that the benefit of the developed jet velocity profile diminishes as jet velocities rise and the air has lesser time to develop prior to exiting. DA - 2009/6/1/ PY - 2009/6/1/ DO - 10.1115/1.3202799 VL - 1 IS - 2 SP - 1-8 LA - en OP - SN - 1948-5085 1948-5093 UR - http://dx.doi.org/10.1115/1.3202799 DB - Crossref ER - TY - JOUR TI - Film Cooling Measurements for Cratered Cylindrical Inclined Holes AU - Lu, Yiping AU - Dhungel, Alok AU - Ekkad, Srinath V. AU - Bunker, Ronald S. T2 - Journal of Turbomachinery AB - Film cooling performance is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes may occur when blades are coated with thermal barrier coating layers by masking the hole area during thermal barrier coating (TBC) spraying, resulting in a hole surrounded by a TBC layer. The film performance and behavior is expected to be different for the cratered holes compared to standard cylindrical holes. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on freestream velocity and film-hole diameter of 11,000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5, and 2.0. The results show that film cooling effectiveness is slightly enhanced by cratering of holes, but a substantial increase in heat transfer enhancement negates the benefits of higher film effectiveness. Three different crater geometries are studied and compared to a base line flush cylindrical hole, a trenched hole, and a typical diffuser shaped hole. Computational fluid dynamics simulation using FLUENT was also performed to determine the jet-mainstream interactions associated with the experimental surface measurements. DA - 2009/1// PY - 2009/1// DO - 10.1115/1.2950055 VL - 131 IS - 1 SP - 011005 SN - 0889-504X 1528-8900 UR - http://dx.doi.org/10.1115/1.2950055 ER - TY - JOUR TI - Film Cooling From a Row of Holes Supplemented With Antivortex Holes AU - Dhungel, Alok AU - Lu, Yiping AU - Phillips, Wynn AU - Ekkad, Srinath V. AU - Heidmann, James T2 - Journal of Turbomachinery AB - The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical antivortex holes, which branch out from the main holes. The antivortex design was originally developed at NASA-Glenn Research Center by James Heidmann, coauthor of this paper. This “antivortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the antivortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the freestream velocity and film hole diameter at four different coolant-to-mainstream blowing ratios of 0.5, 1, 1.5, and 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the antivortex holes are nearer the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other antivortex hole orientations. When the antivortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with antivortex holes placed near the main holes certainly show promising results. DA - 2009/1/22/ PY - 2009/1/22/ DO - 10.1115/1.2950059 VL - 131 IS - 2 LA - en OP - SN - 0889-504X 1528-8900 UR - http://dx.doi.org/10.1115/1.2950059 DB - Crossref ER - TY - JOUR TI - Effect of trench width and depth on film cooling from cylindrical holes embedded in trenches AU - Lu, Y. AU - Dhungel, A. AU - Ekkad, S.V. AU - Bunker, R.S. T2 - Journal of Turbomachinery AB - The present study is an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. Different trench depths are considered with two trench widths. Trench holes can occur when blades are coated with thermal barrier coating (TBC) layers. The film-hole performance and behavior will be different for the trench holes compared to standard cylindrical holes that are flush with the surface. The trench width and depth depend on the mask region and the thickness of the TBC layer. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on freestream velocity and film-hole diameter of 11,000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5, and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to the improved two-dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. Computational fluid dynamics simulation using FLUENT was also performed to determine the jet-mainstream interactions to better understand the surface heat transfer coefficient and film effectiveness distributions. DA - 2009/// PY - 2009/// DO - 10.1115/1.2950057 VL - 131 IS - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77954300524&partnerID=MN8TOARS ER - TY - CONF TI - Numerical prediction of flow and heat transfer rates in metal based microchannels using lattice Boltzmann method AU - Parida, P.R. AU - Ekkad, S.V. C2 - 2009/// C3 - 2008 Proceedings of the ASME Summer Heat Transfer Conference, HT 2008 DA - 2009/// VL - 1 SP - 233-241 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70149096230&partnerID=MN8TOARS ER - TY - CONF TI - Film cooling study of novel orthogonal entrance and shaped exit holes AU - Abraham, S. AU - Navin, A.R. AU - Ekkad, S.V. AB - Film cooling effectiveness depends on several geometrical parameters like location on the airfoil, exit shape, orientation and arrangement of the holes. The focus of this investigation is to propose and explore a new film cooling hole geometry. The adiabatic film cooling effectiveness is determined experimentally, downstream of the exit of the film cooling holes on a flat plate using a steady state IR thermography technique. Coolant holes that are perpendicular to the direction of flow detach from the surface and enhance the heat transfer coefficient on the turbine blade without providing any coolant coverage, while angled holes along the mainstream direction result in superior film cooling effectiveness and lower heat transfer to the surface. The objective of this study is to examine the external cooling effects using coolant holes that are a combination of both angled shaped holes as well as perpendicular holes. The inlet of the coolant hole is kept perpendicular to the direction of flow to enhance the internal side heat transfer coefficient and the exit of the coolant hole is expanded and angled along the mainstream flow to prevent the coolant jet from lifting off from the blade external surface. A total of six different cases with variations in exit shape geometry are investigated at different blowing ratios (BR varying from 0.5 to 2.0). Results suggest that the film cooling effectiveness values obtained from these geometries are comparable with those of conventional angled holes. With the added advantage of enhanced heat transfer coefficient on the coolant channel internal side, as proven earlier by Byerley [3], overall superior cooling is accomplished. Furthermore this shaped hole can be made using the same technology being presently used in the industry. C2 - 2009/// C3 - Proceedings of the ASME Turbo Expo DA - 2009/// DO - 10.1115/GT2009-60003 VL - 3 SP - 829-838 M1 - PART B UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77953215706&partnerID=MN8TOARS ER - TY - CONF TI - Experimental and numerical investigation of convective heat transfer in a gas turbine can combustor AU - Patil, S. AU - Abraham, S. AU - Tafti, D. AU - Ekkad, S. AU - Kim, Y. AU - Dutta, P. AU - Moon, H.-K. AU - Srinivasan, R. AB - Experiments and numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under cold flow conditions in a Reynolds number range between 50,000 and 500,000 with a characteristic swirl number of 0.7. It is observed that the flow field in the combustor is characterized by an expanding swirling flow which impinges on the liner wall close to the inlet of the combustor. The impinging shear layer is responsible for the peak location of heat transfer augmentation. It is observed that as Reynolds number increases from 50,000 to 500,000, the peak heat transfer augmentation ratio (compared to fully-developed pipe flow) reduces from 10.5 to 2.75. This is attributed to the reduction in normalized turbulent kinetic energy in the impinging shear layer which is strongly dependent on the swirl number that remains constant at 0.7 with Reynolds number. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change. C2 - 2009/// C3 - Proceedings of the ASME Turbo Expo DA - 2009/// DO - 10.1115/GT2009-59377 VL - 3 SP - 1363-1371 M1 - PART B UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77953206941&partnerID=MN8TOARS ER - TY - CONF TI - Inclination and Crash Analysis for Hybrid Fuel Cell Scooter AU - Fong, Rey-Yie AU - Cheng, Jung-Ho C2 - 2009/// C3 - Abaqus Taiwan Users’ Conference DA - 2009/// ER - TY - CONF TI - Fuel Cell Stack Damage Evaluation for Hybrid Fuel Cell Scooter under Road Vibration Bumping Impact AU - Fong, Rey-Yie AU - Cheng, Jung-Ho C2 - 2009/// C3 - Abaqus Taiwan Users’ Conference DA - 2009/// ER - TY - THES TI - Design and Failure Prediction of Insert for Composite Sandwich Structures AU - Fong, Rey-Yie AU - Cheng, Jung-Ho DA - 2009/// PY - 2009/// PB - National Taiwan University ER - TY - CONF TI - Sensor networks for in-situ failure identification in woven composites AU - Park, C. AU - Propst, A. AU - Peters, K. AU - Zikry, M.A. AB - This paper presents experimental measurements of the response of woven composite laminates to multiple low-velocity impacts. Damage initiation and progression occur at multiple physical and temporal scales in heterogeneous materials, including fiber breakage, matrix cracking, delamination and matrix relaxation. The sensor networks/interrogators were therefore chosen specifically to provide insight into the order and progression of different failure modes. Measurements of the contact force between the impactor and composite are measured throughout impact. Additionally, the dissipated energy per impact event is also calculated from the impactor velocity. Surface mounted and embedded fiber Bragg grating sensors are used for the measurement of the laminate response. Peak wavelength measurements are performed during impact at 1 kHz, while full-spectral scanning is performed at 5 Hz during relaxation period of the laminate immediately after impact and quasi-statically to measure post-impact residual strain states within the laminate. The results highlight the depth of information embedded within the FBG full-spectral data sensors, as well as the added insight to be gained from combined global-local measurements. C2 - 2009/// C3 - Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems 2009, SMASIS2009 DA - 2009/// DO - 10.1115/SMASIS2009-1283 VL - 2 SP - 477-485 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77953777875&partnerID=MN8TOARS ER - TY - JOUR TI - Nanoscale design of adaptive tribological coatings for gold-ytrium based nanocomposites AU - Krim, J. AU - Dawson, B.D. AU - Barefoot, K. AU - Pan, L. AU - Pearson, J. AU - Zikry, M. AU - Baker, C. AU - Voevodin, A. T2 - Tribology - Materials, Surfaces and Interfaces AB - Nanocomposites hold great promise for space and ambient applications on account of their ability to adapt to and exhibit low friction and wear rates in constantly varying environmental conditions. In order to explore the impact of nanocrystalline grain size and fractal scaling properties on tribological performance, the authors have performed experimental and theoretical studies examining nanotribological properties of gold–ytrium based nanocomposites. These include modelling the impact of grain size on film stress and wear attributes and the documentation of surface region grain size distributions. The authors' modelling results associate smaller grain sizes with lower wear, consistent with experimental observations for the range of grain sizes studied. The findings show promise for nanoscale customisation of coatings so as to tailor them at the nanoscale in an application specific manner. DA - 2009/// PY - 2009/// DO - 10.1179/175158309X12586382418373 VL - 3 IS - 4 SP - 145-150 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77749339040&partnerID=MN8TOARS ER - TY - CONF TI - Nanoscale design of adaptive tribological coatings AU - Pan, L. AU - Dawson, B. AU - Krim, J. AU - Baker, C. AU - Pearson, J. AU - Zikry, M. AU - Vovoedin, A. C2 - 2009/// C3 - 2008 Proceedings of the STLE/ASME International Joint Tribology Conference, IJTC 2008 DA - 2009/// SP - 65-67 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70349869620&partnerID=MN8TOARS ER - TY - CONF TI - High repetition-rate full-spectrum interrogation of FBG sensors for dynamic measurements in composite laminates AU - Kunzler, W. AU - Zhu, Z. AU - Wirthlin, M. AU - Selfridge, R. AU - Schultz, S. AU - Propst, A. AU - Peters, K. AU - Zikry, M. AB - This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict remaining lifetime in composite laminate structures. C2 - 2009/// C3 - Proceedings of SPIE - The International Society for Optical Engineering DA - 2009/// DO - 10.1117/12.816384 VL - 7293 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-66749184331&partnerID=MN8TOARS ER - TY - CONF TI - Dynamic, full-spectral interrogation of fiber bragg grating sensors for impact testing of composite laminates AU - Propst, A. AU - Peters, K. AU - Zikry, M.A. AU - Kunzler, W. AU - Zhu, Z. AU - Wirthlin, M. AU - Selfridge, R. AU - Schultz, S. AB - This paper presents the full-spectral measurement of fiber Bragg grating sensor responses during impact testing of composite laminates. The sensors are embedded in carbon fiber/epoxy laminates which are subjected to multiple low velocity impacts until perforation of the laminate occurs. Applying a recently developed high-speed interrogator, the Bragg grating sensor interrogation is demonstrated at 534 Hz over a 14.9 nm bandwidth. The measurement of the transient response of the grating sensors during impact reveals unique spectral signatures that could not be detected through peak-wavelength monitoring or post-impact full-spectral scanning of the sensors, including local relaxation of the laminate. C2 - 2009/// C3 - Proceedings of SPIE - The International Society for Optical Engineering DA - 2009/// DO - 10.1117/12.835406 VL - 7503 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70449404871&partnerID=MN8TOARS ER - TY - CONF TI - Microstructural modelling of failure modes in crystalline materials AU - Hatem, T.M. AU - Zikry, M.A. C2 - 2009/// C3 - 12th International Conference on Fracture 2009, ICF-12 DA - 2009/// VL - 8 SP - 5923-5932 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84869835552&partnerID=MN8TOARS ER - TY - CONF TI - An Analytical Expression for Predicting the Pressure Drop of Bimodal Filter Media AU - Fotovati, S. AU - Tafreshi, H.V. AU - Pourdeyhimi, B. T2 - American Filtration and Separation Society C2 - 2009/5/4/ C3 - American Filtration and Separation Society CY - Minneapolis, Minnesota DA - 2009/5/4/ PY - 2009/5/4/ ER - TY - CONF TI - Two-dimensional Modeling of Nanoparticle Collection Efficiency in Bimodal Filters AU - Fotovati, S. AU - Tafreshi, H.V. AU - Pourdeyhimi, B. T2 - American Filtration and Separation Society C2 - 2009/5/4/ C3 - American Filtration and Separation Society CY - Minneapolis, Minnesota DA - 2009/5/4/ PY - 2009/5/4/ ER - TY - CONF TI - Three-dimensional Simulation of Particle Filtration in Electrospun Nanofibrous Filters AU - Hosseini, S.A. AU - Tafreshi, H.V. T2 - American Filtration and Separation Society C2 - 2009/5/4/ C3 - American Filtration and Separation Society CY - Minneapolis, Minnesota DA - 2009/5/4/ PY - 2009/5/4/ ER - TY - CONF TI - Modeling Pressure Drop and Collection Efficiency of Micro- and Nanofiber Filters AU - Fotovati, S. AU - Tafreshi, H.V. AU - Pourdeyhimi, B. T2 - Nanofibers For The 3rd Millennium - Nano For Life C2 - 2009/3/11/ C3 - Nanofibers For The 3rd Millennium - Nano For Life CY - Liberec, Czech Republic DA - 2009/3/11/ PY - 2009/3/11/ ER - TY - CONF TI - Modeling Fluid Infiltration in Fibrous Materials AU - Jaganathan, S. AU - Tafreshi, H.V. AU - Pourdeyhimi, B. T2 - Techtextil North America C2 - 2009/4/21/ C3 - Techtextil North America CY - Las Vegas, NV DA - 2009/4/21/ PY - 2009/4/21/ ER - TY - CONF TI - Modeling Performance of Multi-Layer Composite Air Filters AU - Fotovati, S. AU - Tafreshi, H.V. AU - Pourdeyhimi, B. T2 - Techtextil North America C2 - 2009/4/21/ C3 - Techtextil North America CY - Las Vegas, NV DA - 2009/4/21/ PY - 2009/4/21/ ER - TY - JOUR TI - An Investigation of the Radiative Heat Transfer through Nonwoven Fibrous Materials AU - Qashou, Imad AU - Tafreshi, Hooman Vahedi AU - Pourdeyhimi, Behnam T2 - Journal of Engineered Fibers and Fabrics AB - In this study, the surface-to-surface radiation model of the Fluent CFD code is used to investigate the response of a fibrous material to the radiative heat transfer. The unsteady state heat transfer equation is solved for the temperature and heat flux in and around the fibers that constitute a nonwoven fibrous material. For a fixed fiber diameter, it was shown that the higher the fabric's Solid Volume Fraction (SVF), the slower is the material's average temperature rise. Our simulation results also indicate that for a fixed SVF, fiber diameter has a negligible influence on the unsteady transfer of heat through the media. Of particular interest in this paper is the effect of material's thickness on the heat penetration. It is shown that the transient heat transfer exponentially decreases by increasing the material's thickness for fixed SVFs and fiber diameters. The above finding is also in agreement with our experimental study. DA - 2009/3// PY - 2009/3// DO - 10.1177/155892500900400103 VL - 4 IS - 1 SP - 155892500900400 J2 - Journal of Engineered Fibers and Fabrics LA - en OP - SN - 1558-9250 1558-9250 UR - http://dx.doi.org/10.1177/155892500900400103 DB - Crossref ER - TY - ER - TY - JOUR TI - Analytical expressions for predicting permeability of bimodal fibrous porous media AU - Vahedi Tafreshi, H. AU - A Rahman, M.S. AU - Jaganathan, S. AU - Wang, Q. AU - Pourdeyhimi, B. T2 - Chemical Engineering Science AB - Pressure drop is one of the most important characteristics of a fibrous media. While numerous analytical, numerical, and experimental published works are available for predicting the permeability of media made up of fibers with a unimodal fiber diameter distribution (referred to as unimodal media here), there are almost no easy-to-use expressions available for media with a bimodal fiber diameter distribution (referred to as bimodal media). In the present work, the permeability of bimodal media is calculated by solving the Stokes flow governing equations in a series of 3-D virtual geometries that mimic the microstructure of fibrous materials. These simulations are designed to establish a unimodal equivalent diameter for the bimodal media thereby taking advantage of the existing expressions of unimodal materials for permeability prediction. We evaluated eight different methods of defining an equivalent diameter for bimodal media and concluded that the area-weighted average diameter of Brown and Thorpe [2001. Glass-fiber filters with bimodal fiber size distributions. Powder Technology 118, 3–9], volume-weighted resistivity model of Clague and Phillips [1997. A numerical calculation of the hydraulic permeability of three dimensional disordered fibrous media. Physics of Fluids 9 (6), 1562–1572], and the cube root relation of the current paper offer the best predictions for the entire range of mass (number) fractions, 0⩽nc⩽1, with fiber diameter ratios, 1⩽Rcf⩽5, and solidities, 5⩽α⩽15. DA - 2009/// PY - 2009/// DO - 10.1016/j.ces.2008.11.013 VL - 64 IS - 6 SP - 1154-1159 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-59349120565&partnerID=MN8TOARS KW - Bimodal media KW - Permeability modeling KW - Fibrous media KW - Filters ER - TY - JOUR TI - A two-scale modeling of motion-induced fluid release from thin fibrous porous media AU - Ashari, A. AU - Vahedi Tafreshi, H. T2 - Chemical Engineering Science AB - In this work, a two-scale two-phase modeling methodology is presented for studying fluid release from saturated/unsaturated thin fibrous media when brought in contact with a moving solid surface. Our macroscale model is based on the Richards’ equation for two-phase fluid transport in porous media. The required constitutive relationships, capillary pressure and relative permeability as functions of medium's saturation, are obtained through microscale modeling. At microscales, a 3-D model based on fiber diameter, fiber orientation, and medium's solid volume fraction (SVF), is generated to resemble the internal structure of the fibrous sheets and be used in full-morphology analysis as well as microscale permeability simulation. A mass convection boundary condition is considered here to model the fluid transport at the boundary in contact with the target surface. It was shown that the mass convection coefficient, kf, plays a significant role in determining the release rate and is expected to be in the range of 10-6 Effective engine mapping and calibration are contingent upon tight control of the environment in which the mapping and calibration are performed. Among the most important variables to be controlled are the temperatures of coolant and oil that circulate through the engine block. Because of the large time constants associated with thermodynamic systems, controlling these variables often represents a bottleneck in the engine mapping and calibration processes. In this paper, we examine a particular layout for a thermal management unit, which is currently being used in practice. By developing and analyzing a thermodynamic model of the system, we are able to gain insight into the system dynamics and explore special features to optimize the temperature response. In particular, we will show how the overactuation in the system may be leveraged in the presence of hard saturation constraints and different dynamic actuator authorities. We present design and validation results (both simulation and experimental) for the proposed controller, and compare the performance to the baseline controller in order to quantify improvements. DA - 2009/5// PY - 2009/5// DO - 10.1109/tcst.2008.2001267 VL - 17 IS - 3 SP - 540-551 J2 - IEEE Trans. Contr. Syst. Technol. OP - SN - 1063-6536 1558-0865 UR - http://dx.doi.org/10.1109/tcst.2008.2001267 DB - Crossref KW - Automotive control KW - calibration KW - optimal control KW - overactuated systems KW - powetrain control ER - TY - JOUR TI - Quantitative Viscoelasticity Mapping of Human Liver Using Supersonic Shear Imaging: Preliminary In Vivo Feasability Study AU - Muller, Marie AU - Gennisson, Jean-Luc AU - Deffieux, Thomas AU - Tanter, Mickaël AU - Fink, Mathias T2 - Ultrasound in Medicine & Biology AB - This paper demonstrates the feasibility of in vivo quantitative mapping of liver viscoelasticity using the concept of supersonic shear wave imaging. This technique is based on the combination of a radiation force induced in tissues by focused ultrasonic beams and a very high frame rate ultrasound imaging sequence capable of catching in real time the transient propagation of resulting shear waves. The local shear wave velocity is recovered using a dedicated time-of-flight estimation technique and enables the 2-D quantitative mapping of shear elasticity. This imaging modality is performed using a conventional ultrasound probe during a standard intercostal ultrasonographic examination. Three supersonic shear imaging (SSI) sequences are applied successively in the left, middle and right parts of the 2-D ultrasonographic image. Resulting shear elasticity images in the three regions are concatenated to provide the final image covering the entire region-of-interest. The ability of the SSI technique to provide a quantitative and local estimation of liver shear modulus with a millimetric resolution is proven in vivo on 15 healthy volunteers. Liver moduli extracted from in vivo data from healthy volunteers are consistent with those reported in the literature (Young's modulus ranging from 4 to 7.5 kPa). Moreover, liver stiffness estimation using the SSI mode is shown to be fast (less than one second), repeatable (5.7% standard deviation) and reproducible (6.7% standard deviation). This technique, used as a complementary tool for B-mode ultrasound, could complement morphologic information both for fibrosis staging and hepatic lesions imaging. DA - 2009/2// PY - 2009/2// DO - 10.1016/j.ultrasmedbio.2008.08.018 VL - 35 IS - 2 SP - 219-229 J2 - Ultrasound in Medicine & Biology LA - en OP - SN - 0301-5629 UR - http://dx.doi.org/10.1016/j.ultrasmedbio.2008.08.018 DB - Crossref KW - Transient elastography KW - Ultrasound KW - Liver fibrosis KW - Shear wave imaging ER - TY - JOUR TI - A new lamination theory for layered textile composites that account for manufacturing induced effects AU - Pankow, Mark AU - Waas, Anthony M. AU - Yen, Chian-Fong AU - Ghiorse, Seth T2 - Composites Part A: Applied Science and Manufacturing AB - This paper is concerned with the development of a new lamination theory for layered textile composites that can account for manufacturing induced effects. The theory can be used for the calculation of the effective linear elastic extensional and bending stiffnesses of laminated textile composite panels. A representative unit cell (RUC) of the textile architecture is first identified along with its constituents. Tow geometry is represented analytically taking account of tow undulation. Each tow is modeled as a transversely isotropic linear elastic solid and the contribution from each tow to the RUC elastic bending stiffness is obtained by volume averaging, taking account of the volume fraction of each constituent. The formulation is amenable to the incorporation of geometric changes to the textile architecture that occurs through manufacturing induced consolidation. Predictions of the elastic bending stiffness are compared against experimental data, showing a strong correlation between the analytical model and the experimental results. DA - 2009/12// PY - 2009/12// DO - 10.1016/j.compositesa.2009.08.021 VL - 40 IS - 12 SP - 1991-2003 J2 - Composites Part A: Applied Science and Manufacturing LA - en OP - SN - 1359-835X UR - http://dx.doi.org/10.1016/j.compositesa.2009.08.021 DB - Crossref KW - Fabrics/textiles KW - Polymer matrix composites KW - Laminate mechanics KW - Mechanical testing ER - TY - JOUR TI - Hysteretic recurrent neural networks: a tool for modeling hysteretic materials and systems AU - Veeramani, Arun S AU - Crews, John H AU - Buckner, Gregory D T2 - Smart Materials and Structures AB - This paper introduces a novel recurrent neural network, the hysteretic recurrent neural network (HRNN), that is ideally suited to modeling hysteretic materials and systems. This network incorporates a hysteretic neuron consisting of conjoined sigmoid activation functions. Although similar hysteretic neurons have been explored previously, the HRNN is unique in its utilization of simple recurrence to 'self-select' relevant activation functions. Furthermore, training is facilitated by placing the network weights on the output side, allowing standard backpropagation of error training algorithms to be used. We present two- and three-phase versions of the HRNN for modeling hysteretic materials with distinct phases. These models are experimentally validated using data collected from shape memory alloys and ferromagnetic materials. The results demonstrate the HRNN's ability to accurately generalize hysteretic behavior with a relatively small number of neurons. Additional benefits lie in the network's ability to identify statistical information concerning the macroscopic material by analyzing the weights of the individual neurons. DA - 2009/6/3/ PY - 2009/6/3/ DO - 10.1088/0964-1726/18/7/075004 VL - 18 IS - 7 SP - 075004 J2 - Smart Mater. Struct. OP - SN - 0964-1726 1361-665X UR - http://dx.doi.org/10.1088/0964-1726/18/7/075004 DB - Crossref ER - TY - JOUR TI - Organic photodetector with spectral response tunable across the visible spectrum by means of internal optical microcavity AU - An, Kwang Hyup AU - O’Connor, Brendan AU - Pipe, Kevin P. AU - Shtein, Max T2 - Organic Electronics AB - We demonstrate an organic photodetector (OPD) structure in which the active layers and a thick optical spacer are sandwiched between two metallic electrodes, forming a Fabry–Perot resonant cavity. The second resonant mode of this cavity can be positioned by means of an optical spacer so that its maximum intensity overlaps with the donor–acceptor interface, leading to a peak in the external quantum efficiency (EQE) of the OPD for this resonant wavelength. The photoresponse can thus be tuned across the visible spectrum by adjusting the spacer thickness, while the full width half maximum remains approximately 50 nm. Because the active layers can be thin in this approach, the EQE is not sacrificed, and the device can achieve a relatively high response frequency that does not suffer from the inclusion of the optical spacer. We simulate the photoresponse of OPD structure using transfer matrix optical calculations and an exciton diffusion model; our simulation also explicitly accounts for interface roughness measured by atomic force microscopy. Angular dependence of the OPD’s response is also measured and discussed. DA - 2009/9// PY - 2009/9// DO - 10.1016/j.orgel.2009.06.003 VL - 10 IS - 6 SP - 1152-1157 J2 - Organic Electronics LA - en OP - SN - 1566-1199 UR - http://dx.doi.org/10.1016/j.orgel.2009.06.003 DB - Crossref KW - Organic photovoltaic KW - Photodetector KW - Quantum efficiency KW - Spectral tunability KW - Optical microcavity ER - TY - JOUR TI - Characterization of Quasi-static Mechanical Properties of Polymer Nanocomposites Using a New Combinatorial Approach AU - Gershon, Alan L. AU - Kota, Arun K. AU - Bruck, Hugh A. T2 - Journal of Composite Materials AB - Recently, it has become very important to rapidly characterize the processing-structure-property relationships in polymer nanocomposites using minimal quantities of expensive nanoscale fillers. To address this issue, we present a new combinatorial approach developed for characterizing the variation in mechanical properties as a function of filler composition in polymer nanocomposites. The fundamental basis for the combinatorial approach is the generation of compositional gradients through transient operation of a twin-screw extruder (TSE). The compositional variation in the specimens could be rapidly predicted a priori using a convolution process model and was verified a posteriori using pycnometry measurements and thermogravimetric analysis. To characterize the quasi-static mechanical properties along the compositional gradient, sub-scale specimens that are proportional in size to ASTM type I specimens but with a gage section that is a factor of 10 smaller, were tested using a microtensile tester. The properties of the sub-scale specimens processed in the combinatorial approach correlated well with those of sub-scale specimens of similar composition processed in steady-state, thereby indicating that the properties were unaffected by the transient operation of the TSE. Furthermore, the quasi-static mechanical properties of the steady-state ASTM type I standard specimens were compared with those of the sub-scale specimens to determine the effect of specimen size. The results were nearly identical, except the increased size of the ASTM type I standard specimens resulted in substantial reductions in ductility that are most likely due to an increase in the number of processing-related defects. DA - 2009/8/13/ PY - 2009/8/13/ DO - 10.1177/0021998309345311 VL - 43 IS - 22 SP - 2587-2598 J2 - Journal of Composite Materials LA - en OP - SN - 0021-9983 1530-793X UR - http://dx.doi.org/10.1177/0021998309345311 DB - Crossref KW - combinatorial materials science KW - quasi-static mechanical properties KW - polymer nanocomposites KW - twin-screw extrusion KW - sub-scale ASTM type I specimens KW - microtensile testing ER - TY - JOUR TI - Computation vs. Experiment for High-Frequency Low-Reynolds Number Airfoil Plunge AU - Ol, Michael V. AU - Reeder, Mark AU - Fredberg, Daniel AU - McGowan, Gregory Z. AU - Gopalarathnam, Ashok AU - Edwards, Jack R. T2 - International Journal of Micro Air Vehicles AB - We seek to extend the literature on sinusoidal pure-plunge of 2D airfoils at high reduced frequency and low Reynolds number, by including effects of camber and nonzero mean incidence angle. We compare experimental results in a water tunnel using dye injection and 2D particle image velocimetry, with a set of computations in 2D – Immersed Boundary Method and unsteady Reynolds-Averaged Navier Stokes. The Re range is from 10,000 to 60,000, based on free stream velocity and airfoil chord, chosen to cover cases where transition in attached boundary layers would be of some importance, and where transition would only occur in the wake. Generally at high reduced frequency there is no Reynolds number effect. Mean angle of attack has significance, notionally, depending on whether it is below or above static stall. Computations were found to agree well with experimentally-derived velocity contours, vorticity contours and momentum in the wake. As found previously for the NACA0012, varying Strouhal number is found to control the topology of the wake, while varying reduced amplitude and reduced frequency together, but keeping Strouhal number constant, causes wake vortical structures to scale with the reduced amplitude of plunge. Flowfield periodicity – as evinced from comparison of instantaneous and time-averaged particle image velocimetry – is generally attained after two periods of oscillation from motion onset. DA - 2009/6// PY - 2009/6// DO - 10.1260/175682909789498279 VL - 1 IS - 2 SP - 99-119 J2 - International Journal of Micro Air Vehicles LA - en OP - SN - 1756-8293 1756-8307 UR - http://dx.doi.org/10.1260/175682909789498279 DB - Crossref ER - TY - JOUR TI - Closed-form exact solutions of MHD viscous flow over a shrinking sheet AU - Fang, Tiegang AU - Zhang, Ji T2 - Communications in Nonlinear Science and Numerical Simulation AB - In this paper, the magnetohydrodynamic (MHD) flow over a shrinking sheet is solved analytically. The solution is given in a closed-form equation and is an exact solution of the full governing Navier–Stokes equations for the problem. Interesting solution behavior is observed with multiple solution branches for certain parameter domain. DA - 2009/7// PY - 2009/7// DO - 10.1016/j.cnsns.2008.10.005 VL - 14 IS - 7 SP - 2853-2857 J2 - Communications in Nonlinear Science and Numerical Simulation LA - en OP - SN - 1007-5704 UR - http://dx.doi.org/10.1016/j.cnsns.2008.10.005 DB - Crossref KW - Similarity solution KW - Stretching surface KW - Shrinking sheet KW - Navier-Stokes equations KW - Analytical solution KW - Exact solution KW - Magnetohydrodynamics ER - TY - CONF TI - ATOMISTIC STUDIES OF VOID-GROWTH BASED YIELD CRITERIA IN SINGLE CRYSTAL CU AT HIGH STRAIN RATES AU - Dongare, A. M. AU - Rajendran, A. M. AU - LaMattina, B. AU - Zikry, M. A. AU - Brenner, D. W. AU - Elert, Mark AU - Furnish, Michael D. AU - Anderson, William W. AU - Proud, William G. AU - Butler, William T. T2 - SHOCK COMPRESSION OF CONDENSED MATTER 2009: Proceedings of the American Physical Society Topical Group on Shock Compression of Condensed Matter AB - Dynamic fracture of ductile metals is attributed to the nucleation, growth, and coalescence of voids which eventually form the fracture surface. Large‐scale MD simulations are used to model void growth behavior in single crystal Cu at high strain rates. Yielding is studied for systems with various values of void fractions as well as combinations of loading conditions. The calculated yield surface of single crystal Cu for varying void fractions indicates the inability of traditional continuum models to predict void growth at high strain rates. C2 - 2009/// C3 - DA - 2009/// DO - 10.1063/1.3295254 VL - 1195 SP - 769-772 PB - AIP UR - http://dx.doi.org/10.1063/1.3295254 DB - Crossref ER - TY - JOUR TI - Self-assembled ferrofluid lithography: patterning micro and nanostructures by controlling magnetic nanoparticles AU - Chang, Chih-Hao AU - Tan, Chee-Wee AU - Miao, Jianmin AU - Barbastathis, George T2 - Nanotechnology AB - We have developed an alternative self-assembly process to pattern different geometries with user-defined tunability across the micro and nanoscale. In this approach, field-induced assembly of colloidal magnetic nanoparticles within a microfluidic channel is used as a tunable mask for near-field lithography. We have fabricated dot arrays with controllable spacing and micro-ring patterns with 250 nm feature sizes. The proposed process is versatile, cost-effective, and scalable, presenting itself as a promising nanomanufacturing tool. DA - 2009/11/6/ PY - 2009/11/6/ DO - 10.1088/0957-4484/20/49/495301 VL - 20 IS - 49 SP - 495301 J2 - Nanotechnology OP - SN - 0957-4484 1361-6528 UR - http://dx.doi.org/10.1088/0957-4484/20/49/495301 DB - Crossref ER - TY - JOUR TI - Survey on various control techniques in micro grinding processes AU - Xu, C. AU - Tang, Y. AU - Jackson, M.J. T2 - International Journal of Nanomanufacturing AB - Due to the highly demanding geometric accuracy and surface finish for many modern products, grinding processes have been extensively used in manufacturing industry. However, it is also well accepted that grinding is one of the most complicated machining processes due to the high non-linearities, intrinsic uncertainties and time-varying characteristics. Multiple challenging problems exist in the process that limits its overall quality and production in practice. With the increasing demands for higher part geometry accuracy, better surface integrity, more productivity and other desired product parameters (e.g., minimisation of subsurface micro-damage) with less operator intervention, various control methods have been studied and implemented to control position, velocity, force, power, temperature and the material removal rate (MRR) during the grinding process, in order to achieve the desired system performance within certain cost/time. This paper reviews different control strategies in order to provide a guideline for academic researchers and industrial practitioners in improving the final product quality with increased possible process flexibility. DA - 2009/// PY - 2009/// DO - 10.1504/IJNM.2009.027503 VL - 3 IS - 4 SP - 398-408 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-68649101216&partnerID=MN8TOARS ER - TY - CONF TI - On the fluid dynamics of acoustically perturbed non-premixed swirling flames AU - Idahosa, U. AU - Khatami, N. AU - Saha, A. AU - Xu, C. AU - Basu, S. C2 - 2009/// C3 - Fall Meeting of the Eastern States Section of the Combustion Institute 2009 DA - 2009/// SP - 720-725 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84946594823&partnerID=MN8TOARS ER - TY - CONF TI - Geometrical adaptive controller for tool deflection compensation in helical end milling processes AU - Tang, Y. AU - Xu, C. AU - Jackson, M. AB - Geometrical Adaptive Control (GAC) aims to maintain the stability of the geometrical quality of mechanical parts during production. GAC systems can effectively compensate for the machining error induced by cutter deflection during helical end milling processes. The existing GAC systems only deal with deflection compensation in machining of straight surfaces. Deflection in curved surface machining is more complicated, and the effect of surface curvature on deflection should be considered when designing the GAC compensation system. This paper intends to develop a GAC system for cutter deflection in end milling of curved geometries to account for deflection variation induced by workpiece curvature. In this paper, the influence of curved geometry on cutting forces is firstly analyzed; then, the deflection is calculated based on the cantilever beam model. The error space motion control methodology is utilized in GAC design for deflection compensation. Simulation studies are conducted on a two-axis milling system for circular surface, and the results validate the compensation strategy. C2 - 2009/// C3 - Proceedings of the ASME International Manufacturing Science and Engineering Conference 2009, MSEC2009 DA - 2009/// DO - 10.1115/MSEC2009-84218 VL - 2 SP - 377-383 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77953211980&partnerID=MN8TOARS ER - TY - CONF TI - Generation of optimal functions using particle swarm method over discrete intervals AU - Shamieh, F. AU - Xu, C. AB - Particle swarm optimization is a computational learning technique designed to find a global and optimal solution upon or within a function. The output, usually singular, is characteristically accurate as the nature of the system is to maintain a balance of convergence and sample diversity. This paper aims to introduce the process of using a multi-level evaluation approach of particle swarm optimization to generate a solution function. Multiple variable assessment is replaced with sequential interval assessment of repeated variables and pieced together to form the framework of an optimized function. C2 - 2009/// C3 - Annual Conference of the North American Fuzzy Information Processing Society - NAFIPS DA - 2009/// DO - 10.1109/NAFIPS.2009.5156484 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70350402296&partnerID=MN8TOARS ER - TY - JOUR TI - Diamond coated microtools for machining compact bone AU - Jackson, M.J. AU - Whitfield, M.D. AU - Xu, C. AU - Ahmed, W. T2 - International Journal of Nano and Biomaterials AB - The structure of compact bone is heterogeneous and as such, is difficult to shape by cutting tools during clinical surgical practices. The structure of bone can have a devastating effect on the performance of the cutting tool unless it is coated with a thin solid film that is wear resistant. The paper investigates the use of diamond coated cutting tools to prepare bone for prosthetic implants and the implications of their use on the machining characteristics of biological materials. DA - 2009/// PY - 2009/// DO - 10.1504/IJNBM.2009.028340 VL - 2 IS - 6 SP - 505-519 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-73549097118&partnerID=MN8TOARS ER - TY - CONF TI - Characterization of combustion dynamics in swirl stabilized flames AU - Idahosa, U. AU - Saha, A. AU - Xu, C. AU - Basu, S. AB - This paper investigates flame frequency response relative to changes in swirl intensity and equivalence ratio in a non-premixed swirl stabilized burner. The degree of swirl in the burner is characterized by the swirl number (S) provided by circumferentially distributed air supply ports directed tangentially to the main axial air flow. Equivalence ratio variations are induced using varying constant, linear ramp and exponentially decaying fuel (propane) flow rates towards blowoff. The variations in the air speed at the exit of the burner (U) are measured with an anemometer located at the base of the flame. The emission of CH* radicals (I) is used as a marker of flame heat release and is measured using a photomultiplier (PMT). The frequency response of the PMT heat release and burner velocity signals are analyzed in the frequency domain using the Fast Fourier Transform (FFT) and Continuous Wavelet Transform (CWT) methods. Amplification in the power of heat release fluctuation is observed in low swirl flames close to blowoff. This effect is found to be reversed in higher swirl number flames even close to blowoff. In dynamic approaches to blowoff (using ramp and decaying fuel flow rates), the dominant heat release fluctuation frequencies are observed to be similar to perturbation frequencies in lean flames hovering at constant fuel flow rates close to blowoff. C2 - 2009/// C3 - American Society of Mechanical Engineers, Power Division (Publication) PWR DA - 2009/// DO - 10.1115/POWER2009-81168 SP - 517-531 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77952897544&partnerID=MN8TOARS ER - TY - JOUR TI - Adaptive compensation of tool deflection in micromilling processes AU - Tang, Y. AU - Xu, C. AU - Jackson, M.J. T2 - International Journal of Nanomanufacturing AB - This paper proposed a novel adaptive control method to compensate the cutting force induced tool deflection during micromilling processes. Owing to the slenderness of the micromilling cutter, the tool deflects at a certain degree depending on the magnitude of the instantaneous cutting force. The proposed intelligent adaptive control algorithm will adjust the cutting conditions online to compensate the tool deflection and therefore improving the machining accuracy. The numerical simulation results demonstrate the effectiveness of the proposed compensation strategy. DA - 2009/// PY - 2009/// DO - 10.1504/IJNM.2009.027056 VL - 3 IS - 1-2 SP - 159-168 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-68149149709&partnerID=MN8TOARS ER - TY - JOUR TI - A stable hierarchical fuzzy control design for certain non-linear systems based on input-output passivity theory AU - Xu, C. AU - Shin, Y.C. T2 - Control and Intelligent Systems DA - 2009/// PY - 2009/// VL - 37 IS - 2 SP - 103-113 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-69949109741&partnerID=MN8TOARS ER - TY - JOUR TI - A multifunctional high-speed spindle for micromachining medical materials AU - Jackson, M.J. AU - Xu, C. AU - Ahmed, W. T2 - International Journal of Nano and Biomaterials AB - The efficiency of micro cutting tools that are used in high-speed air turbine spindles depends on the rotational speed of the rotor, especially when machining medical materials such as titanium alloys. A high-pressure variation on the surface of the rotor causes the rotor to retard and this severely limits the reliability and durability of high-speed spindles to support new developments in the developing area of micromachining. A variety of spindle designs are proposed and numerical simulations carried out for each design using FLUENT software. The results revealed that changes in the rotor, inlet and outlet geometries affect the pressure distribution on the rotor significantly. The optimum design was identified based on the lowest pressure variation on the rotor surface obtained from the FLUENT results. Spinning the rotor at very high speeds provides a new direction in the development of mechanical micromachining. DA - 2009/// PY - 2009/// DO - 10.1504/IJNBM.2009.028341 VL - 2 IS - 6 SP - 520-539 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-73549119972&partnerID=MN8TOARS ER - TY - CONF TI - A hybrid modeling technique for partially-known systems using linear regression and neural network AU - Joslin, A.J. AU - Xu, C. AB - In this paper a hybrid modeling and system identification method, combining linear least squares regression and artificial neural network techniques, is presented to model a type of dynamic systems which have an incomplete analytical model description. This approach in modeling nonlinear, partially-understood systems is particularly useful to the study of manufacturing processes, where the linear regression portion of the hybrid model is established using a known mathematical model for the process and the neural network is constructed using the residuals from the least squares regression, therefore ensuring a more precise process model for the specific machining setup, tooling selection, workpiece properties, etc. In this paper the method is mathematically proven to give regression coefficients close to those which would be found if only a regression had been performed. The modeling method is then simulated for a macro-scale hard turning process, and the result proves the effectiveness of the proposed hybrid modeling method. C2 - 2009/// C3 - Proceedings of the ASME International Manufacturing Science and Engineering Conference 2009, MSEC2009 DA - 2009/// DO - 10.1115/MSEC2009-84217 VL - 2 SP - 365-375 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77953224712&partnerID=MN8TOARS ER - TY - JOUR TI - Model for the Particle Size, Overpotential, and Strain Dependence of Phase Transition Pathways in Storage Electrodes: Application to Nanoscale Olivines AU - Tang, M. AU - Huang, H.-Y. AU - Meethong, N. AU - Kao, Y.-H. AU - Carter, W. C. AU - Chiang, Y.-M. T2 - Chemistry of Materials AB - In the drive toward improved electrical energy storage for applications ranging from wireless devices to electric vehicles to grid stabilization, nanoscale materials are of growing interest as ion storage electrodes. Nanoscale olivines based on LiMPO4 (M = Fe, Mn, Co, Ni) are one class of compounds for which recent experimental developments reveal very different phase transition and solid-solubility behavior compared to larger particles. The olivines may be an exemplar for generalized behavior for which metastable crystalline or amorphous phases are produced under the large driving forces incurred during electrochemical reactions. Here we use a diffuse-interface thermodynamic model to assess the conditions under which amorphous phase transitions may occur in nanoscale LiMPO4 particles. There are three central conclusions. First, assuming as with similar solids that the amorphous phase has the lower surface energy, it is found that an initially crystalline phase may undergo amorphization during cycling when the particle size is below a critical value. Second, the effect of applied electrical overpotentials on the phase stability is evaluated for the first time, and is found to strongly influence the phase transition pathways of small particles. Third, the tendency to amorphize is significantly affected by the magnitude of the misfit strain between the lithiated and delithiated crystalline phases. It is shown that there exists a critical misfit strain above which the preferred transformation pathway is amorphization, regardless of the particle size. We use these results to interpret experimentally observed behavior of olivines, including data that up to now have been unexplained. DA - 2009/4/28/ PY - 2009/4/28/ DO - 10.1021/cm803172s VL - 21 IS - 8 SP - 1557-1571 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/cm803172s DB - Crossref ER - TY - CHAP TI - Persistence, Consistence and Patience AU - Xu, C. T2 - Tips on Getting an Academic Position PY - 2009/// PB - Lulu Web ER - TY - CHAP TI - Fundamentals of Machining AU - Jackson, M.J. AU - Ahmed, W. AU - Xu, C. T2 - Machining with Nanomaterials PY - 2009/// PB - Springer ER - TY - CHAP TI - Formation of Nanostructured Metals AU - Jackson, M.J. AU - Evans, J. AU - Xu, C. AU - Ahmed, W. T2 - Machining with Nanomaterials PY - 2009/// PB - Springer ER - TY - JOUR TI - A fully discrete, kinetic energy consistent finite-volume scheme for compressible flows AU - Subbareddy, Pramod K. AU - Candler, Graham V. T2 - JOURNAL OF COMPUTATIONAL PHYSICS AB - A robust, implicit, low-dissipation method suitable for LES/DNS of compressible turbulent flows is discussed. The scheme is designed such that the discrete flux of kinetic energy and its rate of change are consistent with those predicted by the momentum and continuity equations. The resulting spatial fluxes are similar to those derived using the so-called skew-symmetric formulation of the convective terms. Enforcing consistency for the time derivative results in a novel density weighted Crank–Nicolson type scheme. The method is stable without the addition of any explicit dissipation terms at very high Reynolds numbers for flows without shocks. Shock capturing is achieved by switching on a dissipative flux term which tends to zero in smooth regions of the flow. Numerical examples include a one-dimensional shock tube problem, the Taylor–Green problem, simulations of isotropic turbulence, hypersonic flow over a double-cone geometry, and compressible turbulent channel flow. DA - 2009/3/20/ PY - 2009/3/20/ DO - 10.1016/j.jcp.2008.10.026 VL - 228 IS - 5 SP - 1347-1364 SN - 0021-9991 KW - Compressible flow KW - Direct numerical simulation KW - Large-eddy simulation KW - Non-dissipative KW - Kinetic energy KW - Implicit time integration KW - Fully discrete ER - TY - JOUR TI - A Discontinuous Galerkin method based on a BGK scheme for the Navier-Stokes equations on arbitrary grids AU - Luo, H. AU - Luo, L. Q. AU - Xu, K. T2 - Advances in Applied Mathematics & Mechanics DA - 2009/// PY - 2009/// DO - 10.1142/9789814313377_0006 VL - 1 IS - 3 SP - 301-318 ER - TY - CONF TI - Sensor networks for in-situ failure identification in woven composites AU - Propst, A. AU - Garrett, R. AU - Park, C. AU - Peters, K. AU - Zikry, M. AB - This paper presents experimental measurements of the response of woven composite laminates to multiple low-velocity impacts. Damage initiation and progression occur at multiple physical and temporal scales in heterogeneous materials, including fiber breakage, matrix cracking, delamination and matrix relaxation. The sensor/interrogators were therefore chosen specifically to provide insight into the order and progression of different failure modes. Measurements of the contact force between the impactor and composite are measured throughout impact. Additionally, the dissipated energy per impact event is also calculated from the impactor velocity. Surface mounted and embedded fiber Bragg grating sensors are used for the measurement of the laminate response. Peak wavelength measurements are performed during impact at 1 kHz, while full-spectral scanning is performed at 5 Hz during relaxation period of the laminate immediately after impact and quasi-statically to measure post-impact residual strain states within the laminate. The results highlight the depth of information embedded within the FBG full-spectral data sensors, as well as the added insight to be gained from combined global-local measurements. C2 - 2009/// C3 - SMASIS 2009, vol 2 DA - 2009/// DO - 10.1117/12.815743 VL - 7293 SP - 477–485 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-66749128673&partnerID=MN8TOARS ER - TY - CONF TI - Quantification of the effectiveness of various conductive and non-conductive epoxies as an attachment method for small SMA wires AU - Furst, S. J. AU - Bumgarner, D. AU - Seelecke, S. AB - The discovery of thermoelastic behavior in shape memory alloys (SMA) such as Nitinol enabled the conceptualization of many applications where actuators and sensors are embedded into a structural component. These so called “adaptive structures” can be extremely compact and energy efficient. SMA wires show characteristics similar to that of muscle fibers, and thus enable replication of an animal’s musculoskeletal system. Also, SMA wires are extremely attractive in the biomedical field where compact robotic elements can reduce the invasiveness of some surgical procedures. Unfortunately, widespread implementation of adaptive structures actuated by small SMA-wires in industry has been hindered by two significant challenges. First, SMA wires exhibit hysteretic behavior during heating and cooling that can be difficult to model without substantial computation. Second, attaching a small (∼50–100 μm diameter) SMA wire is extremely difficult because standard methods such as crimping are infeasible. The goal of this study is to quantify the effectiveness of using adhesives to hold a small SMA wire. A wide range of commercially available adhesives are tested under the conditions relevant to an application where SMA-wires are embedded directly within a structure. Epoxies are tested so that the adhesive will bond to both plastic and metallic elements. The experimental setup is designed to test the failure shear stress between an SMA wire and adhesive. A wire is encapsulated in a small drop of adhesive. Then the area of the wire that is exposed to the adhesive is measured under a microscope and the wire is pulled as a load cell measures the tensile load. The force that causes failure of the bond is recorded and used to calculate the failure shear stress between the adhesive and wire. The effects of using wires with different surface temperatures, and handling procedures (i.e. washing with acetone and handling with latex gloves) are also tested. Measurements under each set of parameters are repeated and quantitative results are obtained. C2 - 2009/// C3 - SMASIS 2009, vol 2 DA - 2009/// DO - 10.1115/smasis2009-1450 SP - 409-418 ER - TY - CONF TI - Electro-mechanical analysis of a biased dielectric EAP actuator AU - York, A. AU - Hodgins, M. AU - Seelecke, S. AB - Dielectric Electro-Active Polymers (DEAP’s) can achieve substantial deformation (>300% strain) while, compared to their ionic counterparts, sustaining large forces. This makes them attractive for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. This paper provides a systematic experimental investigation of the quasi-static and dynamic electro-mechanical properties of a commercially available dielectric EAP actuator. In order to completely characterize the fully coupled behavior force vs. displacement measurements at various constant voltages and force vs. voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the viscoelastic and electrostatic behavior inherent in DEAP material. Typical operating conditions of the actuator require it to have a biased force, such as a spring. Experiments are conducted to observe the actuators performance under these conditions. The force and stroke capabilities are investigated while the actuator is loaded with different springs and at a variety of pre-stretch levels. The resulting behavior of the spring loaded actuator is then correlated to the viscoelastic effects observed during the electro-mechanical characterization. C2 - 2009/// C3 - SMASIS 2009, vol 1 DA - 2009/// DO - 10.1115/smasis2009-1441 SP - 289-297 ER - TY - JOUR TI - Multiscale methods in turbulent combustion: Strategies and computational challenges AU - Echekki, Tarek T2 - Computational Science & Discovery AB - A principal challenge in modeling turbulent combustion flows is associated with their complex, multiscale nature. Traditional paradigms in the modeling of these flows have attempted to address this nature through different strategies, including exploiting the separation of turbulence and combustion scales and a reduced description of the composition space. The resulting moment-based methods often yield reasonable predictions of flow and reactive scalars' statistics under certain conditions. However, these methods must constantly evolve to address combustion at different regimes, modes or with dominant chemistries. In recent years, alternative multiscale strategies have emerged, which although in part inspired by the traditional approaches, also draw upon basic tools from computational science, applied mathematics and the increasing availability of powerful computational resources. This review presents a general overview of different strategies adopted for multiscale solutions of turbulent combustion flows. Within these strategies, some specific models are discussed or outlined to illustrate their capabilities and underlying assumptions. These strategies may be classified under four different classes, including (i) closure models for atomistic processes, (ii) multigrid and multiresolution strategies, (iii) flame-embedding strategies and (iv) hybrid large-eddy simulation–low-dimensional strategies. A combination of these strategies and models can potentially represent a robust alternative strategy to moment-based models; but a significant challenge remains in the development of computational frameworks for these approaches as well as their underlying theories. DA - 2009/// PY - 2009/// DO - 10.1088/1749-4699/2/1/013001 VL - 3 SP - 013001 ER - TY - CONF TI - Measurement and analysis of the annual daylighting performance of a middle school in North Carolina AU - Athalye, R. AU - Eckerlin, H. M. AB - This paper evaluates the measured annual daylighting performance of the Northern Guilford Middle School at Greensboro, North Carolina. A side-daylighting strategy that employs a unique curved interior translucent light-shelf is used in the classrooms. The measured average annual illuminance under clear sky conditions is about 100 foot-candles. However, there is great variation in the space illuminance from season to season. The building occupants react to this variation in ways that cannot be controlled and this ultimately determines how well the design works. Along with the annual measurements, two tests were performed on the side-lit design to determine the effects of individual design elements. The results from these experiments as well as those from the computer modeling of a typical classroom using the side-lit strategy at Northern Guilford are presented in this paper. These results may be extended to any day-lit space with an interior translucent element, located on similar latitude and a comparable solar radiation profile. C2 - 2009/// C3 - ES2009: Proceedings of the ASME 3rd International Conference on Energy Sustainability, Vol 2 DA - 2009/// DO - 10.1115/es2009-90329 SP - 351-361 ER - TY - JOUR TI - Influence of Electrode Characteristics on DC Point-to-Plane Breakdown in High-Pressure Gaseous and Supercritical Carbon Dioxide AU - Lock, Evgeniya H. AU - Saveliev, Alexei V. AU - Kennedy, Lawrence A. T2 - IEEE TRANSACTIONS ON PLASMA SCIENCE AB - Discharges in supercritical conditions is a new field in plasma science. The supercritical phase has distinctive properties that may allow for unique plasma processing applications. In this paper, we study plasma generation in a point-to-plane geometry in the micrometer scale. The effects of needle characteristics, including tip diameter and plane electrode surface roughness, on discharge initiation are studied. The influence of pressure, temperature, and fluid density on breakdown voltage and reduced breakdown electric field are also investigated. DA - 2009/6// PY - 2009/6// DO - 10.1109/tps.2009.2018844 VL - 37 IS - 6 SP - 1078-1083 SN - 1939-9375 KW - Breakdown KW - carbon dioxide KW - microplasma KW - supercritical fluid (SCF) ER - TY - JOUR TI - Modeling the overpotential, particle size and strain dependence of phase transition pathways in battery electrodes: Example in nanoscale olivines AU - Tang, M. AU - Huang, H.-Y. S. AU - Meethong, N. AU - Kao, Y.-H. AU - Carter, W. C. AU - Chiang, Y.-M. T2 - Chemistry of Materials DA - 2009/// PY - 2009/// VL - 21 SP - 1557-1571 ER - TY - JOUR TI - On Diluted-Fuel Combustion Issues in Burning Biogas Surrogates AU - Wilson, David A. AU - Lyons, Kevin M. T2 - JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME AB - This paper describes an analysis of the burning velocity of pure and diluted fuels, with implications for the development and operation of biogas-fueled combustors. Background work in the area of flame stabilization and propagation are introduced from the combustion literature. Fuels examined in this paper were methane and ethylene; the diluents were primarily nitrogen, as well as argon, carbon dioxide, and helium. Trends in terms of burning velocities as functions of equivalence ratio are reported for a variety of fuels. Additionally, flame temperatures and associated burning velocities as a function of diluent composition are reported. Implications for several flame stabilization theories are discussed, as well as point to potential issues in converting combustors to accept biogas as a fuel permitting stable operation. DA - 2009/12// PY - 2009/12// DO - 10.1115/1.4000152 VL - 131 IS - 4 SP - SN - 0195-0738 KW - laminar burning velocity KW - biogas combustion KW - diluted fuels ER - TY - JOUR TI - Improving Data Availability for Better Access Performance: A Study on Caching Scientific Data on Distributed Desktop Workstations AU - Ma, Xiaosong AU - Vazhkudai, Sudharshan S. AU - Zhang, Zhe T2 - JOURNAL OF GRID COMPUTING AB - Client-side data caching serves as an excellent mechanism to store and analyze the rapidly growing scientific data, motivating distributed, client-side caches built from unreliable desktop storage contributions to store and access large scientific data. They offer several desirable properties, such as performance impedance matching, improved space utilization, and high parallel I/O bandwidth. In this context, we are faced with two key challenges: (1) the finite amount of contributed cache space is stretched by the ever increasing scientific dataset sizes and (2) the transient nature of volunteered storage nodes impacts data availability. In this article, we address these challenges by exploiting the existence of external, primary copies of datasets. We propose a novel combination of prefix caching, collective download, and remote partial data recovery (RPDR), to deal with optimal cache space consumption and storage node volatility. Our evaluation, performed on our FreeLoader prototype, indicates that prefix caching can significantly improve the cache hit rate and partial data recovery is better than (or comparable to) many persistent-data availability techniques. DA - 2009/12// PY - 2009/12// DO - 10.1007/s10723-009-9122-7 VL - 7 IS - 4 SP - 419-438 SN - 1572-9184 KW - Desktop grids KW - Storage scavenging KW - Scientific data ER - TY - JOUR TI - Dislocation density crystalline plasticity modeling of lath martensitic microstructures in steel alloys AU - Hatem, T. M. AU - Zikry, M. A. T2 - PHILOSOPHICAL MAGAZINE AB - A three-dimensional multiple-slip dislocation density-based crystalline formulation, specialized finite-element formulations and Voronoi tessellations adapted to martensitic orientations were used to investigate large strain inelastic deformation modes and dislocation density evolution in martensitic microstructures. The formulation is based on accounting for variant morphologies and orientations, retained austenite and initial dislocation densities that are uniquely inherent to martensitic microstructures. The effects of parent austenite orientation and retained austenite were also investigated for heterogeneous fcc/bcc crystalline structures. Furthermore, the formulation was used to investigate microstructures mapped directly from SEM/EBSD images of martensitic steel alloys. The analysis indicates that variant morphology and orientations have a direct effect on dislocation density accumulation and inelastic localization in martensitic microstructures, and that lath directions, orientations and arrangements are critical characteristics of high strength martensitic deformation and behavior. DA - 2009/// PY - 2009/// DO - 10.1080/14786430903185999 VL - 89 IS - 33 SP - 3087-3109 SN - 1478-6443 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70449117497&partnerID=MN8TOARS KW - lath martensite KW - dislocation-densities KW - finite element KW - high strength steel KW - Voronoi tessellation ER - TY - JOUR TI - Deposition and investigation of functionally graded calcium phosphate coatings on titanium AU - Bai, Xiao AU - Sandukas, Stefan AU - Appleford, Mark R. AU - Ong, Joo L. AU - Rabiei, Afsaneh T2 - ACTA BIOMATERIALIA AB - A series of calcium phosphate coatings with graded crystallinity were deposited onto heated titanium substrates using ion beam assisted deposition. The microstructure of the coating was examined using transmission electron microscopy (TEM). The coating thickness was observed to be in a range of 594-694 nm. The degree of crystallinity and microstructural grain size of the coating showed a clear decrease with increasing distance from the substrate-coating interface. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of PO(4)(3-), and X-ray photoelectron spectroscopy (XPS) analysis on the coating top surface showed that the atomic Ca/P ratio was in the range of 1.52+/-0.15 to 1.61+/-0.07. The biological response to the coatings was also evaluated using an osteoblast precursor cell culture test. More cells and a higher integrin expression of cell attachment sites were observed on the coating surface when compared to the control group (blank titanium surface). The pull-off test showed average adhesion strengths at the coating-substrate interface to be higher than 85.12+/-5.37 MPa. Nanoindentation tests indicated that the Young's moduli of all coatings are higher than 91.747+/-3.641 GPa and microhardness values are higher than 5.275+/-0.315 GPa. While the adhesion strength results helped us to identify the best setup for substrate temperature and processing parameters to begin the deposition, the culture test and XPS results helped identifying the optimum parameters for the last stage of deposition. TEM, X-ray diffraction, FTIR and nanoidentation results were used to further evaluate the quality of the coating and optimization of its processing parameters. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.actbio.2009.05.013 VL - 5 IS - 9 SP - 3563-3572 SN - 1878-7568 KW - Calcium phosphate coatings KW - Biomedical implants KW - Bioactivity KW - Adhesion strength ER - TY - JOUR TI - Control of Underwater Vehicles in Full Unsteady Flow AU - Levedahl, Blaine A. AU - Silverberg, L. T2 - IEEE JOURNAL OF OCEANIC ENGINEERING AB - In this paper, a general formulation of the problem of control of underwater vehicles in full unsteady flow is presented. First, a reduced-order model of the coupled fluid vehicle (CFV) system is developed. The inability to observe fluid motion motivates a fluid compensation control (FCC) approach that compensates for the hydrodynamic loads synthesized from surface measurements. The FCC consists of a tracker, a regulator, and a fluid compensator. A condition is provided that guarantees vehicle stability. The tradeoff between regulation and fluid compensation is also examined. A numerical example of an elliptically shaped vehicle illustrates the results. DA - 2009/10// PY - 2009/10// DO - 10.1109/JOE.2009.2027798 VL - 34 IS - 4 SP - 656-668 SN - 1558-1691 KW - Fluid compensation KW - submarine control KW - unmanned underwater vehicle (UUV) control KW - unsteady flow KW - vehicle modeling ER - TY - JOUR TI - A Capacitive Displacement Sensing Technique for Early Detection of Unbalanced Loads in a Washing Machine AU - Ramasubramanian, Melur K. AU - Tiruthani, Karthik T2 - SENSORS AB - Horizontal axis washing machines are water and energy efficient and becoming popular in the USA. Unlike a vertical axis washer, these do not have an agitator and depend solely on tumbling for the agitation of laundry during the wash cycle. However, due to the constant shifting of laundry during washing, the load distribution is often unbalanced during the high speed spin cycle. We present a displacement-based sensing method to detect unbalance early while the spin rate (rpm) is well below the resonance frequency so that corrective actions may be taken prior to the high speed spin cycle. Experimental and analytical characterizations of the sensor configuration are presented. Results show that the displacement sensor is more appropriate than an accelerometer for this application and offer the potential for a simple, reliable, low cost detection of unbalance. DA - 2009/12// PY - 2009/12// DO - 10.3390/s91209559 VL - 9 IS - 12 SP - 9559-9571 SN - 1424-8220 KW - capacitive-displacement-sensor KW - horizontal-axis-washing-machine KW - vibration-detection ER - TY - JOUR TI - Volumetric flame synthesis of well-defined molybdenum oxide nanocrystals AU - Merchan-Merchan, Wilson AU - Saveliev, Alexei V. AU - Desai, Milind T2 - NANOTECHNOLOGY AB - Well-defined faceted inorganic Mo oxide nanocrystals are synthesized in the gas phase using a solid-fed-precursor flame synthesis method. The solid crystals have rectangular cross-section with characteristic size of 10-20 nm and with lengths ranging from 50 nm to a few hundred nanometres. A 1 mm diameter high purity Mo probe introduced in the oxygen-rich part of the flame serves as the material source. A combination of the strong temperature gradient and varying chemical species concentrations within the flame volume provides the ideal conditions for the rapid and direct formation of these unique nanocrystals. Oxidation and evaporation of MoO3 in the oxygen-rich zone are followed by reduction to MoO2 in the lower temperature, more fuel-rich zone. The MoO3 vapours formed are pushed in the direction of the gas flow and transformed into mature well-defined convex polyhedron nanocrystals bounded with six faces resembling rectangular parallelepipeds. DA - 2009/11/25/ PY - 2009/11/25/ DO - 10.1088/0957-4484/20/47/475601 VL - 20 IS - 47 SP - SN - 1361-6528 ER - TY - JOUR TI - Thermal instability in a porous medium layer saturated by a nanofluid AU - Nield, D. A. AU - Kuznetsov, A. V. T2 - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER AB - The onset of convection in a horizontal layer of a porous medium saturated by a nanofluid is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The analysis reveals that for a typical nanofluid (with large Lewis number) the prime effect of the nanofluids is via a buoyancy effect coupled with the conservation of nanoparticles, the contribution of nanoparticles to the thermal energy equation being a second-order effect. It is found that the critical thermal Rayleigh number can be reduced or increased by a substantial amount, depending on whether the basic nanoparticle distribution is top-heavy or bottom-heavy, by the presence of the nanoparticles. Oscillatory instability is possible in the case of a bottom-heavy nanoparticle distribution. DA - 2009/12// PY - 2009/12// DO - 10.1016/j.ijheatmasstransfer.2009.07.023 VL - 52 IS - 25-26 SP - 5796-5801 SN - 1879-2189 KW - Nanofluid KW - Porous medium KW - Instability KW - Natural convection ER - TY - JOUR TI - The Cheng-Minkowycz problem for natural convective boundary-layer flow in a porous medium saturated by a nanofluid AU - Nield, D. A. AU - Kuznetsov, A. V. T2 - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER AB - The Cheng–Minkowycz problem of natural convection past a vertical plate, in a porous medium saturated by a nanofluid, is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. For the porous medium the Darcy model is employed. A similarity solution is presented. This solution depends on a Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. The dependency of the Nusslelt number on these four parameters is investigated. DA - 2009/12// PY - 2009/12// DO - 10.1016/j.ijheatmasstransfer.2009.07.024 VL - 52 IS - 25-26 SP - 5792-5795 SN - 1879-2189 KW - Cheng-Minkowycz problem KW - Natural convection KW - Nanofluid KW - Porous medium KW - Similarity solution ER - TY - JOUR TI - Parametric study of the diversion of a near Earth object on an Earth intersecting trajectory AU - French, David B. AU - Mazzoleni, Andre P. T2 - ACTA ASTRONAUTICA AB - To date, NASA's “Near Earth Object Program” has discovered over 5500 comets and asteroids on trajectories that bring them within “the neighborhood” of Earth's orbit. Nearly 1000 of these objects are classified as “potentially hazardous,” passing within 0.05 astronomical units of Earth's orbit. Discovery rates of such threatening bodies increase each year. Given this multitude of threats, in addition to evidence that the planet has absorbed many impacts over its history, it is reasonable to assume that another object will strike the Earth at some point in the future. Consequently, researchers have studied and proposed several mitigation techniques for such an occurrence. This study seeks to determine how effectively the attachment of a tether and ballast mass would divert the trajectory of such threatening objects. Specifically, the study analyzes the effects over time of such a system on objects of varying orbital semimajor axis and eccentricity, using various tether lengths and ballast masses. It was determined that the technique is most effective for NEOs with high eccentricity and small semimajor axis, and that system performance increases as tether length and ballast mass increase. DA - 2009/12// PY - 2009/12// DO - 10.1016/j.actaastro.2009.04.023 VL - 65 IS - 11-12 SP - 1698-1705 SN - 1879-2030 KW - Tethers KW - Potentially hazardous asteroids KW - Near Earth objects KW - Mitigation ER - TY - JOUR TI - Nanoindentation of model diamond nanocomposites: Hierarchical molecular dynamics and finite-element simulations AU - Pearson, James D. AU - Gao, Guangtu AU - Zikry, Mohammed A. AU - Harrison, Judith A. T2 - COMPUTATIONAL MATERIALS SCIENCE AB - Complementary molecular dynamics (MD) and finite-element (FE) simulations of model diamond nanocomposites (MDN) subjected to nanoindentation were undertaken to understand how contact behavior pertaining to the surface morphology of MDN surfaces can be spanned from the molecular to the continuum scale. The MD simulations determined that the behavior inside the contact region is influenced by atomic-scale features on the tip and surface, indent location, grain tilt and roughness of the MDN surfaces. In addition, if the atomic-scale surface morphology is treated as a surface roughness within the FE simulations, the same grain orientations, and similar elastic properties are used for both MD and FE simulations, there is reasonable agreement between the contact pressures for relatively low indentation loads and shallow substrates. For larger loads, the contact pressures from the FE simulations deviate somewhat from the MD results near the center of the contact. The contact behavior for length scales that are prohibitive for MD models (e.g., deep substrates) was also examined using FE simulations. This allowed for a detailed investigation of how contact conditions and stick-slip events within the contact evolve as a function of contact pressure and continuum surface stresses. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.commatsci.2009.06.007 VL - 47 IS - 1 SP - 1-11 SN - 1879-0801 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70449134804&partnerID=MN8TOARS KW - Molecular dynamics (MD) KW - Finite-element (FE) KW - Simulations KW - Nanoindentation KW - Nanocomposite KW - Model nanocomposite diamond KW - Hierarchical MD-FE modeling KW - Surface roughness KW - Diamond grains ER - TY - JOUR TI - Instability of a slip flow in a curved channel formed by two concentric cylindrical surfaces AU - Avramenko, A. A. AU - Kuznetsov, A. V. T2 - EUROPEAN JOURNAL OF MECHANICS B-FLUIDS AB - Instability of a slip flow in a curved channel formed by two concentric cylindrical surfaces is investigated. Two cases are considered. In the first (Taylor–Couette flow) case the flow is driven by the rotation of the inner cylindrical surface; no azimuthal pressure gradient is applied. In the second case (Dean flow) both cylindrical surfaces are motionless, and the flow is driven by a constant azimuthal pressure gradient. The collocation method is used to find numerically the critical values of the Taylor and Dean numbers, which establish the instability criteria for these two cases. The dependencies of critical values of these numbers on the ratio between the radii of concave and convex walls and on the velocity slip coefficient are investigated. DA - 2009/// PY - 2009/// DO - 10.1016/j.euromechflu.2009.06.003 VL - 28 IS - 6 SP - 722-727 SN - 1873-7390 KW - Slip flow KW - Curved microchannel KW - Linear instability analysis KW - Taylor number KW - Dean number ER - TY - JOUR TI - Hydrogen autoignition in a turbulent jet with preheated co-flow air AU - Echekki, Tarek AU - Gupta, Kamlesh G. T2 - INTERNATIONAL JOURNAL OF HYDROGEN ENERGY AB - The autoignition of hydrogen in a turbulent jet with preheated air is studied computationally using the stand-alone one-dimensional turbulence (ODT) model. The simulations are based on varying the jet Reynolds number and the mixture pressure. Also, computations are carried out for homogeneous autoignition at different mixture fractions and the same two pressure conditions considered for the jet simulations. The simulations show that autoignition is delayed in the jet configuration relative to the earliest autoignition events in homogeneous mixtures. This delay is primarily due to the presence of scalar dissipation associated with the scalar mixing layer in the jet configuration as well as with the presence of turbulent stirring. Turbulence plays additional roles in the subsequent stages of the autoignition process. Pressure effects also are present during the autoignition process and the subsequent high-temperature combustion stages. These effects may be attributed primarily to the sensitivity of the autoignition delay time to the mixture conditions and the role of pressure and air preheating on molecular transport properties. The overall trends are such that turbulence increases autoignition delay times and accordingly the ignition length and pressure further contribute to this delay. DA - 2009/10// PY - 2009/10// DO - 10.1016/j.ijhydene.2009.06.085 VL - 34 IS - 19 SP - 8352-8377 SN - 1879-3487 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70349194387&partnerID=MN8TOARS KW - Turbulent flames KW - One-dimensional turbulence model KW - Turbulent diffusion flames ER - TY - JOUR TI - Free energy calculation of modified base-pair formation in explicit solvent: A predictive model AU - Vendeix, Franck A. P. AU - Munoz, Antonio M. AU - Agris, Paul F. T2 - RNA AB - The maturation of RNAs includes site-specific post-transcriptional modifications that contribute significantly to hydrogen bond formation within RNA and between different RNAs, especially in formation of mismatch base pairs. Thus, an understanding of the geometry and strength of the base-pairing of modified ribonucleoside 5'-monophosphates, previously not defined, is applicable to investigations of RNA structure and function and of the design of novel RNAs. The geometry and free energies of base-pairings were calculated in aqueous solution under neutral conditions with AMBER force fields and molecular dynamics simulations (MDSs). For example, unmodified uridines were observed to bind to uridine and cytidine with significant stability, but the ribose C1'-C1' distances were far short ( approximately 8.9 A) of distances observed for canonical A-form RNA helices. In contrast, 5-oxyacetic acid uridine, known to bind adenosine, wobble to guanosine, and form mismatch base pairs with uridine and cytidine, bound adenosine and guanosine with geometries and energies comparable to an unmodified uridine. However, the 5-oxyacetic acid uridine base paired to uridine and cytidine with a C1'-C1' distance comparable to that of an A-form helix, approximately 11 A, when a H(2)O molecule migrated between and stably hydrogen bonded to both bases. Even in formation of canonical base pairs, intermediate structures with a second energy minimum consisted of transient H(2)O molecules forming hydrogen bonded bridges between the two bases. Thus, MDS is predictive of the effects of modifications, H(2)O molecule intervention in the formation of base-pair geometry, and energies that are important for native RNA structure and function. DA - 2009/12// PY - 2009/12// DO - 10.1261/rna.1734309 VL - 15 IS - 12 SP - 2278-2287 SN - 1469-9001 KW - modified nucleosides KW - base pairs in water KW - wobble recognition KW - refined molecular dynamics simulation ER - TY - CONF TI - A Robust fault tolerant control approach for LTI systems with actuator and sensor faults AU - Cai, X. J. AU - Wu, F. AB - In this paper, we study a robust fault-tolerant control (FTC) problem for linear systems with time varying actuator and sensor faults and propose an parameter-dependent solution by using L 2 gain optimization techniques. Using estimated faults from a fault detection and isolation (FDI) scheme, parameter-dependent robust FTC gain will be scheduled by fault magnitude to stabilize and optimize the faulty system under all possible fault scenarios. The synthesis condition of such a FTC control law will be formulated as linear matrix inequalities (LMIs) and can be solved efficiently by semi-definite programming techniques. A numerical example is used to demonstrate the proposed fault-tolerant control approach for a simple faulty systems with different fault levels and fault estimation error bounds. C2 - 2009/// C3 - CCDC 2009: 21st Chinese Control and Decision Conference, vols 1-6, Proceedings DA - 2009/// DO - 10.1109/ccdc.2009.5191903 SP - 890-895 ER - TY - JOUR TI - Mechanical Properties of Vapor-Liquid-Solid Synthesized Silicon Nanowires AU - Zhu, Yong AU - Xu, Feng AU - Qin, Qingquan AU - Fung, Wayne Y. AU - Lu, Wei T2 - NANO LETTERS AB - The Young's modulus and fracture strength of silicon nanowires with diameters between 15 and 60 nm and lengths between 1.5 and 4.3 mum were measured. The nanowires, grown by the vapor-liquid-solid process, were subjected to tensile tests in situ inside a scanning electron microscope. The Young's modulus decreased while the fracture strength increased up to 12.2 GPa, as the nanowire diameter decreased. The fracture strength also increased with the decrease of the side surface area; the increase rate for the chemically synthesized silicon nanowires was found to be much higher than that for the microfabricated silicon thin films. Repeated loading and unloading during tensile tests demonstrated that the nanowires are linear elastic until fracture without appreciable plasticity. DA - 2009/11// PY - 2009/11// DO - 10.1021/nl902132w VL - 9 IS - 11 SP - 3934-3939 SN - 1530-6984 ER - TY - CONF TI - Intelligent energy management system simulator for PHEVs at municipal parking deck in a smart grid environment AU - Kulshrestha, P. AU - Wang, L. AU - Chow, M. Y. AU - Lukic, S. C2 - 2009/// C3 - 2009 ieee power & energy society general meeting, vols 1-8 DA - 2009/// SP - 2157-2162 ER - TY - JOUR TI - Calibration of a single-mode polymer optical fiber large-strain sensor AU - Kiesel, Sharon AU - Peters, Kara AU - Hassan, Tasnim AU - Kowalsky, Mervyn T2 - MEASUREMENT SCIENCE AND TECHNOLOGY AB - We calibrate the phase shift as a function of applied displacement in a polymethylmethacrylate (PMMA) single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm. The phase sensitivity is measured up to 15.8% nominal strain in the fiber. The measured phase–displacement response is compared to a previous analytical formulation for the large deformation response of the polymer optical fiber strain sensor. The formulation includes both the finite deformation of the optical fiber and nonlinear strain-optic effects at large deformations. Using previously measured values for the linear and nonlinear mechanical response of the fiber, the nonlinear strain-optic effects are calibrated from the current experimental data. This calibration demonstrates that the nonlinearities in the strain-optic effect are of the same order of magnitude as those in the mechanical response of the PMMA optical fiber sensor. DA - 2009/3// PY - 2009/3// DO - 10.1088/0957-0233/20/3/034016 VL - 20 IS - 3 SP - SN - 1361-6501 KW - polymer optical fiber KW - strain sensor KW - large deformation ER - TY - JOUR TI - Nanoindentation and microstructural evolution of polycrystalline gold AU - Ma, Jeong Beom AU - Zikry, M. A. T2 - JOURNAL OF MATERIALS RESEARCH DA - 2009/3// PY - 2009/3// DO - 10.1557/jmr.2009.0133 VL - 24 IS - 3 SP - 1093-1104 SN - 2044-5326 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-63149171212&partnerID=MN8TOARS ER - TY - JOUR TI - Influence of injection parameters on the transition from PCCI combustion to diffusion combustion in a small-bore HSDI diesel engine AU - Fang, T. AU - Coverdill, R. E. AU - Lee, C. -F. F. AU - White, R. A. T2 - INTERNATIONAL JOURNAL OF AUTOMOTIVE TECHNOLOGY DA - 2009/6// PY - 2009/6// DO - 10.1007/s12239-009-0033-1 VL - 10 IS - 3 SP - 285-295 SN - 1976-3832 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67049172714&partnerID=MN8TOARS KW - HSDI diesel engine KW - Conventional diesel combustion KW - PCCI combustion ER - TY - CONF TI - Improved Method for Estimation of Spacecraft Free-Molecular Aerodynamic Properties AU - Fuller, J. D. AU - Tolson, R. H. C2 - 2009/// C3 - Journal of Spacecraft and Rockets DA - 2009/// VL - 46 SP - 938-948 M1 - 5 ER - TY - JOUR TI - Implementing a Remote Laboratory Experience Into a Joint Engineering Degree Program: Aerodynamic Levitation of a Beach Ball AU - Jernigan, Shaphan R. AU - Fahmy, Yusef AU - Buckner, Gregory D. T2 - IEEE TRANSACTIONS ON EDUCATION AB - This paper details a successful and inexpensive implementation of a remote laboratory into a distance control systems course using readily available hardware and software. The physical experiment consists of a beach ball and a dc blower; the control objective is to make the height of the aerodynamically levitated beach ball track a reference trajectory by manipulating the voltage to the blower. MATLAB/Simulink coupled with xPC target serve as the controller platform, while microsoft netmeeting and standard Internet video conferencing equipment are used to interface the distance-learning students with the laboratory equipment. Both local students at North Carolina State University's campus in Raleigh and distance students at the University of North Carolina at Asheville completed the laboratory experiment. In a student survey, distance students participating in the lab remotely rated the experience as favorably as local students. Course grades, including the design project grade, were similar between the two groups. DA - 2009/5// PY - 2009/5// DO - 10.1109/TE.2008.924217 VL - 52 IS - 2 SP - 205-213 SN - 1557-9638 KW - Control KW - distance education KW - e-learning KW - joint degree program KW - levitation KW - remote laboratory ER - TY - JOUR TI - Grain-boundary interactions and orientation effects on crack behavior in polycrystalline aggregates AU - Shi, J. AU - Zikry, M. A. T2 - INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES AB - A dislocation-density grain–boundary interaction scheme has been developed to account for the interrelated dislocation-density interactions of emission, absorption and transmission in GB regions. The GB scheme is based on slip-system compatibility, local resolved shear stresses, and immobile and mobile dislocation-density accumulation at critical GB locations. To accurately represent dislocation-density evolution, a conservation law for dislocation-densities is used to balance dislocation-density absorption, transmission and emission from the GB. The behavior of f.c.c. polycrystalline copper, with different random low and high angle GBs, are investigated for different crack lengths. For aggregates with random low angle GBs, dislocation-density transmission dominates at the GBs, which can indicate that the low angle GB will not significantly change crack growth directions. For aggregates with random high angle GBs, extensive dislocation-density absorption and pile-ups occur. The high stresses associated with this behavior, along the GBs, can result in intergranular crack growth due to potential crack nucleation sites in the GB. DA - 2009/10/15/ PY - 2009/10/15/ DO - 10.1016/j.ijsolstr.2009.07.019 VL - 46 IS - 21 SP - 3914-3925 SN - 1879-2146 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-69249219074&partnerID=MN8TOARS KW - Grain boundaries KW - Dislocation-density grain-boundary interaction KW - Finite elements KW - Crystal plasticity KW - Intergranular crack KW - Transgranular crack ER - TY - JOUR TI - First-principles investigation of the structure and synergistic chemical bonding of Ag and Mg at the Al vertical bar Omega interface in a Al-Cu-Mg-Ag alloy AU - Sun, Lipeng AU - Irving, Douglas L. AU - Zikry, Mohammed A. AU - Brenner, D. W. T2 - ACTA MATERIALIA AB - Density functional theory was used to characterize the atomic structure and bonding of the Al | Ω interface in a Al–Cu–Mg–Ag alloy. The most stable interfacial structure was found to be connected by Al–Al bonds with a hexagonal Al lattice on the surface of the Ω phase sitting on the vacant hollow sites of the Al {1 1 1} matrix plane. The calculations predict that when substituted separately for Al at this interface, Ag and Mg do not enhance the interface stability through chemical bonding. Combining Ag and Mg, however, was found to chemically stabilize this interface, with the lowest-energy structure examined being a bi-layer with Ag atoms adjacent to the Al matrix and Mg adjacent to the Ω phase. This study provides an atomic arrangement for the interfacial bi-layer observed experimentally in this alloy. DA - 2009/7// PY - 2009/7// DO - 10.1016/j.actamat.2009.04.006 VL - 57 IS - 12 SP - 3522-3528 SN - 1873-2453 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-65849380009&partnerID=MN8TOARS KW - Aluminum alloys KW - Density functional theory (DFT) ER - TY - JOUR TI - Asteroid Diversion Using a Long Tether and Ballast AU - French, David B. AU - Mazzoleni, Andre P. T2 - JOURNAL OF SPACECRAFT AND ROCKETS AB - Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields. DA - 2009/// PY - 2009/// DO - 10.2514/1.40828 VL - 46 IS - 3 SP - 645-661 SN - 0022-4650 ER - TY - JOUR TI - A realistic modeling of fluid infiltration in thin fibrous sheets AU - Jaganathan, Sudhakar AU - Tafreshi, Hooman Vahedi AU - Pourdeyhimi, Behnam T2 - JOURNAL OF APPLIED PHYSICS AB - In this paper, a modeling study is presented to simulate the fluid infiltration in fibrous media. The Richards’ equation of two-phase flow in porous media is used here to model the fluid absorption in unsaturated/partially saturated fibrous thin sheets. The required consecutive equations, relative permeability, and capillary pressure as functions of medium’s saturation are obtained via fiber-level modeling and a long-column experiment, respectively. Our relative permeability calculations are based on solving the Stokes flow equations in partially saturated three-dimensional domains obtained by imaging the sheets’ microstructures. The Richards’ equation, together with the above consecutive correlations, is solved for fibrous media inclined with different angles. Simulation results are obtained for three different cases of upward, horizontal, and downward infiltrations. We also compared our numerical results with those of our long-column experiment and observed a good agreement. Moreover, we establish empirical coefficients for the semianalytical correlations previously proposed in the literature for the case of horizontal and downward infiltrations in thin fibrous sheets. DA - 2009/6/1/ PY - 2009/6/1/ DO - 10.1063/1.3141737 VL - 105 IS - 11 SP - SN - 1089-7550 ER - TY - JOUR TI - Study on a ultra-light dual revolute manipulator with high joint torque AU - Choi, Hyeung-Sik AU - Kim, Tae-Hyeung AU - Moon, Woong-Ju AU - Ro, Paul I. T2 - INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING DA - 2009/10// PY - 2009/10// DO - 10.1007/s12541-009-0070-8 VL - 10 IS - 4 SP - 49-56 SN - 2005-4602 KW - Ultra light robot arm KW - Closed chain mechanism KW - Microprocessor KW - FEM KW - Control system ER - TY - JOUR TI - Plasma Chemical Reactor with Exploding Water Jet AU - Shmelev, Vladimir M. AU - Saveliev, Alexei V. AU - Kennedy, Lawrence A. T2 - PLASMA CHEMISTRY AND PLASMA PROCESSING DA - 2009/8// PY - 2009/8// DO - 10.1007/s11090-009-9177-z VL - 29 IS - 4 SP - 275-290 SN - 1572-8986 KW - Pulsed discharges KW - Surface discharges KW - UV sources ER - TY - JOUR TI - Online Switching Control of LFT Parameter-Dependent Systems AU - Dong, Ke AU - Wu, Fen T2 - JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME AB - To improve controlled performance and expand gain-scheduling control capability, we propose a switching control approach of linear fractional transformation parameter-dependent systems using multiple Lyapunov functions combined with online control techniques. At each switching instant, a gain-scheduled controller working for the next switching interval will be designed online. The switching control synthesis condition is formulated as linear matrix inequalities and can be solved efficiently, upon which the controller will be constructed. The online switching control scheme is demonstrated using an uninhabited combat aerospace vehicle problem. DA - 2009/3// PY - 2009/3// DO - 10.1115/1.3023140 VL - 131 IS - 2 SP - SN - 1528-9028 KW - control system synthesis KW - linear matrix inequalities KW - linear systems KW - Lyapunov methods KW - time-varying systems ER - TY - JOUR TI - Nucleation and growth mechanism for flame synthesis of MoO2 hollow microchannels with nanometer wall thickness AU - Merchan-Merchan, Wilson AU - Saveliev, Alexei V. AU - Taylor, Aaron M. T2 - MICRON AB - The growth and morphological evolution of molybdenum-oxide microstructures formed in the high temperature environment of a counter-flow oxy-fuel flame using molybdenum probes is studied. Experiments conducted using various probe retention times show the sequence of the morphological changes. The morphological row begins with micron size objects exhibiting polygonal cubic shape, develops into elongated channels, changes to large structures with leaf-like shape, and ends in dendritic structures. Time of probe–flame interaction is found to be a governing parameter controlling the wide variety of morphological patterns; a molecular level growth mechanism is attributed to their development. This study reveals that the structures are grown in several consecutive stages: material “evaporation and transportation”, “transformation”, “nucleation”, “initial growth”, “intermediate growth”, and “final growth”. XRD analysis shows that the chemical compositions of all structures correspond to MoO2. DA - 2009/12// PY - 2009/12// DO - 10.1016/j.micron.2009.07.002 VL - 40 IS - 8 SP - 821-826 SN - 0968-4328 KW - Microstructures KW - Nanostructures KW - Metal oxides KW - Flame synthesis KW - Growth mechanism ER - TY - JOUR TI - Nonlinear H-infinity Control Designs with Axisymmetric Spacecraft Control AU - Zheng, Qian AU - Wu, Fen T2 - JOURNAL OF GUIDANCE CONTROL AND DYNAMICS AB - In this paper, we study nonlinear control of a spacecraft symmetric about its principal axis with two control torques. Using a computationally efficient H ∞ control design procedure, attitude stabilization and command tracking problems of the axisymmetric spacecraft are solved locally. The proposed nonlinear H ∞ control approach uses higher order Lyapunov functions and reformulates the difficult Hamilton―Jacobian―Isaacs inequalities as semidefinite optimization conditions. Sum-of-squares programming techniques are then applied to obtain computationally tractable solutions, from which nonlinear control laws will be constructed. The nonlinear H ∞ control designs for spacecraft are capable of exploiting the most suitable forms of Lyapunov functions for performance improvement. DA - 2009/// PY - 2009/// DO - 10.2514/1.40060 VL - 32 IS - 3 SP - 850-859 SN - 1533-3884 ER - TY - JOUR TI - Modeling of Lath Martensitic Microstructures and Failure Evolution in Steel Alloys AU - Hatem, T. M. AU - Zikry, M. A. T2 - JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME AB - A multiple-slip dislocation-density-based crystalline formulation, specialized finite-element formulations, and Voronoi tessellations adapted to martensitic orientations were used to investigate dislocation-density activities and crack tip blunting in high strength martensitic steels. The formulation is based on accounting for variant morphologies and orientations, retained austenite, and initial dislocations densities that are uniquely inherent to martensitic microstructures. The effects of variant distributions and arrangements are investigated for different crack and void interaction distributions and arrangements. The analysis indicates that for certain orientations related to specific variant block arrangements, which correspond to random low angle orientations, cracks can be blunted by dislocation-density activities along transgranular planes. For other variant block arrangements, which correspond to random high angle orientations, sharp crack growth can occur due to dislocation activities along intergranular planes. DA - 2009/10// PY - 2009/10// DO - 10.1115/1.3183780 VL - 131 IS - 4 SP - SN - 0094-4289 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77955251717&partnerID=MN8TOARS KW - lath martensite KW - dislocation-densities KW - high strength steel KW - fracture KW - crack blunting ER - TY - JOUR TI - Macroscopic modeling of slow axonal transport of rapidly diffusible soluble proteins AU - Kuznetsov, A. V. AU - Avramenko, A. A. AU - Blinov, D. G. T2 - INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER AB - The purpose of this paper is to develop a macroscopic model of slow axonal transport of soluble proteins which may be transported in axons by both diffusion and active molecular-motor-assisted transport mechanisms. The model relies on the “stop-and-go” hypothesis put forward by Brown et al. [A. Brown, L. Wang, P. Jung, Stochastic simulation of neurofilament transport in axons: the “stop-and-go” hypothesis, Molecular Biology of the Cell 16 (2005) 4243–4255.] according to which the motion of neurofilaments in slow axonal transport does not occur at a constant velocity; instead, neurofilaments move along microtubules alternating between short periods of rapid movement, short on-track pauses, and prolonged off-track pauses, when they temporarily disengage from microtubules. For soluble proteins, diffusion may also play an important role in overall slow axonal transport; to account for this effect governing equations of the dynamic system model developed in Craciun et al. [G. Craciun, A. Brown, A. Friedman, A dynamical system model of neurofilament in axons, Journal of Theoretical Biology 237 (2005) 316–322.] are extended to incorporate diffusivity of off track proteins (proteins unbound to a stationary matrix). The model correctly predicts that the total concentration of organelles forms the bell-shaped wave that spreads out as it propagates toward the axon tip. DA - 2009/4// PY - 2009/4// DO - 10.1016/j.icheatmasstransfer.2009.01.005 VL - 36 IS - 4 SP - 293-296 SN - 1879-0178 KW - Molecular motors KW - Motor-assisted transport KW - Neurons KW - Axons KW - Slow axonal transport KW - Soluble proteins ER - TY - JOUR TI - Integrated experimental, atomistic, and microstructurally based finite element investigation of the dynamic compressive behavior of 2139 aluminum AU - Elkhodary, K. AU - Sun, L. AU - Irving, D.L. AU - Brenner, D.W. AU - Ravichandran, G. AU - Zikry, Mohammed T2 - Journal of Applied Mechanics, Transactions ASME AB - The objective of this study was to identify the microstructural mechanisms related to the high strength and ductile behavior of 2139-Al, and how dynamic conditions would affect the overall behavior of this alloy. Three interrelated approaches, which span a spectrum of spatial and temporal scales, were used: (i) The mechanical response was obtained using the split Hopkinson pressure bar, for strain-rates ranging from 1.0×10−3 s to 1.0×104 s−1. (ii) First principles density functional theory calculations were undertaken to characterize the structure of the interface and to better understand the role played by Ag in promoting the formation of the Ω phase for several Ω-Al interface structures. (iii) A specialized microstructurally based finite element analysis and a dislocation-density based multiple-slip formulation that accounts for an explicit crystallographic and morphological representation of Ω and θ′ precipitates and their rational orientation relations were conducted. The predictions from the microstructural finite element model indicated that the precipitates continue to harden and also act as physical barriers that impede the matrix from forming large connected zones of intense plastic strain. As the microstructural FE predictions indicated, and consistent with the experimental observations, the combined effects of θ′ and Ω, acting on different crystallographic orientations, enhance the strength and ductility, and reduce the susceptibility of 2139-Al to shear strain localization due to dynamic compressive loads. DA - 2009/// PY - 2009/// DO - 10.1115/1.3129769 VL - 76 IS - 5 SP - 1-9 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77952634990&partnerID=MN8TOARS ER - TY - JOUR TI - Finite Element Simulation of Self-Writing Waveguide Formation Through Photopolymerization AU - Anderson, Aliesha AU - Peters, Kara T2 - JOURNAL OF LIGHTWAVE TECHNOLOGY AB - This article presents the simulation of the dynamics of the self-writing waveguide phenomenon in photopolymerizable resin systems using the finite element method. The rate equation of the photopolymerization process, mechanical shrinkage in the resin and lightwave propagation through the waveguide are included in the finite element model. An emphasis is placed on the simulation of processes occuring at multiple time scales and the introduction of mechanical shrinkage through an equivalent body force. Simulation results predict the features of self-writing previously observed including nonuniformities in the final polymerized waveguide. DA - 2009/12/15/ PY - 2009/12/15/ DO - 10.1109/JLT.2009.2031823 VL - 27 IS - 24 SP - 5529-5536 SN - 0733-8724 KW - Photopolymerization KW - polymer optical fiber KW - self-writing KW - sensor ER - TY - JOUR TI - Evaluation of a Shape Memory Alloy Reinforced Annuloplasty Band for Minimally Invasive Mitral Valve Repair AU - Purser, Molly F. AU - Richards, Andrew L. AU - Cook, Richard C. AU - Osborne, Jason A. AU - Cormier, Denis R. AU - Buckner, Gregory D. T2 - ANNALS OF THORACIC SURGERY AB - An in vitro study using explanted porcine hearts was conducted to evaluate a novel annuloplasty band, reinforced with a two-phase, shape memory alloy, designed specifically for minimally invasive mitral valve repair.In its rigid (austenitic) phase, this band provides the same mechanical properties as the commercial semi-rigid bands. In its compliant (martensitic) phase, this band is flexible enough to be introduced through an 8-mm trocar and is easily manipulated within the heart.In its rigid phase, the prototype band displayed similar mechanical properties to commercially available semi-rigid rings. Dynamic flow testing demonstrated no statistical differences in the reduction of mitral valve regurgitation. In its flexible phase, the band was easily deployed through an 8-mm trocar, robotically manipulated and sutured into place.Experimental results suggest that the shape memory alloy reinforced band could be a viable alternative to flexible and semi-rigid bands in minimally invasive mitral valve repair. DA - 2009/10// PY - 2009/10// DO - 10.1016/j.athoracsur.2009.04.133 VL - 88 IS - 4 SP - 1312-1316 SN - 1552-6259 ER - TY - JOUR TI - Effect of protein degradation in the axon on the speed of the bell-shaped concentration wave in slow axonal transport AU - Kuznetsov, A. V. AU - Avramenko, A. A. AU - Blinov, D. G. T2 - INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER AB - This paper investigates the effect of degradation of proteins transported by means of slow axonal transport (due to enzyme-mediated breakdown of proteins) on the speed of the bell-shaped wave of protein concentration propagating toward the synapse of the axon. Another issue investigated in this paper is the effect of protein degradation on the traffic jam caused by a decay of microtubule tracks at a certain location in the axon. The decay of microtubule tracks may be caused by misregulation of microtubule-associated proteins resulting from an imbalance in intracellular signaling or by mutations of these proteins. Axonal swellings caused by such traffic jams hinder axonal transport; they are a likely cause of various neurodegenerative diseases, including Alzheimer's and Parkinson's diseases and the Down syndrome. DA - 2009/8// PY - 2009/8// DO - 10.1016/j.icheatmasstransfer.2009.04.002 VL - 36 IS - 7 SP - 641-645 SN - 1879-0178 KW - Molecular motors KW - Motor-assisted transport KW - Neurons KW - Axons KW - Slow axonal transport KW - Traffic jams KW - Protein degradation KW - Enzymes ER - TY - JOUR TI - Damage identification using electromagnetic waves based on born imaging algorithm AU - Nojavan, S. AU - Yuan, F. G. T2 - Journal of Engineering Mechanics AB - Reconstructing damage geometry with computationally efficient and effective algorithms is of primary importance in establishing a robust structural health monitoring (SHM) system. In this paper, Born imaging algorithm is proposed for three-dimensional (3D) damage imaging of reinforced concrete structures using electromagnetic waves. This algorithm is derived in time domain for inhomogeneous isotropic and lossy structures. In order to reduce the computational cost of the algorithm, different imaging conditions are introduced. Numerical simulations in a 2D transverse magnetic case for a reinforced concrete slab with multiple damages are performed to test the effectiveness of the algorithm. In this simulated study, sensor data, incident field, and back-propagated field are computed via a finite difference time-domain method. It is concluded that the proposed imaging algorithm is capable of efficiently identifying the damages’ geometries and may be employed in a SHM system. DA - 2009/// PY - 2009/// DO - 10.1061/(ASCE)0733-9399(2009)135:7(717) VL - 135 IS - 7 SP - 717-728 ER - TY - JOUR TI - An investigation of interface-sharpening schemes for multi-phase mixture flows AU - Cassidy, Daniel A. AU - Edwards, Jack R. AU - Tian, Ming T2 - JOURNAL OF COMPUTATIONAL PHYSICS AB - This work evaluates several approaches for sharp phase interface-capturing in computations of multi-phase mixture flows. Attention is focused on algebraic interface-capturing strategies that fit directly within a finite-volume MUSCL-type framework, in which dimension-by-dimension reconstruction of interface states based on extrapolated fluid properties is the norm. In this scope, linear, sine-wave, and tangent hyperbola volume-fraction reconstructions are examined for a range of problems, including advection of a volume-fraction discontinuity, the Rayleigh–Taylor instability, a dam-break problem, an axisymmetric jet instability, the Rayleigh instability, and flow within an aerated-liquid injector. An implicit dual-time stepping approach, applied directly to a preconditioned form of the governing equations, is used for time-advancement. The results show that the sharpening strategies are successful in providing two-to-three-cell capturing of volume-fraction discontinuities. DA - 2009/9/1/ PY - 2009/9/1/ DO - 10.1016/j.jcp.2009.02.028 VL - 228 IS - 16 SP - 5628-5649 SN - 1090-2716 KW - Two-phase flow KW - Interface-capturing KW - Incompressible flow ER - TY - JOUR TI - A Learning Method for Multivariable PID Control Synthesis Based on Estimated Plant Jacobian AU - Chung, Byeong-Mook AU - Lim, Yoon-Kyu AU - Buckner, Gregory D. T2 - INTERNATIONAL JOURNAL OF CONTROL AUTOMATION AND SYSTEMS DA - 2009/10// PY - 2009/10// DO - 10.1007/s12555-009-0506-z VL - 7 IS - 5 SP - 737-744 SN - 2005-4092 KW - Hydrofoil catamaran KW - Jacobian sign KW - learning method KW - PID control ER - TY - JOUR TI - Three Experimental Systems to Evaluate Phosphorus Supply from Enhanced Granulated Manure Ash AU - Crozier, C. R. AU - Havlin, J. L. AU - Hoyt, G. D. AU - Rideout, J. W. AU - McDaniel, R. T2 - AGRONOMY JOURNAL AB - Three experimental systems were used to evaluate a new P fertilizer since residual P levels at typical farm sites may make response detection unlikely. The systems were (i) greenhouse with low P soil, (ii) long‐term research sites with preexisting soil P gradients, and (iii) agricultural fields with prior P fertilization based on agronomic recommendations. The new fertilizer (animal waste by‐product, AWP: 5% N, 28% P 2 O 5 , 4% K 2 O, and 1% S) is an enhanced granulated manure ash. Corn ( Zea mays L.), wheat ( Triticum aestivum L.), and soybean [ Glycine max (L.) Merr.] growth, P uptake, and residual soil Mehlich‐3 P were measured with agronomic rates of AWP or triple superphosphate (TSP). Greenhouse corn and wheat P uptake, and soil Mehlich‐3 P increased similarly with either fertilizer at rates equivalent to 0, 10, 20, 40, and 80 kg P ha −1 . In long‐term research sites, grain yield increased with P fertilization in 8 of 12 tests, and was greater with TSP than with AWP in 3 of 12 tests. Plant P uptake increased in all 12 tests, and was greater with TSP in 1 of 12 tests. In previously fertilized agricultural fields, soil Mehlich‐3 P, but not yield, increased due to P fertilization. Fertilizer source differences were infrequent and relatively minor, but possibly due to lower water soluble P content of the AWP (70% versus 78% for TSP). Evaluation of such products requires an appropriate experimental system with low P soils that may be difficult to find on typical North Carolina farms. DA - 2009/// PY - 2009/// DO - 10.2134/agronj2008.0187x VL - 101 IS - 4 SP - 880-888 SN - 0002-1962 ER - TY - JOUR TI - Shear pipe effects and dynamic shear-strain localization in martensitic steels AU - Hatem, T. M. AU - Zikry, M. A. T2 - ACTA MATERIALIA AB - A three-dimensional, multiple-slip, dislocation-density-based crystalline formulation, specialized finite-element formulations, and Voronoi tessellations adapted to martensitic orientations were used to investigate dislocation-density activities and shear-strain localization in high-strength martensitic steels under quasi-static and dynamic loading conditions. The formulation is based on accounting for variant morphologies and orientations, retained austenite, and initial dislocations densities that are uniquely inherent to martensitic microstructures. The effects of variant distributions and arrangements, loading directions, and microcracks on the evolution of shear-strain localization are investigated. The analysis indicates that shear-strain localization occurs due to slip-system compatibilities relative to the loading direction and the long direction of laths, which result in shear-strain accumulation. At specific triple junctions, rotation misalignments due to lattice and slip incompatibilities occur, and these incompatibilities are further exacerbated by the presence of defects, such as microcracks. DA - 2009/9// PY - 2009/9// DO - 10.1016/j.actamat.2009.06.028 VL - 57 IS - 15 SP - 4558-4567 SN - 1873-2453 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67849128240&partnerID=MN8TOARS KW - Lath martensite KW - Dislocation-density KW - High strength steel KW - Shear-strain localization ER - TY - JOUR TI - Regional stabilisation of polynomial non-linear systems using rational Lyapunov functions AU - Zheng, Qian AU - Wu, Fen T2 - INTERNATIONAL JOURNAL OF CONTROL AB - In this article, we propose a new non-linear stabilisation approach based on the popular linear parameter-varying control techniques. The regional state-feedback control problem of polynomial non-linear systems will be studied using rational Lyapunov functions of states. By bounding the variation rates of each state, the domain of attraction will be embedded in the region specified by the non-linear vector field. As a result, the state-feedback stabilisation conditions will be formulated as a set of polynomial matrix inequalities and can be solved efficiently by sum-of-squares programming. The resulting Lyapunov matrix and state-feedback gains are typically state-dependent rational matrix functions. This approach is also extended to a class of output-dependent non-linear systems where the stabilising output-feedback controller can be synthesised using rational Lyapunov functions of outputs. Finally, several examples will be used to demonstrate the proposed stabilisation approach and clarify the effect of various choices of Lyapunov function forms and state constraints. DA - 2009/// PY - 2009/// DO - 10.1080/00207170802627267 VL - 82 IS - 9 SP - 1605-1615 SN - 1366-5820 KW - polynomial non-linear systems KW - rational Lyapunov function KW - domain of attraction KW - regional stabilisation KW - SOS programming ER - TY - JOUR TI - Lyapunov Redesign of Adaptive Controllers for Polynomial Nonlinear Systems AU - Zheng, Qian AU - Wu, Fen T2 - 2009 AMERICAN CONTROL CONFERENCE, VOLS 1-9 AB - In this paper, we study adaptive control redesign problem of polynomial nonlinear systems with matching parametric uncertainties. By transforming the system into its corresponding error dynamics, we will develop an adaptive control scheme in attenuating the effect of the unknown parameters on the controlled output, which is composed of tracking errors and control efforts. To achieve better controlled performance, the Lyapunov functions will be relaxed from quadratic to higher order and the resulting controller gain is generalized from constant to parameter dependent. The synthesis conditions of adaptive control will be formulated as polynomial matrix inequalities and are solvable by recast the resulting conditions into a Sum of Squares (SOS) optimization problem, from which the adaptive control law as well as the parameter adaptation law are derived with zero tracking and parameter estimation errors. An example is provided to demonstrate effectiveness of the proposed adaptive control redesign approach. DA - 2009/// PY - 2009/// DO - 10.1109/acc.2009.5160128 SP - 5144-5149 SN - 2378-5861 KW - Adaptive control KW - parametric uncertainties KW - higher-order Lyapunov function KW - SOS programming ER - TY - CONF TI - Low-temperature combustion within a HSDI eiesel engine using multiple-injection strategies AU - Fang, T. G. AU - Coverdill, R. E. AU - Lee, C. F. F. AU - White, R. A. C2 - 2009/// C3 - Journal of Engineering for Gas Turbines and Power DA - 2009/// VL - 131 M1 - 6 ER - TY - JOUR TI - FE analysis of SMA-based bio-inspired bone-joint system AU - Yang, S. AU - Seelecke, S. T2 - SMART MATERIALS & STRUCTURES AB - This paper presents the finite element (FE) analysis of a bio-inspired bone–joint system. Motivated by the BATMAV project, which aims at the development of a micro-air-vehicle platform that implements bat-like flapping flight capabilities, we study the actuation of a typical elbow joint, using shape memory alloy (SMA) in a dual manner. Micro-scale martensitic SMA wires are used as 'metal muscles' to actuate a system of humerus, elbow joint and radius, in concert with austenitic wires, which operate as flexible joints due to their superelastic character. For the FE analysis, the humerus and radius are modeled as standard elastic beams, while the elbow joint and muscle wires use the Achenbach–Muller–Seelecke SMA model as beams and cable elements, respectively. The particular focus of the paper is on the implementation of the above SMA model in COMSOL. DA - 2009/10// PY - 2009/10// DO - 10.1088/0964-1726/18/10/104020 VL - 18 IS - 10 SP - SN - 0964-1726 ER - TY - JOUR TI - Experimental study of gravitation effects in the flow of a particle-laden thin film on an inclined plane AU - Ward, T. AU - Wey, C. AU - Glidden, R. AU - Hosoi, A. E. AU - Bertozzi, A. L. T2 - Physics of Fluids (Woodbury, N.Y.) DA - 2009/// PY - 2009/// VL - 21 IS - 8 ER - TY - JOUR TI - Combined numerical and experimental investigation on the effect of jet pressure and forming belt geometry on the hydroentanglement process AU - Xiang, P. AU - Kuznetsov, A. V. AU - Seyam, A. M. T2 - JOURNAL OF THE TEXTILE INSTITUTE AB - Hydroentanglement is a mechanical bonding process utilised to produce nonwoven fabrics. A web of loose fibres is put on a forming belt or perforated screen to form an integrated fabric with desired aesthetics by subjecting the web to multiple rows of fine high-pressure water jets. Mechanical performance of hydroentangled nonwovens is determined by the degree of the fibre entanglement, which depends on process parameters. This study presents the results of combined experimental and numerical investigation on the effects of the jet pressure and forming belt geometry on fibre entanglement. Extensive comparisons of simulations with experimental data are reported and analysed to give a clear understanding of the effect of fibreweb and forming belt properties on the critical jet pressure. The modelling results are in good correlation with experimental data for a wide range of jet pressures. The effect of the jet count per unit length on the degree of fibre entanglement is also investigated. DA - 2009/5// PY - 2009/5// DO - 10.1080/00405000701770563 VL - 100 IS - 4 SP - 293-304 SN - 1754-2340 KW - hydroentanglement KW - numerical modeling KW - vorticity KW - critical jet pressure KW - forming belt ER - TY - JOUR TI - Atomic scale simulations of ductile failure micromechanisms in nanocrystalline Cu at high strain rates AU - Dongare, Avinash M. AU - Rajendran, Arunachalam M. AU - LaMattina, Bruce AU - Zikry, Mohammed A. AU - Brenner, Donald W. T2 - PHYSICAL REVIEW B AB - The micromechanisms related to ductile failure during dynamic loading of nanocrystalline Cu are investigated in a series of large-scale molecular-dynamics (MD) simulations. Void nucleation, growth, and coalescence are studied for a nanocrystalline Cu system with an average grain size of 6 nm under conditions of uniaxial tensile strain and triaxial tensile strain at a strain rate of ${10}^{8}\text{ }{\text{s}}^{\ensuremath{-}1}$. The MD simulations of deformation of the nanocrystalline system under conditions of triaxial tensile stress show random nucleation of voids at grain boundaries and/or triple point junctions. The initial shape of the voids is nonspherical due to growth of the voids along the grain boundaries. Void growth is observed to occur by the creation of a shell of disordered atoms around the voids and not by nucleation of dislocations from the void surface. Void coalescence occurs by the shearing of the disordered regions in between the voids. The nucleation and growth of voids result in the relaxation of tensile stresses, after which growth of the voids is slower. The slower growth is accompanied by recrystallization of the surrounding disordered regions resulting in near-spherical shapes of the voids. DA - 2009/9// PY - 2009/9// DO - 10.1103/physrevb.80.104108 VL - 80 IS - 10 SP - SN - 1098-0121 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70349914381&partnerID=MN8TOARS ER - TY - JOUR TI - Near-Earth object threat mitigation using a tethered ballast mass AU - French, D. B. AU - Mazzoleni, A. P. T2 - Journal of Aerospace Engineering AB - The effects of the collision of a near-earth object (NEO) with the Earth could be catastrophic on a local, regional, or global scale depending on the size of the NEO. Therefore, there is considerable interest in determining ways to mitigate the threat posed by these objects. This paper presents a method using the attachment of a tether and ballast mass to alter the trajectory of a NEO on an Earth-intersecting orbit so that it avoids hitting the Earth. Furthermore, a parametric study of such a system is conducted over a wide range of parameters that describe the orbit and the system itself. For each set of parameters, a resulting “miss distance” due to the attachment of the tether and ballast mass is calculated. The results demonstrate that such a system could be used to protect the Earth from Earth-intersecting NEOs. DA - 2009/// PY - 2009/// DO - 10.1061/(ASCE)0893-1321(2009)22:4(460) VL - 22 IS - 4 SP - 460-465 ER - TY - JOUR TI - Microstructural modeling of adaptive nanocomposite coatings for durability and wear AU - Pearson, James D. AU - Zikry, Mohammed A. AU - Wahl, Kathryn J. T2 - WEAR AB - Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally based finite-element techniques. One of the major objectives is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The interrelated effects of microstructural characteristics such as grain shapes and sizes, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion on coating behavior have been studied. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. It is shown by varying the composition, resulting in tradeoffs between lubrication, toughness, and strength, the effects of these critical stresses and strains can be controlled for desired behavior. A mechanistic model to account for experimentally observed transfer film adhesion modes was also developed, and based on these results, it was shown that transfer film bonding has a significant impact on stress and wear behavior. DA - 2009/4/24/ PY - 2009/4/24/ DO - 10.1016/j.wear.2009.02.004 VL - 266 IS - 9-10 SP - 1003-1012 SN - 1873-2577 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-64749097639&partnerID=MN8TOARS KW - Solid lubrication KW - Finite-element modeling KW - Sliding wear KW - Nanocomposite coating KW - Thin-film KW - Transfer film ER - TY - JOUR TI - Microfluidics analysis of nanoparticle mixing in a microchannel system AU - Li, Jie AU - Kleinstreuer, Clement T2 - MICROFLUIDICS AND NANOFLUIDICS DA - 2009/5// PY - 2009/5// DO - 10.1007/s10404-008-0341-1 VL - 6 IS - 5 SP - 661-668 SN - 1613-4990 KW - Microfluidics KW - Nanofluid KW - Micro-mixer KW - Heat and mass transfer KW - Nanodrug delivery ER - TY - JOUR TI - Full-spectrum interrogation of fiber Bragg grating sensors for dynamic measurements in composite laminates AU - Schultz, S. AU - Kunzler, W. AU - Zhu, Z. AU - Wirthlin, M. AU - Selfridge, R. AU - Propst, A. AU - Zikry, M. AU - Peters, K. T2 - SMART MATERIALS AND STRUCTURES AB - This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop-tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict the remaining lifetime in composite laminate structures. DA - 2009/11// PY - 2009/11// DO - 10.1088/0964-1726/18/11/115015 VL - 18 IS - 11 SP - SN - 1361-665X UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70350668824&partnerID=MN8TOARS ER - TY - JOUR TI - Forced convection with counterflow in a circular tube occupied by a porous medium AU - Kuznetsov, A. V. AU - Nield, D. A. T2 - Journal of Porous Media AB - An analytical solution is obtained for forced convection with counterflow in the core and sheath of a circular tube occupied by a saturated porous medium. The Brinkman model is employed for the porous medium. It is found that the effect of counterflow (in contrast to flow in one direction) is to reduce the value of the Nusselt number for large values of the core-sheath coordinate ξ, but to increase it for small values of ξ. In particular, Nu takes a zero minimum value when the mean velocity is zero. DA - 2009/// PY - 2009/// DO - 10.1615/JPorMedia.v12.i7.40 VL - 12 IS - 7 SP - 657-666 ER - TY - JOUR TI - Forced Convection With Laminar Pulsating Counterflow in a Saturated Porous Channel AU - Nield, D. A. AU - Kuznetsov, A. V. T2 - JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME AB - An analytical solution is obtained for forced convection in a parallel-plate channel occupied by a layered saturated porous medium with counterflow produced by pulsating pressure gradients. The case of asymmetrical constant heat-flux boundary conditions is considered, and the Brinkman model is employed for the porous medium. A perturbation approach is used to obtain analytical expressions for the velocity, temperature distribution, and transient Nusselt number for convection produced by an applied pressure gradient that fluctuates with small amplitude harmonically in time about a nonzero mean. It is shown that the fluctuating part of the Nusselt number alters in magnitude and phase as the dimensionless frequency increases. The magnitude increases from zero, goes through a peak, and then decreases to zero. The height of the peak depends on the values of various parameters. The phase (relative to that of the steady component) decreases as the frequency increases. The phase angle at very low frequency can be π/2 or −π/2 depending on the degree of asymmetry of the heating and the values of other parameters. DA - 2009/10// PY - 2009/10// DO - 10.1115/1.3180810 VL - 131 IS - 10 SP - SN - 1528-8943 KW - boundary layers KW - channel flow KW - flow through porous media KW - fluid oscillations KW - forced convection KW - laminar flow KW - pulsatile flow ER - TY - JOUR TI - Fatigue in aluminum-steel and steel-steel composite foams AU - Vendra, Lakshmi AU - Neville, Brian AU - Rabiei, Afsaneh T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - The compression–compression fatigue behavior of two classes of composite metal foams (CMF) manufactured using different processing techniques, was investigated experimentally. Aluminum–steel composite foam processed using gravity casting technique comprises of steel hollow spheres and a solid aluminum alloy matrix. Steel–steel composite foam, processed using powder metallurgy (PM) technique consists of steel hollow spheres packed in a steel matrix. Under compression fatigue loading, the composite foam samples showed a high cyclic stability at maximum stress levels as high as 90 MPa. The deformation of the composite foam samples was divided into three stages – linear increase in strain with fatigue cycles (stage I), minimal strain accumulation in large number of cycles (stage II) and rapid strain accumulation within few cycles culminating in complete failure (stage III). Composite foams under cyclic loading undergo a uniform distribution of deformation, unlike the regular metal foams, which deform by forming collapse bands at weaker sections. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, processing techniques and the bonding strength between the spheres and matrix. DA - 2009/8/20/ PY - 2009/8/20/ DO - 10.1016/j.msea.2009.03.075 VL - 517 IS - 1-2 SP - 146-153 SN - 1873-4936 KW - Composite metal foams KW - Fatigue KW - Mechanical testing KW - Casting KW - Powder processing ER - TY - JOUR TI - Experimental investigation of transition to laminar mixing of a homogeneous viscous liquid in a tilted-rotating tank AU - Ward, Thomas AU - Hourigan, William T2 - CHEMICAL ENGINEERING SCIENCE AB - A tilted and partially filled rotating tank is investigated experimentally at O(1) Reynolds and small (⪡1) capillary numbers, to study the mixing of a viscous homogeneous fluid. Of particular interest is the transition from a previously studied low Reynolds number flow regime [Ward, T., Metchik, A., 2007. Viscous fluid mixing in a titled tank by periodic shear. Chemical Engineering Science 62, 6274–6284], that exhibited two large vortices, to the laminar flow regime which results in additional vortex generation. In the laminar Reynolds number limit O(1) the two primary vortices generated by the liquid rotation axis can interact with the bottom wall, generating two secondary counter-rotating vortices, via a cascade that is qualitatively similar to the well known Moffatt [1964. Viscous and resistive eddies near a sharp corner. Journal of Fluid Mechanics 18, 1–18] vortices in Stokes flow. While the secondary vortices aid in transporting material from the walls to the bulk, they also intensify in magnitude with increasing rotation rate leading to finite sized unmixed regions via the appearance of KAM-like surfaces [Alvarez-Hernández, M.M., Shinbrot, T., Zalc, J., Muzzio, F.J., 2002. Practical chaotic mixing. Chemical Engineering Science 57, 3749–3753]. This suggests that there may be an optimal tilt angle, for a given speed, with which to achieve the maximum mixed cross sectional area within a minimum amount of elapsed time. Experiments are performed using a 90% glycerol, 10% water mixture at two volume portions with angles ranging between 25∘ and 65∘ measured from the horizontal. Laser fluorescence is used to illuminate the vortices via experimental Poincaré mapping [Fountain, G.O., Khakhar, D.V., Ottino, J.M., 1998. Visualization of three dimensional chaos. Science 281, 683–686], and the resulting images are analyzed to determine the mixed cross sectional area versus elapsed time. DA - 2009/12/1/ PY - 2009/12/1/ DO - 10.1016/j.ces.2009.07.032 VL - 64 IS - 23 SP - 4919-4928 SN - 0009-2509 KW - Fluid mixing KW - Periodic shear KW - Laminar flow ER - TY - JOUR TI - Defect-mediated room temperature ferromagnetism in vanadium dioxide thin films AU - Yang, T. H. AU - Nori, S. AU - Zhou, H. H. AU - Narayan, J. T2 - Applied Physics Letters DA - 2009/// PY - 2009/// VL - 95 IS - 10 ER - TY - JOUR TI - Compressible Boundary-Layer Predictions at High Reynolds Number Using Hybrid LES/RANS Methods AU - Choi, Jung-Il AU - Edwards, Jack R. AU - Baurle, Robert A. T2 - AIAA JOURNAL AB - Simulations of compressible boundary-layer flow at three different Reynolds numbers (Re δ = 5.59 × 10 4 , 1.78 × 10 5 , and 1.58 x 10 6 ) are performed using a hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes method. Variations in the recycling/rescaling method, the higher order extension, the choice of primitive variables, the Reynolds-averaged Navier-Stokes to large eddy simulation transition parameters, and the mesh resolution are considered in order to assess the model. The results indicate that the present model can provide good predictions of the mean-flow properties, second-moment statistics, and structural features of the boundary layers considered. Normalized turbulent statistics in the outer layer are found to be independent of Reynolds number, similar to incompressible turbulent boundary layers. DA - 2009/9// PY - 2009/9// DO - 10.2514/1.41598 VL - 47 IS - 9 SP - 2179-2193 SN - 1533-385X ER - TY - JOUR TI - Biodiesel combustion in an optical HSDI diesel engine under low load premixed combustion conditions AU - Fang, Tiegang AU - Lin, Yuan-Chung AU - Foong, Tien Mun AU - Lee, Chia-fon T2 - FUEL AB - An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes for biodiesel blends under different injection strategies. The experimental results indicated that the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation. The ignition and heat release rate peak occurred later with increasing biodiesel content. Fuel impingement on the wall was observed for all test conditions. The liquid penetration became longer and the fuel impingement was stronger with the increase of biodiesel content. Early and late injection timings result in lower flame luminosity due to improved mixing with longer ignition delay. For all the injection timings, lower soot luminosity was seen for biodiesel blends than pure diesel fuel. Furthermore, NOx emissions were dramatically reduced for premixed combustion mode with retarded post-TDC injection strategies. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.fuel.2009.02.033 VL - 88 IS - 11 SP - 2154-2162 SN - 1873-7153 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67651124927&partnerID=MN8TOARS KW - Biodiesel KW - Spray KW - Combustion visualization ER - TY - JOUR TI - Air-fuel mixing and combustion in a small-bore direct injection optically accessible diesel engine using a retarded single injection strategy AU - Fang, Tiegang AU - Coverdill, Robert E. AU - Lee, Chia-fon F. AU - White, Robert A. T2 - FUEL AB - In this paper, the air–fuel mixing and combustion in a small-bore direct injection optical diesel engine were studied for a retarded single injection strategy. The effects of injection pressure and timing were analyzed based on in-cylinder heat release analysis, liquid fuel and vapor fuel imaging by Laser induced exciplex fluorescence technique, and combustion process visualization. NOx emissions were measured in the exhaust pipe. Results show that increasing injection pressure benefits soot reduction while increases NOx emissions. Retarding injection timing leads to simultaneous reduction of soot and NOx emissions with premixed homogeneous charge compression ignition (HCCI) like combustion modes. The vapor distribution in the cylinder is relatively homogeneous, which confirms the observation of premixed combustion in the current studies. The postulated path of these combustion modes were analyzed and discussed on the equivalence ratio-temperature map. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.fuel.2009.05.032 VL - 88 IS - 11 SP - 2074-2082 SN - 0016-2361 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67651097881&partnerID=MN8TOARS KW - High-speed direct injection (HSDI) diesel engine KW - Laser induced exciplex fluorescence (LIEF) technique KW - Homogeneous charge compression ignition (HCCI) combustion KW - Natural flame luminosity ER - TY - JOUR TI - The synthesis and magnetic properties of a nanostructured Ni-MgO system AU - Narayan, J. AU - Nori, Sudhakar AU - Ramachandran, S. AU - Prater, J. T. T2 - JOM DA - 2009/6// PY - 2009/6// DO - 10.1007/s11837-009-0093-8 VL - 61 IS - 6 SP - 76-81 SN - 1543-1851 ER - TY - JOUR TI - The effect of a transition layer between a fluid and a porous medium: shear flow in a channel AU - Nield, D. A. AU - Kuznetsov, A. V. T2 - TRANSPORT IN POROUS MEDIA DA - 2009/7// PY - 2009/7// DO - 10.1007/s11242-009-9342-0 VL - 78 IS - 3 SP - 477-487 SN - 1573-1634 KW - Transition layer KW - Beavers-Joseph condition KW - Shear flow KW - Channel ER - TY - JOUR TI - Slip MHD viscous flow over a stretching sheet - An exact solution AU - Fang, Tiegang AU - Zhang, Ji AU - Yao, Shanshan T2 - COMMUNICATIONS IN NONLINEAR SCIENCE AND NUMERICAL SIMULATION AB - In this paper, the magnetohydrodynamic (MHD) flow under slip condition over a permeable stretching surface is solved analytically. The solution is given in a closed form equation and is an exact solution of the full governing Navier–Stokes equations. The effects of the slip, the magnetic, and the mass transfer parameters are discussed. Results show that there is only one physical solution for any combination of the slip, the magnetic, and the mass transfer parameters. The velocity and shear stress profiles are greatly influenced by these parameters. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.cnsns.2009.02.012 VL - 14 IS - 11 SP - 3731-3737 SN - 1878-7274 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67349181009&partnerID=MN8TOARS KW - Similarity solution KW - Stretching surface KW - Navier-Stokes equations KW - Analytical solution KW - Exact solution KW - Magnetohydrodynamics KW - Slip flow ER - TY - JOUR TI - In-situ impact-induced damage assessment of woven composite laminates through a fibre Bragg grating sensor network AU - Garrett, R. C. AU - Peters, K. J. AU - Zikry, M. A. T2 - AERONAUTICAL JOURNAL AB - Abstract Woven composite specimens with embedded fibre Bragg grating (FBG) sensor networks were impacted at low velocities, while global measurements of contact forces and dissipated energies were obtained from drop tower measurements, and local residual, post-impact strain values were obtained from the FBG sensors. Critical damage events were identified in the global data for these specimens and damage signatures in the residual strain data corresponding to these critical damage events were correlated. The results indicate that the full spectral scan information from the sensor network, although obtainable at a lower scan rate, provide more reliable residual lifetime information than average residual strains. DA - 2009/6// PY - 2009/6// DO - 10.1017/S0001924000003031 VL - 113 IS - 1144 SP - 357-370 SN - 0001-9240 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-68349093775&partnerID=MN8TOARS ER - TY - CONF TI - Hysteretic recurrent neural networks: A tool for modeling hysteretic materials and systems AU - Veeramani, A. S. AU - Crews, J. H. AU - Buckner, G. D. C2 - 2009/// C3 - Smart Materials & Structures DA - 2009/// VL - 18 M1 - 7 ER - TY - JOUR TI - Grain size, grain boundary sliding, and grain boundary interaction effects on nanocrystalline behavior AU - Shi, J. AU - Zikry, M. A. T2 - MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING AB - A dislocation–density grain boundary (GB) interaction scheme, a GB misorientation dependent dislocation–density relation, and a grain boundary sliding (GBS) model are presented to account for the behavior of nanocrystalline aggregates with grain sizes ranging from 25 nm to 200 nm. These schemes are coupled to a dislocation–density multiple slip crystalline plasticity formulation and specialized finite element algorithms to predict the response of nanocrystalline aggregates. These schemes are based on slip system compatibility, local resolved shear stresses, and immobile and mobile dislocation–density evolution. A conservation law for dislocation–densities is used to balance dislocation–density absorption, transmission and emission from the GB. The relation between yield stresses and grain sizes is consistent with the Hall–Petch relation. The results also indicate that GB sliding and grain-size effects affect crack behavior by local dislocation–density and slip evolution at critical GBs. Furthermore, the predictions indicate that GBS increases with decreasing grain sizes, and results in lower normal stresses in critical locations. Hence, GBS may offset strength increases associated with decreases in grain size. DA - 2009/9/15/ PY - 2009/9/15/ DO - 10.1016/j.msea.2009.05.012 VL - 520 IS - 1-2 SP - 121-133 SN - 1873-4936 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67650726010&partnerID=MN8TOARS KW - Grain boundaries KW - Dislocation-density grain boundary interactions KW - Finite elements KW - Crystal plasticity KW - Hall-Petch relation KW - Grain boundary sliding ER - TY - JOUR TI - Effect of the injection angle on liquid spray development in a high-speed direct-injection optical diesel engine AU - Fang, T-G AU - Coverdill, R. E. AU - Lee, C-F F. AU - White, R. A. T2 - PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING AB - In this paper, the spray development and its interaction with the piston geometry were investigated in a small-bore high-speed direct-injection optical diesel engine. The effects of injection angle, injection timing, injection pressure, and injection fuel quantity were studied. The entire liquid spray cycle was visualized by a background-corrected Mie-scattering technique using a high-speed digital video camera synchronized with a high-repetition-rate copper vapour laser. For some conditions, the initial injection velocity was estimated quantitatively. The results show that the injection angle and injection timing predominantly control the spray interaction with the piston geometry and the resulting air—fuel mixing mode. Narrow-angle injection leads to a significantly different air—fuel mixing process from the traditional wide-angle injector. If properly controlled, the narrow-angle direct-injection technique offers more flexibility on injection timing control with the fuel confined in the central bowl region without wetting the cylinder liner. DA - 2009/8// PY - 2009/8// DO - 10.1243/09544070JAUTO1221 VL - 223 IS - D8 SP - 1077-1092 SN - 0954-4070 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-68849127632&partnerID=MN8TOARS KW - narrow-angle direct injection KW - high-speed direct-injection diesel engine KW - Mie scattering KW - spray visualization ER - TY - JOUR TI - Designing a family of reconfigurable vehicles using multilevel multidisciplinary design optimization AU - Ferguson, Scott AU - Kasprzak, Edward AU - Lewis, Kemper T2 - STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION DA - 2009/8// PY - 2009/8// DO - 10.1007/s00158-008-0319-3 VL - 39 IS - 2 SP - 171-186 SN - 1615-1488 KW - Reconfigurable systems KW - Product family design KW - Multilevel optimization KW - Vehicle Design ER - TY - JOUR TI - Computational design of thin-film nanocomposite coatings for optimized stress and velocity accommodation response AU - Pearson, J. D. AU - Zikry, M. A. AU - Wahl, K. T2 - WEAR AB - The tailoring of thin-film coatings comprised of high strength nano-grained constituents is investigated by new microstructurally based finite-element techniques for applications related to the wear, durability, and performance of these coatings over a broad range of temperatures and loading conditions. These coatings are comprised of brittle phases, diamond-like carbon and partially stabilized zirconia and ductile constituents, such as gold and molybdenum. The effects of wear, contact transfer films, grain sizes and distributions, grain spacing and strength are used to determine the optimal thin-film coating compositions. Comparisons are made with experimental measurements pertaining to durability and wear for validation and for the development of design guidelines for thin-film nanocomposite coatings. DA - 2009/6/15/ PY - 2009/6/15/ DO - 10.1016/j.wear.2008.11.027 VL - 267 IS - 5-8 SP - 1137-1145 SN - 1873-2577 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-65949109936&partnerID=MN8TOARS KW - Nanocomposite KW - Thin-film coating KW - Solid lubricant KW - Finite-element modeling ER - TY - JOUR TI - Opposed flow oxy-flame synthesis of carbon and oxide nanostructures on molybdenum probes AU - Merchan-Merchan, Wilson AU - Saveliev, Alexei V. AU - Nguyen, Vu T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - The formation of carbon and metal-oxide nanostructures on molybdenum probes inserted in a counter-flow oxy-fuel flame is studied experimentally. Flame position and probe diameter were varied to achieve a controlled growth of carbon and metal-oxide nanostructures at fuel and oxygen-rich flame zones. Mo probes of 1-mm diameter were introduced in the flame at various heights, starting from the upper hydrocarbon-rich zone on the fuel side of the flame to the oxygen-rich zone on the oxidizer side. High density layers of carbon nanocoils (CNCs) and filamentous structures containing ribbon shapes and straight nanofibers were formed in the upper hydrocarbon-rich flame zone. The formation of carbon micro-trees was observed on the fuel side closer to the flame front. The structures formed in the oxidizer part of the flame were composed of molybdenum-oxides. MoO2 micron-sized channel structures were formed on the oxidizer side in the vicinity of the flame front. The micro-channels had rectangular and square-framed shapes; they were completely hollow, closed, and semi-open with a small circular cavity at their tips. The application of probes with diameters of 0.75 and 0.25 mm resulted in the formation of spectacular 3-D structures with unique and distinct morphologies. DA - 2009/// PY - 2009/// DO - 10.1016/j.proci.2008.07.025 VL - 32 SP - 1879-1886 SN - 1873-2704 KW - Combustion synthesis KW - Carbon nanocoils KW - Carbon nanofibers KW - Metal-oxide whiskers ER - TY - JOUR TI - Experimental and numerical investigation of the peeling force required for the detachment of fabric from the forming belt in the hydroentanglement process AU - Xiang, P. AU - Kuznetsov, A. V. AU - Seyam, A. M. T2 - JOURNAL OF THE TEXTILE INSTITUTE AB - Abstract Hydroentanglement is a fast-growing process for manufacturing non-woven fabrics. In this process, multiple fine jets of highly pressurised water are directed towards a fibreweb composed initially of loose fibres, supported by the forming belt. The impact of the jets causes fibre entanglement in the fibreweb and produces an integrated fabric with desired aesthetics. It is important that, at the end of the process, the fibreweb could be easily separated from the forming wires. In this paper, the peeling force required for the separation of the hydroentangled fabric from the forming wires is measured experimentally. Numerical simulations of the hydroentanglement process are also carried out to predict the probability of fibres to be pushed in the knuckles of the forming wires. The fibres that get caught in the knuckles are mainly responsible for the peeling force of the fabric from the forming wires. The fibreweb is modelled as a porous layer, which is supported by forming wires. By correlating experimental results with simulations, a mathematical model, which is based on simulating average vorticity around the forming wires, is developed to predict the peeling force. The effect of the thickness of the fibreweb layer on the peeling force is investigated. Keywords: hydroentanglementnon-wovenpeeling forcenumerical simulationforming surfacesfluid vorticity Acknowledgements The support provided by the Nonwoven Cooperative Research Center of North Carolina State University is gratefully acknowledged. Helpful discussions with industry advisors to this project: C. Camelio, R. Holmes, F. Noëlle, Dr D. Shiffler and C.B. Widen, are appreciated. DA - 2009/// PY - 2009/// DO - 10.1080/00405000701679723 VL - 100 IS - 2 SP - 99-110 SN - 1754-2340 KW - hydroentanglement KW - non-woven KW - peeling force KW - numerical simulation KW - forming surfaces KW - fluid vorticity ER - TY - JOUR TI - Bio-diesel effects on combustion processes in an HSDI diesel engine using advanced injection strategies AU - Fang, Tiegang AU - Lee, Chia-fon F. T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the combustion process using different fuels including European low sulfur diesel and bio-diesel fuels with advanced multiple injection strategies. Influences of injection timings and fuel types on combustion characteristics and emissions were studied under similar loads. In-cylinder pressure was measured and used for heat release analysis. High-speed combustion videos were captured for all the studied cases using the same frame rate. NOx emissions were measured in the exhaust pipe. Different combustion modes including conventional diesel combustion and low-temperature combustion were observed and confirmed from the heat release rates and the combustion images. Natural luminosity was found consistently lower for bio-diesel than the European low sulfur diesel fuel for all the cases. However, for NOx emissions, under conventional combustion cases such as cases 2 and 3, it was found that bio-diesel leads to increased NOx emissions. Under a certain injection strategy with retarded main injections like case 4 and 5, it is possible to have up to 34% lower NOx emissions for B100 than B0 for case 4 with low-temperature combustion mode. Simultaneous reduction of NOx and natural luminosity was achieved for advanced low-temperature combustion mode. It is hypothesized based on the results that the lower soot generation for bio-diesel fuel is believed due to a lower soot formation rate and a higher soot oxidation rate. The NOx increase problem for bio-diesel fuel can be amended by employing advanced injection strategies with low-temperature combustion modes. DA - 2009/// PY - 2009/// DO - 10.1016/j.proci.2008.07.031 VL - 32 SP - 2785-2792 SN - 1540-7489 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67649256041&partnerID=MN8TOARS KW - Diesel combustion KW - Advanced injection strategy KW - Natural luminosity KW - Bio-diesel KW - Low-temperature combustion ER - TY - JOUR TI - Autonomous Aerobraking Using Thermal Response Surface Analysis AU - Prince, Jill L. AU - Dec, John A. AU - Tolson, Robert H. T2 - JOURNAL OF SPACECRAFT AND ROCKETS AB - Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields. DA - 2009/// PY - 2009/// DO - 10.2514/1.32793 VL - 46 IS - 2 SP - 292-298 SN - 0022-4650 ER - TY - JOUR TI - Ideal Lift Distributions and Flap Angles for Adaptive Wings AU - Gopalarathnam, Ashok AU - Norris, Rachel King T2 - Journal of Aircraft AB - An approach is presented for determining the optimum flap angles and spanwise loading to suit a given flight condition. Multiple trailing-edge flaps along the span of an adaptive wing are set to either reduce drag in rectilinear flight conditions or to limit the wing bending moment at maneuvering conditions. For reducing drag, the flaps are adjusted to minimize induced drag, while simultaneously enabling the wing sections to operate within their respective low-drag ranges. For limiting wing bending moment, the flaps are used to relieve the loading near the wing tips. An important element of the approach is the decomposition of the flap angles into a distribution that can be used to control the spanwise loading for induced-drag control and a constant flap that can used for profile-drag control. The problem is linearized using the concept of basic and additional lift distributions, which enables the use of standard constrained-minimization formulations. The results for flap-angle distributions for different flight conditions are presented for a planar and a nonplanar wing. Postdesign analysis and aircraft-performance simulations are used to validate the optimum flap-angle distributions determined using the current approach. DA - 2009/3// PY - 2009/3// DO - 10.2514/1.38713 VL - 46 IS - 2 SP - 562-571 J2 - Journal of Aircraft LA - en OP - SN - 0021-8669 1533-3868 UR - http://dx.doi.org/10.2514/1.38713 DB - Crossref ER - TY - JOUR TI - Analytical Model for the Characterization of the Guiding Zone Tribotest for Tube Hydroforming AU - Ngaile, Gracious AU - Yang, Chen T2 - JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME AB - Common part failures in tube hydroforming include wrinkling, premature fracture, and unacceptable part surface quality. Some of these failures are attributed to the inability to optimize tribological conditions. There has been an increasing demand for the development of effective lubricants for tube hydroforming due to widespread application of this process. This paper presents an analytical model of the guiding zone tribotest commonly used to evaluate lubricant performance for tube hydroforming. Through a mechanistic approach, a closed-form solution for the field variables contact pressure, effective stress/strain, longitudinal stress/strain, and hoop stress can be computed. The analytical model was validated by the finite element method. In addition to determining friction coefficient, the expression for local state of stress and strain on the tube provides an opportunity for in-depth study of the behavior of lubricant and associated lubrication mechanisms. The model can aid as a quick tool for iterating geometric variables in the design of a guiding zone, which is an integral part of tube hydroforming tooling. DA - 2009/4// PY - 2009/4// DO - 10.1115/1.3090888 VL - 131 IS - 2 SP - SN - 1528-8935 KW - finite element analysis KW - forming processes KW - fracture KW - friction KW - lubricants KW - pipes KW - stress-strain relations ER - TY - JOUR TI - Three-dimensional wall-bounded laminar boundary layer with span-wise cross free stream and moving boundary AU - Fang, Tiegang AU - Lee, Chia-fon F. T2 - ACTA MECHANICA DA - 2009/5// PY - 2009/5// DO - 10.1007/s00707-008-0032-8 VL - 204 IS - 3-4 SP - 235-248 SN - 0001-5970 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67349269485&partnerID=MN8TOARS ER - TY - JOUR TI - Magnetic properties and their dependence on deposition parameters of Co/Al2O3 multilayers grown by pulsed laser deposition AU - Aggarwal, Ravi AU - Nori, Sudhakar AU - Jin, Chunming AU - Pant, Punam AU - Trichy, Gopinath R. AU - Kumar, Dhananjay AU - Narayan, J. AU - Narayan, Roger J. T2 - ACTA MATERIALIA AB - Co/Al2O3 multilayered thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at temperatures from room temperature (RT) to 600 °C. The Co/Al2O3 multilayered thin film grown at RT contains continuous cobalt layers in alumina matrices, with no evidence of island formation. On the other hand, cobalt showed a tendency to form islands in alumina matrices for growth temperatures in the range of 300–600 °C. All the Co/Al2O3 multilayered thin films showed ferromagnetic behavior up to RT. It was observed that variations in the deposition parameters can significantly influence the magnetic properties of Co/Al2O3 multilayers. Depending on the temperature and pulse rate, RT coercivities in the 50–300 Oe range were observed. Films deposited at 600 °C using a laser pulse rate of 10 Hz exhibited a decrease of coercivity with increasing measurement temperature. On the other hand, films deposited at 600 °C using a reduced pulse rate of 2 Hz demonstrated an “anomalous” relationship between low-temperature coercivity and temperature. In these films, coercivity exhibited a weak tendency to increase with temperature. Squareness (Mr/Ms) of the hysteresis loops and its dependence on the temperature was also shown to be strongly affected by the deposition parameters. These observations have been rationalized on the basis of two competing magnetic anisotropies that act along different directions in the material. DA - 2009/4// PY - 2009/4// DO - 10.1016/j.actamat.2009.01.018 VL - 57 IS - 6 SP - 2040-2046 SN - 1359-6454 KW - Magnetic properties KW - Multilayered materials KW - Thin films KW - Pulsed laser deposition ER - TY - JOUR TI - A macroscopic model of traffic jams in axons AU - Kuznetsov, A. V. AU - Avramenko, A. A. T2 - MATHEMATICAL BIOSCIENCES AB - The purpose of this paper is to develop a minimal macroscopic model capable of explaining the formation of traffic jams in fast axonal transport. The model accounts for the decrease of the number density of positively (and negatively) oriented microtubules near the location of the traffic jam due to formation of microtubule swirls; the model also accounts for the reduction of the effective velocity of organelle transport in the traffic jam region due to organelles falling off microtubule tracks more often in the swirl region. The model is based on molecular-motor-assisted transport equations and the hydrodynamic model of traffic jams in highway traffic. Parametric analyses of the model's predictions for various values of viscosity of the traffic flow, variance of the velocity distribution, diffusivity of microtubule-bound and free organelles, rate constants for binding to and detachment from microtubules, relaxation time, and average motor velocities of the retrograde and anterograde transport, are carried out. DA - 2009/4// PY - 2009/4// DO - 10.1016/j.mbs.2009.01.005 VL - 218 IS - 2 SP - 142-152 SN - 1879-3134 KW - Molecular motors KW - Motor-assisted transport KW - Neurons KW - Axons and dendrites KW - Intracellular organelles KW - Traffic jams ER - TY - JOUR TI - The Effects of Grain-boundary Orientations on Failure Behavior in FCC Polycrystalline Systems AU - Jawad, F. F. AU - Zikry, M. A. T2 - INTERNATIONAL JOURNAL OF DAMAGE MECHANICS AB - A multiple-slip rate-dependent crystalline constitutive formulation that is coupled to the evolutionary equations of mobile and immobile dislocation densities is used with specialized finite-element methodologies to obtain a detailed microstructural prediction of the inelastic deformation and interrelated physical mechanisms that affect different failure modes in f.c.c. crystalline materials. The effects of grain and grain-boundary (GB) orientations, grain shape and size, GB strength, and mechanical properties on the inelastic finite deformation and failure mode mechanisms in polycrystalline aggregates with Σ3 and Σ17b GBs have been investigated. Results from this study are consistent with experimental observations that microstructures with desired material properties, such as resistivity to crack nucleation, can be potentially achieved by the control of grain aggregate size and CSL GB orientations. Furthermore, it is also shown that transgranular failure modes can occur in aggregates with a high frequency of Σ3 GBs, whereas intergranular fracture modes can occur with a high frequency of Σ17b GBs. DA - 2009/5// PY - 2009/5// DO - 10.1177/1056789508097547 VL - 18 IS - 4 SP - 341-369 SN - 1530-7921 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-65449169199&partnerID=MN8TOARS KW - grain boundary KW - misorientation KW - coincident site lattice KW - dislocation density KW - intergranular KW - transgranular KW - grain orientation KW - voronoi tessellation ER - TY - JOUR TI - ODT Closure with Extinction and Reignition in Piloted Methane-Air Jet Diffusion Flames AU - Ranganath, Bhargav AU - Echekki, Tarek T2 - COMBUSTION SCIENCE AND TECHNOLOGY AB - Abstract A novel tabulation procedure for reactive scalar statistics based on the one-dimensional turbulence (ODT) is implemented to study extinction and reignition in piloted methane-air jet diffusion flames. The formulation is based on constructing the scalar statistics from stand-alone temporal jet simulations using ODT. The statistics are correlated in terms of two parameters based on a single transported variable: the mean mixture fraction, which measures the extent of mixing between the fuel and oxidizer streams, and the centerline mixture fraction, which measures the extent of entrainment into the fuel jet or the jet evolution downstream. The evolution of momentum and passive scalars is computed using a Reynolds-Averaged Navier-Stokes (RANS) formulation, which uses the 2D table for look-up of the mean density. Other reactive scalars' profiles are obtained from the 2D table and the computed momentum and scalar fields from RANS. Comparison of the computed and the experimental statistics for momentum and scalars shows that the tabulation scheme along with the RANS model yields reasonable predictions of the processes of extinction and reignition in piloted jet diffusion flames. Keywords: ODT-based closurePiloted-jet diffusion flamesTurbulent non-premixed combustion We are grateful to Prof. A. Dreizler for providing us the velocity data for Flames D and F and to Drs. R. S. Barlow and J. F. Frank for providing the scalar data through the TNF workshop Web site. Notes The velocities represent bulk properties at the fuel jet, the pilot, and the co-flow. DA - 2009/// PY - 2009/// DO - 10.1080/00102200802529993 VL - 181 IS - 4 SP - 570-596 SN - 1563-521X UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70349196281&partnerID=MN8TOARS KW - ODT-based closure KW - Piloted-jet diffusion flames KW - Turbulent non-premixed combustion ER - TY - JOUR TI - Hydrogen production in ultrarich combustion of hydrocarbon fuels in porous media AU - Toledo, Mario AU - Bubnovich, Valeri AU - Saveliev, Alexei AU - Kennedy, Lawrence T2 - INTERNATIONAL JOURNAL OF HYDROGEN ENERGY AB - Rich and ultrarich combustion of methane, ethane, and propane inside inert porous media is studied experimentally and numerically to examine the suitability of the concept for hydrogen production. Temperature, velocities, and chemical products of the combustion waves were recorded experimentally at a range of equivalence ratios from stoichiometry (φ = 1.0) to φ = 2.5, for a filtration velocity of 12 cm/s. Two-temperature numerical model based on comprehensive heat transfer and chemical mechanisms is found to be in a good qualitative agreement with experimental data. Partial oxidation products of methane, ethane, and propane (H2, CO, and C2 hydrocarbons) are dominant for ultrarich superadiabatic combustion. The maximum hydrogen yield is close to 50% for all fuels, and carbon monoxide yield is close to 80%. DA - 2009/2// PY - 2009/2// DO - 10.1016/j.ijhydene.2008.12.001 VL - 34 IS - 4 SP - 1818-1827 SN - 1879-3487 KW - Hydrogen production KW - Partial oxidation KW - Filtration combustion KW - Porous media ER - TY - JOUR TI - Forced Convection with Laminar Pulsating Counterflow in a Saturated Porous Circular Tube AU - Kuznetsov, A. V. AU - Nield, D. A. T2 - TRANSPORT IN POROUS MEDIA DA - 2009/4// PY - 2009/4// DO - 10.1007/s11242-008-9271-3 VL - 77 IS - 3 SP - 447-462 SN - 1573-1634 KW - Forced convection KW - Pulsating flow KW - Counterflow KW - Circular tube ER - TY - JOUR TI - Microstructural modeling of nanoidentational polycrsytalline gold with random high angle grain-boundaries AU - Ma, J.B. AU - Zikry, M.A. T2 - Reviews on Advanced Materials Science DA - 2009/// PY - 2009/// VL - 19 IS - 1-2 SP - 78-92 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-64649089133&partnerID=MN8TOARS ER - TY - JOUR TI - Direct extraction of rate-dependent traction-separation laws for polyurea/steel interfaces AU - Zhu, Yong AU - Liechti, Kenneth M. AU - Ravi-Chandar, K. T2 - INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES AB - Polyurea coatings on steel form tough, flexible and chemically resistant surfaces, making them ideal for a variety of applications. An important issue for polyurea coatings in some cases is their adhesion to steel under various loading conditions in aggressive environments. In this paper, adhesion was examined using steel/polyurea/steel sandwich specimens and interfacial fracture mechanics. The mode 1 and mode 2 interfacial fracture behaviors were characterized by two independent traction–separation laws. The traction–separation laws were measured directly by recording the J-integral and the end-opening displacement in the directions normal and tangential to the steel/polyurea interface. In each case, the traction was initially nonzero, increased with increasing separation, reached its peak value and then decreased with further increasing opening. Strong rate-dependent effects were found for both modes of fracture and were attributed to the interfacial behavior. Porosity introduced during the processing of the polyurea affected the traction–separation laws and associated fracture mechanisms. DA - 2009/1/1/ PY - 2009/1/1/ DO - 10.1016/j.ijsolstr.2008.08.019 VL - 46 IS - 1 SP - 31-51 SN - 1879-2146 KW - Polyurea KW - Adhesion KW - Interfacial fracture KW - Cohesive zone model KW - Traction-separation law ER - TY - JOUR TI - The Effect of Strong Heterogeneity on the Onset of Convection in a Porous Medium AU - Nield, D. A. AU - Kuznetsov, A. V. AU - Simmons, Craig T. T2 - TRANSPORT IN POROUS MEDIA DA - 2009/3// PY - 2009/3// DO - 10.1007/s11242-008-9297-6 VL - 77 IS - 2 SP - 169-186 SN - 1573-1634 KW - Heterogeneity KW - Stability KW - Natural convection KW - Computer package ER - TY - JOUR TI - Development of Stable Automated Cruise Flap for an Aircraft with Adaptive Wing AU - Cox, Craig AU - Gopalarathnam, Ashok AU - Hall, Charles E., Jr. T2 - Journal of Aircraft AB - Cruise flaps are devices designed to minimize drag, and previous research has explored using a wing-based pressure differential to automate them. Different presentations of the pressure-differential data tend to lead to the development of different types of controllers for automated cruise flaps. A presentation used by previous researchers led to an unstable drag-minimizing controller, whereas a presentation used in this research leads to a stable controller that implements multiple functions. Techniques previously used for high Reynolds number natural-laminar-flow airfoils are modified for use with the low Reynolds number SD7037 planned for future flight testing. The results of rigid-aircraft simulations are presented, showing the effectiveness of the multifunction controller, which is able to simultaneously reduce drag and alleviate the effects of vertical gusts. DA - 2009/1// PY - 2009/1// DO - 10.2514/1.38684 VL - 46 IS - 1 SP - 301-311 J2 - Journal of Aircraft LA - en OP - SN - 0021-8669 1533-3868 UR - http://dx.doi.org/10.2514/1.38684 DB - Crossref ER - TY - JOUR TI - Cleaving of solid single mode polymer optical fiber for strain sensor applications AU - Abdi, O. AU - Wong, K. C. AU - Hassan, T. AU - Peters, K. J. AU - Kowalsky, M. J. T2 - OPTICS COMMUNICATIONS AB - Abstract Single mode polymer optical fibers (smPOFs) can be applied for measuring large strains in numerous applications, such as civil engineering infrastructure assessment and health monitoring. Because of the large light attenuation of solid smPOFs, small lengths of the fiber would need to be coupled to silica optical fibers (SOFs) for practical applications of the smPOF as a strain sensor. This coupling requires smooth cleaving of the smPOFs. In this work, several cleaving techniques previously demonstrated to provide smooth cross-sections of multimode POFs were applied to the smPOF. From these techniques, hot-knife cutting was determined to be a feasible method for cleaving when the blade was heated to 80 °C and the smPOF heated in the range of 30 °C to 40 °C. In addition, focused ion beam machining which produces high-precision cleaves of the solid smPOF cross-section, was performed to set a bench mark and thus evaluate the quality of cleaving from other methods used in this study. DA - 2009/3/1/ PY - 2009/3/1/ DO - 10.1016/j.optcom.2008.11.046 VL - 282 IS - 5 SP - 856-861 SN - 1873-0310 KW - Cleaving KW - Polymer optical fiber KW - Single mode KW - Strain KW - Sensor ER - TY - JOUR TI - A minimal hydrodynamic model for a traffic jam in an axon AU - Kuznetsov, A. V. AU - Avramenko, A. A. T2 - INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER AB - Traffic jams in long processes of nerve cells (neurons) are linked to such neurodegenerative diseases as Alzheimer's disease and Down syndrome. These traffic jams cause swellings in the neurons' processes that accumulate large amounts of mitochondria, large multi-vesicular bodies, and other types of intracellular organelles, eventually leading to neuron failure and death. The purpose of this paper is to develop a minimal model for a traffic jam in an axon based on a macroscopic (hydrodynamic) approach to modeling of highway traffic and on a macroscopic model of molecular-motor-assisted transport of intracellular organelles on microtubules. DA - 2009/1// PY - 2009/1// DO - 10.1016/j.icheatmasstransfer.2008.09.004 VL - 36 IS - 1 SP - 1-5 SN - 1879-0178 KW - Molecular motors KW - Motor-assisted transport KW - Neurons KW - Axons and dendrites KW - Intracellular organelles KW - Traffic jams ER - TY - JOUR TI - Viscous flow over an unsteady shrinking sheet with mass transfer AU - Fang, Tiegang AU - Zhang, J. AU - Yao, S.-S. T2 - Chinese Physics Letters AB - The unsteady viscous flow over a continuously shrinking surface with mass suction is studied. The solution is fortunately an exact solution of the unsteady Navier–Stokes equations. Similarity equations are obtained through the application of similarity transformation techniques. Numerical techniques are used to solve the similarity equations for different values of the mass suction parameters and the unsteadiness parameters. Results show that multiple solutions exist for a certain range of mass suction and unsteadiness parameters. Quite different flow behaviour is observed for an unsteady shrinking sheet from an unsteady stretching sheet. DA - 2009/// PY - 2009/// DO - 10.1088/0256-307x/26/1/014703 VL - 26 IS - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-66149140214&partnerID=MN8TOARS ER - TY - JOUR TI - Thermally Developing Forced Convection in a Porous Medium Occupied by a Rarefied Gas: Parallel Plate Channel or Circular Tube with Walls at Constant Heat Flux AU - Kuznetsov, A. V. AU - Nield, D. A. T2 - TRANSPORT IN POROUS MEDIA DA - 2009/2// PY - 2009/2// DO - 10.1007/s11242-008-9250-8 VL - 76 IS - 3 SP - 345-362 SN - 1573-1634 KW - Forced convection KW - Thermal development KW - Rarefied gas KW - Graetz problem KW - Parallel plate channel and circular tube ER - TY - JOUR TI - Comparison of analytical and CFD models with regard to micron particle deposition in a human 16-generation tracheobronchial airway model AU - Zhang, Zhe AU - Kleinstreuer, Clement AU - Kim, Chong S. T2 - JOURNAL OF AEROSOL SCIENCE AB - A representative human tracheobronchial tree has been geometrically represented with adjustable triple-bifurcation units (TBUs) in order to effectively simulate local and global micron particle depositions. It is the first comprehensive attempt to compute micron-particle transport in a (Weibel Type A) 16-generation model with realistic inlet conditions. The CFD modeling predictions are compared to experimental observations as well as analytical modeling results. Based on the findings with the validated computer simulation model, the following conclusions can be drawn: (i) Surprisingly, simulated inspiratory deposition fractions for the entire tracheobronchial region (say, G0–G15) with repeated TBUs in parallel and in series agree rather well with those calculated using analytical/semi-empirical expressions. However, the predicted particle-deposition fractions based on such analytical formulas differ greatly from the present simulation results for most local bifurcations, due to the effects of local geometry and resulting local flow features and particle distributions. Clearly, the effects of realistic geometries, flow structures and particle distributions in different individual bifurcations accidentally cancel each other so that the simulated deposition efficiencies during inspiration in a relatively large airway region may agree quite well with those obtained from analytical expressions. Furthermore, with the lack of local resolution, analytical models do not provide any physical insight to the air–particle dynamics in the tracheobronchial region. (ii) The maximum deposition enhancement factors (DEF) may be in the order of 102 to 103 for micron particles in the tracheobronchial airways, implying potential health effects when the inhaled particles are toxic. (iii) The presence of sedimentation for micron particles in lower bronchial airways may change the local impaction-based deposition patterns seen for larger airways and hence reduces the maximum DEF values. (iv) Rotation of an airway bifurcation cause a significant impact on distal bifurcations rather than on the proximal ones. Such geometric effects are minor when compared to the effects of airflow and particle transport/deposition history, i.e., upstream effects. DA - 2009/1// PY - 2009/1// DO - 10.1016/j.jaerosci.2008.08.003 VL - 40 IS - 1 SP - 16-28 SN - 1879-1964 KW - Human tracheobronchial airways KW - Computational analysis KW - Micron particle deposition KW - Deposition efficiency KW - Deposition fraction ER - TY - JOUR TI - An integrated fiberoptic-microfluidic device for agglutination detection and blood typing AU - Ramasubramanian, Melur K. AU - Alexander, Stewart P. T2 - BIOMEDICAL MICRODEVICES DA - 2009/2// PY - 2009/2// DO - 10.1007/s10544-008-9227-y VL - 11 IS - 1 SP - 217-229 SN - 1572-8781 KW - RBC KW - Agglutination KW - Transfusion KW - Cross-matching KW - Scattering KW - Microfluidics KW - Fiberoptics KW - Optointerruption KW - Blood typing ER - TY - JOUR TI - A study on compression-induced morphological changes of nonwoven fibrous materials AU - Jaganathan, S. AU - Tafreshi, H. Vahedi AU - Shim, E. AU - Pourdeyhimi, B. T2 - COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS AB - Pore size is a characteristic parameter that is often defined for fibrous materials used in industrial applications. While there exist many available studies on the pore size distribution of different fibrous materials, the influence of compression load on pore size distribution has not been studied well. Studying the behavior of fibrous materials under compression is important especially because in many applications these materials are subjected to some degree of compression during use. In this work, we present a novel image-based modeling technique to study the changes in the pore size distribution of a fibrous material exposed to compressive load. This was made possible by building a miniature compression cell, and imaging the structure of a hydroentangled fabric under varying levels of compression. The 3D images obtained with Digital Volumetric Imaging were utilized to study the pore size distribution of the material and develop an empirical correlation as a function of compressive stress for these structures. This new correlation indicates that the mean pore diameter of a nonwoven material decreases exponentially with increasing the compressive stress. DA - 2009/4/1/ PY - 2009/4/1/ DO - 10.1016/j.colsurfa.2008.12.019 VL - 337 IS - 1-3 SP - 173-179 SN - 1873-4359 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-59349102148&partnerID=MN8TOARS KW - Fibrous materials KW - Pore size distribution KW - Modeling KW - Compression KW - 3D imaging ER - TY - JOUR TI - A comparison of composite metal foam's properties and other comparable metal foams AU - Rabiei, A. AU - Vendra, L. J. T2 - MATERIALS LETTERS AB - New closed cell composite metal foams are processed using casting and powder metallurgy (PM) techniques. The foam is comprised of steel hollow spheres packed into a random loose arrangement, with the interstitial spaces between spheres occupied with a solid metallic matrix. The characterization of composite metal foams was carried out using monotonic compression, compression–compression fatigue, loading–unloading compression, micro-hardness and nano-hardness testing. The microstructure of the composite metal foams was studied using optical, scanning electron microscopy imaging and electron dispersive spectroscopy. The composite metal foams displayed superior (5–20 times higher) compressive strengths, reported as 105 MPa for cast foams and 127 MPa for PM foams, and much higher energy absorbing capability as compared to other metal foams being produced with similar materials through other technologies. DA - 2009/2/28/ PY - 2009/2/28/ DO - 10.1016/j.matlet.2008.11.002 VL - 63 IS - 5 SP - 533-536 SN - 1873-4979 KW - Casting KW - Composite materials KW - Metal foams KW - Mechanical properties KW - Microstructure KW - Powder metallurgy ER - TY - JOUR TI - Start-up flow in a channel or pipe occupied by a fluid-saturated porous mediaum AU - Avramenko, A. A. AU - Kuznetsov, A. V. T2 - Journal of Porous Media AB - The response of incompressible fluid in a parallel-plate channel or circular pipe, occupied by a fluid-saturated porous medium, to a suddenly imposed time-independent pressure drop is investigated. The Brinkman-expended Darcy equation is used to model momentum transport in the fluid. The problem is solved analytically using the Laplace transformation. The unsteady velocity profiles in a channel or pipe are presented through infinite series solutions. As expected, the flow asymptotically attains the fully developed velocity distribution, which is attained faster for the medium of smaller permeability. DA - 2009/// PY - 2009/// DO - 10.1615/jpormedia.v12.i4.60 VL - 12 IS - 4 SP - 361-367 ER - TY - JOUR TI - Disturbance attenuation by output feedback for linear systems subject to actuator saturation AU - Wu, Fen AU - Zheng, Qian AU - Lin, Zongli T2 - INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL AB - Abstract In this paper, we study the problem of disturbance attenuation by output feedback for linear systems subject to actuator saturation. A nonlinear output feedback, expressed in the form of a quasi‐linear parameter‐varying system with state‐dependent scheduling parameter, is constructed that leads to the attenuation of the effect of the disturbance on the output of the system. The level of disturbance attenuation is measured in terms of the restricted ℒ︁ 2 gain and the restricted ℒ︁ 2 –ℒ︁ ∞ gain over a class of bounded disturbances. Copyright © 2008 John Wiley & Sons, Ltd. DA - 2009/1/25/ PY - 2009/1/25/ DO - 10.1002/rnc.1306 VL - 19 IS - 2 SP - 168-184 SN - 1099-1239 KW - nonlinear control KW - output feedback KW - disturbance rejection KW - actuator saturation KW - L-2 gain KW - L-2-L-infinity gain ER - TY - JOUR TI - A Dynamic Heart System to Facilitate the Development of Mitral Valve Repair Techniques AU - Richards, Andrew L. AU - Cook, Richard C. AU - Bolotin, Gil AU - Buckner, Gregory D. T2 - ANNALS OF BIOMEDICAL ENGINEERING AB - The development of a novel surgical tool or technique for mitral valve repair can be hampered by cost, complexity, and time associated with performing animal trials. A dynamically pressurized model was developed to control pressure and flowrate profiles in intact porcine hearts in order to quantify mitral regurgitation and evaluate the quality of mitral valve repair.A pulse duplication system was designed to replicate physiological conditions in explanted hearts. To test the capabilities of this system in measuring varying degrees of mitral regurgitation, the output of eight porcine hearts was measured for two different pressure waveforms before and after induced mitral valve failure. Four hearts were further repaired and tested. Measurements were compared with echocardiographic images.For all trials, cardiac output decreased as left ventricular pressure was increased. After induction of mitral valve insufficiencies, cardiac output decreased, with a peak regurgitant fraction of 71.8%. Echocardiography clearly showed increases in regurgitant severity from post-valve failure and with increased pressure.The dynamic heart model consistently and reliably quantifies mitral regurgitation across a range of severities. Advantages include low experimental cost and time associated with each trial, while still allowing for surgical evaluations in an intact heart. DA - 2009/4// PY - 2009/4// DO - 10.1007/s10439-009-9653-x VL - 37 IS - 4 SP - 651-660 SN - 1573-9686 KW - Dynamic heart model KW - Mitral regurgitation KW - Mitral valve repair ER - TY - JOUR TI - Invariant-Based Anisotropic Constitutive Models of the Healthy and Aneurysmal Abdominal Aortic Wall AU - Basciano, C. A. AU - Kleinstreuer, C. T2 - JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME AB - The arterial wall is a complex fiber-reinforced composite. Pathological conditions, such as aneurysms, significantly alter the mechanical response of the arterial wall, resulting in a loss of elasticity, enhanced anisotropy, and increased chances of mechanical failure. Invariant-based models of the healthy and aneurysmal abdominal aorta were constructed based on first principles and published experimental data with implementations for several numerical cases, as well as comparisons to current healthy and aneurysmal tissue data. Inherent limitations of a traditional invariant-based methodology are also discussed and compared to the models' ability to accurately reproduce experimental trends. The models capture the nonlinear and anisotropic mechanical responses of the two arterial sections and make reasonable predictions regarding the effects of alterations in healthy and diseased tissue histology. Additionally, the new models exhibit convex and anisotropic monotonically increasing energy contours (suggesting numerical stability) but have potentially the inherent limitations of a covariant theoretical framework. Although the traditional invariant framework exhibits significant covariance, the invariant terms utilized in the new models exhibited limited covariance and are able to accurately reproduce experimental trends. A streamlined implementation is also possible for future numerical investigations of fluid-structure interactions in abdominal aortic aneurysms. DA - 2009/2// PY - 2009/2// DO - 10.1115/1.3005341 VL - 131 IS - 2 SP - SN - 1528-8951 KW - ab initio calculations KW - biomechanics KW - blood vessels KW - diseases KW - elasticity KW - physiological models ER - TY - JOUR TI - An Adjustable Triple-Bifurcation Unit Model for Air-Particle Flow Simulations in Human Tracheobronchial Airways AU - Kleinstreuer, C. AU - Zhang, Z. T2 - JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME AB - A new methodology for a swift and accurate computer simulation of large segments of the human lung airways is presented. Focusing on a representative tracheobronchial (TB) region, i.e., G0–G15, nano- and micron particle transports have been simulated for Qin=30l∕min, employing an experimentally validated computer model. The TB tree was geometrically decomposed into triple-bifurcation units with kinematically adjusted multilevel outlet/inlet conditions. Deposition patterns and maximum concentrations differ greatly between nanoparticles (1⩽dp⩽150nm) and micron particles (1⩽dp⩽10μm), which may relate uniquely to health impacts. In comparison with semi-analytical particle deposition results, it is shown that such simple “lung models” cannot predict local deposition values but can match computer simulation results for the entire TB region within 2.5–26%. The present study revealed that turbulent air-particle flow may propagate to G5 for the assumed inhalation flow rate. Geometry and upstream effects are more pronounced for micron particle deposition than for nanoparticle deposition. DA - 2009/2// PY - 2009/2// DO - 10.1115/1.3005339 VL - 131 IS - 2 SP - SN - 1528-8951 KW - bifurcation KW - computational fluid dynamics KW - flow simulation KW - lung KW - nanoparticles KW - physiological models KW - pneumodynamics KW - turbulence ER - TY - JOUR TI - Inelastic contact behavior of crystalline asperities in rf MEMS devices AU - Rezvanian, O. AU - Zikry, Mohammed T2 - Journal of Engineering Materials and Technology AB - Microelectromechanical systems (MEMS), particularly those with radio frequency (rf) applications, have demonstrated significantly better performance over current electromechanical and solid-state technologies. Surface roughness and asperity microcontacts are critical factors that can affect contact behavior at scales ranging from the nano to the micro in MEMS devices. Recent investigations at the continuum level have underscored the importance of microstructural effects on the inelastic behavior of asperity microcontacts. Hence, a microstructurally based approach that accounts for the inhomogeneous deformation of the asperity microcontacts under cyclic loading and that is directly related to asperity physical scales and anisotropies can provide a detailed understanding of the deformation mechanisms associated with asperity microcontacts so that guidelines can be incorporated in the design and fabrication process to effectively size critical components and forces for significantly improved device durability and performance. A physically based microstructural representation of fcc crystalline materials that couples a multiple-slip crystal plasticity formulation to dislocation densities is used in a specialized finite-element modeling framework. The asperity model and the loading conditions are based on realistic service conditions consistent with rf MEMS with metallic normal contacts. The evolving microstructure, stress fields, contact width, hardness, residual effects, and the localized phenomena that can contribute to failure initiation and evolution in the flattening of single crystal gold asperity microcontacts are characterized for a loading-unloading cycle. It is shown that the nonuniform loading conditions due to asperity geometry and contact loading and the size effects due to asperity dimensions result in significant contribution of the geometrically necessary dislocation densities to stress, deformation, and microstructural evolution of crystalline asperities. This is not captured in modeling efforts based on von Mises continuum plasticity formulations. Residual strains and stresses are shown to develop during the cyclic loading. Localized tensile stress regions are shown to develop due to stress reversal and strain hardening during both loading and unloading regimes. Hardness predictions also indicate that nano-indentation hardness values of the contact material can overestimate the contact force in cases, where a rigid flat surface is pressed on a surface roughness asperity. DA - 2009/// PY - 2009/// DO - 10.1115/1.3026545 VL - 131 IS - 1 SP - 0110021-01100210 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77955373765&partnerID=MN8TOARS ER - TY - JOUR TI - Temperature dependence of asperity contact and contact resistance in gold RF MEMS switches AU - Brown, C AU - Rezvanian, O AU - Zikry, M A AU - Krim, J T2 - Journal of Micromechanics and Microengineering AB - Experimental measurements and modeling predictions were obtained to characterize the electro-mechanical response of two different gold contact radio frequency microelectromechanical system (RF MEMS) switches due to variations in the temperature and applied contact voltage. A three-dimensional surface roughness profile from AFM measurements of the top contact surface of a sample RF MEMS switch was used to obtain modeling predictions of the time-dependent deformation of the asperity microcontacts, real areas of contact, number of asperity microcontacts and constriction resistance. The experimental data indicated a decrease in the overall resistance and a decrease in the creep mechanism at 77 K and 5.6 K when compared to measurements at 293 K. At 293 K, there is more contact area per unit time, and the resistance drop from the increase in real contact area dominates the resistance increase due to asperity heating. At 77 K, the creep rate is reduced, and fewer asperities are in contact. At 5.6 K, the change in contact area over time is small, and the contact resistance measurement is dominated by the Joule heating. The data presented and constriction resistance modeling for gold RF MEMS switches show that temperature plays a significant role in the creep deformation and heating of switch contacts. DA - 2009/1/14/ PY - 2009/1/14/ DO - 10.1088/0960-1317/19/2/025006 VL - 19 IS - 2 SP - 025006 J2 - J. Micromech. Microeng. OP - SN - 0960-1317 1361-6439 UR - http://dx.doi.org/10.1088/0960-1317/19/2/025006 DB - Crossref ER - TY - JOUR TI - Fourier series of half-range functions by smooth extension AU - Morton, Jeremy AU - Silverberg, Larry T2 - APPLIED MATHEMATICAL MODELLING AB - This paper considers Fourier series approximations of one- and two-dimensional functions over the half-range, that is, over the sub-interval [0, L ] of the interval [− L, L ] in one-dimensional problems and over the sub-domain [0, L x ] × [0, L y ] of the domain [− L x , L x ] × [− L y , L y ] in two-dimensional problems. It is shown how to represent these functions using a Fourier series that employs a smooth extension. The purpose of the smooth extension is to improve the convergence characteristics otherwise obtained using the even and odd extensions. Significantly improved convergence characteristics are illustrated in one-dimensional and two-dimensional problems. DA - 2009/2// PY - 2009/2// DO - 10.1016/j.apm.2007.12.009 VL - 33 IS - 2 SP - 812-821 SN - 1872-8480 KW - Fourier series KW - Smooth extension KW - Half-range problems ER - TY - JOUR TI - A hybrid building-block and gridless method for compressible flows AU - Luo, Hong AU - Baum, Joseph D. AU - Loehner, Rainald T2 - INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS AB - Abstract A hybrid building‐block Cartesian grid and gridless method is presented to compute unsteady compressible flows for complex geometries. In this method, a Cartesian mesh based on a building‐block grid is used as a baseline mesh to cover the computational domain, while the boundary surfaces are represented using a set of gridless points. This hybrid method combines the efficiency of a Cartesian grid method and the flexibility of a gridless method for the complex geometries. The developed method is used to compute a number of test cases to validate the accuracy and efficiency of the method. The numerical results obtained indicate that the use of this hybrid method leads to a significant improvement in performance over its unstructured grid counterpart for the time‐accurate solution of the compressible Euler equations. An overall speed‐up factor from six to more than one order of magnitude and a saving in storage requirements up to one order of magnitude for all test cases in comparison with the unstructured grid method are demonstrated. Copyright © 2008 John Wiley & Sons, Ltd. DA - 2009/2/10/ PY - 2009/2/10/ DO - 10.1002/fld.1827 VL - 59 IS - 4 SP - 459-474 SN - 1097-0363 KW - Cartesian grid methods KW - gridless methods KW - building-block methods KW - Euler equations KW - unsteady compressible flows KW - shock waves ER -