@article{chen_sung_shen_tallent_barker_li_2022, title={Bit-GraphBLAS: Bit-Level Optimizations of Matrix-Centric Graph Processing on GPU}, ISSN={["1530-2075"]}, DOI={10.1109/IPDPS53621.2022.00056}, abstractNote={In a general graph data structure like an adjacency matrix, when edges are homogeneous, the connectivity of two nodes can be sufficiently represented using a single bit. This insight has, however, not yet been adequately exploited by the existing matrix-centric graph processing frameworks. This work fills the void by systematically exploring the bit-level representation of graphs and the corresponding optimizations to the graph operations. It proposes a two-level representation named Bit-Block Compressed Sparse Row (B2SR) and presents a series of optimizations to the graph operations on B2SR by leveraging the intrinsics of modern GPUs. Evaluations on NVIDIA Pascal and Volta GPUs show that the optimizations bring up to 40× and 6555× for essential GraphBLAS kernels SpMV and SpGEMM, respectively, making GraphBLAS-based BFS accelerate up to 433×, SSSP, PR, and CC up to 35×, and TC up to 52×.}, journal={2022 IEEE 36TH INTERNATIONAL PARALLEL AND DISTRIBUTED PROCESSING SYMPOSIUM (IPDPS 2022)}, author={Chen, Jou-An and Sung, Hsin-Hsuan and Shen, Xipeng and Tallent, Nathan and Barker, Kevin and Li, Ang}, year={2022}, pages={515–525} }
 @article{li_vallabh_bradford_kim_seyam_2022, title={Development of hull material for high-altitude airship: A parametric study}, volume={1}, ISSN={["1530-7964"]}, DOI={10.1177/07316844211054852}, abstractNote={The development of hull material with ideal properties to meet all the operation requirements has posed the greatest challenge to flying the airship at high altitude for extended periods. Materials developed in our previous study with a laminated structure achieved high strength-to-weight ratio and excellent gas barrier property at a relatively low total weight. To optimize this novel design and obtain a more comprehensive understanding of the laminate properties, a parametric study involving lamination process parameters (temperature and time), and laminate structural parameter (reinforcement fabric construction), was conducted. The effects of lamination parameters on tensile, peel, tear and helium permeability tests were carried out to assess the laminates. It was found that the tensile strength of the laminate is predominantly determined by the fabric reinforcement material properties. The peel and tear strength results showed that increasing the lamination temperature from 185 °C to 200 °C improved respective strength values. Additionally, the analysis of failure modes and tear propagation suggested that laminate samples with progressive failure have better tear resistant property over those with brutal failure. Extremely low helium permeability was achieved, yet the gas barrier property was not affected by the lamination process parameters and fabric type.}, journal={JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, author={Li, Ang and Vallabh, Rahul and Bradford, Philip D. and Kim, David and Seyam, Abdel-Fattah M.}, year={2022}, month={Jan} }
 @article{szoke_devenport_borgoltz_alexander_hari_glegg_li_vallabh_seyam_2022, title={Investigating the Aeroacoustic Properties of Porous Fabrics}, volume={1}, ISSN={["1533-385X"]}, DOI={10.2514/1.J061385}, abstractNote={The aeroacoustic properties of porous fabrics are investigated experimentally with the goal of finding a fabric that serves as an improved interface between wind tunnel flow and quiescent conditions. A total number of eight porous fabrics were investigated, namely, four glass fiber fabrics, two plain-weave Kevlar fabrics, and two modified plain Kevlar fabrics with their pores irregularly clogged. Two custom-made rigs were used to quantify the transmission loss (TL) and self-noise of all fabrics. The pores were found to serve as a low-resistance gateway for sound to pass through, hence enabling a low TL. The TL was found to increase with decreasing open area ratio (OAR), whereas other fabric properties had a minor impact on TL. The thread density was found to be a primary factor in determining the frequency range of porous fabrics’ self-noise, with the OAR potentially playing a secondary role in the self-noise levels. Fabrics with irregular pore distribution showed a more broadband self-noise signature associated with lower frequencies compared to fabrics with periodic pore patterns. Overall, fabrics with an irregular pore distribution or fabrics with increased thread density were identified as two potential ways to obtain superior aeroacoustic behavior compared to commonly used Kevlar fabrics.}, journal={AIAA JOURNAL}, author={Szoke, Mate and Devenport, William J. and Borgoltz, Aurelien and Alexander, W. Nathan and Hari, Nandita and Glegg, Stewart A. L. and Li, Ang and Vallabh, Rahul and Seyam, Abdel-Fattah M.}, year={2022}, month={Jan} }
 @article{li_danladi_vallabh_yakubu_ishiaku_theyson_seyam_2021, title={Cellulose Microfibril and Micronized Rubber Modified Asphalt Binder}, volume={9}, ISSN={["2079-6439"]}, DOI={10.3390/fib9040025}, abstractNote={Cellulose microfibrils (CMFs) and micronized rubber powder (MRP) can be derived from low or negative-cost agricultural/industrial waste streams and offer environment-friendly and cost-effective pathways to develop engineering products. This study investigated the efficacy of adding these micromodifiers on the performance characteristics of asphalt binders. In this work, samples were produced using a mixture of slow-setting anionic asphalt emulsion with various combinations of MRP (at 0, 2 and 10 wt %) and four types of CMFs (hydrophobic and hydrophilic with crystalline ratios of 86% and 95%) at 0, 2 and 5 wt %. The performance of modified asphalt samples was assessed by penetration depth (PD), softening point (SP), and penetration index (PI). Linear regression analysis showed that adding CMFs and/or MRP reduced PD and increased SP values. The type of CMFs significantly affected the performance, which becomes more distinct with the increased weight content of CMFs. While hydrophilic CMFs caused increases in SP and PI values, no clear trend was seen to determine the effect of CMF crystallinity. It was also discovered that the combined addition of CMF and MRP achieved similar PI values at lower total weight content compared to using MRP alone.}, number={4}, journal={FIBERS}, author={Li, Ang and Danladi, Abdu A. and Vallabh, Rahul and Yakubu, Mohammed K. and Ishiaku, Umar and Theyson, Thomas and Seyam, Abdel-Fattah M.}, year={2021}, month={Apr} }
 @article{vallabh_li_bradford_kim_seyam_2021, title={Ultra-lightweight fiber-reinforced envelope material for high-altitude airship}, volume={6}, ISSN={["1754-2340"]}, DOI={10.1080/00405000.2021.1948695}, abstractNote={In this work, fiber-reinforced laminates for the envelope (hull) of high-altitude airships were developed using a novel design concept utilizing ethylene vinyl alcohol (EVOH) as the adhesive component layer with high gas barrier properties. The other component layers of the laminates included poly(p-phenylene benzobisoxazole) (Zylon®) fabric, metalized Mylar® (polyester) and metallized Kapton® (polyimide). The envelope materials were developed in two different strength categories. In the first category, three laminate designs were developed with strength ranging from 945–970 N/cm. The second group had one laminate design with a strength of 702 N/cm. These laminates with basis weights ranging from 103–113 g/m2, are the lightest envelope materials developed to date. As a function of their high strength and low basis weights, the new envelope materials have significantly higher specific strength (ranging from 911–925 kN.m/kg) compared to other envelope constructions published in the open literature. Other outstanding properties of the laminates include low helium permeability ranging from 0.4–8.0 cc/m2.24 hr.1 atm, high tear strength, UV and visible light (UV–Vis) resistance, and high creep resistance.}, journal={JOURNAL OF THE TEXTILE INSTITUTE}, author={Vallabh, Rahul and Li, Ang and Bradford, Philip D. and Kim, David and Seyam, Abdel-Fattah M.}, year={2021}, month={Jun} }
 @article{wang_yildiz_li_aly_qiu_jiang_pui_chen_bradford_2020, title={High temperature carbon nanotube - Nanofiber hybrid filters}, volume={236}, ISSN={["1873-3794"]}, DOI={10.1016/j.seppur.2019.116255}, abstractNote={Novel hybrid filters composed of aligned carbon nanotube (CNT) sheets, sandwiched between electrospun polyimide (PI) nanofiber membranes serving as the supporting layers, were fabricated for the capture of fine particles. The CNT sheets and PI nanofiber membranes were thermally bonded together by melting electrospun polyetherimide (PEI) nanofibers. Two different kinds of filter structures were prepared, where multiple layers of aligned CNT sheets were either stacked together on top of each other or separated from each other by a PEI layer. The filtration performance tests showed that the filtration efficiency increased with increasing number of CNT sheets. The maximum filtration efficiency reached 99.99% at 5.3 cm/s face velocity for 0.3 μm particles by the 4-layer CNT filter, while the pressure drop was only 120 Pa. In mechanical testing, the CNT sheets also reinforced the hybrid filters, even though the PI nanofiber membrane already had relatively high mechanical properties. The tensile strength of the 4-layer CNT hybrid filters was 9 MPa, reaching the highest tier of strength reported for nanofiber membranes. In addition to high efficiency and low pressure drop, the hybrid all-nanofiber filters are also targeted for use in hot gas filtration applications where temperatures reach 200–250 °C.}, journal={SEPARATION AND PURIFICATION TECHNOLOGY}, author={Wang, Qiannan and Yildiz, Ozkan and Li, Ang and Aly, Karim and Qiu, Yiping and Jiang, Qiuran and Pui, David Y. H. and Chen, Sheng-Chieh and Bradford, Philip D.}, year={2020}, month={Apr} }
 @article{aly_li_bradford_2017, title={Compressive piezoresistive behavior of carbon nanotube sheets embedded in woven glass fiber reinforced composites}, volume={116}, ISSN={["1879-1069"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85006298233&partnerID=MN8TOARS}, DOI={10.1016/j.compositesb.2016.11.002}, abstractNote={Due to the difficulties associated with performing compression tests and the complex nature of compression failure, the number of studies that have examined the piezoresistive response of carbon nanotube (CNT) sensing networks in composites under compression loading has been limited. This paper introduces a novel technique for embedding aligned sheets of two millimeter long, interconnected CNTs into the interlaminar region of laminated composite structures to assess the potential of the CNT sheets to function as strain sensing materials for composite structures subjected to axial compression loading. Quasi-static and cyclic compression mechanical loading tests were accompanied by real time electrical resistance change data acquisition and the results suggested that the CNT sheet sensing material composed of six CNT sheets layers exhibited improved sensitivity, stability and repeatability which are vital properties for any successful health monitoring technique. The coupons with six CNT sheets layers embedded exhibited piezoresistivity that showed some linearity in tension and was nonlinear in compression. This piezoresistive response was characterized as anti-symmetric around zero strain all the way until fracture.}, journal={COMPOSITES PART B-ENGINEERING}, author={Aly, Karim and Li, Ang and Bradford, Philip D.}, year={2017}, month={May}, pages={459–470} }
 @article{fang_li_yildiz_shao_bradford_ghosh_2017, title={Enhanced anisotropic response of dielectric elastomer actuators with microcombed and etched carbon nanotube sheet electrodes}, volume={120}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2017.05.067}, abstractNote={Dielectric elastomers (DE), also known as dielectric electroactive polymers offer tremendous potential in a wide-ranging applications including microrobotics and wearable responsive systems. The real-world application of DEs, however, has been limited by a number of factors, including facile means of producing directional stress/strain. As a critical component of the DE actuator, the electrodes should have high electrical conductance under finite in-plane deformation, good electromechanical stability, and ease of shaping based on the design requirements. In this work we investigate highly aligned carbon nanotube (CNT) sheets as electrodes in DE actuators to yield anisotropic electromechanical response. The morphology of CNT sheets were altered by microcombing and selective laser etching to enhance mechanical anisotropy. The enhancement of CNT sheets alignment results in almost pure unidirectional strain of 33% at a relatively moderate electric field. The results demonstrate that the deformation anisotropy of DE actuators can be significantly improved by directional laser etching of the electrodes rather than microcombing alone.}, journal={CARBON}, author={Fang, Xiaomeng and Li, Ang and Yildiz, Ozkan and Shao, Huiqi and Bradford, Philip D. and Ghosh, Tushar K.}, year={2017}, month={Aug}, pages={366–373} }
 @article{aly_li_bradford_2016, title={Strain sensing in composites using aligned carbon nanotube sheets embedded in the interlaminar region}, volume={90}, ISSN={["1878-5840"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84983749060&partnerID=MN8TOARS}, DOI={10.1016/j.compositesa.2016.08.003}, abstractNote={This paper introduces a novel technique for embedding aligned sheets of two millimeters long, interconnected CNTs into the interlaminar region of composite structures. The potential of these embedded CNT sheets to function as damage detecting and strain sensing elements was demonstrated via various mechanical tests that were accompanied by real time electrical resistance change data acquisition. The experimental results suggested that the CNT sheet sensitivity could be further enhanced by an oxygen plasma treatment and also by pre-straining the CNT sheets before embedding them. The samples containing two CNT sheets layers exhibited long term stability, sensitivity and repeatability which are vital features for health monitoring.}, journal={COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING}, author={Aly, Karim and Li, Ang and Bradford, Philip D.}, year={2016}, month={Nov}, pages={536–548} }
 @article{li_bogdanovich_bradford_2015, title={Aligned carbon nanotube sheet piezoresistive strain sensors}, volume={24}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/24/9/095004}, abstractNote={Carbon nanotubes (CNTs) have a unique set of properties that may be useful in the production of next generation structural health monitoring composites. This research introduces a novel CNT based material system for strain and damage sensing applications. An aligned sheet of interconnected CNTs was drawn from a chemical vapor deposition grown CNT array and then bonded to the surface of glass fiber/epoxy composite coupons. Various types of mechanical tests were conducted, accompanied by real-time electrical data acquisition, in order to evaluate the electro-mechanical behavior of the developed sensing material. Specimens were loaded in the longitudinal and transverse CNT sheet orientations to investigate the anisotropy of the piezoresistive effect. The CNT sheets exhibited good sensing stability, linearity, sensitivity and repeatability within a practical strain range; which are crucial sensor features for health monitoring. It was also demonstrated that the CNT orientation in the sheet had a dramatic effect on the sensitivity, thus validating the usefulness of this sensing material for directional strain/damage monitoring. Finally, pre-straining of the CNT sheet sensors was conducted to further enhance the linearity of electro-mechanical response and long-term stability of the sensors during cyclic loading.}, number={9}, journal={SMART MATERIALS AND STRUCTURES}, author={Li, Ang and Bogdanovich, Alexander E. and Bradford, Philip D.}, year={2015}, month={Sep} }
 @article{faraji_stano_yildiz_li_zhu_bradford_2015, title={Ultralight anisotropic foams from layered aligned carbon nanotube sheets}, volume={7}, ISSN={["2040-3372"]}, DOI={10.1039/c5nr03899e}, abstractNote={In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm(-3), the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.}, number={40}, journal={NANOSCALE}, author={Faraji, Shaghayegh and Stano, Kelly L. and Yildiz, Ozkan and Li, Ang and Zhu, Yuntian and Bradford, Philip D.}, year={2015}, pages={17038–17047} }