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An elastic model for bioinspired design of carbon nanotube bundles

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Acta Mechanica Sinica 2015年第2期31卷 205-215页

作者： Xiaoyu Sun Zuoqi zhang Yuanjie Xu yongwei zhang School of Civil Engineering Wuhan University Institute of High Performance Computing A*STARSingapore 138632Singapore

Collagen fibers provide a good example of making strong micro-or mesoscale fibers from nanoscale tropocollagen molecules through a staggered and crosslinked organization in a bottom-up *** the architectural features of collagen fibers has been shown to be a promising approach to develop carbon nanotube（CNT）fibers of high *** the present work,an elastic model is developed to describe the load transfer and failure propagation within the bioinspired CNT bundles,and to establish the relations of the mechanical properties of the bundles with a number of geometrical and physical parameters such as the CNT aspect ratio and longitudinal gap,interface cross-link density,and the functionalizationinduced degradation in CNTs,*** the model,the stress distributions along the CNT-CNT interface as well as in every individual CNT are well captured,and the failure propagation along the interface and its effects on the mechanical properties of the CNT bundles are *** work may provide useful guidelines for the design of novel CNT fibers in practice.

关键词： Carbon nanotube fiber Collagen-mimic design Staggered pattern Interface modification

Orthogonal waveform design with fractional programming on the ambiguity suppression of SAR systems

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Science China(Information Sciences) 2024年第9期67卷 263-279页

作者： Yunkai DENG yongwei zhang Zhimin zhang Wei WANG Heng zhang Department of Space Microwave Remote Sensing System Aerospace Information Research InstituteChinese Academy of Sciences

Waveform diversity(WD) represents a dynamic and transformative technology widely used in radar systems to enhance sensitivity and discrimination capabilities. Recently, WD techniques have been extensively explored for their potential ambiguity suppression within synthetic aperture radar(SAR) *** these, the alternate transmitting mode combined with orthogonal waveforms emerges as a particularly promising solution. This study focuses on optimizing the power spectrum density(PSD) of signals to design and generate an orthogonal waveform pair that achieves both a low cross-correlation-to-autocorrelation ratio(CAR) and satisfactory imaging performance. Initially, we construct a fractional programming model with convex constraints to minimize the CAR. To address this challenge, we introduce an iterative optimization procedure for the PSD variable, which sequentially reduces the CAR. Each optimization step can be efficiently solved using a quadratically constrained quadratic program, ensuring that the resulting computational complexity remains low. Building on the optimized PSD, we established a parametric piecewise linear model to generate an orthogonal waveform pair. This model not only maintains a low CAR but achieves satisfactory imaging performance in real-time applications. Consequently, this orthogonal waveform pair effectively suppresses range ambiguity in SAR systems. Finally, we demonstrated the practicability and effectiveness of the proposed orthogonal waveforms through detailed simulation experiments, specifically targeting ambiguity suppression in conventional quad-polarization SAR systems.

关键词： synthetic aperture radar (SAR) waveform diversity (WD) ambiguity suppression orthogonal waveform fractional programming power spectrum density (PSD)

Remarkable enhancement in failure stress and strain of penta-graphene via chemical functionalization

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Nano Research 2017年第11期10卷 3865-3874页

作者： Yingyan zhang Qingxiang Pei Zhendong Sha yongwei zhang Huajian Gao School of Computing Engineering and Mathematics Western Sydney University Penrith NSW2751 Australia Institute of High Performance Computing A＊STAR Singapore 138632 Singapore International Center for Applied Mechanics State Key Laboratory for Strength and Vibration of Mechanical Structures Xi'an Jiaotong University Xi'an 710049 China School of Engineering Brown University Providence Rhode Island 02912 USA

Penta-graphene （PG）,a newly proposed two-dimensional material composed entirely of carbon pentagons,is believed to possess much lower failure stress and strain than those of *** open question is whether and how these properties can be *** using molecular dynamics simulations,we examine the deformation and failure processes of PG functionalized with different functional *** reveal that complete chemical functionalization leads to remarkable increases in the failure stress and strain of PG by up to 86.6% and 82.4%,*** underlying reason for this enhancement is that the buckled pentagonal rings in pristine and partially functionalized PGs can easily transform into planar polygon rings under stretching;in contrast,complete functionalization of PG strongly stabilizes its structure and prevents such transformation,thereby significantly increasing the failure stress and *** findings suggest a possible route to enhance the mechanical properties of PG for potential applications in nanocomposites and nanodevices.

关键词： penta-graphene mechanical properties chemical functionalization molecular dynamics

Modulating the thermal conductivity of silicon nanowires via surface amorphization

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Science China(Technological Sciences) 2014年第4期57卷 699-705页

作者： LIU XiangJun zhang Gang PEI QingXiang zhang yongwei Institute of High Performance Computing

We perform non-equilibrium molecular dynamics calculations to study the heat transport in crystalline-core amorphous-shell silicon nanowires(SiNWs).It is found that the thermal conductivity of the core-shell SiNWs is closely related to the cross-sectional area ratio of amorphous *** shell amorphization,an 80%reduction in thermal conductivity compared to crystalline SiNWs with the same size can be achieved,due to the non-propagating heat diffusion in the amorphous *** contrast to the strong temperature-dependent thermal conductivity of crystalline SiNWs,the core-shell SiNWs only show weak temperature *** addition,an empirical relation is proposed to accurately predict the thermal conductivity of the core-shell SiNWs based on the rule of *** present work demonstrates that SiNWs with an amorphized shell are promising candidates for thermoelectric applications.

关键词： thermal conductivity thermoelectric molecular dynamics silicon nanowire

Conversion of CH4, steam and O_2 to syngas and hydrocarbons via dielectric barrier discharge

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Journal of Natural Gas Chemistry 2009年第1期18卷 94-97页

作者： Baowei Wang Xu zhang yongwei Liu Genhui XU Key Laboratory for Green Chemical Technology of the Ministry qf Education School qf Chemical Engineering and Technology. Tianjin University Tianjin 300072 China

The conversion of CH4 with oxygen and steam in a dielectric barrier discharge （DBD） was studied in the paper to discuss the effects of different factors, such as the content of feed-in gas, the applied voltage and frequency. The results showed that a lower ratio of CH4 to O2 always resulted in a higher conversion of CH4. When it was 2, the conversion reached 32.43% without steam introduced into the system. The main effect of steam was increasing the selectivity to CO. The reaction was accelerated and the selectivities to CO and hydrocarbons were enhanced by increasing the applied voltage. It was also observed that a higher frequency led to a lower current and then restrained the reaction.

关键词： methane steam oxygen dielectric barrier discharges plasma

Pulling out a peptide chain from β-sheet crystallite: Propagation of instability of H-bonds under shear force

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Acta Mechanica Sinica 2015年第3期31卷 416-424页

作者： Changjian Xu Dechang Li Yuan Cheng Ming Liu yongwei zhang Baohua Ji Biomechanics and Biomaterials Laboratory Department of Applied Mechanics Beijing Institute of Technology Institute of High Performance Computing A*STAR CSIRO - Computational Informatics and Digital Productivity Flagship

Anti-parallel β-sheet crystallite as the main component of silk fibroin has attracted much attention due to its superior mechanical properties. In this study, we examine the processes of pulling a peptide chain from β-sheet crystallite using steered molecular dynamics simulations to investigate the rupture behavior of the crystallite. We show that the failure of β-sheet crystallite was accompanied by a propagation of instability of hydrogen-bonds （H-bonds） in the crystallite. In addition, we find that there is an optimum size of the crystallite at which the H-bonds can work cooperatively to achieve the highest shear strength. In addition, we find that the stiffness of loading device and the loading rates have significant effects on the rupture behavior of β-sheet crystallite. The stiff loading device facilitates the rebinding of the Hbond network in the stick-slip motion between the chains, while the soft one suppresses it. Moreover, the rupture force of β-sheet crystallites decreases with loading rate. Particularly, when the loading rate decreases to a critical value, the rupture force of the β-sheet crystallite becomes independent of the loading rates. This study provides atomistic details of rupture behaviors of β-sheet crystallite, and, therefore, sheds valuable light on the underlying mechanism of the superior mechanical properties of silk fibroin.

关键词： Silk fibroin β-Sheet crystallite - H-bondnetwork Molecular biomechanics Steered moleculardynamics

Aqueous and mechanical exfoliation, unique properties, and theoretical understanding of MoO3 nanosheets made from free-standing a-MoO3 crystals： Raman mode softening and absorption edge blue shift

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Nano Research 2018年第3期11卷 1193-1203页

作者： Hongfei Liu Yongqing Cai Mingyong Han Shifeng Guo Ming Lin Meng Zhao yongwei zhang Dongzhi Chi Institute of Materials Research and Engineering (IMRE) A＊STAR (Agency for Science Technology and Research) 2 Eusionopolis Way Singapore 138634 Singapore Institute of High Performance Computing (IHPC) A ＊STAR (Agency for Science Technology and Research) 1 Fusionopolis Way Singapore 138632 Singapore

Crystalline α-MoO3 belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO3 powders at elevated temperatures. The MoO3 belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional （2D） nanosheets were processed via the scotch-tape and bovine serum albumin （BSA） assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO3 exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo-O-Mo stretching mode （Ag） at - 818 cm^-1, which was accompanied by mode-softening of up to 5 cm^-1 This mode softening, hitherto not reported for 2D α-MoO3 nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO3 nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO3 crystals, illuminate the possibility of further 2D α-MoO3 nanosheet production and lattice dynamic studies.

关键词： α-MoO3 two-dimensionalmaterials exfoliations lattice vibrationaldynamics micro-Raman scattering

Autonomous Landing on Ground Target of UAV by Using Image-Based Visual Servo Control 36

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Autonomous Landing on Ground Target of UAV by Using Image-Ba...

Thermally Evaporated ZnSe for Efficient and Stable Regular/Inverted Perovskite Solar Cells by Enhanced Electron Extraction

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作者： yongwei zhang Yangguang Yu Shengde Jia Xiangke Wang College of Mechatronics ＆ Automation National University of Defense Technology

ISBN: (纸本)9781538629185

This paper addresses the auto landing problem of a quadrotor unmanned aerial vehicle（UAV） equipped with a single down-looking vertically camera on the ground target using image-based visual servo（IBVS） *** features on a ground guidance cooperation mark flat are exploited to recognize and obtain the center pixel position of the mark,without the position and attitude estimation process,and direct compute flight control commands based on pixel level in image by control law,which all running on an onboard *** exploited two control schemes include visual velocity landing control and VICON position landing control to compare the control *** results are provided to illustrate and assess the performance of the proposed visual control strategy.

关键词： Unmanned Aerial Vehicle(UAV) Image-Based Visual Servo(IBVS) Control Automatic Landing VICON

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Energy & Environmental Materials 2023年第5期6卷 440-448页

作者： Xin Li Guibin Shen Xin Ren Ng Zhiyong Liu Yun Meng yongwei zhang Cheng Mu Zhi Gen Yu Fen Lin Solar Energy Research Institute of Singapore(SERIS) National University of SingaporeSingapore 117574Singapore Key Laboratory of Advanced Light Conversion Materials and Biophotonics Department of ChemistryRenmin University of ChinaBeijing 100872China State Key Laboratory of Digital Manufacturing Equipment and Technology Huazhong University of Science and TechnologyWuhan 430074China School of Materials Science and Engineering Nanyang Technological UniversitySingapore 639798Singapore Shandong Provincial Engineering and Technical Center of Light Manipulation and Shandong Provincial Key Laboratory of Optics and Photonic Devices School of Physics and ElectronicsShandong Normal UniversityJinan 250014China Institute of High Performance Computing A^(*)STARSingapore 138632Singapore

Electron transport layers(ETLs)are crucial for achieving efficient and stable planar perovskite solar cells(PSCs).Reports on versatile inorganic ETLs using a simple film fabrication method and applicability for both low-cost planar regular and inverted PSCs with excellent efficiencies(>22%)and high stability are very ***,we employ a novel inorganic ZnSe as ETL for both regular and inverted PSCs to improve the efficiency and stability using a simple thermal evaporation *** TiO_(2)-ZnSe-FAPbl_(3)heterojunction could be formed,resulting in an improved charge collection and a decreased carrier recombination further proved through theoretical *** optimized regular PSCs based on TiO_(2)/ZnSe have achieved 23.25%efficiency with negligible *** addition,the ZnSe ETL can also effectively replace the unstable bathocuproine(BCP)in inverted ***,the ZnSe-based inverted device realizes a champion efficiency of 22.54%.Moreover,the regular device comprising the TiO_(2)/ZnSe layers retains 92%of its initial PCE after 10:00 h under 1 Sun continuous illumination and the inverted device comprising the C_(60)/ZnSe layers maintains over 85%of its initial PCE at 85℃for 10:00 *** highlights one of the best results among universal ETLs in both regular and inverted perovskite photovoltaics.

关键词： high efficiency long-term stability planar regular/inverted perovskite solar cells thermal evaporation ZnSe electron transport layer