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npj Computational Materials 2022年第1期8卷 446-454页

作者： Bo Xu Junkai Deng Xiangdong Ding Jun Sun jefferson zhe liu State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong University710049Xi’anChina Department of Mechanical Engineering The University of MelbourneParkvilleVIC3010Australia

Two-dimensional materials with ferroelectric properties break the size effect of conventional ferroelectric materials and unlock unprecedented potentials of ferroelectric-related application at small length *** first-principles calculations,a sliding-induced ferroelectric-to-antiferroelectric behavior in bilayer group-IV monochalcogenides(MX,with M=Ge,Sn and X=S,Se)is *** this mechanism,the top layer exhibits a reversible intralayer ferroelectric switching,leading to a reversible transition between the ferroelectric and antiferroelectric states in the bilayer *** results show that the interlayer van der Waals interaction,which is usually considered to be weak,can actually generate an in-plane lattice distortion and thus cause the breaking/forming of intralayer covalent bonds in the top layer,leading to the observed anomalous *** unique property has advantages for energy harvesting over existing piezoelectric and triboelectric *** interlayer sliding-induced big polarization change(40μC cm^(−2))and ultrahigh polarization changing rate generate an open-circuit voltage two orders of magnitude higher than that of MoS_(2)-based *** theoretical prediction of power output for this bilayer MXs at a moderate sliding speed 1 m s^(−1)is four orders of magnitude higher than the MoS_(2)nanogenerator,indicating great potentials in energy harvesting applications.

关键词： ferroelectric interlayer layer

Mechanical buckling induced periodic kinking/stripe microstructures in mechanically peeled graphite fla es from HOPG

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Acta Mechanica Sinica 2015年第4期31卷 494-499页

作者： Manrui Ren Ze liu Quan-shui zheng jefferson zhe liu Department of Engineering Mechanics and Center for Nano and Micro Mechanics Tsinghua University Department of Mechanical and Aerospace Engineering Monash University

Mechanical exfoliation is a widely used method to isolate high quality graphene layers from bulk graphite. In our recent experiments, some ordered microstructures, consisting of a periodic alternation of kinks and stripes, were observed in thin graphite flakes that were mechanically peeled from highly oriented pyrolytic graphite. In this paper, a theoretical model is presented to attribute the formation of such ordered structures to the alternation of two mechanical processes during the exfoliation：（1） peeling of a graphite flake and （2） mechanical buckling of the flake being sub- jected to bending. In this model, the width of the stripes L is determined by thickness h of the flakes, surface energy Y, and critical buckling strain ecr. Using some appropriate values of y and ecr that are within the ranges determined by other inde- pendent experiments and simulations, the predicted relations between the stripe width and the flake thickness agree reason- ably well with our experimental measurements. Conversely, measuring the L-h relations of the periodic microstructures in thin graphite flakes could help determine the critical mechan- ical buckling strain εcr and the interface energy γ.

关键词： HOPG Mechanical exfoliation Periodic microstructures Kinking Mechanical buckling

Molecular dynamics simulations of the electric double layer capacitance of graphene electrodes in mono-valent aqueous electrolytes

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Nano Research 2016年第1期9卷 174-186页

作者： Gengping Jiang Chi Cheng Dan Li jefferson zhe liu Department of Mechanical and Aerospace Engineering Monash University VIC 3800 Australia Department of Materials Science and Engineering Monash University VIC 3800 Australia Monash Center forAtomically Thin Materials Monash University VIC 3800 Australia

Electrical double layer （EDL） capacitors based on recently emergent graphene materials have shown several folds performance improvement compared to conventional porous carbon materials, driving a wave of technology breakthrough in portable and renewable energy storage. Accordingly, much interest has been generated to pursue a comprehensive understanding of the fundamental yet elusive double layer structure at file electrode^electrolyte interface. In this paper, we carried out comprehensive molecular dynamics simulations to obtain a com- prehensive picture of how ion type, solvent properties, and charging conditions affect the EDL structure at the graphene electrode surface, and thereby its contribution to capacitance. We show that different symmetrical monovalent aqueous electrolytes M^X- （M~ = Na~, K~, Rb＋, and Cs＋; X- = F-, CI-, and I ） indeed have distinctive EDL structures. Larger ions, such as, Rb＊, Cs＊, C1, and I, undergo partial dehydration and penetrate through the first water layer next to the graphene electrode surfaces under charging. As such, the electrical potential distribution through the EDL strongly depends on the ion type. Interestingly, we further reveal that the water can play a critical role in determining the capacitance value. The change of dielectric constant of water in different electrolytes largely cancels out the variance in electric potential drop across the EDL of different ion type. Our simulation sheds new lights on how the interplay between solvent molecules and EDL structure cooperatively contributes to capacitance, which agrees with our experimental results well.

关键词： graphene supercapacitor molecular dynamicssimulations electric double layerstructures aqueous electrolyte monovalent ions

Control of surface wettability via strain engineering

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Acta Mechanica Sinica 2013年第4期29卷 543-549页

作者： Wei Xiong jefferson zhe liu Zhi-Liang Zhang Quan-Shui zheng Department of Engineering Mechanics and Center for Nano and Micro Mechanics Tsinghua University Department of Mechanical and Aerospace Engineering Monash University Department of Structural Engineering Norwegian University of Science and Technology (NTNU)

Reversible control of surface wettability has wide applications in lab-on-chip systems, tunable optical lenses, and microfluidic tools. Using a graphene sheet as a sam- ple material and molecular dynamic simulations, we demon- strate that strain engineering can serve as an effective way to control the surface wettability. The contact angles 0 of water droplets on a graphene vary from 72.5° to 106° under biaxial strains ranging from -10% to 10% that are applied on the graphene layer. For an intrinsic hydrophilic surface （at zero strain）, the variation of 0 upon the applied strains is more sensitive, i.e., from 0° to 74.8°. Overall the cosines of the contact angles exhibit a linear relation with respect to the strains. In light of the inherent dependence of the contact an- gle on liquid-solid interfacial energy, we develop an analytic model to show the cos 0 as a linear function of the adsorption energy Eads of a single water molecule over the substrate sur- face. This model agrees with our molecular dynamic results very well. Together with the linear dependence of Eads on bi- axial strains, we can thus understand the effect of strains on the surface wettability. Thanks to the ease of reversibly ap- plying mechanical strains in micro/nano-electromechanical systems, we believe that strain engineering can be a promis- ing means to achieve the reversibly control of surface wetta- bility.

关键词： Wettability ~ Strain engineering ~ Molecular dy-namics simulation

Effects of vacancies on interwall spacings of multi-walled carbon nanotubes

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Journal of zhejiang University-Science A(Applied Physics & Engineering) 2010年第10期11卷 714-721页

作者： Ming-du MA jefferson zhe liu Li-feng WANG Lu-ming SHEN Quan-shui zheNG Department of Engineering Mechanics Tsinghua University Beijing 100084 China Department of Mechanical and Aerospace Engineering Monash University Clayton Victoria 3168 Australia Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA School of Civil Engineering University of Sydney NSW 2006 Australia

We use molecular dynamics (MD) simulations to study the effects of vacancies on tube diameters and interwall spacings of multi-walled carbon nanotubes (MWCNTs). Two types of vacancies, double vacancy and three dangling-bond (3DB) single vacancy, are identified to have opposite effects on the tube size change, which explains the inconsistency of the experimentally measured interwall spacings of MWCNTs after electron beam irradiation. A theoretical model to quantitatively predict the shrunk structures of the irradiated MWCNTs is further developed. We also discuss the fabrications of prestressed MWCNTs, in which reduced interwall spacings are desired to enhance the overall elastic modulus and strength.

关键词：多壁碳纳米管间距作者分子动力学电子束照射尺寸变化实验测量定量预测

Hyperspectral image super resolution using deep internal and self-supervised learning

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CAAI Transactions on Intelligence Technology 2024年第1期9卷 128-141页

作者： zhe liu Xian-Hua Han Graduate School of Science and Technology for Innovation Yamaguchi UniversityYamaguchiJapan Graduate School of Artificial Intelligence and Science Rikkyo UniversityTokyoJapan

By automatically learning the priors embedded in images with powerful modelling ca-pabilities,deep learning-based algorithms have recently made considerable progress in reconstructing the high-resolution hyperspectral(HR-HS)*** previously collected large-amount of external data,these methods are intuitively realised under the full supervision of the ground-truth ***,the database construction in merging the low-resolution(LR)HS(LR-HS)and HR multispectral(MS)or RGB image research paradigm,commonly named as HSI SR,requires collecting corresponding training triplets:HR-MS(RGB),LR-HS and HR-HS image simultaneously,and often faces dif-ficulties in *** learned models with the training datasets collected simultaneously under controlled conditions may significantly degrade the HSI super-resolved perfor-mance to the real images captured under diverse *** handle the above-mentioned limitations,the authors propose to leverage the deep internal and self-supervised learning to solve the HSI SR *** authors advocate that it is possible to train a specific CNN model at test time,called as deep internal learning(DIL),by on-line preparing the training triplet samples from the observed LR-HS/HR-MS(or RGB)images and the down-sampled LR-HS ***,the number of the training triplets extracted solely from the transformed data of the observation itself is extremely few particularly for the HSI SR tasks with large spatial upscale factors,which would result in limited reconstruction *** solve this problem,the authors further exploit deep self-supervised learning(DSL)by considering the observations as the unlabelled training ***,the degradation modules inside the network were elaborated to realise the spatial and spectral down-sampling procedures for transforming the generated HR-HS estimation to the high-resolution RGB/LR-HS approximation,and then the reconstruction errors of the observations were formulated for mea

关键词： computer vision deep learning deep neural networks hyperspectral image enhancement

Influences of Graupel Microphysics on CMA-GFS Simulation of Summer Regional Precipitation

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Journal of Meteorological Research 2024年第1期38卷 27-38页

作者： zhe LI Qijun liu Zhanshan MA CMA Earth System Modeling and Prediction Centre China Meteorological Administration(CMA)Beijing 100081

The horizontal resolution of global numerical weather prediction models is continuously developing. However, due to the imperfect precipitation simulation/forecast of these models, the demand for considering riming particles in cloud microphysical schemes in these models is increasing. This study employed the latest versions of global atmospheric reanalysis data (ERA5), the satellite retrieval data of the Global Precipitation Observation Program (GPM),and station precipitation observations to explore the impacts of adding graupel to the cloud microphysical scheme in the China Meteorological Administration-Global Forecast System (CMA-GFS) on summer regional precipitation simulations in four Chinese climate zones. The results verify that the new graupel scheme can enable CMA-GFS to decently predict global graupel distribution, especially in tropical and midlatitude regions. The addition of graupel in the cloud microphysics increases the precipitation simulation in North China, while that in Southwest China is weakened and dispersed. Moreover, graupel scheme increases the precipitation simulations of almost all *** increase in light rain is obvious, and the absolute value of heavy rain is strengthened. This may be because graupel quickly melts into rain after falling out of the zero-temperature layer due to its large mass and fast falling speed, increasing surface precipitation. In summary, the addition of graupel in the cloud microphysical scheme can improve CMA-GFS’s underestimation of strong precipitation.

关键词： graupel cloud microphysical scheme precipitation China Meteorological Administration-Global Forecast System(CMA-GFS) climate zone

Full lifetime demonstration of a Micro-Cathode-Arc thruster evolution characteristics

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Chinese Journal of Aeronautics 2024年第6期37卷 38-49页

作者： zhe ZHANG Zijing ZHAO Xiangyang liu Ningfei WANG School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

Ground lifetime test is the most crucial experiment to assess the performance,*** flight qualification of electric propulsion,and it can bring new insights for understanding the operation *** work demonstrates a full lifetime test of 140000 cycles on a Micro-Cathode-Arc Thruster(μCAT)with 160μs charging time and 86 mJ charging energy.A four-probe resistivity measurement method is utilized to investigate variations in the conductive film thickness and resistivity throughout the thruster *** film parameters show that the lifetime of theμCAT can be divided into three *** the initial stage,the film thickness decreases by 1.2μm and the resistivity increases significantly due to the high discharge intensity and intense film ablation;In the steady stage,the change of the film thickness is within 5%,and the resistivity of the film increases slowly from 0.050Ω·mm to 0.223Ω·*** the end stage,the resistivity exponentially increases from 0.223Ω·mm to 1.176Ω·mm,with the increase accounting for 81%,ultimately resulting in the failure of the thruster open ***,the evolution of discharge parameters,and the variation of plume parameters are measured throughout the *** discharge characteristics also show significant differences in the duration of voltage and current in these three *** results of plume shape and plasma parameters are also well con-sistent with the discharge parameters and film *** results suggest that,for evaluating the steady stage lifetime of thrusters,the film thickness is the best indicator compared to the variations in resistivity and voltage-current *** the end stage,the plasma plume *** duration,and plume parameters can conveniently and clearly characterize the thruster failures and irregularity.

关键词： Electric propulsion Lifetime test Micro-Cathode-Arc Thruster(uCAT) Conductive film Discharge characteristics Plasma parameters

Homological dimensions of gentle algebras via geometric models

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Science China Mathematics 2024年第4期67卷 733-766页

作者： Yu-zhe liu Hanpeng Gao Zhaoyong Huang Department of Mathematics Nanjing UniversityNanjing 210093China School of Mathematical Sciences Anhui UniversityHefei 230601China

Let A=kQ/I be a finite-dimensional basic algebra over an algebraically closed field k,which is a gentle algebra with the marked ribbon surface(SA,MA,ΓA).It is known that SAcan be divided into some elementary polygons{Δi|1≤i≤d}byΓA,which has exactly one side in the boundary of ***■(Δi)be the number of sides ofΔibelonging toΓAif the unmarked boundary component of SAis not a side ofΔi;otherwise,■(Δi)=∞,and let f-Δbe the set of all the non-co-elementary polygons and FA(resp.f-FA)be the set of all the forbidden threads(*** finite length).Then we have(1)the global dimension of A is max1≤i≤d■(Δi)-1=maxΠ∈FAl(Π),where l(Π)is the length ofΠ;(2)the left and right self-injective dimensions of A are 0,if Q is either a point or an oriented cycle with full ***Δi∈f-Δ{1,■(Δi)-1}=max n∈f-F_(A)l(П),otherwise,As a consequence,we get that the finiteness of the global dimension of gentle algebras is invariant under AvellaGeiss(AG)-*** addition,we get that the number of indecomposable non-projective Gorenstein projective modules over gentle algebras is also invariant under AG-equivalence.

关键词： global dimension self-injective dimension gentle algebras marked ribbon surfaces geometric models AG-equivalence

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Development *** in limited urban sprawl:An integrated framework for resolving the urban boundary dilemma in China

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Journal of Geographical Sciences 2024年第7期34卷 1371-1393页

作者： SONG Xiangxiang ZHANG Zuo WANG zhe liu Yanzhong School of Public Administration Central China Normal UniversityWuhan430079China College of Resource and Environmental Engineering Wuhan University of Science and TechnologyWuhan430081China

The strategic delineation of the urban development boundary(UDB)is an effective initiative for efficient land resource allocation and for facilitating planned urban *** align with sustainable development objectives,UDB definitions have evolved to reconcile urban development with ecological *** study presents a UDB delineation framework from an integrated perspective that incorporates both demand-oriented and comprehensive ***,the urban construction land demand area was estimated based on population projections,meanwhile,the ecological red line(ERL)was delineated and integrated into the evaluation of the construction land ***,with the demand area as the simulation target and unsuitable areas as comprehensive constraints,the UDB was delineated by simulating future land use *** proposed framework was applied to Wuhan,a rapidly urbanizing city in central China,where the delineation of the UDB serves the dual purpose of managing the rapid expansion of built-up land and achieving a harmonious balance between urban development imperatives and ecological protection ***,based on the results and analysis,policy implications for the rational spatial planning of Wuhan were proposed,encompassing the spatial patterns and scientific decision-making in ecological conservation and urban *** results demonstrate that the efficacy of adopting a comprehensive perspective in delineating UDB effectively reconciles the competing needs of urban development and *** framework and the policy insights derived in this study could inform spatial planning efforts not only in Wuhan but also in other cities facing the dilemma of urban development and ecological protection.

关键词： urban development boundary(UDB) ecological red line(ERL) urban land suitability land use simulation integrated framework spatial decision-making