检索结果-内蒙古大学图书馆

arXiv 2019年

作者： Zhang, Long Zhang, Zhe Wu, Fengcheng Wang, Danqing Gogna, Rahul Hou, Shaocong Watanabe, Kenji Taniguchi, Takashi Kulkarni, Krishnamurthy Kuo, Thomas Forrest, Stephen R. Deng, Hui Physics Department University of Michigan 450 Church Street Ann ArborMI48109-2122 United States State Key Laboratory of Surface Physics Department of Physics Fudan University Shanghai200433 China Condensed Matter Theory Center Joint Quantum Institute Department of Physics University of Maryland College ParkMD20742 United States Applied Physics Program University of Michigan 450 Church Street Ann ArborMI48109-1040 United States Department of Electrical Engineering and Computer Science University of Michigan 450 Church Street Ann ArborMI48109-1040 United States National Institute for Materials Science Tsukuba Japan

Moiré superlattices formed in van der Waals bilayers have enabled the creation and manipulation of new quantum states, as is exemplified by the discovery of superconducting and correlated insulating states in twisted bilayer graphene near the magic angle. Twisted bilayer semiconductors may lead to tunable exciton lattices and topological states, yet signatures of moiré excitons have been reported only in closely angularly-aligned bilayers. Here we report tuning of moiré lattice in WS2 /MoSe2 bilayers over a wide range of twist angles, leading to the continuous tuning of moiré - lattice induced interlayer excitons and their hybridization with optically bright intralayer excitons. A pronounced revival of the hybrid excitons takes place near commensurate twist angles, 21.8◦ and 38.2◦, due to interlayer tunneling between states connected by a moiré reciprocal lattice vector. From the angle dependence, we obtain the effective mass of the interlayer excitons and the electron inter-layer tunneling strength. These findings pave the way for understanding and engineering rich moiré -lattice induced phenomena in angle-twisted semiconductor van dar Waals heterostructures. Copyright © 2019, The Authors. All rights reserved.

关键词： Excitons

来源：评论

学校读者我要写书评

暂无评论

Observation of Anisotropic Charge Density Wave in Layered 1T-TiSe2

引用

Microscopy and Microanalysis 2018年第S1期24卷 230-231页

作者： Qiao, Qiao Zhou, Songsong Tao, Jing Zheng, Jin-Cheng Wu, Lijun Ciocys, Samuel T Iavarone, Maria Srolovitz, David J Karapetrov, Goran Zhu, Yimei Department of Physics Temple University Philadelphia Pennsylvania 19122 USA Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA Department of Materials Science and Engineering University of Pennsylvania Philadelphia Pennsylvania 19104 USA Department of Physics and Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices Xiamen University Xiamen Fujian 361005 China Department of Physics Drexel University Philadelphia Pennsylvania 19104 USA Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania Philadelphia Pennsylvania 19104 USA

来源：评论

学校读者我要写书评

暂无评论

Stress anisotropy in shear-jammed packings of frictionless disks

引用

Physical Review E 2018年第4期98卷 042906-042906页

作者： Sheng Chen Thibault Bertrand Weiwei Jin Mark D. Shattuck Corey S. O'Hern Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power Engineering Tsinghua University Beijing 100084 China Department of Mechanical Engineering & Materials Science Yale University New Haven Connecticut 06520 USA Laboratoire Jean Perrin UMR 8237 CNRS Sorbonne Université 75005 Paris France Department of Mechanics and Engineering Science Peking University Beijing 100871 China Benjamin Levich Institute and Physics Department The City College of the City University of New York New York New York 10031 USA Department of Physics Yale University New Haven Connecticut 06520 USA Department of Applied Physics Yale University New Haven Connecticut 06520 USA

We perform computational studies of repulsive, frictionless disks to investigate the development of stress anisotropy in mechanically stable (MS) packings at jamming onset. We focus on two protocols for generating MS packings at jamming onset: (1) isotropic compression and (2) applied simple or pure shear strain γ at fixed packing fraction ϕ. MS packings of frictionless disks occur as geometric families (i.e., quasiparabolic segments with positive curvature) in the ϕ−γ plane. MS packings from protocol 1 populate parabolic segments with both signs of the slope, dϕ/dγ>0 and dϕ/dγ<0. In contrast, MS packings from protocol 2 populate segments with dϕ/dγ<0 only. For both simple and pure shear, we derive a relationship between the stress anisotropy and local dilatancy dϕ/dγ obeyed by MS packings along geometrical families. We show that for MS packings prepared using isotropic compression, the stress anisotropy distribution is Gaussian centered at zero with a standard deviation that decreases with increasing system size. For shear jammed MS packings, the stress anisotropy distribution is a convolution of Weibull distributions that depend on strain, which has a nonzero average and standard deviation in the large-system limit. We also develop a framework to calculate the stress anisotropy distribution for packings generated via protocol 2 in terms of the stress anisotropy distribution for packings generated via protocol 1.

关键词： Granular packing Jamming Packing & jamming problems

来源：评论

学校读者我要写书评

暂无评论

Model reduction with memory and the machine learning of dynamical systems

arXiv

引用

arXiv 2018年

作者： Ma, Chao Wang, Jianchun Weinan, E. Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States Department of Mechanics and Aerospace Engineering Southern University of Science and Technology Shenzhen518055 China Beijing Institute of Big Data Research Beijing100871 China

The well-known Mori-Zwanzig theory tells us that model reduction leads to memory effect. For a long time, modeling the memory effect accurately and efficiently has been an important but nearly impossible task in developing a good reduced model. In this work, we explore a natural analogy between recurrent neural networks and the Mori-Zwanzig formalism to establish a systematic approach for developing reduced models with memory. Two training models-a direct training model and a dynamically coupled training model-are proposed and compared. We apply these methods to the Kuramoto-Sivashinsky equation and the Navier-Stokes equation. Numerical experiments show that the proposed method can produce reduced model with good performance on both short-term prediction and long-term statistical properties. Copyright © 2018, The Authors. All rights reserved.

关键词： Recurrent neural networks

来源：评论

学校读者我要写书评

暂无评论

Experiments and simulations of the humidity dependence of friction between nanoasperities and graphite: The role of interfacial contact quality

引用

Physical Review materials 2018年第12期2卷 126001-126001页

作者： Kathryn Hasz Zhijiang Ye Ashlie Martini Robert W. Carpick Department of Materials Science and Engineering University of Pennsylvania 3231 Walnut Street Philadelphia Pennsylvania 19104 USA Department of Mechanical and Manufacturing Engineering Miami University 650 E. High Street Oxford Ohio 45056 USA Department of Mechanical Engineering University of California Merced 5200 North Lake Road Merced California 95343 USA Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania 220 S. 33rd Street Philadelphia Pennsylvania 19104 USA

We use atomic force microscopy and grand canonical Monte Carlo simulations to study stick-slip friction of tetrahedral amorphous carbon probes sliding against highly oriented pyrolytic graphite (HOPG) at relative humidities ranging from <1% to near saturation. Friction varies with humidity in a nonmonotonic manner such that water acts as a lubricant only above a threshold humidity; below that threshold, water increases friction substantially relative to dry sliding. Adhesion forces also show a similar nonmonotonic behavior. A nonmonotonic dependence of friction and adhesion on humidity for single-asperity interfaces has previously been attributed to the humidity-dependent adhesion force due to the water meniscus that forms at the contact, which is presumed to increase the solid-solid contact area. However, our simulations show no such increase in solid-solid contact area, but do show a small, continuous increase in tip-sample separation as humidity increases. Experimentally, no significant change in lateral stiffness is observed with humidity. All of this contradicts the hypothesis that the friction increase is due solely to capillary adhesion increasing the contact area. We show that water molecules are present between the tip and sample in increasing numbers as the humidity increases. From this, we attribute the nonmonotonic friction trend to the changing quality of the contact between the water and the substrate, quantified by the number of water molecules in the interface and their registry with the HOPG surface atoms, which in simulations also shows a nonmonotonic trend with humidity. Hysteresis observed in the variation of friction with humidity in both experiments and simulations is explained by the larger energy barrier for surface desorption of water molecules compared to adsorption.

关键词： Friction Tribology Graphite Water

来源：评论

学校读者我要写书评

暂无评论

Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes

引用

Nature 2018年第7732期563卷 546-550页

作者： Zhifeng Lei Xiongjun Liu Yuan Wu Hui Wang Suihe Jiang Shudao Wang Xidong Hui Yidong Wu Baptiste Gault Paraskevas Kontis Dierk Raabe Lin Gu Qinghua Zhang Houwen Chen Hongtao Wang Jiabin Liu Ke An Qiaoshi Zeng Tai-Gang Nieh Zhaoping Lu Beijing Advanced Innovation Center for Materials Genome Engineering State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing China. Department of Microstructure Physics and Alloy Design Max-Planck-Institut für Eisenforschung Düsseldorf Germany. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing China. College of Materials Science and Engineering Chongqing University Chongqing China. Institute of Applied Mechanics Zhejiang University Hangzhou China. School of Materials Science and Engineering Zhejiang University Hangzhou China. Spallation Neutron Source Oak Ridge National Laboratory Oak Ridge TN USA. Center for High Pressure Science and Technology Advanced Research Pudong Shanghai China. Department of Materials Science and Engineering University of Tennessee Oak Ridge TN USA. Beijing Advanced Innovation Center for Materials Genome Engineering State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing China. luzp@***.

Oxygen, one of the most abundant elements on Earth, often forms an undesired interstitial impurity or ceramic phase (such as an oxide particle) in metallic materials. Even when it adds strength, oxygen doping renders metals brittle. Here we show that oxygen can take the form of ordered oxygen complexes, a state in between oxide particles and frequently occurring random interstitials. Unlike traditional interstitial strengthening, such ordered interstitial complexes lead to unprecedented enhancement in both strength and ductility in compositionally complex solid solutions, the so-called high-entropy alloys (HEAs). The tensile strength is enhanced (by 48.5 ± 1.8 per cent) and ductility is substantially improved (by 95.2 ± 8.1 per cent) when doping a model TiZrHfNb HEA with 2.0 atomic per cent oxygen, thus breaking the long-standing strength-ductility trade-off. The oxygen complexes are ordered nanoscale regions within the HEA characterized by (O, Zr, Ti)-rich atomic complexes whose formation is promoted by the existence of chemical short-range ordering among some of the substitutional matrix elements in the HEAs. Carbon has been reported to improve strength and ductility simultaneously in face-centred cubic HEAs, by lowering the stacking fault energy and increasing the lattice friction stress. By contrast, the ordered interstitial complexes described here change the dislocation shear mode from planar slip to wavy slip, and promote double cross-slip and thus dislocation multiplication through the formation of Frank-Read sources (a mechanism explaining the generation of multiple dislocations) during deformation. This ordered interstitial complex-mediated strain-hardening mechanism should be particularly useful in Ti-, Zr- and Hf-containing alloys, in which interstitial elements are highly undesirable owing to their embrittlement effects, and in alloys where tuning the stacking fault energy and exploiting athermal transformations do not lead to property enhancement. Thes

关键词： High-entropy Alloys (HEA) Interstitial Strengthening Wavy Slip Chemical Short-range Order Double Cross Slip

来源：评论

学校读者我要写书评

暂无评论

Processing-dependent thermal stability of a prototypical amorphous metal oxide

引用

Physical Review materials 2018年第5期2卷 053401-053401页

作者： Li Zeng Mahyar M. Moghadam D. Bruce Buchholz Ran Li Denis T. Keane Vinayak P. Dravid Robert P. H. Chang Peter W. Voorhees Tobin J. Marks Michael J. Bedzyk Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA Department of Materials Science and Engineering Northwestern University Evanston Illinois 60208 USA Northwestern Synchrotron Research Center Argonne Illinois 60439 USA Department of Chemistry Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA

Amorphous metal oxides (AMOs) are important candidate materials for fabricating next-generation thin-film transistors. While much attention has been directed toward the synthesis and electrical properties of AMOs, less is known about growth conditions that allow AMOs to retain their desirable amorphous state when subjected to high operating temperatures. Using in situ x-ray scattering and level-set simulations, we explore the time evolution of the crystallization process for a set of amorphous In2O3 thin films synthesized by pulsed-laser deposition at deposition temperatures (Td) of −50, −25, and 0 °C. The films were annealed isothermally and the degree of crystallinity was determined by a quantitative analysis of the time-evolved x-ray scattering patterns. As expected, for films grown at the same Td, an increase in the annealing temperature TA led to a shorter delay prior to the onset of crystallization, and a faster crystallization rate. Moreover, when lowering the deposition temperature by 25 °C, a 40 °C increase in annealing temperature is needed to achieve the same time interval for the crystals to grow from 10 to 90% volume fraction of the sample. Films grown at Td=0∘C exhibited strong cubic texture after crystallization. A level-set method was employed to quantitatively model the texture that develops in the microstructures and to determine key parameters, such as the interface growth velocity, the nucleation density, and the activation energy. The differences observed in the crystallization processes are attributed to the changes in the atomic structure of the oxide and possible nanocrystalline inclusions that formed during the deposition of the amorphous phase.

关键词： Annealing Crystallization Electron diffraction Laser ablation Numerical techniques X-ray diffraction

来源：评论

学校读者我要写书评

暂无评论

A new local approach to cleavage fracture and its application in a reactor pressure vessel

引用

Procedia Structural Integrity 2018年 13卷 2174-2179页

作者： Guian Qian Wei-Sheng Lei Shunpeng Zhu José Correia Abílio De Jesus State Key Laboratory for Nonlinear Mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China. Applied Materials Inc. 974 East Arques Avenue Sunnyvale CA 94085 USA School of Mechanical and Electrical Engineering University of Electronic Science and Technology of China Chengdu 611731 China Department of Mechanical Engineering Politecnico di Milano Milan 20156 Italy INEGI Faculty of Engineering University of Porto Porto 4200-465 Portugal

The paper presents and applies a local approach to correlate the fracture behavior of a notched and fracture mechanics specimen. The random nature of cleavage fracture process determines that both the microscopic fracture stress and the macroscopic properties including fracture load, fracture toughness and the ductile to brittle transition temperature are all stochastic parameters. This understanding leads to the proposal of statistical assessment of cleavage induced notch toughness of ferritic steels according to a new local approach to cleavage fracture. The temperature independence of the two Weibull parameters in the new model induces a master curve to correlate the fracture load at different temperatures. This proposed index is applied to compare the notch toughness of a ferritic steel with two different microstructures.

关键词： Ferritic steels cleavage fracture notch brittleness statistical model；

来源：评论

学校读者我要写书评

暂无评论

A Brief Review of High Entropy Alloys and Serration Behavior and Flow Units

引用

Journal of Iron and Steel Research International 2016年第1期23卷 2-6页

作者： Yong ZHANG Jun-wei QIAO Peter K.LIAW State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Laboratory of Applied Physics and Mechanics of Advanced Materials College of Materials Science and EngineeringTaiyuan University of Technology Department of Materials Science and Engineering University of Tennessee

Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys（HEAs）and/or multiprincipal-element alloys（MEAs）,are attracting increasing attentions,because the materials with novel properties are being developed,based on the design strategy of the equiatomic ratio,multicomponent,and high entropy of mixing in their liquid or random solution ***,HEAs with the ultrahigh strength and fracture toughness,excellent magnetic properties,high fatigue,wear and corrosion resistance,great phase stability/high resistance to heat-softening behavior,sluggish diffusion effects,and potential superconductivity,etc.,were *** HEAs can even have very high irradiation resistance and may have some self-healing effects,and can potentially be used as the first wall and nuclear fuel cladding *** behaviors and flow units are powerful methods to understand the plastic deformation or fracture of *** methods have been successfully used to study the plasticity of amorphous alloys（also bulk metallic glasses,BMGs）.The flow units are proposed as：free volumes,shear transition zones（STZs）,tension-transition zones（TTZs）,liquid-like regions,soft regions or soft spots,*** flow units in the crystalline alloys are usually dislocations,which may interact with the solute atoms,interstitial types,or substitution ***,the flow units often change with the testing temperatures and loading strain rates,e.g.,at the low temperature and high strain rate,plastic deformation will be carried out by the flow unit of twinning,and at high temperatures,the grain boundary will be the weak area,and play as the flow *** serration shapes are related to the types of flow units,and the serration behavior can be analyzed using the power law and modified power law.

关键词： high entropy alloy bulk metallic glass serration behavior flow unit

来源：评论

学校读者我要写书评

暂无评论

4D Electronic Systems: Transformable, Freestanding 3D Mesostructures Based on Transient materials and Mechanical Interlocking (Adv. Funct. Mater. 40/2019)

引用

Advanced Functional materials 2019年第40期29卷

作者： Yoonseok Park Haiwen Luan Kyeongha Kwon Shiwei Zhao Daniel Franklin Heling Wang Hangbo Zhao Wubin Bai Jong Uk Kim Wei Lu Jae‐Hwan Kim Yonggang Huang Yihui Zhang John A. Rogers Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA Department of Mechanical Engineering Department of Civil and Environmental Engineering Department of Materials Science and Engineering Northwestern University Evanston IL 60208 USA School of Aeronautic Science and Engineering Beihang University Beijing 100191 P. R. China School of Chemical Engineering Sungkyunkwan University (SKKU) Suwon 16419 Republic of Korea Frederick Seitz Materials Research Laboratory Department of Materials Science and Engineering University of Illinois at Urbana–Champaign Urbana IL 61801 USA Center for Bio‐Integrated Electronics Department of Mechanical Engineering Department of Civil and Environmental Engineering Department of Materials Science and Engineering Northwestern University Evanston IL 60208 USA Center for Flexible Electronics Technology Applied Mechanics Laboratory Department of Engineering Mechanics Tsinghua University Beijing 100084 P. R. China Department of Materials Science and Engineering Biomedical Engineering Neurological Surgery Chemistry Mechanical Engineering Electrical Engineering and Computer Science Simpson Querrey Institute and Feinberg Medical School Center for Bio‐Integrated Electronics Northwestern University Evanston Evanston IL 60208 USA

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：