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PT-symmetry-protected Dirac states in strain-induced hidden MoS2 monolayer

Physical Review B 2019年第23期100卷 235435-235435页

作者： Meiling Xu Guohui Zhan Siyu Liu Dongqin Zhang Xin Zhong Ziyang Qu Yinwei Li Aijun Du Haijun Zhang Yanchao Wang Laboratory of Quantum Materials Design and Application School of Physics and Electronic Engineering Jiangsu Normal University Xuzhou 221116 China State Key Laboratory of Superhard Materials & Innovation Center for Computational Physics Methods and Software College of Physics Jilin University Changchun 130012 China National Laboratory of Solid State Microstructures School of Physics Nanjing University Nanjing 210093 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China Department of Physics China Jiliang University Hangzhou Zhejiang 310018 People's Republic of China Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education Jilin Normal University Changchun 130103 China School of Chemistry Physics and Mechanical Engineering Queensland University of Technology Gardens Point Campus Brisbane QLD 4001 Australia

Two-dimensional (2D) materials have recently attracted significant interest in condensed-matter physics and materials science due to rich intriguing physics and potential applications. Here, by first-principles calculations, we discover a phase of transition-metal dichalcogenides (MoS2 and its family) named the 1H′ phase. We demonstrate that 1H′MoS2 monolayer has multiple topological phase transitions from a topologically trivial insulator state to a 2D type-II Dirac semimetal state, and then to a 2D ideal type-I semimetal state under a moderate tensile strain. The Dirac points are protected by the coexistence of space-inversion (P) and time-reversal (T) symmetry. Our results highlight a family of nonhoneycomb 2D Dirac semimetals with potential application in nanoelectronics.

关键词： Edge states First-principles calculations Topological materials

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Experimental investigation of multiplicity correlation between prompt neutrons and photons in the spontaneous fission of 252Cf

arXiv

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arXiv 2019年

作者： Marin, Stefano Protopopescu, Vladimir A. Vogt, Ramona Marcath, Matthew J. Hua, Michael Y. Talou, Patrick Schuster, Patricia F. Clarke, Shaun D. Pozzi, Sara A. Department of Nuclear Engineering and Radiological Sciences University of Michigan Ann ArborMI48109 United States Oak Ridge National Laboratory Oak RidgeTN United States Physics Division Lawrence Livermore National Laboratory LivermoreCA United States Physics Department University of California DavisCA United States Monte Carlo Methods Codes and Applications Group Los Alamos National Laboratory Los AlamosNM87545 United States XCP-5 Computational Physics Division Los Alamos National Laboratory Los AlamosNM87545 United States

Excited nuclear fragments are emitted during nuclear fission. The de-excitation of fission fragments takes place as sequential emission of neutrons followed by photons. Particle emission dissipates the intrinsic and rotational excitation energies of the fragment until a long-lived state is reached. Both the number of neutrons and the number of photons emitted during de-excitation are dependent on the initial excitation energy, angular momentum, and parity of the radiating fission fragment. A correlation between neutron and photon multiplicities following fission is thus expected. We perform linear regression analysis of the data collected by the Chi-Nu array at the LANSCE facility in Los Alamos National laboratory. We have developed analytic expressions to determine the bias introduced by background sources and the misclassification of particles by our pulse shape discrimination capable organic scintillation detectors. Additionally, we have developed perturbative techniques to derive corrections to the binomial-response model. We use the perturbative techniques to correct the experimentally-determined neutron-photon correlations for the effects of photon-neutron pileup. We have experimentally determined an event-by-event covariance, cov(Nn, Nγ), of −0.33 ± 0.05 between the neutron and photon multiplicities emitted following the spontaneous fission of 252Cf. The result suggests the existence of a small event-by-event competition of neutron and photon emission in fission. We compare our result with previous analyses and model calculations. Copyright © 2019, The Authors. All rights reserved.

关键词： Neutrons

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High-pressure modulated structures in beryllium chalcogenides

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Physical Review B 2019年第1期100卷 014102-014102页

作者： Xiaolei Feng Pengyue Gao Xue Li Min Wu Hui Wang Jian Lv Simon A. T. Redfern Hanyu Liu Yanming Ma Innovation Center of Computational Physics Methods and Software & State Key Laboratory for Superhard Materials College of Physics Jilin University Changchun 130012 China Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai 201203 China Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ United Kingdom College of Materials sciences and Engineering Zhejiang University of Technology 310014 China Asian School of the Environment Nanyang Technological University Singapore 639798 International Center of Future Science Jilin University Changchun 130012 China

Structure searches of beryllium chalcogenides (BeS, BeSe, and BeTe) at high pressures using a swarm intelligence algorithm, in conjunction with density functional theory, reveal modulated polymorphs, unusual for such simple binary compounds. Apart from the well-known cubic (space group F4¯3m, zinc-blende structure) to hexagonal closed-packed (space group P63/mmc, nickel-arsenide structure) structural transition, a further transition at higher pressure to an orthorhombic structure is predicted for BeS and BeSe. The orthorhombic phase is space group Cmca in BeS and Pnma before finally adopting Cmca in BeSe, each accompanied by the onset of modulation of the atomic arrangement. The amplitude of displacements associated with the modulation increases with increasing pressure and molecular dynamics simulations show the modulated structure to become stable at least to 300 GPa and 2000 K. This unusual structural modulation is not seen, however, in BeTe, which instead transforms to a C2/m phase. Links are drawn between the modulated phases of BeS and BeSe and the high-pressure modulated phases of their parent chalcogens. Our results provide key insights into understanding the modulation in binary compounds at high pressure.

关键词： Chemical bonding Crystal structure Electronic structure Phase transitions Pressure effects Structural properties Chalcogenides Density functional calculations High-throughput calculations

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Use of a full-motion flight simulator for teaching aircraft performance and dynamics 55

Use of a full-motion flight simulator for teaching aircraft ...

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55th AIAA Aerospace Sciences Meeting

作者： Dannenhoffer, John F. Green, Melissa A. Aerospace Computational Methods Laboratory Mechanical and Aerospace Engineering Syracuse University SyracuseNY13244 United States Green Fluids Laboratory Mechanical and Aerospace Engineering Syracuse University SyracuseNY13244 United States

ISBN: (数字)9781624104473

ISBN: (纸本)9781624104473

In the teaching of aircraft performance and dynamics, one often resorts to the use of empirical data that is \obtained from flight test data". The method by which this data is obtained is often not described well (if at all) to the students. In addition, many students of aerospace engineering have never been in the cockpit of an aircraft and are unaware of the fundamental operation of an aircraft. To fill this gap, some universities have at their disposal a real aircraft in which students can y to get first-hand experience at flying. For these students, this is a unique opportunity, but there is some inherent risk involved. Syracuse University is in possession of a 6-DOF full-motion-base flight simulator. For the past six years, this flight simulator has been integrated into the Aircraft Performance and Dynamics course, which is typically taken in the fall semester of the student's senior year. The way in which this flight simulator is used in the Aircraft Performance and Dynamics course is described, together with a review of the impact of the flight simulator on several of the ABET-related Student Outcomes. © 2017 by John F. Dannenhoffer, III. Published by the American Institute of Aeronautics and Astronautics, Inc.

关键词： Flight Instructor Aircraft Performance Flight Test Programme Cessna Code of Federal Regulations Elevator Trim Dutch Roll Six Degree of Freedom Aerospace engineering Stability Derivatives

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Corrigendum to “Hybrid Lattice Boltzmann-Finite Difference model for low Mach number combustion simulation” [Combustion and Flame 209(2019) 394-404]

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Combustion and Flame 2020年 219卷 44-44页

作者： S.A. Hosseini H. Safari N. Darabiha D. Thévenin M. Krafczyk Laboratory of Fluid Dynamics and Technical Flows University of Magdeburg “Otto von Guericke” Magdeburg D-39106 Germany Laboratoire EM2C CNRS CentraleSupélec Université Paris-Saclay 3 rue Joliot Curie Gif-sur-Yvette Cedex 91192 France International Max Planck Research School (IMPRS) for Advanced Methods in Process and Systems Engineering Magdeburg Germany Institute for Computational Modeling in Civil Engineering Technische Universität Braunschweig Germany

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Ultrahigh-pressure induced decomposition of silicon disulfide into silicon-sulfur compounds with high coordination numbers

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Physical Review B 2019年第18期99卷 184106-184106页

作者： Yuanzheng Chen Xiaolei Feng Jiao Chen Xinyong Cai Bai Sun Hongyan Wang Huarong Du Simon A. T. Redfern Yu Xie Hanyu Liu School of Physical Science and Technology Key Laboratory of Advanced Technologies of Materials Southwest Jiaotong University Chengdu 610031 China The Institute for Disaster Management and Reconstruction Sichuan University Chengdu 610207 China Center for High Pressure Science and Technology Advanced Research (HPSTAR) Beijing 100094 China Department of Earth Sciences University of Cambridge Cambridge CB2 3EQ United Kingdom Department of Mechanics and Mechatronics Engineering Centre for Advanced Materials Joining Waterloo Institute of Nanotechnology and Department of Physics and Astronomy University of Waterloo Waterloo Ontario Canada N2L 3G1 Innovation Center for Computational Physics Methods and Software & State Key Lab of Superhard Materials College of Physics Jilin University Changchun 130012 China

Silicon disulfide, SiS2, is thought to occur in interstellar dust and is of fundamental interest more generally among the silicon chalcogenides as a comparator to SiO2, an important component of terrestrial planets. However, the high-pressure behaviors of silicon sulfides are unclear. Here, using an efficient structure search method, we systematically explore the structural evolution of different Si-S stoichiometries up to 250 GPa. SiS2 is found to be stable below 155 GPa, above which it decomposes into two compounds, SiS and SiS3. SiS adopts a high-symmetry cubic structure consisting of eightfold-coordinated silicon in face-sharing SiS8 polyhedra, while SiS3 crystallizes in a rhombohedral structure containing ninefold-coordinated SiS9 polyhedra. Analyses suggest that the Si eightfold-coordination environment could be a common feature for group IV–VI compounds under high pressure. Our findings provide insights on the nature of Si-S compounds under ultrahigh pressure.

关键词： Chemical bonding Pressure effects Structural properties Density functional calculations

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Thermodynamic and Kinetic Properties of Shocks in Two-Dimensional Yukawa Systems

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Physical Review Letters 2017年第2期118卷 025001-025001页

作者： M. Marciante M. S. Murillo Computational Physics and Methods Group Los Alamos National Laboratory Los Alamos New Mexico 87544 USA Department of Computational Mathematics Science and Engineering Michigan State University East Lansing Michigan 48824 USA

Particle-level simulations of shocked plasmas are carried out to examine kinetic properties not captured by hydrodynamic models. In particular, molecular dynamics simulations of 2D Yukawa plasmas with variable couplings and screening lengths are used to examine shock features unique to plasmas, including the presence of dispersive shock structures for weak shocks. A phase-space analysis reveals several kinetic properties, including anisotropic velocity distributions, non-Maxwellian tails, and the presence of fast particles ahead of the shock, even for moderately low Mach numbers. We also examine the thermodynamics (Rankine-Hugoniot relations) of recent experiments [Phys. Rev. Lett. 111, 015002 (2013)] and find no anomalies in their equations of state.

关键词： High-energy-density plasmas Shock waves & discontinuities in plasma

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A Promising Carbon/g‐C3N4Composite Negative Electrode for a Long‐Life Sodium‐Ion Battery

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Angewandte Chemie 2019年第39期131卷

作者： Guo‐Ming Weng Yu Xie Hang Wang Christopher Karpovich Jason Lipton Junqing Zhu Jaemin Kong Lisa D. Pfefferle André D. Taylor Department of Chemical and Biomolecular Engineering New York University Brooklyn New York 11201 USA Department of Chemical and Environmental Engineering Yale University New Haven Connecticut 06511 USA Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education) & Innovation Center for Computational Physics Methods and Software & State Key Laboratory of Superhard Materials College of Physics Jilin University Changchun 130012 China

2D graphitic carbon nitride (g‐C 3 N 4 ) nanosheets are a promising negative electrode candidate for sodium‐ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g‐C 3 N 4 exhibits poor electronic conductivity, low reversible Na‐storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na + ion diffusion barrier in the innate g‐C 3 N 4 nanosheet. A facile one‐pot heating of a mixture of low‐cost urea and asphalt is strategically applied to yield stacked multilayer C/g‐C 3 N 4 composites with improved Na‐storage capacity (about 2 times higher than that of g‐C 3 N 4 , up to 254 mAh g −1 ), rate capability, and cyclability. A C/g‐C 3 N 4 sodium‐ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g −1 .

关键词： Komposite Graphitisches Kohlenstoffnitrid Nanoschichten Natrium-Ionen-Batterien 2D-Materialien

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Prototype balloon for inspection of offshore platforms powered by renewable energy controlled by electronics prototyping platform

Prototype balloon for inspection of offshore platforms power...

引用

Offshore Technology Conference Asia 2016, OTCA 2016

作者： Albino, Ribeiro Neto Landau, Luiz National Service for Industrial Training - SENAI FIRJAN Laboratory for Computational Methods in Engineering LAMCE COPPE UFRJ Brazil Laboratory for Computational Methods in Engineering LAMCE COPPE UFRJ Brazil

ISBN: (纸本)9781510830721

The purpose of this research is the development of a prototype balloon anchored to a vessel for inspection of offshore platforms and monitoring of environmental damage with the use of solar panels, infrared camera and controlled by an Arduino platform. The possible environmental damage in offshore platforms require continuous monitoring as prevention and for repairs in case of accident, in this study the tool used for monitoring must provide continuous and uninterrupted monitoring of activities at a lower cost of operation. The method applied was the use of a balloon anchored to a vessel for continuous monitoring using an infrared camera as prevention and assistance for repairs in case of accidents occurring in open sea and various other situations in environmental damage inspections. The balloon will use helium gas for floating and a powertrain only for forced positioning, as the most part of the time it will be conducted with the wind to the sides, up and down through remotely controlled rudder. The use of other monitoring devices show several limitations when compared to the use of balloons, their great advantage is the autonomy compared to a drone (approximately 20 minutes) and the cost of operating a helicopter, thus, the cost-benefit enables its construction. The use of solar panels as a power source for batteries is an efficient solution for keeping its load, being applied for the continuous operation of equipment. The Arduino platform is a resource for various applications and its use in this prototype applies for the control and management of the following components that will be part of the monitoring balloon: solar plates, various sensors, GPS, motors and servo motors. © 2016, Offshore Technology Conference

关键词： Monitoring

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Visual simulator of remotely operated vehicle rov for training and qualification of new operators

Visual simulator of remotely operated vehicle rov for traini...

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Offshore Technology Conference Asia 2016, OTCA 2016

作者： Neto, Albino Ribeiro Landau, Luiz National Service for Industrial Training - SENAI FIRJAN Laboratory for Computational Methods in Engineering LAMCE COPPE UFRJ Brazil Laboratory for Computational Methods in Engineering LAMCE COPPE UFRJ Brazil

ISBN: (纸本)9781510830721

This work aims to build a visual simulator of low cost remotely operated vehicle (ROV) to be used as part of the initial training and qualification of new operators in the maintenance of wellheads, Christmas trees and monitoring the seabed. Besides the simulation of normal operation of the machine, the most common defects and failures that occur during operation will be implemented. The use of simulation in Virtual Reality in a three-dimensional synthetic environment was used enabling the operator to make choices, manipulate and visualize the equipment. The software used in the simulator allowed its development without the need of traditional programming knowledge. In this particular case the programming was done in a visual way by connecting pre-programmed blocks, thus enabling the drastic reduction of the development time of its application and eventual costs. The use of simulators to complement traditional training has been proven an efficient tool in the training of professionals in various fields. In some case studies previously analyzed, the comparison to traditional training methods in offshore operations and the excellent cost-benefit allows its development. The development of the simulator aims beyond a virtual training, but also the possibility of offering a low-cost tool compared to training with use of real equipment and even with other similar simulators already developed. © 2016, Offshore Technology Conference

关键词： Simulators

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