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Multiple unpinned Dirac points in group-Va single-layers with phosphorene structure

npj Computational Materials 2016年第1期2卷 142-148页

作者： Yunhao Lu Di Zhou Guoqing Chang Shan Guan Weiguang Chen Yinzhu Jiang Jianzhong Jiang Xue-sen Wang Shengyuan A Yang Yuan Ping Feng Yoshiyuki Kawazoe Hsin Lin School of Materials Science and Engineering Zhejiang UniversityHangzhouChina State Key Laboratory of Silicon Materials Zhejiang UniversityHangzhouChina Centre for Advanced 2D Materials and Graphene Research Centre National University of SingaporeSingaporeSingapore Department of Physics National University of SingaporeSingaporeSingapore Research Laboratory for Quantum Materials Singapore University of Technology and DesignSingaporeSingapore College of Physics and Electronic Engineering Zhengzhou Normal UniversityZhengzhouChina New Industry Creation Hatchery Center Tohuku UniversitySendaiJapan Institute of Thermophysics Siberian Branch of Russian Academy of SciencesNovosibirskRussia

Emergent Dirac fermion states underlie many intriguing properties of graphene,and the search for them constitutes one strong motivation to explore two-dimensional(2D)allotropes of other ***,the ultrathin layers of black phosphorous,has been a subject of intense investigations recently,and it was found that other group-Va elements could also form 2D layers with similar puckered lattice ***,by a close examination of their electronic band structure evolution,we discover two types of Dirac fermion states emerging in the low-energy *** pair of(type-I)Dirac points is sitting on high-symmetry lines,while two pairs of(type-II)Dirac points are located at generic k-points,with different anisotropic dispersions determined by the reduced symmetries at their *** fully-unpinned(type-II)2D Dirac points are discovered for the first *** the absence of spin-orbit coupling(SOC),we find that each Dirac node is protected by the sublattice symmetry from gap opening,which is in turn ensured by any one of three point group *** SOC generally gaps the Dirac nodes,and for the type-I case,this drives the system into a quantum spin Hall insulator *** suggest possible ways to realise the unpinned Dirac points in strained phosphorene.

关键词： structure spectrum Dirac

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Cache-Friendly design for Complex Spatially-Variable Coefficient Stencils on Many-Core Architectures

Cache-Friendly Design for Complex Spatially-Variable Coeffic...

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International Conference on High Performance Computing

作者： Jiarui Fang Haohuan Fu Guangwen Yang National Supercomputing Center in Wuxi Ministry of Education Key Lab. for Earth System Modeling Tsinghua University Tsinghua National Laboratory for Information Science and Technology (TNList)

ISBN: (纸本)9781509054121

Many-core architectures, such as the NVIDIA graphics processing unit and Intel Xeon Phi, which are characterized by high computation resources but limited on-chip memory capacity, have been used to significantly accelerate various computationally demanding tasks. Stencil operators are naturally suitable for such architectures because of their parallel calculation patterns. However, only simple stencils with points distributed along the axes and with constant coefficients have been fully investigated. This study first provides insights into optimization strategies for stencils with complex shapes, including off-axial points and spatially variable coefficients. Through our proposed stencil-decomposition schemes, we maintain read-only coefficients in on-chip caches to avoid unvectorized memory access. To alleviate the resulting severe cache-starvation situation, a generalized cache-friendly design for many-core architecture is proposed. It can reduce cache miss times and cache space consumption. The proposed methodology significantly improves the performance of stencil operations in a real seismic imaging application and introduces a new option to write highly efficient memory-bound stencil-like loops.

关键词： Computer architecture Graphics processing units Mathematical model Shape system-on-chip Imaging Computational modeling

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F-CNN: An FPGA-based framework for training Convolutional Neural Networks

F-CNN: An FPGA-based framework for training Convolutional Ne...

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International Conference on Application Specific systems (ASAP), Architectures and Processors

作者： Wenlai Zhao Haohuan Fu Wayne Luk Teng Yu Shaojun Wang Bo Feng Yuchun Ma Guangwen Yang Ministry of Education Key Laboratory for Earth System Modeling and Center for Earth System Science Tsinghua University China Tsinghua National Laboratory for Information Science and Technology China Department of Computing Imperial college London UK Department of Automatic Test and Control Harbin Institute of Technology China Department of Computer Science and Technology Tsinghua University China

ISBN: (纸本)9781509015047

This paper presents a novel reconfigurable framework for training Convolutional Neural Networks (CNNs). The proposed framework is based on reconfiguring a streaming datapath at runtime to cover the training cycle for the various layers in a CNN. The streaming datapath can support various parameterized modules which can be customized to produce implementations with different trade-offs in performance and resource usage. The modules follow the same input and output data layout, simplifying configuration scheduling. For different layers, instances of the modules contain different computation kernels in parallel, which can be customized with different layer configurations and data precision. The associated models on performance, resource and bandwidth can be used in deriving parameters for the datapath to guide the analysis of design trade-offs to meet application requirements or platform constraints. They enable estimation of the implementation specifications given different layer configurations, to maximize performance under the constraints on bandwidth and hardware resources. Experimental results indicate that the proposed module design targeting Maxeler technology can achieve a performance of 62.06 GFLOPS for 32-bit floating-point arithmetic, outperforming existing accelerators. Further evaluation based on training LeNet-5 shows that the proposed framework achieves about 4 times faster than CPU implementation of Caffe and about 7.5 times more energy efficient than the GPU implementation of Caffe.

关键词： Training Field programmable gate arrays Convolution Computational modeling Bandwidth Neural networks Runtime

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Large eddy simulation of turbulent flow in the rod bundle with different spacer grids 23

Large eddy simulation of turbulent flow in the rod bundle wi...

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23rd International Conference on Nuclear Engineering: Nuclear Power - Reliable Global Energy, ICONE 2015

作者： Wei, Zonglan Yu, Zhang Liu, Songtao Science and Technology on Reactor System Design Technology Laboratory NPIC Chengdu Sichuan China Nuclear Power Design and Research Sub-Institute NPIC Chengdu Sichuan China

ISBN: (纸本)9784888982566

Large eddy simulation(LES) of the swirling flow in the rod bundle subchannels with spacer grids are presented. According to the rod bundle flow benchmark experiment, the 5×5 rod bundle with a split-type spacer grid is simulated by this transient simulation with a fine hybrid mesh. Mean velocity components, RMS (root mean square) velocity components and turbulent kinetic energy profiles at different locations downstream the mixing vanes are compared between the experiment and simulation results. LES results can reproduce the mixing turbulent flow velocity field well. We also have studied the influence of the mixing vanes' bending degree on the subchannel flow structures by using LES to simulate the 3×3 rod bundle with the typical PWR spacer grid. The mixing vanes' bending degree is modified to 35°and 40°based on the original spacer grid, whose mixing vanes' bending degree is 30°. The larger bending degree produces a stronger mean coolant mixing effect, while larger pressure loss and fluctuation come together with this effect. The increased pressure loss would generate additional flow resistance, and larger fluctuation of coolant flow would make the mixing effect unstable, as well as would cause flow-induced vibration and grid-to-rod fretting phenomena. The LES method is a viable tool to optimize the spacer grid design and provide transient flow field data for mechanical analysis. Copyright © 2015 by JSME.

关键词： Mixing

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Fire compartment partitioning approaches for fire probabilistic safety analysis of a high-temperature gas-cooled reactor 8

Fire compartment partitioning approaches for fire probabilis...

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8th International Topical Meeting on High Temperature reactor technology, HTR 2016

作者： Geng, Yuhao Zhao, Jun Tong, Jiejuan Wang, Wei Di Maio, Francesco Zio, Enrico Institute of Nuclear and New Energy Technology Collaborative Innovation Center of Advanced Nuclear Energy Technology Key Laboratory of Advanced Reactor Engineering and Safety Ministry of Education Tsinghua University Beijing100084 China Energy Department Politecnico di Milano Via La Masa 34 Milano20156 Italy System Science and the Energetic Challenge Fondation EDF-Electricite de France Ecole Centrale Supelec Paris Chatenay-Malabry Cedex Paris92295 France

ISBN: (纸本)9780894487323

Fire compartment partitioning is the foundational task in Fire Probabilistic Safety Analysis (FPSA), that requires approaches able to balance analytical accuracy and computational burden. In this work, two fire compartment partitioning approaches are illustrated and applied to an electric building of a High-Temperature Gas-Cooled reactor (HTGR, e.g., HTR-PM), and the quantified risks of the compartments obtained with the two approaches are compared. The results show that risk is insensitive to the utilized fire compartment partitioning approach, making the FPSA tasks easier to be performed.

关键词： Fires

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Study On Adaptive Electromagnetic Balancing Ability Improvement By Field Balancing For Motorized Spindle

Study On Adaptive Electromagnetic Balancing Ability Improvem...

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The 29th International Congress on Condition Monitoring and Diagnostic Engineering Management

作者： HW Fan XH Zhang MQ Jing H Liu BJ Shi HW Ma QH Mao School of Mechanical Engineering Xi'an University of Science and Technology Key Laboratory of Education Ministry for Modern Design & Rotor-bearing System School of Mechanical Engineering Xi'an Jiaotong University

Motorized spindle is widely used in the high-speed machine tools,which has the greatly high machining quality and ***,the dynamic performance of high-speed motorized spindle can be reduced by rotor unbalance,because the unbalance-induced vibration is very sensitive for the rotating speed increase of machine tool *** order to correct unbalance in the rotating condition and without human interference,an electromagnetic adaptive balancing system is ***,the electromagnetic balancing device has the limited balancing ability in itself,so it is very necessary to carry out the field balancing to improve the online active balancing *** on the single-plane balancing scheme,a field balancing program was developed and the corresponding balancing test was *** results show the field balancing is effective for the improvement of electromagnetic active balancing *** research work provides a new rotor balancing strategy for the high-speed precision motorized spindle.

关键词： motorized spindle online active balancing electromagnetic balancing device adaptive balancing method balancing ability field balancing

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Balance Compensation Study of Electromagnetic Active Balancer for Motorized Spindle

Balance Compensation Study of Electromagnetic Active Balance...

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2016 13th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI)

作者： Bijia Shi Minqing Jing Hongwei Fan Heng Liu Qian Wang Key Laboratory of Education Ministry for Modern Design & Rotor-bearing System School of Mechanical Engineering Xi'an Jiaotong University School of Mechanical Engineering Xi'an University of Science and Technology

With the increase of rotating speed, the rotor unbalance of the modern rotating machinery becomes more sensitive. The on-line active balance is an ideal balancing mode for precision machines. Electromagnetic balancer is a non-contact new-structure balancing device in the on-line balancing field, as it can reliably work in high-speed condition and keep the position balanceable after turning down. Balance ability is an important indicator evaluating the performance of a balancer. This paper studies a new electromagnetic balancer carrying permanent magnet for the motorized spindle. Because the counterweight disk is the primary moving element of the balancer, its balance compensation value and distribution are mainly discussed in this paper. Based on the existing disk structure, the balance ability of disks with different structure is researched. The two counterweight disks with the same compensation value and distribution angle, the two disks have the same compensation value and different distribution angles, the two disks have different compensation values and the same distribution angle are analysed. The calculation results demonstrate that the first scheme is proven better in the balance ability and can be easily developed.

关键词： Motorized spindle Active balancing Counterweight disk Electromagnetic balancer Balance ability

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Study on Unbalance Magnetic Pull of the Motorized Spindle under Different Rotor Eccentricities

Study on Unbalance Magnetic Pull of the Motorized Spindle un...

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2016 13th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI)

作者： Jin Wang Minqing Jing Hongwei Fan Heng Liu Bijia Shi Key Laboratory of Education Ministry for Modern Design & Rotor-bearing System School of Mechanical Engineering Xi'an Jiaotong University School of Mechanical Engineering Xi'an University of Science and Technology

High-speed precision machining is one of the important development directions of modern machining technology, high-speed spindle system is widely used in high-speed machining, and motorized spindle is the main choice of the high-speed machine tool spindle. The electromagnetic force caused by rotor unbalance is one of main vibration sources of motorized spindle. Firstly, the research on the frequency spectrum characteristic of electromagnetic force under different rotor eccentricities is very necessary to suppress electromagnetic vibration. An electromagnetic finite element model was built for a motorized spindle based on Ansoft Maxwell in this paper. The electromagnetic force spectrum variation under the static and dynamic eccentricities is studied. The Unbalance Magnetic Pull(UMP) of the motorized spindle under different rotating speeds and different eccentricities are analysed. The results show that the motorized spindle with the static or dynamic eccentricity both produces new components in the electromagnetic force. Simultaneously, the eccentricity increase positively results in the increase of UMP amplitude. The UMP is constant under the rotor static eccentricity, which has a small impact on rotor vibration, while the frequency of UMP under the rotor dynamic eccentricity is the rotating frequency, which will increase the motorized spindle vibration. Finally, by the experiment the correctness of theoretical analysis and simulation are verified. This work provides a theoretical foundation for the fault diagnosis and dynamic balance of the motorized spindle.

关键词： Machine tool motorized spindle Unbalance Magnetic Pull(UMP) Rotor eccentricity Finite element analysis Frequency spectrum analysis

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Application of STPA to the digital reactor protection system in NPP for system safety analysis 23

Application of STPA to the digital reactor protection system...

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23rd International Conference on Nuclear Engineering: Nuclear Power - Reliable Global Energy, ICONE 2015

作者： Liu, Zhaohui Wu, Zhiqiang Yang, Xiaohua School of Computer Science and Technology University of South China Hengyang421001 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610041 China

ISBN: (纸本)9784888982566

In NPP, the digital control system which integrated software and hardware are increasingly used to improve dependability and introduce new functionality. Traditional safety analysis can get a good result when handling accidents caused by component failures, but software does not fail in this way. STPA is a new hazard analysis technique based on systems theory rather than reliability theory. It considers the system as a whole (include the hardware and software) to analyze failure and causality of systems and treats safety as a control problem rather than a failure problem. Being a safety-critical system, RPS in NPP needs to be considered carefully in system safety. So, we adopt this new approach to analyze the design process. From the analysis results, we found that causal factors leading to safety accidents identified by STPA included all the hazards identified by the fault tree analysis. Furthermore, there are some causal factors that were identified by STPA only. We utilize these results of the analysis on causation factor to refine the safety requirements and reduce the occurrences of the hazardous scenarios. Copyright © 2015 by JSME.

关键词： Fault tree analysis

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Study of a fully vacuum-sealed calcium atomic beam tube for optical frequency standard

Study of a fully vacuum-sealed calcium atomic beam tube for ...

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IEEE International Frequency Control Symposium

作者： Haijun Chen Youhuan Liang Jianqing Yang Zhongzheng Liu Jinjun Feng Xiaogang Zhang Shengnan Zhang Jingbiao Chen National Key Laboratory of Science and Technology on Vacuum Electronics Beijing Vacuum Electronics Research Institute Beijing China Communication System and Network Peking University Beijing China

ISBN: (纸本)9781509020928

Optical frequency standard is regarded as the future quantum frequency standard. With no laser cooling system, the calcium atomic beam optical frequency standard has the potential to be miniaturized and engineered, while providing a better performance than cesium clock and hydrogen clock. This paper presents the design and fabrication of a fully vacuum-sealed calcium beam tube with a smaller size and lighter weight. So far one testing has operated continuously for more than 15 months. We believe this study has laid a foundation for practicability and engineering of the calcium atomic beam optical frequency standard.

关键词： Calcium Atomic beams Laser beams Electron tubes Atom optics Standards Optical device fabrication

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