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arXiv 2023年

作者： Wan, Wei Hu, Shengshan Li, Minghui Lu, Jianrong Zhang, Longling Zhang, Leo Yu Jin, Hai School of Cyber Science and Engineering Huazhong University of Science and Technology China School of Software Engineering Huazhong University of Science and Technology China School of Information and Communication Technology Griffith University Australia School of Computer Science and Technology Huazhong University of Science and Technology China National Engineering Research Center for Big Data Technology and System Services Computing Technology and System Lab Hubei Key Laboratory of Distributed System Security China Hubei Engineering Research Center on Big Data Security China Cluster and Grid Computing Lab

Federated learning (FL) is a nascent distributed learning paradigm to train a shared global model without violating users' privacy. FL has been shown to be vulnerable to various Byzantine attacks, where malicious participants could independently or collusively upload well-crafted updates to deteriorate the performance of the global model. However, existing defenses could only mitigate part of Byzantine attacks, without providing an all-sided shield for FL. It is difficult to simply combine them as they rely on totally contradictory assumptions. In this paper, we propose FPD, a four-pronged defense against both non-colluding and colluding Byzantine attacks. Our main idea is to utilize absolute similarity to filter updates rather than relative similarity used in existingI works. To this end, we first propose a reliable client selection strategy to prevent the majority of threats in the bud. Then we design a simple but effective score-based detection method to mitigate colluding attacks. Third, we construct an enhanced spectral-based outlier detector to accurately discard abnormal updates when the training data is not independent and identically distributed (non-IID). Finally, we design update denoising to rectify the direction of the slightly noisy but harmful updates. The four sequentially combined modules can effectively reconcile the contradiction in addressing non-colluding and colluding Byzantine attacks. Extensive experiments over three benchmark image classification datasets against four state-of-the-art Byzantine attacks demonstrate that FPD drastically outperforms existing defenses in IID and non-IID scenarios (with 30% improvement on model accuracy). © 2023, CC BY.

关键词： Classification (of information)

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An ab-initio study on engineering quantum anomalous Hall effect in compensated antiferromagnet MnBi2Te4

arXiv

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arXiv 2024年

作者： Li, Zeyu Han, Yulei Qiao, Zhenhua International Centre for Quantum Design of Functional Materials CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics Department of Physics University of Science and Technology of China Anhui Hefei230026 China Hefei National Laboratory University of Science and Technology of China Hefei230088 China Department of Physics Fuzhou University Fujian Fuzhou350108 China

Recently, the quantum anomalous Hall effect (QAHE) has been theoretically proposed in compensated antiferromagnetic systems by using the magnetic topological insulator model [see arXiv:2404.13305 (2024)]. However, the related and systematic study based on a realistic material system is still limited. As the only experimentally realized antiferromagnetic topological insulator, MnBi2Te4 becomes a vital platform for exploring various topological states. In this work, by using the comprehensive first-principles calculations, we demonstrate that the QAHE can also be realized in compensated antiferromagnetic even-septuple-layer MnBi2Te4 without combined parity-time (PT) symmetry. Using a magnetic topological insulator model, the layer-resolved Chern number is calculated to further understand the physical origin of different Chern numbers. The application of external hydrostatic pressure can strengthen the Te-Te quasicovalent bond due to the dramatic compression of the van der Waals gap. Thus, the resulting topological nontrivial gap can exceed the room-temperature energy scale in a wide range of pressures. Additionally, we find that constructing MnBi2Te4/CrI3 heterostructure can realize the compensated antiferromagnetic configurations with QAHE. Our findings illustrate the realization of QAHE in compensated antiferromagnetic even-septuple-layer MnBi2Te4 and provide a reliable strategy to obtain the corresponding magnetic configurations. Copyright © 2024, The Authors. All rights reserved.

关键词： Hydrostatic pressure

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Experimental Study on Droplet Behavior and Mechanisms During Reflooding in a Single-Rod Channel

SSRN

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SSRN 2022年

作者： Chen, Mingjing Liu, Hanzhou Chen, Deqi Zhong, Lei Liu, Haidong Yu, Hongxing Yu, Ruan Feng, Peng Key Laboratory of Low-grade Energy Utilization Technologies and Systems Chongqing University Ministry of Education Chongqing 400044 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610041 China Key Laboratory of Aerospace Thermophysics Ministry of Industry and Information Technology School of Energy Science and Engineering Harbin Institute of Technology Harbin150001 China

Discrete droplets have received extensive attention in reflooding processes under Loss Of Coolant Accident (LOCA) conditions due to their large vapor-liquid interface area, droplet collision, droplet evaporation, and other behaviors that have a significant impact on the heat transfer of Dispersed Flow Film Boiling (DFFB). Unfortunately, the accurate prediction of the characteristics of droplet velocity and distribution under DFFB cannot be achieved at present, due to the lack of sufficient visual data support. For this reason, a visualization experiment of high-temperature surface reflooding in a single-rod channel was carried out. In this paper, the effect of the thermal parameter, such as input heat flux on the transient droplet behavior, which include the droplet size and velocity, has been analaysed in detail. Furthermore, to provide physical support for building droplet distribution models containing more physical mechanisms in the future, several droplet formation and breakup mechanisms, which include the Helmholtz instability, capillary breakage and rewetting area sputter, has been discussed in this paper. © 2022, The Authors. All rights reserved.

关键词： Drop breakup

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Broadband Wide-Angle Linear-to-Circular Polarization Converter Based on Metal Strips Loaded Metasurface

Broadband Wide-Angle Linear-to-Circular Polarization Convert...

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International Applied Computational Electromagnetics Society Symposium (ACES)

作者： Jingwen Wang Shasha Deng Weidong Chen Zhongxiang Zhang Chang Chen School of Information Science and Technology University of Science and Technology of China Hefei China Key Laboratory of simulation and design for Electronic information system Hefei Normal University Hefei China

A transmissive broadband wide-angle linear-to-circular polarization converter based on metal strips loaded metasurface is proposed in this paper. The converter is composed of three metallic layers separated by dielectric substrates and the metal strips printed on each layer keep orthogonal to each other. To further investigate the operating mechanism of the design, equivalent circuit models are presented. Moreover, the converter is verified to be effective in polarization conversion through the full-wave simulation. With the insertion loss less than 2 dB and 3 dB, the simulation 3-dB axial ratio (AR) bandwidth keeps 67% and 76%, respectively. Furthermore, at an increased incident angle of 40°, the device can still maintain an AR bandwidth over 47% at 2 dB insertion loss, which manifests the validity and rationality of the converter design.

关键词： Strips Computational modeling Metals Insertion loss Bandwidth Metasurfaces Broadband communication

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An Efficiency Optimization Control Method for Three-Phase Interleaved DC-DC Converter

An Efficiency Optimization Control Method for Three-Phase In...

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IEEE Asia Power and Energy Engineering Conference (APEEC)

作者： Jinxin Wang Renyong Peng Chen Cai Haitao Yu Meiyuan Chen Yiyi Liu Ke Wu Shihan Tang Hongyang Wei Jie Chen Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu China

Because of the environmental friendliness of electric vehicles, research on electric vehicles has become a hot spot in recent years. How to charge electric vehicles faster is critical to the widespread use of electric vehicles. Electric vehicle integrated power unit can use bidirectional DC-DC converter for driving to achieve integrated charging. In order to improve the power density and efficiency of the integrated system, the bidirectional DC-DC for electric vehicle driving uses three-phase interleaved parallel technology. This paper proposes a method to select different interleaved phase numbers according to different output powers of the converter to improve the working efficiency of three-phase interleaved parallel DC-DC converters. This method improves the efficiency of the three-phase interleaved parallel converter under light load and widens the high-efficiency working area of the converter. Finally, simulations and experimental results are conducted to validate the efficiency of the design.

关键词： Power system measurements Simulation DC-DC power converters Switches Electric vehicles Software Electron tubes

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Influence of Different Factors on Fault Current Under DC Side Fault of Photo voltaic Grid Connected system

Influence of Different Factors on Fault Current Under DC Sid...

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IEEE Conference on Energy Internet and Energy system Integration (EI2)

作者： Yongyi Luo Xianguo Qing Renyong Peng Yuzhao Huangfu Ao Cui Zhaosu Wang Zhiqiang Zhang Ziheng Peng Chengyu Liao Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu China

ISBN: (纸本)9781665434263

Modular multilevel converter (MMC) has many advantages, such as low loss, flexible control and so on, which has been widely used in photovoltaic grid connected system. However, the photovoltaic output has some instability, and the damping of the flexible DC system is also low, which puts forward a severe test for the stable operation of the power grid. Firstly, this paper describes the basic structure of the photovoltaic system connected by MMC. Secondly, the photovoltaic grid connected system model based on PSCAD illustrates the fault current characteristics under DC side fault, and simulates and analyzes the influence of different factors in the system on the fault current.

关键词： Photovoltaic systems Analytical models Multilevel converters system integration Power grids Internet Circuit faults

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A Band Stop Decoupling Structure for Circularly Polarized Antennas With Different Intervals

A Band Stop Decoupling Structure for Circularly Polarized An...

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International Applied Computational Electromagnetics Society Symposium (ACES)

作者： Yuhang Ding Shasha Deng Weidong Chen Zhongxiang Zhang Chang Chen School of Information Science and Technology University of Science and Technology of China Hefei China Key Laboratory of simulation and design for Electronic information system Hefei Normal University Hefei China

In this paper, a novel band stop decoupling structure (BSDS) for circularly polarized microstrip antenna array with different intervals to realize mutual coupling reduction is proposed. The BSDS is composed of complementary split-rings resonator (CSRRs) and split-rings resonator (SRRs), where the CSRRs block TM waves by electric resonance and the SRRs block TE waves by magnetic resonance, respectively. The proposed design is verified by the simulation and the results indicate that the isolation enhancement more than 35 dB can be obtained at the center frequency of 3.4 GHz when the center spacing is 0.37 $\lambda$0. Futhermore, when the center spacing reduces to 0.26 $\lambda$0, the mutual coupling remains below 25 dB. Besides, the BSDS can improve the radiation pattern offset without affecting the gain and the backward radiation of antennas.

关键词： Mutual coupling Microstrip antenna arrays Surface waves Simulation Magnetic resonance Microstrip antennas Scattering parameters

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Learning Pre-Grasp Manipulation of Flat Objects in Cluttered Environments using Sliding Primitives

Learning Pre-Grasp Manipulation of Flat Objects in Cluttered...

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IEEE International Conference on Robotics and Automation (ICRA)

作者： Jiaxi Wu Haoran Wu Shanlin Zhong Quqin Sun Yinlin Li State Key Laboratory of Turbulence and Complex Systems Intelligent Biomimetic Design Lab College of Engineering Peking University Beijing China Department of Automation University of Science and Technology of China Heifei China State Key Laboratory of Management and Control for Complex System Institute of Automation Chinese Academy of Science Beijing China Science and Technology on Thermal Energy and Power Laboratory Wuhan China

Flat objects with negligible thicknesses like books and disks are challenging to be grasped by the robot because of the width limit of the robot's gripper, especially when they are in cluttered environments. Pre-grasp manipulation is conducive to rearranging objects on the table and moving the flat objects to the table edge, making them graspable. In this paper, we formulate this task as Parameterized Action Markov Decision Process, and a novel method based on deep reinforcement learning is proposed to address this problem by introducing sliding primitives as actions. A weight-sharing policy network is utilized to predict the sliding primitive's parameters for each object, and a Q-network is adopted to select the acted object among all the candidates on the table. Meanwhile, via integrating a curriculum learning scheme, our method can be scaled to cluttered environments with more objects. In both simulation and real-world experiments, our method surpasses the existing methods and achieves pre-grasp manipulation with higher task success rates and fewer action steps. Without fine-tuning, it can be generalized to novel shapes and household objects with more than 85% success rates in the real world. Videos and supplementary materials are available at https://***/view/pre-grasp-sliding.

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Enhanced Toughness and Ductility of T91 Steel after Exposure to Liquid Lbe Saturated by Oxygen at 350-500 °C

SSRN

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SSRN 2024年

作者： Zhou, Zhikun Tian, Chenwen Dong, Wenbo Du, Juan Liu, Yunpeng Wahab, Magd Abdel Chen, Ziguang Department of Engineering Mechanics School of Aerospace Engineering Huazhong University of Science and Technology Wuhan430074 China Laboratory Soete Faculty of Engineering and Architecture Ghent University Technologiepark Zwijnaarde 46 ZwijnaardeB-9052 Belgium Institute of Intelligent Manufacturing Jianghan University Wuhan430056 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China College of Engineering Yuan Ze University Taiwan Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment 1037 Luoyu Road Wuhan430074 China

The mechanical tensile properties of T91 steel after being oxidized in liquid LBE saturated by oxygen at 350-500 °C for up to 1,000 h are studied. Duplex oxide scales are found on T91 steels after the LBE exposure, and the thickness evolution is revealed. Oxidized T91 steels with surface oxide scale yield enhanced toughness and ductility, which is mainly attributed to the inner oxide layer. We show that the enhancing effect relies on the presence of the oxide scale, not its thickness. The possible enhancing effect of the oxide scale on the toughness of T91 steel by impeding the dislocation from emitting out of the steel surfaces is discussed and qualitatively verified by micro-scale elastoplastic simulations based on a newly proposed discrete dislocation dynamics and peridynamics superposition scheme. © 2024, The Authors. All rights reserved.

关键词： Ductility

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Dynamically confined single-atom catalytic sites within a porous heterobilayer for CO oxidation via electronic antenna effects

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Physical Review B 2023年第20期107卷 205421-205421页

作者： Bojie Jiang Feixiang Zhang Yueyang Wang Xinlian Xue Jinlei Shi Xingju Zhao Lili Zhang Rui Pang Xiaoyan Ren Shunfang Li Zhenyu Zhang Key Laboratory of Material Physics Ministry of Education School of Physics and Microelectronics Zhengzhou University Zhengzhou 450001 China International Center for Quantum Design of Functional Materials (ICQD) Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China Hefei Anhui 230026 China

Suppression of clustering of single-atom catalysts during chemical reaction is a long-standing challenge in heterogeneous catalysis, largely due to the prevailing design scheme that the catalytic atoms are anchored onto the supporting surfaces. Here we use first-principles approaches to establish a different design principle, where the single-atom catalytic centers are dynamically sandwiched between a porous g-C3N4/MoS2 heterobilayer as a prototypical system. We show that many of the transition metals can be well stabilized as dispersive single atoms within the porous centers. Moreover, the single atoms migrate out of their sandwiched homes in O2 activation and CO oxidation, and successfully return home after the reaction is completed. In such a dynamical process the single atoms function as electronic antennas, facilitating the charge donation to or acceptance from the reactants, while effectively lowering the reaction barriers. These findings are instructive in establishing high-performance single-atom catalysts upon two-dimensional porous materials.

关键词： Chemical kinetics, dynamics & catalysis Chemical reactions Ab initio molecular dynamics Density functional calculations Electronic structure

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