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arXiv 2021年

作者： Zhu, Wenqing Li, Zhi Shu, Hua Gao, Huajian Wei, Xiaoding State Key Laboratory for Turbulence and Complex System Department of Mechanics and Engineering Science College of Engineering Peking University Beijing100871 China School of Mechanical and Aerospace Engineering College of Engineering Nanyang Technological University 70 Nanyang Drive 637457 Singapore Shanghai Institute of Laser Plasma China Academy of Engineering Physics Shanghai201102 China Institute of High Performance Computing A*STAR 138632 Singapore Beijing Innovation Center for Engineering Science and Advanced Technology Peking University Beijing100871 China Peking University Nanchang Innovation Institute Nanchang330000 China

Theoretical predictions of the ideal strength of materials range from E/30 to E/10 (E is Young’s modulus). However, despite intense interest over the last decade, the value of the ideal strength that can be attained experimentally for metals remains a mystery (1-5). In this study, we demonstrated the unprecedented strength of an amorphous Cu-Zr alloy that surpassed the E/10 limit. Laser-induced shock experiments were conducted on Cu50Zr50 to explore its strength and failure mechanisms at ultrahigh strain rates. The material demonstrated a high spall strength of 9.8 GPa, approximately 1/13 of its P-wave modulus (~ E/6), at strain rates greater than 107 s−1, which sets a new record for the elastic limit of metallic materials. Electron microscopy and large-scale molecular dynamics simulations revealed that void nucleation and growth, not shear-banding, comprised the major failure mechanism for metallic glasses at extremely fast strain rates. A new model for void formation under the control of surface energy explained the rate dependence of the material strength. The results of this study reveal new possible ways to use the amorphous phase in nanostructured metals in future applications under demanding mechanical conditions. Copyright © 2021, The Authors. All rights reserved.

关键词： Copper alloys

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Method for constructing multi-dimensional feature map of malicious code

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Journal of Physics: Conference Series 2021年第4期1748卷

作者： Haocong Ma Ji Zhang Junhua Zhou Xiang Zhai Junjie Xue Hang Ji State Key Laboratory of Intelligent Manufacturing System Technology Beijing Institute of Electronic System Engineering Beijing 100854 China Beijing Complex Product Advanced Manufacturing Engineering Research Center Beijing simulation Center Beijing 100854 China Science and Technology on Space System Simulation Laboratory Beijing Simulation Center Beijing 100854 China School of Computer Science and Technology Beijing Institute of Technology Beijing 100081 China

Malicious code is characterized by a large number of types, rapid increase in number, continuous update of transmission routes, and continuous enhancement of back analysis and back detection methods. Therefore, how to effectively detect and analyze malicious code has been a problem of great concern. This paper studies the features of binary file and disassembly file of malicious code, introduces the concept of information gain, and proposes a method to construct the multi-dimensional characteristic graph of malicious code. Finally, the convolutional neural network is used to classify the multi-dimensional feature graph of malicious code, which provides a new idea for the feature extraction of malicious code.

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Observation of negative THz photoconductivity in large area type-Ⅱ Dirac semimetal PtTe2

arXiv

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arXiv 2020年

作者： Suo, Peng Zhang, Huiyun Yan, Shengnan Zhang, Wenjie Fu, Jibo Lin, Xian Hao, Song Jin, Zuanming Zhang, Yuping Zhang, Chao Miao, Feng Liang, Shi-Jun Ma, Guohong Department of Physics Shanghai University Shanghai200444 China College of Electronics and Information Engineering Shandong University of Science and Technology Qingdao266590 China National Laboratory of Solid State Microstructures School of Physics Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing210093 China School of Physics University of Wollongong WollongongNSW2522 Australia Terahertz Technology Innovation Research Institute Terahertz Spectrum and Imaging Technology Cooperative Innovation Center Shanghai Key Lab of Modern Optical System University of Shanghai for Science and Technology 516 JunGong Road Shanghai200093 China STU SIOM Joint Laboratory for Superintense Lasers and the Applications Shanghai201210 China

As a newly emergent type-Ⅱ Dirac semimetal, Platinum Telluride (PtTe2) stands out from other 2D noble-transition-metal dichalcogenides for the unique band structure and novel physical properties, and has been studied extensively. However, the ultrafast response of low energy quasiparticle excitation in terahertz (THz) frequency remains nearly unexplored yet. Herein we employ optical pump-terahertz (THz) probe spectroscopy (OPTP) to systematically study the photocarrier dynamics of PtTe2 thin films with varying pump fluence, temperature, and film thickness. Upon photoexcitation the THz photoconductivity (PC) of PtTe2 films show abrupt increase initially, while the THz PC changes into negative value in a subpicosecond time scale, followed by a prolonged recovery process that lasted a few ns. The magnitude of both positive and negative THz PC response shows strongly pump fluence dependence. We assign the unusual negative THz PC to the formation of small polaron due to the strong electron-phonon (e-ph) coupling, which is further substantiated by temperature and film thickness dependent measurements. Moreover, our investigations give a subpicosecond time scale of sequential carrier cooling and polaron formation. The present study provides deep insights into the underlying dynamics evolution mechanisms of photocarrier in type-Ⅱ Dirac semimetal upon photoexcitation, which is crucial importance for designing PtTe2-based optoelectronic devices. Copyright © 2020, The Authors. All rights reserved.

关键词： Photoconductivity

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CeO 2 quantum dots/LZU1 Z-scheme heterojunction for photocatalytic selective oxidative coupling of benzylamines

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Journal of Rare Earths 2024年

作者： Yezi Hu Rusong Sang Feng Chu Zewen Shen Guixia Zhao Junrong Yue Xiubing Huang MOE Key Laboratory of Resources and Environmental System Optimization College of Environmental Science and Engineering North China Electric Power University Beijing 102206 China State Key Laboratory of Multi Phase Complex System Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China Beijing Advanced Innovation Center for Materials Genome Engineering Beijing Key Laboratory of Function Materials for Molecule & Structure Construction School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Imines play a pivotal role as multifunctional intermediates in pharmaceutical and biological applications, and their selective synthesis under mild conditions has attracted increasing interest. In this study, a covalent-organic frameworks (COFs) modified with CeO 2 quantum dots (QDs) were prepared through a simple chemical reaction using LZU1 COFs and Ce(NO 3 ) 3 ·6H 2 O serving as precursors. The optimized 5CeO 2 QDs@LZU1 decorated with about 3.9 wt% CeO 2 QDs demonstrates excellent performance in the photocatalytic selective oxidative of amines in visible light conditions, achieving nearly 100% benzylamine conversion and over 99% imine selectivity within 6 h, which is significantly superior to that of pure LZU1 and CeO 2 . The remarkable enhancement in activity is mainly attributed to the fact that the interaction between CeO 2 QDs and LZU1 COF in 5CeO 2 QDs@LZU1 improves the visible light response and concurrently promotes the separation efficiency of photogenerated e ‒ and h + pairs. Broad substrate scope also provides a prospect for the industrial synthesis of various imines. Our findings not only expand the application range of COFs by incorporating QDs but also lay the groundwork for their further rational design and optimization.

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Nanodevices: Record‐Low‐Threshold Lasers Based on Atomically Smooth Triangular Nanoplatelet Perovskite (Adv. Funct. Mater. 2/2019)

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advanced Functional Materials 2019年第2期29卷

作者： Guohui Li Tao Che Xingqi Ji Shaoding Liu Yuying Hao Yanxia Cui Shengzhong Liu Key Lab of Advanced Transducers and Intelligent Control System of Ministry of Education College of Physics and Optoelectronics Key Laboratory of Interface Science and Engineering in Advanced Materials Taiyuan University of Technology Taiyuan 030024 P. R. China State Key Laboratory of Quantum Optics and Quantum Optics Devices Shanxi University Taiyuan 030006 P. R. China Key Laboratory of Applied Surface and Colloid Chemistry National Ministry of Education Shaanxi Engineering Lab for Advanced Energy Technology School of Materials Science and Engineering Shaanxi Normal University Xi'an 710119 P. R. China

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Nonequilibrium Effects on Rapid Directional Solidification Microstructures During Additive Manufacturing: A Quantitative Phase Field Study

SSRN

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SSRN 2024年

作者： Li, Leiji Xiao, Fei Li, Zhu He, Shiyu Liu, Yang Cai, Xiaorong Hou, Ruihang Zhou, Ying Zuo, Shungui Zhang, Chongfeng Gao, Jinzhong Shen, Xiaopeng Zhu, Tianchi Gu, Yijia Jin, Xuejun State Key Lab of Metal Matrix Composite School of Materials Science and Engineering Shanghai Jiao Tong University 800 Dong Chuan Road Shanghai200240 China Institute of Medical Robotics Shanghai Jiao Tong University Shanghai200240 China National Key Laboratory of Aerospace Mechanism Aerospace System Engineering Shanghai 3805 Jin Du Road Shanghai201108 China Department of Materials Science and Engineering Missouri University of Science and Technology RollaMO65409 United States National Engineering Research Center of Advanced Magnetic Resonance Technologies for Diagnosis and Therapy School of Materials Science and Engineering Shanghai Jiao Tong University 800 Dong Chuan Road Shanghai200240 China Department of Materials Science and Engineering Graduate School of Engineering Osaka University 2-1 Yamada-oka Osaka Suita565-0871 Japan Shanghai Key Laboratory of Materials Laser Processing and Modification China

Fusion-based metal additive manufacturing (AM) is a technology that builds objects layer by layer, with rapid solidification referring to the quick transition of material from liquid to solid. During this process, solute trapping, a nonequilibrium effect characterized by velocity-dependent partition coefficient, significantly influences microstructure kinetics, morphology, and phase formation. This study utilizes the latest quantitative phase field (PF) model to systematically investigate the solute trapping, solute drag, and their effects on pattern formation during rapid solidification at velocities relevant to AM, in both one and two dimensions. Under different temperature gradients and pulling velocities, we observed that the growth mode transits from planar to cellular to dendritic, then back to cellular, and finally to planar, which is consistent with classic solidification theory. A solidification microstructure selection map is constructed based on PF simulations. Furthermore, we compared primary dendritic/cell spacing calculated by the PF model with theoretical models. The simulated morphologies and arm spacing showed good agreement with experimental observations for Al-4Si and Ti-20Nb alloys during rapid solidification. These results demonstrate the potential of the PF model for predicting and controlling microstructure formation under rapid solidification conditions in the melt pool of AM processes. © 2024, The Authors. All rights reserved.

关键词： Morphology

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Lattice dynamics of the topological Dirac semimetal LaAgSb2 with charge density wave ordering

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Physical Review B 2020年第20期102卷 205103-205103页

作者： Ratnadwip Singha Sudeshna Samanta Tara Shankar Bhattacharya Swastika Chatterjee Shubhankar Roy Lin Wang Achintya Singha Prabhat Mandal Saha Institute of Nuclear Physics HBNI 1/AF Bidhannagar Kolkata 700 064 India Center for High Pressure Science and Technology Advanced Research Shanghai 201 203 China Micro-Nano System Center School of Information Science and Technology Fudan University Shanghai 200 433 China Department of Physics Bose Institute 93/1 Acharya Prafulla Chandra Road Kolkata 700 009 India Department of Earth Sciences Indian Institute of Science Education and Research Kolkata 741 246 India Vidyasagar Metropolitan College 39 Sankar Ghosh Lane Kolkata 700 006 India Center for High Pressure Science (CHiPS) State Key Laboratory of Metastable Materials Science and Technology Yanshan University Qinhuangdao Hebei 066 004 China

LaAgSb2 is a rare material that offers the opportunity to investigate the complex interplay between charge density wave (CDW) ordering and topology-protected electronic band structure. As both of these phenomena are governed by the structural symmetries, a comprehensive study of the lattice dynamics is highly desirable. In this paper, we present the results of temperature- and pressure-dependent Raman spectroscopy and x-ray diffraction in single crystalline LaAgSb2. Our results confirm that Raman spectroscopy is a highly sensitive tool to probe the CDW-ordering phenomenon, particularly the low-temperature second CDW transition in LaAgSb2, which appears as a very weak anomaly in most experiments. The crystal-orientation-dependent measurements provide the evolution of Raman modes with crystallographic symmetries and can be further studied through group symmetry analysis. The low-temperature x-ray diffraction data show the emergence of structural modulations corresponding to the CDW instability. The combined high-pressure Raman spectroscopy and synchrotron x-ray diffraction reveal multiple structural phase transitions through lowering of crystalline symmetries, which are also expected to lead to electronic topological transitions.

关键词： Charge density waves Lattice dynamics Phonons Pressure effects Topological phases of matter Density functional theory Raman spectroscopy X-ray diffraction

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Lead-Free Nanocrystals: Bright Blue Light-Emitting Doped Cesium Bromide Nanocrystals: Alternatives of Lead-Free Perovskite Nanocrystals for White LEDs (advanced Optical Materials 10/2019)

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advanced Optical Materials 2019年第10期7卷

作者： Zhiwen Yang Zhao Jiang Xinyi Liu Xiaochuan Zhou Jianhua Zhang Wanwan Li State Key Lab of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240 P. R. China Key Laboratory of Advanced Display and System Applications Ministry of Education Shanghai University Shanghai 200072 China

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Enhancing Plasticity in BCC Mg-Li-Al Alloys Through Controlled Precipitation at Grain Boundaries

SSRN

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SSRN 2024年

作者： Ji, Fan Xin, Tongzheng Zhao, Yuhong Yang, Wenkui Bai, Guoning Tang, Song Guo, Enyu Zhou, Mengran Shi, Qingyu Cui, Luqing Chen, Long-Qing He, Binbin Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China Instrumental Analysis Center Dalian University of Technology Dalian116024 China School of Materials Science and Engineering Dalian University of Technology Dalian116024 China Beijing Advanced Innovation Center for Materials Genome Engineering University of Science and Technology Beijing Beijing100083 China School of Materials Science and Engineering Collaborative Innovation Center of Ministry of Education Shanxi Province for High-performance Al/Mg Alloy Materials North University of China Taiyuan030051 China Institute of Materials Intelligent Technology Liaoning Academy of Materials Shenyang110004 China Herbert Gleiter Institute of Nanoscience School of Materials Science and Engineering Nanjing University of Science and Technology Jiangsu210094 China State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment Department of Mechanical Engineering Tsinghua University Beijing100084 China Key Laboratory for Advanced Materials Processing Technology Ministry of Education Beijing100084 China The National Key Laboratory of Aerospace Power System and Plasma Technology Xi'an Jiaotong University Xi’an710049 China School of Mechanical Engineering Xi'an Jiaotong University Xi’an710049 China Department of Materials Science and Engineering The Pennsylvania State University University ParkPA16802 United States

This study investigates the improvement of plasticity in body-centered cubic magnesium (Mg)-lithium (Li)-aluminum (Al) alloys, crucial for lightweight structural applications. The ternary Mg-Li-Al alloys exhibits high strength but low ductility. Precipitates at grain boundaries in these alloys, linked to reduced plasticity, are examined for their crystal structure and composition. advanced microscopic techniques reveal the transformation of precipitates and the development of specific structures at grain boundaries. Thermodynamics of element diffusion at grain boundaries are explored through first-principles calculations, and a phase-field simulation models precipitate evolution. Molecular dynamics simulations elucidate nanoscale mechanisms governing the transition from brittle to ductile fracture modes during artificial aging. The D03-Mg3Al at grain boundaries is a brittle phase, and through a 170°C aging treatment, it induces the precipitation of lamellar α-Mg phase with D03-Mg3Al as nucleation sites. The occupancy energy of Al atoms at Li sites in α-Mg is found to be lower than that in D03-Mg3Al, leading to the dissolution of D03-Mg3Al. The α-Mg, characterized by a stronger metallic nature, exhibits a better-matched modulus with the matrix and enhanced dislocation mobility. The precipitation of α-Mg plays a pivotal role in significantly improving the ductility of the alloy. This work contributes to the understanding of the complex interplay between alloy composition, grain boundary precipitates, and plasticity, as well as brings insights to guide interfacial control in the development of advanced Mg-Li-Al alloys for structural applications. © 2024, The Authors. All rights reserved.

关键词： Grain boundaries

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Frontoparietal connectivity neurofeedback training for promotion of working memory: An fNIRS study in healthy male participants

arXiv

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arXiv 2020年

作者： Xia, Meiyun Xu, Pengfei Yang, Yuanbin Jiang, Wenyu Wang, Zehua Gu, Xiaolei Yang, Mingxi Li, Deyu Li, Shuyu Dong, Guijun Wang, Ling Wang, Daifa School of Biological Science and Medical Engineering Beihang University Beijing100083 China College of Computer Science Sichuan Normal University Chengdu610101 China Beijing Advanced Innovation Center for Biomedical Engineering Beihang University Beijing100083 China State Key Laboratory of Virtual Reality Technology and System Beihang University Beijing100083 China Department of Rehabilitation Medicine Wangjing Hospital China Academy of Chinese Medical Sciences Beijing100102 China Department of Neurological Rehabilitation Guangxi Jiangbin Hospital Nanning530021 China School of Sports and Health Shandong Sport University Jinan250102 China

Neurofeedback cognitive training is a promising tool used to promote cognitive functions effectively and efficiently. In this study, we investigated a novel functional near-infrared spectroscopy (fNIRS)based frontoparietal functional connectivity (FC) neurofeedback training paradigm related to working memory, involving healthy adults. Compared with conventional cognitive training studies, we chose the frontoparietal network, a key brain region for cognitive function modulation, as neurofeedback, yielding a strong targeting effect. In the experiment, 10 participants (test group) received three cognitive training sessions of 15 min using fNIRS-based frontoparietal FC as neurofeedback, and another 10 participants served as the control group. Frontoparietal FC was significantly increased in the test group (p = 0.03), and the cognitive functions (memory and attention) were significantly promoted compared with the control group (accuracy of 3-back test: p = 0.0005, reaction time of 3-back test: p = 0.0009). After additional validations on long-term training effect and on different patient populations, the proposed method exhibited considerable potential to be developed as a fast, effective, and widespread training approach for cognitive function enhancement. Copyright © 2020, The Authors. All rights reserved.

关键词： Brain

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