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Transfer matrix method for free and forced vibrations of multi-level functionally graded material stepped beams with different boundary conditions

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Applied Mathematics and Mechanics(English Edition) 2024年第6期45卷 983-1000页

作者： Xiaoyang SU Tong HU Wei ZHANG Houjun KANG Yunyue CONG Quan YUAN School of Civil engineering and Architecture Guangxi UniversityNanning 530004China Scientific Research Center of engineering Mechanics Guangxi UniversityNanning 530004China state key laboratory of Featured Metal Materials and Life-Cycle safety for Composite Structures Guangxi UniversityNanning 530004China

Functionally graded materials(FGMs)are a novel class of composite materials that have attracted significant attention in the field of engineering due to their unique mechanical *** study aims to explore the dynamic behaviors of an FGM stepped beam with different boundary conditions based on an efficient solving *** the assumptions of the Euler-Bernoulli beam theory,the governing differential equations of an individual FGM beam are derived with Hamilton’s principle and decoupled via the separation-of-variable ***,the free and forced vibrations of the FGM stepped beam are solved with the transfer matrix method(TMM).Two models,i.e.,a three-level FGM stepped beam and a five-level FGM stepped beam,are considered,and their natural frequencies and mode shapes are *** demonstrate the validity of the method in this paper,the simulation results by ABAQUS are also *** this basis,the detailed parametric analyses on the frequencies and dynamic responses of the three-level FGM stepped beam are carried *** results show the accuracy and efficiency of the TMM.

关键词： transfer matrix method(TMM) free vibration forced vibration functionally graded material(FGM) stepped beam

A novel domain decomposition-based model for efficient dynamic predictions of large composite machine tools

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Science China(Technological Sciences) 2024年第6期67卷 1765-1782页

作者： YU YangBo JI Yu Lei CHEN YanRen XU Kun BI QingZhen state key laboratory of Mechanical System and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai200240China

We propose a large combined moving component composed of carbon fiber reinforced polymer(CFRP)laminates for making lightweight machine tools with high dynamic *** accurate dynamic prediction of composite machine tools is essential for the new generation machine *** paper aims to address two challenges in numerical dynamic modeling and the design of composite machine tools to enhance development efficiency.(1)Anisotropic composite laminates,which form the composite machine tool,exhibit coupling in various *** propose the generalized continuity condition of the boundary to tackle this dynamic modeling challenge.(2)Composite machine tools feature numerous composite-metal coupled *** mechanical model correction of isotropic metals is performed to address their *** take the example of a five-axis gantry machine tool with composite moving parts,establish a dynamic model for efficient prediction,and verify it through simulation and *** proposed method yields remarkable results,with an average relative error of only 3.85%in modal frequency prediction and a staggering 99.7%reduction in solution time compared to finite element *** further discuss the dynamic performance of the machine tool under varied stacking angles and layer numbers of the composite machine *** propose general design criteria for composite machine tools to consider the modal frequency and manufacturing cost of machine tools.

关键词： machine tool dynamics carbon fiber reinforced polymer composite laminates

Health benefits from the rapid reduction in ambient exposure to air pollutants after China's clean air actions:progress in efficacy and geographic equality

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National Science Review 2024年第2期11卷 103-113页

作者： Tao Xue Ruohan Wang Meng Wang Yanying Wang Dan Tong Xia Meng Conghong Huang Siqi Ai Fangzhou Li Jingyuan Cao Mingkun Tong Xueqiu Ni Hengyi Liu Jianyu Deng Hong Lu Wei Wan Jicheng Gong Shiqiu Zhang Tong Zhu Institute of Reproductive and Child Health National Health Commission Key Laboratory of Reproductive Health/Department of Epidemiology and Biostatistics Ministry of Education Key Laboratory of Epidemiology of Major Diseases(PKU) School of Public Health Peking University Health Science Centre state Environmental Protection key laboratory of Atmospheric Exposure and Health Risk Management and Center for Environment and Health Peking University Advanced Institute of Information Technology Peking University Department of Epidemiology and Environmental Health School of Public Health and Health ProfessionsUniversity at Buffalo state key Joint laboratory of Environment simulation and Pollution Control College of Environmental Sciences and EngineeringPeking University Department of Earth System Science Tsinghua University School of Public Health Key Laboratory of Public Health Safety of the Ministry of Education and Key Laboratory of Health Technology Assessment of the Ministry of HealthFudan University College of Land Management Nanjing Agricultural University National&Local Joint engineering Research Center for Rural Land Resources Use and Consolidation Clean Air Asia

Clean air actions （CAAs） in China have been linked to considerable benefits in public ***,whether the beneficial effects of CAAs are equally distributed geographically is *** high-resolution maps of the distributions of major air pollutants (fine particulate matter[PM2.5]and ozone[O3]) and population,we aimed to track spatiotemporal changes in health impacts from,and geographic inequality embedded in,the reduced exposures to PM2.5and O3from 2013 to *** used a method established by the Global Burden of Diseases *** analyzing the changes in loss of life expectancy（LLE） attributable to PM2.5and O3,we calculated the gain of life expectancy （GLE） to quantify the health benefits of the air-quality ***,we assessed the geographic inequality embedded in the GLE using the Gini index （GI）.Based on risk assessments of PM2.5and O3,during the first stage of CAAs（2013 to 2017）,the mean GLE was 1.87 *** of the sum of the GLE was disproportionally distributed in about one quarter of the population exposed （GI 0.44）.During the second stage of CAAs（2017 to 2020）,the mean GLE increased to 3.94 months and geographic inequality decreased （GI 0.18）.According to our assessments,CAAs were enhanced,from the first to second stages,in terms of not only preventing premature mortality but also ameliorating health *** enhancements were related to increased sensitivity to the health effects of air pollution and synergic control of PM2.5and *** findings will contribute to optimizing future CAAs.

关键词： clean air action public health inequality fine particulate matter ozone

The mechanisms of enhanced thickness-dependent DC breakdown strength of EP/MWCNTs nanocomposites

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High Voltage 2024年第2期9卷 440-452页

作者： Zhen Li He Gao Longfei Zhang Shouming Wang Ji Liu Shengtao Li key laboratory of engineering Dielectrics and Its Application Ministry of EducationHarbin University of Science and TechnologyHarbinChina state key laboratory of Electrical Insulation and Power Equipment Xi'an Jiaotong UniversityXi'anChina

Owing to advanced power electronic and electrical applications developing towards miniaturisation and integration,the thickness-dependent DC breakdown mechanism of epoxy/multiwall-carbon-nanotube nanocomposites is under *** results indicate that the breakdown strength of nanocomposites containing 0.05 wt%multiwall-carbon-nanotubes rises by~18%,and the breakdown strength falls exponentially with increasing *** clarify the microscopic mechanism,a simulation model of DC breakdown,including carriers transport and segmental dynamics,is developed,and the accordant simulation results with experimental results indicate that the thickness-dependent DC breakdown of epoxy/multiwall-carbon-nanotube nanocomposites is determined both by segment chain dynamics and charge *** to the breakdown model analysis,the effects of multiwall-carbon-nanotube on enhanced breakdown strength are caused by the increased amount of deep traps in the interfacial region,while the influence of thickness is attributed to the enlarged segment chain displacement and electric field distortion as the voltage raising time increases.

关键词： strength breakdown nanocomposites

Subpicosecond laser ablation behavior of a magnesium target and crater evolution:Molecular dynamics study and experimental validation

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Chinese Physics B 2024年第7期33卷 613-622页

作者：江国龙周霞 state key laboratory of Structural Analysis for Industrial Equipment Department of Engineering MechanicsFaculty of Vehicle Engineering and MechanicsDalian University of TechnologyDalian 116024China

The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics(MD) simulations and *** simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms,which has laser-induced high ***,under high fluence and short pulse width laser irradiation,the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the *** addition,Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg[0001].The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by *** results show that,under multiple pulsed laser irradiation,not only does the crater depth increase linearly with the pulse number,but also the quadratic term and constant term of the fitted crater profile curve increase linearly.

关键词： laser-material interaction molecular dynamics(MD)simulation ablation crater morphology magnesium

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Underestimated benefits of NO_(x) control in reducing SNA and O_(3) based on missing heterogeneous HONO sources

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Frontiers of Environmental Science & engineering 2024年第3期18卷 57-67页

作者： Shuping Zhang Haotian Zheng Jun Liu Yao Shi Tianzeng Chen Chaoyang Xue Fenfen Zhang Yueqi Jiang Xiangping Zhang Shovan Kumar Sahu Biwu Chu Jia Xing state key Joint laboratory of Environment simulation and Pollution Control School of EnvironmentTsinghua UniversityBeijing 100084China China Academy of Civil Aviation Science and Technology Beijing 100028China state key Joint laboratory of Environment simulation and Pollution Control Research Center for Eco-Environmental SciencesChinese Academy of SciencesBeijing 100085China Yellow River Institute of Hydraulic Research Zhengzhou 450003China Centre for Climate Research Singapore Meteorological Service SingaporeSingapore 537054Singapore

Substantial NO_(x) emission mitigation is crucial for the synergistic reduction of particulate matter and ozone(O_(3))pollution in *** traditional air quality model does not consider heterogeneous HONO chemistry,leading to uncertainties in estimating the benefits of NO_(x) *** studies have shown that the parameterization of heterogeneous HONO formation increases both the simulated value of sulfate–nitrate–ammonium(SNA)and that of O_(3),thus adding the heterogeneous reactions of HONO into air quality models inevitably leads to changes in the estimated benefits of NO_(x) *** we investigated the changes in SNA and O_(3)concentrations from NO_(x) emission reduction before and after adding heterogeneous HONO reactions in the Community Multi-Scale Air Quality(CMAQ)*** heterogeneous HONO reactions in the simulation improved the benefits of NO_(x) reduction in terms of SNA control in *** 80%NO_(x) reduction,the reduction in SNA increased from 36.9%without considering heterogeneous HONO reactions to 42.8%with heterogeneous HONO *** reduction in the maximum daily 8h average(MDA8)O_(3)in summer caused by NO_(x) reduction increased slightly from 4.7%to 5.2%after adding heterogeneous HONO *** results in this study highlight the enhanced effectiveness of NO_(x) controls for the reduction of SNA and O_(3)after considering heterogeneous HONO formation in a complex chemical ambient,demonstrating the importance of NO_(x) controls in reducing PM2.5 and O_(3)pollution in China.

关键词： Heterogeneous HONO NO_(x) reduction PM_(2.5) O_(3)

UAV swarm air combat maneuver decision-making method based on multi-agent reinforcement learning and transferring

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Science China(Information Sciences) 2024年第8期67卷 49-66页

作者： Zhiqiang ZHENG Chen WEI Haibin DUAN state key laboratory of Virtual Reality Technology and Systems School of Automation Science and Electrical Engineering Beihang University

During short-range air combat involving unmanned aircraft vehicle(UAV) swarms, UAVs must make accurate maneuver decisions based on information from both enemy and friendly UAVs. This dual requirement of competition and cooperation presents a significant challenge in the field of unmanned air combat. In this paper, a method based on multi-agent reinforcement learning(MARL) is proposed to address this issue. An actor network containing three subnetworks that can handle different types of situational information is designed. Hence, the results from simpler one-on-one scenarios are leveraged to enhance the complex swarm air combat training process. Separate state spaces for local and global information are designed for the actor and critic networks. A detailed reward function is proposed to encourage *** prevent lazy participants in air combat, a reward assignment operation is applied to distribute these dense rewards. simulation testing and ablation experiments demonstrate that both the transfer operation and reward assignment operation can effectively deal with the swarm air combat scenario, and reflect the effectiveness of the proposed method.

关键词： multi-agent reinforcement learning reward assignment short-range air combat transfer UAV swarm

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Study on Dynamic Mechanical Behavior of Al-Mg-Si Alloy

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Journal of Wuhan University of Technology(Materials Science) 2024年第2期39卷 454-462页

作者：陶小旺 LIU Jibo LIU Xianbin CHEN Jianbin WANG Yonggang 汪小锋 key laboratory of Impact and safety engineering Ministry of EducationNingbo UniversityNingbo 315211China Ningbo Zhanci New Material Co. Ltd.Ningbo 315338China

The dynamic mechanical behavior of Al-Mg-Si alloy was investigated under different strain rates by mechanical property and microstructure characterization,constitutive behavior analysis and numerical simulation in the present *** the strain rate increases,the yield strength,ultimate tensile strength and elongation increase first,then remain almost constant,and finally *** alloy always exhibits a typical ductile fracture mode,not depending on the strain ***,as the strain rate increases,the number of dimples gradually *** deformation can refine grains,however,the grain structure is slightly affected by the strain *** optimized Johnson-Cook constitutive equation was used to describe the mechanical behavior and obtained by fitting the true stress-strain *** parameter C was described by a function related to the strain *** fitting true stress-strain curves by the JC model agree very well with the experimental true stress-strain *** true stress-strain curves calculated by the finite element numerical simulation agree well with the experimental true stress-strain curves.

关键词： Al-Mg-Si alloy strain rate mechanical property microstructure Johnson-Cook model finite element simulation

High Efficiency Formamidinium-Cesium Perovskite-Based Radio-Photovoltaic Cells

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Energy & Environmental Materials 2024年第1期7卷 164-171页

作者： Runlong Gao Rui Chen Pengying Wan Xiao Ouyang Qiantao Lei Qi Deng Xinyu Guan Guangda Niu Jiang Tang Wei Chen Zonghao Liu Xiaoping Ouyang Linyue Liu Sino-French Institute of Nuclear engineering and Technology Sun Yat-Sen University state key laboratory of Intense Pulsed Radiation simulation and Effect Northwest Institute of Nuclear Technology Wuhan National laboratory for Optoelectronics Huazhong University of Science and Technology School of Microelectronics Xi’an Jiaotong University Shanghai Institute of Applied Physics Chinese Academy of Sciences key laboratory of Beam Technology of Ministry of Education College of Nuclear Science and Technology Beijing Normal University

Radio-photovoltaic cell is a micro nuclear battery for devices operating in extreme environments,which converts the decay energy of a radioisotope into electric energy by using a phosphor and a photovoltaic *** phosphors with high light yield and good environmental stability have been developed,but the performance of radio-photovoltaic cells remains far behind expectations in terms of power density and power conversion efficiency,because of the poor photoelectric conversion efficiency of traditional photovoltaic converters under low-light conditions.

关键词： formamidinium-cesium perovskite phosphor photovoltaic converter power conversion efficiency radio-photovoltaic cell