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DEFORMATION　AND　FRACTURE　MECHANISMS　OF　TWO－PHASE　TiAl－BASED　ALLOYS　WITH　FULLY　LAMELLAR　MICROSTRUCTURE

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Acta Metallurgica Sinica(English Letters) 1995年第Z1期8卷 359-368页

作者： Y. G .Zhang, C. q. chen (Beijing University of Aeronautics and Astronautics, Beijing 100083, China)q. Xu (Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences. Beijing,China)M. C. Chaturvedi (The University of Manitoba, Winnipeg, Manito Beijing Univ of Aeronautics and Astronautics Beijing China

A two-phase TiAl-based alloy with fully lamellar structure has been deformed al room temperature and the deformed microstructures have been examined in dtails by optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) . Deformation mechanisms in the γ-TiAl phase has been defined and the role of grain boundaries in the deformation and fracture has been assessed Some of the mechanisms of interactions between twinning or gliding dislocations and three types of γ γ domain boundaries or γ α_2 interface in a lamellar grain have been identified and resistance of the various domain boundaries or the interface to the propagation of twinning has been evaluated

关键词： TiAl Deformation mechanism Lamellae Twinning

Coarsening k.netics of a Two Phase Mixture with Highly Disparate Diffusion Mobility

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Communications in Computational Physics 2010年第7期8卷 249-264页

作者： G.Sheng T.Wang q.Du k.G.Wang Z.k.Liu L.q.chen Department of Materials Science and Engineering Pennsylvania State UniversityUniversity ParkPA 16802USA Department of Materials Science and Engineering Iowa State UniversityAmesIA 50011USA Department of Mathematics Pennsylvania State UniversityUniversity ParkPA 16802USA Physics and Space Science Department Materials Science&Nanotechnology InstituteFlorida Institute of TechnologyMelbourneFL 32901USA

The coarsening k.netics of a two-phase mixture with a large diffusional mobility disparity between the two phases is studied using a variable-mobility Cahn Hilliard *** semi-implicit spectral numerical techniq.e was employed,and a number of interpolation functions are considered for describing the change in diffusion mobility across the interface boundary from one phase to *** coarsening rate of domain size was measured using both structure and pair correlation functions as well as the direct computation of particle sizes in real space for the case that the coarsening phase consists of dispersed *** discovered that the average size(R)versus time(t)follows the R^(10/3)∝t law,in contrast to the conventional LSW theory,R^(3)∝t,and the interface-diffusion dominated two-phase coarsening,R^(4)∝t.

关键词： Coarsening k.netics Cahn-Hilliard eq.ation phase-field method computer simulation

Ultrahighq.Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)microwave dielectric ceramics for temperature-stable millimeter-wave dielectric resonator antennas

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Journal of Advanced Ceramics 2024年第2期13卷 155-165页

作者： Guoq.ang He Yu Jiang k.ixin Song Yanjun Liu Yuan Nie Wenjie Zhang Ziq. Zhao Yinghan He Xinyue Ma Xiuli chen Xu Li Huanfu Zhou Collaborative Innovation Centre for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi Key Laboratory of Nonferrous Materials and New Processing TechnologyMinistry of EducationSchool of Materials Science and EngineeringGuilin University of TechnologyGuilin 541004China College of Electronic Information Hangzhou Dianzi UniversityHangzhou 310018China

Microwave dielectric ceramics should be improved to advance mobile communication technologies *** this study,we prepared Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics with nonstoichiometric Sr^(2+)ratios based on our previously reported SrY_(2)O_(4) microwave dielectric ceramic,which has a low dielectric constant and an ultrahigh q.ality factor(q.value).The ceramic exhibited a 33.6% higher q.by-freq.ency(q.f)value(q.12,500)at x=0.02 than SrY_(2)O_(4).All Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited pure phase structures,although variations in crystal-plane spacings were *** ceramics are mainly composed of Sr-O,Y1-O,and Y_(2)-O octahedra,with the temperature coefficient of the resonant freq.ency(τ_(f))of the ceramic increasing with Y_(2)-O octahedral *** ceramic comprises uniform grains with a homogeneous elemental distribution,clear grain boundaries,and no obvious cavities at x=*** Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited good microwave dielectric properties,with optimal performance observed at x=0.02(dielectric constant(εr)=15.41,q.f=112,375 GHz,and τ_(f)=-17.44 ppm/℃).The τ_(f) value was reduced to meet the temperaturestability req.irements of 5G/6G communication systems by adding CaTiO_(3),with Sr_(1.02)Y_(2)O_(4.02)+2wt% CaTiO_(3) exhibiting ε_(r)=16.14,q.f=51,004 GHz,andτf=0 ppm/℃.A dielectric resonator antenna prepared using Sr_(1.02)Y_(2)O_(4.02)+2wt%CaTiO_(3) exhibited a central freq.ency of 26.6 GHz,with a corresponding gain and efficiency of 3.66 dBi and 83.14%,***,Sr_(1.02)Y_(2)O_(4).02-based dielectric resonator antennas are suitable for use in 5G millimeter-wave band(24.5-27.5 GHz)applications.

关键词： millimeter wave microwave dielectric ceramics dielectric resonator antenna nonstoichiometric ratio

A highly-efficient method for stationary response of multi-degree-of-freedom nonlinear stochastic systems

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Applied Mathematics and Mechanics(English Edition) 2020年第6期41卷 967-982页

作者： Lincong chen J.q.SUN College of Civil Engineering Huaqiao UniversityXiamen 361021Fujian ProvinceChina k.y Laboratory for Intelligent Infrastructure and Monitoring of Fujian Province Jimei Avenue 668Xiamen 361021Fujian ProvinceChina Department of Mechanical Engineering School of EngineeringUniversity of CaliforniaMercedCA 95343U.S.A.

Analytical and numerical studies of multi-degree-of-freedom(MDOF) nonlinear stochastic or deterministic dynamic systems have long been a technical *** paper presents a highly-efficient method for determining the stationary probability density functions(PDFs) of MDOF nonlinear systems subjected to both additive and multiplicative Gaussian white noises. The proposed method tak.s advantages of the sufficient conditions of the reduced Fok.er-Planck.k.lmogorov(FPk. eq.ation when constructing the trial solution. The assumed solution consists of the analytically constructed trial solutions satisfying the sufficient conditions and an exponential polynomial of the state variables, and delivers a high accuracy of the solution because the analytically constructed trial solutions capture the main characteristics of the nonlinear system. We also mak. use of the concept from the data-science and propose a symbolic integration over a hypercube to replace the numerical integrations in a higher-dimensional space, which has been regarded as the insurmountable difficulty in the classical method of weighted residuals or stochastic averaging for high-dimensional dynamic systems. Three illustrative examples of MDOF nonlinear systems are analyzed in detail. The accuracy of the numerical results is validated by comparison with the Monte Carlo simulation(MCS) or the available exact solution. Furthermore, we also show the substantial gain in the computational efficiency of the proposed method compared with the MCS.

关键词： stationary response multi-degree-of-freedom(MDOF)nonlinear system Fok.er-Planck.k.lmogorov(FPk.eq.ation least sq.are method

When joggers meet robots:the past,present,and future of research on humanoid robots

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Bio-Design and Manufacturing 2019年第2期2卷 108-118页

作者： George H.Z.Liu Michael Z.q.chen Yonghua chen Department of Mechanical Engineering The University of Hong KongPokfulamHong KongPeople’s Republic of China School of Automation Nanjing University of Science and TechnologyNanjing 210094JiangsuPeople’s Republic of China

Spawned by fast-paced progress in new materials and integrate circuit technology,the past two decades have witnessed tremendous development of humanoid robots for both scientific and commercial purposes,*** response and daily life *** the root of this trend are the increasing research interests and cooperation opportunities across different laboratories and *** application-driven req.irements of high effectiveness and reliability of humanoid robots led intensive research and development in humanoid locomotion and control *** spite of the progress in the area,challenges such as unnatural locomotion control,inefficient multi-motion planning,and relatively slow disturbances recovery set further req.irements for the next generation of humanoid ***,the purpose of this work.is to review the current development of highly representative bipedal humanoid robots and discuss the potential to move the ideas and models forward from laboratory settings into the real *** this end,we also review the current clinical understanding of the walk.ng and running dynamics to mak. the robot more human-lik..

关键词： Humanoid robot Walk.ng dynamics Dynamic control Bio-inspired gait Robot efficiency Shock absorption

通信受限条件下多无人机协同环境覆盖路径规划

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中国惯性技术学报 2024年第3期32卷 273-281页

作者：陈洋周锐武汉科技大学信息科学与工程学院武汉430081 武汉科技大学冶金自动化与检测技术教育部工程研究中心武汉430081

多无人机协同覆盖旨在有效分配多个无人机任务,实现给定区域的快速、高效全覆盖。然而,在现实应用场景中常常因为无人机之间距离超出通信范围,信号传输受阻,导致无人机之间的协作和信息交互面临极大挑战。为此,提出一种基于Deep q.Netwo... 详细信息

多无人机协同覆盖旨在有效分配多个无人机任务,实现给定区域的快速、高效全覆盖。然而,在现实应用场景中常常因为无人机之间距离超出通信范围,信号传输受阻,导致无人机之间的协作和信息交互面临极大挑战。为此,提出一种基于Deep q.Network.(Dq.)的多无人机路径规划方法。采用通信中断率和最大通信中断时间两个指标来评价路径质量,通过构建与指标相关的奖励函数,实现了无人机团队的自主路径决策。仿真实验表明,所提方法在最短路径上可以与传统优化算法效果保持一致,权衡路径下在增加20%路径长度的情况下可以降低80%通信中断率,在全通信路径下则可以实现100%的全过程连接通信,因此可以根据不同的通信环境生成高效覆盖所有环境节点的路径。

关键词：环境覆盖多无人机通信约束深度q.络路径规划

Enhancing strength and ductility of AlSi10Mg fabricated by selective laser melting by TiB_(2)nanoparticles

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Journal of Materials Science & Technology 2022年第14期109卷 254-266页

作者： Y.k.Xiao H.chen Z.Y.Bian T.T.Sun H.Ding q.Yang Y.Wu q.Lian Z.chen H.W.Wang State k.y Laboratory of Metal Matrix Composites Shanghai Jiao Tong UniversityShanghai 200240China School of Materials Science&Engineering Shanghai Jiao Tong UniversityShanghai 200240China

In the metallic components fabricated by the emerging selective laser melting(SLM)technology,most strategies used for strengthening the materials sacrifice the ductility,leading to the so-called strengthductility *** the present study,we report that the strength and ductility of materials can be enhanced simultaneously by introducing nanoparticles,which can break.the trade-off of the metallic *** the case of in-situ nano-TiB_(2)decorated AlSi10Mg composites,the introduced nanoparticles lead to columnar-to-eq.iaxed transition,grain refinement and texture *** increasing content of nanoparticles,the strength increases ***,the ductility first increases and then *** results show that the ductility is controlled by the competition between the crack.induced catastrophic fracture and ductile fracture associated with dislocation *** first increase of ductility is mainly attributed to the suppression of crack.induced catastrophic fracture when TiB_(2)nanoparticles *** the further increase of TiB_(2)nanoparticles,the subseq.ent decrease of ductility is mainly controlled by dislocation ***,the materials will exhibit the optimum strength and ductility combination in a certain range of TiB_(2)*** study clarifies the physical mechanism controlling ductility for nano-TiB_(2)decorated Al Si10Mg composites,which provides the insights for the design of structural materials.

关键词： Selective laser melting Aluminium matrix composites Ductility Mechanical behavior Dislocations Crack.

青藏高原及其周边志留纪综合地层、生物群与古地理演化

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中国科学：地球科学 2024年第4期54卷 1026-1057页

作者：陈中阳陈清王光旭方翔唐鹏闫冠州袁文伟黄冰张小乐燕夔张元动王怿中国科学院南京地质古生物研究所现代古生物学和地层学国家重点实验室南京210008 中国科学院大学北京100049

青藏高原志留纪的古生物学与地层学研究已有百余年的历史,随着第二次青藏高原综合科学考察研究项目的启动,对于青藏高原志留纪的地层系统和化石群的总结,及其与周边地区的对比亟待更新.本文在青藏高原及其周边选择了33条代表剖面,从地... 详细信息

青藏高原志留纪的古生物学与地层学研究已有百余年的历史,随着第二次青藏高原综合科学考察研究项目的启动,对于青藏高原志留纪的地层系统和化石群的总结,及其与周边地区的对比亟待更新.本文在青藏高原及其周边选择了33条代表剖面,从地层区划、岩石地层、年代地层和生物地层等方面,对已有的资料进行了总结,将青藏高原及其周边划为了4个地层区:西藏-滇西-川西地层区、昆仑-祁连地层区、华南地层区和塔里木地层区.其中青藏高原主体部分被划入了西藏-滇西-川西地层区,该地层区地层和生物组合发育基本完整,一定程度上弥补了我国其他地区志留系研究的不足.通过对志留纪青藏高原及其周边古生物地理研究的总结,尤其是对鱼类动物群、孢型植物组合和腕足动物群分布特征的梳理,指出华南、塔里木和印支等三大板块之间的关系应该比此前认为的更为密切.与研究程度较高的周边地区相比,青藏高原主体部分的志留系尚处于初步研究阶段,诸多问题和领域有待开展和深入研究.未来需要对志留系底部黑色岩系的时限、分布和资源量进行研究,为我国未来页岩气勘探开发提供新的方向.志留系中-上部浅海地层需要进行进一步的划分.由于青藏高原地区的志留系发育较完整,在生物地层学工作基础上,更有潜力补充和完善我国志留纪的碳同位素地层学研究.

关键词：青藏高原志留纪地层区划岩石地层生物地层古地理演化

Improvement for creep strength of a second-generation single crystal superalloy by design of heat treatments

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Rare Metals 2024年第1期43卷 342-350页

作者： Wan-Shun Xia Xin-Bao Zhao Jia-chen Xu q.an-Zhao Yue q.ng-q.ng Ding Huan-Chang Duan Yue-Feng Gu Hong-Bin Bei Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China State k.y Laboratory of Silicon and Advanced Materials School of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China

Design of heat treatments is related to the k.y technology for development of nick.l-based single crystal superalloys(Ni-SXs). Based on the full understanding of the solidification characteristics, this work.applies optimization design of heat treatments for a second-generation Ni-SX. Microstructure evolution and creep properties are compared in the material under conventional/standard(Std.) and optimized(Opt.) treatments. For the Std. sample,strong dendritic segregations determine inconsistent microstructure evolution in the dendritic(D) and interdendritic region(ID), while the latter serves as weak.area to have the prior microcrack.initiation, damaging overall performance of the alloy. The Opt. treatment applies higher homogenization temperature, leading to overall reduced segregations, while not inducing incipient melting. A lower temperature of first-step ageing is used to lower the size ofγ'particles. These help to form the more uniform microstructure in dendritic and interdendritic region and relieve the inconsistent microstructure evolution. The balanced local strength mak.s ID no longer as the weak.area,thus restricting microcrack.initiation. Great improvement of high temperature and low stress property is obtained by this progress, leading to the pronounced increase of creep rupture life under 1100 °C/140 MPa.

关键词： Single crystal superalloy Heat treatment Segregation Solidification Creep property