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Acta Mechanica Sinica 2007年第5期23卷 495-501页

作者： Xiwen Zhang Zhaohui Yao Yan Zhang Shangdong Xu Department of engineering Mechanics Tsinghua University Beijing 100084 China institute of Heart Pulmonary and Vascular Diseases Capital University of Medical Science Affiliated Beijing Anzhen Hospital Beijing 100029 China

Pulsatile flow fields in rigid abdominal aortic aneurysm （AAA） models were investigated numerically, and the simulation results are found in good agreement with particle image velocimetry （PIV） measurements. There are one or more vortexes in the AAA bulge, and a fairly high wall shear stress exists at the distal end, and thus the AAA is in danger of rupture. Medical treatment consists of inserting a vascular stent-graft in the AAA, which would decrease the blood impact to the inner walls and reduce wall shear stress so that the rupture could be prevented. A new computational model, based on porous medium model, was developed and results are documented. Therapeutic effect of the stent-graft was verified numerically with the new model.

关键词： Abdominal aortic aneurysm Numerical simulation Particle image velocimetry Wall shear stress Stent-graft

Quantitative micro-electrochemical study of duplex stainless steel 2205 in 3.5wt%NaCl solution

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International Journal of Minerals,Metallurgy and Materials 2022年第11期29卷 2053-2063页

作者： Shuangyu Cai Keke Lu Xinnan Li Lei Wen Feifei Huang Ying Jin National Center for Materials Service Safety University of Science and Technology BeijingBeijing 100083China Nuclear Equipment Division Beijing Institute of Nuclear EngineeringChina Nuclear Power Engineering Co.Ltd.Beijing 100840China Innovation Group of Marine engineering Materials and Corrosion Control Southern Marine Science and Engineering Guangdong LaboratoryZhuhai 519080China

Duplex stainless steels(DSSs)are suffering from various localized corrosion attacks such as pitting,selective dissolution,crevice corrosion during their service *** is of great value to quantitatively analyze and grasp the micro-electrochemical corrosion behavior and related mechanism for DSSs on the micrometer or even smaller *** this work,scanning Kelvin probe force microscopy(SKPFM)and energy dispersive spectroscopy(EDS)measurements were performed to reveal the difference between the austenite phase and ferrite phase in microregion of DSS *** traditional electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization(PDP)tests were employed for micro-electrochemical characterization of DSS 2205 with different proportion phases inϕ40 andϕ10μm micro *** of them can only be utilized for qualitative or semi-quantitative micro-electrochemical characterization of DSS *** perturbation method was employed for quantitative micro-electrochemical characterization of DSS *** is more,the applicable conditions of coulostatic perturbation were analyzed in depth by establishing a detailed electrochemical interface circuit.A series of microregion coulostatic perturbations for DSS 2205 with different proportion phases inϕ10μm micro holes showed that as the austenite proportion increases,the corresponding polarization resistance of microregion increases linearly.

关键词： duplex stainless steel 2205 quantitative micro-electrochemical study electrochemical impedance spectroscopy coulostatic perturbation scanning Kelvin probe force microscopy

Variability of urban fractional vegetation cover and its driving factors in 328 cities in China

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Science China Earth Sciences 2024年第2期67卷 466-482页

作者： Fei FENG Xin YANG Baoquan JIA Xiaoting LI Xianwen LI Chengyang XU Kaicun WANG Research Centre of Urban Forestry Key Laboratory for Silviculture and Forest Ecosystem of State Forestry and Grassland AdministrationBeijing Forestry UniversityBeijing100083China State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing Normal UniversityBeijing100875China Research institute of Forestry Chinese Academy of ForestryBeijing100091China School of Architecture Tsinghua UniversityBeijing100084China College of Urban and Environmental Sciences Sino-French Institute for Earth System ScienceInstitute of Carbon NeutralityPeking UniversityBeijing100871China

Urban green space promotes the health of urban residents,enhances urban ecosystem biodiversity,mitigates environmental pollution,and attenuates urban heat island ***,urban vegetation cover is highly heterogeneous and difficult to *** this study,the variation of urban fractional vegetation cover(FVC)in 328 cities in China from 1990 to2022 was quantified based on Landsat satellite data at a 30-m *** was found that from 1990 to 2005,due to increases in building density and impervious surfaces in cities,the national mean urban vegetation cover decreased from 0.38 to ***2005,urban vegetation cover began to reverse,reaching 0.45 in *** increasing trend was most pronounced in newly built urban *** decrease in average urban vegetation cover before 2005 was mainly due to the expansion of low vegetation cover areas,while the increase in urban vegetation cover after 2005 manifested as the expansion of high vegetation cover *** reversal in the trend of urban vegetation cover change after 2004 is related to the gradual implementation of national policies requiring increased urban green space *** urban gross domestic product(GDP)showed the highest correlation with changes in urban vegetation *** large and medium-sized cities,the top three factors influencing vegetation cover were GDP,urban population,and ***,for cities in arid/semi-arid regions,changes in vegetation cover were more sensitive to climatic factors(such as precipitation).Although the urban vegetation cover in China has substantially increased in recent years,the urban green space in small-sized cities and in the old urban districts of large-sized cities still have room to improve.

关键词： Urban vegetation Urban vegetation cover Urbanization Remote sensing

Multilayered electret films based triboelectric nanogenerator

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Nano Research 2016年第5期9卷 1442-1451页

作者： Tao Zhou Limin Zhang Fei Xue Wei Tang Chi Zhang Zhong Lin wang beijing institute of Nanoenergy and Nanosystems Chinese Academy of Sciences National Center for Nanoscience and Technology Beijing 100083 China School of Material Science and engineering Georgia Institute of Technology Atlanta Georgia 30332 USA

A triboelectric nanogenerator （TENG） is a simple and cost effective device that converts ambient mechanical energy into electricity based on the surface contact electrification of thin films. The limited surface charge density may affect the overall performance of the TENG. In this paper, a novel electret film based TENG （E-TENG） fabricated by corona charging is proposed that greatly enhances the effective surface charge density of the thin films as compared to those subjected to contact electrification. The short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENG have been investigated, using different corona charging voltages, pinpoint distances and times in order to explore the optimum experimental conditions. The short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENG are found to be about seven times larger than those of the ordinary polytetrafluoroethylene （PTFE） film based TENG. Based on corona charging, several multilayered E-TENGs have been fabricated, and the short-circuit current, transferred electric charge density, and open-circuit voltage of the E-TENGs with different number of layers are studied for achieving optimal performances. This work offers an effective approach for improving the effective surface charge density and thereby increasing the output capability of the TENG, which would greatly promote TENG applications in self-powered portable electronics and sensor networks.

关键词： triboelectric nanogenerator electret thin film corona charging energy harvesting

Effect of molybdenum content on the microstructure and corrosion behavior of FeCoCrNiMox high-entropy alloys

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Journal of Materials Science & Technology 2020年第11期42卷 64-73页

作者： Chunduo Dai Tianliang Zhao Cuiwei Du Zhiyong Liu Dawei Zhang institute for Advanced Materials and Technology University of Science and Technology BeijingBeijing 100083China Key Laboratory for Corrosion and Protection of The Ministry of Education(MOE) Beijing 100083China beijing Advanced Innovation Center for Materials Genome engineering University of Science and Technology BeijingBeijing 100083China Materials Genome institute of Shanghai University Shanghai 200444China

The effect of Mo content on the microstructure revolution and corrosion behavior of cast FeCoCrNiMox high-entropy alloys in chloride environments were *** indicate that FeCoCrNi and FeCoCrNiMo0.1 alloys are in single FCC solid *** precipitates form in FeCoCrNiMo0.3 and increase in FeCoCrNiMo0.6 *** occurs on FeCoCrNi and FeCoCrNiMo0.1 alloys while FeCoCrNiMo0.3 and FeCoCrNiMo0.6 alloys suffer from preferential localized corrosion at the regions depleted in Cr and *** higher Cr2O3/Cr(OH)3 ratio and the incorporation of Mo oxides make the passive film more protective and the corrosion resistance of the FeCoCrNiMo0.1 alloy is thus *** correlation between microstructure and corrosion behavior and the corresponding corrosion mechanism were clarified.

关键词： High-entropy alloys Corrosion behavior Precipitate

OUTPUT-FEEDBACK CONTROL FOR NONHOLONOMIC systemS WITH LINEAR GROWTH CONDITION

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Journal of systems Science & Complexity 2011年第5期24卷 862-874页

作者： Guiling JU Weihai SUN Yuqiang WU Department of Mathematics Armored Force Engineering Institute Beijing 100072 China. institute of Automation Qufu Normal University Qufu 273165 China

This paper deals with the stabilization of the nonholonomic systems with strongly nonlinear uncertainties. The objective is to design an output feedback law such that the closed-loop system is globally asymptotically regulated at the origin. The systematic strategy combines the input-state scaling technique with the backstepping technique. A novel switching control strategy based on the output measurement of the first subsystem is employed to make the subsystem far away from the origin. The simulation demonstrates the effectiveness of the proposed controller.

关键词： Backstepping global asymptotic stabilization input-state scaling nonholonomic systemwith uncertainties switching control strategy.

Phase separation in Sr doped BiMnO_3

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Chinese Physics B 2014年第3期23卷 446-450页

作者：李冠男饶光辉黄清镇高庆庆骆军刘广耀李静波梁敬魁 beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences School of Materials Science and engineering Guilin University of Electronic Technology NIST center for Neutron Research National Institute of Standards and Technology School of Materials Science and engineering Beijing Institute of Technology

Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and physical property measurements. All the experiments indicate that a phase separation occurs at the temperature coinciding with the reported charge ordering temperature （Tco） in the literature. Below the reported TCO, both the phases resulting from the phase separation crystallize in the orthorhombically distorted perovskite structure with space group Imma. At lower temperature, these two phases order in the CE-type antiferromagnetic structure and the A-type antiferromagnetic structure, respectively. However, a scrutiny of the high-resolution NPD and XRD data at different temperatures and the electron diffraction exper- iment at 300 K did not manifest any evidence of a long-range charge ordering （CO） in our investigated samples, suggesting that the anomalies of physical properties such as magnetization, electric transport, and lattice parameters at the TCO might be caused by the phase separation rather than by a CO transition.

关键词： phase separation neutron/X-ray powder diffraction charge/orbital order

Enhanced thermoelectric performance of n-type TiCoSb halfHeusler by Ta doping and Hf alloying

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Rare Metals 2021年第1期40卷 40-47页

作者： Rui-Fang Wang Shan Li Wen-Hua Xue Chen Chen Yu-Mei Wang Xing-Jun Liu Qian Zhang School of Materials Science and engineering Institute of Materials Genome and Big DataHarbin Institute of TechnologyShenzhen 518055China beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of ScienceBeijing 100190China

The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping,while the pristine TiCoSb is intrinsically *** is thus desired to obtain a comparable n-type counterpart through optimization of electron *** this work,n-type Ti_(0.9-x)HfxTa_(0.1)CoSb half-Heuslers were fabricated by arc melting,ball milling,and spark plasma *** optimized carrier concentration,together with a decreased lattice thermal conductivity,was obtained by Ta doping at the Ti site,leading to a peak figure of merit(ZT)of 0.7 at 973 K in Ti_(0.9)Ta_(0.1)-*** further alloying Hf at the Ti site,the lattice thermal conductivity was significantly reduced without deteriorating the power *** a result,a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300-973 K were achieved in Ti_(0.6)Hf_(0.3)Ti_(0.1)*** work demonstrates that n-type TiCoSb-based halfHeuslers are promising thermoelectric materials.

关键词： Thermoelectric Half-Heusler N-type TiCoSb

First-principles study of solute diffusion in Ni3Al

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Chinese Physics B 2017年第9期26卷 126-132页

作者：刘少华李孜王崇愚 School of Materials Science and engineering Tsinghua UniversityBeijing 100084China institute of Applied Physics and Computational Mathematics Beijing 100088China Department of Physics Tsinghua UniversityBeijing 100084China

Using first-principles calculations in combination with Wagner–Schottky and kinetic Monte Carlo methods, the diffusion behaviors of solutes via various vacancy-mediated diffusion mechanisms in L12 γ-Ni3Al were investigated. The formation energies of the point defects and the migration energies for solutes were calculated. Adding alloying elements can decrease the defect-formation energies of NiAl, increase the defect-formation energies of AlNi, and have little effect on the formation energy of VNi. The migration energies of solutes are related with the site preference and the diffusion mechanism. The diffusion coefficients of Ni, Al, and solutes were calculated, and the concentration of antisite defects plays a crucial role in the elemental diffusion.

关键词： nickel-based superalloy diffusion Ni3Al first-principles

Galerkin-based quasi-smooth manifold element(QSME)method for anisotropic heat conduction problems in composites with complex geometry

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Applied Mathematics and Mechanics(English Edition) 2024年第1期45卷 137-154页

作者： Pan WANG Xiangcheng HAN Weibin WEN Baolin WANG Jun LIANG School of Civil engineering Central South UniversityChangsha 410083China institute of Advanced Structure Technology Beijing Institute of TechnologyBeijing 100081China School of Science Harbin Institute of TechnologyShenzhen 518055Guangdong ProvinceChina

The accurate and efficient analysis of anisotropic heat conduction problems in complex composites is crucial for structural design and performance evaluation. Traditional numerical methods, such as the finite element method(FEM), often face a trade-off between calculation accuracy and efficiency. In this paper, we propose a quasi-smooth manifold element(QSME) method to address this challenge, and provide the accurate and efficient analysis of two-dimensional(2D) anisotropic heat conduction problems in composites with complex geometry. The QSME approach achieves high calculation precision by a high-order local approximation that ensures the first-order derivative *** results demonstrate that the QSME method is robust and stable, offering both high accuracy and efficiency in the heat conduction analysis. With the same degrees of freedom(DOFs), the QSME method can achieve at least an order of magnitude higher calculation accuracy than the traditional FEM. Additionally, under the same level of calculation error, the QSME method requires 10 times fewer DOFs than the traditional FEM. The versatility of the proposed QSME method extends beyond anisotropic heat conduction problems in complex composites. The proposed QSME method can also be applied to other problems, including fluid flows, mechanical analyses, and other multi-field coupled problems, providing accurate and efficient numerical simulations.

关键词： anisotropic heat conduction quasi-smooth manifold element(QSME) composite with complex geometry numerical simulation finite element method(FEM)