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Incipient plasticity and activation volume of dislocation nucleation for TiZrNbTaMo high-entropy alloys characterized by nanoindentation

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Journal of Materials Science & Technology 2019年第5期35卷 812-816页

作者： Shao-Ping Wang jian xu Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences 72 Wenhua Road Shenyang 110016 China University of Chinese Academy of Sciences 19(A) Yuquan Road Beijing 100049 China

With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys(HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation behavior in these solid-solution alloys. It is shown that the maximum shear stress (max)required for dislocation nucleation is determined to be 1/16-1/12 and 1/18-1/14 of shear modulus for the TiZrNbTa and TiZrNbTaMo HEAs, respectively, which is nearly comparative to the theoretical shear stress of these alloys. The activation volumes of dislocation nucleation the TiZrNbTa and TiZrNbTaMo HEAs are determined to be 1.2 b^3 for and 1.3 b^3, respectively, which is substantially irrespective of alloying with Mo. Furthermore, activation volumes of these two HEAs are on the order of cubic burger’s vector and only one-third of the value for TiZrHfNb HEA, suggesting that a heterogeneous nucleation of dislocation took place in a way of direct atom-vacancy exchange, rather than of the cooperative motion of several atoms. These findings reveal the unique feature in deformation of BCC solid-solution complex alloys.

关键词： High-entropy alloys Nanoindentation Refractory metals BCC phase Incipient plasticity

Changes in enzymes activity, substrate utilization pattern and diversity of soil microbial communities under cadmium pollution

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Journal of Environmental Sciences 2005年第5期17卷 802-807页

作者： Muhammad Akmal WANG Hai-zhen WU jian-jun xu jian-ming xu De-fu Institute of Soil and grater Resources and Environmental Science Zhejiang University Hangzhou 310029 China

Heavy metal pollution has received increasing attention in recent years mainly because of the public awareness of environmental issues. In this study we have evaluated the effect of cadmium （Cd） on enzymes activity, substrate utilization pattern and diversity of microbial communities in soil spiked with 0, 20, 40, 60, 80, and 100 mg/kg Cd, during 60 d of incubation at 25℃. Enzyme activities determined at 0, 15, 30, 45, and 60 d after heavy metal application（DAA） showed marked declines for various Cd treatments, and up to 60 DAA, 100 mg/kg Cd resulted in 50.1%, 47.4%, and 39.8% decreases in soil urease, acid phosphatase and dehydrogenase activities, respectively to control. At 60 DAA, substrate utilization pattern of soil microbial communities determined by inoculating Biolog ECO plates indicated that Cd addition had markedly inhibited the functional activity of soil microbial communities and multivariate analysis of sole carbon source utilization showed significantly different utilization patterns for 80 and 100 mg/kg Cd treatments. The structural diversity of soil microbial communities assessed by PCR-DGGE method at 60 DAA, illustrated that DGGE patterns in soil simplified with increasing Cd concentration, and clustering of DGGE profiles for various Cd treatments revealed that they had more than 50% difference with that of control.

关键词： enzyme activity microbial community soil cadmium

Dynamic fracture toughness of high strength metals under impact loading:increase or decrease

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Acta Mechanica Sinica 2011年第4期27卷 559-566页

作者： Ze-jian xu Yu-Long Li State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology 100081 Beijing China School of Aeronautics Northwestern Polytechnical University 710072 Xi'an China

An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness （DFT） of high strength metals always increases with the loading rate on the order of TPa.m1/2.s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar （SHPB） apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMnSiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor （DSIF） and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experimentsneed to be performed in a comparatively large striker velocity range.

关键词： Dynamic fracture. Fracture toughness Loadingrate effect - Hopkinson pressure bar High strength metal

A method to study interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel

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International Journal of Minerals,Metallurgy and Materials 2012年第9期19卷 821-826页

作者： Yuan-zhi Zhu jian-ping xu The Key Laboratory of the Ministry of Education of China for Ferrous Metallurgy and Resources Utilization Wuhan University of Science and Technology Wuhan 430081 China School of Materials and Metallurgy Wuhan University of Science and Technology Wuhan 430081 China

A novel diffusion couple method was used to investigate the interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel and its effects on phase transformation at the interface. It is discovered that the content of arsenic has great effect on grain growth and phase transformation at high temperature. When the arsenic content is no more than lwt%, there is no obvious grain growth and no obvious ferrite transitional region formed at the diffusion interface. However, when the arsenic content is no less than 5wt%, the grain grows very rapidly. In addition, the arsenic-enriched ferrite transitional layer forms at the diffusion interface in the hot-rolling process, which results from a slower diffusion rate of arsenic atoms than that of carbon in ferrite.

关键词： low carbon steel alloy steel arsenic diffusion bonding phase transformation grain growth

Suppression of oscillatory congestion via trunk link bandwidth and control gain in star network

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Applied Mathematics and Mechanics(English Edition) 2019年第1期40卷 25-48页

作者： Sainan WANG Shu ZHANG jian xu School of Aerospace Engineering and Applied Mechanics Tongji University

The time delay-induced instability in an Internet congestion control model is investigated. The star topology is considered, and the link bandwidth ratio and the control gain are selected as the tunable parameters for congestion suppression. The stability switch boundary is obtained by the eigenvalue analysis for the linearized system around the equilibrium. To investigate the oscillatory congestion when the equilibrium becomes unstable, the center manifold reduction and the normal form theory are used to study the periodic oscillation induced by the delay. The theoretical analysis and numerical simulation show that the ratio between bandwidths of the trunk link and the regular link,rather than these bandwidths themselves, is crucial for the stability of the congestion control system. The present results demonstrate that it is not always effective to increase the link bandwidth ratio for stabilizing the system, and for some certain delays, adjusting the control gain is more efficient.

关键词： Internet congestion control Hopf bifurcation delayed differential equation stability normal form

Organophosphate esters in sediment from Taihu Lake,China:Bridging the gap between riverine sources and lake sinks

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Frontiers of Environmental Science & Engineering 2022年第3期16卷 35-47页

作者： Wenping Zhang Changsheng Guo Jiapei Lv xu Li jian xu State Key Laboratory of Environmental Criteria and Risk Assessment Chinese Research Academy of Environmental SciencesBeijing 100012China State Environmental Protection Key Laboratory of Ecological Effect and Risk Assessment of Chemicals Chinese Research Academy of Environmental SciencesBeijing 100012China Center for Environmental Health Risk Assessment and Research Chinese Research Academy of Environmental SciencesBeijing 100012China

Surface sediment samples from Taihu Lake in China and its inflow rivers,along with two lake sediment core samples,were collected and analyzed for organophosphate esters(OPEs).The concentrations of total OPEs varied from 28.60 ng/g to 158.72 ng/g(median:54.25 ng/g)in river surface sediment and from 62.57 ng/g to 326.84 ng/g(median:86.37 ng/g)in lake *** phosphate(TnBP)was the predominant compound in river surface sediment,and tris(2-butoxyethyl)phosphate was predominant in lake *** contamination occurred in the north-west region,which was related to the high level of urbanization and high usage of *** sediment–water partition coefficients of OPEs(log_(Koc))were calculated,showing a significant correlation with logKow(p<0.05).The concentration and composition of OPEs in two sediment cores varied due to the different sampling locations,with more OPE species found in the northern region than in the southern *** component analysis and positive matrix factorization indicated that sewage discharges,vehicle emissions,and atmospheric deposition were the possible sources of OPEs in Taihu Lake ***(1-chloro-2-propyl)phosphate,tris(2-chloroethyl)phosphate,and TnBP were the main OPEs causing ecological risks.

关键词： Organophosphate esters Partition Vertical distribution Composition profile Positive matrix factorization

An introduction and guidance for neurodynamics

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Science Bulletin 2015年第22期60卷 1969-1971页

作者： Jun Ma jian xu Department of Physics Lanzhou University of Technology chool of Aerospace Engineering and Applied Mechanics Tongji University

Diseases associated with nervous system have brought much pain and anxiety for *** a result,clinical diagnosis such as big data analysis based on functional magnetic resonance imaging(f MRI)[1],computational neurodynamics,and cognitive neurodynamics have been paid much *** is believed that potential mechanism for abnormality[2]in nervous system could be discerned by detecting dynamic behavior of central

关键词：神经动力学中枢神经系统功能性磁共振成像数据分析 fMRI 临床诊断理论物理认知功能

Fin performance of 3-D aerator devices with backward lateral deflectors

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Journal of Hydrodynamics 2020年第2期32卷 410-413页

作者： jian-rong xu jian-hua Wu Yu Peng Fei Ma Powerchina Huadong Engineering Corporation Limited Hangzhou311122China College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing210098China

In the present work,a 3-D aerator device with backward lateral deflectors,called BLD-3-D aerator device,is developed,and the lateral cavity and fin performance of the BLD-3-D aerator device are experimentally *** findings show that,the relative lateral cavity length with backward lateral deflectors is shorter than that with current lateral deflectors under the same approach flow conditions,and on the basis of the results of the relative cavity length ratio between the lateral and bottom aerators the BLD-3-D aerator device is of remarkable performance for the water fin control thanks to the decrease of the relative lateral cavity length.

关键词： Aerator backward lateral deflector BLD-3-D aerator device cavity water fin

Incorporating multi-kernel function and Internet verification for Chinese person name disambiguation

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Frontiers of Computer Science 2016年第6期10卷 1026-1038页

作者： Ruifeng xu Lin GUI Qin LU Shuai WANG jian xu Shenzhen Engineering Laboratory of Performance Robots at Digital Stage Harbin Institute of Technology Shenzhen Graduate School Shenzhen 518055 China Department of Computing The Hong Kong Polytechnic University Hong Kong China

The study on person name disambiguation aims to identify different entities with the same person name through document linking to different entities. The traditional disambiguation approach makes use of words in documents as features to distinguish different entities. Due to the lack of use of word order as a feature and the limited use of external knowledge, the traditional approach has performance limitations. This paper presents an approach for named entity disambiguation through entity linking based on a multi- kernel function and Internet verification to improve Chinese person name disambiguation. The proposed approach extends a linear kernel that uses in-document word features by adding a string kernel to construct a multi-kernel function. This multi-kernel can then calculate the similarities between an input document and the entity descriptions in a named per- son knowledge base to form a ranked list of candidates to different entities. Furthermore, Internet search results based on keywords extracted from the input document and entity descriptions in the knowledge base are used to train classifiers for verification. The evaluations on CIPS-SIGHAN 2012 person name disambiguation bakeoff dataset show that the use of word orders and Internet knowledge through a multi-kernel function can improve both precision and recall and our system has achieved state-of-the-art performance.

关键词： Chinese person name disambiguation Internet verification string kemel multi-kemel function machine learning