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What Security Questions Do Developers Ask？ A Large-Scale Study of Stack Overflow Posts

Journal of Computer Science & Technology 2016年第5期31卷 910-924页

作者： xin-Li Yang David Lo xin Xia Zhi-Yuan wan Jian-Ling Sun College of Computer Science and Technology Zhejiang University Hangzhou 310027 China School of Information Systems Singapore Management University Singapore Singapore

Security has always been a popular and critical topic. With the rapid development of information technology, it is always attracting people＇s attention. However, since security has a long history, it covers a wide range of topics which change a lot, from classic cryptography to recently popular mobile security. There is a need to investigate security-related topics and trends, which can be a guide for security researchers, security educators and security practitioners. To address the above-mentioned need, in this paper, we conduct a large-scale study on security-related questions on Stack Overflow. Stack Overflow is a popular on-line question and answer site for software developers to communicate, collaborate, and share information with one another. There are many different topics among the numerous questions posted on Stack Overflow and security-related questions occupy a large proportion and have an important and significant position. We first use two heuristics to extract from the dataset the questions that are related to security based on the tags of the posts. And then we use an advanced topic model, Latent Diriehlet Allocation （LDA） tuned using Genetic Algorithm （GA）, to cluster different security-related questions based on their texts. After obtaining the different topics of security-related questions, we use their metadata to make various analyses. We summarize all the topics into five main categories, and investigate the popularity and difficulty of different topics as well. Based on the results of our study, we conclude several implications for researchers, educators and practitioners.

关键词： security Stack Overflow empirical study topic model

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3D atomic-scale growth characteristics of {10-12} twin in magnesium

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Journal of Magnesium and Alloys 2019年第3期7卷 474-486页

作者： xin wan Jing Zhang Xueyan Mo Fusheng Pan College of Materials Science and Engineering Chongqing UniversityChongqing 400044China National Engineering Research Center for Magnesium Alloys Chongqing 400044China

In this work,we carried out three-dimensional(3D)atomic-scale study on the growth characteristics of{10-12}twin in magnesium(Mg).The study was performed by MD simulations on Mg single crystals with an initial twin nucleus structures.A detailed atomistic analysis reveals that a stabilized 3D{10-12}twin nucleus is bounded by basal/prismatic(BP)interfaces,prismatic/basal(PB)interfaces,and{10-11}***,a{10-12}twin boundary(TB)occurs at the junction of the BP and PB interface with the growth of the twin *** this process,two twinning mechanisms are involved:a pure-shuffle mechanism in which{10-11}interface migration along the[11-20]direction is mediated by atomic shuffle,and a glide-shuffle mechanism in which BP/PB and{10-12}TB movements are realized by the migration of disconnections along the relevant *** addition,we systematically investigate the stress state associated with the activation of twinning,aiming to discover the intrinsic relationship of the elastic stress field to twin growth on an atomic *** results suggest that the elastic stress in the matrix is an important driving force for twin growth,much similar to what stress does for a *** addition,it is rather remarkable that the{10-11}interface has a greater ability to migrate than other interfaces,and this is thought to be a main factor for the rapid growth of a{10-12}twin.

关键词： Molecular dynamics {10-12}twinning 3D growth Twin-related interfaces

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Effect of austempering time on microstructure and properties of a low-carbon bainite steel

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International Journal of Minerals,Metallurgy and Materials 2020年第3期27卷 340-346页

作者： man Liu Guang Xu Jun-yu Tian Qing Yuan xin Chen The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and Technology

The effect of austempering time after the bainitic transformation on the microstructure and property in a low-carbon bainite steel was investigated by metallography and dilatometry. The results showed that by prolonging the austempering time after the bainite transformation, the amount of large-size martensite/austenite islands decreased, but no significant change of the amount and morphology of bainite were observed. In addition, more austenite with a high carbon content was retained by prolonging the holding time at the bainite transformation ***, with a longer holding time, the elongation was improved at the expense of a small decrease in tensile strength. Finally, the Avrami equation B(RF) = 1-exp(-0.0499 × t^0.7616) for bainite reaction at 350℃ was obtained for the tested steel. The work provided a reference for tailoring the properties of low-carbon steels.

关键词： austempering time retained austenite martensite/austenite island low-carbon bainite transformation kinetics

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Biofiltration and disinfection codetermine the bacterial antibiotic resistome in drinking water:A review and meta-analysis

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Frontiers of Environmental Science & Engineering 2020年第1期14卷 23-34页

作者： Kun wan Wenfang Lin Shuai Zhu Shenghua Zhang xin Yu Key Laboratory of Urban Environment and Health.Institute of Urban Environment Chinese Academy of SciencesXiamen 361021China University of Chinese Academy of Sciences Beijing 100049China Beijing Guohuan Tsinghua Environmental Engineering Design&Research Institute Co. Ltd.Beijing 100084China

The bacterial antibiotic resistome(BAR)is one of the most serious contemporary medical *** BAR problem in drinking water is receiving growing *** this study,we focused on the distribution,changes,and health risks of the BAR throughout the drinking water treatment *** extracted the antibiotic resistance gene(ARG)data from recent publications and analyzed ARG profiles based on diversity,absolute abundance,and relative *** absolute abundance of ARG was found to decrease with water treatment processes and was positively correlated with the abundance of 16S rRNA(r=0.963,/?<0.001),indicating that the reduction of ARG concentration was accompanied by decreasing *** treatment processes,biofiltration and chlorination were discovered to play important roles in shaping the bacterial antibiotic *** exhibited positive effects in controlling the diversity of ARG,while biofiltration,especially granular activated carbon filtration,increased the diversity of *** biofiltration and chlorination altered the structure of the resistome by affecting relative ARG *** addition,we analyzed the mechanism behind the impact of biofiltration and chlorination on the bacterial antibiotic *** intercepting influent ARG-carrying bacteria,biofilters can enrich various ARGs and maintain ARGs in *** further selects bacteria co-resistant to chlorine and ***,we proposed the BAR health risks caused by biofiltration and chlorination in water *** reduce potential BAR risk in drinking water,membrane filtration technology and water boiling are recommended at the point of use.

关键词： Drinking water treatment Antibiotic resistance gene Biofiltration Chlorination

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Identification of the optimal doping position of hetero-atoms in chalcogen-doped Fe-N-C catalysts for oxygen reduction reaction

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Particuology 2024年第6期89卷 99-108页

作者： Weihao Liu Huanhuan He Qingtao Liu xin wan Jianglan Shui School of Materials Science and Engineering Beihang UniversityBeijing100191China School of Space and Environment Beihang UniversityBeijing102206China Tianmushan Laboratory Hangzhou310023China

The excellent oxygen reduction reaction(ORR)activity of Fe–N–C catalysts in acidic media makes them potential for low-cost proton exchange membrane fuel *** recent years,it has been shown that heteroatoms(B,O,S,P,Cl,F,etc.)can be used as electron-withdrawing groups to modulate the planar structure and electron distribution of the Fe–Nx active sites to achieve simultaneous improvement of catalytic activity and ***,the optimal location of the heteroatoms remains ***,taking chalcogen heteroatoms(S and Se)as an example,we control the doping positions and investigate their effect on the ORR performance of the Fe–N–C *** first coordination shell of the iron single atom is identified as the optimal doping *** optimized catalysts Fe–N_(3)Se_(1)/NC and Fe–N_(3)Se_(1)/NC demonstrate improved activity and stability in both half cells and fuel *** work provides insights into the enhancement mechanism of heteroatom doping in single-atom catalysts.

关键词： Oxygen reduction reaction Fe-N-C catalysts Hetero-atom doping Doping position Enhancement mechanism

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Tunable Cis-cisoid Helical Conformation of Poly(3,5-disubstibuted phenylacetylene)s Stabilized by Interaction

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Chinese Journal of Polymer Science 2020年第7期38卷 685-695,I0005页

作者： Sheng wang Si-Liang Cai Jie Zhang xin-Hua wan Beijing National Laboratory for Molecular Sciences Key Laboratory of Polymer Chemistry and Physics of Ministry of EducationCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing 100871China

A series of novel cis poly(phenylacetylene)s(PPAs)substituted at meta-position(s)by two alkoxycarbonyl pendants,Le.,sP-Me-C8/rP-Me-C8,P-Me-C12,sP-Et-C4,sP-2C4 and sP-Oct-C4,were synthesized under the catalysis of[Rh(nbd)Cl]2(nbd=norbornadiene).The dependence of elongation,screw sense,and stimuli response of helical polyene backbone on the structure of pendant,solvent,and temperature was systematically investigated in both solution and solid *** of n→π*interaction between vicinal carbonyl groups,sP-Me-C8/rP-Me-C8 could adopt contracted cis-cisoid helix in THF,toluene,CH2Cl2,and *** an intramolecular interaction was sensitive to the hydrogen bond donating ability of solvent and temperature,but insensitive to the dielectric constant and polarity of *** poly(3-methoxycarbonyl-5-alkoxycarbonylphenylacetylene),the longer the chiral alkyl chain was,the easier the stable cis-cisoid helix could be ***,when the methoxycarbonyl was changed to ethoxycarbonyl,sec-butyloxycarbonyl,and octyloxycarbonyl pendant groups,only cistransoid helix was obtained at room temperature due to the increased steric ***,lowering temperature was found to facilitate the stabilization of n→π*interactions,and reversible temperature-dependent stereomutations were achieved in sP-Me-C8 and sP-Et-C4depending on the solvent where they were *** results suggested that the long alkyl chain,small pendant size,and lower temperature favored the stabilization of intramolecular n→π*interactions and the formation of contracted,cis-cisoid helices for poly(3,5-diestersubstituted phenylacetylene)s.

关键词： Polyphenylacetylenes Cis-cisoid,Cis-transoid n→π*Interactions,Helical conformation

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Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

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Defence Technology（防务技术） 2021年第5期17卷 1592-1601页

作者： Yasir Mahmood Peng-wan Chen I.A.Bataev xin Gao State Key Lab of Explosion Science and Technology Beijing Institute of Technology100081PR China Novosibirsk State Technical University K.Marks 20630073NovosibirskRussia

Explosive welding technique is widely used in many *** technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding *** plays an important role to improve the welding quality and control energy loss during the collision *** this paper,the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium *** details of welded composite plate were observed through optical and scanning electron ***-base plate interface morphology showed a wavy structure with solid melted regions inside the ***,the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of CueTi,***,Cu_(2)Ti,CuTi_(2),Cu_(4)Ti,*** study the mechanical properties of composite plates,mechanical tests were conducted,including the tensile test,bending test,shear test and Vickers hardness *** simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method,Euler and Arbitrary Lagrangian-Eulerian *** multi-physics process of explosive welding,including detonation,jetting and interface morphology,was observed with ***,simulated plastic strain,temperature and pressure profiles were analysed to understand the welding *** results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent *** the collision point,both alloys behave like fluids,resulting in the formation of a wavy morphology with vortices,which is in good agreement with the experimental results.

关键词： Explosive welding Ti6Al4V/CP-Ti/Cu Smooth particle hydrodynamic(SPH) Microstructure Mechanical properties

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Computing the Number of k-Component Spanning Forests of a Graph with Bounded Treewidth

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Journal of the Operations Research Society of China 2019年第2期7卷 385-394页

作者： Peng-Fei wan xin-Zhuang Chen Department of Applied Mathematics School of ScienceNorthwestern Polytechnical UniversityXi’an 710029China School of Mathematics and Statistics Yulin UniversityYulin 719000ShaanxiChina

Let G be a graph on n vertices with bounded *** use fk(G)to denote the number of spanning forests of G with k *** a tree decomposition of width at most p of G,we present an algorithm to compute fk(G)for k=1,2,…,*** r... 详细信息

关键词： Spanning tree Spanning forest Bounded treewidth Dynamic programming

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Reduced precision solution criteria for nonlinear model predictive control with the feasibility-perturbed sequential quadratic programming algorithm

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Journal of Zhejiang University-Science C(Computers and Electronics) 2011年第11期12卷 919-931页

作者： Jiao-na wan Zhi-jiang SHAO Ke-xin wan Xue-yi FANG Zhi-qiang wanG Ji-xin QIAN State Key Lab of Industrial Control Technology Institute of Industrial Control Department of Control Science and Engineering Zhejiang University Hangzhou 310027 China

We propose a novel kind of termination criteria, reduced precision solution (RPS) criteria, for solving optimal control problems (OCPs) in nonlinear model predictive control (NMPC), which should be solved quickly for new inputs to be applied in time. Computational delay, which may destroy the closed-loop stability, usually arises while non-convex and nonlinear OCPs are solved with differential equations as the constraints. Traditional termination criteria of optimization algorithms usually involve slow convergence in the solution procedure and waste computing resources. Considering the practical demand of solution precision, RPS criteria are developed to obtain good approximate solutions with less computational cost. These include some indices to judge the degree of convergence during the optimization procedure and can stop iterating in a timely way when there is no apparent improvement of the solution. To guarantee the feasibility of iterate for the solution procedure to be terminated early, the feasibility- perturbed sequential quadratic programming (FP-SQP) algorithm is used. Simulations on the reference tracking performance of a continuously stirred tank reactor (CSTR) show that the RPS criteria efficiently reduce computation time and the adverse effect of computational delay on closed-loop stability.

关键词： Nonlinear model predictive control (NMPC) Computational delay Termination criteria Continuously stirred tankreactor (CSTR)

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NUMERICAL SIMULATION OF BED TOPOGRAPHY CHANGES INDUCED BY DEEP WATER NAVIGATION CHANNEL PROJECT IN THE YANGTZE ESTUARY

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Journal of Hydrodynamics 2003年第4期15卷 46-53页

作者： ZhangJing-xin LiuHua HeYou-sheng ZhangFu-ran QiDing-man SchoolofCivilEngineeringandMechanics ShanghaiJiaotongUniversityShanghai200030China ResearchCenterofEstuarineandCoastalSciences Shanghai201201China

A study on the mathematical modeling of the two dimensional, time-dependentvariation of bottom topography caused by the spur dikes of the deep water navigation channel projectin the Yangtze estuary is reported. The hydro-dynamic flows are computed using the DELFT3D whichserves as the base of computation of sediment transport and bottom deformation. A model of finesediment transport is developed and implemented in an orthogonal curvilinear coordinate system bythe finite difference method. Using the observed water depth of the North Channel of Yangtze estuaryfrom 2001 to 2002, the model is calibrated and validated to determine the parameters in thesediment model. The computational results of the changes of the bed in the North Channel induced bythe spur dikes coincide with the measured data except the area near the structures.

关键词： tidal flow sediment transport yangtze estuary mathematical model

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