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A refined deviatoric hardening plastic model for sand

Journal of Rock Mechanics and Geotechnical Engineering 2024年第7期16卷 2813-2821页

作者： Min Wang Tongming Qu Yuntian feng Teng Liang Liangtong zhan MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering Zhejiang UniversityHangzhou310058China Department of Civil and Environmental Engineering Hong Kong University of Science and TechnologyKowloon999077Hong KongChina Zienkiewicz Centre for Computational Engineering College of EngineeringSwansea UniversitySwanseaWalesSA18EPUK Center for Hypergravity Experimental and Interdisciplinary Research Zhejiang UniversityHangzhou310058China

The classical deviatoric hardening models are capable of characterizing the mechanical response of granular materials for a broad range of degrees of *** work finds that it has limitations in accurately predicting the volumetric deformation characteristics under a wide range of confining/consolidation *** issue stems from the pressure independent hardening law in the classical deviatoric hardening *** overcome this problem,we propose a refined deviatoric hardening model in which a pressure-dependent hardening law is developed based on experimental *** between numerical results and laboratory triaxial tests indicate that the improved model succeeds in capturing the volumetric deformation behavior under various confining/consolidation pressure conditions for both dense and loose ***,to examine the importance of the improved deviatoric hardening model,it is combined with the bounding surface plasticity theory to investigate the mechanical response of loose sand under complex cyclic loadings and different initial consolidation *** is proved that the proposed pressure-dependent deviatoric hardening law is capable of predicting the volumetric deformation characteristics to a satisfactory degree and plays an important role in the simulation of complex deformations for granular geomaterials.

关键词： Elasto-plastic deformation Isotropic hardening Deviatoric plastic strain Granular material Kinematic hardening Bounding surface

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A Lightweight Dynamic Enforcement of Privacy Protection for Android

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Journal of Computer Science & Technology 2019年第4期34卷 901-923页

作者： Zi-Peng zhang Ming fu Xin-Yu feng School of Computer Science and Technology University of Science and Technology of ChinaHefei 230026China OS Kernel Laboratory Huawei Technologies Co.Ltd.Shanghai 200135China State Key Laboratory for Novel Software Technology Nanjing UniversityNanjing 210023China

Inter-process communication(IPC)provides a message passing mechanism for information exchange between *** has been long believed that IPCs can be abused by malware writers to launch collusive information leak using two or more *** work on privacy protection focuses on the simple information leak caused by the individual applications and lacks effective approaches to preventing the collusive information leak caused by IPCs between multiple *** this paper,we propose a hybrid approach to prevent the collusive information leak based on information flow *** approach combines static information flow analysis and dynamic runtime checking *** leak caused by individual processes is prevented through static information flow control,and dynamic checking is done at runtime to prevent the collusive information *** a combination may effectively reduce the runtime overhead of pure dynamic checking,and reduce false-alarms in pure static *** develop this approach based on an abstract and simplified programming model,and formalize a novel definition of the leak-freedom property as our target security property.A simulation-based proof technique is used to prove that our approach is able to guarantee *** proofs are mechanized in Coq.

关键词： privacy protection dynamic runtime checking static information flow control Android verification

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Numerical simulation of flow in swirl injector for power-law fluid

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航空动力学报 2012年第4期27卷 890-899页

作者： WANG feng fu Qing-fei YANG Li-jun School of Astronautics Northwestern Polytechnical UniversityXi'an 710072China School of Astronautics Beijing University of Aeronautics and AstronauticsBeijing 100191China

In order to investigate the flow characteristics of swirl injectors for gelled propellants,which actually behaved as non-Newtonian power-law fluid,a swirl axisymmetric model was established to solve Navier-Stokes equations and VOF(volume of fluid) equation,and the power-law constitutive equation was used to describe the rheology characteristics of the gelled *** film thickness and velocity distribution in the swirl injector under different flow conditions were studied *** simulation results show that the increased geometry characteristic parameter of the swirl injector contributes to the decrease of liquid film *** liquid film thickness is almost independent of the pressure *** rheologic parameters have great influences on the inner flow of swirl injector: by increasing the fluid consistency index K and power index n,both the axial and the swirl velocities decrease dramatically;higher fluid consistency index K and power index n make the liquid film thickness *** the viscosity is large enough,the air core in the injector would vanish.

关键词： numerical simulation gelled propellants power-law fluid swirl injector inner flow

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Influence of Nb Content on Microstructure and Mechanical Properties of a 7%Ni Steel

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Acta Metallurgica Sinica(English Letters) 2018年第9期31卷 975-982页

作者： Hong-Wei Cao Xing-Hong Luo Guo-feng zhan Shi Liu School of Materials Science and Engineering University ofScience and Technology of ChinaShenyang 110016China CAS Key Laboratory of Nuclear Materials and SafetyAssessment Institute of Metal ResearchChinese Academyof SciencesShenyang 110016China Research and Development Center of Wuhan Iron and Steel(Group)Corp Wuhan 430080China

The influence of Nb content on the microstructure and cryogenic mechanical properties of a 7%Ni steel was investigated within the Nb content range from 0 to 0.05%. The microstructure was characterized by optical microscope, scanning electron microscope, transmission electron microscopy and X-ray diffraction, and the low-temperature mechanical property tests were conducted. The Nb addition can effectively refine the prior austenite grains and microstructure of the steel. Fine niobium precipitates with a diameter of about 10-50 nm were observed. They tend to be spherical and locate mainly in the vicinity of grain boundaries. Although there are considerable amounts of reversed austenite forming at grain boundaries in the specimen containing the highest Nb content, no Nb element was detected in such reversed austenite, which implies that Nb element did not affect the formation of the reversed austenite directly. Mechanical test results suggest that the strength of the 7%Ni steel is not simply in relation to the prior austenite grain size, but also depends on the amount of reversed austenite. On the other hand, the grain refinement, enhanced with increasing Nb content, has a good effect on cryogenic toughness.

关键词： 7%Ni steel Nb content Niobium precipitate Reversed austenite Cryogenic mechanical properties

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New progress in understanding the origins of modern humans in China

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Science China Earth Sciences 2017年第12期60卷 2160-2170页

作者： GAO Xing PENG Fei fu QiaoMei LI feng Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences Institute of Vertebrate Paleontology and PaleoanthropologyChinese Academy of SciencesBeijing 100044 University of the Chinese Academy of Sciences Beijing 100049China Department of Early Prehistory and Quaternary Ecology University of TubingenTubingen 72070Germany

Hypotheses concerning the origins of modern humans have been intensively debated, and two competing models, the recent "Out-of-Africa" and "Multiregional Evolution" paradigms, have dominated research and discussions for decades. Evidence from China has played a fundamental role in this debate: regional continuity and replacement by populations in-migrated from Africa have both been suggested and supported mainly by paleoanthropologists and geneticists, respectively. As more evidence has accumulated, new results obtained, and more scholars from various disciplines become involved, supporters of the recent "Out-of-Africa" model agree more or less with the "Multiregional Evolution" model regarding the complex history of modern humans and their interbreeding with other archaic populations(e.g., Neandertals). Recent discoveries of new human fossils, Paleolithic archaeological materials, and ancient DNA evidence in China have yielded a large body of information regarding the formation and development of modern humans in this region. However, controversies continue, including that most molecular biologists insist on the replacement of archaic populations by modern humans dispersed from Africa, while most paleoanthropologists and archaeologists propose an enhanced "Continuity with Hybridization" model. In this paper, we compile new results and progress in China and present the current debates and issues on the origins of modern humans. Finally, we offer several suggestions for future studies.

关键词： China Origins of modern humans Modern behavior Recent out-of-Africa Continuity with hybridization Interdisciplinary research

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Phonon damping in one-dimensional lattices with asymmetric interactions

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Science China(Physics,Mechanics & Astronomy) 2022年第11期65卷 62-67页

作者： Sihan feng Weicheng fu Yong zhang Hong Zhao Department of Physics Xiamen UniversityXiamen 361005China Department of Physics Tianshui NormalUniversityTianshui 74100lChina Lanzhou Center for Theoretical Physics Key Laboratory of Theoretical Physics of Gansu ProvinceLanzhou UniversityLanzhou 730oooChina

The symmetry of interparticle interaction plays an important role in determining the energy transport and diffusion behavior of one-dimensional(1D) lattices, not only in the process of hydrodynamics but also in the process of kinetics. In this paper, we study the relaxation properties of phonons in 1D lattices with asymmetric and symmetric interparticle interactions, exemplified by the famous Fermi-Pasta-Ulam-Tsingou model. Asymmetric interparticle interactions(AIIs) lead to larger damping rates of phonons as compared to symmetric ones in the low-temperature limit, and the difference gradually vanishes when the temperature increases. Moreover, in lattices with AIIs, the dependence of the damping rate Γ of phonons still follows a power-law on the wave number q, i.e., Γ ~q^(γ) for small q. In particular, at low temperatures, AIIs result in γ ≈ 1, which is out of the predictions of 3/2 ≤ γ ≤ 2 from various theories. Our results provide insights into understanding the anomalous heat conduction observed in 1D chains and ultra-low phonon heat conduction found in certain solids.

关键词： phonons heat conduction damping rate renormalization Fermi-Pasta-Ulam-Tsingou model

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Recent advances in statistical methodologies in evaluating program for high-dimensional data

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Applied Mathematics(A Journal of Chinese Universities) 2022年第1期37卷 131-146页

作者： zhan Ming-feng CAI Zong-wu FANG Ying LIN Ming Wang Yanan Institute for Studies in Economics and fujian Key Laboratory of Statistical Sciences Xiamen UniversityXiamen 361005China Department of Economics University of KansasLawrenceKS 66045USA Department of Statistics and Data Science Xiamen UniversityXiamen 361005China

The era of big data brings opportunities and challenges to developing new statistical methods and models to evaluate social programs or economic policies or interventions. This paper provides a comprehensive review on some recent advances in statistical methodologies and models to evaluate programs with high-dimensional data. In particular, four kinds of methods for making valid statistical inferences for treatment effects in high dimensions are addressed. The first one is the so-called doubly robust type estimation, which models the outcome regression and propensity score functions simultaneously. The second one is the covariate balance method to construct the treatment effect estimators. The third one is the sufficient dimension reduction approach for causal inferences. The last one is the machine learning procedure directly or indirectly to make statistical inferences to treatment effect. In such a way, some of these methods and models are closely related to the de-biased Lasso type methods for the regression model with high dimensions in the statistical literature. Finally, some future research topics are also discussed.

关键词： causal inference covariate balance de-biased Lasso dimension reduction doubly robust high dimensions machine learning treatment effect

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Perspective on low-temperature electrolytes for LiFePO 4-based lithium-ion batteries

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International Journal of Minerals,Metallurgy and Materials 2023年第1期30卷 1-13页

作者： Xianglong Chen Yudong Gong Xiu Li feng zhan Xinhua Liu Jianmin Ma School of Resources Environment and MaterialsGuangxi UniversityNanning 530004China Peking University Science Park Beijing 100871China School of Materials and Energy University of Electronic Science and Technology of ChinaChengdu 611731China School of Transportation Science and Engineering Beihang UniversityBeijing 100871China

The olivine-type lithium iron phosphate(LiFePO_(4))cathode material is promising and widely used as a high-performance lithium-ion battery cathode material in commercial batteries due to its low cost,environmental friendliness,and high *** present,LiFePO_(4)/C sec-ondary batteries are widely used for electronic products,automotive power batteries,and other occasion-related applications with good thermal stability,stable cycle performance,and low room-temperature self-discharge ***,LiFePO_(4)-based battery applications are seriously limited when they are operated in a cold *** outcome is due to a considerable decrease in Li+transport capabilities within the elec-trode,particularly leading to a dramatic decrease in the electrochemical capacity and power performance of the ***,the design of low-temperature electrolytes is important for the further commercial application of LiFePO_(4) *** paper reviews the key factors for the poor low-temperature performance of LiFePO_(4)-based batteries and the research progress of low-temperature ***-cial attention is paid to electrolyte components,including lithium salts,cosolvents,additives,and the development of new *** factors affecting the anode are also ***,according to the current research progress,some viewpoints are summarized to provide suitable modification methods and research suggestions for improving the practicability of LiFePO_(4)/C commercial batteries at low temperat-ures in the future.

关键词： lithium-ion batteries LiFePO_(4) electrolytes low-temperature electrochemical performance

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Pre-reduction of WO_(3)-Co_(3)O_(4)by H_(2)-C_(2)H_4 in a fluidized bed

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Chinese Journal of Chemical Engineering 2024年第2期66卷 273-284页

作者： Huijun Shang Hengli Li Weijun Li feng Pan zhan Du State Key Laboratory of Multiphase Complex Systems Institute of Process EngineeringChinese Academy of Sciences(CAS)Beijing 100190China College of Chemical Engineering Nanjing Technology UniversityNanjing 211816China School of Chemistry and Chemical Engineering Shihezi UniversityShihezi 832003China College of Chemical Engineering University of Chinese Academy of SciencesBeijing 100049China Chinalco Environmental Protection and Energy Conservation Group Co. Ltd.Xiong’an 071700China

In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been *** study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon *** results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are *** pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)

关键词： Fluidization WO_(3)-Co_(3)O_(4) Reduction Carbon deposition Rate equation

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High thermoelectric properties with low thermal conductivity due to the porous structure induced by the dendritic branching in n-type PbS

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Nano Research 2022年第5期15卷 4739-4746页

作者： Zhenyu Zhu Janak Tiwari Tianli feng zhan Shi Yue Lou Biao Xu School of Chemistry and Chemical Engineering Nanjing University of Science and TechnologyNanjing 210094China Department of Mechanical Engineering The University of UtahSalt Lake CityUT 84112USA State Key Laboratory of Inorganic Synthesis and Preparative Chemistry College of ChemistryJilin UniversityChangchun 130012China State Key Laboratory of Coordination Chemistry School of Chemistry and Chemical EngineeringNanjing UniversityNanjing 210000China

PbS-based thermoelectric materials have attracted extensive attention in recent years for the advantages of earth abundancy and low cost,which is considered to be a substitute for traditional PbTe ***,their high thermal conductivity restricts its ***,in order to improve their thermoelectric performance from reducing the thermal conductivity,a kind of dendritic PbS with controlled crystal grain and morphology are obtained by solution *** adjusting the amount of surfactant(CTAB),the specific formation process of dendrites is *** sintering,the dendritic PbS nanoparticles are easy to form porous structure due to the overlapping and staggered arrangement of dendritic *** comparison,we also prepare a kind of regular octahedral PbS and a dense packing arrangement is formed because of the integrity of the octahedral ***-based Boltzmann transport equation is used to prove the crucial role of porous structure in scattering ***,a maximum zT=1.0 at 773 K in n-type PbS is obtained,which still keep a high-speed growth and is expected to get higher zT value in a higher temperature *** work may shed light to other thermoelectric materials from the formation of porous structure to reduce the thermal conductivity.

关键词： thermoelectric materials lead sulfide solution synthesis porous structure

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