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Slip in Couette flow with pressure gradient:Theoretical and experimental investigation of hydrodynamic characteristics considering slip effect

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Journal of Hydrodynamics 2020年第1期32卷 107-115页

作者： Xin Zhao Chao Wei Shi-hua yuan Science and Technology on Vehicle Transmission Laborator Bejing Institute of TechnologyBeijing 10081China

A new slip velocity model based on molecular potential theory and macro-force analysis,which is applied in Couette flow with pressure gradient,is built *** model is validated by later being introduced in hydrodynamic system to predict film distribution,which shows a good agreement with experimental data obtained from multi-beam intensity-based tests with Fe and Cu ball materials under accurate controlled temperature,load and different wall *** show that the slip length for Fe case is ignorable so it seems like no slip,but for Cu case,the slip length is large to make 20%discrepancy with no slip simulation and also behaves ***,during the experimental cases when both Fe and Cu ball velocities rise from-133 mm/s to 1330 mm/s,the slip velocity changes its direction with entrainment velocity and thus contributes to first enhance and then diminish the hydrodynamic film,but due to slip length on Cu case varying largely than that on Fe case,the film from Cu case and from Fe case has a clear cross-point between uh=80 mm/s and uh=220 m m/s(ub is the ball speed).The results above support strongly that Cu surface will lead to stronger slip than Fe case because of its smaller solid-liquid interaction,and obviously slip will influence hydrodynamic characteristics prominently.

关键词： Slip Couette flow with pressure gradient hydrodynamic characteristic

Ferroelectricity survives in the sub-nanometer scale

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Science China Materials 2023年第5期66卷 2105-2106页

作者： Yiqian Liu yuan-hua Lin State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Ultrathin materials with maintained functionalities are the prerequisites for the device miniaturization and *** materials are key ingredients in nonvolatile memories as information storage media and in field-effect transistors as gate dielectrics[1],and therefore their thickness scaling enables the high-capacity and energy-efficient ***,the longstanding problem for ultrathin ferroelectrics is that the strong depolarizing field can cancel ferroelectricity[2].In traditional barium titanates,the ultrathin film turns paraelectric without spontaneous polarizations[2,3].Moreover,realizing switchable ferroelectric behaviors is even more challenging because of the unsuppressed leakage *** recent years,although some studies have demonstrated that ferroelectricity can be stabilized in several nanometers in perovskites and fluorites[4-6],there still lacks direct evidence to confirm that ultrathin ferroelectrics have macroscopic hysteresis loops and polarization switching,which is the foundation of the practical usage of ultrathin ferroelectrics.

关键词： polarization ferroelectric maintained

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

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International Journal of Minerals,Metallurgy and Materials 2010年第3期17卷 297-306页

作者： Long-gang Hou yuan-hua Cai hua Cui Ji-shan Zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.

关键词： hypereutectic Al-Si alloy spray forming cast microstructure phase transformation

Impact of Information Security Policies on Email-Virus Propagation

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Tsinghua Science and Technology 2005年第z1期10卷 803-810页

作者： yuan hua CHEN Guoqing School of Economics and Management Tsinghua University Beijing 100084 China School of Economics and Management Tsinghua University Beijing 100084 China

Aimed at tracing out the email-virus propagation rules in communication network, this paper extends the traditional epidemiological model (i. e., SEIR) by taking into account the behavior of email users, such as email checking frequency and anti-virus information security policies, and discusses the factors that affect the email-virus propagation in an organization. With the extended SEIR model, namely E-SEIR, three aspects of information security policies (i. e., immunization, information security training,and user recovery support) are investigated in terms of their impacts on the email virus propagation. The results show that the E-SEIR model is suitable to reflect the propagation pattern of email virus, and may also be used in anti-virus policies simulation and evaluation.

关键词： email virus propagation simulation E-SEIR model information security policy epidemiological

Time-Inconsistent Stochastic LQ Problem with Regime Switching

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Journal of Systems Science & Complexity 2020年第6期33卷 1733-1754页

作者： SI Binbin NI yuan-hua ZHANG Ji-Feng College of Artificial Intelligence Nankai UniversityTianjin 300350China Key Laboratory of IntelligentRobotics of Tianjin Tianjin 300350China Key Laboratory of Systems and Control Academy of Mathematics and Systems ScienceChinese Academy ofSciencesBeijing 100190China School of Mathematical Sciences University of Chinese Academy of SciencesBeijing 100049China

This paper investigates a time-inconsistent stochastic linear-quadratic problem with regime switching that is characterized via a finite-state Markov ***-loop equilibrium control is studied in this paper whose existence is characterized via Markov-chain-modulated forward-backward stochastic difference equations and generalized Riccati-like equations with jumps.

关键词： Forward-backward stochastic difference equation open-loop equilibrium control regime switching stochastic linear-quadratic problem time inconsistency

Graph partitioning algorithm for opportunistic routing in large-scale wireless network

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The Journal of China Universities of Posts and Telecommunications 2009年第4期16卷 42-46页

作者： LI Yan-hua LIU yuan-an Wireless Communication Center Beijing University of Posts and Telecommunications Beijing 100876 China

Opportunistic routing takes advantage of the broadcast nature of wireless communications by forwarding data through a set of opportunistic paths instead of one ＇best＇ path in traditional routing. However, using the global scheduling opportunistic scheme like the existing opportunistic routing protocol （ExOR） would consume considerable transmission latency and energy in large-scale wireless topologies. In this article, a graph partitioning algorithm is proposed, namely, minimum cut with laplacians （MCL）, to divide the Ad-hoc network topology into subgraphs with minimized edge cuts across them. Then the existing opportunistic routing can be applied locally in each subgraph. In this way, forwarders in different subgraphs can transmit simultaneously, and each node only needs to maintain a local forwarder list instead of a global one. The simulations show that using MCL scheme in the opportunistic routing can reduce the end-to-end delay by about 49%, and increase the life time of the wireless node by about 39%.

关键词： opportunistic routing graph partitioning wireless routing mobile Ad-hoc network

New Proposals for Application of Terahertz Imaging Technique in Chinese Medicine

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Chinese Journal of Integrative Medicine 2022年第4期28卷 366-373页

作者： BAI Shan-shan YANG hua-yuan School of Acupuncture Moxibustion and Tuina Shanghai University of Traditional Chinese MedicineShanghai201203China

The rapid development of terahertz technology promotes the realization of various terahertz imaging *** technology features terahertz waves as good non-invasive illumination sources due to their high spectral resolution,penetration and *** terahertz imaging technique(TIT)has gradually been extended from the biomedical field to the field of Chinese medicine(CM),and it has become a powerful tool for seeking scientific evidence for CM theories with the use of modern science and *** paper reviews the current application of TITs in the field of CM research,and most importantly offers novel proposals for the application of TITs in CM research from the perspective of CM syndrome objectification and acupuncture research and cites existing reports as reference to the feasibility of these new proposals.

关键词： terahertz Chinese medicine syndrome objectification meridians acupuncture moxibustion new proposals

Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

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International Journal of Minerals,Metallurgy and Materials 2013年第7期20卷 659-664页

作者： yuan-hua Cai Cong Wang Ji-shan Zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing

Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy （OM）, field emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM）, tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast A1-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like ~/5-A1FeSi white intermetallics, and Chinese script-like a-A1FeSi compounds. During high temperature homogenization treatment, only harmful needle-like ^-A1FeSi phase undergoes fragmentation and spheroidizing at its tips, and the destruc- tive needle-like 5-phase does not show any morphological and size changes. Phase transitions from ^-A1FeSi to ^-A1FeSi and from 6-A1FeSi to [3-A1FeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

关键词： aluminum alloys zinc hardening mechanical properties microstructure

TOWARDS EXPLORING WHEN AND WHAT PEOPLE REVIEWED FOR THEIR ONLINE SHOPPING EXPERIENCES

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Journal of Systems Science and Systems Engineering 2018年第3期27卷 367-393页

作者： Liangqiang Li hua yuan Yu Qian Peiji Shao School of Management and Economics University of Electronic Science and Technology of China Chengdu 611731 China

Web 2.0 technologies have attracted an increasing number of people with various backgrounds to become active online writers and viewers. As a result, exploring reviewers＇ opinions from a huge number of online reviews has become more important and simultaneously more difficult than ever before. In this paper, we first present a methodological framework to study the ＂purchasing-reviewing＂ behavior dynamics of online customers. Then, we propose a review-to-aspect mapping method to explore reviewers＇ opinions from the massive and sparse online reviews. The analytical and experimental results with real data demonstrate that online customers can be sectioned into groups in accordance with their reviewing behaviors and that people within the same group may have similar reviewing motivations and concerns for an online shopping experience.

关键词： E-commerce online review review dynamics opinion mining