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Palladium-catalyzed highly regioselective Heck reaction of aryl nonaflates with electron-rich olefins

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Chinese Chemical Letters 2008年第9期19卷 1017-1020页

作者： Dan xu Zhi Hua Liu Wei Jun Tang Jun Mo Li Jin xu Department of Chemistry Renmin University of China Beijing 100872 China

Highly efficient palladium-catalyzed Heck coupling of aryl nonaflates with electron-rich vinyl ethers, and enamides is described. These reactions afforded exclusively the branched products in good yields. The results ... 详细信息

关键词： Aryl nonaflates Electron-rich Palladium Heck reaction Regioselectivity

Geometry Effects on Aerodynamics Performance of a Low Aspect Ratio Turbine Nozzle

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Journal of Thermal Science 2004年第4期13卷 289-296页

作者： Naixing Chen Hongwu Zhang Yanji xu Weiguang Huang Chinese Acad Sci Inst Engn Thermophys Beijing 100080 Peoples R China

This paper describes the influence of some geometric parameters on aerodynamics performance of a low-aspect-ratio turbine blading designed by a novel method developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. This is a part of the study on aerodynamics optimization of turbomachinery. It follows the development of the basic ideas in the turbomachinery aerodynamics research project at the institute. The present paper concentrates mainly on the effects of geometry, such as stagger angle, leading and trailing edge thickness, maximum thickness and its location on adiabatic efficiency, total pressure ratio and mass flow rate. The study was performed and assessed for a low-aspect ratio turbine nozzle using 3D steady Reynolds-averaged N.S. solver. Using the knowledge of the flow physics analysis an optimized turbine nozzle was obtained.

关键词： 3D aerodynamics of turbomachinery turbine design optimization geometry effect.

Analysis of Review Helpfulness Based on Consumer Perspective

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Tsinghua Science and Technology 2015年第3期20卷 293-305页

作者： Yuanlin Chen Yueting Chai Yi Liu Yang xu National Engineering Laboratory for E-Commerce Technologies Tsinghua University DNSLAB China Internet Network Information Center

When consumers make purchase decisions, they generally refer to the reviews generated by other consumers who have already purchased similar products in order to get more information. Online transaction platforms provide a highly convenient channel for consumers to generate and retrieve product reviews. In addition, consumers can also vote reviews perceived to be helpful in making their decision. However, due to diverse characteristics, consumers can have different preferences on products and reviews. Their voting behavior can be influenced by reviews and existing review votes. To explore the influence mechanism of the reviewer, the review, and the existing votes on review helpfulness, we propose three hypotheses based on the consumer perspective and perform statistical tests to verify these hypotheses with real review data from Amazon. Our empirical study indicates that review helpfulness has significant correlation and trend with reviewers, review valance, and review votes. In this paper, we also discuss the implications of our findings on consumer preference and review helpfulness.

关键词： consumer preference online decision making review helpfulness behavior analysis

Nonlocal thermo-elastic constitutive relation of fibre-reinforced composites

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Acta Mechanica Sinica 2020年第1期36卷 176-187页

作者： Linjuan Wang Jifeng xu Jianxiang Wang Bhushan LKarihaloo State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering ScienceCollege of EngineeringPeking UniversityBeijing100871China CAPT-HEDPS and IFSA Collaborative Innovation Center of MoECollege of EngineeringPeking UniversityBeijing100871China Beijing Aeronautical Science and Technology Research Institute Beijing100083China School of Engineering Cardiff UniversityCardiffCF243AAUK

The effective properties of composite materials have been predicted by various micromechanical *** composite materials of constituents which are described by the classical governing equations of the local form,the conventional micromechanical schemes usually give effective properties of the local ***,it is recognized that under general loading conditions,spatiotemporal nonlocal constitutive equations may better depict the macroscopic behavior of these *** this paper,we derive the thermo-elastic dynamic effective governing equations of a fibre-reinforced composite in a coupled spatiotemporal integral *** coupled equations reduce to the spatial nonlocal peridynamic formulation when the microstructural inertial effects are *** static deformation and steady-state heat conduction,we show that the integral formulation is superior at capturing the variations of the average displacement and temperature in regions of high gradients than the conventional micromechanical *** approach can be applied to analogous multi-field coupled problems of composites.

关键词： Nonlocal theory Thermoelasticity Composite materials Constitutive equations

Moduli of Polarized Calabi–Yau Pairs

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Acta Mathematica Sinica,English Series 2020年第6期36卷 631-637页

作者： János KOLLáR Chen Yang xu Princeton University Princeton NJ 08544-1000USA MIT CambridgeMA 02139-4307USA

We prove that the irreducible components of the moduli space of polarized Calabi–Yau pairs are projective.

关键词： Polarized Calabi–Yau stable pairs Moduli spaces

Physics performance of the STAR zero degree calorimeter at relativistic heavy ion collider

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Nuclear Science and Techniques 2016年第6期27卷 144-149页

作者： Yi-Fei xu Jin-Hui Chen Yu-Gang Ma Ai-Hong Tang Zhang-Bu xu Yu-Hui Zhu Shanghai Institute of Applied Physics Chinese Academy ofSciencesShanghai 201800China University of Chinese Academy of Sciences Beijing 100049China ShanghaiTech University Shanghai 200031China Brookhaven National Laboratory UptonNY 11973USA

The zero degree calorimeter(ZDC) at RHICSTAR was installed in the year *** running for more than 10 years,the performance of the STAR-ZDC cannot maintain a proper status because of the radiation *** ZDC on RHIC-BRAHMS had been moved to STAR in 2011 after some *** present here the result of the tests as well as the physical performance of those ZDC modules between the 2011 and 2015 RHIC *** excellent energy resolution of the ZDC in heavy ion collision provides a good candidate for future detector development,such as the CSR experiment at CAS-Lanzhou facility.

关键词：物理性能重离子对撞机零度量热计相对论企业社会责任 RHIC 能量分辨率

Failure Modes of Lead Free Solder Bumps Formed by Induction Spontaneous Heating Reflow

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Journal of Materials Science & Technology 2007年第1期23卷 61-67页

作者： Mingyu LI Hongbo xu Jongmyung KIM Hongbae KIM Shenzhen Graduate School Harbin Institute of Technology Shenzhen 518055 China Jeonnam Provincial College Jeonnam 517-802 Korea

The shear failure modes and respective failure mechanism of Sn3.5Ag and Sn3.0Ag0.5Cu lead-free solder bumping on Au/Ni/Cu metallization formed by induction spontaneous heating reflow process have been investigated through the shear test after aging at 120℃ for 0, 1, 4, 9 and 16 d. Different typical shear failure behaviors have been found in the loading curves （shear force vs displacement）. From the results of interracial morphology analysis of the fracture surfaces and cross-sections, two main typical failure modes have been identified. The probabilities of the failure modes occurrence are inconsistent when the joints were aged for different times. The evolution of the brittle NiaSn4 and Cu-Ni-Au-Sn layers and the grains coarsening of the solder bulk are the basic reasons for the change of shear failure modes.

关键词： Induction spontaneous heating reflow Lead free solder Shear test Failure mode

An efficient and highly available framework of data recency enhancement for eventually consistent data stores

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Frontiers of Computer Science 2017年第1期11卷 88-104页

作者： Yu TANG Hailong SUN xu WANG xudong LIU School of Computer Science and Engineering Beihang University Beijing 100191 China

Data items are usually replicated in modem dis- tributed data stores to obtain high performance and avail- ability. However, the availability-consistency and latency- consistency trade-offs exist in data replication, thus system designers intend to choose weak consistency models, such as eventual consistency, which may result in stale reads. Since stale data items may lead to serious application semantic problems, we consider how to increase the probability of data recency which provides a uniform view on recent versions of data items for all clients. In this work, we propose HARP, a framework that can enhance data recency of eventually con- sistent distributed data stores in an efficient and highly avail- able way. Through detecting possible stale reads under fail- ures or not, HARP can perform reread operations to elim- inate stale results only when needed based on our analysis on write/read processes. We also present solutions on how to deal with some practical anomalies in HARP, including de- layed, reordered and dropped messages and clock drift, and show how to extend HARP to multiple datacenters. Finally we implement HARP based on Cassandra, and the experi- ments show that HARP can effectively eliminate stale reads, with a low overhead （less than 6.9%） compared with original eventually consistent Cassandra.

关键词： eventual consistency high availability data recency stale read

Dislocation-mediated migration of interphase boundaries

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Journal of Materials Science & Technology 2019年第11期35卷 2714-2726页

作者： Zhipeng Sun Fuzhi Dai Ben xu Wenzheng Zhang School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Science and Technology of Advanced Functional Composite Laboratory Aerospace Research Institute of Materials and Processing TechnologyBeijing 100076China Key Laboratory of Advanced Materials(MOE) State Key Laboratory of New Ceramics and Fine ProcessingChina

Faceted interphase boundaries(IPBs)are commonly observed in lath-shaped precipitates in alloys consisting of simple face-centred cubic(fcc),body centred-cubic(bcc)or hexagonal closed packed(hcp)phases,which normally contain one or two sets of parallel *** influence of these dislocations on interface migration and possible accompanying long-range strain field remain *** elucidate this,we carried out atomistic simulations to investigate the dislocation-mediated migration processes of IPBs in a pure-iron *** results show that the migration of these IPBs is accompanied with the slip of interfacial dislocations,even in high-index slip planes,with two migration modes were observed:the first mode is the uniform migration mode that occurs only when all of the dislocations slip in a common slip plane.A shear-coupled interface migration was observed for this *** other interfaces propagate in the stick-slip migration mode that occurs when the dislocations glide on different slip planes,involving dislocation reaction or tangling.A quantitative relationship was established to link the atomic displacements with the dislocation structure,slip plane,and interface *** macroscopic shear deformation due to the effect of overall atomic displacement shows a good agreement with the results obtained based on the phenomenological theory of martensite *** findings have general implications for the understanding of phase transformations and the surface relief effect at the atomic scale.

关键词： Interphase boundary migration O-line interface Shear-coupled interface migration Dislocation gliding Atomic displacement