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An efficient approach for continuous density queries

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Frontiers of Computer Science 2012年第5期6卷 581-595页

作者： Jie WEN Xiaofeng MENG Xing HAO Jianliang xu School of Information Renmin University of ChinaBeijing 100872China Department of Computer Science Hong Kong Baptist UniversityHong KongChina

In location-based services, a density query re- turns the regions with high concentrations of moving objects （MOs）. The use of density queries can help users identify crowded regions so as to avoid congestion. Most of the exist- ing methods try very hard to improve the accuracy of query results, but ignore query efficiency. However, response time is also an important concern in query processing and may have an impact on user experience. In order to address this issue, we present a new definition of continuous density queries. Our approach for processing continuous density queries is based on the new notion of a safe interval, using which the states of both dense and sparse regions are dynamically main- tained. Two indexing structures are also used to index candi- date regions for accelerating query processing and improving the quality of results. The efficiency and accuracy of our approach are shown through an experimental comparison with snapshot density queries.

关键词： continuous density queries safe interval query efficiency

WARRANTY STRATEGY IN A SUPPLY CHAIN WHEN TWO RETAILER'S EXTENDED WARRANTIES BUNDLED WITH THE PRODUCTS

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Journal of Systems Science and Systems Engineering 2015年第3期24卷 364-388页

作者： Yiwen Bian Shuai Yan Wei Zhang Hao xu SHU-UTS SILC(Sydney Institute of Language & Commerce) Business School Shanghai University School of Management Zhejiang University School of Business Anhui University

We in this paper examine warranty strategy in a two-stage supply chain consisting of a manufacturer and two competing retailers. The manufacturer produces two substitute products and markets them through the two retailers to a group of consumers, respectively. For each type of products, the manufacRtrer＇s base warranty and a retailer＇s extended warranty are bundled with the product. We use game theoretic models to explore the interactions between the two types of warranties and the competition between the retailers. For this purpose, two scenarios are considered： no retailer and both the two retailers providing the extended warranties, respectively. In each scenario, the manufacturer＇s base warranties are assumed to be offered. Our results show that when the retailers offer their extended warranties, the manufacturer has no incentive to offer the base warranties; otherwise, the manufacturer has to provide the base warranties. The competition between retailers in terms of the product substitutability has no impact on warranty decisions, but affects all players＇ profits in the supply chain. The manufacturer can provide a longer warranty length and higher customer welfare to a customer than the retailers do, if it is more efficient than the retailers in warranty cost-efficiency, and vice versa.

关键词： Base warranty extended warranty supply chain competition.

Bi Layer Formation at the Anode Interface in Cu/Sn-58Bi/Cu Solder Joints with High Current Density

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Journal of Materials Science & Technology 2012年第1期28卷 46-52页

作者： Hongwen He Haiyan Zhao Fu Guo Guangchen xu Department of Mechanical Engineering Tsinghua University Beijing 100084 China College of Materials Science and Engineering Beijing University of Technology Beijing 100124 China

Bi layer formation in Cu/Sn-58Bi/Cu solder joints was investigated with different current densities and solder thickness. Uniform and continuous Bi layers were formed at the anode interface which indicated that Bi was the main diffusing species migrating from the cathode to the anode. The electromigration force and Joule heating took on the main driving forces for Bi diffusion and migration. In addition, two appearance types of Bi layers, planar-type and groove-type, were found during current stressing. The morphology and thickness of Bi layers were affected by current density and current stressing time.

关键词： Bi layer formation Current density Electromigration Joule heating

BACH： A Bandwidth-Aware Hybrid Cache Hierarchy Design with Nonvolatile Memories

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Journal of Computer Science & Technology 2016年第1期31卷 20-35页

作者： Jishen Zhao Cong xu Tao Zhang Yuan Xie Department of Computer Engineering University of California at Santa Cruz Santa Cruz CA 95064 U.S.A. Hewlet-Packard Labs Palo Alto CA 94304 U.S.A. NVIDIA Corporation Santa Clara CA 95050 U.S.A. Department of Electrical and Computer Engineering University of California at Santa Barbara Santa Barbara CA 93106 U.S.A.

Limited main memory bandwidth is becoming a fundamental performance bottleneck in chipmultiprocessor （CMP） design. Yet directly increasing the peak memory bandwidth can incur high cost and power consumption. In this paper, we address this problem by proposing a memory, a bandwidth-aware reconfigurable cache hierarchy, BACH, with hybrid memory technologies. Components of our BACH design include a hybrid cache hierarchy, a reconfiguration mechanism, and a statistical prediction engine. Our hybrid cache hierarchy chooses different memory technologies with various bandwidth characteristics, such as spin-transfer torque memory （STT-MRAM）, resistive memory （ReRAM）, and embedded DRAM （eDRAM）, to configure each level so that the peak bandwidth of the overall cache hierarchy is optimized. Our reconfiguration mechanism can dynamically adjust the cache capacity of each level based on the predicted bandwidth demands of running workloads. The bandwidth prediction is performed by our prediction engine. We evaluate the system performance gain obtained by BACH design with a set of multithreaded and multiprogrammed workloads with and without the limitation of system power budget. Compared with traditional SRAM-based cache design, BACH improves the system throughput by 58% and 14% with multithreaded and multiprogrammed workloads respectively.

关键词： memory bandwidth hybrid cache reconfigurable cache nonvolatile memory

Numerical Simulation of 2D Supersonic Magnetohydrodynamic Channel and Study on Hall Effect

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Chinese Journal of Aeronautics 2011年第2期24卷 136-144页

作者： ZHENG Xiaomei LU Haoyu xu Dajun CAI Guobiao School of Astronautics Beihang University Beij'ing 100191 China

In this research effort,numerical simulation of two-dimensional magnetohydrodynamic（MHD） channel is performed and Hall effect is *** computational model consists of the Navier-Stokes（N-S） equations coupled with electrical-magnetic source terms,Maxwell equations and the generalized Ohm＇s *** conditions for the electrical potential equation considering Hall effect are *** start with,the MHD channel with single-pair electrodes is studied and flow of the electric current is in accordance with physical *** the MHD channel with five-pair electrodes is numerically *** results show that the electrical current concentrates on the downstream of the anode and the upstream of the cathode due to Hall effect,and the flow field becomes *** the current value of the magnetic interaction parameter,the electrical-magnetic force affects the flow remarkably,decreasing the outlet Mach number and increasing the outlet pressure;what＇s more,the flow structure in the channel becomes extremely *** of MHD channels with continual electrodes and segmented electrodes are *** results show that performance of the MHD channel with segmented electrodes is better than that with continual electrodes with the increase of Hall parameter.

关键词： hypersonic vehicles scramjet magnetohydrodynamics Hall effect numerical simulation

Interannual modulation of intraseasonal sea level variability along the southern coast of Java

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Science China Earth Sciences 2018年第1期61卷 1-12页

作者： CAO GuoJiao HE YiJun WEI Zexun xu TengFei School of Marine Sciences Nanjing University of Information Science & Technology Nanjing 210044 China First Institute of Oceanography State Oceanic Administration Qingdao 266061 China Laboratory for Regional Oceanography and Numerical Modeling Qingdao National Laboratory for Marine Science and Technology Qingdao 266237 China jiangsu Research Center for Ocean Survey and Technology Nanjing 210044 China

The intraseasonal variability(ISV) of sea level anomalies(SLAs) along the southern coast of Java and its interannual modulation were studied based on a gridded SLA product produced from the Archiving, Validation, and Interpretation of Satellite Oceanography dataset. This ISV is induced by the propagation of intraseasonal Kelvin waves derived from the central equatorial Indian Ocean(EIO). Wavelet analysis and empirical mode decomposition of intraseasonal SLAs along the southern coast of Java showed interannual variability, with weaker ISV events during El Ni years and positive Indian Ocean Dipole(IOD) years than during normal years. This interannual modulation of the ISV is influenced by the El Ni-Southern Oscillation teleconnection via the Walker Circulation and eastern Indian Ocean upwelling connected to IOD events. The anomalously weaker Walker Circulation during El Ni events generates anomalous surface easterlies over the central-eastern tropical Indian Ocean that produce upwelling Kelvin waves in the EIO and offshore water transport along the southern coasts of Sumatra and Java, resulting in negative SLAs along the southern coast of Java. These negative SLAs damp the positive SLAs induced by the eastward propagation of downwelling Kelvin waves from the central EIO during the following March–May of El Ni years. Similar features of SLAs and sea surface wind anomalies also occur during positive IOD years. Consequently, the sea level ISV along the southern coast of Java is weaker in El Ni and positive IOD years.

关键词： Intraseasonal variability Sea level Interannual variability Kelvin waves Indian Ocean

Cathodic reduction process of Al-Cu-Y alloy in fluoride-oxide eutectic system via molten salt electrolysis

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Journal of Rare Earths 2018年第3期36卷 324-330页

作者： xu Wang Chunfa Liao Yunfen Jiao Hao Tang School of Metallurgy and Chemical Engineering Jiangxi University of Science and Technology

Al-Cu-Y alloys were prepared by molten salt electrolysis in fluoride-oxide system composed of electrolyte（Na3 AlF6-AlF3-LiF-MgF2） and oxide（Al2 O3-CuO-Y2 O3）. Cathodic reduction process of Al2 O3,CuO and Y2 O3 were analyzed by cyclic voltammetry and chronoamperometry. Components and phase composition of alloy samples prepared by potentiostatic electrolysis were characterized by scanning electron microscopy and energy dispersive spectroscopy. The results show that the Al-Cu-Y alloy can be prepared in the AIF3-NaF-5 wt%LiF-5 wt%MgF2（NaF/AlF3 = 2.2, molecular ratio） eutectic system with mixed oxide（Al2 O3-CuO-Y2 O3） through 2 h at the conditions of a temperature of 1208 K, cell voltage3.0 V, cathode current density 0.7 A/cm^2. Al（Ⅲ） and Cu（Ⅱ） ions can be reduced to zero valence Al（0） and Cu（0） directly on carbonaceous electrode surface by instantaneous nucleation, respectively, the reduction process is controlled by diffusion. The reduction potential of Y（Ⅲ） ions is close to the active ions of fluoride melts, but strengthened phase AI3 Y can be formed through electrochemical reduction and alloyed process with active Al（Ⅲ） and Cu（Ⅱ） ions, meanwhile, the Al2 Cu and Al3 Y phases are distributed at the grain boundary of Al matrix.

关键词： Fluoride-oxide eutectic Al-Cu-Y alloy Molten salt electrolysis Cyclic voltammetry Electrode process Rare earths

An investigation into the three-dimensional cloud structure over East Asia from the CALIPSO-GOCCP Data

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Science China Earth Sciences 2015年第12期58卷 2236-2248页

作者： YIN JinFang WANG DongHai xu HuanBin ZHAI GuoQing State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing Institute of Applied Meteorology Department of Earth Science Zhejiang University

The spatial distribution of clouds and their seasonal variations, and the three-dimensional(3D) cloud structures over East Asia have been analyzed with the CALIPSO-GOCCP data during the period from 2007 to 2012. The results show that there is a large cloud fraction greater than 0.7 over southern China, and the largest cloud fraction appears in southwest China. Besides, a large cloud fraction occurs over the southeast of the Tibetan Plateau. The total and high cloud fractions show notable variations with seasons, while the middle and low cloud fractions vary a little. As for cloud vertical structure, significant differences of the cloud vertical distributions are observed between over land and ocean. Cloud fractions and the height of the maximum cloud fractions decline gradually with the increasing latitude, except for the vertical-latitude profiles over the Tibetan Plateau regions. The longitude-vertical cross sections show similar patterns from the longitude 70° E to 140° E, except the profiles with large cloud fractions over the Tibetan Plateau. From the horizontal distribution patterns and vertical structures of the clouds over East Asia, it is concluded that the huge terrain of the Tibetan Plateau has significant impacts on the cloud formation over the Tibetan Plateau region and the areas to the east. At last, the clouds from the CALIPSO-GOCCP observations are compared to those from the ERA-Interim reanalysis data. The results indicate that the ERA-Interim reanalysis data provide reasonable spatial distribution patterns and the vertical structures in terms of the total cloud fraction over East Asia. However, the total cloud fraction was underestimated about 20% by the ERA-Interim reanalysis data over most parts of East Asia, especially over the neighboring areas east of the Tibetan Plateau. Additionally, the ERA-interim reanalysis data overestimate the cloud fractions at each level in the vertical direction.

关键词： CALIPSO cloud fraction cloud three-dimension structure ERA-interim reanalysis data

Enhanced dechlorination of 2,4-dichlorophenol by recoverable Ni/Fe–Fe_3O_4 nanocomposites

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Journal of Environmental Sciences 2016年第10期28卷 92-101页

作者： Cancan xu Rui Liu Lvjun Chen Jialu Tang Zhejiang Provincial Key Laboratory of Water Science and Technology Department of Environment Yangtze Delta Region Institute of Tsinghua University School of Environment Tsinghua University

Ni/Fe-Fe3O4 nanocomposites were synthesized for dechlorination of 2,4-dichlorophenol （2,4-DCP）. The effects of the Ni content in Ni/Fe-Fe3O4 nanocomposites, solution pH, and common dissolved ions on the dechlorination efficiency were investigated, in addition to the reusability of the nanocomposites. The results showed that increasing content of Ni in Ni/Fe-FesO4 nanocomposites, from 1 to 5 wt.%, greatly increased the dechlorination efficiency; the Ni/Fe-Fe3O4 nanocomposites had much higher dechlorination efficiency than bare Ni/Fe nanoparticles. Ni content of S wt.% and initial pH below 6.0 was found to be the optimal conditions for the catalytic dechlorination of 2,4-DCP. Both 2,4-DCP and the intermediate product 2-chlorophenol （2-CP） were completely removed, and the concentra- tion of the final product phenol was close to the theoretical phenol production from complete dechlorination of 20 mg/L of 2,4-DCP, after 3 hr reaction at initial pH value of 6.0, 3 g/L Ni/Fe-Fe3O4, S wt.% Ni content in the composite, and temperature of 22℃ 2,4-DCP dechlorination was enhanced by C1- and inhibited by NO3- and SO42-. The nanocomposites were easily separated from the solution by an applied magnetic field. When the catalyst was reused, the removal efficiency of 2,4-DCP was almost 100% for the first seven uses, and gradually decreased to 75% in cycles 8-10. Therefore, the Ni/Fe-Fe3O4 nanocomposites can be considered as a potentially effective tool for remediation of Pollution bv 2.4-DCP.

关键词： Ni/Fe-Fe3O4 nanocomposites2 4-DichlorophenolCatalytic dechlorinationRecoverableCommon dissolved ions