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Preserving location privacy without exact locations in mobile services

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Frontiers of Computer Science 2013年第3期7卷 317-340页

作者： Xiao PAN xiaofeng meng School of Economics and Management Shijiazhuang Tiedao University Shijiazhuang 050043 China School of Information Renmin University of China Beijing 100872 China

Privacy preservation has recently received considerable attention in location-based services （LBSs）. A large number of location cloaking algorithms have been proposed for protecting the location privacy of mobile users. However, most existing cloaking approaches assume that mobile users are trusted. And exact locations are required to protect location privacy, which is exactly the information mobile users want to hide. In this paper, we propose a p-anti-conspiration privacy model to anonymize over semi-honest users. Further- more, two k＊NNG-based cloaking algorithms, vk＊NNCA and ek＊NNCA, are proposed to protect location privacy without exact locations. The efficiency and effectiveness of the pro- posed algorithms are validated by a series of carefully designed experiments. The experimental results show that the price paid for location privacy protection without exact locations is small.

关键词： location privacy semi-honest users privacy preservation location-based services

Fast computation of scattering from 3D complex structures by MLFMA

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Journal of Systems Engineering and Electronics 2008年第5期19卷 872-877页

作者： Hu Jun Nie Zaiping Que xiaofeng meng Min Coll. of Electronic Engineering Univ. of Electronic Science and Technology of China Chengdu 610054 P. R. China

This paper introduces the research work on the extension of multilevel fast multipole algorithm （MLFMA） to 3D complex structures including coating object, thin dielectric sheet, composite dielectric and conductor, cavity. The impedance boundary condition is used for scattering from the object coated by thin lossy material. Instead of volume integral equation, surface integral equation is applied in case of thin dielectric sheet through resistive sheet boundary condition. To realize the fast computation of scattering from composite homogeneous dielectric and conductor, the surface integral equation based on equivalence principle is used. Compared with the traditional volume integral equation, the surface integral equation reduces greatly the number of unknowns. To computc conducting cavity with electrically large aperture, an electric field integral equation is applied. Some numerical results are given to demonstrate the validity and accuracy of the present methods.

关键词： impedance boundary condition equivalence theory surface integral equation dielectric cavity.

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

Efficient processing of partially specified twig pattern queries

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Science in China(Series F) 2009年第10期52卷 1830-1847页

作者： ZHOU JunFeng meng xiaofeng LING TokWang School of Information Renmin University of China Beijing 100872 China Department of Computer Science and Technology Yanshan University Qinhuangdao 066004 China School of Computing National University of Singapore 117590 Singapore

As huge volumes of data are organized or exported in tree-structured form, it is quite necessary to extract useful information from these data collections using effective and efficient query processing methods. A natural way of retrieving desired information from XML documents is using twig pattern （TP）, which is, actually, the core component of existing XML query languages. Twig pattern possesses the inherent feature that query nodes on the same path have concrete precedence relationships. It is this feature that makes it infeasible in many actual scenarios. This has driven the requirement of relaxing the complete specification of a twig pattern to express more flexible semantic constraints in a single query expression. In this paper, we focus on query evaluation of partially specified twig pattern （PSTP） queries, through which we can reap the most flexibility of specifying partial semantic constraints in a query expression. We propose an extension to XPath through introducing two Samepath axes to support partial semantic constraints in a concise but effective way. Then we propose a stack based algorithm, pTwigStack, to process a PSTP holistically without deriving the concrete twig patterns and then processing them one by one. Further, we propose two DTD schema based optimization methods to improve the performance of pTwigStack algorithm. Our experimental results on various datasets indicate that our method performs significantly better than existing ones when processing PSTPs.

关键词： XML database query processing partially specified twig pattern holistic twig join XPath

Vertical nanowires enhanced X-ray radiation damage of cells

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Journal of Materials Science & Technology 2023年第14期145卷 7-13页

作者： Liyuan Zheng Qingxuan Li Shandong Xu xiaofeng meng Xinqi Chen Ming Su Department of Chemical Engineering Northeastern UniversityBostonMassachusetts 02115United States Wenzhou Institute of Biomaterials and Engineering Chinese Academy of Sciencesand Wenzhou Medical UniversityWenzhou 325001China College of Sciences Beijing Forestry UniversityBeijing 100083China Department of Mechanical Engineering Northwestern UniversityEvanstonIllinois 60208United States

Cell behavior is affected by nanostructured surface,but it remains unknown how ionizing radiation af-fects cells on nanostructured *** paper reports an experimental investigation of X-ray radiation induced damage of cells placed on an array of vertically aligned silicon nanowires.X-ray photoelectrons and secondary electrons produced from nanowire array are measured and compared to those from flat silicon *** cell functions including morphology,viability,adhesion and proliferation have been examined and found to be drastically affected when cells are exposed to X-ray radiation,compared to those sitting on flat substrate and those only exposed to *** enhanced cell damage on nanowires upon X-ray exposure is attributed to nanowire enhanced production of photoelectrons including Auger electrons and secondary electrons,which have high escaping probability from sharp tips of *** escaped photoelectrons ionize water molecules and generate hydroxyl free radicals that can damage DNAs of *** inference of this work is that the contrast in scanning electron microscopy is useful in assessing the effects of nanomaterials for enhanced X-ray radiation therapy.

关键词： Edge enhancement Silicon nanowire array X-ray radiation Photoelectron Cell damage

Identify Implicit Communities by Graph Clustering

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Wuhan University Journal of Natural Sciences 2006年第5期11卷 1109-1113页

作者： YANG Nan meng xiaofeng School of Information Renmin University of ChinaBeijing 100872 China

How to find these communities is an important research work. Recently, community discovery are mainly categorized to HITS algorithm, bipartite cores algorithm and maximum flow/minimum cut framework. In this paper, we proposed a new method to extract communities. The MCL algorithm, which is short for the Markov Cluster Algorithm, a fast and scalable unsupervised cluster algorithm is used to extract communities. By putting mirror deleting procedure behind graph clustering, we decrease comparing cost considerably. After MCL and mirror deletion, we use community member select algorithm to produce the sets of community candidates. The experiment and results show the new method works effectively and properly.

关键词： Web community link analysis graph clustering MCL

Common patterns of online collective attention flow

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Science China(Information Sciences) 2017年第5期60卷 258-260页

作者： Yong LI xiaofeng meng Qiang ZHANG Jiang ZHANG Changqing WANG School of Information Renmin University of China College of Computer Science and Engineering Northwest Normal University School of Systems Science Beijing Normal University DNSLAB China Internet Network Information Center

Dear editor,During the past two decades,we have witnessed the explosive growth of the World Wide *** understand the common patterns of how this complex artificial software system evolves has been a more and more important and active research area for scientists[1].If we see the Web as a virtual tissue,according to the metabolic theory,the website must absorb"energy"to grow,reproduce,and *** are interested in the following questions:

关键词： Common patterns of online collective attention flow line view node

Microwave propagation in air drilling

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Petroleum Science 2010年第3期7卷 390-396页

作者： meng xiaofeng Chen Yijian Zhou Jing meng Yingfeng Physics Department Beijing Normal University Beijing 100875 China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum University Chengdu Sichuan 610500 China

This paper examines the feasibility in air drilling of transmitting down-hole signals by using microwaves. Firstly the basic theory of microwave propagation in the drill-pipe or casing was studied, including power loss, cutoff wavelength, and dust scattering. Theoretical analysis indicates that the microwave propagation distance in a cb214mm casing can easily reach 5,000 m. When the effect of dust particles is taken into account, the propagation distance decreases to 2,000 m. We conducted both laboratory experiments and field tests in casings commonly used in oil fields. The field tests show that the effective propagation distance of microwave in the casing is about 1,300 m. The experimental results do not match well with theoretical prediction, but are acceptable. In future commercial applications, by applying multiple relay amplifiers, the microwave propagation distance could be long enough for most drilling wells.

关键词： Microwave waveguide drill-pipe casing air drilling

TwigStack^+:Holistic Twig Join Pruning Using Extended Solution Extension

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Wuhan University Journal of Natural Sciences 2007年第5期12卷 855-860页

作者： ZHOU Junfeng XIE Min meng xiaofeng School of Information Renmin University of China Beijing 100872 China Department of Computer Science and Technology Yanshan University Qinhuangdao 066004 Hebei China

XML has been used extensively in many applications as a de facto standard for information representation and exchange over internet. Huge volumes of data are organized or exported in tree-structured form and the desired information can be got by traversing the whole tree structure using a twig pattern query. A new definition, Extended Solution Extension, is proposed in this paper to check the usefulness of an element from both forward and backward directions. Then a novel Extended Solution Extension based algorithm, TwigStack^＋, is also proposed to reduce the query processing cost, simply because it can check whether other elements can be processed together with the current one. Compared with existing methods, query evaluation cost can be largely reduced. The experimental results on various datasets indicate that the proposed algorithm performs significantly better than the existing ones.

关键词： XML database holistic join