Free-riders impact on throughputs of peer-to-peer file-sharing systems

In a peer-to-peer file-sharing system, a free-rider is a node which downloads files from its peers but does not share files to other nodes. Analyzing the free-riders’ impact on system throughputs is essential in examining the performance of peer-to-peer file-sharing systems. We find that the free-riders’ impact largely depends on nodes behavior, including their online time and greed of downloading files. We extend an existing peer-to-peer system model and classify nodes according to their behavior. We focus on two peer-to-peer architectures: centralized indexing and distributed hash tables. We find that when the cooperators in a system are all greedy in downloading files, the system throughput has little room to increase while the cooperators throughput degrade badly with the increasing percent of greedy free-riders in the system. When all the cooperators are non-greedy with long average online time, the system throughput has much room to increase and the cooperators throughput degrade little with a high percent of greedy free-riders in the system. We also find that if a system can tolerate a high percent of greedy free-riders without suffering much throughput degradation, the system must contain some non-greedy cooperators that contribute great idle service capacity to the system. Foundation item: the National High Technology Research and Development Program (863) of China (No. 2007AA01Z457), and the Shanghai Science and Technology Development Funds (No. 07QA14033)     

Security analysis of application layer protocols on wireless local area networks

This paper aims at analyzing the security issues that lie in the application layer (AL) protocols when users connect to the Internet via a wireless local area network (WLAN) through an access point. When adversaries launch deauthentication flood attacks cutting users’ connection, the connection managers will automatically research the last access point’s extended service set identifier (ESSID) and then re-establish connection. However, such re-connection can lead the users to a fake access point with the same ESSID set by attackers. As the attackers hide behind users’ access points, they can pass AL’s authentication and security schemes, e.g. secure socket layer (SSL). We have proved that they can even spy on users’ account details, passwords, data and privacy.     

Delphi语言在计算机机房实践教学中的应用

本文介绍了在Delphi开发环境下,通过Windows API两函数调用的编程,实现了学生机与教师机之间的网络通讯连接和文件的拷贝,满足了学生在计算机机房上课时向教师机上传电子作业的功能。     

Scheduling for Uncertain Data Broadcast in Mobile Networks

With the increasing popularity of wireless sensor network and GPS (global positioning system) , uncertain data as a new type of data brings a new challenge for the traditional data processing methods. Data broadcast is an effective means for data dissemination in mobile networks. In this paper, the definition of the mean uncertainty ratio of data is presented and a broadcasting scheme is proposed for uncertain data dissemination. Simulation results show that the scheme can reduce the uncertainty of the broadcasted uncertain data effectively at the cost of a minor increase in data access time, in the case of no transmission error and presence of transmission errors. As a result, lower uncertainty of data benefits the qualities of the query results based on the data.     

一种高效的移动云服务环境下隐私保护认证协议

为了解决移动云服务环境的互相认证和隐私保护问题,设计了一种改进的移动云服务环境下隐私保护认证协议.该协议结合基于身份的签密技术和多服务器认证技术,保证用户只需注册一次,就可以访问多个移动云服务提供者,同时认证过程不需要可信第三方参与;该协议在移动终端未使用计算复杂度高的双线性对运算和映射到域上的hash运算,其计算效率显著提高. 通过理论分析和实验结果可知:该协议与目前已有的同类协议相比,在移动端的计算时间为45.242 s,其计算效率约为已有同类协议的2倍;具有用户匿名和不可追踪等安全性质;能够抵抗错误口令登录、更改攻击.      

Threshold signature scheme with threshold verification based on multivariate linear polynomial

Secret sharing schemes are multi-party protocols related to key establishment. They also facilitate distributed trust or shared control for critical activities (e.g., signing corporate cheques and opening bank vaults), by gating the critical action on cooperation from t(t ∈ Z ⁺) of n(n ∈ Z ⁺) users. A (t, n) threshold scheme (t < n) is a method by which a trusted party computes secret shares Γ _i (1 ⩽ i ⩽ n) from an initial secret Γ ₀ and securely distributes Γ _i to user. Any t or more users who pool their shares may easily recover Γ ₀, but any group knowing only t−1 or fewer shares may not. By the ElGamal public key cryptophytes and the Schnorr’s signature scheme, this paper proposes a new (t, n) threshold signature scheme with (k,m) (k,m ∈ Z ⁺) threshold verification based on the multivariate linear polynomial.     

On the algorithms of adaptive neural network-based speed control of switched reluctance machines

AbstractA switched reluctance machine(SRM)drive is a time-varying,strongly nonlinear system.High performance control can no longer be achieved by using linear techniques.This paper describes the back-propagation (BP)neural network-based proportional-integral-derivative(PID)speed control of the SRM.It’s the interest of this paper to explore the utilization of the prior empirical knowledge as guidance in the initializing and training of the neural networks.The purpose is to make the networks less sensitive on the initial weights.Two modified algorithms are presented and simulation experiments show some interesting findings about their control effects and their corresponding sensitivity on the initial weights of the networks.     

作为地铁接驳手段的公共自行车使用特性分析

本文以苏州公共自行车为研究对象,利用刷卡数据及问卷调查数据分析公共自行车作为地铁接驳手段的使用特性.研究发现,地铁型站点公共自行车的用车时长较短且较为离散,与其他类型站点有显著差异.在接驳地铁的出行者中,公共自行车经常使用者的平均学历较高,也非低收入人群.利用离散选择模型分析地铁接驳方式选择行为可知,接驳方式使用时间是最重要的影响因素,年龄、职业和出行目的等对公共自行车的选择均有显著影响.研究还发现,经常使用公共自行车的出行者在接驳地铁时同样也倾向于选择公共自行车,而不使用者则倾向于选择步行或公交车.     

一种基于手机信令的通勤OD 训练方法

针对基站定位精度低、信令采样间隔长、轨迹不连续的手机信令,提出一种职 住及通勤OD(origin-destination)计算框架.对用户单日手机轨迹按时间排序,标识每个轨 迹点的进出时间及停留时间,剔除长距离漂移轨迹点,对邻近轨迹点进行空间聚合.将全 天划分为多个时窗,叠加用户多日轨迹,计算稳定指数并识别用户在各时窗内的多日稳 定点.综合工作日与节假日稳定点判断用户居住地、工作地.采用基于常住人口的扩样方 法,对街道通勤OD矩阵进行扩样.模型结果与重庆主城常住人口分布、2014 年居民出行 调查结果吻合.     

基于干扰对准的LTE上行虚拟MIMO系统

提出在LTE上行采用2×2模式的虚拟MIMO（VirtualMIMO,V—MIMO）系统,即一个两天线的基站同时支持两个单天线的用户,并在此基础上,提出一种基于传输延时的干扰对准算法．这种算法将基站的双天线的接收信号按照奇、偶时隙分离,从而将期望信号与干扰信号分离．应用本文算法一个两天线的基站可以支持3个甚至4个用户同时接入LTE网络的上行链路．     

Chosen ciphertext secure identity-based broadcast encryption in the standard model

To give concurrent consideration both the efficiency and the security (intensity of intractable problem) in the standard model, a chosen ciphertext secure identity-based broadcast encryption is proposed. Against the chosen ciphertext security model, by using identity (ID) sequence and adding additional information in ciphertext, the self-adaptive chosen identity security (the full security) and the chosen ciphertext security are gained simultaneously. The reduction of scheme’s security is the decisional bilinear Diffie-Hellman (BDH) intractable assumption, and the proof of security shows that the proposed scheme is indistinguishable against adaptive chosen ciphertext attacks in the standard model under the decisional BDH intractable assumption. So the security level is improved, and it is suitable for higher security environment.     

Precise zero-knowledge arguments with poly-logarithmic efficiency

Precise zero-knowledge was introduced by Micali and Pass in STOC’06. This notion captures the idea that the view of a verifier can be reconstructed in almost same time. Following the notion, they constructed some precise zero-knowledge proofs and arguments, in which the communicated messages are polynomial bits. In this paper, we employ the new simulation technique introduced by them to provide a precise simulator for a modified Kilian’s zero-knowledge arguments with poly-logarithmic efficiency (this modification addressed by Rosen), and as a result we show this protocol is a precise zero-knowledge argument with poly-logarithmic efficiency. We also present an alternative construction of the desired protocols.     

Effects of Friends' Information Interaction on Travel Decisions

Many existing studies focus on the effects of traffic information from ATIS on travel choices. Research on the effect of friends' travel information on people's travel choice is uncommon, yet needed. In this paper, behavioral experiments are conducted to discuss what the effects of information interaction with friends can bring on individual travel decision behavior. The experimental results concluded that when the rate of friends' information interaction reaches 33.3%, the whole system is at an optimal level. Furthermore, users reach an optimum when the rate of friends' travel information interaction is 75%. The average time and cost per person is increasing when the whole system optimum transfers to the user optimum. Moreover, adjustments of departure time at the system optimum are more dispersed than at the user optimum, while travel choice changes are more concentrated.     

基于微信公众平台在线练习系统研究与开发

文中主要提出基于微信公众号环境下开发新型在线练习系统,运用微信跨平台特性实现用户在各类网络终端如安卓系统手机、苹果系统手机、PAD等随时随地进行在线学习与练习的目标。     

Location and design decisions of facilities in a distribution system with elastic customer demand

This paper describes a bi-level programming model that seeks to simultaneously optimize location and design decisions of facilities in a distribution system in order to realize company’s maximal total profit subject to the constraints on the facility capacity and the investment budget. In the upper-level problem, two-echelon integrated competitive/uncompetitive capacitated facility location model, which involves facility location and design, is presented. In the lower-level problem, customer is assumed to patronize store based on facility utility which is expressed by service time cost in the store and its travel cost to customer. Customer’s facility choice behavior is presented by a stochastic user equilibrium assignment model with elastic demand. Since such a distribution system design problem belongs to a class of NP-hard problem, a genetic algorithm (GA)-based heuristic procedure is presented. Finally, a numerical example is used to illustrate the application of the proposed model and some parameter sensitivity analyses are presented.     

Directed proxy signature in the standard model

A directed signature is a type of signature with restricted verification ability. Directed signatures allow only a designated verifier to check the validity of the signature issued to him, and at the time of trouble or if necessary, any third party can verify the signature with the help of the signer or the designated verifier. Directed signature schemes are widely used in situations where the receiver’s privacy should be protected. Proxy signatures allow an entity to delegate its signing capability to another entity in such a way that the latter can sign message on behalf of the former when the former is not available. Proxy signature schemes have found numerous practical applications such as distributed systems and mobile agent applications. In this paper, we firstly define the notion of the directed proxy signature by combining the proxy signature and directed signature. Then, we formalize its security model and present a concrete scheme in the standard model. Finally, we use the techniques from provable security to show that the proposed scheme is unforgeable under the gap Diffie-Hellman assumption, and invisible under the decisional Diffie-Hellman assumption.     

放射式轨道路网的系统出行成本研究

探讨放射式轨道路网下的系统出行成本，能够为评价轨道交通服务水平、确定合理的线路数量和运营参数提供理论支持。基于研究区域人口密度服从Clark 分布，建立了系统出行成本模型。模型将乘客在步行时间、车站等待时间和车上等待时间换算为费用作为系统出行成本的一部分，结合运营商的运营和维护成本得到系统人均出行总成本。以成都市为例，通过模型分析确定最优发车频率为13 veh/h、轨道线路数为5条，较符合实际情况，验证了模型的有效性。     

基于半马尔科夫链的中小堤坝WSN节点能耗研究

无线传感器网络技术的引入,为中小型堤坝监测技术的发展提供了新思路。由于无线传感器网络节点采用电池供电,而堤坝环境中的数据监测条件比较苛刻,电源更换相对困难,无线传感器网络节点能耗的优化在延长整个无线传感器网络生命周期过程中显得尤为重要。本文介绍了无线传感器网络中节点能耗的主要分布,并提出了降低节点能量消耗的策略。借助半马尔可夫链理论建立了节点能耗的数学模型,分析了WSN节点的能耗情况,在保证正常数据通信的情况下,通过对节点状态的管理,延长节点的睡眠时间,从而达到降低整个网络能耗的目的。     

城市环境中共享（街道）空间概念演变综述

通过综述城市设计与交通工程学科文献,从新西兰视角明确共享空间概念的起源和演变。综述过程包括研究公众期望变化背景下的公共道路空间的功能与使用以及如何与一些相互关联的街道设计方法(如交通稳静化和自适应道路)联系起来。这些方法从机动车时代初期就被用于最小化机动车影响。应用于城市活动中心的公共道路环境中的共享空间概念,正逐渐被城市规划师、交通工程师和管理部门所接受。共享空间不同于传统道路,它鼓励通过少量物理隔离使全体道路使用者合理地使用同一道路空间。为了以安全有效的方式实现共享空间,在设计上需要通过促进步行与骑行活动来降低机动车主导性,同时应将道路空间作为场所来利用而非仅仅出于其机动性与可达性目的。基于交通稳静化街道与共享空间在基础概念上的差异,认为共享空间由一些设计要素组成,若缺少这些要素,公共街道将难以对全体道路使用者发挥其真正的共享空间功能。     

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车载导航系统（IVNS）能提供实时有效交通信息辅助驾驶人选择最佳路径.为了探讨IVNS的市场渗透率对路网运行效益（交通效益和环境效益两方面）的影响,本文运用宏观动态交通网络模型METANET建立仿真平台,用反馈式动态交通分配模型描述IVNS路径诱导下驾驶人的行为,以总排队时间和总耗费时间作为交通效益评价指标,用反映速度—加速度关系的机动车排放和燃油消耗关系模型——VT-Micro 模型计算机动车排放量和燃油消耗量,并用货币价值量化排放减少带来的直接经济效益(包括大气污染治理费用和燃油消耗节省).对一个算例路网进行仿真,仿真结果表明：IVNS能够有效均衡路网交通,改善路网交通拥挤,尽管使NOx排放增加,却降低了HC、CO排放,减少了燃油消耗,带来了巨大的经济效益.综合考虑IVNS市场渗透率的交通效益和环境效益,建议可将市场渗透率控制在0.2~0.3左右.研究旨在为相关部门设计评价IVNS,优化路网运行效益提供辅助决策依据.