多媒体教室网络接入设计与实现

伴随着教育信息化的发展,网络已经成为多媒体教学必不可少的教学手段.因此,对未接入网络的教学区教学设备进行网络布线、管理及升级显得非常必要.本文阐述了学院教学楼多媒体教室网络接入的设计思想和实施方案,对项目实施中的难点和关键点进行了深入分析和研究实现,为云空间的教学手段提供了优质的保障.     

Relationship of Margin Rule and Volatility in Chinese Copper Futures Markets

Different from western markets, the margin rates in Chinese futures markets are raised when contract approaches maturity. This paper concentrates on the effect of this time dependent margin rule on volatility. Open interest, another candidate in the margin rule, is also included in our model to investigate its necessity as one of the factors of the rise of margin rates. With the popular copper contract in Shanghai Futures Exchange (SHFE) , our test results suggest that margin levels have a significant positive effect on volatility, yet open interest has little to do with volatility. The implication is that the rise of margin rate approaching maturity virtually deteriorates the degree of market risks, and open interest is not a necessary factor for the margin rule. It indicates that the policy tool, represented by margin rates, has significantly greater influence on volatility than the market element, represented by open interest.     

A simulation study of service differentiation for the bandwidth request scheme in fixed IEEE 802.16 network

Various flexible mechanisms related to quality of service (QoS) provisioning have been specified for uplink traffic at the medium access control (MAC) layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation (SD) is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better. Foundation item: the National Basic Research Program (973) of China (No. 2005C13321804)     

In-home power line communication media access control protocol based on collision resolution

Most existing media access control (MAC) protocols in power line communication (PLC) networks just discard the colliding data packets when collision occurs. The collision deteriorates throughput and delay performance of system under high traffic conditions. This article presents a novel media access scheme with fast collision resolution for in-home power line networks. It works by first recognizing the colliding stations through detecting the inserted unique ID sequence ahead of data packets, then the source nodes retransmitting their packets immediately after the collision slot. The proposed protocol maintains the benefits of ALOHA systems. It needs no scheduling overhead and is suitable for bursty sources, such as multimedia data packets. Computer simulations have demonstrated that this approach can achieve high throughput due to its ability of resolving collisions.     

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公路客运快递业（简称客运快递）已经成为公路客运业的一项重要附属业务,但是,较低的网点密度和安全性限制了客运快递的发展。为了发现问题,明确客户对客运快递的喜好,增强客运快递市场竞争力,首先针对快递客户实施调查,研究客户对快递业务各种属性的重视程度。然后,利用调查数据构建分析客户选择快递方式的行为模型,并基于模型分析客户的选择行为,计算客户对客运快递网点密度的敏感度。最后,提出整合客运快递和公交首末站点资源的建议,为客运快递企业扩大市场份额提供营销策略。     

图书馆开放型一站式服务模式的实施及对策

本文介绍了图书馆开放型一站式服务模式的基本内涵、建设过程与实施办法,并对该模式的应用提出了建议。     

机场旅客进出场交通方式选择的双层规划模型

以机场出发旅客为研究对象,在分析多种交通方式下旅客进出场出行费用对其交通方式选择影响基础上,应用双层规划模型描述了机场旅客进出场交通方式选择问题,并利用基于灵敏度分析的启发式方法对模型进行求解．模型综合考虑了交通系统的收益和旅客的利益．通过算例可以看出,应用双层规划模型描述机场旅客进出场交通方式选择问题是合理的,所采用的方法是可行有效的,对于制定多模式交通运输价格策略、缓解大型机场地面交通拥挤等具有现实意义．     

枢纽机场衔接公路网优化理论与方法研究

公路方式是我国枢纽机场与城市衔接的主要交通方式。枢纽机场衔接公路网的优化,能维持该区域客运交通运输网络高效运转,是综合运输体系中的关键技术。我国面临枢纽机场衔接公路网优化理论不完善和经验缺乏的问题。从系统工程角度,分析国内外大型机场地面交通衔接的现状和发展趋势,阐述枢纽机场地面交通衔接集聚特征及集疏运机理,探讨枢纽机场衔接影响因素（制约性、结构性、比例性）和衔接公路网优化准则,提出枢纽机场衔接公路网优化的核心问题和研究方向。     

基于UG/Open的齿轮参数化建模

在UGNX环境下,建立参数化齿轮模型,并存储为模板文件,然后利用UG/Open进行二次开发,实现了通过对话框输入参数,直接建立渐开线圆柱斜齿轮的三维模型。     

铁路计算机网络安全系统建设和应用

铁路计算机网络安全系统基于"应用分区、网络分层、安全分级"的思想,实现铁路计算机网络基础设施、网络边界和局域网环境的安全保障.介绍构成铁路计算机网络安全系统平台的铁路行业数字证书认证、统一用户管理和资源管理、访问控制、病毒防护和应用系统的安全服务5个子系统及其应用,并结合铁路信息化发展提出进一步建设铁路计算机网络安全保障体系的构想.