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针对无线协作多播网络中的能量效率问题,设计了一种基于功率控制的能效优化策略。通过采用功率控制因子来限制系统总的能耗,按照最小信噪比原则进行中继节点选择,来增加系统吞吐量。该策略合理分配了基站和中继节点的功率,扩大了系统的覆盖范围,提高了发射效率。仿真结果表明了,与传统传输机制相比,完全搜索算法和变功率中继选择算法在效率方面有了较大提高,而时间分配算法则找到了最优的转发时间比例。 相似文献
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针对单源单中继多用户多输入多输出下行系统,提出一种基于规则块对角化的收发处理设计.考虑源端无法获得第二跳的信道信息和用户无法获得第一跳的信道信息的场景,对源-中继链路和中继-用户链路进行独立的收发处理设计.在中继处采用传统的规则块对角化方法抑制用户间干扰和噪声,并基于最小均方误差准则联合接收矩阵设计改进的迭代优化算法.仿真结果表明,该算法收敛较快,且很好地降低了低信噪比区域的误码率. 相似文献
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提出单源、多中继、单目的节点的放大转发中继系统中一种新的中继选择算法.考虑源端通过反馈获得第一跳链路过时(延时)的瞬时信道状态信息,推导了中继选择方案的中断概率闭式表达,并基于该表达式,以最小化条件中断概率为目标,提出利用信道相关性信息辅助的中继选择新方案.仿真验证了新方案相比于传统方案有明显的性能增益. 相似文献
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针对传统的密集型多路网络流均衡调度中,普遍存在着平均带宽利用率较低、能量消耗较大等问题。提出基于分布式计算的密集型多路网络流均衡调度方法。通过对密集型多路网络流进行分析,将网络节点跳数信息和多路网络流负载信息相结合作为网络流选择和切换的标准,获取网络流选择的决策函数。根据现阶段密集型多路网络流负载均衡状态对网络中过载链路上的数据流进行调度,利用链路粘值来获得网络数据流对调度任务的拒绝程度,减小调度对流性能的影响,实现多路网络流均衡调度。实验结果表明,所提方法平均带宽利用率较高、能量消耗较低。 相似文献
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在面向Internet接入无线Mesh网络(WMN)中,数据流在Mesh一侧的传输具有汇聚特性,终点大都为网关,因此最后一跳无线链路成为了WMN的瓶颈;同时不平衡的数据转发导致局部性能过低,也加剧了网络容量的低效问题. 提出基于层次模型的路由转发策略,该路由策略通过平衡因子控制上层节点负载的均衡,从而提高WMN整体网络容量. 仿真结果表明,采用层次化路由策略使得整体网络容量比HWMP提高了近20%,管理帧开销降至HWMP的40%. 相似文献
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为解决多用户MIMO-OFDM网络反馈链路所面临的反馈链路开销大与频谱效率低的问题,提出了一种基于稀疏重构的多用户MIMO网络联合反馈策略。该策略将压缩感知应用于多用户MIMO-OFDM网络有限反馈,首先在接收端对由信道估计得出的信道状态信息进行稀疏重构,以最大程度降低反馈链路开销,然后观测矩阵自适应地反馈到发送端,在发送端通过压缩感知重构策略重构原始信道信息,有效降低了反馈链路处理复杂度和传输的数据量。仿真结果表明,在反馈量相同的前提下,该策略的反馈开销和频谱率性能都优于传统有限反馈机制,降低了通信链路的整体开销,并一定程度上改善了网络拥塞。 相似文献
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由于无线网路中链路质量的不稳定、信号的广播传输模式和节点之间存在的相互干扰，针对提高无线网状网络性能的信道分配和路由选择将更加复杂。采用多信道成为一种可选的提高网络容量的方法。本文提出了一种基于2.4GHz 802.11无线网状网络的一种固定信道分配方法，采用了多输入多输出技术使得网络中的数据流以流水线的方式进行传输。在这个场景下多条并行的流可以同时被激活，以此来提升UDP和TCP的传输性能。通过对802.11b网络中1、6和11三个相互不重叠的信道的分配，该信道分配算法在空间上实现邻居节点之间的干扰最小化，其中信道1和11被分配给网状网络的主干传输部分，信道6被分配给用户接入网络。文章最后通过NS2仿真实验，并对本文提出的算法进行了分析。实验结果证明网络的平均吞吐率有大幅度提升，且多跳传输的延迟也被降低。 相似文献
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移动自组织网络(MANET)是一类连接移动设备的自适应无线网络,为提高网络传输质量优化链路状态,文中以高负载MANET为背景环境,提出基于灰色区域预测的自适应多路径改进路由算法。以OLSR路由协议为基础,与卡尔曼滤波预测法相结合对链路网络连接状态实行估测,在链路失效前计算新路由,减少计算新路由耗时;估测链路时效性时对网络中灰色区域进行处理,邻居节点为灰色区域内直接判定为无效节点,确保存在稳定通信链路。基于上述稳定通信链路,以衡量链路质量为标准,采用多路径冗余传输及多路径负载均衡改进路由算法提高端到端传输可靠性;运用多路径冗余传输方式,提升端到端递交率;利用多路径负载均衡传输方式使更多节点参与转发,提高端到端吞吐量。实验证明,运用文中自适应多路径改进路由算法可有效提升网络传输质量。 相似文献
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A research group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol-a chemical found in the skins of red grapes in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said. 相似文献
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《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
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Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors. 相似文献
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《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
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A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells suggesting that China's projected climate warming could decrease the pest's numbers. The study was published in Proceedings of the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007. 相似文献
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Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction. 相似文献
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Active biological molecules functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery disease diagnosis therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction. 相似文献
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Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies. 相似文献
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Puay Tang 《The Information Society》1998,14(1):19-31
The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means. 相似文献
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Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 相似文献