Mathematical Analysis of Energy Efficiency in IEEE 802.11 DCF     

高波杨宇航  马惠业 《天津大学学报(英文版)》2005,11(5):332-337

The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.  相似文献   

三角债清理的图论模型分析     

陈爱珍 《忻州师范学院学报》2006,22(5):129-131

三角债是我国当前经济领域中存在的一个突出问题。文章建立了三角债的图论模型,并证明了任一债务网络皆可转换为最小债务网络,从而简化了三角债清理工作。  相似文献   

基于遗传算法和BP神经网络的优化设计方法   总被引：5，自引：0，他引：5  

于文莉  陈亚军  周伟忠  于文华 《湖州师范学院学报》2004,26(2):56-58

随着生产规模的复杂化、多维化和非线性等复杂特性的增加，对生产中高效的优化技术要求也越来越迫切，利用并行遗传算法和BP网络的优点，提出采用遗传算法的并行搜索和解空间搜索的优点进行网络参数的选取，利用BP网络简单和可塑性强的优点来优化样本空间，以取得整体的优化效率。  相似文献   

Factors affecting the career progress of academic accountants in Australia: Cross-institutional and gender perspectives     

Nava Subramaniam 《Higher Education》2003,46(4):507-542

Since the late 1980s, Australian highereducation has undergone significant reforms andpolicy changes based on economic rationalismand modernisation of management. This paperexamines the outcomes of the reform processesbased on the career attributes, status andperceptions of work environment of academicaccountants in Australian universities.Similarities and differences between academicaccountants are explored fromcross-institutional and gender perspectives.The data provide insight into a number ofsystemic inequalities between the older andmore established universities and the neweruniversities. In specific, across-institutional analysis based on fouruniversity types: Sandstones/Redbricks,Gumtrees, Unitechs and New (Marginson 1999)indicates that academic accountants in Newuniversities employ a much lower proportion ofstaff with PhD qualification, a weakerpublication profile, and perceive greaterbarriers for conducting research in terms of ashortage of research mentors, colleagues withresearch experience, and post-graduatestudents. Further, the commitment to flexiblelearning and delivery strategies iscomparatively stronger in Unitechs, and posesadditional demands on accounting academics'overall workload. Perceptions of gender-baseddiscrimination by female academic accountantsare generally stronger than their malecounterparts, particularly, in Newuniversities. These results raise severalissues for academic accountants at both theinstitutional and individual level in terms ofequal employment opportunities, management ofresearch programmes, development of teachingstrategies and individual time management.  相似文献   

加强信息网络环境下的图书馆建设     

喻绍贤 《哈尔滨学院学报》2002,23(10):135-136

信息网络的迅速发展，对图书馆提出了严峻挑战的同时也带来机遇。图书馆要面对时代变化，不断进行自身建设，才能适应社会发展需要。  相似文献   

EBF网络特征映射和恢复及其在鲁棒话者识别中的应用     

李昕  郑宇  江芳泽 《上海大学学报(英文版)》2002,6(4)

The performance of speaker verification systems is often compromised under real-world environments. For example, variations in handset characteristics could cause severe performance degradation. This paper presents a novel method to overcome this problem by using a non-linear handset mapper. Under this method, a mapper is constructed by training an elliptical basis function network using distorted speech features as inputs and the corresponding clean features as the desired outputs. During feature recuperation, clean features are recovered by feeding the distorted features to the feature mapper. The recovered features are then presented to a speaker model as if they were derived from clean speech. Experimental evaluations based on 258 speakers of the TIMIT and NTIMIT corpuses suggest that the feature mappers improve the verification performance remarkably.  相似文献   

Metaphor,Transferred Epithet与Personification辨析     

于少萍  彭家玉 《十堰职业技术学院学报》2001,14(1):7-8

本文认为隐喻、移位法与拟人法这三个英语辞格是人类思维中三种性质不同的方式的产物，并分析了其表现形式的不同。  相似文献   

Modeling water and carbon fluxes above summer maize field in North China Plain with back-propagation neural networks     

Qin Z  Su GL  Yu Q  Hu BM  Li J 《Journal of Zhejiang University. Science. B》2005,6(5):418-426

INTRODUCTION Dynamics of carbon and water vapor fluxesexchange between the atmosphere and the ecosystembiosphere, depend on complex and non-liner interplayamong physiological, ecological, biochemical andedaphic factors and meteorological conditions (Jarvis,1995; Leuning et al., 1995). There are many studiesquantifying the fluxes across different time and spacescales as well as assessing the environment con-straints on them by some kinds of biophysical orempirical models whose resul…  相似文献   

移动自组网AODV多路径路由研究     

范业仙 《宁德师专学报(自然科学版)》2007,19(2):141-144

AODV协议是唯一通过IETF批准成为RFC文档的移动自组网按需控制路由协议．分析AODV路由协议工作过程及优缺点，并介绍了几种典型的基于AODV的多路径路由改进协议，最后对这些多路径协议进行优缺点分析及性能比较。  相似文献   

Hybrid ants-like search algorithms for P2P media streaming distribution in ad hoc networks     

ZUO Dong-hong DU Xu YANG Zong-kai 《浙江大学学报(A卷英文版)》2007,8(8):1191-1198

Media streaming delivery in wireless ad hoc networks is challenging due to the stringent resource restrictions,po-tential high loss rate and the decentralized architecture. To support long and high-quality streams,one viable approach is that a media stream is partitioned into segments,and then the segments are replicated in a network and served in a peer-to-peer(P2P) fashion. However,the searching strategy for segments is one key problem with the approach. This paper proposes a hybrid ants-like search algorithm(HASA) for P2P media streaming distribution in ad hoc networks. It takes the advantages of random walks and ants-like algorithms for searching in unstructured P2P networks,such as low transmitting latency,less jitter times,and low unnecessary traffic. We quantify the performance of our scheme in terms of response time,jitter times,and network messages for media streaming distribution. Simulation results showed that it can effectively improve the search efficiency for P2P media streaming distribution in ad hoc networks.  相似文献