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飞机航班延误已成为困扰国内外航空运输业的一道世界性的难题.针对航空公司对航班延误分析的迫切需要,通过分析机场跑道的当前容量,应用排队论中的M/G/1模型,对机场起降飞机进行延误分析,提出一种评估机场跑道上航班延误的新方法,并用首都机场的实际数据进行验证.算例分析结果表明,此方法可为航空公司以及机场在航班安排方面提供有效的参考. 相似文献
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目前航班延误现象时有发生,旅客对航空公司的航班动态监控和运行控制能力的要求越来越高。基于数据链通信的航班动态监控技术越来越受到关注,本文对ADS—B的数据链分类及其在航班动态监控中的应用状况进行了分析和讨论。 相似文献
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随着XML文档大量涌现,如何有效地管理和查询XML数据已经成为亟待解决的问题。结合数据库发展的需要,研究了在关系数据库中利用物化视图和查询重写技术存储和查询XML文档。基于视图的查询重写技术是查询优化的一个重要技术,利用缓存的视图结果回答新查询不需要访问源数据库进行查询,能够节省查询处理时间。通过对物化视图、视图缓存、查询重写等技术进行研究,讨论如何利用关系数据库中缓存的物化视图来回答查询的问题,并实现了基于物化视图的XML数据查询系统原型。系统中使用扩展的模式匹配算法实现对多分支路径的模式匹配,解决了重写是否存在的问题,并通过模式匹配算法的匹配结果,来判断是否可以构造补偿表达式。通过构造补偿表达式算法得到重写结果,进而通过数据库中缓存的视图完成查询。 相似文献
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谢丰奕 《卫星电视与宽带多媒体》2014,(8):40-42
除了美国捷蓝航空公司,Viasat公司根据今年3月签订的一项协议,未来一年内也将透过欧洲首颗高容量宽带通信卫星Eutelsat Ka-Sat 9A(9°E),在以色列航空公司(ELAL)航班飞机上推出Exede空中卫星宽带服务.而ELAL也因此将成为继爱尔兰航空公司之后欧洲第2家提供Ka波段卫星宽带服务的商业航空公司. 相似文献
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蒋理陆春燕夏洋章啸可 《无线互联科技》2018,(21):69-70
航班数据是航空公司运行的重要组成部分,将繁杂的数据高效地展示出来,可以有效地提升航空公司运行效率,也可以使客户更有效地了解相关信息。文章介绍了一种航班数据可视化展示的软件系统,详细介绍了从数据获取到展示的过程。 相似文献
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基于客户/服务器的两级语义数据缓存机制在OLAP环境中的应用 总被引:1,自引:0,他引:1
在联机分析处理(OLAP)环境中,为了提高多维查询的响应速度,服务器需要特殊的查询优化技术,比较流行的做法是,服务器动态地有选择地对查询结果进行缓存。本文在客户端也引入相同的缓存机制,这种方法能有效地降低服务器载荷;对于在数据仓库进行增量维护时,客户/服务器中两级缓存中语义数据的一致性问题及其对查询的影响进行了研究。 相似文献
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在移动计算环境中,移动主机与服务器连接状态的多变性,限制了移动主机的查询处理。在移动主机中对查询数据进行语义缓存,将提高移动主机对服务器资源的利用效率以及可用性。文章在语义缓存的基础上引入了有效期,在查询导出的精确匹配、包含匹配和相交匹配基础上,给出了查询结果有效性的充分条件,从而保证查询结果的有效。 相似文献
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One of the key research fields of content-centric networking (CCN) is to develop more efficient cache replacement policies to improve the hit ratio of CCN in-network caching. However, most of existing cache strategies designed mainly based on the time or frequency of content access, can not properly deal with the problem of the dynamicity of content popularity in the network. In this paper, we propose a fast convergence caching replacement algorithm based on dynamic classification method for CCN, named as FCDC. It develops a dynamic classification method to reduce the time complexity of cache inquiry, which achieves a higher caching hit rate in comparison to random classification method under dynamic change of content popularity. Meanwhile, in order to relieve the influence brought about by dynamic content popularity, it designs a weighting function to speed up cache hit rate convergence in the CCN router. Experimental results show that the proposed scheme outperforms the replacement policies related to least recently used (LRU) and recent usage frequency (RUF) in cache hit rate and resiliency when content popularity in the network varies. 相似文献
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Hou Y.T. Jianping Pan Bo Li Panwar S.S. 《Selected Areas in Communications, IEEE Journal on》2004,22(1):134-150
Caching is an important means to scale up the growth of the Internet. Weak consistency is a major approach used in Web caching and has been deployed in various forms. The paper investigates some fundamental properties and performance issues associated with an expiration-based caching system. We focus on a hierarchical caching system based on the time-to-live expiration mechanism and present a basic model for such system. By analyzing the intrinsic timing behavior of the basic model, we derive important performance metrics from the perspectives of the caching system and end users, respectively. Based on the results for the basic model, we introduce threshold-based and randomization-based techniques to enhance and generalize the basic model further. Our results offer some important insights into a hierarchical caching system based on the weak consistency paradigm. 相似文献
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Chen-Lung Chan Shih-Yu Huang Jia-Shung Wang 《Communications, IEEE Transactions on》2007,55(11):2142-2151
Proxy-caching strategies, especially prefix caching and interval caching, are commonly used in video-on-demand (VOD) systems to improve both the system performance and the playback experience of users. However, because these caching strategies are designed for homogeneous clients, they do not perform well in the real world where clients are heterogeneous (i.e., different available network bandwidths and different sizes of client-side buffers). This paper investigates the problems caused by heterogeneous client-side buffers. We analyze the theoretical performance of these caching strategies, and then, derive cost functions to measure the corresponding performance gains. Based on these analytical results, we develop a caching strategy that employs both prefix caching and interval caching to minimize the input bandwidth of a proxy. The simulation results demonstrate that the bandwidth requirements of a proxy implementing our caching strategy are significantly lower compared to adopting prefix caching or interval caching alone. 相似文献
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文章研究了基于TTL的Web缓存层次过滤效果,业务量性质对基于TTL的动态Web缓存系统的性能有重要影响。在层次缓存中,由于只有错失的请求才会被转发给下一级缓存,因而逐级对业务量存在过滤作用,业务量性质随之改变。文章利用仿真研究了基于TTL的动态Web缓存层次过滤对业务量的影响。重点考察了请求到达间隔模型及对象流行度分布的变化。 相似文献
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基于区块链的边缘缓存技术可以实现更大范围的内容共享并提高缓存内容的使用效率。针对不同运营商各自建设边缘设备,缓存内容相互隔离,难以共享信息的问题,该文提出一种基于联盟链的边缘缓存系统框架并设计了内容共享和交易流程,实现了不同运营商之间的内容共享。此外,为了降低高维缓存节点的共识开销,设计了基于内容缓存的部分实用拜占庭容错(pPBFT)共识机制,仅选取缓存相关内容的联盟链节点作为验证智能合约的执行节点。最后,将运营商内容共享所带来的收益进行量化并构建为最大化收益的优化问题。通过所提出的内容缓存算法,得到了最优缓存决策的闭式表达式和与内容流行度相关的最优缓存策略。仿真结果表明,在该框架中所提出的共识机制和缓存策略能够有效增加运营商的缓存收益。 相似文献
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在基于transcoding代理的流媒体服务系统中,CPU和网络是两种潜在的瓶颈资源.本文提出了一种有资源适应性的transcoding代理缓存机制,统一考虑CPU和网络的资源需求,以提高系统的服务能力.首先推导了多版本缓存策略下网络收益和CPU收益的计算方法.通过引入一个时变的影响因子 α (t),给出了缓存系统聚合资源收益的表达.在此基础上给出了单个对象的缓存价值函数,并设计了RAC替换算法.实验表明RAC具有较好的资源适应性和系统吞吐率. 相似文献
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This paper introduces the caching strategy and service policy optimization problem in a cache-satellite distribution service and formulates it as a mathematical optimization problem. A number of system performances like hit rate, cache disk space, bandwidth gain, bandwidth requirements for the satellite channel and latency experienced by the clients were modeled into a mathematical formulation. To show how the optimal caching and service policy responds to the system parameter changes, computational experiments were performed on a hypothetical market having forty ISPs and one billion Web documents. It was found that the correlation between document size and popularity is most influential and the concentration of popularity appeared to be the main factor determining the sensitivity of the optimal caching levels and the corresponding system performances like hit rate and byte hit rate. The achieved hit rate ranged between 64 and 74% with the corresponding caching levels of 25 to 40%. Based on these findings, the importance of caching strategy and service policy optimization was discussed and a number of further research issues were suggested. 相似文献
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随着P2P文件共享应用的泛滥,P2P应用大量占用了基础网络运营商的核心带宽,并在影响运营商利润的同时影响了P2P技术的继续发展.本文介绍了一种P2P流量优化技术--P2P缓存系统.通过对P2P流量进行缓存过滤,可使P2P流量占用的核心网络带宽大大降低,从而解决P2P文件共享同基础网络运营的矛盾.本文讨论了P2P缓存系统所面临的主要问题,并提出了相关的解决方案. 相似文献