移动Ad hoc网络路由协议及其性能比较

由于Ad hoc网络自身的特殊性,其路由协议的设计与传统固定网络有很大不同.首先说明了Adhoc网络中提供高效路由算法的难点,然后讨论了Ad hoc网络中路由协议设计的几种策略,接着介绍了几种典型的Ad hoc路由协议,最后通过实验分析比较了4种路由协议的性能,并给出了结论.     

基于按需距离向量与最佳链路状态的Ad hoc网络路由协议

Ad hoc网络是一种无线特定网络,没有固定的路由器,对Ad hoc网络的关注不断的升温并促使其逐步走向实际应用.笔者阐述了Ad hoc网络路由研究现状、路由协议要求及应用,阐述了已被IESG通过并成为RFC标准的基于按需距离向量与最佳链路状态的Ad hoc网络路由协议的技术关键、特点及其应用.     

基于模型分析的城市环境下车载移动Ad hoc网络路由协议改进策略

在Manhattan移动模型的基础上,深入分析了车载移动Ad hoc网络路由协议的性能问题. 结合AODV路由协议,提出了一种可以量化分析车载Ad hoc网络路由断链率和路由负载的模型. 模型分析指出,传统的移动Ad hoc网络路由协议应用于车载Ad hoc网络时性能会严重下降. 针对这一问题,提出了一种基于车辆运动方向信息的类AODV路由协议DBAP,将车辆的运动方向信息作为其路由发现过程中的辅助参数,从而显著地增强了路由稳定性. 仿真结果验证了模型的正确性,同时证明了本文所提出的DBAP路由协议在城市车载环境中具有较低的路由负载和路由断链率,在协议性能等方面相对于AODV协议具有显著提高.     

Ad hoc 网络技术研究

Ad hoc网络是一种多跳、无中心的无线自组网络.它不需依赖任何预先设置的固定的网络设施,而能被迅速展开;而且具有灵活、机动、自适应和高抗毁等特性.基于Ad hoc网络的研究现状,讨论了Ad hoc网络所涉及的网络体系结构、路由协议、网络安全、功率控制和节能技术等问题.     

移动ad hoc网络安全按需路由协议

Ad hoc网络按需路由协议的安全问题是近年来的研究热点.本文在分析了ad hoc网络按需路由协议遭受攻击的特点的基础上,结合典型的安全按需路由协议,对采用不同的路由算法的按需路由协议特点进行了探讨,得出了不同的安全对策,同时给出了一个通用的安全Ad hoc网络按需协议设计准则.     

Linux环境下Ad hoc网络的实现及性能分析

主要提出在Linux操作系统下实现Ad hoc网络的方案.在现有的可以用于Ad hoc网络的路由协议中选择动态源路由（DSR）作为实现协议,建成了由多个节点组成的运行DSR路由协议的试验网,在试验网上对Ad hoc网中的数据传输和语音会议进行了测试.最后对测得的数据进行了分析,并提出了改进方案.     

浅谈Ad Hoc无线网络的路由协议

文章首先简单介绍了Ad hoc网的概貌,然后介绍了Ad hoc网络的主要路由协议,并给出了各个协议的优、缺点,为选择适合于特殊环境的路由协议提供了一定的参考。     

基于NS的Ad hoc网络路由协议性能仿真

Ad hoc无线网络是一组无线移动主机组成的一个没有任何基础设施或集中管理设备的临时网络。文中介绍了Ad hoc无线网络的路由协议，并利用网络仿真软件NS，对两种典型的路由协议AODV(Ad hoc on Demand Distance Vector Routing，Ad hoc网络的距离矢量路由算法)和DSR(Dynamic Source Routing，动态源路由协议)进行了仿真实验，并给出了结果。     

Ad Hoc网络中典型路由协议比较

目的:为了以后设计更加高效实用的Ad hoc网络路由协议。方法:通过对几种典型的Ad hoc网络路由协议进行说明、分析和综合比较。结果:路由协议中DSDV、DSR、AODV以及TORA各优缺点。结论:整体性能DSR路由协议最优。     

移动Ad hoc网络中黑洞问题的研究

移动Ad hoc网络在民用设施和国防事业方面得到广泛应用,动态变化的拓扑结构是Ad hoc网络的一大特征,也正是这种动态性使得Ad hoc网络特别容易受到安全方面的攻击.文章剖析了AODV路由协议的工作过程,针对协议中存在的黑洞问题,提出了一种新的解决方案,该方案不仅有效地解决了黑洞问题而且可以消除一些现有解决方案所存...     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.