网络拓扑结构对IP组播效率影响的研究

研究了不同网络拓扑结构对IP组播效率的影响,给出了一种度量组播效率的方法,并进行了分析与仿真.结果表明:在随机选择组播树根节点的情况下,平均节点度越大的网络,组播效率越低;限制组播路由的通过性和适当选择组播根节点的位置能够有效提高组播效率;有源最短路径树在不同网络拓扑下的性能差异较大,并且不是一种能够适合于各种网络结构的高效组播树构建算法.     

NoC体系结构的面积和性能优化方法研究

片上网络Network-on-chip(NoC)是片上系统System-on-chip(SoC)的一种新的设计方法。NoC可以为SoC系统提供大规模的通信系统。基于NoC的系统能很好地适应在现在复杂SoC设计中常使用的多异步时钟。NoC方法带来一种全新的片上通信方法,显著改善传统总线式系统的性能。基于NoC的发展现状,研究当代关于NoC体系结构的面积和性能优化提出的各种方法,主要从MarioP.Vestias等人提出的基于GNoC结构的面积和性能优化方法展开研究。GNoC可以通过改变路由器的数量、配置路由器来满足特定的通信需求和选择路由器和IP核之间的互连方式以满足特定应用。     

一种评价通信网节点重要性的新方法——节点孤立法

提出了一种评价通信网节点重要性的新方法--节点孤立法,并提出了节点核度积的概念,认为通信网中最重要的节点是孤立后所对应的节点核度积最大的节点.该方法考虑了网络的连接状况,并且动态地考虑了网络中所有节点相互通信的最短路径总长度的增加值.该方法是基于全网性能对节点重要性进行评价,通过比较节点的核度积,判断通信网中任意两个节点的相对重要性,而且使用了一种模2的矩阵运算方法,可以快速得到节点通信的最短路径.理论分析和仿真实验结果表明,该方法的计算复杂度和对节点重要性评价的准确性优于其它算法.     

HCONoC: a novel high-performance hierarchical optical network on chip

针对传统的片上电互连在带宽、时延等方面遇到的问题,提出一种基于光分组交换技术的分层簇的光片上网络(HCONoC).设计了该网络的拓扑结构连接方式、布局方法、节点编址命名方法以及扩展方式等.为HCONoC的不同层次结构分别构建了新的无阻塞片上光路由器结构,并分析了损耗特性.根据网络拓扑的具体特点和编址方式,设计了有效的路由算法,可提高网络吞吐同时减少时延.最后,使用OPNET搭建仿真平台,对所提网络结构的时延和吞吐性能进行了仿真,结果表明该网络结构在本地流量模式下显示出更强的性能优势.     

一种面向复杂嵌入式系统的互连网络研究

提出了一种结构简单,具有分形特征的基三分层互连网络.讨论了适合于基三分层网络的节点编码方案,给出了网络中任意两个节点之间最短路径的求解算法和网络平均最短距离的估计值.针对复杂嵌入式系统的特点,分析了基三分层网络的成本、可靠性和实时性.将基三分层网络与常见的嵌入式实时互连拓扑结构进行了比较,结果表明基三分层网络可靠性较高,具有较高的性价比,适合作为通信局部性较高的嵌入式实时互连网络.     

树形网络子图中心度的研究

研究具有树形网络拓扑结构的子图中心度,通过仿真分析得到节点数固定的树形网络拓扑结构的子图中心度与网络拓扑结构的最大度之间的关系,以及在度序列相同的情况下不同拓扑结构对子图中心度的影响,仿真结果显示这种方法更能清楚的显示网络的局部聚类和无标度特性。     

一种Ad Hoc网络拓扑控制算法

分析了Ad Hoc网络的性能与拓扑结构的密切相关性和网络特点,提出了一种适用于Ad Hoc网络的基于计算几何方法和功率控制技术的分布式拓扑控制算法.该算法利用天线判断邻居节点方向,构建局部网络拓扑;采用计算几何法减少邻居数,简化拓扑结构;使用对称机制保障节点间的双向连通,兼顾网络连通性;通过调整功率实现具有健壮性的网络拓扑优化控制.仿真结果表明,该算法在满足网络覆盖度和连通性的前提下,形成了优化的拓扑结构,能够节约能量,延长节点寿命,减少相互干扰,提高信道利用率,降低传输时延,增加吞吐量,改善了网络整体性能.     

IP核心网络实现VOIP的负载规划

描述了下一代IP核心网络中VOIP网络负载能力的规划方法 ,对IP核心网络中影响语音质量的链路负载能力作出了定量分析。介绍并比较了两种规划其负载能力的策略———基于信息量矩阵的最短路径传输通道策略和满足最坏负荷情况的最短路径传输通道策略 ,以便从网络拓扑结构、路由选择和连接允许控制考虑 ,提供一个灵活的框架 ,对IP核心网实现VOIP提供一些规划参考建议     

基于聚类的物流节点模型及其自适应蚁群算法

综合考虑物流服务节点区域的空间属性和成本约束,基于物流服务节点波及范围,分析备选服务节点选择过程及其运行成本特征,构建了物流服务节点布局优化模型。将物流服务节点选择映射为一个聚类过程,提出解决物流服务节点选择问题的自适应蚁群聚类算法。以物流系统总成本最低为聚类准则,描述了物流节点布局模型的求解过程,并对服务节点布局参数进行仿真实验,验证模型及算法的鲁棒性和选择效率。     

中国国内航空网络的分形特征研究

为进一步探索中国航空网络拓扑结构的复杂性,以2015和2019年夏秋航季国内航班正班计划数据为例,以分形理论为基础,对中国航空网络分形特征进行实证分析。研究表明,中国航空网络具有较高的聚类系数和较短的平均路径长度,且度服从幂律分布,其具有小世界特征和无标度特征。度度相关性表现为负相关,网络为异配的。盒子尺寸l_B与最小盒子数N_B在双对数图中线性关系显著,表明中国航空网络在结构上具有自相似功能模块,具有分形特征。与2015年网络结构比较,2019年网络的平均最短路径和聚类系数均下降,而节点数和节点平均度增大,无权盒维数由2015年的5.065增长到5.079,加权盒维数从2.164增长到2.262,中国航空网络的分形结构随时间推移逐步演进,网络整体结构在趋好。     

Efficient Routing Protection Algorithm Based on Optimized Network Topology

Network failures are unavoidable and occur frequently. When the network fails, intra-domain routing protocols deploying on the Internet need to undergo a long convergence process. During this period, a large number of messages are discarded, which results in a decline in the user experience and severely affects the quality of service of Internet Service Providers (ISP). Therefore, improving the availability of intra-domain routing is a trending research question to be solved. Industry usually employs routing protection algorithms to improve intra-domain routing availability. However, existing routing protection schemes compute as many backup paths as possible to reduce message loss due to network failures, which increases the cost of the network and impedes the methods deployed in practice. To address the issues, this study proposes an efficient routing protection algorithm based on optimized network topology (ERPBONT). ERPBONT adopts the optimized network topology to calculate a backup path with the minimum path coincidence degree with the shortest path for all source purposes. Firstly, the backup path with the minimum path coincidence with the shortest path is described as an integer programming problem. Then the simulated annealing algorithm ERPBONT is used to find the optimal solution. Finally, the algorithm is tested on the simulated topology and the real topology. The experimental results show that ERPBONT effectively reduces the path coincidence between the shortest path and the backup path, and significantly improves the routing availability.     

Geometry and topology optimization of sheet metal profiles by using a branch‐and‐bound framework

In this paper well established procedures from partial differential equation (PDE)‐constrained and discrete optimization are combined in a new way to find an optimal design of a multi‐chambered profile. Given a starting profile design, a load case and corresponding design constraints (e.g. sheet thickness, chamber sizes), the aim is to find an optimal subdivision into a predefined number of chambers with optimal shape subject to structural stiffness. In the presented optimization scheme a branch‐and‐bound tree is generated with one additional chamber in each level. Before adding the next chamber, the geometry of the profile is optimized. Then a relaxation of a topology optimization problem is solved. Based on this relaxation, a best fitting feasible topology subject to manufacturability conditions is determined using a new mixed integer method employing shortest paths. To improve the running time, the finite element simulations for the geometry optimization and topology relaxation are performed with different levels of accuracy. Finally, numerical experiments are presented including different starting geometries, load scenarios and mesh sizes.     

Evolution of meso-structures and mechanical properties of granular materials under triaxial compression state from complex network perspective

The evolution of the network connection of granular materials is investigated by performing a series of numerical simulations in triaxial compression tests with different initial porosities by discrete element method (DEM). Results of evolution characteristics of complex network are reported for both dense and loose assembles. The simulation focuses on the influence of porosity on connectivity evolution, and reveals the correlation between the parameters in macro and mesoscale. Kinds of properties are studied, including degree and its distribution, clustering coefficient, network density and the average shortest path. The results demonstrate the phenomenon of dilataion due to shear deformation are able to be reflected by those mesocope parameters mentioned. Specifically, in the process of the dilatation, the rate of contact disintegration exceeds the rate of contact creation, which means the loss of connectivity, thus the values of some properties decrease, like degree, clustering coefficient and network density, but some increase like the average shortest path. Additionally, the bridging of macro and mesoscope are built regarding the parameters of the Cam-Clay model and complex network. From the results, the parameter M (determined by q?=?Mp′ at critical state) and the reference parameter \( {\text{T}} \) (\( T_{j}^{s} = L_{j}^{s} \left( {1 - \log_{{D_{j}^{s} }} t} \right) \), calculated according to the average degree \( D_{j}^{s} \) and shortest path \( L_{j}^{s} \) of the critical state) have a positive correlation. And a linear relationship between the slope of isotropic virgin-consolidation λ and the rate of decline of the average shortest path upon loading is represented as well. These achievements are the first step in an ongoing study of establishing the multi-scale constitutive from complex network perspective.     

飞机座舱低光照度对飞行员视觉工效的影响

目的研究飞机座舱低光照度对飞行员视觉工效的影响,确定飞行员视觉工效最佳的低光照环境。方法采用客观实验与主观量表相结合的方法对12名被试进行试验。结果被试在视觉实验过程中,实验结果受光照环境的影响。反应准确率最高、平均注视时间最短、主观评价得分最高的均为50Lux的光照环境,反应时间最短的是10Lux的光照环境,眼跳速度最快的是30Lux的光照环境。视觉工效综合评价的结果表明50Lux时视觉工效最佳。结论飞机座舱不同的光照度对飞行员视觉作业的结果存在一定的差异性,相对而言,50Lux的光照环境对飞行员的视觉工效最佳。     

An integrated approach for the concurrent determination of the block layout and the input and output point locations based on the contour distance

This paper presents an integrated approach for the facilities design problem. It develops a method for the concurrent determination of the block layout, the locations of departmental input and output (I/O) points using the contour distances between the I/O points, and the material flow paths between the I/O points. The topology of block layouts is represented using two linear sequences (sequence-pair), which allows the layout to have either a slicing or a non-slicing structure. The block layout is obtained from the sequence-pair with a linear programming formulation. Three heuristic methods are then presented to determine for a given block layout the locations of the I/O points on the perimeters of the departments. The flow paths from output to input points are found by determining the shortest paths that follow the perimeters of the departments. The linear programming algorithm, the shortest path algorithm, and the I/O point location heuristics are embedded into a simulated annealing algorithm that modifies the sequence-pair to obtain a high-quality layout based on the contour distances between the I/O points. Results of computational experiments show that the performance of this integrated algorithm compares favourably with those of algorithms using a sequential approach and is capable of solving industrial-sized problems in acceptable computation time.     

Dynamic state-dependent dispatching for wafer fabrication

A dynamic state-dependent dispatching (DSDD) heuristic for a wafer fabrication plant is presented. The DSDD heuristic dynamically uses different dispatching rules according to the state of a production system. Rather than developing new rules, the DSDD heuristic combines and modifies existing rules. This heuristic first classifies workstations into dynamic bottlenecks and non-dynamic bottlenecks. Dynamic bottleneck workstations apply a revised two-boundary dispatching rule when their queue length exceeds the average obtained from simulation using constant lot-release policy and first-in, first-out dispatching rule. Otherwise, the shortest expected processing time until next visit dispatching rule is used. A revised FGCA (FGCA+) dispatching rule is used for all non-dynamic bottlenecks workstations. Simulation results demonstrate that the DSDD heuristic obtains the best performance among the compared six dispatching rules in terms of average and standard deviation of cycle time and work-in-process.     

Tenure and turnover of academics in six undergraduate programs in the United States

The mobility of faculty members in different undergraduate programs is influenced by different factors, and so inter-program variability can be expected in mobility rates. This study makes use of course catalogs for the collection of data related to the tenure and turnover of academics from six undergraduate programs in the United States. Included in the study are 34 universities ranked in the top 100 US universities according to USNews for which a minimum of 15 years of course catalogs are available. For the study, 1345 course catalogs were used to attain information about 19,353 faculty members. It was found that economics faculty members have the shortest average tenure and economics programs have the highest turnover among all six programs, while physics and chemistry are the least mobile programs. The other three programs—history, mathematics and political science—fall somewhere in between. Private and high ranking universities are less mobile than public and low ranking universities respectively. It is found that turnover rates fell and average tenures increased after the 1970s.