使用IP/NetBEUI组合协议建造跨VLAN的VoD网站的方法

介绍一种使用IP和NetBEUI组合协议建造Intranet内部VoD（视频点播）网站的简 便技术。并已成功地运用这一技术建成了莆田学院的VoD网站。     

未来VoD系统的发展方向及技术方案

随着宽带技术及视频技术的飞速发展,在不久的将来视频点播系统VoD交得到大规模的应用与推广。目前关于VoD系统的研究及实现技术方式很多,文章系统地介绍了各主要部分关键技术的未来发展方向及可能采取的最佳技术方案。     

低成本可扩展的分布式VoD系统体系结构研究*

考虑视频点播（VoD）系统的成本代价要求,给出了一种基于普通PC机的、高性价比的分布式VoD系统方案,论述了系统的体系结构、动态扩展及其负载平衡机制。实验数据表明,系统能有效地解决传统集中式VoD系统的瓶颈问题,具有良好的可扩展性,能够满足大规模VoD应用的要求。     

数字化校园中高清流媒体VoD系统的架构

流媒体视频点播系统已经成为下一步网络应用的重要发展方向。结合校园网络结构特点,针对VoD系统中的重要瓶颈问题,分析了VoD服务系统架构,论证了系统架构中应采用的IP组播技术,并对视频片源的转制和实验结果进行了讨论。     

低成本可扩展的分布式VoD系统体系结构研究

考虑视频点播(VoD)系统的成本代价要求,给出了一种基于普通PC机的、高性价比的分布式VoD系统方案,论述了系统的体系结构、动态扩展及其负载平衡机制.实验数据表明,系统能有效地解决传统集中式VoD系统的瓶颈问题,具有良好的可扩展性,能够满足大规模VoD应用的要求.     

基于BitTorrent的P2P-VoD系统设计与实现

针对在互联网上提供大规模VoD服务的困难,提出一种采用P2P技术的VoD系统VoDBB,该系统能以较小的服务器代价实现大规模的VoD应用.VoDBB通过修改BitTorrent的片段选择算法改进系统播放连续度,加入后备流媒体服务器和相应的下载源选择算法保障服务质量(QoS),并通过磁盘管理模块和锚点机制支持用户交互操作.仿真实验结果表明,该系统能提供良好的用户观看体验,降低流媒体服务器负载,并具有很强的扩展能力.     

分布式多服务器结构VoD系统的容错技术研究

分布式多服务器结构的VoD系统采用分布式存储技术将视频文件分块存储于不同的服务器上,如果没有良好的容错措施,某一服务器的故障将会导致整个系统无法运行。文章从算法角度分析了奇偶校验纠错法和线性编码法两种技术,分别适用于分布式多服务器结构的VoD系统在一个和多个服务器节点崩溃时恢复数据。     

基于代理的视频点播系统设计

视频点播（Video-on-Demand,VoD)是现代网络上的一个重要多媒体应用。在传统的集中式视频点播系统中，如果用户数目过多，将会出现服务器I/O及网络带宽的瓶颈，而采用基于代理服务器的分布式体系结构，可以把VoD系统的负载分布到放置在网络不同位置的各个代理服务器上，能很好地解决系统瓶颈问题，阐述了基于代理的VoD系统的特点，设计原则，以及设计的关键问题，并提出了一种基于代理服务器的VoD系统模型。     

一种集群分布式VoD系统的实现

随着宽带网络的大规模普及和高清视频文件点播需求的大量增加,VoD服务成为宽带网络的重要应用之一。如何降低VoD系统的成本和带宽是运营商普遍关注的问题。描述了一种基于集群架构的低成本分布式VoD系统的实现,并对其核心的最小连接调度算法与影片动态分布模型进行了详细介绍。     

一种高性能和高可用的集群VoD系统的设计及其实现

随着分布式系统、网络技术和多媒体技术的迅速发展,使得联机访问异地巨量媒体数据成为可能,从而形成了当前研究和开发的热点——分布式媒体服务系统。优化VoD系统的性能以及降低系统的成本是设计VoD系统的一个重要挑战。描述了一种基于PC机集群系统的高性能、高可用性以及低成本的集群VoD系统——CVoD的设计及其实现。对该系统进行的性能测试表明,每个节点能够服务大约90个近似于DVD质量的视频流;随着集群系统规模的扩大,该系统能够服务的客户端和系统中的服务器节点的个数基本上成正比,限制系统性能进一步扩展的关键因素是网络带宽大小的限制。实验结果证明CVoD具有很好的性能可扩展性以及良好的可用性。     

Motion of a rigid cylinder between parallel plates in stokes flow : Part 1: Motion in a quiescent fluid and sedimentation

A general numerical scheme for solution of two-dimensional Stokes equations in a multiconnected domain of arbitrary shape [1, 2] is applied to the motion of a rigid circular cylinder between plane parallel boundaries. Numerically generated boundary-conforming coordinates are used to transform the flow domain into a domain with rectilinear boundaries. The transformed Stokes equations in vorticity-stream function form are then solved on a uniform grid using an iterative algorithm. In Part I coefficients of the resistance matrix representing the forces and torque on the cylinder due to its translational motion parallel or perpendicular to the boundaries or due to rotation about its axis are calculated. The solutions are obtained for a wide range of particle radii and positions across the channel. It is found that the force on a particle translating parallel to the boundaries without rotation exhibits a minimum at a position between the channel centerline and the wall and a local maximum on the centerline.

The resistance matrix is utilized to calculate translational and angular velocities of a free particle settling under gravity in a vertical channel. It is found that the translational velocity has a maximum at some lateral position and a minimum on the centerline; the particle angular velocity is opposite in sign to that of a particle rolling along the nearer channel wall except when the gap between the particle and the wall is very small. These results are compared with existing analytical solutions for a small cylindrical particle situated on the channel centerline, and with solutions of related 3-D problems for a spherical particle in a circular tube and in a place channel. It is shown that the behavior of cylindrical and spherical particles in a channel in many cases is qualitatively different. This is attributed to different flow patterns in these two cases. The motion of a spherical particle in a circular tube has qualitative and quantitative features similar to those for a cylindrical particle in a plane channel.     

Developing a vision-based auto-recharging system for mobile robots

This article describes a vision-based auto-recharging system that guides a mobile robot moving toward a docking station. The system contains a docking station and a mobile robot. The docking station contains a docking structure, a control device, a charger, a safety detection device, and a wireless RF interface. The mobile robot contains a power detection module (voltage and current), an auto-switch, a wireless RF interface, a controller, and a camera. The controller of the power detection module is a Holtek chip. The docking structure is designed with one active degree of freedom and two passive degrees of freedom. For image processing, the mobile robot uses a webcam to capture a real-time image. The image signal is transmitted to the controller of the mobile robot via a USB interface. We use an Otsu algorithm to calculate the distance and orientation of the docking station from the mobile robot. In the experiment, the proposed algorithm guided the mobile robot to the docking station.     

High-Order Accurate Adaptive Kernel Compression Time-Stepping Schemes for Fractional Differential Equations

We present a goal-oriented a posteriori error estimator for finite element approximations of a class of homogenization problems. As a rule, homogenization problems are defined through the coupling of a macroscopic solution and the solution of auxiliary problems. In this work we assume that the homogenized problem is known and that it depends on a finite number of auxiliary problems. The accuracy in the goal functional depends therefore on the discretization error of the macroscopic and the auxiliary solutions. We show that it is possible to compute the error contributions of all solution components separately and use this information to balance the different discretization errors. Additionally, we steer a local mesh refinement for both the macroscopic problem and the auxiliary problems. The high efficiency of this approach is shown by numerical examples. These include the upscaling of a periodic diffusion tensor, the case of a Stokes flow over a porous bed, and the homogenization of a fuel cell model which includes the flow in a gas channel over a porous substrate coupled with a multispecies nonlinear transport equation.     

The probabilistic orienteering problem

The probabilistic orienteering problem (POP) is defined on a directed graph where a cost is associated with each arc and a prize is associated with each node. Moreover, each node will be available for visit only with a certain probability. A server starts from a fixed origin, has a given budget to visit a subset of nodes, and ends at a fixed destination. In a first stage, a node subset has to be selected and a corresponding a priori path has to be determined such that the server can visit all nodes in the subset and reach the destination without exceeding the budget. The list of available nodes in the subset is then revealed. In a second stage, the server follows the a priori path by skipping the absent nodes. The POP consists in determining a first-stage solution that maximizes the expected profit of the second-stage path, where the expected profit is the difference between the expected total prize and the expected total cost.We discuss the relevance of the problem and formulate it as a linear integer stochastic problem. We develop a branch-and-cut approach for the POP and several matheuristic methods, corresponding to different strategies to reduce the search space of the exact method. Extensive computational tests on instances with up to 100 nodes show the effectiveness of the exact method and the efficiency of the matheuristics in finding high quality solutions in a few minutes. Moreover, we provide an extended analysis on a subset of instances to show the value of explicitly modeling the stochastic information in the problem formulation.     

HelSweeper: Screw-sweeps of canal surfaces

A tube is a solid bounded by the union of a one-parameter family of circles that may be decomposed into canal-surfaces and planar disks or annuli. A screw-sweep is the region swept by a shape during a screw motion. HelSweeper computes the boundary of a screw-sweep of an arbitrary union of tubes and polyhedra. To do so, it generates a superset of faces, splits them at their intersections, and selects the face portions that form the desired boundary. The novelty of the proposed approach lies in the fact that the faces contributed to this superset by a tube are each a screw-sweeps of a rigid curve (generator), which is the locus of grazing points, and that each grazing point is formulated as the intersection of a circle of the tube with a corresponding screw-plane. Hence, each such face is a one-parameter family of helices, each being the screw-sweep of a grazing point.     

ROD-based hybrid TH precoding and combining for mmWave large-scale MIMO systems

Hybrid precoding is one of key techniques for millimeter wave (mmWave) large-scale multiple-input multiple-output (MIMO) systems. This paper considers a nonlinear hybrid precoding architecture which consists of a nonlinear unit, a reductive digital precoder and a constant modulus radio frequency (RF) precoder, and presents a novel hybrid Tomlinson-Harashima (TH) precoding and combining algorithm. Firstly, due to the intractability of the sum rates maximization problem for such a nonlinear hybrid precoding architecture, a tractable three-stage optimization problem is constructed through the lower bound of the sum rates, which allows the digital precoding matrix, the RF precoding matrix and the RF combining matrix to be optimized sequentially and independently. Then, in order to solve the three-stage optimization problem effectively, a novel row orthogonal decomposition (ROD) is defined. Based on the ROD, it is interesting that the necessary and sufficient condition of the optimal digital precoding matrix can be obtained, and a near-optimal RF precoding matrix can be derived. Finally, the optimization of the RF combining matrix is reformulated as a unimodular quadratic programming and solved by a generalized power method. Theoretical analyses and simulations indicate that the proposed ROD-based hybrid TH precoding and combining algorithm can offer a higher sum rates and a lower bit error rate with a comparable complexity in comparison to the previous works.     

Exact combinatorial bounds on the probability of overfitting for empirical risk minimization

Three general methods for obtaining exact bounds on the probability of overfitting are proposed within statistical learning theory: a method of generating and destroying sets, a recurrent method, and a blockwise method. Six particular cases are considered to illustrate the application of these methods. These are the following model sets of predictors: a pair of predictors, a layer of a Boolean cube, an interval of a Boolean cube, a monotonic chain, a unimodal chain, and a unit neighborhood of the best predictor. For the interval and the unimodal chain, the results of numerical experiments are presented that demonstrate the effects of splitting and similarity on the probability of overfitting.     

Formatting texts accessed randomly

Full-text systems that access text randomly cannot normally determine the format operations in effect for a given target location. The problem can be solved by viewing the format marks as the non-terminals in a format grammar. A formatted text can then be parsed using the grammar to build a data structure that serves both as a parse tree and as a search tree. While processing a retrieved segment, a full-text system can follow the search tree from root to leaf, collecting the format marks encountered at each node to derive the sequence of commands active for that segment. The approach also supports the notion of a ‘well formatted’ document and provides a means for verifying the well-formedness of a given text. To illustrate the approach, a sample set of format marks and a sample grammar are given suitable for formatting and parsing the article as a sample text.