The multimedia multicasting problem

This paper explores the problems associated with the multicasting of continuous media to support multimedia group applications. The interaction between multicasting and the delivery of multiple time-correlated continuous-media streams with real-time delay requirements poses various new and interesting problems in research on communication protocols and architectures. We describe these problems, and identify where the opportunities are for effective solutions, all in the context of providing an overview of the current state of research in multimedia multicasting. The issues we discuss include quality of service, resource reservations, routing, error and traffic control, heterogeneity, and the use of hierarchical coding and open-loop control techniques.     

Group Decision Making on Urban Planning Using Desktop Multimedia Conferencing

Recent developments on multimedia systems and networking technology show that using desktop multimedia conferencing for group decision making on wide area networks such as the Internet is possible. In this paper we review the design, hardware and software requirements and organizational issues in a desktop multimedia conferencing system. We draw on our experiences from multiple multimedia conferences on the Internet and in particular we focus on a case study on urban planning using desktop multimedia conferencing on the Internet. Further we discuss implications for further research on desktop multimedia conferencing.     

多媒体视频会议系统的关键技术研究

多媒体视频会议系统是近年来国际上将“视频图像、语音等多媒体信息数字处理”与“数字通信传输技术”最新成果相结合的产物，它集计算机的交互性、通信的分布性以及电视的真实性为一体，具有明显的优越性，因而成为当今计算机领域的一个研究热点。本文主要讨论了该系统的组成、原理及关键技术，尤其是图像压缩技术的研究。     

超级电容器碳电极材料的制备及性能

以普通煤焦油沥青为前驱体,KOH为活化剂,采用化学活化法,在500~1 000℃下制备了超级电容器用活性炭电极材料,分析了温度对材料微观结构的影响。通过循环伏安、交流阻抗和恒流充放电等方法,分析了不同多孔活性炭在有机电解液中的电化学行为。在500~700℃内,比电容随活化温度的升高而升高,700℃下活化的活性炭的比电容最高;活化温度在700℃以上,活性炭的比电容降低。在700~1 000℃下制备的活性炭,在有机电解液中表现出良好的电化学行为。     

基于Windows流媒体技术的网络屏幕广播

在介绍Windows流媒体技术的基础上．利用WindowsMedia成功地实现了屏幕图像在Internet/Intranet上的广播。     

Dynamic Modeling and Simulation of Impact in Tether Net/Gripper systems

The objective of this paper is to study the dynamic modeling andsimulation of a tether-net/gripper system during an impact, while it isbeing deployed or retrieved by a winch on a satellite orbiting aroundearth. We stick to Tether-Net system but the analysis is applicable toTether-Gripper systems too. We assume that the net is deployed from thesatellite in orbit and the motion is restricted to the orbital plane.This net captures a second satellite and tows it. The motion of atether-net system can be broken down into the following phases: (i)Phase 1: Net is shot out from the satellite with the tether completelyslack, (ii) Phase 2: Net comes to a location where the tether is tautwhile the drum on the orbiter is locked, (iii) Phase 3: Drum is unlockedand the net moves with the tether, (iv) Phase 4: Net captures a body.The continua (tether) is modeled using mode functions and coordinates.The theory of impulse and momentum can be used to model Phases 1, 2, and4 of motion of the tether-net system. The dynamics of the motion of thesystem in phase 3 is characterized by differential and algebraicequations (DAEs). Matlab ODE solvers were used to solve these DAEs.     

泡沫铝制备过程中增粘剂的选择

研究了铝熔体中添加不同种类增粘剂后的增粘效果,并通过对制备泡沫体的宏观观测和微观检测,研究了铝熔体增粘方式对泡沫体结构的影响及各种增粘剂的增粘机理. 结果表明:铝熔体中加入金属钙、镁、氧化铝和粉煤灰后,其物相组成发生改变,增粘剂存在形式和增粘机理不同,得到的泡沫体在结构上差别也很大.     

Numerical modelling of void inclusions in porous media

Numerical modelling of porous flow in a low‐permeability matrix with high‐permeability inclusions is a challenging task because the large ratio of permeabilities ill‐conditions the finite element system of equations. We propose a coupled model where Darcy flow is used for the porous matrix and potential flow is used for the inclusions. We discuss appropriate interface conditions in detail and show that the head drop in the inclusions can be prescribed in a very simple way. Algorithmic aspects are treated in full detail. Numerical examples show that this coupled approach precludes ill‐conditioning and is more efficient than heterogeneous Darcy flow. Copyright © 2003 John Wiley & Sons, Ltd.     

A stabilized volume‐averaging finite element method for flow in porous media and binary alloy solidification processes

A stabilized equal‐order velocity–pressure finite element algorithm is presented for the analysis of flow in porous media and in the solidification of binary alloys. The adopted governing macroscopic conservation equations of momentum, energy and species transport are derived from their microscopic counterparts using the volume‐averaging method. The analysis is performed in a single domain with a fixed numerical grid. The fluid flow scheme developed includes SUPG (streamline‐upwind/Petrov–Galerkin), PSPG (pressure stabilizing/Petrov–Galerkin) and DSPG (Darcy stabilizing/Petrov–Galerkin) stabilization terms in a variable porosity medium. For the energy and species equations a classical SUPG‐based finite element method is employed. The developed algorithms were tested extensively with bilinear elements and were shown to perform stably and with nearly quadratic convergence in high Rayleigh number flows in varying porosity media. Examples are shown in natural and double diffusive convection in porous media and in the directional solidification of a binary‐alloy. Copyright © 2004 John Wiley & Sons, Ltd.     

微细粒浸染型金矿碱性介质浮选法研究

介绍了微细粒浸染型金矿石浮选富集的一种新方法———以碳酸钠作为pH调整剂的碱性介质浮选法,并研究了这种方法浮选富集矿石过程中各种因素的影响。研究表明,在弱碱性矿浆中(pH值7 5～8 5)能够较好地实现载金矿物与脉石矿物的浮选分离。