天下视频Flash 制作下载转换通

宽带流行了,播客兴起了,FLV吃香了,菜鸟也坐不住了,迅即抱回了DV,开通了播客。历经N天修炼,Flash视频终于成为菜鸟的拿手好菜之一。播客的兴起,使得Flash视频(FLV)格式大行其道。究其原因,不外乎FLV视频避免了不安装特定视频插件就     

基于ERP的企业管理信息系统设计

对目前流行的ERP进行了分析,研究了ERP系统的特性,提出了基于ERP的管理信息系统的开发方法,并结合实际应用,开发了系统的各功能模块,设计了基于B/S和C/S两种结构相结合的系统体系结构,开发过程中结合了两种系统架构的优点,有效的提高了系统的安全性和扩展性.最后通过系统的正常运行,验证了系统设计思路的合理性.     

射频仿真目标模拟系统误差分析及补偿

阐明了近场效应产生的原理,推导了二元定向公式,并对其进行了建模仿真,得出其对系统精度的影响程度.建立了阵面及转台回转中心关系的模型,利用模型推导了幅度误差和相位误差对目标位置精度的影响,然后对衰减器与移相器幅相漂移产生的原因进行了分析,并提出了各种误差的补偿办法.最后给出了系统误差产生的顺序.     

无线互联 纺织未来

因特网的发展引起了新的产业革命,变革了经济的运行模式,刺激了广大企业的创新意识,促进了教育的普及和提高,大大改变发展中国家的工业化模式,甚至会改变国家之间的力量对比。不仅如此,互联网还造就了崭新的一代群体。就像60年代电视改变了人们的娱乐方式,造就了“电视一代”;80年代电脑改变了人们的工作方式,促成了“电脑一代”一样,九十年代Internet改变了人们获取信息的方式,诞生了“网络一代”。互联网对人类社会的影响是深刻而长远的,即给人们带来挑战,更给人们带来机遇。     

基于RFID技术的装备信息自动管理系统设计与实现

介绍了有源射频识别系统的硬件结构,设计了一套基于单片机AT89C2051和发射芯片nRF905的射频识别系统,在此基础上实现了装备信息自动管理系统,给出了系统硬件电路设计,并提供了射频读写器的软件流程图和射频标签读写方式的控制方法.最后对系统性能进行了测试,验证了其稳定性.     

基于Systemview的OFDM系统仿真分析

正交频分复用被看作是第四代移动通信的核心技术之一,在高速数据传输中得到了广泛的应用.本文介绍了OFDM的基本原理,给出了OFDM系统的基本框架,并基于Systeinview建立了OFDM系统的仿真模型.分析了采用编码和交织的系统性能并给出了仿真结果.为进一步研究OFDM系统性能提供了一个通用的平台.     

产品外形协同设计系统的研究与实现*

提出了协同设计工作模式,给出了系统的工作流程,定义了用户的权限分配,研究了基于交互日志的传输方式,讨论了协同设计过程中的实时更新机制.最后采用了基于MVC的体系结构构建了一个原型系统,该系统在实际应用中,验证了该技术思路的正确性.     

GSM短信息的通信业务性能研究

GSM短信息通信系统提供了一个技术成熟的通信平台,其良好的开放性为用户根据公示的规范、利用集成了标准化协议和硬件接口的模块、以较低的成本快速构建网络控制系统创造了条件.针对此项应用,对短信息的通信业务性能进行了研究,通过短信息的存储转发、漫游、确认机制,分析了它的通信可靠性;介绍了短信息逻辑信道和物理信道的映射,分析了延时特性,提出了确定性和随机性时延的划分;计算了基站的短信息吞吐量;总结了短信息可提供的安全性措施,为控制系统中通信网络的选择、设计提供参考.     

以网民权利为基础

为什么微软要惩治盗版了,我们就黑屏了？为什么国家要保护青少年了,我们就绿坝了？为什么一款游戏换运营商了,我们就得重新打怪升级了？     

电脑迷俱乐部

天天PCFAN当你拿到这本杂志时,也许重庆已经迎来了初春,肆虐了一个月的倒春寒应该结束了吧。对了,今年就是2012年了,手中没有"船票"的同学是时候去订票了!     

The importance of introducing a waiting time for Lattice Monte Carlo simulations of a polymer translocation process

For a standard Lattice Monte Carlo (LMC) simulation of a random walker subject to a bias, it is impossible to obtain both a correct mean velocity and diffusion coefficient. To correct this, a modified LMC algorithm has been developed where the introduction of a probability of remaining in the current state allows for a distribution of intervals between jumps. In this paper, we demonstrate the impact of this modification for a first-passage problem: the translocation of a polymer through a nanopore. We find that while either approach yields the correct mean first-passage time, the incorporation of a waiting time is necessary to obtain the correct spread of times.     

A Combined Feedforward–Feedback Control Strategy for Improving the Dynamics of a Flexible Mechanism

Modern high-speed mechanisms often experience undesirable vibrations,which may render a required accuracy unattainable or, even worse, leadto a failure of the whole process. Instead of suppressing the vibrationby a stiffer design, active control methods may greatly improve thesystem performance and lead the way to a reduction of the mechanism'sweight.We investigate a four-bar-linkage mechanism and show that byintroducing an additional degree of freedom for a controlled actuatorand providing a suitable control strategy, the dynamically inducedinaccuracies can be substantially reduced and new reference paths bedescribed. The modeling of the four-bar-linkage mechanism as a hybridmultibody system and the modeling of the complete system including theactuator is briefly explained. From the combined feedforward–feedbackoptimal control approach presented in [11], a time-varying outputcontrol law is derived that leads to a very good system performancefor both a regulating and a tracking problem. The experimental resultsshow the effectiveness of the applied control strategies.     

A path following problem for a class of non-holonomic control systems with noise

This paper deals with a path following problem for a system affected by noise and proposes a dynamic inversion-based controller that makes use of the error between the real position and a suitable path location. An estimate of such error is given in terms of the noise bounds, showing the practical stability of the closed loop system. The results presented in this article apply to a subclass of Chaplygin control systems which includes several common mechanical systems. As an example the developed strategy has been applied to maneuver a kinematic model of a system moving in a 3-dimensional space in such a way that a point located at a positive distance from its center of geometry is driven towards a given path.     

A case study of a difficult refinement: a fast dictionary for a spell-checking program

We present a difficult refinement of a dictionary for a spell-checker. It represents a realistic problem and shows how a calculational approach using a relation known as a coupling invariant can improve the process of refinement over the conventional posit-and-prove approach. The paper concludes with a brief discussion of the advantages of the approach we adopt. We also hope that the paper will contribute a difficult refinement to the rather sparse corpus of such case studies in the literature—especially those using the calculational approach.     

GF(2~N)上线性化多项式根的存在性

给出了判断有限域上某元素为线性化多项式根的方法。在此基础上,将线性化多项式根的求解问题归结为有限域上简单方程的求解,使得可以方便地用计算机求解线性化多项式的根。     

A Simulation Model of the Price Bargaining Rules in Vertical Relationships

This paper analyzes the dynamics of the price and quantity bargaining betweenfour agents, in a current industrial structure, with a special attention tothe price bargaining. The structure combines a bilateral monopoly in a marketfor inputs, and a duopoly in a final market. After a simplified presentationof a model which proposes equilibrium solutions to the bargaining, we presentthe protocol and the results of an experiment whose objective is twofold. Thefirst one is to test the assumptions of the model. The second one is toidentify behavioral models and bargaining rules for a work of simulation. Theexperimental results do not confirm the solutions of the theoretical model,which predicted a Nash solution for the price bargaining, and used the cournotconjecture in the quantity bargaining. A detailed analysis of the resultsleads to some observations useful to parameterize a simulation model. Thesimulation runs a systematic analysis of the dynamics of the bargaining rulesin this structure.     

Design of switched linear systems in the presence of actuator saturation and L-infinity disturbances

This paper considers the problem of disturbance tolerance/rejection of a switched system resulting from a family of linear systems subject to actuator saturation and L-infinity disturbances. For a given set of linear feedback gains, a given switching scheme and a given bound on the L-infinity norm of the disturbances, conditions are established, in terms of linear or bilinear matrix inequalities, under which a set of a certain form is invariant for a given switched linear system in the presence of actuator saturation and L-infinity disturbances, and the closed-loop system possesses a certain level of disturbance rejection capability. With these conditions, the design of feedback gains and switching scheme can be formulated and solved as constrained optimization problems. Disturbance tolerance is measured by the largest bound on the disturbances for which the trajectories starting from a given set remain bounded. Disturbance rejection is measured either by the L-infinity norm of the system output or by the system’s ability to steer its state into and/or keep it within a small neighborhood of the origin. In the event that all systems in the family are identical, the switched system reduces to a single system under a switching feedback law. Simulation results show that such a single system under a switching feedback law could have stronger disturbance tolerance/rejection capability than a single linear feedback law can.     

Error estimate for quasistatic history-dependent contact model

In this paper we consider a mathematical model which describes a quasistatic process for a viscoelastic body in contact with an obstacle or a foundation. The variational formulation of the problem is in the form of a system coupling a nonlinear integral equation with a history-dependent hemivariational inequality. We establish a fully discrete scheme of the abstract problem and derive a result on error estimate.     

A hybrid system approach for supporting digital libraries

A digital library (DL) consists of a database which contains library information and a user interface which provides a visual window for users to search relevant information stored in the database. Thus, an abstract structure of a digital library can be defined as a combination of a special purpose database and a user-friendly interface. This paper addresses one of the fundamental aspects of such a combination. This is the formal data structure for linking an object oriented database with hypermedia to support digital libraries. It is important to establish a formal structure for a digital library in order to efficiently maintain different types of library information. This article discusses how to build an object oriented hybrid system to support digital libraries. In particular, we focus on the discussion of a general purpose data model for digital libraries and the design of the corresponding hypermedia interface. The significant features of this research are, first, a formalized data model to define a digital library system structure; second, a practical approach to manage the global schema of a library system; and finally, a design strategy to integrate hypermedia with databases to support a wide range of application areas. Received: 15 December 1997 / Revised: June 1999     

A Nonlinear Integral Defined on Partition and its Application to Decision Trees

Nonlinear integrals play an important role in information fusion. So far, all existing nonlinear integrals of a function with respect to a set function are defined on a subset of a space. In many of the problems with information fusion, such as decision tree generation in inductive learning, we often need to deal with the function defined on a partition of the space. Motivated by minimizing the classification information entropy of a partition while generating decision trees, this paper proposes a nonlinear integral of a function with respect to a nonnegative set function on a partition, and provides the conclusion that the sum of the weighted entropy of the union of several subsets is not less than the sum of the weighted entropy of a single subset. It is shown that selecting the entropy of a single attribute is better than selecting the entropy of the union of several attributes in generating rules by decision trees.