基于FPGA的单片机的系统的设计

本文在阐述可编程逻辑器件特点及其发展趋势的基础上,利用EDA的硬件和软件技术,研究和设计了基于FPGA的8051单片机的片上系统。本文采用VHDL语言,应用先进的自顶向下的设计方法,在Active—HDL5．1编程环境下,应用层次化的设计思路,模块化的设计方法进行设计。     

计算机病毒的预防的思考

计算机病毒随着计算机的普及也渗透到信息化办公的各个领域,带给计算机操作系统难以防范的困扰。为使计算机信息安全有保障,研讨计算机的病毒的防范措施迫在眉睫。针对计算机病毒如何预防进行探究,并分析应对措施。     

行走的空间 当代的游牧

当“游牧”这个词之于人们已渐行渐远,一所“行走住房”（Walking House）正从德国慢慢走在返回丹麦的路上。“行走住房”呈横向的六角柱体形,柱体形状隐含了一种趋动的姿态,而六个硬朗的棱角似乎又暗示着游走和远行从来并非轻易。实际上“行走住房”的移动不是靠柱体本身的滚动,而是依赖底部六个支架——六只“脚”——以拟人化的方式前进。对比常见的交通工具,例如汽车、火车和轨道交通,因为这一组“脚”,“行走住房”显示出一种同人类本身更紧密的亲缘关系。     

山里的小学山里的孩子山里的老师

秦岭七十二道峪,其中一峪为“秀龙峪”,是传说中汉朝皇帝刘秀避难之地。该峪有一下峪村,村里的四组有一所当年部队驻扎时拥建的小学。     

营林工作的可持续发展的探讨

森林以其独特的性质特点,使自身既可为人类社会的当代发展享用,又可以为人类的后代存续造福。然而,若森林得不到有效的维护,那么以上两种利处就无法得到实现。所以,我们要加大对森林可持续发展的认识程度,使森林成为改善人类福利的重要保证。这本身也体现了林业的可持续发展理念。我国政府对生态建设和林业建设给予了很高的注视程度。在相关的法律、政策上都有明确的规定,以保障林业的健康发展。同时,在资金的投入上,也相对有力,从而取得了可喜的治理成果。然而,由于长期以来存在的一些制度上的问题．我国的林业可持续发展也受到了一定的影响。     

艺术的都市人 都市人的艺术

<正>自古以来,城市不仅是人类财富与权利的中心,更是人类智慧与文明的汇集地。一代又一代的都市人不仅创造着物质财富,更在城市文化的熏陶下,创造了属于自己的灿烂精神文明。艺术是人类文明创造出的一朵奇葩,自城市诞生以来,它就一直伴随着都市人。从古代城市的辉煌遗迹到现代都市的热闹繁华,虽然都市人和艺术都经历着时代的变迁和发展,但是,都市人与艺术之间的密切关系却未曾改变。都市人创造了属于他们自己的艺术,而艺术也带给了     

艺术的都市人 都市人的艺术

自古以来,城市不仅是人类财富与权利的中心,更是人类智慧与文明的汇集地。一代又一代的都市人不仅创造着物质财富,更在城市文化的熏陶下,创造了属于自己的灿烂精神文明。艺术是人类文明创造出的一朵奇葩,自城市诞生以来,它就一直伴随着都市人。从古代城市的辉煌遗迹到现代都市的热闹繁华,虽然都市人和艺术都经历着时代的变迁和发展,但是,都市人与艺术之间的密切关系却未曾改变。     

工业光纤的更好的经济效益

当美国国家航空航天局（NASA）兰利研究中心的研究人员观察电磁干扰如何潜在影响飞行导航和通信系统时,得到了一些惊人的结果。举个例子,来自一些超宽带信号的干扰可能会在没有预警的情况下突然消除飞机无线电。电磁干扰（EMI）也可能会导致无线电导航系统给出错误的读数。电磁干扰也可以影响距离测量设备,在某些情况下,读出的距离可能远离一整个海里。也许最令人担忧的是,严重的电磁干扰会中断空中防撞系统显示屏上的飞机图像。     

刍议高速公路的合理收费的标准

近几年，高速公路的快速发展，极大地促进了整个社会经济的发展。论文阐述了合理制定高速公路收费标准的重要性以及收费标准制定的因素，并对高速公路收费问题产生的原因进行深入分析，并提出相应的对策建议。     

基于gtkmm的linux下的图形界面开发的研究

目前,在linux环境下开发图形化界面已受到广泛关注,先简要介绍一下GTK,GTK+与gtkmm的区别,然后重点介绍gtkmm与glade相结合来开发C++图形界面应用程序。     

两类排队网络的逼近研究

本文给出了两类排队网络。一类是容量有限的队列网络,我们证明了在高负荷下,标准化的队长过程弱收敛于半鞅反射的布朗运动：另一类是带有反馈的多类顾客多服务台队列网络,我们获得了队列网络中负荷过程的扩散逼近。     

一类Kelly-型排队网络的稳定性

排队网络可以用来模拟诸如通信网络这样的复杂系统。对排队网络的研究中的一个主要议题是建立其在某些特殊的规则下稳定的充要条件。本文的研究对象是一类具有两类顾客输入的Kelly-型排队网络。利用流体模型以及Lyapunov函数等工具,建立了该排队网络在所有非闲置的规则下稳定的充分条件。最后,对条件的充分性作了说明。     

Heuristic analysis of closed queueing networks

In this paper we consider closed queueing networks having M single server queueing stations with arbitrary interconnections and general service time distributions. Here we propose an iterative approximation procedure, based on a decomposition approximation. Numerical results are reported to demonstrate the accuracy of the method. We also discuss the sensitivity of the results to the initial guess for the server utilizations.     

Generalized queueing network analysis of integrated supply chains

Supply chain networks are formed from complex interactions between several companies whose aim is to produce and deliver goods to the customers at specified times and places. Computing the total lead time for customer orders entering such a complex network of companies is an important exercise. In this paper we present analytical models for evaluating the average lead times of make-to-order supply chains. In particular, we illustrate the use of generalized queueing networks to compute the mean and variance of the lead time. We present four interesting examples and develop queueing network models for them. The first two examples consider pipeline supply chains and compute the variance of lead time using queueing network approximations available in the literature. This analysis indicates that for the same percentage increase in variance, an increase at the downstream facility has a far more disastrous effect than the same increase at an upstream facility. Through another example, we illustrate the point that coordinated improvements at all the facilities is important and improvements at individual facilities may not always lead to improvements in the supply chain performance. The existing literature on approximate methods of analysis of forkjoin queueing systems assumes heavy traffic and requires tedious computations. We present here two tractable approximate analytical methods for lead time computation in a class of fork-join queueing systems. Our method is based on the results presented by Clarke in 1961. For the case where the 'joining' servers of the queueing system are of the type D/N/1, we present an easy to use approximate method and illustrate its use in evaluating decisions regarding logistics (for instance, who should own the logistics fleet-the manufacturer or the vendor?) and computing simple upper bounds for delivery reliability, that is the probability that customer desired due dates are met.     

Modelling, analysis, and acceleration of a printed circuit board fabrication process

Product design and fabrication constitute an important business activity in any manufacturing firm. Designing an optimized product fabrication process is an important problem in itself and is of significant practical and research interest. In this paper, we look into a printed circuit board (PCB) fabrication process and investigate ways in which the fabrication cycle time can be minimized. Single class queueing networks constitute the modelling framework for our study. The model developed in this paper and the analysis experiments carried out are based on extensive data collected on a PCB fabrication company located in Bangalore, India. This is a representative PCB fabrication company involving multiple, concurrent fabrication works with contention for human/technical resources. Our model seeks to capture faithfully the flow of the fabrication process in this company and such other organisations, using queueing networks. Using the model developed, we explore how the cycle times can be reduced using input control, load balancing, and variability reduction. The model presented is sufficiently generic and conceptual; its scope extends beyond that of a PCB fabrication organization.     

Analysis of finite-buffer state-dependent bulk queues

In this paper, we consider a general state-dependent finite-buffer bulk queue in which the rates and batch sizes of arrivals and services are allowed to depend on the number of customers in queue and service batch sizes. Such queueing systems have rich applications in manufacturing, service operations, computer and telecommunication systems. Interesting examples include batch oven processes in the aircraft and semiconductor industry; serving of passengers by elevators, shuttle buses, and ferries; and congestion control mechanisms to regulate transmission rates in packet-switched communication networks. We develop a unifying method to study the performance of this general class of finite-buffer state-dependent bulk queueing systems. For this purpose, we use semi-regenerative analysis to develop a numerically stable method for calculating the limiting probability distribution of the queue length process. Based on the limiting probabilities, we present various performance measures for evaluating admission control and batch service policies, such as the loss probability for an arriving group of customers and for individual customers within a group. We demonstrate our method by means of numerical examples.     

Multi-class queueing models for performance analysis of computer systems

Queueing models, networks of queues in particular, have been found especially useful for estimating the performance of computer systems. Networks of queues with multiple customer classes provide a flexible framework for modelling computer systems, where a rich set of analytical results and techniques are available. When because of the complexity of the system being modelled the analytical results cannot be applied directly, they often point to fairly accurate approximation schemes. In this paper, we present a brief survey of some of the important results and techniques from the theory of multi-class queueing networks. We also present a case study to illustrate how these results and techniques are used in a real-life situation where many of the modelling constraints are violated.     

Modelling of material handling systems for facility design in manufacturing environments with job-specific routing

Traditionally, flow times distance is used as a surrogate for cost in facility design. However, this performance measure does not fully capture the impact of facility design decisions on operational performance measures such as cycle time and work-in-progress in the system, which are often more meaningful for managers, especially in a manufacturing environment. To better measure operational performance, modelling of material handling systems using a queueing network must be integrated in the facility design process. A number of approaches are discussed in the facility design literature for modelling material flow using queueing networks. In these approaches, Poisson arrival or Markovian job routing assumptions have been used. However, for many manufacturing environments, these assumptions lead to an inaccurate estimation of the material handling system's performance and thus lead to poor facility designs. Incorporating more general queueing results for non-Markovian systems is difficult, however, because the facility design process must investigate a large number of potential solutions and thus the results from the queueing models for the material handling system must be quickly obtained. In this paper, the need for more general queueing models of material handling systems in facility design is confirmed. Then, an approach based on multi-class queueing models is adapted to capture the change in variability of the system performance caused by both different arrangements of workstations in the facility and different arrival processes to the workstations due to the job routing in a computationally efficient manner. The proposed modelling approach is shown to provide more accurate results than previous methods used in facility design based on numerical comparisons with results from discrete-event simulation.     

Approximations for the time spent in a dynamic job shop with applications to due-date assignment

In this paper we develop approximations for the distribution of the total time spent in a dynamic job shop. In particular, using an exponential limit theorem and an heuristic decomposition of open queueing networks, we show that for a large class of dynamic job shops, the total time spent in a dynamic job shop can be approximated by an exponential random variable with an appropriate mean. Approximations for job shops that do not belong to this class are also developed. Numerical results show that the proposed approximations are in general very good. Application of these approximations in the assignment of due-dates is also illustrated.