An Approximate Model of Multistage Automatic Transfer Lines with Possible Scrapping Of Workpieces

We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.     

Linear control rules for production control of semiconductor fabs

We consider the problem of reducing the cycle time required for producing wafers at a given rate in high-volume single-product semiconductor fabs. Based on theoretical results, we propose a new method of input control that uses intersecting hyperplanes to decide when to release a new lot into the wafer fab. The release control rules constructed thus are said to belong to the class of linear control rules. We provide numerical examples to demonstrate that our method gives nearly optimal results for flowline and probabilistic reentrant flowline models. We then propose the linear control rule called descending control (DEC) and give a hybrid simulation-optimization procedure for determining DEC rules in real-life settings. We provide numerical results for the HP development fab model of Wein     

On some queueing models of time division multiple access communication system

In this paper we consider a general queueing model for a time division multiple access communication channel and establish the relationship between the steady-state probability distribution of the number of packets in the buffer at various observation epochs. These results are derived using the theory of embedded Markov chain and discrete state level crossing analysis. We also provide a table describing the relationship between the results given here and the results available in the literature.     

Fabless-foundry partnership: models and analysis of coordinationissues

The fabless-foundry partnership for integrated circuit (IC) manufacturing business is expected to grow from 12% in 1995 to approximately 17% (i.e., $45B) of the total IC market in 2000. The growth of this market will be even more significant for subquarter micron technologies-whose growth is driven by the multimedia industry. The customer base will extend beyond traditional fabless IC companies into vertically integrated IC manufacturers and system vendors. Given the rate of growth and the high technology profile of products, substantial investments in capital, technology, and skilled workforce have to be dedicated and managed effectively for ensuring a successful partnership. In this paper, we outline the potential coordination problems that may arise in such partnerships, and propose a framework for analyzing issues related to yield information sharing and yield improvement. Our analysis indicates that fabless-foundry contracts that are based on a fixed number of good dies, and better yield information are more profitable     

Discrete-Time Analysis of Integrated Voice/Data Multiplexers With and Without Speech Activity Detectors

Discrete-time analysis of two schemes for multiplexing voice and data is presented. In each scheme voice and data are multiplexed using the movable boundary frame allocation scheme. In the first scheme, speech activity detectors (SAD's) are not used, and hence, the variations in the voice traffic are only due to the on/off characteristics of voice. In the second scheme, SAD's are employed so that talker silences can he utilized for transmission of additional voice and/or data. In this scheme, the multiplexer performs digital speech interpolation as well as movable boundary frame allocation. The performance measures considered are probability of loss for voice calls, probability of speech clipping, speech packet rejection ratio, and the expected data message delay. In the case of the multiplexer with SAD, a tradeoff exists between data message delay and speech interpolation advantage. Some numerical examples are presented which illustrate the performance of the two multiplexers.     

A general software reliability model for performance prediction

In this paper we give a general Markov process formulation for a software reliability model and present expressions for software performance measures. We discuss a general model and derive the maximum likelihood estimates for the required parameters of this model. The generality of this model is demonstrated by showing that the Jelinski-Moranda model and the Non-Homogeneous Poisson Process (NHPP) model are both very special cases of our model. In this process we also correct some errors in a previous paper of the NHPP model.     

Determination of Optimal Buffer Storage Capacities and Optimal Allocation in Multistage Automatic Transfer Lines

One way to improve the efficiency of automatic transfer lines is to provide intermediate storage buffers. These buffers divide the transfer line into stages, each with one or more machines. The machines in a stage are completely integrated, whereas, the stages are partially decoupled. Here, we study a problem related to buffer storage allocation. The objective is to find optimal distribution of a total storage space among the intermediate buffers. This is formulated as a dynamic programming problem and a heuristic solution is presented.     

Software reliability models: A review

In this paper we review several software reliability models and provide an extensive listing of papers dealing with software reliability modelling and their applications. The models discussed are grouped into two broad categories: empirical and analytical models. Analytical models are further subdivided into static and dynamic models, and the general theory behind these models are reviewed. Based on the observations made in this review, we provide suggestions for future research.     

Optimal Design of Internet-Based Auctions

Online auctions are a profitable, exciting, and dynamic part of electronic commerce, and behave in ways, which do not match classical auction theory. This paper models an online auction in terms of a Markov chain on a state space defined by the current price of the item and the number of bidders who have been previously bumped. It provides a mathematical model, some approximations, which were necessary to convert it into a tractable problem and solutions to a small and a medium-sized theoretical auction. The model results were validated through a comparison with real-world online auction data, showing promise as a predictor of final auction prices. The results of the auction model are also useful in solving an optimization problem that incorporates inventory management considerations in determining optimal auction size.