Ahmed M. Mohamed

Transient Model for Jackson Networks and Its Approximation

Jackson networks have been very successful in so many areas in modeling parallel and distributed systems. However, the ability of Jackson networks to predict performance with system changes remains an open question, since they do not apply to systems where there are population size constraints. Also, the product-form solution of Jackson networks assumes steady state systems with exponential service centers and FCFS queueing discipline. In this paper, we present a transient model for Jackson networks. The model is applicable under any population size. This model can be used to study the transient behavior of Jackson networks and if the number of tasks to be executed is large enough, the model accurately approaches the product-form solution (steady state solution). Finally, an approximation to the transient model using the steady state solution is presented.

What Makes a Good Summary

One of the biggest challenges for intelligence analysts who participate in prevention or response to a terrorism act is to quickly find relevant information from massive amounts of data. Along with research on information retrieval and filtering, text summarization is an effective technique to help intelligence analysts shorten their time to find critical information and make timely decisions. Multi-document summarization is particularly useful as it serves to quickly describe a collection of information. The obvious shortcoming lies in what it cannot capture especially in more diverse collections. Thus, the question lies in the adequacy and/or usefulness of such summarizations to the target analyst. In this chapter, we report our experimental study on the sensitivity of users to the quality and content of multi-document summarization. We used the DUC 2002 collection for multi-document summarization as our testbed. Two groups of document sets were considered: (I) the sets consisting of closely correlated documents with highly overlapped content; and (II) the sets consisting of diverse documents covering a wide scope of topics. Intuitively, this suggests that creating a quality summary would be more difficult for the latter case. However, human evaluators were discovered to be fairly insensitive to this difference. This occurred when they were asked to rank the performance of various automated summarizers. In this chapter, we examine and analyze our experiments in order to better understand this phenomenon and how we might address it to improve summarization quality. In particular, we present a new metric based on document graphs that can distinguish between the two types of document sets.

Transient performance model for parallel and distributed systems

In studying or designing parallel and distributed systems one should have available a robust analytical model that includes the major parameters that determine the system performance. Jackson networks have been very successful in modeling parallel and distributed systems. However, Jackson networks have their limitations. In particular, the product-form solution of Jackson networks assumes steady state and exponential service centers with certain specialized queueing discipline. In this paper, we present a performance model that can be used to study the transient behavior of parallel and distributed systems with finite workload. When the number of tasks to be executed is large enough, the model approaches the product-form of Jackson networks (steady state solution). We show how to use the model to analyze the performance of parallel and distributed systems. We also use the model to show to what extent the product-form solution of Jackson networks can be used.

ABSTRACT: Many Applications of Mobile Ad Hoc

In studying or designing parallel and distributedsystems one should have available a robust analyticalmodel that includes the major parameters thatdetermines the system performance. Jackson networkshave been very successful in modeling parallel anddistributed systems. However, Jackson networks havetheir limitations. In particular, the product-form solutionof Jackson networks assumes steady state andexponential service centers with certain specializedqueueing discipline. In this paper, we present aperformance model that can be used to study thetransient behavior of parallel and distributed systemswith finite workload. When the number of tasks to beexecuted is large enough, the model approaches theproduct-form of Jackson networks (steady state solution).We show how to use the model to analyze theperformance of parallel and distributed systems. Wealso use the model to show to what extent the product-formsolution of Jackson networks can be used.