1,720,972 research outputs found
An invariance in the priority queue with generalized server vacations and structured batch arrivals
No full textShanthikumar (Shanthikumar, J.G. Level crossing analysis of priority queues and a conservation identity for vacation models. Nav. Res. Log. 1989, 36, 797-806) studied the priority M/G/1 queue with server vacations and found that the difference between the waiting time distribution under the non-preemptive priority (NPP) and that under the preemptive-resume priority (PRP) is independent of the vacation policy. We extend this interesting property: (i) to the generalized vacations which includes the two vacation policies considered by Shanthikumar; (ii) to the structured batch Poisson arrival process; and (iii) to the discrete-time queues.Korea Research Foundation Grant
(KRF-2002-070-C00021
Waiting-time distribution of a discrete-time multiserver queue with correlated arrivals and deterministic service times: D-MAP/D/k system
No full textWe derive the waiting-time distribution of a discrete-time multiserver queue with correlated arrivals and deterministic (or constant) service times. We show that the procedure for obtaining the waiting-time distribution of a multiserver queue is reduced to that of a single-server queue. We present a complete solution to the waiting-time distribution of D-MAP/D/k queue together with some computational results. (C) 2002 Elsevier Science B.V. All rights reserved.BK 21 project, the Department of Industrial Engineering, KAIST, NSER
On the queue length distribution for the GI/G/1/K/V-M queue
No full textWe present a transform-free distribution of the steady-state queue length for the GI/G/1/K queueing system with multiple vacations under exhaustive FIFO service discipline. The method we use is a modified supplementary variable technique and the result we obtain is expressed in terms of conditional expectations of the remaining service time, the remaining interarrival time, and the remaining vacation, conditional on the queue length at the embedded points. The case K --> infinity is also considered.Korea Research Foundation Grant
(KRF-2002-070-C00021
Analysis of the queue-length distribution for the discrete-time batch-service Geo/G(a,Y)/1/K queue
No full textIn this paper, we consider a discrete-time finite-capacity queue with Bernoulli arrivals and batch services. In this queue, the single server has a variable service capacity and serves the customers only when the number of customers in system is at least a certain threshold value. For this queue, we first obtain the queue-length distribution just after a service completion, using the embedded Markov chain technique. Then we establish a relationship between the queue-length distribution just after a service completion and that at a random epoch, using elementary 'rate-in = rate-out' arguments. Based on this relationship, we obtain the queue-length distribution at a random (as well as at an arrival) epoch, from which important performance measures of practical interest, such as the mean queue length, the mean waiting time, and the loss probability, are also obtained. Sample numerical examples are presented at the end. (c) 2006 Elsevier B.V. All rights reserved.Korean Research Foundation Grant
(KRF-2005-041-C00071
Growth behavior of rounded (Ti,W)C and faceted WC grains in a Co matrix during liquid phase sintering
No full textGrowth behavior of two different types of grains, faceted and rounded, in the same liquid matrix has been studied in the 70(25TiC-75WC)-30Co (wt%) system. Powder samples were sintered above the eutectic temperature for various times under a carbon saturated condition. (Ti,W)C grains with a rounded shape and WC grains with a faceted shape coexisted in the same Co-based liquid. With increasing sintering time the average size of (Ti,W)C grains increased continuously and very large WC grains appeared. The growth of rounded (Ti,W)C grains followed a cubic law indicating diffusion-controlled growth. On the other hand, the growth of the faceted WC grains resulted in a bimodal grain size distribution, showing abnormal grain growth. With increased initial size, however, abnormal growth of WC grains was suppressed. This growth behavior of WC grains could be explained using growth theories of faceted crystals and was also confirmed by a calculation using their growth equations. The present investigation thus shows that the growth behavior of one type of grain is not affected by the other type of grain in the same matrix and is governed only by whether the grain shape is faceted or rounded. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Comparisons between low Reynolds number two-equation models for computation of a shockwave-turbulent-boundary layer interaction
No full textA comparative study is made on the performance of several low Reynolds number k-epsilon models and the k-omega model in predicting the shockwave-turbulent-boundary layer interaction over a supersonic compression ramp of 16 degrees, 20 degrees and 24 degrees at a Mach numbers of 2.85, 2.79 and 2.84, respectively. The model equations are numerically solved by a higher order upwind scheme with the 3rd order MUSCL type TVD. The computational results reveal that all of the low Reynolds number k-epsilon models, particularly those employing y+ in their damping functions give erroneously large skin friction in the redeveloping region. It is also interesting to note that the k-epsilon models, when adjusted and based on DNS data, do not perform better, as expected, than the conventional low Reynolds number k-epsilon models. The k-omega model which does not adopt a low Reynolds number modification, brings about reasonably accurate skin friction, but with a later onset of pressure rise. By recasting the omega equation into the general form of the epsilon equation, it is inferred that the turbulent cross diffusion term between k and epsilon is critical to guarantee better performance of the k-omega model for the skin friction prediction in the redeveloping region. Finally, an asymptotic analysis of a fully developed incompressible channel flow, with the k-epsilon and the k-omega models, reveals that the cross diffusion mechanism inherent in the k-omega model contributes to the better performance of the k-omega model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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