5,952 research outputs found
Petri net modeling and scheduling for cyclic job shops with blocking
No full textCyclic scheduling is an effective scheduling method in the repetitive discrete manufacturing environment. We investigate the scheduling problem for general cyclic job shops with blocking where each machine has an input buffer of finite capacity. We develop Petri net models for the-shops. We propose a sequential buffer control policy that restricts the jobs to enter the input buffer of the next machine in a specified sequence. We show that the scheduling model of a cyclic shop with finite buffers under such a buffer control policy can be transformed into a scheduling model of a cyclic shop with no buffer that can be modeled as a timed marked graph. In addition, we characterize the structural properties for deadlock detection. Finally, we present a mixed integer programming model to find an optimal deadlock-free schedule that minimizes the cycle time. (C) 1998 Elsevier Science Ltd. All rights reserved.
A tabu search procedure for periodic job shop scheduling
No full textWe consider job shops where an identical mixture of items is repetitively produced. We discuss the sequencing problem that finds the processing order at each machine that maximizes the throughput rate of the mixtures or equivalently minimizes the cycle time. We present an effective tabu search procedure for the problem. To do this, we characterize the neighborhood structure that generates feasible solutions by reversing the order of two operations on a critical circuit in the associated graph. We develop an efficient method of approximately evaluating the cycle times of neighborhood solutions. Computational results are reported. Copyright (C) 1996 Elsevier Science Lt
A known-signal detector based on ranks in weakly dependent noise
No full textLocally optimum rank detection of known signals under a weakly dependent noise model is considered in this paper. The weakly dependent noise model is known to be useful for modeling inter-user interference, which is important in the synthesis and analysis of mobile communication systems. For good weak-signal detection performance under any specified noise probability density function, the locally optimum detector is derived based on signs and ranks of the observation. It is also shown that the locally optimum rank detector has the same asymptotic performance as the locally optimum rank detector which uses the actual values of the observations.Ministry of Information and Communication (MIC) under grant from the University Basic Research Fun
Extrapair paternity and the evolution of bird song
No full textBird song is usually considered to have evolved in the context of sexual selection. Because extrapair paternity is a major component of sexual selection, mating advantages at the social level for males that produce songs of high quality may be transformed into higher success in extrapair paternity. Therefore, males with longer and more complex songs should suffer less from extrapair paternity intraspecifically, whereas species with high rates of extrapair paternity, reflecting intense sperm competition, should produce more elaborate songs. Although some intraspecific studies demonstrated a negative link between features of songs and extrapair paternity in own nest, others failed to detect such a relationship. Contrary to expectation, a meta-analysis of all studies revealed no significant intraspecific evidence for songs being associated with extrapair paternity. In addition, in comparative analyses based on generalized least squares (GLS) models, we found that no measures of song complexity and temporal output were significantly related to extrapair paternity interspecifically, even when potentially confounding factors such as social mating system, life history, migration, habitat, or sexual dichromatism were held constant. Only plumage dichromatism was significantly related to extrapair paternity. The absence of both intra- and interspecific relationships between measures of song variability and extrapair paternity suggests that factors other than postmating sexual selection have been the important evolutionary forces shaping differences in song. Copyright 2004.bird song; evolution; extrapair paternity; generalized least squares; meta-analysis; repertoire size; sexual selection
Comparison of gliding bacteria isolated from fish in North-American and other areas of the Pacific Rim.
No full text
- …
