The Effect of Restricting Cycle Times in the Economic Lot Scheduling Problem

The economic lot scheduling problem (ELSP) involves specifying economic cycle times for each of several products produced by a set of machines. The extensive, usually experimentally based, literature on the ELSP indicates that it may be desirable to restrict the possible choice of cycle times for each product to a small and very structured set of possible cycle times. In this paper we examine the economic impacts of such a restriction and give evidence that is highly supportive of this type of restriction; in particular, the “powers of 2” sets of possible cycle times used in practice appear to be very desirable from an economic viewpoint.     

The edge dislocation inside an elliptical inclusion

The plane elasticity problem of an edge dislocation located within an elliptical inclusion in an unbounded matrix is considered. A general solution to this problem is obtained in terms of complex potential functions and all coefficients in the series representation of these potential functions are explicitly obtained. Convergence of these series is thus assured. Two specific cases of this general solution are considered in detail. The first case considers a very long, thin inclusion corresponding physically to the geometry of typical crazes in glassy polymers. the second case considers the almost circular inclusion representative of a number of crystal defects and imperfections. For the second case, expressions for the resultant force on the dislocation agree with results previously obtained for the limiting circular inclusions.     

A pictorial index mechanism for model-based matching

We are currently developing unified query processing strategies for image databases. To perform this task, model-based representations of images by content are being used, as well as a hierarchical generalization of a relatively new object-recognition technique called data-driven indexed hypotheses. As the name implies, it is index-based, from which its efficiency derives. Earlier approaches to data-driven model-based object recognition techniques were not capable of handling complex image data containing overlapping, partially visible, and touching objects due to the limitations of the features used for building models. Recently, a few data-driven techniques capable of handling complex image data have been proposed. In these techniques, as in traditional databases, iconic index structures are employed to store the image and shape representation in such a way that searching for a given shape or image feature can be conducted efficiently. Some of these techniques handle the insertion and deletion of shapes and/or image representations very efficiently and with very little influence on the overall system performance. However, the main disadvantage of all previous data-driven implementations is that they are main memory based. In the present paper, we describe a secondary memory implementation of data-driven indexed hypotheses along with some performance studies we have conducted.     

The effects of shearing on the rheological behaviour of thixotropic bentonite muds

The bentonite muds, widely used in civil engineering and in the oil industry, have a Binghamian and thixotropic behaviour that impedes their flow. It has been shown that vibrations, whatever may be their characteristics, are ineffective for improving this flow. Techniques aimed at applying large and slow shearing actions are no better: the thixotropy reduces considerably the size of the flow zone in the vicinity of the shearing surface, even with low concentrations of mud. It is now obvious that if one wishes to cause a large zone of bentonite mud to flow, it is necessary to reduce the thixotropy with the help of appropriate additives.     

Effect of grain-boundary crystallization on the high-temperature strength of silicon nitride

Si₃N₄ specimens having the composition 88.7 wt% Si₃N₄-4.9wt% SiO₂-6.4wt% Y₂O₃ (85.1 mol% Si₃N₄-11.1 mol% SiO₂-3.8mol% Y₂O₃) were sintered at 2140° C under 25 atm N₂ for 1 h and then subjected to a 5 h anneal at 1500° C. Crystallization of an amorphous grainboundary phase resulted in the formation of Y₂Si₂O₇. The short-time 1370° C strength of this material was compared with that of material of the same composition having no annealing treatment. No change in strength was noted. This is attributed to the refractory nature of the yttrium-rich grain-boundary phase (apparently identical in both glassy and crystalline phases) and the subsequent domination of the failure process by common processing flaws.Chemical analysis of the medium indicated 5.25 wt% O₂, 0.46 wt% C, 0.8 wt% Al, and expressed in p.p.m. 670 Ca, 30 Cu, 2000 Fe, <2 Ti, 370 Cr, 130 Mg, 90 Mn, <10 V, <20 Zr, 2000 Mo, 240 Ni, 130 Zn, <30 Pb, <60 Sn.     

CREATING A STRATEGIC CAPABILITIES ARCHITECTURE

A strategic capabilities architecture is the primary basis for a firm's sustainable competitive advantage. When managers think in terms of such an architecture, the creation of new information systems, training programs, capital projects, and management approaches becomes more focused and has greater impact.     

Thread prioritization: A thread scheduling mechanism for multiple-context parallel processors

Multiple-context processors provide register resources that allow rapid context switching between several threads as a means of tolerating long communication and synchronization latencies. When scheduling threads on such a processor, we must first decide which threads should have their state loaded into the multiple contexts, and second, which loaded thread is to execute instructions at any given time. In this paper we show that both decisions are important, and that incorrect choices can lead to serious performance degradation. We propose thread prioritization as a means of guiding both levels of scheduling. Each thread has a priority that can change dynamically, and that the scheduler uses to allocate as many computation resources as possible to critical threads. We briefly describe its implementation, and we show simulation performance results for a number of simple benchmarks in which synchronization performance is critical.     

Modeling reuse across the software life cycle

This article reports strong correlations between reuse levels of software products across the life cycle and presents models of reuse levels across the life cycle. These models can be used to estimate reuse levels of one life cycle object given reuse levels of others, or to predict reuse levels of later life cycle objects given reuse levels of earlier ones. The models have been developed from survey data collected from 113 respondents from 29 organizations about their own and their organizations' levels of reuse of life cycle objects. Usage scenarios for the models are presented, as are methods for customizing and improving the models.     

Using affine closure to find legal reordering transformations

We present a unified framework for applying iteration reordering transformations. This framework is able to represent traditional transformations such as loop interchange, loop skewing and loop distribution as well as compositions of these transformations. Using a unified framework rather than a sequence of ad-hoc transformations makes it easier to analyze and predict the effects of these transformations. Our framework is based on the idea that all reordering transformations can be represented as a mapping from the original iteration space to a new iteration space. An optimizing compiler would use our framework by finding a mapping that both corresponds to a legal transformation and produces efficient code. We present the mapping selection problem as a search problem by decomposing it into a sequence of smaller choices. We then characterize the set of all legal mappings by defining a search tree. As part of this process we use a new operation called affine closure.     

Complete Boolean Satisfiability Solving Algorithms Based on Local Search

Boolean satisfiability (SAT) is a well-known problem in computer science, artificial intelligence, and operations research. This paper focuses on the satisfiability problem of Model RB structure that is similar to graph coloring problems and others. We propose a translation method and three effective complete SAT solving algorithms based on the characterization of Model RB structure. We translate clauses into a graph with exclusive sets and relative sets. In order to reduce search depth, we determine search order using vertex weights and clique in the graph. The results show that our algorithms are much more effective than the best SAT solvers in numerous Model RB benchmarks, especially in those large benchmark instances.