Elsa Costa e Silva

Sequence based heuristics for two-dimensional bin packing problems

This article addresses several variants of the two-dimensional bin packing problem. In the most basic version of the problem it is intended to pack a given number of rectangular items with given sizes in rectangular bins in such a way that the number of bins used is minimized. Different heuristic approaches (greedy, local search, and variable neighbourhood descent) are proposed for solving four guillotine two-dimensional bin packing problems. The heuristics are based on the definition of a packing sequence for items and in a set of criteria for packing one item in a current partial solution. Several extensions are introduced to deal with issues pointed out by two furniture companies. Extensive computational results on instances from the literature and from the two furniture companies are reported and compared with optimal solutions, solutions from other five (meta)heuristics and, for a small set of instances, with the ones used in the companies.

Integrating two-dimensional cutting stock and lot-sizing problems

The two-dimensional cutting stock problem (2DCSP) consists in the minimization of the number of plates used to cut a set of items. In industry, typically, an instance of this problem is considered at the beginning of each planning time period, what may result in solutions of poor quality, that is, excessive waste, when a set of planning periods is considered. To deal with this issue, we consider an integrated problem, in which the 2DCSP is extended from the solution in only a single production planning period to a solution in a set of production planning periods. The main difference of the approach in this work and the ones in the literature is to allow sufficiently large residual plates (leftovers) to be stored and cut in a subsequent period of the planning horizon, which may further help in the minimization of the waste. We propose two integrated integer programming models to optimize the combined two-dimensional cutting stock and lot-sizing problems, minimizing the total cost, which includes material, waste and storage costs. Two heuristics based on the industrial practice to solve the problem were also presented. Computational results for the proposed models and for the heuristics are presented and discussed.

Beyond links: Understanding meaning and control in political blogs

The use of hyperlinks in blogs produces hypertexts, which are characterized by an irregular and not sequential organization. Contrary to the narrative structures in which the author exercises his authority by setting an order of events, hypertexts compromise the integrity of authorship. Blog hyperlinking thus challenges traditional notion of authorship and control exercised over the speech produced. Political contexts, such as those inhabited by politicians and news providers, are quite sensitive to these compromises as control over meanings is seen as problematic. The use of a hyperlink can be seen as willingness to renounce to full control, but acknowledging its presence is insufficient to analyze its effects in the meaning of the posts. This article argues that a qualitative assessment of links is necessary if a full understanding of hyperlinks implications is to be provided. It proposes a model of analysis with three levels of compromising: referential, accessory, and compulsory.The use of hyperlinks in blogs produces hypertexts, which are characterized by an irregular and not sequential organization. Contrary to the narrative structures in which the author exercises his authority by setting an order of events, hypertexts compromise the integrity of authorship. Blog hyperlinking thus challenges traditional notion of authorship and control exercised over the speech produced. Political contexts, such as those inhabited by politicians and news providers, are quite sensitive to these compromises as control over meanings is seen as problematic. The use of a hyperlink can be seen as willingness to renounce to full control, but acknowledging its presence is insufficient to analyze its effects in the meaning of the posts. This article argues that a qualitative assessment of links is necessary if a full understanding of hyperlinks implications is to be provided. It proposes a model of analysis with three levels of compromising: referential, accessory, and compulsory.

HEURISTICS WITH STOCHASTIC NEIGHBORHOOD STRUCTURES FOR TWO-DIMENSIONAL BIN PACKING AND CUTTING STOCK PROBLEMS

This paper proposes a heuristic with stochastic neighborhood structures (SNS) to solve two-stage and three-stage two-dimensional guillotine bin packing and cutting stock problems. A solution is represented as a sequence of items which are packed into existing or new stacks, shelves or bins according to previously defined criteria. Moreover, SNS comprises three random neighborhood structures based on modifying the current sequence of items. These are called cut-and-paste, split, and swap blocks and are applied one by one in a fixed order to try to improve the quality of the current solution. Both benchmark instances and real-world instances provided by furniture companies were utilized in the computational tests. Particularly, all benchmark instances are bin packing instances (i.e., the demand of each item type is small), and all real-world instances are classified into bin packing instances and cutting stock instances (i.e., the demand of each item type is large). The computational results obtained by the proposed method are compared with lower bounds and with the solutions obtained by a deterministic Variable Neighborhood Descent (VND) meta-heuristic. The SNS provide solutions within a small percentage of the optimal values, and generally make significant improvements in cutting stock instances and slight to moderate improvements in bin packing instances over the VND approach.

The Influence of BMI and Predictors of Disordered Eating and Life Satisfaction on Postmenopausal Women

This study aims to compare eating behaviors, body satisfaction, exercise, and life satisfaction between normal-weight and overweight postmenopausal women and to examine the predictors of disordered eating and life satisfaction among postmenopausal women (n = 294). The overweight group had more eating disordered behavior, more body dissatisfaction, and lower physical quality of life. The increase of age predicted less disordered eating. Higher BMI, the perception of an ideal weight lower than the current one, lower body satisfaction, and physical quality of life predicted disordered eating. Higher body satisfaction, less psychosocial discomfort, and a greater degree of sexual symptom discomfort predicted life satisfaction.

A Hybrid Heuristic Based on Column Generation for Two- and Three- Stage Bin Packing Problems

We address two two-dimensional bin packing problems where the bins are rectangular and have the same size. The items are also rectangular and all of them must be packed with the objective of minimizing the number of bins. In the first problem, the two-stage problem, the items must be packed in levels. In the second problem, the restricted 3-stage problem, items can be grouped in stacks which are packed in levels.

The Politics of Playing Along: Radio and Regulation in Democratic Europe

The loss of localism has been a common trend in most radio markets in Europe and the United States. Deregulation of ownership led to a concentration phenomenon that has affected local radios in several western democracies. New forms of regulation have been considered as possible ways to stop the erosion of localism by applying rules to markets in the defense of diversity, pluralism, and the local dimension. This article analyses the local radio market in Portugal, by assessing the changes in the legislation and by examining the regulatory action that can, according to its remit, act preventively to avoid market forces to harm these principles.