Two-level network design with intermediate facilities: An application to electrical distribution systems

We consider the two-level network design problem with intermediate facilities. This problem consists of designing a minimum cost network respecting some requirements, usually described in terms of the network topology or in terms of a desired flow of commodities between source and destination vertices. Each selected link must receive one of two types of edge facilities and the connection of different edge facilities requires a costly and capacitated vertex facility. We propose a hybrid decomposition approach which heuristically obtains tentative solutions for the vertex facilities number and location and use these solutions to limit the computational burden of a branch-and-cut algorithm. We test our method on instances of the power system secondary distribution network design problem. The results show that the method is efficient both in terms of solution quality and computational times.     

Self-Directed Gambling Changes: Trajectory of Problem Gambling Severity in Absence of Treatment

Most problem gamblers do not seek formal treatment, recovering on their own through cognitive re-appraisal or self-help strategies. Although barriers to treatment have been extensively studied, there is a paucity of research on self-directed changes in problem gambling and very few studies have examined these changes prospectively. The aim of this study was to examine the trajectory of gambling severity and behavior change over an 18-month period, among a sample of non-treatment seeking/attending problem gamblers recruited from the community (N?=?204) interested in quitting or reducing gambling. Separate mixed effects models revealed that in absence of formal treatment, significant reductions in gambling severity, frequency, and amount gambled could be observed over the course of a 6 to 9-month period and that changes experienced within the first 12 months were maintained for an extended 6 months. Problem gambling severity at baseline was significantly associated with changes in severity over time, such that participants with more severe gambling problems demonstrated greater reductions in their gambling severity over time. A total of 11.1% of participants gambled within a low-risk threshold at 18 months, although 28.7% of the sample reported consecutive gambling severity scores below problem levels for the duration of 1 year or longer. The findings suggest that among problem gamblers motivated to quit or reduce their gambling, significant self-directed changes in gambling severity can occur over a relatively short time. Additional prospective studies are needed to document the role of specific self-help tools or thought processes in exacting gambling changes.     

Noise analysis in professional office chairs

The noise caused by the movement of users on their chairs in the work environment may indicate structural weaknesses and risk, and still significantly reduce productivity by increasing employees stress level. By understanding the activities to be developed in a work place one may understand what should be necessary to a good development, thereafter a search for improvement of labor activity with the aim of better use of resources in the operation of product use may be done. The analysis of the incremental variation of noise in professional chairs aims to identify its origin and the time the emission of noise starts during the period of use, its development and the major causative agents. Determining the characteristics of the sound of different materials and adjustments mechanisms of the chair can determine how different materials interact with each other. The measurement of these noises in an acoustic isolated room using directional microphones, if recorded and analyzed properly makes it possible to investigate and orientate to suspect elements in order to propose solutions and identify the quality of other similar chairs. Based on the results recommendations can be established for the orientation of users, managers and people responsible for the acquisition of the products, inducing them to review the employment of materials and the choice of the processes of production. These aspects are not covered in the Brazilian ergonomics norms and standards in the use of chairs.     

Bayesian multivariate GARCH models with dynamic correlations and asymmetric error distributions

The main goal in this paper is to develop and apply stochastic simulation techniques for GARCH models with multivariate skewed distributions using the Bayesian approach. Both parameter estimation and model comparison are not trivial tasks and several approximate and computationally intensive methods (Markov chain Monte Carlo) will be used to this end. We consider a flexible class of multivariate distributions which can model both skewness and heavy tails. Also, we do not fix tail behaviour when dealing with fat tail distributions but leave it subject to inference.     

Optimizing the Collections Process in Consumer Credit

This paper builds a dynamic programming model to optimize the collections process in consumer credit. It determines which collections actions should be undertaken and how long they should be performed, including theoretical results about the form of the optimal policy under certain conditions. Finally, a case study is described based on data from the collections department of a European bank.     

A Metropolis algorithm to obtain co-sufficient samples with applications in conditional tests

ABSTRACT

Conditional tests are constructed by conditioning a fit measure to a minimal sufficient statistic. To calculate the p-value of these tests, Monte Carlo methods with co-sufficient samples can be used. In this paper we show how to simulate co-sufficient samples when the data distribution belongs to the exponential family with doubly transitive sufficient statistics. The proposed method is illustrated using the beta distribution.     

Annualized hours as a capacity planning tool in make-to-order or assemble-to-order environment: An agricultural implements company case

Capacity planning is one of the most important elements for an efficient production planning and control system. It is even more important when the main strategies to fulfil sales requirements are make-to-order (MTO) or assemble-to-order (ATO). Neither MTO or ATO companies keep finished products in stock which means that production level is driven by actual sales figures. Therefore, it is very important to have an available capacity as flexible as possible to meet sales requirements. Annualized hours (AH) is a work time control system that helps in increasing the flexibility of available capacity. The main rule of the AH system is to hire employees to work a certain number of hours on a yearly basis. Following some other pre-defined rules and limits, the AH system allows a company to adjust weekly available time in order to reduce idle capacity or to fulfil requirements that could mean overtime. This paper proposes a linear programming model to plan the operations using AH. This model has been implemented in a company that produces agricultural implements, showing that it is very simple to use. It is producing excellent practical results.     

Achieve Boston: a citywide innovation in professional development

Achieve Boston is a broad-based collaborative effort to improve the overall quality of programs for children and youth by establishing a professional development infrastructure that supports those who work with young people during the out-of-school-time hours.     

Production planning and control for remanufacturing: literature review and analysis

This article reviews the literature on production planning and control (PPC) for remanufacturing. The objectives are threefold: to determine whether the gaps identified by Guide (Guide Jr, V.D.R., 2000. Production planning and control for remanufacturing: industry practice and research needs. Journal of Operations Management, 18, 467–483) on the subject with respect to the main complicating characteristics of remanufacturing have been fulfilled; to classify the literature based on an appropriate structure to obtain a better understanding of the subject identifying sources of future research and to provide a useful source for scholars and practitioners. Seventy-six papers were examined and classified. It was found that none of the studies deals simultaneously with all of the complicating characteristics, and that more practical research is needed. In addition it was found that we lack studies regarding forecasting and aggregate planning considering disassembly of returned products, material matching restrictions or stochastic routings, master production scheduling considering material matching restrictions or stochastic routings, ordering system and capacity planning considering material matching restrictions and inventory control and management considering stochastic routings.