Uma metaheurística para a programação de projectos com multi-modos e recursos limitados

Este artigo apresenta uma nova abordagem (MM-GAV-FBI), aplicável ao problema da programação de projectos com restrições de recursos e vários modos de execução por actividade, problema conhecido na literatura anglo-saxónica por MRCPSP. Cada projecto tem um conjunto de actividades com precedências tecnológicas definidas e um conjunto de recursos limitados, sendo que cada actividade pode ter mais do que um modo de realização. A programação dos projectos é realizada com recurso a um esquema de geração de planos (do inglês Schedule Generation Scheme - SGS) integrado com uma metaheurística. A metaheurística é baseada no paradigma dos algoritmos genéticos. As prioridades das actividades são obtidas a partir de um algoritmo genético. A representação cromossómica utilizada baseia-se em chaves aleatórias. O SGS gera planos não-atrasados. Após a obtenção de uma solução é aplicada uma melhoria local. O objectivo da abordagem é encontrar o melhor plano (planning), ou seja, o plano que tenha a menor duração temporal possível, satisfazendo as precedências das actividades e as restrições de recursos. A abordagem proposta é testada num conjunto de problemas retirados da literatura da especialidade e os resultados computacionais são comparados com outras abordagens. Os resultados computacionais validam o bom desempenho da abordagem, não apenas em termos de qualidade da solução, mas também em termos de tempo útil.As the complexity of projects increases, the requirement of an organized planning and scheduling process is enhanced. The need for organized planning and scheduling of a construction project is influenced by a variety of factors (e.g., project size and number of project activities). To plan and schedule a construction project, activities must be defined sufficiently. The level of detail determines the number of activities contained within the project plan and schedule. So, finding feasible schedules which efficiently use scarce resources is a challenging task within project management. In this context, the well-known Resource Constrained Project Scheduling Problem (RCPSP) has been studied during the last decades. In the RCPSP the activities of a project have to be scheduled such that the makespan of the project is minimized. So, the technological precedence constraints have to be observed as well as limitations of the renewable resources required to accomplish the activities. Once started, an activity may not be interrupted. This problem has been extended to a more realistic model, the multi-mode resource constrained project scheduling problem (MRCPSP), where each activity can be performed in one out of several modes. Each mode of an activity represents an alternative way of combining different levels of resource requirements with a related duration. Each renewable resource has a limited availability such as manpower and machines for the entire project. The objective of the MRCPSP problem is minimizing the makespan. While the exact methods are available for providing optimal solution for small problems, its computation time is not feasible for large-scale problems. This paper presents a genetic algorithm-based approach (MM-GAV-FBI) for the multi-mode resource constrained project scheduling problem. The idea of this new approach is integrating a genetic algorithm with a schedule generation scheme. This study also proposes applying a local search procedure trying to improve the initial solution. The chromosome representation of the problem is based on random keys. The schedule is constructed using a schedule generation scheme (SGS) in which the priorities of the activities are defined by the genetic algorithm. The experimental results of MM-GAV-FBI on project instances show that this approach is an effective method for solving the MRCPSP

Project scheduling under multiple resources constraints using a genetic algorithm

The resource constrained project scheduling problem (RCPSP) is a difficult problem in combinatorial optimization for which extensive investigation has been devoted to the development of efficient algorithms. During the last couple of years many heuristic procedures have been developed for this problem, but still these procedures often fail in finding near-optimal solutions. This paper proposes a genetic algorithm for the resource constrained project scheduling problem. The chromosome representation of the problem is based on random keys. The schedule is constructed using a heuristic priority rule in which the priorities and delay times of the activities are defined by the genetic algorithm. The approach was tested on a set of standard problems taken from the literature and compared with other approaches. The computational results validate the effectiveness of the proposed algorithm

A two-level genetic algorithm for the multi-mode resource-constrained project scheduling problem

This paper presents a genetic algorithm for the multimode resource-constrained project scheduling problem (MRCPSP), in which multiple execution modes are available for each of the activities of the project. The objective function is the minimization of the construction project completion time. To solve the problem, is applied a two-level genetic algorithm, which makes use of two separate levels and extend the parameterized schedule generation scheme by introducing an improvement procedure. It is evaluated the quality of the schedule and present detailed comparative computational results for the MRCPSP, which reveal that this approach is a competitive algorithm

MULTIOBJECTIVE OPTIMIZATION: TIME-COST APPLICATION IN CONSTRUCTION

INTRODUCTION AND BACKGROUND In today´s market-driven economy, the ability to minimize the time and/or cost of a project could determine the profitability and even the survival of a construction company. The increasing acceptance of alternative tenders and different project delivery systems, such as design and build, management contracting, build-operate-transfer, partnering, etc., allows greater flexibility in construction duration. This also means that both construction time and cost should be considered concomitantly at the estimation and planning and stages Several approaches to solve the time-cost optimization (TCO) problem have been proposed in the last years: mathematical, heuristic and search methods

Multiplex PCR for the discrimination of vaginal bacterial population

Bacterial vaginosis is one of the most common disorders in women of reproductive age worldwide and while not life-threatening, it leads to increased risk of more serious gynecologic infections and pre-term labor. It is a pathology which has been recognized to possess several microorganisms involved such as Lactobacillus species, Gardnerella vaginalis, Atopobium vaginae, and other anaerobic bacteria of difficult identification, whose fragile balance may determine the appearance or not the pathology. Currently diagnosis is made mostly based on symptoms and is variable dependent on the symptoms which the physician judge to be most important for diagnosis, and laboratory culture techniques for the identification of bacterial strains present is very time consuming and not always successful in identifying most microorganisms present. In order to have a better understanding of the aetiology of BV and thus be able to identify better tools for the correct diagnosis of this pathology, more effective tools for identification of bacteria commonly associated with the vaginal flora are need. The use of new molecular biology techniques, such as PCR, has begun to be extensively developed for the study of pathologies such as BV. Besides conventional PCR there have been key developments made to this techniques such as multiplex PCR (allowing the detection of the presence of several strains of organisms in a single reaction) and qPCR which allows the fast quantification of organism which would otherwise take many days to quantify using traditional microbiology techniques. Here we describe the development of a multiplex PCR assay for the identification of 3 of the most commonly studied bacterial strains for the diagnosis of BV: Lactobacillus spp., G. vaginalis and A. vaginae

The influence of scavengers on VOC emissions in particleboards made from pine and poplar

This paper studies the performance of scavengers on Volatile Organic Compound (VOC) emissions from wood-based composites. Particleboards made from maritime pine (Pinus pinaster Ait.) and European poplar (Populus spp.) were produced with a UF resin doped with melamine and two scavengers, sodium metabisulfite and urea. VOC emission was measured according to EN ISO 16000. Particleboards made from pine present much higher total VOC (TVOC) emissions than boards made from poplar. Pine emits a higher amount of terpenes, but also aldehydes, acids and terpenoids, while poplar emits mainly acetic acid. Sodium metabisulfite showed an excellent ability to reduce aldehydes emission, which represents nearly 50 % of total emission of particleboards made from pine. When sodium metabisulfite was applied to particleboards made from poplar, reduction of TVOCs was not significant due to the low contribution of aldehydes to TVOCs. Urea presents a low reduction in TVOCs for both wood species

Evaluation of bonding performance of amino polymers using ABES

In this paper, the use of Automated Bonding Evaluation System (ABES) for evaluation of bonding strength of wood adhesives is presented. A simple reactive model is proposed, which considers the phenomena involved during resin cure: formation of wood-resin-wood bonds. In the present study, experimental data of a standard urea-formaldehyde (UF) resin using different catalysts, phosphoric acid and ammonium sulphate, are presented and discussed. The proposed can be applied to wood adhesives, namely formaldehyde-based resins under different temperatures. The model fits well to experimental data, presenting high determination coefficient values

Programa multidisciplinar de monitorização de curto termo para apoio ao planeamento e gestão da zona costeira

A zona costeira do noroeste de Portugal tem vindo a sofrer processos erosivos de modo progressivo que têm preocupado os responsáveis políticos e os cidadãos em geral. Esta realidade é especialmente notória nas zonas costeiras com altas pressões de ocupação. A zona costeira de Vila Nova de Gaia apresenta ocupação intensa, tendo vários segmentos que evidenciam elevada vulnerabilidade à erosão costeira. Com o objectivo de avaliar os segmentos mais vulneráveis foi implementado um programa global de monitorização iniciado em 2007. Pretende-se avaliar as tendências de evolução morfodinâmica do sistema costeiro, incluindo prépraia, praia e dunas. Este programa compreendeu a realização de duas campanhas anuais, durante dois anos, utilizando um conjunto de metodologias de monitorização inovadoras: observações de campo, fotografias aéreas, levantamentos topográficos com um sistema móvel com DGPS e câmaras de vídeo; levantamentos batimétricos utilizando uma embarcação autónoma flutuante; recolha de amostras de sedimentos e realização de perfis de praia. A informação produzida foi processada para utilização na avaliação da vulnerabilidade à erosão e produção das cartas de risco associadas, as quais estão em fase de elaboração. Todos os dados são processados e analisados em ambiente SIG. Neste artigo são apresentados resultados obtidos nas quatro campanhas de monitorização, incluindo aspectos da morfodinâmica local com base na análise dos Modelos Digitais de Terreno e as principais mudanças morfológicas e sedimentares verificadas no período de monitorização