Algoritmos de aproximação para problemas de roteamento e conectividade com múltiplas funções de distância

Orientador: Lehilton Lelis Chaves PedrosaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: Nesta dissertação, estudamos algumas generalizações de problemas clássicos de roteamento e conectividade cujas instâncias são compostas por um grafo completo e múltiplas funções de distância. Por exemplo, existe o Problema do Caixeiro Alugador (CaRS), no qual um viajante deseja visitar um conjunto de cidades alugando um ou mais carros disponíveis. Cada carro tem uma função de distância e uma taxa de retorno ao local do aluguel. CaRS é uma generalização do Problema do Caixeiro Viajante (TSP). Nós lidamos com esses problemas usando algoritmos de aproximação, que são algoritmos eficientes que produzem soluções com garantia de qualidade. Neste trabalho, são apresentadas duas abordagens, uma baseada em uma redução linear que preserva o fator de aproximação e outra baseada na construção de instâncias de dois problemas distintos. Os problemas considerados são o Steiner TSP, o Problema do Passeio com Coleta de Prêmios e o Problema da Floresta Restrita. Generalizamos cada um desses problemas considerando múltiplas funções de distância e, para cada um deles, apresentamos um algoritmo de aproximação com fator O(logn), onde n é o número de vértices (cidades). Essas aproximações são assintoticamente ótimas, já que não há algoritmos com fator o(log n), a não ser que P = NPAbstract: In this dissertation, we study some generalizations of classical routing and connectivity problems whose instances are composed of a complete graph and multiple distance functions. As an example, there is the Traveling Car Renter Problem (CaRS) in which a traveler wants to visit a set of cities by renting one or more available cars. Each car is associated to a distance function and a service fee to return to the rental location. CaRS is a generalization of the Traveling Salesman Problem (TSP). We deal with these problems using approximation algorithms which are efficient algorithms that produce solutions with quality guarantee. In this work, two approaches are presented, one based on a linear reduction that preserves the approximation factor and the other based on the construction of instances of two distinct problems. The studied problems are the Steiner TSP, the Profitable Tour Problem, and the Constrained Forest Problem. We generalize these problems by considering multiple distance functions and, for each of them, we present an O(log n)-approximation algorithm, where n is the number of vertices (cities). The factor is asymptotically optimal, since there is no approximation algorithm with factor o(log n) unless P = NPMestradoCiência da ComputaçãoMestra em Ciência da Computação001CAPE

REMIND2.1: transformation and innovation dynamics of the energy-economic system within climate and sustainability limits

This paper presents the new and now open-source version 2.1 of the REgional Model of INvestments and Development (REMIND). REMIND, as an integrated assessment model (IAM), provides an integrated view of the global energy–economy–emissions system and explores self-consistent transformation pathways. It describes a broad range of possible futures and their relation to technical and socio-economic developments as well as policy choices. REMIND is a multiregional model incorporating the economy and a detailed representation of the energy sector implemented in the General Algebraic Modeling System (GAMS). It uses non-linear optimization to derive welfare-optimal regional transformation pathways of the energy-economic system subject to climate and sustainability constraints for the time horizon from 2005 to 2100. The resulting solution corresponds to the decentralized market outcome under the assumptions of perfect foresight of agents and internalization of external effects. REMIND enables the analyses of technology options and policy approaches for climate change mitigation with particular strength in representing the scale-up of new technologies, including renewables and their integration in power markets. The REMIND code is organized into modules that gather code relevant for specific topics. Interaction between different modules is made explicit via clearly defined sets of input and output variables. Each module can be represented by different realizations, enabling flexible configuration and extension. The spatial resolution of REMIND is flexible and depends on the resolution of the input data. Thus, the framework can be used for a variety of applications in a customized form, balancing requirements for detail and overall runtime and complexity

Impact of land tenure arrangements, Bt cotton adoption and market participation on welfare of farm households in rural Pakistan

Pakistan is the fourth largest cotton producing country. Cotton and cotton products contribute about 3.2% to GDP and 60-65 % to foreign exchange earnings of the country. In this dissertation three important aspects of cotton production and marketing are focused, i.e. adoption and impact of Bt cotton, land rights’ influence on farmers’ decision to invest in land improvement measures and efficiency level, and cotton farmers’ market participation. Cross sectional data was collected from 325 cotton farmers in Pakistan during 2007. The Propensity score matching approach was employed to estimate the adoption and impact of Bt cotton technology. The empirical results indicate that Bt cotton adopter farmers were getting 50-60 kgs per acre higher yields, household income was higher in the range of Rupees 16500-17000, while the demand for pesticide was less in the range of 0.62-0.68 liters. The probability of adopters being poor was found to be lower by 13-14%. The land rights results indicate that owner cultivated lands exhibit the higher levels of technical, allocative and economic efficiency compared to fixed-renters and sharecroppers. The net returns are positive and significant for the farmers selling at market compared to farmers selling at farm gate. From the empirical results it can be concluded that targeting the small scale farmers with Bt cotton technology can help them a way out of poverty, as well as land reforms in favour of tenants and small scale farmers can help them increase their efficiency level. Similarly, regarding farmers’ market participation, small-scale farmers can be linked to the markets by investing in human capital, improving the village infrastructure and readdressing the formal credit programme

Plasma Ignition in Underwater Gas Bubbles.

The ignition of plasma in underwater gas bubbles is a promising method of injecting chemically reactive species into liquids for applications in environmental remediation. To date, these studies have been limited to bubbles attached to the surface of the electrode. This dissertation proposes that plasma can be ignited in bubbles that are separated from the electrode by first deforming the shape of the bubble's dielectric boundary. This approach exploits a phenomenon termed the shape effect, in which the distortion of the dielectric boundary distorts and enhances the applied electric field in the volume of the bubble. The purpose of this dissertation was two-fold: (1) to demonstrate the shape effect by exciting strong deformations in underwater bubbles, and (2) investigate the fundamental mechanisms responsible for plasma formation in isolated bubbles. To accomplish this goal, an experimental apparatus was developed, capable of confining the bubble, deforming the shape of the bubble, and igniting plasma within the bubble interior. The apparatus utilizes ultrasonic acoustic standing waves to trap the bubble at a fixed position underwater and apply electric fields using electrodes that are mounted on a 3D translation stage. In general, it was observed that electric fields in the range 10-25 kV/cm were capable of exciting bubbles into a wide variety of nonlinear deformations, including resonant capillary waves on the bubble surface, spherical harmonic perturbations, and in some cases the complete breakup of the bubble into multiple fragments. Simulations of the electric field in these deformed bubbles indicate that the enhancement of the applied field could be as large as a factor of 10-50. A thorough investigation of fundamental discharge mechanisms in bubble filled liquids was also undertaken. It was shown that in a specific range of voltage and electrode geometry, a new type of streamer is observed that travels through the both liquid and the bubble gas. Under careful adjustment of the operating conditions, the plasma could actually be confined to the bubble when driven by a 12 kV pulse. It was further observed that this isolated bubble plasma could be ignited much easier using a repetitively pulsed voltage source.PHDNuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99808/1/bsso_1.pd

Evaluating urban services using economic valuation techniques :towards better urban environmental quality and promotion of sustainable development

PhD ThesisThis PhD thesis examines and evaluates the importance of urban services in environmental quality using economic evaluation techniques. It is a consensus that one of the features of countries that are under development is the rapid growth of urbanization. Rapid urbanization is followed by an intense demand for qualitative and quantitative development in physical dimensions and urban systems. An efficient urban management system is required to tackle and solve the problems of urbanization, using appropriate policies, methods and data to ensure that not only has the urban population got access to the labour market, housing and urban services, but also urban environments are organized to enhance the quality of life for its citizens. Consequently, this research seeks to assess and define a method to help local authorities and policy makers in affective decision making and efficient city management. Thus, the main objective of this thesis is to establish a non-market benefits valuation models for use in current and future policy applications with the aim of better built environment quality and promoting sustainable development. This research shows that allocating appropriate urban services plays a key role in promoting urban environmental quality, and fostering essential amenities such as comfort, safety, aesthetic, attractiveness etc. to citizens. Distribution and accessibility of urban services plays an important role in people’s movements, forming the city size, shape, and density, and importantly living quality in the city. This research reveals how economic valuation techniques can be used to define the market and the value of the urban services and assesses public preferences by determining willingness to pay for better access to preferred urban services. By employing the perspective of welfare economics to identify the structure of public preferences, including preference differences between socioeconomic groups, this study provides valuable information which should help to inform public policy deliberations over city management and land use planning objectives of promoting sustainable development and increasing quality of life and environment

Proceedings of the inaugural construction management and economics ‘Past, Present and Future’ conference CME25, 16-18 July 2007, University of Reading, UK

This conference was an unusual and interesting event. Celebrating 25 years of Construction Management and Economics provides us with an opportunity to reflect on the research that has been reported over the years, to consider where we are now, and to think about the future of academic research in this area. Hence the sub-title of this conference: “past, present and future”. Looking through these papers, some things are clear. First, the range of topics considered interesting has expanded hugely since the journal was first published. Second, the research methods are also more diverse. Third, the involvement of wider groups of stakeholder is evident. There is a danger that this might lead to dilution of the field. But my instinct has always been to argue against the notion that Construction Management and Economics represents a discipline, as such. Granted, there are plenty of university departments around the world that would justify the idea of a discipline. But the vast majority of academic departments who contribute to the life of this journal carry different names to this. Indeed, the range and breadth of methodological approaches to the research reported in Construction Management and Economics indicates that there are several different academic disciplines being brought to bear on the construction sector. Some papers are based on economics, some on psychology and others on operational research, sociology, law, statistics, information technology, and so on. This is why I maintain that construction management is not an academic discipline, but a field of study to which a range of academic disciplines are applied. This may be why it is so interesting to be involved in this journal. The problems to which the papers are applied develop and grow. But the broad topics of the earliest papers in the journal are still relevant today. What has changed a lot is our interpretation of the problems that confront the construction sector all over the world, and the methodological approaches to resolving them. There is a constant difficulty in dealing with topics as inherently practical as these. While the demands of the academic world are driven by the need for the rigorous application of sound methods, the demands of the practical world are quite different. It can be difficult to meet the needs of both sets of stakeholders at the same time. However, increasing numbers of postgraduate courses in our area result in larger numbers of practitioners with a deeper appreciation of what research is all about, and how to interpret and apply the lessons from research. It also seems that there are contributions coming not just from construction-related university departments, but also from departments with identifiable methodological traditions of their own. I like to think that our authors can publish in journals beyond the construction-related areas, to disseminate their theoretical insights into other disciplines, and to contribute to the strength of this journal by citing our articles in more mono-disciplinary journals. This would contribute to the future of the journal in a very strong and developmental way. The greatest danger we face is in excessive self-citation, i.e. referring only to sources within the CM&E literature or, worse, referring only to other articles in the same journal. The only way to ensure a strong and influential position for journals and university departments like ours is to be sure that our work is informing other academic disciplines. This is what I would see as the future, our logical next step. If, as a community of researchers, we are not producing papers that challenge and inform the fundamentals of research methods and analytical processes, then no matter how practically relevant our output is to the industry, it will remain derivative and secondary, based on the methodological insights of others. The balancing act between methodological rigour and practical relevance is a difficult one, but not, of course, a balance that has to be struck in every single paper