This thesis deals with the problem of locating emergency vehicles in an urban area. An optimization model is formulated that extends previous work by allowing stochastic travel times, unequal vehicle utilizations, and backup service. The heart of the model is a procedure similar to the Hypercube approximation model. Ten pair-wise interchange heuristics are developed and tested on 240 test problems. Demand and service time components of the test data have been generated using characteristics of the Tucson Emergency Medical System. Geographical components of the test data have been generated using actual city shapes as models. It is believed that these test problems are more indicative of actual emergency vehicle location problems than those previously presented in the literature.

I examine local bias in hedge fund portfolio selection, using Section 13-F original and confidential holding filings. Using Coval and Moskowitz (1999) measure, I find that local bias is present among U.S.-based hedge funds. The holdings of funds are on average 20-67 km closer to hedge funds than the market. I also find that size and leverage of a company serve as determinants of local bias, with the preference of hedge funds for smaller and more levered local companies. I suggest an alternative model for assessment of local bias that yields results further supporting the hypothesis of the existence of local bias among hedge funds. I do not find a positive effect of local bias on performance. Moreover, in some periods I find a strong negative effect of local bias both on raw and risk-adjusted returns. I argue that these findings suggest that the origins of local bias should not be looked for in information asymmetry, and rather may be attributed to perceived informational advantage, flight to familiarity, and some endogenous factors of hedge fund locality.

On April 27, 1802, I gave a shout of joy ... It was seven years ago I proposed to myself a problem which I have not been able to solve directly, but for which I had found by chance a solution, and I knew that it was correct, without being able to prove it. The matter often returned to my mind and I had sought twenty times unsuccessfully for this solution. For some days I had carried the idea about with me continually. At last, I do not know how, I found it, together with a large number of curious and new considerations concerning the theory of probability. Andre Marie Ampere. Facility location problems (or plant location problems) are general models that can be used when a set of clients has to be served by facilities. More precisely, we are given a set of potential facility locations and a set of clients. The optimization problem is to select a subset of the locations at which to place facilities and then to assign clients to theses facilities so as to minimize total cost. Most formulations considered in this thesis can be viewed as general models that can be applied to a wide range of context and practical situations. However, as this research has been partly initiated by the interest of the author in telecommunication network design we will introduce these models by considering problems in this particular area. In the context of telecommunication network design an application of discrete location theory is the optimization of access networks with concentrators. Typically, we have a number of terminal points that must be connected to a service point. An obvious solution is to use a dedicated link for each terminal (star network). However, it is clear that this solution can be very expensive when the number of terminals is large and when they are far from the service point. Access networks are often constructed by inserting concentrators between the terminals and the service point. Many terminals are connected to a facility which in turn is connected by a single link to the service point. The objective is to build a network that will provide the service at minimum cost. If no extra constraints are involved the mmimum cost network problem can be expressed as an uncapacitated facility location problem (UFL). If the number of terminals that can be connected to a concentrator is limited we obtain a so-called capacitated facility location problem (CFL). CFL can be extended to consider various types of concentrators with various capacities. This problem is the multi-capacitated facility location problem (MCFL). MCFL is a straightforward model for low speed packet switched data networks typical among which are networks connecting sellingpoint terminals to a database. For other networks, the problem may involve various traffic constraints. In chapter 1 we present those problems and compare solutions obtained by Lagrangian relaxation and simulated annealing algorithms. The architecture mentioned above can be extended with more than one hierarchical level of concentrator. Unfortunately, we pay for this cost saving through a decrease of reliability. Therefore, the number of levels is often limited to one or two. In chapter 2 we study an extension of UFL and CFL to two levels of concentrators. Obviously, the structure of a network changes according to the way requirements vary with time. In order to plan investments and to develop strategies, the evolution of a network has to be determined for several years ahead (typically four or five years). In this case the main questions to answer are: Where and when to establish concentrators and of what size? In chapter 3 we study this problem for the dynamic version of UFL. Now, with the network optimization problem, there naturally arises the problem of allocating the total minimum cost among customers fairly. Namely, we would like to allocate the cost in such a way that no subgroup of users would have incentive to withdraw and build their own network. The standard way to approach such a problem is by the means of cooperative game theory. In chapter 4 we study the core of location games derived from UFL and CFL, and in chapter 5 we propose methods to compute the nucleolus of these games.

No description available.

Spatial facility location problems (SFLPs) involve the placement of facilities in continuous demand regions. One approach to solving SFLPs is to aggregate demand into discrete points, and then solve the point-based model as a conventional facility location problem (FLP) according to a surrogate model. Solution performance is measured in terms of the percentage of continuous space actually covered in the original SFLP. In this dissertation I explore this approach and examine factors contributing to solution quality. Three error sources are discussed: point representation spacing, multiple possible solutions to the surrogate point-based model, and round-off errors induced by the computer representation of numbers. Some factors—including boundary region surrogate points and surrogate point location—were also found to make significant contributions to coverage errors. A surrogate error measure using a point-based surrogate model was derived to characterize relationships among spacing, facility coverage area, and spatial coverage error. Locating continuous space facilities with full coverage is important but challenging. Demand surrogate points were initially used as a continuous space for constructing the MIP model, and a point-based surrogate FLP was enhanced for extracting multiple solutions with additional constraints that were found to reduce coverage error. Next, a best initial solution was applied to a proposed heuristic algorithm to serve as an improvement procedure. Algorithm performance was evaluated and applied to a problem involving the location of emergency warning sirens in the city of Dublin, Ohio. The effectiveness of the proposed method for solving this and other facility location/network design problems was demonstrated by comparing the results with those reported in recently published papers.

Two lightning detectors, of the magnetic direction finder type, form part of a two station system for determining the position of lightning strikes. The detectors are on a baseline of approximately 600 m, and the ultimate aim of the system is to accurately detect and map lightning within a radius of 30 km. Although no real time capability is present, the archive data collected from each separate station is used to find the offset errors in the azimuthal orientation, as well as in time (using processes described in Appendix A). The relative offset errors are determined by shifting the time and azimuthal information for one station’s data and calculating the maximum possible matching records (within certain time and azimuth criteria) for each incremental shift. An analysis of the peaks in total matching records, when plotted against the relevant shift increments, is performed in order to obtain the values of the offset errors. Between the two individual stations, the relative offset in orientation is found to be 24.5 degrees, and in time to be 0.001305 days (112.75 seconds). The individual stations, as well as the triangulated data calculated from matching records, can also be calibrated using data from the South African Weather Service Lightning Detection Network (SAWSLDN). Individual station calibration indicated an offset of +6.4 degrees and 0.00575 days (496.8 seconds) for Station 1, with the offsets for Station 2 determined as +29.4 degrees and −0.000105 days (9.07 seconds). Comparison of triangulated data to SAWSLDN data yields unexpected results with regard to resultant shifts, which may point to an error or anomaly in the triangulation calculations. A detailed analysis of the storm data is contained in Appendix B of the dissertation.

Esse trabalho, pertencente à disciplina de Gestão de Operações, é um esforço no sentido de recortar a questão tributária da teoria sobre localização de centros de distribuição, e discutir esse tema sob a visão do ICMS, principal imposto brasileiro aplicado à distribuição de mercadorias. A questão tributária é um elemento usualmente citado como fator presente nas escolhas de localização de unidades produtivas e centros de distribuição. Entretanto, essa variável é ainda considerada como periférica, sendo pouco explorada em pesquisas acadêmicas relacionadas à literatura localizacional. Foram estabelecidos os objetivos de identificar a presença do ICMS nas escolhas por centros de distribuição e encontrar elementos que possam evidenciar afirmações sobre a influência desse imposto nas decisões de quatro empresas do setor de defensivos agrícolas. A metodologia empregada nesse trabalho foi a de estudo de casos múltiplos, baseado na observação e descrição de processos cronológicos de decisão reais, com o suporte de um roteiro de questões para a realização das entrevistas com os responsáveis pela gestão de distribuição A escolha do setor de defensivos deve-se à presença de fortes benefícios fiscais relativos ao ICMS, como isenção de pagamento para faturamento intra-estadual. A pesquisa conseguiu identificar a divisão dos fatores influenciadores da decisão em dois blocos, extra tributários e tributários, sendo os extra correspondentes aos fatores logísticos comumente estudados em pesquisas, como prazos de entrega, custos de transporte e armazenagem e os tributários ligados especificamente ao ICMS. Os resultados encontrados permitem dizer que o ICMS foi um fator presente em todos os processos de decisão, variando segundo as perspectivas financeiras relacionadas às perdas por créditos não aproveitados, implicações legais, vantagens competitivas de preços e custos de transações decorrentes de acordos especiais com clientes. A pesquisa aponta uma afirmação baseada em evidências encontradas nas quatro empresas estudadas de que qualquer decisão por centro de distribuição passa pela validação da área tributária. Além disso, comportamentos e aspectos técnicos semelhantes foram observados na organização e estrutura dos projetos para definir centros de distribuição. Outra importante conclusão é de que existe um grau de conhecimento e consciência comum sobre a influência desse imposto sobre as operações das empresas. Do ponto de vista acadêmico, a grande contribuição desse trabalho é a afirmação de que, dados os mecanismos de fomento, cobrança e compensações do ICMS, as empresas do setor de defensivos podem ter que adotar estratégias de localização que sobrepujam vantagens logísticas. E essa é, provavelmente, uma verdade para qualquer setor onde estejam presentes benefícios fiscais e alto valor agregado das mercadorias comercializadas. O aprofundamento sobre tais estratégias que as empresas devem adotar para lidar com o ICMS é a principal recomendação desse trabalho para futuros estudos acadêmicos. / This research, which belongs to the Operations Management subject, is an effort towards investigating the tax issue, inserted in the distribution centers location theory and discussing this theme under ICMS perspective, the main tax regarding goods circulation in Brazil. The tax issue is usually mentioned as one of the aspects to be considered when choosing the localization of manufacturing units and distribution centers. However, this topic is still considered less relevant than other logistics features and therefore is not deeply studied by academic researches related to location literature. There were established the objectives of identifying the presence of ICMS on the decisions concerning distributions centers localizations and finding elements that could be evidences of affirmations regarding its influence on the decisions in four companies of crop protection products. The methodology is a multiple cases study, based on observation and description of real and chronological decision processes, supported by a script of questions to interview the responsible ones for distribution functions. The choice of the crop protection business is due to the strong existence of tax benefits on this field concerning ICMS, such as payment exemption in case of intra state distribution. It was possible to identify two groups of factors, the logistics and the tax ones, being the logistics factors frequently studied as the freight, warehousing costs and lead times issues and the tax factor associated to the specific ICMS subject. The results found allow to state that ICMS was an important variable in all decision processes assuming four perspectives: financial, related to losses due to credits not consumed; legal implications, prices competitiveness advantage and transactions costs regarding special customer agreements. Based on evidences found in the four analyzed companies, this research confirms that any location decision has to be validated by the tax management. In addition, similar behavior and technical aspects were observed on the organization and structure of projects to define distribution centers. Other important conclusion is the common conscience shared among the four companies about the ICMS influence on their operations. From an academic perspective, the main contribution of this study is the affirmation that, given the foment, charging and compensations mechanisms of the ICMS, the companies from the crop protection business analyzed might have to adopt localization strategies that overcomes the logistical advantages. And this is, probably, truth to any sector whereas tax benefits and high value commercialized goods are present. The deep study about those strategies that companies have to adopt to deal with ICMS is the main recommendation of this essay for future academic researches.

Electrical transmission and distribution networks are prone to short circuit faults since they span over long distances to deliver the electrical power from generating units to where the energy is required. These faults are usually caused by vegetation growing underneath bare overhead conductors, large birds short circuiting the phases, mechanical failure of pin-type insulators or even insulation failure of cables due to wear and tear, resulting in creepage current. Short circuit faults are highly undesirable for distribution network companies since they cause interruption of supply, thus affecting the reliability of their network, leading to a loss of revenue for the companies. Therefore, accurate offline fault location is required to quickly tackle the repair of permanent faults on the system so as to improve system reliability. Moreover, it also provides a tool to identify weak spots on the system following transient fault events such that these future potential sources of system failure can be checked during preventive maintenance. With these aims in mind, a novel fault location technique has been developed to accurately determine the location of short circuit faults in a distribution network consisting of feeders and spurs, using only the phase currents measured at the outgoing end of the feeder in the substation. These phase currents are analysed using the Discrete Wavelet Transform to identify distinct features for each type of fault. To achieve better accuracy and success, the scheme firstly uses these distinct features to train an Artificial Neural Network based algorithm to identify the type of fault on the system. Another Artificial Neural Network based algorithm dedicated to this type of fault then identifies the location of the fault on the feeder or spur. Finally, a series of Artificial Neural Network based algorithms estimate the distance to the point of fault along the feeder or spur. The impact of wind farm connections consisting of doubly-fed induction generators and permanent magnet synchronous generators on the accuracy of the developed algorithms has also been investigated using detailed models of these wind turbine generator types in Simulink. The results obtained showed that the developed scheme allows the accurate location of the short circuit faults in an active distribution network. Further sensitivity tests such as the change in fault inception angle, fault impedance, line length, wind farm capacity, network configuration and white noise confirm the robustness of the novel fault location technique in active distribution networks.

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Includes bibliographies. / by Julia Marie Wondolleck. / M.C.P.

Our increased reliance on localization devices such as GPS navigation has led to an increased demand for localization solutions in all environments, including indoors. Indoor localization has received considerable attention in the last several years for a number of application areas including first responder localization to targeted advertising and social networking. The difficult multipath encountered indoors degrades the performance of RF based localization solutions and so far no optimal solution has been published. This dissertation presents an algorithm called Coherent Array Reconciliation Tomography (CART), which is a Direct Positioning Algorithm (DPA) that incorporates signal fusion to perform a simultaneous leading edge and position estimate for a superior localization solution in a high multipath environment. The CART algorithm produces position estimates that are near optimal in the sense that they achieve nearly the best theoretical accuracy possible using an Impulse Radio (IR) Ultra-Wideband (UWB) waveform. Several existing algorithms are compared to CART including a traditional two step Leading Edge Detection (LED) algorithm, Singular value Array Reconciliation Tomography (SART), and Transactional Array Reconciliation Tomography (TART) by simulation and experimentation. As shown under heavy simulated multipath conditions, where traditional LED produces a limited solution and the SART and TART algorithms fail, the CART algorithm produces a near statistically optimal solution. Finally, the CART algorithm was also successfully demonstrated experimentally in a laboratory environment by application to the fire fighter homing device that has been a part of the ongoing research at Worcester Polytechnic Institute (WPI).