699,964 research outputs found

    Procurement in infrastructure : what does theory tell us ?

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    Infrastructure has particular challenges in public procurement, because it is highly complex and customized and often requires economic, political and social considerations from a long time horizon. To deliver public infrastructure services to citizens or taxpayers, there are a series of decisions that governments have to make. The paper provides a minimum package of important economic theories that could guide governments to wise decision-making at each stage. Theory suggests that in general it would be a good option to contract out infrastructure to the private sector under high-powered incentive mechanisms, such as fixed-price contracts. However, this holds under certain conditions. Theory also shows that ownership should be aligned with the ultimate responsibility for or objective of infrastructure provision. Public and private ownership have different advantages and can deal with different problems. It is also shown that it would be a better option to integrate more than one public task (for example, investment and operation) into the same ownership, whether public or private, if they exhibit positive externalities.Public Sector Economics&Finance,Debt Markets,Infrastructure Economics,Contract Law,Transport Economics Policy&Planning

    A Scalable Algorithm For Sparse Portfolio Selection

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    The sparse portfolio selection problem is one of the most famous and frequently-studied problems in the optimization and financial economics literatures. In a universe of risky assets, the goal is to construct a portfolio with maximal expected return and minimum variance, subject to an upper bound on the number of positions, linear inequalities and minimum investment constraints. Existing certifiably optimal approaches to this problem do not converge within a practical amount of time at real world problem sizes with more than 400 securities. In this paper, we propose a more scalable approach. By imposing a ridge regularization term, we reformulate the problem as a convex binary optimization problem, which is solvable via an efficient outer-approximation procedure. We propose various techniques for improving the performance of the procedure, including a heuristic which supplies high-quality warm-starts, a preprocessing technique for decreasing the gap at the root node, and an analytic technique for strengthening our cuts. We also study the problem's Boolean relaxation, establish that it is second-order-cone representable, and supply a sufficient condition for its tightness. In numerical experiments, we establish that the outer-approximation procedure gives rise to dramatic speedups for sparse portfolio selection problems.Comment: Submitted to INFORMS Journal on Computin

    Designing direct subsidies for water and sanitation services - Panama : a case study

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    As an alternative to traditional subsidy schemes in utility sectors, direct subsidy programs have several advantages: they are transparent, they are explicit, and they minimize distortions of the behavior of both the utility, and the customers. At the same time, defining practical eligibility criteria for direct subsidy schemes is difficult, and identifying eligible households may entail substantial administrative costs. The authors, using a case study from Panama, discuss some of the issues associated with the design of direct subsidy systems for water services. The conclude that: 1) There is a need to assess - rather than assume - the need for a subsidy. A key test of affordability, and thus of the need for a subsidy, is to compare the cost of the service, with some measure of household willingness to pay. 2) The initial assessment must consider the affordability of connection costs as well as the affordability of the service itself. Connection costs may be prohibitive for poor households with no credit, suggesting a need to focus subsidies on providing access, rather than ongoing water consumption. 3) A key issue in designing a direct subsidy scheme is its targeting properties. Poverty is a complex phenomenon, and difficult to measure. Eligibility must therefore be based on easily measurable proxy variables, and good proxies are hard to find. In choosing eligibility criteria for a subsidy, it is essential to verify what proportion of the target group fails to meet the criteria (errors of exclusion) and what proportion of non-target groups is inadvertently eligible for the benefits (errors of inclusion). 4) administrative costs are roughly the same no matter what the level of individual subsidies, so a scheme that pays beneficiaries very little, will tend not to be cost-effective. It is important to determine what proportion of total program costs will be absorbed by administrative expenses. 5) Subsidies should not cover the full cost of the service, and should be contingent on beneficiaries paying their share of the bill. Subsidiesfor consumption above a minimum subsistence level, should be avoided. Subsidies should be provided long enough before eligibility is reassessed to avoid"poverty trap"problems. 6) The utility or concessionaire can be helpful in identifying eligible candidates, because of its superior information on the payment histories of customers. It will also have an incentive to do so, since it has an interest in improving poor payment records. Thought should therefore be given at the design stage to the role of the service provider in the implementation of the subsidy scheme. 7) The administrative agency's responsibilities, the sources of funding, and the general principles guiding the subsidy system should have a clear legal basis, backed by regulations governing administrative procedures. 8) To reduce administrative costs, and avoid duplication of effort, it would be desirable for a single set of institutional arrangements to be used to determine eligibility for all welfare, and subsidy programs in a given jurisdiction, whether sub-national, or national.Sanitation and Sewerage,Environmental Economics&Policies,Health Economics&Finance,Public Health Promotion,Economic Theory&Research,Town Water Supply and Sanitation,Environmental Economics&Policies,Health Economics&Finance,Poverty Assessment,Water Supply and Sanitation Governance and Institutions

    Planning and Control Concepts for Material Handling Systems

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    Iris Vis was born in 1974 in Leidschendam. May 2002 - Assistant professor at the School of Economics and Business Administration, Vrije Universiteit Amsterdam 1999, Visiting scholar at Georgia Institute of Technology, School of Industrial and Systems Engineering, october - december September 1997 - May 2002, Ph.D. candidate at the Rotterdam School of Management/Faculteit Bedrijfskunde, Erasmus University Rotterdam Research Areas logistics, material handling systems, cross-docking centres, number of vehicles, scheduling, storage and retrieval, container terminalsThe purpose of this research is the development of new concepts for different planning and control problems within material handling centres, like warehouses and container terminals. Problems discussed, are, for example: (i) the determination of the number of vehicles required to transport all loads in time (ii) scheduling of storage and retrieval requests. Techniques from Operations Research are used to model and solve above mentioned problems. Firstly, a polynomial time algorithm (minimum flow algorithm) is developed to solve the problem of the determination of the minimum number of vehicles to transport all loads at known time instants. An extension of this problem is the determination of the minimum number of vehicles required if every job has a time window. In this case, a release time and a due time are given for every job. This problem can be formulated as an integer linear programming model and a set partitioning model. A dynamic programming model is developed to solve the scheduling of retrieval and storage requests for a storage and retrieval machine working in multiple parallel aisles. All developed methods will be applied within a semi-automated container terminal. For the internal transportation of containers from ship to stack (storage) and vice versa and for inter terminal transport Automated Guided Vehicles (AGVs) will be used. Also stacking will be done in an automatic way by Automated Stacking Cranes (ASCs). Simulation studies are performed to test the methods developed

    Estimation And Inference For Convex Functions And Computational Efficiency In High Dimensional Statistics

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    Optimization and statistics are intrinsically intertwined with each other. Optimization has been the ends of some statistical problems, like estimation and inference for the minimizer and the minimum of convex functions, and the means for other statistical problems, like computational concerns in high dimensional statistics. In this dissertation, we consider both optimization-related problems.Estimation and inference for the minimizer and minimum of convex functions have been longstanding problems with wide application in economics and health care. But existing approaches are insufficient due to their asymptotic nature and/or incapability of characterizing function-specific difficulty. We investigate the problems under non-asymptotic frameworks that characterize function-specific difficulty and propose adaptive computational-efficient optimal methods. The first two parts of the dissertation address these problems, briefly summarized as follows. • The first part focuses on univariate convex functions. We develop computationally efficient adaptive optimal procedures under local minimax framework and discover a novel Uncertainty Principle that provides a fundamental limit on how well the minimizer and minimum can be estimated simultaneously for any convex regression function. • The second part focuses on multivariate additive convex functions. Under function-specific benchmarks, we propose computationally efficient optimal methods and establish their optimality. Computational efficiency is another optimization-related problem of increasingly importance in statistics, especially in the AI age where the scale of data is big and the requirement on computational time is high. To achieve the balance between running time and statistical accuracy, we propose a framework that provides theoretically guaranteed optimization methods together with the analysis of interplay between running time and statistical accuracy for a class of high-dimensional problems in the third part of the dissertation. Our framework consists of three parts, statistical-optimization interplay analysis, which characterizes optimization induced statistical error in a more essential way, optimization template algorithm, and optimization convergence analysis. We showcase the power of our framework through three example problems, where we get novel results for the first two and show that our framework adapts to the degenerate case through the third example

    How labour organization may affect technology adoption: an analytical framework analysing the case of integrated pest management

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    Integrated Pest Management (IPM) is an important component of sustainable agriculture. Farmers who switch from a more capital-intensive pesticide-based pest management strategy to IPM have to substitute capital with labour. The adoption of IPM will therefore depend, among other things, on the opportunity costs of labour. A simple model analyses the trade-off between IPM and current farmers' best practice in developing countries. Modifications of the model include different forms of labour organization in pest management, such as owner operated and short- and long-term labour contracts. The implications are that agricultural policies, environmental policies, and labour market policies can go hand in hand. Unfortunately, this will be more likely at a higher level of original pesticide use and hence a higher level of environmental costs

    Tunnel/Predictor Display for Trajectory Control in Hypersonic Flight

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    A tunnel/predictor display which presents guidance information in a 3-dimensional format is considered for improving trajectory control in hypersonic flight. The displayed 3-dimensional information comprises a tunnel image and a predictor for indicating the aircraft position at a specified time ahead. The 3-dimensional guidance information is introduced to support the pilot in controlling the flight path. It is considered that piloting problems can be avoided which exist with conventional trajectory control techniques due to path-attitude decoupling. A predictor control law is constructed which yields controlled element properties (predictor-aircraft system) requiring minimum pilot compensation. This predictor control law forms the basis of the trajectory control improvement goal. Results from hypersonic flight simulation tests at the NASA Dryden Flight Research Center are presented for experimental verification. This paper is an outcome of a joint research effort of the NASA Dryden Flight Research Center, and the Institute of Flight Mechanics and Flight Control of the Technische Universität München and the Department of Aeronautics, Naval Architecture and Railway Vehicles (former Department of Aircraft and Ships at the Budapest University of Technology and Economics

    The Effects of Mandating Benefits Packages

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    [Excerpt] The purpose of this paper is to inform policymakers and the public about the potential labor market consequences of government mandating of employee benefits. Both theoretical and empirical economic arguments for and against benefit mandating are presented and assessed. In view of the continuing policy debate over health care and parental leave, these two areas are the focus of special attention in the discussion below
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