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Preventive maintenance and upgrade system: Optimizing the whole performance system by components' replacement or rearrangement

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INTERNATIONAL JOURNAL OF PRODUCTION ECONOMICS 2008年第1期112卷 236-244页

作者： Rachaniotis, N. P. Pappis, C. P. Univ Piraeus Dept Ind Management Piraeus 18534 Greece

A decision-making model for reassembling different deteriorating subsystems and components of a complex system from used and new parts is proposed. The objective is to find the proper reassembly policies in a period of time so as to maximize the systems' overall performance values, under limited budget, and reassembly and compatibility constraints. Environmental gains are incurred from these policies, since the used components' life cycle, at least in some cases, is extended instead of ending by entering the waste stream. A stochastic dynamic programming approach is proposed, and an example in the case of personal computers is presented. (c) 2007 Elsevier B.V. All rights reserved.

关键词： reassembly benchmarking deteriorating components stochastic dynamic programming

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Optimal harvesting of stochastic spatial resources

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JOURNAL OF ENVIRONMENTAL ECONOMICS AND MANAGEMENT 2008年第1期56卷 1-18页

作者： Costello, Christopher Polasky, Stephen Donald Bren Sch Environm Sci & Management Dept Econ Santa Barbara CA 93117 USA Univ Minnesota Dept Appl Econ Minneapolis MN 55455 USA

We characterize the optimal harvest of a renewable resource in a generalized stochastic spatially explicit model. Despite the complexity of the model, we are able to obtain sharp analytical results. We find that the optimal harvest rule in general depends upon dispersal patterns of the resource across space, and only in special circumstances do we find a modified golden rule of growth that is independent of dispersal patterns. We also find that the optimal harvest rule may include closure of some areas to harvest, either on a temporary or permanent basis (biological reserves). Reserves alone cannot correct open access, but may, under sufficient spatial heterogeneity and connectivity, increase profits if appropriate harvest controls are in place outside of reserves. (C) 2008 Elsevier Inc. All rights reserved.

关键词： marine reserves spatial externalities stochastic dynamic programming renewable resources bioeconomic modeling

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Optimal management of molds in stored corn

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AGRICULTURAL SYSTEMS 2008年第3期98卷 220-227页

作者： Yigezu, Yigezu A. Alexander, Corinne E. Preckel, Paul V. Maier, D. E. Woloshuk, C. P. Mason, L. J. Lawrence, J. Moog, D. J. Purdue Univ Dept Agr Econ W Lafayette IN 47907 USA Kansas State Univ Dept Grain Sci & Ind Manhattan KS 66506 USA Purdue Univ Dept Bot & Plant Pathol W Lafayette IN 47907 USA Purdue Univ Dept Entomol W Lafayette IN USA Purdue Univ Dept Agr & Biol Engn W Lafayette IN 47907 USA

Long term storage of corn is becoming more common due to the recent increase in the demand for corn by ethanol plants. Infection of maize kernels by toxigenic fungi remains a challenging storage problem despite decades of research. Experts in storage management propose the use of a combination of preventive and monitoring-based responsive strategies in response to mold risks. In this paper, a stochastic dynamic programming model is solved to determine the expected profitability and optimal combination. timing, and intensity of the proposed mold management strategies using farmers' existing infrastructure. The results show that even with relatively high monitoring costs, maintaining high quality grain using a monitoring-based optimal mold management strategy costs less than the benefit it fetches. The current typical practice by Indiana farmers of aerating the grain until the end of December and doing nothing thereafter bears a high risk of economic losses if grain is to be stored until later during the summer. Generally, the optimal mold management strategy depends on monitoring the biophysical conditions of the grain and the time period under consideration. If the in-bin temperature is high and less than 5% of kernels are mold damaged, then aerating when the outside temperature is at least 3 degrees C less than the in-bin temperature and continuing to store the grain is the optimal strategy. (C) 2008 Elsevier Ltd. All rights reserved.

关键词： Mold management Stored corn Expected profitability Integrated pest management Monitoring Aeration stochastic dynamic programming

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The need for speed: informed land acquisitions for conservation in a dynamic property market

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ECOLOGY LETTERS 2008年第11期11卷 1169-1177页

作者： McDonald-Madden, Eve Bode, Michael Game, Edward T. Grantham, Hedley Possingham, Hugh P. Univ Queensland Ctr Appl Environm Decis Anal Sch Integrat Biol St Lucia Qld 4072 Australia Univ Melbourne Ctr Appl Environm Decis Anal Dept Bot Parkville Vic 3010 Australia

Land acquisition is a common approach to biodiversity conservation but is typically subject to property availability on the public market. Consequently, conservation plans are often unable to be implemented as intended. When properties come on the market, conservation agencies must make a choice: purchase immediately, often without a detailed knowledge of its biodiversity value;survey the parcel and accept the risk that it may be removed from the market during this process;or not purchase and hope a better parcel comes on the market at a later date. We describe both an optimal method, using stochastic dynamic programming, and a simple rule of thumb for making such decisions. The solutions to this problem illustrate how optimal conservation is necessarily dynamic and requires explicit consideration of both the time period allowed for implementation and the availability of properties.

关键词： Biodiversity conservation planning decision theory property market stochastic dynamic programming surveying threatened species

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A specialized inventory problem in banks: Optimizing retail sweeps

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PRODUCTION AND OPERATIONS MANAGEMENT 2008年第3期17卷 285-295页

作者： Nair, Suresh K. Anderson, Richard G. Univ Connecticut Sch Business Storrs CT 06269 USA Fed Reserve Bank St Louis St Louis MO 63102 USA

Deposits held at Federal Reserve Banks are an essential input to the business activity of most depository institutions in the United States. Managing these deposits is an important and complex inventory problem for two reasons. First, Federal Reserve regulations require that depository institutions hold certain amounts of such deposits at the Federal Reserve Banks to satisfy statutory reserve requirements against customers' transaction accounts (demand deposits and other checkable deposits). Second, some inventory of such deposits is essential for banks to operate one of their core lines of business: furnishing payment services to households and firms. Because the Federal Reserve does not pay interest on such deposits used to satisfy statutory reserve requirements, banks seek to minimize their inventory of such deposits. In 1994, the banking industry introduced a new inventory management tool for such deposits, the retail deposit sweep program, which avoids the statutory requirement by reclassifying transaction deposits as savings deposits. This is an interesting inventory problem for fungible items, where the conversion process is reversible. We examine two methods for operating such sweeps programs within the limits of Federal Reserve regulations, and we develop a stochastic dynamic programming model to implement one such method, the threshold method.

关键词： retail banking sweeps Regulation D required reserves stochastic dynamic programming

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Decision support program for long term production planning of hydro-power plants with major reservoirs

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UPB Scientific Bulletin, Series D: Mechanical Engineering 2008年第4期70卷 137-146页

作者： Popa, Radu Dragomirescu, Andrei Popa, Bogdan Faculty of Power Engineering University Politehnica Bucharest Romania

The paper presents a decision support program who takes into consideration the system which consists in the ten important reservoirs with the associated hydropower plants. This program enables the selection of the strategic operation policy for the next month, or for a certain number of oncoming months, depending on reservoirs levels at the beginning of the month, and on the average monthly anticipated affluent flows;it suggests the most suitable operation solution according to an optimization model of stochastic dynamic programming.

关键词： decision support program stochastic dynamic programming optimal hydropower reservoir operation

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MULTIPLE HYPOTHESIS TESTING AND THE DECLINING-POPULATION PARADIGM IN STELLER SEA LIONS

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ECOLOGICAL APPLICATIONS 2008年第8期18卷 1932-1955页

作者： Wolf, Nicholas Mangel, Marc MRAG Amer Santa Cruz CA 95062 USA Univ Calif Santa Cruz Ctr Stock Assessment Res Santa Cruz CA 95064 USA Univ Calif Santa Cruz Dept Appl Math & Stat Santa Cruz CA 95064 USA

We describe a novel spatially and temporally detailed approach for determining the cause or causes of a population decline, using the western Alaskan population of Steller sea lions (Eumetopias jubatus) as an example. Existing methods are mostly based on regression, which limits their utility when there are multiple hypotheses to consider and the data are sparse and noisy. Our likelihood-based approach is unbiased with regard to sample size, and its posterior probability landscape allows for the separate consideration of magnitude and certainty for multiple factors simultaneously. As applied to Steller sea lions, the approach uses a stochastic population model in which the vital rates (fecundity, pup survival, non-pup survival) at a particular rookery in each year are functions of one or more local conditions (total prey availability, species composition of available prey,fisheries activity, predation risk indices). Three vital rates and four scaling functions produce twelve nonexclusive hypotheses, of which we considered 10;we assumed a priori that fecundity would not be affected by fishery activities or predation. The likelihood of all the rookery- and year-specific census data was calculated by averaging across sample paths, using backward iteration and a beta-binomial structure for observation error. We computed the joint maximum likelihood estimates (MLE) of parameters associated with each hypothesis and constructed marginal likelihood curves to examine the support for each effect. We found strong support for a positive effect of total prey availability on pup recruitment, negative effects of prey species composition (pollock fraction) on fecundity and pup survival, and a positive effect of harbor seal density (our inverse proxy for predation risk) on non-pup survival. These results suggest a natural framework for adaptive management;for example, the areas around some of the rookeries could be designated as experimental zones where fishery quotas are contingent

关键词： aerial survey beta-binomial observation error declining-population paradigm Eumetopias jubatus killer whales multiple-hypothesis testing optimal foraging Steller sea lions stochastic dynamic programming walleye pollock

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Managing beyond the invader: manipulating disturbance of natives simplifies control efforts

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JOURNAL OF APPLIED ECOLOGY 2008年第4期45卷 1143-1151页

作者： Firn, Jennifer Rout, Tracy Possingham, Hugh P. Buckley, Yvonne M. Univ Queensland Sch Integrat Biol St Lucia Qld 4072 Australia Univ Melbourne Sch Bot Melbourne Vic 3010 Australia CSIRO Sustainable Ecosyst St Lucia Qld 4067 Australia

1. Invasive plants have negative impacts on ecosystems worldwide. Several ecological studies have identified disturbance as a causative mechanism of plant invasions. Changes to natural disturbances and/or newly imposed disturbances can favour an invader over native species especially those that are better adapted to prior conditions. 2. To link the disturbance ecology of invasives to their management, we investigated the benefit of incorporating actions that manipulate disturbance (natural or imposed) into control efforts. We developed a simple model that describes the dynamics of an invader whose establishment is preferentially favoured by disturbance. 3. The model includes the probability of disturbance differentially affecting sites occupied by natives and invaders. Invaded sites are disturbed by alternative control measures, which act to kill and/or remove above-ground biomass and reduce the seed bank. We couched the model in a decision theory tool, stochastic dynamic programming, and applied it to the management of Mimosa pigra, a pan-tropical invasive perennial shrub. 4. We found that targeting the above-ground biomass of the invader (current population) was optimal when the probability of disturbance of native sites and the invader seed bank size were low to moderate. When both the rate of disturbance of native sites and invader seed banks were high, the best measure was that with the highest probability of reducing the seed bank (future populations). This measure was optimal despite its trade-off of having the highest probability of reinvasion. 5. Synthesis and applications. Manipulation of disturbance regimes in both native and invaded sites can simplify control efforts. If there is a high probability that native vegetation will be disturbed, then management efforts should focus on future populations by attempting to reduce the size of the invader seed bank. This complicates control, as seed bank size is difficult to measure and reducing it requires intensi

关键词： integrated weed management Mimosa pigra stochastic dynamic programming seed bank dynamics weed control population dynamics decision-making seed dispersal

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Lazy Planning under Uncertainty by Optimizing Decisions on an Ensemble of Incomplete Disturbance Trees

Lazy Planning under Uncertainty by Optimizing Decisions on a...

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8th European Workshop on Reinforcement Learning

作者： Defourny, Boris Ernst, Damien Wehenkel, Louis Univ Liege Dept Elect Engn & Comp Sci B-4000 Liege Belgium

ISBN: (纸本)9783540897217

This paper addresses the problem of solving discrete-time optimal sequential decision making problems having a disturbance space W composed of a finite number of elements. In this context, the problem of finding from an initial state x(0) all optimal decision strategy can be stated as all optimization problem which aims at finding an optimal combination of decisions attached to the nodes of a disturbance tree modeling all possible sequences of disturbances w(0), w(1),..., W(T-1) C W(T) over the optimization horizon T. A significant drawback of this approach is that the resulting optimization problem has a search space which is the Cartesian product of O(vertical bar W vertical bar(T-1)) decision spaces U, which makes the approach computationally impractical as soon as the optimization horizon grows, even if W has just a handful of elements. To circumvent this difficulty, we propose to exploit an ensemble of randomly generated incomplete disturbance trees of controlled complexity, to solve. their induced optimization problems in parallel, and to combine their predictions at time t = 0 to obtain a (near-)optimal first-stage decision. Because this approach postpones the determination of the decisions for subsequent stages until additional information about the realization of the uncertain process becomes available, we. call it lazy. Simulations carried out on a robot corridor navigation problem show that even for small incomplete trees, this approach can lead to near-optimal decisions.

关键词： stochastic dynamic programming Ensemble methods

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A stochastic dynamic programming model with fuzzy storage states for reservoir operations

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ADVANCES IN WATER RESOURCES 2004年第11期27卷 1105-1110页

作者： Mousavi, SJ Mahdizadeh, K Afshar, A Univ Sci & Technol Dept Civil Engn Hydrostruct Res Ctr Tehran 16844 Iran Amirkabir Univ Technol Dept Civil Engn Tehran Iran

Application of stochastic dynamic programming (SDP) models to reservoir optimization calls for state variables discretization. Reservoir storage volume is an important variable whose discretization has a pronounced effect on the computational efforts. The error caused by storage volume discretization is examined by considering it as a fuzzy state variable. In this approach, the point-to-point transitions between storage volumes at the beginning and end of each period are replaced by transitions between storage intervals. This is achieved by using fuzzy arithmetic operations with fuzzy numbers. In this approach, instead of aggregating single-valued crisp numbers, the membership functions of fuzzy numbers are combined. Running a simulation model with optimal release policies derived from fuzzy and non-fuzzy SDP models shows that a fuzzy SDP with a coarse discretization scheme performs as well as a classical SDP having much finer discretized space. It is believed that this advantage in the fuzzy SDP model is due to the smooth transitions between storage intervals which benefit from soft boundaries. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： fuzzy set theory reservoir operations smooth transition stochastic dynamic programming

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