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Optimal Strategy (optimal + strategy)
Selected AbstractsOptimal Strategy of Selective Cerebral Perfusion During Aortic Arch ConstructionARTIFICIAL ORGANS, Issue 7 2010Bingyang Ji MD No abstract is available for this article. [source] To breathe or not to breathe: optimal strategies for finding prey in a dark, three-dimensional environmentJOURNAL OF ANIMAL ECOLOGY, Issue 5 2008MARK HINDELL The use of sophisticated telemetry logging devices has revealed that short-finned pilot whales employ energetic sprints to chase down their deep-dwelling prey. These sprints are costly in terms of energy, and therefore oxygen, which is a valuable resource for an animal that has to hold its breath while hunting. This finding highlights the challenges faced by ecologists when trying to develop foraging models for marine predators because many of the key parameters, such as movements in three dimensions, marine prey fields and metabolic adaptations of diving animals, remain largely unknown. [source] The Buyer's Option in Multi-Unit Ascending Auctions: The Case of Wine Auctions at DrouotJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 4 2005Philippe Février This paper studies multi-unit ascending (English) auctions with a buyer's option. The buyer's option gives the winner of an auction the right to purchase any number of units at the winning price. We develop a theoretical model and derive the optimal strategies for the bidders. The model predicts various behavioral implications (e.g., the winner never exercises the option, the price declines,) that are tested using a unique data set on wine auctions held at the Paris-based auction house Drouot. We also analyze why the buyer's option is used. Estimating the model in a structural econometric way, and using counterfactual comparisons, we find that the buyer's option does not affect the seller's revenue (relative to a system where the units are auctioned sequentially without the option). Drouot, however, saves a lot of time with the option and this effect represents a considerable amount of money. The time-saving effect seems thus to be the primary purpose of the buyer's option. [source] SOLVING DYNAMIC WILDLIFE RESOURCE OPTIMIZATION PROBLEMS USING REINFORCEMENT LEARNINGNATURAL RESOURCE MODELING, Issue 1 2005CHRISTOPHER J. FONNESBECK ABSTRACT. An important technical component of natural resource management, particularly in an adaptive management context, is optimization. This is used to select the most appropriate management strategy, given a model of the system and all relevant available information. For dynamic resource systems, dynamic programming has been the de facto standard for deriving optimal state-specific management strategies. Though effective for small-dimension problems, dynamic programming is incapable of providing solutions to larger problems, even with modern microcomputing technology. Reinforcement learning is an alternative, related procedure for deriving optimal management strategies, based on stochastic approximation. It is an iterative process that improves estimates of the value of state-specific actions based in interactions with a system, or model thereof. Applications of reinforcement learning in the field of artificial intelligence have illustrated its ability to yield near-optimal strategies for very complex model systems, highlighting the potential utility of this method for ecological and natural resource management problems, which tend to be of high dimension. I describe the concept of reinforcement learning and its approach of estimating optimal strategies by temporal difference learning. I then illustrate the application of this method using a simple, well-known case study of Anderson [1975], and compare the reinforcement learning results with those of dynamic programming. Though a globally-optimal strategy is not discovered, it performs very well relative to the dynamic programming strategy, based on simulated cumulative objective return. I suggest that reinforcement learning be applied to relatively complex problems where an approximate solution to a realistic model is preferable to an exact answer to an oversimplified model. [source] Rendez-vous search on a rectangular latticeNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2007William H. Ruckle Abstract In a rendez-vous search two or more teams called seekers try to minimize the time needed to find each other. In this paper, we consider s seekers in a rectangular lattice of locations where each knows the configuration of the lattice, the distribution of the seekers at time 0, and its own location, but not the location of any other. We measure time discretely, in turns. A meeting takes place when the two seekers reach the same point or adjacent points. The main result is that for any dimension of lattice, any initial distribution of seekers there are optimal strategies for the seekers that converge (in a way we shall make clear) to a center. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007 [source] A search game on a cyclic graphNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2004Kensaku Kikuta Abstract There is a finite cyclic graph. The hider chooses one of all nodes except the specified one, and he hides an (immobile) object there. At the beginning the seeker is at the specified node. After the seeker chooses an ordering of the nodes except the specified one, he examines each nodes in that order until he finds the object, traveling along edges. It costs an amount when he moves from a node to an adjacent one and also when he checks a node. While the hider wishes to maximize the sum of the traveling costs and the examination costs which are required to find the object, the seeker wishes to minimize it. The problem is modeled as a two-person zero-sum game. We solve the game when unit costs (traveling cost + examination cost) have geometrical relations depending on nodes. Then we give properties of optimal strategies of both players. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004. [source] Dynamic optimization and Skiba sets in economic examplesOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 5-6 2001Wolf-Jürgen Beyn Abstract We discuss two optimization problems from economics. The first is a model of optimal investment and the second is a model of resource management. In both cases the time horizon is infinite and the optimal control variables are continuous. Typically, in these optimal control problems multiple steady states and periodic orbits occur. This leads to multiple solutions of the state,costate system each of which relates to a locally optimal strategy but has its own limiting behaviour (stationary or periodic). Initial states that allow different optimal solutions with the same value of the objective function are called Skiba points. The set of Skiba points is of interest, because it provides thresholds for a global change of optimal strategies. We provide a systematic numerical method for calculating locally optimal solutions and Skiba points via boundary value problems. In parametric or higher dimensional systems Skiba curves (or manifolds) appear and we show how to follow them by a continuation process. We apply our method to the models above where Skiba sets consist of points or curves and where optimal solutions have different stationary or periodic asymptotic behaviour. Copyright © 2001 John Wiley & Sons, Ltd. [source] Influence of Drive Cycle Length on Initiation of Ventricular Fibrillation During Implantable Cardioverter Defibrillator Threshold TestingPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 9 2006NEIL K. SANGHVI Background: Programmed electrical stimulation of the heart as a method to induce tachyarrhythmias has been described since the 1960s. To date, no study has examined optimal drive cycle length in the induction of ventricular fibrillation (VF) during defibrillation threshold testing after implantable cardioverter-defibrillator placement. We hypothesized that longer drive cycle length, by means of the longer action potential duration, would promote intramyocardial phase 2 reentry and facilitate induction of VF. Methods: Fifty consecutive implants were randomized in a prospective crossover format for this study. The group consisted of 40 men and 10 women, with each patient receiving either a 400 or 600 ms initial drive train prior to 1.2 J internal shock on the T wave with a goal to induce ventricular fibrillation. The timing of the T wave shock was determined by measuring the interval from the beginning of the QRS to the apex of the T wave in lead II. Successful inductions were defibrillated via the cardioverter defibrillator. Patients were then crossed over and the protocol repeated. Results: Twenty of 23 (87%) patients were successfully induced into VF in the initial 400 ms drive train arm whereas 22 of 27 (81%) were successfully induced in the 600 ms arm. Thus, a total of 44 (88%) patients were successfully induced at 400 ms, 41 (82%) patients were successfully induced at 600 ms, and 2 (4%) patients were not inducible at either cycle length, but were inducible with 50 Hz ventricular stimulation. However, no significant difference was noted between the two groups. Conclusion: No investigation to date has questioned whether a relationship exists between drive cycle length and initiation of ventricular fibrillation. Our study addresses this question, though negative for difference between 400 and 600 ms drive trains. Further research into optimal strategies for inducing ventricular fibrillation will minimize patient sedation time and discomfort while undergoing defibrillator threshold testing. [source] Using a Discrete-event Simulation to Balance Ambulance Availability and Demand in Static Deployment SystemsACADEMIC EMERGENCY MEDICINE, Issue 12 2009Ching-Han Wu EMT-P Abstract Objectives:, To improve ambulance response time, matching ambulance availability with the emergency demand is crucial. To maintain the standard of 90% of response times within 9 minutes, the authors introduce a discrete-event simulation method to estimate the threshold for expanding the ambulance fleet when demand increases and to find the optimal dispatching strategies when provisional events create temporary decreases in ambulance availability. Methods:, The simulation model was developed with information from the literature. Although the development was theoretical, the model was validated on the emergency medical services (EMS) system of Tainan City. The data are divided: one part is for model development, and the other for validation. For increasing demand, the effect was modeled on response time when call arrival rates increased. For temporary availability decreases, the authors simulated all possible alternatives of ambulance deployment in accordance with the number of out-of-routine-duty ambulances and the durations of three types of mass gatherings: marathon races (06:00,10:00 hr), rock concerts (18:00,22:00 hr), and New Year's Eve parties (20:00,01:00 hr). Results:, Statistical analysis confirmed that the model reasonably represented the actual Tainan EMS system. The response-time standard could not be reached when the incremental ratio of call arrivals exceeded 56%, which is the threshold for the Tainan EMS system to expand its ambulance fleet. When provisional events created temporary availability decreases, the Tainan EMS system could spare at most two ambulances from the standard configuration, except between 20:00 and 01:00, when it could spare three. The model also demonstrated that the current Tainan EMS has two excess ambulances that could be dropped. The authors suggest dispatching strategies to minimize the response times in routine daily emergencies. Conclusions:, Strategies of capacity management based on this model improved response times. The more ambulances that are out of routine duty, the better the performance of the optimal strategies that are based on this model. [source] Robustness of shortfall risk minimising strategies in the binomial modelPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Gino Favero In this paper we study the dependence on the loss function of the strategy which minimises the expected shortfall risk when dealing with a financial contingent claim in the particular situation of a binomial model. After having characterised the optimal strategies in the particular cases when the loss function is concave, linear or strictly convex, we analyse how optimal strategies change when we approximate a loss function with a sequence of suitable loss functions. [source] Valuation and optimal strategies of convertible bondsTHE JOURNAL OF FUTURES MARKETS, Issue 9 2006Szu-Lang Liao This article presents a contingent claim valuation of a callable convertible bond with the issuer's credit risk. The optimal call, voluntary conversion, and bankruptcy strategies are jointly determined by shareholders and bondholders to maximize the equity value and the bond value, respectively. This model not only incorporates tax benefits, bankruptcy costs, refunding costs, and a call notice period, but also takes account of the issuer's debt size and structure. The numerical results show that the predicted optimal call policies are generally consistent with recent empirical findings; therefore, calling convertible bonds too late or too early can be rational. © 2006 Wiley Periodicals, Inc. Jrl Fut Mark 26:895,922, 2006 [source] Phase-dependent and task-dependent modulation of stretch reflexes during rhythmical hand tasks in humansTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Ruiping Xia Phase-dependent and task-dependent modulation of reflexes has been extensively demonstrated in leg muscles during locomotory activity. In contrast, the modulation of reflex responses of hand muscles during rhythmic movement is poorly documented. The objective of this study was to determine whether comparable reflex modulation occurs in muscles controlling finger motions during rhythmic, fine-motor tasks akin to handwriting. Twelve healthy subjects performed two rhythmic tasks while reflexes were evoked by mechanical perturbations applied at various phases of each task. Electromyograms (EMGs) were recorded from four hand muscles, and reflexes were averaged during each task relative to the movement phase. Stretch reflexes in all four muscles were found to be modulated in amplitude with respect to the phase of the rhythmic tasks, and also to vary distinctly with the tasks being conducted. The extent and pattern of reflex modulation differed between muscles in the same task, and between tasks for the same muscle. Muscles with a primary role in each task showed a higher correlation between reflex response and background EMG than other muscles. The results suggest that the modulation patterns observed may reflect optimal strategies of central,peripheral interactions in controlling the performance of fine-motor tasks. As with comparable studies on locomotion, the phase-dependency of the stretch reflexes implies a dynamically fluctuating role of proprioceptive feedback in the control of the hand muscles. The clear task-dependency is also consistent with a dynamic interaction of sensory feedback and central programming, presumably adapted to facilitate the successful performance of the different fine-motor tasks. [source] An optimal investment and consumption model with stochastic returnsAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 1 2009Xikui Wang Abstract We consider a financial market consisting of a risky asset and a riskless one, with a constant or random investment horizon. The interest rate from the riskless asset is constant, but the relative return rate from the risky asset is stochastic with an unknown parameter in its distribution. Following the Bayesian approach, the optimal investment and consumption problem is formulated as a Markov decision process. We incorporate the concept of risk aversion into the model and characterize the optimal strategies for both the power and logarithmic utility functions with a constant relative risk aversion (CRRA). Numerical examples are provided that support the intuition that a higher proportion of investment should be allocated to the risky asset if the mean return rate on the risky asset is higher or the risky asset return rate is less volatile. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimal conservation planning for migratory animals: integrating demographic information across seasonsCONSERVATION LETTERS, Issue 3 2010Justin Sheehy Abstract Conservation strategies for migratory animals are typically based on ad-hoc or simple ranking methods and focus on a single period of the annual cycle. We use a density-dependent population model to examine one-time land purchase strategies for a migratory population with a breeding and wintering grounds. Under equal rates of habitat loss, we show that it is optimal to invest more, but never solely, in the habitat with the higher density dependence to habitat cost ratio. When there are two habitats that vary in quality within a season, the best strategy is to invest only in one habitat. Whether to purchase high- or low-quality habitat depends on the general life history of the species and the ratio of habitat quality to habitat cost. When carry-over effects are incorporated, it is almost always optimal to invest in high-quality habitat during the season that produces the carry-over effect. We apply this model to a threatened warbler population and show the optimal strategy is to purchase more breeding than wintering habitat despite the fact that breeding habitat is over ten times more expensive. Our model provides a framework for developing year-round conservation strategies for migratory animals and has important implications for long-term planning and management. [source] Offshore Remanufacturing with Variable Used Product ConditionDECISION SCIENCES, Issue 1 2010Michael R. Galbreth ABSTRACT We consider the acquisition and production decisions of a remanufacturer who acquires used products of variable condition and allocates remanufacturing activity to domestic and offshore facilities. The problem is formulated as a multicommodity network flow model with economies of scale and product obsolescence. We show that the remanufacturer's optimal strategy can be chosen from a finite set of simple policies in which each product is routed to a facility based on its condition. We then numerically investigate the impact of key parameters on optimal decisions regarding offshore remanufacturing. [source] Incomplete Adoption of a Superior InnovationECONOMICA, Issue 268 2000Harvey E. Lapan We consider a model in which an innovating monopolist of a technologically superior intermediate input must sell this product to final output producers. Prior research shows that, with complete information, the monopolist's optimal strategy will lead to complete adoption of this technologically superior innovation. In this article we show that, when the price of some competitively supplied input used in the final product market is endogenous and is altered by adoption of the innovation, then the optimal pricing strategy of the monopolist may lead to incomplete innovation. Thus, the standard result of complete adoption of the superior technology is partly attributable to the partial equilibrium nature of prior models. [source] From unambiguous quantum state discrimination to quantum state filteringFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2-3 2003J.A. Bergou Unambiguous discrimination among nonorthogonal but linearly independent quantum states is possible with a certain probability of success. Here, we consider a new variant of that problem. Instead of discriminating among all of the N different states, we now ask for less. We want to unambiguously assign the state to one of two complementary subsets of the set of N given non-orthogonal quantum states, each occurring with given a priori probabilities. We refer to the special case when one subset contains only one state and the other contains the remaining N -1 states as unambiguous quantum state filtering. We present an optimal analytical solution for the special case of N=3, and discuss the optimal strategy to unambiguously distinguish |,1, from the set {|,2,,|,3,}. For unambiguous filtering the subsets need not be linearly independent. We briefly discuss how to construct generalized interferometers (multiports) which provide a fully linear optical implementation of the optimal strategy. [source] Is central neck dissection necessary for the treatment of lateral cervical nodal recurrence of papillary thyroid carcinoma?HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 10 2007Jong-Lyel Roh MD Abstract Background: Although the pattern of cervical lymph node metastases from papillary thyroid carcinoma (PTC) has been described, little is known about the pattern of lateral cervical nodal recurrence. The aim of this study was to establish the optimal strategy for neck dissection in patients who underwent reoperation for lateral cervical recurrence of PTC. Methods: We reviewed the records of 22 patients who underwent neck dissection for lateral nodal recurrence of thyroid cancer between 2002 and 2004. Eight patients had thyroid remnants or recurrent tumors in the bed and 6 had undergone lateral neck dissection prior to referral. Patients underwent comprehensive dissection of the posterolateral and ipsilateral (n = 10) or bilateral (n = 12) central neck. The pattern of nodal recurrence and postoperative morbidity were analyzed. Results: All patients had lateral compartment involvement, 91% at mid-lower, 45% at upper, and 18% at posterior sites. Central nodes were involved in 86% of patients: 82% at ipsilateral paratracheal, 32% at pretracheal, 27% at superior mediastinal, and 2 patients at contralateral sites. Skip lateral recurrence with no positive central nodes was rarely observed (14%). Postoperative vocal cord palsy (n = 1) and hypoparathyroidism (n = 5) developed only in patients undergoing bilateral central compartment dissection. Conclusions: The inclusion of comprehensive ipsilateral central and lateral neck dissection in the reoperation for patients with lateral neck recurrence of PTC is an optimal surgical strategy. © 2007 Wiley Periodicals, Inc. Head Neck, 2007 [source] The Opportunistic Approach to DisinflationINTERNATIONAL FINANCE, Issue 1 2002Athanasios Orphanides This paper explores the theoretical foundations of a new approach to monetary policy. Proponents of this approach hold that, when inflation is moderate but still above the long-run objective, the central bank should not take deliberate anti-inflation action but, rather, should wait for exogenous circumstances , such as favourable supply shocks and unforeseen recessions , to deliver the desired reduction in inflation. While waiting for such circumstances to arise, the central bank should aggressively resist incipient increases in inflation. This strategy has come to be known as ,the opportunistic approach to disinflation'. We deduce policy maker preferences that rationalize the opportunistic approach as the optimal strategy for disinflation in the context of a model that is standard in other respects. The policy maker who is endowed with these preferences tends to focus on stabilizing output when inflation is low, but on fighting inflation when inflation is high. We contrast the opportunistic approach to a more conventional strategy derived from strictly quadratic preferences. [source] The Frequency of Financial Analysts' Forecast Revisions: Theory and Evidence about Determinants of Demand for Predisclosure InformationJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 7-8 2008Craig W. Holden Abstract:, A fundamental property of a financial market is its degree of price informativeness. A major determinant of price informativeness is predisclosure information collected by financial analysts and then privately disseminated to clients, who make the recommended trades. We develop a dynamic model of the analyst's optimal strategy of forecast revision frequency with endogenous analysts and endogenous traders. We then empirically test the model's predictions. We find that forecast revision frequency is positively associated with earnings variability, trading volume, and earnings response coefficients, and negatively associated with skewness of trading volume. Thus, we find strong empirical support for our dynamic model. [source] Ehealth: Market Potential and Business StrategiesJOURNAL OF COMPUTER-MEDIATED COMMUNICATION, Issue 4 2001Pamela Whitten Due to the economic and social priorities afforded health services in the United States, research on new delivery modalities such as the Internet is gaining in popularity. Claims of the Internet's potential range from a promise to revolutionize the fundamental way health care is delivered to a tool for empowering patients through enhanced interaction with providers (Rice, 2001). Even though a great amount of attention has been given to e-health activity, the preponderance of publications to date has focused on the Internet as a source of health information. However important this form of e-health is, this type of service simply does not face the same constraints that must be addressed by those actually delivering health care services or tightly regulated pharmaceutical products. In this paper, we examine e-health by focusing explicitly on the delivery of health care products and services. Our examination of e-health activity is guided by two broad research questions. First, we ask what the potential is for the development of online health care services by examining its potential in major health care service and product sectors. Second, based upon case studies of two online health service firms, we seek to understand the emerging strategies of firms that are attempting to enter the health care market with an entirely online approach. Our examination of current e-health trends, as well as our two case studies, demonstrates the tremendous potential for health-related commercial activity on the Internet. However, our examination of the barriers facing ehealth from the US health system also pointed out the almost insurmountable challenges. We therefore conclude that a "click and mortar" model may perhaps be the optimal strategy for e-health. [source] Peer-to-Peer File Sharing and the Market for Digital Information GoodsJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 2 2010Ramon Casadesus-Masanell We study competitive interaction between two alternative models of digital content distribution over the Internet: peer-to-peer (p2p) file sharing and centralized client,server distribution. We present microfoundations for a stylized model of p2p file sharing where all peers are endowed with standard preferences and show that the endogenous structure of the network is conducive to sharing by a significant number of peers, even if sharing is costlier than freeriding. We build on this model of p2p to analyze the optimal strategy of a profit-maximizing firm, such as Apple, that offers content available at positive prices. We characterize the size of the p2p network as a function of the firm's pricing strategy, and show that the firm may be better off setting high prices, allowing the network to survive, and that the p2p network may work more efficiently in the presence of the firm than in its absence. [source] Review article: infliximab therapy for inflammatory bowel disease , seven years onALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2006P. RUTGEERTS Summary Infliximab, the chimeric monoclonal IgG1 antibody to tumour necrosis factor, is indicated for refractory luminal and fistulizing Crohn's disease and extra-intestinal manifestations of inflammatory bowel disease. Recently, the active ulcerative colitis trials (ACT) studies have shown that infliximab is also efficacious to treat ulcerative colitis resistant to standard therapy. Induction with 5 mg/kg infliximab at weeks 0, 2 and 6 is advocated. The response to infliximab is improved when concomitant immunosuppressive therapy is given. As the majority of patients will relapse if not retreated, a long-term strategy is necessary. Although episodic therapy can be used, the optimal strategy is systematic maintenance treatment with 5 mg/kg intravenous (i.v.) every 8 weeks. Long-term maintenance therapy with infliximab results in a reduction of the rate of complications, hospitalizations and surgeries associated with Crohn's disease. Safety problems with the monoclonal antibody infliximab treatment mainly concern the formation of antibodies to infliximab, which may lead to infusion reactions, loss of response and serum sickness-like delayed infusion reactions. Latent tuberculosis needs to be screened for. The rate of other opportunistic infections is slightly increased mainly in patients treated concomitantly with immunosuppression. There is no evidence that malignancy rates in patients treated with antitumour necrosis factor strategies are increased. [source] THE COST OF ILLIQUIDITY AND ITS EFFECTS ON HEDGINGMATHEMATICAL FINANCE, Issue 4 2010L. C. G. Rogers Though liquidity is commonly believed to be a major effect in financial markets, there appears to be no consensus definition of what it is or how it is to be measured. In this paper, we understand liquidity as a nonlinear transaction cost incurred as a function of rate of change of portfolio. Using this definition, we obtain the optimal hedging policy for the hedging of a call option in a Black-Scholes model. This is a more challenging question than the more common studies of optimal strategy for liquidating an initial position, because our goal requires us to match a random final value. The solution we obtain reduces in the case of quadratic loss to the solution of three partial differential equations of Black-Scholes type, one of them nonlinear. [source] MODELING LIQUIDITY EFFECTS IN DISCRETE TIMEMATHEMATICAL FINANCE, Issue 1 2007Umut Çetin We study optimal portfolio choices for an agent with the aim of maximizing utility from terminal wealth within a market with liquidity costs. Under some mild conditions, we show the existence of optimal portfolios and that the marginal utility of the optimal terminal wealth serves as a change of measure to turn the marginal price process of the optimal strategy into a martingale. Finally, we illustrate our results numerically in a Cox,Ross,Rubinstein binomial model with liquidity costs and find the reservation ask prices for simple European put options. [source] Classical and Impulse Stochastic Control of the Exchange Rate Using Interest Rates and ReservesMATHEMATICAL FINANCE, Issue 2 2000Abel Cadenillas We consider the problem of a Central Bank that wants the exchange rate to be as close as possible to a given target, and in order to do that uses both the interest rate level and interventions in the foreign exchange market. We model this as a mixed classical-impulse stochastic control problem, and provide for the first time a solution to that kind of problem. We give examples of solutions that allow us to perform an interesting economic analysis of the optimal strategy of the Central Bank. [source] Anesthesia for free vascularized tissue transferMICROSURGERY, Issue 2 2009Natalia Hagau M.D., Ph.D. Anesthesia may be an important factor in maximizing the success of microsurgery by controlling the hemodynamics and the regional blood flow. The intraanesthetic basic goal is to maintain an optimal blood flow for the vascularized free flap by: increasing the circulatory blood flow, maintaining a normal body temperature to avoid peripheral vasoconstriction, reducing vasoconstriction resulted from pain, anxiety, hyperventilation, or some drugs, treating hypotension caused by extensive sympathetic block and low cardiac output. A hyperdynamic circulation can be obtained by hypervolemic or normovolemic hemodilution and by decrease of systemic vascular resistance. The importance of proper volume replacement has been widely accepted, but the optimal strategy is still open to debate. General anesthesia combined with various types of regional anesthesia is largely preferred for microvascular surgery. Maintenance of homeostasis through avoidance of hyperoxia, hypocapnia, and hypovolemia (all factors that can decrease cardiac output and induce local vasoconstriction) is a well-established perioperative goal. As the ischemia,reperfusion injury could occur, inhalatory anesthetics as sevoflurane (that attenuate the consequences of this process) seem to be the anesthetics of choice. © 2008 Wiley-Liss, Inc. Microsurgery, 2009. [source] Optimal search for a moving target with the option to waitNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2009János Flesch Abstract We investigate the problem in which an agent has to find an object that moves between two locations according to a discrete Markov process (Pollock, Operat Res 18 (1970) 883,903). At every period, the agent has three options: searching left, searching right, and waiting. We assume that waiting is costless whereas searching is costly. Moreover, when the agent searches the location that contains the object, he finds it with probability 1 (i.e. there is no overlooking). Waiting can be useful because it could induce a more favorable probability distribution over the two locations next period. We find an essentially unique (nearly) optimal strategy, and prove that it is characterized by two thresholds (as conjectured by Weber, J Appl Probab 23 (1986) 708,717). We show, moreover, that it can never be optimal to search the location with the lower probability of containing the object. The latter result is far from obvious and is in clear contrast with the example in Ross (1983) for the model without waiting. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 [source] The dynamic transshipment problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2001Yale T. Herer Abstract We investigate the strategy of transshipments in a dynamic deterministic demand environment over a finite planning horizon. This is the first time that transshipments are examined in a dynamic or deterministic setting. We consider a system of two locations which replenish their stock from a single supplier, and where transshipments between the locations are possible. Our model includes fixed (possibly joint) and variable replenishment costs, fixed and variable transshipment costs, as well as holding costs for each location and transshipment costs between locations. The problem is to determine how much to replenish and how much to transship each period; thus this work can be viewed as a synthesis of transshipment problems in a static stochastic setting and multilocation dynamic deterministic lot sizing problems. We provide interesting structural properties of optimal policies which enhance our understanding of the important issues which motivate transshipments and allow us to develop an efficient polynomial time algorithm for obtaining the optimal strategy. By exploring the reasons for using transshipments, we enable practitioners to envision the sources of savings from using this strategy and therefore motivate them to incorporate it into their replenishment strategies. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48:386,408, 2001 [source] Optimal foraging when predation risk increases with patch resources: an analysis of pollinators and ambush predatorsOIKOS, Issue 5 2010Emily I. Jones Pollinators and their predators share innate and learned preferences for high quality flowers. Consequently, pollinators are more likely to encounter predators when visiting the most rewarding flowers. I present a model of how different pollinator species can maximize lifetime resource gains depending on the density and distribution of predators, as well as their vulnerability to capture by predators. For pollinator species that are difficult for predators to capture, the optimal strategy is to visit the most rewarding flowers as long as predator density is low. At higher predator densities and for pollinators that are more vulnerable to predator capture, the lifetime resource gain from the most rewarding flowers declines and the optimal strategy depends on the predator distribution. In some cases, a wide range of floral rewards provides near-maximum lifetime resource gains, which may favor generalization if searching for flowers is costly. In other cases, a low flower reward level provides the maximum lifetime resource gain and so pollinators should specialize on less rewarding flowers. Thus, the model suggests that predators can have qualitatively different top-down effects on plant reproductive success depending on the pollinator species, the density of predators, and the distribution of predators across flower reward levels. [source] | |||||||||||||||||||||||||