perishable inventory theory a review this paper reviews the relevant literature on the problem of determining suitable ordering policies for both fixed life perishable inventory and inventory subject to continuous exponential decay we consider both deterministic and stochastic demand for single and multiple products both optimal and sub optimal order policies are discussed in addition a brief review of the application of these models to blood bank management is included the review concludes with a discussion of some of the interesting open research questions in the area

optimal supply diversification under general supply risks we analyze a planning model for a firm or public organization that needs to cover uncertain demand for a given item by procuring supplies from multiple sources the necessity to employ multiple suppliers arises from the fact that when an order is placed with any of the suppliers only a random fraction of the order size is usable the model considers a single demand season with a given demand distribution where all supplies need to be ordered simultaneously before the start of the season the suppliers differ from one another in terms of their yield distributions their procurement costs and capacity levels the planning model determines which of the potential suppliers are to be retained and what size order is to be placed with each we consider two versions of the planning model in the first the service constraint model scm the orders must be such that the available supply of usable units covers the random demand during the season with at least a given probability in the second version of the model the total cost model tcm the orders are determined so as to minimize the aggregate of procurement costs and end of the season inventory and shortage costs in the classical inventory model with a single fully reliable supplier these two models are known to be equivalent but the equivalency breaks down under multiple suppliers with unreliable yields for both the service constraint and total cost models we develop a highly efficient procedure that generates the optimal set of suppliers as well as the optimal orders to be assigned to each most importantly these procedures generate a variety of important qualitative insights for example regarding which sets of suppliers allow for a feasible solution both when they have ample supply and when they are capacitated and how various model parameters influence the selected set of suppliers the aggregate order size and the optimal cost values

optimality of myopic ordering policies for inventory model with stochastic supply this paper addresses a discrete time inventory model where the maximum amount of supply from which instantaneous replenishment orders can be made is a random variable optimal ordering policies are characterized as critical number policies with monotone increasing optimal critical values a sufficient condition is then presented for myopic ordering policies to be optimal

why don t poor countries catch up a cross national test of an institutional explanation early neoclassical analyses predicted that poor countries would grow faster than wealthy countries because of technological advances and diminishing returns to capital in the latter the reverse has occurred poor countries are falling back rather than catching up we suggest here that deficient institutions underlie this divergence employing various indicators of institutional quality including the rule of law the pervasiveness of corruption and the risk of expropriation and contract repudiation we show that the ability of poor countries to catch up is determined in large part by the institutional environment in which economic activity in these countries takes place jel o00 o10

optimal dynamic scheduling policy for a make to stock production system this paper considers the dynamic scheduling problem of a single server make to stock queue with two products for the case of poisson demands and exponential production times we show that it is optimal to produce the product with the larger b index when it is backordered if the production times are identically distributed the optimal policy can further be characterized by monotone switching curves we also prove that a base stock policy coupled with a switching curve is optimal for some initial inventory levels a simple linear switching rule for determining production priority is proposed and compared with other heuristic policies in a computational experiment

continuous review inventory models where random lead time depends on lot size and reserved capacity the processing time of large orders is in many industries longer than that of small orders this renders supply lead times in such settings to be increasing in the order size yet that pattern is not re ected in existing inventory control models especially those allowing for random lead times this work aims at rectifying the situation our setting is an order quantity reorder point model with backordering where the shortage penalty is incurred per unit per unit time the processing time of each unit is random the processing time of a lot is correlated with its size for the case where lead time is proportional to the lot size we obtain a closed form solution that is unlike the classical q r model where lead time is independent of lot size no iterations are required here we also analyze a case where the processing time exhibits economies of scale in the lot size finally we consider a situation where a customer can secure shorter processing times by reserving capacity at the supplier s manufacturing facility 2000 elsevier science b v all rights reserved

a periodic review production planning model with uncertain capacity and uncertain demand optimality of extended myopic policies increasing product complexity manufacturing environment complexity and an increased emphasis on product quality are all factors leading to uncertainties in production processes these uncertainties are in the form of unplanned machine maintenance varying production yields and rework among others in planning for production an adequate model must incorporate these uncertainties into the representation of the production process this paper treats the aggregate planning problem for a single product with random demand and random capacity in the single period problem random capacity does not affect the optimal policy but results in a unimodal nonconvex cost function in the multiple period and infinite horizon settings order up to policies that are dependent on the distribution of capacity are shown to be optimal in spite of a nonconvex cost in the infinite horizon setting an intuitive description of the situation leads to the notion of a class of extended myopic policies requiring the consideration o

the structure of periodic review policies in the presence of random yield this work provides a comprehensive analysis of a general periodic review production inventory model with random variable yield existence of an order point whose value does not depend on yield being random is proved in the single period case without specifying the yield model and using a very general cost structure when yield is a random multiple of lot size the nonorder up to optimal policy is characterized for a finite horizon model the finite horizon value functions are shown to converge to the solution of an infinite horizon functional equation and the infinite horizon order point is shown to be no smaller than when yield is certain

incorporating fuel constraints and electricity spot prices into the stochastic unit commitment problem the electric power industry is going through deregulation as a result the load on the generating units of a utility is becoming increasingly unpredictable furthermore electric utilities may need to buy power or sell their production to a power pool that serves as a spot market for electricity these trading activities expose utilities to volatile electricity prices in this paper we present a stochastic model for the unit commitment that incorporates power trading into the picture our model also accounts for fuel constraints and prices that may vary with electricity prices and demand the resulting model is a mixed integer program that is solved using lagrangian relaxation and bender s decomposition using this solution approach we solve problems with 729 demand scenarios on a single processor to within 0 1 of the optimal solution in less than 10 minutes our numerical results indicate that significant savings can be achieved when the spot market is entered into the problem and when stochastic policy is adopted instead of a deterministic one

a panel data analysis of the fungibility of foreign aid the donor community has been increasingly concerned that development assistance intended for crucial social and economic sectors might be used directly or indirectly to fund unproductive military and other expenditures the link between foreign aid and public spending is not straightforward because some aid may be fungible this article empirically examines the impact of foreign aid on the recipient s public expenditures using cross country samples of annual observations for 1971 90 for the base sample of 14 developing countries it finds that aid is not fungible at the aggregate level and there is no associated tax relief increasing the number of countries however makes aid fungible moreover results based on the main sample indicate that aid is fungible in three out of five sectors examined developing country governments receiving earmarked concessionary loans for agriculture education and energy reduce their own resources going to these sectors and use them elsewhere only loans to the transport and communication sector are fully spent on the purposes intended by donors because most aid appears to be fungible the rate of return on a specific donor funded project tells little about the impact of that assistance a better approach may be to tie foreign aid to an overall public expenditure program that provides adequate resources to crucial sectors

the political realities of african management abstract amidst the outburst of concern for public management in africa there is frequently a failure to distinguish among its components policy making leadership general internal administration and bureaucratic hygiene accounting procurement the merit system etc each of these four areas is different in the importance that it has for project performance the knowledge base that is available for improving it and the way in which it is affected by african political and social structures as a consequence those seeking to improve public management on the continent frequently are mistaken in the priorities that they establish and import inappropriate management technologies

determining the optimal size of supply base with the consideration of risks of supply disruptions abstract determining the optimal size of the supply base has haunted managers for years a small supply base gives rise to the risk of supply disruption whereas a large supply base increases the fixed cost in this paper we consider the risks of supply disruption due to occurrence of super semi super and unique events in order to formulate a model to determine the optimal size of supply base we depict the model in a decision tree like structure and forward a tabular method of solution that obviates the need avoids evaluation of a majority of non optimal solutions and thus overcomes the problem of dimensionality

integrated safety stock optimization for multiple sourced stockpoints facing variable demand and lead time abstract the safety stock placement problem of a multi stage supply chain comprising multiple sourced stockpoints is addressed in this paper each stockpoint faces variability in its downstream demand and suppliers lead time the maximum among these suppliers lead time is determined by employing concepts of order statistics it is required to find the fill rate and safety stocks at each stockpoint that leads to satisfying the end customer service level at minimum safety stock placement cost hence the fill rates and the safety amounts are decided from a global supply chain perspective two models are proposed a decentralized safety stock placement model and a centralized consolidation model the decentralized model finds the safety amounts at each stockpoint required to face its underlying lead time demand variability the consolidation model finds the consolidated safety amounts that will be kept in the relevant consolidation center at each stage a benders decomposition technique is developed to handle the nonlinearity and binary restrictions involved in the safety stock consolidation model strategies proposed by the consolidation model achieve 45 2 62 reduction in safety amounts that results in a cost savings ranging between 22 2 44 2 as compared to the strategies proposed by the decentralized model

ordering quantity decisions considering uncertainty in supply chain logistics operations abstract this research seeks to determine the optimal order amount for a retailer given uncertainty in a supply chain s logistics network due to unforeseeable disruption or various types of defects e g shipping damage missing parts and misplacing products mixture distribution models characterize problems from solitary failures and contingent events causing network to function ineffectively the uncertainty in the number of good products successfully reaching distribution centers dcs and retail stores poses a challenge in deciding product order amounts because the commonly used ordering plan developed for maximizing expected profits does not allow retailers to address concerns about contingencies this research proposes two improved procedures with risk averse characteristics towards low probability and high impact events several examples illustrate the impact of a dc s operation policies and model assumptions on a retailer s product ordering plan and resulting sales profit

carrier portfolio management for shipping seasonal products many seasonal products are transported via ocean carriers from origin to destination markets the shipments arriving earlier in the market may sell at higher prices but faster shipping services can be costly in this paper we study a newsvendor type shipper who transports and sells seasonal products to an overseas market where the selling price declines over time a set of vessels with different schedules and freight rates are available to choose from our analysis demonstrates that a portfolio of vessels has two distinct effects on mitigating uncertainties in both demand and vessels arrival schedules while these two portfolio effects have been previously understood as separate issues in the literature to find the optimal portfolio in our problem we first show that when vessels arrive in a deterministic sequence the optimal portfolio can either be derived in closed form in the single demand setting or computed efficiently with a variation of the shortest path algorithm in the multi demand sett

just in time purchasing single or multiple sourcing abstract we consider two just in time jit purchasing models one utilizing a few sources and the other using the more conventional single source we address the issue of splitting a large order quantity into multiple deliveries taking account of the increase in the aggregate ordering transportation and inspection costs for multiple sourcing we formulate and solve a mathematical programming problem to obtain the optimal selection of suppliers and the size of the split orders for single sourcing we provide a procedure that yields the optimal number of deliveries

speculative production and anticipative reservation of reactive capacity by a multi product newsvendor in this paper the optimal sourcing decisions of a multi product newsvendor prior to the selling season of the products are studied to satisfy the uncertain demands the newsvendor can either utilize speculative production or anticipatively reserve capacity during the selling season when demand has become known the newsvendor can utilize its reserved capacity and reactively satisfy demand uncovered by its speculative production for the case where capacity for speculative production may be limited but potential reservation of reactive capacity is unlimited two capacity reservation settings are analyzed and compared in the first one capacity for each product has to be reserved separately while in the second setting one joint capacity reservation for all products is permitted which can then be allocated to the different products optimally during the selling season for the case of separate individual reservations the optimal strategies are analytically derived and structural insights concerning their existence are presented as the model allowing for joint reservation can not be tackled analytically in general an approximation based on an lp formulation is used through a numerical example insights on the value of the increased flexibility induced by joint reservation the cost premium acceptable for joint reservation and the relative levels of capacity reservation in the two settings are given

lower bounds for multi echelon stochastic inventory systems we establish lower bounds on the minimum cost of managing certain production distribution networks with setup costs at all stages and stochastic demands these networks include serial assembly and one warehouse multi retailer systems we obtain the bounds through novel cost allocation schemes we evaluate the bounds performance for one warehouse multi retailer systems by comparing them with simple heuristic policies the bounds are quite tight for systems with a small number of retailers we also present simplified proof of known optimality results for serial and assembly systems

the impact of cost uncertainty on the location of a distribution center abstract the location of a distribution center dc is a key consideration for the design of supply chain networks when deciding on it firms usually allow for transportation costs but not supplier prices we consider simultaneously the location of a dc and the choice of suppliers offering different possibly random prices for a single product a buying firm attempts to minimize the sum of the price charged by a chosen supplier and inbound and outbound transportation costs no costs are incurred for switching suppliers we first derive a closed form optimal location for the case of a demand populated unit line between two suppliers offering deterministic prices we then let one of the two suppliers offer a random price if the price follows a symmetric and unimodal distribution the optimal location is closer to the supplier with a lower mean price we also show the dominance of high variability the buyer can decrease the total cost more for higher price variability for any location the dominance result holds for normal uniform and gamma distributions we propose an extended model with more than two suppliers on a plane and show that the dominance result still holds from numerical examples for a line and a plane we observe that an optimal location gets closer to the center of gravity of demands as the variability of any supplier s price increases

optimal commodity trading with a capacitated storage asset this paper considers the so called warehouse problem with both space and injection withdrawal capacity limits this is a foundational problem in the merchant management of assets for the storage of commodities such as energy sources and natural resources when the commodity spot price evolves according to an exogenous markov process this work shows that the optimal inventory trading policy of a risk neutral merchant is characterized by two stage and spot price dependent basestock targets under some assumptions these targets are monotone in the spot price and partition the available inventory and spot price space in each stage into three regions where it is respectively optimal to buy and inject do nothing and withdraw and sell in some cases of practical importance one can easily compute the optimal basestock targets the structure of the optimal policy is nontrivial because in each stage the merchant s qualification of high selling and low buying commodity prices in general depends on the merchant s inventory availability this is a consequence of the interplay between the capacity and space limits of the storage asset and brings to light the nontrivial nature of the interface between trading and operations a computational analysis based on natural gas data shows that mismanaging this interface can yield significant value losses moreover adapting the merchant s optimal trading policy to the spot price stochastic evolution has substantial value this value can be almost entirely generated by reacting to the unfolding of price uncertainty that is by sequentially reoptimizing a model that ignores this source of uncertainty

optimal production planning with emissions trading emissions trading is a market based mechanism for curbing emissions and it has been implemented in europe north america and several other parts of the world to study its impact on production planning we develop a dynamic production model where a manufacturer produces a single product to satisfy random market demands the manufacturer has access to both a green and a regular production technology of which the former is more costly but yields fewer emissions to comply with the emissions regulations the manufacturer can buy or sell the allowances in each period via forward contracts in an outside market with stochastic trading prices while needing to keep a nonnegative allowance account balance at the end of the planning horizon we first derive several important structural properties of the model and based upon them we characterize the optimal emissions trading and production policies that minimize the manufacturer s expected total discounted cost in particular the optimal emissions trading pol

coordination mechanisms of supply chain systems supply chain management scm has become an important management paradigm as supply chain members are often separate and independent economic entities a key issue in scm is to develop mechanisms that can align their objectives and coordinate their activities so as to optimize system performance in this paper we provide a review of coordination mechanisms of supply chain systems in a framework that is based on supply chain decision structure and nature of demand this framework highlights the behavioral aspects and information need in the coordination of a supply chain the identification of these issues points out several directions of future research in this area

diversification under supply uncertainty supply chain management is becoming an increasingly important issue especially when in most industries the cost of materials purchased comprises 40 60 of the total sales revenue despite the benefits cited for single sourcing in the popular literature there is enough evidence of industries having two three sources for most parts in this paper we address the operational issue of quantity allocation between two uncertain suppliers and its effects on the inventory policies of the buyer based on the type of delivery contract a buyer has with the suppliers we suggest three models for the supply process model i is a one delivery contract with all of the order quantity delivered either in the current period with probability or in the next period with probability 1 model ii is also a one delivery contract with a random fraction of the order quantity delivered in the current period the portion of the order quantity not delivered is cancelled model iii is similar to model ii with the remaining quantity delivered in the next period we derive the optimal ordering policies that minimize the total ordering holding and penalty costs with backlogging we show that the optimal ordering policy in period n for each of these models is as follows for x a n order nothing for vi n x a n use only one supplier and for x vi n order from both suppliers for the limiting case in the single period version of model i we derive conditions under which one would continue ordering from one or the other or both suppliers for model ii we give sufficient conditions for not using the second more expensive supplier when the demand and yield distributions have some special form for the single period version of models ii and iii with equal marginal ordering costs we show that the optimal order quantities follow a ratio rule when demand is exponential and yields are either normal or gamma distributed

adjustment strategies for a fixed delivery contract we consider a long term contractual agreement between buyer and seller in whichq units are delivered to the buyer at regular time intervals it must be true that the delivery quantity q is less than the mean demand per period in order to manage the inventory the buyer has the option of adjusting the delivery quantity upwards just prior to a delivery but must pay a premium to do so demand is assumed random and we model the system in a continuous review setting we show that the equations one must solve to find optimal adjustment strategies are intractable a diffusion approximation is developed which when coupled with the solution to an even simpler deterministic version of the problem yields very simple but effective approximations extensive computations are included to compare the performance of the optimal and approximate policies we also empirically derive a formula for computingq whose accuracy is established computationally we prove that the fixed delivery contract results in lower variance of orders to the seller we also include a computational study to find the unit cost discount that equalizes the expected costs for the fixed delivery contract and the base stock contract for a large parameter set

cvar constrained planning of renewable generation with consideration of system inertial response reserve services and demand participation abstract integration of renewable generation can lead to both diversification of energy sources which can improve the overall economic performance of the power sector and cost increase due to the need for further resources to provide flexibility and thus secure operation from unpredictable variable and asynchronous generation in this context we propose a cost risk model that can properly plan generation and determine efficient technology portfolios through balancing the benefits of energy source diversification and cost of security of supply through the provision of various generation frequency control and demand side services including preservation of system inertia levels we do so through a scenario based cost minimization framework where the conditional value at risk cvar associated with costs under extreme scenarios of fossil fuel prices combined with hydrological inflows is constrained the model can tackle problems with large data sets e g 8760 hours and 1000 scenarios since we use linear programming and propose a benders based method adapted to deal with cvar constraints in the master problem through several analyses including the chilean main electricity system we demonstrate the effects of renewables on hedging both fossil fuel and hydrological risks effects of security of supply on costs risks and renewable investment and the importance of demand side services in limiting risk exposure of generation portfolios through encouraging risk mitigating renewable generation investment

competition in the supply option market this paper develops a multiattribute competition model for procurement of short life cycle products in such an environment the buyer installs dedicated production capacity at the suppliers before demand is realized final production orders are decided after demand materializes of course the buyer is reluctant to bear all the capacity and inventory risk and thus signs flexible contracts with several suppliers we model the suppliers offers as option contracts where each supplier charges a reservation price per unit of capacity and an execution price per unit of delivered supply these two parameters illustrate the trade off between total price and flexibility of a contract which are both important to the buyer we model the interaction between suppliers and the buyer as a game in which the suppliers are the leaders and the buyer is the follower specifically suppliers compete to provide supply capacity to the buyer and the buyer optimizes its expected profit by selecting one or more suppliers we characterize the suppliers equilibria in pure strategies for a class of customer demand distributions in particular we show that this type of interaction gives rise to cluster competition that is in equilibrium suppliers tend to be clustered in small groups of two or three suppliers each such that within the same group all suppliers use similar technologies and offer the same type of contract finally we show that in equilibrium supply chain inefficiencies i e the loss of profit due to competition are at most 25 of the profit of a centralized supply chain

allocating production capacity among multiple products we consider the problem of allocating production capacity among multiple items assuming that a fixed proportion of overall capacity can be dedicated exclusively to the production of each item given a capacity allocation production of each item follows a base stock policy i e each demand triggers a replenishment order to restore safety stocks to target levels we present procedures for choosing base stock levels and capacity allocations that are asymptotically optimal our objective is to minimize holding and backorder costs or to minimize holding costs subject to a service level constraint asymptotic optimality refers to large backorder penalties or stringent service level constraints numerical results indicate that our rules perform very well even far from the asymptotic regime a further approximation step results in allocation rules based on heavy traffic limits these too perform well

sabotaging civil service reform in aid dependent countries are donors to blame summary international development assistance has focused increasing resources on raising civil service capacity in low income country administrations plagued by low pay poor establishment controls and the absence of merit based human resource practice at the same time donors sabotage civil service capacity development over the longer term notwithstanding international accords calling on donors to curtail this behavior collective action problems constrain donors from dismantling the projectized aid infrastructure that fragments government institutions we identify practical implications of this collective action dilemma and explore alternative reform approaches we examine an agency level civil service reform acsr in cambodia in comparative perspective showing how strategic incremental introduction of merit based incentives yielded benefits in one ministry but faltered when the pilot was expanded to other agencies to the extent that the accumulated acsr experiences have achieved some albeit limited traction they may offer a small but significant beacon for those seeking to move forward on civil service reform under difficult conditions

optimal replenishment and rework with multiple unreliable supply sources we study a production inventory system with multiple unreliable supply sources through inspection and rework the system can improve the quality of the units received from the supply sources there are two interleaved decisions the replenishment quantities from the sources and the inspection rework quantities among the units received we show the optimal solution to the replenishment decision can be efficiently derived from a greedy algorithm and inspection rework is optimally applied to a single source identified by the algorithm furthermore in the case of linear cost functions it is optimal to place orders from two supply sources i e dual sourcing the results extend to the infinite horizon case where an order up to policy is optimal the model also readily adapts to situations in which the supply imperfection takes the form of a reduced delivery quantity yield loss

optimal procurement strategies for online spot markets abstract spot markets have emerged for a broad range of commodities and companies have started to use them in addition to their traditional long term procurement contracts forward contracts in comparison to forward contracts spot markets offer products at essentially negligible lead time but typically command a higher expected price for this added flexibility while also exhibiting substantial price uncertainty in our research we analyze the resulting procurement challenge and quantify the benefits of using spot markets from a supply chain perspective we develop and solve mathematical models that determine the optimal order quantity to purchase via forward contracts and the optimal quantity to purchase via spot markets we analyze the most general situation where commodities can be both bought and sold via a spot market and derive closed form results for this case we compare the obtained results to the reference scenario of pure contract sourcing and we include results for situations where the use of spot markets is restricted to either buying or selling only our approaches can be used by decision makers to determine optimal procurement strategies based on key parameters such as demand and spot price volatilities correlation between demand and spot prices and risk aversion the results of our analysis demonstrate that significant profit improvements can be achieved if a moderate fraction of the commodity demand is procured via spot markets the results also show that companies who use spot markets can offer a higher expected service level but that they might experience a higher variability in profits than companies who do not use spot markets we illustrate our analytical results with numerical examples throughout the paper

aid dependence and the quality of governance cross country empirical tests aid dependence can potentially undermine the quality of governance and public sector institutions by weakening accountability encouraging rent seeking and corruption fomenting conflict over control of aid funds siphoning off scarce talent from the bureaucracy and alleviating pressures to reform inefficient policies and institutions analyses of cross country data in this paper provide evidence that higher aid levels erode the quality of governance as measured by indices of bureaucratic quality corruption and the rule of law these findings support the need for donors to develop less costly and less intrusive ways of disseminating state of the art knowledge on public sector reform in developing countries

understanding economic policy reform one of the eventual consequences of the global debt crisis was a wave of market oriented economic reforms this paper discusses the state of our knowledge on the political economy of this process why were inefficient and often unsustainable policies maintained for so long why are so many governments reforming now after decades of adherence to policies of an opposite kind have the reformers internalized the correct lessons from the east asian experience finally are there any helpful rules for reformers to follow in guiding their policies through complicated political terrain

robust optimal policies of production and inventory with uncertain returns and demand abstract we consider an inventory and production planning problem with uncertain demand and returns in which the product return process is integrated into the manufacturing process over a finite planning horizon we first propose an inventory control model for the return and remanufacturing processes with consideration of the uncertainty of the demand and returns then a robust optimization approach is applied to deal with the uncertainty of the problem through formulating a robust linear programming model moreover properties on the robust optimization model are studied and an equivalent robust optimization model based on duality theory is obtained which allows the solutions to be derived more efficiently finally we provide a set of numerical examples to verify the effectiveness of the approach and analyze the effects of the key parameters on the solutions

coordinated supply chain management abstract historically the three fundamental stages of the supply chain procurement production and distribution have been managed independently buffered by large inventories increasing competitive pressures and market globalization are forcing firms to develop supply chains that can quickly respond to customer needs to remain competitive these firms must reduce operating costs while continuously improving customer service with recent advances in communications and information technology as well as a rapidly growing array of logistics options firms have an opportunity to reduce operating costs by coordinating the planning of these stages in this paper we review the literature addressing coordinated planning between two or more stages of the supply chain placing particular emphasis on models that would lend themselves to a total supply chain model finally we suggest directions for future research

an analysis of risk and return in the defense market its impact on weapon system competition with growing austerity pressures from the administration congress and the general public the government s procurement policy has called for increased use of dual source competition as a means of reducing acquisition costs in practice however this policy has produced mixed results the cause seems to be an inadequate understanding of the peculiarities of competition in the government s market this paper examines the risk and return available in the defense market and relates it to the industry s propensity to compete the results show that intelligent observation of the industry s capacity utilization rate would contribute to the development of a more efficient acquisition policy

strong formulations for multistage stochastic self scheduling unit commitment with the increasing penetration of renewable energy into the power grid system the volatility of real time electricity prices increases significantly this brings challenges for independent power producers to provide optimal bidding strategies the traditional approaches of only attending the day ahead market might not be profitable enough without taking advantage of real time price volatility in this paper we study the optimal bidding strategies for the independent power producers utilizing self scheduling strategies to participate in the real time market considering real time electricity price volatility with the objective of maximizing the total expected profit considering the correlations of renewable energy generation outputs among different time periods the correlations of real time prices are captured in our modeling framework in which we explore a multistage stochastic scenario tree to formulate the price uncertainties accordingly the derived multistage stochastic self scheduling unit com

optimal ordering policies with two suppliers when lead times and demands are all stochastic abstract splitting orders among several suppliers is a common practice earlier theoretical studies considered only the strategy of splitting an order equally among the suppliers they concentrated on the effects of order splitting on reducing the effective lead time demand and safety stocks but the effects on the overall ordering policy have not been considered this paper presents a procedure for determining the optimal order policy i e the total order quantity reorder point and proportion of split between two suppliers the optimization objective is minimize the sum of annual holding and order costs subject to a maximum stockout risk our procedure handles any stochastic form of daily demand and lead times some interesting observation from our solutions are i the major advantage of order splitting is in the reduction of cycle inventory cost whereas the safety stock reduction is usually unimportant contrary to earlier findings ii although intuitively one might use suppliers with the shortest mean lead times lower cost is actually achieved if the second supplier s mean lead time is suitably larger than the first s this often means excluding suppliers with the lowest mean lead times iii the optimal proportion of order split varies with among other factors the difference in the suppliers mean lead times

responsive pricing under supply uncertainty consider a retailer orders a seasonal product from a supplier and sells the product over a selling season while the product demand is known to be a linear function of price the supply yield is uncertain and is distributed according to a general discrete probability distribution this paper presents a two stage stochastic model for analyzing two pricing policies no responsive pricing and responsive pricing under the no responsive pricing policy the retailer would determine the order quantity and the retail price before the supply yield is realized under the responsive pricing policy the retailer would specify the order quantity first and then decide on the retail price after observing the realized supply yield therefore the responsive pricing policy enables the retailer to use pricing as a response mechanism for managing uncertain supply our analysis suggests that the retailer would always obtain a higher expected profit under the responsive pricing policy in addition to examining the impact of yield distribution and system parameters on the optimal order quantities retail prices and profits under these two pricing policies we analyze two issues arising from responsive pricing the first issue deals with the case in which the retailer can place an emergency order with an alternative source after observing the realized yield while the second issue deals with a situation in which the retailer has to allocate his order among multiple suppliers

newsvendor with multiple options of expediting we consider a manufacturer facing single period inventory planning problem with uncertain demand and multiple options of expediting the demand comes at a certain time in the future the manufacturer may order the product in advance with a relatively low cost she can order additional amount by expediting after the demand is realized there are a number of expediting options each of which corresponds to a certain delivery lead time and a unit procurement price the unit procurement price is decreasing over delivery lead time the selling price is also decreasing over time in this paper we assume that the manufacturer must deliver all products to the customer in a single shipment the problem can be formulated as a profit maximization problem we develop structural properties and show how the optimal solution can be identified efficiently in addition we compare our model with the classical newsvendor model and obtain a number of managerial insights

self commitment of combined cycle units under electricity price uncertainty day ahead energy market clearing relies on a deterministic equivalent model with a limited time horizon which may lead to inefficient scheduling of generating units from the point of view of generators for this reason generators may wish to assume the risk of self committing their units with the hope of securing greater profits this phenomenon may reduce the room for economic signals in the day ahead market in this paper we investigate the influence of risk aversion and price volatility on the decision of generators to self commit units we present a stochastic programming model for self committing combined cycle units under price uncertainty with a conditional value at risk criterion we use benders decomposition to solve the problem and present results on a case study to draw conclusions

selecting a portfolio of suppliers under demand and supply risks we analyze a planning model for a firm or public organization that needs to cover uncertain demand for a given item by procuring supplies from multiple sources each source faces a random yield factor with a general probability distribution the model considers a single demand season all supplies need to be ordered before the start of the season the planning problem amounts to selecting which of the given set of suppliers to retain and how much to order from each so as to minimize total procurement costs while ensuring that the uncertain demand is met with a given probability the total procurement costs consist of variable costs that are proportional to the total quantity delivered by the suppliers and a fixed cost for each participating supplier incurred irrespective of his supply level each potential supplier is characterized by a given fixed cost and a given distribution of his random yield factor the yield factors at different suppliers are assumed to be independent of the season s demand which is described by a general probability distribution determining the optimal set of suppliers the aggregate order and its allocation among the suppliers on the basis of the exact shortfall probability is prohibitively difficult we have therefore developed two approximations for the shortfall probability although both approximations are shown to be highly accurate the first based on a large deviations technique ldt has the advantage of resulting in a rigorous upper bound for the required total order and associated costs the second approximation is based on a central limit theorem clt and is shown to be asymptotically accurate whereas the order quantities determined by this method are asymptotically optimal as the number of suppliers grows most importantly this clt based approximation permits many important qualitative insights

are windfalls a curse abstract a puzzling feature of temporary terms of trade booms is that some countries have responded to such windfalls by running current account deficits furthermore those countries that ran current account deficits failed to attain greater post boom growth rates indicating the deficits were consumed or invested in low quality projects the point we make is that the structure of the fiscal process is critical in determining outcomes if fiscal control is unitary then the consumption smoothing effect is operative and representative agent models of the current account have predictive power however if control is divided among several fiscal claimants a voracity effect appears which counteracts the consumption smoothing effect leading to a deterioration of the current account in response to a positive temporary shock we model the interaction among fiscal claimants as a dynamic game and show that in equilibrium aggregate appropriation increases more than the windfall itself this results in a deterioration of the current account we also show that all the windfall is dissipated with the country experiencing no increase in welfare 1998 elsevier science b v

procuring fast delivery sole sourcing with information asymmetry this paper studies a queuing model in which a buyer sources a good or service from a single supplier chosen from a pool of suppliers the buyer seeks to minimize the sum of her procurement and operating costs the latter of which depends on the suppliers lead time the selected supplier can regulate his lead time but faster lead times are costly although the buyer selects the supplier to source from possibly via an auction and dictates the contractual terms the buyers bargaining power is limited by asymmetric information the buyer only has an estimate of the suppliers costs while the suppliers know their costs precisely we identify a procurement mechanism that minimizes the buyers total cost procurement plus operating this mechanism is not simple it is a numerically derived nonlinear menu of contracts therefore we study several simpler mechanisms e g one that charges a late fee and one that specifies a fixed lead time requirement no menus no nonlinear functions we find that simple mechanisms are nearly optimal generally within 1 of optimal because asymmetric information conveys significant protection to the supplier i e the supplier is able to retain most of the benefit of having a lower cost renegotiation is another concern with the optimal mechanism because it does not minimize the supply chains cost the firms can be both better off if they throw away the contract and start over interestingly we find that the potential gain from renegotiation is relatively small with either the optimal or our simple mechanisms we conclude that our simple mechanisms are quite attractive along all relevant dimensions buyers performance supply chain performance simplicity and robustness to renegotiation

bureaucratic corruption and the rate of temptation do wages in the civil service affect corruption and by how much abstract this paper presents what is to our knowledge the first empirical estimate of the effect of pay in the civil service on corruption first we show that theory is ambiguous on the relationship between civil service pay and corruption then we examine the issue using a new data set on wages for low income countries we find evidence of a statistically and economically significant relationship between relative civil service pay and corruption in regressions based on cross country averages where we control for a wide array of variables the relationship implies that a rather large increase in wages is required to eradicate corruption solely by raising wages

managing global sourcing inventory performance the use of global suppliers has increased considerably over the last three decades operations management theory establishes that global sourcing requires more units of inventory but since these units are often procured at a lower cost from global suppliers the capital invested in inventory and the consequent financial burden may increase or decrease with global sourcing this study provides rigorous firm level empirical evidence that links the global sourcing practices of public u s firms and their inventory investments we process bill of lading manifests customs forms to extract information on over half a million sea shipments from global suppliers to u s public firms and link this information with quarterly financial data from the compustat database we provide stylized facts on the participation of different firms and sectors in global trade using a simultaneous equation model we find that an increase in global sourcing results in an increase in inventory investment a 10 shift in sourcing from domestic to global suppliers increases the inventory investment by 8 8 for an average firm in our sample we also find that increasing the number of suppliers can mitigate this increase in inventory investment for example going from single to dual sourcing reduces inventory investment by about 11 we illustrate the use of our estimates to identify the impact of changing global sourcing strategy on inventory investment and operational performance metrics this paper was accepted by martin lariviere operations management

single versus multiple supplier sourcing strategies successful supply chain management necessitates an effective sourcing strategy to combat uncertainties in both supply and demand in particular supply disruption results in excessive downtime of production resources upstream and downstream supply chain repercussions and eventually a loss in the market value of the firm in this paper we analyze single period single product sourcing decisions under demand uncertainty our approach integrates product prices supplier costs supplier capacities historical supplier reliabilities and firm specific inventory costs a unique feature of our approach is the integration of a firm specific supplier diversification function we also extend our analysis to examine the impact of minimum supplier order quantities our results indicate that single sourcing is a dominant strategy only when supplier capacities are large relative to the product demand and when the firm does not obtain diversification benefits in other cases we find that multiple sourcing is an optimal sourcing strategy we also characterize a non intuitive trade off between supplier minimum order quantities costs and supplier reliabilities finally we examine the robustness of our results through an extensive numerical analysis of the key parameters of our model

sole versus dual sourcing in stochastic lead time s q inventory models when supply lead times are uncertain the simultaneous procurement from two sources offers savings in inventory holding and shortage costs economies are achieved if these savings outweigh the increase in ordering costs in this paper we analyze dual sourcing in the context of the reorder point order quantity inventory model with constant demand and stochastic lead times and compare it with single sourcing two cases are studied using the uniform and the exponential distributions which may be thought of as two extreme ways of representing stochastic lead times in our two vendor model the order quantity is split equally between the two vendors and the split orders are placed simultaneously when the inventory position reaches the reorder level a comparison of the total expected costs suggests that when the uncertainty in the lead times is high and the ordering costs are low dual sourcing could be cost effective

production control in the face of storable raw material random supply and an outside market we study a periodic review production inventory control problem where both the supply of raw material and demand for the finished product are exogenous and random the raw material can be stored for future use can be purchased from or sold to an outside market we study both the lost sales and backlogging cases under both strict convex and linear raw material purchasing selling costs convexity of the purchasing selling cost implies that the more the firm purchases from or sells to the outside market the more expensive or less valuable the raw material becomes for all cases we find the partial characterizations for the optimal policies which all turn out to be very intuitively appealing in particular for each of the linear cost cases the optimal policy degenerates into a combination of two base stock policies one for the raw material inventory and the other for the finished product inventory

a continuous review model for an inventory system with two supply modes in this paper we develop an approximate model of an inventory control system in which there exist two options for resupply with one having a shorter lead time because the optimal policy appears to be extremely complex we consider a reasonable extension of the standard q r policy to allow for two different lot sizes q1 and q2 and two different reorder levels r1 and r2 expressions for the expected on hand inventory and the expected backorders are developed and a procedure for determining the policy parameters is given the model is validated by simulation and calculations are included which compare the average annual cost with and without emergency ordering

optimal self scheduling of a thermal producer in short term electricity markets by milp this paper addresses the problem of the self scheduling of a thermal electricity producer in day ahead energy and reserves markets a 0 1 mixed integer linear formulation of the producer self scheduling problem is provided which allows a realistic and accurate modeling of the unit s operating phases a novel unit start up modeling is presented in which three different start up types are modeled hot warm and cold each with distinct start up cost synchronization time soak time and predefined start up power output trajectories all dependent on the unit s prior reservation time test results address the effect of the energy and reserves market clearing prices on the producer units day ahead commitment status and profits

dynamic replenishment production and pricing decisions in the face of supply disruption and random price sensitive demand abstract we study a joint decision problem for replenishment production pricing strategies in the face of both supply and demand uncertainties the supply of the raw material suffers from a potential supply disruption while the demand for the finished goods is price sensitive and random we assume that the raw material is storable and unfilled demands are fully backordered we characterize the optimal policies for raw material replenishment finished goods production and pricing we find that the optimal replenishment policy is an order up to type for a given finished goods stock level while it is a threshold type for a given raw material stock level for either a given finished goods stock level or a given raw material stock level the optimal production policy is a threshold type and the optimal pricing policy is a modified list price type respectively

periodic review production models with variable capacity random yield and uncertain demand we investigate a production planning problem in a periodic review environment with variable production capacity random yields and uncertain demand the implications of random yields and variable capacity for lot sizing previously have been explored separately but not jointly many production environments are likely to be subject to both types of uncertainties to minimize the total discounted expected costs production holding and shortage costs we formulate the problem as a stochastic dynamic program for the finite horizon problem we prove that the objective function is quasi convex and that the structure of the optimal policy is characterized by a single critical point for the initial stock level at each period that is if the initial stock is greater than this critical point the optimal planned production is zero otherwise it is greater than zero expressions for solving the critical point and the optimal planned production are obtained we further show that the solution for the finite horizon problem converges to that of the infinite horizon problem