on the structure of lost sales inventory models we provide a new approach to the structural analysis of the standard lost sales inventory system this approach is we think easier to work with than the original one we also derive new bounds on the optimal policy then we show that more variable demand leads to higher cost finally we extend the analysis to several important variations of the basic model

progress along the path evolving issues in the measurement of genuine saving more than 10 years since a practical linkage between sustainable development and a measure of national wealth expanded to include natural and environmental resources was first posited the empirical estimation of adjusted net savings dubbed genuine saving has evolved considerably in this paper we take stock of both progress achieved and the challenges that remain we begin by recalling the key points made in pearce and atkinson 1993 ecol econ 8 103 which presented the first cross country estimates of savings rates adjusted to reflect depletion and degradation of the environment we then briefly summarise the evolution of the theoretical argument linking savings and sustainability however the main focus of this paper is an aspect that concerned david pearce greatly namely the evolution of the measurement of genuine savings we identify and consider the empirical evidence with regard to two particular measurement issues the valuation of exhaustible resources and environmental degradation common to the both issues are concerns about measuring changes in national wealth in real world economies

the great indian calorie debate explaining rising undernourishment during india s rapid economic growth abstract the prevalence of undernourishment in india the percent of people consuming insufficient calories to meet their energy requirements has been rising steadily since the mid 1980s paradoxically this period has been one of robust poverty reduction and rapid economic growth the reasons for the apparent reductions in calorie consumption underlying increased undernourishment have been the subject of intense debate both within india and internationally this paper critically reviews this debate finding that is has taken place outside of the context of india s recent nutrition and epidemiological transitions which appear to have brought with them increased not decreased food consumption the debate has also taken place under the unchallenged assumption that the data on which the conflicting trends are based collected as part of the country s household consumption and expenditure surveys hcess are reliable the paper provides supporting literature and empirical evidence that a probable key source of the calorie decline is incomplete collection of data on food consumed away from peoples homes which is widespread and rapidly increasing complete measurement of this food source in the hcess of all developing countries is vital for accurate measurement of both undernourishment and poverty and for resolving the indian calorie debate

how much demand should be fulfilled we study the inventory replenishment of a product whose demand can be manipulated by restricting the supply this research is motivated by a novel marketing tactic employed by manufacturers of fashion and luxury items such a tactic combines innovative marketing with deliberate understocking in an attempt to create shortages i e waitlists that add to the allure and sense of exclusivity of a product and stimulate its demand we model the problem as a finite horizon periodic review system where demand in each period is a decreasing function of the net ending inventory in the previous period although the optimal structure can be complex in general under certain conditions we are able to characterize the optimal policy as a state dependent monotone base stock policy we compare this policy with the optimal policy for the case in which demand is independent of the net inventory we also show that understocking is optimal in various scenarios we then propose a novel strategy called the inventory withholding strategy to further explore the wait list effect by making customers wait even when there is inventory on hand to satisfy them our numerical experiments study the impact of various model parameters in combination with the wait list effect on the optimal policy and the corresponding expected profits

does a procurement service provider generate value for the buyer through information about supply risks we consider a supply chain with one buyer and two suppliers who are subject to disruptions and whose likelihoods of disruption are their private information in such a setting does the buyer benefit from engaging the services of a better informed procurement service provider psp compared to procuring directly from the suppliers intuition might suggest that hiring a psp is always the right choice because the psp s knowledge of the supply base improves supplier selection and management on the other hand earlier studies prove that using a psp purely for its superior knowledge about supply costs is always worse for a buyer than contracting with the suppliers directly our answer to this research question is more nuanced contrary to the findings of earlier studies we find that the buyer may benefit from using a psp we identify quantify and explain all of the benefits and the costs of using a psp and describe conditions under which the benefits exceed the costs the benefits of using a psp are deriv

towards an operational sustainability criterion abstract this paper examines the concept of sustainability and its implications for environmental policy analysis it builds on the premise that present society holds a moral obligation to pass on a world of undiminished life opportunities to members of future generations maintaining life opportunities in turn can be achieved by maintaining or improving a diverse set of resources and capabilities that support a person s freedom to define and pursue her own conception of the good life on an operational level this framework points to the following guideline for environmental policy protecting the rights of future generations requires either the conservation of environmental resources or compensatory measures including the provision of substitute technologies that ensure the fair and proportionate sharing of net benefits over intergenerational time scales in this framework resource depletion is permissible only if with reasonable certainty it would generate a pareto improvement relative to a baseline scenario involving strict resource conservation

integrating replenishment decisions with advance demand information there is a growing consensus that a portfolio of customers with different demand lead times can lead to higher more regular revenues and better capacity utilization customers with positive demand lead times place orders in advance of their needs resulting inadvance demand information this gives rise to the problem of finding effective inventory control policies under advance demand information we show that state dependent s s and base stock policies are optimal for stochastic inventory systems with and without fixed costs the state of the system reflects our knowledge of advance demand information we also determine conditions under which advance demand information has no operational value a numerical study allows us to obtain additional insights and to evaluate strategies to induce advance demand information

managing supply uncertainty under supply chain cournot competition abstract we study the cournot competition between two supply chains that are subject to supply uncertainty each supply chain consists of a retailer and an exclusive supplier which has random yield we examine how the levels of supply uncertainty and competition intensity affect the equilibrium decisions of ordering quantity contract offering and centralization choice we show that a retailer should order more if its competing retailer s supply becomes less reliable or if its own supply becomes more reliable a supply chain with reliable supply can take great advantage of the high supply risk of its competing chain furthermore for decentralized chains we characterize the optimal wholesale price contracts with linear penalty under different supply risks and competition scenarios finally we show that supply chain centralization is a dominant strategy and it always makes the customers better off nevertheless if the supply risk is low and the chain competition is intensive centralization could actually decrease the supply chain profit compared with the case where both chains do not choose centralization this results in a prisoner s dilemma on the other hand if the supply risk is high and or the competition level is low centralization always increases the supply chain profit the desirability of supply chain centralization is enhanced by high supply uncertainty or low chain competition

customer order information leadtimes and inventories we have an inventory to manage the scenario is standard in all respects save one instead of arriving unannounced customers provide advance warning of their demands how should we use this information and what is its effect on system performance the answers turn out to be strikingly simple there are very simple policies which perform effectively in some cases optimally also such demand leadtimes improve performance in precisely the same way that replenishment leadtimes degrade it

natural resource accounting for indian states illustrating the case of forest resources abstract our main objective is to set out and apply a seea based methodology to reflect the true value of forest resources in india s national and state accounts we establish that a top down approach using available national databases is both feasible and desirable from a policy perspective in this paper we address four components of value creation in forests timber production carbon storage fuelwood usage and the harvesting of non timber forest products the results of our analysis suggest that prevailing measures of national income in india underestimate the contribution of forests to income the income accounts of the northeastern states in particular are significantly understated by these traditional gdp gsdp measures we are also able to identify some states which performed poorly in the context of our sustainability framework reflecting natural capital losses due to degradation and deforestation our results highlight the need to integrate natural resource accounting into the national accounting framework in order to generate appropriate signals for sustainable forest management and for the conservation of forest resources which are widely used by the poor in india as well as being significant stores of national wealth

wealth as a criterion for sustainable development in this article the authors define sustainable development as an economic programme along which social well being does not decline over time it can be shown that the requirement is equivalent to the maintenance of a comprehensive measure of wealth where an economy s wealth is defined to be the social worth of its entire array of capital assets including natural capital using data published by the world bank on the world s poorest regions countries which would be regarded as having performed well if judged on the basis of such indices as gnp per head or the human development index are found to have grown poorer a few alarmingly so

changes in social welfare and sustainability theoretical issues and empirical evidence abstract we analyze the time derivative of a ramsey koopmans social welfare function r k swf as an indicator of genuine investment and current change in social welfare csw conditions when feedback or arbitrary rules are used for selecting policy variables in non optimizing economies when policy variables are selected arbitrarily their accounting prices should determine current csw in addition to the accounting prices of the economy s assets and genuine investment should be adjusted accordingly we use our theoretical framework to characterize csw conditions for non optimizing economies based on direct estimation of accounting prices we use our theoretical model to provide empirical evidence regarding the csw conditions for the greek economy

inventory control with markovian capacity and the option of order rejection we consider a stochastic inventory control problem with markovian capacity and the option of order rejection we show its optimal policy to be the combination of a capacity dependent modified base stock production policy and a capacity dependent critical point order acceptance policy when capacity is stochastically monotone we show that the policy parameters change over the current capacity level in an intuitive way all these results can be extended to the infinite horizon case with or without cost discounting our computational study substantiates the benefits from both exploiting the markovian behavior of the capacity and rejecting orders when necessary

validating the usage of household food acquisition surveys to assess the consumption of ultra processed foods evidence from brazil our ability to research dietary changes over time and their effects on health is limited by challenges in accurately measuring food consumption in countries where dietary surveys are scarce and rarely nationally representative household budget surveys may serve asa useful alternative for assessing food consumption the objective of this study was to evaluate how well household acquisition data reflects the actual intake of ultra processed foods using data from the 2008 to 2009 brazilian household budget survey the food acquisition module was conducted for all households selected for the survey n 55 970 and a subsample corresponding to 25 of the households n 13 569 was randomly selected for the individual food intake module which was conducted for all individuals aged 10years or older n 34 003 ultra processed foods were defined as formulations made by the food industry mostly or entirely from substances extracted from foods or obtained with the further processing of constituents of foods or through chemical synthesis with little if any whole food examples included candies cookies chips sugar sweetened beverages and ready to eat dishes our results showed an important agreement between the estimates of ultra processed food consumption obtained from household acquisition data and individual intake inside the home data particularly for the relative of total energy consumption of these foods our study thus indicates that household budget surveys are quite promising for tracking population level changes in the consumption of ultra processed foods the trend toward increased consumption of food away from home in other low and middle income countries indicates that future household budget surveys should include the collection of these data

national food security assessment through the analysis of food consumption data from household consumption and expenditure surveys the case of brazil s pesquisa de orcamento familiares 2008 09 by analyzing the food consumption data from the 2008 09 pesquisa de orcamentos familiares in brazil we demonstrate that failing to account for food consumed for free at school may significantly distort the assessment of the distribution of food consumption among households and therefore the assessment of the extent of food insecurity in the country the results of our analysis enabled a revision of the fao estimate of the prevalence of undernourishment in brazil and provide useful suggestions for better design of food consumption modules to be included in household consumption and expenditure surveys hces additionally we identify areas for further research on food consumption data to improve national food security assessments

valuing nature lessons learned and future research directions this paper critically reviews the literature on environmental valuation of ecosystem services across the range of global biomes the main objective of this review is to assess the policy relevance of the information encompassed by the wide range of valuation studies that have been undertaken so far published and other studies now cover most ecosystems with aquatic and marine contexts attracting the least attention there is also a predominance of single function valuation studies studies valuing multiple functions and uses and studies which seek to capture the before and after states as environmental changes take place are rare by and large it is the latter types of analyses that are most important as aids to more rational decision taking in ecosystem conservation versus development situations involving different stakeholders local national and global aggregate global scale estimates of ecosystems value are problematic given the fact that only marginal values are consistent with conventional decision aiding tools such as economic cost benefit analysis in general valuation data provide prima facie support for the hypothesis that net ecosystem service value diminishes with biodiversity and ecosystem loss balmford et al 2002 science 297 p 950 future research effort should include complementary research on multiple ecosystem services that seeks to capture the temporal disturbance profile and its causal factors the explicit recognition of multiple interdependent ecosystem services and values poses both conceptual and empirical research challenges it would serve to transform the practice of research in this sub field via the a priori assumption of multiple and inter dependent use instead of independent single use this line of reasoning can then be extended to the institutional arrangements that determine which values are captured new institutional processes and arrangements are probably required in order to best realise benefit streams from multiple ecosystem use and non use provision across a range of different stakeholders

price drivers and structural breaks in european carbon prices 2005 2007 this article aims at characterizing the daily price fundamentals of european union allowances euas traded since 2005 as part of the emissions trading scheme ets the presence of two structural changes on april 2006 following the disclosure of 2005 verified emissions and on october 2006 following the european commission announcement of stricter phase ii allocation allows to isolate distinct fundamentals evolving overtime the results extend previous literature by showing that eua spot prices react not only to energy prices with forecast errors but also to unanticipated temperatures changes during colder events besides the sub period decomposition of the pilot phase gives a better grasp of institutional and market events that drive allowance price changes

toward a new welfare economics for sustainability the debate over various definitions of sustainability has for the most part been conducted within the framework of traditional welfare economics discussion has centered on technical issues imbedded within the functional forms of various optimization models especially the coefficient of the elasticity of substitution and the social discount rate two more basic problems are 1 intractable theoretical difficulties within welfare economics call into question the results of traditional models of sustainability regarding intergenerational welfare and 2 equating per capita consumption with welfare contradicts empirical evidence suggesting that the link between happiness and wealth income is relatively weak alternative approaches to measuring well being are being developed and these have great potential to move the sustainability debate forward

inventory control in a fluctuating demand environment we present an inventory model where the demand rate varies with an underlying state of the world variable this variable can represent economic fluctuations or stages in the product life cycle for example we derive some basic characteristics of optimal policies and develop algorithms for computing them in addition we show that certain monotonicity patterns in the problem data are reflected in the optimal policies

development ecological resources and their management a study of complex dynamic systems abstract human well being depends to a large extent on services provided by ecological systems in poor countries this dependence is more transparent than in industrialised countries where the dependence is more indirect effective management of these systems requires a good understanding of their properties and in particular a knowledge of the dynamics of the systems in the article the dynamics of one simple system is analysed economically the system is a lake and the interaction between the run off of nutrients into the lake and the growth of either algae eutrophication in lakes in northern europe and north america or water hyacinths in lakes in southern and eastern sfrica is studied it turns out that the dynamics exhibit bifurcation points so that there are two basins of attraction if the system flips to one basin and it is regarded desirable to return to the other basin there will be hysteresis assuming that there are different users of the lake a differential game is constructed that captures the strategic interests of the users the resulting equilibrium shows first the conventional negative externality that will force the system to a different basin od attraction finally we investigate the use of a tax for bringing back the system to a pareto optimum

net national product as an indicator of sustainability net national product nnp can potentially serve several objectives among others to measure value added and to be an indicator of welfare in the aftermath of the world commission on environment and development however it also seems important to investigate whether the concept of nnp can serve as an indicator of sustainability my point of departure following hicks 1946 ch 14 is therefore to require that nnp should measure what can be consumed in the present period without reducing future consumption possibilities and in line with this to argue that the nnp should equal the maximum per capita consumption level that can be sustained if sufficiently many facilitating assumptions are made then a concept of nnp that serves as an exact indicator of sustainability can easily be constructed for instance for a closed economy with a constant population a stationary technology and with only one capital good it follows that the present does not reduce future consumption possibilities if and only if it does not decrease the stock of the single capital good hence under the assumption that the one capital good k is identical to the one consumption good x nnp defined as y x k measures the maximal sustainable consumption at time t because then x y is equivalent to k the purpose of this note is to establish that with multiple capital goods it is not in general possible to construct an exact indicator of sustainability on the

food counts measuring food consumption and expenditures in household consumption and expenditure surveys this special issue presents new evidence on the impact of survey design choices on the quality and availability of data collected in household consumption and expenditure surveys hces the 13 studies in this issue analyze how different survey design options affect the quality of the data being collected and the implications for statistical inference and policy analysis the studies offer practical insights into survey design for national statistical offices and survey practitioners worldwide and also provide policymakers with improved tools and a better understanding of poverty food security and nutrition for effective policymaking

benefits of leadtime information and of its combination with demand forecast information abstract this paper studies both the benefits of leadtime information and the interrelationships among demand forecast information leadtime uncertainty and leadtime information for improving inventory control performance to this end it explicitly incorporates both leadtime information and demand forecast information into an inventory model although they have conventionally been dealt with individually in the literature specifically it considers a periodic review inventory model with uncertain leadtimes in which both leadtime information and demand forecast information are available the leadtime information is modeled as the information of the arrival of outstanding orders and the demand forecast information as the martingale model of forecast evolution mmfe the paper analyzes the way to use both leadtime information and demand forecast information for inventory control operations specifically under certain conditions the optimality of the state dependent base stock policy is shown and an effective heuristic policy is developed it also derives some managerial insights for exploiting both leadtime information and demand forecast information in the case where leadtimes are uncertain for instance while leadtime information itself significantly improves inventory control performance it also enhances the benefits of demand forecast information specifically the benefits of demand forecast information may significantly decrease as leadtime uncertainty increases however the decrease of the benefits of demand forecast information may be alleviated with leadtime information

capital theory and the measurement of sustainable development an indicator of weak sustainability the measurement of sustainable development is not without considerable difficulties yet this should not detract from the positive advances that can be made in this direction in this paper we present one form that a weak sustainability indicator can take derived from a simple but intuitive savings rule it incorporates the idea that the level of overall capital stock should be non decreasing although subject to qualification at this stage some interesting results emerge from the application of the rule to 18 countries

the welfare economic theory of green national accounts this paper takes a critical look at the literature on green national accounts the problem studied is to find a linear index of economic variables that responds to perturbations in the same direction as social well being the thesis of a large literature that net national product which is a flow is that index in closed economies is shown in some interpretations to be simply false and in others to suffer from deep estimation problems it is argued that capital depreciation using shadow prices should certainly be included in national accounts but that the right welfare index is a comprehensive measure of wealth defined as the shadow value of an economy s stock of all capital assets it is shown that comprehensive wealth is usable as a criterion for policy evaluation as well as for determining sustainable economic development

ecosystem services and regional development an application to sweden this study carries out interregional comparisons of development and sustainable use of natural capital with and without inclusion of non marketed ecosystem services a simple dynamic model of an open economy shows that appropriate adjustment of conventional income accounts includes flow and stock components but excludes explicit entrance of pollution calculations are made for swedish regions and for two types of ecosystem services pollution sequestration and recreational services provided by three types of ecosystems forests agricultural landscape and wetlands when comparing the adjusted and non adjusted regional income accounts it is shown that the two measurements generate significantly different pictures of regional income and growth regions that are traditionally considered as relatively less growth promoting are shown to hold important sources of wealth from natural capital while counties that are rich in conventional accounts fall behind when adjusting for values of changes in natural capital

resource accounting in measures of unsustainability challenging the world bank s conclusions the world bank has recently published acomprehensive study of environmental and resourceaccounting covering 103 countries world bank1997a the study concludes that many sub saharan northern african and middle east countries have hadnegative genuine saving rates over the last 20years and therefore fail to pass the test of weaksustainability this paper argues that the bank sconclusions depend on a method for computing usercosts from resource exploitation that is challengedby two competing ones the el serafy method andthe method of repetto et al and is inferior to oneof its rivals resource rents are re computed usingthe el serafy method for 14 countries and thesub saharan and northern african and middle eastregions the results are that both regions andalmost all countries either stop exhibiting signs ofunsustainability or their unsustainability can beexplained without having recourse to resourceaccounting however for congo ecuador gabon nigeria mauritania and trinidad and tobago there isa lesson these countries did not adequately use theopportunities they were given through their naturalresource endowments and should learn from theirmistake for the future depletion of their remainingreserves of natural resources

the role of inventory in delivery time competition the paper operationalizes the notion of shortage cost by considering the behavior of customers and competing firms and examines the role of inventory in response time competition we start with a single firm production control model in which customers are characterized by their preferences of price quality and delivery time the optimal production inventory policy and the optimal choice between make to order and make to stock operations are determined in simple newsboy like formulas the basic model is then extended to an n firm market game in which firms compete for orders from the aspect of early delivery one could think of this setting as an oligopoly racing market the analysis shows that competition can breed a demand for produce to stock just as other economic phenomena such as economies of scale uncertainty or seasonality can induce make to stock and that delivery time competition increases the buyer s welfare while decreasing the producer s welfare

a production inventory system with markovian capacity and outsourcing option we study the optimal production inventory outsourcing policy for a firm with markovian in house production capacity that faces independent stochastic demand and has the option to outsource we find very simple optimal policy forms under fairly reasonable assumptions in addition when the capacity markov process is stochastically monotone the policy parameters decrease in the firm s current capacity level under additional assumptions all these results extend to the infinite horizon and undiscounted cost cases we analyze comparative statics and the necessity of some technical conditions and discuss when the outsourcing option is more valuable

evaluating projects and assessing sustainable development in imperfect economies we are interested in three related questions 1 how should accounting prices be estimated 2 how should we evaluate policy change in an imperfect economy 3 how can we check whether intergenerational well being will be sustained along a projected economic programme we do not presume that the economy is convex nor do we assume that the government optimizes on behalf of its citizens we show that the same set of accounting prices should be used both for policy evaluation and for assessing whether or not intergenerational welfare along a given economic path will be sustained we also show that a comprehensive measure of wealth computed in terms of the accounting prices can be used as an index for problems 2 and 3 above the remainder of the paper is concerned with rules for estimating the accounting prices of several specific environmental natural resources transacted in a few well known economic institutions

inventory control in a lost sales setting with information about supply lead times abstract supply chain collaboration using advancements in information technology is on the rise and this includes sharing of information between suppliers and buyers in this paper we study the value of information about the development of supply lead times from a buyer s perspective we consider a periodically reviewed single item inventory system in a lost sales setting where at most one order can be outstanding at a time we compare the performance of an inventory model assuming informed lead times to a model assuming uninformed independent and identically distributed lead times we employ the dynamic programming approach to find the best state dependent ordering policy to minimize the expected average total cost per time unit our numerical results show that acquiring information about the development of supply lead times is of value in general the best policy suggested by the model assuming informed lead times causes lower average cost than the model assuming uninformed lead times

national account of timber and forest environmental resources in sweden this paper outlines an extension of the national account of income from forest resources in sweden 1987 incorporating changes in timber inventories production of nonmarketed timber and nontimber goods and depletion or improvement in vital environmental stocks such as soil nutrients biodiversity and carbon sinks the total net value added provided by forest resources and forestry labour 1987 is estimated to 22 billions sek this is one third more than the contribution of forestry to ordinary gnp

you are what and where you eat capturing food away from home in welfare measures consumption of food away from home is rapidly growing across the developing world surprisingly the majority of household surveys around the world haven not kept up with its pace and still collect limited information on it the implications for poverty and inequality measurement are far from clear and the direction of the impact cannot be established a priori since consumption of food away from home affects both food consumption and the poverty line this paper exploits rich data on food away from home collected as part of the national household survey in peru shedding light to the extent to which welfare measures differ depending on whether they properly account for food away from home peru is a relevant context with the average peruvian household spending 28 percent of their food budget on food away from home by 2010 the analysis indicates that failure to account for the consumption of food away from home has important implications for poverty and inequality measures as well as the understanding of who the poor are first accounting for food away from home results in extreme poverty rates that are 18 percent higher and moderate poverty rates that are 16 percent lower these results are also consistent in fact more pronounced with poverty gap and severity measures second consumption inequality measured by the gini coefficient decreases by 1 3 points when food away from home is included a significant reduction finally inclusion of food away from home results in a reclassification of households from poor to non poor status and vice versa 20 percent of the poor are different when the analysis includes consumption of food away from home this effect is large enough that a standard poverty profile analysis results in significant differences between the poverty classification based on whether food away from home is included or not the differences cover many dimensions including demographics education and labor market characteristics taken together the results indicate that a serious rethinking of how to deal with the consumption of food away from home in measuring well being is urgently needed to properly estimate and understand poverty around the world

the time path of scarcity rent in the theory of exhaustible resources there is now a consensus in the literature on resource economics that a depletable resource should command a price in excess of its marginal extraction cost simply to reflect the opportunity cost of using a unit of it today rather that conserving it for the future but how this excess is to change along an optimal or competitive equilibrium path of resource use is still an unresolved question this might at first seem puzzling since according to the fundamental theorem of economics of exhaustible resources or hotelling i 93 i rule on an optimal path price minus marginal extraction cost also termed interchangeably as scarcity rent user cost or royalty should steadily grow over time at the social rate of discount however the literature contains sharply contrasting views on the subject for example kay and mirrlees 1975 have argued that since along an optimal path the scarcity rent grows exponentially as a finite stock of a resourcexnears exhaustion then situations in which the resource stock is still very large and yet the price greatly exceeds the marginal extraction cost should indicate that the price is significantly above its optimal level and that the resource is overconserved in stark contrast to this view heal i976 has argued that as the resource stock nears exhaustion the difference between price and marginal cost or what he termed social cost of extraction falls monotonically to zero hanson i980 analyses the same model as heal s but unlike heal who assumes the unit extraction cost to be convex he postulates it to be concave and yet like heal concludes that the scarcity rent will be monotonically declining over time solow and wan i976 analyse a still different situation where resource deposits differ in quality and the unit extraction cost increases as higher grade deposits are exhausted and extraction proceeds to lower grades they show that along an optimal path the shadow price of a resource must rise at the real rate of interest despite differential extraction costs but that the difference between price and the marginal extraction cost or what they call degradation charge declines monotonically over time to zero these sharply differing conclusions suggest that far from being resolved the question of how scarcity rent changes over time is much in want of a close scrutiny the need for such a scrutiny becomes even stronger once it is noted

capital gains and net national product in open economies it is shown within a given framework that with the world economy following an egalitarian path the aggregate capital gains being positive is equivalent to the interest rate tending to decrease this result is of importance for the concept of net national product in open economies in particular with positive aggregate capital gains an open economy cannot sustain consuming the return on its capital stocks since some part of the return must be used to augment the country s national wealth it is established that a country s share of world wide sustainable consumption equals its share of worldwide wealth

the effect of leadtime uncertainty in a simple stochastic inventory model we study a basic continuous time single item inventory model where demands form a compound poisson process and leadtimes are stochastic the performance measure of interest is the long run average cost order costs are linear so a base stock policy is optimal we focus on the behavior of the optimal base stock level in response to stochastically larger or more variable leadtimes we also investigate the behavior of the corresponding long run average costs we show that a stochastically larger leadtime requires a higher optimal base stock level however a stochastically larger leadtime may not necessarily result in a higher optimal average cost because sometimes the variability effects may dominate on the other hand a more variable leadtime always leads to a higher optimal average cost the effect of leadtime variability on optimal policies depends on the inventory cost structure a more variable leadtime requires a higher optimal base stock level if and only if the unit penalty holding cost rate is high low similar results regarding the effect of leadtime demand are also discussed in this latter case the compound poisson assumption is not necessary

inventory control with information about supply conditions this paper presents an inventory control model which includes a markovian model of the supply system as that system evolves over time so do the replenishment leadtimes the optimal policy has the same structure as in standard models but its parameters change dynamically to reflect current supply conditions in this setting contrary to conventional wisdom a longer leadtime does not necessarily imply more inventory the leadtime is important but so is a concept we call order coverage

optimal policies for inventory systems with finite capacity and partially observed markov modulated demand and supply processes we analyze a single item periodic review inventory system with random yield and finite capacity operating in a random environment the primary objective is to extend the model of gallego and hu 2004 to the more general case when the environment is only partially observable although our analysis is specific to inventory systems it can also be applied to production systems by replacing the fixed capacity supplier with a fixed capacity producer using sufficient statistics we consider single period multiple period and infinite period problems to show that a state dependent modified inflated base stock policy is optimal moreover we show that the multiple period cost converges to the infinite period cost as the length of the planning horizon increases

hicksian income from resource extraction in an open economy we derive a measure of national income defined in terms of maximum sustainable per capita consumption if population and interest rates are constant the income generated by natural resource extraction is the return on resource wealth defined as the present value of future resource rents with a growing population or declining interest rate sustainability requires net increases in wealth over time the income from extraction of nonrenewable resources can exceed resource rents contrary to the conclusions of el serafy 1989 and repetto et al 1989 finally we present an example illustrating the hazard of consuming the full increment of hicksian income

s s policies for a dynamic inventory model with stochastic lead times this study analyzes a stochastic lead time inventory model under the assumptions that a replenishment orders do not cross in time and b the lead time distribution for a given order is independent of the number and sizes of outstanding orders the study extends the existing literature on the finite horizon version of the model and yields an intuitively appealing dynamic program that is nearly identical to one that would apply in a transformed model with all lead times fixed at zero hence many results that have been derived for fixed lead time models generalize easily conditions for the optimality of myopic base stock policies and for the optimality of s s policies are established for both finite and infinite planning horizons the infinite horizon model analysis is extended by adapting the fixed lead time results for the efficient computation of optimal and approximately optimal s s policies

inventory management with random supply and imperfect information a hidden markov model in most of the papers on inventory models operating in a random environment the state of the environment in each period is assumed to be fully observed with perfect information however this assumption is not realistic in most real life situations and we provide a remedy in this paper by assuming that the environment is only partially observed with imperfect information we accomplish this by analyzing two formulations of single item models with periodic review and random supply in a random environment in the first one supply is random due to random capacity of production and random availability of transportation we show that state dependent base stock policy is optimal if the capacity and all costs are observed while demand and availability are unobserved in the second model we consider a model with random availability only with fixed ordering cost we show that state dependent s s policy is optimal if the availability process is observable