optimal pricing and lot sizing under conditions of perishability finite production and partial backordering and lost sale abstract perishable products constitute a sizable component of inventories common questions in a production and selling situation involving a perishable or a non perishable product are what should be the price and what should be the size of the replenishment when demand for the product is price sensitive pricing and lot sizing decisions are interdependent similarly when a product is highly perishable the demand may need to be backlogged to avoid costs due to deterioration i e perishability and backlogging are complementary conditions in this paper we consider the pricing and lot sizing problem for a perishable good under finite production exponential decay and partial backordering and lost sale the backlogging phenomenon in the literature is often modeled using backordering and lost sale costs these cost parameters however are not easy to estimate in practice in this paper we use a new approach to model backlogging of demand in this approach customers are viewed to be impatient the backlogging option gets used only when it is economic to do so we extend the analysis presented for a perishable product to the case in which the product is non perishable

diffusion and spillover of new technology a heterogeneous agent model for cassava in west africa understanding what determines the geographic spread of innovations can help guide the funding and implementation of research and extension programs our approach uses household survey data as model parameters to simulate behavior across the entire surveyed population and avoid the aggregation bias associated with representative farm models such a heterogeneous agent approach allows us to infer the distribution of a technology s impacts across one set of households and predict the potential for spreading to another set that shares similar characteristics with respect to natural resource endowments and farming systems we apply the technique to new cassava varieties in west africa finding a strongly poverty alleviating impact with substantial spillover potential from nigeria to neighboring countries

efficiency of research investments in the presence of international spillovers wheat research in developing countries expenditures on agricultural research in the public sector including the international agricultural research centers iarcs have stagnated and in some cases declined sharply in recent years this has focused attention on issues of efficiency of agricultural research systems especially the number size scope type and locations of their programs this paper examines the issue of research efficiency through a case study of wheat improvement research in developing countries the basic premise of this study is that the optimal level of research investment should be determined in a global model that incorporates direct research spill ins an analytical framework is developed to determine the threshold levels of crop production in a country or a region within a country needed to justify crop improvement research programs of different sizes in the presence of spill ins from abroad spill in coefficients are estimated from yield performance of varieties of different origins grown across a range of environments the model is then applied to analyze the efficiency of current investments in 69 wheat improvement research programs in 35 developing countries a major conclusion of the paper is that given the magnitude of potential spill ins from the international research system many wheat research programs could significantly increase the efficiency of resource use by reducing the size of their wheat research programs and focusing on the screening of varieties developed elsewhere 2000 elsevier science b v all rights reserved

a production lot size inventory model for deteriorating items and arbitrary production and demand rates abstract in this paper we present a method for finding the optimal replenishment schedule for the production lot size model with deteriorating items where demand and production are allowed to vary with time in an arbitrary way and in which shortages are allowed the method is illustrated by a numerical example

deteriorating inventory model with quantity discount pricing and partial backordering inventory models with quantity discount pricing and partial backordering although common in practice have received very little attention from researchers the objective of this study is to develop a deterministic inventory model with quantity discount pricing and partial backordering when the product in stock deteriorates with time most retailers make pricing decisions of their products at certain times of the year and these decisions affect demand in this study the demand rate is assumed to decrease as price for the product increases unlike traditional inventory models that seek to minimize cost the objective of this study is to maximize profit the findings of this study are particularly relevant to retailers of deteriorating products in a competitive environment a numerical example is given to illustrate the theory

joint inventory allocation and pricing decisions for perishable products abstract we jointly determine the price and the inventory allocation for a perishable product with a predetermined lifetime we assume that the price of the product increases as the time when it perishes approaches as in the airline industry demand for the product is price sensitive to maximize the expected revenue we developed a discrete time dynamic programming model to obtain the optimal prices and the optimal inventory allocations for the product with a two period lifetime we then proposed three heuristics when the lifetime is longer than two periods the computational results showed that the expected revenues from the proposed heuristics were very close to that of the optimal solution we extended these results to i the case where the price for the product consistently decreases and ii the case where the price for the product first increases and later decreases

an eoq model with partial backordering and advance payments for an evaporating item abstract in the classic economic order quantity model the purchasing cost of an order is paid at the time of its receipt in some cases retailers ask purchasers to pay all or a fraction of the purchasing cost in advance and may allow them to divide the prepayment into several equal sized parts in this paper an economic order quantity model for an evaporating item with partial backordering and partial consecutive prepayments is developed with a real case study of a gasoline station real numerical examples illustrate the proposed model and the solution method

integrating deterioration and lifetime constraints in production and supply chain planning a survey abstract items with short lifetimes that are subject to deterioration are important in the business world research has a long tradition in integrating deterioration and value loss effects into mathematical models for inventory planning and control where such effects are understood as a general loss or shrinkage of inventory however there has been little work in the modeling of lifetime restrictions of items to prevent wastage and disposals especially in a dynamic planning context globalization and other trends extend the consideration of single companies to whole supply chains implying increased coordination and information needs this is important as planning decisions impact lead times and thus the quality of items in the whole supply chain products that exceed their useful lifetime can impose high costs due to inventory loss or the need to rework them this implies increased utilization of scarce resources e g machine time metals and or energy thereby increasing co 2 levels we survey the state of the art regarding depreciation effects and the modeling of lifetime constraints as well as a classification of models following business planning functions of the value chain a critical evaluation of approaches and their limitations is provided highlighting directions for future research

review of inventory systems with deterioration since 2001 abstract this paper presents an up to date review of the advances made in the field of inventory control of perishable items deteriorating inventory the last extensive review on this topic dates back to 2001 goyal s k and giri b c recent trends in modeling of deteriorating inventory european journal of operational research 134 1 16 since then over two hundred articles on this subject have been published in the major journals on inventory control indicating the need for a new review we use the classification of goyal and giri based on shelf life characteristics and demand characteristics contributions are highlighted by discussing main system characteristics including price discounts backordering or lost sales single or multiple items one or two warehouses single or multi echelon average cost or discounted cash flow and payment delay

optimal stopping and restarting production times for an eoq model with deteriorating items and time dependent partial backlogging abstract yan and cheng j operational res soc 49 1998 1288 1295 presented a general production inventory model with production rate product demand rate and deterioration rate all considered as functions of the time their model allows for shortages and partial backlogging of the unsatisfied demand at a constant rate in this paper we extend the results of yan and cheng to cover the case where the backlogging rate is a time dependent function and we propose an algorithm for the solution of this problem we also propose some conditions which we believe to be necessary for the validity for some of yan s and cheng s statements the paper closes with numerical examples which cover each one of the cases considered in the paper

the production inventory problem of a product with time varying demand production and deterioration rates abstract in this paper we consider the production inventory problem in which the demand production and deterioration rates of a product are assumed to vary with time shortages of a cycle are allowed to be backlogged partially two models are developed for the problem by employing different modeling approaches over an infinite planning horizon solution procedures are derived for determining the optimal replenishment policies a procedure to find the near optimal operating policy of the problem over a finite time horizon is also suggested

impacts of food crop improvement research evidence from sub saharan africa abstract the paper reviews and summarizes evidences of impacts of crop improvement research of major food crops in africa it provides evidence of increased availability of improved varieties of major food crops to farmers in africa increased food production in regions where adoption has occurred and positive returns to research investment indicating that agricultural research in africa has had productivity increasing impacts on its agriculture however research impacts vary considerably across countries and regions within a country as a result of agroclimatic factors and policy environment which affects the supply of seeds and other inputs and the continuity and stability of research investments the paper points to a number of important issues both internal and external to the agricultural research system organization that need to be addressed if agricultural research is to provide a stimulus for modernizing african agriculture given the small size of food crop production area in many african countries it is important for research systems to take full advantage of research spill ins from regional and international research organizations there is a great potential to increase the efficiency of research systems by improving the coordination among members of national research systems and continuing improvements in collaborations between narss and regional and international organizations

uncertainty and optimal social security systems this paper examines the annuity aspect of social security within the framework of an overlapping generations model the duration of life is assumed to be uncertain under a fully funded system demand for social security is determined by each generation so as to maximize expected lifetime utility taking into account the welfare of future generations under a pay as you go system with intergenerational transfers demand for retirement benefits by the working population takes into account taxes paid by descendants it is shown that the two modes of finance are equivalent in terms of all real aggregates effects of changes in expected lifetime and in the birth rate are analyzed starting at the optimal level a compulsory balanced increase in social security taxes and benefits is shown to increase short run savings

econometric estimation of a global spillover matrix for wheat varietal technology abstract an econometric approach using international and national yield trial data is employed to estimate a spillover matrix for wheat varietal technology the global spillover matrix is estimated based on international yield trial data from 1979 1980 to 1987 1988 that include 195 international trial locations and 209 wheat varieties the locations were classified across countries using the cimmyt s wheat megaenvironment system and varieties were classified by both their environmental and institutional origin the model gave good explanatory power and confirmed the location specificity hypothesis at least for the varieties developed by national programs nars the spillover matrix shows that nars varieties developed in the home environment generally perform better on average than varieties developed in other megaenvironments also the matrix is not symmetric cimmyt varieties perform better on average in irrigated and high rainfall environments than nars varieties developed for these environments the yield advantage of cimmyt varieties in many test megaenvironments indicates the potential of cimmyt varieties to spill over to these test megaenvironments results also indicate that national programs are efficient in selecting from among imported technologies analysis of international data is complemented by the analysis of country level data for pakistan and kenya that confirms the above results the country level analysis however indicates that cimmyt germplasm does not do so well in some sub environments such as the irrigated short duration environment the results of the spillover matrix have implications for the design of crop breeding programs both at the national and international levels information provided by the spillover matrix can be utilized by national programs to deploy their resources more efficiently by following a mixed strategy of direct importation of technology in some environments and local development of technologies in other environments which are unique to the country

returns to public sector plant breeding in the presence of spill ins and private goods the case of bean research in michigan this article illustrates a methodology for assessing economic returns to a publicly funded breeding program in the presence of private sector investments and spill ins from other contemporary public institutions and past research efforts the approach consists of determining yield gains from bean improvement research applying these yield gain estimates to measure benefits attributable to different institutional players and time periods and then assessing the benefit cost ratios of investments in a bean improvement program since 1980 by michigan state university msu the results indicate that investments in msu s bean breeding program have yielded benefits to costs ratio in the range of 0 7 to 2 2 depending on the attribution rule used to estimate the benefits the estimated benefit cost ratios reported in this study are lower bound estimates as they do not account for potential benefits from area planted to msu varieties outside of michigan spillover effects which was 1 5 times greater than the area planted to msu bred varieties within michigan in the period 1998 2002 the implications of the increasingly privatized bean seed markets for the role of public sector research in bean improvement research are discussed

approximation algorithms for deterministic continuous review inventory lot sizing problems with time varying demand this work deals with the continuous time lot sizing inventory problem when demand and costs are time dependent we adapt a cost balancing technique developed for the periodic review version of our problem to the continuousreview framework we prove that the solution obtained costs at most twice the cost of an optimal solution we study the numerical complexity of the algorithm and generalize the policy to several important extensions while preserving its performance guarantee of two finally we propose a modified version of our algorithm for the lot sizing model with some restricted settings that improves the worst case bound

how many parts to make at once reprinted from factory the magazine of management volume 10 number 2 february 1913 pp 135 136 152 interest on capital tied up in wages material and overhead sets a maximum limit to the quantity of parts which can be profitably manufactured at one time set up costs on the job fix the minimum experience has shown one manager a way to determine the economical size of lots

an inventory model with deteriorating items quantity discount pricing and time dependent partial backlogging abstract wee international journal of production economics 59 1999 511 in his interesting paper presented a deterministic inventory model with the following characteristics quantity discount schemes for the unit cost partial backlogging at a fixed rate deterioration of stock in time and demand rate being a linear function of the selling price in this article we generalize the work of wee 1999 more specifically we consider a model where the demand rate is a convex decreasing function of the selling price and the backlogging rate is a time dependent function which ensures that the rate of backlogged demand increases as the waiting time to the following replenishment point decreases

approximation methods for the uncapacitated dynamic lot size problem we provide worst case error bounds for several approximation methods heuristics product aggregation and partitioning of the planning horizon for the uncapacitated dynamic lot size problem we propose two managerially oriented heuristics and show that they have a relative wont case error bound equal to two and develop similar analyses for methods known as the least cost per unit heuristic the part period balancing heuristic and an economic order quantity heuristic expressed in terms of a time supply of demand we also show how errors introduced by partitioning of the planning horizon in multi product multi facility problems are bounded by product set up costs and how errors introduced by product aggregation are bounded by set up costs holding costs and demands the latter results suggest methods for product aggregation that minimize the worst case error bounds

exploring strategic priorities for regional agricultural r d investments in east and central africa the 11 countries of east and central africa have diverse but overlapping agroclimatic conditions and could potentially benefit from spillovers of agricultural technology across country borders this article uses high resolution spatial data on actual and potential yields for 15 major products across 12 development domains to estimate the total benefits available from the spread of new agricultural technologies around the region market responses and welfare gains are estimated using the dynamic research evaluation for management model taking account of current and future projections of local and international demand results suggest which crops countries and agroclimatic regions offer the largest total benefits downloadable data and program files permit different assumptions and additional information to be considered in the ongoing process of strategic priority setting

a comparison between two pricing and lot sizing models with partial backlogging and deteriorated items abstract recently abad 2003 optimal pricing and lot sizing under conditions of perishability finite production and partial backordering and lost sale european journal of operational research 144 677 685 studied the pricing and lot sizing problem for a perishable good under finite production exponential decay partial backordering and lost sale in this article we extend his model by adding not only the backlogging cost but also the cost of lost goodwill we then analytically compare the net profits per unit time between abad s 2003 model and goyal and giri s 2003 the production inventory problem of a product with time varying demand production and deterioration rates european journal of operational research 147 549 557 model in abad s model the cycle starts with an instant production to accumulate stocks then stops production to use up stocks and finally restarts production to meet the unsatisfied demands by contrast in goyal and giri s model the cycle begins with a period of shortages then starts production until accumulated inventory reaches certain level and finally stops production and uses up inventory our theoretical results show that there is no dominant one between these two models furthermore we provide certain conditions under which one model has more net profit per unit time than the other finally we give several numerical examples to illustrate the results

risk inflation and the stock market most explanations for the decline in share values over the past two decades have focused on the concurrent increase in inflation this paper considers an alternative explanation a substantial increase in the riskiness of capital investments we show that the variance of firms real gross marginal return on capital has increased significantly increasing the relative riskiness of investors returns on equity and that this can explain a large part of the market decline we also assess the effects of increase in the mean and variance of the inflation rate and a decline in firms expected return on capital this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item

social security taxation and intergenerational risk sharing the life cycle hypothesis has become the dominant mode used to analyze the effects of a social security system on private saving the labor leisure choice and social welfare as both barro and samuelson indicate a fully funded social security program in a world of certainty would drive out an equivalent amount of private saving if the interest rate is r the effects of a payment of a dollar into the social security pool while young would just offset the effects of receiving 1 r dollars as a transfer when retired papers by diamond hi and samuelson among others have examined the effects of non fully funded social security schemes in a growing economy a non fully funded program can be used to alter the private sector s saving rate and hence the capital labor ratio social security then can be used as a policy tool for achieving the or some variant of the golden rule growth path this abstract was borrowed from another version of this item

saving social security and uncertainty since alteration of the saving behavior of the present working generation may have such a significant impact on capital stock growth some concern has arisen about the effect of the social security system on saving behavior in response to this concern numerous empirical and theoretical analyses have been forthcoming most of the theoretical analyses either in the form of overlapping generations models 9 11 or simpler life cycle models 6 15 have indicated that unless specific parameter values utility functions and in some cases production functions are chosen the effect of a social security system on saving is indeterminate for example kurz 11 has shown that the introduction of a simple pay as you go social security system in an overlapping generations model in which individuals do not have a leisure choice will not have a predictable effect on the steady state level of the capital stock unless parameter values and the form of the production function are known similarly in life cycle models that include a leisure choice the effect of social security is difficult to determine although feldstein 6 shows that when the leisure choice is suppressed in such a model a social security system will have a negative impact on saving this indeterminacy has not been completely resolved by empirical work although the bulk of evidence 7 8 10 12 tends to support the view that social security has depressed saving in the past unfortunately with the exception of the work of sheshinski and weiss 16 little of the theoretical analysis deals with the effect on saving behavior of participants who are faced with uncertainty about future prices wages and social security benefits sheshinski and weiss have shown that in an overlapping generations model with uncertain lifetimes the effect of increasing the role of social security through balanced increases in benefits and contributions will actually lead to an increase in saving their analysis however does not include a leisure choice nor does it deal with other forms of uncertainty facing participants consequently we still lack more complete answers to the following basic questions will the introduction of a social security program in the presence of uncertainty

the adequacy of savings this paper uses newly available data from the social security administration s retirement history survey to examine the adequacy of saving this data source is particularly rich survey data for respondents covering the ydars 1969 197 1 and 1953 have been matched with social security earnings records covering the years dating back to 1951 in addition to information on the path of lifetime earnhngs the survey contains extensive data on individual asset holdings the evidence indicates that surprisingly few couples currantly suffer significant reductions in their standard of living in their old age this appears due in large part to our compulsory savings institutions the social security and private pension systems these institutions have succeeded in redistributing the lifetime consumption of private individuals from their youth to their old age this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this item this abstract was borrowed from another version of this i this abstract was borrowed from another version of this item

dynamic version of the economic lot size model this article originally appeared in management science october 1958 volume 5 number 1 pp 89 96 published by the institute of management sciences a forward algorithm for a solution to the following dynamic version of the economic lot size model is given allowing the possibility of demands for a single item inventory holding charges and setup costs to vary over n periods we desire a minimum total cost inventory management scheme which satisfies known demand in every period disjoint planning horizons are shown to be possible which eliminate the necessity of having data for the full n periods

optimal pricing and lot sizing under conditions of perishability and partial backordering we formulate a generalized model of dynamic pricing and lot sizing by a reseller who sells a perishable good we assume that when it is economic to backlog demand the reseller can plan for periods of shortage during which demand can be partially backordered when the good is highly perishable the reseller may need to backlog demand in order to market the good at a reasonable price we present a simple solution procedure for solving the optimization problem the procedure entails solving first a single nonlinear equation and then if required two nonlinear equations

on a finite horizon production lot size inventory model for deteriorating items an optimal solution abstract a generalized production lot size inventory model for deteriorating items over a finite planning horizon is considered the demand production and deteriorating rates are assumed to be known and continuous functions of time shortages are allowed and completely backlogged the conditions under which the system total cost attains its unique global minimum are derived an example which illustrate the applicability of theoretical results is also introduced

public agricultural r d design and technological spill ins a dynamic model the paper presents a dynamic model for the analysis of the national agricultural research systems narss strategy in a context of increasing globalisation both intersectoral and international technology spill ins may greatly affect the nars design and this paper proposes an analytical framework for its study when major spill ins are present these spill ins are calculated by applying the yale technology concordance ytc methodology a var vec model is then specified to detect empirically given the calculated spill ins what nars design prevails in a dynamic framework the model is estimated for the italian agriculture data and provides evidence of close dependency on external r d sources

uncertain inflation and social security indexation abstract this paper provides a theoretical analysis of the effects of the insurance feature of social security indexation on portfolio allocation and the stability of income and consumption of the retiree within the framework of a life cycle model of allocation under uncertainty the paper shows that the magnitudes of such effects depend on the importance of social security in total wealth the covariance of real portfolio returns with the inflation rate and more importantly whether there exists market failure in providing for inflation insurance