innovation in the energy sector lessons learnt from r d expenditures and patents in selected iea countries abstract long time series of the iea and international patent offices offer a huge potential for scientific investigations of the energy innovation process thus this paper deals with a broad literature review on innovation drivers and barriers and an analysis of the knowledge induced by public research and development expenditures r d and patents in the energy sector the cumulative knowledge stock induced by public r d expenditures in 14 investigated iea countries is 102 3 bn eur in 2013 nuclear energy has the largest share of 43 9 bn eur followed by energy efficiency accounting for 14 9 bn eur fossil fuels with 13 5 bn eur and renewable energy with 12 1 bn eur a regression analysis indicates a linear relation between the gdp and the cumulative knowledge with each billion eur of gdp leading to an additional knowledge of 3 1 mil eur however linearity is not given for single energy technologies further the results show that appropriate public r d funding for research and development associated with a subsequent promotion of the market diffusion of a niche technology may lead to a breakthrough of the respective technology

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

the contribution of tourism development to economic growth in the korean economy abstract this study investigates the causal relations between tourism growth and economic expansion for the korean economy by using engle and granger two stage approach and a bivariate vector autoregression var model two principle results emerge from this study first the results of a cointegration test indicate that there is no long run equilibrium relation between two series second the outcomes of granger causality test imply the one way causal relationship of economic driven tourism growth the hypothesis of tourism led economic growth is not held in the korean economy this consequence is supported by testing the sensitivity of causality test under different lag selections along with the optimal lag

technical note note on myopic heuristics for the random yield problem bollapragada and morton 1999 present several well performing heuristics for solving the periodic inventory problem with random yield and demand their approach is essentially based on a transformation of the single period problem into a standard newsvendor problem with deterministic yield and random demand which however is supply dependent in our note we show that their evaluation of the respective optimality condition is not correct this explains the steady deterioration of their myopic heuristics for parameter constellations that correspond to increasing service levels some computational investigations reveal that the performance of the heuristics can become quite poor if service levels are high and exceed those values for which results are reported in the original study nonetheless up to now these heuristics are still the best ones available for solving the joint random yield problem

age based vs stock level control policies for a perishable inventory system abstract in this study we investigate the impact of modified lotsize reorder control policy for perishables which bases replenishment decisions on both the inventory level and the remaining lifetimes of items in stock we derive the expressions for the key operating characteristics of a lost sales perishable inventory model operating under the proposed age based policy and examine the sensitivity of the optimal policy parameters with respect to various system parameters we compare the performance of the suggested policy to that of the classical q r type policy through a numerical study over a wide range of system parameters our findings indicate that the age based policy is superior to the stock level policy for slow moving perishable inventory systems with high service levels

power approximation for computing s s policies using service level the paper presents an analytic approximation for computing s s policies for single items under periodic review with fixed ordering costs linear holding costs and a service level requirement the replenishment lead time is fixed and unfilled demand is backlogged the approximation is similar to ehrhardt s power approximation however we do not assume the knowledge of shortage costs which are difficult to estimate in practice we define a service level which measures the average backlog relative to the average demand this quantity is easy to understand and frequently used in practice the resulting power approximation policies are easy to compute and require only knowledge of the mean and variance of demand computational results show that the approximation gives a service level which is within one percentage point of the required service level in most cases furthermore the expected total costs of the approximation taking into consideration a penalty cost for stockouts are well within one percent of optimal

empirically driven hierarchical classification of stock keeping units this paper proposes a hierarchical multi criteria classification method developed for inventory management purposes and applied in a case study of the spare parts business of a household appliance manufacturer the classification method is built on the basis of six dimensions resulting in 12 different classes of spare parts for which differentiated forecasting and inventory policies are proposed and tested the results of our simulation study demonstrate the reduction of the total logistics costs by about 20 whilst still achieving the specified target service level for each class even more importantly the proposed approach is simple enough to be understood and applied by company managers thus increasing the probability of its adoption in the same or similar fashion in other real world settings

critical number policies for inventory models with periodic data we consider an infinite horizon in problem with stochastic demands where the data vary periodically karlin karlin s 1960a dynamic inventory policy with varying stochastic demands management sci 6 231 258 karlin s 1960b optimal policy for dynamic inventory process with stochastic demands subject to seasonal variations j siam8 611 629 shows that a periodic critical number policy is optimal and presents an algorithm for computing the critical numbers assuming discounted costs here we develop an alternative conceptually simpler approach to these problems the results include a proof of the optimality of such policies for the average cost case and a qualitative description of the behavior of the optimal policy as smoothing fluctuations in the data

is there a relationship between international trade and international travel this paper investigates for the first time whether there is a relationship between international trade and international travel flows using time series econometric techniques using data for australia and four important travel and trading partners the usa the uk nz and japan the paper tests three specific hypotheses that business travel leads to international trade that international trade leads to international travel and that international travel other than business travel leads to international trade using cointegration and granger causality approaches the paper finds support for prior beliefs that there is a relationship between international travel and international trade and suggests that this may be a fruitful area for further research

international travelling and trade further evidence for the case of spanish wine based on fractional vector autoregressive specifications this article deals with the relationship between international travelling and trade for this purpose we focus on a particular case study the connection between the spanish wine exports to germany and the german travellers to spain unlike previous studies we use a methodology based on fractional vector autoregressive var models which permits us to compute the impulse responses in a similar way as in the standard var case the results show that the orders of integration of the two series are constrained between 0 and 1 being higher for the arrivals series than for the exports the impulse response analysis reveals that an increase in travelling produces a positive initial impact on trade though it tends to disappear in the long run

leadtime reduction in a q r inventory system an agency perspective abstract we examine the problem of designing and implementing a continuous review q r inventory system from an agency perspective in which the agent s effort influences the item s replenishment leadtime our results are as follows if the agent is risk neutral a linear or quadratic contract achieves first best for a risk averse agent with an exponential utility function assuming a normal leadtime distribution we determine the optimal linear contract extensive numerical experiments suggest that ignoring the possible influence of the agent on the replenishment leadtime can be costly but that the cost penalty of ignoring agency can be significantly reduced by a simple contract

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

does corporate r d investment affect firm environmental performance evidence from g 6 countries the rate of climate change due to global warming has become a substantial concern and appeared as a real world phenomenon in the recent years however it is imperative to know how business enterprises alter such concern recent studies involve a variety of firm level factors to create a robust link between business enterprises environmental and financial performance however little is known regarding the role of research and development r d investment on firms environmental performance using a firm level data for the period 2004 2016 from g 6 countries this study empirically investigates how r d investment affects the firm environmental performance measured by energy and carbon emissions intensities we find that r d investment improves the firm s environmental performance consistent with the theoretical argument of natural resource based view nrbv our findings are robust to alternative econometric specifications alternative variable specifications and sub samples our findings offer novel insights to the policymakers business managers and regulators

energy research and r d indicators an lmdi decomposition analysis for the iea big 5 in energy research abstract the literature has always shown that there are two important factors in the improvement of a country s research output gross domestic product gdp and r d expenditures taking the discussion a step further and in an effort to provide policy recommendations on what is needed to boost research capacity this paper aims at decomposing the change in energy research papers of five countries australia canada germany uk and us into four factors gdp r d intensity ratio of total r d to gdp energy r d rate of return or productivity number of energy related papers per unit of energy r d expenditure and energy r d priority share of energy r d to total r d expenditure the findings show a general trend in the sign of the four effects on research for all five countries energy r d productivity energy r d priority and gdp are mostly found to be positive contributors while the r d intensity a negative one this pattern has exceptions that are more prominent during periods where economic growth is constrained for example during 2008 09 the results have policy implications not only for these five countries but also for developing countries low gdp that aim at contributing more to the energy related research output globally

the value of real time yield information in multi stage inventory systems exact and heuristic approaches abstract we consider a random yield inventory system where a company has access to real time information about the actual yield realizations to contribute to a better understanding of the value of this information we develop a mathematical model of the inventory system and derive structural properties we build on these properties to develop an optimal solution approach that can be used to solve small to medium sized problems to solve large problems we develop two heuristics we conduct numerical experiments to test the performances of our approaches and to identify conditions under which real time yield information is particularly beneficial our research provides the approaches that are necessary to implement inventory control policies that utilize real time yield information the results can also be used to estimate the cost savings that can be achieved by using real time yield information the cost savings can then be compared against the required investments to decide if such an investment is profitable

growth effects of leisure tourism and the level of economic development abstractthis study examines 1 whether leisure tourism can contribute to economic growth and 2 if it does whether its growth effects are constant across levels of economic development leisure tourism differs from business tourism in the causal relation with economic growth in addition the natural and heritage related resources for leisure tourism are limited and not reproducible this notion has a significant implication for the relationship between the growth effects of leisure tourism and the level of economic development thus the current study focuses on leisure tourism and controls for the effects of business tourism as an economy grows the growth effects of leisure tourism are expected to diminish due to a lack of continued productivity improvement in the tourism industry the empirical findings in this research reveal that leisure tourism contributes to economic growth at an early stage of economic development but its contribution becomes weaker as the economy develops

tractable q r heuristic models for constrained service levels the fill rate the proportion of demand that is satisfied from stock is a viable alternative in inventory models to the hard to quantify penalty cost however a number of difficulties have impeded its implementation among them that the existing cycle based approximate solutions do not reflect the possibility of multiple outstanding orders and that the optimal policy cannot be found directly but must be iteratively calculated we show that for a large family of leadtime demand distributions the optimal policy depends on only two parameters the fill rate and the economic order quantity eoq scaled by the standard deviation of demand over the constant leadtime if we then assume that the leadtime demand is normally distributed we can use the asymptotic results as the eoq goes to zero and to positive infinity to fit atheoretic curves for the order quantity q and the reorder point r these fitted curves yield a good q r policy without iteration we also find that among the set of simple heuristics the limit form as eoq goes to positive infinity provides a better alternative to simply setting q equal to the eoq

tourism trade and growth the case of cyprus although the relationship between international trade and economic growth has found a wide application area in the literature over the years this can not be said about tourism and growth or trade and tourism this study employs the bounds test for cointegration and granger causality tests to investigate a long run equilibrium relationship between tourism trade and real income growth and the direction of causality among themselves for cyprus results reveal that tourism trade and real income growth are cointegrated thus a long run equilibrium relationship can be inferred between these three variables on the other hand granger causality test results suggest that real income growth stimulates growth in international trade both exports and imports and international tourist arrivals to the island furthermore growth in international trade both exports and imports also stimulates an increase in international tourist arrivals to cyprus and finally real import growth stimulate growth in real export

analysis of order up to level inventory systems with compound poisson demand abstract we analyse a single echelon single item inventory system where the demand and the lead time are stochastic demand is modelled as a compound poisson process and the stock is controlled according to a continuous time order up to out level policy we propose a method for determining the optimal out level for cost oriented inventory systems where unfilled demands are backordered we first establish an analytical characterization of the optimal out level the actual calculation is based on a numerical procedure the accuracy of which can be set as highly as desired by means of a numerical investigation we show that the method is very efficient in calculating the optimal out level we compare our results with those obtained using an approximation proposed in the literature and we show that there is a significant difference in accuracy for slow moving items our work allows insights to be gained on stock control related issues for both fast and slow moving stock keeping units skus

is there a relationship between public expenditures in energy r d and carbon emissions per gdp an empirical investigation abstract energy innovation plays a crucial role in the reduction of carbon emissions in order to design climate and energy policies that promote the development deployment and diffusion of new energy technologies policy makers not only require a theoretical understanding of the energy innovation system but also empirical evidence of the effects that policy actions have had this paper focuses on public energy r d a traditional and controversial option among the various climate technology policies and empirically analyses its relationship with carbon emissions per gdp i e carbon intensity and its two components energy intensity and the carbon factor evidence of the causality links that have prevailed in 13 advanced economies over the 1980 2004 period has been obtained through dynamic panel models our findings confirm that government r d spending is not sufficient by itself to boost the energy innovation process public energy r d has been successful in improving energy efficiency at country level but it has failed to have a significant impact on the carbon factor and carbon intensity at the same time the formation of energy r d budgets is found to be significantly affected by carbon trends

causality cointegration and control abstract the first sections of the paper show that causality tests can be relevant when considering the effectiveness of a control mechanism rejecting some results in earlier papers the relevance comes from a more careful consideration of what information is available to whom and when compared to previous work the final section of the paper extends this analysis to cointegrated variables when causality is a necessary consequence

inventory problems with perishable items fixed lifetimes and backlogging our model deals with a single product and a single stock location with poisson demand the replenishment leadtime from the external supplier is fixed the lifetime of the product is also fixed and aging is assumed to begin when the order is placed when the age of a unit has reached its lifetime the unit is useless and thus discarded from the system the replenishment policy is assumed to be an order up to s policy demand that cannot be met immediately is backordered we consider three different cases where the service requirements are represented by 1 backorder costs per unit 2 a service level constraint 3 backorder costs per unit and time unit cases 1 and 2 are solved exactly while an approximation is developed for case 3 we show how the results from an earlier paper assuming lost sales can be used to solve the considered problems our results are compared to the results in a related paper considering q r policies c 2009 elsevier b v all rights reserved less

forecasting long haul tourism demand for hong kong using error correction models forecasting accuracy is particularly important when forecasting tourism demand on account of the perishable nature of the product this study compares a range of forecasting models in the context of predicting annual tourist flows into hong kong from the major long haul markets of the us the uk germany and major short haul markets of china japan and taiwan econometric forecasting models considered included error correction models ecms based on permanent income life cycle pi lc hypothesis pi lc ecm and alternative cointegration approaches engle and granger 1987 johansen 1988 and ordinary least square ols approaches both autoregressive integrated moving average arima and no change model hereafter naive models are used as a benchmark time series model for accuracy comparisons it was hypothesized that pi lc ecm is a better forecasting model particularly for long haul tourism demand the objective of this article is to investigate whether the application of pi lc ecm could improve the

tourism expansion tourism uncertainty and economic growth new evidence from taiwan and korea abstract this study examines the causal relationship between tourism expansion and economic growth in two asian countries taiwan and south korea an egarch m model with uncertainty factors is employed to examine the direction of causality between tourism expansion and economic growth as well as the impulse impacts of uncertainty on both variables the results indicate that the tourism led economic growth hypothesis is supported for taiwan while a reciprocal causal relationship is found for south korea the significant impacts of uncertainty on growth are also identified

order quantities for perishable inventory control with non stationary demand and a fill rate constraint abstract we study the practical decision problem of fresh food production with a long production lead time to decide every period e g week how many items to produce when a batch is ready for use its items have a fixed shelf life after which the items become waste in the sense that they cannot be sold anymore the demand for fresh food products is uncertain and highly fluctuating mainly caused by price promotions of retail organisations we focus on cases where a so called cycle fill rate service level requirement applies we investigate the generation of a production plan that fixes the timing and quantity of the production for a finite time horizon to minimise waste one issues the oldest items first i e a fifo issuing policy in case of out of stock sales are lost we model this decision problem as a stochastic programming sp model the objective of our study is to find order quantities for the sp model that approximately meet cycle fill rate service level requirements while keeping outdating low to find approximate solutions for the sp model an milp model is developed the milp model is a deterministic approximation that generates feasible replenishment quantities in less than a second with a scenario based minlp approach optimal solutions are generated for a large sample of demand paths as a benchmark for the milp solutions we show that the milp model is suitable for practical use if the setup cost is such that the replenishment cycles in the production plan are close to or of the same length as the maximum shelf life in those cases the expected total costs are close to the costs of the optimal solution and the average fill rate is close to the required one

the stochastic dynamic production inventory lot sizing problem with service level constraints abstract this paper addresses the multi period single item inventory lot sizing problem with stochastic demands under the static dynamic uncertainty strategy of bookbinder and tan manage sci 34 1988 1096 in the static dynamic uncertainty strategy the replenishment periods are fixed at the beginning of the planning horizon but the actual orders are determined only at those replenishment periods and will depend upon the demand that is realised their solution heuristic was a two stage process of firstly fixing the replenishment periods and then secondly determining what adjustments should be made to the planned orders as demand was realised we present a mixed integer programming formulation that determines both in a single step giving the optimal solution for the static dynamic uncertainty strategy the total expected inventory holding ordering and direct item costs during the planning horizon are minimised under the constraint that the probability that the closing inventory in each time period will not be negative is set to at least a certain value this formulation includes the effect of a unit variable purchase production cost which was excluded by the two stage bookbinder tan heuristic an evaluation of the accuracy of the heuristic against the optimal solution for the case of a zero unit purchase production cost is made for a wide variety of demand patterns coefficients of demand variability and relative holding cost to ordering cost ratios the practical constraint of non negative orders and the existence of the unit variable cost mean that the replenishment cycles cannot be treated independently and so the problem cannot be solved as a stochastic form of the wagner whitin problem applying the shortest route algorithm

optimal ordering and pricing policy for demand functions that are separable into price and inventory age abstract we formulate and analyze two models for determining the optimal pricing order quantity and replenishment period for items whose demand function is separable into components of price and inventory age the first model assumes a multiplicative demand function we provide conditions which are satisfied by most common price dependent demand functions to reduce the three variable profit maximization problem into a single variable problem which can be solved using an efficient line search method next we show that a genuine additive model cannot exist and instead suggest and analyze a pseudo additive model however this model is more limited than the multiplicative model in its ability to incorporate various combinations of price and inventory age effects and reduction of the maximization problem into a single variable problem is more complicated except in the case of a linear price effect which is further analyzed for both models we show that the optimal solution satisfies the first order condition for equilibrium under a monopoly with a modification that includes inventory holding costs we solve numerical examples to illustrate the solution procedures

myopic heuristics for the random yield problem we consider a single item periodic review inventory problem with random yield and stochastic demand the yield is proportional to the quantity ordered with the multiplicative factor being a random variable the demands are stochastic and are independent across the periods but they need not be stationary the holding penalty and ordering costs are linear any unsatisfied demands are backlogged two cases for the ordering cost are considered the ordering cost can be proportional to either the quantity ordered e g in house production or the quantity received e g delivery by an external supplier random yield problems have been addressed previously in the literature but no constructive solutions or algorithms are presented except for simple heuristics that are far from optimal in this paper we present a novel analysis of the problem in terms of the inventory position at the end of a period this analysis provides interesting insights into the problem and leads to easily implementable and highly accurate myopic heuristics a detailed computational study is done to evaluate the heuristics the study is done for the infinite horizon case with stationary yields and demands and for the finite horizon case with a 26 period seasonal demand pattern the best of our heuristics has worst case errors of 3 0 and 5 0 and average errors of 0 6 and 1 2 for the infinite and finite horizon cases respectively

an approximation to the continuous review inventory model with perishable items and lead times a continuous review perishable inventory model based on approximations to the expected outdating the expected shortage quantity and the expected inventory level is developed to determine a best q r ordering policy under a positive order leadtime when the total expected average cost per unit time is minimized the approximation method is simple and verified by a comparison with the weiss model the results reveal that the mean absolute deviation from the optimal total expected average cost per unit time is only 0 58 this paper also compares the proposed model to the conventional model with no perishability a value is given to the item lifetime indicating when an approximate answer approaches closely to the conventional ordering policy finally a simulation model written in simscript ii 5 is used to validate the approximate results

on the bias of intermittent demand estimates forecasting and inventory control for intermittent demand items has been a major problem in the manufacturing and supply environment croston operational research quarterly 23 1972 289 proposed a method according to which intermittent demand estimates can be built from constituent events croston s method has been reported to be a robust method but has shown more modest benefits in forecasting accuracy than expected in this research one of the causes of this unexpected performance has been identified as a first step towards improving croston s method certain limitations are identified in croston s approach and a correction in his derivation of the expected estimate of demand per time period is presented in addition a modification to his method that gives approximately unbiased demand per period estimates is introduced all the conclusions are confirmed by means of an extended simulation experiment where croston s and revised croston s methods are compared the forecasting accuracy comparison corresponds to a situation of an inventory control system employing a re order interval or product group review

investigating causality in international air freight and business travel the case of australia few studies have examined the link between air cargo and business travel despite there being a generally accepted understanding that these two variables are inextricably related to each other thi

how to promote the growth of new energy industry at different stages abstract china is currently the world s largest emitter of carbon dioxide co2 vigorously developing new energy sources has become an important way to reduce co2 emissions therefore more and more scholars have studied effective ways to promote the development of new energy industry however most of the existing research use single equation linear models or static models to study the driving forces of the new energy industry this not only ignores the large number of dynamic relationships between economic variables but also produces endogeneity problems in order to overcome the shortcomings of existing research this paper uses vector autoregressive model to study the new energy industry the results show that energy consumption structure has a positive effect on the new energy industry in the short run but the effect is limited in the long run the impact of the agriculture industry is gradually narrowing over time due to the gradual reduction of crop acreage however the influence of economic growth is positive both in the short and long run this is due to the gradual optimization of industrial structure technological progress produces a similar impact owing to continued investment in research and development funding as well as research and development personnel

technical note linear inflation rules for the random yield problem analysis and computations in this paper we propose a simple heuristic approach for the inventory control problem with stochastic demand and multiplicative random yield our heuristic tries to find the best candidate within a class of policies that are referred to in the literature as the linear inflation rule lir policies our approach is computationally fast easy to implement and intuitive to understand moreover we find that in a significant number of instances our heuristic performs better than several other well known heuristics that are available in the literature

the nature of the relationship between international tourism and international trade the case of german imports of spanish wine this article deals with the relationship between international trade and tourism we focus on the effect that german tourism to spain has on german imports of spanish wine due to the different stochastic properties of the series under analysis which display different orders of integration a methodology is used based on long memory regression models where tourism is supposed to be exogenous the period covered is january 1998 to november 2004 the results show that tourism has an effect on wine imports that lasts between 2 and 9 months disaggregating the imports across the different types of wine it is observed that only for red wines from navarra penedus and valdepenas and to a certain extent for sparkling wine tourism produces an effect on future import demand from a policy making perspective our results imply that the impact of tourism on the host economy is not only direct and short term but also oblique and delayed thus reinforcing the case for tourism as a means for economic development

inventory models with minimal service level constraints abstract this paper investigates inventory models in which the stockout cost is replaced by a minimal service level constraint slc that requires a certain level of service to be met in every period the minimal service level approach has the virtue of simplifying the computation of an optimal ordering policy because the optimal reorder level is solely determined by the minimal slc and demand distributions it is found that above a certain critical service level the optimal s s policy collapses to a simple base stock or order up to level policy which is independent on the cost parameters this shows the minimal slc models to be qualitatively different from their shortage cost counterparts we also demonstrate that the imputed shortage cost transforming a minimal slc model to a shortage cost model does not generally exist the minimal slc approach is extended to models with negligible set up costs the optimality of myopic base stock policies is established under mild conditions

does tourism promote cross border trade we estimate a simultaneous bivariate qualitative choice model of arizona agribusiness firms propensity to trade and visit as a tourist the cross border state of sonora mexico venture business visits quantified through the tourism equation were found to have the largest impact on a firm s propensity to trade tourist visits have a greater impact on trade when combined with other firm attributes such as age perceived need for geographic diversity foreign language fluency and firm size than if considered alone our results suggest that there is a role for government agencies to play in overcoming imperfect information related to trade opportunities through facilitating exploratory business venture and tourist visits

continuous review s s policies with lost sales a method is developed to calculate an s s policy that minimizes the average stationary cost in an inventory system with constant lead time fixed order cost linear holding cost per unit time linear penalty cost per unit short discrete compound poisson demand and lost sales it is assumed that at most one order is outstanding or equivalently that s s s the procedure is compared to several easier to compute approximate solutions including one that assumes backordering examples are given that reveal that although the backorder solution is different than the lost sales one the cost penalty of using it in the lost sales situation is small

poverty human development and growth an emerging consensus this paper considers several issues relevant to the debate on the extent to which poverty or development progress in general should be measured by income or by a broader set of objectives issues covered here are practical implications of the two approaches for poverty reduction efforts the impact of growth on basic social indicators and how national achievement on social indicators is best measured sri lanka and pakistan countries often cited in this debate are used as examples

concepts for safety stock determination under stochastic demand and different types of random production yield abstract we consider a manufacturer s stochastic production inventory problem under periodic review and present methods for safety stock determination to cope with uncertainties that are caused by stochastic demand and different types of yield randomness following well proven inventory control concepts for this problem type we focus on a critical stock policy with a linear order release rule a central parameter of this type of policy is given by the safety stock value when non zero manufacturing lead times are taken into account in the random yield context it turns out that safety stocks have to be determined that vary from period to period we present a simple approach for calculating these dynamic safety stocks for different yield models additionally we suggest approaches for determining appropriate static safety stocks that are easier to apply in practice in a simulation study we investigate the performance of the proposed safety stock variants

inventory service level measures convexity and approximation we argue that standard approximations for two often used inventory service level measures may perform poorly in many situations then we confirm the long standing conjecture that the relatively exact formulas for these quantities are convex functions of the relevant control variables both results suggest the exact expressions should be seriously considered in practical work

does a common currency promote countries growth via trade and tourism the main aim of this study is to contribute to the debate on the effects of a common currency in particular the impact of a common currency on growth via trade and tourism is explored for a panel dataset which includes 179 countries as destination and 30 oecd countries as origin over the period 1995 2006 this research contributes to previous work in three ways i tourism is included as an additional channel for a common currency to promote growth ii the heterogeneity of countries is addressed by dividing the sample into three groups of countries by income and iii up to date data including the case of the euro are considered the results obtained suggest that a common currency strengthens economic growth by promoting not only international trade but also tourism

effects of correlation on intermittent demand forecasting and stock control abstract this study investigates the effects of three different types of correlation on forecasting and stock control of intermittent demand items applying appropriate forecasting and stock control methods to theoretically generated compound poisson demand data we show that correlation in intermittent demand does play a role in forecast quality and stock control performance negative autocorrelation levels lead to higher service levels than positive values while cost does not significantly change our results also show that high intermittency levels intensify these changes in service level we also show that cross correlation produces results in the opposite direction of autocorrelation in size or intervals that is positive negative cross correlation leads to higher lower service levels

approximations for the relative outdating of perishable products by combining stochastic modeling simulation and regression modeling abstract in this paper we derive approximations for the expected amount of outdating waste in an inventory system with perishable products periodic review positive lead time fixed case pack sizes and a first in first out withdrawal policy demand is discrete and stochastic demand which is not met from inventory on hand will be lost the approximations can be used to evaluate how the amount of outdating can be reduced by changing the safety stock and or the product and demand characteristics we first derive approximations in an analytical way and then use regression to improve these approximations the final approximation is very fast and performs very well the mean and standard deviation of the approximation error are equal to 0 01 and 0 78 moreover the approximation is applicable in situations with parameter settings which are frequently encountered in practice and for which no other approximations have been derived in the literature before

optimal inventory policy for a perishable item with demand function sensitive to price and time abstract we formulate a model for determining the optimal pricing order quantity and replenishment period for perishable items with price dependent and time dependent demand the items have a fixed shelf life and the demand rate decreases linearly in the selling price and polynomially over the time after replenishment until it vanishes either at the reservation price or at expiration time we prove that the three variable profit maximization problem can be reduced into a single variable problem in which the variable is the duration of the replenishment period we show that the profit function is strictly pseudo concave and provide means of obtaining the optimal policy three numerical examples are presented to demonstrate the model accompanied by a sensitivity analysis

s 1 s policies for perishable inventory we consider s 1 s policies for a single item whose lifetime is fixed and known with certainty demands are generated by a stationary poisson process and there is a positive leadtime for replenishment we believe this study gives the only analysis for perishables with a positive order leadtime the analysis involves the derivation of the stationary distribution of the s dimensional stochastic process corresponding to the time elapsed since the last s orders were placed this distribution is then used to obtain an expression for the expected cost rate of operating the system in steady state as a function of s a computer program has been developed to compute optimal s values and expected annual costs we report a computation for a variety of system parameters which show some of the unusual features of the problem finally we show how this model can be used in the context of a problem of optimizing availability of operating equipment subject to scheduled maintenance as well as random failure

social rate of return to r d on various energy technologies where should we invest more a study of g7 countries abstract the importance of investment in research and development r d in the energy sector is indisputable especially considering the benefits of new technologies to sustainability security and environmental protection however the nature and potential of various energy technologies that are capable of improving the energy and environmental conditions globally is a challenging task for governments and policy makers that have to make decisions on the allocation of funds in r d to do so the optimal resource allocation to r d should be determined by estimating the social rate of return for r d investments this paper aims to estimate the social rate of return of r d on various energy applications and technologies such as energy efficiency fossil fuels renewable energy sources and nuclear for the g7 countries the results show that primarily r d investment on energy efficiency technologies and nuclear are the ones that yield high social benefits for all g7 countries while exactly the opposite holds for fossil fuels

on the empirical performance of t s s heuristics the periodic t s s policies have received considerable attention from the academic literature determination of the optimal parameters is computationally prohibitive and a number of heuristic procedures have been put forward however these heuristics have never been compared in an extensive empirical study such an investigation on 3055 skus is carried out in this paper our study provides insights into the performance of t s s heuristics also in relation to demand forecasting the results show that naddor s heuristic is best able to minimize the total cost however the normal and power approximations achieve more efficient solutions in that backorder volumes are smaller at the same inventory levels indicating the potentially superior performance of these methods if the balancing of holding and backorder costs can be improved the results also show that for all heuristics the sba variant of the croston forecasting method significantly outperforms croston as well as single exponential smoothing ses

do we really understand the development of china s new energy industry abstract countries all over the world have realized that the key to resolving the dilemma between accelerated energy consumption and reduction in carbon dioxide emission is to actively develop new energy industry many scholars have conducted in depth investigation into the main driving forces of the new energy industry however they often adhere to an assumption that the effect of the driving forces on new energy industry is constant across areas ignoring the spatial heterogeneity in economic phenomena geographically weighted regression gwr model and the use of local sample data to implement parameter estimation can make up for the inadequacies of existing research therefore this paper uses the gwr model to carefully investigate the new energy industry the results show that the impact of economic growth on the new energy industry in the eastern region is higher than in the central and western regions owing to the differences in economic structure and fixed asset investment the impact of foreign energy dependence continuously declines from the eastern region to the central and western regions this is attributable to the differences in natural gas and oil imports technological progress has a similar effect on account of the differences in r d funding and r d personnel investments however the impact of the agriculture industry in the central region is higher than in the eastern and western regions due to the differences in crop acreage and agricultural output this study improves our understanding of the new energy industry and would help local authorities to formulate targeted policies for promoting the growth of new energy industry