make to order or make to stock model and application some firms make all their products to order while others make them to stock there are a number of firms that maintain a middle ground where some items are made to stock and others are made to order this paper was motivated by a consumer product company faced with the decision about which items to make to stock and which ones to make to order and the inventory and production policy for the make to stock items the production environment is characterized by multiple items setup times between the production of consecutive items limited capacity and congestion effects in such an environment making an item to order reduces inventory costs for that item but might increase the lot size and inventory costs for the items made to stock also lead times increase because of congestion effects resulting in higher safety stocks for make to stock items and lower service levels for make to order items thus leading to a complex trade off we develop a nonlinear integer programming formulation of the problem we present an efficient heuristic to solve the problem which was motivated by key results for a special case of the problem without congestion effects that can be solved optimally we also develop a lower bound to evaluate the performance of the heuristic a computational study indicates that the heuristic performs well we discuss the application of the model in a large firm and the resulting insights we also provide insights into the impact of various problem parameters on the make to order versus make to stock decisions using a computational study in particular we find that the average number of setups of an item selected for make to stock production is always less than half the average number of setups of the item if it were to be made to order also factors other than an item s demand such as its setup time processing time and unit holding cost impact the make to order versus make to stock decision

scheduling the production of several items with random demands in a single facility consider the problem of scheduling the production of several items in a single facility that can produce only one item at a time this problem occurs since it is often economic to produce several items in a single facility the objective is to reduce the long run average holding backorder and setup costs we assume that demands are random with constant expected rates we allow backorders and charge holding and backlogging costs at linear time weighted rates items are produced at continuous constant rates setup times and setup costs are item dependent constants these parameters however are independent of the order of setups a real time scheduling tool is developed in three steps first with demands replaced by their expectations we compute an optimal or near optimal target cyclic schedule next we study the problem of scheduling the facility after a single disruption perturbs the inventories the goal is to recover the target cyclic schedule at minimal excess over the average cost of the cyclic schedule we formulate this as a control problem and obtain a linear recovery policy that is optimal for a large configuration of disruptions finally we select safety stocks to minimize the long run average cost of following the target schedule with the recovery policy we show that optimal safety stocks are unique and have the property that in the long run the proportion of time that an item is in stock is the ratio of backorder to holding plus backorder cost we present an example that integrates the cyclic schedule the control policy and the safety stocks

determination of safety stocks for cyclic schedules with stochastic demands abstract this paper considers the problem of scheduling the production of multiple items each with random demand on a single facility we show how the variance in demand during lead time can be estimated and present a model for determination of safety stocks and order up to levels for a fixed cyclic sequence both with and without idle time for systems with idle time we present a control model to make the decision to produce next item in sequence or idle the facility the performance of the model is tested in a simulation study

myths and facts of the utility death spiral abstract as the electricity industry is changing worldwide the swift expansion of basic forms of distributed generation dg particularly photovoltaic deployment threatens the current utility business models that during the transitional stages may challenge the reliability of electricity systems and societal welfare these findings are matters of major concern to policy makers as the shift towards more decentralized power systems must be sustainable and although this brings great opportunities it also pauses important challenges the transition calls for policy and regulation attention for some researchers dg development should be accompanied with design changes to distribution tariffs the addition of connection charge and modifications to net metering while for others certain of these measures could discourage dg investments in this context and given multiple uncertainties the authors propose a system dynamics model to examine the effect of the diffusion of photovoltaic technology on the revenues of utilities and customers the paper concludes that for the colombian case it is possible under certain conditions to attain a balance between social welfare and the aversion of the utility death spiral through systemic interventions

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

job matching and on the job training conventional analysis predicts that workers pay part of their on the job training costs by accepting a lower starting wage and subsequently realize a return to this investment in the form of greater wage growth missing from the conventional treatment of on the job training is a discussion of the process by which heterogeneous workers are matched to jobs requiring varying amounts of training this matching process constitutes a key feature of the on the job training model presented in this article and tested with a unique data set containing extensive information concerning on the job training employer search wages and wage and productivity growth

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

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

lot sizing and lead time decisions in production inventory systems traditionally lot sizing decisions in inventory management trade off the cost of placing orders against the cost of holding inventory however when these lot sizes are to be produced in a finite capacity production inventory system the lot size has an important impact on the lead times which in turn determine inventory levels and costs in this paper we study the lot sizing decision in a production inventory setting where lead times are determined by a queueing model that is linked endogenously to the orders placed by the inventory model assuming a continuous review s s inventory policy we develop a procedure to obtain the distribution of lead times and the distribution of inventory levels when lead times are endogenously determined by the inventory model this procedure allows to determine the optimal inventory parameters within the class of s s policies that minimize the expected ordering and inventory related costs over time we numerically show that ignoring the endogeneity of lead times may lead to inappropriate lot sizing decisions and significantly higher costs this cost discrepancy is very outspoken if the lot size based on the economic order quantity deviates significantly from desirable production lot sizes in these cases the endogenous treatment of lead times is of particular importance

flexible lot sizing in hybrid make to order make to stock production planning abstract hybrid make to order make to stock production systems are difficult to control batch production of make to stock products allows for efficient capacity usage but fixed batch sizes can make the system less responsive to make to order customers using markov decision process modeling we show that the optimal policy for such hybrid systems varies the lot size in response to make to order backlogs as well as stock levels we evaluate the performance of this flexible lot sizing policy for a two product hybrid system we find that it leads to savings of up to 23 compared to policies that use either completely or partly fixed lot sizes we also find that flexible lot sizing is especially beneficial for systems with a low load and where make to stock is important in terms of production capacity usage and cost

wages and the composition of experience this paper provides evidence on the relation between alternative forms of experience and wages using data drawn from the national longitudinal survey of youth prior labor market experience is segmented into mutually exclusive categories based on industry and occupation to examine how subsequent employers value skills acquired on previous jobs we find that most forms of experience including tenure at the current job provide a comparable return however the wage return to prior experience in a different occupation and industry is significantly lower such career changes constitute over half of all prior work experience among workers in their mid 30s

the u s investment tax credit for solar energy alternatives to the anticipated 2017 step down abstract solar photovoltaic pv installations in the united states have been deployed at a rapid pace in recent years a development that is attributed in significant part to the federal investment tax credit itc yet this credit is scheduled to step down from 30 to 10 at the beginning of 2017 for corporate investors for a sample of five u s states and different segments of the solar industry we find that the anticipated itc step down in 2017 would increase the levelized cost of solar power by a significant margin raising the specter of a cliff for the solar industry our analysis identifies and evaluates an alternative phase down scenario that would reduce the itc gradually over time and eliminate it completely by 2024 for this alternative phase down scenario it is shown that solar pv would remain broadly competitive provided the solar industry can maintain the pace of cost reductions demonstrated in past years

comparison of dynamic scheduling policies for hybrid make to order and make to stock production systems with stochastic demand we examine the previously under researched problem of scheduling a single stage capacitated hybrid make to order mto and make to stock mts production system with stochastic demand we build on the economic lot scheduling problem elsp literature and make some modifications to incorporate mto products at the tactical level target cycles kept long enough to trade off changeover and inventory costs are calculated while at the operational level the general idea is to try and follow these target cycles and make adjustments to them in order to a avoid stock outs for nits products and b have short lead time for mto products while keeping the overall costs as low as possible through an extensive simulation study we evaluate various run out time scheduling and sequencing heuristics and provide a more complete understanding and managerial insights in the case of hybrid mto mts environment with stochastic demand it is clear that the methods that perform well for pure mts situations do not necessarily perform well for hybrid mto mts situation c 2004 elsevier b v all rights reserved

a single item continuous review inventory problem with space restriction abstract with today s high cost of land acquisition observed in most countries management can no longer afford large storage facilities to house their products for this reason one of the main concerns of inventory managers is to ensure that enough storage space is available upon the delivery of a product they therefore have to determine the least cost ordering policy so as to meet demand and taking into account the space limitation in this paper we investigate the problem of a single item continuous review inventory problem in the presence of a space restriction when the demand is stochastic through a sensitivity analysis study it is found that ordering cost storage capacity average demand per unit time and holding cost rate are the most influential problem parameters on the expected inventory costs it is also shown numerically that a simple solution based on economic order quantity is performing very well with an average and maximum cost penalty of 0 19 and 2 03 respectively

cyclical schedules vs dynamic sequencing replenishment dynamics and inventory efficiency abstract this paper addresses the efficiency of fixed sequence cyclical scheduling systems relative to that of dynamically sequenced order point methods of production control the criterion for comparison is the aggregate inventory required to achieve a target fill rate taking into account the alternative replenishment dynamics arising under the respective systems a simulation analysis demonstrates that cyclical scheduling may have smaller aggregate inventory requirement when the production process is highly utilized and when this utilization is due to demand for a small number of items having large setup times

intra firm wage compression and coverage of training costs evidence from linked employer employee data the author uses german linked employer employee data to estimate the impact of intra firm wage dispersion on the probability that establishments pay for further training about half of all establishments in the estimation sample cover all direct and indirect training costs which contradicts the standard human capital approach with perfect labor markets the main finding of cross section panel and instrumental variable probit estimations is that establishments with larger intra firm wage compression are more likely to cover all direct and indirect training costs which is consistent with theoretical considerations of the new training literature about imperfect labor markets

quality investment and price decision in a risk averse supply chain abstract in this paper we investigate quality investment and price decision of a make to order mto supply chain with uncertain demand in international trade due to volatility of orders from buyers the supplier and the manufacturer in the supply chain are subject to financial risk in contrast to the general assumption that players in a supply chain are risk neutral in quality investment and price decision we consider the risk averse behavior of the players in three different supply chain strategies vertical integration vi manufacturer s stackelberg ms and supplier s stackelberg ss the study shows that both supply chain strategy and risk averse behavior have significant impacts on quality investment and pricing compared to a risk neutral supply chain a risk averse supply chain has lower same and higher quality of products in vi ms and ss respectively also we derive the conditions under which the supply chain strategy is implemented in a decentralized setting a numerical study is used to illustrate some related issues

integrated lot sizing and safety stock placement in a network of production facilities abstract in a network of production facilities safety stock placement is determined at the network level to hedge against uncertainty in demand while considering the production cycle time pct of each stage as an exogenous parameter the lot sizing policy at each stage affects setup time capacity and is a major determinant of queuing behavior and pct this paper integrates strategic safety stock placement and tactical lot sizing which are typically optimized independently we model the integrated problem to minimize system wide production and inventory costs subject to meeting service level requirements of external customers we establish bounds for optimal lot sizes and extend existing safety stock placement dynamic programming algorithm to solve the integrated problem based on numerical experiments we assess the value of integrating the two decisions and find that integration leads to smaller lot sizes shorter lead times and favors pooling of safety stocks the setup cost setup time and the added value at a production stage are the most significant factors in determining the amount of savings generated through integration in addition simulation studies show that integration reduces pct variability and decreases the fraction of delayed items

inefficient hiring in entry level labor markets hiring inexperienced workers generates information about their abilities if this information is public workers obtain its benefits if workers cannot compensate firms for hiring them firms will hire too few inexperienced workers i determine the effects of hiring workers and revealing more information about their abilities through a field experiment in an online marketplace i hired 952 randomly selected workers giving them either detailed or coarse public evaluations both hiring workers and providing more detailed evaluations substantially improved workers subsequent employment outcomes under plausible assumptions the experiment s market level benefits exceeded its cost suggesting that some experimental workers had been inefficiently unemployed

future proof tariff design recovering sunk grid costs in a world where consumers are pushing back abstract traditional analysis of distribution network tariff design assumes a lack of alternatives to grid connection for the fulfilment of consumers electricity needs this is radically changing with breakthroughs in two technologies 1 photovoltaics pv enable domestic and commercial consumers to self produce energy 2 batteries allow consumers and self producers to gain control over their grid energy and capacity parameters contributing to the state of the art the grid cost recovery problem for the distribution system operator dso is modelled as a non cooperative game between consumers in this game the availability and costs of the two named technologies strategically interact with tariff structures four states of the world for user s access to technologies are distinguished and three tariff structures are evaluated the assessed distribution network tariff structures are energy volumetric charges with net metering energy volumetric charges for both injection and withdrawal and capacity based charges results show that in a state of the world with new technology choices for grid users both efficiency and equity issues can arise when distribution network charges are ill designed

dividing the costs and returns to general training data from the national longitudinal survey of youth indicate that the employer often pays the explicit costs of not only on site training but also off site general training although few of these costs appear to be passed on to workers in the form of a lower wage while in training completed spells of general training paid for by previous employers have a larger wage effect than completed spells of general training paid for by the current employer a model where contract enforcement considerations cause employers to share the costs and returns to purely general training can explain these findings

how feed in remuneration design shapes residential pv prosumer paradigms as part of their clean technology and decarbonization strategies numerous countries have introduced feed in remuneration fir schemes to spur the deployment of solar photovoltaics pv however in the light of rising retail electricity prices and falling costs for rooftop solar installations in recent years policy makers and regulators face the difficult task of deciding when and how these schemes should be amended or phased out to understand how such actions might shape the role of residential solar and the resulting economics in a changing electricity system we study how the design of fir schemes affects optimal pv system sizes to illustrate our approach we draw on empirical data on the fir policies of net metering and feed in tariffs from california and germany between 2005 and 2016 using a techno economic model and a conceptual framework we show that fir design and its interplay with retail electricity prices and pv system costs jointly determine whether residential pv installations are economic how they are sized and which prosumer paradigms they spur our analysis holds numerous implications for policy makers and advisors responsible for redesigning or adapting existing fir mechanisms as well as for the stakeholders of an emerging ecosystem based on residential solar pv

the unemployment volatility puzzle the role of matching costs revisited recently pissarides 2009 has argued that the standard search model with sunk xed matching costs increases unemployment volatility without introducing an unrealistic wage response in new matches we revise the role of matching costs and show that when these costs are not sunk and therefore can be partially passed on to new hired workers in the form of lower wages the amplication mechanism of xed matching

the strategic use of capacity slack in the economic lot scheduling problem with random demand growing interest in designing systems with capacity slack as one form of flexibility raises many questions about its use and its usefulness in the framework of the economic lot scheduling problem with stochastic demand we develop on optimization based model that considers capacity slack safety stock and overtime explicitly and has the objective of minimizing the expected cost per unit time of inventory overtime and where applicable setup costs the solution is a continuous time production plan that consists of a time dependent inventory trajectory for each of the parts including the placement of planned idle time in the schedule we consider schedule stability to be desirable because of potential effects on upstream and downstream operations in multistage production settings thus the plan also has certain characteristics that contribute to achieving stability our results on the relative merits of capacity slack and safety stock indicate that capacity slack in the form of planned idle time is

investment in general training the role of information and labour mobility following the seminal work of becker i964 it is widely accepted in the literature that firms will be unwilling to finance training which workers may use in other firms this paper takes issue with this prediction and suggests that firms will frequently share in the cost of such general training 1 becker argues that a firm which pays for the training of workers in skills of potential use to other firms will lose these workers since other firms bear none of the costs of general training they can attract a worker with such training by outbidding the firm which trained him recognising this absence of property rights over an investment in general training firms will refuse to provide it hence if general training is to take place the trainee will have to pay for it if potential trainees are unwilling or unable to pay general training will not take place a shortage in general training is likely to emerge this may be especially pronounced in developing countries 2 in contrast the outlook for

firm sponsored general education and mobility frictions evidence from hospital sponsorship of nursing schools and faculty this study asks why hospitals provide direct financial support to nursing schools and faculty this support is striking because nursing education is clearly general clearly paid by the firm and information asymmetries appear minimal using aha and survey data i find hospitals employing a greater share of their msa s registered nurses are more likely to provide direct financial support to nursing schools and faculty net of size and other institutional controls given the institutional context i interpret this result as unusually specific evidence that technologically general skill training may be made de facto specific by imperfect and costly mobility

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

cost competitiveness of residential solar pv the impact of net metering restrictions abstract the policy of net metering allows operators of residential and commercial solar pv systems to sell surplus electricity back to their utility at the going retail rate this policy has recently been criticized on the grounds that it provides a subsidy for residential and commercial solar installations a subsidy that is paid for by all ratepayers in response public utility commissions have begun to take up this regulatory issue this paper presents a theoretical and empirical analysis of the effects of net metering restrictions we examine the impact that overage tariffs ot will have on the size of future residential pv investments overage tariffs credit electricity generated by the solar system but not consumed by the household and thus transferred back to the utility at a rate below the going retail electricity rate our calculations focus on three representative locations in the states of california nevada and hawaii we find that if overage electricity is credited at some rate set at or above the levelized cost of electricity lcoe there would be sufficient incentives for investors in residential solar pv to continue in the current mode of solar rooftop installations even though the profitability of these investments might be reduced substantially at the same time we find that the lcoe is a tipping point insofar as overage tariffs set below that level would have a sharply negative effect on the individual size and overall volume of new rooftop installations

some ideas regarding reserving supplier capacity and selecting replenishment quantities in a project context abstract in this paper we consider the context of a major project whose execution takes several periods specifically we are interested in the procurement policy for a resource material commodity or engineered item that is used throughout the project two types of uncertainty are considered namely i uncertainty in the requirements period by period and ii uncertainty in the capacity period by period of the supplier providing the resource there is the possibility of paying a premium to reserve dedicated capacity that can vary from period to period hence the first group of decision variables are the capacities to reserve period by period there is typically a long lead time involved so that all the capacities must be reserved prior to the first replenishment decision the second class of decision variables encompasses the procurement quantities period of period these decisions can be made as the project progresses we present some general approaches to dealing with this complex problem as well as some important insights

lot size effects on process lead time lead time demand and safety stock abstract a comprehensive process lot sizing order point model is developed in which queuing relationships are used to endogenously model the effects of lot size on the lead time demand distribution the model is used to examine the effect of shortage penalty on the optimal lot size when the model reflects job queuing dynamics arising from the lot size decision a coordinated policy of safety stock adjustment and lead time reduction through lot size adjustment is shown be more efficient than responding to changes in the shortage penalty parameter solely through adjustment of safety stock

general training by firms apprentice contracts and public policy workers will not pay for general on the job training if contracts are not enforceable firms may if there are mobility frictions private information about worker productivities however prevents workers who quit receiving their marginal products elsewhere their new employers then receive external benefits from their training in this paper training firms increase profits by offering apprenticeships which commit firms to high wages for those trainees retained on completion at these high wages only good workers are retained this signals their productivity and reduces the external benefits if they subsequently quit regulation of apprenticeship length a historically important feature enhances efficiency appropriate subsidies enhance it further

the economic returns to an mba because mba programs require work experience before admittance prior wages can be exploited to disentangle the return to the degree from unobserved productivity we find that controlling for individual fixed effects generally reduces the estimated returns to an mba particularly for those in top programs however for full time mba students attending schools outside of the top 25 the estimated returns are higher when we control for individual fixed effects we show that there is some evidence that those who take the gmat but do not obtain an mba are stronger in dimensions such as workplace skills that are not easily measured

why do temporary help firms provide free general skills training the majority of u s temporary help supply ths firms offer nominally free unrestricted computer skills training a practice inconsistent with the competitive model of training i propose and test a model in which firms offer general training to induce self selection and perform screening of worker ability the model implies and the data confirm that firms providing training attract higher ability workers yet pay them lower wages after training thus beyond providing spot market labor ths firms sell information about worker quality to their clients the rapid growth of ths employment suggests that demand for worker screening is rising

integrated management of inventory and production systems based on floating decoupling point and real time information a simulation based analysis abstract globalisation has transformed market conditions reducing lead times and increasing both the degree of product differentiation and price competition to cope with this issue new hybrid order fulfilment strategies have emerged which integrate the make to stock mts and build to order bto strategies and whose aim is to simultaneously improve opposite objectives such as the stock level and the lead time furthermore companies face frequent challenges of sharing updated information and avoiding the lack of coordination between the different company subsystems this work focuses on relatively recent fulfilment strategies based on the floating decoupling point fdp which uses real time information to operate the main objectives of this work are the study of the influence of different sources of real time information about the available products and select the most suitable configuration of these systems regarding the inventory control policy and the source of real time information the stochastic nature of the process makes simulation an appropriate tool to achieve valuable results the simulation studies have been carried out following a full factorial design of experiments doe experimental results show that the strategies based on the fdp are very sensitive to the real time information these systems achieve the best performance when the inventory control policy uses simultaneously demand forecasting and real time information of available products corresponding to the work in process wip and finished goods inventory fgi in contrast system performance deteriorates significantly when real time information of available products in the wip has not been taken into account

you paid for the skills now keep them tuition reimbursement and voluntary turnover does investing in employees marketable skills reduce turnover this study uses insights from human capital theory to explain how general skill development and promotion relate to voluntary turnover data from 9 439 salaried employees of a large manufacturer show that participation in tuition reimbursement reduces turnover while employees are in school voluntary turnover increases when individuals earn graduate degrees but is significantly reduced if they are subsequently promoted

relational knowledge transfers an expert must train a novice the novice initially has no cash so he can only pay the expert with the accumulated surplus from his production at any time the novice can leave the relationship with his acquired knowledge and produce on his own the sole reason he does not is the prospect of learning in future periods the pro t maximizing relationship is structured as an apprenticeship in which all production generated during training is used to compensate the expert knowledge transfer takes a simple form in the rst period the expert gifts the novice a positive level of knowledge which is independent of the players discount rate after that the novice s total value of knowledge grows at the players discount rate until all knowledge has been transferred the ine ciencies that arise from this contract are caused by the expert s arti cially slowing down the rate of knowledge transfer rather than by her reducing the total amount of knowledge eventually transferred we show that these ine ciencies are larger the more patient the players are finally we study the impact of knowledge externalities across players

technical change and the returns and investments in firm level training evidence from thailand abstract this paper examines determinants of investments in and returns to training with focus on technical changes using employee panel data in thai manufacturing industries empirical findings demonstrate significant returns to both on the job and off the job training in first difference fixed effect estimation of wage equations controlling for technical changes which differentially influence training investments and the returns first returns to informal on the job training are robust contrary to findings from developed countries second technical change induces both on the job and off the job training and controlling for technical change makes returns to on the job training even larger implications for training and education policies are discussed

are small scale grid connected photovoltaic systems a cost effective policy for lowering electricity bills and reducing carbon emissions a technical economic and carbon emission analysis this research discusses findings from technical simulations and economic models of 1kw p and 3kw p grid connected photovoltaic pv systems supplying a rural home electricity load in parallel with the electricity network in western australia wa the technical simulations are based on electricity billing consumption monitoring an energy audit data combined with 15min interval load and pv system performance for commercially available technologies and balance of system components using long term meteorological input data the economic modelling uses 2010 market prices for capital costs operational costs electricity tariffs subsidies and is based on discounted cash flow analyses which generate a final net present value npv for each system against network electricity costs in australian dollars aud over a 15 year investment horizon the results suggest that current market prices generate a negative npv a net private loss even with the current government subsidies which lead to higher home electricity costs than conventional network electricity use additionally the private costs of carbon emission mitigation aud tco 2 e 1 for the grid connected pv system simulations and models were around aud 600 700 tco 2 e 1 a particularly expensive option when compared to existing large scale renewable energy mitigation activities

testing some predictions of human capital theory new training evidence from britain we confront the predictions of various theories with new training data from the british household panel survey we find that employer financed training is associated with significantly higher wages at current and future firms with a larger impact in future firms this is consistent with human capital theory with credit constraints and with the new training literature assuming imperfectly competitive labor markets

training systems and labor mobility a comparison between germany and sweden the mobility effect of general and specific training is a key issue in the debate on the design of educational systems using data from two retrospective life history surveys we compare general school based vocational training and specific apprenticeship training with regard to inter firm inter occupational and inter industrial mobility the results show that workers with school based degrees display greater occupational mobility while no difference in firm and industrial mobility can be discerned this suggests that apprenticeships do not eliminate job search at labor market entry that they reduce occupational mobility and that responsiveness to structural change is similar under both training systems

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

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

product line competition customization vs proliferation we study a market with customers who have heterogeneous preferences for product attributes we consider two types of firms that compete on price and product variety a traditional firm which chooses a limited set of product configurations and a customizing firm which can produce any configuration to order the traditional firm carries product inventories and experiences a lead time delay the customizing firm does not carry inventory and its customers incur waiting costs until they receive their orders we assume that the customizing firm has limited capacity in the short run e g when it does not outsource production to high volume manufacturers we derive the equilibrium for a duopoly competition between the customizing firm and the traditional firm study its characteristics and compare it to a monopoly we characterize conditions that favor customization under competition we find that the customizing firm s profit is not monotone in the market size and its ease of customization similarly a

the stochastic economic lot scheduling problem cyclical base stock policies with idle times in this paper we discuss stochastic economic lot scheduling problems elsp i e settings where several items need to be produced in a common facility with limited capacity under significant uncertainty regarding demands production times setup times or combinations thereof we propose a class of production inventory strategies for stochastic elsps and describe how a strategy which minimizes holding backlogging and setup costs within this class can be effectively determined and evaluated the proposed class of strategies is simple but rich and effective when the facility is assigned to a given item production continues until either a specific target inventory level is reached or a specific production batch has been completed the different items are produced in a given sequence or rotation cycle possibly with idle times inserted between the completion of an item s production batch and the setup for the next item an optimal strategy within the class can be determined and all relevant performance measures can be evaluated in just a few cpu seconds using a 486 based pc we also derive a number of easily computable lower bounds for the optimal cost value and establish a comparison with deterministic elsps

lot sizes in a capacity constrained facility a simulation study of stationary stochastic demand abstract this paper considers the scheduling of several different items on a single machine in literature known as the economic lot scheduling problem elsp one of the characteristics of this problem is that the demand rate is deterministic and constant however in a practical situation demand usually varies in this paper we examine if a deterministic model can be used if demand is stationary stochastic a dynamic programming approach from bomberger manage sci 12 11 1966 778 and a heuristic method from segerstedt int j production econom 59 1 3 1999 469 are used to calculate lot sizes for four items the production of these items is simulated with different variations in demand rates our conclusion is that a deterministic model of this kind can be used in a practical situation where the demand rate is stationary stochastic but the models must be complemented by a decision rule which item to produce and when to produce it in our tests the heuristic method and the dynamic programming approach perform rather similarly with respect to costs and inventory levels but the dynamic programming approach results in more backorders when there is small variation in demand rates this study indicates that the model used for determination of lot sizes is of less importance than the decision rule used for identification of the item to produce and when to produce it

time of day pricing and the levelized cost of intermittent power generation abstract an important characteristic of most renewable energy sources is intermittency in their ability to generate electricity yet intermittency is usually ignored in life cycle cost calculations intended to assess the competitiveness of electric power from renewable as opposed to dispatchable energy sources such as fossil fuels this paper demonstrates that for intermittent renewable power sources a traditional life cycle cost calculation should be appended by a correction factor which we term the co variation coefficient it captures any synergies or complementarities between the time varying patterns of electricity generation and pricing we estimate the co variation coefficient for specific settings in the western united states our estimates imply that the benchmark of cost competitiveness for solar photovoltaic pv power is 10 to 15 lower than previous average life cycle cost analyses have suggested in contrast the generation pattern of wind power exhibits complementarities with electricity pricing schedules yielding a cost assessment that is higher than that suggested by traditional calculations for the specific settings we study the corresponding magnitude of the markup is 10 to 15

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

determination of an order up to policy in the stochastic economic lot scheduling model we consider a production inventory problem with compound renewal item demand the model consists of stockpoints one for each item controlled according to r s policies and one machine which replenishes them the replenishment orders are produced with a fixed rate on the machine with significant setup times and costs which are stochastic and sequence dependent the time between the release and the production of the replenishment order is called the waiting time we develop analytical approximations for the first two moments of this waiting time the order up to levels and the average physical inventory levels for all stockpoints given the target fill rates these analytical approximations allows for a quick evaluation of the waiting time which is important when optimization of the system is considered

general productivity growth in a theory of quits and layoffs an efficient matching model of quits and layoffs is developed to account for several empirical regularities differences between quits and layoffs over the life and business cycles and across demographic groups are generated by differential rates of general productivity growth the standard approach to quits and layoffs based on wage rigidity is shown to be incapable of accounting for many of the empirical regularities although a formal test rejects a structural prediction of the efficient turnover model the specification does well in predicting both the level of and time series variation in the fraction of separations labeled quits