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This study evaluated wheat production effects on carbon (C) fractions and soil organic C (SOC) molecular composition of a semiarid Plinthustalf in a trial established near Bethlehem. Treatments applied for 20 consecutive years included two straw management (unburned and burned), three tillage (no-tillage, ploughing and stubble mulch) and two weed control (chemical and mechanical) methods. Samples collected from 0-50 mm depth of specific treatment combinations were analyzed for SOC, soil inorganic C (SIC), permanganate oxidizable C (POXC), cold (CWEC) and hot (HWEC) water extractable C, extractable humic substances ([C.sub.EX]), humic acids, fulvic acids ([C.sub.FA]) and SOC functional groups. Humification (HI) and polymerization (PI) indices and alkyl C/O-alkyl C ratios were calculated. No-tillage combinations demonstrated potential to reverse losses of soil C fractions in the O-50 mm layer. Increased POXC, CWEC, [C.sub.EX] and [C.sub.FA] revealed the labile nature of accumulated SOC in no-tillage, suggesting that SOC therein could be rapidly lost if no-tilled soils were again cultivated. Although the HI and PI were not always significant, their decrease in the no-tillage combinations suggest minimal decomposition, which is a benefit in Plinthustalfs with low storage capacity. Positive correlations between SIC and SOC fractions implied that an increase in SOC fractions protected SIC, resulting in its accumulation in no-tillage combinations. Functional groups seemed to mimic fractionated SOC fractions because O-alkyl C decreased with concomitant increase in alkyl, aromatic and carbonyl C. These responses highlighted that no-tillage combinations could be ideal to restore SOC quality in drought-prone agro-ecosystems dominated by sandy soils. Additional keywords: carbon fractions, functional groups, nuclear magnetic resonance, semiarid regions, soil management., Introduction Declining soil fertility and increasing atmospheric carbon (C) can be a signal of escalating pressure on arable lands and lack of sustainable management practices to rehabilitate soils of prolonged [...]

Abstract. We formulate and analyze a stylized dynamic model of a price-taking firm that manages production and capacity, uses only internal financing, and faces stochastic market environments. The firm has [...]

Abstract. We consider the problem of managing production in a production-inventory system where a firm is subject to an allowance (a limit) on either the amount of input it can [...]

We give an efficient algorithm for computing a Cournot equilibrium when the producers are confined to integers, the inverse demand function is linear, and costs are quadratic. The method also [...]

Operation practices, commonly deals with design, management, planning, coordination, and control of resources, are the elements in the operational strategies of an organization. These operation practices are improvement programs in organizations that are carried out to achieve competitive advantage in terms of cost, speed of delivery, quality, flexibility, and innovation. There are many service improvement programs that have been undertaken by the government of Malaysia, however, local authorities are still receiving criticisms and complaints from the public stating the inability of local authorities to deliver services that meet the customers' needs. Empirical studies showed that operation practices have an influence on the performance of an organization. However, most studies only focused on specific operation practices such as quality management practices, just in time practices and human resource management practices This study, therefore, focused on examining the relationship between operational practices and performance of local authorities in Peninsular Malaysia. This study uses a cross-sectional design to identify the service operation practice and organization performance measured in one occasion to obtain data and identify relationships between variables studied. Unit of analysis of this study is the departments in the organization of local authorities and respondents are directors or heads of department. The study population was all the departments (416 departments) in the City Council and the Municipal Council in Peninsular Malaysia. Stratified sampling method was used to select 300 departments based on the characteristics of local authorities in Peninsular Malaysia. This study collected data from a total of 202 respondents who are directors or department heads of 300 selected City Councils and Municipal Councils in Peninsular Malaysia. The findings showed that the dimensions of leadership practices have a significant influence on performance. Findings of this study also show that organizational culture practices have a positive and significant influence on performance. In this study, organizational culture is defined as the practice of shared values, beliefs, attitudes, and norms practiced in the department that is conducive to the welfare of workers as employees, recognition, appreciation and listening to workers. Findings of this study also noted a positive and significant influence of the push-pull orientation in service operations with performance. The government should, therefore, emphasize local governments' ability in the push and pull orientation to improve their performance. New services development and design is the process of preparing a new delivery system procedure or making an investment in organizational resources to facilitate the service delivery organization. JEL Classifications: H70 Keywords: Leadership, Culture, Service Design, Development, Performance Corresponding Author's Email Address: abdullah.a@umk.edu.my, INTRODUCTION Operations management commonly deals with design, management, planning, coordination, and control of resources needed for the production of goods and services. Operation practices have a significant influence on an [...]

Should OM research become more relevant? I provide my own perspective on this question and some practical ideas for our community to explore. This article is based on my Manufacturing [...]

Introduction and summary Today's footprints of motor vehicle production (1) in Europe and North America appear at first glance to be remarkably similar: In both regions, plants producing motor vehicles [...]

We use a detailed data set from the U.S. auto industry spanning from 2002 to 2009 and a variety of econometric methods to characterize the relationship between the availability of [...]

Whereas theoretical studies on dynamic pricing typically assume that consumers are either fully strategic or fully myopic, systematic empirical investigations into how consumers behave under dynamic pricing contexts are relatively [...]

This essay, based on my 2013 MSOM Distinguished Fellow lecture, presents my view on new opportunities and challenges for research in operations management. Key words: operations management; research; impact on [...]

Consider a set of manufacturers, all of which can subcontract part of their workload to a third party. For C we assume that every manufacturer as well as the third [...]

In this paper, we examine the relationship between inventory levels and one-year-ahead earnings of retailers using publicly available financial data. We use benchmarking metrics obtained from operations management literature to [...]

We consider an appointment-based service system (e.g., an outpatient clinic) for which appointments need to be scheduled before the service session starts. Patients with scheduled appointments may or may not [...]

Recent cases of product adulteration by foreign suppliers have compelled many manufacturers to rethink approaches to deterring suppliers from cutting corners, especially when manufacturers cannot fully monitor and control the [...]

To help a firm reduce inefficiencies associated with equipment capacity planning, we propose I dual--mode equipment procurement (DMEP) framework. DMEP combines dual--source (i.e., a less-expensive-but-slower base mode and a faster-but-more-expensive [...]

In recent years, algorithms have been developed to help automate the production of dynamic system models. Part of this effort has been the development of algorithms that use modeling metrics for generating minimum complexity models with realization preserving structure and parameters. Existing algorithms, add or remove ideal compliant elements from a model and consequently do not equally emphasize the contribution of the other fundamental physical phenomena, i.e., ideal inertial or resistive elements, to the overall system behavior Furthermore, these algorithms have only been developed for linear or linearized models, leaving the automated production of models of nonlinear systems unresolved. Other model reduction techniques suffer from similar limitations due to linearity or the requirement that the reduced models be realization preserving. This paper presents a new modeling metric, activity, which is based on energy. This metric is used to order the importance of all energy elements in a system model. The ranking of the energy elements provides the relative importance of the model parameters and this information is used as a basis to reduce the size of the model and as a type of parameter sensitivity information for system design. The metric is implemented in an automated modeling algorithm called model order reduction algorithm (MORA) that can automatically generate a hierarchical series of reduced models that are realization preserving based on choosing the energy threshold below which energy elements are not included in the model. Finally, MORA is applied to a nonlinear quarter car model to illustrate that energy elements with low activity can be eliminated from the model resulting in a reduced order model with physically meaningful parameters, which also accurately predicts the behavior of the full model The activity metric appears to be a valuable metric for automating the reduction of nonlinear system models--providing in the process models that provide better insight and may be more numerically efficient. [DOI: 10.1115/1.4002473]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jpubeco.2010.04.002 Byline: Bruno Deffains (a)(b), Jean Mercier Ythier (c)(d)(e) Keywords: Organ transplants; Donation; Public goods; Production organization; Rotten kid theorem Abstract: Most organ transplants are from dead donors. National transplant organizations exhibit considerable differences in terms of their donor population rates. Spain's organization is by far the most efficient in this respect. We argue that much of the productivity advantage of Spain's transplant organization proceeds from an efficient organization of the production chain, from organ procurement to transplantation. Transplants from dead donors are analogous to a common resource for the transplant community. Their circulation through the national transplant organization creates public good externalities between the care units in charge of organ retrieval and those in charge of transplantation. A socially efficient production of transplant care services obtains through an optimal control, by the national transplant agency, of both the circulation and the production of transplants. In particular, transplant shortage makes the rotten kid theorem fail in this context. The analysis also produces a natural measure of public good externalities, evaluated from the standpoint of care units. Author Affiliation: (a) Universite de Paris Pantheon-Assas (Ermes), France (b) European Business School, Wiesbaden, Germany (c) Universite de Metz, France (d) BETA (CNRS), Strasbourg, France (e) IDEP, Marseille, France Article History: Received 14 February 2009; Revised 26 March 2010; Accepted 5 April 2010

Production split and merge operations are widely used in many manufacturing systems to increase production capacity and variety, improve product quality, and carry out scheduling and control activities. This article presents analytical methods to analyze split and merge production systems with exponential machine reliability models, operating under circulate, strictly circulate, priority, and percentage split/merge policies. In addition to developing the recursive procedures for performance analysis, the structural properties of the systems and the impacts of routing policies on system performance are investigated. Keywords: Split, merge, throughput, percentage, priority, circulate, strictly circulate, 1. Introduction In modern manufacturing systems, split and merge structures are often used to increase production capacity and variety, improve product quality, and carry out scheduling and control activities. The [...]

A set of manufacturers outsources certain operations to a single third party following the announcement of a booking price for each available day of production. Knowing these costs, manufacturers book [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2009.03.007 Byline: Onur Kaya Keywords: Supply chain management; Remanufacturing; Demand substitution Abstract: We consider a manufacturer producing original products using virgin materials and remanufactured products using returns from the market where the amount of returns depend on the incentive offered by the manufacturer. We determine the optimal value of this incentive and the optimal production quantities in a stochastic demand setting with partial substitution. We analyze 3 different models in centralized and decentralized settings where the collection process of the returns is managed by a collection agency in the decentralized setting. We also analyze contracts to coordinate the decentralized systems and determine the optimal contract parameters. Finally, we present our computational study to observe the effect of different parameters on the system performance. Author Affiliation: Department of Industrial Engineering, Onur Kaya, Koc University, Eng 206, Sariyer, Istanbul 34450, Turkey Article History: Received 5 June 2008; Accepted 4 March 2009

In this paper, we present a Markovian modelling framework that can describe any serial production system with rework. Each production stage is represented by a state in the Markov chain. Absorbing states indicate the events of scrapping a product at a production stage or the completion of the finished product. Generalizable formulae for the final absorption probabilities are derived that represent: (1) the probability that an unfinished product is scrapped at a certain production stage and (2) the yield of the system. We also derive various expected costs and quantities associated with ali products ending in any absorbing state, as well as the equivalent costs and quantities for finished products. The applicability of our modelling framework is demonstrated in a real-life manufacturing environment in the food-packing industry. Journal of the Operational Research Society (2010) 61, 342-351. doi: 10.1057/jors.2008.186 Published online 4 March 2009 Keywords: serial production systems; rework; Markov chains

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2008.05.018 Byline: Ardeshir J. Dalal (a), Moawia Alghalith (b) Keywords: Multiplicative output uncertainty; Price uncertainty; Comparative statics; Ross increasing relative risk aversion; Quadratic utility; Stein's Lemma Abstract: While production decisions in the presence of price uncertainty have been extensively studied, this is not so for the case in which the level of production is itself uncertain. In this paper,we provide a decision analysis under multiplicative production uncertainty, both with and without price uncertainty. We depict equilibrium and obtain comparative statics results with the aid of a diagram based on the difference between expected price and marginal cost. Comparative statics results are obtained for the model with production uncertainty alone and also for simultaneous price and production uncertainty (including two special cases). We first derive results based on the Arrow-Pratt coefficients of risk aversion, and then supplement these with the Ross measure of relative risk aversion, since this proves useful in the presence of multiple sources of uncertainty. We find that increases in risk (both price and production) or input prices reduce expected output. However, expected output supply is an increasing function of (expected) price only for 'low' levels of risk aversion, and in general the relationship is ambiguous. Author Affiliation: (a) Missouri State University, Department of Economics, Strong Hall 351, Springfield, MO 65897, United States (b) University of the West Indies, St. Augustine, Trinidad and Tobago Article History: Received 21 September 2006; Accepted 9 May 2008

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1744-7976.2008.01137.x Byline: Oliver Musshoff (1), Norbert Hirschauer (2) Abstract: Mathematical programming has for a long time been recognized as a powerful tool. Despite its capacity for solving constrained optimization problems under uncertainty, some methodological obstacles have persisted over the years. The main problem is that the eventually complex results of an unbiased statistical analysis (multiple correlated stochastic variables with different distributions and nonadditive links between) cannot be adequately accounted for within minimization of total absolute deviation (MOTAD) or expected value-variance (EV) models that rely on the algorithmic determination of the variability measure. In this paper, we develop a methodological hybrid consisting of Monte Carlo simulation and genetic algorithms: the Monte Carlo simulation facilitates the easy representation of diverse stochastic processes and correlation, and the genetic algorithm ensures that the optimization procedure remains applicable even in the case of complex stochastic information. This hybrid approach is applied to the production-planning problem of a German crop farm. Variant calculations are used to account for the unknown risk attitude of the farmer. Model results demonstrate that optimized production programs and expected total gross margins are not only highly sensitive to the risk attitude, but also to the stochastic processes that are estimated (or assumed) for various activities. We furthermore find evidence that the hybrid approach is able to generate considerable improvement in farm-program decisions and outperforms planning models that assume static distributions. La programmation mathematique est reconnue depuis longtemps comme etant un outil puissant. Malgre sa capacitea resoudre des problemes d'optimisation avec contraintes en situation d'incertitude, certains obstacles methodologiques ont persiste au fil du temps. Le principal probleme reside dans le fait que les resultats eventuellement complexes d'une analyse statistique non biaisee (plusieurs variables aleatoires correlees avec differentes distributions et des liens non additifs entre elles) ne peuvent etre adequatement representes dans les modeles MOTAD et E-V qui dependent de la determination algorithmique de la mesure de la variabilite. Dans le present article, nous avons elabore une methode hybride a partir d'une simulation de Monte Carlo et d'algorithmes genetiques: la simulation de Monte Carlo facilite la representation de divers processus stochastiques et de diverses correlations, et l'algorithme genetique assure que la procedure d'optimisation demeure applicable meme dans le cas d'information stochastique complexe. Cette methode hybride est appliquee au probleme de planification de la production auquel est confrontee une exploitation de cultures en Allemagne. Des calculs de variantes sont utilises pour tenir compte de l'attitude inconnue du producteur quant au risque. Les resultats du modele indiquent que les programmes de production optimises et les marges brutes totales prevues ne sont pas uniquement sensibles a l'attitude face aux risques mais aussi aux processus stochastiques qui sont estimes (ou supposes) pour diverses activites. Nous avons egalement trouve que la methode hybride peut ameliorer considerablement les decisions concernant les programmes agricoles et qu'elle est superieure aux modeles de planification qui supposent des distributions statiques. Author Affiliation: (1)Georg-August-Universitat Gottingen, Faculty of Agricultural Sciences, Department for Agricultural Economics and Rural Development, Platz der Gottinger Sieben 5, D-37073 Gottingen, Germany (corresponding author: phone: +49(0)551-39-4842; fax: +49(0)551-39-22030; e-mail:oliver.musshoff@agr.uni-goettingen.de). (2)Martin-Luther-Universitat Halle-Wittenberg, Faculty of Natural Sciences III, Institute of Agricultural and Nutritional Sciences, Ludwig-Wucherer-Str. 2, D-06108 Halle (Saale), Germany (phone: +49(0)345-55-22362; fax: +49(0)345-55-27110; e-mail:norbert.hirschauer@landw.uni-halle.de).

This paper describes and discusses a Plackett-Burman experiment aimed at increasing supermarket sales of a top-selling national magazine. The experiment involved 10 factors relating to in-store advertising and the location [...]

Forecasting highly uncertain demand signals is an important component for successfully managing inventory in semiconductor supply chains. We present a control-relevant approach to the problem that tailors a forecasting model to its end-use purpose, which is to provide forecast signals for a tactical inventory management policy based on model predictive control (MPC). The success of the method hinges on a control-relevant prefiltering operation applied to demand estimation data that emphasizes a goodness-of-fit in regions of time and frequency most important for achieving desired levels of closed-loop performance. A multi-objective formulation is presented that allows the supply-chain planner to generate demand forecasts that minimize inventory deviation, starts change variance, or their weighted combination when incorporated in an MPC decision policy. The benefits obtained from this procedure are demonstrated on a case study drawn from the final stage of a semiconductor manufacturing supply chain. Index Terms--Forecasting, inventory control, predictive control, production management, supply-chain management (SCM).

A service encounter is an experience that extends over time. Therefore, its effective management must include the control of the timing of the delivery of each of the service's elements [...]

A computationally effective analysis of the throughput performance of a closed-loop multi-vehicle automated material handling system (AMHS) used in highly automated 300 mm wafer fabrication facilities (fabs) is presented. A probabilistic model is developed, based on a detailed description of AMHS operations, and the system is analyzed as an extended Markov chain. The model represents vehicle operations on the closed-loop considering the possibility of vehicle blocking. This analysis provides essential parameters such as the vehicle blocking probabilities and the throughput capacity of the AMHS. A numerical example is analyzed and simulated using AutoMod to demonstrate and validate the stochastic model. Keywords: Material handling, Markov chains, blocking, semiconductor manufacturing, 1 Introduction Consider a discrete vehicle-based material handling system serving multiple machines on a simple closed loop. Move requests arrive randomly, requiring material transfer between machines located on the loop, [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2007.06.037 Byline: E. Mohebbi Keywords: Inventory; Production; Limited capacity; Random environments; Markov-modulated processes; Level crossings Abstract: This note presents an extension of our earlier paper on a production-inventory system with limited storage capacity in a multi-state random environment [i.e., E. Mohebbi, A production-inventory model with randomly changing environmental conditions, Eur. J Res. 174 (2006) 539-552]. More specifically, it assumes that the production rate as well as the occurrence rate and batch sizes of a compound Poisson demand stream are influenced by the state of a continuous-time homogeneous Markov chain representing the random environment. We present an adaptation of the system-point method of level crossings which yields the limiting distribution of inventory level (stock-on-hand) for a two-parameter production control policy when stockouts are lost. Author Affiliation: Department of Management/MIS, College of Business, University of West Florida, Pensacola, FL 32514, USA Article History: Received 17 January 2006; Accepted 17 June 2007

The problem of scheduling material-handling hosts in automated electroplaing lines to maximize the throughput is considered. An electroplating line processes indential products eyclically in a series of tanks. The transfer of products between tanks is performed by one or more hoists mounted on an overhead track. A system consisting of two hoists is considered in this work. The scheduling problem in this system is significantly more difficult than that with one hoist as it involves additional decisions concening the assignment of tasks to hoists and additional constraints to ensure that there are no collisions between hoists. a meheuristic algoithm to solve the problem is proposed. The algorithm generates sequences of product transfer tasks in the production cycle and assigns the tasks in sequence to the hoists. A linear programming model is developed to find an optimal schedule for each given hoist assignment. The results of computational experiement are presented and discussed demonstrating the effective and efficiency of the proposed algorithm. Keywords: Cyclic hoist scheduling, two hoists, heuristies, linear programming, 1. Introduction Material-handling devices such as automated guided vehicles, robots and hoists are widely used to transfer parts between workstations in advanced manufacturing facilities. It is essential to consider these [...]

The problem of lagging productivity growth in US has attracted the attention of researchers in the recent past. It is contended that productivity growth is the source of growth in real income per capita (Dew-Becker & Gordon, 2005). Though researches debate about the causes of productivity slow down during the 1970s (Denison, 1979; Norsworthy, Harper and Kunze, 1979) and acceleration during 1990s (Jorgenson & Stiroh, 2000; Oliner & Sichel, 2000; Gordon, 2003), economists try to find ways of increasing total productivity growth. The present paper postulates that 'vicious circle of low productivity' is the basic cause of stagnant growth a model is developed to break this vicious circle. Based on the premise that the employer may have to offer higher 'wage' to attract and retain 'competent and productive workers', and based on efficiency wage models (Solow, 1979, Shapiro & Stiglitz, 1984; and Libenstein, 1963), the present model attempts to break the vicious circle of low productivity., INTRODUCTION 'Productivity growth raises our standard of living and plays a central role in our competitiveness in the worldwide economy. Productivity growth will be even more important as new technologies [...]

The classic economic production quantity (EPQ) model assumes that all items produced by a manufacturing process during a production run are of perfect quality. Due to deterioration or other factors, the production process may shift and produce some items of a lesser quality. In this study, we assume that during production, items are screened and classified as type A for perfect quality or type B otherwise. For simplicity, we assume that the percentage of type A items produced is constant so that the production rates for the both types of items are constants. The demands for both types are assumed to be known with certainty and are constant over time. Inventory models that account for the production of such an item are presented. The optimal operating policy that maximizes the total profit for the EPQ model under the effect of imperfect quality items is derived. Explicit expression for the optimal production quantity is obtained and the uniqueness of the optimal solution is demonstrated. Various variations of the model are investigated. Numerical examples illustrating the models are also given., 1. INTRODUCTION The classic economic production quantity (EPQ) model assumes that 100% of the items produced by a manufacturing process during a production run are of perfect quality. Due to [...]

Every atom's mass defect is distinctive, and linear combinations of things in nature seldom overlap. For a combination of carbon, hydrogen, nitrogen, oxygen, and sulfur, every mass is unique. Our [...]

The Philippines' Maynilad Water Services Inc. has gone bankrupt, while Manila Water Company Inc. is now a stock exchange-listed company after being given concession contracts in 1997. The study shows that privatization success of urban water utilities is affected by corporate governance and operations and financial management.

In this paper, we take the econometric approach to productivity measurement in United States manufacturing, using KLEM data over the period from 1953 to 2001. We are also interested in technical change bias, price elasticities, and elasticities of substitution in the U.S. manufacturing industry. We present an empirical comparison and evaluation of the effectiveness of four well-known flexible cost functions--the locally flexible generalized Leontief (see Diewert [1971. An application of the Shephard duality theorem: a generalized Leontief production function. Journal of Political Economy 79, 481-507]), translog (see Christensen et al. [1975. Transendendal logarithmic utility functions. American Economic Review 65, 367-364]), and normalized quadratic (see Diewert and Wales [1987. Flexible functional forms and global curvature conditions. Econometrica 55, 43-68])--and the globally flexible asymptotically ideal model (see Barnett et al. [1991. Seminonparametric Bayesian estimation of the asymptotically ideal production model. Journal of Econometrics 49, 5-50]), the latter modified to introduce technical change by means of Thomsen's [2000. Short cuts to dynamic factor demand modelling. Journal of Econometrics 97, 1-23] factor-augmenting efficiency index approach. JEL classification: C22; F33 Keywords: Flexible functional forms; Technical change; Generalized Leontief (GL); Translog; Normalized quadratic (NQ); Asymptotically ideal model (AIM)

Studies of productivity in the operations and engineering management literature have typically focused on identifying the drivers of productivity and how best to manage resources. To date, the issues of [...]

This article analyzes production models of the export-oriented maquila in Mexico, understood as the combinations between technological level and work organization system, labor relations flexibility, manpower characteristics, and business strategies, using for the first time the special module of the ENESTYC representative survey and information resulting from field work in 200 establishments. This work proposes that the maquila crisis in Mexico at the beginning of this century was not only because of the economic recession in the United States and Chinese competition but also because of the structural limitations of the sector's main production models, which have contributed to a crisis in labor productivity growth. Keywords: maquila; productivity; work conditions; production model