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Cost Parameters (cost + parameter)
Selected AbstractsLeaf stomatal responses to vapour pressure deficit under current and CO2 -enriched atmosphere explained by the economics of gas exchangePLANT CELL & ENVIRONMENT, Issue 8 2009GABRIEL G. KATUL ABSTRACT Using the economics of gas exchange, early studies derived an expression of stomatal conductance (g) assuming that water cost per unit carbon is constant as the daily loss of water in transpiration (fe) is minimized for a given gain in photosynthesis (fc). Other studies reached identical results, yet assumed different forms for the underlying functions and defined the daily cost parameter as carbon cost per unit water. We demonstrated that the solution can be recovered when optimization is formulated at time scales commensurate with the response time of g to environmental stimuli. The optimization theory produced three emergent gas exchange responses that are consistent with observed behaviour: (1) the sensitivity of g to vapour pressure deficit (D) is similar to that obtained from a previous synthesis of more than 40 species showing g to scale as 1 , m log(D), where m ? [0.5,0.6], (2) the theory is consistent with the onset of an apparent ,feed-forward' mechanism in g, and (3) the emergent non-linear relationship between the ratio of intercellular to atmospheric [CO2] (ci/ca) and D agrees with the results available on this response. We extended the theory to diagnosing experimental results on the sensitivity of g to D under varying ca. [source] Optimization of a finned heat sink array based on thermoeconomic analysisINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007S. Z. Shuja Abstract The design and specification of heat sinks for electronic systems is not easily accomplished through the use of standard thermal design and analysis tools since geometric and boundary conditions are not typically known in advance. A second-law based thermoeconomic optimization procedure is presented for a finned heat sink array. This involves including costs associated with material, and irreversible losses due to heat transfer and pressure drop. The influence of important physical, geometrical and unit cost parameters on the overall finned array are optimized for some typical operating conditions that are representative of electronic cooling applications. The optimized cost results are presented in terms of ReD, ReL, ,P / ,H, and q for a finned system in a graphical form. In addition the methodology of obtaining optimum parameters for a finned heat sink system which will result in minimum operating cost is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd. [source] The costs of heparin-induced thrombocytopenia: a patient-based cost of illness analysisJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2009T. WILKE Summary.,Background and objectives:,Due to the complexity of heparin-induced thrombocytopenia (HIT), currently available cost analyses are rough estimates. The objectives of this study were quantification of costs involved in HIT and identification of main cost drivers based on a patient-oriented approach. Methods:,Patients diagnosed with HIT (1995,2004, University-hospital Greifswald, Germany) based on a positive functional assay (HIPA test) were retrieved from the laboratory records and scored (4T-score) by two medical experts using the patient file. For cost of illness analysis, predefined HIT-relevant cost parameters (medication costs, prolonged in-hospital stay, diagnostic and therapeutic interventions, laboratory tests, blood transfusions) were retrieved from the patient files. The data were analysed by linear regression estimates with the log of costs and a gamma regression model. Mean length of stay data of non-HIT patients were obtained from the German Federal Statistical Office, adjusted for patient characteristics, comorbidities and year of treatment. Hospital costs were provided by the controlling department. Results and conclusions:,One hundred and thirty HIT cases with a 4T-score ,4 and a positive HIPA test were analyzed. Mean additional costs of a HIT case were 9008 ,. The main cost drivers were prolonged in-hospital stay (70.3%) and costs of alternative anticoagulants (19.7%). HIT was more costly in surgical patients compared with medical patients and in patients with thrombosis. Early start of alternative anticoagulation did not increase HIT costs despite the high medication costs indicating prevention of costly complications. An HIT cost calculator is provided, allowing online calculation of HIT costs based on local cost structures and different currencies. [source] Optimal control of a production-inventory system with both backorders and lost salesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 3 2010Saif Benjaafar Abstract We consider the optimal control of a production inventory-system with a single product and two customer classes where items are produced one unit at a time. Upon arrival, customer orders can be fulfilled from existing inventory, if there is any, backordered, or rejected. The two classes are differentiated by their backorder and lost sales costs. At each decision epoch, we must determine whether or not to produce an item and if so, whether to use this item to increase inventory or to reduce backlog. At each decision epoch, we must also determine whether or not to satisfy demand from a particular class (should one arise), backorder it, or reject it. In doing so, we must balance inventory holding costs against the costs of backordering and lost sales. We formulate the problem as a Markov decision process and use it to characterize the structure of the optimal policy. We show that the optimal policy can be described by three state-dependent thresholds: a production base-stock level and two order-admission levels, one for each class. The production base-stock level determines when production takes place and how to allocate items that are produced. This base-stock level also determines when orders from the class with the lower shortage costs (Class 2) are backordered and not fulfilled from inventory. The order-admission levels determine when orders should be rejected. We show that the threshold levels are monotonic (either nonincreasing or nondecreasing) in the backorder level of Class 2. We also characterize analytically the sensitivity of these thresholds to the various cost parameters. Using numerical results, we compare the performance of the optimal policy against several heuristics and show that those that do not allow for the possibility of both backordering and rejecting orders can perform poorly.© 2010 Wiley Periodicals, Inc. Naval Research Logistics 2010 [source] Locational tying of complementary retail itemsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2009Bacel Maddah Abstract We study a selling practice that we refer to as locational tying (LT), which seems to be gaining wide popularity among retailers. Under this strategy, a retailer "locationally ties" two complementary items that we denote by "primary" and "secondary." The retailer sells the primary item in an appropriate "department" of his or her store. To stimulate demand, the secondary item is offered in the primary item's department, where it is displayed in very close proximity to the primary item. We consider two variations of LT: In the multilocation tying strategy (LT-M), the secondary item is offered in its appropriate department in addition to the primary item's department, whereas in the single-location tying strategy (LT-S), it is offered only in the primary item's location. We compare these LT strategies to the traditional independent components (IC) strategy, in which the two items are sold independently (each in its own department), but the pricing/inventory decisions can be centralized (IC-C) or decentralized (IC-D). Assuming ample inventory, we compare and provide a ranking of the optimal prices of the four strategies. The main insight from this comparison is that relative to IC-D, LT decreases the price of the primary item and adjusts the price of the secondary item up or down depending on its popularity in the primary item's department. We also perform a comparative statics analysis on the effect of demand and cost parameters on the optimal prices of various strategies, and identify the conditions that favor one strategy over others in terms of profitability. Then we study inventory decisions in LT under exogenous pricing by developing a model that accounts for the effect of the primary item's stock-outs on the secondary item's demand. We find that, relative to IC-D, LT increases the inventory level of the primary item. We also link the profitability of different strategies to the trade-off between the increase in demand volume of the secondary item as a result of LT and the potential increase in inventory costs due to decentralizing the inventory of the secondary item. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 [source] Capacity allocation with traditional and Internet channelsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 8 2006Yue Dai Abstract In this paper we study a capacity allocation problem for two firms, each of which has a local store and an online store. Customers may shift among the stores upon encountering a stockout. One question facing each firm is how to allocate its finite capacity (i.e., inventory) between its local and online stores. One firm's allocation affects the decision of the rival, thereby creating a strategic interaction. We consider two scenarios of a single-product single-period model and derive corresponding existence and stability conditions for a Nash equilibrium. We then conduct sensitivity analysis of the equilibrium solution with respect to price and cost parameters. We also prove the existence of a Nash equilibrium for a generalized model in which each firm has multiple local stores and a single online store. Finally, we extend the results to a multi-period model in which each firm decides its total capacity and allocates this capacity between its local and online stores. A myopic solution is derived and shown to be a Nash equilibrium solution of a corresponding "sequential game." © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] Focusing on Customer Time in Field Service: A Normative ApproachPRODUCTION AND OPERATIONS MANAGEMENT, Issue 2 2007Aruna Apte Although customer convenience should be rightfully considered a central element in field services, the customer experience suggests that service enterprises rarely take the customer's preferred time into account in making operational and scheduling decisions. In this paper we present the results of our exploratory research into two interrelated topics: the explicit inclusion of customer time in nonemergency field service delivery decisions and the analysis of trade-off between the customer's convenience and field service provider's cost. Based on prior research in service quality we identify and illustrate two time-based performance metrics that are particularly appropriate for assessing service quality in nonemergency field services: performance and conformance quality. To determine vehicle routes, we develop a hybrid heuristic derived from the existing and proven heuristic methods. A numerical example closely patterned after real-life data is generated and used within a computational experiment to investigate alternate policies for promise time windows. Our experiment shows that over a reasonable range of customer cost parameters the policy of shorter promise time windows reduces the combined total cost incurred by the provider and the customers and should be considered a preferred policy by the field service provider. Managerial implications of this result are discussed. [source] Demand and Production Management with Uniform Guaranteed Lead TimePRODUCTION AND OPERATIONS MANAGEMENT, Issue 4 2005Uday S. Rao Recently, innovation-oriented firms have been competing along dimensions other than price, lead time being one such dimension. Increasingly, customers are favoring lead time guarantees as a means to hedge supply chain risks. For a make-to-order environment, we explicitly model the impact of a lead time guarantee on customer demands and production planning. We study how a firm can integrate demand and production decisions to optimize expected profits by quoting a uniform guaranteed maximum lead time to all customers. Our analysis highlights the increasing importance of lead time for customers, as well as the tradeoffs in achieving a proper balance between revenue and cost drivers associated with lead-time guarantees. We show that the optimal lead time has a closed-form solution with a newsvendor-like structure. We prove comparative statics results for the change in optimal lead time with changes in capacity and cost parameters and illustrate the insights using numerical experimentation. [source] Duncan's model for X, -control charts: sensitivity analysis to input parametersQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 1 2010Cinzia Mortarino Abstract Duncan's model is a well-known procedure to build a control chart with specific reference to the production process it has to be applied to. Although many papers report true applications proving the procedure's noteworthy economic advantages over control charts set purely on the basis of standard statistical criteria, this method is often perceived only as an academic exercise. Perhaps the greater barrier preventing its practical application stems from the difficulty in making cost items explicit. In this paper a sensitivity analysis is proposed for misspecification in the cost parameters for optimal solutions of Duncan's model. While similar contributions published in the literature perform sensitivity analyses with a one-factor-at-a-time scheme, the original contribution of this paper is represented by the focus given on interactions among changes in values of different cost parameters. The results obtained here denote that all factors significantly affect optimal solutions through quite complicated interactions. This should not, in our opinion, discourage the implementation of Duncan's model, pointing conversely to its robust versions, already available in the current literature. Copyright © 2009 John Wiley & Sons, Ltd. [source] Case for postoperative surveillance following colorectal cancer resectionANZ JOURNAL OF SURGERY, Issue 1-2 2004Tim R. Worthington Over 4 years have elapsed since the first National Health and Medical Research Council (NHMRC) guidelines were published for the management of patients after potentially curative resection of colorectal cancer. New information has now been published indicating that more intensive follow up than was originally recommended might provide a survival benefit for patients. This new information should be considered when formulating new NHMRC guidelines. In particular, meta-analyses of published individual trials have suggested a survival advantage that was not evident in the individual studies. There have been significant developments in chemotherapy with new individual agents and use of agents in combination that have proved far more effective than previous protocols. The therapeutic effect of these developments is the downstaging of some patients with metastatic disease, which was previously unresectable, to undergo resection. Furthermore, there is now some evidence that palliation of patients with advanced disease is more effective if commenced before the development of symptoms and this needs to be considered in the assessment of the benefits of follow up. There have been limited studies of cost-effectiveness, but international analyses suggest that the costs associated with more intensive follow-up regimes are within the accepted cost parameters associated with the management of many other conditions. [source] A new approach to the qualitative evaluation of functional disability in dementiaINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 11 2003X. Kurz Abstract Background Dementia patients suffer from the progressive deterioration of cognitive and functional abilities. Instrumental disabilities usually appear in the earlier stages of the disease while basic disabilities appear in the more advanced stages. In order to differentiate between mild, moderate and severe patients both instrumental and basic functional disabilities should be taken into account simultaneously. Objectives The objective of this study was to find a new method for classifying dementia patients based on their disabilities by using a basic and an instrumental Activities of Daily Living (ADL) scale. Methods Functional disability was assessed in a Belgian cohort of dementia patients using the Katz and Lawton Instrumental Activities of Daily Living (IADL) scales. A k -means derived clustering method allocated patients to disability clusters according to their Katz and Lawton scores. In order to validate the classification, we compared socio-demographic, clinical and costs parameters between the groups. Results The clustering method allocated patients between three clusters: dependent, non-dependent with instrumental functional disability (ND-IFD) and non-dependent. Dependence, as defined by these clusters, significantly correlates with age, residential setting, MMSE, patient's quality of life and costs. Conclusion This new classification of patients suffering from dementia will provide better understanding of functional disabilities and will complement the evaluation of disease severity based on cognitive function. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||