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Optimal Number (optimal + number)
Selected AbstractsOptimal number of matings in two aphidophagous ladybirdsECOLOGICAL ENTOMOLOGY, Issue 1 2006Omkar Abstract., 1.,The present study was designed to identify the optimal number of matings required for maximum fecundity and egg viability in two aphidophagous ladybirds, Cheilomenes sexmaculata and Propylea dissecta. 2.,For this purpose, ladybirds were subjected to different numbers of matings and the reproductive responses were recorded thereafter. 3.,The Gompertz model was used to draw asymptotic graphs for fecundity and per cent egg viability in both ladybird species. Ninety-five per cent and 50% of maximum theoretical fecundity and per cent egg viability were predicted from the model. 4.,Ninety-five per cent maximum theoretical fecundity was obtained after 13.25 and 12.95 matings in C. sexmaculata and P. dissecta, respectively; and 8.95 and 11.25 matings were required for 95% maximum theoretical per cent egg viability in C. sexmaculata and P. dissecta, respectively. 5.,The results of these experiments clearly support the existence of an optimal number of matings in these two ladybird species leading to maximum adult fitness. [source] Traffic Estimation and Optimal Counting Location Without Path Enumeration Using Bayesian NetworksCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2008Enrique Castillo A combination (bi-level) of an OD-pair matrix estimation model based on Bayesian networks, and a Wardrop-minimum-variance model, which identifies origins and destinations of link flows, is used to estimate OD-pair and unobserved link flows based on some observations of links and/or OD-pair flows. The Bayesian network model is also used to select the optimal number and locations of the links counters based on maximum correlation. Finally, the proposed methods are illustrated by their application to the Nguyen,Dupuis and the Ciudad Real networks. [source] A Risk-Cost Optimized Maintenance Strategy for Corrosion-Affected Concrete StructuresCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2007Chun-Qing Li It is also observed that some severely deteriorated concrete structures survive for many years without maintenance. This raises the question of why and how to maintain corrosion-affected concrete structures, in particular in the climate of an increasing scarcity of resources. The present article attempts to formulate a maintenance strategy based on risk-cost optimization of a structure during its whole service life. A time-dependent reliability method is employed to determine the probability of exceeding a limit state at each phase of the service life. To facilitate practical application of the formulated maintenance strategy, an algorithm is developed and programmed in a user-friendly manner with a worked example. A merit of the proposed maintenance strategy is that models used in risk assessment for corrosion-affected concrete structures are related to some of the design criteria used by practitioners. It is found in the article that there exists an optimal number of maintenances for cracking and delamination that returns the minimum total cost for the structure in its whole life. The maintenance strategy presented in the article can help structural engineers, operators, and asset managers develop a cost-effective management scheme for corrosion-affected concrete structures. [source] Optimal number of matings in two aphidophagous ladybirdsECOLOGICAL ENTOMOLOGY, Issue 1 2006Omkar Abstract., 1.,The present study was designed to identify the optimal number of matings required for maximum fecundity and egg viability in two aphidophagous ladybirds, Cheilomenes sexmaculata and Propylea dissecta. 2.,For this purpose, ladybirds were subjected to different numbers of matings and the reproductive responses were recorded thereafter. 3.,The Gompertz model was used to draw asymptotic graphs for fecundity and per cent egg viability in both ladybird species. Ninety-five per cent and 50% of maximum theoretical fecundity and per cent egg viability were predicted from the model. 4.,Ninety-five per cent maximum theoretical fecundity was obtained after 13.25 and 12.95 matings in C. sexmaculata and P. dissecta, respectively; and 8.95 and 11.25 matings were required for 95% maximum theoretical per cent egg viability in C. sexmaculata and P. dissecta, respectively. 5.,The results of these experiments clearly support the existence of an optimal number of matings in these two ladybird species leading to maximum adult fitness. [source] Inter-sexual differences in the immune response of Eurasian kestrel nestlings under food shortageECOLOGY LETTERS, Issue 1 2002Juan A. Fargallo When resources are limited, parents should decide the optimal number, size, and sex of progeny, and offspring should decide the optimal allocation of resources to different costly functions, such as growth and immunity. We manipulated clutch sizes of Eurasian kestrels by one egg to estimate possible cumulative effects of incubation and chick rearing costs on parental body condition, feeding effort, and offspring viability. No obvious effects of clutch size manipulations on feeding effort were found while feeding effort was adjusted to the original clutch size. Enlarged and control nests suffered from higher nestling mortality than reduced nests, and chicks of the enlarged group were in poorer body condition than chicks of the reduced group. Controlling for body mass, male chicks exhibited lower cell-mediated immunity assessed by a cutaneous hypersensitivity response than females, but only in treatments suffering from food restrictions, as indicated by chick starvation. These novel results reveal inter-sexual differences in physiological strategies in early life, suggesting sex-related differences in susceptibility to disease and consequently in survival prospects of offspring. [source] New knowledge extraction technique using probability for case-based reasoning: application to medical diagnosisEXPERT SYSTEMS, Issue 1 2006Yoon-Joo Park Abstract: Case-based reasoning (CBR) has been used in various problem-solving areas such as financial forecasting, credit analysis and medical diagnosis. However, conventional CBR has the limitation that it has no criterion for choosing the nearest cases based on the probabilistic similarity of cases. It uses a fixed number of neighbors without considering an optimal number for each target case, so it does not guarantee optimal similar neighbors for various target cases. This leads to the weakness of lowering predictability due to deviation from desired similar neighbors. In this paper we suggest a new case extraction technique called statistical case-based reasoning. The main idea involves a dynamic adaptation of the optimal number of neighbors by considering the distribution of distances between potential similar neighbors for each target case. In order to do this, our technique finds the optimal distance threshold and selects similar neighbors satisfying the distance threshold criterion. We apply this new method to five real-life medical data sets and compare the results with those of the statistical method, logistic regression; we also compare the results with the learning methods C5.0, CART, neural networks and conventional CBR. The results of this paper show that the proposed technique outperforms those of many other methods, it overcomes the limitation of conventional CBR, and it provides improved classification accuracy. [source] The effects of pay and job satisfaction on the labour supply of hospital consultantsHEALTH ECONOMICS, Issue 12 2007Divine Ikenwilo Abstract There is little evidence about the responsiveness of doctors' labour supply to changes in pay. Given substantial increases in NHS expenditure, new national contracts for hospital doctors and general practitioners that involve increases in pay, and the gradual imposition of a ceiling on hours worked through the European Working Time Directive, knowledge of the size of labour supply elasticities is crucial in examining the effects of these major changes. This paper estimates a modified labour supply model for hospital consultants, using data from a survey of consultants in Scotland. Rigidities in wage setting within the NHS mean that the usual specification of the labour supply model is extended by the inclusion of job quality (job satisfaction) in the equation explaining the optimal number of hours worked. Generalised Method of Moments estimation is used to account for the endogeneity of both earnings and job quality. Our results confirm the importance of pay and non-pay factors on the supply of labour by consultants. The results are sensitive to the exclusion of job quality and show a slight underestimation of the uncompensated earnings elasticity (of 0.09) without controlling for the effect of job quality, and 0.12 when we controlled for job quality. Pay increases in the new contract for consultants will only result in small increases in hours worked. Small and non-significant elasticity estimates at higher quantiles in the distribution of hours suggest that any increases in hours worked are more likely for consultants who work part time. Those currently working above the median number of hours are much less responsive to changes in earnings. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimal solid shell element for large deformable composite structures with piezoelectric layers and active vibration controlINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2005X. G. Tan Abstract In this paper, we present an optimal low-order accurate piezoelectric solid-shell element formulation to model active composite shell structures that can undergo large deformation and large overall motion. This element has only displacement and electric degrees of freedom (dofs), with no rotational dofs, and an optimal number of enhancing assumed strain (EAS) parameters to pass the patch tests (both membrane and out-of-plane bending). The combination of the present optimal piezoelectric solid-shell element and the optimal solid-shell element previously developed allows for efficient and accurate analyses of large deformable composite multilayer shell structures with piezoelectric layers. To make the 3-D analysis of active composite shells containing discrete piezoelectric sensors and actuators even more efficient, the composite solid-shell element is further developed here. Based on the mixed Fraeijs de Veubeke,Hu,Washizu (FHW) variational principle, the in-plane and out-of-plane bending behaviours are improved via a new and efficient enhancement of the strain tensor. Shear-locking and curvature thickness locking are resolved effectively by using the assumed natural strain (ANS) method. We also present an optimal-control design for vibration suppression of a large deformable structure based on the general finite element approach. The linear-quadratic regulator control scheme with output feedback is used as a control law on the basis of the state space model of the system. Numerical examples involving static analyses and dynamic analyses of active shell structures having a large range of element aspect ratios are presented. Active vibration control of a composite multilayer shell with distributed piezoelectric sensors and actuators is performed to test the present element and the control design procedure. Copyright © 2005 John Wiley & Sons, Ltd. [source] A distributed adaptive guard channel reservation scheme for cellular networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2007H.K. Pati Abstract In this paper, a distributed adaptive guard channel reservation (DAGCR) scheme is proposed to give priority to handoff calls. This scheme is built upon the concept of guard channels and it uses an adaptive algorithm to search automatically the optimal number of guard channels to be reserved at each base station. The quality-of-service (QoS) parameters used are the new and handoff call blockings. Simulation studies are performed to compare the present algorithm with the static guard channel policy. Simulation results show that this proposed algorithm guarantees the handoff call blocking probability to remain below the targeted threshold up to a substantially high offered load with a minimal blocking to new calls up to a moderate offered load and also shows significantly high channel utilization in all offered load conditions. This scheme is examined over a wide range of offered load. Thus, it seems the proposed scheme is very useful in controlling the blocking performances in wireless cellular networks. Copyright © 2006 John Wiley & Sons, Ltd. [source] Clustering with artificial neural networks and traditional techniquesINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 4 2003G. Tambouratzis In this article, two clustering techniques based on neural networks are introduced. The two neural network models are the Harmony theory network (HTN) and the self-organizing logic neural network (SOLNN), both of which are characterized by parallel processing, a distributed architecture, and a large number of nodes. After describing their clustering characteristics and potential, a comparison to classical statistical techniques is performed. This comparison allows the creation of a correspondence between each neural network clustering technique and particular metrics as used by the corresponding statistical methods, which reflect the affinity of the clustered patterns. In particular, the HTN is found to perform the clustering task with an accuracy similar to the best statistical methods, while it is further capable of proposing an optimal number of groups into which the patterns may be clustered. On the other hand, the SOLNN combines a high clustering accuracy with the ability to cluster higher-dimensional patterns without a considerable increase in the processing time. © 2003 Wiley Periodicals, Inc. [source] Hyperspectral NIR image regression part II: dataset preprocessing diagnosticsJOURNAL OF CHEMOMETRICS, Issue 3-4 2006James Burger Abstract When known reference values such as concentrations are available, the spectra from near infrared (NIR) hyperspectral images can be used for building regression models. The sets of spectra must be corrected for errors, transformed to reflectance or absorbance values, and trimmed of bad pixel outliers in order to build robust models and minimize prediction errors. Calibration models can be computed from small (<100) sets of spectra, where each spectrum summarizes an individual image or spatial region of interest (ROI), and used to predict large (>20,000) test sets of spectra. When the distributions of these large populations of predicted values are viewed as histograms they provide mean sample concentrations (peak centers) as well as uniformity (peak widths) and purity (peak shape) information. The same predicted values can also be viewed as concentration maps or images adding spatial information to the uniformity or purity presentations. Estimates of large population statistics enable a new metric for determining the optimal number of model components, based on a combination of global bias and pooled standard deviation values computed from multiple test images or ROIs. Two example datasets are presented: an artificial mixture design of three chemicals with distinct NIR spectra and samples of different cheeses. In some cases it was found that baseline correction by taking first derivatives gave more useful prediction results by reducing optical problems. Other data pretreatments resulted in negligible changes in prediction errors, overshadowed by the variance associated with sample preparation or presentation and other physical phenomena. Copyright © 2007 John Wiley & Sons, Ltd. [source] The function of mate choice in sticklebacks: optimizing Mhc genetics,JOURNAL OF FISH BIOLOGY, Issue 2003M. Milinski Sexual reproduction is an evolutionary ,puzzle'. A sexual female ,throws away' half of her genes (during meiosis), and ,fills up' what she lost with genes from a male. Thus, sexual reproduction can only be successful if the offspring with the new mixture of genes should be more than twice as fit as if she had just made a copy of herself. A challenging hypothesis assumes that infectious diseases select for females that reshuffle the immune genes for their offspring in each generation. The required increase in quality could be achieved by females selectively ,smelling out' suitable immune-genes (i.e. Mhc alleles) in potential partners, which, in combination with the female's genes, offer optimal resistance against quickly changing infectious diseases. It was found that most three spined sticklebacks Gasterosteus aculeatus in natural populations around Plön, Germany, had intermediate instead of maximal numbers of different Mhc class IIB alleles. Furthermore, fish with an intermediate number of different Mhc alleles were infected with the lowest number of both parasite species and parasites per species. This suggests that Mhc heterozygosity was optimized instead of maximized. Can this immunogenetic optimum be achieved through female choice? In a flow channel design that allowed the detection of olfactory signals only, it was found that female three-spined sticklebacks that were ready to spawn preferred males as mates that in combination with their Mhc alleles would allow the production of offspring with the optimal number of Mhc alleles. Thus, mate choice in three-spined sticklebacks could have the two-fold advantage over asexual reproduction that is required to maintain sexual reproduction. The interaction of olfactory with visual signals in three-spined stickleback mate choice is discussed. The three-spined stickleback is a suitable model organism for studying the evolution of sexual reproduction in relation to optimizing offspring immune genetics although other fishes may be as suitable. [source] Effect of cell number on mesenchymal stem cell transplantation in a canine disc degeneration modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 10 2010Kenji Serigano Abstract Transplantation of mesenchymal stem cells (MSCs) inhibits the progression of disc degeneration in animal models. We know of no study to determine the optimal number of cells to transplant into the degenerated intervertebral disc (IVD). To determine the optimal donor cell number for maximum benefit, we conducted an in vivo study using a canine disc degeneration model. Autologous MSCs were transplanted into degenerative discs at 105, 106, or 107,cells per disc. The MSC-transplanted discs were evaluated for 12 weeks using plain radiography, magnetic resonance imaging, and gross and microscopic evaluation. Preservation of the disc height, annular structure was seen in MSC-transplantation groups compared to the operated control group with no MSC transplantation. Result of the number of remaining transplanted MSCs, the survival rate of NP cells, and apoptosis of NP cells in transplanted discs showed both structural microenvironment and abundant extracellular matrix maintained in 106 MSCs transplanted disc, while less viable cells were detected in 105 MSCs transplanted and more apoptotic cells in 107 MSCs transplanted discs. The results of this study demonstrate that the number of cells transplanted affects the regenerative capability of MSC transplants in experimentally induced degenerating canine discs. It is suggested that maintenance of extracellular matrix by its production from transplanted cells and/or resident cells is important for checking the progression of structural disruption that leads to disc degeneration. Published by Wiley Periodicals, Inc. J Orthop Res 28:1267,1275, 2010 [source] Optimal carbon source switching strategy for the production of PHA copolymersAICHE JOURNAL, Issue 3 2001Nikolaos V. Mantzaris During polymerization in a nongrowing cell population of Ralstonia eutropha, alternating between two different carbon sources (fructose and fructose/valeric acid) could lead to the production of block copolymers consisting of blocks of homo-poly-3-hydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) copolymer. The problem of finding the optimal number of carbon source switches and corresponding switching times that maximize the final concentration of diblock copolymers (PHB-PHBV and PHBV-PHB) was addressed. It was mathematically formulated in the mixed-integer nonlinear programming (MINLP) framework, which allows the decomposition of the original problem into the primal and master problems. The primal problem corresponds to the original problem for a fixed number of carbon source switches, whereas the master problem consists of finding the number of carbon source switches that maximizes the optimum solutions of all possible primal problems. The global optimum was obtained for 39 carbon source switches. It corresponds to a mass fraction of 50.6% of final diblock copolymer concentration over the final total polymer concentration. [source] Stabilized Record Base for Implant TreatmentJOURNAL OF PROSTHODONTICS, Issue 7 2010Susan S. Nimmo DDS Abstract It is important to obtain an accurate interocclusal record for the restoration of patients undergoing implant treatment. Atrophic alveolar bone in the mandible not only limits the placement of implants, but also contributes to deficient ridge morphology resulting in unstable record bases. Securing the record base to the implants is a useful way to obtain an accurate registration. The technique presented in this article uses two widely spaced implants as the optimal number of implants to stabilize record bases. [source] THE MEULLENET-OWENS RAZOR SHEAR (MORS) FOR PREDICTING POULTRY MEAT TENDERNESS: ITS APPLICATIONS AND OPTIMIZATIONJOURNAL OF TEXTURE STUDIES, Issue 6 2008Y.S. LEE ABSTRACT The Meullenet-Owens Razor Shear (MORS), recently developed for the assessment of poultry meat tenderness, is a reliable instrumental method. Three different studies were conducted to (1) investigate the adaptation of MORS to an Instron InSpec 2200 tester (InSpec); (2) optimize the number of replications necessary per fillet to obtain a reliable instrumental tenderness mean; and (3) test the efficacy of a blunt version of MORS (BMORS). In study 1, the tenderness of 157 cooked broiler breast fillets was predicted by the MORS performed with both a texture analyzer (MORS standard) and InSpec. The correlation coefficient of 0.95 was reported for the MORS energy obtained from the both tests, indicating that the MORS performed with an InSpec is equivalent to that performed on the more expensive texture analyzer. In study 2, eight shears were taken on each cooked fillet (101 fillets) to determine a recommended number of shears per fillet for the MORS. The composite hypothesis test was conducted considering the average of 8 shears as Y (representative estimated tenderness of a fillet) and the average of 2, 3, 4, 5, 6 or 7 as X (potentials for recommended number of shears). The results showed that the optimal number of replications of the MORS for a reliable estimate of tenderness to be four shears or greater per fillet. A blunt version of MORS (BMORS) was introduced in study 3. A total of 288 broilers (576 fillets) were deboned at eight different postmortem deboning times. Tenderness of cooked fillets was assessed by both the MORS and BMORS on the same individual fillets. Both methods were equivalent in performance for predicting broiler breast meat tenderness, giving a correlation coefficient of 0.99 with all instrumental parameters obtained from both methods. Tenderness intensity perceived by consumers was slightly more highly correlated to BMORS energy (r = ,0.90) than MORS energy (r = ,0.87). The BMORS was recommended to use especially for tough meat because of its better discrimination ability among tough meat. Overall, both the MORS and BMORS were proven to be reliable predictors for broiler breast meat tenderness. PRACTICAL APPLICATIONS The incidence of tough meat has been a major issue the poultry industry faces. Therefore, the need to ensure consumer acceptance and the increased recognition of the importance of tenderness has led to the development of instrumental methods for monitoring meat tenderness. To date, a great deal of efforts has been devoted to the development of such instrumental methods. One promising method is the Meullenet-Owens Razor Shear (MORS). The method has gained in popularity for predicting poultry meat tenderness because of its high reliability as well as simplicity compared with that of other industry standards (Warner-Bratzler shear or Allo-Kramer shear). The MORS is not only as reliable as the industry standards, but also more rapid because of the elimination of the sample cutting steps. The application of the MORS will be of benefit to the poultry industry as it could significantly save labor or time to implement for routine quality control. [source] Tree Basal Growth Response to Flooding in a Bottomland Hardwood Forest in Central Ohio,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2008Christopher J. Anderson Abstract:, Tree basal growth in response to flooding regime was evaluated at a 5.2-ha bottomland forest along the Olentangy River in central Ohio. Tree-ring analysis was used to develop a 14-year basal area increment (BAI) (cm2/year) series for 42 canopy trees (representing 10 species) throughout the bottomland. Mean annual BAI was evaluated relative to the frequency and duration of bankfull (>70 m3/s) and high-flood (>154 m3/s) river discharge for a given water year (October 1-September 30) and growing season (April 1-September 30). A significant polynomial relationship was detected between the number of days of high-flood river discharge over a combined two-year period (Year i + Year i , 1) and mean annual BAI. No significant relationships were detected when only the concurrent-year or previous-year flood regimes were considered or when growing season was considered. A similar relationship was detected when duration of high-flood discharge days and BAI were both evaluated in two-year increments (Year i + Year i , 1). Mean annual BAI was most influenced by boxelder (Acer negundo) which was the dominant species and exhibited strong agreement with the overall BAI series. In each case, the resulting parabolic curve of tree basal growth in response to flooding suggests an optimal number of flooding days, a response to perturbation consistent with the subsidy-stress model. Dendrochronology may be a useful tool for managers looking to restore environmental flows to regulated rivers. [source] Variable but predictable prey availability affects predator breeding success: natural versus experimental evidenceJOURNAL OF ZOOLOGY, Issue 4 2008A. Millon Abstract Food supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life-history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis. [source] Estimation of gene frequency and heterozygosity from pooled samplesMOLECULAR ECOLOGY RESOURCES, Issue 3 2002K. Ritland Abstract Pooling of DNA samples can significantly reduce the effort of population studies with DNA markers. I present a statistical model and numerical method for estimating gene frequency when pooled DNA is assayed for the presence/absence of alleles. Analytical and Monte-Carlo methods examined estimation variance and bias, and hence optimal pool size, under a triangular allele frequency distribution. For gene frequency of rarer alleles, the optimal number of pooled individuals is approximately the inverse of the gene frequency. For heterozygosity, the optimal pool is approximately half the allele number; this results in pools containing, on average, 60% of possible alleles. [source] Optimal production and maintenance policy for imperfect production systemsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2006Chih-Hsiung Wang Abstract A joint optimization of the production run length and preventive maintenance (PM) policy is studied for a deteriorating production system where the in-control period follows a general probability distribution with non-decreasing failure rate. In the literature, the sufficient conditions for the optimality of the equal-interval PM schedule is explored to derive an optimal production run length and an optimal number of PM actions. Nevertheless, an exhaustive search may arise. In this study, based on the assumption that the conditions for the optimality of the equal-interval PM schedule hold, we derive some structural properties for the optimal production/PM policy, which increases the efficiency of the solution procedure. These analyses have implications for the practical application of the production/PM model to be more available in practice. A numerical example of gamma shift distribution with non-decreasing failure rates is used to illustrate the solution procedure, leading to some insight into the management process. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] The economic lot size of the integrated vendor-buyer inventory system derived without derivativesOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 3 2002P.C. Yang Abstract In previous modellings of the integrated vendor,buyer system, the buyer's economic order quantity and the vendor's optimal number of deliveries are derived by setting the first derivatives to zero and solving the simultaneous equations. The Hessian matrix of second derivatives is used to prove the convexity of the objective function. This procedure can be difficult for students who lack the background of differential calculus. This study develops algebraically the optimal policy of the integrated vendor,buyer inventory system without using differential calculus. A significant cost reduction is also achieved when Goyal's model is modified. Copyright © 2002 John Wiley & Sons, Ltd. [source] Social Optimal Location of Facilities with Fixed Servers, Stochastic Demand, and CongestionPRODUCTION AND OPERATIONS MANAGEMENT, Issue 6 2009Ignacio Castillo We consider two capacity choice scenarios for the optimal location of facilities with fixed servers, stochastic demand, and congestion. Motivating applications include virtual call centers, consisting of geographically dispersed centers, walk-in health clinics, motor vehicle inspection stations, automobile emissions testing stations, and internal service systems. The choice of locations for such facilities influences both the travel cost and waiting times of users. In contrast to most previous research, we explicitly embed both customer travel/connection and delay costs in the objective function and solve the location,allocation problem and choose facility capacities simultaneously. The choice of capacity for a facility that is viewed as a queueing system with Poisson arrivals and exponential service times could mean choosing a service rate for the servers (Scenario 1) or choosing the number of servers (Scenario 2). We express the optimal service rate in closed form in Scenario 1 and the (asymptotically) optimal number of servers in closed form in Scenario 2. This allows us to eliminate both the number of servers and the service rates from the optimization problems, leading to tractable mixed-integer nonlinear programs. Our computational results show that both problems can be solved efficiently using a Lagrangian relaxation optimization procedure. [source] DESIGNING A MARKET STRUCTURE WHEN FIRMS COMPETE FOR THE RIGHT TO SERVE THE MARKET,THE JOURNAL OF INDUSTRIAL ECONOMICS, Issue 3 2005Michel Mougeot In many industries, a regulator designs an auction to select ex-ante the firms that compete ex-post on the product market. This paper considers the optimal market structure when firms incur sunk costs before entering the market and when the government is not able to regulate firms in the market. We prove that a free entry equilibrium results in an excessive entry when the entry costs are private information. Then, we consider an auction mechanism selecting the firms allowed to serve the market and show that the optimal number of licences results in the socially optimal market structure. When all the potential candidates are actual bidders, the optimal number of firms in the market increases with the number of candidates and decreases with the social cost of public funds. When the market size is small, as the net profit in the market decreases with the number of selected firms, entry is endogenous. As increasing competition in the market reduces competition for the market, the optimal structure is more concentrated than in the previous case. [source] Diagnostic phototesting in polymorphous light eruption: the optimal number of irradiationsBRITISH JOURNAL OF DERMATOLOGY, Issue 6 2005I.J. Schornagel No abstract is available for this article. [source] A Study of Industry Evolution in the Face of Major Environmental Disturbances: Group and Firm Strategic Behaviour of Spanish Banks, 1983,1997,BRITISH JOURNAL OF MANAGEMENT, Issue 3 2004JoséÁngel Zúñiga-Vicente This paper examines the story of the evolution of a specific industry through the application of dynamic strategic group analysis. In particular, we analyse the relationship between major environmental disturbances and changes that have occurred over time in the competitive structure of the industry regarding two closely related central questions. First, the way in which these environmental transformations have influenced group patterns and stability, and second, the way in which such environmental disturbances has affected the strategic positioning of individual firms. We resort to alternative theoretical perspectives in an attempt to answer both questions. The empirical setting is the population of Spanish banks over the period 1983,1997. We make use of a new grouping algorithm , the Model-based Clustering or MCLUST , which may be enormously fruitful in future empirical works on strategic groups. This method allows researchers to obtain the optimal number of groupings over time in a much more objective way than the cluster techniques used until now. Compared to previous dynamic studies that only consider the largest firms, our research illustrates how a richer analysis of an industry dynamics can be obtained by using a dynamic analysis of strategic groups. Our results show that while there have been no industry-wide identical groupings year to year, there is an important strategic stability at group and firm-level punctuated by a high degree of strategic instability at times of major environmental disturbances. [source] Effect of the number of lymph nodes sampled on postoperative survival of lymph node-negative esophageal cancerCANCER, Issue 6 2008Alexander J. Greenstein MD Abstract BACKGROUND The presence of lymph node (LN) metastases in esophageal cancer has important prognostic and treatment implications. However, the optimal number of LNs that should be examined for accurate staging is controversial. In the current study, the association between survival and the number of LNs evaluated was examined in patients who underwent resection of lymph node-negative (American Joint Committee on Cancer [AJCC] TNM stage I-IIA) esophageal cancer. METHODS All patients were identified who underwent surgery for lymph node-negative esophageal cancer between 1988 and 2003 from the Surveillance, Epidemiology, and End Results cancer registry. Patients were classified into 3 groups by the number of negative LNs sampled during surgery (,10 LNs, 11-17 LNs, and ,18 LNs). Esophageal cancer-specific survival was compared among these LN groups using Kaplan-Meier curves. Stratified and Cox regression analyses were used to evaluate the association between survival and the number of negative LNs after adjusting for potential confounders. RESULTS A total of 972 patients were included in the study. Disease-specific survival rates increased with a higher number of negative LNs. The 5-year disease-specific survival rate was 55% among patients with ,10 negative LNs, compared with 66% and 75%, respectively, for those with 11 to 17 negative LNs and ,18 negative LNs. The number of negative LNs was found to be significantly associated with survival in analyses stratified by tumor status. On multivariate regression controlling for age, race/ethnicity, sex, histology, tumor status, and postoperative radiotherapy, a higher number of negative LNs was found to be independently associated with higher disease-specific survival. CONCLUSIONS The presence of LN metastases in patients with esophageal cancer appears to have important prognostic and treatment implications. Data from the current study suggest that patients undergoing surgical resection for esophageal cancer should have at least 18 LNs removed. Cancer 2008. © 2008 American Cancer Society. [source] A phenotypically distinct subset of immature B cells exhibits partial activation, increased survival, and preferential expression of VhS107EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 12 2003Emily Abstract We have observed that immature B cells (IgMlowIgD,) in the bone marrow of adult BALB/c mice exhibit heterogeneity, with a distinct subpopulation (,4,10%) expressing the CD43/S7 surface protein. These CD43/S7+ immature B cells often express other surface antigens associated with B cell activation (CD5, CD11b, PD-1). Generation of optimal numbers of CD43/S7+ immature B cells requires expression of a functional Btk protein, consistent with activation as a requisite for the CD43/S7+ immature B cell phenotype. Like typical CD43/S7, immature B cells, the CD43/S7+ immature B cells are predominantly resting cells, which are derived from cycling bone marrow B cell precursors. The CD43/S7+ immature B cell population exhibits enhanced survival in vivo upon administration of the apoptosis-inducing corticosteroid, dexamethasone. Finally, CD43/S7+ immature B cells show a fourfold increase in incidence of VhS107 , heavy chain expression compared to the CD43/S7, immature B cells. Therefore, in adult murine bone marrow, the presence of a phenotypically distinct immature B cellpopulation can be demonstrated which has undergone partial activation leading to increased survival and BCR-dependent Vh repertoire selection. [source] Suboptimal engagement of the T-cell receptor by a variety of peptide,MHC ligands triggers T-cell anergyIMMUNOLOGY, Issue 1 2010Scheherazade Sadegh-Nasseri Summary T cells recognize antigen via the T-cell receptor (TCR) and produce a spectrum of responses that range from activation to anergy or cell death. The variety of outcomes may be dictated by the strength of the signals transmitted upon cognate recognition of the TCR. The physiological outcome of TCR engagement is determined by several factors, including the avidity of the ligand for TCR, the duration of engagement, and the presence and nature of accessory molecules present on antigen-presenting cells (APCs). In this review, we discuss a model of anergy induced by presentation of low densities of peptide,major histocompatibility complex (MHC) ligand in CD4+ T cells and compare it to anergy induced by altered peptide ligands in an effort to identify a unifying mechanism. We suggest that altered peptide ligand (APL) and low densities of agonist ligands induce anergy by engaging less than optimal numbers of TCRs. The physiological impacts of anergy in memory CD4+ T cells are discussed. [source] B Cells Help Alloreactive T Cells Differentiate Into Memory T CellsAMERICAN JOURNAL OF TRANSPLANTATION, Issue 9 2010Y.-H. Ng B cells are recognized as effector cells in allograft rejection that are dependent upon T cell help to produce alloantibodies causing graft injury. It is not known if B cells can also help T cells differentiate into memory cells in the alloimmune response. We found that in B-cell-deficient hosts, differentiation of alloreactive T cells into effectors was intact whereas their development into memory T cells was impaired. To test if B cell help for T cells was required for their continued differentiation into memory T cells, activated T cells were sorted from alloimmunized mice and transferred either with or without B cells into naïve adoptive hosts. Activated T cells cotransferred with B cells gave rise to more memory T cells than those transferred without B cells and upon recall, mediated accelerated rejection of skin allografts. Cotransfer of B cells led to increased memory T cells by enhancing activated CD4 T-cell proliferation and activated CD8 T-cell survival. These results indicate that B cells help alloreactive T-cell differentiation, proliferation and survival to generate optimal numbers of functional memory T cells. [source] | |||||||||||||||||||||||||