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Simulation Shows (simulation + shows)
Selected AbstractsA queuing model for due date control in a multiserver repair shopNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2001Joris Keizers This paper deals with a repair shop with multiple parallel servers, which has to carry out planned overhauls. Each overhaul consists of a large number of maintenance jobs. The overhaul process is interrupted by randomly arriving emergency jobs. To control the delivery performance of the overhauls, knowledge about the overhaul makespan distribution should be available. Using a 2-dimensional Markov model, we derive the first and second moment of the overhaul makespan analytically for the case that the repair times of all overhaul jobs are identically and exponentially distributed. For the case of nonidentical repair time distributions, an approximation is presented. Simulation shows that the makespan distribution fitted on these moments gives an excellent approximation. © John Wiley & Sons, Inc. Naval Research Logistics 48: 281,282, 2001 [source] Assessment of Agreement under Nonstandard Conditions Using Regression Models for Mean and VarianceBIOMETRICS, Issue 1 2006Pankaj K. Choudhary Summary The total deviation index of Lin (2000, Statistics in Medicine19, 255,270) and Lin et al. (2002, Journal of the American Statistical Association97, 257,270) is an intuitive approach for the assessment of agreement between two methods of measurement. It assumes that the differences of the paired measurements are a random sample from a normal distribution and works essentially by constructing a probability content tolerance interval for this distribution. We generalize this approach to the case when differences may not have identical distributions,a common scenario in applications. In particular, we use the regression approach to model the mean and the variance of differences as functions of observed values of the average of the paired measurements, and describe two methods based on asymptotic theory of maximum likelihood estimators for constructing a simultaneous probability content tolerance band. The first method uses bootstrap to approximate the critical point and the second method is an analytical approximation. Simulation shows that the first method works well for sample sizes as small as 30 and the second method is preferable for large sample sizes. We also extend the methodology for the case when the mean function is modeled using penalized splines via a mixed model representation. Two real data applications are presented. [source] On-line cell lysis and DNA extraction on a microfluidic biochip fabricated by microelectromechanical system technologyELECTROPHORESIS, Issue 9 2008Xing Chen Dr. Abstract Integrating cell lysis and DNA purification process into a micrototal analytical system (,TAS) is one critical step for the analysis of nucleic acids. On-chip cell lysis based on a chemical method is realized by sufficient blend of blood sample and the lyzing reagent. In this paper two mixing models, T-type mixing model and sandwich-type mixing model, are proposed and simulation of those models is conducted. Result of simulation shows that the sandwich-type mixing model with coiled channel performs best and this model is further used to construct the microfluidic biochip for on-line cell lysis and DNA extraction. The result of simulation is further verified by experiments. It asserts that more than 80% mixing of blood sample and lyzing reagent which guarantees that completed cell lysis can be achieved near the inlet location when the cell/buffer velocity ratio is less than 1:5. After cell lysis, DNA extraction by means of a solid-phase method is implemented by using porous silicon matrix which is integrated in the biochip. During continuous flow process in the microchip, rapid cell lysis and PCR-amplifiable genomic DNA purification can be achieved within 20,min. The potential of this microfluidic biochip is illustrated by pretreating a whole blood sample, which shows the possibility of integration of sample preparation, PCR, and separation on a single device to work as portable point-of-care medical diagnostic system. [source] Array antenna assisted doppler spread compensator for OFDMEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2002Minoru Okada This paper proposes a novel array-antenna-assisted Doppler spread compensator for orthogonal frequency division multiplexing (OFDM), which is sensitive to fast time-variation of the radio propagation channel. In the proposed compensator, a linear array antenna is installed on top of the vehicle. The compensator estimates the received signal at a certain point on the linear array antenna by using space domain interpolation. Because the relative position of the estimated receiving point with respect to the ground does not change during the effective symbol duration of an OFDM signal, the time variation due to the movement of the vehicle can be compensated for. Computer simulation shows that the compensator can compensate for the bit error rate performance degradation due to time-variation of the channel when the velocity of the vehicle is up to 180km/h and a two-element array antenna is used at the carrier frequency of 600 MHz. The bit error rate performance can be further improved by using a four-element array antenna. [source] Understanding hydrological processes with scarce data in a mountain environmentHYDROLOGICAL PROCESSES, Issue 12 2008A. Chaponnière Abstract Performance of process-based hydrological models is usually assessed through comparison between simulated and measured streamflow. Although necessary, this analysis is not sufficient to estimate the quality and realism of the modelling since streamflow integrates all processes of the water cycle, including intermediate production or redistribution processes such as snowmelt or groundwater flow. Assessing the performance of hydrological models in simulating accurately intermediate processes is often difficult and requires heavy experimental investments. In this study, conceptual hydrological modelling (using SWAT) of a semi-arid mountainous watershed in the High Atlas in Morocco is attempted. Our objective is to analyse whether good intermediate processes simulation is reached when global-satisfying streamflow simulation is possible. First, parameters presenting intercorrelation issues are identified: from the soil, the groundwater and, to a lesser extent, from the snow. Second, methodologies are developed to retrieve information from accessible intermediate hydrological processes. A geochemical method is used to quantify the contribution of a superficial and a deep reservoir to streamflow. It is shown that, for this specific process, the model formalism is not adapted to our study area and thus leads to poor simulation results. A remote-sensing methodology is proposed to retrieve the snow surfaces. Comparison with the simulation shows that this process can be satisfyingly simulated by the model. The multidisciplinary approach adopted in this study, although supported by the hydrological community, is still uncommon. Copyright © 2007 John Wiley & Sons, Ltd. [source] Sensitivity of the regional climate of East/Southeast Asia to convective parameterizations in the RegCM3 modelling system.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2008Part 1: Focus on the Korean peninsula Abstract This study investigates the capability of the regional climate model, RegCM3, to simulate fine-scale regional climate over a narrow peninsula or archipelago. The model is run in one-way double-nested mode with one mother domain and two nested domains. The mother domain encompasses the eastern and southern regions of Asia and adjacent oceans with a grid spacing of 60 km. The first nested domain focuses on the Korean peninsula and the second one covers the Philippine archipelago with a grid spacing of 20 km. The simulation spans a period of 5 years and 1 month, from November 2000 to December 2004. The sensitivity of the two convection schemes, namely, the Grell scheme (Grell) and the MIT-Emanuel scheme (EMU), is studied. Model results obtained with both the Grell and EMU show reasonable performance in capturing the seasonal variation and the spatial characteristics of the East Asian monsoon. However, the Grell simulation appears to have persistent cold and dry biases in the summer season. There is a definite improvement in these model deficiencies by the implementation of EMU. Although the temperature fields in the Grell and EMU simulations are essentially the same in terms of the spatial distribution, the EMU simulation is quantitatively in better agreement with the observed estimates, indicating a substantial reduction in the cold bias. Further, in comparison with the Grell simulation, the EMU simulation shows an improvement in the timing and amplitude of the rain band propagating northward. The spatial distributions of precipitation also have good quality, capturing the localized maxima over Korea. The frequency distributions of daily temperature and precipitation simulated by EMU are closer to observations than those of the Grell simulation. It is found that the convective precipitation derived from different convection parameterizations is a major contributor to the performance of the model in summer. Copyright © 2008 Royal Meteorological Society [source] Managing QoS requirements for video streaming: from intra-node to inter-nodeINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2006Y. Bai Abstract Streaming video over IP networks has become increasingly popular; however, compared to traditional data traffic, video streaming places different demands on quality of service (QoS) in a network, particularly in terms of delay, delay variation, and data loss. In response to the QoS demands of video applications, network techniques have been proposed to provide QoS within a network. Unfortunately, while efficient from a network perspective, most existing solutions have not provided end-to-end QoS that is satisfactory to users. In this paper, packet scheduling and end-to-end QoS distribution schemes are proposed to address this issue. The design and implementation of the two schemes are based on the active networking paradigm. In active networks, routers can perform user-driven computation when forwarding packets, rather than just simple storing and forwarding packets, as in traditional networks. Both schemes thus take advantage of the capability of active networks enabling routers to adapt to the content of transmitted data and the QoS requirements of video users. In other words, packet scheduling at routers considers the correlation between video characteristics, available local resources and the resulting visual quality. The proposed QoS distribution scheme performs inter-node adaptation, dynamically adjusting local loss constraints in response to network conditions in order to satisfy the end-to-end loss requirements. An active network-based simulation shows that using QoS distribution and packet scheduling together increases the probability of meeting end-to-end QoS requirements of networked video. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical analysis on thermal characteristics for chip scale package by integrating 2D/3D modelsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2009Ping Yang Abstract The objective of this paper is to investigate stress and strain of a special scale package-substrate on chip for reliability evaluation or manufacture strategy in deep-seated situation. A two-dimensional model with one-half of cross-section (2D model) and a three-dimensional model with one-fourth of whole package (3D model) were built, respectively, to simulate the thermal stress and strain of CSP-SOC under the condition of the standard industry thermal cycling temperature ,40 to125°C. The different locations can be processed by using the two models, respectively, based on different modeling simplified modes. By using 2D model, the numerical simulation shows that the maximum deformation of the prototype occurs in printed circuit board (PCB), the maximum stress and strain occurs in the outer solder balls. In the meantime, by the results of 3D model, the simulation shows that the maximum elastic strain occurs in the interface between the solder balls and PCB, the minimum strain occurs in the underfill tape, the maximum packaging stress occurs in the edge area of the chip. The result from 3D model maybe more impersonal to reflect the stress and strain characteristics because the third direction is considered in modeling. The analysis by integrating the 2D model and 3D model can get a more comprehensive profile for the thermal investigation of chip scale package (CSP) than by using any single model. The investigation built a basis for improving reliability in engineering design of CSP product. Copyright © 2008 John Wiley & Sons, Ltd. [source] Species-level selection reduces selfishness through competitive exclusionJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2007D. J. RANKIN Abstract Adaptation does not necessarily lead to traits which are optimal for the population. This is because selection is often the strongest at the individual or gene level. The evolution of selfishness can lead to a ,tragedy of the commons', where traits such as aggression or social cheating reduce population size and may lead to extinction. This suggests that species-level selection will result whenever species differ in the incentive to be selfish. We explore this idea in a simple model that combines individual-level selection with ecology in two interacting species. Our model is not influenced by kin or trait-group selection. We find that individual selection in combination with competitive exclusion greatly increases the likelihood that selfish species go extinct. A simple example of this would be a vertebrate species that invests heavily into squabbles over breeding sites, which is then excluded by a species that invests more into direct reproduction. A multispecies simulation shows that these extinctions result in communities containing species that are much less selfish. Our results suggest that species-level selection and community dynamics play an important role in regulating the intensity of conflicts in natural populations. [source] Application of the preconditioned GMRES to the Crank-Nicolson finite-difference time-domain algorithm for 3D full-wave analysis of planar circuitsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008Y. Yang Abstract The increase of the time step size significantly deteriorates the property of the coefficient matrix generated from the Crank-Nicolson finite-difference time-domain (CN-FDTD) method. As a result, the convergence of classical iterative methods, such as generalized minimal residual method (GMRES) would be substantially slowed down. To address this issue, this article mainly concerns efficient computation of this large sparse linear equations using preconditioned generalized minimal residual (PGMRES) method. Some typical preconditioning techniques, such as the Jacobi preconditioner, the sparse approximate inverse (SAI) preconditioner, and the symmetric successive over-relaxation (SSOR) preconditioner, are introduced to accelerate the convergence of the GMRES iterative method. Numerical simulation shows that the SSOR preconditioned GMRES method can reach convergence five times faster than GMRES for some typical structures. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1458,1463, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23396 [source] Optimization of a small to-can package electrical design for SFF/SFP optical transceiver modulesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2004Sang-Hoon Lee Abstract In this paper, we present an optimum TO-38 package design for SFF/SFP optical transceiver modules in order to improve the 3-dB bandwidth. The frequency response of the TO-38 package is measured and compared to simulation where the 3-dB-bandwidth was 3.5 GHz. For a higher operating bandwidth (>15 GHz), new optimized physical geometries for the TO-can package, such as bonding wires, leads, and material, are suggested. The optimal result of simulation shows that this TO-can package can be used at a higher-bit-rate optical module of 10 Gb/s. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 239,242, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11340 [source] Directly measuring early exercise premiums using American and European S&P 500 Index optionsTHE JOURNAL OF FUTURES MARKETS, Issue 3 2003Michael Dueker The Chicago Board Options Exchange concurrently listed European-style and American-style options on the Standard and Poor's 500 Index from April 2, 1986 through June 20, 1986. This unique time period allows for a direct measurement of the early exercise premium in American-style index options. In this study, using ask quotes, we find average early exercise premiums ranging from 5.04 to 5.90% for calls, and from 7.97 to 10.86% for puts. Additionally, we are able to depict a potentially useful functional form of the early exercise premium. As in previous studies, we find some instances of negative early exercise premiums. However, a trading simulation shows that traders must be able to trade within the bid,ask spread to profit from these apparent arbitrage opportunities. © 2003 Wiley Periodicals, Inc. Jrl Fut Mark 23:287,313, 2003 [source] Exact, Distribution Free Confidence Intervals for Late Effects in Censored Matched PairsBIOMETRICAL JOURNAL, Issue 1 2009Shoshana R. Daniel Abstract When comparing censored survival times for matched treated and control subjects, a late effect on survival is one that does not begin to appear until some time has passed. In a study of provider specialty in the treatment of ovarian cancer, a late divergence in the Kaplan,Meier survival curves hinted at superior survival among patients of gynecological oncologists, who employ chemotherapy less intensively, when compared to patients of medical oncologists, who employ chemotherapy more intensively; we ask whether this late divergence should be taken seriously. Specifically, we develop exact, permutation tests, and exact confidence intervals formed by inverting the tests, for late effects in matched pairs subject to random but heterogeneous censoring. Unlike other exact confidence intervals with censored data, the proposed intervals do not require knowledge of censoring times for patients who die. Exact distributions are consequences of two results about signs, signed ranks, and their conditional independence properties. One test, the late effects sign test, has the binomial distribution; the other, the late effects signed rank test, uses nonstandard ranks but nonetheless has the same exact distribution as Wilcoxon's signed rank test. A simulation shows that the late effects signed rank test has substantially more power to detect late effects than do conventional tests. The confidence statement provides information about both the timing and magnitude of late effects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Proposed Monetary Regime for Small Commodity Exporters: Peg the Export Price (,PEP')INTERNATIONAL FINANCE, Issue 1 2003Jeffrey Frankel On the one hand, the big selling points of floating exchange rates , monetary independence and accommodation of terms of trade shocks , have not lived up to their promise. On the other hand, proposals for credible institutional monetary commitments to nominal anchors have each run aground on their own peculiar shoals. Rigid pegs to the dollar are dangerous when the dollar appreciates. Money targeting does not work when there is a velocity shock. CPI targeting is not viable when there is a large import price shock. And the gold standard fails when there are large fluctuations in the world gold market. This paper advances a new proposal called PEP: peg the export price. Most applicable for countries that are specialized in the production of a particular mineral or agricultural product, the proposal calls on them to commit to fix the price of that commodity in terms of domestic currency. A series of simulations shows how such a proposal would have worked for oil producers over the period 1970,2000. The paths of real oil prices, exports, and debt are simulated under alternative regimes. An illustrative finding is that countries that suffered a declining world market in oil or other export commodities in the late 1990s would under the PEP proposal have automatically experienced a depreciation and a boost to exports when it was most needed. The argument for PEP is that it simultaneously delivers automatic accommodation to terms of trade shocks, as floating exchange rates are supposed to do, while retaining the credibility-enhancing advantages of a nominal anchor, as dollar pegs are supposed to do. [source] Modelling of anisotropic damage in brittle rocks under compression dominated stressesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2002Y.F. Lu Abstract A new model for describing induced anisotropic damage in brittle rocks is proposed. Although phenomenological, the model is based on physical grounds of micromechanical analysis. Induced damage is represented by a second rank tensor, which is related to the density and orientation of microcracks. Damage evolution is related to the propagation condition of microcracks. The onset of microcrack coalescence leading to softening behaviour is also considered. The effective elastic compliance of the damaged material is obtained from a specific form of Gibbs potential. Irreversible damage-related strains due to residual opening of microcracks after unloading are also captured. All the model's parameters could be determined from conventional triaxial compression tests. The proposed model is applied to a typical brittle rock. Comparison between test data and numerical simulations shows an overall good agreement. The proposed model is able to describe the main features related to induced microcracks in brittle geomaterials. Copyright © 2002 John Wiley & Sons, Ltd. [source] Counting elephants in Montane forests: some sources of errorAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009Hilde Vanleeuwe Abstract The dung count method is widely used to estimate elephant numbers in forests. It was developed in the lowland forests of Central Africa but it is also used in Montane forests in eastern Africa. Using data collected on Mount Kenya and computer simulations, this paper explores the following issues associated with dung surveys in Montane forests: ,,High rainfall at 3000 m altitude on Mount Kenya was expected to accelerate dung pile decay but no significant difference was found between 3000 and 2500 m where less rain falls, possibly because high rainfall at 3000 m is counteracted by lower temperatures; ,,Physical obstacles make it difficult to walk long, straight transects in Montane forests. Deviating from a straight line pushes the distribution of distance measurements from dung piles to the transect centre line (pdist) towards a negative exponential (NE), which complicates data analysis and may give inaccurate estimates. Using short transects largely alleviate this problem; ,,Analysis of dung count simulations shows that the expected sightability curve of pdist pushes towards a NE with increasing numbers of obstacles blocking the view, even along perfectly straight transects; ,,Extrapolating measured dung density to map area on Mount Kenya resulted in an underestimate of c. 13%. An unstratified correction of map area to ground area for Montane areas would be biased because of the strong tendency for elephants to avoid steeply sloping areas. Résumé La méthode par comptage des crottes est largement utilisée pour estimer le nombre des éléphants en forêt. Elle a été mise au point dans les forêts de basse altitude d'Afrique centrale, mais elle est aussi employée dans les forêts de montagne d'Afrique de l'Est. Utilisant les données collectées sur le Mont Kenya et des simulations informatiques, cet article explore les questions suivantes liées au comptage des crottes dans les forêts de montagne: ,,Les fortes chutes de pluies à 3 000 mètres d'altitude sur le Mont Kenya étaient censées accélérer la décomposition des tas de crottes, mais on n'a pas trouvé de différence significative entre 3 000 et 2 500 mètres où il tombe moins de pluie, peut-être parce que les fortes pluies à 3 000 mètres sont compensées par de plus basses températures; ,,Les obstacles physiques rendent plus difficiles de marcher le long de transects rectilignes dans les forêts de montagne. Le fait de dévier de la ligne droite pousse la distribution des mesures des distances entre les tas de crottes et la ligne droite du transect (pdist) vers un modèle exponentiel négatif (EN) qui complique l'analyse des données et peut donner des estimations inexactes. Le fait de recourir à des transects courts réduit considérablement ce problème; ,,L'analyse des simulations de comptages de crottes montre que la courbe de visibilité attendue de pdist pousse vers un EN lorsque le nombre d'obstacles bloquant la vue augmente, même le long de transects parfaitement rectilignes; ,,L'extrapolation de la densité mesurée des crottes sur une carte du Mont Kenya a abouti à une sous-estimation d'environ 13%. Une correction non stratifiée de la surface cartographiée des zones montagneuses vers une surface plane serait biaisée étant donné que les éléphants ont fortement tendance àéviter les zones escarpées et glissantes. [source] | |||||||||||||||||||