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Terms modified by Queue Selected AbstractsOn Estimation in M/G/c/c QueuesINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 6 2001Mei Ling Huang We derive the minimum variance unbiased estimator (MVUE) and the maximum likelihood estimator (MLE) of the stationary probability function (pf) of the number of customers in a collection of independent M/G/c/c subsystems. It is assumed that the offered load and number of servers in each subsystem are unknown. We assume that observations of the total number of customers in the system are utilized because it may be impractical or impossible to observe individual server occupancies. Both estimators depend on the R distribution (the distribution of the sum of independent right truncated Poisson random variables) and R numbers. [source] Priority-Driven Acoustic Modeling for Virtual EnvironmentsCOMPUTER GRAPHICS FORUM, Issue 3 2000Patrick Min Geometric acoustic modeling systems spatialize sounds according to reverberation paths from a sound source to a receiver to give an auditory impression of a virtual 3D environment. These systems are useful for concert hall design, teleconferencing, training and simulation, and interactive virtual environments. In many cases, such as in an interactive walkthrough program, the reverberation paths must be updated within strict timing constraints - e.g., as the sound receiver moves under interactive control by a user. In this paper, we describe a geometric acoustic modeling algorithm that uses a priority queue to trace polyhedral beams representing reverberation paths in best-first order up to some termination criteria (e.g., expired time-slice). The advantage of this algorithm is that it is more likely to find the highest priority reverberation paths within a fixed time-slice, avoiding many geometric computations for lower-priority beams. Yet, there is overhead in computing priorities and managing the priority queue. The focus of this paper is to study the trade-offs of the priority-driven beam tracing algorithm with different priority functions. During experiments computing reverberation paths between a source and a receiver in a 3D building environment, we find that priority functions incorporating more accurate estimates of source-to-receiver path length are more likely to find early reverberation paths useful for spatialization, especially in situations where the source and receiver cannot reach each other through trivial reverberation paths. However, when receivers are added to the environment such that it becomes more densely and evenly populated, this advantage diminishes. [source] Network-aware selective job checkpoint and migration to enhance co-allocation in multi-cluster systems,CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13 2009William M. Jones Abstract Multi-site parallel job schedulers can improve average job turn-around time by making use of fragmented node resources available throughout the grid. By mapping jobs across potentially many clusters, jobs that would otherwise wait in the queue for local resources can begin execution much earlier; thereby improving system utilization and reducing average queue waiting time. Recent research in this area of scheduling leverages user-provided estimates of job communication characteristics to more effectively partition the job across system resources. In this paper, we address the impact of inaccuracies in these estimates on system performance and show that multi-site scheduling techniques benefit from these estimates, even in the presence of considerable inaccuracy. While these results are encouraging, there are instances where these errors result in poor job scheduling decisions that cause network over-subscription. This situation can lead to significantly degraded application performance and turnaround time. Consequently, we explore the use of job checkpointing, termination, migration, and restart (CTMR) to selectively stop offending jobs to alleviate network congestion and subsequently restart them when (and where) sufficient network resources are available. We then characterize the conditions and the extent to which the process of CTMR improves overall performance. We demonstrate that this technique is beneficial even when the overhead of doing so is costly. Copyright © 2009 John Wiley & Sons, Ltd. [source] Lesser Bear: A lightweight process library for SMP computers,scheduling mechanism without a lock operationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 10 2002Hisashi Oguma Abstract We have designed and implemented a lightweight process (thread) library called ,Lesser Bear' for SMP computers. Lesser Bear has thread-level parallelism and high portability. Lesser Bear executes threads in parallel by creating UNIX processes as virtual processors and a memory-mapped file as a huge shared-memory space. To schedule thread in parallel, the shared-memory space has been divided into working spaces for each virtual processor, and a ready queue has been distributed. However the previous version of Lesser Bear sometimes requires a lock operation for dequeueing. We therefore proposed a scheduling mechanism that does not require a lock operation. To achieve this, each divided space forms a link topology through the queues, and we use a lock-free algorithm for the queue operation. This mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source] An analysis of VI Architecture primitives in support of parallel and distributed communicationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2002Andrew Begel Abstract We present the results of a detailed study of the Virtual Interface (VI) paradigm as a communication foundation for a distributed computing environment. Using Active Messages and the Split-C global memory model, we analyze the inherent costs of using VI primitives to implement these high-level communication abstractions. We demonstrate a minimum mapping cost (i.e. the host processing required to map one abstraction to a lower abstraction) of 5.4 ,s for both Active Messages and Split-C using four-way 550 MHz Pentium III SMPs and the Myrinet network. We break down this cost to the use of individual VI primitives in supporting flow control, buffer management and event processing and identify the completion queue as the source of the highest overhead. Bulk transfer performance plateaus at 44 Mbytes/s for both implementations are due to the addition of fragmentation requirements. Based on this analysis, we present the implications for the VI successor, Infiniband. Copyright © 2002 John Wiley & Sons, Ltd. [source] System Complexity As a Measure of Safe Capacity for the Emergency DepartmentACADEMIC EMERGENCY MEDICINE, Issue 11 2006Daniel J. France PhD Objectives System complexity is introduced as a new measure of system state for the emergency department (ED). In its original form, the measure quantifies the uncertainty of demands on system resources. For application in the ED, the measure is being modified to quantify both workload and uncertainty to produce a single integrated measure of system state. Methods Complexity is quantified using an information-theoretic or entropic approach developed in manufacturing and operations research. In its original form, complexity is calculated on the basis of four system parameters: 1) the number of resources (clinicians and processing entities such as radiology and laboratory systems), 2) the number of possible work states for each resource, 3) the probability that a resource is in a particular work state, and 4) the probability of queue changes (i.e., where a queue is defined by the number of patients or patient orders being managed by a resource) during a specified time period. Results An example is presented to demonstrate how complexity is calculated and interpreted for a simple system composed of three resources (i.e., emergency physicians) managing varying patient loads. The example shows that variation in physician work states and patient queues produces different scores of complexity for each physician. It also illustrates how complexity and workload differ. Conclusions System complexity is a viable and technically feasible measurement for monitoring and managing surge capacity in the ED. [source] Delay analysis of a probabilistic priority disciplineEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2002Yuming Jiang In computer networks, the Strict Priority (SP) discipline is perhaps the most common and simplest method to schedule packets from different classes of applications, each with diverse performance requirements. With this discipline, however, packets at higher priority levels can starve packets at lower priority levels. To resolve this starvation problem, we propose to assign a parameter to each priority queue in the SP discipline. The assigned parameter determines the probability or extent by which its corresponding queue is served when the queue is polled by the server. We thus form a new packet service discipline, referred to as the Probabilistic Priority (PP) discipline. By properly adjusting the assigned parameters, not only is the performance of higher priority classes satisfied, but also the performance of lower priority classes can be improved. This paper analyzes the delay performance of the PP discipline. A decomposition approach is proposed for calculating the average waiting times and their bounds are studied. Two approximation approaches are proposed to estimate the waiting times. Simulation results that validate the numerical analysis are presented and examined. A numerical example which demonstrates the use of the PP discipline to achieve service differentiation is presented. This example also shows how the assigned parameters can be determined from the results of analysis mentioned above. [source] On the application of forking nodes to product-form queueing networks,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2008Essia H. Elhafsi Abstract We define a ,forking node' as a service centre with one input feeding two outputs (each served by its own queue) under the control of an internal path-selection (PS) policy. We assume that both outputs lead to paths through which a packet reaches its final destination. However, the mean downstream delays on the two paths may be different and the PS policy should favour the path with the lower downstream delay. Using simulation, we compare the performance of this system under a variety of random, deterministic, state-dependent PS policies, including threshold-based and join-shortest-queue with bias (JSQ + b). We show that JSQ + b has better performance than the other alternatives. Moreover, if the input process to the forking node is Poisson, standard time series analysis techniques show that its two outputs are very close to being independent Poisson processes. Thus, if we find an accurate and efficient ,offline' analytical performance model for JSQ + b forking node, we can extend the applicability of product-form queueing networks to include such forking nodes. For this reason, we present several ways of modelling the performance of a JSQ + b node, using bounds, and compare their results on example networks. We establish a closed-form expression relating the bias b and the delays of the downstream paths. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dynamic buffer management using per-queue thresholdsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2007B. Gazi Abstract Shared buffer switches consist of a memory pool completely shared among output ports of a switch. Shared buffer switches achieve low packet loss performance as buffer space is allocated in a flexible manner. However, this type of buffered switches suffers from high packet losses when the input traffic is imbalanced and bursty. Heavily loaded output ports dominate the usage of shared memory and lightly loaded ports cannot have access to these buffers. To regulate the lengths of very active queues and avoid performance degradations, threshold-based dynamic buffer management policy, decay function threshold, is proposed in this paper. Decay function threshold is a per-queue threshold scheme that uses a tailored threshold for each output port queue. This scheme suggests that buffer space occupied by an output port decays as the queue size of this port increases and/or empty buffer space decreases. Results have shown that decay function threshold policy is as good as well-known dynamic thresholds scheme, and more robust when multicast traffic is used. The main advantage of using this policy is that besides best-effort traffic it provides support to quality of service (QoS) traffic by using an integrated buffer management and scheduling framework. Copyright © 2006 John Wiley & Sons, Ltd. [source] Performance analysis of IEEE 802.11 DCF with stochastic reward nets,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2007R. Jayaparvathy Abstract In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11-based wireless local area networks (WLANs). We consider the distributed co-ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN-based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on,off traffic model and taking into account the freezing of the back-off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd. [source] DRED: a random early detection algorithm for TCP/IP networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2002James Aweya Abstract It is now widely accepted that a RED [2] controlled queue certainly performs better than a drop-tail queue. But an inherent weakness of RED is that its equilibrium queue length cannot be maintained at a preset value independent of the number of TCP active connections. In addition, RED's optimal parameter setting is largely correlated with the number of connections, the round-trip time, the buffer space, etc. In light of these observations, we propose DRED, a novel algorithm which uses the basic ideas of feedback control to randomly discard packets with a load-dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The benefits of stabilized queues in a network are high resources utilization, predictable maximum delays, more certain buffer provisioning, and traffic-load-independent network performance in terms of traffic intensity and number of connections. Copyright © 2002 John Wiley & Sons, Ltd. [source] Simulation and discrete event optimization for automated decisions for in-queue flightsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 5 2010D. Dimitrakiev The paper discusses simulation and optimization of in-queue flights, analyzed as discrete-event systems. Simulation is performed in a platform, based on MATLAB program functions and SIMULINK dynamic models. Regime optimization aims to maximize the controllability of the queue and minimize the fuel consumption of each aircraft (AC). Because of mutual preferential independence, a hierarchical additive value function is constructed, consisting of fuzzily estimated parameter value functions and weight coefficients and a multicriteria decision problem is solved under strict certainty. Two optimization algorithms are applied: one that finds the regime that leads to maximally preferred consequence and another that finds the regime with minimum total fuel consumption among those whose control parameters are set at their most preferred levels. A comparison between the two algorithms is proposed. A scheme describes how the optimization procedures can be used multiple times during the execution of the flight with respect to the occurrence of discrete events. Simulation results are also proposed for the discussed algorithms and procedures. © 2010 Wiley Periodicals, Inc. [source] Prioritized e-mail servicing to reduce non-spam delay and loss: A performance analysisINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2008Muhammad N. Marsono This paper proposes a prioritized e-mail servicing on e-mail servers to reduce the delay and loss of non-spam e-mails due to queuing. Using a prioritized two-queue scheme, non-spam e-mails are queued in a fast queue and given higher service priority than spam e-mails that are queued in a slow queue. Four prioritized e-mail service strategies for the two-queue scheme are proposed and analyzed. We modeled these four strategies using discrete-time Markov chain analysis under different e-mail traffic loads and service capacities. Non-spam e-mails can be delivered within a small delay, even under heavy e-mail loadings and high spam-to-non-spam a priori. Results from our analysis of the two-queue scheme show that it gives non-spam delay and loss probability two orders of magnitude smaller than the typical single-queue approach during heavy spam traffic. Moreover, prioritized e-mail servicing protects e-mail servers from spam attacks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Modelling congestion in closed queueing networksINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 4-5 2000P.K. Pollett Abstract We will consider the problem of identifying regions of congestion in closed queueing networks with state-dependent service rates. A particular queue will be called a bottleneck if the number of customers in that queue grows without bound as the total number of customers in the network becomes large. We will review methods for identifying potential bottlenecks, with a view to controlling congestion. We will see that the problem of identifying bottlenecks can be reduced to one of finding them in an isolated subnetwork with suitably modified routing intensities. Several special cases will be studied, illustrating a range of behaviour. For example, it is possible for a subnetwork to be congested, yet each queue in that subnetwork is not strictly a bottleneck. [source] Observing freeway ramp merging phenomena in congested trafficJOURNAL OF ADVANCED TRANSPORTATION, Issue 2 2007Majid Sarvi This work conducts a comprehensive investigation of traffic behavior and characteristics during freeway ramp merging under congested traffic conditions. On the Tokyo Metropolitan Expressway, traffic congestion frequently occurs at merging bottleneck sections, especially during heavy traffic demand. The Tokyo Metropolitan Expressway public corporation, generally applies different empirical strategies to increase the flow rate and decrease the accident rate at the merging sections. However, these strategies do not rely either on any behavioral characteristics of the merging traffic or on the geometric design of the merging segments. There have been only a few research publications concerned with traffic behavior and characteristics in these situations. Therefore, a three-year study is undertaken to investigate traffic behavior and characteristics during the merging process under congested situations. Extensive traffic data capturing a wide range of traffic and geometric information were collected using detectors, videotaping, and surveys at eight interchanges in Tokyo Metropolitan Expressway. Maximum discharged flow rate from the head of the queue at merging sections in conjunction with traffic and geometric characteristics were analyzed. In addition, lane changing maneuver with respect to the freeway and ramp traffic behaviors were examined. It is believed that this study provides a thorough understanding of the freeway ramp merging dynamics. In addition, it forms a comprehensive database for the development and implementation of congestion management techniques at merging sections utilizing Intelligent Transportation System. [source] An equity-based passenger flow control model with application to Hong Kong-Shenzhen border-crossingJOURNAL OF ADVANCED TRANSPORTATION, Issue 2 2002Hai Yang Cross-border passengers from Hong Kong to Shenzhen by the east Kowloon-Canton Railway (KCR) through the Lo Wu customs exceed nearly 200 thousand on a special day such as a day during the Chinese Spring Festival. Such heavy passenger demand often exceeds the processing and holding capacity of the Lo Wu customs for many hours a day. Thus, passengers must be metered off at all entrance stations along the KCR line through ticket rationing to restrain the number of passengers waiting at Lo Wu within its safe holding capacity. This paper proposes an optimal control strategy and model to deal with this passenger crowding and control problem. Because the maximum passenger checkout rate at Lo Wu is fixed, total passenger waiting time is not affected by the control strategy for given time-dependent arriving rates at each station. An equity-based control strategy is thus proposed to equalize the waiting times of passengers arriving at all stations at the same time. This equity is achieved through optimal allocation of the total quota of tickets to all entrance stations for each train service. The total ticket quota for each train service is determined such that the capacity constraint of the passenger queue at Lo Wu is satisfied. The control problem is formulated as a successive linear programming problem and demonstrated for the KCR system with partially simulated data. [source] Divorce, dispersal and incest avoidance in the cooperatively breeding superb fairy-wren Malurus cyaneusJOURNAL OF ANIMAL ECOLOGY, Issue 2 2003Andrew Cockburn Summary 1Between 1988 and 2001, we studied social relationships in the superb fairy-wren Malurus cyaneus (Latham), a cooperative breeder with male helpers in which extra-group fertilizations are more common than within-pair fertilizations. 2Unlike other fairy-wren species, females never bred on their natal territory. First-year females dispersed either directly from their natal territory to a breeding vacancy or to a foreign ,staging-post' territory where they spent their first winter as a subordinate. Females dispersing to a foreign territory settled in larger groups. Females on foreign territories inherited the territory if the dominant female died, and were sometimes able to split the territory into two by pairing with a helper male. However, most dispersed again to obtain a vacancy. 3Females dispersing from a staging post usually gained a neighbouring vacancy, but females gaining a vacancy directly from their natal territory travelled further, perhaps to avoid pairing or mating with related males. 4Females frequently divorced their partner, although the majority of relationships were terminated by the death of one of the pair. If death did not intervene, one-third of pairings were terminated by female-initiated divorce within 1000 days. 5Three divorce syndromes were recognized. First, females that failed to obtain a preferred territory moved to territories with more helpers. Secondly, females that became paired to their sons when their partner died usually divorced away from them. Thirdly, females that have been in a long relationship divorce once a son has gained the senior helper position. 6Dispersal to avoid pairing with sons is consistent with incest avoidance. However, there may be two additional benefits. Mothers do not mate with their sons, so dispersal by the mother liberates her sons to compete for within-group matings. Further, divorcing once their son has become a breeder or a senior helper allows the female to start sons in a queue for dominance on another territory. Females that do not take this option face constraints on their ability to recruit more sons into the local neighbourhood. [source] Priority waiting lists: Is there a clinically ordered queue?JOURNAL OF EVALUATION IN CLINICAL PRACTICE, Issue 4 2005Boris G. Sobolev PhD [source] The effects of information on a queue with balking and phase-type service timesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2008Pengfei Guo Abstract This article generalizes the models in Guo and Zipkin, who focus on exponential service times, to systems with phase-type service times. Each arriving customer decides whether to stay or balk based on his expected waiting cost, conditional on the information provided. We show how to compute the throughput and customers' average utility in each case. We then obtain some analytical and numerical results to assess the effect of more or less information. We also show that service-time variability degrades the system's performance. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008 [source] Analysis of a finite-buffer bulk-service queue with discrete-Markovian arrival process: D-MAP/Ga,b/1/NNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2003M.L. Chaudhry Abstract Discrete-time queues with D-MAP arrival process are more useful in modeling and performance analysis of telecommunication networks based on the ATM environment. This paper analyzes a finite-buffer discrete-time queue with general bulk-service rule, wherein the arrival process is D-MAP and service times are arbitrarily and independently distributed. The distributions of buffer contents at various epochs (departure, random, and prearrival) have been obtained using imbedded Markov chain and supplementary variable methods. Finally, some performance measures such as loss probability and average delay are discussed. Numerical results are also presented in some cases. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 345,363, 2003. [source] Designing a belt conveyor controller in a bottling plant using fuzzy logic and genetic algorithmsPACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2001Marcello Braglia Abstract This paper presents an industrial case study relevant to a fuzzy logic controller designed via a properly developed genetic algorithm. We consider an example of a fuzzy logic-based industrial process-controller. In particular, we deal with the problem of controlling the speed of a belt conveyor for glass containers in a bottling plant. The primary objective of the controller is to guarantee the continuous feed to the filling station, in the presence of frequent gaps between bottles. The secondary objective is to reduce the impact speed between arriving bottles and those standing in the queue, in order to reduce the plant noise. High-performance parameters of the fuzzy controller are found by a properly developed genetic algorithm. The results provided by Monte Carlo simulations demonstrate that, with such controllers, it is possible to achieve both the objectives mentioned above. Copyright © 2001 John Wiley & Sons, Ltd. [source] Large deviations of multiclass M/G/1 queues,THE CANADIAN JOURNAL OF STATISTICS, Issue 3 2009André Dabrowski Abstract Consider a multiclass M/G/1 queue where queued customers are served in their order of arrival at a rate which depends on the customer class. We model this system using a chain with states represented by a tree. Since the service time distribution depends on the customer class, the stationary distribution is not of product form so there is no simple expression for the stationary distribution. Nevertheless, we can find a harmonic function on this chain which provides information about the asymptotics of this stationary distribution. The associated h -transformation produces a change of measure that increases the arrival rate of customers and decreases the departure rate thus making large deviations common. The Canadian Journal of Statistics 37: 327,346; 2009 © 2009 Statistical Society of Canada Considérons une file d'attente M/G/1 multicatégorie où les consommateurs dans la file d'attente sont servis selon leur ordre d'arrivée à un taux dépendant de leur catégorie de consommateurs. Nous modélisons ce système en utilisant une chaîne où les états sont représentés à l'aide d'un arbre. Puisque la distribution du temps de service dépend du type de consommateurs, la distribution stationnaire ne peut pas s'écrire sous la forme d'un produit. Par conséquent, il n'existe pas d'expression simple pour représenter la distribution stationnaire. Cependant, nous pouvons obte-nir une transformation harmonique de cette chaîne contenant de l'information sur les propriétés asymptotiques de cette distribution stationnaire. La transformation- h associée conduit à un chan-gement de mesure qui augmente le taux d'arrivée et décroît le taux de service ce qui augmente la probabilité de grandes déviations. La revue canadienne de statistique 37: 327,346; 2009 © 2009 Société statistique du Canada [source] Distribution sensitivity in a highway flow modelAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 6 2009Andrew M. Ross, Article first published online: 13 FEB 200 Abstract We examine a model of traffic flow on a highway segment, where traffic can be impaired by random incidents (usually, collisions). Using analytical and numerical methods, we show the degree of sensitivity that the model exhibits to the distributions of service times (in the queueing model) and incident clearance times. Its sensitivity to the distribution of time until an incident is much less pronounced. Our analytical methods include an M/Gt/, analysis (Gt denotes a service process whose distribution changes with time) and a fluid approximation for an M/M/c queue with general distributions for the incident clearance times. Our numerical methods include M/PH2/c/K models with many servers and with phase-type distributions for the time until an incident occurs or is cleared. We also investigate different time scalings for the rate of incident occurrence and clearance. Copyright © 2009 John Wiley & Sons, Ltd. [source] HST experience in data managementASTRONOMISCHE NACHRICHTEN, Issue 6-8 2004R. Albrecht Abstract The data generated by the Hubble Space Telescope pose a series of special requirements for the analysis process. The Hubble Space Telescope (HST) is being operated in a semi-autonomous, pre-programmed manner, executing a queue of observing requests. Calibration is being done "institutionally", i.e. not in response to individual observing programs, but in the same manner for all users. Data products are being generated for the observers, and they are ingested in the HST science data archives, to make them available for further exploitation through the Virtual Observatory. Added value products can be generated by combining data from different programs. Interactive analysis tools are being supplied to support users in the optimum exploitation of the data. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Automatic data reduction and archiving for STELLAASTRONOMISCHE NACHRICHTEN, Issue 6-8 2004Article first published online: 13 OCT 200, M. Weber Abstract The data is collected at the observatory, each data product is registered and a queue is set up to transfer the highest priority observations first. Optionally, lossy compression (e.g. White 1994) can be used to boost transfer speeds for time critical observations. Once the data has been transferred, the reduction process is started at the control-center in Potsdam. The type of reduction steps required can be specified by the user or a default pipeline setup can be used. The users can be notified about the status of their observations in any desired detail. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Versatile Birth,Death Model Applicable to Four Distinct ProblemsAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 1 2004J. Gani Summary This paper revisits a simple birth,death model which arises in slightly different forms in four distinct stochastic problems. These are the barbershop queue, coupon collecting, vocabulary usage and geological dating. Discrete and continuous time Markov chains are used to characterize these problems. Somewhat different questions are posed for each particular case, and practical results are derived for each process. The paper concludes with some comments on the versatility of this applied probability model. [source] Dissection of the Late Steps in Aureothin BiosynthesisCHEMBIOCHEM, Issue 1 2006Markus Müller Part of the queue. Biosynthesis of the cytostatic polyketide aureothin (1) in Streptomyces thioluteus was found to involve two tailoring steps (see scheme). Mutational biosynthesis of nor -deoxyaureothin (,- 2) and a hydroxylated derivative (3), together with biotransformation experiments revealed a well-defined order for the polyketide-tailoring steps. Regioselective ,-pyrone methylation was found to be the penultimate biosynthetic step prior to furan-ring formation. [source] The Optimization of Signal Settings on a Signalized Roundabout Using the Cross-entropy MethodCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2008Mike Maher It is an iterative process that consists of generating solutions from some probability distribution whose parameter values are updated in each iteration using information from the best solutions found in that iteration. The article applies the method to the problem of the optimization of signal settings on a signalized roundabout. The performance of any given set of timings is evaluated using the cell transmission model, a deterministic macroscopic traffic flow model that permits the modeling of the spatial extent of queues and the possibility of "blocking back." The results from the investigations are encouraging, and show that the CEM has the potential to be a useful technique for tackling global optimization problems. [source] Lesser Bear: A lightweight process library for SMP computers,scheduling mechanism without a lock operationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 10 2002Hisashi Oguma Abstract We have designed and implemented a lightweight process (thread) library called ,Lesser Bear' for SMP computers. Lesser Bear has thread-level parallelism and high portability. Lesser Bear executes threads in parallel by creating UNIX processes as virtual processors and a memory-mapped file as a huge shared-memory space. To schedule thread in parallel, the shared-memory space has been divided into working spaces for each virtual processor, and a ready queue has been distributed. However the previous version of Lesser Bear sometimes requires a lock operation for dequeueing. We therefore proposed a scheduling mechanism that does not require a lock operation. To achieve this, each divided space forms a link topology through the queues, and we use a lock-free algorithm for the queue operation. This mechanism is applied to Lesser Bear and evaluated by experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source] System Complexity As a Measure of Safe Capacity for the Emergency DepartmentACADEMIC EMERGENCY MEDICINE, Issue 11 2006Daniel J. France PhD Objectives System complexity is introduced as a new measure of system state for the emergency department (ED). In its original form, the measure quantifies the uncertainty of demands on system resources. For application in the ED, the measure is being modified to quantify both workload and uncertainty to produce a single integrated measure of system state. Methods Complexity is quantified using an information-theoretic or entropic approach developed in manufacturing and operations research. In its original form, complexity is calculated on the basis of four system parameters: 1) the number of resources (clinicians and processing entities such as radiology and laboratory systems), 2) the number of possible work states for each resource, 3) the probability that a resource is in a particular work state, and 4) the probability of queue changes (i.e., where a queue is defined by the number of patients or patient orders being managed by a resource) during a specified time period. Results An example is presented to demonstrate how complexity is calculated and interpreted for a simple system composed of three resources (i.e., emergency physicians) managing varying patient loads. The example shows that variation in physician work states and patient queues produces different scores of complexity for each physician. It also illustrates how complexity and workload differ. Conclusions System complexity is a viable and technically feasible measurement for monitoring and managing surge capacity in the ED. [source] | ||||||||||||||||||||||||||||