Journal of special operations medicine : a peer reviewed journal for SOF medical professionals, 2014
Current guidelines for mass-casualty triage do not explicitly use information about resource avai... more Current guidelines for mass-casualty triage do not explicitly use information about resource availability. Even though this limitation has been widely recognized, how it should be addressed remains largely unexplored. The authors present a novel framework developed using operations research methods to account for resource limitations when determining priorities for transportation of critically injured patients. To illustrate how this framework can be used, they also develop two specific example methods, named ReSTART and Simple-ReSTART, both of which extend the widely adopted triage protocol Simple Triage and Rapid Treatment (START) by using a simple calculation to determine priorities based on the relative scarcity of transportation resources. The framework is supported by three techniques from operations research: mathematical analysis, optimization, and discrete-event simulation. The authors? algorithms were developed using mathematical analysis and optimization and then extensiv...
We present a new method for obtaining confidence intervals in steady-state simulation. In our rep... more We present a new method for obtaining confidence intervals in steady-state simulation. In our replicated batch means method, we do a small number of independent replications to estimate the steady-state mean of the underlying stochastic process. In order to obtain a variance estimator, we further group the observations from these replications into non-overlapping batches. We show that for large sample
ABSTRACT We consider a queueing system with multiple stations attended by a single flexible serve... more ABSTRACT We consider a queueing system with multiple stations attended by a single flexible server. An order arriving at this system needs to go through each station only once but there is no particular precedence relationship among these stations. One can also think of this system as an assembly system where each station processes a different component of an order and once all the components associated with an order are processed they are assembled instantaneously. A holding cost is charged for keeping the orders in the system and there is a penalty associated with the switches of the server between stations. Our objective is to minimize the long-run average costs by dynamically assigning the server to stations based on the system state. Using sample-path arguments, we provide partial characterizations of the optimal policy and provide sufficient conditions under which a simple state-independent policy that works on one order at a time is optimal. We also propose three simple threshold policies and present a numerical study that provides supporting evidence for the superior performance of our double-threshold heuristic.
ABSTRACT For a tandem line of finite, single-server queues operating under the production blockin... more ABSTRACT For a tandem line of finite, single-server queues operating under the production blocking mechanism, we study the effects of pooling several adjacent stations and the associated servers into a single station with a single team of servers. We assume that the servers are cross-trained (so that they can work at several different stations) and that two or more servers can cooperate on the same job. For such a system, we provide sufficient conditions on the service times and sizes of the input and output buffers at the pooled station under which pooling will decrease the departure time of each job from the system (and hence increase the system throughput). We also show that pooling decreases the total number of jobs in the system at any given time and the sojourn time of each job in the system if the departure time of each job from the system is decreased by pooling and there is an arrival stream at the first station. Moreover, we provide sufficient conditions under which pooling will improve the holding cost of each job in the system incurred before any given time, and extend our results to closed tandem lines and to queueing networks with either a more general blocking mechanism or probabilistic routing. Finally, we present a numerical study aimed at quantifying the improvements in system performance obtained through pooling and at understanding which stations should be pooled to achieve the maximum benefit. Our results suggest that the improvements gained by pooling may be substantial and that the bottleneck station should be among the pooled stations in order to obtain the greatest benefit.
We present a new method for obtaining confidence intervals in steady-state simulation. In our rep... more We present a new method for obtaining confidence intervals in steady-state simulation. In our replicated batch means method, we perform a small number of independent replications to estimate the steady-state mean of the underlying stochastic process. In order to obtain a variance estimator, we further group the observations from these replications into nonoverlapping batches. We show that for large sample
ACM Transactions on Modeling and Computer Simulation, 2006
Independent replications (IR) and batch means (BM) are two of the most widely used variance-estim... more Independent replications (IR) and batch means (BM) are two of the most widely used variance-estimation methods for simulation output analysis. Andradottir and Argon (2002) proposed the method of replicated batch means (RBM), which com- bines good characteristics of IR and BM. The current paper gives analytical results for the mean and variance of the RBM estimator for a class of processes having an initial transient with an additive form. Along the way, we provide complementary extensions of the main variance result in the Andradottir and Argon paper. An example illustrates our findings.
Journal of special operations medicine : a peer reviewed journal for SOF medical professionals, 2014
Current guidelines for mass-casualty triage do not explicitly use information about resource avai... more Current guidelines for mass-casualty triage do not explicitly use information about resource availability. Even though this limitation has been widely recognized, how it should be addressed remains largely unexplored. The authors present a novel framework developed using operations research methods to account for resource limitations when determining priorities for transportation of critically injured patients. To illustrate how this framework can be used, they also develop two specific example methods, named ReSTART and Simple-ReSTART, both of which extend the widely adopted triage protocol Simple Triage and Rapid Treatment (START) by using a simple calculation to determine priorities based on the relative scarcity of transportation resources. The framework is supported by three techniques from operations research: mathematical analysis, optimization, and discrete-event simulation. The authors? algorithms were developed using mathematical analysis and optimization and then extensiv...
We present a new method for obtaining confidence intervals in steady-state simulation. In our rep... more We present a new method for obtaining confidence intervals in steady-state simulation. In our replicated batch means method, we do a small number of independent replications to estimate the steady-state mean of the underlying stochastic process. In order to obtain a variance estimator, we further group the observations from these replications into non-overlapping batches. We show that for large sample
ABSTRACT We consider a queueing system with multiple stations attended by a single flexible serve... more ABSTRACT We consider a queueing system with multiple stations attended by a single flexible server. An order arriving at this system needs to go through each station only once but there is no particular precedence relationship among these stations. One can also think of this system as an assembly system where each station processes a different component of an order and once all the components associated with an order are processed they are assembled instantaneously. A holding cost is charged for keeping the orders in the system and there is a penalty associated with the switches of the server between stations. Our objective is to minimize the long-run average costs by dynamically assigning the server to stations based on the system state. Using sample-path arguments, we provide partial characterizations of the optimal policy and provide sufficient conditions under which a simple state-independent policy that works on one order at a time is optimal. We also propose three simple threshold policies and present a numerical study that provides supporting evidence for the superior performance of our double-threshold heuristic.
ABSTRACT For a tandem line of finite, single-server queues operating under the production blockin... more ABSTRACT For a tandem line of finite, single-server queues operating under the production blocking mechanism, we study the effects of pooling several adjacent stations and the associated servers into a single station with a single team of servers. We assume that the servers are cross-trained (so that they can work at several different stations) and that two or more servers can cooperate on the same job. For such a system, we provide sufficient conditions on the service times and sizes of the input and output buffers at the pooled station under which pooling will decrease the departure time of each job from the system (and hence increase the system throughput). We also show that pooling decreases the total number of jobs in the system at any given time and the sojourn time of each job in the system if the departure time of each job from the system is decreased by pooling and there is an arrival stream at the first station. Moreover, we provide sufficient conditions under which pooling will improve the holding cost of each job in the system incurred before any given time, and extend our results to closed tandem lines and to queueing networks with either a more general blocking mechanism or probabilistic routing. Finally, we present a numerical study aimed at quantifying the improvements in system performance obtained through pooling and at understanding which stations should be pooled to achieve the maximum benefit. Our results suggest that the improvements gained by pooling may be substantial and that the bottleneck station should be among the pooled stations in order to obtain the greatest benefit.
We present a new method for obtaining confidence intervals in steady-state simulation. In our rep... more We present a new method for obtaining confidence intervals in steady-state simulation. In our replicated batch means method, we perform a small number of independent replications to estimate the steady-state mean of the underlying stochastic process. In order to obtain a variance estimator, we further group the observations from these replications into nonoverlapping batches. We show that for large sample
ACM Transactions on Modeling and Computer Simulation, 2006
Independent replications (IR) and batch means (BM) are two of the most widely used variance-estim... more Independent replications (IR) and batch means (BM) are two of the most widely used variance-estimation methods for simulation output analysis. Andradottir and Argon (2002) proposed the method of replicated batch means (RBM), which com- bines good characteristics of IR and BM. The current paper gives analytical results for the mean and variance of the RBM estimator for a class of processes having an initial transient with an additive form. Along the way, we provide complementary extensions of the main variance result in the Andradottir and Argon paper. An example illustrates our findings.
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