Ana Paula Iannoni

An optimization approach for ambulance location and the districting of the response segments on highways

In this paper we present a method to optimize the configuration and operation of emergency medical systems on highways. Different from the approaches studied in the previous papers, the present method can support two combined configuration decisions: the location of ambulance bases along the highway and the districting of the response segments. For example, this method can be used to make decisions regarding the optimal location and coverage areas of ambulances in order to minimize mean user response time or remedy an imbalance in ambulance workloads within the system. The approach is based on embedding a well-known spatially distributed queueing model (hypercube model) into a hybrid genetic algorithm to optimize the decisions involved. To illustrate the application of the proposed method, we utilize two case studies on Brazilian highways and validate the findings via a discrete event simulation model.

Incorporating priorities for waiting customers in the hypercube queuing model with application to an emergency medical service system in Brazil

Emergency medical services (EMS) assist different classes of patients according to their medical seriousness. In this study, we extended the well-known hypercube model, based on the theory of spatially distributed queues, to analyze systems with multiple priority classes and a queue for waiting customers. Then, we analyzed the computational results obtained when applying this approach to a case study from an urban EMS in the city of Ribeirao Preto, Brazil. We also investigated some scenarios for this system studying different periods of the day and the impact of increasing the demands of the patient classes. The results showed that relevant performance measures can be obtained to analyze such a system by using the analytical model extended to deal with queuing priority. In particular, it can accurately evaluate the average response time for each class of emergency calls individually, paying particular attention to high priority calls.

Análise do sistema logístico de recepção de cana-de-açúcar: um estudo de caso utilizando simulação discreta

Os sistemas logisticos sao hoje fundamentais para melhorar a eficiencia operacional de usinas de cana-de-acucar, pois atuam na integracao de operacoes agricolas e industriais. O presente artigo apresenta um estudo do sistema de recepcao de cana em uma das maiores usinas do Brasil, a Usina Sao Martinho, localizada na regiao de Ribeirao Preto, SP. O trabalho foi desenvolvido com o objetivo de analisar o desempenho desse sistema, compreendido da balanca ate as moendas, e investigar configuracoes e politicas alternativas para sua operacao. Em razao das diversas fontes de incerteza e da complexidade operacional do sistema, o metodo utilizado teve por base tecnicas de simulacao discreta. As principais medidas de desempenho avaliadas sao relacionadas ao tempo medio em que os veiculos permanecem no sistema de recepcao e a quantidade media de cana descarregada nas moendas por unidade de tempo.

A tutorial on hypercube queueing models and some practical applications in Emergency Service Systems

This paper presents some extensions and applications of hypercube queueing models todescribe server-to-customer type Emergency Service Systems. The classical hypercube is a well-known spatially distributed queueing model effective in analyzing these systems, based on Markovian analysis approximations. Experience has shown that each real life Emergency Service System may have its own unique characteristics so that each system may require a particular hypercube queueing model incorporating those characteristics. Some of these distinctive characteristics are considered in the extensions presented in this tutorial such as dispatch policy based on random selection of the server to take an incoming call; partial cooperation among servers whereby depending on where the call is coming from, some servers cannot take the call; servers with additional workload coming from walk-in nonemergency customers such as in customer-to-server systems; existence of calls requiring the dispatch of more than one server; existence of more than one type of servers in the system, for instance paramedical and medical units in emergency medical systems. In this study, we present a set of these models based on the smallest non-trivial service systems. For each model, the construction of the system of equations for equilibrium hypercube state probabilities and the evaluation of particular operational characteristics are described.

Modelo de fila hipercubo com múltiplo despacho e backup parcial para análise de sistemas de atendimento médico emergenciais em rodovias

The hypercube is a spatially distributed queuing model based on Markovian analysis approximations to analyze the configuration and operation of server-to-customer emergency systems, in which servers travel to the locations of the customers. In the present study we adapt the model to analyze emergency medical systems (EMS) on highways operating with particular dispatching policies, which considers that only certain ambulances in the system can service calls in a given region (partial backup), and two or more identical or distinct ambulances can simultaneously service a single call (multiple dispatch). We also consider the situations in which an ambulance is busy in its base servicing a non-emergency call (i.e. it does not need to travel along the highway). Computational results of the model application to a case study of an EMS operating on highways in Sao Paulo state are presented and analyzed.

Towards hypercube queuing models for dispatch policies with priority in queue and partial backup

This work extends the hypercube queuing model to address users in-queue priorities.The extended model also considers the partial backup of servers.It is motivated by an emergency maintenance service of an agro-industry in Brazil.To reduce the computational burden an approximate method is also developed.The findings suggest promising perspectives for real-life applications. This work extends the hypercube queuing model to explicitly address users in-queue priorities, as well as the partial backup of servers. To reduce the computational burden an approximate method is also developed. The study is motivated by an emergency maintenance service system found within the agricultural stage of the sugarcane agro-industry in Brazil. An example is used to illustrate the issues of priority in queue and partial backup. In order to show the importance and effectiveness of our proposed models we conducted additional experiments by varying the user arrival rates as well as eliminating the in-queue priorities. The study shows that selected adaptations and extensions of both the hypercube model and the approximate method are capable of representing similar emergency systems. The findings from the illustrative examples suggest promising perspectives for real-life applications in sugar and ethanol plants, and other agro-industries.

Otimização da localização das bases de ambulâncias e do dimensionamento das suas regiões de cobertura em rodovias

In this paper we combine extensions of the hypercube queueing model with genetic algorithms to optimize the configuration and operation of emergency medical systems on highways. Initially we present a method to locate the ambulance bases along the highway so that the main system performance measures are optimized. Then we extend the approach to support combined decisions: the location of ambulance bases and the districting of the covering regions of each base on the highway. For instance, the approach can search for locals to place the ambulance bases and determine the sizes of their operation areas, such that the mean user response time and/or the ambulance workload imbalance are minimized. To illustrate the application of the proposed methods, we analyze the results of two case studies of Brazilian highways.

Extensão do modelo hipercubo para análise de sistemas de atendimento médico emergencial com prioridade na fila

Em alguns sistemas de atendimento medico emergencial, a demanda pelo servico pode ser alta devido ao atendimento a pacientes em diferentes estados, desde mais graves ate mais leves. Nesses sistemas, pode haver formacao de filas de usuarios aguardando atendimento, e a necessidade de se considerar explicitamente politicas de prioridade nesse atendimento torna-se importante. Neste trabalho propoe-se uma extensao do classico modelo hipercubo de filas espacialmente distribuidas para considerar fila com prioridade. Para verificar a viabilidade e a aplicabilidade dessa abordagem, utilizam-se dados de um estudo de caso realizado no SAMU de Ribeirao Preto-SP. Foram analisados dois cenarios que consideram dois aspectos relevantes: o impacto dos atendimentos de remocao de pacientes e o aumento da demanda nas diversas classes de chamados dos usuarios do sistema. O foco e no tempo medio de resposta aos chamados dos usuarios, considerado como uma medida de desempenho importante do sistema, principalmente aos chamados de classes com alta prioridade. Os resultados mostram que a abordagem pode ser utilizada para analisar satisfatoriamente sistemas com prioridade de fila.

Analyzing an emergency maintenance system in the agriculture stage of a Brazilian sugarcane mill using an approximate hypercube method

Abstract In this paper, we present and apply an approximate hypercube queuing method to analyze an emergency maintenance system within the agricultural stage of Brazil’s sugarcane industry. We incorporate differentiated service rates in the approximate hypercube method to deal with significant travel times as well as partial backup and priority in queue to mimic the dispatch policies of the system. We then applied this method using data from a case study conducted in an existing sugar and alcohol mill. We also investigated an alternative scenario for this system, as proposed by the company‘s managers, whereby the number of servers increases. The results showed that the method is an efficient way to investigate the original configuration as well as an alternative scenario for the case study. Furthermore, the method might be useful in larger applications and/or similar agro-industries.