717 research outputs found
Analysis of Two Stage M[X1],M[X2]/G1,G2/1 Retrial G-queue with Discretionary Priority Services, Working Breakdown, Bernoulli Vacation, Preferred and Impatient Units
In this paper, we study M[X1] , M[X2] /G1 ,G2 /1 retrial queueing system with discretionary priority services. There are two stages of service for the ordinary units. During the first stage of service of the ordinary unit, arriving priority units can have an option to interrupt the service, but, in the second stage of service it cannot interrupt. When ordinary units enter the system, they may get the service even if the server is busy with the first stage of service of an ordinary unit or may enter into the orbit or leave the system. Also, the system may breakdown at any point of time when the server is in regular service period. During the breakdown period, the interrupted priority unit will get the fresh service at a slower rate but the ordinary unit can not get the service and the server will go for repair immediately. During the ordinary unit service period, the arrival of negative unit will interrupt the service and it may enter into an orbit or leave the system. After completion of each priority unit’s service, the server goes for a vacation with a certain probability. We allow reneging to happen during repair and vacation periods. Using the supplementary variable technique, the Laplace transforms of time-dependent probabilities of system state are derived. From this, we deduce the steady-state results. Also, the expected number of units in the respective queues and the expected waiting times, are computed. Finally, the numerical results are graphically expressed
(R1984) Analysis of M^[X1], M^[X2]/G1, G_2^(a,b)/1 Queue with Priority Services, Server Breakdown, Repair, Modified Bernoulli Vacation, Immediate Feedback
In this investigation, the steady state analysis of two individualistic batch arrival queues with immediate feedback, modified Bernoulli vacation and server breakdown are introduced. Two different categories of customers like priority and ordinary are to be considered. This model propose nonpreemptive priority discipline. Ordinary and priority customers arrive as per Poisson processes. The server consistently afford single service for priority customers and the general bulk service for the ordinary customers and the service follows general distribution. The ordinary customers to be served only if the batch size should be greater than or equal to a , else the server should not start service until a customers have accumulated. Meanwhile priority queue is empty; the server becomes idle or go for vacation. If server gets breakdown while the priority customers are being served, they may wait in the head of the queue and get fresh service after repair completion, but in case of ordinary customers they may leave the system. After completion of each priority service, customer may rejoin the system as a feedback customer for receiving regular service because of inappropriate quality of service. Supplementary variable technique and probability generating function are generally used to solve the Laplace transforms of time-dependent probabilities of system states. Finally, some performance measures are evaluated and express the numerical results
Performance analysis of priority queueing systems in discrete time
The integration of different types of traffic in packet-based networks spawns the need for traffic differentiation. In this tutorial paper, we present some analytical techniques to tackle discrete-time queueing systems with priority scheduling. We investigate both preemptive (resume and repeat) and non-preemptive priority scheduling disciplines. Two classes of traffic are considered, high-priority and low-priority traffic, which both generate variable-length packets. A probability generating functions approach leads to performance measures such as moments of system contents and packet delays of both classes
Developing a Lean Based Model for a Hospital Pharmacy Environment
Lean strategies have become necessary in healthcare due primarily to two factors: a demand for efficiency and a need to reduce medical error. The case for the necessity of a lean program is based on trends of increasing costs and decreasing revenues resulting from government intervention. Profit margin per patient has been reduced, and therefore more patients per time period must be seen in order to meet profitability goals. Preventable medical error is shown to be a leading cause of death.
Current research in the area of hospital and healthcare efficiency proves that a parallel exists between healthcare efficiency today and the state of efficiency in manufacturing during the late 70’s and early 80’s. In the 70’s and 80’s, MRP technology came into vogue as a means for attacking complicated problems with expensive, complicated, technology-based solutions. Today, many hospitals hope to solve their efficiency and human error problems by implementing computer based delivery, order-filling, and data systems. Better manufacturers made a move away from complicated solutions, toward lean practices focused on instead of simplifying the problems; healthcare should then do the same.
A generic lean methodology geared toward the differing nuances of healthcare is developed. Lean is offered as a solution to both efficiency and medical error (on the basis that visual systems reduce error and that lean reduces stress, a major contributor to human error). A connection between stress and lean has been found by prior research and is taken a step further and connected with human error. This is based on research showing that stress cases the potential for human error in skilled workers to increase by 2-5 times
Purpose in the Machine: Do Traffic Simulators Produce Distributionally Equivalent Outcomes for Reinforcement Learning Applications?
Traffic simulators are used to generate data for learning in intelligent
transportation systems (ITSs). A key question is to what extent their modelling
assumptions affect the capabilities of ITSs to adapt to various scenarios when
deployed in the real world. This work focuses on two simulators commonly used
to train reinforcement learning (RL) agents for traffic applications, CityFlow
and SUMO. A controlled virtual experiment varying driver behavior and
simulation scale finds evidence against distributional equivalence in
RL-relevant measures from these simulators, with the root mean squared error
and KL divergence being significantly greater than 0 for all assessed measures.
While granular real-world validation generally remains infeasible, these
findings suggest that traffic simulators are not a deus ex machina for RL
training: understanding the impacts of inter-simulator differences is necessary
to train and deploy RL-based ITSs.Comment: 12 pages; accepted version, published at the 2023 Winter Simulation
Conference (WSC '23
Evaluation of traffic performance at roundabouts
Dissertação de mestrado integrado em Engenharia CivilRoundabouts have evolved into one of the most common forms of crossings. Their success in
resolving traffic issues and enhancing junction performance has been critical to their adoption.
In ancient times, roundabouts were the subject of study by many scientists who transformed
the traffic principles by which they were governed and today they are considered one of the
most widely implemented alternatives worldwide.
Speed reduction, greater safety, shorter wait times, and higher capacity as compared to any
other at-grade junction. These characteristics have resulted in their deployment all over the
world.
This dissertation aims to study and compare the performance of various models to assess the
capacity of a roundabout. Thus, a comparison of the capacity calculation models developed in
different countries to estimate the performance of roundabouts is done, relying its assessment
on numerous elements ranging from geometric attributes to driving behaviour. Furthermore,
several performance measures such as delay, degree of saturation, and others are evaluated,
which will allow comparing empirical, analytical and simulation models.
In this work, a microsimulation model for roundabouts with the application of the PTV VISSIM
software is applied. Vissim is considered a tool that simplifies road network research and
analysis. allowing to analyze the performance of a roundabout through the evaluation of
several indicators in different parts of the roundabout such as entries, exits and conflicting
carriageway. Finally, a case study of the roundabout performance in the city of Guimaraes,
Portugal, under its geometric and traffic features is done based on real traffic data.As rotundas têm evoluído para uma das formas mais comuns de cruzamentos. O sucesso das
rotundas na resolução de questões de tráfego e na melhoria do desempenho dos cruzamentos,
em termos de eficiência e segurança, tem sido crítico para a sua adopção. No inicio da
implementação de interseções giratórias, as rotundas eram objecto de estudo por muitos
cientistas que alteraram os princípios de trânsito pelos quais eram governadas, passando por
alterar a ordem de prioridade para quem entrava circulava no interior da rotunda, que alterou
completamente o projeto, dimensionamento e avaliação do desempenho deste tipo de
soluções.
Características como a redução da velocidade, a segurança, a redução dos tempos de espera e
a maior capacidade em comparação com outros tipos de cruzamento tornaram as rotundas
uma excelente solução para serem implementadas em diversos contextos rodoviários, que
resultou na sua disseminação e forte implantação em todo o mundo.
Neste contexto, o objectivo desta dissertação é estudar e caracterizar os modelos mais comuns
para avaliar o desempenho deste tipo de interseções. Para esse efeito, é feita uma comparação
de modelos de cálculo de capacidade desenvolvidos em diferentes países para estimar o
desempenho de rotundas, tendo por base a avaliação de diversos elementos geométricos e de
circulação do tráfego. No processo comparativo são avaliadas várias medidas de desempenho,
tais como o atraso, grau de saturação, comprimento das filas de espera, entre outras.
Neste trabalho são comparados modelos empíricos e analíticos com os modelos de
microssimulação. Para este efeito, foi desenvolvido um estudo de caso numa rotunda da
cidade de Guimarães, Portugal, tendo sido utilizado o software PTV VISSIM, que é considerada
uma ferramenta que simplifica o estudo e análise do funcionamento de uma rede rodoviária,
particularmente ao nível das interseções. Os resultados mostraram uma grande semelhança
entre os modelos de capacidade empíricos e analíticos, assim como, destes com o modelo de
microssimulação
Cellular Automata Models of Road Traffic
In this paper, we give an elaborate and understandable review of traffic
cellular automata (TCA) models, which are a class of computationally efficient
microscopic traffic flow models. TCA models arise from the physics discipline
of statistical mechanics, having the goal of reproducing the correct
macroscopic behaviour based on a minimal description of microscopic
interactions. After giving an overview of cellular automata (CA) models, their
background and physical setup, we introduce the mathematical notations, show
how to perform measurements on a TCA model's lattice of cells, as well as how
to convert these quantities into real-world units and vice versa. The majority
of this paper then relays an extensive account of the behavioural aspects of
several TCA models encountered in literature. Already, several reviews of TCA
models exist, but none of them consider all the models exclusively from the
behavioural point of view. In this respect, our overview fills this void, as it
focusses on the behaviour of the TCA models, by means of time-space and
phase-space diagrams, and histograms showing the distributions of vehicles'
speeds, space, and time gaps. In the report, we subsequently give a concise
overview of TCA models that are employed in a multi-lane setting, and some of
the TCA models used to describe city traffic as a two-dimensional grid of
cells, or as a road network with explicitly modelled intersections. The final
part of the paper illustrates some of the more common analytical approximations
to single-cell TCA models.Comment: Accepted for publication in "Physics Reports". A version of this
paper with high-quality images can be found at: http://phdsven.dyns.cx (go to
"Papers written"
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