Analysis of some Stochastic models in inventories and Queues

The thesis entitled Analysis of Some Stochastic Models in Inventories and Queues. This thesis is devoted to the study of some stochastic models in Inventories and Queues which are physically realizable, though complex. It contains a detailed analysis of the basic stochastic processes underlying these models. In this thesis, (s,S) inventory systems with nonidentically distributed interarrival demand times and random lead times, state dependent demands, varying ordering levels and perishable commodities with exponential life times have been studied. The queueing system of the type Ek/Ga,b/l with server vacations, service systems with single and batch services, queueing system with phase type arrival and service processes and finite capacity M/G/l queue when server going for vacation after serving a random number of customers are also analysed. The analogy between the queueing systems and inventory systems could be exploited in solving certain models. In vacation models, one important result is the stochastic decomposition property of the system size or waiting time. One can think of extending this to the transient case. In inventory theory, one can extend the present study to the case of multi-item, multi-echelon problems. The study of perishable inventory problem when the commodities have a general life time distribution would be a quite interesting problem. The analogy between the queueing systems and inventory systems could be exploited in solving certain models.

Queueing Models with Vacations and Working Vacations

The objective of the study of \Queueing models with vacations and working vacations" was two fold; to minimize the server idle time and improve the e ciency of the service system. Keeping this in mind we considered queueing models in di erent set up in this thesis. Chapter 1 introduced the concepts and techniques used in the thesis and also provided a summary of the work done. In chapter 2 we considered an M=M=2 queueing model, where one of the two heterogeneous servers takes multiple vacations. We studied the performance of the system with the help of busy period analysis and computation of mean waiting time of a customer in the stationary regime. Conditional stochastic decomposition of queue length was derived. To improve the e ciency of this system we came up with a modi ed model in chapter 3. In this model the vacationing server attends the customers, during vacation at a slower service rate. Chapter 4 analyzed a working vacation queueing model in a more general set up. The introduction of N policy makes this MAP=PH=1 model di erent from all working vacation models available in the literature. A detailed analysis of performance of the model was provided with the help of computation of measures such as mean waiting time of a customer who gets service in normal mode and vacation mode.

Applying Data mining using Statistical Techniques for Career Selection

For years, choosing the right career by monitoring the trends and scope for different career paths have been a requirement for all youngsters all over the world. In this paper we provide a scientific, data mining based method for job absorption rate prediction and predicting the waiting time needed for 100% placement, for different engineering courses in India. This will help the students in India in a great deal in deciding the right discipline for them for a bright future. Information about passed out students are obtained from the NTMIS ( National technical manpower information system ) NODAL center in Kochi, India residing in Cochin University of science and technology

Escala NEDOCS para medir congestión en urgencias: estudio de validación en Colombia

Introducción: En Colombia, no existe una herramienta para cuantificar el grado de congestión de los servicios de urgencias que sea aplicable a su realidad. Por esta razón, este trabajo busca determinar si la escala NEDOCS es una herramienta válida para medir el grado de congestión en este medio. Métodos: Se calculó la escala durante un período de tres semanas, durante 6 veces en el día a la misma hora en las tres instituciones. Para la validación, se comparó la escala NEDOCS contra dos escalas tipo Likert de 6 preguntas. Además, se describió el porcentaje de la demanda no atendida y del número de quejas. Resultados: Para la escala, la variabilidad se explica en 88 %. Por otro lado, la correlación entre la severidad en la congestión de los últimos 3 ítems de la escala con las opiniones subjetivas fue directa y significativa (r = 1,000., p < 0.000). Se obtuvo una correspondencia significativa con las siguientes variables: a) disponibilidad de camas (r = 0.7, p < 0.001); b) promedio de tiempo de espera, (r = 0,56, p < 0.021). Discusión: Dado que no existe gold standard, las mediciones de la escala en comparación con las opiniones del personal arrojan que la escala NEDOCS aplicada en los servicios de urgencias colombianos es útil para medir congestión. Se observó como fenómeno especial que el personal se encuentra acostumbrado a “vivir con la congestión”, por lo cual el personal considera como congestión del servicio los momentos de alto stress laboral.

Comparación de parámetros de atención en una escala de triage de 5 niveles con los parámetros estándar

Introducción: La escala de severidad en emergencias es una herramienta que ofrece seguridad a pacientes en servicios de urgencias. Este trabajo evalúa la aplicación de la escala ESI 4.0 en términos de oportunidad de atención y consumo de recursos en la Fundación Santa Fé de Bogotá, para comparar los resultados con parámetros estándar. Metodología Estudio observacional analítico de corte transversal. Se incluyeron 385 pacientes aleatorizados por nivel de atención. Se tomaron datos demográficos y variables como consumo de recursos y destino del paciente para su descripción y análisis. Resultados: El promedio de edad fue 44.9 años IC95%42.9–46.9, el 54.5% fueron mujeres. Se encontró un tiempo promedio de espera para nivel 1 de 1.39 min, para el nivel 2 de 22.9 min 2, para el nivel 3 de 41.9 min, para el nivel 4 de 56.9 min y para el nivel 5 de 52.1 min. El tiempo promedio de estancia en urgencias fue 5.9 horas y el 78.9% consumió recursos. Al comparar los tiempos con estándares mundiales en el nivel 1, 2 y 3 son significativamente mayores (P<0,05), en el nivel 4 es similar (p0,51) y en el nivel 5 es significativamente menor (p=0,00) Discusión: La escala ESI 4.0 es una herramienta segura, con un comportamiento similar en oportunidad de atención y consumo de recursos con respecto a los estándares de cuidado en los servicios de urgencias.

Determinantes sociais condicionantes das altas clínicas dos utentes da rede nas UCCI: um estudo de caso

Introdução: O adiamento das altas clínicas nas Unidades de Cuidados Continuados Integrados (UCCI) por motivos sociais é actualmente considerado um dos principais motivos que impedem a integração atempada de novos clientes na Rede Nacional de Cuidados Continuados, RNCC, daqui em diante designada como a REDE. Este atraso tem impacto ao nível da recuperação e estabilização dos utentes, bem como ao nível de eficiência e eficácia da UCCI, não podendo deixar de se considerarem os aspectos sociais e económicos. Objectivo Geral: Identificar os determinantes que influenciam as altas clínicas em UCCI. Métodos e População do Estudo: Este é um estudo de caso colectivo, em que os dados observacionais, transversais, são recolhidos por meio de questionário de auto-relato (por cada área de intervenção directa) e por análise dos processos de consulta de pacientes. O objecto desta pesquisa abrange dois grupos: o grupo de amostra composto por 70 profissionais de saúde que lidam directamente com os utentes e o grupo amostra composto de utentes internados na UCCI L Nostrum, com alta clínica entre 1/1/2011 e 31/12/2012, e que foram integrados através da REDE. Foram recolhidos os dados de 293 utentes sendo objecto de estudo os casos de 83 utentes integrados através da REDE e com prolongamento de internamento por motivos sociais. Resultados: Na percepção dos profissionais de saúde, as respostas institucionais apresentam-se como a condicionante mais indicada, tanto para os utentes em geral, com 22 indicações (88%) como para os utentes da REDE, com 10 indicações (40%). Relativamente aos motivos familiares há referência de 76% para os utentes em geral e de 36% para os utentes da REDE. Os motivos económicos também apresentam, para os profissionais inquiridos, um valor expressivo (68%) nos utentes em geral, estando nos da REDE este factor condicionante a par com os motivos familiares (36%). Os motivos estruturais têm menor expressão tanto nos utentes em geral (32%) como nos utentes da REDE (16%). “Outros” para os utentes em geral, refere-se a dependência funcional (4%). Nos motivos familiares, para os utentes em geral, 23 (92%) foi mais vezes indicada a insuficiência de suporte familiar, para os utentes da REDE, 13 (52%). A ausência de suporte familiar, para os utentes em geral, representa 48% das respostas, seguindo-se o suporte inadequado (28%) e a ausência de cuidadores (24%). Para os utentes da REDE, o suporte inadequado apresenta-se como segundo motivo (7%), seguindo-se a ausência de suporte familiar (16%). Na percepção dos profissionais, os utentes da REDE estão também condicionados pela distância geográfica (8%) da sua área residencial. Em termos estruturais, os motivos mais assinalados pelos profissionais para a generalidade dos utentes foram as barreiras físicas à mobilidade (80%) e a habitação sem condições básicas de habitabilidade (78%). Os mesmos motivos foram assinalados para os utentes da REDE, barreiras físicas à mobilidade (40%) e habitação sem condições de habitabilidade (28%). No entanto, relativamente aos utentes em geral, a ausência de habitação (29%) e a distância geográfica (4%) também foram motivos assinalados. Dos motivos económicos percebidos pelos profissionais, a insuficiência de rendimentos é o factor mais assinalado pela generalidade dos utentes (84%) e pelos da REDE (68%), seguida da percepção da capacidade de reposta limitada das instituições, 64% para a generalidade dos utentes e 28% para os da REDE e por fim os tipos de respostas insuficientes para as necessidades individuais dos utentes (20% dos utentes em geral e 12% da REDE). No total dos dois anos, 2011 e 2012, verificaram-se na UCCI L Nostrum 293 prorrogações (100%) das quais 210 (71,6%) foram consideradas dentro do prazo e justificadas com motivos clínicos, enquanto 83 (28,3%) foram efectivamente protelamentos por motivos sociais, tendo em conta que nestes casos os utentes já não tinham critérios clínicos que justificassem a sua permanência na UCCI. Das 210 prorrogações consideradas dentro do prazo e justificadas com motivos clínicos, 93 (44,3%) foram-no por tempo de espera para transferência de UCCI. Em 2011, dos 146 utentes com alta protelada (100%), 50 utentes (34,2%) permaneceram na UCCI por motivos sociais, enquanto em 2012 houve registo de 33 casos de protelamento (22,4%) em 147 (100%) altas prorrogadas. Conclusões: Dos factores identificados como motivo de protelamento nos 83 utentes, estritamente por motivos sociais, destaca-se o protelamento de alta por espera de integração em equipamento/resposta adequada, nomeadamente lar ou serviços de apoio domiciliário (79,5%), seguindo-se a insuficiência de rendimentos do utente/familiares para contratação de serviços ou resposta institucional (74,7%), a inexistência de condições habitacionais para regresso ao domicílio (63,9%) e a insuficiência de suporte familiar (54,2%). Regista-se também a inadequação do suporte familiar (31,3%), a inexistência de suporte familiar (28,9%) e, em menor percentagem, a ausência de condições estruturais (13,3%). A ausência de domicílio (sem abrigo) (8,4%) e a ausência de rendimentos (4,8%) também foram factores inibidores da alta clínica. Dos 293 utentes identificados que tiveram protelamento da alta por motivos sociais verificou-se que 144 (49,1%) dos utentes permaneceram unicamente pela existência de condicionantes institucionais e familiares/estruturais. Aspectos éticos: ao longo deste estudo, foram assegurados e respeitados, todos os procedimentos de garantia da confidencialidade e rigor na recolha dos dados, e a não interferência nas dinâmicas da instituição, dos utentes e dos profissionais.

Modeling cumulative evidence for freedom from disease with applications to BSE surveillance trials

This investigation deals with the question of when a particular population can be considered to be disease-free. The motivation is the case of BSE where specific birth cohorts may present distinct disease-free subpopulations. The specific objective is to develop a statistical approach suitable for documenting freedom of disease, in particular, freedom from BSE in birth cohorts. The approach is based upon a geometric waiting time distribution for the occurrence of positive surveillance results and formalizes the relationship between design prevalence, cumulative sample size and statistical power. The simple geometric waiting time model is further modified to account for the diagnostic sensitivity and specificity associated with the detection of disease. This is exemplified for BSE using two different models for the diagnostic sensitivity. The model is furthermore modified in such a way that a set of different values for the design prevalence in the surveillance streams can be accommodated (prevalence heterogeneity) and a general expression for the power function is developed. For illustration, numerical results for BSE suggest that currently (data status September 2004) a birth cohort of Danish cattle born after March 1999 is free from BSE with probability (power) of 0.8746 or 0.8509, depending on the choice of a model for the diagnostic sensitivity.

Evaluation of the cumulative evidence for freedom from BSE in birth cohorts

Substantial resources are used for surveillance of bovine spongiform encephalopathy (BSE) despite an extremely low detection rate, especially in healthy slaughtered cattle. We have developed a method based on the geometric waiting time distribution to establish and update the statistical evidence for BSE-freedom for defined birth cohorts using continued surveillance data. The results suggest that currently (data included till September 2004) a birth cohort of Danish cattle born after March 1999 is free from BSE with probability (power) of 0.8746 or 0.8509, depending on the choice of a model for the diagnostic sensitivity. These results apply to an assumed design prevalence of 1 in 10,000 and account for prevalence heterogeneity. The age-dependent, diagnostic sensitivity for the detection of BSE has been identified as major determinant of the power. The incorporation of heterogeneity was deemed adequate on scientific grounds and led to improved power values. We propose our model as a decision tool for possible future modification of the BSE surveillance and discuss public health and international trade implications.

Subcontract and supply enquiries in the tender process of contractors

In the tender process, contractors often rely on subcontract and supply enquiries to calculate their bid prices. However, this integral part of the bidding process is not empirically articulated in the literature. Over 30 published materials on the tendering process of contractors that talk about enquiries were reviewed and found to be based mainly on experiential knowledge rather than systematic evidence. The empirical research here helps to describe the process of enquiries precisely, improve it in practice, and have some basis to support it in theory. Using a live participant observation case study approach, the whole tender process was shadowed in the offices of two of the top 20 UK civil engineering construction firms. This helped to investigate 15 research questions on how contractors enquire and obtain prices from subcontractors and suppliers. Forty-three subcontract enquiries and 18 supply enquiries were made across two different projects with average value of 7m. An average of 15 subcontract packages and seven supply packages was involved. Thus, two or three subcontractors or suppliers were invited to bid in each package. All enquiries were formulated by the estimator, with occasional involvement of three other personnel. Most subcontract prices were received in an average of 14 working days; and supply prices took five days. The findings show 10 main activities involved in processing enquiries and their durations, as well as wasteful practices associated with enquiries. Contractors should limit their enquiry invitations to a maximum of three per package, and optimize the waiting time for quotations in order to improve cost efficiency.

Computing journey start times with recurrent traffic conditions

n this study, the authors discuss the effective usage of technology to solve the problem of deciding on journey start times for recurrent traffic conditions. The developed algorithm guides the vehicles to travel on more reliable routes that are not easily prone to congestion or travel delays, ensures that the start time is as late as possible to avoid the traveller waiting too long at their destination and attempts to minimise the travel time. Experiments show that in order to be more certain of reaching their destination on time, a traveller has to leave early and correspondingly arrive early, resulting in a large waiting time. The application developed here asks the user to set this certainty factor as per the task in hand, and computes the best start time and route.

Transmathematical basis of infinitely scalable pipeline machines

We describe infinitely scalable pipeline machines with perfect parallelism, in the sense that every instruction of an inline program is executed, on successive data, on every clock tick. Programs with shared data effectively execute in less than a clock tick. We show that pipeline machines are faster than single or multi-core, von Neumann machines for sufficiently many program runs of a sufficiently time consuming program. Our pipeline machines exploit the totality of transreal arithmetic and the known waiting time of statically compiled programs to deliver the interesting property that they need no hardware or software exception handling.

A moving point approach to model shallow ice sheets: a study case with radially-symmetrical ice sheets

Predicting the evolution of ice sheets requires numerical models able to accurately track the migration of ice sheet continental margins or grounding lines. We introduce a physically based moving point approach for the flow of ice sheets based on the conservation of local masses. This allows the ice sheet margins to be tracked explicitly and the waiting time behaviours to be modelled efficiently. A finite difference moving point scheme is derived and applied in a simplified context (continental radially-symmetrical shallow ice approximation). The scheme, which is inexpensive, is validated by comparing the results with moving-margin exact solutions and steady states. In both cases the scheme is able to track the position of the ice sheet margin with high precision.

A moving-point approach to model shallow ice sheets: a study case with radially symmetrical ice sheets

Predicting the evolution of ice sheets requires numerical models able to accurately track the migration of ice sheet continental margins or grounding lines. We introduce a physically based moving-point approach for the flow of ice sheets based on the conservation of local masses. This allows the ice sheet margins to be tracked explicitly. Our approach is also well suited to capture waiting-time behaviour efficiently. A finite-difference moving-point scheme is derived and applied in a simplified context (continental radially symmetrical shallow ice approximation). The scheme, which is inexpensive, is verified by comparing the results with steady states obtained from an analytic solution and with exact moving-margin transient solutions. In both cases the scheme is able to track the position of the ice sheet margin with high accuracy.

Vasectomy within the public health services in Campinas, Sao Paulo, Brazil

Objective: To describe some of the characteristics of men who underwent a vasectomy in the public health network of Campinas, Sao Paulo, Brazil. Methods: A descriptive study including 202 men randomly selected from a list of all the men vasectomized between 1998 and 2004 in the public health network. Results: Most of the men were 30 years of age or older when vasectomized, had completed elementary school and had two or more children of both sexes. Most of the men came from the lowest income segment of the population: 47.6% in 1998-1999 and 61.3% in 2003-2004. Although the men knew various contraceptive methods, 51.2% reported that their partners were using combined oral contraceptives at the time of surgery. Most men initially sought information on vasectomy at health-care clinics where care was provided by a multidisciplinary team; most received counselling, however, 47.9% of the men waited more than 4 months for the vasectomy. Conclusions: The profile of the vasectomized men in this study appears to indicate that the low-income population from Campinas, Sao Paulo, Brazil has access to vasectomy; however, the waiting time for vasectomy reveals that difficulties exist in obtaining this contraceptive method in the public health service.

QoS Evaluation of BandwidthSchedulers in IPTV Networks OfferedSRD Fluid Video Traffic

Internet protocol TV (IPTV) is predicted to be the key technology winner in the future. Efforts to accelerate the deployment of IPTV centralized model which is combined of VHO, encoders, controller, access network and Home network. Regardless of whether the network is delivering live TV, VOD, or Time-shift TV, all content and network traffic resulting from subscriber requests must traverse the entire network from the super-headend all the way to each subscriber's Set-Top Box (STB).IPTV services require very stringent QoS guarantees When IPTV traffic shares the network resources with other traffic like data and voice, how to ensure their QoS and efficiently utilize the network resources is a key and challenging issue. For QoS measured in the network-centric terms of delay jitter, packet losses and bounds on delay. The main focus of this thesis is on the optimized bandwidth allocation and smooth datatransmission. The proposed traffic model for smooth delivering video service IPTV network with its QoS performance evaluation. According to Maglaris et al [5] First, analyze the coding bit rate of a single video source. Various statistical quantities are derived from bit rate data collected with a conditional replenishment inter frame coding scheme. Two correlated Markov process models (one in discrete time and one incontinuous time) are shown to fit the experimental data and are used to model the input rates of several independent sources into a statistical multiplexer. Preventive control mechanism which is to be include CAC, traffic policing used for traffic control.QoS has been evaluated of common bandwidth scheduler( FIFO) by use fluid models with Markovian queuing method and analysis the result by using simulator andanalytically, Which is measured the performance of the packet loss, overflow and mean waiting time among the network users.