On Queues with Interruptions and Repeat or Resumption of Service

This thesis entitled' On Queues with Interruptions and Repeat or Resumption of Service' introduces several new concepts into queues with service interruption. It is divided into Seven chapters including an introductory chapter. The following are keywords that we use in this thesis: Phase type (PH) distribution, Markovian Arrival Process (MAP), Geometric Distribution, Service Interruption, First in First out (FIFO), threshold random variable and Super threshold random variable. In the second chapter we introduce a new concept called the 'threshold random variable' which competes with interruption time to decide whether to repeat or resume the interrupted service after removal of interruptions. This notion generalizes the work reported so far in queues with service interruptions. In chapter 3 we introduce the concept of what is called 'Super threshold clock' (a random variable) which keeps track of the total interruption time of a customer during his service except when it is realized before completion of interruption in some cases to be discussed in this thesis and in other cases it exactly measures the duration of all interruptions put together. The Super threshold clock is OIl whenever the service is interrupted and is deactivated when service is rendered. Throughout this thesis the first in first out service discipline is followed except for priority queues.

Queues with Customer Induced Interruption

In this thesis we have introduced and studied the notion of self interruption of service by customers. Service interruption in queueing systems have been extensively discussed in literature (see, Krishnamoorthy, Pramod and Chakravarthy [38]) for the most recent survey. So far all work reported deal with cases in which service interruptions are generated by sources other than customers. However, there are situations where interruptions are due to the customers rather than the system. Such situations are especially arise at doctors clinic, banks, reservation counter etc. Our attempt is to quantify a few of such problems. Systematically we have proceed from single server queue (in Chapter 2) to multi-server queues (Chapter 3). In Chapte 4, we have studied a very general multiserver queueing model with service interruption and protection of service phases. We also introduced customer interruption in a retrial setup (in Chapter 5). All models (from Chapter 2 to Chapter 4) that were analyzed involve 'non-preemptive priority' for interrupted customers where as in the model discussed in Chapter 5 interruption of service by customers is not encouraged. So the interrupted customers cannot access the server as long as there are primary customers in the system. In Chapter 5 we have obtained an explicit expression for the stability condition of the system. In all models analyzed in this thesis, we have assumed that no more than one interruption is allowed for a customer while in service. Since the models are not analytically tractable, a large number of numerical illustrations were given in each chapter it illustrate the working of the systems. We can extend the models discussed in this thesis to several directions. For example some of the models can be analyzed with both server induced and customer induced interruptions the results for which are not available till date. Another possible extension of work is to the case where there is no bound on the number of interruptions a customer is permitted to have before service completion. More complex is the case where a customer is permitted to have a nite number (K ≥ 2) of We can extend the models discussed in this thesis to several directions.

Palvelutasopoikkeamariskin kustannusvaikutusten määrittäminen tietoliikennepalveluiden tuotannossa

Tutkimuksen päämääränä oli selvittää laadullisin menetelmin millaisia kustannusvaikutuksia laajavaikutteiset palvelutasopoikkeamat, eli erilaiset viat tai häiriöt tietoliikennepalveluissa aiheuttavat kohdeyrityksen tietoliikennepalveluiden tuotannossa. Tutkimus muistutti lähtökohdiltaan paljolti riskianalyysia, sillä sen tavoitteina oli tunnistaa merkittävimmät palvelutasopoikkeamien aiheuttajat, arvioida palvelutasopoikkeaman kustannusvaikutuksia ja pohtia millaisin toimin ja kustannuksin palvelutasopoikkeamia voitaisiin ehkäistä. Tutkimusongelmaa lähestyttiin jakamalla palvelutasopoikkeaman kustannusvaikutukset viankorjauksesta aiheutuviin välittömiin ja asiakasvaikutusten kautta mahdollisesti syntyviin välillisiin kustannuksiin. Välillisiä kustannuksia aiheuttaviksi ilmiöiksi tunnistettiin palvelukatkon aiheuttama liikennetulomenetys, nykyisten tai potentiaalisten asiakkaiden menettäminen ja nykyisten asiakkaiden alentunut ostohalukkuus. Yhteenvetona tutkimuksessa tehtyihin havaintoihin perustuen välilliset kustannukset eivät osoittautuneet niin merkittäviksi kuin tutkimuksen aloitusvaiheessa oletettiin, mutta lisätutkimus aiheesta voi olla perusteltua.

Valor percebido e a nova lógica dominante de serviço : estudo da indústria brasileira de equipamentos de refrigeração para transporte de cargas

Levitt (1960) apresentou o termo Miopia em Marketing e discutiu sobre o perigo de as organizações centralizarem seu foco no produto e descuidarem da real necessidade dos clientes, já que o produto é apenas um meio para atender à necessidade do cliente e não o fim em si. Na mesma linha, Shostack (1977), quase duas décadas mais tarde, enfatizou a urgência de se entender a posição do Marketing na economia pós-industrial de serviços, em que a lógica tradicional focada em produtos não mais atendia adequadamente o mercado. Portanto, não é recente a visão de que a posse do bem físico é secundária para o atendimento das necessidades do consumidor, sendo fundamental pensar no benefício que o bem proporciona ao cliente quando do seu uso. Mais recentemente, Vargo e Lusch (2004a) retomaram a discussão sobre a importância de as organizações atentarem para as necessidades dos clientes em vez de apenas focarem na transação, ou seja, na ideia de troca de um produto por um valor monetário. Estes autores emergiram novamente com a ideia de que as empresas precisam entregar benefícios aos seus clientes e a que apropriação do serviço gerado pela oferta da empresa é mais importante do que a transferência de posse do bem físico. Eles retomam, desta forma, as ideias de Levitt e Shostack e as modificam para criar a Service-Dominant Logic ou S-D Logic, como eles denominam. A ênfase desta proposta é que o Marketing deixe de considerar a transação de produtos ou serviços como central para a criação de valor, para uma lógica centrada no serviço produzido pelo bem – produto ou serviço. Assim, passa ser fundamental entender como o valor é percebido pelo cliente na fase de uso e focar os esforços na geração desse valor, possibilitando, assim, que empresas que entendam as reais necessidades do mercado, criem vantagem competitiva sustentável. Considerando a proposta destes autores, este trabalho testou a aplicação deste conceito na indústria de equipamentos de refrigeração para transporte de cargas com temperatura controlada no Brasil. Foram entrevistados seis importantes transportadores de carga frigorificada do país, os quais foram questionados sobre o valor do serviço usufruído pela posse do bem em contraposição ao valor percebido de usufruir o serviço sem ter que comprar o bem para tal. Os entrevistados associam muito valor à posse do bem, pois, para eles, isso garante que o serviço não sofrerá interrupções, algo muito valioso para eles. Isso evidencia uma falta de confiança nas alternativas possíveis à compra do ativo pela empresa. A confiança no prestador do serviço é, portanto, elemento chave na avaliação dos benefícios, reforçando achados de estudos anteriores. Foram identificadas diferenças de atribuição de valor para as propostas alternativas de fornecimento em razão da relevância do serviço de transporte refrigerado para a empresa – negócio central ou função de apoio para o negócio central da empresa.

Dual resource transfers and interruption in external debt service

Externai debt service requires a dual resource transfer. Trade surpluses have to be generated in order to make foreign exchange revenues available for debt repayment. In addition, with developing countries' externai debt being largely a public liability, debt service requires that resources can be effectively transferred from the private to the public sector. This paper derives a statistical model for dealing with dual constraints in the presence of binary dependent variables and applies it to the dual resource transfer problem. The results from the estimation of the model for a sample of 31 middle-income developing countries in the period of 1980 to 1990, strongly support the hypothesis that both externai and fiscal constraints are important in explaining externai debt service disruptions.

Transandean railroads: the interruption of service and prospects for resumption

Building the infrastructure and then operating a railroad which starts on the Pacific coast of South America and which, a few score kilometres inland, must climb close to 4,000 metres above sea level in the Andes mountains has always presented challenges both for the civil engineers responsible for its construction and for the managers in charge of its operation.As at mid-2001, two of the four transandean railroads that ran 20 years ago are out of service, owing to adverse weather conditions, and a third is not operating as a result of institutional problems.Nevertheless, two of the three railroads that are now shut down could resume service soon. Furthermore, there is a possibility that a new transandean railroad could be built that would cross the Andes mountains further south, at an altitude of less than 1,750 meters.

Amending the Selective training and service act of 1940. Hearings before the Committee on military affairs, House of representatives, Seventy-seventh Congress, first session, on H.R. 4949, H.R. 4257, H.R. 4989 and S. 1524, to provide for the common defense and to prevent stoppages or interruption in the productin of munitions in industrial plants, and for other purposes,

Andrew J. May, chairman.

ON (s,S) inventory policy with/without retrial and interruption of services/production

In this thesis we have developed a few inventory models in which items are served to the customers after a processing time. This leads to a queue of demand even when items are available. In chapter two we have discussed a problem involving search of orbital customers for providing inventory. Retrial of orbital customers was also considered in that chapter; in chapter 5 also we discussed retrial inventory model which is sans orbital search of customers. In the remaining chapters (3, 4 and 6) we did not consider retrial of customers, rather we assumed the waiting room capacity of the system to be arbitrarily large. Though the models in chapters 3 and 4 differ only in that in the former we consider positive lead time for replenishment of inventory and in the latter the same is assumed to be negligible, we arrived at sharper results in chapter 4. In chapter 6 we considered a production inventory model with production time distribution for a single item and that of service time of a customer following distinct Erlang distributions. We also introduced protection of production and service stages and investigated the optimal values of the number of stages to be protected.

Analytical and Monte Carlo approaches to evaluate probability distributions of interruption duration

Regulatory authorities in many countries, in order to maintain an acceptable balance between appropriate customer service qualities and costs, are introducing a performance-based regulation. These regulations impose penalties-and, in some cases, rewards-that introduce a component of financial risk to an electric power utility due to the uncertainty associated with preserving a specific level of system reliability. In Brazil, for instance, one of the reliability indices receiving special attention by the utilities is the maximum continuous interruption duration (MCID) per customer.This parameter is responsible for the majority of penalties in many electric distribution utilities. This paper describes analytical and Monte Carlo simulation approaches to evaluate probability distributions of interruption duration indices. More emphasis will be given to the development of an analytical method to assess the probability distribution associated with the parameter MCID and the correspond ng penalties. Case studies on a simple distribution network and on a real Brazilian distribution system are presented and discussed.

Determinants of CD4 cell count decline after treatment interruption

Patients who had started HAART (Highly Active Anti-Retroviral Treatment) under previous aggressive DHHS guidelines (1997) underwent a life-long continuous HAART that was associated with many short term as well as long term complications. Many interventions attempted to reduce those complications including intermittent treatment also called pulse therapy. Many studies were done to study the determinants of rate of fall in CD4 count after interruption as this data would help guide treatment interruptions. The data set used here was a part of a cohort study taking place at the Johns Hopkins AIDS service since January 1984, in which the data were collected both prospectively and retrospectively. The patients in this data set consisted of 47 patients receiving via pulse therapy with the aim of reducing the long-term complications. ^ The aim of this project was to study the impact of virologic and immunologic factors on the rate of CD4 loss after treatment interruption. The exposure variables under investigation included CD4 cell count and viral load at treatment initiation. The rates of change of CD4 cell count after treatment interruption was estimated from observed data using advanced longitudinal data analysis methods (i.e., linear mixed model). Using random effects accounted for repeated measures of CD4 per person after treatment interruption. The regression coefficient estimates from the model was then used to produce subject specific rates of CD4 change accounting for group trends in change. The exposure variables of interest were age, race, and gender, CD4 cell counts and HIV RNA levels at HAART initiation. ^ The rate of fall of CD4 count did not depend on CD4 cell count or viral load at initiation of treatment. Thus these factors may not be used to determine who can have a chance of successful treatment interruption. CD4 and viral load were again studied by t-tests and ANOVA test after grouping based on medians and quartiles to see any difference in means of rate of CD4 fall after interruption. There was no significant difference between the groups suggesting that there was no association between rate of fall of CD4 after treatment interruption and above mentioned exposure variables. ^

Quality of experience of adaptive video streaming: investigation in service parameters and subjective quality assessment methodology

The usage of HTTP adaptive streaming (HAS) has become widely spread in multimedia services. Because it allows the service providers to improve the network resource utilization and user׳s Quality of Experience (QoE). Using this technology, the video playback interruption is reduced since the network and server status in addition to capability of user device, all are taken into account by HAS client to adapt the quality to the current condition. Adaptation can be done using different strategies. In order to provide optimal QoE, the perceptual impact of adaptation strategies from point of view of the user should be studied. However, the time-varying video quality due to the adaptation which usually takes place in a long interval introduces a new type of impairment making the subjective evaluation of adaptive streaming system challenging. The contribution of this paper is two-fold: first, it investigates the testing methodology to evaluate HAS QoE by comparing the subjective experimental outcomes obtained from ACR standardized method and a semi-continuous method developed to evaluate the long sequences. In addition, influence of using audiovisual stimuli to evaluate the video-related impairment is inquired. Second, impact of some of the adaptation technical factors including the quality switching amplitude and chunk size in combination with high range of commercial content type is investigated. The results of this study provide a good insight toward achieving appropriate testing method to evaluate HAS QoE, in addition to designing switching strategies with optimal visual quality.

[principles Of Universality, Comprehensiveness And Equity In A Hearing Health Care Service].

This article analyzed whether the practices of hearing health care were consistent with the principles of universality, comprehensiveness and equity from the standpoint of professionals. It involved qualitative research conducted at a Medium Complexity Hearing Health Care Center. A social worker, three speech therapists, a physician and a psychologist constituted the study subjects. Interviews were conducted as well as observation registered in a field diary. The thematic analysis technique was used in the analysis of the material. The analysis of interviews resulted in the construction of the following themes: Universality and access to hearing health, Comprehensive Hearing Health Care and Hearing Health and Equity. The study identified issues that interfere with the quality of service and run counter to the principles of Brazilian Unified Health System. The conclusion reached was that a relatively simple investment in training and professional qualification can bring about significant changes in order to promote a more universal, comprehensive and equitable health service.

A retrospective study of Traumatic Dental Injuries in a Brazilian dental urgency service

Epidemiologic aspects of traumatic dental injuries (TDI) were evaluated in the permanent dentition in a sample of 847 patients treated at the Dental Urgency Service of the Dental School of the Federal University of Goiás, Brazil, between May 2000 and May 2008. The statistical treatment analyzed data from frequency distribution and chi-square test. The level of significance was set at 5% for all analyses. The results showed a higher incident among males (610; 72.01%) with mean age of 6-10 year-old. Uncomplicated crown fracture (without pulp exposure) (502; 26.95%), avulsion (341; 18.30%) and complicated crown fracture (with pulp exposure) (330; 17.71%) were the most prevalent TDI. The prevalence of trauma throughout the years showed proportionality, being observed a larger number of cases between July and September (249; 29.39%). The most affected teeth were the maxillary central incisors (65.65%), followed by the maxillary left lateral incisors (19.67%). In 311 participants (18.25%), only one tooth was involved, while in most patients (536; 81.75%), TDI occurred in more than one tooth. Significant proportion (82.27%) of traumatized teeth presented completely formed root apex. The main etiologic factors involved in TDI were falls (51.71%), traffic accidents (22.90%) and violence (5.67%). Based on the obtained data, it may be concluded that accurate policies of TDI prevention must be established, capable of stimulating the exposure of appropriate protocols for management of these lesions. The prevalence of TDI in Goiânia subpopulation is compared to the prevalence reported in epidemiological studies in others populations.

The Process of Simulation Authoring/Creation by Chemistry Teachers: A Service Learning Experience

Two case studies are presented to describe the process of public school teachers authoring and creating chemistry simulations. They are part of the Virtual Didactic Laboratory for Chemistry, a project developed by the School of the Future of the University of Sao Paulo. the documental analysis of the material produced by two groups of teachers reflects different selection process for both themes and problem-situations when creating simulations. The study demonstrates the potential for chemistry learning with an approach that takes students' everyday lives into account and is based on collaborative work among teachers and researches. Also, from the teachers' perspectives, the possibilities of interaction that a simulation offers for classroom activities are considered.