Retrial Queues with Orbital Search

Queueing system in which arriving customers who find all servers and waiting positions (if any) occupied many retry for service after a period of time are retrial queues or queues with repeated attempts. This study deals with two objectives one is to introduce orbital search in retrial queueing models which allows to minimize the idle time of the server. If the holding costs and cost of using the search of customers will be introduced, the results we obtained can be used for the optimal tuning of the parameters of the search mechanism. The second one is to provide insight of the link between the corresponding retrial queue and the classical queue. At the end we observe that when the search probability Pj = 1 for all j, the model reduces to the classical queue and when Pj = 0 for all j, the model becomes the retrial queue. It discusses the performance evaluation of single-server retrial queue. It was determined by using Poisson process. Then it discuss the structure of the busy period and its analysis interms of Laplace transforms and also provides a direct method of evaluation for the first and second moments of the busy period. Then it discusses the M/ PH/1 retrial queue with disaster to the unit in service and orbital search, and a multi-server retrial queueing model (MAP/M/c) with search of customers from the orbit. MAP is convenient tool to model both renewal and non-renewal arrivals. Finally the present model deals with back and forth movement between classical queue and retrial queue. In this model when orbit size increases, retrial rate also correspondingly increases thereby reducing the idle time of the server between services

Impact of Self-generation of Priorities and Non-preemptive Service in Single/Multiserver Queues

In this thesis we have studied a few models involving self-generation of priorities. Priority queues have been extensively discussed in literature. However, these are situations involving priority assigned to (or possessed by) customers at the time of their arrival. Nevertheless, customers generating into priority is a common phenomena. Such situations especially arise at a physicians clinic, aircrafts hovering over airport running out of fuel but waiting for clearance to land and in several communication systems. Quantification of these are very little seen in literature except for those cited in some of the work indicated in the introduction. Our attempt is to quantify a few of such problems. In doing so, we have also generalized the classical priority queues by introducing priority generation ( going to higher priorities and during waiting). Systematically we have proceeded from single server queue to multi server queue. We also introduced customers with repeated attempts (retrial) generating priorities. All models that were analyzed in this thesis involve nonpreemptive service. Since the models are not analytically tractable, a large number of numerical illustrations were produced in each chapter to get a feel about the working of the systems.

El problema de conceptualización del terrorismo dentro de la disciplina de las Relaciones Internacionales: Un análisis desde la perspectiva histórico conceptual

Los hechos ocurridos durante el 11 de septiembre de 2001 se constituyeron como un momento fundamental en los intentos de conceptualización del terrorismo internacional dentro de la disciplina de las Relaciones Internacionales. A raíz del 9/11 tuvo lugar la resemantización del concepto de terrorismo internacional en función del terrorismo religioso y del fundamentalismo islámico. Lo anterior, marco una ruptura en el campo de experiencia y en el horizonte de expectativas del concepto mismo, pues este último adquirió un nuevo uso discursivo, y por ende, político. Por eso, ante la necesidad de emprender un análisis discursivo de los usos del concepto de terrorismo internacional, se evidencia cómo al estar inmersos en determinados juegos del lenguaje, el uso discursivo de este concepto termina por convertirse en una herramienta de acción política que promueve una forma de vida.

Apoyo social e ideación suicida en pacientes con cáncer

El diagnóstico de cáncer ha sido asociado con un alto riesgo de presentar ideación suicida en comparación con la población no oncológica, sin embargo se ha considerado al apoyo social como un factor protector para la ocurrencia de esta conducta. La presente investigación tuvo como objetivo identificar la relación entre el apoyo social percibido y la ideación suicida en 90 pacientes oncológicos adultos en Bogotá, bajo la hipótesis de que a mayor apoyo social percibido, menor presencia de ideación suicida. Se midió la variable de apoyo social a través del cuestionario Duke UNC y la ideación suicida a través de cuatro instrumentos: Escala de Ideación Suicida (SSI), Escala de Desesperanza de Beck (BHS), el ítem 9 del Inventario de Depresión de Beck (BDI-IA) y una entrevista semiestructurada. Los resultados mostraron que no existe relación entre el apoyo social percibido y la ideación suicida. Por otro lado se identificó una prevalencia de suicidio entre 5,6% y 22,77%, confirmando que el paciente con cáncer considera el suicidio y es fundamental evaluar esta variable en esta población. Se considera importante continuar con la realización de investigaciones que permitan generalizar los resultados a la población oncológica colombiana.