On the irrelevant disorder regime of pinning models

Recent results have lead to substantial progress in understanding the role of disorder in the (de)localization transition of polymer pinning models. Notably, there is an understanding of the crucial issue of disorder relevance and irrelevance that is now rigorous. In this work, we exploit interpolation and replica coupling methods to obtain sharper results on the irrelevant disorder regime of pinning models. In particular, in this regime, we compute the first order term in the expansion of the free energy close to criticality and this term coincides with the first order of the formal expansion obtained by field theory methods. We also show that the quenched and quenched averaged correlation length exponents coincide, while, in general, they are expected to be different. Interpolation and replica coupling methods in this class of models naturally lead to studying the behavior of the intersection of certain renewal sequences and one of the main tools in this work is precisely renewal theory and the study of these intersection renewals.Comment: Published in at http://dx.doi.org/10.1214/09-AOP454 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

The general distributional Little's law and its applications

"March 1991."Includes bibliographical references (p. 31-32).Research supported by the Leaders for Manufacturing Program at MIT and Draper Laboratory.Dimitris Bertsimas, Daisuke Nakazato

The general distributional Little's law and its applications

"March 1991."Includes bibliographical references (p. 31-32).Research supported by the Leaders for Manufacturing Program at MIT and Draper Laboratory.Dimitris Bertsimas, Daisuke Nakazato

International migration for employment and domestic labour market development:: the jordanian experience.

Following a review and evaluation of previous research in the field of international migration for employment, it is argued that the extent to which such migration is beneficial depends critically on how it is organized and by whom. The development of Jordan's traditional image as a regional labour supplier is traced from the early twentieth century and is explained largely in terms of a response to repeated economic and political crises. A case study of the Kuwait labour market is used to demonstrate the recent (post-1978) collapse in Jordanian labour migration and to establish the changing character of the international labour market. The central role assumed by international emigration for employment in the Jordanian economy and the problems; and policy constraints which that places on labour market management are illustrated. An attempt is made to identify scarce skills and to assess the development and utility of the government's policy response towards labour shortages. The scale and characteristics of labour inflows into the Jordanian labour market are established. This reveals the complex role of immigrant workers in an emigrant economy and demonstrates the need for a substantial revision of the 'replacement' labour migration model. The parallel themes of primary labour emigration and secondary labour immigration are explored in a detailed case study of local labour markets and agricultural development in the East Jordan Valley. A concluding chapter summarises the problems of manpower planning and of labour market information: gathering under conditions of heightened uncertainty

Unreliable Retrial Queues in a Random Environment

This dissertation investigates stability conditions and approximate steady-state performance measures for unreliable, single-server retrial queues operating in a randomly evolving environment. In such systems, arriving customers that find the server busy or failed join a retrial queue from which they attempt to regain access to the server at random intervals. Such models are useful for the performance evaluation of communications and computer networks which are characterized by time-varying arrival, service and failure rates. To model this time-varying behavior, we study systems whose parameters are modulated by a finite Markov process. Two distinct cases are analyzed. The first considers systems with Markov-modulated arrival, service, retrial, failure and repair rates assuming all interevent and service times are exponentially distributed. The joint process of the orbit size, environment state, and server status is shown to be a tri-layered, level-dependent quasi-birth-and-death (LDQBD) process, and we provide a necessary and sufficient condition for the positive recurrence of LDQBDs using classical techniques. Moreover, we apply efficient numerical algorithms, designed to exploit the matrix-geometric structure of the model, to compute the approximate steady-state orbit size distribution and mean congestion and delay measures. The second case assumes that customers bring generally distributed service requirements while all other processes are identical to the first case. We show that the joint process of orbit size, environment state and server status is a level-dependent, M/G/1-type stochastic process. By employing regenerative theory, and exploiting the M/G/1-type structure, we derive a necessary and sufficient condition for stability of the system. Finally, for the exponential model, we illustrate how the main results may be used to simultaneously select mean time customers spend in orbit, subject to bound and stability constraints

International Mobility of Highly-Qualified People in APEC

An important aspect of the global knowledge-based economy is the emergence of a new trend where certain groups of highly-qualified workers have become increasingly mobile internationally. Reaching the goal of being more innovative economy requires that the highly-qualified workforce is of sufficient quantity and quality to support the expansion of innovative activities by firms. Many industrialized countries compete strategically in attracting these workers. It is necessary that the economic policy discussion surrounding the international mobility of skilled labour must take into consideration the wide variety of ways the migration of labour affects the economy. Numerous drivers, policy and non-policy induced, are at work. Attention must now turn towards the links between these movements and the regulating institutions; the performance in the trade of goods and services, FDI, human capital formation and multinational enterprises location, and income convergence among countries. This paper focuses on four key issues: First, it examines the global trends in the international migratory flows of highly qualified persons (HQPs), focusing on APEC economies. Second, it discusses the fundamental non-policy drivers of the increased HQP flows in the new global economy. Third, it reviews the literature on the economic costs and benefits associated with cross-country movement of HQPs and the main factors conditioning these costs and benefits. Finally, it addresses the question of how policy in APEC economies has adjusted or should adjust to the increased international HQP mobility.International migration, Skilled workers, Labour mobility