Optimal railway infrastructure maintenance and repair policies to manage risk under uncertainty with adaptive control

The aim of this paper is to apply two adaptive control formulations under uncertainty, say open-loop and closed-loop, to the process of developing maintenance and repair policies for railway infrastructures. To establish the optimal maintenance and repair policies for railway lines, we use a previous design of risk model based on two factors: the criticality and the deterioration ratios of the facilities. Thus, our theory benefits from the Reliability Centered Management methodology application, but it also explicitly models uncertainty in characterizing a facility deterioration rate to decide the optimal policy to maintain the railway infrastructures. This may be the major contribution of this work. To verify the models presented, a computation study has been developed and tested for a real scenario: the railway line Villalba-Cercedilla in Madrid (Spain). Our results demonstrate again that applying any adaptive formulation, the cost of the railway lines maintenance shown is decreased. Moreover applying a Closed Loop Formulation the cost associated to the risk takes smaller values (40% less cost for the same risk than the deterministic approach), but with an Open Loop formulation the generated risk in the railway line is also smaller

El concepto de software libre

El software libre es cada vez más habitual en casi cualquier entorno informático. Sin embargo, es también un gran desconocido. En este artículo se exponen las condiciones que tiene que cumplir un programa para ser considerado como software libre, compiladas en varias definiciones. A partir de ellas se repasa brevemente su historia y se exploran algunas de sus características y consecuencias. También se comentan algunos aspectos relacionados con las licencias de software libre que son tan fundamentales para su existencia.El programari lliure és cada vegada més habitual en qualsevol entorn informàtic. Tanmateix, és també un gran desconegut. En aquest article s'exposen les condicions que ha de complir un programa per a ser considerat com a programari lliure, compilades en diverses definicions. A partir d'elles es repassa breument la seva història i s'exploren algunes de les seves característiques i conseqüències. També es comenten alguns aspectes relacionats amb les llicències de programari lliure que són tan bàsiques per a la seva existència.Free, open source software is increasingly more usual in almost any computing environment. However, it is also a great unknown: not many people knows what it truly is. This paper presents the conditions that some piece of software has to comply with to be considered as free or open source software, which are compiled in several definitions. Starting from them, its history is briefly exposed, and some of its characteristics and consequences are explored. In addition, some aspects related to free software licensing are commented, since they are so fundamental for its very existence

Threshold unit root models

One of the main criticisms of unit root models is based on the theoretical fact that economic variables measured in rates cannot have unit roots. Nevertheless, standard unit root tests do not reject the existence of unit roots in many of those variables. In this paper we present a class of threshold models capable of replicating the behavior of economic variables such as unemployment, inflation and interest rates. Depending on the values of a threshold variable these models can have either a unit root or a stable root. However, despite the presence of the unit root, we prove they are stationary and geometrically ergodic. Least squares estimates of the parameters of these models are shown to be consistent and asymptotically normal. We propose the supremum of a e test in order to test the null of no threshold against the alternative of threshold when the threshold value is unknown. The limiting distribution is derived under the null of I (0) as well as under the null of 1(1). Critical values for both asymptotic distributions are computed and a finite sample study of the performance (size and power) of the tests developed in this paper is made. The paper concludes with an application to interest rates

Virtual cluster scheduling through the scheduling graph

This paper presents an instruction scheduling and cluster assignment approach for clustered processors. The proposed technique makes use of a novel representation named the scheduling graph which describes all possible schedules. A powerful deduction process is applied to this graph, reducing at each step the set of possible schedules. In contrast to traditional list scheduling techniques, the proposed scheme tries to establish relations among instructions rather than assigning each instruction to a particular cycle. The main advantage is that wrong or poor schedules can be anticipated and discarded earlier. In addition, cluster assignment of instructions is performed using another novel concept called virtual clusters, which define sets of instructions that must execute in the same cluster. These clusters are managed during the deduction process to identify incompatibilities among instructions. The mapping of virtual to physical clusters is postponed until the scheduling of the instructions has finalized. The advantages this novel approach features include: (1) accurate scheduling information when assigning, and, (2) accurate information of the cluster assignment constraints imposed by scheduling decisions. We have implemented and evaluated the proposed scheme with superblocks extracted from Speclnt95 and MediaBench. The results show that this approach produces better schedules than the previous state-of-the-art. Speed-ups are up to 15%, with average speed-ups ranging from 2.5% (2-Clusters) to 9.5% (4-Clusters).Peer ReviewedPostprint (published version

A unified modulo scheduling and register allocation technique for clustered processors

This work presents a modulo scheduling framework for clustered ILP processors that integrates the cluster assignment, instruction scheduling and register allocation steps in a single phase. This unified approach is more effective than traditional approaches based on sequentially performing some (or all) of the three steps, since it allows optimizing the global code generation problem instead of searching for optimal solutions to each individual step. Besides, it avoids the iterative nature of traditional approaches, which require repeated applications of the three steps until a valid solution is found. The proposed framework includes a mechanism to insert spill code on-the-fly and heuristics to evaluate the quality of partial schedules considering simultaneously inter-cluster communications, memory pressure and register pressure. Transformations that allow trading pressure on a type of resource for another resource are also included. We show that the proposed technique outperforms previously proposed techniques. For instance, the average speed-up for the SPECfp95 is 36% for a 4-cluster configuration.Peer ReviewedPostprint (published version

La dinámica demográfica y el planeamiento urbano en Vigo desde 1960. Impacto del proceso de industrialización desarrollista

The intense process of industrialization and technocrat planning territorial of the years 1960, have modified the demographic dynamics and the urban structure of the city of Vigo deeply. Theses policies serves as base to study the impacts taken place on the demographic evolution into the city, and the planning figures that should order the populational and physical growth of Vigo. The intense flow inmigratory, a planning ineffective and great floor consumer cause an unbalanced urban development from a demographic point of view, and disordered from the urbanístic perspective.El intenso proceso de industrialización desarrollista y de planificación territorial tecnócrata de los años 1960 ha modificado profundamente la dinámica demográfica y la estructura urbana de la ciudad de Vigo. Estas políticas dirigistas sirven de base para estudiar, por un lado, los impactos producidos sobre la evolución demográfica municipal y en el espacio intraurbano y, por otro, las figuras de planeamiento que deben ordenar y encauzar el crecimiento poblacional y físico de Vigo. El intenso flujo inmigratorio y un planeamiento ineficaz y gran consumidor de suelo provocan un desarrollo urbano desequilibrado desde un punto de vista demográfico y caótico y desordenado desde el urbanístico

Observation of a continuous interior crisis in the Hindmarsh-Rose neuron model.

Interior crises are understood as discontinuous changes of the size of a chaotic attractor that occur when an unstable periodic orbit collides with the chaotic attractor. We present here numerical evidence and theoretical reasoning which prove the existence of a chaos-chaos transition in which the change of the attractor size is sudden but continuous. This occurs in the Hindmarsh¿Rose model of a neuron, at the transition point between the bursting and spiking dynamics, which are two different dynamic behaviors that this system is able to present. Moreover, besides the change in attractor size, other significant properties of the system undergoing the transitions do change in a relevant qualitative way. The mechanism for such transition is understood in terms of a simple one-dimensional map whose dynamics undergoes a crossover between two different universal behavior