Optimal maintenance policy of a machine subject to failure

Optimal maintenance policies for a machine with degradation in performance with age and subject to failure are derived using optimal control theory. The optimal policies are shown to be, normally, of bang-coast nature, except in the case when probability of machine failure is a function of maintenance. It is also shown, in the deterministic case that a higher depreciation rate tends to reverse this policy to coast-bang. When the probability of failure is a function of maintenance, considerable computational effort is needed to obtain an optimal policy and the resulting policy is not easily implementable. For this case also, an optimal policy in the class of bang-coast policies is derived, using a semi-Markov decision model. A simple procedure for modifying the probability of machine failure with maintenance is employed. The results obtained extend and unify the recent results for this problem along both theoretical and practical lines. Numerical examples are presented to illustrate the results obtained.

Analysis of the consolidation of preloaded clays

Precompression, wherein the probable settlements are achieved at an accelerated pace through preloading, well before the construction is take up, has been widely used in areas of ground improvement with respect to soft clays. By applying a temporary surcharge load in excess or less than the permanent load, the soil achieves higher initial effective stress and when the final load is applied, the soil experiences, lower load increment ratio or negative load increment ratio. In this paper, based on the laboratory experiments conducted on cochin marine clays and Mangalore marine clays, attempts have been made to analyse the volume change behaviour of preloaded clays. It has been brought out that for a preloaded clay, the final load increment ratio has an important role in its behaviour. Effective preloading not only reduces the final settlement due to primary, the secondary consolidation settlement also gets reduced.

Adaptive power optimization of on-chip SNUCA cache on tiled chip multicore architecture using remap policy

Advances in technology have increased the number of cores and size of caches present on chip multicore platforms(CMPs). As a result, leakage power consumption of on-chip caches has already become a major power consuming component of the memory subsystem. We propose to reduce leakage power consumption in static nonuniform cache architecture(SNUCA) on a tiled CMP by dynamically varying the number of cache slices used and switching off unused cache slices. A cache slice in a tile includes all cache banks present in that tile. Switched-off cache slices are remapped considering the communication costs to reduce cache usage with minimal impact on execution time. This saves leakage power consumption in switched-off L2 cache slices. On an average, there map policy achieves 41% and 49% higher EDP savings compared to static and dynamic NUCA (DNUCA) cache policies on a scalable tiled CMP, respectively.

Loss ratio of the EDF scheduling policy with early discarding technique

This paper considers a firm real-time M/M/1 system, where jobs have stochastic deadlines till the end of service. A method for approximately specifying the loss ratio of the earliest-deadline-first scheduling policy along with exit control through the early discarding technique is presented. This approximation uses the arrival rate and the mean relative deadline, normalized with respect to the mean service time, for exponential and uniform distributions of relative deadlines. Simulations show that the maximum approximation error is less than 4% and 2% for the two distributions, respectively, for a wide range of arrival rates and mean relative deadlines. (C) 2013 Elsevier B.V. All rights reserved.

Analysis of an queue operated under the FCFS policy with exact admission control

In this article, we present an exact theoretical analysis of an system, with arbitrary distribution of relative deadline for the end of service, operated under the first come first served scheduling policy with exact admission control. We provide an explicit solution to the functional equation that must be satisfied by the workload distribution, when the system reaches steady state. We use this solution to derive explicit expressions for the loss ratio and the sojourn time distribution. Finally, we compare this loss ratio with that of a similar system operating without admission control, in the cases of some common distributions of the relative deadline.

SEP-Optimal Transmit Power Policy for Peak Power and Interference Outage Probability Constrained Underlay Cognitive Radios

In underlay cognitive radio (CR), a secondary user (SU) can transmit concurrently with a primary user (PU) provided that it does not cause excessive interference at the primary receiver (PRx). The interference constraint fundamentally changes how the SU transmits, and makes link adaptation in underlay CR systems different from that in conventional wireless systems. In this paper, we develop a novel, symbol error probability (SEP)-optimal transmit power adaptation policy for an underlay CR system that is subject to two practically motivated constraints, namely, a peak transmit power constraint and an interference outage probability constraint. For the optimal policy, we derive its SEP and a tight upper bound for MPSK and MQAM constellations when the links from the secondary transmitter (STx) to its receiver and to the PRx follow the versatile Nakagami-m fading model. We also characterize the impact of imperfectly estimating the STx-PRx link on the SEP and the interference. Extensive simulation results are presented to validate the analysis and evaluate the impact of the constraints, fading parameters, and imperfect estimates.

A simulation-based algorithm for optimal pricing policy under demand uncertainty

We propose a simulation-based algorithm for computing the optimal pricing policy for a product under uncertain demand dynamics. We consider a parameterized stochastic differential equation (SDE) model for the uncertain demand dynamics of the product over the planning horizon. In particular, we consider a dynamic model that is an extension of the Bass model. The performance of our algorithm is compared to that of a myopic pricing policy and is shown to give better results. Two significant advantages with our algorithm are as follows: (a) it does not require information on the system model parameters if the SDE system state is known via either a simulation device or real data, and (b) as it works efficiently even for high-dimensional parameters, it uses the efficient smoothed functional gradient estimator.

Appraisal of observational method for consolidation analysis

Two of the aims of laboratory one-dimensional consolidation tests are prediction of the end of primary settlement, and determination of the coefficient of consolidation of soils required for the time rate of consolidation analysis from time-compression data. Of the many methods documented in the literature to achieve these aims, Asaoka's method is a simple and useful tool, and yet the most neglected one since its inception in the geotechnical engineering literature more than three decades ago. This paper appraises Asaoka's method, originally proposed for the field prediction of ultimate settlement, from the perspective of laboratory consolidation analysis along with recent developments. It is shown through experimental illustrations that Asaoka's method is simpler than the conventional and popular methods, and makes a satisfactory prediction of both the end of primary compression and the coefficient of consolidation from laboratory one-dimensional consolidation test data.

Laboratory determination of coefficient of consolidation from pore water pressure measurement

In the recent past, many studies have been carried out on the determination of coefficient of consolidation (c(v)) from the time (t)-deformation (d) data obtained from conventional consolidation tests. Several researchers have also proposed different curve fitting procedures for determining cv from the t-d data. It is anticipated that the cv values obtained from the t-d data may be influenced by initial and secondary compressions. Nevertheless, the pore water pressure data measured during the consolidation process will be independent of initial and secondary compressions. In this study, the conventional Asaoka (1978) method is extended to evaluate cv and end-of-primary (EOP) consolidation from the pore water pressure data measured from laboratory experiments. Laboratory experiments were carried out on the modified one-dimensional consolidation apparatus on different remoulded clay samples measuring pore water pressure during the consolidation process. The cv and EOP computed from the proposed approach have been compared with the results of the t-d data and found to be in good agreement.

Familia romana e identidad femenina en época de Augusto

Resumen: Hacia el 167 a.C., un joven Polibio, se sorprendía de que Roma hubiera podido afi rmar su poderío en la península, resistir los ataques cartagineses y acabar imponiendo sus leyes en Oriente. Probablemente –explica P. Grimal– en ello también haya infl uido que las costumbres y tradiciones romanas contribuían a asegurar una superioridad sobre el resto de las culturas y hacían de Roma una ciudad única entre todas. La familia y la mujer constituyeron parte fundamental dentro de la consolidación de esa estructura socio política y de ello heredaríamos, especialmente a nivel normativo, una sólida tradición jurídico-romana. Sin embargo, la época imperial representó un grave período de crisis en el cual, tomar esposa, dar hijos a la patria y controlar los patrimonios, se convirtió en una importante reafi rmación moral, jurídica y política para la sociedad de su tiempo. En esta forma, se analizarán brevemente algunos conceptos y leyes relevantes –cuyos ecos volveremos a encontrar refl ejados a lo largo y ancho de la España cristiana medieval– los cuales nos ayudarán a adentrarnos en la cotidianidad de este singular período, sus emancipadas mujeres aristocráticas y el derecho privado.

Gasto público social : conceptos y alcances

Resumen: La definición del gasto público social, a pesar de ser un concepto difundido, no encuentra consenso en la literatura. En este sentido, los países utilizan definiciones operativas y ello imposibilita las comparaciones. Las modalidades de intervención del Estado en la política social, son: a) centralización y descentralización y b) tipos de políticas: universalización y focalización. El problema de la descentralización se ubica en un contexto más amplio que debería solucionarse con cambios sustanciales en la coparticipación federal, avanzando tanto en la descentralización de ingresos como en las responsabilidades de recaudación local. La focalización facilita la universalidad que es la esencia misma de la política social. En la práctica es imposible llegar a la universalidad con instrumentos tradicionales y la focalización es la herramienta útil para llegar a las personas más pobres, que en el largo plazo, deben ser sujetos de carácter universal.

Propiedad privada, abasto y regulación del comercio y la circulación de mercancías en la campaña de Buenos Aires : desde fines de la colonia al gobierno de Martín Rodríguez

Resumen: El artículo indaga en la fiscalidad sobre el comercio interior de Buenos Aires y su relación con la consolidación de la propiedad privada en la campaña. A partir de un estudio de caso, se examinan las particularidades de las imposiciones fiscales sobre las actividades comerciales en el ámbito rural identificando cambios y continuidades en las formas de recaudación y gravamen. Este análisis se combina con el de los problemas que las prácticas ilegales vinculadas al abasto de ganado presentó tanto en su circulación en la campaña como en su introducción a los mercados citadinos. Ambas cuestiones son contrastadas con lo sucedido a partir de 1822, cuando durante el gobierno de Martín Rodríguez tanto el comercio como la circulación de ganado en el Hinterland intentarían ser regulados con mayor énfasis a fin de asegurar el respeto de la propiedad privada en el mundo rural.