Catálogo de publicaciones - libros

Failures in repairable systems are often described by means of renewal or non-homogeneous Poisson processes, depending upon the repair policy. In the former case repairs bring the system reliability back to its initial value, whereas in the latter they restore the same reliability the system had just before the failure. We focus on the latter process, illustrating some properties and applications, mainly in a Bayesian framework.

We present new efficient schemes of Rosenbrock’s type for numerical solution of differential-algebraic stiff systems. For these schemes, we develop an algorithm for accuracy control.

It is well known that discontinuities in pipe networks give reflections to pressure waves that can be analysed to find the time delay between the original signal and the reflected one. A leak in a pipe will also give a reflection point, though possibly a more diffuse one. It is a reasonably straightforward task (using, say, a cross correlation) to measure the time delay of the first reflection, but more complicated methods are required to extract data about further reflections from, for example, the end of the pipe which has a leak in it.

Cepstrum techniques were used to find the common pipe lengths in the network. Latterly, this has been used in conjunction with wavelet analysis to filter the data. Finally, continuous wavelets are being used. These help to explain many of the results that have previously been produced. These were conducted on both real (experimental) and modelled networks.

In this paper we compare several different strategies for robust design when the experiment is carried out via a computer simulator.

We consider oil-water flow in porous media, with a dynamic capillary pressure relation. This leads to a pseudo-parabolic degenerate regularisation of the Buckley-Leverett (BL) equation. It is known that linear pseudo-parabolic regularisations of BL lead to shock solutions that do not satisfy the Oleinik condition. In this note we analyse the existence of travelling wave solutions that violate the Oleinik condition, taking special care of the degeneracy of the problem.

Electronic products tend to be economically outdated before their technical end-of-life has been reached. The ability to analyze and predict the (remaining) technical life of a product would make it possible either to re-use sub-assemblies in the manufacture process of new products, or to design products for which the technical and economical life match. This requires models to predict and monitor performance degradation profiles. In this paper we report on designed experiments to obtain such models. We show how wavelet analysis can be used to extract features from electrical signals. These features are analyzed using the Analysis of Variance in order to establish relations between these features and performance degradation.

Large area uniform plasmas are essential in microelectronics processing. Motivated by this application, a macroscopic model is proposed as a framework for investigating the occurrence of instabilities in high frequency plasma discharges for parallel plate geometries. This paper will concentrate on the formation of stationary, spatially inhomogeneous patterns.

The preparation of simulation models from CAD models is still a difficult task since shape changes are often required to adapt a component or a mechanical system to the hypotheses and specifications of the simulation task. Detail removal or idealization operations are among the current treatments performed during the preparation of simulation models. In this paper we introduce the concept of simplification features, which allows a user to improve the efficiency of the analysis model generation process. As a result, form feature semantics and simulation data are attached to a polyhedral model during the preparation phase to ease the Finite Element(FE) details identification and removal as well as to maintain the consistency between a CAD model and its associated F.E models.

The effects of discretisation parameters on the performance of a space-time VMS FEM are investigated. A moving-wave solution of the one-dimensional viscous Burgers equation is used to limit the influence of SGS modelling errors. Factors influencing the magnitude of the implicit SGS model are discussed.

We present a continuous wavelet analysis of count data with time-varying intensities. The objective is to extract intervals with significant intensities from background intervals. This includes the precise starting point of the significant interval, its exact duration and the (average) level of intensity. We allow multiple change points in the intensity curve, without specifying the number of change points in advance. We extend the classical (discretised) continuous Haar wavelet analysis towards an unbalanced (i.e., asymmetric) version. This additional degree of freedom allows more powerful detection. Locations of intensity change points are identified as persistent local maxima in the wavelet analysis at the successive scales. We illustrate the approach with simulations on low intensity data. Although the method is presented here in the context of Poisson (count) data, most ideas (apart from the specific Poisson normalization) apply for the detection of multiple change points in other circumstances (such as additive Gaussian noise) as well.