Journal of Computational Methods in Sciences and Engineering

This paper focuses on a combination of two disclosure limitation techniques, additive noise and multiplicative bias, and studies their efficacy in protecting confidentiality of continuous microdata. A Bayesian intruder model is extensively simulated in order to assess the performance of these disclosure limitation techniques as a function of key parameters like the variability amongst profiles in the original data, the amount of users prior information, the amount of bias and noise introduced in the data. The results of the simulation offer insight into the degree of vulnerability of data on continuous random variables and suggests some guidelines for effective protection measures.

The paper discusses two Post Keynesian models in a closed economy, for the credit market and the reserve market respectively. The models are grounded on the idea that (a) bank loans create deposits and (b) deposits make monetary reserves. The main differences between these monetary models are due to different assumptions about the state of expectations of agents involved in the money supply process.

In this paper we consider a spatial economic model along the lines of the new economic geography literature. The evolution equations of the model are of the transport-diffusion type. We propose a finite difference method to study the behavior of the economy across space and time. The emergence of economic agglomerations is adressed as well as their evolution over time when they happen.

The relaxed Burnett system, recently introduced in as a hydrodynamical approximation of the Boltzmann equation, is numerically solved. Due to the stiffness of this system and the severe CFL condition for large Mach numbers, a fully implicit Runge-Kutta method has been used. In order to reduce computing time, we apply a parallel stiff ODE solver based on 4-stage Radau IIA IRK. The ODE solver is combined with suitable first order upwind and second order MUSCL relaxation schemes for the spatial derivatives. Speedup results and comparisons to DSMC and Navier-Stokes approximations are reported for a 1D shock profile.

Optimization of a complete 2D flying sails configuration is considered. An optimum shape design problem is then defined considering the maximization of the drive force on the sails and a complete flow modelling including accurate turbulent effects. The corresponding numerical algorithm is based on a gradient descent method coupled with a discrete shape grid-point parametrization. The descent direction is obtained by an exact computation of an incomplete discrete gradient associated with a multi-level strategy. The numerical behavior of the present formulation has been illustrated by the optimization of a real 2D configuration of an America's Cup yacht.

The recent introduction of new star catalogues referred to the new ICRF reference frame gives special interest to the study of the orientation errors of this freferences frame with respect to the dynamical reference frame defined by means of planetary theory. Several methods can be used for this purpose. One of them is based in an optimal control method where the residuals given from the differences between the calculated and observated positions for a set of minor planets on a long time-span, and we use the residual function as cost function. This method requires a previous correction of the elements of the asteroids in order to consider the most precise calculated positions. For this purpose a set of observated positions asteroids in the time span 1836–1996 are taken. From this initial correction we compare the calculated and observated positions from a differential rotation with a linear correction in time around each axis an a model of correction is got.

This paper introduces a method to build a classifier based on labelled and unlabelled data. We set up the Expectation-Maximization (EM) algorithm steps for the particular case of the naive Bayes approach and show empirical work for the restricted web page database. Original contributions includes the application of the EM algorithm to simulated data in order to see the behavior of the algorithm for different numbers of labelled and unlabelled data, and to study the effect of the sampling mechanism for the unlabelled data on the results.

The measurement of the surface tension associated with the interface between two immiscible liquids requires the use of non-trivial experimental procedures. The Axisymmetric Drop Shape Analysis (ADSA) method has been used by several laboratories because it provides good results over a wide range of situations. In the ADSA method, the theoretical prediction for a drop equilibrium shape is fitted to experimental contours to find the surface tension value. Based on this idea, in the present paper the advantages of using liquid bridges instead of drops are discussed. The sensitivity of both the drop and the liquid bridge equilibrium shapes to the surface tension value is studied from the numerical solution of the Young-Laplace equation. The results show that the use of liquid bridges could lead to better results, especially if non-axisymmetric configurations are considered. The optimal values of the experimental parameters are found, and a numerical algorithm developed to calculate the surface tension value from a liquid bridge photograph is described.

A structural optimization method based on the homogenization approach (the homogenization design method) has been applied to the modeling of the recently produced biomorphic composite materials. The design itself involves a structural optimization problem which is solved under a set of equality and inequality constraints on the state variables (displacements) and design parameters (lengths of the layers in the microstructure and angle of cell rotation). Primal-dual Newton-type interior-point method with proper optimality criteria is applied to the resulting nonconvex nonlinear optimization problem.

We determine the class of one-dimensional stochastic differential equations with a strong solution that can be represented as a functional of Brownian motion. For this class we detail the corresponding solution and transition density. Sharp conditions for explosion to occur are determined.

The Taylor series method is one of the earliest analytic-numeric algorithms for approximate solution of initial value problems for ordinary differential equations. The main idea of the rehabilitation of these algorithms is based on the approximate calculation of higher derivatives using well-known technique for the partial differential equations. In some cases such algorithms will be much more complicated than a R-K methods, because it will require more function evaluation than well-known classical algorithms. However these evaluations can be accomplished fully parallel and the coefficients of truncated Taylor series can be calculated with matrix-vector operations. For large systems these operations suit for the parallel computers. The approximate solution is given as a piecewise polynomial function defined on the subintervals of the whole interval and the local error of this solution at the interior points of the subinterval is less than that one at the end point. This property offers different facility for adaptive error control. This paper describes several above-mentioned algorithms and examines its consistency and stability properties. It demonstrates some numerical test results for stiff systems herewith we attempt to prove the efficiency of these new-old algorithms.

In this paper we present a specific software package to bifurcation analysis. Specifically for locating fixed points of maps defined on R and their variation with respect to parameters. Also this program allows both detecting and analyzing bifurcations under higher order conditions. We deal mainly with discrete-time systems and give only brief remarks on the continuous time case.

Nowadays, one of the main topics in Engineering is, undoubtedly, the Automatic Control of Systems. Probably, the most important problem in this area is how to guarantee the stability of a closed loop control system. The Routh-Hurwith Criterion, RHC, provides one of the most powerful algorithm for analyzing the mentioned stability, even when it depends on an adjustable parameter. It has been developed a computational system in Mathematica, which, applying this Criterion, is able to analyze the stability of every Continuous System which can be modelled by transfer functions in the way of quotient of real coefficients polynomials.

A new powerful approach to compute the eigenfunctions of the finite two-dimensional Fourier transform is developed and analysed. The numerical technique is a generalization of an earlier method developed for ordinary prolate spheroidal wave functions. Special considerations are given to the problem of singularities and the procedure to locate the eigenvalues. It is demonstrated that the computations are fundamentally improved by the introduction of appropriate auxiliary differential equations.

In this abstract it is presented the assesment of two different methods devoted to the evaluation of the configuration space for planar revolute manipulators. The formalism proposed in [3] for the evaluation of the C-space, when applied to planar revolute manipulators, is compared to a new method, which provides both better results and a way to generalize the evaluation for any kind of robotic structure.

In the very recent period Magnetic Resonance Spectroscopy (MRS) and Spectroscopic Imaging (MRSI) have become key diagnostic modalities for neuro-oncology. MRS and MRSI are now applied extensively for initial detection of brain tumours, for histopathologic classification, tumour localization and grading, as well as for assessment of response to therapy and for follow-up surveillance, striving, in particular, for earlier identification of recurrence. In this paper we review the current state of the art of MRS and MRSI for brain tumour diagnostics, highlighting the achievements, as well as remaining dilemmas.

Clearly, MRS and MRSI represent an important advance for the detection and characterisation of tumours of the brain. However, there are still important shortcomings of the present applications of MRS and MRSI in neuro-oncology. First of all, very few of the currently assessed metabolite concentrations or ratios unequivocally distinguish intra-cerebral tumours from normal brain tissue. Moreover, changes in each of the metabolite concentrations and ratios are non-specific for cancer of the brain. In other words, non-neoplastic processes such as infection, stroke, demyelinating disorders, inter alia, frequently show spectral changes that are identical to those seen in brain tumours. Histopathological characterization and tumour grading, both crucial for clinical decision-making, have been greatly aided by MRS and MRSI. However, there are numerous contradictory findings in the literature.

We demonstrate in this paper that many of the shortcomings of MRS and MRSI for neuro-oncology are directly related to the reliance upon the conventional Fourier-based framework for data analysis. We review the distinct advantages of the Fast Padé Transform (FPT) relative to the Fast Fourier Transform (FFT). Our focus is on those salient features of the FPT that are of critical clinical relevance for achieving an overall improved diagnostic performance of MRS and MRSI. These features are extremely stable and rapid convergence, as well as highly accurate quantification estimates of spectra from in vivo MRS time signals, as presently illustrated for data from the brain of a healthy volunteer. The next, and urgently needed step, is to more widely apply the FPT to in vivo MRS and MRSI signals from patients with brain tumours with the aim of tackling, in actual practice, the diagnostic dilemmas still plaguing neuro-oncology.

In this paper we consider simple methods for the numerical solution of Cauchy singular integral equations with conjugation based on quadratures. They use collocation at a set of nodes which is graded toward the endpoints, to accomodate for the presence of the singularity. Our numerical experience reveals that the theoretical stability findings are indeed of practical applicability, as the empirical condition number is seen very often to reach a plateau, whose asymptotic value is indeed very low.