Some known models in phase separation theory (Hele-Shaw, nonlocal mean curvature motion) and their approximations by means of Cahn-Hilliard and nonlocal Allen-Cahn equations are proposed as a tool to generate planar curve-shortening flows without shrinking. This procedure can be seen as a level set approach to area-preserving geometric flows in the spirit of Sapiro and Tannenbaum [38], with application to shape recovery. We discuss the theoretical validation of this method and its implementation to problems of shape recovery in Computer Vision. The results of some numerical experiments on image processing are presented.

We present a numerical study of anisotropic statistical fluctuations in homogeneous turbulent flows. We give an argument to predict the dimensional scaling exponents, (p+j)/3, for the projections of p-th order structure function in the j-th sector of the rotational group. We show that measured exponents are anomalous, showing a clear deviation from the dimensional prediction. Dimensional scaling is subleading and it is recovered only after a random reshuffling of all velocity phases, in the stationary ensemble. This supports the idea that anomalous scaling is the result of a genuine inertial evolution, independent of large-scale behavior.

We study the on-line version of the well known problem of scheduling a set of $n$ independent multiprocessor tasks with prespecified processor allocations on a set of identical processors in order to minimize the makespan. Recently, it has been proven that even in the off-line case with unit processing time tasks no polynomial time approximation algorithm can be found with approximation factor $m^{{1}/{2}-\eps}$ for any $\eps >0$, unless \NP=\ZPP. We first study simple approximation and on-line algorithms based on the classical first-fit technique. Then, by using a split-round technique, we give a $3 \sqrt{m}$-approximation algorithm for the off-line version of the problem. Finally, we adapt this algorithm to the on-line case, in the paradigm of tasks arriving over time, and show that its competitive ratio is bounded by $(6\sqrt{m}+1)$. Due to the conducted experimental results, which also analyzed here, we conclude that our algorithms can also perform well in practice.

PELCR is an environment for lambda-terms reduction on parallel/distributed computing systems. The computation performed in this environment is a distributed graph rewriting and a major optimization to achieve efficient execution consists of a message aggregation technique exhibiting the potential for strong reduction of the communication overhead. In this paper we discuss the interaction between the effectiveness of aggregation and the schedule sequence of rewriting operations. Then we present a Priority Based (BP) scheduling algorithm well suited for the speci c aggregation technique. Results on a classical benchmark lambda-term demonstrate that PB allows PELCR to achieve up to 88% of the ideal speedup while executing on a shared memory parallel architecture.

Conservative linear equations arise in many areas of application, including continuum mechanics or high-frequency geometrical optics approximations. This kind of equations admits most of the time solutions which are only bounded measures in the space variable known as duality solutions. In this paper, we study the convergence of a class of finite-differences numerical schemes and introduce an appropriate concept of consistency with the continuous problem. Some basic examples including computational results are also supplied.

This paper is devoted to a numerical simulation of the classical WKB system arising in geometric optics expansions. It contains the nonlinear eikonal equation and a linear conservation law whose coefficient can be discontinuous. We address the problem of treating it in such a way superimposed signals can be reproduced by means of the kinetic formulation of ``multibranch solutions'' originally due to Brenier and Corrias. Some existence and uniqueness results are given together with computational test-cases of increasing difficulty displaying up to five multivaluations.

We propose here a well-balanced numerical scheme for the one-dimensional Goldstein-Taylor system which is endowed with all the stability properties inherent to the continuous problem and works in both rarefied and diffusive regimes.

This paper investigates the behavior of numerical schemes for nonlinear conservation laws with source terms. We concentrate on two significant examples: relaxation approximations and genuinely nonhomogeneous scalar laws. The main tool in our analysis is the extensive use of weak limits and nonconservative products which allow us to describe accurately the operations achieved in practice when using Riemann-based numerical schemes. Some illustrative and relevant computational results are provided.

We consider the Cauchy problem for $n\times n$ strictly hyperbolic systems of nonresonant balance laws $$ \left\{\begin{array}{c} u_t+f(u)_x=g(x,u), \qquad x \in \reali, t>0\\ u(0,.)=u_o \in \L1 \cap \BV(\reali; \reali^n), \\ | \la_i(u)| \geq c > 0 \mbox{ for all } i\in \{1,\ldots,n\}, \\ |g(.,u)|+\norma{\nabla_u g(.,u)}\leq \om \in \L1\cap\L\infty(\reali), \\ \end{array}\right. $$ each characteristic field being genuinely nonlinear or linearly degenerate. Assuming that $\|\om\|_{\L1(\reali)}$ and $\|u_o\|_{\BV(\reali)}$ are small enough, we prove the existence and uniqueness of global entropy solutions of bounded total variation as limits of special wave-front tracking approximations for which the source term is localized by means of Dirac masses. Moreover, we give a characterization of the resulting semigroup trajectories in terms of integral estimates.

This paper focuses on a new method to compute fitness function (ff) values in genetic algorithms for bus network optimization. In the proposed methodology, a genetic algorithm is used to generate iteratively new populations (sets of bus networks). Each member of the population is evaluated by computing a number of performance indicators obtained by the analysis of the assignment of the O/D demand associated to the considered networks. Thus, ff values are computed by means of a multicriteria analysis executed on the performance indicators so found. The goal is to design a heuristic algorithm that allows to achieve the best bus network satisfying both the transport demand and supply.

Recently algebraic polynomials have been considered as wavelets and handled by wavelet techniques. In the unified approach for the construction of polynomial wavelets by Fischer and Prestin, the actual implementation of decomposition, reconstruction and/or compression schemes required at each level the inversion of generalized Grammian matrices, in general not orthogonal. In this context the present paper works out necessary and sufficient conditions for the polynomial wavelets to be orthogonal to each other. Furthermore it shows how these computable characterizations lead to attractive decomposition and reconstruction algorithms based on orthogonal matrices. Finally the special case of Bernstein--Szego weight functions is studied in detail.

This paper describes a new fast line-by-line radiative transfer scheme which computes top of the atmosphere spectral radiance and its Jacobians with respect to any set of geophysical parameters both for clear and cloudy sky, and presents the software which implements the procedure. The performance of the code has been evaluated with respect to accuracy and speediness through a comparison with a state-of-art line-by-line radiative transfer model. The new code is well suited for nadir viewing satellite and airplane infrared sensors with a sampling rate in the range 0.1-2 cm-1.

The mapping properties of the Cauchy singular integral operator with constant coefficients are studied in couples of spaces equipped with weighted uniform norms. Recently weighted Besov type spaces got more and more interest in approximation theory and, in particular, in the numerical analysis of polynomial approximation methods for Cauchy singular integral equations on an interval. In a scale of pairs of weighted Besov spaces the authors state the boundedness and the invertibility of the Cauchy singular integral operator. Such result was not expected for a long time and it will affect further investigations essentially. The technique of the paper is based on properties of the de la Vallee Poussin operator constructed with respect to some Jacobi polynomials.

We present computer simulations of the HIV infection based on a sophisticated cellular automata model of the immune response. The infection progresses following the well known three-phases dynamics observed in patients, that is, acute, silent and acquired immunodeficiency. Antigenic shift and selection of escape viral mutants with low transcription rate explain the long-term course of the asymptomatic phase, while the immunodeficiency status appears to be the consequence of a drastic reduction in T helper cell repertoire