We deal with the emergence of the horizontal three-dimensional convection flow from an asymptotic mechanical equilibrium in a parallelepipedic box with rigid walls and a very small horizontal temperature gradient. The non-linear stability bound is associated with a variational problem. It is proved that this problem is equivalent to the eigenvalue problem governing the linear stability pf the asymptotic basic conduction state and so the two bounds, the linear one and the non-linear one, coincide. Finally, the eigenvalue problem is reduced to a system consisting of a polynomial equation and a trascendental equation. The numerical solution of this system yields the common stability bound. Its physical interpretation and comparison with the three-dimensional case is provided for various aspect ratios in the two-dimensional horizontal directions. (C) 1999 Elsevier Science Ltd. All rights reserved.

A vast literature exists on the Benard flow, the vertical thermal convection flow, but almost no result is known on the horizontal counterpart. On account of the wide range of applications in geophysics, astrophysics, metereology, and material science; we think that the horizontal thermal convection flow deserves as much consideration as the Benard problem. The present study is the first step towards the description of the bifurcation pattern of the horizontal thermal convection flow. We present several flow configurations of an incompressible Navier-Stokes fluid contained in a 4 × 1 × 1 parallelepipedic box with open top and vertical transversal walls at different temperature. The flow induced by the buoyancy force and the thermocapillary effects at the fluid/air interface is numerically computed within the Boussinesq approximation. The velocity-vorticity formulation with a fully implicit finite difference method are implemented in a parallel computational code. The strong coupling of the discrete equations ensures the correct mass balance at each time step and provides true-transient numerical flows. For fluids at Prandtl number Pr = 0.015 (semiconductors and liquid metals), we describe the changes in shape of the main vortex and the intensity of the speed of the flow versus variations of the Grashof number. In the case of absence of thermocapillary effects, we observe that as Gr increases, the flow exhibits more and more three-dimensional effects. When we add the thermocapillary effects, we observe an increase of the speed of the flow with the formation of a steep boundary layer around the liquid/air interface.

The exit-time statistics of experimental turbulent data is analyzed. By looking at the exit-time moments (inverse structure functions) it is possible to have a direct measurement of scaling properties of the laminar statistics. It turns out that the inverse structure functions show a much more extended intermediate dissipative range than the structure functions, leading to the first clear evidence of the existence of such a range of scales. [S1063-651X(99)51012-X].

We study the coherent dynamics of globally coupled maps showing macroscopic chaos. With this term we indicate the hydrodynamical-like irregular behavior of some global observables, with typical times much longer than the times related to the evolution of the single (or microscopic) elements of the system. The usual Lyapunov exponent is not able to capture the essential features of this macroscopic phenomenon. Using the recently introduced notion of finite size Lyapunov exponent, we characterize, in a consistent way, these macroscopic behaviors. Basically, at small values of the perturbation we recover the usual (microscopic) Lyapunov exponent, while at larger values a sort of macroscopic Lyapunov exponent emerges, which can be much smaller than the former. A quantitative characterization of the chaotic motion at hydrodynamical level is then possible, even in the absence of the explicit equations for the time evolution of the macroscopic observables, (C) 1999 Elsevier Science B.V. All rights reserved.

An algorithm for the approximate evaluation of the Hilbert transform has been prposed. The convergence of the procedure is proved. The stability of the algorithm is considered and some numerical examples are given.

A new approach to encoding knowledge in a integrated environment, by means of research paths, is shown.

The noisy trigonometric moment problem for a finite linear combination of box functions is considered, and a research program, possibly leading to a superresolving method, is outlined and some initial steps are performed. The method is based on the remark that the poles of the Padè approximant to the Z-transform of the noiseless moments show, asymptotically, a regular pattern in the complex plane. The pattern can be described by a set of arcs, connecting points on the unit circle, and a pole density function defined on the arcs. When a moderate noise affects the moments, more arcs are needed to describe the pole pattern, but the noiseless pattern is slightly deformed, still allowing its identification. When this identification is possible, a very effective noise filter and moment extrapolator should be easily constructed. In this paper only some preliminary steps of the above research program are performed. Specifically, the case of one box function is considered. A method for computing the pole patterns, based on the solution of a singular integral equation of Cauchy type, is developed. The method is general enough to be used also for several box functions. Some numerical results, showing the feasibility of the program, are discussed.

In this paper, the modal analysis model, made up by a linear combination of complex exponential functions, is considered. Padè approximants to the Z-transform of a noisy sample are then considered, and the asymptotic locus of their poles is studied. It turns out that this locus is strongly related to the complex exponentials of the model. By exploiting these properties, powerful methods for estimating the model parameters can be devised, which have both denoising and super-resolution capabilities.

A mathematical model for the removal of subsoil pollutant by bioventing is exposed

With road traffic in Europe forecast to increase, strategies are needed to keep transportation sector growth within the bounds imposed by a sustainable development. Research is contributing through a large number of projects dealing with transport-environment interactions. This paper reviews international research activities in this field, focusing on technological innovations, air and noise pollution prediction models, and existing tools for socioeconomic evaluation of traffic impacts on the environment. In particular, research projects of the Second Special Project on Transport (PFT2) of the Italian National Research Council (CNR) are outlined.

REFIR is a Fourier Transform Spectrometer designed to measure the upwelling IR Earth's emission from space in the spectral range 100 to 1000 cm -1 with an unapodized spectral resolution of about 0.5 cm -1. One of the main scientific objectives of REFIR is to monitor the far IR planetary emission and the principal drivers of this emission, with particular attention being paid to the poorly understood mid and upper troposphere. The expected retrieval performance for temperature and water vapor profiles, from a subset of REFIR measurements, is evaluated and presented in this paper. ©2003 Copyright SPIE - The International Society for Optical Engineering.

Inversion of the radiative transfer equation to retrieve the vertical profile of temperature from high resolution radiance spectra is an important problem in remote sensing of atmosphere. Because of its non linearity and ill conditioning, regularization techniques have been resorted in order to reduce the error of the retrieval. In this paper Generalized Singular Value Decomposition (GSVD) and Truncated Generalized Singular Value Decomposition (TGSVD) have been used to solve the linear model; the optimal regularization parameter for the proper amount of smoothing have been chosen by the L-curve criterion. A significant test problem has been worked out with reference to the Infrared Atmospheric Sounding Interferometer (IASI). The effectiveness of the methods to reduce variance and bias in the output profile has been addressed. We show that GSVD plus L-curve criterion or TGSVD plus L-curve are really effective in reducing error, variance and bias of the retrieved profile.

CHIARA (Convolution of High-resolution Interferograms for Advanced Retrieval in the Atmosphere) is an integrated tool intended for the simulation and inversion of spectra. In this paper application of CHIARA to IMG spectra is presented and discussed.

The spinodal decomposition of binary mixtures in uniform shear flow is studied in the context of the time-dependent Ginzburg-Landau equation, approximated at one-loop order. We show that the structure factor obeys a generalized dynamical scaling with different growth exponents alpha(x) = 5/4 and alpha(y) = 1/4 in the flow and in the shear directions, respectively. The excess viscosity Delta eta after reaching a maximum relaxes to zero as gamma(-2)t(-3/2), gamma being the shear rate. Delta eta and other observables exhibit log-time periodic oscillations which can be interpreted as due to a growth mechanism where stretching and breakup of domains cyclically occur.

We show how a lattice-Boltzmann approach can be extended to ternary fluid mixtures with the aim of modeling the diverse behavior of oil-water-surfactant systems. We model the mixture using a Ginzburg-Landau free energy with two scalar order parameters which allows us to define a lattice-Boltzmann scheme in the spirit of the Cahn-Hilliard approach to nonequilibrium dynamics. Results are presented for the spontaneous emulsification of an oil-water droplet and for spinodal decomposition in the presence of a surfactant.