In this paper we deal with high oscillatory systems and numerical methods for the approximation of their solutions. Some classical schemes developed in the literature are recalled and a recent approach based on the expression of the oscillatory solution by means of the exponential map is considered. Moreover we introduce a new method based on the Cayley map and provide some numerical tests in order to compare the different approaches

In particolare nell'ultima fase, il progetto e' stato orientato alla caratterizzazione di processi di transizione liquido/solido in presenza di deformazioni della fase solida. Su segnalazione di esperti in Scienza dei Materiali, sono state svolte delle simulazioni numeriche per individuare l'entita' dell'effetto di tali deformazioni sul processo. Stiamo lavorando su un test che portera' auspicabilmente a chiarire la necessita' che il modello matematico includa anche la descrizione delle deformazioni.

The approximation of a function affected by noise in several dimensions suffers from the so-called "curse of dimensionality". In this paper a Fourier series method based on regularization is developed both for uniform and random design when a restriction on the complexity of the curve such as additivity is considered in order to circumvent the problem. Optimal convergence theorems are stated and numerical experiments are shown on several test problems available in the literature together with comparisons with alternative methods. © 2002 Elsevier Science B.V. All rights reserved.

Remote sensing of atmosphere is changing rapidly thanks to the development of high spectral resolution infrared space-born sensors. The aim is to provide more and more accurate information on the lower atmosphere, as requested by the World Meteorological Organization (WMO), to improve reliability and time span of weather forecasts plus Earth's monitoring. In this paper the performance of the Infrared Atmospheric Sounding Interferometer (IASI) is analyzed looking directly at the products: temperature and water vapour.

A novel mesoscopic simulation technique -multi-particle collision dynamics- which has been suggested very recently, is used to study the two-dimensional flow around a square and a circular cylinder. The method is described and new proper boundary conditions are proposed to deal with wall collisions. The flow is analyzed in a wide range of Reynolds numbers in order to cover both the steady and unsteady regimes, resulting in symmetric steady vortices and periodic vortex shedding, respectively. The numerical results for integral flow parameters, such as the recirculation length, the drag and lift coefficients, the Strouhal number, as well as the spatial dependence of the velocity field, are compared with previous numerical and experimental studies. The qualitative and quantitative agreement is very good, validating the method as a promising technique to describe the hydrodynamic effects of solvent on embedded particles.

The phase separation of two-dimensional binary mixtures has been studied through numerical Langevin simulations based on a Ginzburg-Landau free energy. We have considered not symmetric mixtures with and without imposed shear flow. In the sheared case our main results are as follows: (1) domains are distorted by the flow; (2) the structure factor has four peaks; (3) excess viscosity shows a peak whose position is independent of shear rate but its height decreases increasing shear rate.

A computational approach has been developed to assess the power of paramagnetism-based backbone constraints with respect to the determination of the tertiary structure, once the secondary structure elements are known. This is part of the general assessment of paramagnetism-based constraints which are known to be relevant when used in conjunction with all classical constraints. The paramagnetism-based constraints here investigated are the pseudocontact shifts, the residual dipolar couplings due to self-orientation of the metalloprotein in high magnetic fields, and the cross correlation between dipolar relaxation and Curie relaxation. The relative constraints are generated by back-calculation from a known structure. The elements of secondary structure are supposed to be obtained from chemical shift index. The problem of the reciprocal orientation of the helices is addressed. It is shown that the correct fold can be obtained depending on the length of the α-helical stretches with respect to the length of the non helical segments connecting the α-helices. For example, the correct fold is straightforwardly obtained for the four-helix bundle protein cytochrome b 562, while the double EF-hand motif of calbindin D9k is hardly obtained without ambiguity. In cases like calbindin D9k, the availability of datasets from different metal ions is helpful, whereas less important is the location of the metal ion with respect to the secondary structure elements.

Bioventing is an in site remediation technique, which is useful for decontaminating polluted subsoil. Air is injected into the subsoil to enhance the bacteria biodegradation activity. A multiphase mathematical model describing the removal of hydrocarbon in the unsaturated zone will be described and the problem of the optimal design of a decontamination intervention will be formulated. In order to simplify the computational approach to the problem, a conjecture will be introduced, affirming that control of the subsoil airflow field allows the pollutant removal phenomenon to be controlled. Different objective functions, useful for evaluating the airflow field, will be introduced and their characteristics will be examinated with a numerical test.