Il Nuovo Cimento C

The Imager proposed for the gamma-ray satellite project INTEGRAL is based on a multilayer two-dimensional array of CsI(TI) elements viewed by Si photodiodes. The total active area is ≈2500 cm2. The operative energy interval ranges from 0.05 to 10 MeV. A prototype version of this instrument, ready to be tested on a ballon-borne experiment, has been realized. In this article the expected performances of the instrument are presented, toghether with the first calibration results of the prototype.

We study nonlinear interactions in measured surface wave trains obtained in the Northern Adriatic Sea about 16 kilometres from Venice, Italy.Nonlinear Fourier analysis is discussed in terms of the exact spectral solution to the Korteweg-deVries (KdV) equation as given by theinverse scattering transform (IST). For the periodic and/or quasi-periodic boundary conditions assumed herein, the approach may be viewed as a nonlinear, broad-banded generalization of the ordinary, linear Fourier transform. In particular, we study solition interactions, their properties and the nonlinear dynamics of the radiation (or oscillation) modes as found from the inverse scattering transform analysis. We also conduct a number of computer experiments in which measured wave trains are numerically propagated forward in time toward shallow water and backward in time into deep water in order to assess how the nonlinear wave dynamics are influenced by propagation over variable bathymetry. On this basis we develop a scenario for the evolution of nonlinear wave trains, initially far offshore in deep water, as they propagate into shallow water regions. The deep-water waves have a small Ursell number and are hence not very nonlinear; as they propagate toward shallow water, the Ursell number gradually increases in the numerical experiments by about an order of magnitude. A useful parameterization of nonlinearity in these studies is the «spectral modulus,» a number between 0 and 1, which is associated with each IST spectral frequency. Small values of the modulus mean that a particular spectral component is linear (a sine wave); large values of the modulus (≈1) indicate that the component is nonlinear (a soliton). There is a systematic increase of the modulus as the waves propagate into shallow water where nonlinear effects predominate; we describe how the modulus varies as a function of spectral frequency during this shoaling process. The results suggest that the effect of increasing nonlinearity «saturates» the IST spectrum (i.e. the modulus ≈1 for all frequencies) to that virtually all spectral components become solitons in sufficiently shallow water.

This paper presents a study based on a second-order interpretation of wave «energy» spectra, which may explain the build-up of low-and high-frequency peaks for wave spectra measured in shallow water. A comparison between this interpretative model and laboratory data, which were obtained in a bidimensional wave flume, is also given in the paper.

Abbiamo analizzato i profili della concentrazione del carbonato di calcio (CaCO3) in quattro cores di sedimenti recenti del Mar Ionio, che coprono un intervallo di ∼5000 anni, ed il profilo della termoluminescenza (TL) in uno di questi cores che copre un intervallo di ∼2000 anni. La velocità di sedimentazione è stata determinata con grande precisione utilizzando metodi radiometrici e di tefroanalisi e si è dimostrata costante ed identica per i quattro cores. I profili di CaCO3 e di TL sono stati così trasformati in serie temporali. La precisione delle scale temporali ha permesso l'analisi accurata di significative ciclicità presenti nelle serie temporali ottenute e di individuare la loro possibile origine solare. Le serie di CaCO3 sono perfettamente riproducibili e rivelano, in particolare, le periodicità di circa 90 anni (ciclo di Gleissberg) e di circa 200 anni presenti anche nel14C degli anelli degli alberi. Questa periodicità è accompagnata da due bande laterali che suggeriscono che l'onda di 200 anni è modulata da una componente con periodo di ∼2000 anni, come si trova anche nel radiocarbonio. L'analisi della serie temporale di TL rivela ben definite periodicità a 137.7 a, 59 a, 28.5 a, 22 a, 12.06 a, 10.8 a, che hanno notevoli corrispondenze con le periodicità trovate nelle macchie solari e nelle aurore. Inoltre, il battimento delle due onde con periodo decennale produce un treno d'onda con periodo di 11.4 a ed una modulazione d'ampiezza di 206 a già citata, ed i nodi del treno d'onda coincidono con i minimi delle macchie solari. I risultati ottenuti indicano un possibile meccanismo comune, di origine solare e/o climatica che controlla indici differenti in reservoirs terrestri.

This work analyses the setting-up of an optical head which allows the visualization of a section of the distribution of the flux of energy along the focal axis of optical systems in general and of solar concentrators in particular. A circular-type solar concentrator, with the reflector consisting of a plastic lamina aspirated by means of a pump, has been built. The distribution of the energy flux in the focus of this concentrator has been calculated by the theoretical method. Results are compared with experimental data obtained by means of the optical head.

We solve the one-dimensional diffusion equation for the hadronic cosmic-ray component in the atmosphere assuming for the interaction mean free path a ln2 E-dependence on the energy and comparing with mountain experimental data.

We consider the perturbation of a stratified rotating fluid due to the crossing of a mountain ridge. The behaviour of the solutions is examined in the primitive Navier-Stokes equations in linear form studied by Queney. We produce the Green's functions of the problem at ground level at any distance from the perturbing ridge; in this sense it is an extension of the theory presented by Pierrehumbert. Furthermore, we discuss the relative contribution of the different terms and we examine the behaviour of small-scale waves with altitude. This work is also relevant for the parametrization of the subgrid physical effect in large numerical models, like the barrier effect of the Alps or the Rocky Mountains.