Meccanismi di regressione e frammentazione dell’habitat nelle praterie di Posidonia oceanica

The aim of this PhD is to describe the current health status and the temporal evolution of P. oceanica meadows of Latium coast, describing their mode of regression through the analysis of the upper and lower limits position and the application of some principles and metrics of landscape ecology. Studies on landscape fragmentation have typically been conducted in terrestrial habitats, such as forests, where indices are used to quantify habitat loss and fragmentation in relation to changes in abundance and/or community structure of associated organisms (Lord and Norton 1990; Saunders et al. 1991; Opdam et al. 1993; Reed et al. 1996; Jorge and Garcia 1997; Trzcinski et al. 1999). There are numerousindices available to quantify terrestrial landscape fragmentation, yet presently there is a general consensus about the application of these indices, however no individual index can capture the full complexity of spatial atterns, multiple indices are required for analysing landscape configuration (Saura, 2002). Indices that quantify ecologically important spatial patterns are necessary for achieving the goal of landscape ecology: ‘to elucidate the relationship between andscape patterns and ecological processes’ (Turner, 1989). Although landscape indices have been also been used to quantify spatial patterns of various aquatic habitats (Bell and Hicks 1991; Irlandi 1994, 1997; Irlandi et al. 1995; Garrabou et al. 1998; Kendrick et al. 1999; Hovel and Lipcius 2001), such as seagrass. Seagrass ecosystems occur over broad spatial scales (tens to hundreds of kilometres) and are characterised by a continuum from fragmented patches to continuous meadows (Sleeman, 2005). Given the high ecological significance of seagrasses, it is necessary to define reliable measures that can be used by researchers and resource managers to identify fragmentation and quantify spatial change in relation to ecological processes (Sleeman, 2005)

Resistive Plate Chambers with Gd-coated electrodes as thermal neutron detectors

Abstract Resistive Plate Chambers (RPCs) are wide spread, cheap, easy-to-build and large size detectors, used mainly to reveal ionising particles in high-energy physics experiments. Here a technique, consisting in coating the inner surface of the bakelite electrodes with a mixture of linseed oil and Gd 2 O 3 is reported. This allows to make RPCs sensitive also to thermal neutrons, making them suitable to be employed for industrial, medical or de-mining applications. Thermal neutron-sensitive RPCs can be operated at atmospheric pressure, are lightweighted, have low γ -ray sensitivity and are easy to handle even when large areas have to be covered. This paper reports the results of the first test of this detector, performed at the Geel Linear Accelerator (GELINA) in Belgium

First determination of the one-proton induced Non-Mesonic Weak Decay width of p-shell {\Lambda}-Hypernuclei

Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.Comment: 16 pages, 3 figures, 2 table

Σ−p\Sigma^- p emission rates in K−K^- absorptions at rest on 6^6Li, 7^7Li, 9^{9}Be, 13^{13}C and 16^{16}O

An experimental study of the $K^-_{stop}A\rightarrow \Sigma^- p A'$ reaction on $A=^6$Li, $^7$Li, $^9$Be, $^{13}$C and $^{16}$O $p$-shell nuclei is presented. The data were collected by the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy). Emission rates for the reaction in the mentioned nuclei are measured and compared with the few existing data. The spectra of several observables are discussed; indications of Quasi-Free absorptions by a $(np)$ pair embedded in the $A$ nucleus can be obtained from the study of the missing mass distributions.Comment: Version accepted by PR

High-energy gamma rays emission in coincidence with light charged particles from the32S +74Ge reaction at 210 MeV

High-energyγ-rays from the32S+74Ge reaction at 210 MeV bombarding energy were measured in coincidence with light charged particles detected in a large area hodoscope. Experimental results show that energeticγ-rays in coincidence with light charged particles are essentially emitted in the compound nucleus decay. The parameters of the giant dipole resonance (GDR) have been extracted from alineshape analysis of the experimentalγ-ray spectrum. The derived values of mean energyED, widthΓ and strengthS are in good agreement with results from previous experiments on Sn isotopes obtained by using different experimental techniques

Performance of ALICE pixel prototypes in high energy beams

The two innermost layers of the ALICE inner tracking system are instrumented with silicon pixel detectors. Single chip assembly prototypes of the ALICE pixels have been tested in high energy particle beams at the CERN SPS. Detection efficiency and spatial precision have been studied as a function of the threshold and the track incidence angle. The experimental method, data analysis and main results are presented.Comment: 10 pages, 9 figures, contribution to PIX2005 Workshop, Bonn (Germany), 5-8 September 200