Un Metodo per la valutazione su base statistica della vulnerabilit\ue0 di attraversamenti fluviali in alvei coerenti

La valutazione dell\u2019evoluzione temporale dello scavo nella sezione contratta di restringimenti d\u2019alveo, causati dalla presenza di attraversamenti, pu\uf2 porgere informazioni preziose sia in fase di progettazione di nuove opere sia in fase di verifica della stabilit\ue0 di attraversamenti esistenti. Il presente lavoro si propone di presentare un modello matematico per la stima della progressione temporale della profondit\ue0 di scavo di contrazione in corrispondenza di ponti, in condizioni di assenza di trasporto solido, moto vario e materiale d\u2019alveo coeso. Applicando il metodo con riferimento a serie temporali sintetiche egualmente probabili di deflussi fluviali, di estensione pari alla vita attesa dell\u2019opera, \ue8 possibile inoltre valutare la distribuzione di probabilit\ue0 dello scavo di contrazione, pervenendo cos\uec ad una stima su base statistica della vulnerabilit\ue0 dell\u2019attraversamento

Stochastic Flow Analysis for Predicting River Scour of Cohesive Soils

Damage to bridge crossings during flood events endangers the lives of the traveling public and causes costly disruptions to traffic flow. The most common causes of bridge collapse are scouring of the streambed and banks and erosion of highway embankments. This study couples a synthetic river flow simulation technique with a scour model for cohesive soils and determines the expected scour depth for a given lifetime of the bridge. A fractionally differenced autoregressive integrated moving average model generates synthetic streamflow sequences of the same length as the expected lifetime of the bridge. The scour model predicts the progression of scour depth through time in a multilayered soil. The model is used to determine the scour depth associated with different replicates of the synthetic flow sequences of the same length as the lifetime of the bridge. The probability distribution of scour depth is estimated by repeating this simulation procedure over a number of independent realizations of streamflow series for a given life of the bridge. This approach provides a framework for the probabilistic design and risk analysis of bridge foundations subjected to scour

Absorption systems at z similar to 2 as a probe of the circumgalactic medium: a probabilistic approach

We characterize the properties of the intergalactic medium (IGM) around a sample of galaxies extracted from state-of-the-art hydrodynamical simulations of structure formation in a cosmological volume of 25 Mpc comoving at z similar to 2. The simulations are based on two different subresolution schemes for star formation and supernova feedback: the Multi-Phase Particle Integrator (MUPPI) scheme and the Effective Model. We develop a quantitative and probabilistic analysis based on the apparent optical depth method of the properties of the absorbers as a function of impact parameter from their nearby galaxies: in such a way, we probe different environments from circumgalactic medium to low-density filaments. Absorbers' properties are then compared with a spectroscopic observational data set obtained from high-resolution quasar spectra. Our main focus is on the N-C IV-N-H I relation around simulated galaxies: the results obtained with MUPPI and the Effective model are remarkably similar, with small differences only confined to regions at impact parameters b = [1 - 3] x r(vir). Using C IV as a tracer of the metallicity, we obtain evidence that the observed metal absorption systems have the highest probability to be confined in a region of 150-400kpc around galaxies. Near-filament environments have instead metallicities too low to be probed by present-day telescopes, but could be probed by future spectroscopical studies. Finally, we compute C IV covering fractions which are in agreement with observational data

ESPRESSO: A High Resolution Spectrograph for the Combined Coud\ue9 Focus of the VLT

In the frame of the call for proposal for the E-ELT instrumentation studies, the CODEX team carried out the feasibility study for a spectrograph for extremely stable Doppler measurements. The CODEX project and its scientific goals are described in [L. Pasquini, S. Cristiani et al. in Messenger 122, 10 (2005)]. During the development of this study, the CODEX team recognized that a CODEX-like instrument would be of high scientific interest also on the VLT. The ESPRESSO concept was born. The contribution by J. Liske in this volume highlights the direct links between the two instruments (see also [J. Liske, A. Grazian, E. Vanzella et al. in 2008MNRAS.tmp..460L, in press])