University of Perugia

About: University of Perugia is a education organization based out in Perugia, Umbria, Italy. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 13365 authors who have published 39516 publications receiving 1265601 citations. The organization is also known as: Universitá degli Studi di Perugia & Universita degli Studi di Perugia.

REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

Abstract: Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initia l fireball Lorentz factor 0. We aim to provide a direct measure of 0. Methods. The early-time afterglow light curve carries information about 0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afte rglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 0∼ 400, fully confirming the highly relativistic nature of GRB fi reballs. The deceleration radius was inferred to be Rdec≈ 10 17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.

Aggregation of Organic Dyes on TiO2 in Dye-Sensitized Solar Cells Models: An ab Initio Investigation

Abstract: A density functional theory (DFT), time-dependent DFT, and ab initio second order Moller−Plesset perturbation theory study of the aggregation of the metal free indoline D102 and D149 dyes on extended TiO2 models is reported. By selecting the relevant dimeric arrangements on the TiO2 surface and evaluating, at the same time, the associated spectroscopic response, an almost quantitative description of the extremely different aggregation behavior of the two dyes is provided. Nicely reproducing the experimental evidence, the present results predict strong aggregation interactions and a sizable red-shift of the absorption band in the case of D102, while negligible effects for D149. Our results open the possibility of computationally screening the various aggregation patterns and predicting the corresponding optical response, thus paving the way to an effective molecular engineering of further enhanced sensitizers for solar cell applications.

Normal faults, normal friction?

Abstract: Debate continues as to whether normal faults may be seismically active at very low dips (d , 308) in the upper continental crust. An updated compilation of dip estimates (n 5 25) has been prepared from focal mechanisms of shallow, intracontinental, normal-slip earthquakes (M . 5.5; slip vector raking 90 86 308 in the fault plane) where the rupture plane is unambiguously discriminated. The dip distribution for these moderate-to-large normal fault ruptures extends from 658 . d . 308, corresponding to a range, 258 , ur , 608, for the reactivation angle between the fault and inferred vertical s1. In a comparable data set previously obtained for reverse fault ruptures (n 5 33), the active dip distribution is 108 , d5u r , 608. For vertical and horizontal s1 trajectories within extensional and compressional tectonic regimes, respectively, dip-slip reactivation is thus restricted to faults oriented at ur # 608 to inferred s1. Apparent lockup at ur 608 in each dip distribution and a dominant 30 86 58 peak in the reverse fault dip distribution, are both consistent with a friction coefficient ms 0.6, toward the bottom of Byerlee’s experimental range, though localized fluid overpressuring may be needed for reactivation of less favorably oriented faults.

The first fermi lat supernova remnant catalog

Abstract: To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope (LAT). Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude allows us to determine an upper limit of 22% on the number of GeV candidates falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, we demonstrate the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. We model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.