Compton dragged gamma-ray bursts: the spectrum

Recently several studies have jointly analysed data from different cosmological probes with the motivation of estimating cosmological parameters. Here we generalize this procedure to allow freedom in the relative weights of various probes. This is done by including in the joint χ ² function a set of 'hyper-parameters', which are dealt with using Bayesian considerations. The resulting algorithm, which assumes uniform priors on the log of the hyper-parameters, is very simple: instead of minimizing     (where     is per data set j ) we propose to minimize     (where N _j is the number of data points per data set j ). We illustrate the method by estimating the Hubble constant H ₀ from different sets of recent cosmic microwave background (CMB) experiments (including Saskatoon, Python V, MSAM1, TOCO and Boomerang ). The approach can be generalized for combinations of cosmic probes, and for other priors on the hyper-parameters.     

Fault plane orientations of microearthquakes at Mt. Etna from the inversion of P-wave rise times

A crucial point in the analysis of tectonic earthquakes occurring in a volcanic area is the inference of the orientation of the structures along which the ruptures occur. These structures represent zones of weakness which could favor the migration of melt toward the surface and the assessment of their geometry is a fundamental step toward efficient evaluation of volcanic risk. We analyzed a high-quality dataset of 171 low-magnitude, tectonic earthquakes that occurred at Mt. Etna during the 2002–2003 eruption. We applied a recently developed technique aimed at inferring the source parameters (source size, dip and strike fault) and the intrinsic quality factor Q_p of P waves from the inversion of rise times. The technique is based on numerically calibrated relationships among the rise time of first P waves and the source parameters for a circular crack rupturing at a constant velocity. For the most of the events the directivity source effect did not allow us to constrain the fault plane orientation. For a subset of 45 events with well constrained focal mechanisms we were able to constrain the “true” fault plane orientation. The level of resolution of the fault planes was assessed through a non linear analysis based on the random deviates technique. The significance of the retrieved fault plane solutions and the fit of the assumed source model to data were assessed through a χ-square test. Most of the retrieved fault plane solutions agree with the geometrical trend of known surface faults. The inferred source parameters and Q_p are in agreement with the results of previous studies.     

Influence of Marble’s Texture on its Mechanical Behavior

This research work studied the influence of texture on the mechanical properties of crystalline rocks at the scale of the laboratory sample. The experiments were performed on a marble varying in texture, so that the study was conducted on homogeneous (entirely xenoblastic or totally granoblastic) and heterogeneous (mix of the two textures) specimens. The mechanical behavior of the homogeneous and heterogeneous samples was investigated with static and dynamic, destructive and nondestructive tests, in natural conditions, at the laboratory temperature, and at higher temperatures. The specimens were heated to 100, 200, and 300 °C, in order to examine the effect of heating temperature on the elastic modulus and P-waves velocity. As a result, the pure granoblastic marble exhibits values of the elastic modulus, P-waves velocity, and strengths, both in natural conditions and on heated specimens, lower than xenoblastic samples. Such different behavior can be explained by a higher grain boundaries porosity of the granoblastic marble. On heterogeneous samples, only the Rock Impact Hardness Number (RIHN) appears able to highlight the dependence of the mechanical properties on the rock texture. In particular, the impact strength improves with increasing the percentage of xenoblastic texture inside the specimen.     

The power of blazar jets

We estimate the power of relativistic, extragalactic jets by modelling the spectral energy distribution of a large number of blazars. We adopt a simple one-zone, homogeneous, leptonic synchrotron and inverse Compton model, taking into account seed photons originating both locally in the jet and externally. The blazars under study have an often dominant high-energy component which, if interpreted as due to inverse Compton radiation, limits the value of the magnetic field within the emission region. As a consequence, the corresponding Poynting flux cannot be energetically dominant. Also the bulk kinetic power in relativistic leptons is often smaller than the dissipated luminosity. This suggests that the typical jet should comprise an energetically dominant proton component. If there is one proton per relativistic electrons, jets radiate around 2–10 per cent of their power in high-power blazars and 3–30 per cent in less powerful BL Lacs.     

Climate forcings and climate sensitivities diagnosed from atmospheric global circulation models

Understanding the historical and future response of the global climate system to anthropogenic emissions of radiatively active atmospheric constituents has become a timely and compelling concern. At present, however, there are uncertainties in: the total radiative forcing associated with changes in the chemical composition of the atmosphere; the effective forcing applied to the climate system resulting from a (temporary) reduction via ocean-heat uptake; and the strength of the climate feedbacks that subsequently modify this forcing. Here a set of analyses derived from atmospheric general circulation model simulations are used to estimate the effective and total radiative forcing of the observed climate system due to anthropogenic emissions over the last 50 years of the twentieth century. They are also used to estimate the sensitivity of the observed climate system to these emissions, as well as the expected change in global surface temperatures once the climate system returns to radiative equilibrium. Results indicate that estimates of the effective radiative forcing and total radiative forcing associated with historical anthropogenic emissions differ across models. In addition estimates of the historical sensitivity of the climate to these emissions differ across models. However, results suggest that the variations in climate sensitivity and total climate forcing are not independent, and that the two vary inversely with respect to one another. As such, expected equilibrium temperature changes, which are given by the product of the total radiative forcing and the climate sensitivity, are relatively constant between models, particularly in comparison to results in which the total radiative forcing is assumed constant. Implications of these results for projected future climate forcings and subsequent responses are also discussed.     

X-ray spectra produced by a hot plasma containing cold clouds

We compute the hard X-ray spectra from a hot plasma pervaded by small cold dense clouds. The main cooling mechanism of the plasma is Compton cooling by the soft thermal emission from the clouds. We compute numerically the equilibrium temperature of the plasma together with the escaping spectrum. The spectrum depends mainly on the amount of cold clouds filling the hot phase. The clouds covering factor is constrained to be low in order to produce spectra similar to those observed in Seyfert galaxies and X-ray binaries, implying that an external reflector is required in order to reproduce the full range of observed reflection amplitudes. We also derive analytical estimates for the X-ray spectral slope and reflection amplitude using an escape probability formalism.     

Analysis of two-decade meteorological and air quality trends in Rome (Italy)

Theoretical and Applied Climatology - The extreme temperature events are a concern in recent years due to climate variability particularly in India as there is an increase in the temperature...     

On the Lagrangian and Eulerian Time Scales of Turbulence Within a Two-Dimensional Array of Obstacles

Boundary-Layer Meteorology - Fields of Lagrangian ( $$T^{L}$$ ) and Eulerian ( $$T^{E}$$ ) time scales of the turbulence within a regular array of two-dimensional obstacles of unit aspect ratio...