On the evolution of the cosmic supernova rates     

Piero Madau  Massimo Della Valle  & Nino Panagia 《Monthly notices of the Royal Astronomical Society》1998,297(1):L17-L22

The Galactic radio-emitting X-ray binary Cygnus X-3 is known to be a source of large-scale radio jets associated with periods of intense radio flaring. These jets have been found to have an expansion velocity of ∼0.3 c and are believed (on kinematic grounds) to lie close to the plane of the sky. We present new observations of Cygnus X-3 using the VLBA at 15 GHz. These observations, which included the detection of two small flares, show an additional kind of behaviour with apparent superluminal expansion along both major and minor axes. Evidence for superluminal activity has been found in a number of X-ray binary systems such as GRS 1915+105 and GRO J1655−40 with their superluminal radio jets. Apparently similar morphologies of the Galactic and extragalactic jet sources have led to the X-ray binaries being described as 'micro-quasars'. The superluminal expansion seen in our results appears to be different in nature from these other two sources, and a number of mechanisms are presented and discussed.  相似文献   

On the clustering phase transition in self-gravitating N-body systems     

Monica Cerruti-Sola  Piero Cipriani  Marco Pettini 《Monthly notices of the Royal Astronomical Society》2001,328(1):339-352

The thermodynamic behaviour of self-gravitating N -body systems has been worked out by borrowing a standard method from molecular dynamics. The link between dynamics and thermodynamics is made in the microcanonical ensemble of statistical mechanics. Through the computation of basic thermodynamic observables and of the equation of state in the     plane, the clustering phase transition appears to be of the second-order type. The dynamical–microcanonical averages are compared with their corresponding canonical ensemble averages, obtained through standard Monte Carlo computations. The latter seem to have completely lost any information about the phase transition. Finally, our results – obtained in a 'microscopic' framework – are compared with some existing theoretical predictions – obtained in a 'macroscopic' (thermodynamic) framework: qualitative and quantitative agreement is found, with an interesting exception.  相似文献   

Evidence forr-process elements in HR 8911     

Piero Galeotti 《Astrophysics and Space Science》1974,31(1):193-201

The results of a spectral analysis of some high-dispersion plates of the peculiar star HR 8911 ( Piscium) are reported, and the observational evidence for somer-only elements in the atmosphere of this object is discussed.Many uranium lines were observed, so that the presence of this element may be considered certain. The presence of uranium and of some elements with mass number around theA195 peak gives strong evidence for anr-process mechanism which originated the elemental peculiarities in this object. The implications about the origin of peculiar stars are discussed on the ground of an explosive origin of ther-process elements observed in this star. Finally, the uncommon element holmium seems very likely to be present in the atmosphere of this peculiar star.  相似文献   

Globular clusters, satellite galaxies and stellar haloes from early dark matter peaks   总被引：1，自引：0，他引：1  

Ben Moore  Juerg Diemand  Piero Madau  Marcel Zemp  Joachim Stadel 《Monthly notices of the Royal Astronomical Society》2006,368(2):563-570

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Aerogel keystones: Extraction of complete hypervelocity impact events from aerogel collectors     

Andrew J. Westphal  Christopher Snead  Anna Butterworth  Giles A. Graham  John P. Bradley  Sa&#x;a Bajt  Patrick G. Grant  Graham Bench  Sean Brennan  Piero Pianetta 《Meteoritics & planetary science》2004,39(8):1375-1386

Abstract— In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon and the first samples of contemporary interstellar dust ever collected. Although sophisticated laboratory instruments exist for the analysis of Stardust samples, techniques for the recovery of particles and particle residues from aerogel collectors remain primitive. Here, we describe our recent progress in developing techniques for extracting small volumes of aerogel, which we have called “keystones,” which completely contain particle impacts but minimize the damage to the surrounding aerogel collector. These keystones can be fixed to custom‐designed micromachined silicon fixtures (so called “microforklifts”). In this configuration, the samples are self‐supporting, which can be advantageous in situations where interference from a supporting substrate is undesirable. The keystones may also be extracted and placed onto a substrate without a fixture. We have also demonstrated the capability of homologously crushing these unmounted keystones for analysis techniques that demand flat samples.  相似文献   

Observations and box model analysis of radon-222 in the atmospheric surface layer at L’Aquila,Italy: March 2009 case study   总被引：1，自引：1，他引：0  

Giovanni Pitari  Eleonora Coppari  Natalia De Luca  Piero Di Carlo 《Environmental Earth Sciences》2014,71(5):2353-2359

Two years of radon-222 observations collected at L’Aquila (Italy) in the atmospheric surface layer during 2004–2006 were analyzed in correlation with meteorological data and other atmospheric tracers. A box model was developed to better understand the mechanisms of diurnal and seasonal variability of the tracer and to indirectly assess the magnitude of the monthly averaged radon soil flux in the L’Aquila measurement site. The model was successfully validated with measurements, with a 0.8 average correlation coefficient between hourly values for the whole period of radon observations. Measurements taken during March 2009 were analyzed to find possible signs of perturbation due to the ongoing seismic activity that would have reached its peak on the 6 April 2009 destructive earthquake. Contrary to the professed (and unpublished) dramatic increases of radon activity unofficially announced to the inhabitants at that time, the study presented here shows that no radon activity increase took place in L’Aquila with respect to a previous ‘seismically unperturbed’ year (same month with similar meteorological conditions), but that an average 30 % decrease was experienced. This conclusion is reached from a direct comparison of observed data and also as a result of the previously validated radon box model constrained by actual meteorological data, from which an indirect estimate of a 17 % reduction of the radon soil flux is obtained.  相似文献   

Analytical prediction of ultimate moment and curvature of RC rectangular sections in compression     

Piero Colajanni  Marinella Fossetti  Maurizio Papia 《Bulletin of Earthquake Engineering》2013,11(6):2055-2078

This paper presents closed form expressions linking the ultimate bearing capacity to the ultimate curvature of rectangular RC sections subjected to axial load and bending moment acting in one of the two symmetry planes of the section. With respect to possible simplified formulations the following effects are also considered: confinement of the concrete, hardening of the longitudinal reinforcement, and presence of reinforcing bars distributed orthogonally to the neutral axis. The formulation is proposed in dimensional terms after a preliminary definition of the geometrical and mechanical parameters governing the structural response of the class of sections considered. The analytical expressions derived using the proposed approach also allow one to determine the compression level that makes the ultimate bending moment maximum as well as to evaluate the curvature corresponding to the first yielding of the principal reinforcement in tension. Comparing this value of curvature with the ultimate one, an approximate estimation of the available ductility of curvature of the section can be made. The analytical procedure is validated by comparing the results with those obtained using a typical numerical approach. Some experimental results are also considered.  相似文献   

Data reconstruction and homogenization for reducing uncertainties in high-resolution climate analysis in Alpine regions     

Emanuele Eccel  Piero Cau  Roberto Ranzi 《Theoretical and Applied Climatology》2012,110(3):345-358

Analysis of climatic series needs pre-processing to attain spatial- and time-consistent homogeneity. The latter, in high-resolution investigations, can rely on the strong correlations among series, which in turn requires a strict fulfilment of the quality standard in terms of completeness. Fifty-nine daily precipitation and temperature series of 50?years from Trentino, northern Italy, were pre-processed for climatic analysis. This study describes: (1) the preliminary gap-filling protocol for daily series, based on geostatistical correlations on both horizontal and vertical domains; (2) an algorithm to reduce inhomogeneity owing to the systematic snowfall underestimation of rain gauges; and (3) the processing protocol to take into account any source of undocumented inhomogeneity in series. This was performed by application of the t test and F-test of R code RHtestV2. This pre-processing shows straightforward results; correction of snowfall measurements re-evaluates attribution of patterns of altitudinal trends in time trends; homogenization increases the strength of the climatic signal and reduces the scattering of time trends, assessed over a few decades, of a factor of 2.  相似文献   

Numerical modelling of centrifuge tests on tunnel–soil systems     

Glenda Abate  Maria Rossella Massimino  Michele Maugeri 《Bulletin of Earthquake Engineering》2015,13(7):1927-1951

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Erratum to: Influence of frequency content and amplitude of input motion in DSSI investigated by shaking table tests     

Giovanni Biondi  Maria Rossella Massimino  Michele Maugeri 《Bulletin of Earthquake Engineering》2015,13(6):1871-1871

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