5,551 research outputs found
Semi-Teleparallel Theories of Gravitation
A class of theories of gravitation that naturally incorporates preferred
frames of reference is presented. The underlying space-time geometry consists
of a partial parallelization of space-time and has properties of Riemann-Cartan
as well as teleparallel geometry. Within this geometry, the kinematic
quantities of preferred frames are associated with torsion fields. Using a
variational method, it is shown in which way action functionals for this
geometry can be constructed. For a special action the field equations are
derived and the coupling to spinor fields is discussed.Comment: 14 pages, LaTe
Determining the Physical Properties of the B Stars I. Methodology and First Results
We describe a new approach to fitting the UV-to-optical spectra of B stars to
model atmospheres and present initial results. Using a sample of lightly
reddened stars, we demonstrate that the Kurucz model atmospheres can produce
excellent fits to either combined low dispersion IUE and optical photometry or
HST FOS spectrophotometry, as long as the following conditions are fulfilled:
1) an extended grid of Kurucz models is employed,
2) the IUE NEWSIPS data are placed on the FOS absolute flux system using the
Massa & Fitzpatrick (1999) transformation, and
3) all of the model parameters and the effects of interstellar extinction are
solved for simultaneously.
When these steps are taken, the temperatures, gravities, abundances and
microturbulence velocities of lightly reddened B0-A0 V stars are determined to
high precision. We also demonstrate that the same procedure can be used to fit
the energy distributions of stars which are reddened by any UV extinction curve
which can be expressed by the Fitzpatrick & Massa (1990) parameterization
scheme.
We present an initial set of results and verify our approach through
comparisons with angular diameter measurements and the parameters derived for
an eclipsing B star binary. We demonstrate that the metallicity derived from
the ATLAS 9 fits to main sequence B stars is essentially the Fe abundance. We
find that a near zero microturbulence velocity provides the best-fit to all but
the hottest or most luminous stars (where it may become a surrogate for
atmospheric expansion), and that the use of white dwarfs to calibrate UV
spectrophotometry is valid.Comment: 17 pages, including 2 pages of Tables and 6 pages of Figures.
Astrophysical Jounral, in pres
The waveform similarity approach to identify dependent events in instrumental seismic catalogues
In this paper, waveform similarity analysis is adapted and implemented in a declustering
procedure to identify foreshocks and aftershocks, to obtain instrumental catalogues that are
cleaned of dependent events and to perform an independent check of the results of traditional
declustering techniques.
Unlike other traditional declustering methods (i.e. windowing techniques), the application
of cross-correlation analysis allows definition of groups of dependent events (multiplets) characterized
by similar location, fault mechanism and propagation pattern. In this way the chain of
intervening related events is led by the seismogenetic features of earthquakes. Furthermore, a
time-selection criterion is used to define time-independent seismic episodes eventually joined
(on the basis of waveform similarity) into a single multiplet. The results, obtained applying
our procedure to a test data set, show that the declustered catalogue is drawn by the Poisson
distribution with a degree of confidence higher than using the Gardner and Knopoff method.
The declustered catalogues, applying these two approaches, are similar with respect to the
frequency–magnitude distribution and the number of earthquakes.
Nevertheless, the application of our approach leads to declustered catalogues properly related
to the seismotectonic background and the reology of the investigated area and the success of
the procedure is ensured by the independence of the results on estimated location errors of the
events collected in the raw catalogue
The Mw 6.3, 2009 L’Aquila earthquake: source, path and site effects from spectral analysis of strong motion data
The strong motion data of 2009 April 6 L’Aquila (Central Italy) earthquake (Mw = 6.3) and of
12 aftershocks (4.1 ≤ Mw ≤ 5.6) recorded by 56 stations of the Italian strong motion network
are spectrally analysed to estimate the source parameters, the seismic attenuation, and the site
amplification effects. The obtained source spectra for S wave have stress drop values ranging
from 2.4 to 16.8 MPa, being the stress drop of the main shock equal to 9.2 MPa. The spectral
curves describing the attenuation with distance show the presence of shoulders and bumps,
mainly around 50 and 150 km, as consequence of significant reflected and refracted arrivals
from crustal interfaces. The attenuation in the first 50 km is well described by a quality factor
equal to Q( f ) = 59 f 0.56 obtained by fixing the geometrical spreading exponent to 1. Finally,
the horizontal-to-vertical spectral ratio provides unreliable estimates of local site effects for
those stations showing large amplifications over the vertical component of motion
Radar array diagnosis from undersampled data using a compressed sensing/sparse recovery technique
A Compressed Sensing/Sparse Recovery approach is adopted in this paper for the accurate diagnosis of fault array elements from undersampled data. Experimental validations on a slotted waveguide test array are discussed to demonstrate the effectiveness of the proposed procedure in the failures retrieval from a small set of measurements with respect to the number of radiating elements. Due to the sparsity feature of the proposed formulation, the method is particularly appealing for the diagnostics of large arrays, typically adopted for radar applications
Cherenkov Flashes and Fluorescence Flares on Telescopes: New lights on UHECR Spectroscopy while unveiling Neutrinos Astronomy
Cherenkov Telescopes (as Magic, Hess and Veritas), while pointing
horizontally should reveal also the fluorescence flare tails of nearby
down-going air-showers. Such air-showers, born at higher (tens km) altitudes,
are growing and extending up to lowest atmospheres (EeVs) or up to higher (few
km) quotas (PeVs). Viceversa, as it has been foreseen and only recently
observed, the opposite takes place. Fluorescence Telescopes made for UHECR
detection may be blazed by inclined Cherenkov lights. The geomagnetic splitting
may tag the energy as well as the inclined shower footprint as seen in a recent
peculiar event in AUGER. Additional stereoscopic detection may define the event
origination distance and its consequent primary composition, extending our
understanding on UHECR composition, while unveling a novel tau Neutrino
Astronomy.Comment: 5 pages, 5 figures, Preprint submitted to Nuclear Instruments and
Methods A. Only editorial format chang
Comparison between empirical predictive equations calibrated at global and national scale and the Italian strong-motion data
In Italy in the last years many ground motion prediction equations (hereinafter GMPEs) were calibrated both at national and regional scale using weak and strong motion data recorded in the last 30 years by several networks. Moreover many of the Italian strongest earthquakes were included in global datasets in order to calibrate GMPEs suitable to predict ground-motion at very large scale. In the last decade the Sabetta and Pugliese (1996) relationships represented a reference for the ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by RAN (Italian Accelerometric Network), and more recently by other regional networks (e.g. RAIS, Strong motion network of Northern Italy), are collected in ITACA (ITalian ACcelerometric Archive). Considering Italian strong-motion data with Mw  4.0 and distance (Joyner-Boore or epicentral) up to 100 km, new GMPEs were developed by Bindi et al. (2009), aimed at replacing the older Italian relationships. The occurrence of the recent 23rd December 2008, Mw 5.4, Parma (Northern Italy) earthquake and the 6th April 2009, Mw 6.3, L’Aquila earthquake, allowed to upgrade the ITACA data set and gave us the possibility to validate the predictive capability of many GMPEs, developed using Italian, European and global data sets. The results are presented in terms of quality of performance (fit between recorded and predicted values) using the maximum likelihood approach as explained in Spudich et al. (1999). Considering the strong-motion data recorded during the L’Aquila sequence the considered GMPEs, in average, overestimate the observed data, showing a dependence of the residuals with distance in particular at higher frequencies. An improvement of fit is obtained comparing all Italian strong-motion data included in ITACA with the European GMPEs calibrated by Akkar and Bommer (2007 a,b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies
Wide Band Permittivity Measurements of Palm (Phoenix canariensis) and Rhynchophorus ferrugineus (Coleoptera: Curculionidae) for RF Pest Control
Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)
We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand
2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet
at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo
2.3m optical spectroscopy, and analysed using a spherical, non-LTE,
line-blanketed code. Our study reveals exceptional stellar parameters:
T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt
a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and
O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination
line studies. We confirm that Sand 2 is more chemically enriched in carbon than
LMC WC stars, and is expected to undergo a supernova explosion within the next
50,000 yr.Comment: 17 pages, 4 figures, AASTeX preprint format. This paper will appear
in a special issue of ApJ Letters devoted to the first scientific results
from the FUSE missio
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