377 research outputs found
On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg II k
line at 2796.34 A. The work is based on a selection of 230 stars observed by
both the IUE and HIPPARCOS satellites, covering a wide range of spectral type
and absolute visual magnitudes. The Wilson-Bappu relationship here provided is
considered to represent an improvement over previous recent results for the
considerably larger data sample used as well as for a proper consideration of
the measurement errors. No evidence has been found for a possible dependence of
the WB effect on stellar metallicity and effective temperature.Comment: 8 pages, 8 figures Accepted for publication on A&
A study of the Mg II 2796.34 A emission line in late--type normal, and RS CVn stars
We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.Comment: 10 pages, 7 figures, latex, to be published in A&
Stochastic simulation of destruction processes in self-irradiated materials
Self-irradiation damages resulting from fission processes are common
phenomena observed in nuclear fuel containing (NFC) materials. Numerous
-decays lead to local structure transformations in NFC materials. The
damages appearing due to the impacts of heavy nuclear recoils in the subsurface
layer can cause detachments of material particles. Such a behaviour is similar
to sputtering processes observed during a bombardment of the material surface
by a flux of energetic particles. However, in the NFC material, the impacts are
initiated from the bulk. In this work we propose a two-dimensional mesoscopic
model to perform a stochastic simulation of the destruction processes occurring
in a subsurface region of NFC material. We describe the erosion of the material
surface, the evolution of its roughness and predict the detachment of the
material particles. Size distributions of the emitted particles are obtained in
this study. The simulation results of the model are in a qualitative agreement
with the size histogram of particles produced from the material containing
lava-like fuel formed during the Chernobyl nuclear power plant disaster.Comment: 11 pages, 8 figure
UN SISTEMA DI ACQUISIZIONE E CONDIVISIONE DEI DATI SISMICI TRA L’INTERNATIONAL MONITORING SYSTEM DEL CTBTO E LA RETE NAZIONALE CENTRALIZZATA DELL’INGV
UN SISTEMA DI ACQUISIZIONE E CONDIVISIONE DEI DATI SISMICI TRA L’INTERNATIONAL MONITORING SYSTEM DEL CTBTO
E LA RETE NAZIONALE CENTRALIZZATA DELL’ING
Entropy: From Black Holes to Ordinary Systems
Several results of black holes thermodynamics can be considered as firmly
founded and formulated in a very general manner. From this starting point we
analyse in which way these results may give us the opportunity to gain a better
understanding in the thermodynamics of ordinary systems for which a
pre-relativistic description is sufficient. First, we investigated the
possibility to introduce an alternative definition of the entropy basically
related to a local definition of the order in a spacetime model rather than a
counting of microstates. We show that such an alternative approach exists and
leads to the traditional results provided an equilibrium condition is assumed.
This condition introduces a relation between a time interval and the reverse of
the temperature. We show that such a relation extensively used in the black
hole theory, mainly as a mathematical trick, has a very general and physical
meaning here; in particular its derivation is not related to the existence of a
canonical density matrix. Our dynamical approach of thermodynamic equilibrium
allows us to establish a relation between action and entropy and we show that
an identical relation exists in the case of black holes. The derivation of such
a relation seems impossible in the Gibbs ensemble approach of statistical
thermodynamics. From these results we suggest that the definition of entropy in
terms of order in spacetime should be more general that the Boltzmann one based
on a counting of microstates. Finally we point out that these results are
obtained by reversing the traditional route going from the Schr\"{o}dinger
equation to statistical thermodynamics
Incomplete normalization of probability on multifractals
This work is an extension of the incomplete probability theory from the
simple case of monofractals previously studied to the more general case of
multifractals which can occur in the phase space without equiprobable
partition.Comment: 10 pages, to appear in Physica A (2007
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