7,166 research outputs found
Strong evidences for a nonextensive behavior of the rotation period in Open Clusters
Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices derived from the modified Kawaler's
parametrization, and , obtained from rotational velocity distribution. These
's are related through a heuristic single relation given by , where is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression , where
and denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between and cluster age . Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index .Comment: 6 pages and 2 figures, accepted to EPL on October 17, 201
The Distance to the M31 Globular Cluster System
The distance to the centroid of the M31 globular cluster system is determined
by fitting theoretical isochrones to the observed red-giant branches of
fourteen globular clusters in M31. The mean true distance modulus of the M31
globular clusters is found to be 24.47 +/- 0.07 mag. This is consistent with
distance modulii for M31 that have been obtained using other distance
indicators.Comment: 11 pages, 2 postscript figures, uses aaspp4.sty, to be published in
the May 1998 Astronomical Journa
A nonextensive insight to the stellar initial mass function
the present paper, we propose that the stellar initial mass distributions as
known as IMF are best fitted by -Weibulls that emerge within nonextensive
statistical mechanics. As a result, we show that the Salpeter's slope of
2.35 is replaced when a -Weibull distribution is used. Our results
point out that the nonextensive entropic index represents a new approach
for understanding the process of the star-forming and evolution of massive
stars.Comment: 5 pages, 2 figures, Accepted to EP
The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics
We prove that the distributional limit of the normalised number of returns to
small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical
systems is compound Poisson. The returns to small balls around a fixed point in
the phase space correspond to the occurrence of rare events, or exceedances of
high thresholds, so that there is a connection between the laws of Return Times
Statistics and Extreme Value Laws. The fact that the fixed point in the phase
space is a repelling periodic point implies that there is a tendency for the
exceedances to appear in clusters whose average sizes is given by the Extremal
Index, which depends on the expansion of the system at the periodic point.
We recall that for generic points, the exceedances, in the limit, are
singular and occur at Poisson times. However, around periodic points, the
picture is different: the respective point processes of exceedances converge to
a compound Poisson process, so instead of single exceedances, we have entire
clusters of exceedances occurring at Poisson times with a geometric
distribution ruling its multiplicity.
The systems to which our results apply include: general piecewise expanding
maps of the interval (Rychlik maps), maps with indifferent fixed points
(Manneville-Pomeau maps) and Benedicks-Carleson quadratic maps.Comment: To appear in Communications in Mathematical Physic
Predictive value of pulse pressure variation for fluid responsiveness after maneuver to change tidal volume in patients with protective ventilatory strategy
Determining Heavy Mass Parameters in Supersymmetric SO(10) Models
Extrapolations of soft scalar mass parameters in supersymmetric theories can
be used to explore elements of the physics scenario near the grand unification
scale. We investigate the potential of this method in the lepton sector of
SO(10) which incorporates right-handed neutrino superfields. The method is
exemplified in two models by exploring limits on the precision that can be
expected from coherent LHC and e+e- collider analyses in the reconstruction of
the fundamental scalar mass parameters at the unification scale and of the
D-terms related to the breaking of grand unification symmetries. In addition,
the mass of the third-generation right-handed neutrino can be estimated in
seesaw scenarios. Even though the models are simplified and not intended to
account for all aspects of a final comprehensive SO(10) theory, they provide
nevertheless a valid base for identifying essential elements that can be
inferred on the fundamental high-scale theory from high-energy experiments.Comment: 26 pp LaTeX; version published in Phys. Rev.
Material orgânico de superfície em solos florestais sob diferentes paisagens da Mata Atlântica.
O bioma Mata Atlântica é considerado um ?hotspot? por conter uma alta diversidade de espécies e um alto grau de endemismo. Além de abrigar grande parte da população brasileira, este bioma encontra-se altamente fragmentado e é considerado um bioma estratégico para a conservação. Nesse sentido, a utilização de ferramentas simples para a avaliação dos processos geobioquímicos, como a serapilheira (Formas de Humus) parecem interessantes. Portanto, o trabalho tem como alvo avaliar e quantificar as Formas de Humus em gradiente altitudinal. Para esse fim, foram escolhidos 3 municípios da paisagem da Mata Atlântica em diferentes altitudes, e avaliados o material orgânico de superfície de dois sistemas (Natural e Plantios de Eucalipto) em cada município. Os resultados mostram uma clara diferença entre os estoques da serapilheira com a altitude, sendo entre os sistemas naturais, os do município de Friburgo com os maiores estoques. Mudanças nos estoques de serapilheira, como quantidade de galhos, dos plantios de Eucalipto parecem responder positivamente a estrutura e a idade dos sistemas. Os resultados também mostram associações positivas entre quantidade de material fresco e quantidade de raízes finas. Por fim, o estudo com serapilheira, a luz das Formas de Humus, pode ajudar a diagnosticar e classificar sistemas
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