11,522 research outputs found
Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC10001893
KIC10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the
Kepler spacecraft in its primary mission. In addition to tens of pulsation
frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks
at very low frequencies, which is too low to be explained in terms of g modes.
The most convincing explanation is that we are seeing the orbital modulation of
three Earth-size planets (or planetary remnants) in very tight orbits, which
are illuminated by the strong stellar radiation. The orbital periods are
P1=5.273, P2=7.807, and P3=19.48 hours, and the period ratios P2/P1=1.481 and
P3/P2=2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of
the main pulsation modes of the star at 210.68 {\mu}Hz corresponds to the third
harmonic of the orbital frequency of the inner planet, suggesting that we see,
for the first time in an sdB star, g-mode pulsations tidally excited by a
planetary companion. The extreme planetary system that emerges from the Kepler
data is very similar to the recent discovery of two Earth-size planets orbiting
the sdB pulsator KIC05807616 (Charpinet et al. 2011a).Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Fractional Hamiltonian analysis of higher order derivatives systems
The fractional Hamiltonian analysis of 1+1 dimensional field theory is
investigated and the fractional Ostrogradski's formulation is obtained. The
fractional path integral of both simple harmonic oscillator with an
acceleration-squares part and a damped oscillator are analyzed. The classical
results are obtained when fractional derivatives are replaced with the integer
order derivatives.Comment: 13 page
Evidence for Halo Kinematics among Cool Carbon-Rich Dwarfs
This paper reports preliminary yet compelling kinematical inferences for N ~
600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of
the Galactic halo. The study uses a spectroscopically and non-kinematically
selected sample of stars from the SDSS, and cross-correlates these data with
three proper motion catalogs based on Gaia DR1 astrometry to generate estimates
of their 3-D space velocities. The fraction of stars with halo-like kinematics
is roughly 30% for distances based on a limited number of parallax
measurements, with the remainder dominated by the thick disk, but close to 60%
of the sample lie below an old, metal-poor disk isochrone in reduced proper
motion. An ancient population is consistent with an extrinsic origin for C/O >1
in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts
lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux
from younger white dwarf companions. For an initial stellar mass function that
favors low-mass stars as in the Galactic disk, the dC stars are likely to be
the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.Comment: 7 pages, 1 table, and 3 figures. Accepted to MNRA
Coarsening Dynamics of a One-Dimensional Driven Cahn-Hilliard System
We study the one-dimensional Cahn-Hilliard equation with an additional
driving term representing, say, the effect of gravity. We find that the driving
field has an asymmetric effect on the solution for a single stationary
domain wall (or `kink'), the direction of the field determining whether the
analytic solutions found by Leung [J.Stat.Phys.{\bf 61}, 345 (1990)] are
unique. The dynamics of a kink-antikink pair (`bubble') is then studied. The
behaviour of a bubble is dependent on the relative sizes of a characteristic
length scale , where is the driving field, and the separation, ,
of the interfaces. For the velocities of the interfaces are
negligible, while in the opposite limit a travelling-wave solution is found
with a velocity . For this latter case () a set of
reduced equations, describing the evolution of the domain lengths, is obtained
for a system with a large number of interfaces, and implies a characteristic
length scale growing as . Numerical results for the domain-size
distribution and structure factor confirm this behavior, and show that the
system exhibits dynamical scaling from very early times.Comment: 20 pages, revtex, 10 figures, submitted to Phys. Rev.
A case of pediatric paraparesis secondary to an idiopathic acute transverse myelitis
Introduction: Acute transverse myelitis (ATM) refers to a frequently idiopathic, segmental spinal cord inflammation. It is a rare condition, in particular in children, and not previously reported in a family retinitis pigmentosa (RP) clinical setting. Case Report: An 11-year-old
previously healthy girl, with a family history of RP, presented with a subacute flaccid paraparesis, with bilateral, up to the fourth dorsal level, mixed sensory hypoesthesia and autonomic dysfunction. Brain and spinal cord magnetic resonance imaging (MRI) showed
an extensive, T2-hyperintense, non-contrast
enhancing lesion from the second to fifth
dorsal levels. Cerebrospinal fluid (CSF) and lab studies were normal, as the ophthalmologic observation. Treated with high-dose corticosteroids and intensive physical therapy,a significant recovery could be seen. Conclusion:Early pharmacological and physical treatment
is fundamental and may indeed change the
prognosis of this disease ATM. The family history of RP, although probably incidental, brings nevertheless the issue of a possible etiological contribution, or pathologic common pathways
Anomalous Roughening in Experiments of Interfaces in Hele-Shaw Flows with Strong Quenched Disorder
We report experimental evidences of anomalous kinetic roughening in the
stable displacement of an oil-air interface in a Hele-Shaw cell with strong
quenched disorder. The disorder consists on a random modulation of the gap
spacing transverse to the growth direction (tracks). We have performed
experiments varying average interface velocity and gap spacing, and measured
the scaling exponents. We have obtained beta=0.50, beta*=0.25, alpha=1.0,
alpha_l=0.5, and z=2. When there is no fluid injection, the interface is driven
solely by capillary forces, and a higher value of beta around beta=0.65 is
measured. The presence of multiscaling and the particular morphology of the
interfaces, characterized by high slopes that follow a L\'evy distribution,
confirms the existence of anomalous scaling. From a detailed study of the
motion of the oil--air interface we show that the anomaly is a consequence of
different local velocities over tracks plus the coupling in the motion between
neighboring tracks. The anomaly disappears at high interface velocities, weak
capillary forces, or when the disorder is not sufficiently persistent in the
growth direction. We have also observed the absence of scaling when the
disorder is very strong or when a regular modulation of the gap spacing is
introduced.Comment: 14 pages, 17 figure
Análise quantitativa e comparativa do teor de minerais em vinhos do Vale do Submédio São Francisco (VSSF).
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