10,589 research outputs found
A Gamma Doradus Candidate In Eclipsing Binary BD And?
The BVR photometric light curves of the eclipsing binary BD And were obtained
in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the
photometric solutions were derived. The results show that BD And is a detached
binary system, whose components have a little temperature difference of about
40 K. By analyzing photometric available light minimum times, we also derived
an update ephemeris and found for the first time a possible periodic
oscillation with an amplitude of 0.011 days and a period of 9.6 years. The
results indicate that the periodic oscillation could be caused by a third
component physically attached to the eclipsing binary. After removing the light
variations due to the eclipses and proximity effects, the light-curve
distortions are further explained by the pulsation of the primary component
with a dominant period of 1 day. In accordance with the position of the primary
component on the Hertzsprung-Russell diagram and its pulsation period, the
primary component of BD And could be an excellent gamma Doradus candidate. It
is rarely phenomenon that a component of the eclipsing binary system is a gamma
Doradus variable.Comment: 34 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1112.1916 by other authors without attributio
Absolute Properties of An Overcontact Binary HH Boo
We obtained multi-colour light curves of HH Boo. We analysed the orbital
period variation of the system. The analysis indicated that there is possible
mass transfer from the second component to the primary or mass loss with
-5.04x10-7 Msun per year. Re-analysing the available radial velocity curve, we
analysed the light curves. The inclination (i) of the system was found to be
69.71(0.16) deg, while the semi-major axis (a) was computed as 2.246(0.064)
Rsun. The mass of the primary component was found to be 0.92(0.08) Msun, while
it was obtained as 0.58(0.06) Msun for the secondary component. The radius of
the primary component was computed as 0.98(0.03) Rsun, while it was computed as
0.80(0.02) Rsun for the secondary component. We demonstrated that HH Boo should
be a member of the A-type subclass of W UMa binaries.Comment: 20 pages, 5 figures, 4 table
Ballistic conductance of magnetic Co and Ni nanowires with ultrasoft pseudo-potentials
The scattering-based approach for calculating the ballistic conductance of
open quantum systems is generalized to deal with magnetic transition metals as
described by ultrasoft pseudo-potentials. As an application we present
quantum-mechanical conductance calculations for monatomic Co and Ni nanowires
with a magnetization reversal. We find that in both Co and Ni nanowires, at the
Fermi energy, the conductance of electrons is blocked by a magnetization
reversal, while the states (one per spin) are perfectly transmitted.
electrons have a non-vanishing transmission in a small energy window below the
Fermi level. Here, transmission is larger in Ni than in Co.Comment: 9 pages, 6 figures, to appear in PR
Boundary Asymptotic Analysis for an Incompressible Viscous Flow: Navier Wall Laws
We consider a new way of establishing Navier wall laws. Considering a bounded
domain of R N , N=2,3, surrounded by a thin layer ,
along a part 2 of its boundary , we consider a
Navier-Stokes flow in with
Reynolds' number of order 1/ in . Using
-convergence arguments, we describe the asymptotic behaviour of the
solution of this problem and get a general Navier law involving a matrix of
Borel measures having the same support contained in the interface 2. We
then consider two special cases where we characterize this matrix of measures.
As a further application, we consider an optimal control problem within this
context
Phonons Softening in Tip-Stretched Monatomic Nanowires
It has been shown in recent experiments that electronic transport through a
gold monatomic nanowire is dissipative above a threshold voltage due to
excitation of phonons via the electron-phonon interaction. We address that data
by computing, via density functional theory, the zone boundary longitudinal
phonon frequency of a perfect monatomic nanowire during its mechanical
elongation. The theoretical frequency that we find for an ideally strained
nanowire is not compatible with experiment if a uniformly distributed stretch
is assumed. With the help of a semi-empirical Au-Au potential, we model the
realistic nanowire stretching as exerted by two tips. In this model we see that
strain tends to concentrate in the junctions, so that the mean strain of the
nanowire is roughly one half of the ideal value. With this reduced strain, the
calculated phonon softening is in much better agreement with experiment.Comment: 9 pages,3 figures, Surface Science, in pres
Evolution of the ISM of Starburst galaxies: the SN heating efficiency
The interstellar medium heated by SN explosions may acquire an expansion
velocity larger than the escape velocity and leave the galaxy through a
supersonic wind. SN ejecta are transported out of the galaxies by such winds
which thus affect the chemical evolution of the galaxies. The effectiveness of
the processes mentioned above depends on the heating efficiency (HE) of the
SNe, that is a matter of debate. We have constructed a simple semi-analytic
model, considering the essential ingredients of a SB environment which is able
to qualitatively trace the thermalisation history of the ISM in a SB region and
determine the HE evolution. We find that, as long as the mass-loss rate of the
clouds remains larger than the rate at which the SNRs interact one with each
other, the SN heating efficiency remains very small, as radiative cooling of
the gas dominates. We conclude that the HE value has a time-dependent trend
that is sensitive to the initial conditions of the system.Comment: 17 pages, 18 figures, A&A accepte
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