890 research outputs found
Electromagnetic Modes in Deformed Nuclei
A strength function method is adopted to describe a coupling between electric
and magnetic modes of different multipolarity. The collective vibrations are
analysed for a separable residual interaction in the framework of the
random-phase approximation. The coupling between and giant resonances
is considered as an illustrative example.Comment: 7 pages (latex), 1 figure (ps file), an invited talk at the workshop
"Symmetries and Spin - Praha 98", to be published in Czech.J.Phys., 199
Hydrodynamic simulations of irradiated secondaries in dwarf novae
We investigate numerically the surface flow on the secondary star during
outbursts. We use a simple model for the irradiation and the geometry of the
secondary star: the irradiation temperature is treated as a free parameter and
the secondary is replaced by a spherical star with a space-dependent Coriolis
force that mimics the effect of the Roche geometry. The Euler equations are
solved in spherical coordinates with the TVD-MacCormack scheme. We show that
the Coriolis force leads to the formation of a circulation flow from high
latitude region to the close vicinity of the point. However no heat can
be efficiently transported to the region due to the rapid radiative
cooling of the hot material as it enters the equatorial belt shadowed from
irradiation. Under the assumption of hydrostatic equilibrium, the Coriolis
force could lead to a moderate increase of the mass transfer rate by pushing
the gas in the vertical direction at the point, but only during the
initial phases of the outburst (about 15 -- 20 orbital periods). We conclude
that the Coriolis force does not prevent a flow from the heated regions of the
secondary towards the region, at least during the initial phase of an
outburst, but the resulting increase of the mass transfer rate is moderate, and
it is unlikely to be able to account for the duration of long outbursts.Comment: 11 pages, 11 figures, accepted for publication in A&
Permutation Entropy and Signal Energy Increase the Accuracy of Neuropathic Change Detection in Needle EMG
Background and Objective. Needle electromyography can be used to detect the number of changes and morphological changes in motor unit potentials of patients with axonal neuropathy. General mathematical methods of pattern recognition and signal analysis were applied to recognize neuropathic changes. This study validates the possibility of extending and refining turns-amplitude analysis using permutation entropy and signal energy. Methods. In this study, we examined needle electromyography in 40 neuropathic individuals and 40 controls. The number of turns, amplitude between turns, signal energy, and “permutation entropy” were used as features for support vector machine classification. Results. The obtained results proved the superior classification performance of the combinations of all of the above-mentioned features compared to the combinations of fewer features. The lowest accuracy from the tested combinations of features had peak-ratio analysis. Conclusion. Using the combination of permutation entropy with signal energy, number of turns and mean amplitude in SVM classification can be used to refine the diagnosis of polyneuropathies examined by needle electromyography
Decoding of the light changes in eclipsing Wolf-Rayet binaries I. A non-classical approach to the solution of light curves
We present a technique to determine the orbital and physical parameters of
eclipsing eccentric Wolf-Rayet + O-star binaries, where one eclipse is produced
by the absorption of the O-star light by the stellar wind of the W-R star. Our
method is based on the use of the empirical moments of the light curve that are
integral transforms evaluated from the observed light curves. The optical depth
along the line of sight and the limb darkening of the W-R star are modelled by
simple mathematical functions, and we derive analytical expressions for the
moments of the light curve as a function of the orbital parameters and the key
parameters of the transparency and limb-darkening functions. These analytical
expressions are then inverted in order to derive the values of the orbital
inclination, the stellar radii, the fractional luminosities, and the parameters
of the wind transparency and limb-darkening laws. The method is applied to the
SMC W-R eclipsing binary HD 5980, a remarkable object that underwent an
LBV-like event in August 1994. The analysis refers to the pre-outburst
observational data. A synthetic light curve based on the elements derived for
the system allows a quality assessment of the results obtained.Comment: Accepted for publication in Astronomy & Astrophysic
The Rossiter-McLaughlin effect and analytic radial velocity curves for transiting extrasolar planetary systems
A transiting extrasolar planet sequentially blocks off the light coming from
the different parts of the disk of the host star in a time dependent manner.
Due to the spin of the star, this produces an asymmetric distortion in the line
profiles of the stellar spectrum, leading to an apparent anomaly of the radial
velocity curves, known as the Rossiter - McLaughlin effect. Here, we derive
approximate but accurate analytic formulae for the anomaly of radial velocity
curves taking account of the stellar limb darkening. The formulae are
particularly useful in extracting information of the projected angle between
the planetary orbit axis and the stellar spin axis, \lambda, and the projected
stellar spin velocity, V sin I_s. We create mock samples for the radial curves
for the transiting extrasolar system HD209458, and demonstrate that constraints
on the spin parameters (V sin I_s, \lambda) may be significantly improved by
combining our analytic template formulae and the precision velocity curves from
high-resolution spectroscopic observations with 8-10 m class telescopes. Thus
future observational exploration of transiting systems using the Rossiter -
McLaughlin effect is one of the most important probes to better understanding
of the origin of extrasolar planetary systems, especially the origin of their
angular momentum.Comment: 39 pages, 16 figures, Accepted to ApJ. To match the published version
(ApJ 623, April 10 issue
Two New Tidally Distorted White Dwarfs
We identify two new tidally distorted white dwarfs (WDs), SDSS
J174140.49+652638.7 and J211921.96-001825.8 (hereafter J1741 and J2119). Both
stars are extremely low mass (ELM, < 0.2 Msun) WDs in short-period, detached
binary systems. High-speed photometric observations obtained at the McDonald
Observatory reveal ellipsoidal variations and Doppler beaming in both systems;
J1741, with a minimum companion mass of 1.1 Msun, has one of the strongest
Doppler beaming signals ever observed in a binary system (0.59 \pm 0.06%
amplitude). We use the observed ellipsoidal variations to constrain the radius
of each WD. For J1741, the star's radius must exceed 0.074 Rsun. For J2119, the
radius exceeds 0.10 Rsun. These indirect radius measurements are comparable to
the radius measurements for the bloated WD companions to A-stars found by the
Kepler spacecraft, and they constitute some of the largest radii inferred for
any WD. Surprisingly, J1741 also appears to show a 0.23 \pm 0.06% reflection
effect, and we discuss possible sources for this excess heating. Both J1741 and
J2119 are strong gravitational wave sources, and the time-of-minimum of the
ellipsoidal variations can be used to detect the orbital period decay. This may
be possible on a timescale of a decade or less.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journa
The minimum period problem in cataclysmic variables
We investigate if consequential angular momentum losses (CAML) or an
intrinsic deformation of the donor star in CVs could increase the CV bounce
period from the canonical theoretical value ~65 min to the observed value
min, and if a variation of these effects in a CV population
could wash out the theoretically predicted accumulation of systems near the
minimum period (the period spike). We are able to construct suitably mixed CV
model populations that a statisticial test cannot rule out as the parent
population of the observed CV sample. However, the goodness of fit is never
convincing, and always slightly worse than for a simple, flat period
distribution. Generally, the goodness of fit is much improved if all CVs are
assumed to form at long orbital periods. The weighting suggested by King,
Schenker & Hameury (2002) does not constitute an improvment if a realistically
shaped input period distribution is used. Put your abstract here.Comment: 10 pages, Latex, 13 postscript figures, Accepted for publication in
MNRA
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