802 research outputs found
Idling Magnetic White Dwarf in the Synchronizing Polar BY Cam. The Noah-2 Project
Results of a multi-color study of the variability of the magnetic cataclysmic
variable BY Cam are presented. The observations were obtained at the Korean
1.8m and Ukrainian 2.6m, 1.2m and 38-cm telescopes in 2003-2005, 56
observational runs cover 189 hours. The variations of the mean brightness in
different colors are correlated with a slope dR/dV=1.29(4), where the number in
brackets denotes the error estimates in the last digits. For individual runs,
this slope is much smaller ranging from 0.98(3) to 1.24(3), with a mean value
of 1.11(1). Near the maximum, the slope becomes smaller for some nights,
indicating more blue spectral energy distribution, whereas the night-to-night
variability has an infrared character. For the simultaneous UBVRI photometry,
the slopes increase with wavelength from dU/dR=0.23(1) to dI/dR=1.18(1). Such
wavelength dependence is opposite to that observed in non-magnetic cataclysmic
variables, in an agreement to the model of cyclotron emission. The principal
component analysis shows two (with a third at the limit of detection)
components of variablitity with different spectral energy distribution, which
possibly correspond to different regions of emission. The scalegram analysis
shows a highest peak corresponding to the 200-min spin variability, its quarter
and to the 30-min and 8-min QPOs. The amplitudes of all these components are
dependent on wavelength and luminosity state. The light curves were fitted by a
statistically optimal trigonometrical polynomial (up to 4-th order) to take
into account a 4-hump structure. The dependences of these parameters on the
phase of the beat period and on mean brightness are discussed. The amplitude of
spin variations increases with an increasing wavelength and with decreasing
brightnessComment: 30pages, 11figures, accepted in Cent.Eur.J.Phy
Rigidity of cosmic acceleration in a class of k-essence cosmologies
We study the structural stability of a cosmic acceleration (inflation) in a
class of k-essence cosmologies against changes in the shape of the potential.
Those models may be viewed as generalized tachyon cosmologies and this analysis
extends previous results on the structural stability of cosmic acceleration in
tachyon cosmologies. The study considers both phantom and non-phantom cases.
The concepts of rigidity and fragility are defined through a condition on the
functional form of the Hubble factor. Given the known result of the existence
of inflationary (non-phantom) and super-inflationary (phantom) attractors we
formulate the question of their structural stability. We find that those
attractors are rigid in the sense that they never change as long as the
conditions for inflation or super-inflation are met.Comment: 10 page
Hyperbolic Chaos of Turing Patterns
We consider time evolution of Turing patterns in an extended system governed
by an equation of the Swift-Hohenberg type, where due to an external periodic
parameter modulation long-wave and short-wave patterns with length scales
related as 1:3 emerge in succession. We show theoretically and demonstrate
numerically that the spatial phases of the patterns, being observed
stroboscopically, are governed by an expanding circle map, so that the
corresponding chaos of Turing patterns is hyperbolic, associated with a strange
attractor of the Smale-Williams solenoid type. This chaos is shown to be robust
with respect to variations of parameters and boundary conditions.Comment: 4 pages, 4 figure
Secondary electron emission yield in the limit of low electron energy
Secondary electron emission (SEE) from solids plays an important role in many
areas of science and technology.1 In recent years, there has been renewed
interest in the experimental and theoretical studies of SEE. A recent study
proposed that the reflectivity of very low energy electrons from solid surface
approaches unity in the limit of zero electron energy2,3,4, If this was indeed
the case, this effect would have profound implications on the formation of
electron clouds in particle accelerators,2-4 plasma measurements with
electrostatic Langmuir probes, and operation of Hall plasma thrusters for
spacecraft propulsion5,6. It appears that, the proposed high electron
reflectivity at low electron energies contradicts to numerous previous
experimental studies of the secondary electron emission7. The goal of this note
is to discuss possible causes of these contradictions.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
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