575 research outputs found
Quantum interference in the classically forbidden region: a parametric oscillator
We study tunneling between period two states of a parametrically modulated
oscillator. The tunneling matrix element is shown to oscillate with the varying
frequency of the modulating field. The effect is due to spatial oscillations of
the wave function and the related interference in the classically forbidden
region. The oscillations emerge already in the ground state of the oscillator
Hamiltonian in the rotating frame, which is quartic in the momentum.Comment: Submitted to PR
Double-layered monopolar order in Tb2Ti2O7 spin liquid
Ho2Ti2O7 and Dy2Ti2O7 spin ices exhibit elementary excitations akin to
magnetic monopoles. Here we focus on Tb2Ti2O7 spin liquid, where correlated
magnetic moments keep fluctuating down to very low temperatures. Using a
monopole picture, we have re-analyzed the field-induced magnetic structure
previously determined by neutron diffraction in Tb2Ti2O7. We show that under a
high field applied along a [110] direction, Tb2Ti2O7 orders as a three
dimensional arrangement of monopole and antimonopole double layers. In
contrast, Ho2Ti2O7 spin ice in the same conditions behaves as a monopole-free
state. By symmetry analysis we derived the distortions compatible with the
observed magnetic structure of Tb2Ti2O7 which can be related to the appearance
of the double-layered monopolar order.Comment: 6 pages, 6 figures, submitted for publicatio
Gravitational orientation of the orbital complex, Salyut-6--Soyuz
A simple mathematical model is proposed for the Salyut-6-Soyuz orbital complex motion with respect to the center of mass under the one-axis gravity-gradient orientation regime. This model was used for processing the measurements of the orbital complex motion parameters when the above orientation region was implemented. Some actual satellite motions are simulated and the satellite's aerodynamic parameters are determined. Estimates are obtained for the accuracy of measurements as well as that of the mathematical model
Collective processes in relativistic plasma and their implications for gamma-ray burst afterglows
We consider the effects of collective plasma processes on synchrotron
emission from highly relativistic electrons. We find, in agreement with Sazonov
(1970), that strong effects are possible also in the absence of a
non-relativistic plasma component, due to the relativistic electrons (and
protons) themselves. In contrast with Sazonov, who infers strong effects only
in cases where the ratio of plasma frequency to cyclotron frequency is much
larger than the square of the characteristic electron Lorentz factor, nu_p/nu_B
>> gamma^2, we find strong effects also for 1 << nu_p/nu_B << gamma^2. The
modification of the spectrum is prominent at frequencies nu < nu_{R*} = nu_p
min[gamma, (nu_p/nu_B)^(1/2)], where nu_{R*} generalizes the Razin-Tsytovich
frequency, nu_R = gamma nu_p, to the regime nu_p/nu_B << gamma^2. Applying our
results to gamma-ray burst (GRB) plasmas, we predict a strong modification of
the radio spectrum on minute time scale following the GRB, at the onset of
fireball interaction with its surrounding medium, in cases where the ratio of
the energy carried by the relativistic electrons to the energy carried by the
magnetic field exceeds ~ 10^5. Plausible electron distribution functions may
lead to negative synchrotron reabsorption, i.e to coherent radio emission,
which is characterized by a low degree of circular polarization. Detection of
these effects would constrain the fraction of energy in the magnetic field,
which is currently poorly determined by observations, and, moreover, would
provide a novel handle on the properties of the environment into which the
fireball expands.Comment: 28 pages, 1 figure, submitted to Ap
Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud
In 2003-2012, the INTEGRAL observatory has performed long-term observations
of the Large Magellanic Cloud (LMC). At present, this is one of the deepest
hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20
sources of different natures have been detected. We present the results of a
statistical analysis of the population of high-mass X-ray binaries in the LMC
and active galactic nuclei (AGNs) observed in its direction. The hard X-ray
luminosity function of high-mass X-ray binaries is shown to be described by a
power law with a slope alpha~1.8, that in agreement with the luminosity
function measurements both in the LMC itself, but made in the soft X-ray energy
band, and in other galaxies. At the same time, the number of detected AGNs
toward the LMC turns out to be considerably smaller than the number of AGNs
registered in other directions, in particular, toward the source 3C 273. The
latter confirms the previously made assumption that the distribution of matter
in the local Universe is nonuniform.Comment: 5 pages, 5 figures, will be published in Astronomy Letters, 2012,
Vol. 38, No. 8, p. 492--49
Multiphoton antiresonance in large-spin systems
We study nonlinear response of a spin with easy-axis anisotropy. The
response displays sharp dips or peaks when the modulation frequency is
adiabatically swept through multiphoton resonance. The effect is a consequence
of a special symmetry of the spin dynamics in a magnetic field for the
anisotropy energy . The occurrence of the dips or peaks is
determined by the spin state. Their shape strongly depends on the modulation
amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps
in the response as function of frequency. The results bear on the dynamics of
molecular magnets in a static magnetic field.Comment: Submitted to PR
Preparation and Characterization of a-SiC:H Absorber Layer for Semi-transparent Solar Cells
AbstractThis paper reports on device-quality silicon-carbon alloy (a-SiC:H) application as an absorber material in semi-transparent solar cells. Films with an optical bandgap ranging from 2 to 2.3 eV were prepared by plasma enhanced chemical vapour deposition (PECVD). The n-i-p structures with undoped SiC:H layers deposited under the same experimental conditions were also fabricated and characterized. The optimized devices showed forward current-voltage characteristics with a diode ideality factor in the range from 1.4 to 1.8, and an open circuit voltage up to 0.92 V. The density of deep defect states in a SiC:H was estimated from the transient current measurements and correlated with the optical bandgap
Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey
We present the results of our optical identifications of four hard X-ray
sources from the Swift all-sky survey. We obtained optical spectra for each of
the program objects with the 6-m BTA telescope (Special Astrophysical
Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their
nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT
J2341.0+7645) are shown to belong to the class of cataclysmic variables
(suspected polars or intermediate polars). The measured emission line width
turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of
extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems.
Apart from line broadening, we have detected a change in the positions of the
line centroids for SWIFT J2341.0+7645, which is most likely attributable to the
orbital motion of the white dwarf in the binary system. The other two program
objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in
origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift
z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all
sources in the 0.6-10 keV energy band obtained from XRT/Swift data.Comment: 9 pages, 6 figures, will be published in Astronomy Letters, 38, No.5,
pp.281-289 (2012
Contribution of the Accretion Disk, Hot Corona, and Obscuring Torus to the Luminosity of Seyfert Galaxies: Integral and Spitzer Observations
We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spitzer mid-infrared (MIR) observations of a complete sample of 68 nearby active galactic nuclei (AGNs) from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal-to-noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L 15 ÎŒmâL0.74 ± 0.06 HX. Assuming that the observed MIR emission is radiation from an accretion disk reprocessed in a surrounding dusty torus that subtends a solid angle decreasing with increasing luminosity (as inferred from the declining fraction of obscured AGNs), the intrinsic disk luminosity, L Disk, is approximately proportional to the luminosity of the corona in the 2-300 keV energy band, L Corona, with the L Disk/L Corona ratio varying by a factor of 2.1 around a mean value of 1.6. This ratio is a factor of ~2 smaller than for typical quasars producing the cosmic X-ray background. Therefore, over three orders of magnitude in luminosity, HX radiation carries a large, and roughly comparable, fraction of the bolometric output of AGNs. We estimate the cumulative bolometric luminosity density of local AGNs at ~(1-3) Ă 1040 erg sâ1 Mpcâ3. Finally, the Compton temperature ranges between kT c â 2 and â6 keV for nearby AGNs, compared to kT c â 2 keV for typical quasars, confirming that radiative heating of interstellar gas can play an important role in regulating SMBH growth
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