335 research outputs found
Solar limb darkening in the far infrared and its relation to the temperature of the chromosphere Final report, 1 Sep. 1967 - 31 Aug. 1968
Limb darkening measurements for analysis of solar infrared spectrum and chromospheric temperatur
A new approach to electromagnetic wave tails on a curved spacetime
We present an alternative method for constructing the exact and approximate
solutions of electromagnetic wave equations whose source terms are arbitrary
order multipoles on a curved spacetime. The developed method is based on the
higher-order Green's functions for wave equations which are defined as
distributions that satisfy wave equations with the corresponding order
covariant derivatives of the Dirac delta function as the source terms. The
constructed solution is applied to the study of various geometric effects on
the generation and propagation of electromagnetic wave tails to first order in
the Riemann tensor. Generally the received radiation tail occurs after a time
delay which represents geometrical backscattering by the central gravitational
source. It is shown that the truly nonlocal wave-propagation correction (the
tail term) takes a universal form which is independent of multipole order. In a
particular case, if the radiation pulse is generated by the source during a
finite time interval, the tail term after the primary pulse is entirely
determined by the energy-momentum vector of the gravitational field source: the
form of the tail term is independent of the multipole structure of the
gravitational source. We apply the results to a compact binary system and
conclude that under certain conditions the tail energy can be a noticeable
fraction of the primary pulse energy. We argue that the wave tails should be
carefully considered in energy calculations of such systems.Comment: RevTex, 28 pages, 5 eps figures, http://www.tpu.ee/~tony/texdocs/, 4
changes made (pp. 2, 4, 22, 24), 2 references adde
Three and four current reversals versus temperature in correlation ratchets with a simple sawtooh potential
Transport of Brownian particles on a simple sawtooth potential subjected to
both unbiased thermal and nonequilibrium symmetric three-level Markovian noise
is considered. The new effects of three and four current reversals as a
function of temperature are established in such correlation ratchets. The
parameter space coordinates of the fixed points associated with these current
reversals and the necessary and sufficient conditions for the existence of the
novel current reversals are found.Comment: 4 pages, 5 figures; some changes introduced; accepted for publication
in Physical Review
Can Schwarzschildean gravitational fields suppress gravitational waves?
Gravitational waves in the linear approximation propagate in the
Schwarzschild spacetime similarly as electromagnetic waves. A fraction of the
radiation scatters off the curvature of the geometry. The energy of the
backscattered part of an initially outgoing pulse of the quadrupole
gravitational radiation is estimated by compact formulas depending on the
initial energy, the Schwarzschild radius, and the location and width of the
pulse. The backscatter becomes negligible in the short wavelength regime.Comment: 18 pages, Revtex. Added three references; a new comment in Sec. 7;
several misprints corrected. To appear in the Phys. Rev.
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