1,557 research outputs found
State transition of a non-Ohmic damping system in a corrugated plane
Anomalous transport of a particle subjected to non-Ohmic damping of the power
in a tilted periodic potential is investigated via Monte Carlo
simulation of generalized Langevin equation. It is found that the system
exhibits two relative motion modes: the locking state and the running state.
Under the surrounding of sub-Ohmic damping (), the particle should
transfer into a running state from a locking state only when local minima of
the potential vanish; hence the particle occurs a synchronization oscillation
in its mean displacement and mean square displacement (MSD). In particular, the
two motion modes are allowed to coexist in the case of super-Ohmic damping
() for moderate driving forces, namely, where exists double centers
in the velocity distribution. This induces the particle having faster
diffusion, i.e., its MSD reads . Our result shows that the effective power index
can be enhanced and is a nonmonotonic function of the
temperature and the driving force. The mixture effect of the two motion modes
also leads to a breakdown of hysteresis loop of the mobility.Comment: 7 pages,7 figure
Resonant interaction between gravitational waves, electromagnetic waves and plasma flows
In magnetized plasmas gravitational and electromagnetic waves may interact
coherently and exchange energy between themselves and with plasma flows. We
derive the wave interaction equations for these processes in the case of waves
propagating perpendicular or parallel to the plasma background magnetic field.
In the latter case, the electromagnetic waves are taken to be circularly
polarized waves of arbitrary amplitude. We allow for a background drift flow of
the plasma components which increases the number of possible evolution
scenarios. The interaction equations are solved analytically and the
characteristic time scales for conversion between gravitational and
electromagnetic waves are found. In particular, it is shown that in the
presence of a drift flow there are explosive instabilities resulting in the
generation of gravitational and electromagnetic waves. Conversely, we show that
energetic waves can interact to accelerate particles and thereby \emph{produce}
a drift flow. The relevance of these results for astrophysical and cosmological
plasmas is discussed.Comment: 12 pages, 1 figure, typos corrected and numerical example adde
Variational bounds for the shear viscosity of gelling melts
We study shear stress relaxation for a gelling melt of randomly crosslinked,
interacting monomers. We derive a lower bound for the static shear viscosity
, which implies that it diverges algebraically with a critical exponent
. Here, and are the critical exponents of
percolation theory for the correlation length and the gel fraction. In
particular, the divergence is stronger than in the Rouse model, proving the
relevance of excluded-volume interactions for the dynamic critical behaviour at
the gel transition. Precisely at the critical point, our exact results imply a
Mark-Houwink relation for the shear viscosity of isolated clusters of fixed
size.Comment: 5 pages; CHANGES: typos corrected, some references added; version as
publishe
HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography
We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet
around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star
with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We
measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV
observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J .
Based on theoretical stellar evolution models, the host star has a mass and
radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively.
Spectroscopic observations made with Keck-I/HIRES during a partial transit
event show the Doppler shadow of HAT-P-57b moving across the average spectral
line profile of HAT-P- 57, confirming the object as a planetary system. We use
these observations, together with analytic formulae that we derive for the line
profile distortions, to determine the projected angle between the spin axis of
HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible
solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at
95% confidence, and with relative probabilities for the two modes of 26% and
74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object
located 2.7" from HAT-P-57 consisting of two point sources separated in turn
from each other by 0.22". The H and L -band magnitudes of the companion stars
are consistent with their being physically associated with HAT-P-57, in which
case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57
is the most rapidly rotating star, and only the fourth main sequence A star,
known to host a transiting planet.Comment: 18 pages, 14 figures, 5 tables, accepted for publication in A
Gravitational Optics: Self-phase modulation and harmonic cascades
Nonlinear wave interaction of low amplitude gravitational waves in flat
space-time is considered. Analogy with optics is established. It is shown that
the flat metric space-time is equivalent to a centro-symmetric optical medium,
with no second order susceptibility. The lowest order nonlinear effects are
those due to the third order nonlinearity and include self-phase modulation and
high harmonic generation. These processes lead to an efficient energy dilution
of the gravitational wave energy over an increasingly large spectral range.Comment: 12 pages, REVTEX
A direct D-bar reconstruction algorithm for recovering a complex conductivity in 2-D
A direct reconstruction algorithm for complex conductivities in
, where is a bounded, simply connected Lipschitz
domain in , is presented. The framework is based on the
uniqueness proof by Francini [Inverse Problems 20 2000], but equations relating
the Dirichlet-to-Neumann to the scattering transform and the exponentially
growing solutions are not present in that work, and are derived here. The
algorithm constitutes the first D-bar method for the reconstruction of
conductivities and permittivities in two dimensions. Reconstructions of
numerically simulated chest phantoms with discontinuities at the organ
boundaries are included.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in [insert name of journal]. IOP Publishing Ltd is
not responsible for any errors or omissions in this version of the manuscript
or any version derived from it. The Version of Record is available online at
10.1088/0266-5611/28/9/09500
HATS-8b: A Low-Density Transiting Super-Neptune
HATS-8b is a low density transiting super-Neptune discovered as part of the
HATSouth project. The planet orbits its solar-like G dwarf host (V=14.03
0.10 and T =5679 50 K) with a period of 3.5839 d. HATS-8b is the
third lowest mass transiting exoplanet to be discovered from a wide-field
ground based search, and with a mass of 0.138 0.019 M it is
approximately half-way between the masses of Neptune and Saturn. However
HATS-8b has a radius of 0.873 (+0.123,-0.075) R, resulting in a bulk
density of just 0.259 0.091 g.cm. The metallicity of the host star
is super-Solar ([Fe/H]=0.210 0.080), arguing against the idea that low
density exoplanets form from metal-poor environments. The low density and large
radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and
in addition to this there is an excellent reference star of near equal
magnitude at just 19 arcsecond separation on the sky. These factors make
HATS-8b an exciting target for future atmospheric characterization studies,
particularly for long-slit transmission spectroscopy.Comment: 11 pages, 7 figures, accepted for publication in A
Gravitational radiation from compact binary systems: gravitational waveforms and energy loss to second post-Newtonian order
We derive the gravitational waveform and gravitational-wave energy flux
generated by a binary star system of compact objects (neutron stars or black
holes), accurate through second post-Newtonian order () beyond the lowest-order quadrupole approximation. We cast the
Einstein equations into the form of a flat-spacetime wave equation together
with a harmonic gauge condition, and solve it formally as a retarded integral
over the past null cone of the chosen field point. The part of this integral
that involves the matter sources and the near-zone gravitational field is
evaluated in terms of multipole moments using standard techniques; the
remainder of the retarded integral, extending over the radiation zone, is
evaluated in a novel way. The result is a manifestly convergent and finite
procedure for calculating gravitational radiation to arbitrary orders in a
post-Newtonian expansion. Through second post-Newtonian order, the radiation is
also shown to propagate toward the observer along true null rays of the
asymptotically Schwarzschild spacetime, despite having been derived using flat
spacetime wave equations. The method cures defects that plagued previous
``brute- force'' slow-motion approaches to the generation of gravitational
radiation, and yields results that agree perfectly with those recently obtained
by a mixed post-Minkowskian post-Newtonian method. We display explicit formulae
for the gravitational waveform and the energy flux for two-body systems, both
in arbitrary orbits and in circular orbits. In an appendix, we extend the
formalism to bodies with finite spatial extent, and derive the spin corrections
to the waveform and energy loss.Comment: 59 pages ReVTeX; Physical Review D, in press; figures available on
request to [email protected]
HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars
We report the discovery of HATS-15 b and HATS-16 b, two massive transiting
extrasolar planets orbiting evolved ( Gyr) main-sequence stars. The
planet HATS-15 b, which is hosted by a G9V star ( mag), is a hot
Jupiter with mass of and radius of
, and completes its orbit in nearly 1.7 days.
HATS-16 b is a very massive hot Jupiter with mass of and radius of ; it orbits around
its G3 V parent star ( mag) in days. HATS-16 is slightly
active and shows a periodic photometric modulation, implying a rotational
period of 12 days which is unexpectedly short given its isochronal age. This
fast rotation might be the result of the tidal interaction between the star and
its planet.Comment: 16 pages, 8 figures, submitted to PAS
HATS-7b: A Hot Super Neptune Transiting a Quiet K Dwarf Star
IW ../submit_V2/abstract.txt ( Row 1 Col 1 6:48 Ctrl-K H for help We report
the discovery by the HATSouth network of HATS-7b, a transiting Super-Neptune
with a mass of 0.120+/-0.012MJ, a radius of 0.563+/-(0.046,0.034)RJ, and an
orbital period of 3.1853days. The host star is a moderately bright
(V=13.340+/-0.010mag, K_S=10.976+/-0.026mag) K dwarf star with a mass of
0.849+/-0.027Msun , a radius of 0.815+/-(0.049,-0.035)Rsun, and a metallicity
of [Fe/H]=+0.250+/-0.080. The star is photometrically quiet to within the
precision of the HATSouth measurements and has low RV jitter. HATS-7b is the
second smallest radius planet discovered by a wide-field ground-based transit
survey, and one of only a handful of Neptune-size planets with mass and radius
determined to 10% precision. Theoretical modeling of HATS-7b yields a
hydrogen-helium fraction of 18+/-4% (rock-iron core and H2-He envelope), or
9+/-4% (ice core and H2-He envelope), i.e.it has a composition broadly similar
to that of Uranus and Neptune, and very different from that of Saturn, which
has 75% of its mass in H2-He. Based on a sample of transiting exoplanets with
accurately (<20%) determined parameters, we establish approximate power-law
relations for the envelopes of the mass-density distribution of exoplanets.
HATS-7b, which, together with the recently discovered HATS-8b, is one of the
first two transiting super-Neptunes discovered in the Southern sky, is a prime
target for additional follow-up observations with Southern hemisphere
facilities to characterize the atmospheres of Super-Neptunes (which we define
as objects with mass greater than that of Neptune, and smaller than halfway
between that of Neptune and Saturn, i.e. 0.054 MJ<Mp<0.18 MJ).Comment: 11 pages, accepted for publication by Ap
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