9,903 research outputs found
Planet migration and gap formation by tidally-induced shocks
Gap formation in a gas disk triggered by disk-planet tidal interaction is
considered. Density waves launched by the planet are assumed to be damped as a
result of their nonlinear evolution leading to shock formation and its
subsequent dissipation. As a consequence wave angular momentum is transferred
to the disk,leading to evolution of its surface density. Planetary migration is
an important ingredient of the theory; effects of the planet-induced surface
density perturbations on the migration speed are considered. A gap is assumed
to form when a stationary solution for the surface density profile is no longer
possible in the frame of reference migrating with the planet. An analytical
limit on the planetary mass necessary to open a gap in an inviscid disk is
derived. The critical mass turns out to be smaller than mass M_1 for which
planetary Hill's radius equals disk scaleheight by a factor of at least Q^{5/7}
(Q is the Toomre stability parameter) depending on the strength of the
migration feedback. In viscous disks the critical planetary mass could vary
from about 0.1M_1 to M_1, depending on the disk viscosity. This implies that a
gap could be formed by a planet with mass 1-10 times bigger than the Earth mass
depending on the disk aspect ratio, viscosity, and planet's location in the
nebula.Comment: AASTeX, 31 pages, 7 figures, 1 table, submitted to Ap
The mechanism of double exponential growth in hyper-inflation
Analyzing historical data of price indices we find an extraordinary growth
phenomenon in several examples of hyper-inflation in which price changes are
approximated nicely by double-exponential functions of time. In order to
explain such behavior we introduce the general coarse-graining technique in
physics, the Monte Carlo renormalization group method, to the price dynamics.
Starting from a microscopic stochastic equation describing dealers' actions in
open markets we obtain a macroscopic noiseless equation of price consistent
with the observation. The effect of auto-catalytic shortening of characteristic
time caused by mob psychology is shown to be responsible for the
double-exponential behavior.Comment: 9 pages, 5 figures and 2 tables, submitted to Physica
A Magnetohydrodynamic Boost for Relativistic Jets
We performed relativistic magnetohydrodynamic simulations of the hydrodynamic
boosting mechanism for relativistic jets explored by Aloy & Rezzolla (2006)
using the RAISHIN code. Simulation results show that the presence of a magnetic
field changes the properties of the shock interface between the tenuous,
overpressured jet () flowing tangentially to a dense external medium.
Magnetic fields can lead to more efficient acceleration of the jet, in
comparison to the pure-hydrodynamic case. A ``poloidal'' magnetic field
(), tangent to the interface and parallel to the jet flow, produces both a
stronger outward moving shock and a stronger inward moving rarefaction wave.
This leads to a large velocity component normal to the interface in addition to
acceleration tangent to the interface, and the jet is thus accelerated to
larger Lorentz factors than those obtained in the pure-hydrodynamic case.
Likewise, a strong ``toroidal'' magnetic field (), tangent to the
interface but perpendicular to the jet flow, also leads to stronger
acceleration tangent to the shock interface relative to the pure-hydrodynamic
case. Overall, the acceleration efficiency in the ``poloidal'' case is less
than that of the ``toroidal'' case but both geometries still result in higher
Lorentz factors than the pure-hydrodynamic case. Thus, the presence and
relative orientation of a magnetic field in relativistic jets can significant
modify the hydrodynamic boost mechanism studied by Aloy & Rezzolla (2006).Comment: 25 pages, 10 figures, accepted for publication in Ap
Ac Susceptibility and Static Magnetization Measurements of CeRuSi at Small Magnetic Fields and Ultra Low Temperatures
The magnetic properties of CeRuSi at microkelvin temperatures (down
to 170 K) and ultra small magnetic fields ( mT) are
investigated experimentally for the first time. The simultaneously measured ac
susceptibility and static magnetization show neither evidence of the magnetic
ordering, superconductivity down to the lowest temperatures nor conventional
Landau Fermi-Liquid behavior. The results imply the magnetic transition
temperature in undoped CeRuSi is very close to absolute 0 K. The
possibility for proximity of CeRuSi to the quantum critical point
without any doping is discussed.Comment: 4 pages, 3 figures; accepted for publication in Phys. Rev. B (Rapid
Communication) and scheduled issue on 1st of May 200
Aligned Molecular Clouds towards SS433 and L=348.5 degrees; Possible Evidence for Galactic "Vapor Trail" Created by Relativistic Jet
We have carried out a detailed analysis of the NANTEN 12CO(J=1-0) dataset in
two large areas of ~25 square degrees towards SS433 (l~40 degree) and of ~18
square degrees towards l~348.5 degree, respectively. We have discovered two
groups of remarkably aligned molecular clouds at |b|~1--5 degree in the two
regions. In SS433, we have detected 10 clouds in total, which are well aligned
nearly along the axis of the X-ray jet emanating from SS433. These clouds have
similar line-of-sight velocities of 42--56 km s^-1 and the total projected
length of the feature is ~300 pc, three times larger than that of the X-ray
jet, at a distance of 3 kpc. Towards l~348.5 degree, we have detected four
clouds named as MJG348.5 at line-of-sight velocities of -80 -- -95 km s^-1 in
V_LSR, which also show alignment nearly perpendicular to the Galactic plane.
The total length of the feature is ~400 pc at a kinematic distance of 6 kpc. In
the both cases, the CO clouds are distributed at high galactic latitudes where
such clouds are very rare. In addition, their alignments and coincidence in
velocity should be even rarer, suggesting that they are physically associated.
We tested a few possibilities to explain these clouds, including protostellar
outflows, supershells, and interactions with energetic jets. Among them, a
favorable scenario is that the interaction between relativistic jet and the
interstellar medium induced the formation of molecular clouds over the last
~10^5-6 yrs. It is suggested that the timescale of the relativistic jet may be
considerably larger, in the order of 10^5-6 yrs, than previously thought in
SS433. The driving engine of the jet is obviously SS433 itself in SS433,
although the engine is not yet identified in MJG348.5 among possible several
candidates detected in the X-rays and TeV gamma rays.Comment: 29 pages, 10 figures, already published in PASJ, 2008,60, 71
Impact of elastic heterogeneity on the propagation of vibrations at finite temperatures in glasses
Some aspects of how sound waves travel through disordered solids are still
unclear. Recent work has characterized a feature of disordered solids which
seems to influence vibrational excitations at the mesoscales, local elastic
heterogeneity. Sound waves propagation has been demonstrated to be strongly
affected by inhomogeneous mechanical features of the materials which add to the
standard anharmonic couplings, amounting to extremely complex transport
properties at finite temperatures. Here, we address these issues for the case
of a simple atomic glass former, by Molecular Dynamics computer simulation. In
particular, we focus on the transverse components of the vibrational
excitations in terms of dynamic structure factors, and characterize the
temperature dependence of sound dispersion and attenuation in an extended
frequency range. We provide a complete picture of how elastic heterogeneity
determines transport of vibrational excitations, also based on a direct
comparison of the numerical data with the predictions of the heterogeneous
elastic theory.Comment: 14 pages, 5 figures, 1 tabl
Star Forming Dense Cloud Cores in the TeV {\gamma}-ray SNR RX J1713.7-3946
RX J1713.7-3946 is one of the TeV {\gamma}-ray supernova remnants (SNRs)
emitting synchrotron X rays. The SNR is associated with molecular gas located
at ~1 kpc. We made new molecular observations toward the dense cloud cores,
peaks A, C and D, in the SNR in the 12CO(J=2-1) and 13CO(J=2-1) transitions at
angular resolution of 90". The most intense core in 13CO, peak C, was also
mapped in the 12CO(J=4-3) transition at angular resolution of 38". Peak C shows
strong signs of active star formation including bipolar outflow and a
far-infrared protostellar source and has a steep gradient with a
r^{-2.20.4} variation in the average density within radius r. Peak C and
the other dense cloud cores are rim-brightened in synchrotron X rays,
suggesting that the dense cloud cores are embedded within or on the outer
boundary of the SNR shell. This confirms the earlier suggestion that the X rays
are physically associated with the molecular gas (Fukui et al. 2003). We
present a scenario where the densest molecular core, peak C, survived against
the blast wave and is now embedded within the SNR. Numerical simulations of the
shock-cloud interaction indicate that a dense clump can indeed survive shock
erosion, since shock propagation speed is stalled in the dense clump.
Additionally, the shock-cloud interaction induces turbulence and magnetic field
amplification around the dense clump that may facilitate particle acceleration
in the lower-density inter-clump space leading to the enhanced synchrotron X
rays around dense cores.Comment: 22 pages, 7 figures, to accepted in The Astrophysical Journal. A full
color version with higher resolution figures is available at
http://www.a.phys.nagoya-u.ac.jp/~sano/ApJ10/ms_sano.pd
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