17,692 research outputs found
Relativistic J-matrix method
The relativistic version of the J-matrix method for a scattering problem on
the potential vanishing faster than the Coulomb one is formulated. As in the
non-relativistic case it leads to a finite algebraic eigenvalue problem. The
derived expression for the tangent of phase shift is simply related to the
non-relativistic case formula and gives the latter as a limit case. It is due
to the fact that the used basis set satisfies the ``kinetic balance
condition''.Comment: 21 pages, RevTeX, accepted for publication in Phys. Rev.
XMM-Newton observations of the Perseus Cluster I: The temperature and surface brightness structure
We present preliminary results of the XMM-Newton 50 ksec observation of the
Perseus cluster. The global east/west asymmetry of the gas temperature and
surface brightness distributions, approximately aligned with the chain of
bright galaxies, suggests an ongoing merger, although the modest degree of the
observed asymmetry certainly excludes a major merger interpretation. The chain
of galaxies probably traces the filament along which accretion has started some
time ago and is continuing at the present time. A cold and dense (low entropy)
cluster core like Perseus is probably well "protected" against the penetration
of the gas of infalling groups and poor clusters whereas in non-cooling core
clusters like Coma and A1367, infalling subclusters can penetrate deeply into
the core region. In Perseus, gas associated with infalling groups may be
stripped completely at the outskirts of the main cluster and only compression
waves (shocks) may reach the central regions. We argue that the passage of such
a wave(s) can qualitatively explain the overall horseshoe shaped appearance of
the gas temperature map (the hot horseshoe surrounds the colder, low entropy
core) as well as other features of the Perseus cluster core. As compression
waves traverse the cluster core, they can induce oscillatory motion of the
cluster gas which can generate multiple sharp "edges", on opposite sides or the
central galaxy. Gas motions induced by mergers may be a natural way to explain
the high frequency of "edges" seen in clusters with cooling cores.Comment: 16 pages, 14 figures, submitted to Ap
SPH Simulations of Galactic Gaseous Disk with Bar: Distribution and Kinematic Structure of Molecular Clouds toward the Galactic Center
We have performed Smoothed Particle Hydrodynamic (SPH) simulations to study
the response of molecular clouds in the Galactic disk to a rotating bar and
their subsequent evolution in the Galactic Center (GC) region. The Galactic
potential in our models is contributed by three axisymmetric components
(massive halo, exponential disk, compact bulge) and a non-axisymmetric bar.
These components are assumed to be invariant in time in the frame corotating
with the bar. Some noticeable features such as an elliptical outer ring, spiral
arms, a gas-depletion region, and a central concentration have been developed
due to the influence of the bar. The rotating bar induces non-circular motions
of the SPH particles, but hydrodynamic collisions tend to suppress the random
components of the velocity. The velocity field of the SPH particles is
consistent with the kinematics of molecular clouds observed in HCN (1-0)
transition; these clouds are thought to be very dense clouds. However, the l-v
diagram of the clouds traced by CO is quite different from that of our SPH
simulation, being more similar to that obtained from simulations using
collisionless particles. The diagram of a mixture of collisional and
collisionless particles gives better reproduction of the kinematic structures
of the GC clouds observed in the CO line. The fact that the kinematics of HCN
clouds can be reproduced by the SPH particles suggests that the dense clouds in
the GC are formed via cloud collisions induced by rotating bar.Comment: 31 pages, 10 pigures, accepted for publication in Ap
Two-band ferromagnetic Kondo-lattice model for local-moment half-metals
We introduce a two-band Kondo-lattice model to describe ferromagnetic
half-metals with local magnetic moments. In a model study, the electronic and
magnetic properties are presented by temperature dependent magnetization
curves, band-structures, spin polarizations and plasma frequencies. These are
obtained from numerically evaluated equations, based on the single-electron
Green functions. We show that the mutual influence between the itinerant
electrons and the local magnetic moments is responsible for several phase
transitions of the half-metals, namely first and second order magnetic phase
transitions, as well as half-metal to semiconductor and half-metal to semimetal
transitions.Comment: 10 pages, 5 figures, submitted to Journal of Physics: Condensed
Matte
Type IIB instanton as a wave in twelve dimensions
0-brane of type IIA string theory can be interpreted as a dimensional
reduction of a gravitational wave in 11 dimensions. We observe that a similar
interpretation applies also to the D-instanton background of type IIB theory:
it can be viewed as a reduction (along one spatial and one time-like direction)
of a wave in a 12-dimensional theory. The instanton charge is thus related to a
linear momentum in 12 dimensions. This suggests that the instanton should play
as important role in type IIB theory as the 0-brane is supposed to play in type
IIA theory.Comment: 7 pages, harvmac (minor corrections and a reference added
Ion-neutral sympathetic cooling in a hybrid linear rf Paul and magneto-optical trap
Long range polarization forces between ions and neutral atoms result in large
elastic scattering cross sections, e.g., 10^6 a.u. for Na+ on Na or Ca+ on Na
at cold and ultracold temperatures. This suggests that a hybrid ion-neutral
trap should offer a general means for significant sympathetic cooling of atomic
or molecular ions. We present SIMION 7.0 simulation results concerning the
advantages and limitations of sympathetic cooling within a hybrid trap
apparatus, consisting of a linear rf Paul trap concentric with a Na
magneto-optical trap (MOT). This paper explores the impact of various heating
mechanisms on the hybrid system and how parameters related to the MOT, Paul
trap, number of ions, and ion species affect the efficiency of the sympathetic
cooling
DEVELOPMENT OF UHTREX GAS-BEARING COMPRESSORS
Two helium blowers operating on hydrodynamic gas bearing and suitable for highly contaminated systems are described. The cleanup loop blower easily met its design conditions (15-psi pressure rise at 120 lb/hr), as did the main loop blower (8 psi at 10,250 lb/hr). Hydrostatic journal bearings raise the rotor assembly to avoid wear during starting and stopping. (D.C.W.
Second Order General Slow-Roll Power Spectrum
Recent combined results from the Wilkinson Microwave Anisotropy Probe (WMAP)
and Sloan Digital Sky Survey (SDSS) provide a remarkable set of data which
requires more accurate and general investigation. Here we derive formulae for
the power spectrum P(k) of the density perturbations produced during inflation
in the general slow-roll approximation with second order corrections. Also,
using the result, we derive the power spectrum in the standard slow-roll
picture with previously unknown third order corrections.Comment: 11 pages, 1 figure ; A typo in Eq. (38) is fixed ; References
expanded and a note adde
Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 microns
We report a 4.8 sigma detection of water absorption features in the day side
spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)
spectra taken at 3.2 microns with CRIRES on the VLT to trace the
radial-velocity shift of the water features in the planet's day side atmosphere
during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite
considerable telluric contamination in this wavelength regime, we detect the
signal within our uncertainties at the expected combination of systemic
velocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),
and determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to
the stellar continuum. We find no evidence of significant absorption or
emission from other carbon-bearing molecules, such as methane, although we do
note a marginal increase in the significance of our detection to 5.1 sigma with
the inclusion of carbon dioxide in our template spectrum. This result
demonstrates that ground-based, high-resolution spectroscopy is suited to
finding not just simple molecules like CO, but also to more complex molecules
like H2O even in highly telluric contaminated regions of the Earth's
transmission spectrum. It is a powerful tool that can be used for conducting an
immediate census of the carbon- and oxygen-bearing molecules in the atmospheres
of giant planets, and will potentially allow the formation and migration
history of these planets to be constrained by the measurement of their
atmospheric C/O ratios.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Excitation of a Kaluza-Klein mode by parametric resonance
In this paper we investigate a parametric resonance phenomenon of a
Kaluza-Klein mode in a -dimensional generalized Kaluza-Klein theory. As the
origin of the parametric resonance we consider a small oscillation of a scale
of the compactification around a today's value of it. To make our arguments
definite and for simplicity we consider two classes of models of the
compactification: those by () and those by (, ). For these models we show that
parametric resonance can occur for the Kaluza-Klein mode. After that, we give
formulas of a creation rate and a number of created quanta of the Kaluza-Klein
mode due to the parametric resonance, taking into account the first and the
second resonance band. By using the formulas we calculate those quantities for
each model of the compactification. Finally we give conditions for the
parametric resonance to be efficient and discuss cosmological implications.Comment: 36 pages, Latex file, Accepted for publication in Physical Review
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