23,912 research outputs found
R-process and alpha-elements in the Galactic disk: Kinematic correlations
Recent studies of elemental abundances in the Galactic halo and in the
Galactic disk have underscored the possibility to kinematically separate
different Galactic subcomponents. Correlations between the galactocentric
rotation velocity and various element ratios were found, providing an important
means to link different tracers of star formation and metal enrichment to the
Galactic components of different origin (collapse vs. accretion). In the
present work we determine stellar kinematics for a sample of 124 disk stars,
which we derive from their orbits based on radial velocities and proper motions
from the the literature. Our stars form a subsample of the Edvardsson et al.
(1993) sample and we concentrate on three main tracers: (i) Europium as an
r-process element is predominantly produced in Supernovae of type II. (ii)
Likewise, alpha-elements, such as Ca, Si, Mg, are synthesised in SNe II,
contrary to iron, which is being produced preferentially in SNe Ia. (iii) The
s-process element Barium is a measure of the relative contribution of AGB stars
to the Galaxy's enrichment history and has been shown to be an indicator for
distinguishing between thin and thick disk stars. All such studies reveal,
basically, that stars with low galactocentric rotational velocity tend to have
high abundances of alpha-elements and Eu, but lower abundances of, e.g., Ba.Comment: 5 pages, 2 figures, Poster contribution to appear in "Planets To
Cosmology: Essential Science In Hubble's Final Years", proceedings of the May
2004 STScI Symposium, M. Livio (ed.), (Cambridge University Press
Analysis of pressure distortion testing
The development of a distortion methodology, method D, was documented, and its application to steady state and unsteady data was demonstrated. Three methodologies based upon DIDENT, a NASA-LeRC distortion methodology based upon the parallel compressor model, were investigated by applying them to a set of steady state data. The best formulation was then applied to an independent data set. The good correlation achieved with this data set showed that method E, one of the above methodologies, is a viable concept. Unsteady data were analyzed by using the method E methodology. This analysis pointed out that the method E sensitivities are functions of pressure defect level as well as corrected speed and pattern
On the mechanism for orbital-ordering in KCuF3
The Mott insulating perovskite KCuF3 is considered the archetype of an
orbitally-ordered system. By using the LDA+dynamical mean-field theory (DMFT)
method, we investigate the mechanism for orbital-ordering (OO) in this
material. We show that the purely electronic Kugel-Khomskii super-exchange
mechanism (KK) alone leads to a remarkably large transition temperature of T_KK
about 350 K. However, orbital-order is experimentally believed to persist to at
least 800 K. Thus Jahn-Teller distortions are essential for stabilizing
orbital-order at such high temperatures.Comment: 4 pages, 5 figure
On the temperature dependence of correlation functions in the space like direction in hot QCD
We study the temperature dependence of quark antiquark correlations in the
space like direction. In particular, we predict the temperature dependence of
space like Bethe-Salpeter amplitudes using recent Lattice gauge data for the
space like string potential. We also investigate the effect of the space like
string potential on the screening mass and discuss possible corrections which
may arise when working with point sources.Comment: 15 pages 8 figures (not included, will be sent on request),
(SUNY-NTG-94-3
Interaction-assisted propagation of Coulomb-correlated electron-hole pairs in disordered semiconductors
A two-band model of a disordered semiconductor is used to analyze dynamical
interaction induced weakening of localization in a system that is accessible to
experimental verification. The results show a dependence on the sign of the
two-particle interaction and on the optical excitation energy of the
Coulomb-correlated electron-hole pair.Comment: 4 pages and 3 ps figure
The luminosity function of Palomar 5 and its tidal tails
We present the main sequence luminosity function of the tidally disrupted
globular cluster Palomar 5 and its tidal tails. For this work we analyzed
imaging data obtained with the Wide Field Camera at the INT (La Palma) and data
from the Wide Field Imager at the MPG/ESO 2.2 m telescope at La Silla down to a
limiting magnitude of approximately 24.5 mag in B. Our results indicate that
preferentially fainter stars were removed from the cluster so that the LF of
the cluster's main body exhibits a significant degree of flattening compared to
other GCs. This is attributed to its advanced dynamical evolution. The LF of
the tails is, in turn, enhanced with faint, low-mass stars, which we interpret
as a consequence of mass segregation in the cluster.Comment: 4 pages, 3 figures, to be published in the proceedings of the
conference "Satellites and tidal streams" held at La Palma, Canary Islands,
May 26 - 30, 200
A Two-Parameter Recursion Formula For Scalar Field Theory
We present a two-parameter family of recursion formulas for scalar field
theory. The first parameter is the dimension . The second parameter
() allows one to continuously extrapolate between Wilson's approximate
recursion formula and the recursion formula of Dyson's hierarchical model. We
show numerically that at fixed , the critical exponent depends
continuously on . We suggest the use of the independence as a
guide to construct improved recursion formulas.Comment: 7 pages, uses Revtex, one Postcript figur
Off-diagonal disorder in the Anderson model of localization
We examine the localization properties of the Anderson Hamiltonian with
additional off-diagonal disorder using the transfer-matrix method and
finite-size scaling. We compute the localization lengths and study the
metal-insulator transition (MIT) as a function of diagonal disorder, as well as
its energy dependence. Furthermore we investigate the different influence of
odd and even system sizes on the localization properties in quasi
one-dimensional systems. Applying the finite-size scaling approach in
conjunction with a nonlinear fitting procedure yields the critical parameters
of the MIT. In three dimensions, we find that the resulting critical exponent
of the localization length agrees with the exponent for the Anderson model with
pure diagonal disorder.Comment: 12 pages including 4 EPS figures, accepted for publication in phys.
stat. sol. (b
- âŠ