1,134 research outputs found
Ensemble Density Functional Theory for Inhomogeneous Fractional Quantum Hall Systems
The fractional quantum Hall effect (FQHE) occurs at certain magnetic field
strengths B*(n) in a two-dimensional electron gas of density n at strong
magnetic fields perpendicular to the plane of the electron gas. At these
magnetic fields strengths, the system is incompressible, i.e., there is a
finite cost in energy for creating charge density fluctuations in the bulk,
while the boundary of the electron gas has gapless modes of density waves. The
bulk energy gap arises because of the strong electron-electron interactions.
While there are very good models for infinite homogeneous systems and for the
gapless excitations of the boundary of the electron gas, computational methods
to accurately model finite, inhomogeneous systems with more then about ten
electrons have not been available until very recently. We will here review an
ensemble density functional approach to studying the ground state of large
inhomogeneous spin polarized FQHE systems.Comment: 23 pages (revtex), 6 Postscript figures. To be published in Int. J.
Quant. Chem. (invited talk at the 1996 Sanibel Symposium
A new Tolman test of a cosmic distance duality relation at 21 cm
Under certain general conditions in an expanding universe, the luminosity
distance (d_L) and angular diameter distance (d_A) are connected by the
Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use
of objects of known surface brightness, to test this relation. In this letter,
we propose the use of redshifted 21 cm signal from disk galaxies, where neutral
hydrogen (HI) masses are seen to be almost linearly correlated with surface
area, to conduct a new Tolman test. We construct simulated catalogs of
galaxies, with the observed size-luminosity relation and realistic redshift
evolution of HI mass functions, likely to be detected with the planned Square
Kilometer Array (SKA). We demonstrate that these observations may soon provide
the best implementation of the Tolman test to detect any violation of the
Etherington relation.Comment: 4 pages, 2 figures, 1 table, v2: published versio
Information Across the Atlantic: a bibliography for company information in the US and UK
Laws in various countries demand a variety of information to be provided. This bibliography presents a variety of sources necessary to a researcher seeking information on United States and/or United Kingdom companies. It was created to aid library or information professionals in need of company information from these two countries. Research was conducted both in the US and the UK. Materials or resources were examined primarily in Oxford University libraries and the University of North Carolina at Chapel Hill. The bibliography is annotated and arranged by the following categories: basic company directories, company ownership and personnel, company financial information, Internet resources, and newspapers and periodicals. Its purpose is to identify key sources for finding both public and private company information in both countries
Weak Lensing Detection of Cl 1604+4304 at z = 0.90
We present a weak lensing analysis of the high-redshift cluster Cl 1604+4304.
At z=0.90, this is the highest-redshift cluster yet detected with weak lensing.
It is also one of a sample of high-redshift, optically-selected clusters whose
X-ray temperatures are lower than expected based on their velocity dispersions.
Both the gas temperature and galaxy velocity dispersion are proxies for its
mass, which can be determined more directly by a lensing analysis. Modeling the
cluster as a singular isothermal sphere, we find that the mass contained within
projected radius R is 3.69+-1.47 * (R/500 kpc) 10^14 M_odot. This corresponds
to an inferred velocity dispersion of 1004+-199 km/s, which agrees well with
the measured velocity dispersion of 989+98-76 km/s (Gal & Lubin 2004). These
numbers are higher than the 575+110-85 km/s inferred from Cl 1604+4304 X-ray
temperature, however all three velocity dispersion estimates are consistent
within ~ 1.9 sigma.Comment: Revised version accepted for publication in AJ (January 2005). 2
added figures (6 figures total
Galois covers of the open p-adic disc
This paper investigates Galois branched covers of the open -adic disc and
their reductions to characteristic . Using the field of norms functor of
Fontaine and Wintenberger, we show that the special fiber of a Galois cover is
determined by arithmetic and geometric properties of the generic fiber and its
characteristic zero specializations. As applications, we derive a criterion for
good reduction in the abelian case, and give an arithmetic reformulation of the
local Oort Conjecture concerning the liftability of cyclic covers of germs of
curves.Comment: 19 pages; substantial organizational and expository changes; this is
the final version corresponding to the official publication in Manuscripta
Mathematica; abstract update
Keck spectroscopy of CLASS gravitational lenses
We present the optical spectra of four newly discovered gravitational lenses
from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried
out using the Low Resolution Imaging Spectrograph on the W. M. Keck-I Telescope
as part of a program to study galaxy-scale gravitational lenses. From our
spectra we found the redshift of the background source in CLASS B0128+437
(z_s=3.1240+-0.0042) and the lensing galaxy redshifts in CLASS B0445+123
(z_l=0.5583+-0.0003) and CLASS B0850+054 (z_l=0.5883+-0.0006). Intriguingly, we
also discovered that CLASS B0631+519 may have two lensing galaxies
(z_l,1=0.0896+-0.0001, z_l,2=0.6196+-0.0004). We also found a single
unidentified emission line from the lensing galaxy in CLASS B0128+437 and the
lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS
B0445+123 and CLASS B0631+519 (l,2) to be early-type galaxies with Einstein
Radii of 2.8-3.0 h^{-1} kpc. The deflector in CLASS B0850+054 is a late-type
galaxy with an Einstein Radius of 1.6 h^{-1} kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA
The intermediate-redshift galaxy cluster CL 0048-2942. Stellar populations
We present a detailed study of the cluster CL 0048-2942, located at z~0.64,
based on a photometric and spectroscopic catalogue of 54 galaxies in a 5 x 5
square arcmin region centred in that cluster. Of these, 23 galaxies were found
to belong to the cluster. Based on this sample, the line-of-sight velocity
dispersion of the cluster is approximately 680 +- 140 km/s. We have performed
stellar population synthesis in the cluster members as well as in the field
galaxies of the sample and found that there are population gradients in the
cluster with central galaxies hosting mainly intermediate/old populations
whereas galaxies in the cluster outskirts show clearly an increase of younger
populations, meaning that star formation is predominantly taking place in the
outer regions of the cluster. In a general way, field galaxies seem to host
less evolved stellar populations than cluster members. In fact, in terms of
ages, young supergiant stars dominate the spectra of field galaxies whereas
cluster galaxies display a dominant number of old and intermediate age stars.
Following the work of other authors (e.g. Dressler et al. 1999) we have
estimated the percentage of K+A galaxies in our sample and found around 13% in
the cluster and 10% in the field. These values were estimated through means of
a new method, based on stellar population synthesis results, that takes into
account all possible absorption features in the spectrum and thus makes optimal
use of the data.Comment: Accepted by Astronomy & Astrophysics. 24 pages, 10 figures, 10 tables
(figures 3, 4, 5 and tables 1, 3, 4, 5, 6, 7, 8 will be available in
electronic format only in the A&A published version
Spin-ensemble density-functional theory for inhomogeneous quantum Hall systems
We have developed an ensemble density-functional theory that includes spin degrees of freedom for non-uniform quantum Hall systems. We have applied this theory using a local-spin-density approximation to study the edge reconstruction of parabolically confined quantum dots. For a Zeeman splitting below a certain critical value, the edge of a completely polarized maximum density droplet reconstructs into a spin-unpolarized structure. For larger Zeeman splittings, the edge remains polarized and develops an exchange hole
A Study of Nine High-Redshift Clusters of Galaxies: IV. Photometry and Sp ectra of Clusters 1324+3011 and 1604+4321
New photometric and spectroscopic observations of galaxies in the directions
of three distant clusters are presented as part of our on-going high-redshift
cluster survey. The clusters are CL1324+3011 at z = 0.76, CL1604+4304 at z =
0.90, and CL1604+4321 at z = 0.92. The observed x-ray luminosities in these
clusters are at least a factor of 3 smaller than those observed in clusters
with similar velocity dispersions at z <= 0.4. These clusters contain a
significant population of elliptical-like galaxies, although these galaxies are
not nearly as dominant as in massive clusters at z <= 0.5. We also find a large
population of blue cluster members. Defining an active galaxy as one in which
the rest equivalent width of [OII] is greater than 15 Angstroms, the fraction
of active cluster galaxies, within the central 1.0 Mpc, is 45%. In the field
population, we find that 65% of the galaxies with redshifts between z = 0.40
and z = 0.85 are active, while the fraction is 79% for field galaxies at z >
0.85. The star formation rate normalized by the rest AB B-band magnitude, SFRN,
increases as the redshift increases at a given evolving luminosity. At a given
redshift, however, SFRN decreases linearly with increasing luminosity
indicating a remarkable insensitivity of the star formation rate to the
intrinsic luminosity of the galaxy over the range -18 >= ABB >= -22. Cluster
galaxies in the central 1 Mpc regions exhibit depressed star formation rates.
We are able to measure significant evolution in the B-band luminosity function
over the range 0.1 <= z <= 1. The characteristic luminosity increases by a
factor of 3 with increasing redshift over this range.Comment: 64 pages, 18 figures, accepted for publication in the Astronomical
Journal on May 25, 2001. Scheduled to appear in Sept 2001 issu
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