1,383 research outputs found
Clusters and Superclusters in the Las Campanas Redshift Survey
Two-dimensional high-resolution density field of galaxies of the Las Campanas
Redshift Survey (LCRS) with a smoothing length 0.8 Mpc/h is used to extract
clusters and groups of galaxies, and a low-resolution field with a smoothing
length 10 Mpc/h to find superclusters of galaxies. Properties of these density
field (DF) clusters and superclusters are studied and compared with the
properties of Abell clusters and superclusters, and LCRS loose groups. We
calculate the DF-cluster luminosity function, and show that most luminous
clusters in high-density environments are about ten times brighter than most
luminous clusters in low-density environments. We present a catalogue of
DF-superclusters and show that superclusters that contain Abell clusters are
richer and more luminous than superclusters without Abell clusters. A pdf file
of the paper with high-resolution figures is available in Tartu Observatory
web-site (http://www.aai.ee/~maret/cosmoweb.html)Comment: 19 pages LaTeX text, 15 PostScript Figures, submitted to Astronomy
and Astrophysic
The AMIGA sample of isolated galaxies. V. Quantification of the isolation
The AMIGA project aims to build a well defined and statistically significant
reference sample of isolated galaxies in order to estimate the environmental
effects on the formation and evolution of galaxies. The goal of this paper is
to provide a measure of the environment of the isolated galaxies in the AMIGA
sample, quantifying the influence of the candidate neighbours identified in our
previous work and their potential effects on the evolution of the primary
galaxies. Here we provide a quantification of the isolation degree of the
galaxies in this sample. Our starting sample is the Catalogue of Isolated
Galaxies (CIG). We used two parameters to estimate the influence exerted by the
neighbour galaxies on the CIG galaxy: the local number density of neighbour
galaxies and the tidal strength affecting the CIG galaxy. We show that both
parameters together provide a comprehensive picture of the environment. For
comparison, those parameters have also been derived for galaxies in denser
environments such as triplets, groups and clusters. The CIG galaxies show a
continuous spectrum of isolation, as quantified by the two parameters, from
very isolated to interacting. The fraction of CIG galaxies whose properties are
expected to be influenced by the environment is however low (159 out of 950
galaxies). The isolated parameters derived for the comparsion samples gave
higher values than for the CIG and we found clear differences for the average
values of the 4 samples considered, proving the sensitivity of these
parameters. The environment of the galaxies in the CIG has been characterised,
using two complementary parameters quantifying the isolation degree, the local
number density of the neighbour galaxies and the tidal forces affecting the
isolated galaxies. (Abridged)Comment: 10 pages, 12 figures, proposed for acceptance A&
Efficacy of gold weight implants in facial nerve palsy: quantitative alterations in blinking
AbstractDeficient eyelid closure is a major visual threat to patients with unresolved facial nerve palsy. Gold weight implants assisted eyelid closure in patients with paresis of the orbicularis oculi, ameliorating patient complaints of dry eye, excessive tearing, and corneal epithelial breakdown. We used dynamic measures to assess the efficacy of upper eyelid gold weight implantation surgery for facial nerve palsy. The search coil technique was used to record spontaneous blinks bilaterally in six patients, before and after unilateral gold weight implantations into the upper eyelid in severe facial nerve palsy. In uncomplicated facial nerve palsy, the amplitude of blink down-phases for the paretic eyelid was 28.6±5.7% of the amplitude of the contralateral, normal eyelid. Following corrective surgery, closure of the paretic eyelid improved to 42.6±7.5% (P<0.05). There was not a commensurate increase in the peak velocity of blink down-phases, suggesting that gold weight effects are mediated by a passive improvement in blink dynamics
River Restoration in the Twenty-First Century: Data and Experiential Knowledge to Inform Future Efforts
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71999/1/j.1526-100X.2007.00243.x.pd
Computation of Mixed Type Functional Differential Boundary Value Problems
This is the published version, also available here: http://dx.doi.org/10.1137/040603425.We study boundary value differential-difference equations where the difference terms may contain both advances and delays. Special attention is paid to connecting orbits, in particular to the modeling of the tails after truncation to a finite interval, and we reformulate these problems as functional differential equations over a bounded domain. Connecting orbits are computed for several such problems including discrete Nagumo equations, an Ising model, and Frenkel--Kontorova type equations. We describe the collocation boundary value problem code used to compute these solutions, and the numerical analysis issues which arise, including linear algebra, boundary functions and conditions, and convergence theory for the collocation approximation on finite intervals
Photometric validation of a model independent procedure to extract galaxy clusters
By means of CCD photometry in three bands (Gunn g, r, i) we investigate the
existence of 12 candidate clusters extracted via a model independent peak
finding algorithm (\cite{memsait}) from DPOSS data. The derived color-magnitude
diagrams allow us to confirm the physical nature of 9 of the cluster
candidates, and to estimate their photometric redshifts. Of the other
candidates, one is a fortuitous detection of a true cluster at z~0.4, one is a
false detection and the last is undecidable on the basis of the available data.
The accuracy of the photometric redshifts is tested on an additional sample of
8 clusters with known spectroscopic redshifts. Photometric redshifts turn out
to be accurate within z~0.01 (interquartile range).Comment: A&A in pres
A 120-Mpc Periodicity in the Three-Dimensional Distribution of Galaxy Superclusters
Using a new compilation of available data on galaxy clusters and
superclusters we present evidence for a quasiregular three-dimensional network
of rich superclusters and voids, with the regions of high density separated by
about 120 Mpc. We calculate the power spectrum for clusters of galaxies; it has
a peak on the wavelength equal to the step of the network; the excess in the
amplitude of the spectrum over that of the cold dark matter model is by a
factor of 1.4. The probability that the spectrum can be formed within the
framework of the standard cosmogony is very small. If the cluster distribution
reflects the distribution of all matter (luminous and dark), then there must
exists some hithero unknown process that produces regular structure on large
scales.Comment: Tex, 6 pages, 2 PostScript figures embedded, accepted by Nature on
November 19, 199
Global survey of star clusters in the Milky Way: III. 139 new open clusters at high Galactic latitudes
Context. An earlier analysis of the Milky Way Star Cluster (MWSC) catalogue revealed an apparent lack of old (t Ăą?€ 1 Gyr) open clusters in the solar neighbourhood (d Ăą?„ 1 kpc). Aims. To fill this gap we undertook a search for hitherto unknown star clusters, assuming that the missing old clusters reside at high Galactic latitudes | b | > 20Ă°. Methods. We were looking for stellar density enhancements using a star count algorithm on the 2MASS point source catalogue. To increase the contrast between potential clusters and the field, we applied filters in colour-magnitude space according to typical colour-magnitude diagrams of nearby old open clusters. The subsequent comparison with lists of known objects allowed us to select thus far unknown cluster candidates. For verification they were processed with the standard pipeline used within the MWSC survey for computing cluster membership probabilities and for determining structural, kinematic, and astrophysical parameters. Results. In total we discovered 782 density enhancements, 524 of which were classified as real objects. Among them 139 are new open clusters with ages 8.3 < log (t [yr]) < 9.7, distances d< 3 kpc, and distances from the Galactic plane 0.3 <Z< 1 kpc. This new sample has increased the total number of known high latitude open clusters by about 150%. Nevertheless, we still observe a lack of older nearby clusters up to 1 kpc from the Sun. This volume is expected to still contain about 60 unknown clusters that probably escaped our detection algorithm, which fails to detect sparse overdensities with large angular size
Modeling of Covalent Bonding in Solids by Inversion of Cohesive Energy Curves
We provide a systematic test of empirical theories of covalent bonding in
solids using an exact procedure to invert ab initio cohesive energy curves. By
considering multiple structures of the same material, it is possible for the
first time to test competing angular functions, expose inconsistencies in the
basic assumption of a cluster expansion, and extract general features of
covalent bonding. We test our methods on silicon, and provide the direct
evidence that the Tersoff-type bond order formalism correctly describes
coordination dependence. For bond-bending forces, we obtain skewed angular
functions that favor small angles, unlike existing models. As a
proof-of-principle demonstration, we derive a Si interatomic potential which
exhibits comparable accuracy to existing models.Comment: 4 pages revtex (twocolumn, psfig), 3 figures. Title and some wording
(but no content) changed since original submission on 24 April 199
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