4,264 research outputs found
The Redshift Evolution of Clustering in the HDF
We present a correlation function analysis for the catalogue of photometric
redshifts obtained from the Hubble Deep Field image by Fernandez-Soto et al.,
1998. By dividing the catalogue into redshift bins of width we
measured the angular correlation function as a function of redshift
up to . From these measurements we derive the trend of the
correlation length . We find that is roughly constant with
look-back time up to , and then increases to higher values at
z\simgt 2.4. We estimate the values of , assuming
, and different geometries. For
we find Mpc, in good
agreement with the values obtained from analysis of the Lyman Break Galaxies.Comment: 6 pages, 4 postscript figures, version to appear on MNRA
Correlations in the Spatial Power Spectrum Inferred from Angular Clustering: Methods and Application to APM
We reconsider the inference of spatial power spectra from angular clustering
data and show how to include correlations in both the angular correlation
function and the spatial power spectrum. Inclusion of the full covariance
matrices loosens the constraints on large-scale structure inferred from the APM
survey by over a factor of two. We present a new inversion technique based on
singular value decomposition that allows one to propagate the covariance matrix
on the angular correlation function through to that of the spatial power
spectrum and to reconstruct smooth power spectra without underestimating the
errors. Within a parameter space of the CDM shape Gamma and the amplitude
sigma_8, we find that the angular correlations in the APM survey constrain
Gamma to be 0.19-0.37 at 68% confidence when fit to scales larger than k=0.2h
Mpc^-1. A downturn in power at k<0.04h Mpc^-1 is significant at only 1-sigma.
These results are optimistic as we include only Gaussian statistical errors and
neglect any boundary effects.Comment: 37 pages, LaTex, 9 figures. Submitted to Ap
Angular correlations of galaxy distribution
We study the angular correlations of various galaxy catalogs (CfA1, SSRS1,
Perseus-Pisces, APM Bright Galaxies and Zwicky). We find that the angular
correlation exponent is rather than as
usually found by the standard correlation function . We
identify the problem in the artificial decay of . Moreover we
find that no characteristic angular scale is present in any of the analyzed
catalogs. Finally we show that all the available data are consistent with each
other and the angular distribution of galaxies is quite naturally compatible
with a fractal structure with .Comment: 16 pages, latex, 3 postscript figures. Accepted for publication in
Astrophysical Journal Letters. This paper is also available at
http://www.phys.uniroma1.it/DOCS/PIL/pil.htm
Transatlantic Issues: Report from Scotland
Several bioethical topics received a great deal of news coverage here in Scotland in 2009. Three important issues with transatlantic connections are the swine flu outbreak, which was handled very differently in Scotland, England, and America; the U.S. debate over healthcare reform, which drew the British National Health Service (NHS) into the controversy; and the release to Libya of the Lockerbie bomber, which at first glance might not seem particularly bioethical, but which actually hinged on the very public discussion of the prisoner’s medical records. On a national level, there have been attempts in both Scotland and England to change the law on assisted suicide, where success looks more likely than ever. This paper discusses each of these issues and hopefully will raise awareness of how these issues were dealt with in the United Kingdom and its component countries
Temporally Asymmetric Fluctuations are Sufficient for the Operation of a Correlation Ratchet
It has been shown that the combination of a broken spatial symmetry in the
potential (or ratchet potential) and time correlations in the driving are
crucial, and enough to allow transformation of the fluctuations into work. The
required broken spatial symmetry implies a specific molecular arrangement of
the proteins involved. Here we show that a broken spatial symmetry is not
required, and that temporally asymmetric fluctuations (with mean zero) can be
used to do work, even when the ratchet potential is completely symmetric.
Temporal asymmetry, defined as a lack of invariance of the statistical
properties under the operation to temporal inversion, is a generic property of
nonequilibrium fluctuation, and should therefore be expected to be quite common
in biological systems.Comment: 17 pages, ps figures on request, LaTeX Article Forma
Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data
The Southern Abell Redshift Survey contains 39 clusters of galaxies with
redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z =
0.0845. SARS covers the region 0 21h (while
avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the
Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected
from the Automatic Plate Measuring Facility galaxy catalog with
extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the
Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects
concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are
reported in the fields of these 39 clusters of galaxies.Comment: 20 pages, 5 figures, accepted for publication in the Astronomical
Journal, Table 2 can be downloaded in its entirety from
http://trotsky.arc.nasa.gov/~mway/SARS1/sars1-table2.cs
The local space density of dwarf galaxies
We estimate the luminosity function of field galaxies over a range of ten
magnitudes (-22 < M_{B_J} < -12 for H_0 = 100 km/s/Mpc) by counting the number
of faint APM galaxies around Stromlo-APM redshift survey galaxies at known
distance. The faint end of the luminosity function rises steeply at M_{B_J}
\approx -15, implying that the space density of dwarf galaxies is at least two
times larger than predicted by a Schechter function with flat faint-end slope.
Such a high abundance of dwarf galaxies at low redshift can help explain the
observed number counts and redshift distributions of faint galaxies without
invoking exotic models for galaxy evolution.Comment: 20 pages, 5 included postscript figures, uses AAS LaTex macros.
Accepted for publication in the Astrophysical Journal. Two figures and
associated discussion added; results and conclusions unchange
Multi-band quantum ratchets
We investigate directed motion in non-adiabatically rocked ratchet systems
sustaining few bands below the barrier. Upon restricting the dynamics to the
lowest M bands, the total system-plus-bath Hamiltonian is mapped onto a
discrete tight-binding model containing all the information both on the intra-
and inter-well tunneling motion. A closed form for the current in the
incoherent tunneling regime is obtained. In effective single-band ratchets, no
current rectification occurs. We apply our theory to describe rectification
effects in vortex quantum ratchets devices. Current reversals upon variation of
the ac-field amplitude or frequency are predicted.Comment: Accepted for publication in Physical Review Letter
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