664 research outputs found
Interpreting the Clustering of Radio Sources
We develop the formalism required to interpret, within a CDM framework, the
angular clustering of sources in a deep radio survey. The effect of nonlinear
evolution of density perturbations is discussed as is the effect of the assumed
redshift distribution of sources. We also investigate what redshift ranges
contribute to the clustering signal at different angular scales. Application of
the formalism is focussed on the clustering detected in the FIRST survey but
measurements made for other radio surveys are also investigated. We comment on
the implications for the evolution of clustering.Comment: 7 pages latex, 6 figures, to appear in MNRAS, replaced version
corrects typo in expression for w(theta
Clustering of HI galaxies in HIPASS and ALFALFA
We investigate the clustering of HI-selected galaxies in the ALFALFA survey
and compare results with those obtained for HIPASS. Measurements of the angular
correlation function and the inferred 3D-clustering are compared with results
from direct spatial-correlation measurements. We are able to measure clustering
on smaller angular scales and for galaxies with lower HI masses than was
previously possible. We calculate the expected clustering of dark matter using
the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA
sample is somewhat more anti-biased with respect to dark matter than the HIPASS
sample.Comment: 5 Pages 4 Figures accepted by MNRA
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Rule of Law in Iran: Independence of the Judiciary, Bar Association, Lawyers and Iran’s Compliance with International Human Rights Obligations
The Angular Two-Point Correlation Function for the FIRST Radio Survey
The FIRST (Faint Images of the Radio Sky at Twenty Centimeters) survey now
covers 1550 square degrees of sky where and
. This yields a catalog of 138,665 sources
above the survey threshold of 1 mJy, about one third of which are in
double-lobed and multi-component sources. We have used these data to obtain the
first high-significance measurement of the two-point angular correlation for a
deep radio sample. We find that the correlation function between
and is well fitted by a power law of the form
where and . On small scales
(), double and multi-component sources are shown to have a
larger clustering amplitude than that of the whole sample. Sources with flux
densities below 2 mJy are found to have a shallower slope than that obtained
for the whole sample, consistent with there being a significant contribution
from starbursting galaxies at these faint fluxes. The cross-correlation of
radio sources and Abell clusters is determined. A preliminary approach to
inferring spatial information is outlined.Comment: 22 pages, latex, 4 figures. To appear in Astrophysical Journal.
Replaced paper contains a revised value for the the spatial correlation
function amplitude (r_0
Figure rotation of dark halos in CDM simulations
We investigate the figure rotation of dark matter halos identified in Lambda
CDM simulations. We find that when strict criteria are used to select suitable
halos for study, 5 of the 222 halos identified in our z=0 simulation output
undergo coherent figure rotation over a 5h^{-1}Gyr period. We discuss the
effects of varying the selection criteria and find that pattern speeds for a
much larger fraction of the halos can be measured when the criteria are
relaxed. Pattern speeds measured over a 1h^{-1}Gyr period follow a log-normal
distribution, centred at Omega_p = 0.25h rad/Gyr with a maximum value of 0.94h
rad/Gyr. Over a 5h^{-1}Gyr period, the average pattern speed of a halo is about
0.1h rad/Gyr and the largest pattern speed found is 0.24h rad/Gyr. Less than
half of the selected halos showed alignment between their figure rotation axis
and minor axis, the exact fraction being somewhat dependent on how one defines
a halo. While the pattern speeds observed are lower than those generally
thought capable of causing spiral structure, we note that coherent figure
rotation is found over very long periods and argue that further simulations
would be required before strong conclusions about spiral structure in all
galaxies could be drawn. We find no correlation between halo properties such as
total mass and the pattern speed.Comment: accepted to MNRAS, 8 page
Prediction of exercise capacity and training prescription from the 6-minute walk test and rating of perceived exertion
Walking tests, such as the 6-min walk test (6MWT), are popular methods of estimating peak oxygen uptake (VO(2)peak) in clinical populations. However, the strength of the distance vs. VO(2)peak relationship is not strong, and there are no equations for estimating ventilatory threshold (VT), which is important for training prescription and prognosis. Since the 6MWT is often limited by walking mechanics, prediction equations that include simple additional predictors, such as the terminal rating of perceived exertion (RPE), hold the potential for improving the prediction of VO(2)max and VT. Therefore, this study was designed to develop equations for predicting VO(2)peak and VT from performance during the 6MWT, on the basis of walking performance and terminal RPE. Clinically stable patients in a cardiac rehabilitation program (N = 63) performed the 6MWT according to the American Thoracic Society guidelines. At the end of each walk, the subject provided their terminal RPE on a 6–20 Borg scale. Each patient also performed a maximal incremental treadmill test with respiratory gas exchange to measure VO(2)peak and VT. There was a good correlation between VO(2)peak and 6MWT distance (r = 0.80) which was improved by adding the terminal RPE in a multiple regression formula (6MWT + RPE, R(2) = 0.71, standard error of estimate, SEE = 1.3 Metabolic Equivalents (METs). The VT was also well correlated with walking performance, 6MWT distance (r = 0.80), and was improved by the addition of terminal RPE (6MWT + RPE, R(2) = 0.69, SEE = 0.95 METs). The addition of terminal RPE to 6MWT distance improved the prediction of maximal METs and METs at VT, which may have practical applications for exercise prescription
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