420 research outputs found
Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy
Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
to ) and couplings (from to ).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen
Ătude comparative tensiomĂštre automatique versus doppler Ă ultrasons dans la mesure de lâindex de pression systolique Ă la cheville (Ipsc)
ObjectifLâĂ©valuation de lâindex de pression systolique Ă la cheville (IPSC) est la mĂ©thode non invasive la plus simple de dĂ©pistage de lâartĂ©riopathie des membres infĂ©rieurs (AOMI) mais reste peu usitĂ©e en pratique courante, car elle est chronophage, implique un Ă©quipement et une formation appropriĂ©s. Le but de notre Ă©tude est dâĂ©valuer la validitĂ© et la fiabilitĂ© de la mesure de lâIPSC Ă lâaide dâun tensiomĂštre automatique par comparaison avec les rĂ©sultats obtenus par doppler continu, mĂ©thode de rĂ©fĂ©rence. MĂ©thodes Les patients de 65 ans et plus hospitalisĂ©s au CHU dâAngers de juillet 2008 à mars 2009 en mĂ©decine interne et nâayant pas dâAOMI documentĂ©e au moment de lâinclusion ont participĂ© Ă lâĂ©tude. Les critĂšres dâexclusion Ă©taient la prĂ©sence dâune fibrillation auriculaire et une incompressibilitĂ© des artĂšres distales des membres infĂ©rieurs. Pour chaque patient, lâIPSC a Ă©tĂ© Ă©valuĂ© par tensiomĂštre automatique et par la mĂ©thode Doppler de rĂ©fĂ©rence ; ces mesures Ă©tant faites par le mĂȘme examinateur. La concordance entre les deux mesures Ă©tait apprĂ©ciĂ©e par la mĂ©thode de Bland et Altman et le coefficient de corrĂ©lation intraclasse (ICC). RĂ©sultats Sur 287 patients participant Ă lâĂ©tude, 221 ont Ă©tĂ©s inclus. Cinquante-six (25 %) de ces patients avaient un IPSC < 0,90. La concordance entre les deux mĂ©thodes Ă©tait mĂ©diocre : ICC Ă 0,35 ± 0,08 et moyenne Ă 0,08 ± 0,26 selon la mĂ©thode de Bland et Altman. Conclusion La mĂ©thode de dĂ©pistage de lâAOMI par mesure de lâIPSC par tensiomĂštre automatique ne peut ĂȘtre retenue comme une alternative Ă la mĂ©thode Doppler
Observing the high redshift universe using the VIMOS-IFU
We describe the advantages of using Integral Field Spectroscopy to observe
deep fields of galaxy. The VIMOS Integral Field Unit is particularly suitable
for this kind of studies thanks to its large field-of-view (~ 1 arcmin^2).
After a short description of the VIMOS-IFU data reduction, we detail the main
scientific issues which can be addressed using observations of the Hubble Deep
Field South with a combination of Integral Field Spectroscopy and broad band
optical and Near-Infrared imaging.Comment: 4 pages, accepted for publishing in AN (ref. proc. of Euro3D Science
workshop, IoA Cambridge, May 2003
Number counts and clustering properties of bright Distant Red Galaxies in the UKIDSS Ultra Deep Survey Early Data Release
We describe the number counts and spatial distribution of 239 Distant Red
Galaxies (DRGs), selected from the Early Data Release of the UKIDSS Ultra Deep
Survey. The DRGs are identified by their very red infrared colours with
(J-K)AB>1.3, selected over 0.62 sq degree to a 90% completeness limit of
KAB~20.7. This is the first time a large sample of bright DRGs has been studied
within a contiguous area, and we provide the first measurements of their number
counts and clustering. The population shows strong angular clustering,
intermediate between those of K-selected field galaxies and
optical/infrared-selected Extremely Red Galaxies. Adopting the redshift
distributions determined from other recent studies, we infer a high correlation
length of r0~11 h-1 Mpc. Such strong clustering could imply that our galaxies
are hosted by very massive dark matter halos, consistent with the progenitors
of present-day L>L* elliptical galaxies.Comment: 5 pages, 4 figures, revised version accepted to MNRAS.
Higher-resolution figures available from the authors on reques
An improved lower bound for (1,<=2)-identifying codes in the king grid
We call a subset of vertices of a graph a -identifying
code if for all subsets of vertices with size at most , the sets
are distinct. The concept of
identifying codes was introduced in 1998 by Karpovsky, Chakrabarty and Levitin.
Identifying codes have been studied in various grids. In particular, it has
been shown that there exists a -identifying code in the king grid
with density 3/7 and that there are no such identifying codes with density
smaller than 5/12. Using a suitable frame and a discharging procedure, we
improve the lower bound by showing that any -identifying code of
the king grid has density at least 47/111
The Halo Mass-Bias Redshift Evolution in the CDM Cosmology
We derive an analytic model for the redshift evolution of linear-bias,
allowing for interactions and merging of the mass-tracers, by solving a second
order differential equation based on linear perturbation theory and the
Friedmann-Lemaitre solutions of the cosmological field equations. We then study
the halo-mass dependence of the bias evolution, using the dark matter halo
distribution in a CDM simulation in order to calibrate the free
parameters of the model. Finally, we compare our theoretical predictions with
available observational data and find a good agreement. In particular, we find
that the bias of optical QSO's evolve differently than those selected in X-rays
and that their corresponding typical dark matter halo mass is and \magcir 5 \times 10^{13} h^{-1} M_{\odot},
respectively.Comment: 8 pages, 5 figures, accepted for publication in Ap
The VIRMOS deep imaging survey: I. overview and survey strategy
This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging
survey in four fields totalling more than 17 deg^2, conducted with the 30x40
arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose
survey used for a variety of science goals, including surveys of very high
redshift galaxies and weak lensing studies.
Four high galactic latitude fields, each 2x2 deg^2, have been selected along
the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of
the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while
the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is
covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively.
The data is pipeline processed at the Terapix facility at the Institut
d'Astrophysique de Paris to produce large mosaic images. The catalogs produced
contain the positions, shape, total and aperture magnitudes for the 2.175
million objects. The depth measured (3sigma in a 3 arc-second aperture) is
I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful
quality control has been applied on the data as described in joint papers.
These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a
large spectroscopic survey of the distant universe (Le F\`evre et al., 2003).
First results from the CFH12K-VIRMOS survey have been published on weak lensing
(e.g. van Waerbeke & Mellier 2003).
Catalogs and images are available through the VIRMOS database environment
under Oracle ({\tt http://www.oamp.fr/virmos}). They will be open for general
use on July 1st, 2003.Comment: 17 pages including 9 figures, submitted to A&
On the evolution of clustering of 24um-selected galaxies
This paper investigates the clustering properties of a complete sample of
1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping
region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the
two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z
sample) as it is in these regions were we expect the mid-IR population to be
dominated by intense dust-enshrouded activity such as star formation and black
hole accretion. Investigations of the angular correlation function produce a
correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the
low-z one. Comparisons with physical models reveal that the high-z sources are
exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable
to those which locally host groups-to-clusters of galaxies, and are very common
within such (rare) structures. Conversely, lower-z galaxies are found to reside
in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems.
While recent studies have determined a strong evolution of the 24um luminosity
function between z~2 and z~0, they cannot provide information on the physical
nature of such an evolution. Our clustering results instead indicate that this
is due to the presence of different populations of objects inhabiting different
structures, as active systems at z<~1.5 are found to be exclusively associated
with low-mass galaxies, while very massive sources appear to have concluded
their active phase before this epoch. Finally, we note that the small-scale
clustering data seem to require steep profiles for the distribution of galaxies
within their halos. This is suggestive of close encounters and/or mergers which
could strongly favour both AGN and star-formation activity.Comment: 13 pages, 8 figures, to appear in MNRA
The Canada-France Deep Fields III: Photometric Redshift Distribution to I(AB) ~ 24
We compute accurate redshift distributions to I(AB) = 24 and R(AB) = 24.5
using photometric redshifts estimated from six-band UBVRIZ photometry in the
Canada-France Deep Fields-Photometric Redshift Survey (CFDF-PRS). Our
photometric redshift algorithm is calibrated using hundreds of CFRS
spectroscopic redshifts in the same fields. The dispersion in redshift is
\sigma/(1+z) \la 0.04 to the CFRS depth of I(AB) = 22.5, rising to \sigma/(1+z)
\la 0.06 at our nominal magnitude and redshift limits of I(AB) = 24 and z \le
1.3, respectively. We describe a new method to compute N(z) that incorporates
the full redshift likelihood functions in a Bayesian iterative analysis and we
demonstrate in extensive Monte Carlo simulations that it is superior to
distributions calculated using simple maximum likelihood redshifts. The
field-to-field differences in the redshift distributions, while not unexpected
theoretically, are substantial even on 30' scales. We provide I(AB) and R(AB)
redshift distributions, median redshifts, and parametrized fits of our results
in various magnitude ranges, accounting for both random and systematic errors
in the analysis.Comment: 19 Pages, 8 Tables, 13 Figures. Replaced to match published version.
Main results unchange
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