865 research outputs found
Cosmic Microwave Background Polarization
Cosmic microwave background (CMB) anisotropy is our richest source of
cosmological information; the standard cosmological model was largely
established thanks to study of the temperature anisotropies. By the end of the
decade, the Planck satellite will close this important chapter and move us
deeper into the new frontier of polarization measurements. Numerous
ground--based and balloon--borne experiments are already forging into this new
territory. Besides providing new and independent information on the primordial
density perturbations and cosmological parameters, polarization measurements
offer the potential to detect primordial gravity waves, constrain dark energy
and measure the neutrino mass scale. A vigorous experimental program is
underway worldwide and heading towards a new satellite mission dedicated to CMB
polarization.Comment: Review given at TAUP 2005; References added; Additional reference
Dark energy constraints and correlations with systematics from CFHTLS weak lensing, SNLS supernovae Ia and WMAP5
We combine measurements of weak gravitational lensing from the CFHTLS-Wide
survey, supernovae Ia from CFHT SNLS and CMB anisotropies from WMAP5 to obtain
joint constraints on cosmological parameters, in particular, the dark energy
equation of state parameter w. We assess the influence of systematics in the
data on the results and look for possible correlations with cosmological
parameters.
We implement an MCMC algorithm to sample the parameter space of a flat CDM
model with a dark-energy component of constant w. Systematics in the data are
parametrised and included in the analysis. We determine the influence of
photometric calibration of SNIa data on cosmological results by calculating the
response of the distance modulus to photometric zero-point variations. The weak
lensing data set is tested for anomalous field-to-field variations and a
systematic shape measurement bias for high-z galaxies.
Ignoring photometric uncertainties for SNLS biases cosmological parameters by
at most 20% of the statistical errors, using supernovae only; the parameter
uncertainties are underestimated by 10%. The weak lensing field-to-field
variance pointings is 5%-15% higher than that predicted from N-body
simulations. We find no bias of the lensing signal at high redshift, within the
framework of a simple model. Assuming a systematic underestimation of the
lensing signal at high redshift, the normalisation sigma_8 increases by up to
8%. Combining all three probes we obtain -0.10<1+w<0.06 at 68% confidence
(-0.18<1+w<0.12 at 95%), including systematic errors. Systematics in the data
increase the error bars by up to 35%; the best-fit values change by less than
0.15sigma. [Abridged]Comment: 14 pages, 10 figures. Revised version, matches the one to be
published in A&A. Modifications have been made corresponding to the referee's
suggestions, including reordering of some section
The Drift Chambers Of The Nomad Experiment
We present a detailed description of the drift chambers used as an active
target and a tracking device in the NOMAD experiment at CERN. The main
characteristics of these chambers are a large area, a self supporting structure
made of light composite materials and a low cost. A spatial resolution of 150
microns has been achieved with a single hit efficiency of 97%.Comment: 42 pages, 26 figure
The DICE calibration project: design, characterization, and first results
We describe the design, operation, and first results of a photometric
calibration project, called DICE (Direct Illumination Calibration Experiment),
aiming at achieving precise instrumental calibration of optical telescopes. The
heart of DICE is an illumination device composed of 24 narrow-spectrum,
high-intensity, light-emitting diodes (LED) chosen to cover the
ultraviolet-to-near-infrared spectral range. It implements a point-like source
placed at a finite distance from the telescope entrance pupil, yielding a flat
field illumination that covers the entire field of view of the imager. The
purpose of this system is to perform a lightweight routine monitoring of the
imager passbands with a precision better than 5 per-mil on the relative
passband normalisations and about 3{\AA} on the filter cutoff positions. The
light source is calibrated on a spectrophotometric bench. As our fundamental
metrology standard, we use a photodiode calibrated at NIST. The radiant
intensity of each beam is mapped, and spectra are measured for each LED. All
measurements are conducted at temperatures ranging from 0{\deg}C to 25{\deg}C
in order to study the temperature dependence of the system. The photometric and
spectroscopic measurements are combined into a model that predicts the spectral
intensity of the source as a function of temperature. We find that the
calibration beams are stable at the level -- after taking the slight
temperature dependence of the LED emission properties into account. We show
that the spectral intensity of the source can be characterised with a precision
of 3{\AA} in wavelength. In flux, we reach an accuracy of about 0.2-0.5%
depending on how we understand the off-diagonal terms of the error budget
affecting the calibration of the NIST photodiode. With a routine 60-mn
calibration program, the apparatus is able to constrain the passbands at the
targeted precision levels.Comment: 25 pages, 27 figures, accepted for publication in A&
The Dynamic Processing of CD46 Intracellular Domains Provides a Molecular Rheostat for T Cell Activation
Adequate termination of an immune response is as important as the induction of an appropriate response. CD46, a regulator of complement activity, promotes T cell activation and differentiation towards a regulatory Tr1 phenotype. This Tr1 differentiation pathway is defective in patients with MS, asthma and rheumatoid arthritis, underlying its importance in controlling T cell function and the need to understand its regulatory mechanisms. CD46 has two cytoplasmic tails, Cyt1 and Cyt2, derived from alternative splicing, which are co-expressed in all nucleated human cells. The regulation of their expression and precise functions in regulating human T cell activation has not been fully elucidated.Here, we first report the novel role of CD46 in terminating T cell activation. Second, we demonstrate that its functions as an activator and inhibitor of T cell responses are mediated through the temporal processing of its cytoplasmic tails. Cyt1 processing is required to turn T cell activation on, while processing of Cyt2 switches T cell activation off, as demonstrated by proliferation, CD25 expression and cytokine secretion. Both tails require processing by Presenilin/γSecretase (P/γS) to exert these functions. This was confirmed by expressing wild-type Cyt1 and Cyt2 tails and uncleavable mutant tails in primary T cells. The role of CD46 tails was also demonstrated with T cells expressing CD19 ectodomain-CD46 C-Terminal Fragment (CTF) fusions, which allowed specific triggering of each tail individually.We conclude that CD46 acts as a molecular rheostat to control human T cell activation through the regulation of processing of its cytoplasmic tails
Constraints on Cosmological Models and Reconstructing the Acceleration History of the Universe with Gamma-Ray Burst Distance Indicators
Gamma-ray bursts (GRBs) have been regarded as standard candles at very high
redshift for cosmology research. We have proposed a new method to calibrate GRB
distance indicators with Type Ia supernova (SNe Ia) data in a completely
cosmology-independent way to avoid the circularity problem that had limited the
direct use of GRBs to probe cosmology [N. Liang, W. K. Xiao, Y. Liu, and S. N.
Zhang, Astrophys. J. 685, 354 (2008).]. In this paper, a simple method is
provided to combine GRB data into the joint observational data analysis to
constrain cosmological models; in this method those SNe Ia data points used for
calibrating the GRB data are not used to avoid any correlation between them. We
find that the CDM model is consistent with the joint data in the
1- confidence region, using the GRB data at high redshift calibrated
with the interpolating method, the Constitution set of SNe Ia, the cosmic
microwave background radiation from Wilkinson Microwave Anisotropy Probe five
year observation, the baryonic acoustic oscillation from the spectroscopic
Sloan Digital Sky Survey Data Release 7 galaxy sample, the x-ray baryon mass
fraction in clusters of galaxies, and the observational Hubble parameter versus
redshift data. Comparing to the joint constraints with GRBs and without GRBs,
we find that the contribution of GRBs to the joint cosmological constraints is
a slight shift in the confidence regions of cosmological parameters to better
enclose the CDM model. Finally, we reconstruct the acceleration
history of the Universe up to with the distance moduli of SNe Ia and GRBs
and find some features that deviate from the CDM model and seem to
favor oscillatory cosmology models; however further investigations are needed
to better understand the situation.Comment: 14 pages, 9 figures, 2 tables; v3: the revised version, fig. 6 and
some discussions added, accepted for for publication in Phys. Rev. D; v4: the
published version (Phys. Rev. D 81, 083518, 2010
Non-perturbative scalar gauge-invariant metric fluctuations from the Ponce de Leon metric in the STM theory of gravity
We study our non-perturbative formalism to describe scalar gauge-invariant
metric fluctuations by extending the Ponce de Leon metric.Comment: accepted in Eur. Phys. J.
A Study of Strange Particles Produced in Neutrino Neutral Current Interactions in the NOMAD Experiment
Results of a detailed study of strange particle production in neutrino
neutral current interactions are presented using the data from the NOMAD
experiment. Integral yields of neutral strange particles (K0s, Lambda,
Lambda-bar) have been measured. Decays of resonances and heavy hyperons with an
identified K0s or Lambda in the final state have been analyzed. Clear signals
corresponding to K* and Sigma(1385) have been observed. First results on the
measurements of the Lambda polarization in neutral current interactions have
been obtained.Comment: Accepted for publication in Nuclear Physics B as a rapid
communicatio
Next-to-leading order QCD evolution of transversity fragmentation functions
We derive the next-to-leading order splitting kernels for the scale evolution
of fragmentation functions for transversely polarized quarks into transversely
polarized hadrons.Comment: 9 pages, LaTe
The Nearby Supernova Factory
The Nearby Supernova Factory (SNfactory) is an ambitious project to find and
study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at
redshifts 0.03<z<0.08. This program will provide an exceptional data set of
well-studied SNe in the nearby smooth Hubble flow that can be used as
calibration for the current and future programs designed to use SNe to measure
the cosmological parameters. The first key ingredient for this program is a
reliable supply of Hubble-flow SNe systematically discovered in unprecedented
numbers using the same techniques as those used in distant SNe searches. In
2002, 35 SNe were found using our test-bed pipeline for automated SN search and
discovery. The pipeline uses images from the asteroid search conducted by the
Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction
techniques and analysis have allowed us to increase our effective SN discovery
rate to ~12 SNe/month in 2003.Comment: 7 pages, 3 figures to be published in New Astronomy Review
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