Search results for "observation"
showing 10 items of 1586 documents
Non-Gaussian Signatures in the Lens Deformations of the CMB Sky. A New Ray-Tracing Procedure
2003
We work in the framework of an inflationary cold dark matter universe with cosmological constant, in which the cosmological inhomogeneities are considered as gravitational lenses for the CMB photons. This lensing deforms the angular distribution of the CMB maps in such a way that the induced deformations are not Gaussian. Our main goal is the estimation of the deviations with respect to Gaussianity appeared in the distribution of deformations. In the new approach used in this paper, matter is evolved with a particle-mesh N-body code and, then, an useful ray-tracing technique designed to calculate the correlations of the lens deformations induced by nonlinear structures is applied. Our appro…
A new stochastic approach to cumulative weak lensing
2009
We study the weak gravitational lensing effects caused by a stochastic distribution of dark matter halos. We develop a simple approach to calculate the magnification probability distribution function which allows us to easily compute the magnitude bias and dispersion for an arbitrary data sample and a given universe model. As an application we consider the effects of single-mass large-scale cosmic inhomogeneities to the SNe magnitude-redshift relation, and conclude that such structures could bias the PDF enough to affect the extraction of cosmological parameters from the limited size of present-day SNe data samples. We also release turboGL, a simple and very fast (<= 1s) Mathematica code…
Evolution of polarization orientations in a flat universe with vector perturbations: CMB and quasistellar objects
2007
Various effects produced by vector perturbations (vortical peculiar velocity fields) of a flat Friedmann-Robertson-Walker background are considered. In the presence of this type of perturbations, the polarization vector rotates. A formula giving the rotation angle is obtained and, then, it is used to prove that this angle depends on both the observation direction and the emission redshift. Hence, rotations are different for distinct quasars and also for the Cosmic Microwave Background (CMB) radiation coming along different directions (from distinct points of the last scattering surface). As a result of these rotations, some correlations could appear in an initially random field of quasar po…
Current cosmological bounds on neutrino masses and relativistic relics
2004
We combine the most recent observations of large-scale structure (2dF and SDSS galaxy surveys) and cosmic microwave anisotropies (WMAP and ACBAR) to put constraints on flat cosmological models where the number of massive neutrinos and of massless relativistic relics are both left arbitrary. We discuss the impact of each dataset and of various priors on our bounds. For the standard case of three thermalized neutrinos, we find an upper bound on the total neutrino mass sum m_nu < 1.0 (resp. 0.6) eV (at 2sigma), using only CMB and LSS data (resp. including priors from supernovae data and the HST Key Project), a bound that is quite insensitive to the splitting of the total mass between the th…
Measuring the cosmological background of relativistic with the Wilkinson Microwave Anisotropy Probe
2003
We show that the first year results of the Wilkinson Microwave Anisotropy Probe (WMAP) constrain very efficiently the energy density in relativistic particles in the Universe. We derive new bounds on additional relativistic degrees of freedom expressed in terms of an excess in the effective number of light neutrinos $\ensuremath{\Delta}{N}_{\mathrm{eff}}.$ Within the flat \ensuremath{\Lambda}CDM scenario, the allowed range is $\ensuremath{\Delta}{N}_{\mathrm{eff}}l6$ (95% confidence level) using WMAP data only, or $\ensuremath{-}2.6l\ensuremath{\Delta}{N}_{\mathrm{eff}}l4$ with the prior ${H}_{0}=72\ifmmode\pm\else\textpm\fi{}8\mathrm{km}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{Mpc}}^{\ensure…
Imaging Performance of FIGARO-IV, A Large Area γ-Ray Telescope Above 100 MeV.
1995
We are developing a new telescope, named FIGARO-IV, for γ-ray astronomy above 100 MeV, in which the electron-positron pairs, produced by photons in lead converters, are tracked in several independent planes of Limited Streamer Tubes (LST). Because of its large sensitive area and good angular resolution, this telescope is well suitable, and competitive with respect to satellite-based detectors as EGRET, to localise discrete γ-ray sources in a relatively short observation time, to detect high-energy γ-ray bursts and to investigate both periodic and random time variability on -ray sources.
Meßfehlerschätzung bei der MR-tomographischen Volumetrie des linken Ventrikels mit Mehrschicht-Technik
1992
A multi-slice technique for MRT measurements of the left ventricular volume is much faster than the use of single-slice methods and is therefore better tolerated, leaving time for additional measurements. The end-diastolic left ventricular volume can be reliably measured by this method (123.3 +/- 13.5 ml vs. 124.1 +/- ml). The end-systolic volume is consistently overestimated by 23.7 +/- 18.3% compared with the reference value obtained by single slice measurements (47.9 +/- 8.9 ml vs 39.1 +/- 7.9 ml). Correspondingly, stroke volume and ejection fraction is underestimated on average by 10.6 +/- 9.7% and 10.6 +/- 7.6% respectively).
Optical peregrine soliton generation in standard telecommunication fibers
2011
By combining real time characterization with cut-back measurements, we provide the first direct observation of Peregrine-like soliton longitudinal evolution dynamics and report a new effect associated with the breakup of a Peregrine soliton into two subpulses, each providing similar characteristics of localization upon finite background. Experimental results are in good agreement with simulations.
Direct Observation of the StrangebBaryonΞb−
2007
We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psi…
Kinematics of Magnetic Bright Features in the Solar Photosphere
2016
S. Jafarzadeh et. al.