1,237 research outputs found
Building analytical three-field cosmological models
A difficult task to deal with is the analytical treatment of models composed
by three real scalar fields, once their equations of motion are in general
coupled and hard to be integrated. In order to overcome this problem we
introduce a methodology to construct three-field models based on the so-called
"extension method". The fundamental idea of the procedure is to combine three
one-field systems in a non-trivial way, to construct an effective three scalar
field model. An interesting scenario where the method can be implemented is
within inflationary models, where the Einstein-Hilbert Lagrangian is coupled
with the scalar field Lagrangian. We exemplify how a new model constructed from
our method can lead to non-trivial behaviors for cosmological parameters.Comment: 11 pages, and 3 figures, updated version published in EPJ
Constraining Omega with Cluster Evolution
We show that the evolution of the number density of rich clusters of galaxies
breaks the degeneracy between Omega (the mass density ratio of the universe)
and sigma_{8} (the normalization of the power spectrum), sigma_{8}Omega^{0.5}
\simeq 0.5, that follows from the observed present-day abundance of rich
clusters. The evolution of high-mass (Coma-like) clusters is strong in Omega=1,
low-sigma_{8} models (such as the standard biased CDM model with sigma_{8}
\simeq 0.5), where the number density of clusters decreases by a factor of \sim
10^{3} from z = 0 to z \simeq 0.5; the same clusters show only mild evolution
in low-Omega, high-sigma_{8} models, where the decrease is a factor of \sim 10.
This diagnostic provides a most powerful constraint on Omega. Using
observations of clusters to z \simeq 0.5-1, we find only mild evolution in the
observed cluster abundance. We find Omega = 0.3 \pm 0.1 and sigma_{8} = 0.85
\pm 0.15 (for Lambda = 0 models; for Omega + Lambda = 1 models, Omega = 0.34
\pm 0.13). These results imply, if confirmed by future surveys, that we live in
a low-den sity, low-bias universe.Comment: 14 pages, 3 Postscript figures, ApJ Letters, accepte
Network Awareness of P2P Live Streaming Applications
Early P2P-TV systems have already attracted millions of users, and many new commercial solutions are entering this market. Little information is however available about how these systems work. In this paper we present large scale sets of experiments to compare three of the most successful P2P-TV systems, namely PPLive, SopCast and TVAnts. Our goal is to assess what level of "network awareness" has been embedded in the applications, i.e., what parameters mainly drive the peer selection and data exchange. By using a general framework that can be extended to other systems and metrics, we show that all applications largely base their choices on the peer bandwidth, i.e., they prefer high-bandwidth users, which is rather intuitive. Moreover, TVAnts and PPLive exhibits also a preference to exchange data among peers in the same autonomous system the peer belongs to. However, no evidence about preference versus peers in the same subnet or that are closer to the considered peer emerges. We believe that next-generation P2P live streaming applications definitively need to improve the level of network-awareness, so to better localize the traffic in the network and thus increase their network-friendliness as wel
Do broad absorption line quasars live in different environments from ordinary quasars?
We select a sample of traditionally defined broad absorption line
quasars (BALQs) from the Fifth Data Release quasar catalog of the Sloan Digital
Sky Survey. For a statistically homogeneous quasar sample with , the BAL quasar fraction is and is almost constant with
redshift. We measure the auto-correlation of non-BAL quasars (nonBALQs) and the
cross-correlation of BALQs with nonBALQs using this statistically homogeneous
sample, both in redshift space and using the projected correlation function. We
find no significant difference between the clustering strengths of BALQs and
nonBALQs. Assuming a power-law model for the real space correlation function
, the correlation length for nonBALQs is ; for BALQs, the cross-correlation length is . Our clustering results suggest that BALQs live in similar
large-scale environments as do nonBALQs.Comment: accepted for publication in Ap
Painful Scalp Ulcers
A arterite temporal é um vasculite sistémica que afecta vasos de médio e grande calibre,
em particular a artéria temporal.
Os autores apresentam o caso de um doente observado por ulceraçÔes extensas e dolorosas
da regiĂŁo parieto-temporal direita, com cefaleia hemicraniana homolateral, amaurose
fugaz e claudicação mandibular. As artérias temporais eram espessadas, dolorosas e sem
pulso Ă palpação. Analiticamente, registou-se anemia normocĂtica e normocrĂłmica e velocidade de sedimentação de 63 mm na primeira hora. No exame histopatolĂłgico observou-se um processo inflamatĂłrio transmural, com cĂ©lulas gigantes. O exame oftalmolĂłgico revelou compromisso da acuidade visual com maior expressĂŁo Ă direita.
Perante o diagnĂłstico de arterite temporal, instituiu-se corticoterapia com prednisolona
1 mg/Kg/dia. A melhoria clĂnica foi significativa, embora com persistĂȘncia das queixas oftalmolĂłgicas.
Este caso reforça a importĂąncia do diagnĂłstico precoce desta patologia e da sua terapĂȘutica atempada, minimizando a ocorrĂȘncia de sequelas definitivas
Clustering Analyses of 300,000 Photometrically Classified Quasars--II. The Excess on Very Small Scales
We study quasar clustering on small scales, modeling clustering amplitudes
using halo-driven dark matter descriptions. From 91 pairs on scales <35 kpc/h,
we detect only a slight excess in quasar clustering over our best-fit
large-scale model. Integrated across all redshifts, the implied quasar bias is
b_Q = 4.21+/-0.98 (b_Q = 3.93+/-0.71) at ~18 kpc/h (~28 kpc/h). Our best-fit
(real-space) power index is ~-2 (i.e., ), implying
steeper halo profiles than currently found in simulations. Alternatively,
quasar binaries with separation <35 kpc/h may trace merging galaxies, with
typical dynamical merger times t_d~(610+/-260)m^{-1/2} Myr/h, for quasars of
host halo mass m x 10^{12} Msolar/h. We find UVX quasars at ~28 kpc/h cluster
>5 times higher at z > 2, than at z < 2, at the level. However, as
the space density of quasars declines as z increases, an excess of quasar
binaries (over expectation) at z > 2 could be consistent with reduced merger
rates at z > 2 for the galaxies forming UVX quasars. Comparing our clustering
at ~28 kpc/h to a \xi(r)=(r/4.8\Mpch)^{-1.53} power-law, we find an upper
limit on any excess of a factor of 4.3+/-1.3, which, noting some caveats,
differs from large excesses recently measured for binary quasars, at
. We speculate that binary quasar surveys that are biased to z > 2
may find inflated clustering excesses when compared to models fit at z < 2. We
provide details of 111 photometrically classified quasar pairs with separations
<0.1'. Spectroscopy of these pairs could significantly constrain quasar
dynamics in merging galaxies.Comment: 12pages, 3 figures, 2 tables; uses amulateapj; accepted to Ap
Cosmic homogeneity demonstrated with luminous red galaxies
We test the homogeneity of the Universe at with the Luminous Red
Galaxy (LRG) spectroscopic sample of the Sloan Digital Sky Survey. First, the
mean number of LRGs within completely surveyed LRG-centered spheres of
comoving radius is shown to be proportional to at radii greater than
. The test has the virtue that it does not rely
on the assumption that the LRG sample has a finite mean density; its results
show, however, that there \emph{is} such a mean density. Secondly, the survey
sky area is divided into 10 disjoint solid angular regions and the fractional
rms density variations of the LRG sample in the redshift range
among these () regions is found to be 7
percent of the mean density. This variance is consistent with typical biased
\lcdm models and puts very strong constraints on the quality of SDSS
photometric calibration.Comment: submitted to Ap
- âŠ