1,888,038 research outputs found
n-Heptane hydroconversion over sulfated-zirconia-supported molybdenum carbide catalysts
Tertiary Education Trust Fund (TETFUND) NigeriaPeer reviewedPublisher PD
Large-angle non-Gaussianity in simulated high-resolution CMB maps
A detection or nondetection of primordial non-Gaussianity by using the cosmic
microwave background radiation (CMB) offers a way of discriminating
inflationary scenarios and testing alternative models of the early universe.
This has motivated the considerable effort that has recently gone into the
study of theoretical features of primordial non-Gaussianity and its detection
in CMB data. Among such attempts to detect non-Gaussianity, there is a
procedure that is based upon two indicators constructed from the skewness and
kurtosis of large-angle patches of CMB maps, which have been proposed and used
to study deviation from Gaussianity in the WMAP data. Simulated CMB maps
equipped with realistic primordial non-Gaussianity are essential tools to test
the viability of non-Gaussian indicators in practice, and also to understand
the effect of systematics, foregrounds and other contaminants. In this work we
extend and complement the results of our previous works by performing an
analysis of non-Gaussianity of the high-angular resolution simulated CMB
temperature maps endowed with non-Gaussianity of the local type, for which the
level of non-Gaussianity is characterized by the dimensionless parameter
Comment: 8 pages, 3 figure
Newtonian Perturbations on Models with Matter Creation
Creation of Cold Dark Matter (CCDM) can macroscopically be described by a
negative pressure, and, therefore, the mechanism is capable to accelerate the
Universe, without the need of an additional dark energy component. In this
framework we discuss the evolution of perturbations by considering a
Neo-Newtonian approach where, unlike in the standard Newtonian cosmology, the
fluid pressure is taken into account even in the homogeneous and isotropic
background equations (Lima, Zanchin and Brandenberger, MNRAS {\bf 291}, L1,
1997). The evolution of the density contrast is calculated in the linear
approximation and compared to the one predicted by the CDM model. The
difference between the CCDM and CDM predictions at the perturbative
level is quantified by using three different statistical methods, namely: a
simple -analysis in the relevant space parameter, a Bayesian
statistical inference, and, finally, a Kolmogorov-Smirnov test. We find that
under certain circumstances the CCDM scenario analysed here predicts an overall
dynamics (including Hubble flow and matter fluctuation field) which fully
recovers that of the traditional cosmic concordance model. Our basic conclusion
is that such a reduction of the dark sector provides a viable alternative
description to the accelerating CDM cosmology.Comment: Physical Review D in press, 10 pages, 4 figure
Genetic and Phenotypic Parameters of Body Weight in Ettawa Grade Goats
The aim of this study was to estimate genetic and phenotypic parameters of growth traits consisting of birth weight (BW), weaning weight (WW), 6 mo body weight (6WM), 12 mo body weight (12WM), and 18 mo body weight (18WM) of Ettawa Grade goats. The number of goat used to determine growth traits of BW, WW, 6WM, 12WM, and 18WM were 316; 316; 259; 259 and 165 heads, respectively. Data were analyzed using General Linear Model (GLM) to identify non-genetic effect. Estimation of genetic and phenotypic parameters including heritability, repeatability, genetic and phenotypic correlation were calculated using Restricted Maximum Likelihood and GLM. Genetic trends were calculated using the regression of mean breeding values on birth year. The results showed that parity and type of birth had significant (P<0.05) influence on all growth traits. Estimated heritability of birth, weaning, 6WM, 12WM, and 18WM were 0.54±0.12; 0.35±0.07; 0.37±0.09; 0.68±0.16 and 0.63±0.19, respectively. Estimated repeatability of WW, 6WM, 12WM and 18WM, WW, 6WM, 12WM and 18WM were 0.98±0.01; 0.97±0.01; 0.94±0.03; 0.71±0.12 and 0.91±0.04, respectively. The genetic trends for traits of BW and 18MW were decreased fluctuatively. However, the WW, 6MW, 12MW were increased fluctuatively. The high and positive genetic correlations between all growth traits and 12WM traits in this study indicated that selection for high 12WM will improve genetic merit in Ettawa Grade goats
Classification of Energy Momentum Tensors in Dimensional Space-times: a Review
Recent developments in string theory suggest that there might exist extra
spatial dimensions, which are not small nor compact. The framework of a great
number of brane cosmological models is that in which the matter fields are
confined on a brane-world embedded in five dimensions (the bulk). Motivated by
this we review the main results on the algebraic classification of second order
symmetric tensors in 5-dimensional space-times. All possible Segre types for a
symmetric two-tensor are found, and a set of canonical forms for each Segre
type is obtained. A limiting diagram for the Segre types of these symmetric
tensors in 5-D is built. Two theorems which collect together some basic results
on the algebraic structure of second order symmetric tensors in 5-D are
presented. We also show how one can obtain, by induction, the classification
and the canonical forms of a symmetric two-tensor on n-dimensional (n > 5)
spaces from its classification in 5-D spaces, present the Segre types in n-D
and the corresponding canonical forms. This classification of symmetric
two-tensors in any n-D spaces and their canonical forms are important in the
context of n-dimensional brane-worlds context and also in the framework of 11-D
supergravity and 10-D superstrings.Comment: LaTex2e, 18 pages. To appear in Braz.J.Phys (2004
Longitudinal and Transverse Form Factors from C
Electron scattering form factors from C have been studied in the
framework of the particle-hole shell model. Higher configurations are taken
into account by allowing particle-hole excitations from the 1 and 1
shells core orbits up to the 1 shell. The inclusion of the higher
configurations modifies the form factors markedly and describes the
experimental data very well in all momentum transfer regions.Comment: 5 pages, 5 figures, 3 tables, late
Observation of metastable hcp solid helium
We have produced and observed metastable solid helium-4 below its melting
pressure between 1.1 K and 1.4 K. This is achieved by an intense pressure wave
carefully focused inside a crystal of known orientation. An accurate density
map of the focal zone is provided by an optical interferometric technique.
Depending on the sample, minimum density achieved at focus corresponds to
pressures between 2 and 4 bar below the static melting pressure. Beyond, the
crystal undergoes an unexpected instability much earlier than the predicted
spinodal limit. This opens a novel opportunity to study this quantum crystal in
an expanded metastable state and its stability limits.Comment: deuxi\`eme versio
Anisotropic thermal emission from magnetized neutron stars
The thermal emission from isolated neutron stars is not well understood. The
X-ray spectrum is very close to a blackbody but there is a systematic optical
excess flux with respect to the extrapolation to low energy of the best
blackbody fit. This fact, in combination with the observed pulsations in the
X-ray flux, can be explained by anisotropies in the surface temperature
distribution.We study the thermal emission from neutron stars with strong
magnetic fields in order to explain the origin of the anisotropy. We find
(numerically) stationary solutions in axial symmetry of the heat
transportequations in the neutron star crust and the condensed envelope. The
anisotropy in the conductivity tensor is included consistently. The presence of
magnetic fields of the expected strength leads to anisotropy in the surface
temperature. Models with toroidal components similar to or larger than the
poloidal field reproduce qualitatively the observed spectral properties and
variability of isolated neutron stars. Our models also predict spectral
features at energies between 0.2 and 0.6 keV.Comment: 18 pages, 19 figures, version accepted for publication in A&
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