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Analysis of LOFT Tests L2-2, L2-3 and L3-0
This paper describes LOFT Tests L2-2, L2-3, and L3-0 and presents conclusions reached from analysis of these tests. The LOFT L2 series of tests, called the power ascension series, originally consisted of six tests. The first four tests, L2-1 through L2-4, were identical except for step-wise increases in core power for each test. Comparison of these tests, and the nonnuclear Test L1-5, was planned to evaluate the effect of core power on system and ECC behavior during large cold leg break LOCA's. Tests L2-5 and L2-6 were to provide parametric investigations of the effect of loss of offsite power and prepressurized fuel. Prior to the start of the L2 series, it was decided Test L2-1 was not necessary due to the information learned from the LOFT nonnuclear tests and PBF lead rod tests. Tests L2-2 and L2-3 are described. The posttest analysis of Tests L2-2 and L2-3 is discussed, and conclusions reached from the comparisons of the experimental data to computer calculations presented. In addition, the results and implications of computer calculations on a commercial size PWR with the same model used for LOFT are presented. Finally, Test L3-0 is described and conclusions reached from it introduced
Inflationary Perturbations: the Cosmological Schwinger Effect
This pedagogical review aims at presenting the fundamental aspects of the
theory of inflationary cosmological perturbations of quantum-mechanical origin.
The analogy with the well-known Schwinger effect is discussed in detail and a
systematic comparison of the two physical phenomena is carried out. In
particular, it is demonstrated that the two underlying formalisms differ only
up to an irrelevant canonical transformation. Hence, the basic physical
mechanisms at play are similar in both cases and can be reduced to the
quantization of a parametric oscillator leading to particle creation due to the
interaction with a classical source: pair production in vacuum is therefore
equivalent to the appearance of a growing mode for the cosmological
fluctuations. The only difference lies in the nature of the source: an electric
field in the case of the Schwinger effect and the gravitational field in the
case of inflationary perturbations. Although, in the laboratory, it is
notoriously difficult to produce an electric field such that pairs extracted
from the vacuum can be detected, the gravitational field in the early universe
can be strong enough to lead to observable effects that ultimately reveal
themselves as temperature fluctuations in the Cosmic Microwave Background.
Finally, the question of how quantum cosmological perturbations can be
considered as classical is discussed at the end of the article.Comment: 49 pages, 6 figures, to appear in a LNP volume "Inflationary
Cosmology
Nutritional knowledge amongst an adult South African sample of low socioeconomic status
The aim of this study was to determine the socioeconomic predictors of nutritional knowledge
(NK) based on total household income, educational level and employment status. A secondary
aim was to determine the relationship between NK and the body mass indexes (BMI) of children.
Using a cross-sectional study, 39 participants enrolled in the Prospective Urban Rural
Epidemiological (PURE) study were purposively sampled for data on their childrenâs age,
gender, height and weight. A semi-structured researcher-generated questionnaire was used to
collect sociodemographic information and assess NK. Pearson correlation assessed the
relationship between the parentâs NK and their childâs BMI. Linear regression analysis was used
to test predictive relationships. The Alpha level was set at p < 0.05. Regression analysis showed
that 2.5% of the variance (R2 = 0.25) was based on NK and was significant (p < 0.05).
Employment status was a significant predictor (p = -0.038) of NK, when controlling for total
household income and education level. Parents of underweight children had the lowest NK. In
conclusion, there was a positive correlation between the childrenâs BMI and their parents NK,
but this was not significant. Employment status was a significant predictor of NK. Public health
practitioners should develop interventions based on NK, which might benefit black parents,
especially those of low socioeconomic status
Inflationary Cosmological Perturbations of Quantum-Mechanical Origin
This review article aims at presenting the theory of inflation. We first
describe the background spacetime behavior during the slow-roll phase and
analyze how inflation ends and the Universe reheats. Then, we present the
theory of cosmological perturbations with special emphasis on their behavior
during inflation. In particular, we discuss the quantum-mechanical nature of
the fluctuations and show how the uncertainty principle fixes the amplitude of
the perturbations. In a next step, we calculate the inflationary power spectra
in the slow-roll approximation and compare these theoretical predictions to the
recent high accuracy measurements of the Cosmic Microwave Background radiation
(CMBR) anisotropy. We show how these data already constrain the underlying
inflationary high energy physics. Finally, we conclude with some speculations
about the trans-Planckian problem, arguing that this issue could allow us to
open a window on physical phenomena which have never been probed so far.Comment: Review Article, 47 pages, 3 figures. Lectures given at the 40th
Karpacz Winter School on Theoretical Physics (Poland, Feb. 2004), submitted
to Lecture Notes in Physic
Improved Estimates of Cosmological Perturbations
We recently derived exact solutions for the scalar, vector and tensor mode
functions of a single, minimally coupled scalar plus gravity in an arbitrary
homogeneous and isotropic background. These solutions are applied to obtain
improved estimates for the primordial scalar and tensor power spectra of
anisotropies in the cosmic microwave background.Comment: 31 pages, 4 figures, LaTeX 2epsilon, this version corrects an
embarrasing mistake (in the published version) for the parameter q_C.
Affected eqns are 105, 109-110, 124, 148-153 and 155-15
Evolution of cosmological perturbations in non-singular string cosmologies
In a class of non-singular cosmologies derived from higher-order corrections
to the low-energy bosonic string action, we derive evolution equations for the
most general cosmological scalar, vector and tensor perturbations. In the large
scale limit, the evolutions of both scalar and tensor perturbations are
characterised by conserved quantities, the usual curvature perturbation in the
uniform-field gauge and the tensor-type perturbed metric. The vector
perturbation is not affected, being described by the conservation of the
angular momentum of the fluid component in the absence of any additional
dissipative process. For the scalar- and tensor-type perturbations, we show
how, given a background evolution during kinetic driven inflation of the
dilaton field, we can obtain the final power spectra generated from the vacuum
quantum fluctuations of the metric and the dilaton field during the inflation.Comment: 11 pages, 2 figures, submitted to Phys. Rev.
WKB approximation for inflationary cosmological perturbations
A new method for predicting inflationary cosmological perturbations, based on
the Wentzel-Kramers-Brillouin (WKB) approximation, is presented. A general
expression for the WKB scalar and tensor power spectra is derived. The main
advantage of the new scheme of approximation is that it is valid even if the
slow-roll conditions are violated. The method is applied to power-law
inflation, which allows a comparison with an exact result. It is demonstrated
that the WKB approximation predicts the spectral indices exactly and the
amplitude with an error lower than 10%, even in regimes far from
scale-invariance. The new method of approximation is also applied to a
situation where the slow-roll conditions hold. It is shown that the result
obtained bears close resemblance with the standard slow-roll calculation.
Finally, some possible improvements are briefly mentioned.Comment: 11 pages, 1 figure, RevTeX; minor changes, reference added (v2);
typos corrected (v3
Scalar perturbation spectra from warm inflation
We present a numerical integration of the cosmological scalar perturbation
equations in warm inflation. The initial conditions are provided by a
discussion of the thermal fluctuations of an inflaton field and thermal
radiation using a combination of thermal field theory and thermodynamics. The
perturbation equations include the effects of a damping coefficient
and a thermodynamic potential . We give an analytic expression for the
spectral index of scalar fluctuations in terms of a new slow-roll parameter
constructed from . A series of toy models, inspired by spontaneous
symmetry breaking and a known form of the damping coefficient, lead to a
spectrum with on large scales and on small scales.Comment: 12 pages, 5 figures, RevTeX 4, revised with extra figure
Cosmological parameter estimation and the inflationary cosmology
We consider approaches to cosmological parameter estimation in the
inflationary cosmology, focussing on the required accuracy of the initial power
spectra. Parametrizing the spectra, for example by power-laws, is well suited
to testing the inflationary paradigm but will only correctly estimate
cosmological parameters if the parametrization is sufficiently accurate, and we
investigate conditions under which this is achieved both for present data and
for upcoming satellite data. If inflation is favoured, reliable estimation of
its physical parameters requires an alternative approach adopting its detailed
predictions. For slow-roll inflation, we investigate the accuracy of the
predicted spectra at first and second order in the slow-roll expansion
(presenting the complete second-order corrections for the tensors for the first
time). We find that within the presently-allowed parameter space, there are
regions where it will be necessary to include second-order corrections to reach
the accuracy requirements of MAP and Planck satellite data. We end by proposing
a data analysis pipeline appropriate for testing inflation and for cosmological
parameter estimation from high-precision data.Comment: 15 pages RevTeX file with figures incorporated. Slow-roll inflation
module for use with the CAMB program can be found at
http://astronomy.cpes.susx.ac.uk/~sleach/inflation/ This version corrects a
typo in the definition of z_S (after Eq.1) and supersedes the journal versio
Primordial power spectrum from WMAP
The observed angular power spectrum of the cosmic microwave background
temperature anisotropy, , is a convolution of a cosmological radiative
transport kernel with an assumed primordial power spectrum of inhomogeneities.
Exquisite measurements of over a wide range of multipoles from the
Wilkinson Microwave Anisotropy Probe (WMAP) has opened up the possibility to
deconvolve the primordial power spectrum for a given set of cosmological
parameters (base model). We implement an improved (error sensitive)
Richardson-Lucy deconvolution algorithm on the measured angular power spectrum
from WMAP assuming a concordance cosmological model. The most prominent feature
of the recovered is a sharp, infra-red cut off on the horizon scale. The
resultant spectrum using the recovered spectrum has a likelihood far
better than a scale invariant, or, `best fit' scale free spectra
( {\it w.r.t.} Harrison Zeldovich, and, {\it w.r.t.} power law with ). The recovered has a
localized excess just below the cut-off which leads to great improvement of
likelihood over the simple monotonic forms of model infra-red cut-off spectra
considered in the post WMAP literature. The recovered , in particular,
the form of infra-red cut-off is robust to small changes in the cosmological
parameters. We show that remarkably similar form of infra-red cutoff is known
to arise in very reasonable extensions and refinements of the predictions from
simple inflationary scenarios. Our method can be extended to other cosmological
observations such as the measured matter power spectrum and, in particular, the
much awaited polarization spectrum from WMAP.Comment: 20 pages, 12 figures, uses Revtex4, Matches version accepted to Phys.
Rev. D. More extensive discussion of the method in the appendix, references
added and typos correcte