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 children’s 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 parent’s NK and their child’s 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 children’s 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 $\Gamma$ and a thermodynamic potential $V$. We give an analytic expression for the spectral index of scalar fluctuations in terms of a new slow-roll parameter constructed from $\Gamma$. A series of toy models, inspired by spontaneous symmetry breaking and a known form of the damping coefficient, lead to a spectrum with $n_s>1$ on large scales and $n_s<1$ 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, $C_l$, is a convolution of a cosmological radiative transport kernel with an assumed primordial power spectrum of inhomogeneities. Exquisite measurements of $C_l$ 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 $P(k)$ is a sharp, infra-red cut off on the horizon scale. The resultant $C_l$ spectrum using the recovered spectrum has a likelihood far better than a scale invariant, or, `best fit' scale free spectra ($\Delta\ln{\cal L}=25$ {\it w.r.t.} Harrison Zeldovich, and, $\Delta\ln{\cal L}=11$ {\it w.r.t.} power law with $n_s=0.95$). The recovered $P(k)$ 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 $P(k)$, 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