Non-Gaussianity from violation of slow-roll in multiple inflation

Multiple inflation is a model based on N=1 supergravity wherein there are sudden changes in the mass of the inflaton because it couples to 'flat direction' scalar fields which undergo symmetry breaking phase transitions as the universe cools. The resulting brief violations of slow-roll evolution generate a non-gaussian signal which we find to be oscillatory and yielding f_NL ~ 5-20. This is potentially detectable by e.g. Planck but would require new bispectrum estimators to do so. We also derive a model-independent result relating the period of oscillations of a phase transition during inflation to the period of oscillations in the primordial curvature perturbation generated by the inflaton.Comment: 21 pages, 6 figures; Clarifying comments and references added; Accepted for publication in JCA

Running Spectral Index from Inflation with Modulations

We argue that a large negative running spectral index, if confirmed, might suggest that there are abundant structures in the inflaton potential, which result in a fairly large (both positive and negative) running of the spectral index at all scales. It is shown that the center value of the running spectral index suggested by the recent CMB data can be easily explained by an inflaton potential with superimposed periodic oscillations. In contrast to cases with constant running, the perturbation spectrum is enhanced at small scales, due to the repeated modulations. We mention that such features at small scales may be seen by 21 cm observations in the future.Comment: 7 pages, 6 figures, v2: published in JCA

Perturbation Theory in k-Inflation Coupled to Matter

We consider k-inflation models where the action is a non-linear function of both the inflaton and the inflaton kinetic term. We focus on a scalar-tensor extension of k-inflation coupled to matter for which we derive a modified Mukhanov-Sasaki equation for the curvature perturbation. Significant corrections to the power spectrum appear when the coupling function changes abruptly along the inflationary trajectory. This gives rise to a modification of Starobinsky's model of perturbation features. We analyse the way the power spectrum is altered in the infrared when such features are present.Comment: 20 pages, 1 figur

Comparison of the Elemental Structure and Emission Characteristics of Selected PVC and Non PVC Ceiling Materials Available in Nigerian Markets

The recurring fire outbreak in buildings in Nigeria is quite alarming, just as the shift to the use of PVC as a choice for ceiling material due to its aesthetic appearance is on the increase. Hence this study determined the emission characteristics PVC and non-PVC samples. This was done with a view to establishing their suitability as ceiling materials in building designs for tropical countries and providing thermal and combustion data for building stakeholders that could help to checkmate man made fire disasters. This experiment involves the burning of a consistent mass, 50g of 6 samples of 3 PVC and 3 non-PVC in an open furnace where the combustion is carefully controlled. It investigates the flue gasses concentration emitted in the cause of fire outbreak and its effect on occupants. It responds to the question in mind that not only visible flame kills but also toxicity from flue gas can be detrimental to health of victims. The results showed that PVC samples are unwelcome in terms of their emission characteristics which were due to their elemental makeup of their composites such as PVC recorded highest Carbon composition of 77.9% and lowest oxygen composition of 18.0 %. VOCs are cancerous, cause dizziness, rapid heartbeat, vomiting and eventual death. Benzene, a known VOC, is used in making PVC which is a human carcinogen compound. Ceiling materials that will achieve low noxious emission and as well fire retardant should be investigated and employed for use. These materials can be improved upon to achieve environmental friendly building materials

Iodine source apportionment in the Malawian diet

The aim of this study was to characterise nutritional-I status in Malawi. Dietary-I intakes were assessed using new datasets of crop, fish, salt and water-I concentrations, while I status was assessed for 60 women living on each of calcareous and non-calcareous soils as defined by urinary iodine concentration (UIC). Iodine concentration in staple foods was low, with median concentrations of 0.01 mg kg−1 in maize grain, 0.008 mg kg−1 in roots and tubers, but 0.155 mg kg−1 in leafy vegetables. Freshwater fish is a good source of dietary-I with a median concentration of 0.51 mg kg−1. Mean Malawian dietary-Iodine intake from food, excluding salt, was just 7.8 μg d−1 compared to an adult requirement of 150 μg d−1. Despite low dietary-I intake from food, median UICs were 203 μg L−1 with only 12% defined as I deficient whilst 21% exhibited excessive I intake. Iodised salt is likely to be the main source of dietary I intake in Malawi; thus, I nutrition mainly depends on the usage and concentration of I in iodised salt. Drinking water could be a significant source of I in some areas, providing up to 108 μg d−1 based on consumption of 2 L d−1

Learning Environment, Motivation and Self-regulated Learning Among Students in Technical Fields.

The way students perceive their learning environment has been suggested to influence the attitude of students to their learning and their academic performance. The attitude of the students is evident in their displayed motivation and self-regulated learning skills. In this study the influences of the learning environment on students’ motivation and self-regulated learning are investigated. Data for the study were drawn from a questionnaire survey of architecture and engineering students in a University in Nigeria. The number of students that responded to the questionnaires was 343. The findings suggest high influence of the learning environment on students’ motivation and self-regulated learning. The students’ motivation was also found to influence their self-regulated learning. The aspects of the learning environment that influence motivation and self-regulated learning were identified. The findings of the study suggest the importance of confidence inspired in learning environment setting and the need to introduce constraints to motivate and encourage students in this field to self-regulate. Keywords: Architecture, Engineering, Learning Environment, Motivation, Self-regulated learnin

Reconstruction of the Primordial Power Spectrum by Direct Inversion

We introduce a new method for reconstructing the primordial power spectrum, $P(k)$, directly from observations of the Cosmic Microwave Background (CMB). We employ Singular Value Decomposition (SVD) to invert the radiation perturbation transfer function. The degeneracy of the multipole $\ell$ to wavenumber $k$ linear mapping is thus reduced. This enables the inversion to be carried out at each point along a Monte Carlo Markov Chain (MCMC) exploration of the combined $P(k)$ and cosmological parameter space. We present best--fit $P(k)$ obtained with this method along with other cosmological parameters.Comment: 23 pages, 9 figure

Fields Annihilation and Particles Creation in DBI inflation

We consider a model of DBI inflation where two stacks of mobile branes are moving ultra relativistically in a warped throat. The stack closer to the tip of the throat is annihilated with the background anti-branes while inflation proceeds by the second stack. The effects of branes annihilation and particles creation during DBI inflation on the curvature perturbations power spectrum and the scalar spectral index are studied. We show that for super-horizon scales, modes which are outside the sound horizon at the time of branes collision, the spectral index has a shift to blue spectrum compared to the standard DBI inflation. For small scales the power spectrum approaches to its background DBI inflation value with the decaying superimposed oscillatory modulations.Comment: First revision: minor changes, the background spectral index is corrected, new references are added. Second revision: minor changes, new references are added, accepted for publication in JCA