Aspects of a spherically symmetric model of the post-decoupling universe

Bibliography: pages 84-88.The central aim of this thesis is to consider aspects of the spherically symmetric Lemaitre-Tolman-Bondi (LTB) solution as a model of the post-decoupling universe. To do this comprehensively is a massive task and is not our aim here. Indeed, far from it, we will concentrate on select instances of this programme and attempt in some places to indicate possibilities for further study. There are many solutions of the EFE which satisfy what we consider to be 'reasonable criteria' for a cosmology and others that do not. The LTB solution may be accepted as a reasonable cosmological model because ■ It allows non-empty solutions. ■ It allows expanding solutions. ■ It has a homogeneous and isotropic limit. ■ It allows for inhomogeneity

Multimodality in science education as productive pedagogy in a PGCE programme

Initial teacher education programmes such as the Postgraduate Certificate in Education (PGCE) in South Africa are undergoing significant changes with the introduction of a new policy regime. This paper briefly outlines the policy changes advanced for teacher education programmes in South Africa. It examines productive pedagogies as a conceptual framework to underpin such a restructured programme. It then proposes that multiple representations can serve as a productive pedagogy of enactment in the science classroom because it engages the student with higher-order thinking skills, connects them with the world beyond the classroom in a supportive environment, and values difference by affording students multiple opportunities to develop a deep understanding of concepts. Some examples are given and the broader implications for classroom practice are discussed

An empirical evaluation of students' perceptions of the nature of science : a comparison between groups

In 1991 Evans and Schibeci used a modified Views of Science-Technology-Society (VOSTS) instrument to assess 434 Australian students' views on selected aspects of the Science-Technology-Society (STS) theme. In South Africa , Parker and Rochford (1995), and the writer Edwards et al. (1997) conducted and published further corroborative studies with more than 1400 students. Set in the context of the debate on the "traditional" and "contemporary" models of the nature of science (after Palmquist and Finley, 1997), this study measures, compares and interprets the response patterns of five convenient sample groups to 26 items on the modified VOSTS instrument. The three subscales measure students' perceptions of the definition of science, scientific method and how scientific knowledge changes. The reliability of the instrument was computed for Cape Town students using Cronbach's coefficient which yielded α = 0.78; and its content had been shown to be inherently valid at the time it was developed. A self-completion questionnaire was administered by the writer to four Cape Town student samples in 1995 during normal periods of instruction at two high schools, a technikon and a college of education. The samples comprised 320 year 10 high school science students, 340 year 12 high school science students, 108 electrical engineering students, and 55 first year college of education science students respectively. The 434 year 10 Australian students' (sample 5) responses were compared with the responses of their South African counterparts. In order to determine statistically significant differences between the response frequencies of the sample groups on the 26 items, the χ² - test statistic was used

Large Scale Inhomogeneity Versus Source Evolution -- Can We Distinguish Them Observationally?

We reconsider the issue of proving large scale spatial homogeneity of the universe, given isotropic observations about us and the possibility of source evolution both in numbers and luminosities. Two theorems make precise the freedom available in constructing cosmological models that will fit the observations. They make quite clear that homogeneity cannot be proven without either a fully determinate theory of source evolution, or availability of distance measures that are independent of source evolution. We contrast this goal with the standard approach that assumes spatial homogeneity a priori, and determines source evolution functions on the basis of this assumption.Comment: mn style, mn.sty file included, mn.sty file remove

Dynamical studies in relativistic cosmology

Bibliography: leaves 158-167.We conduct three investigations in Relativistic Cosmology that is the Einstein Field Equations applied to the largest scales with source field typically taken to be a perfect fluid and fundamental observers comoving with the preferred fluid four-velocity. We show using a tetrad analysis of the evolution equations for the dynamical variables and all the constraints these satisfy in classical General Relativity, that there are no new consistent perfect fluid cosmologies with the kinematic variables and the electric and/or magnetic parts of the Weyl curvature all rotationally symmetric about a common axis in an open neighbourhood Ա of an event. The consistent solutions of this kind are either locally rotationally symmetric, or most generally are subcases of the Szekeres model-an inhomogeneous dust model with no Killing symmetries. This result and its obvious future generalisations provides an input into the equivalence problem in cosmology necessary for a mathematically consistent understanding of probability and a measure set for universes required in quantum cosmology, for instance. We investigate such generalisations and find that similar results hold under some further assumptions dependent on the level of generalisation. In particular, we examine situations where either the electric part or the magnetic part of the free gravitational field are not rotationally symmetric, and also make a brief comment on the most general case where only the shear is rotationally symmetric. We use a tetrad analysis to show that the well-known result that holds for relativistic shear-free dust cosmologies in Einstein's classical theory either the expansion vanishes or the flow is irrotational - has an analogue in the Kaluza-Klein universe model, which has its roots presumably in string theory (or M-theory), recently proposed by Randall and Sundrum. The Big Bang singularity of General Relativity can not be avoided in these so-called brane universes in the situation where we neglect non-local tidal effects on the dynamics by allowing the vorticity to spin up as the singularity is approached in shear-free cases. Moreover, we show that in the general case of a shearing perfect fluid, the singularity at the start of the universe is approached even more strongly than in classical General Relativity in the case of no tidal interaction. Finally, we reconsider the issue of proving large scale spatial homogeneity of the universe in classical General Relativity, given isotropic observations about us and the possibility of source evolution both in numbers and luminosities. We use a spherically symmetric dust universe model (compatible with observations) for our investigation and we solve the field equations on the null cone analytically for the first time. Two theorems make precise the freedom available in constructing cosmological models that will fit the observations. They make quite clear that homogeneity cannot be proven without either a fully determinate theory of source evolution, or availability of distance measures that are independent of source evolution. We contrast this goal with the standard approach that assumes spatial homogeneity a priori, and determines source evolution functions on the basis of this assumption

Partially locally rotationally symmetric perfect fluid cosmologies

We show that there are no new consistent cosmological perfect fluid solutions when in an open neighbourhood ${\cal U}$ of an event the fluid kinematical variables and the electric and magnetic Weyl curvature are all assumed rotationally symmetric about a common spatial axis, specialising the Weyl curvature tensor to algebraic Petrov type D. The consistent solutions of this kind are either locally rotationally symmetric, or are subcases of the Szekeres dust models. Parts of our results require the assumption of a barotropic equation of state. Additionally we demonstrate that local rotational symmetry of perfect fluid cosmologies follows from rotational symmetry of the Riemann curvature tensor and of its covariant derivatives only up to second order, thus strengthening a previous result.Comment: 20 pages, LaTeX2.09 (10pt), no figures; shortened revised version, new references; accepted for publication in Classical and Quantum Gravit

Developing pre-service science teachers’ pedagogy in an inquiry-based classroom: examining their representational competence and fluency

The manner in which science is communicated is important to the way in which concepts are understood by the recipient. Multiple representations involving verbal, graphical, symbolic or experimental modes can help students to better understand science phenomena. In this study the representational competence and fluency of pre-service science teachers (N=82), who were paired to present a model that illustrates series or parallel circuits, were analysed. In addition, the extent to which simulations constrain or afford understanding in the domain was also examined. The results indicate that 56% of pre-service science teachers use simulations to afford a better understanding of electric circuits while 59% can construct an appropriate model to demonstrate concepts in direct-current electricity. However, only 7% incorporate symbolic representations to show an enhanced understanding. There is also a need for students to improve their verbal skills to better explain concepts. Some implications of this study are outlined.Institute for Science and Technology Education (ISTE

Identifying factors of risk management for the construction industry

Abstract: Delays and cost overruns are recurrent in construction projects. Risk management (RM) has been developed to curtain risks associated with construction projects. However, there is no consensus of what factors should constitute RM for construction projects. Therefore, this paper scrutinises preceding studies on the theme of RM and establish core risk management factors (RMFs) that are indispensable to make the concept valuable in the construction industry (CI). A literature search related to RM was conducted in order to identify common RMF. It was indicated that there is still misunderstanding and disagreement over the factors that should constitute RM in construction. However, the RMFs of organisational environment, defining objectives, resource requirement, risk measurement, risk identification, risk assessment, risk response and action planning, communication, monitoring, review and continuous improvement dominate the literature. Identifying RMF that can effortlessly be understood and implemented will contribute to ameliorating the current RM status and boosting the body of knowledge

An appraisal of critical risk factors in construction projects in South Africa : perspective of contractors

Abstract: The significant impact of construction projects on a nation has been characterized in literature in terms of infrastructure development and job creation. These projects are nevertheless associated with various risks that need to be managed to ensure successful delivery. Hence, the identification of these risk factors is of utmost importance. Therefore, this study aimed at assessing contractors‘ perception of critical risk factors in construction projects in Gauteng (South Africa). Explorative and questionnaire survey methods were employed to obtain data from literature and construction professionals all practising in Gauteng. Results revealed that supply of faulty materials, poor communication between involved parties, financial failure of the contractor, working at dangerous areas and closure were the five critical risk factors in construction projects. It is obvious from the results that the knowledge of the identified critical risk factors furnishes invaluable information to the construction contractor concerning what risk variables to focus attention on in construction activities. The paper contributes to the identification of critical risk factors in construction projects from an objective point

Pathophysiology of COVID-19 and its potential therapeutics

A series of acute and atypical serious respiratory illnesses were reported in December 2019 from Wuhan, a city of China. It spread to other places and became a global pandemic involving more than 200 countries of the world. Soon, it was discovered that this atypical respiratory illness was caused by a novel corona virus. It was named as the severe acute respiratory syndrome corona virus-2 (SARS-CoV-2) and the disease caused by it as corona virus disease-19 (COVID-19). Since COVID-19 is a new viral disease, world is still struggling to find out a permanent remedy to control this serious health problem. It seems prudent to study or have a look on the pathophysiology of SARS CoV-2 in the light of available research. Further, a review on pathophysiology may give an insight on the potential therapeutic options. Being a new virus and having potential to cause significant morbidity and mortality in short span of time various approved drugs are being repurposed for the treatment of COVID-19