Traversable Wormholes in (2+1) and (3+1) Dimensions with a Cosmological Constant

Macroscopic traversable wormhole solutions to Einstein's field equations in $(2+1)$ and $(3+1)$ dimensions with a cosmological constant are investigated. Ensuring traversability severely constrains the material used to generate the wormhole's spacetime curvature. Although the presence of a cosmological constant modifies to some extent the type of matter permitted (for example it is possible to have a positive energy density for the material threading the throat of the wormhole in $(2+1)$ dimensions), the material must still be ``exotic'', that is matter with a larger radial tension than total mass-energy density multiplied by $c^2$. Two specific solutions are applied to the general cases and a partial stability analysis of a $(2+1)$ dimensional solution is explored.Comment: 19 pgs. WATPHYS TH-93/0

Transactional Distance Theory: A Critical View of the Theoretical and Pedagogical Underpinnings of E-Learning

This chapter provides a critical look at the literature surrounding Distance Education and targets Transactional Distance Theory. It will examine in detail the three components: structure, interaction (or dialogue) and autonomy. The structure necessary for successful distance learning starts the chapter. Next, interaction (or dialogue) is introduced and the complexity of this in relation to the student experience is discussed. Finally, autonomy is explored in detail. This overview will relate specifically to the student perspective. Alternative approaches, links to seminal authors and a critical viewpoint is taken throughout

How can I improve my practice as a university lecturer in the development and delivery of a distance learning module in a post graduate diploma in clinical education?

EdD ThesisAbstract: How can I improve as a practitioner of distance learning? With the uptake of distance learning (DL), which has been marginal for most academics, teaching contexts, traditional power structures and relationships have changed, leaving lecturers potentially disenfranchised. Proliferate literature was found addressing DL in medical education, although the practical application for academics was scarce. Unsurprisingly, the most cited article in Medical Teacher in 2010 was: ‘The Failure of e-Learning Research to Inform Educational Practice, and What We Can Do About It’ (Personal communication, Medical Teacher, October 24, ). My experience suggested DL was a disruptive technology to individuals and the organisational culture of higher education. The related research question and aim of this study were: Research Question How can I improve my practice as a University Lecturer in the development and delivery of a distance learning module in a post graduate diploma in clinical education? Research Aim To critically and systematically examine, and make informed changes to, the design and delivery of a post-graduate distance clinical education module. I hoped to inform educational practice: primarily, my own, by improving my practice as a university DL practitioner. Based on the literature of organisations and DL, I examined and evaluated the complex process of developing and then delivering an asynchronous fully online module. Maintaining an action research methodology, this study underwent two cycles. The first cycle focused on planning of the module, the second on delivery. These cycles informed my own practice, guided further development and resulted in subsequent change. Data collection consisted of documentary analysis of meetings, interviews with staff and students, formal student evaluations, web analytics and personal reflection. Data analysis incorporated both quantitative and qualitative methods to triangulate the research findings and ensure the research aim was addressed. Within this inquiry, new competencies for academics including leadership and management were exposed. Barriers to staff progress included changes and ambiguity in roles, lack of leadership and unpreparedness for responsibilities, time, and workload. Student barriers included time, fear, relevance of learning, isolation and increased autonomy. Explicit planning, organisational support and working within communities were requisite to create a ‘sustaining’ technology representing an improvement on current practices for both groups. Avoiding traditional workload assumptions that are erroneous and inaccurate, this study provides new models of organisational roles and responsibilities. Time, workload, and changing expectations of staff and students are addressed whilst uncompromisingly focusing on informing and improving practice.The School of Medical Sciences Education Development, Newcastle University

Generating potentials via difference equations

The condition for pressure isotropy, for spherically symmetric gravitational fields with charged and uncharged matter, is reduced to a recurrence equation with variable, rational coefficients. This difference equation is solved in general using mathematical induction leading to an exact solution to the Einstein field equations which extends the isotropic model of John and Maharaj. The metric functions, energy density and pressure are well behaved which suggests that this model could be used to describe a relativistic sphere. The model admits a barotropic equation of state which approximates a polytrope close to the stellar centre.Comment: 11 pages, To appear in Math. Meth. Appl. Sc

Heart & Matter: Fermentation in a Time of Crisis

In Heart & Matter, I explore contemporary artisan movements from the perspectives of the artisans that animate these movements, considering how people draw on this emergent category of alternate labor and identity to navigate crises of social, economic, and personal precariousness within the artisan industry. Moving from North Carolina to Okinawa, Tokyo to Chicago, my collaborators shared the quotidian anxiety of how to keep their crafts - and the businesses, livelihoods, and identities tied up in those crafts – relevant, viable, and even successful. Toward survival, my interlocutors engaged in practices of resilience, innovation, and collaboration, elemental threads that wove their working philosophies of craft. At the visceral intersection of ethnography and apprenticeship, I trace a working ethos of emergent artisanship that captures the hopes and anxieties, the successes and failures, the everyday lives and works of craftspeople confronting uncertain frontiers of vocation and taste. By way of introduction, Every Scar a Lesson outlines and demonstrates my primary methodology, an itinerant series of participant observations from the perspective of formal and informal apprenticeship, or what I call a wandering apprenticeship. Storms Within, Storms Without examines the resilience crucial to meeting and overcoming the difficulties of craft livelihoods. Despite the ease many associate with industry (even some of those within the industry), being a craftsperson is not easy. The ups and downs of a craft livelihood can be overwhelming, and I trace some of the strategies – ethical or otherwise - craftspeople use to resist defeat. Fortune and Glory contemplates the fickleness of innovation. I discuss the environmentally contingent, cooperative nature of creativity and the possibilities and limitations such a nature enacts. I consider the value innovation can bring to a craft venture, and also the potential consequences to business and craftsperson when the well of innovation runs dry. Ouroboros explores the phenomenon of collaboration, touching on the practice of collaborative production, the communal ethos among craftspeople, and the broader concerns of working with and within a community. This chapter reflects both on the creative potential of the craft community, and on its pressures.Doctor of Philosoph

The Wahlquist metric cannot describe an isolated rotating body

It is proven that the Wahlquist perfect fluid space-time cannot be smoothly joined to an exterior asymptotically flat vacuum region. The proof uses a power series expansion in the angular velocity, to a precision of the second order. In this approximation, the Wahlquist metric is a special case of the rotating Whittaker space-time. The exterior vacuum domain is treated in a like manner. We compute the conditions of matching at the possible boundary surface in both the interior and the vacuum domain. The conditions for matching the induced metrics and the extrinsic curvatures are mutually contradictory.Comment: 13 pages, 0 figure

Algorithmic construction of static perfect fluid spheres

Perfect fluid spheres, both Newtonian and relativistic, have attracted considerable attention as the first step in developing realistic stellar models (or models for fluid planets). Whereas there have been some early hints on how one might find general solutions to the perfect fluid constraint in the absence of a specific equation of state, explicit and fully general solutions of the perfect fluid constraint have only very recently been developed. In this article we present a version of Lake's algorithm [Phys. Rev. D 67 (2003) 104015; gr-qc/0209104] wherein: (1) we re-cast the algorithm in terms of variables with a clear physical meaning -- the average density and the locally measured acceleration due to gravity, (2) we present explicit and fully general formulae for the mass profile and pressure profile, and (3) we present an explicit closed-form expression for the central pressure. Furthermore we can then use the formalism to easily understand the pattern of inter-relationships among many of the previously known exact solutions, and generate several new exact solutions.Comment: Uses revtex4. V2: Minor clarifications, plus an additional section on how to turn the algorithm into a solution generalization technique. This version accepted for publication in Physical Review D. Now 7 page

Traversable Wormholes Construction in 2+1 Dimensions

We study traversable Lorentzian wormholes in the three-dimensional low energy string theory by adding some matter source involving a dilaton field. It will be shown that there are two-different types of wormhole solutions such as BTZ and black string wormholes depending on the dilaton backgrounds, respectively. We finally obtain the desirable solutions which confine exotic matter near the throat of wormhole by adjusting NS charge.Comment: 12 pages, 4 figures, JHEP style, one reference adde

Static circularly symmetric perfect fluid solutions with an exterior BTZ metric

In this work we study static perfect fluid stars in 2+1 dimensions with an exterior BTZ spacetime. We found the general expression for the metric coefficients as a function of the density and pressure of the fluid. We found the conditions to have regularity at the origin throughout the analysis of a set of linearly independent invariants. We also obtain an exact solution of the Einstein equations, with the corresponding equation of state $p=p(\rho)$, which is regular at the origin.Comment: 10 pages, 1 figure, revtex 4. This paper is in honor of Alberto Garcia's sixtieth birthday. Accepted by Gen. Rel. Gra