Thermodynamics of D0-branes in matrix theory

We examine the matrix theory representation of D0-brane dynamics at finite temperature. In this case, violation of supersymmetry by temperature leads to a non-trivial static potential between D0-branes at any finite temperature. We compute the static potential in the 1-loop approximation and show that it is short-ranged and attractive. We compare the result with the computations in superstring theory. We show that thermal states of D0-branes can be reproduced by matrix theory only when certain care is taken in integration over the moduli space of classical solutions in compactified time.Comment: 13 pages, 1 figur

Combinatorics of Boundaries in String Theory

We investigate the possibility that stringy nonperturbative effects appear as holes in the world-sheet. We focus on the case of Dirichlet string theory, which we argue should be formulated differently than in previous work, and we find that the effects of boundaries are naturally weighted by $e^{-O(1/g_{\rm st})}$.Comment: 12 pages, 2 figures, LaTe

Mitochondria and apoptosis: a quick take on a long view

Fifteen years of apoptosis research have led to the widely accepted idea that the major form of programmed cell death in mammals proceeds via the mitochondria, and that mitochondrial control of apoptosis is regulated by a specialized family of proteins known as the Bcl-2 family. Here we will consider some very recent data that has shed new insight into the regulation of these proteins and the impact of mitochondrial dynamics on mitochondrial outer membrane permeabilization (MOMP) and apoptosis

Remarks on the Classical Size of D-Branes

We discuss different criteria for `classical size' of extremal Dirichlet p-branes in type-II supergravity. Using strong-weak coupling duality, we find that the size of the strong-coupling region at the core of the (p<3)-branes, is always given by the asymptotic string scale, if measured in the weakly coupled dual string metric. We also point out how the eleven-dimensional Planck scale arises in the classical 0-brane solution, as well as the ten-dimensional Planck scale in the D-instanton solution.Comment: 8 pp, harvma

On the properties of colossal magnetoresistive perovskite manganites : an experimental and theoretical investigation

This thesis investigates the properties of colossal magnetoresistive perovskite manganites from a theoretical and experimental point of view. In light of the failings of the double-exchange mechanism which has traditionally been used to explain the physics of colossal magnetoresistive manganites, we investigate the properties of these materials using the current carrier density collapse (CCDC) theory. We show that the CCDC theory can adequately explain the resistivity of perovskite manganites when subjected to zero external magnetic field and when in the presence of an applied magnetic field, thus accounting for the large negative magnetoresistance in these materials. Also the theory in conjunction with a generic phase seperation model allows us to explain the resistivity and for the first time, specific heat in disordered manganites. Experimental investigations into La0.75 Sr0.25 MnO3 have been undertaken. Homemade samples of La0.75 Sr0.25 MnO3 have been produced. Different annealing treatments have allowed us to produce samples with different crystallite sizes, as determined by Rietveld refinement. The effects of crystallite size upon the resistivity, magnetoresistance, magnetic properties and specific heat have been investigated. The resistivity, magnetoresistance and magnetic properties are in qualitative agreement with the CCDC theory, and the specific heat data are seen to be in quantitative agreement with the CCDC theory. We find no results that are in contradiction to the CCDC theory.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Strong coupling expansion of chiral models

A general precedure is outlined for an algorithmic implementation of the strong coupling expansion of lattice chiral models on arbitrary lattices. A symbolic character expansion in terms of connected values of group integrals on skeleton diagrams may be obtained by a fully computerized approach.Comment: 2 pages, PostScript file, contribution to conference LATTICE '9

The group structure of non-Abelian NS-NS transformations

We study the transformations of the worldvolume fields of a system of multiple coinciding D-branes under gauge transformations of the supergravity Kalb-Ramond field. We find that the pure gauge part of these NS-NS transformations can be written as a U(N) symmetry of the underlying Yang-Mills group, but that in general the full NS-NS variations get mixed up non-trivially with the U(N). We compute the commutation relations and the Jacobi identities of the bigger group formed by the NS-NS and U(N) transformations.Comment: Latex, 11 pages. v2: Typos corrected; version to appear in JHEP

D-Branes on K3-Fibrations

B-type D-branes are constructed on two different K3-fibrations over IP_1 using boundary conformal field theory at the rational Gepner points of these models. The microscopic CFT charges are compared with the Ramond charges of D-branes wrapped on holomorphic cycles of the corresponding Calabi-Yau manifold. We study in particular D4-branes and bundles localized on the K3 fibers, and find from CFT that each irreducible component of a bundle on K3 gains one modulus upon fibration over IP_1. This is in agreement with expectations and so provides a further test of the boundary CFT.Comment: 16p, harvmac, tables.tex; typos corrected, refs added, discussion about moduli spaces improve