1,741 research outputs found
STRINGY EVIDENCE FOR D=11 STRUCTURE IN STRONGLY COUPLED TYPE II-A SUPERSTRING
Witten proposed that the low energy physics of strongly coupled D=10 type-IIA
superstring may be described by D=11 supergravity. To explore the stringy
aspects of the underlying theory we examine the stringy massive states. We
propose a systematic formula for identifying non-perturbative states in D=10
type-IIA superstring theory, such that, together with the elementary excited
string states, they form D=11 supersymmetric multiplets multiplets in SO(10)
representations. This provides hints for the construction of a weakly coupled
D=11 theory that is dual to the strongly coupled D=10 type IIA superstring.Comment: LaTeX, revtex, 2-column, 10 pages
Charge and mass effects on the evaporation of higher-dimensional rotating black holes
To study the dynamics of discharge of a brane black hole in TeV gravity
scenarios, we obtain the approximate electromagnetic field due to the charged
black hole, by solving Maxwell's equations perturbatively on the brane. In
addition, arguments are given for brane metric corrections due to backreaction.
We couple brane scalar and brane fermion fields with non-zero mass and charge
to the background, and study the Hawking radiation process using well known low
energy approximations as well as a WKB approximation in the high energy limit.
We argue that contrary to common claims, the initial evaporation is not
dominated by fast Schwinger discharge.Comment: Published version. Minor typos corrected. 29 pages, 5 figure
Heterotic-type IIA duality with fluxes
In this paper we study a possible non-perturbative dual of the heterotic
string compactified on K3 x T^2 in the presence of background fluxes. We show
that type IIA string theory compactified on manifolds with SU(3) structure can
account for a subset of the possible heterotic fluxes. This extends our
previous analysis to a case of a non-perturbative duality with fluxes.Comment: 26 pages, minor corrections; version to appear in JHE
Intrinsic Geometry of D-Branes
We obtain forms of Born-Infeld and D-brane actions that are quadratic in
derivatives of and linear in by introducing an auxiliary
`metric' which has both symmetric and anti-symmetric parts, generalising the
simplification of the Nambu-Goto action for -branes using a symmetric
metric. The abelian gauge field appears as a Lagrange multiplier, and solving
the constraint gives the dual form of the dimensional action with an
form gauge field instead of a vector gauge field. We construct the dual action
explicitly, including cases which could not be covered previously. The
generalisation to supersymmetric D-brane actions with local fermionic symmetry
is also discussed.Comment: 10 pages, LaTeX, no figures. Minor correction; version to appear in
Physics Letters
Do work placements improve final year academic performance or do high-calibre students choose to do work placements?
This study investigates whether the completion of an optional sandwich work placement enhances student performance in final year examinations. Using Propensity Score Matching, our analysis departs from the literature by controlling for self-selection. Previous studies may have overestimated the impact of sandwich work placements on performance because it might be the case that high-calibre students choose to go on placement. Our results, utilising a large student data set, indicate that self-selection is present, but the effects of a placement on student performance still have an impact. This robust finding is found to be of a remarkably similar magnitude across two UK universities
Geometric Actions for D-Branes and M-Branes
New forms of Born-Infeld, D-brane and M theory five-brane actions are found
which are quadratic in the abelian field strength. The gauge fields couple both
to a background or induced metric and a new auxiliary metric, whose elimination
reproduces the non-polynomial Born-Infeld action. This is similar to the
introduction of an auxiliary metric to simplify the Nambu-Goto string action.
This simplifies the quantisation and dualisation of the gauge fields.Comment: LaTeX, 9 pages, no figures. Minor corrections; version to appear in
Physics Letters
DNA hybridization catalysts and catalyst circuits
Practically all of life's molecular processes, from chemical synthesis to replication, involve enzymes that carry out their functions through the catalysis of metastable fuels into waste products. Catalytic control of reaction rates will prove to be as useful and ubiquitous in
DNA nanotechnology as it is in biology. Here we present experimental results on the control of the decay rates of a metastable DNA "fuel". We show that the fuel complex can be induced to decay with a rate about 1600 times faster than it would decay spontaneously. The original DNA hybridization catalyst [15] achieved a maximal speed-up of roughly 30. The fuel complex discussed here can therefore serve as the basic ingredient for an improved DNA hybridization catalyst. As an example application for DNA hybridization catalysts, we propose a method for implementing arbitrary digital logic circuits
The trans-activation domain of the sporulation response regulator Spo0A revealed by X-ray crystallography
Sporulation in Bacillus involves the induction of scores of genes in a temporally and spatially co-ordinated programme of cell development. Its initiation is under the control of an expanded two-component signal transduction system termed a phosphorelay. The master control element in the decision to sporulate is the response regulator, Spo0A, which comprises a receiver or phosphoacceptor domain and an effector or transcription activation domain. The receiver domain of Spo0A shares sequence similarity with numerous response regulators, and its structure has been determined in phosphorylated and unphosphorylated forms. However, the effector domain (C-Spo0A) has no detectable sequence similarity to any other protein, and this lack of structural information is an obstacle to understanding how DNA binding and transcription activation are controlled by phosphorylation in Spo0A. Here, we report the crystal structure of C-Spo0A from Bacillus stearothermophilus revealing a single alpha -helical domain comprising six alpha -helices in an unprecedented fold. The structure contains a helix-turn-helix as part of a three alpha -helical bundle reminiscent of the catabolite gene activator protein (CAP), suggesting a mechanism for DNA binding. The residues implicated in forming the sigma (A)-activating region clearly cluster in a flexible segment of the polypeptide on the opposite side of the structure from that predicted to interact with DNA. The structural results are discussed in the context of the rich array of existing mutational data
The holy blood and the holy grail: Myths of scientific racism and the pursuit of excellence in sport
Despite the continuing publication of research that suggests there is no scientific basis to 'race' as a biological category, theories of racial difference continue to be invoked within sport to explain the perceived dominance of black athletes. In the case of John Entine's controversial 'Taboo: why black athletes dominate sports and why we are afraid to talk about it' or undergraduate textbooks that suggest 'racial differences' in physique may significantly affect athletic performance, scientific racism is normalised in sport. In this article, the relationship between scientific racism and sport will be examined. Qualitative research with current sport scientists is used to investigate the socio-ethical tensions within the subject field of sport science between professionalism, scientism and the demand from external interests to produce results that help people in sport win medals. It will be shown that these tensions, combined with the history of race as a category in sport science, combine to create the discourse of scientific knowledge that reflects, rather than challenges, folk genetics of black athletic physicality
Heterotic String Compactifications on Half-flat Manifolds II
In this paper, we continue the analysis of heterotic string compactifications
on half-flat mirror manifolds by including the 10-dimensional gauge fields. It
is argued, that the heterotic Bianchi identity is solved by a variant of the
standard embedding. Then, the resulting gauge group in four dimensions is still
E6 despite the fact that the Levi-Civita connection has SO(6) holonomy. We
derive the associated four-dimensional effective theories including matter
field terms for such compactifications. The results are also extended to more
general manifolds with SU(3) structure.Comment: 31 page
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