31 research outputs found
Global properties of an exact string theory solution in two and four dimensions
This paper discusses global properties of exact (in alpha prime) string
theory solutions: A deformed black hole solution in two dimensions and a
Taub-NUT type solution in four dimensions. These models are exact by virtue of
having CFT descriptions in terms of heterotic coset models. The analysis
includes analytic continuations of the metric, motion of test particles, and
the T-duality which acts as a map between different regions of the extended
solutions, rendering the physical spacetimes non-singular.Comment: 16 pages, 3 figures; v2: minor corrections, as printed in journa
A pedestrian approach to the high energy limits of branes and other gravitational systems
In this article we study limits of models that contain a dimensionful
parameter such as the mass of the relativistic point-particle. The limits are
analogous to the massless limit of the particle and may be thought of as high
energy limits. We present the ideas and work through several examples in a
(hopefully) pedagogical manner. Along the way we derive several new results.Comment: 19 pages, 1 figur
The N=8 Supergravity Hamiltonian as a Quadratic Form
We conjecture that the light-cone Hamiltonian of N=8 Supergravity can be
expressed as a quadratic form. We explain why this rewriting is unique to
maximally supersymmetric theories. The N=8 quartic interaction vertex is
constructed and used to verify that this conjecture holds to second order in
the coupling constant.Comment: 23 pages, minor corrections in appendix
The Exact Geometry of a Kerr-Taub-NUT Solution of String Theory
In this paper we study a solution of heterotic string theory corresponding to
a rotating Kerr-Taub-NUT spacetime. It has an exact CFT description as a
heterotic coset model, and a Lagrangian formulation as a gauged WZNW model. It
is a generalisation of a recently discussed stringy Taub-NUT solution, and is
interesting as another laboratory for studying the fate of closed timelike
curves and cosmological singularities in string theory. We extend the
computation of the exact metric and dilaton to this rotating case, and then
discuss some properties of the metric, with particular emphasis on the
curvature singularities.Comment: 14 pages, 3 figure
A note on fermions in holographic QCD
We study the fermionic sector of a probe D8-brane in the supergravity
background made of D4-branes compactified on a circle with supersymmetry broken
explicitly by the boundary conditions. At low energies the dual field theory is
effectively four-dimensional and has proved surprisingly successful in
recovering qualitative and quantitative properties of QCD. We investigate
fluctuations of the fermionic fields on the probe D8-brane and interpret these
as mesinos (fermionic superpartners of mesons). We demonstrate that the masses
of these modes are comparable to meson masses and show that their interactions
with ordinary mesons are not suppressed.Comment: 21+1 pp, 1 figure; v2: typos corrected, refs. adde
An Exact String Theory Model of Closed Time-Like Curves and Cosmological Singularities
We study an exact model of string theory propagating in a space-time
containing regions with closed time-like curves (CTCs) separated from a finite
cosmological region bounded by a Big Bang and a Big Crunch. The model is an
non-trivial embedding of the Taub-NUT geometry into heterotic string theory
with a full conformal field theory (CFT) definition, discovered over a decade
ago as a heterotic coset model. Having a CFT definition makes this an excellent
laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and
the Milne/Misner-type chronology horizon which separates them. In an effort to
uncover the role of stringy corrections to such geometries, we calculate the
complete set of alpha' corrections to the geometry. We observe that the key
features of Taub-NUT persist in the exact theory, together with the emergence
of a region of space with Euclidean signature bounded by time-like curvature
singularities. Although such remarks are premature, their persistence in the
exact geometry is suggestive that string theory theory is able to make physical
sense of the Milne/Misner singularities and the CTCs, despite their
pathological character in General Relativity. This may also support the
possibility that CTCs may be viable in some physical situations, and may be a
natural ingredient in pre-Big-Bang cosmological scenarios.Comment: 37 pages, 4 figures. V2: discussion of computation of metric refined,
references adde
A Note on D-brane - Anti-D-brane Interactions in Plane Wave Backgrounds
We study aspects of the interaction between a D-brane and an anti-D-brane in
the maximally supersymmetric plane wave background of type IIB superstring
theory, which is equipped with a mass parameter mu. An early such study in flat
spacetime (mu=0) served to sharpen intuition about D-brane interactions,
showing in particular the key role of the ``stringy halo'' that surrounds a
D-brane. The halo marks the edge of the region within which tachyon
condensation occurs, opening a gateway to new non-trivial vacua of the theory.
It seems pertinent to study the fate of the halo for non--zero mu. We focus on
the simplest cases of a Lorentzian brane with p=1 and an Euclidean brane with
p=-1, the D--instanton. For the Lorentzian brane, we observe that the halo is
unaffected by the presence of non--zero mu. This most likely extends to other
(Lorentzian) p. For the Euclidean brane, we find that the halo is affected by
non-zero mu. As this is related to subtleties in defining the exchange
amplitude between Euclidean branes in the open string sector, we expect this to
extend to all Euclidean branes in this background.Comment: 14 pages, LaTeX, 2 eps figures. v2: a reference and some clarifying
remarks added; v3: Considerably revised version; halo unaffected by plane
wave background for Lorentzian branes, but Euclidean branes' halo is modifie
Blood cell gene expression associated with cellular stress defense is modulated by antioxidant-rich food in a randomised controlled clinical trial of male smokers
Background
Plant-based diets rich in fruit and vegetables can prevent development of several chronic age-related diseases. However, the mechanisms behind this protective effect are not elucidated. We have tested the hypothesis that intake of antioxidant-rich foods can affect groups of genes associated with cellular stress defence in human blood cells. Trial registration number: NCT00520819 http://clinicaltrials.gov.
Methods
In an 8-week dietary intervention study, 102 healthy male smokers were randomised to either a diet rich in various antioxidant-rich foods, a kiwifruit diet (three kiwifruits/d added to the regular diet) or a control group. Blood cell gene expression profiles were obtained from 10 randomly selected individuals of each group. Diet-induced changes on gene expression were compared to controls using a novel application of the gene set enrichment analysis (GSEA) on transcription profiles obtained using Affymetrix HG-U133-Plus 2.0 whole genome arrays.
Results
Changes were observed in the blood cell gene expression profiles in both intervention groups when compared to the control group. Groups of genes involved in regulation of cellular stress defence, such as DNA repair, apoptosis and hypoxia, were significantly upregulated (GSEA, FDR q-values < 5%) by both diets compared to the control group. Genes with common regulatory motifs for aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (AhR/ARNT) were upregulated by both interventions (FDR q-values < 5%). Plasma antioxidant biomarkers (polyphenols/carotenoids) increased in both groups.
Conclusions
The observed changes in the blood cell gene expression profiles suggest that the beneficial effects of a plant-based diet on human health may be mediated through optimization of defence processes
Selection and peer-review under responsibility of SINTEF Energi AS Planning Tool for Clustering and Optimised Grid Connection of Offshore Wind Farms
Abstract A planning tool for clustering and optimised grid connection of offshore wind farms is presented and described in some detail. This tool is suitable for high level, strategic planning of clustering and grid connection of future offshore wind farms that are planned in the proximity of each other. This tool is an upgraded version of a previously developed tool for offshore grid expansion planning. The use of the upgraded tool is demonstrated with an example that considers the Kriegers Flak area, with results indicating benefits of interconnecting wind farms across country borders and using a hybrid AC and DC transmission system to shore