3,047 research outputs found
Multidimensional perfect fluid cosmology with stable compactified internal dimensions
Multidimensional cosmological models in the presence of a bare cosmological
constant and a perfect fluid are investigated under dimensional reduction to
4-dimensional effective models. Stable compactification of the internal spaces
is achieved for a special class of perfect fluids. The external space behaves
in accordance with the standard Friedmann model. Necessary restrictions on the
parameters of the models are found to ensure dynamical behavior of the external
(our) universe in agreement with observations.Comment: 11 pages, Latex2e, uses IOP packages, submitted to Class.Quant.Gra
Explaining the Electroweak Scale and Stabilizing Moduli in M Theory
In a recent paper \cite{Acharya:2006ia} it was shown that in theory vacua
without fluxes, all moduli are stabilized by the effective potential and a
stable hierarchy is generated, consistent with standard gauge unification. This
paper explains the results of \cite{Acharya:2006ia} in more detail and
generalizes them, finding an essentially unique de Sitter (dS) vacuum under
reasonable conditions. One of the main phenomenological consequences is a
prediction which emerges from this entire class of vacua: namely gaugino masses
are significantly suppressed relative to the gravitino mass. We also present
evidence that, for those vacua in which the vacuum energy is small, the
gravitino mass, which sets all the superpartner masses, is automatically in the
TeV - 100 TeV range.Comment: 73 pages, 39 figures, Minor typos corrected, Figures and References
adde
Symmetric Strategy Improvement
Symmetry is inherent in the definition of most of the two-player zero-sum
games, including parity, mean-payoff, and discounted-payoff games. It is
therefore quite surprising that no symmetric analysis techniques for these
games exist. We develop a novel symmetric strategy improvement algorithm where,
in each iteration, the strategies of both players are improved simultaneously.
We show that symmetric strategy improvement defies Friedmann's traps, which
shook the belief in the potential of classic strategy improvement to be
polynomial
Geometric structure of the generic static traversable wormhole throat
Traversable wormholes have traditionally been viewed as intrinsically
topological entities in some multiply connected spacetime. Here, we show that
topology is too limited a tool to accurately characterize a generic traversable
wormhole: in general one needs geometric information to detect the presence of
a wormhole, or more precisely to locate the wormhole throat. For an arbitrary
static spacetime we shall define the wormhole throat in terms of a
2-dimensional constant-time hypersurface of minimal area. (Zero trace for the
extrinsic curvature plus a "flare-out" condition.) This enables us to severely
constrain the geometry of spacetime at the wormhole throat and to derive
generalized theorems regarding violations of the energy conditions-theorems
that do not involve geodesic averaging but nevertheless apply to situations
much more general than the spherically symmetric Morris-Thorne traversable
wormhole. [For example: the null energy condition (NEC), when suitably weighted
and integrated over the wormhole throat, must be violated.] The major technical
limitation of the current approach is that we work in a static spacetime-this
is already a quite rich and complicated system.Comment: 25 pages; plain LaTeX; uses epsf.sty (four encapsulated postscript
figures
Experimental and numerical analysis of mold filling in rotational molding
This work focuses on the development of a numerical mold filling simulation for the rotational molding process. In the rotational molding process, a dry fiber preform is placed in a mold and impregnated with a thermoset matrix under rotation. Additionally, metallic load introduction elements can be inserted into the mold and joined with co-curing or form-fit, resulting in hybrid drive shafts or tie rods. The numerical model can be used to simulate the impregnation of the preform. Based on the resin transfer molding process, an OpenFOAM solver is extended for the rotational molding process. Permeability, kinetic and curing models are selected and adapted to the materials used. A wireless measurement solution with a capacitive sensor is developed to validate the model. Comparisons between measurements and numerically calculated impregnation times to reach the capacitive sensor with the matrix show good quality of the developed model. The average deviation between calculated result and measured mean values in the experiment is 43.8% the maximum deviation is 65.8% . The model can therefore be used to predict the impregnation progress and the curing state
Polynomial Hamiltonian form of General Relativity
Phase space of General Relativity is extended to a Poisson manifold by
inclusion of the determinant of the metric and conjugate momentum as additional
independent variables. As a result, the action and the constraints take a
polynomial form. New expression for the generating functional for the Green
functions is proposed. We show that the Dirac bracket defines degenerate
Poisson structure on a manifold, and a second class constraints are the Casimir
functions with respect to this structure. As an application of the new
variables, we consider the Friedmann universe.Comment: 33 pages, 1 figure, corrected reference
Metabolomics in CGIAR Research Program on Roots, Tubers and Bananas (RTB).
The CGIAR Research Program on Roots, Tubers and Bananas (RTB) is supporting investments in metabolomics in collaboration with the Fraser lab at Royal Holloway University London (RHUL). The metabolome is the global collection of all low molecular weight chemical compounds that are produced by cell metabolism in different sizes, polarity and quantities. It thus provides a direct functional readout of the cell’s physiological status and activity under specific environmental settings. Metabolomics research in RTB has involved metabolite profiling for making significant marker-trait associations, assessment of genetic diversity and varietal identification. Therefore, this has included screening young plantlets as proxies for mature end-product quality (roots, tubers and banana fruits), identifying potential biomarkers for abiotic stress tolerance and for product-quality traits. In this paper, we review the main findings of this work, and discuss the implications for breeding programs in the RTB Program
Stable Topologies of Event Horizon
In our previous work, it was shown that the topology of an event horizon (EH)
is determined by the past endpoints of the EH. A torus EH (the collision of two
EH) is caused by the two-dimensional (one-dimensional) set of the endpoints. In
the present article, we examine the stability of the topology of the EH. We see
that a simple case of a single spherical EH is unstable. Furthermore, in
general, an EH with handles (a torus, a double torus, ...) is structurally
stable in the sense of catastrophe theory.Comment: 21 pages, revtex, five figures containe
Classification and Moduli Kahler Potentials of G_2 Manifolds
Compact manifolds of G_2 holonomy may be constructed by dividing a
seven-torus by some discrete symmetry group and then blowing up the
singularities of the resulting orbifold. We classify possible group elements
that may be used in this construction and use this classification to find a set
of possible orbifold groups. We then derive the moduli Kahler potential for
M-theory on the resulting class of G_2 manifolds with blown up co-dimension
four singularities.Comment: 30 pages, Latex, references adde
G_2 Domain Walls in M-theory
M-theory is considered in its low-energy limit on a G_2 manifold with
non-vanishing flux. Using the Killing spinor equations for linear flux, an
explicit set of first-order bosonic equations for supersymmetric solutions is
found. These solutions describe a warped product of a domain wall in
four-dimensional space-time and a deformed G_2 manifold. It is shown how these
domain walls arise from the perspective of the associated four-dimensional N=1
effective supergravity theories. We also discuss the inclusion of membrane and
M5-brane sources.Comment: 30 pages, Late
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