8,753 research outputs found
New Gauged N=8, D=4 Supergravities
New gaugings of four dimensional N=8 supergravity are constructed, including
one which has a Minkowski space vacuum that preserves N=2 supersymmetry and in
which the gauge group is broken to . Previous gaugings used the
form of the ungauged action which is invariant under a rigid symmetry
and promoted a 28-dimensional subgroup ( or the
non-semi-simple contraction ) to a local gauge group. Here, a
dual form of the ungauged action is used which is invariant under
instead of and new theories are obtained by gauging 28-dimensional
subgroups of . The gauge groups are non-semi-simple and are different
real forms of the groups, denoted , and the new
theories have a rigid SU(2) symmetry. The five dimensional gauged N=8
supergravities are dimensionally reduced to D=4. The gauge
theories reduce, after a duality transformation, to the
gauging while the gauge theory reduces to the gauge
theory. The new theories are related to the old ones via an analytic
continuation. The non-semi-simple gaugings can be dualised to forms with
different gauge groups.Comment: 33 pages. Reference adde
Metal honeycomb to porous wireform substrate diffusion bond evaluation
Two nondestructive techniques were used to evaluate diffusion bond quality between a metal foil honeycomb and porous wireform substrate. The two techniques, cryographics and acousto-ultrasonics, are complementary in revealing variations of bond integrity and quality in shroud segments from an experimental aircraft turbine engine
Computer program for determining mass properties of a rigid structure
A computer program was developed for the rapid computation of the mass properties of complex structural systems. The program uses rigid body analyses and permits differences in structural material throughout the total system. It is based on the premise that complex systems can be adequately described by a combination of basic elemental shapes. Simple geometric data describing size and location of each element and the respective material density or weight of each element were the only required input data. From this minimum input, the program yields system weight, center of gravity, moments of inertia and products of inertia with respect to mutually perpendicular axes through the system center of gravity. The program also yields mass properties of the individual shapes relative to component axes
An experimental study of the temporal statistics of radio signals scattered by rain
A fixed-beam bistatic CW experiment designed to measure the temporal statistics of the volume reflectivity produced by hydrometeors at several selected altitudes, scattering angles, and at two frequencies (3.6 and 7.8 GHz) is described. Surface rain gauge data, local meteorological data, surveillance S-band radar, and great-circle path propagation measurements were also made to describe the general weather and propagation conditions and to distinguish precipitation scatter signals from those caused by ducting and other nonhydrometeor scatter mechanisms. The data analysis procedures were designed to provide an assessment of a one-year sample of data with a time resolution of one minute. The cumulative distributions of the bistatic signals for all of the rainy minutes during this period are presented for the several path geometries
Moody's Correlated Binomial Default Distributions for Inhomogeneous Portfolios
This paper generalizes Moody's correlated binomial default distribution for
homogeneous (exchangeable) credit portfolio, which is introduced by Witt, to
the case of inhomogeneous portfolios. As inhomogeneous portfolios, we consider
two cases. In the first case, we treat a portfolio whose assets have uniform
default correlation and non-uniform default probabilities. We obtain the
default probability distribution and study the effect of the inhomogeneity on
it. The second case corresponds to a portfolio with inhomogeneous default
correlation. Assets are categorized in several different sectors and the
inter-sector and intra-sector correlations are not the same. We construct the
joint default probabilities and obtain the default probability distribution. We
show that as the number of assets in each sector decreases, inter-sector
correlation becomes more important than intra-sector correlation. We study the
maximum values of the inter-sector default correlation. Our generalization
method can be applied to any correlated binomial default distribution model
which has explicit relations to the conditional default probabilities or
conditional default correlations, e.g. Credit Risk, implied default
distributions. We also compare some popular CDO pricing models from the
viewpoint of the range of the implied tranche correlation.Comment: 29 pages, 17 figures and 1 tabl
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Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To assess whether blue-light filtering spectacle lenses impart effects on visual function, provide protection to the macula, or both. We will also examine potential effects on the sleep-wake cycle
Effect of hydrogen on the strength and microstructure of selected ceramics
Ceramics in monolithic form and as composite constituents in the form of fibers, matrices, and coatings are currently being considered for a variety of high-temperature applications in aeronautics and space. Many of these applications involve exposure to a hydrogen-containing environment. The compatibility of selected ceramics in gaseous high-temperature hydrogen is assessed. Environmental stability regimes for the long term use of ceramic materials are defined by the parameters of temperature, pressure, and moisture content. Thermodynamically predicted reactions between hydrogen and several monolithic ceramics are compared with actual performance in a controlled environment. Morphology of hydrogen attack and the corresponding strength degradation is reported for silicon carbide, silicon nitride, alumina, magnesia, and mullite
Spacetime-Filling Branes and Strings with Sixteen Supercharges
We discuss branes whose worldvolume dimension equals the target spacetime
dimension, i.e. ``spacetime-filling branes''. In addition to the D9-branes,
there are 9-branes in the NS-NS sectors of both the IIA and IIB strings. The
worldvolume actions of these branes are constructed, via duality, from the
known actions of branes with codimension larger than zero. Each of these types
of branes is used in the construction of a string theory with sixteen
supercharges by modding out a type II string by an appropriate discrete
symmetry and adding 32 9-branes. These constructions are related by a web of
dualities and each arises as a different limit of the Horava-Witten
construction.Comment: 43 pages, LaTeX, 8 figures, uses html.sty, version to appear in Nucl.
Phys.
Weakly nonlinear theory of grain boundary motion in patterns with crystalline symmetry
We study the motion of a grain boundary separating two otherwise stationary
domains of hexagonal symmetry. Starting from an order parameter equation
appropriate for hexagonal patterns, a multiple scale analysis leads to an
analytical equation of motion for the boundary that shares many properties with
that of a crystalline solid. We find that defect motion is generically opposed
by a pinning force that arises from non-adiabatic corrections to the standard
amplitude equation. The magnitude of this force depends sharply on the
mis-orientation angle between adjacent domains so that the most easily pinned
grain boundaries are those with an angle between four and eight degrees.
Although pinning effects may be small, they do not vanish asymptotically near
the onset of this subcritical bifurcation, and can be orders of magnitude
larger than those present in smectic phases that bifurcate supercritically
Scaling Cosmologies from Duality Twisted Compactifications
Oscillating moduli fields can support a cosmological scaling solution in the
presence of a perfect fluid when the scalar field potential satisfies
appropriate conditions. We examine when such conditions arise in
higher-dimensional, non-linear sigma-models that are reduced to four dimensions
under a generalized Scherk-Schwarz compactification. We show explicitly that
scaling behaviour is possible when the higher-dimensional action exhibits a
global SL(n,R) or O(2,2) symmetry. These underlying symmetries can be exploited
to generate non-trivial scaling solutions when the moduli fields have
non-canonical kinetic energy. We also consider the compactification of
eleven-dimensional vacuum Einstein gravity on an elliptic twisted torus.Comment: 21 pages, 3 figure
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