203 research outputs found
Dynamics of supertubes
We find the evolution of arbitrary excitations on 2-charge supertubes, by
mapping the supertube to a string carrying traveling waves. We argue that when
the coupling is increased from zero the energy of excitation leaks off to
infinity, and when the coupling is increased still further a new set of long
lived excitations emerge. We relate the excitations at small and large
couplings to excitations in two different phases in the dual CFT. We conjecture
a way to distinguish bound states from unbound states among 3-charge BPS
geometries; this would identify black hole microstates among the complete set
of BPS geometries.Comment: 50 pages, 3 figure
MULTILAYER MICROSTRIP ANTENNA QUALITY FACTOR OPTIMIZATION FOR BANDWIDTH ENHANCEMENT
The impedance bandwidth, one of the important characteristics of microstrip patch antennas, can be significantly improved by using a multilayer dielectric configuration. In this paper the focus is on bandwidth enhancement technique of a multilayer patch antenna for X-band applications. In order to enhance the bandwidth, antenna losses are contained by controlling those quality factors which can have a significant impact on the bandwidth for a given permittivity and thickness of the substrate. This has been achieved by conformal transformation of the multidielectric microstrip antenna. For the ease of analysis Wheelers transformation is used to map the complex permittivity of a multilayer substrate to a single layer. Method of Moments and Finite Difference Time Domain approaches are used for the computation of results
X-ray diffraction studies on Mycobacterium smegmatis DNA
This article does not have an abstract
Elastic Shape Models for Face Analysis Using Curvilinear Coordinates
International audienceThis paper studies the problem of analyzing variability in shapes of facial surfaces using a Rie- mannian framework, a fundamental approach that allows for joint matchings, comparisons, and deformations of faces under a chosen metric. The starting point is to impose a curvilinear coordinate system, named the Darcyan coordinate system, on facial surfaces; it is based on the level curves of the surface distance function measured from the tip of the nose. Each facial surface is now represented as an indexed collection of these level curves. The task of finding optimal deformations, or geodesic paths, between facial surfaces reduces to that of finding geodesics between level curves, which is accomplished using the theory of elastic shape analy- sis of 3D curves. Elastic framework allows for nonlinear matching between curves and between points across curves. The resulting geodesics provide optimal elastic deformations between faces and an elastic metric for comparing facial shapes. We demonstrate this idea using examples from FSU face databas
Branes wrapping Black Holes
We examine the dynamics of extended branes, carrying lower dimensional brane
charges, wrapping black holes and black hole microstates in M and Type II
string theory. We show that they have a universal dispersion relation typical
of threshold bound states with a total energy equal to the sum of the
contributions from the charges. In near-horizon geometries of black holes,
these are BPS states, and the dispersion relation follows from supersymmetry as
well as properties of the conformal algebra. However they break all
supersymmetries of the full asymptotic geometries of black holes and
microstates. We comment on a recent proposal which uses these states to explain
black hole entropy.Comment: 41 pages, 2 figures;v2: references adde
Scalar propagator in the pp-wave geometry obtained from AdS_5 X S^5
We compute the propagator for massless and massive scalar fields in the
metric of the pp-wave. The retarded propagator for the massless field is found
to stay confined to the surface formed by null geodesics. The algebraic form of
the massive propagator is found to be related in a simple way to the form of
the propagator in flat spacetime.Comment: Latex, 12 pages, some typos in Section 5.2 fixe
Constructing "hair" for the three charge hole
It has been found that the states of the 2-charge extremal D1-D5 system are
given by smooth geometries that have no singularity and no horizon
individually, but a `horizon' does arise after `coarse-graining'. To see how
this concept extends to the 3-charge extremal system, we construct a
perturbation on the D1-D5 geometry that carries one unit of momentum charge
. The perturbation is found to be regular everywhere and normalizable, so we
conclude that at least this state of the 3-charge system behaves like the
2-charge states. The solution is constructed by matching (to several orders)
solutions in the inner and outer regions of the geometry. We conjecture the
general form of `hair' expected for the 3-charge system, and the nature of the
interior of black holes in general.Comment: 37 pages, 7 figures LaTex, Minor revision in the discussio
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