601 research outputs found
A stereographic representation of Knoop hardness anisotropy
Indentation direction parameter for hardness anisotropy representation of single crystal on stereographic triangl
The Parallelometer: a mechanical device to study curvature
A simple mechanical device is introduced, the parallelometer, that can be
used to measure curvatures of surfaces. The device can be used as a practical
illustration of parallel transport of a vector and to study Berry phase shift
when it is carried along a loop on the surface. Its connection to the Foucault
pendulum is discussed. The experimental results can be successfully compared
with the theoretical expectations. The experiment is inexpensive and
conceptually easy to perform and understand for a beginner
Choptuik scaling in six dimensions
We perform numerical simulations of the critical gravitational collapse of a
spherically symmetric scalar field in 6 dimensions. The critical solution has
discrete self-similarity. We find the critical exponent \gamma and the
self-similarity period \Delta.Comment: 8 pages, 3 figures RevTe
Collapse of a Circular Loop of Cosmic String
We study the collapse of a circular loop of cosmic string. The gravitational
field of the string is treated using the weak field approximation. The
gravitational radiation from the loop is evaluated numerically. The memtric of
the loop near the point of collapse is found analytically.Comment: 15 page
Homothetic Self-Similar Solutions of the Three-Dimensional Brans-Dicke Gravity
All homothetic self-similar solutions of the Brans-Dicke scalar field in
three-dimensional spacetime with circular symmetry are found in closed form.Comment: latex, five pages, without figur
Gravitating Fluxbranes
We consider the effect that gravity has when one tries to set up a constant
background form field. We find that in analogy with the Melvin solution, where
magnetic field lines self-gravitate to form a flux-tube, the self-gravity of
the form field creates fluxbranes. Several exact solutions are found
corresponding to different transverse spaces and world-volumes, a dilaton
coupling is also considered.Comment: 14 pages, 5 figure
Spherically symmetric scalar field collapse in any dimension
We describe a formalism and numerical approach for studying spherically
symmetric scalar field collapse for arbitrary spacetime dimension d and
cosmological constant Lambda. The presciption uses a double null formalism, and
is based on field redefinitions first used to simplify the field equations in
generic two-dimensional dilaton gravity. The formalism is used to construct
code in which d and Lambda are input parameters. The code reproduces known
results in d = 4 and d = 6 with Lambda = 0. We present new results for d = 5
with zero and negative Lambda.Comment: 16 pages, 6 figures, typos corrected, presentational changes, PRD in
pres
Extremal dyonic black holes in D=4 Gauss-Bonnet gravity
We investigate extremal dyon black holes in the Einstein-Maxwell-dilaton
(EMD) theory with higher curvature corrections in the form of the Gauss-Bonnet
density coupled to the dilaton. In the same theory without the Gauss-Bonnet
term the extremal dyon solutions exist only for discrete values of the dilaton
coupling constant . We show that the Gauss-Bonnet term acts as a dyon hair
tonic enlarging the allowed values of to continuous domains in the plane
the second parameter being the magnetic charge. In the limit of the
vanishing curvature coupling (a large magnetic charge) the dyon solutions
obtained tend to the Reissner-Nordstr\"om solution but not to the extremal
dyons of the EMD theory. Both solutions have the same values of the horizon
radius as a function of charges. The entropy of new dyonic black holes
interpolates between the Bekenstein-Hawking value in the limit of the large
magnetic charge (equivalent to the vanishing Gauss-Bonnet coupling) and twice
this value for the vanishing magnetic charge. Although an expression for the
entropy can be obtained analytically using purely local near-horizon solutions,
its interpretation as the black hole entropy is legitimate only once the global
black hole solution is known to exist, and we obtain numerically the
corresponding conditions on the parameters. Thus, a purely local analysis is
insufficient to fully understand the entropy of the curvature corrected black
holes. We also find dyon solutions which are not asymptotically flat, but
approach the linear dilaton background at infinity. They describe magnetic
black holes on the electric linear dilaton background.Comment: 19 pages, 3 figures, revtex
Janis-Newman-Winicour and Wyman solutions are the same
We show that the well-known most general static and spherically symmetric
exact solution to the Einstein-massless scalar equations given by Wyman is the
same as one found by Janis, Newman and Winicour several years ago. We obtain
the energy associated with this spacetime and find that the total energy for
the case of the purely scalar field is zero.Comment: 9 pages, LaTex, no figures, misprints corrected, to appear in Int. J.
Mod. Phys.
Ricci flows, wormholes and critical phenomena
We study the evolution of wormhole geometries under Ricci flow using
numerical methods. Depending on values of initial data parameters, wormhole
throats either pinch off or evolve to a monotonically growing state. The
transition between these two behaviors exhibits a from of critical phenomena
reminiscent of that observed in gravitational collapse. Similar results are
obtained for initial data that describe space bubbles attached to
asymptotically flat regions. Our numerical methods are applicable to
"matter-coupled" Ricci flows derived from conformal invariance in string
theory.Comment: 8 pages, 5 figures. References added and minor changes to match
version accepted by CQG as a fast track communicatio
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