19,068 research outputs found
The near-horizon geometry of dilaton-axion black holes
Static black holes of dilaton-axion gravity become singular in the extreme
limit, which prevents a direct determination of their near-horizon geometry.
This is addressed by first taking the near-horizon limit of extreme rotating
NUT-less black holes, and then going to the static limit. The resulting
four-dimensional geometry may be lifted to a Bertotti-Robinson-like solution of
six-dimensional vacuum gravity, which also gives the near-horizon geometry of
extreme Kaluza-Klein black holes in five dimensions.Comment: 2 pages, "mprocl.sty" with Latex 2.09, contribution to the 9th Marcel
Grossmann meeting (MG9), Rome, July 200
Friction measuring apparatus Patent
Kinetic and static friction force measurement between magnetic tape and magnetic head surface
On the invertibility of mappings arising in 2D grid generation problems
In adapting a grid for a Computational Fluid Dynamics problem one uses a mapping from the unit square onto itself that is the solution of an elliptic partial differential equation with rapidly varying coefficients. For a regular discretization this mapping has to be invertible. We will show that such result holds for general elliptic operators (in two dimensions). The Carleman-Hartman-Wintner Theorem will be fundamental in our proof. We will also explain why such a general result cannot be expected to hold for the (three-dimensional) cube
On a Dirichlet problem related to the invertibility of mappings arising in 2D grid generation problems
this paper depends strongly on a theorem of Carleman-HartmanWintner. This theorem is only true in two dimensional domains. In fact a straightforward generalization to more than two dimensional domains cannot be true. A counterexample to the proof of [15]forthe three dimensional case can be found by using a special harmonic function due to Kellogg [12]. This function is shown in [2]. A direct counterexample can be found in [13]. 2 Main result on smooth domain
Compaction and mobility in randomly agitated granular assemblies
We study the compaction and mobility properties of a dense granular material
under weak random vibration. By putting in direct contact millimetric glass
beads with piezoelectric transducers we manage to inject energy to the system
in a disordered manner with accelerations much smaller than gravity, resulting
in a slow compaction dynamics and no convection. We characterize the mobility
inside the medium by pulling through it an intruder grain at constant velocity.
We present an extensive study of the relation between drag force and velocity
for different vibration conditions and sizes of the intruder.Comment: 4 pages, 6 figures, to appear in the proceedings of Powders and
Grains 200
Rotating non-asymptotically flat black rings in charged dilaton gravity
We derive new rotating, non-asymptotically flat black ring solutions in
five-dimensional Einstein-Maxwell-dilaton gravity with dilaton coupling
constant which arises from a six-dimensional Kaluza-Klein
theory. As a limiting case we also find new rotating, non-asymptotically flat
five-dimensional black holes. The solutions are analyzed and the mass, angular
momentum and charge are computed. A Smarr-like relation is found. It is shown
that the first law of black hole thermodynamics is satisfied.Comment: 21 pages, LaTeX; v2 a reference added, typos correcte
Evolution of midplate hotspot swells: Numerical solutions
The evolution of midplate hotspot swells on an oceanic plate moving over a hot, upwelling mantle plume is numerically simulated. The plume supplies a Gaussian-shaped thermal perturbation and thermally-induced dynamic support. The lithosphere is treated as a thermal boundary layer with a strongly temperature-dependent viscosity. The two fundamental mechanisms of transferring heat, conduction and convection, during the interaction of the lithosphere with the mantle plume are considered. The transient heat transfer equations, with boundary conditions varying in both time and space, are solved in cylindrical coordinates using the finite difference ADI (alternating direction implicit) method on a 100 x 100 grid. The topography, geoid anomaly, and heat flow anomaly of the Hawaiian swell and the Bermuda rise are used to constrain the models. Results confirm the conclusion of previous works that the Hawaiian swell can not be explained by conductive heating alone, even if extremely high thermal perturbation is allowed. On the other hand, the model of convective thinning predicts successfully the topography, geoid anomaly, and the heat flow anomaly around the Hawaiian islands, as well as the changes in the topography and anomalous heat flow along the Hawaiian volcanic chain
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