1,213 research outputs found
Dynamic roughening of the magnetic flux landscape in YBaCuO
We study the magnetic flux landscape in YBaCuO thin films as
a two dimensional rough surface. The vortex density in the superconductor forms
a self-affine structure in both space and time. This is characterized by a
roughness exponent and a growth exponent .
This is due to the structure and distribution of flux avalanches in the
self-organized critical state, which is formed in the superconductor. We also
discuss our results in the context of other roughening systems in the presence
of quenched disorder.Comment: 13 pages, 7 figures, accepted for publication in Physica
The Torus Universe in the Polygon Approach to 2+1-Dimensional Gravity
In this paper we describe the matter-free toroidal spacetime in 't Hooft's
polygon approach to 2+1-dimensional gravity (i.e. we consider the case without
any particles present). Contrary to earlier results in the literature we find
that it is not possible to describe the torus by just one polygon but we need
at least two polygons. We also show that the constraint algebra of the polygons
closes.Comment: 18 pages Latex, 13 eps-figure
Winding Solutions for the two Particle System in 2+1 Gravity
Using a PASCAL program to follow the evolution of two gravitating particles
in 2+1 dimensions we find solutions in which the particles wind around one
another indefinitely. As their center of mass moves `tachyonic' they form a
Gott-pair. To avoid unphysical boundary conditions we consider a large but
closed universe. After the particles have evolved for some time their momenta
have grown very large. In this limit we quantize the model and find that both
the relevant configuration variable and its conjugate momentum become discrete.Comment: 15 pages Latex, 4 eps figure
The 2+1 Kepler Problem and Its Quantization
We study a system of two pointlike particles coupled to three dimensional
Einstein gravity. The reduced phase space can be considered as a deformed
version of the phase space of two special-relativistic point particles in the
centre of mass frame. When the system is quantized, we find some possibly
general effects of quantum gravity, such as a minimal distances and a foaminess
of the spacetime at the order of the Planck length. We also obtain a
quantization of geometry, which restricts the possible asymptotic geometries of
the universe.Comment: 59 pages, LaTeX2e, 9 eps figure
Avalanches and Self-Organized Criticality in Superconductors
We review the use of superconductors as a playground for the experimental
study of front roughening and avalanches. Using the magneto-optical technique,
the spatial distribution of the vortex density in the sample is monitored as a
function of time. The roughness and growth exponents corresponding to the
vortex landscape are determined and compared to the exponents that characterize
the avalanches in the framework of Self-Organized Criticality. For those
situations where a thermo-magnetic instability arises, an analytical non-linear
and non-local model is discussed, which is found to be consistent to great
detail with the experimental results. On anisotropic substrates, the anisotropy
regularizes the avalanches
- …