2,894 research outputs found
The pair annihilation reaction D + D --> 0 in disordered media and conformal invariance
The raise and peel model describes the stochastic model of a fluctuating
interface separating a substrate covered with clusters of matter of different
sizes, and a rarefied gas of tiles. The stationary state is obtained when
adsorption compensates the desorption of tiles. This model is generalized to an
interface with defects (D). The defects are either adjacent or separated by a
cluster. If a tile hits the end of a cluster with a defect nearby, the defect
hops at the other end of the cluster changing its shape. If a tile hits two
adjacent defects, the defect annihilate and are replaced by a small cluster.
There are no defects in the stationary state.
This model can be seen as describing the reaction D + D -->0, in which the
particles (defects) D hop at long distances changing the medium and annihilate.
Between the hops the medium also changes (tiles hit clusters changing their
shapes). Several properties of this model are presented and some exact results
are obtained using the connection of our model with a conformal invariant
quantum chain.Comment: 8 pages, 12figure
Exact Polynomial Eigenmodes for Homogeneous Spherical 3-Manifolds
Observational data hints at a finite universe, with spherical manifolds such
as the Poincare dodecahedral space tentatively providing the best fit.
Simulating the physics of a model universe requires knowing the eigenmodes of
the Laplace operator on the space. The present article provides explicit
polynomial eigenmodes for all globally homogeneous 3-manifolds: the Poincare
dodecahedral space S3/I*, the binary octahedral space S3/O*, the binary
tetrahedral space S3/T*, the prism manifolds S3/D_m* and the lens spaces
L(p,1).Comment: v3. Final published version. 27 pages, 1 figur
Topology of the Universe: background and recent observational approaches
Is the Universe (a spatial section thereof) finite or infinite? Knowing the
global geometry of a Friedmann-Lema\^{\i}tre (FL) universe requires knowing
both its curvature and its topology. A flat or hyperbolic (``open'') FL
universe is {\em not} necessarily infinite in volume.
Multiply connected flat and hyperbolic models are, in general, as consistent
with present observations on scales of 1-20{\hGpc} as are the corresponding
simply connected flat and hyperbolic models. The methods of detecting multiply
connected models (MCM's) are presently in their pioneering phase of development
and the optimal observationally realistic strategy is probably yet to be
calculated. Constraints against MCM's on ~1-4 h^{-1} Gpc scales have been
claimed, but relate more to inconsistent assumptions on perturbation statistics
rather than just to topology. Candidate 3-manifolds based on hypothesised
multiply imaged objects are being offered for observational refutation.
The theoretical and observational sides of this rapidly developing subject
have yet to make any serious contact, but the prospects of a significant
detection in the coming decade may well propel the two together.Comment: 5 pages, proceedings of the Workshop ``Cosmology: Observations
Confront Theories,'' 11-17 Jan 1999, IIT Kharagpur, West Bengal, to appear in
Pramana - Journal of Physic
Circles in the Sky: Finding Topology with the Microwave Background Radiation
If the universe is finite and smaller than the distance to the surface of
last scatter, then the signature of the topology of the universe is writ large
on the microwave background sky. We show that the microwave background will be
identified at the intersections of the surface of last scattering as seen by
different ``copies'' of the observer. Since the surface of last scattering is a
two-sphere, these intersections will be circles, regardless of the background
geometry or topology. We therefore propose a statistic that is sensitive to all
small, locally homogeneous topologies. Here, small means that the distance to
the surface of last scatter is smaller than the ``topology scale'' of the
universe.Comment: 14 pages, 10 figures, IOP format. This paper is a direct descendant
of gr-qc/9602039. To appear in a special proceedings issue of Class. Quant.
Grav. covering the Cleveland Topology & Cosmology Worksho
Optical properties of the vibrations in charged C molecules
The transition strengths for the four infrared-active vibrations of charged
C molecules are evaluated in self-consistent density functional theory
using the local density approximation. The oscillator strengths for the second
and fourth modes are strongly enhanced relative to the neutral C
molecule, in good agreement with the experimental observation of ``giant
resonances'' for those two modes. Previous theory, based on a ``charged
phonon'' model, predicted a quadratic dependence of the oscillator strength on
doping, but this is not borne out in our calculations.Comment: 10 pages, RevTeX3.
Skylab floating ice experiment
The author has identified the following significant results. Coupling of the aircraft data with the ground truth observations proved to be highly successful with interesting results being obtained with IR and SLAR passive microwave techniques, and standard photography. Of particular interest were the results of the PMIS system which operated at 10.69 GHz with both vertical and horizontal polarizations. This was the first time that dual polarized images were obtained from floating ice. In both sea and lake ice, it was possible to distinguish a wide variety of thin ice types because of their large differences in brightness temperatures. It was found that the higher brightness temperature was invariably obtained in the vertically polarized mode, and as the age of the ice increases the brightness temperature increases in both polarizations. Associated with this change in age, the difference in temperature was observed as the different polarizations decreased. It appears that the horizontally polarized data is the most sensitive to variations in ice type for both fresh water and sea ice. The study also showed the great amount of information on ice surface roughness and deformation patterns that can be obtained from X-band SLAR observations
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