810 research outputs found
Global quantum Hall phase diagram from visibility diagrams
We propose a construction of a global phase diagram for the quantum Hall
effect. This global phase diagram is based on our previous constructions of
visibility diagrams in the context of the Quantum Hall Effect. The topology of
the phase diagram we obtain is in good agreement with experimental observations
(when the spin effect can be neglected). This phase diagram does not show
floating.Comment: LaTeX2e, 9 pages, 5 eps figure
Linear Connections on the Two Parameter Quantum Plane
We apply a recently proposed definition of a linear connection in non
commutative geometry based on the natural bimodule structure of the algebra of
differential forms to the case of the two-parameter quantum plane. We find that
there exists a non trivial family of linear connections only when the two
parameters obeys a specific relation.Comment: 7 pages, Te
Boundary-induced inhomogeneity of particle layers in the solidification of suspensions
When a suspension freezes, a compacted particle layer builds up at the
solidification front with noticeable implications on the freezing process. In a
directional solidification experiment of monodispersed suspensions in thin
samples, we evidence a link between the thickness of this layer and the sample
depth. We attribute it to an inhomogeneity of particle density induced by the
sample plates. A mechanical model enables us to relate it to the layer
thickness with a dependency on the sample depth and to select the distribution
of particle density that yields the best fit to our data. This distribution
involves an influence length of sample plates of about nine particle diameters.
These results clarify the implications of boundaries on suspension freezing.
They may be useful to model polydispersed suspensions since large particles
could play the role of smooth boundaries with respect to small ones.Comment: 16 pages, 13 figure
Galactic Structure and Radioactivity Source Distributions
A probable sky map of the emission from a short-lived isotrope produced by
massive stars is presented. The model is based on the nonaxisymmetric component
of a dust distribution model developed to reproduce Galactic FIR emission.
Features seen in COMPTEL observations are qualitatively reproduced.Comment: 6 pages w/ 4 figures, invited conference paper for "Radioactivities
in Astronomy" to be published in New Astronom
Vortex in Maxwell-Chern-Simons models coupled to external backgrounds
We consider Maxwell-Chern-Simons models involving different non-minimal
coupling terms to a non relativistic massive scalar and further coupled to an
external uniform background charge. We study how these models can be
constrained to support static radially symmetric vortex configurations
saturating the lower bound for the energy. Models involving Zeeman-type
coupling support such vortices provided the potential has a "symmetry breaking"
form and a relation between parameters holds. In models where minimal coupling
is supplemented by magnetic and electric field dependant coupling terms, non
trivial vortex configurations minimizing the energy occur only when a non
linear potential is introduced. The corresponding vortices are studied
numericallyComment: LaTeX file, 2 figure
Visibility diagrams and experimental stripe structure in the quantum Hall effect
We analyze various properties of the visibility diagrams that can be used in
the context of modular symmetries and confront them to some recent experimental
developments in the Quantum Hall Effect. We show that a suitable physical
interpretation of the visibility diagrams which permits one to describe
successfully the observed architecture of the Quantum Hall states gives rise
naturally to a stripe structure reproducing some of the experimental features
that have been observed in the study of the quantum fluctuations of the Hall
conductance. Furthermore, we exhibit new properties of the visibility diagrams
stemming from the structure of subgroups of the full modular group.Comment: 8 pages in plain TeX, 7 figures in a single postscript fil
The static potential in QED with non-minimal coupling
Here we study the effect of the non-minimal coupling j^{\mu}\eps
\partial^{\nu} A^{\alpha} on the static potential in multiflavor QED.
Both cases of four and two components fermions are studied separately at
leading order in the expansion. Although a non-local Chern-Simons term
appears, in the four components case the photon is still massless leading to a
confining logarithmic potential similar to the classical one. In the two
components case, as expected, the parity breaking fermion mass term generates a
traditional Chern-Simons term which makes the photon massive and we have a
screening potential which vanishes at large inter-charge distance. The extra
non-minimal couplings have no important influence on the static potential at
large inter-charge distances. However, interesting effects show up at finite
distances. In particular, for strong enough non-minimal coupling we may have a
new massive pole in the photon propagator while in the opposite limit there may
be no poles at all in the irreducible case. We also found that, in general, the
non-minimal couplings lead to a finite range {\bf repulsive} force between
charges of opposite signs.Comment: 19 pages and 7 figure
Galactic Spiral Structure
We describe the structure and composition of six major stellar streams in a
population of 20 574 local stars in the New Hipparcos Reduction with known
radial velocities. We find that, once fast moving stars are excluded, almost
all stars belong to one of these streams. The results of our investigation have
lead us to re-examine the hydrogen maps of the Milky Way, from which we
identify the possibility of a symmetric two-armed spiral with half the
conventionally accepted pitch angle. We describe a model of spiral arm motions
which matches the observed velocities and composition of the six major streams,
as well as the observed velocities of the Hyades and Praesepe clusters at the
extreme of the Hyades stream. We model stellar orbits as perturbed ellipses
aligned at a focus in coordinates rotating at the rate of precession of
apocentre. Stars join a spiral arm just before apocentre, follow the arm for
more than half an orbit, and leave the arm soon after pericentre. Spiral
pattern speed equals the mean rate of precession of apocentre. Spiral arms are
shown to be stable configurations of stellar orbits, up to the formation of a
bar and/or ring. Pitch angle is directly related to the distribution of orbital
eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve
to form bars and rings. We show that orbits of gas clouds are stable only in
bisymmetric spirals. We conclude that spiral galaxies evolve toward grand
design two-armed spirals. We infer from the velocity distributions that the
Milky Way evolved into this form about 9 Gyrs ago.Comment: Published in Proc Roy Soc A. A high resolution version of this file
can be downloaded from http://papers.rqgravity.net/SpiralStructure.pdf. A
simplified account with animations begins at
http://rqgravity.net/SpiralStructur
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