139 research outputs found
Haldane fractional statistics in the fractional quantum Hall effect
We have tested Haldane's ``fractional-Pauli-principle'' description of
excitations around the state in the FQHE, using exact results for
small systems of electrons. We find that Haldane's prediction
for quasiholes and quasiparticles, respectively, describes our results well
with the modification rather than . We also find
that this approach enables us to better understand the {\it energetics\/} of
the ``daughter'' states; in particular, we find good evidence, in terms of the
effective interaction between quasiparticles, that the states and
4/13 should not be stable.Comment: 9 pages, 3 Postscript figures, RevTex 3.0. (UCF-CM-93-005
Estimating the Spatial Extent of Attractors of Iterated Function System
Technical Report for Period January 1993 - April 1993From any given Iterated Function System, a small set of balls that cover the fractal attractor can
be simply determined. This gives a priori bounds on the region of space in which the attractor may be
constructed.Naval Postgraduate SchoolApproved for public release; distribution is unlimited
Inferring Pattern and Disorder in Close-Packed Structures from X-ray Diffraction Studies, Part I: epsilon-Machine Spectral Reconstruction Theory
In a recent publication [D. P. Varn, G. S. Canright, and J. P. Crutchfield,
Phys. Rev. B {\bf 66}:17, 156 (2002)] we introduced a new technique for
discovering and describing planar disorder in close-packed structures (CPSs)
directly from their diffraction spectra. Here we provide the theoretical
development behind those results, adapting computational mechanics to describe
one-dimensional structure in materials. By way of contrast, we give a detailed
analysis of the current alternative approach, the fault model (FM), and offer
several criticisms. We then demonstrate that the computational mechanics
description of the stacking sequence--in the form of an
epsilon-machine--provides the minimal and unique description of the crystal,
whether ordered, disordered, or some combination. We find that we can detect
and describe any amount of disorder, as well as materials that are mixtures of
various kinds of crystalline structure. Underlying this approach is a novel
method for epsilon-machine reconstruction that uses correlation functions
estimated from diffraction spectra, rather than sequences of microscopic
configurations, as is typically used in other domains. The result is that the
methods developed here can be adapted to a wide range of experimental systems
in which spectroscopic data is available.Comment: 26 pages, 23 figures, 8 tables, 110 citations;
http://www.santafe.edu/projects/CompMech/papers/ipdcpsi.htm
Inferring Pattern and Disorder in Close-Packed Structures from X-ray Diffraction Studies, Part II: Structure and Intrinsic Computation in Zinc Sulphide
In the previous paper of this series [D. P. Varn, G. S. Canright, and J. P.
Crutchfield, Physical Review B, submitted] we detailed a
procedure--epsilon-machine spectral reconstruction--to discover and analyze
patterns and disorder in close-packed structures as revealed in x-ray
diffraction spectra. We argued that this computational mechanics approach is
more general than the current alternative theory, the fault model, and that it
provides a unique characterization of the disorder present. We demonstrated the
efficacy of computational mechanics on four prototype spectra, finding that it
was able to recover a statistical description of the underlying modular-layer
stacking using epsilon-machine representations. Here we use this procedure to
analyze structure and disorder in four previously published zinc sulphide
diffraction spectra. We selected zinc sulphide not only for the theoretical
interest this material has attracted in an effort to develop an understanding
of polytypism, but also because it displays solid-state phase transitions and
experimental data is available.Comment: 15 pages, 14 figures, 4 tables, 57 citations;
http://www.santafe.edu/projects/CompMech/papers/ipdcpsii.htm
Analytical solution for the Fermi-sea energy of two-dimensional electrons in a magnetic field: lattice path-integral approach and quantum interference
We derive an exact solution for the total kinetic energy of noninteracting
spinless electrons at half-filling in two-dimensional bipartite lattices. We
employ a conceptually novel approach that maps this problem exactly into a
Feynman-Vdovichenko lattice walker. The problem is then reduced to the analytic
study of the sum of magnetic phase factors on closed paths. We compare our
results with the ones obtained through numerical calculations.Comment: 5 pages, RevTe
Acoustic interactions in arrays of spherical elastic shells
The article of record as published may be located at http://dx.doi.org/10.1121/1.401233The acoustical performance of a submerged linear array of spherical transducers is examined by combining the T-Matrix method of solving for multiple acoustic interactions among separate bodies with a model for the transducers as thin spherical elastic shells. This approach solves the fully coupled problem of the response of the array to internal forcing. The results show that the assumptions giving rise to the Chebyshev criteria for optimal arrays of point sources appear to apply well even for large spheres at low frequencies. However, at frequencies near or above the lowest resonant frequency the directional pattern may be degraded, depending on the material of the shells
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The effects of heat treatments on ectomycorrhizal resistant propagules and their ability to colonize bioassay seedlings
The effect of disturbance on the resistant propagule community (RPC) of ectomycorrhizal
fungi has been given relatively little attention. In this study we investigate the effects of
heat, one important factor of fire disturbances, on the ability of ectomycorrhizal RPC fungi
to colonize Pinus jeffreyi seedlings in greenhouse bioassays. Prior to planting the seed, soils
were collected from an old growth mixed-conifer forest in the southern Sierra Nevada, California,
USA and then subjected to four heat treatments of none, 45 C, 60 C, and 75 C.
After eight months, seedlings were harvested and the ectomycorrhizal fungi colonizing
the roots were characterized by molecular methods (PCR-RFLP and DNA sequencing). Rhizopogon
species increased in dominance on seedlings grown in soils receiving the 75 C
heat treatment. One species significantly increased in frequency, Rhizopogon olivaceotinctus,
and two species (Cenococcum geophilum and Wilcoxina sp.) significantly decreased in frequency
in the 75 C treatment. The increase of R. olivaceotinctus, coupled with other features
of its behavior, suggests that substantial heat disturbances may benefit this species
in competing for roots.Keywords: Rhizopogon, Phoenicoid fungi, Ruderal species, Basidiospores, Heat disturbanc
Exclusion statistics for fractional quantum Hall states on a sphere
We discuss exclusion statistics parameters for quasiholes and quasielectrons
excited above the fractional quantum Hall states near . We
derive the diagonal statistics parameters from the (``unprojected'') composite
fermion (CF) picture. We propose values for the off-diagonal (mutual)
statistics parameters as a simple modification of those obtained from the
unprojected CF picture, by analyzing finite system numerical spectra in the
spherical geometry.Comment: 9 pages, Revtex, 4 Postscript figures. Universality of the statistics
parameters is stressed, 2 figs adde
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