23,529 research outputs found
Persistence in a Random Bond Ising Model of Socio-Econo Dynamics
We study the persistence phenomenon in a socio-econo dynamics model using
computer simulations at a finite temperature on hypercubic lattices in
dimensions up to 5. The model includes a ` social\rq local field which contains
the magnetization at time . The nearest neighbour quenched interactions are
drawn from a binary distribution which is a function of the bond concentration,
. The decay of the persistence probability in the model depends on both the
spatial dimension and . We find no evidence of ` blocking\rq in this model.
We also discuss the implications of our results for possible applications in
the social and economic fields. It is suggested that the absence, or otherwise,
of blocking could be used as a criterion to decide on the validity of a given
model in different scenarios.Comment: 11 pages, 4 figure
Common Structures in Simplicial Quantum Gravity
The statistical properties of dynamically triangulated manifolds (DT mfds) in
terms of the geodesic distance have been studied numerically. The string
susceptibility exponents for the boundary surfaces in three-dimensional DT mfds
were measured numerically. For spherical boundary surfaces, we obtained a
result consistent with the case of a two-dimensional spherical DT surface
described by the matrix model. This gives a correct method to reconstruct
two-dimensional random surfaces from three-dimensional DT mfds. Furthermore, a
scaling property of the volume distribution of minimum neck baby universes was
investigated numerically in the case of three and four dimensions, and we
obtain a common scaling structure near to the critical points belonging to the
strong coupling phase in both dimensions. We have evidence for the existence of
a common fractal structure in three- and four-dimensional simplicial quantum
gravity.Comment: 10 pages, latex, 6 ps figures, uses cite.sty and psfig.st
Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC
Rotational excitation of isotopologues of HCN and HNC by thermal
electron-impact is studied using the molecular {\bf R}-matrix method combined
with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are
obtained for electron temperatures in the range 56000 K and for transitions
among all levels up to J=8. Hyperfine rates are also derived using the
infinite-order-sudden (IOS) scaling method. It is shown that the dominant
rotational transitions are dipole allowed, that is those for which . The hyperfine propensity rule is found to be stronger
than in the case of HeHCN collisions. For dipole allowed transitions,
electron-impact rates are shown to exceed those for excitation of HCN by He
atoms by 6 orders of magnitude. As a result, the present rates should be
included in any detailed population model of isotopologues of HCN and HNC in
sources where the electron fraction is larger than 10, for example in
interstellar shocks and comets.Comment: 12 pages, 4 figures, accepted in MNRAS (2007 september 3
Solving -means on High-dimensional Big Data
In recent years, there have been major efforts to develop data stream
algorithms that process inputs in one pass over the data with little memory
requirement. For the -means problem, this has led to the development of
several -approximations (under the assumption that is a
constant), but also to the design of algorithms that are extremely fast in
practice and compute solutions of high accuracy. However, when not only the
length of the stream is high but also the dimensionality of the input points,
then current methods reach their limits.
We propose two algorithms, piecy and piecy-mr that are based on the recently
developed data stream algorithm BICO that can process high dimensional data in
one pass and output a solution of high quality. While piecy is suited for high
dimensional data with a medium number of points, piecy-mr is meant for high
dimensional data that comes in a very long stream. We provide an extensive
experimental study to evaluate piecy and piecy-mr that shows the strength of
the new algorithms.Comment: 23 pages, 9 figures, published at the 14th International Symposium on
Experimental Algorithms - SEA 201
Activation gaps for the fractional quantum Hall effect: realistic treatment of transverse thickness
The activation gaps for fractional quantum Hall states at filling fractions
are computed for heterojunction, square quantum well, as well as
parabolic quantum well geometries, using an interaction potential calculated
from a self-consistent electronic structure calculation in the local density
approximation. The finite thickness is estimated to make 30% correction
to the gap in the heterojunction geometry for typical parameters, which
accounts for roughly half of the discrepancy between the experiment and
theoretical gaps computed for a pure two dimensional system. Certain model
interactions are also considered. It is found that the activation energies
behave qualitatively differently depending on whether the interaction is of
longer or shorter range than the Coulomb interaction; there are indications
that fractional Hall states close to the Fermi sea are destabilized for the
latter.Comment: 32 pages, 13 figure
Common Structures in 2,3 and 4D Simplicial Quantum Gravity
Two kinds of statistical properties of dynamical-triangulated manifolds (DT
mfds) have been investigated. First, the surfaces appearing on the boundaries
of 3D DT mfds were investigated. The string-susceptibility exponent of the
boundary surfaces () of 3D DT mfds with topology
near to the critical point was obtained by means of a MINBU (minimum neck baby
universes) analysis; actually, we obtained .
Second, 3 and 4D DT mfds were also investigated by determining the
string-susceptibility exponent near to the critical point from measuring the
MINBU distributions. As a result, we found a similar behavior of the MINBU
distributions in 3 and 4D DT mfds, and obtained . The existence of common structures in simplicial
quantum gravity is also discussed.Comment: 3 pages, latex, 3 ps figures, uses espcrc2.sty. Talk presented at
LATTICE97(gravity
A first principles investigation of cubic BaRuO: A Hund's metal
A first-principles investigation of cubic-BaRuO, by combining density
functional theory with dynamical mean-field theory and a hybridization
expansion continuous time quantum Monte-Carlo solver, has been carried out.
Non-magnetic calculations with appropriately chosen on-site Coulomb repulsion,
and Hund's exchange, , for single-particle dynamics and static
susceptibility show that cubic-BaRuO is in a spin-frozen state at
temperatures above the ferromagnetic transition point. A strong red shift with
increasing of the peak in the real frequency dynamical susceptibility
indicates a dramatic suppression of the Fermi liquid coherence scale as
compared to the bare parameters in cubic-BaRuO. The self-energy also shows
clear deviation from Fermi liquid behaviour that manifests in the
single-particle spectrum. Such a clean separation of energy scales in this
system provides scope for an incoherent spin-frozen (SF) phase, that extends
over a wide temperature range, to manifest in non-Fermi liquid behaviour and to
be the precursor for the magnetically ordered ground state.Comment: 10 pages, 12 figures, 1 tabl
Optical properties of a two-dimensional electron gas at even-denominator filling fractions
The optical properties of an electron gas in a magnetic field at filling
fractions \nu = {1\over 2m} (m=1,2,3...) are investigated using the composite
fermion picture. The response of the system to the presence of valence-band
holes is calculated. The shapes of the emission spectra are found to differ
qualitatively from the well-known electron-hole results at zero magnetic field.
In particular, the asymmetry of the emission lineshape is found to be sensitive
to the hole-composite fermion plane separation.Comment: 17 pages, LaTeX, 7 figures. This revised version is to appear in
Physical Review
- …