18,985 research outputs found
"Exact" Algorithm for Random-Bond Ising Models in 2D
We present an efficient algorithm for calculating the properties of Ising
models in two dimensions, directly in the spin basis, without the need for
mapping to fermion or dimer models. The algorithm gives numerically exact
results for the partition function and correlation functions at a single
temperature on any planar network of N Ising spins in O(N^{3/2}) time or less.
The method can handle continuous or discrete bond disorder and is especially
efficient in the case of bond or site dilution, where it executes in O(L^2 ln
L) time near the percolation threshold. We demonstrate its feasibility on the
ferromagnetic Ising model and the +/- J random-bond Ising model (RBIM) and
discuss the regime of applicability in cases of full frustration such as the
Ising antiferromagnet on a triangular lattice.Comment: 4.2 pages, 5 figures, accepted for publication in Phys. Rev. Let
Noise Predictions for STM in Systems with Local Electron Nematic Order
We propose that thermal noise in local stripe orientation should be readily
detectable via STM on systems in which local stripe orientations are strongly
affected by quenched disorder. Stripes, a unidirectional, nanoscale modulation
of electronic charge, are strongly affected by quenched disorder in
two-dimensional and quasi-two-dimensional systems. While stripe orientations
tend to lock to major lattice directions, dopant disorder locally breaks
rotational symmetry. In a host crystal with otherwise rotational
symmetry, stripe orientations in the presence of quenched disorder map to the
random field Ising model. While the low temperature state of such a system is
generally a stripe glass in two dimensional or strongly layered systems, as the
temperature is raised, stripe orientational fluctuations become more prevalent.
We propose that these thermally excited fluctuations should be readily
detectable in scanning tunneling spectroscopy as {\em telegraph noise} in the
high voltage part of the local curves. We predict the spatial, temporal,
and thermal evolution of such noise, including the circumstances under which
such noise is most likely to be observed. In addition, we propose an in-situ
test, amenable to any local scanning probe, for assessing whether such noise is
due to correlated fluctuations rather than independent switchers.Comment: 8 pages, 8 figure
Leading-Log Effects in the Resonance Electroweak Form Factors
We study log corrections to inelastic scattering at high Bjorken x for Q^2
from 1 to 21 GeV^2. At issue is the presence of log corrections, which can be
absent if high x scattering has damped gluon radiation. We find logarithmic
correction of the scaling curve extrapolated to low Q^2 improves the duality
between it and the resonance plus background data in the Delta region,
indicating log corrections exist in the data. However, at W > 2 GeV and high x,
the data shows a (1-x)^3 form. Log corrections in one situation but not in
another can be reconciled by a W- or Q^2- dependent higher twist correction.Comment: 13 pages, report nos. RPI-94-N90 and WM-94-106, revtex, two figures
(available by fax or post
Integration of multi-scale biosimulation models via light-weight semantics
Currently, biosimulation researchers use a variety of computational environments and languages to model biological processes. Ideally, researchers should be able to semi- automatically merge models to more effectively build larger, multi-scale models. How- ever, current modeling methods do not capture the underlying semantics of these models sufficiently to support this type of model construction. In this paper, we both propose a general approach to solve this problem, and we provide a specific example that demon- strates the benefits of our methodology. In particular, we describe three biosimulation models: (1) a cardio-vascular fluid dynamics model, (2) a model of heart rate regulation via baroreceptor control, and (3) a sub-cellular-level model of the arteriolar smooth mus- cle. Within a light-weight ontological framework, we leverage reference ontologies to match concepts across models. The light-weight ontology then helps us combine our three models into a merged model that can answer questions beyond the scope of any single model
Sonic boom characteristics of proposed supersonic and hypersonic airplanes
Sonic boom characteristics of proposed supersonic and hypersonic aircraf
Inclusive neutrino scattering off deuteron from threshold to GeV energies
Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret
the neutrino oscillation results in long baseline neutrino experiments. There
are rather large uncertainties in the cross section, due to insufficient
knowledge on the role of two-body weak currents. Purpose: Determine the role of
two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV
energies. Methods: Calculate cross sections for inclusive neutrino scattering
off deuteron induced by neutral and charge-changing weak currents, from
threshold up to GeV energies, using the Argonne potential and
consistent nuclear electroweak currents with one- and two-body terms. Results:
Two-body contributions are found to be small, and increase the cross sections
obtained with one-body currents by less than 10% over the whole range of
energies. Total cross sections obtained by describing the final two-nucleon
states with plane waves differ negligibly, for neutrino energies
MeV, from those in which interaction effects in these states are fully
accounted for. The sensitivity of the calculated cross sections to different
models for the two-nucleon potential and/or two-body terms in the weak current
is found to be weak. Comparing cross sections to those obtained in a naive
model in which the deuteron is taken to consist of a free proton and neutron at
rest, nuclear structure effects are illustrated to be non-negligible.
Conclusion: Contributions of two-body currents in neutrino-deuteron
quasi-elastic scattering up to GeV are found to be smaller than 10%. Finally,
it should be stressed that the results reported in this work do not include
pion production channels.Comment: 30 pages, 17 figures; publishe
Evaluating matrix elements relevant to some Lorenz violating operators
Carlson, Carone and Lebed have derived the Feynman rules for a consistent
formulation of noncommutative QCD. The results they obtained were used to
constrain the noncommutativity parameter in Lorentz violating noncommutative
field theories. However, their constraint depended upon an estimate of the
matrix element of the quark level operator (gamma.p - m) in a nucleon. In this
paper we calculate the matrix element of (gamma.p - m), using a variety of
confinement potential models. Our results are within an order of magnitude
agreement with the estimate made by Carlson et al. The constraints placed on
the noncommutativity parameter were very strong, and are still quite severe
even if weakened by an order of magnitude.Comment: 4 pages, 3 figures, RevTex, minor change
Experimental and Theoretical Results for Weak Charge Current Backward Proton Production
In this paper, we do three things in the study of deuteron break-up by high
energy neutrino beams. (1) We present previously unpublished data on neutrino
induced backward protons from deuteron targets; (2) we calculate the
contributions from both the two-nucleon (2N) and six-quark (6q) deuteron
components, which depend upon the overall normalization of the part that is 6q;
and (3) we suggest other signatures for distinguishing the 2N and 6q clusters.
We conclude that the 6q cluster easily explains the shape of the high momentum
backward proton spectrum, and its size is nicely explained if the amount of 6q
is one or a few percent by normalization of the deuteron. There is a crossover,
above which the 6q contribution is important or dominant, at 300--400 MeV/c
backward proton momentum.Comment: 8 pages, 5 figure
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