32,829 research outputs found
Development of improved adhesives for use at cryogenic temperatures to minus423 deg F Final summary report, 11 Jul. 1963 - 31 Aug. 1965
Improved polyurethane and epoxy resins for use as adhesives at cryogenic temperature
Exchange Monte Carlo Method and Application to Spin Glass Simulations
We propose an efficient Monte Carlo algorithm for simulating a
``hardly-relaxing" system, in which many replicas with different temperatures
are simultaneously simulated and a virtual process exchanging configurations of
these replica is introduced. This exchange process is expected to let the
system at low temperatures escape from a local minimum. By using this algorithm
the three-dimensional Ising spin glass model is studied. The ergodicity
time in this method is found much smaller than that of the multi-canonical
method. In particular the time correlation function almost follows an
exponential decay whose relaxation time is comparable to the ergodicity time at
low temperatures. It suggests that the system relaxes very rapidly through the
exchange process even in the low temperature phase.Comment: 10 pages + uuencoded 5 Postscript figures, REVTe
A New Approach to Spin Glass Simulations
We present a recursive procedure to calculate the parameters of the recently
introduced multicanonical ensemble and explore the approach for spin glasses.
Temperature dependence of the energy, the entropy and other physical quantities
are easily calculable and we report results for the zero temperature limit. Our
data provide evidence that the large increase of the ergodicity time is
greatly improved. The multicanonical ensemble seems to open new horizons for
simulations of spin glasses and other systems which have to cope with
conflicting constraints
Grundstate Properties of the 3D Ising Spin Glass
We study zero--temperature properties of the 3d Edwards--Anderson Ising spin
glass on finite lattices up to size . Using multicanonical sampling we
generate large numbers of groundstate configurations in thermal equilibrium.
Finite size scaling with a zero--temperature scaling exponent describes the data well. Alternatively, a descriptions in terms of Parisi
mean field behaviour is still possible. The two scenarios give significantly
different predictions on lattices of size .Comment: LATEX 9pages,figures upon request ,SCRI-9
A Pulsed Synchrotron for Muon Acceleration at a Neutrino Factory
A 4600 Hz pulsed synchrotron is considered as a means of accelerating cool
muons with superconducting RF cavities from 4 to 20 GeV/c for a neutrino
factory. Eddy current losses are held to less than a megawatt by the low
machine duty cycle plus 100 micron thick grain oriented silicon steel
laminations and 250 micron diameter copper wires. Combined function magnets
with 20 T/m gradients alternating within single magnets form the lattice. Muon
survival is 83%.Comment: 4 pages, 1 figures, LaTeX, 5th International Workshop on Neutrino
Factories and Superbeams (NuFact 03), 5-11 Jun 2003, New Yor
Enhanced Pairing in the "Checkerboard" Hubbard Ladder
We study signatures of superconductivity in a 2--leg "checkerboard" Hubbard
ladder model, defined as a one--dimensional (period 2) array of square
plaquettes with an intra-plaquette hopping and inter-plaquette hopping
, using the density matrix renormalization group method. The highest
pairing scale (characterized by the spin gap or the pair binding energy,
extrapolated to the thermodynamic limit) is found for doping levels close to
half filling, and . Other forms of modulated
hopping parameters, with periods of either 1 or 3 lattice constants, are also
found to enhance pairing relative to the uniform two--leg ladder, although to a
lesser degree. A calculation of the phase stiffness of the ladder reveals that
in the regime with the strongest pairing, the energy scale associated with
phase ordering is comparable to the pairing scale.Comment: 9 pages, 9 figures; Journal reference adde
Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming
We simulate by lattice Boltzmann the nonequilibrium steady states of
run-and-tumble particles (inspired by a minimal model of bacteria), interacting
by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic
interactions barely perturb the steady state found without them, but for
particles in a harmonic trap such a state is quite changed if the run length is
larger than the confinement length: a self-assembled pump is formed. Particles
likewise confined in a narrow channel show a generic upstream flux in
Poiseuille flow: chiral swimming is not required
The RFOFO Ionization Cooling Ring for Muons
Practical ionization cooling rings could lead to lower cost or improved
performance in neutrino factory or muon collider designs. The ring modeled here
uses realistic three-dimensional fields. The performance of the ring compares
favorably with the linear cooling channel used in the second US Neutrino
Factory Study. The normalized 6D emittance of an ideal ring is decreased by a
factor of approximately 240, compared with a factor of only 15 for the linear
channel. We also examine such \textit{real-world} effects as windows on the
absorbers and rf cavities and leaving empty lattice cells for injection and
extraction. For realistic conditions the ring decreases the normalized 6D
emittance by a factor of 49.Comment: 27 pages, 18 figures and 5 tables. Submitted to Phys. Rev. ST-A
Entropy-based analysis of the number partitioning problem
In this paper we apply the multicanonical method of statistical physics on
the number-partitioning problem (NPP). This problem is a basic NP-hard problem
from computer science, and can be formulated as a spin-glass problem. We
compute the spectral degeneracy, which gives us information about the number of
solutions for a given cost and cardinality . We also study an extension
of this problem for partitions. We show that a fundamental difference on
the spectral degeneracy of the generalized () NPP exists, which could
explain why it is so difficult to find good solutions for this case. The
information obtained with the multicanonical method can be very useful on the
construction of new algorithms.Comment: 6 pages, 4 figure
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