102,059 research outputs found
Comment on "Evidence for nontrivial ground-state structure of 3d +/- J spin glasses"
In a recent Letter [Europhys. Lett. 40, 429 (1997)], Hartmann presented
results for the structure of the degenerate ground states of the
three-dimensional +/- J spin glass model obtained using a genetic algorithm. In
this Comment, I argue that the method does not produce the correct
thermodynamic distribution of ground states and therefore gives erroneous
results for the overlap distribution. I present results of simulated annealing
calculations using different annealing rates for cubic lattices with
N=4*4*4spins. The disorder-averaged overlap distribution exhibits a significant
dependence on the annealing rate, even when the energy has converged. For fast
annealing, moments of the distribution are similar to those presented by
Hartmann. However, as the annealing rate is lowered, they approach the results
previously obtained using a multi-canonical Monte Carlo method. This shows
explicitly that care must be taken not only to reach states with the lowest
energy but also to ensure that they obey the correct thermodynamic
distribution, i.e., that the probability is the same for reaching any of the
ground states.Comment: 2 pages, Revtex, 1 PostScript figur
Growth and structural characterization of pyramidal site-controlled quantum dots with high uniformity and spectral purity
This work presents some fundamental features of pyramidal site-controlled
InGaAs Quantum Dots (QDs) grown by MetalOrganic Vapour Phase Epitaxy on
patterned GaAs (111)B substrate. The dots self-form inside pyramidal recesses
patterned on the wafer via pre-growth processing. The major advantage of this
growth technique is the control it provides over the dot nucleation posi-tion
and the dimensions of the confined structures onto the sub-strate. The
fundamental steps of substrate patterning and the QD forma-tion mechanism are
described together with a discussion of the structural particulars. The
post-growth processes, including sur-face etching and substrate removal, which
are required to facili-tate optical characterization, are discussed. With this
approach extremely high uniformity and record spectral purity are both
achieved
Direct sampling of complex landscapes at low temperatures: the three-dimensional +/-J Ising spin glass
A method is presented, which allows to sample directly low-temperature
configurations of glassy systems, like spin glasses. The basic idea is to
generate ground states and low lying excited configurations using a heuristic
algorithm. Then, with the help of microcanonical Monte Carlo simulations, more
configurations are found, clusters of configurations are determined and
entropies evaluated. Finally equilibrium configuration are randomly sampled
with proper Gibbs-Boltzmann weights.
The method is applied to three-dimensional Ising spin glasses with +- J
interactions and temperatures T<=0.5. The low-temperature behavior of this
model is characterized by evaluating different overlap quantities, exhibiting a
complex low-energy landscape for T>0, while the T=0 behavior appears to be less
complex.Comment: 9 pages, 7 figures, revtex (one sentence changed compared to v2
School Bus Monitors in Western New York
The New York State Department of Education defines a “bus monitor” (also commonly referred to as a “bus aide”) as any person employed for the purpose of assisting children to safely embark and disembark from a school bus which is owned, leased or contracted for by a public school district or board of cooperative educational services, and for the purpose of assisting the school bus driver with maintaining proper student behavior on such school bus
Double polarisation experiments in meson photoproduction
One of the remaining challenges within the standard model is to gain a good
understanding of QCD in the non-perturbative regime. A key step towards this
aim is baryon spectroscopy, investigating the spectrum and the properties of
baryon resonances. To gain access to resonances with small partial
width, photoproduction experiments provide essential information. Partial wave
analyses need to be performed to extract the contributing resonances. Here, a
complete experiment is required to unambiguously determine the contributing
amplitudes. This involves the measurement of carefully chosen single and double
polarisation observables. In a joint endeavour by MAMI, ELSA, and Jefferson
Laboratory, a new generation of experiments with polarised beams, polarised
proton and neutron targets, and particle detectors have been performed
in recent years. Many results of unprecedented quality were recently published
by all three experiments, and included by the various partial wave analysis
groups in their analyses, leading to substantial improvements, e.g. a more
precise determination of resonance parameters. An overview of recent results is
given, with an emphasis on results from the CBELSA/TAPS experiment, and their
impact on our understanding of the nucleon excitation spectrum is discussed.Comment: 6 pages, 5 figures, Proceedings of MESON2016. arXiv admin note: text
overlap with arXiv:1601.0132
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