818 research outputs found
Notes on \u3ci\u3eTaeniogonalos Gundlachii\u3c/i\u3e (Hymenoptera: Trigonalidae) From Wisconsin
This is the first report of Taeniogonalos gundlachii (Cresson) (Hymenoptera: Trigonalidae) from Wisconsin and of this hyperparasitoid reared from the initial host Euchaetes egle (Drury) (Lepidoptera: Arctiidae). Data are provided from 30 Malaise trap specimens and from a single reared specimen
Creep dynamics of elastic manifolds via exact transition pathways
We study the steady state of driven elastic strings in disordered media below
the depinning threshold. In the low-temperature limit, for a fixed sample, the
steady state is dominated by a single configuration, which we determine exactly
from the transition pathways between metastable states. We obtain the dynamical
phase diagram in this limit. At variance with a thermodynamic phase transition,
the depinning transition is not associated with a divergent length scale of the
steady state below threshold, but only of the transient dynamics. We discuss
the distribution of barrier heights, and check the validity of the dynamic
phase diagram at small but finite temperatures using Langevin simulations. The
phase diagram continues to hold for broken statistical tilt symmetry. We point
out the relevance of our results for experiments of creep motion in elastic
interfaces.Comment: 14 pages, 18 figure
Depinning exponents of the driven long-range elastic string
We perform a high-precision calculation of the critical exponents for the
long-range elastic string driven through quenched disorder at the depinning
transition, at zero temperature. Large-scale simulations are used to avoid
finite-size effects and to enable high precision. The roughness, growth, and
velocity exponents are calculated independently, and the dynamic and
correlation length exponents are derived. The critical exponents satisfy known
scaling relations and agree well with analytical predictions.Comment: 6 pages, 5 figure
A Rapid Dynamical Monte Carlo Algorithm for Glassy Systems
In this paper we present a dynamical Monte Carlo algorithm which is
applicable to systems satisfying a clustering condition: during the dynamical
evolution the system is mostly trapped in deep local minima (as happens in
glasses, pinning problems etc.). We compare the algorithm to the usual Monte
Carlo algorithm, using as an example the Bernasconi model. In this model, a
straightforward implementation of the algorithm gives an improvement of several
orders of magnitude in computational speed with respect to a recent, already
very efficient, implementation of the algorithm of Bortz, Kalos and Lebowitz.Comment: RevTex 7 pages + 4 figures (uuencoded) appended; LPS preprin
Phase diagram of the bose Hubbard model
The first reliable analytic calculation of the phase diagram of the bose gas
on a -dimensional lattice with on-site repulsion is presented. In one
dimension, the analytic calculation is in excellent agreement with the
numerical Monte Carlo results. In higher dimensions, the deviations from the
Monte Carlo calculations are larger, but the correct shape of the Mott
insulator lobes is still obtained. Explicit expressions for the energy of the
Mott and the ``defect'' phase are given in a strong-coupling expansion.Comment: RevTeX 3.
Critical exponents of the driven elastic string in a disordered medium
We analyze the harmonic elastic string driven through a continuous random
potential above the depinning threshold. The velocity exponent beta = 0.33(2)
is calculated. We observe a crossover in the roughness exponent zeta from the
critical value 1.26 to the asymptotic (large force) value of 0.5. We calculate
directly the velocity correlation function and the corresponding correlation
length exponent nu = 1.29(5), which obeys the scaling relation nu = 1/(2-zeta),
and agrees with the finite-size-scaling exponent of fluctuations in the
critical force. The velocity correlation function is non-universal at short
distances.Comment: 4 pages, 3 figures. corrected references and typo
Off-diagonal long-range order, cycle probabilities, and condensate fraction in the ideal Bose gas
We discuss the relationship between the cycle probabilities in the
path-integral representation of the ideal Bose gas, off-diagonal long-range
order, and Bose--Einstein condensation. Starting from the Landsberg recursion
relation for the canonic partition function, we use elementary considerations
to show that in a box of size L^3 the sum of the cycle probabilities of length
k >> L^2 equals the off-diagonal long-range order parameter in the
thermodynamic limit. For arbitrary systems of ideal bosons, the integer
derivative of the cycle probabilities is related to the probability of
condensing k bosons. We use this relation to derive the precise form of the
\pi_k in the thermodynamic limit. We also determine the function \pi_k for
arbitrary systems. Furthermore we use the cycle probabilities to compute the
probability distribution of the maximum-length cycles both at T=0, where the
ideal Bose gas reduces to the study of random permutations, and at finite
temperature. We close with comments on the cycle probabilities in interacting
Bose gases.Comment: 6 pages, extensive rewriting, new section on maximum-length cycle
Universal Scaling of the Conductivity at the Superfluid-Insulator Phase Transition
The scaling of the conductivity at the superfluid-insulator quantum phase
transition in two dimensions is studied by numerical simulations of the
Bose-Hubbard model. In contrast to previous studies, we focus on properties of
this model in the experimentally relevant thermodynamic limit at finite
temperature T. We find clear evidence for deviations from w_k-scaling of the
conductivity towards w_k/T-scaling at low Matsubara frequencies w_k. By careful
analytic continuation using Pade approximants we show that this behavior
carries over to the real frequency axis where the conductivity scales with w/T
at small frequencies and low temperatures. We estimate the universal dc
conductivity to be 0.45(5)Q^2/h, distinct from previous estimates in the T=0,
w/T >> 1 limit.Comment: Accepted for publication in PR
Notes on \u3ci\u3eTaeniogonalos Gundlachii\u3c/i\u3e (Hymenoptera: Trigonalidae) From Wisconsin
This is the first report of Taeniogonalos gundlachii (Cresson) (Hymenoptera: Trigonalidae) from Wisconsin and of this hyperparasitoid reared from the initial host Euchaetes egle (Drury) (Lepidoptera: Arctiidae). Data are provided from 30 Malaise trap specimens and from a single reared specimen
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