2,179 research outputs found
Turnaround Time Between ILLiad’s Odyssey and Ariel Delivery Methods: A Comparison
Interlibrary loan departments are frequently looking for ways to reduce turnaround time. The advent of electronic delivery in the past decade has greatly reduced turnaround time for articles, but recent developments in this arena have the potential to decrease that time even further. The ILLiad ILL management system has an electronic delivery component, Odyssey, with a Trusted Sender setting that allows articles to be sent to patrons without borrowing staff intervention, provided the lending library is designated as a Trusted Sender, or this feature is enabled for all lenders. Using the tracking data created by the ILLiad management system, the turnaround time for two delivery methods, Ariel and Odyssey, was captured for two different academic institutions. With the Trusted Sender setting turned on, Odyssey delivery was faster than Ariel for the institutions studied
Multifractality of self-avoiding walks on percolation clusters
We consider self-avoiding walks (SAWs) on the backbone of percolation
clusters in space dimensions d=2, 3, 4. Applying numerical simulations, we show
that the whole multifractal spectrum of singularities emerges in exploring the
peculiarities of the model. We obtain estimates for the set of critical
exponents, that govern scaling laws of higher moments of the distribution of
percolation cluster sites visited by SAWs, in a good correspondence with an
appropriately summed field-theoretical \varepsilon=6-d-expansion (H.-K. Janssen
and O. Stenull, Phys. Rev. E 75, 020801(R) (2007)).Comment: 4 page
Evidence of Unconventional Universality Class in a Two-Dimensional Dimerized Quantum Heisenberg Model
The two-dimensional - dimerized quantum Heisenberg model is
studied on the square lattice by means of (stochastic series expansion) quantum
Monte Carlo simulations as a function of the coupling ratio
\hbox{}. The critical point of the order-disorder quantum
phase transition in the - model is determined as
\hbox{} by finite-size scaling for up to
approximately quantum spins. By comparing six dimerized models we
show, contrary to the current belief, that the critical exponents of the
- model are not in agreement with the three-dimensional classical
Heisenberg universality class. This lends support to the notion of nontrivial
critical excitations at the quantum critical point.Comment: 4+ pages, 5 figures, version as publishe
Cross-correlations in scaling analyses of phase transitions
Thermal or finite-size scaling analyses of importance sampling Monte Carlo
time series in the vicinity of phase transition points often combine different
estimates for the same quantity, such as a critical exponent, with the intent
to reduce statistical fluctuations. We point out that the origin of such
estimates in the same time series results in often pronounced
cross-correlations which are usually ignored even in high-precision studies,
generically leading to significant underestimation of statistical fluctuations.
We suggest to use a simple extension of the conventional analysis taking
correlation effects into account, which leads to improved estimators with often
substantially reduced statistical fluctuations at almost no extra cost in terms
of computation time.Comment: 4 pages, RevTEX4, 3 tables, 1 figur
Comprehensive quantum Monte Carlo study of the quantum critical points in planar dimerized/quadrumerized Heisenberg models
We study two planar square lattice Heisenberg models with explicit
dimerization or quadrumerization of the couplings in the form of ladder and
plaquette arrangements. We investigate the quantum critical points of those
models by means of (stochastic series expansion) quantum Monte Carlo
simulations as a function of the coupling ratio . The
critical point of the order-disorder quantum phase transition in the ladder
model is determined as improving on previous
studies. For the plaquette model we obtain
establishing a first benchmark for this model from quantum Monte Carlo
simulations. Based on those values we give further convincing evidence that the
models are in the three-dimensional (3D) classical Heisenberg universality
class. The results of this contribution shall be useful as references for
future investigations on planar Heisenberg models such as concerning the
influence of non-magnetic impurities at the quantum critical point.Comment: 10+ pages, 7 figures, 4 table
Error estimation and reduction with cross correlations
Besides the well-known effect of autocorrelations in time series of Monte
Carlo simulation data resulting from the underlying Markov process, using the
same data pool for computing various estimates entails additional cross
correlations. This effect, if not properly taken into account, leads to
systematically wrong error estimates for combined quantities. Using a
straightforward recipe of data analysis employing the jackknife or similar
resampling techniques, such problems can be avoided. In addition, a covariance
analysis allows for the formulation of optimal estimators with often
significantly reduced variance as compared to more conventional averages.Comment: 16 pages, RevTEX4, 4 figures, 6 tables, published versio
Monte Carlo Study of Cluster-Diameter Distribution: A New Observable to Estimate Correlation Lengths
We report numerical simulations of two-dimensional -state Potts models
with emphasis on a new quantity for the computation of spatial correlation
lengths. This quantity is the cluster-diameter distribution function
, which measures the distribution of the diameter of
stochastically defined cluster. Theoretically it is predicted to fall off
exponentially for large diameter , , where
is the correlation length as usually defined through the large-distance
behavior of two-point correlation functions. The results of our extensive Monte
Carlo study in the disordered phase of the models with , 15, and on
large square lattices of size , , and , respectively, clearly confirm the theoretically predicted behavior.
Moreover, using this observable we are able to verify an exact formula for the
correlation length in the disordered phase at the first-order
transition point with an accuracy of about for all considered
values of . This is a considerable improvement over estimates derived from
the large-distance behavior of standard (projected) two-point correlation
functions, which are also discussed for comparison.Comment: 20 pages, LaTeX + 13 postscript figures. See also
http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm
2D Potts Model Correlation Lengths: Numerical Evidence for at
We have studied spin-spin correlation functions in the ordered phase of the
two-dimensional -state Potts model with , 15, and 20 at the
first-order transition point . Through extensive Monte Carlo
simulations we obtain strong numerical evidence that the correlation length in
the ordered phase agrees with the exactly known and recently numerically
confirmed correlation length in the disordered phase: . As a byproduct we find the energy moments in the ordered phase
at in very good agreement with a recent large -expansion.Comment: 11 pages, PostScript. To appear in Europhys. Lett. (September 1995).
See also http://www.cond-mat.physik.uni-mainz.de/~janke/doc/home_janke.htm
A Matrix Kato-Bloch Perturbation Method for Hamiltonian Systems
A generalized version of the Kato-Bloch perturbation expansion is presented.
It consists of replacing simple numbers appearing in the perturbative series by
matrices. This leads to the fact that the dependence of the eigenvalues of the
perturbed system on the strength of the perturbation is not necessarily
polynomial. The efficiency of the matrix expansion is illustrated in three
cases: the Mathieu equation, the anharmonic oscillator and weakly coupled
Heisenberg chains. It is shown that the matrix expansion converges for a
suitably chosen subspace and, for weakly coupled Heisenberg chains, it can lead
to an ordered state starting from a disordered single chain. This test is
usually failed by conventional perturbative approaches.Comment: 4 pages, 2 figure
Scaling of the superfluid density in superfluid films
We study scaling of the superfluid density with respect to the film thickness
by simulating the model on films of size ()
using the cluster Monte Carlo. While periodic boundary conditions where used in
the planar () directions, Dirichlet boundary conditions where used along the
film thickness. We find that our results can be scaled on a universal curve by
introducing an effective thickness. In the limit of large our scaling
relations reduce to the conventional scaling forms. Using the same idea we find
scaling in the experimental results using the same value of .Comment: 4 pages, one postscript file replaced by one Latex file and 5
postscript figure
- …