572 research outputs found
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
Scaling of the specific heat in superfluid films
We study the specific heat of the model on lattices with (i.e. on lattices representing a film geometry) using the
Cluster Monte--Carlo method. In the --direction we apply Dirichlet boundary
conditions so that the order parameter in the top and bottom layers is zero. We
find that our results for the specific heat of various thickness size
collapse on the same universal scaling function. The extracted scaling function
of the specific heat is in good agreement with the experimentally determined
universal scaling function using no free parameters.Comment: 4 pages, uuencoded compressed PostScrip
The XY Model and the Three-state Antiferromagnetic Potts model in Three Dimensions: Critical Properties from Fluctuating Boundary Conditions
We present the results of a Monte Carlo study of the three-dimensional XY
model and the three-dimensional antiferromagnetic three-state Potts model. In
both cases we compute the difference in the free energies of a system with
periodic and a system with antiperiodic boundary conditions in the
neighbourhood of the critical coupling. From the finite-size scaling behaviour
of this quantity we extract values for the critical temperature and the
critical exponent nu that are compatible with recent high statistics Monte
Carlo studies of the models. The results for the free energy difference at the
critical temperature and for the exponent nu confirm that both models belong to
the same universality class.Comment: 13 pages, latex-file+2 ps-files KL-TH-94/8 and CERN-TH.7290/9
A Monte Carlo study of leading order scaling corrections of phi^4 theory on a three dimensional lattice
We present a Monte Carlo study of the one-component model on the
cubic lattice in three dimensions. Leading order scaling corrections are
studied using the finite size scaling method. We compute the corrections to
scaling exponent with high precision. We determine the value of the
coupling at which leading order corrections to scaling vanish. Using
this result we obtain estimates for critical exponents that are more precise
than those obtained with field theoretic methods.Comment: 20 pages, two figures; numbers cited from ref. 23 corrected, few
typos correcte
Churn, Baby, Churn: Strategic Dynamics Among Dominant and Fringe Firms in a Segmented Industry
This paper integrates and extends the literatures on industry evolution and dominant firms to develop a dynamic theory of dominant and fringe competitive interaction in a segmented industry. It argues that a dominant firm, seeing contraction of growth in its current segment(s), enters new segments in which it can exploit its technological strengths, but that are sufficiently distant to avoid cannibalization. The dominant firm acts as a low-cost Stackelberg leader, driving down prices and triggering a sales takeoff in the new segment. We identify a “churn” effect associated with dominant firm entry: fringe firms that precede the dominant firm into the segment tend to exit the segment, while new fringe firms enter, causing a net increase in the number of firms in the segment. As the segment matures and sales decline in the segment, the process repeats itself. We examine the predictions of the theory with a study of price, quantity, entry, and exit across 24 product classes in the desktop laser printer industry from 1984 to 1996. Using descriptive statistics, hazard rate models, and panel data methods, we find empirical support for the theoretical predictions
Quench Induced Vortices in the Symmetry Broken Phase of Liquid He
Motivated by the study of cosmological phase transitions, our understanding
of the formation of topological defects during spontaneous symmetry-breaking
and the associated non-equilibrium field theory has recently changed.
Experiments have been performed in superfluid He to test the new ideas
involved. In particular, it has been observed that a vortex density is seen
immediately after pressure quenches from just below the transition.
We discuss possible interpretations of these vortices, conclude they are
consistent with our ideas of vortex formation and propose a modification of the
original experiments.Comment: 29 pages, RevTeX with one EPS figur
Invaded cluster simulations of the XY model in two and three dimensions
The invaded cluster algorithm is used to study the XY model in two and three
dimensions up to sizes 2000^2 and 120^3 respectively. A soft spin O(2) model,
in the same universality class as the 3D XY model, is also studied. The static
critical properties of the model and the dynamical properties of the algorithm
are reported. The results are K_c=0.45412(2) for the 3D XY model and
eta=0.037(2) for the 3D XY universality class. For the 2D XY model the results
are K_c=1.120(1) and eta=0.251(5). The invaded cluster algorithm does not show
any critical slowing for the magnetization or critical temperature estimator
for the 2D or 3D XY models.Comment: 30 pages, 11 figures, problem viewing figures corrected in v
N-vector spin models on the sc and the bcc lattices: a study of the critical behavior of the susceptibility and of the correlation length by high temperature series extended to order beta^{21}
High temperature expansions for the free energy, the susceptibility and the
second correlation moment of the classical N-vector model [also known as the
O(N) symmetric classical spin Heisenberg model or as the lattice O(N) nonlinear
sigma model] on the sc and the bcc lattices are extended to order beta^{21} for
arbitrary N. The series for the second field derivative of the susceptibility
is extended to order beta^{17}. An analysis of the newly computed series for
the susceptibility and the (second moment) correlation length yields updated
estimates of the critical parameters for various values of the spin
dimensionality N, including N=0 [the self-avoiding walk model], N=1 [the Ising
spin 1/2 model], N=2 [the XY model], N=3 [the Heisenberg model]. For all values
of N, we confirm a good agreement with the present renormalization group
estimates. A study of the series for the other observables will appear in a
forthcoming paper.Comment: Revised version to appear in Phys. Rev. B Sept. 1997. Revisions
include an improved series analysis biased with perturbative values of the
scaling correction exponents computed by A. I. Sokolov. Added a reference to
estimates of exponents for the Ising Model. Abridged text of 19 pages, latex,
no figures, no tables of series coefficient
Quantum-state control in optical lattices
We study the means to prepare and coherently manipulate atomic wave packets
in optical lattices, with particular emphasis on alkali atoms in the
far-detuned limit. We derive a general, basis independent expression for the
lattice operator, and show that its off-diagonal elements can be tailored to
couple the vibrational manifolds of separate magnetic sublevels. Using these
couplings one can evolve the state of a trapped atom in a quantum coherent
fashion, and prepare pure quantum states by resolved-sideband Raman cooling. We
explore the use of atoms bound in optical lattices to study quantum tunneling
and the generation of macroscopic superposition states in a double-well
potential. Far-off-resonance optical potentials lend themselves particularly
well to reservoir engineering via well controlled fluctuations in the
potential, making the atom/lattice system attractive for the study of
decoherence and the connection between classical and quantum physics.Comment: 35 pages including 8 figures. To appear in Phys. Rev. A. March 199
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