10,656 research outputs found
Mapping functions and critical behavior of percolation on rectangular domains
The existence probability and the percolation probability of the
bond percolation on rectangular domains with different aspect ratios are
studied via the mapping functions between systems with different aspect ratios.
The superscaling behavior of and for such systems with exponents
and , respectively, found by Watanabe, Yukawa, Ito, and Hu in [Phys. Rev.
Lett. \textbf{93}, 190601 (2004)] can be understood from the lower order
approximation of the mapping functions and for and ,
respectively; the exponents and can be obtained from numerically
determined mapping functions and , respectively.Comment: 17 pages with 6 figure
The intermediate evolution phase in case of truncated selection
Using methods of statistical physics, we present rigorous theoretical
calculations of Eigen's quasispecies theory with the truncated fitness
landscape which dramatically limits the available sequence space of a
reproducing quasispecies. Depending on the mutation rates, we observe three
phases, a selective one, an intermediate one with some residual order and a
completely randomized phase. Our results are applicable for the general case of
fitness landscape.Comment: 8 page
Geometry, thermodynamics, and finite-size corrections in the critical Potts model
We establish an intriguing connection between geometry and thermodynamics in
the critical q-state Potts model on two-dimensional lattices, using the q-state
bond-correlated percolation model (QBCPM) representation. We find that the
number of clusters of the QBCPM has an energy-like singularity for q different
from 1, which is reached and supported by exact results, numerical simulation,
and scaling arguments. We also establish that the finite-size correction to the
number of bonds, has no constant term and explains the divergence of related
quantities as q --> 4, the multicritical point. Similar analyses are applicable
to a variety of other systems.Comment: 12 pages, 6 figure
The Growth Of Highly Doped p-GaN On Sapphire By RF Plasma-Assisted Molecular Beam Epitaxy.
In this paper, we present the study of the electrical, structural and optical properties of p-type GaN grown on sapphire by RF plasma-assisted molecular beam epitaxy
(RF-MBE)
A Quantum Scattering Interferometer
The collision of two ultra-cold atoms results in a quantum-mechanical
superposition of two outcomes: each atom continues without scattering and each
atom scatters as a spherically outgoing wave with an s-wave phase shift. The
magnitude of the s-wave phase shift depends very sensitively on the interaction
between the atoms. Quantum scattering and the underlying phase shifts are
vitally important in many areas of contemporary atomic physics, including
Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic
clocks, and magnetically-tuned Feshbach resonances. Precise measurements of
quantum scattering phase shifts have not been possible until now because, in
scattering experiments, the number of scattered atoms depends on the s-wave
phase shifts as well as the atomic density, which cannot be measured precisely.
Here we demonstrate a fundamentally new type of scattering experiment that
interferometrically detects the quantum scattering phase shifts of individual
atoms. By performing an atomic clock measurement using only the scattered part
of each atom, we directly and precisely measure the difference of the s-wave
phase shifts for the two clock states in a density independent manner. Our
method will give the most direct and precise measurements of ultracold
atom-atom interactions and will place stringent limits on the time variations
of fundamental constants.Comment: Corrected formatting and typo
The 6-vertex model of hydrogen-bonded crystals with bond defects
It is shown that the percolation model of hydrogen-bonded crystals, which is
a 6-vertex model with bond defects, is completely equivalent with an 8-vertex
model in an external electric field. Using this equivalence we solve exactly a
particular 6-vertex model with bond defects. The general solution for the
Bethe-like lattice is also analyzed.Comment: 13 pages, 6 figures; added references for section
Experimental Evidence for Efimov Quantum States
Three interacting particles form a system which is well known for its complex
physical behavior. A landmark theoretical result in few-body quantum physics is
Efimov's prediction of a universal set of weakly bound trimer states appearing
for three identical bosons with a resonant two-body interaction. Surprisingly,
these states even exist in the absence of a corresponding two-body bound state
and their precise nature is largely independent of the particular type of the
two-body interaction potential. Efimov's scenario has attracted great interest
in many areas of physics; an experimental test however has not been achieved.
We report the observation of an Efimov resonance in an ultracold thermal gas of
cesium atoms. The resonance occurs in the range of large negative two-body
scattering lengths and arises from the coupling of three free atoms to an
Efimov trimer. We observe its signature as a giant three-body recombination
loss when the strength of the two-body interaction is varied near a Feshbach
resonance. This resonance develops into a continuum resonance at non-zero
collision energies, and we observe a shift of the resonance position as a
function of temperature. We also report on a minimum in the recombination loss
for positive scattering lengths, indicating destructive interference of decay
pathways. Our results confirm central theoretical predictions of Efimov physics
and represent a starting point from which to explore the universal properties
of resonantly interacting few-body systems.Comment: 8 pages, 4 figures, Proceedings of ICAP-2006 (Innsbruck
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