623 research outputs found
Uniform semiclassical wave function for coherent 2D electron flow
We find a uniform semiclassical (SC) wave function describing coherent
branched flow through a two-dimensional electron gas (2DEG), a phenomenon
recently discovered by direct imaging of the current using scanned probed
microscopy. The formation of branches has been explained by classical
arguments, but the SC simulations necessary to account for the coherence are
made difficult by the proliferation of catastrophes in the phase space. In this
paper, expansion in terms of "replacement manifolds" is used to find a uniform
SC wave function for a cusp singularity. The method is then generalized and
applied to calculate uniform wave functions for a quantum-map model of coherent
flow through a 2DEG. Finally, the quantum-map approximation is dropped and the
method is shown to work for a continuous-time model as well.Comment: 9 pages, 7 figure
Characterizing the learning effect in response to biofeedback aimed at reducing tibial acceleration during running
Increased tibial acceleration has been found to be an important risk factor for tibial stress
fractures. Interventions aimed at reducing this variable which found a beneficial effect include the
use of biofeedback in gait retraining. However, no studies have focused on the time participants
take to modify tibial acceleration, therefore we aimed to find the start of a learning plateau in this
study. Six participants ran on a treadmill while multisensory feedback was given. A single-subject
analysis was used to characterise the learning effects. All participants changed peak tibial
acceleration within the first step of running in the feedback condition. Two participants further
reduced tibial acceleration to reach a plateau within 120 steps. In four of the six participants a strong
effect of the feedback was still present after a week. Further research is needed to optimise the use
of biofeedback in reducing the prevalence of tibial stress fractures
Conductance of a Quantum Point Contact in the presence of a Scanning Probe Microscope Tip
Using the recursive Green's function technique, we study the coherent
electron conductance of a quantum point contact in the presence of a scanning
probe microscope tip. Images of the coherent fringe inside a quantum point
contact for different widths are obtained. It is found that the conductance of
a specific channel is reduced while other channels are not affected as long as
the tip is located at the positions correspending to that channel. Moreover,
the coherent fringe is smoothed out by increasing the temperature or the
voltage across the device. Our results are consistent with the experiments
reported by Topinka et al.[Science 289, 2323 (2000)].Comment: 5 page
A C*-Algebraic Model for Locally Noncommutative Spacetimes
Locally noncommutative spacetimes provide a refined notion of noncommutative
spacetimes where the noncommutativity is present only for small distances. Here
we discuss a non-perturbative approach based on Rieffel's strict deformation
quantization. To this end, we extend the usual C*-algebraic results to a
pro-C*-algebraic framework.Comment: 13 pages, LaTeX 2e, no figure
Small eigenvalues of the staggered Dirac operator in the adjoint representation and Random Matrix Theory
The low-lying spectrum of the Dirac operator is predicted to be universal,
within three classes, depending on symmetry properties specified according to
random matrix theory. The three universal classes are the orthogonal, unitary
and symplectic ensemble. Lattice gauge theory with staggered fermions has
verified two of the cases so far, unitary and symplectic, with staggered
fermions in the fundamental representation of SU(3) and SU(2). We verify the
missing case here, namely orthogonal, with staggered fermions in the adjoint
representation of SU(N_c), N_c=2, 3.Comment: 3 pages, revtex, 2 postscript figure
Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy
Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
to ) and couplings (from to ).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen
Periodic orbit effects on conductance peak heights in a chaotic quantum dot
We study the effects of short-time classical dynamics on the distribution of
Coulomb blockade peak heights in a chaotic quantum dot. The location of one or
both leads relative to the short unstable orbits, as well as relative to the
symmetry lines, can have large effects on the moments and on the head and tail
of the conductance distribution. We study these effects analytically as a
function of the stability exponent of the orbits involved, and also numerically
using the stadium billiard as a model. The predicted behavior is robust,
depending only on the short-time behavior of the many-body quantum system, and
consequently insensitive to moderate-sized perturbations.Comment: 14 pages, including 6 figure
INSIG1 influences obesity-related hypertriglyceridemia in humans
In our analysis of a quantitative trait locus (QTL) for plasma triglyceride (TG) levels [logarithm of odds (LOD) = 3.7] on human chromosome 7q36, we examined 29 single nucleotide polymorphisms (SNPs) across INSIG1, a biological candidate gene in the region. Insulin-induced genes (INSIGs) are feedback mediators of cholesterol and fatty acid synthesis in animals, but their role in human lipid regulation is unclear. In our cohort, the INSIG1 promoter SNP rs2721 was associated with TG levels (P = 2 Ă 10â3 in 1,560 individuals of the original linkage cohort, P = 8 Ă 10â4 in 920 unrelated individuals of the replication cohort, combined P = 9.9 Ă 10â6). Individuals homozygous for the T allele had 9% higher TG levels and 2-fold lower expression of INSIG1 in surgical liver biopsy samples when compared with individuals homozygous for the G allele. Also, the T allele showed additional binding of nuclear proteins from HepG2 liver cells in gel shift assays. Finally, the variant rs7566605 in INSIG2, the only homolog of INSIG1, enhances the effect of rs2721 (P = 0.00117). The variant rs2721 alone explains 5.4% of the observed linkage in our cohort, suggesting that additional, yet-undiscovered genes and sequence variants in the QTL interval also contribute to alterations in TG levels in humans
Meson screening masses from lattice QCD with two light and the strange quark
We present results for screening masses of mesons built from light and
strange quarks in the temperature range of approximately between 140 MeV to 800
MeV. The lattice computations were performed with 2+1 dynamical light and
strange flavors of improved (p4) staggered fermions along a line of constant
physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The
lattices had temporal extents Nt = 4, 6 and 8 and aspect ratios of Ns / Nt \geq
4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass
remains almost equal to the corresponding zero temperature pseudo-scalar (pole)
mass. At temperatures around 3Tc (Tc being the transition temperature) the
continuum extrapolated pseudo-scalar screening mass approaches very close to
the free continuum result of 2 \pi T from below. On the other hand, at high
temperatures the vector screening mass turns out to be larger than the free
continuum value of 2 \pi T. The pseudo-scalar and the vector screening masses
do not become degenerate even for a temperature as high as 4Tc. Using these
mesonic spatial correlation functions we have also investigated the restoration
of chiral symmetry and the effective restoration of the axial symmetry. We have
found that the vector and the axial-vector screening correlators become
degenerate, indicating chiral symmetry restoration, at a temperature which is
consistent with the QCD transition temperature obtained in previous studies. On
the other hand, the pseudo-scalar and the scalar screening correlators become
degenerate only at temperatures larger than 1.3Tc, indicating that the
effective restoration of the axial symmetry takes place at a temperature larger
than the QCD transition temperature.Comment: Published versio
The QCD thermal phase transition in the presence of a small chemical potential
We propose a new method to investigate the thermal properties of QCD with a
small quark chemical potential . Derivatives of the phase transition point
with respect to are computed at for 2 flavors of p-4 improved
staggered fermions with on a lattice. The resulting
Taylor expansion is well behaved for the small values of relevant for RHIC phenomenology, and predicts a critical curve
in reasonable agreement with estimates obtained using exact
reweighting. In addition, we contrast the case of isoscalar and isovector
chemical potentials, quantify the effect of on the equation of
state, and comment on the complex phase of the fermion determinant in QCD with
.Comment: 26 pages, 25 figures, minor modificatio
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