217 research outputs found
Monte Carlo Simulations of Interacting Anyon Chains
A generalized version of the valence-bond Monte Carlo method is used to study
ground state properties of the 1+1 dimensional quantum -state Potts models.
For appropriate values of these models can be used to describe interacting
chains of non-Abelian anyons --- quasiparticle excitations of certain exotic
fractional quantum Hall states.Comment: 4 pages, 5 figure
Spin-S bilayer Heisenberg models: Mean-field arguments and numerical calculations
Spin-S bilayer Heisenberg models (nearest-neighbor square lattice
antiferromagnets in each layer, with antiferromagnetic interlayer couplings)
are treated using dimer mean-field theory for general S and high-order
expansions about the dimer limit for S=1, 3/2,...,4. We suggest that the
transition between the dimer phase at weak intraplane coupling and the Neel
phase at strong intraplane coupling is continuous for all S, contrary to a
recent suggestion based on Schwinger boson mean-field theory. We also present
results for S=1 layers based on expansions about the Ising limit: In every
respect the S=1 bilayers appear to behave like S=1/2 bilayers, further
supporting our picture for the nature of the order-disorder phase transition.Comment: 6 pages, Revtex 3.0, 8 figures (not embedded in text
Impact of EMG Changes in Continuous Vagal Nerve Monitoring in High-Risk Endocrine Neck Surgery
Background: Continuous vagal intraoperative neuromonitoring (CIONM) of the recurrent laryngeal nerve (RLN) may reduce the risk of RLN lesions during high-risk endocrine neck surgery such as operation for large goiter potentially requiring transsternal surgery, advanced thyroid cancer, and recurrence. Methods: Fifty-five consecutive patients (41 female, median age 61 years, 87 nerves at risk) underwent high-risk endocrine neck surgery. CIONM was performed using the commercially available NIM-Response 3.0 nerve monitoring system with automatic periodic stimulation (APS) and matching endotracheal tube electrodes (Medtronic Inc.). All CIONM events (decreased amplitude/increased latency) were recorded. Results: APS malfunction occurred on three sides (3 %). A total of 138 CIONM events were registered on 61 sides. Of 138, 47 (34 %) events were assessed as imminent (13 events) or potentially imminent (34 events) lesions, whereas 91 (66 %) were classified as artifacts. Loss of signal was observed in seven patients. Actions to restore the CIONM baseline were undertaken in 58/138 (42 %) events with a median 60 s required per action. Four RLN palsies (3 transient, 1 permanent) occurred: one in case of CIONM malfunction, two sudden without any significant previous CIONM event, and one without any CIONM event. The APS vagus electrode led to temporary damage to the vagus nerve in two patients. Conclusions: CIONM may prevent RLN palsies by timely recognition of imminent nerve lesions. In high-risk endocrine neck surgery, CIONM may, however, be limited in its utility by system malfunction, direct harm to the vagus nerve, and particularly, inability to indicate RLN lesions ahead in time.publishedVersio
Disorder and Impurities in Hubbard-Antiferromagnets
We study the influence of disorder and randomly distributed impurities on the
properties of correlated antiferromagnets. To this end the Hubbard model with
(i) random potentials, (ii) random hopping elements, and (iii) randomly
distributed values of interaction is treated using quantum Monte Carlo and
dynamical mean-field theory. In cases (i) and (iii) weak disorder can lead to
an enhancement of antiferromagnetic (AF) order: in case (i) by a
disorder-induced delocalization, in case (iii) by binding of free carriers at
the impurities. For strong disorder or large impurity concentration
antiferromagnetism is eventually destroyed. Random hopping leaves the local
moment stable but AF order is suppressed by local singlet formation. Random
potentials induce impurity states within the charge gap until it eventually
closes. Impurities with weak interaction values shift the Hubbard gap to a
density off half-filling. In both cases an antiferromagnetic phase without
charge gap is observed.Comment: 16 pages, 9 figures, latex using vieweg.sty (enclosed); typos
corrected, references updated; to appear in "Advances in Solid State
Physics", Vol. 3
The questionnaire for urinary incontinence diagnosis (QUID): Validity and responsiveness to change in women undergoing non-surgical therapies for treatment of stress predominant urinary incontinence
Aims The Questionnaire for Urinary Incontinence Diagnosis (QUID), a 6-item urinary incontinence (UI) symptom questionnaire, was developed and validated to distinguish stress and urge UI. This study's objective was to evaluate QUID validity and responsiveness when used as a clinical trial outcome measure. Methods Participants enrolled in a multi-center trial of non-surgical therapy (continence pessary, pelvic floor muscle training or combined) for stress-predominant UI and completed baseline and 3-month diaries, the Urinary Distress Inventory (UDI) and QUID. Data from all treatment groups were pooled. QUID internal consistency (Cronbach's Α) and convergent/discriminant validity (Pearson correlations) were evaluated. Responsiveness to change was assessed with 3-month score outcomes and distribution-based measurements. Results Four hundred forty-four women (mean age 50) were enrolled with stress (N = 200) and mixed (N = 244) UI; 344 had 3-month data. Baseline QUID Stress and Urge scores (both scaled 0–15, larger values indicating worse UI) were 8.4 ± 3.2 and 4.5 ± 3.3, respectively. Internal consistency of QUID Total, Stress, and Urge scores was 0.75, 0.64 and 0.87, respectively. QUID Stress scores correlated moderately with UDI-Stress scores (r = 0.68, P  < 0.0001) and diary stress UI episodes (r = 0.41, P  < 0.0001). QUID Urge scores correlated moderately with UDI-Irritative scores (r = 0.68, P  < 0.0001) and diary urge UI episodes (r = 0.45, P  < 0.0001). Three-month QUID Stress and Urge scores improved (4.1 ± 3.4 and 2.2 ± 2.7, both P  < 0.0001). QUID Stress score effect size (1.3) and standardized response mean (1.2) suggested a large change after therapy. Conclusion The QUID has acceptable psychometric characteristics and may be used as a UI outcome measure in clinical trials. Neurourol. Urodynam. 29:727–734, 2010. © 2010 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77446/1/20818_ftp.pd
Phase Correlations in Cosmic Microwave Background Temperature Maps
We study the statistical properties of spherical harmonic modes of
temperature maps of the cosmic microwave background. Unlike other studies,
which focus mainly on properties of the amplitudes of these modes, we look
instead at their phases. In particular, we present a simple measure of phase
correlation that can be diagnostic of departures from the standard assumption
that primordial density fluctuations constitute a statistically homogeneous and
isotropic Gaussian random field, which should possess phases that are uniformly
random on the unit circle. The method we discuss checks for the uniformity of
the distribution of phase angles using a non-parametric descriptor based on the
use order statistics, which is known as Kuiper's statistic. The particular
advantage of the method we present is that, when coupled to the judicious use
of Monte Carlo simulations, it can deliver very interesting results from small
data samples. In particular, it is useful for studying the properties of
spherical harmonics at low l for which there are only small number of
independent values of m and which therefore furnish only a small number of
phases for analysis. We apply the method to the COBE-DMR and WMAP sky maps, and
find departures from uniformity in both. In the case of WMAP, our results
probably reflect Galactic contamination or the known variation of
signal-to-noise across the sky rather than primordial non-Gaussianity.Comment: 18 pages, 4 figures, accepted for publication in MNRA
Effect of an Electron-phonon Interaction on the One-electron Spectral Weight of a d-wave Superconductor
We analyze the effects of an electron-phonon interaction on the one-electron
spectral weight A(k,omega) of a d_{x^2-y^2} superconductor. We study the case
of an Einstein phonon mode with various momentum-dependent electron-phonon
couplings and compare the structure produced in A(k,omega) with that obtained
from coupling to the magnetic pi-resonant mode. We find that if the strength of
the interactions are adjusted to give the same renormalization at the nodal
point, the differences in A(k,omega) are generally small but possibly
observable near k=(pi,0).Comment: 10 pages, 14 figures (color versions of Figs. 2,4,10,11,12 available
upon request
Towards a large-scale quantum simulator on diamond surface at room temperature
Strongly-correlated quantum many-body systems exhibits a variety of exotic
phases with long-range quantum correlations, such as spin liquids and
supersolids. Despite the rapid increase in computational power of modern
computers, the numerical simulation of these complex systems becomes
intractable even for a few dozens of particles. Feynman's idea of quantum
simulators offers an innovative way to bypass this computational barrier.
However, the proposed realizations of such devices either require very low
temperatures (ultracold gases in optical lattices, trapped ions,
superconducting devices) and considerable technological effort, or are
extremely hard to scale in practice (NMR, linear optics). In this work, we
propose a new architecture for a scalable quantum simulator that can operate at
room temperature. It consists of strongly-interacting nuclear spins attached to
the diamond surface by its direct chemical treatment, or by means of a
functionalized graphene sheet. The initialization, control and read-out of this
quantum simulator can be accomplished with nitrogen-vacancy centers implanted
in diamond. The system can be engineered to simulate a wide variety of
interesting strongly-correlated models with long-range dipole-dipole
interactions. Due to the superior coherence time of nuclear spins and
nitrogen-vacancy centers in diamond, our proposal offers new opportunities
towards large-scale quantum simulation at room temperatures
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