47 research outputs found
Entropic uncertainty measure for fluctuations in two-level electron-phonon models
Two-level electron-phonon systems with reflection symmetry linearly coupled
to one or two phonon modes (exciton and E Jahn-Teller model)
exhibit strong enhancement of quantum fluctuations of the phonon coordinates
and momenta due to the complex interplay of quantum fluctuations and
nonlinearities inherent to the models. We show that for the complex correlated
quantum fluctuations of the anisotropic two-level systems the Shannon entropies
of phonon coordinate and momentum and their sum yield their proper global
description. On the other hand, the variance measures of the Heisenberg
uncertainties suffer from several shortcomings to provide proper description of
the fluctuations. Wave functions, related entropies and variances were
determined by direct numerical simulations. Illustrative variational
calculations were performed to demonstrate the effect on an analytically
tractable exciton model.Comment: 14 pages, 10 figs, published in Eur.Phys.J 38 B (2004) 25-3
Level-dynamic approach to the excited spectra of the Jahn-Teller model - kink-train lattice and 'glassy' quantum phase
The dynamics of excited phonon spectra of the Exe Jahn-Teller (hereafter, JT)
model mapped onto the generalized Calogero-Moser (gCM) gas of pseudoparticles
implies a complex interplay between nonlinearity and fluctuations of
quasiparticle trajectories. A broad crossover appears in a pseudotime
(interaction strength) between the initial oscillator region and the nonlinear
region of the kink-train lattice as a superlattice of the kink-antikink gCM
trajectories. The local nonlinear fluctuations, nuclei (droplets) of the
growing kink phase arise at the crossover, forming a new intermediate droplet
"glassy" phase as a precursor of the kink phase. The "glassy" phase is related
to a broad maximum in the entropy of the probability distributions of
pseudoparticle accelerations, or level curvatures. The kink-train lattice phase
with multiple kink-antikink collisions is stabilised by long-range correlations
when approaching a semiclassical limit. A series of bifurcations of
nearest-level spacings were recognised as signatures of pre-chaotic behaviour
at the quantum level in the kink phase. Statistical characteristics can be seen
to confirm the coexistence within all of the spectra of both regularity and
chaoticity to a varying extent (nonuniversality). Regions are observed within
which one of the phases is dominant.Comment: 10 pages, 8 figures; published in European Physical Journal B; see
also: cond-mat/050968
Ising instability of a Holstein phonon mode in graphene
We study the thermal distribution of phonons in a graphene sheet. Due to the
two electronic bands there are two out-of-plane phonon modes with respect to
the two sublattices. One of these modes undergoes an Ising transition by
spontaneously breaking the sublattice symmetry. We calculate the critical
point, the renormalization of the phonon frequency and the average lattice
distortion. This transition might be observable in Raman scattering and in
transport properties.Comment: 5 pages, 2 figure
Influence of plastic deformation inhomogeneity on corrosion resistance of TIN plates
Thin steel sheets are used in the production of food packaging, especially for long-term storage. Reducing the thickness of steel sheets and increasing the speed of the drawing process in the manufacture of packaging often decrements its plastic deformation stability. These changes bring about the need to use evaluation methods able to determine mechanical and plastic properties of steel sheets quickly and at a low cost. Two types of tin-plated steel sheets were used for experimental research into the influence of plastic deformation on their corrosion resistance. The paper compares the results of the uniaxial tension test and the biaxial tension test of tin-plated sheet properties
Simulation of Jahn-Teller-Dicke Magnetic Structural Phase Transition with Trapped Ions
We study theoretically the collective Ee Jahn-Teller-Dicke
distortion in a system of trapped ions. We focus in the limit of infinite range
interactions in which an ensemble of effective spins interacts with two
collective vibrational modes with U(1) symmetric couplings. Our model is
exactly solvable in the thermodynamical limit and it is amenable to be solved
by exact numerical diagonalization for a moderate number of ions. We show that
trapped ions are ideally suited to study the emergence of spontaneous symmetry
breaking of a continuous symmetry and magnetic structural phase transition in a
mesoscopic system.Comment: 19 pages, 7 figure
Frequency splitting of intervalley phonons in graphene
We study the thermal distribution of intervalley phonons in a graphene sheet.
These phonons have two components with the same frequency. The degeneracy of
the two modes is preserved by weak electron-phonon coupling. A sufficiently
strong electron-phonon coupling, however, can result in a splitting into an
optical and an acoustic phonon branch, which creates a fluctuating gap in the
electronic spectrum. We describe these effects by treating the phonon
distribution within a saddle-point approximation. Fluctuations around the
saddle point indicate a Berezinskii-Kosterlitz-Thouless transition of the
acoustic branch. This transition might be observable in the polarization of
Raman scattered light.Comment: 5 pages, 1 figur
Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).
Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)