68 research outputs found
GW quasi-particle spectra from occupied states only
We introduce a method that allows for the calculation of quasi-particle
spectra in the GW approximation, yet avoiding any explicit reference to empty
one-electron states. This is achieved by expressing the irreducible
polarizability operator and the self-energy operator through a set of linear
response equations, which are solved using a Lanczos-chain algorithm. We first
validate our approach by calculating the vertical ionization energies of the
benzene molecule and then show its potential by addressing the spectrum of a
large molecule such as free-base tetraphenylporphyrin.Comment: 4 pages, 3 figure
Vortex configurations and critical parameters in superconducting thin films containing antidot arrays: Nonlinear Ginzburg-Landau theory
Using the non-linear Ginzburg-Landau (GL) theory, we obtain the possible
vortex configurations in superconducting thin films containing a square lattice
of antidots. The equilibrium structural phase diagram is constructed which
gives the different ground-state vortex configurations as function of the size
and periodicity of the antidots for a given effective GL parameter
. Giant-vortex states, combination of giant- and multi-vortex
states, as well as symmetry imposed vortex-antivortex states are found to be
the ground state for particular geometrical parameters of the sample. The
antidot occupation number is calculated as a function of related
parameters and comparison with existing expressions for the saturation number
and with experimental results is given. For a small radius of antidots a
triangular vortex lattice is obtained, where some of the vortices are pinned by
the antidots and some of them are located between them. Transition between the
square pinned and triangular vortex lattices is given for different values of
the applied field. The enhanced critical current at integer and rational
matching fields is found, where the level of enhancement at given magnetic
field directly depends on the vortex-occupation number of the antidots. For
certain parameters of the antidot lattice and/or temperature the critical
current is found to be larger for higher magnetic fields.
Superconducting/normal phase boundary exhibits different regimes as
antidots are made larger, and we transit from a plain superconducting film to a
thin-wire superconducting network. Presented results are in good agreement with
available experiments and suggest possible new experiments.Comment: 15 pages and 20 figure
A Magnetic Flux Tube Oscillation Model for QPOs in SGR Giant Flares
Giant flares from soft gamma-ray repeaters (SGRs) are one of the most violent
phenomena in neutron stars. Quasi-periodic oscillations (QPOs) with frequencies
ranging from 18 to 1840 Hz have been discovered in the tails of giant flares
from two SGRs, and were ascribed to be seismic vibrations or torsional
oscillations of magnetars. Here we propose an alternative explanation for the
QPOs in terms of standing sausage mode oscillations of flux tubes in the
magnetar coronae. We show that most of the QPOs observed in SGR giant flares
could be well accounted for except for those with very high frequencies (625
and 1840 Hz).Comment: 15 pages,1 figures,1 table, accepted for publication in The
Astrophysical Journa
Temporal Dissociation between Myeloperoxidase (MPO)-Modified LDL and MPO Elevations during Chronic Sleep Restriction and Recovery in Healthy Young Men
OBJECTIVES: Many studies have evaluated the ways in which sleep disturbances may influence inflammation and the possible links of this effect to cardiovascular risk. Our objective was to investigate the effects of chronic sleep restriction and recovery on several blood cardiovascular biomarkers. METHODS AND RESULTS: Nine healthy male non-smokers, aged 22-29 years, were admitted to the Sleep Laboratory for 11 days and nights under continuous electroencephalogram polysomnography. The study consisted of three baseline nights of 8 hours sleep (from 11 pm to 7 am), five sleep-restricted nights, during which sleep was allowed only between 1 am and 6 am, and three recovery nights of 8 hours sleep (11 pm to 7 am). Myeloperoxidase-modified low-density lipoprotein levels increased during the sleep-restricted period indicating an oxidative stress. A significant increase in the quantity of slow-wave sleep was measured during the first recovery night. After this first recovery night, insulin-like growth factor-1 levels increased and myeloperoxidase concentration peaked. CONCLUSIONS: We observed for the first time that sleep restriction and the recovery process are associated with differential changes in blood biomarkers of cardiovascular disease
Optimal representation of the polarization propagator for large-scale GW calculations
Quasiparticle calculations based on the GW approximation are enhanced by introducing an optimal basis set for the polarization propagator, based on a Wannier representation of the one-electron wave functions, thus allowing the treatment of substantially larger systems. Our method is validated by calculating the vertical ionization energies of the benzene molecule and the band structure of bulk silicon. Its potentials are then demonstrated by addressing the quasiparticle spectrum of a model structure of vitreous silica, as well as of the tetraphenylporphyrin molecule
Operating characteristics of the negative expiratory pressure technique in predicting obstructive sleep apnoea syndrome in snoring patients
Background: This study examines the operating characteristics of the expiratory flow response to a negative pressure (NEP) applied to the mouth in the prediction of obstructive sleep apnoea syndrome (OSAS) in snoring patients. Methods: Two hundred and thirty eight patients with normal spirometric values were studied. Full laboratory polysomnography was performed and an NEP of –5 cm H(2)O was applied in the sitting and supine positions. Results: A significant correlation was found between the degree of flow limitation measured by NEP in both positions (expressed as the percentage of the expired tidal volume over which NEP induced flow did not exceed spontaneous flow) and the apnoea-hypopnoea index (AHI). This correlation was significantly higher in the supine position (p<0.0001) where an expiratory flow limitation cut off value of ⩾27.5% of the tidal volume produced a sensitivity of 81.9% and a specificity of 69.1% in predicting OSAS. Conclusion: These findings show that the degree of instability of the upper airway measured by NEP is correlated with the severity of OSAS. NEP had moderate sensitivity and specificity and may be useful in predicting OSAS in a clinic based population
- …