36,660 research outputs found
Electron-magnon scattering in elementary ferromagnets from first principles: lifetime broadening and band anomalies
We study the electron-magnon scattering in bulk Fe, Co, and Ni within the
framework of many-body perturbation theory implemented in the full-potential
linearized augmented-plane-wave method. To this end, a -dependent
self-energy ( self-energy) describing the scattering of electrons and
magnons is constructed from the solution of a Bethe-Salpeter equation for the
two-particle (electron-hole) Green function, in which single-particle Stoner
and collective spin-wave excitations (magnons) are treated on the same footing.
Partial self-consistency is achieved by the alignment of the chemical
potentials. The resulting renormalized electronic band structures exhibit
strong spin-dependent lifetime effects close to the Fermi energy, which are
strongest in Fe. The renormalization can give rise to a loss of quasiparticle
character close to the Fermi energy, which we attribute to electron scattering
with spatially extended spin waves. This scattering is also responsible for
dispersion anomalies in conduction bands of iron and for the formation of
satellite bands in nickel. Furthermore, we find a band anomaly at a binding
energy of 1.5~eV in iron, which results from a coupling of the quasihole with
single-particle excitations that form a peak in the Stoner continuum. This band
anomaly was recently observed in photoemission experiments. On the theory side,
we show that the contribution of the Goldstone mode to the self-energy is
expected to (nearly) vanish in the long-wavelength limit. We also present an
in-depth discussion about the possible violation of causality when an
incomplete subset of self-energy diagrams is chosen
Factorization in hard diffraction
In this talk, I reviewed the role of factorization in diffraction hard
scattering.Comment: Talk presented at the Ringberg Workshop on ``New Trends in HERA
Physics 2001''. 10 pages, 6 postscript figures. Misprints correcte
Electrical read-out of the local nuclear polarization in the quantum Hall effect
It is demonstrated that the now well-established `flip-flop' mechanism of
spin exchange between electrons and nuclei in the quantum Hall effect can be
reversed. We use a sample geometry which utilizes separately contacted edge
states to establish a local nuclear spin polarization --close to the maximum
value achievable-- by driving a current between electron states of different
spin orientation. When the externally applied current is switched off, the
sample exhibits an output voltage of up to a few tenths of a meV, which decays
with a time constant typical for the nuclear spin relaxation. The surprizing
fact that a sample with a local nuclear spin polarization can act as a source
of energy and that this energy is well above the nuclear Zeeman splitting is
explained by a simple model which takes into account the effect of a local
Overhauser shift on the edge state reconstruction.Comment: Submitted to Phys. Rev. Let
Waveform sampling using an adiabatically driven electron ratchet in a two-dimensional electron system
We utilize a time-periodic ratchet-like potential modulation imposed onto a
two-dimensional electron system inside a GaAs/AlGaAs
heterostructure to evoke a net dc pumping current. The modulation is induced by
two sets of interdigitated gates, interlacing off center, which can be
independently addressed. When the transducers are driven by two identical but
phase-shifted ac signals, a lateral dc pumping current results, which
strongly depends on both, the phase shift and the waveform of the
imposed gate voltages. We find that for different periodic signals, the phase
dependence closely resembles . A simple linear model of
adiabatic pumping in two-dimensional electron systems is presented, which
reproduces well our experimental findings.Comment: 3 figure
Influenza Vaccination Coverage Rates in 5 European Countries: a Population-Based Cross-Sectional Analysis of the Seasons 02/03, 03/04 and 04/05
Introduction:: Influenza continues to be a considerable health problem in Europe. Vaccination is the only preventive measure, reducing mortality and morbidity of influenza in all age groups Objectives:: The objective of this survey was to assess and compare the level of influenza vaccination coverage during three consecutive influenza seasons (02/03, 03/04, 04/05) in the five European countries United Kingdom, France, Italy, Germany and Spain, understand the driving forces and barriers to vaccination now and 3 years ago and determine vaccination intentions for the following winter. Methods:: We conducted a random-sampling, telephone-based household survey among non-institutionalized individuals representative of the population aged 14 and over. The surveys used the same questionnaire for all three seasons. The data were subsequently pooled. Four target groups were determined for analysis: (1) persons aged 65 and over; (2) people working in the medical field; (3) persons suffering from chronic illness and (4) a group composed of persons aged 65 and over or working in the medical field or suffering from a chronic illness. Results:: The overall sample consisted of 28,021 people. The influenza vaccination coverage rate increased from 21.0% in season 02/03 to 23.6% in season 03/04 and then to 23.7% in season 04/05. The differences between the seasons are statistically significant (p = 0.01). The highest rate over all countries and seasons had Germany in season 04/05 with 26.5%, Spain had in season 02/03 with 19.3% the lowest rate totally. The coverage rate in the target group composed of person's aged 65 and over or working in the medical field or suffering from a chronic illness was 49.7% in season 02-04 and 50.0% in season 04/05. The driving forces and barriers to vaccination did not change over the years. The most frequent reasons for being vaccinated given by vaccines were: influenza, considered to be a serious illness which people wanted to avoid, having received advise from the family doctor or nurse to be vaccinated and not wanting to infect family and friends. Reasons for not being vaccinated mentioned by people who have never been vaccinated were: not expecting to catch influenza, not having considered vaccination before and not having received a recommendation from the family doctor to be vaccinated. Options encouraging influenza vaccination are: recommendation by the family doctor or nurse, more available information on the vaccine regarding efficacy and tolerance and more information available about the disease. The adjusted odds ratio of receiving influenza vaccine varied between 2.5 in Germany and 6.3 in the United Kingdom in any risk group. Conclusion:: The vaccination coverage rate increased from the first season (21.0%) to the third season (23.7%) by 2.6%. The family doctor is the most important source of encouragement for people to be vaccinated against influenza. It seems that the public would be more likely to be vaccinated if they had more information on the efficacy and tolerance of the vaccine, as well as the disease. We therefore suggest that family doctors be better informed on influenza vaccine and the disease itself, so that they can actively inform their patients on these topic
Incidental threat during visuospatial working memory in adolescent anxiety: an emotional memory-guided saccade task
BackgroundPediatric anxiety disorders are among the most common psychiatric mental illnesses in children and adolescents, and are associated with abnormal cognitive control in emotional, particularly threat, contexts. In a series of studies using eye movement saccade tasks, we reported anxiety-related alterations in the interplay of inhibitory control with incentives, or with emotional distractors. The present study extends these findings to working memory (WM), and queries the interaction of spatial WM with emotional stimuli in pediatric clinical anxiety.
MethodsParticipants were 33 children/adolescents diagnosed with an anxiety disorder, and 22 age-matched healthy comparison youths. Participants completed a novel eye movement task, an affective variant of the memory-guided saccade task. This task assessed the influence of incidental threat on spatial WM processes during high and low cognitive load.
ResultsHealthy but not anxious children/adolescents showed slowed saccade latencies during incidental threat in low-load but not high-load WM conditions. No other group effects emerged on saccade latency or accuracy.
ConclusionsThe current data suggest a differential pattern of how emotion interacts with cognitive control in healthy youth relative to anxious youth. These findings extend data from inhibitory processes, reported previously, to spatial WM in pediatric anxiety
Contact tracing and epidemics control in social networks
A generalization of the standard susceptible-infectious-removed (SIR)
stochastic model for epidemics in sparse random networks is introduced which
incorporates contact tracing in addition to random screening. We propose a
deterministic mean-field description which yields quantitative agreement with
stochastic simulations on random graphs. We also analyze the role of contact
tracing in epidemics control in small-world networks and show that its
effectiveness grows as the rewiring probability is reduced.Comment: 4 pages, 4 figures, submitted to PR
Reconstruction of nuclear quadrupole interaction in (In,Ga)As/GaAs quantum dots observed by transmission electron microscopy
A microscopic study of the individual annealed (In,Ga)As/GaAs quantum dots is
done by means of high-resolution transmission electron microscopy. The
Cauchy-Green strain-tensor component distribution and the chemical composition
of the (In,Ga)As alloy are extracted from the microscopy images. The image
processing allows for the reconstruction of the strain-induced electric-field
gradients at the individual atomic columns extracting thereby the magnitude and
asymmetry parameter of the nuclear quadrupole interaction. Nuclear magnetic
resonance absorption spectra are analyzed for parallel and transverse mutual
orientations of the electric-field gradient and a static magnetic field.Comment: 8 pages, 6 figure
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