530 research outputs found

### Ab initio study of canted magnetism of finite atomic chains at surfaces

By using ab initio methods on different levels we study the magnetic ground
state of (finite) atomic wires deposited on metallic surfaces. A
phenomenological model based on symmetry arguments suggests that the
magnetization of a ferromagnetic wire is aligned either normal to the wire and,
generally, tilted with respect to the surface normal or parallel to the wire.
From a first principles point of view, this simple model can be best related
to the so--called magnetic force theorem calculations being often used to
explore magnetic anisotropy energies of bulk and surface systems. The second
theoretical approach we use to search for the canted magnetic ground state is
first principles adiabatic spin dynamics extended to the case of fully
relativistic electron scattering. First, for the case of two adjacent Fe atoms
an a Cu(111) surface we demonstrate that the reduction of the surface symmetry
can indeed lead to canted magnetism. The anisotropy constants and consequently
the ground state magnetization direction are very sensitive to the position of
the dimer with respect to the surface. We also performed calculations for a
seven--atom Co chain placed along a step edge of a Pt(111) surface. As far as
the ground state spin orientation is concerned we obtain excellent agreement
with experiment. Moreover, the magnetic ground state turns out to be slightly
noncollinear.Comment: 8 pages, 5 figures; presented on the International Conference on
Nanospintronics Design and Realizations, Kyoto, Japan, May 2004; to appear in
J. Phys.: Cond. Matte

### Spin currents and spin dynamics in time-dependent density-functional theory

We derive and analyse the equation of motion for the spin degrees of freedom
within time-dependent spin-density-functional theory (TD-SDFT). Results are (i)
a prescription for obtaining many-body corrections to the single-particle spin
currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an
exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for
calculating, from TD-SDFT, the torque exerted by spin currents on the spin
magnetization, (iv) a novel exact constraint on approximate xc functionals, and
(v) the discovery of serious deficiencies of popular approximations to TD-SDFT
when applied to spin dynamics.Comment: now includes discussion of OEP and GGA; to appear in Phys. Rev. Let

### Pion-Lambda-Sigma Coupling Extracted from Hyperonic Atoms

The latest measurements of the atomic level width in Sigma-hyperonic Pb atom
offer the most accurate datum in the region of low-energy Sigma-hyperon
physics. Atomic widths are due to the conversion of Sigma-nucleon into
Lambda-nucleon. In high angular momentum states this conversion is dominated by
the one-pion exchange. A joint analysis of the data of the scattering of
negative-Sigma on proton converting into a Lambda and a neutron and of the
atomic widths allows to extract a pseudovector pion-hyperon-Sigma coupling
constant of 0.048 with a statistical error of +-0.005 and a systematic one of
+-0.004. This corresponds to a pseudoscalar coupling constant of 13.3 with a
statistical uncertainty of 1.4 and a systematic one of 1.1.Comment: 12 pages, 1 figure, Use of Revtex.st

### Stochastic Resonance of Ensemble Neurons for Transient Spike Trains: A Wavelet Analysis

By using the wavelet transformation (WT), we have analyzed the response of an
ensemble of $N$ (=1, 10, 100 and 500) Hodgkin-Huxley (HH) neurons to {\it
transient} $M$-pulse spike trains ($M=1-3$) with independent Gaussian noises.
The cross-correlation between the input and output signals is expressed in
terms of the WT expansion coefficients. The signal-to-noise ratio (SNR) is
evaluated by using the {\it denoising} method within the WT, by which the noise
contribution is extracted from output signals. Although the response of a
single (N=1) neuron to sub-threshold transient signals with noises is quite
unreliable, the transmission fidelity assessed by the cross-correlation and SNR
is shown to be much improved by increasing the value of $N$: a population of
neurons play an indispensable role in the stochastic resonance (SR) for
transient spike inputs. It is also shown that in a large-scale ensemble, the
transmission fidelity for supra-threshold transient spikes is not significantly
degraded by a weak noise which is responsible to SR for sub-threshold inputs.Comment: 20 pages, 4 figure

### Dynamics of defect formation

A dynamic symmetry-breaking transition with noise and inertia is analyzed.
Exact solution of the linearized equation that describes the critical region
allows precise calculation (exponent and prefactor) of the number of defects
produced as a function of the rate of increase of the critical parameter. The
procedure is valid in both the overdamped and underdamped limits. In one space
dimension, we perform quantitative comparison with numerical simulations of the
nonlinear nonautonomous stochastic partial differential equation and report on
signatures of underdamped dynamics.Comment: 4 pages, LaTeX, 4 figures. Submitted to Physical Revie

### Building light nuclei from neutrons, protons, and pions

In these lectures I first explain, in a rather basic fashion, the
construction of effective field theories. I then discuss some recent
developments in the application of such theories to two- and three-nucleon
systems.Comment: 54 pages, uses czjphys.cls. Lectures given at 14th Summer School
"Understanding the Structure of Hadrons", Prague, July 2001. To appear in
Czechoslovak Journal of Physic

### New reference ranges for interpreting forced expiratory manoeuvres in infants and implications for clinical interpretation: a multicentre collaboration

The raised volume rapid thoracoabdominal compression (RVRTC) technique is commonly used to obtain full forced expiratory manoeuvres from infants, but reference equations derived from 'in-house' equipment have been shown to be inappropriate for current commercially available devices

### The three- and four-nucleon systems from chiral effective field theory

Recently developed chiral nucleon-nucleon (NN) forces at next-to-leading
order (NLO) that describe NN phase shifts up to about 100 MeV fairly well have
been applied to 3N and 4N systems. Faddeev-Yakubovsky equations have been
solved rigorously. The chiral NLO forces depend on a momentum cut-off \Lambda
lying between 540-600 MeV/c. The resulting 3N and 4N binding energies are in
the same range as found using standard NN potentials. In additon, low-energy 3N
scattering observables are very well reproduced like for standard NN forces.
Surprisingly, the long standing A_y-puzzle is resolved at NLO. The cut-off
dependence of the scattering observables is rather mild.Comment: 4 pp, revtex, 3 figure

### Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials

The sensitivity of nucleon-nucleus elastic scattering to the off-shell
behavior of realistic nucleon-nucleon interactions is investigated when
on-shell equivalent nucleon-nucleon potentials are used. The study is based on
applications of the full-folding optical model potential for an explicit
treatment of the off-shell behavior of the nucleon-nucleon effective
interaction. Applications were made at beam energies between 40 and 500 MeV for
proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris
potential and its local on-shell equivalent as obtained with the
Gelfand-Levitan and Marchenko inversion formalism for the two nucleon
Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering
show small fluctuations in the corresponding observables. This implies that
off-shell features of the NN interaction cannot be unambiguously identified
with these processes. Inversion potentials were also constructed directly from
NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in
proton-nucleus scattering above 200 MeV provide a superior description of the
observables relative to those obtained from current realistic NN potentials.
Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.

### Early Lung Function Testing in Infants with Aortic Arch Anomalies Identifies Patients at Risk for Airway Obstruction

BACKGROUND: Aortic arch anomalies (AAA) are rare cardio-vascular anomalies. Right-sided and double-sided aortic arch anomalies (RAAA, DAAA) are distinguished, both may cause airway obstructions. We studied the degree of airway obstruction in infants with AAA by neonatal lung function testing (LFT). PATIENTS AND METHODS: 17 patients (10 RAAA and 7 DAAA) with prenatal diagnosis of AAA were investigated. The median (range) post conception age at LFT was 40.3 (36.6-44.1) weeks, median body weight 3400 (2320-4665) g. Measurements included tidal breathing flow-volume loops (TBFVL), airway resistance (R(aw)) by bodyplethysmography and the maximal expiratory flow at functional residual capacity (V'(max)FRC) by rapid thoracic-abdominal compression (RTC) technique. V'(max)FRC was also expressed in Z-scores, based on published gender-, age and height-specific reference values. RESULTS: Abnormal lung function tests were seen in both RAAA and DAAA infants. Compared to RAAA infants, infants with DAAA had significantly more expiratory flow limitations in the TBFVL, (86% vs. 30%, p<0.05) and a significantly increased R(aw) (pâ=â0.015). Despite a significant correlation between R(aw) and the Z-score of V'(max)FRC (râ=â0.740, p<0.001), there were no statistically significant differences in V'(max)FRC and it's Z-scores between RAAA and DAAA infants. 4 (24%) infants (2 RAAA, 2 DAAA) were near or below the 10(th) percentile of V'(max)FRC, indicating a high risk for airway obstruction. CONCLUSION: Both, infants with RAAA and DAAA, are at risk for airway obstruction and early LFT helps to identify and to monitor these infants. This may support the decision for therapeutic interventions before clinical symptoms arise

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