13,528 research outputs found
Deformations in VLBI antennas
A study is presented of deformations in antennas with the emphasis on their influence on VLBI measurements. The GIFTS structural analysis program has been used to model the VLBI antenna in Fairbanks (Alaska). The report identifies key deformations and studies the effect of gravity, wind, and temperature. Estimates of expected deformations are given
Electronic and phononic Raman scattering in detwinned YBaCuO and YCaBaCuO: s-wave admixture to the -wave order parameter
Inelastic light (Raman) scattering has been used to study electronic
excitations and phonon anomalies in detwinned, slightly overdoped
YBaCuO and moderately overdoped
YCaBaCuO single crystals. In both samples
modifications of the electronic pair-breaking peaks when interchanging the a-
and b-axis were observed. The lineshapes of several phonon modes involving
plane and apical oxygen vibrations exhibit pronounced anisotropies with respect
to the incident and scattered light field configurations. Based on a
theoretical model that takes both electronic and phononic contributions to the
Raman spectra into account, we attribute the anisotropy of the
superconductivity-induced changes in the phonon lineshapes to a small s-wave
admixture to the pair wave-function. Our theory allows us to
disentangle the electronic Raman signal from the phononic part and to identify
corresponding interference terms. We argue that the Raman spectra are
consistent with an s-wave admixture with an upper limit of 20 percent.Comment: accepted in Phys. Rev. B, 11 page
Scaling behavior of spin transport in hydrogenated graphene
We calculate the spin transport of hydrogenated graphene using the
Landauer-B\"uttiker formalism with a spin-dependent tight-binding Hamiltonian.
The advantages of using this method is that it simultaneously gives information
on sheet resistance and localization length as well as spin relaxation length.
Furthermore, the Landauer-B\"uttiker formula can be computed very efficiently
using the recursive Green's function technique. Previous theoretical results on
spin relaxation time in hydrogenated graphene have not been in agreement with
experiments. Here, we study magnetic defects in graphene with randomly aligned
magnetic moments, where interference between spin-channels is explicitly
included. We show that the spin relaxation length and sheet resistance scale
nearly linearly with the impurity concentration. Moreover, the spin relaxation
mechanism in hydrogenated graphene is Markovian only near the charge neutrality
point or in the highly dilute impurity limit
Is my ODE a Painleve equation in disguise?
Painleve equations belong to the class y'' + a_1 {y'}^3 + 3 a_2 {y'}^2 + 3
a_3 y' + a_4 = 0, where a_i=a_i(x,y). This class of equations is invariant
under the general point transformation x=Phi(X,Y), y=Psi(X,Y) and it is
therefore very difficult to find out whether two equations in this class are
related. We describe R. Liouville's theory of invariants that can be used to
construct invariant characteristic expressions (syzygies), and in particular
present such a characterization for Painleve equations I-IV.Comment: 8 pages. Based on talks presented at NEEDS 2000, Gokova, Turkey, 29
June - 7 July, 2000, and at the AMS-HKMS joint meeting 13-16 December, 2000.
Submitted to J. Nonlin. Math. Phy
Duration of heart failure and the risk of atrial fibrillation: different mechanisms at different times?
Chronic heart failure increases the risk of atrial fibrillation (AF), with the prevalence of AF paralleling the severity of heart failure.1 Factors that underlie this increased susceptibility to AF may include electrical, structural, and neurohumoral changes.2 In AF, it is recognized that atrial electrophysiological remodelling occurs and contributes to the perpetuation of the arrhythmia, most notably the decrease of effective refractory period (ERP) which predisposes to re-entry by shortening the wavelength. Does heart failure cause similar changes in atrial electrophysiology that predispose to the arrhythmia
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