952 research outputs found
Optical Constants of Magnesium Oxide in the Far Ultraviolet
Optical constants of magnesium oxide in far ultraviole
Optical Constants of Lithium Fluoride in the Far Ultraviolet
Optical constants of lithium fluoride in far ultraviole
Dynamical excitonic effects in metals and semiconductors
The dynamics of an electron--hole pair induced by the time--dependent
screened Coulomb interaction is discussed. In contrast to the case where the
static electron--hole interaction is considered we demonstrate the occurrence
of important dynamical excitonic effects in the solution of the Bethe--Salpeter
equation.This is illustrated in the calculated absorption spectra of noble
metals (copper and silver) and silicon. Dynamical corrections strongly affect
the spectra, partially canceling dynamical self--energy effects and leading to
good agreement with experiment.Comment: Accepted for publication on Phys. Rev. Let
Rapid characterisation of large earthquakes by multiple seismic broadband arrays
An automatic procedure is presented to retrieve rupture parameters for large earthquakes along the Sunda arc subduction zone. The method is based on standard array analysis and broadband seismograms registered within 30°–100° epicentral distance. No assumptions on source mechanism are required. By means of semblance the coherency of <i>P</i> waveforms is analysed at separate large-aperture arrays. Waveforms are migrated to a 10°&times;10° wide source region to study the spatio-temporal evolution of earthquakes at each array. The multiplication of the semblance source maps resulting at each array increases resolution. Start, duration, extent, direction, and propagation velocity are obtained and published within 25 min after the onset of the event. First preliminary results can be obtained even within 16 min. Their rapid determination may improve the mitigation of the earthquake and tsunami hazard. Real-time application will provide rupture parameters to the GITEWS project (German Indonesian Tsunami Early Warning System). The method is applied to the two <i>M</i>8.0 Sumatra earthquakes on 12 September 2007, to the <i>M</i>7.4 Java earthquake on 2 September 2009, and to major subduction earthquakes that have occurred along Sumatra and Java since 2000. Obtained rupture parameters are most robust for the largest earthquakes with magnitudes <i>M</i>&ge;8. The results indicate that almost the entire seismogenic part of the subduction zone off the coast of Sumatra has been ruptured. Only the great Sumatra event in 2004 and the <i>M</i>7.7 Java event on 17 July 2006 could reach to or close to the surface at the trench. Otherwise, the rupturing was apparently confined to depths below 25 km. Major seismic gaps seem to remain off the coast of Padang and the southern tip of Sumatra
Critical properties of the double exchange ferromagnet Nd0.4Pb0.4MnO3
Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3
single crystal in the temperature range around T_C (Curie temperature) which
embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported.
The magnetic data analyzed in the critical region using the Kouvel-Fisher
method give the values for the T_C =156.47 +/- 0.06 K and the critical
exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of
magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of
initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547
+/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical
exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b
f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The
exponent values are very close to those expected for the universality class of
3D Heisenberg ferromagnets with short-range interactions.Comment: 19 pages, including 6 figure
Spin relaxation times of 2D holes from spin sensitive bleaching of inter-subband absorption
We present spin relaxation times of 2D holes obtained by means of spin
sensitive bleaching of the absorption of infrared radiation in p-type
GaAs/AlGaAs quantum wells (QWs). It is shown that the saturation of
inter-subband absorption of circularly polarized radiation is mainly controlled
by the spin relaxation time of the holes. The saturation behavior has been
determined for different QW widths and in a wide temperature range with the
result that the saturation intensity substantially decreases with narrowing of
the QWs. Spin relaxation times are derived from the measured saturation
intensities by making use of calculated (linear) absorption coefficients for
direct inter-subband transitions. It is shown that spin relaxation is due to
the D'yakonov-Perel' mechanism governed by hole-hole scattering. The problem of
selection rules is addressed.Comment: 14 pages, 5 figure
Effect of varying material anisotropy on critical current anistropy in vicinal YBaCuO thin films
The high cuprate superconductors are noted for their anisotropic
layered structure, certain of these materials indeed tend toward the limit of a
Lawrence-Doniach superconductor. However, YBaCuO has a
smaller anisotropy than would be expected from its interlayer spacing. This is
due to the cuprate chains in the structure. To investigate the influence of the
chain oxygen on transport properties critical current versus applied field
angle measurements were performed on fully oxygenated and de-oxygenated
YBaCuO thin films and optimally oxygenated
YCaBaCuO thin films. The films were grown
on 10 mis-cut SrTiO substrates to enable the intrinsic vortex
channelling effect to be observed. The form of the vortex channelling minimum
observed in field angle dependent critical current studies on the films was
seen to depend on film oxygenation. The vortex channelling effect is dependent
on a angular dependent cross-over to a string-pancake flux line lattice. The
results obtained appear to be consistent with the prediction of Blatter et al.
[Rev. Mod. Phys., 66 (4): 1125 (1994)] that increased superconducting
anisotropy leads to the kinked string-pancake lattice existing over a smaller
angular range.Comment: To be submitted to AP
The silence of self-knowledge
Gareth Evans famously affirmed an explanatory connection between answering the question whether p and knowing whether one believes that p. This is commonly interpreted in terms of the idea that judging that p constitutes an adequate basis for the belief that one believes that p. This paper formulates and defends an alternative, more modest interpretation, which develops from the suggestion that one can know that one believes that p in judging that p
Electronic Structure and Lattice Relaxation Related to Fe in Mgo
The electronic structure of Fe impurity in MgO was calculated by the linear
muffin-tin orbital--full-potential method within the conventional local-density
approximation (LDA) and making use of the LDA+ formalism. The importance of
introducing different potentials, depending on the screened Coulomb integral
, is emphasized for obtaining a physically reasonable ground state of the
Fe ion configuration. The symmetry lowering of the ion electrostatic
field leads to the observed Jahn--Teller effect; related ligand relaxation
confined to tetragonal symmetry has been optimized based on the full-potential
total energy results. The electronic structure of the Fe ion is also
calculated and compared with that of Fe.Comment: 13 pages + 4 PostScript figures, Revtex 3.0, SISSA-CM-94-00
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