5,857 research outputs found
Strategy Options for Disaster Risk Reduction Through Institutional Improvements and Enhanced Financial Sustainability: Recommendations
This presentation was commissioned by the Natural Disaster Network of the Regional Policy Dialogue for the V Hemispheric Meeting celebrated on June 13th and 14th, 2005.Disasters, Management Network GestiĂłn de la Red
Anomalies of the infrared-active phonons in underdoped YBCO as an evidence for the intra-bilayer Josephson effect
The spectra of the far-infrared c-axis conductivity of underdoped YBCO
crystals exhibit dramatic changes of some of the phonon peaks when going from
the normal to the superconducting state. We show that the most striking of
these anomalies can be naturally explained by changes of the local fields
acting on the ions arising from the onset of inter- and intra-bilayer Josephson
effects.Comment: Revtex, epsf, 6 pages, 3 figures encapsulated in tex
Fourier multipliers for Triebel-Lizorkin spaces on compact Lie groups
We investigate the boundedness of Fourier multipliers on a compact Lie group when acting on Triebel-Lizorkin spaces. Criteria are given in terms of the H\"ormander-Mihlin-Marcinkiewicz condition. In our analysis, we use the difference structure of the unitary dual of a compact Lie group. Our results cover the sharp H\"ormander-Mihlin theorem on Lebesgue spaces and also other historical results on the subject
Oscillating singular integral operators on compact Lie groups revisited
Fefferman (Acta Math 24:9–36, 1970, Theorem 2′) has proved the weak (1,1) boundedness for a class of oscillating singular integrals that includes the oscillating spectral multipliers of the Euclidean Laplacian Δ , namely, operators of the form Tθ(-Δ):=(1-Δ)-nθ4ei(1-Δ)θ2,0≤θ<1.The aim of this work is to extend Fefferman’s result to oscillating singular integrals on any arbitrary compact Lie group. We also consider applications to oscillating spectral multipliers of the Laplace–Beltrami operator. The proof of our main theorem illustrates the delicate relationship between the condition on the kernel of the operator, its Fourier transform (defined in terms of the representation theory of the group) and the microlocal/geometric properties of the group
Anemia hemolĂtica inmunomediada : caso clĂnico
En el presente artĂculo se describe un caso clĂnico de anemia hemolĂtica inmunomediada, su diagnĂłstico, tratamiento y evoluciĂłn.In this report one cas of inmunomediated haemolytic is described and the diagnostic, therapy and evolution
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
Electron--Electron Scattering in Quantum Wires and it's Possible Suppression due to Spin Effects
A microscopic picture of electron-electron pair scattering in single mode
quantum wires is introduced which includes electron spin. A new source of
`excess' noise for hot carriers is presented. We show that zero magnetic field
`spin' splitting in quantum wires can lead to a dramatic `spin'-subband
dependence of electron--electron scattering, including the possibility of
strong suppression. As a consequence extremely long electron coherence lengths
and new spin-related phenomena are predicted. Since electron bands in III-V
semiconductor quantum wires are in general spin-split in zero applied magnetic
field, these new transport effects are of general importance.Comment: 11 pages, LaTeX and APS-RevteX 2, Rep.No. GF66,Figures from author,
Physical Review Letters, scheduled for 7 June 199
Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry
Modulated electroreflectance spectroscopy of semiconductor
self-assembled quantum dots is investigated. The structure is modeled as dots
with lens shape geometry and circular cross section. A microscopic description
of the electroreflectance spectrum and optical response in terms of an external
electric field () and lens geometry have been considered. The field
and lens symmetry dependence of all experimental parameters involved in the
spectrum have been considered. Using the effective mass formalism
the energies and the electronic states as a function of and dot
parameters are calculated. Also, in the framework of the strongly confined
regime general expressions for the excitonic binding energies are reported.
Optical selection rules are derived in the cases of the light wave vector
perpendicular and parallel to . Detailed calculation of the Seraphin
coefficients and electroreflectance spectrum are performed for the InAs and
CdSe nanostructures. Calculations show good agreement with measurements
recently performed on CdSe/ZnSe when statistical distribution on size is
considered, explaining the main observed characteristic in the
electroreflectance spectra
Electronic, vibrational, and thermodynamic properties of ZnS (zincblende and rocksalt structure)
We have measured the specific heat of zincblende ZnS for several isotopic
compositions and over a broad temperature range (3 to 1100 K). We have compared
these results with calculations based on ab initio electronic band structures,
performed using both LDA and GGA exchange- correlation functionals. We have
compared the lattice dynamics obtained in this manner with experimental data
and have calculated the one-phonon and two-phonon densities of states. We have
also calculated mode Grueneisen parameters at a number of high symmetry points
of the Brillouin zone. The electronic part of our calculations has been used to
investigate the effect of the 3d core electrons of zinc on the spin-orbit
splitting of the top valence bands. The effect of these core electrons on the
band structure of the rock salt modification of ZnS is also discussed.Comment: 33pages, 16 Figures, submitted to Phys. Rev.
Path-integral molecular dynamics simulation of 3C-SiC
Molecular dynamics simulations of 3C-SiC have been performed as a function of
pressure and temperature. These simulations treat both electrons and atomic
nuclei by quantum mechanical methods. While the electronic structure of the
solid is described by an efficient tight-binding Hamiltonian, the nuclei
dynamics is treated by the path integral formulation of statistical mechanics.
To assess the relevance of nuclear quantum effects, the results of quantum
simulations are compared to others where either the Si nuclei, the C nuclei or
both atomic nuclei are treated as classical particles. We find that the
experimental thermal expansion of 3C-SiC is realistically reproduced by our
simulations. The calculated bulk modulus of 3C-SiC and its pressure derivative
at room temperature show also good agreement with the available experimental
data. The effect of the electron-phonon interaction on the direct electronic
gap of 3C-SiC has been calculated as a function of temperature and related to
results obtained for bulk diamond and Si. Comparison to available experimental
data shows satisfactory agreement, although we observe that the employed
tight-binding model tends to overestimate the magnitude of the electron-phonon
interaction. The effect of treating the atomic nuclei as classical particles on
the direct gap of 3C-SiC has been assessed. We find that non-linear quantum
effects related to the atomic masses are particularly relevant at temperatures
below 250 K.Comment: 14 pages, 15 figure
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