45,106 research outputs found
Optical phonons in new ordered perovskite Sr2Cu(Re0.69Ca0.31) Oy system observed by infrared reflectance spectroscopy
We report infrared reflectivity spectra for a new correlated cupric oxide
system Sr2Cu(Re0.69Ca0.31)Oy with y ~ 0.6 at several temperatures ranging
between 8 and 380 K. The reflectivity spectrum at 300 K comprises of several
optical phonons. A couple of residual bands located around 315 and 653 cm-1
exhibit exceptionally large intensity as compared to the other ones. The
overall reflectivity spectrum lifts up slightly with increasing temperature.
The energy and damping factor of transverse-optical phonons are determined by
fitting the imaginary dielectric constant by Lorentz oscillator model and
discussed as a function of temperature in terms of lattice anharmonicity.Comment: 9 pages, 3 figures, presented at ISS2005, to appear in Physica
Laser ignition of an optically sensitised secondary explosive by a diode laser
As a green technology, laser ignition of a relatively insensitive secondary
explosive has been experimentally investigated. The explosive, hexanitrostilbene
(HNS), was doped with one of two optical sensitizers, carbon black or a laser
absorbing dye, and a continuous-wave (CW) infrared diode laser was used as the
igniting source. The ignition sensitivities of HNS with each of the two optical
sensitizers were analysed and compared in terms of: optical power threshold for
ignition, ignition delay and full burn delay at various laser powers. The results
have shown that both the chemical dye and carbon black optically sensitize
the explosive with similar efficiencies. In contrast to the carbon black, the dye
provides wavelength specificity and selectivity in the laser ignition process and its
solubility in some specific solvents improves the coating of the explosive material.
It was therefore concluded that the laser absorbing dye is a better candidate for
optical sensitization in laser ignition than the commonly used carbon black. The
combination of laser ignition sensitivity with wavelength selectivity potentially
offers higher reliability and safety at a low optical power for future ignitors of
secondary explosives
Generalized Parton Distributions from Hadronic Observables
We propose a physically motivated parametrization for the unpolarized
generalized parton distributions, H and E, valid at both zero and non-zero
values of the skewness variable, \zeta. At \zeta=0, H and E are determined
using constraints from simultaneous fits of experimental data on both the
nucleon elastic form factors and the deep inelastic structure functions.
Lattice calculations of the higher moments constrain the parametrization at
\zeta > 0. Our method provides a step towards a model independent extraction of
generalized distributions from the data that is alternative to the mathematical
ansatz of double distributions.Comment: 4 pages, 2 figures, to appear in the proceedings of DIS 200
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