65,362 research outputs found
Average-Atom Model for X-ray Scattering from Warm Dense Matter
A scheme for analyzing Thomson scattering of x-rays by warm dense matter,
based on the average-atom model, is developed. Emphasis is given to x-ray
scattering by bound electrons. Contributions to the scattered x-ray spectrum
from elastic scattering by electrons moving with the ions and from inelastic
scattering by free and bound electrons are evaluated using parameters (chemical
potential, average ionic charge, free electron density, bound and continuum
wave functions, and occupation numbers) taken from the average-atom model. The
resulting scheme provides a relatively simple diagnostic for use in connection
with x-ray scattering measurements. Applications are given to dense hydrogen,
beryllium, aluminum, titanium, and tin plasmas. At high momentum transfer,
contributions from inelastic scattering by bound electrons are dominant
features of the scattered x-ray spectrum for aluminum, titanium, and tin.Comment: 22 pages, 10 figures Presentation at Workshop IV: Computational
Challenges in Warm Dense Matter at IPAM (UCLA) May 21 - 25, 201
Using the X-FEL to understand X-ray Thomson scattering for partially ionized plasmas
For the last decade numerous researchers have been trying to develop
experimental techniques to use X-ray Thomson scattering as a method to measure
the temperature, electron density, and ionization state of high energy density
plasmas such as those used in inertial confinement fusion. With the advent of
the X-ray free electron laser (X-FEL) at the SLAC Linac Coherent Light Source
(LCLS) we now have such a source available in the keV regime. One challenge
with X-ray Thomson scattering experiments is understanding how to model the
scattering for partially ionized plasmas. Most Thomson scattering codes used to
model experimental data greatly simplify or neglect the contributions of the
bound electrons to the scattered intensity. In this work we take the existing
models of Thomson scattering that include elastic ion-ion scattering and the
electron-electron plasmon scattering and add the contribution of the bound
electrons in the partially ionized plasmas. Except for hydrogen plasmas almost
every plasma that is studied today has bound electrons and it is important to
understand their contribution to the Thomson scattering, especially as new
X-ray sources such as the X-FEL will allow us to study much higher Z plasmas.
Currently most experiments have looked at hydrogen or beryllium. We will first
look at the bound electron contributions to beryllium by analysing existing
experimental data. We then consider several higher Z materials such as Cr and
predict the existence of additional peaks in the scattering spectrum that
requires new computational tools to understand. For a Sn plasma we show that
the bound contributions changes the shape of the scattered spectrum in a way
that would change the plasma temperature and density inferred by the
experiment.Comment: 13th International Conference on X-ray Lasers Paris, France June 10,
2012 through June 15, 201
Perfluoro (Imidoylamidine) diamidines
Perfluoroether triazine elastomers having improved properties are prepared from oligomeric imidoylamidines that were in turn, prepared by the process of: (1) reacting a perfluorodinitrile with liquid ammonia to yield a perfluorodiamidine, (2) isolating the perfluorodiamidine, (3) reacting the isolated diamidine with a perfluorodinitrile to yield a perfluoro(imidoylamidine) dinitrile, and then repeating the steps to sequentially grow an oligomer of desired molecular size. The isolated amidine and nitrile intermediates are also disclosed. The elastomers can be fashioned into seals, gaskets, and sealing components and the like
Process for preparing perfluorotriazine elastomers and precursors thereof
Perfluoroether triazine elastomers having improved properties and utility in seals, gaskets, sealing components and the like are prepared from oligomeric imidoylamidines that have, in turn, been prepared by the process of (1) reacting a perfluorodinitrile with liquid ammonia to yield a perfluorodiamidine, (2) isolating the perfluorodiamidine, (3) reacting the isolated diamidine with a perfluorodinitrile to yield a perfluoror(imidoylamidine) dinitrile, and then repeating step (1), (2), and (3) to sequentially grow an oligomer of desired molecular size. The isolated amidine and nitrile intermediates are also described
Local Density of States and Angle-Resolved Photoemission Spectral Function of an Inhomogeneous D-wave Superconductor
Nanoscale inhomogeneity seems to be a central feature of the d-wave
superconductivity in the cuprates. Such a feature can strongly affect the local
density of states (LDOS) and the spectral weight functions. Within the
Bogoliubov-de Gennes formalism we examine various inhomogeneous configurations
of the superconducting order parameter to see which ones better agree with the
experimental data. Nanoscale large amplitude oscillations in the order
parameter seem to fit the LDOS data for the underdoped cuprates. The
one-particle spectral function for a general inhomogeneous configuration
exhibits a coherent peak in the nodal direction. In contrast, the spectral
function in the antinodal region is easily rendered incoherent by the
inhomogeneity. This throws new light on the dichotomy between the nodal and
antinodal quasiparticles in the underdoped cuprates.Comment: 5 pages, 9 pictures. Phys. Rev. B (in press
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