33,069 research outputs found
Approximate Coulomb distortion effects in (e,e'p) reactions
In this paper we apply a well-tested approximation of electron Coulomb
distortion effects to the exclusive reaction (e,e'p) in the quasielastic
region. We compare the approximate treatment of Coulomb distortion effects to
the exact distorted wave Born approximation evaluated by means of partial wave
analysis to gauge the quality of our approximate treatment. We show that the
approximate M\"oller potential has a plane-wave-like structure and hence
permits the separation of the cross section into five terms which depend on
bilinear products of transforms of the transition four current elements. These
transforms reduce to Fourier transforms when Coulomb distortion is not present,
but become modified with the inclusion of Coulomb distortion. We investigate
the application of the approximate formalism to a model of 208Pb(e,e'p) using
Dirac-Hartree single particle wave functions for the ground state and
relativistic optical model wave functions for the continuum proton. We show
that it is still possible to extract, albeit with some approximation, the
various structure functions from the experimentally measured data even for
heavy nuclei.Comment: 32 pages, 11 figures, 19 reference
Extraction of Structure Functions from Quasielastic Electron Scattering (e,e') from Medium and Heavy Nuclei
Using a relativistic mean-field single particle knock-out model for (e,e')
reactions on nuclei, we investigate approximate treatments of Coulomb
distortion effects and the extraction of longitudinal and transverse structure
functions. We show that an effective momentum approximation (EMA) when coupled
with a focusing factor provides a good description of the transverse
contributions to the (e,e') cross sections for electron energies above 300 MeV
on 208Pb. This approximation is not as good for the longitudinal contributions
even for incident electron eneriges above 1 GeV and if one requires very
precise extraction of longitudinal and transverse structure functions in the
quasielastic region it is necessary to utilize distortion factors based on a
nuclear model and a more accurate inclusion of Coulomb distortion effects.Comment: 5 pages, 7 figures, submitted to Phys. Rev.
Coulomb Distortion Effects for Electron or Positron Induced Reactions in the Quasielastic Region
In response to recent experimental studies we investigate Coulomb distortion
effects on reactions from medium and heavy nuclei for the case of
electrons and positrons. We extend our previously reported full DWBA treatment
of Coulomb distortions to the case of positrons for the
reaction in the quasielastic region for a particular nuclear model. In
addition, we use previously reported successful approaches to treating Coulomb
corrections in an approximate way to calculate the Coulomb distortion effects
for reactions for both electrons and positrons for the case of a
simple nuclear model for quasielastic knock-out of nucleons. With these results
in hand we develop a simple {\em ad-hoc} approximation for use in analyzing
experiments, and discuss methods of extracting the ``longitudinal structure
function" which enters into evaluation of the Coulomb sum rule. These
techniques are generally valid for lepton induced reactions on nuclei with
momentum transfers greater than approximately 300 .Comment: 18 pages, 6 figure
y-scaling in Quasielastic Electron Scattering from Nuclei
A relativistic single particle model is used to calculate the inclusive
reaction from 12, 40, 56, 197, and 208 nuclei in the quasielastic
region. We have shown that this model provides a very good description of the
available experimental cross sections when they are dominated by the
quasielastic process. In this paper we use this model to investigate the
dependence of -scaling on electron kinematics, particularly the electron
scattering angle, for a range of squared four momentum transfer
(GeV/c). In this kinematic domain, Coulomb distortion of the electron does
not significantly affect scaling, but final state interactions of the knocked
out nucleon do affect scaling particularly when the nucleons have lower
energies. In general, we find that scaling works for this reaction, but at
lower values of the four momentum transfer, the scaling function does have some
dependence on the electron scattering angle. We also consider a modification of
y-scaling to include small binding energy effects as a function of Z and A and
show that there is some improvement in scaling.Comment: 21 pages, 11 figure
A Compendium of Core Lexicon Checklists
Core Lexicon (CoreLex) is a relatively new approach assessing lexical use in discourse. CoreLex examines the specific lexical items used to tell a story, or how typical lexical items are compared with a normative sample. This method has great potential for clinical utilization because CoreLex measures are fast, easy to administer, and correlate with microlinguistic and macrolinguistic discourse measures. The purpose of this article is to provide clinicians with a centralized resource for currently available CoreLex checklists, including information regarding development, norms, and guidelines for use
Macroeconomic impacts of demographic change in Scotland : a computable general equilibrium analysis
This paper combines a multi-period economic Computable General Equilibrium (CGE) modelling framework with a demographic model to analyse the macroeconomic impact of the projected demographic trends in Scotland. Demographic trends are defined by the existing fertility-mortality rates and the level of annual net-migration. We employ a combination of a demographic and a CGE simulation to track the impact of changes in demographic structure upon macroeconomic variables under different scenarios for annual migration. We find that positive net migration can cancel the expected negative impact upon the labour market of other demographic changes. (Pressure on wages, falling employment). However, the required size of the annual net-migration is far higher than the current trends. The policy implication suggested by the results is that active policies are needed to attract migrants. We nevertheless report results when varying fertility and mortality assumptions. The impact of varying those assumptions is rather small
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