716 research outputs found
Convergence analysis of the scaled boundary finite element method for the Laplace equation
The scaled boundary finite element method (SBFEM) is a relatively recent
boundary element method that allows the approximation of solutions to PDEs
without the need of a fundamental solution. A theoretical framework for the
convergence analysis of SBFEM is proposed here. This is achieved by defining a
space of semi-discrete functions and constructing an interpolation operator
onto this space. We prove error estimates for this interpolation operator and
show that optimal convergence to the solution can be obtained in SBFEM. These
theoretical results are backed by a numerical example.Comment: 15 pages, 3 figure
Proton Electromagnetic Form Factor Ratios at Low Q^2
We study the ratio of the proton at very small
values of . Radii commonly associated with these form factors are not
moments of charge or magnetization densities. We show that the form factor
is correctly interpretable as the two-dimensional Fourier transformation
of a magnetization density. A relationship between the measurable ratio and
moments of true charge and magnetization densities is derived. We find that
existing measurements show that the magnetization density extends further than
the charge density, in contrast with expectations based on the measured
reduction of as increases.Comment: 4 pages 3 figures We have corrected references, figures and some
typographical error
Proton emission induced by polarized photons
The proton emission induced by polarized photons is studied in the energy
range above the giant resonance region and below the pion emission threshold.
Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of
various observables to final state interaction, meson exchange currents and
short range correlations is analyzed. We found relevant effects due to the
virtual excitation of the resonance.Comment: 12 pages, 11 figures, 1 tabl
Transverse momentum dependent parton distributions in a light-cone quark model
The leading twist transverse momentum dependent parton distributions (TMDs)
are studied in a light-cone description of the nucleon where the Fock expansion
is truncated to consider only valence quarks. General analytic expressions are
derived in terms of the six amplitudes needed to describe the three-quark
sector of the nucleon light-cone wave function. Numerical calculations for the
T-even TMDs are presented in a light-cone constituent quark model, and the role
of the so-called pretzelosity is investigated to produce a nonspherical shape
of the nucleon.Comment: references added and typos corrected; version to appear in Phys. Rev.
Measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons using recoil polarization in parallel kinematics
We propose a new method for measuring longitudinal amplitudes for
electroproduction of pseudoscalar mesons that exploits a symmetry relation for
polarization observables in parallel kinematics. This polarization technique
does not require variation of electron scattering kinematics and avoids the
major sources of systematic errors in Rosenbluth separation.Comment: intended for Phys. Rev. C as a Brief Repor
Many-body effects in 16O(e,e'p)
Effects of nucleon-nucleon correlations on exclusive reactions on
closed-shell nuclei leading to single-hole states are studied using
( MeV, ) as an example. The quasi-hole wave
function, calculated from the overlap of translationally invariant many-body
variational wave functions containing realistic spatial, spin and isospin
correlations, seems to describe the initial state of the struck proton
accurately inside the nucleus, however it is too large at the surface. The
effect of short-range correlations on the final state is found to be largely
cancelled by the increase in the transparency for the struck proton. It is
estimated that the values of the spectroscopic factors obtained with the DWIA
may increase by a few percent due to correlation effects in the final state.Comment: 21 Pages, PHY-7849-TH-9
Temporary employment of first-generation migrants in the Netherlands
Hervorming Sociale Regelgevin
Formation of quark phases in compact stars and SN explosion
We describe possible scenarios of quark deconfinement in compact stars and we
analyze their astrophysical implications. The quark deconfinement process can
proceed rapidly, as a strong deflagration, releasing a huge amount of energy in
a short time and generating an extra neutrino burst. If energy is transferred
efficiently to the surface, like e.g. in the presence of convective
instabilities, this burst could contribute to revitalize a partially failed SN
explosion. We discuss how the neutrino observations from SN1987A would fit in
this scenario. Finally, we focus on the fate of massive and rapidly rotating
progenitors, discussing possible time separations between the moment of the
core collapse and the moment of quark deconfinement. This mechanism can be at
the basis of the interpretation of gamma ray bursts in which lines associated
with heavy elements are present in the spectrum.Comment: 9 pages, 3 figures, Proceedings "6th International Conference on
Perspectives in Hadronic Physics", May 2008, Triest
Momentum distributions and spectroscopic factors of doubly-closed shell nuclei in correlated basis function theory
The momentum distributions, natural orbits, spectroscopic factors and
quasi-hole
wave functions of the C12, O16, Ca40, Ca48, and Pb208 doubly closed shell
nuclei, have been calculated in the framework of the Correlated Basis Function
theory, by using the Fermi hypernetted chain resummation techniques. The
calculations have been done by using the realistic Argonne v8' nucleon-nucleon
potential, together with the Urbana IX three-body interaction. Operator
dependent correlations, which consider channels up to the tensor ones, have
been
used. We found noticeable effects produced by the correlations. For high
momentum values, the momentum distributions show large enhancements with
respect to the independent particle model results. Natural orbits occupation
numbers are depleted by about the 10\% with respect to the independent particle
model values. The effects of the correlations on the spectroscopic factors are
larger on the more deeply bound states.Comment: Modified version of the previous paper (there are new figures). The
paper has been accepted for publication in Physical Review
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