10 research outputs found
The Single-Particle Spectral Function of
The influence of short-range correlations on the -wave single-particle
spectral function in is studied as a function of energy. This
influence, which is represented by the admixture of high-momentum components,
is found to be small in the -shell quasihole wave functions. It is therefore
unlikely that studies of quasihole momentum distributions using the
reaction will reveal a significant contribution of high momentum components.
Instead, high-momentum components become increasingly more dominant at higher
excitation energy. The above observations are consistent with the energy
distribution of high-momentum components in nuclear matter.Comment: 5 pages, RevTeX, 3 figure
Momentum Distribution in Nuclear Matter and Finite Nuclei
A simple method is presented to evaluate the effects of short-range
correlations on the momentum distribution of nucleons in nuclear matter within
the framework of the Green's function approach. The method provides a very
efficient representation of the single-particle Green's function for a
correlated system. The reliability of this method is established by comparing
its results to those obtained in more elaborate calculations. The sensitivity
of the momentum distribution on the nucleon-nucleon interaction and the nuclear
density is studied. The momentum distributions of nucleons in finite nuclei are
derived from those in nuclear matter using a local-density approximation. These
results are compared to those obtained directly for light nuclei like .Comment: 17 pages REVTeX, 10 figures ps files adde
Momentum and Energy Distributions of Nucleons in Finite Nuclei due to Short-Range Correlations
The influence of short-range correlations on the momentum and energy
distribution of nucleons in nuclei is evaluated assuming a realistic
meson-exchange potential for the nucleon-nucleon interaction. Using the
Green-function approach the calculations are performed directly for the finite
nucleus O avoiding the local density approximation and its reference to
studies of infinite nuclear matter. The nucleon-nucleon correlations induced by
the short-range and tensor components of the interaction yield an enhancement
of the momentum distribution at high momenta as compared to the Hartree-Fock
description. These high-momentum components should be observed mainly in
nucleon knockout reactions like leaving the final nucleus in a state
of high excitation energy. Our analysis also demonstrates that non-negligible
contributions to the momentum distribution should be found in partial waves
which are unoccupied in the simple shell-model. The treatment of correlations
beyond the Brueckner-Hartree-Fock approximation also yields an improvement for
the calculated ground-state properties.Comment: 12 pages RevTeX, 7 figures postscript files appende
Hole Spectral Function and 2p1h Response Propagator.
The fragmentation of one-nucleon knock-out strength at low energies is considered from the viewpoint of the two particle-one hole (and two hole-one particle) response propagator. The aim is to deal with particle-particle (and hole-hole) as well as particle-hole collectivity simultaneously. This is achieved on a Tamm-Dancoff level by the so-called Faddeev approximation of the 2p1h propagator. Results of this approach illustrate the relevance of this consistent treatment of both particle-particle (hole-hole) and particle-hole collectivity. A further extension, within the framework of 2p1h RPA which was sometimes applied in the past, has serious unsolved problems, some of which are discussed in detail
The changing face of the dodo (Aves: Columbidae:Raphus cucullatus): iconography of the Walghvogel of Mauritius
The dodo (Raphus cucullatus) was a large, flightless pigeon endemic to the island of Mauritius (Indian Ocean). Its unusual appearance was recorded in several 17th-century depictions of live or recently killed birds. It became extinct at the end of the 17th century, and in some subsequent accounts, it was even considered as non-existent. Dodo images became rare from the mid-17th century, but its inclusion in Lewis Carroll’s Alice’s Adventures in Wonderland initiated a change, establishing it as an icon to a much wider public. Since then, illustrations of dodos have been used in all kinds of media, arguably making it the most iconic extinct bird. Here we analyse how the dodo image evolved from 1600 to 2013, using 2D-geometric morphometrics. Our results show that in particular cartoons, animations and logos tend to put an extreme emphasis on the bulging anterior part of the beak, and that the beak is strongly hooked. The variation in dodo images has increased since 1865, culminating in an explosion of shapes during the past decades. The often exaggerated, cartoonesque depiction of the dodo is in line with the long-held but incorrect popular belief that it was a clumsy, tragic bird destined for extinction