43,371 research outputs found
Cities in fiction: Perambulations with John Berger
This paper explores selected novels by John Berger in which cities play a central role. These cities are places, partially real and partially imagined, where memory, hope, and despair intersect. My reading of the novels enables me to trace important themes in recent discourses on the nature of contemporary capitalism, including notions of resistance and universality. I also show how Berger?s work points to a writing that can break free from the curious capacity of capitalism to absorb and feed of its critique
Microscopic Determinations of Fission Barriers, (MEAN-Field and Beyond)
With a help of the selfconsistent Hartree-Fock-Bogoliubov (HFB) approach with
the D1S effective Gogny interaction and the Generator Coordinate Method (GCM)
we incorporate the transverse collective vibrations to the one-dimensional
model of the fission-barrier penetrability based on the traditional WKB method.
The average fission barrier corresponding to the least-energy path in the
two-dimensional potential energy landscape as function of quadrupole and
octupole degrees of freedom is modified by the influence of the transverse
collective vibrations along the nuclear path to fission. The set of transverse
vibrational states built in the fission valley corresponding to a successively
increasing nuclear elongation produces the new energy barrier which is compared
with the least-energy barrier. These collective states are given as the
eigensolutions of the GCM purely vibrational Hamiltonian. In addition, the
influence of the collective inertia on the fission properties is displayed, and
it turns out to be the decisive condition for the possible transitions between
different fission valleys.Comment: 12 pages, 5 figures, presented at XIII Workshop of Nuclear Physics,
Kazimierz Dolny, 2006 (Poland
Recursive Construction of Higgs-Plus-Multiparton Loop Amplitudes: The Last of the Phi-nite Loop Amplitudes
We consider a scalar field, such as the Higgs boson H, coupled to gluons via
the effective operator H tr G_{mu nu} G^{mu nu} induced by a heavy-quark loop.
We treat H as the real part of a complex field phi which couples to the
self-dual part of the gluon field-strength, via the operator phi tr G_{SD mu
nu} G_{SD}^{mu nu}, whereas the conjugate field phi^dagger couples to the
anti-self-dual part. There are three infinite sequences of amplitudes coupling
phi to quarks and gluons that vanish at tree level, and hence are finite at one
loop, in the QCD coupling. Using on-shell recursion relations, we find compact
expressions for these three sequences of amplitudes and discuss their analytic
properties.Comment: 63 pages, 7 figures; v2 references added; v3 minor typos corrected
and note added; v4 fixed error in eq. (7.11) (lower limit of sum should be
l=2, not l=3), also affecting eqs. (7.14), (8.20), (8.21), (8.27) and (8.28
Two-particle spatial correlations in superfluid nuclei
We discuss the effect of pairing on two-neutron space correlations in
deformed nuclei. The spatial correlations are described by the pairing tensor
in coordinate space calculated in the HFB approach. The calculations are done
using the D1S Gogny force. We show that the pairing tensor has a rather small
extension in the relative coordinate, a feature observed earlier in spherical
nuclei. It is pointed out that in deformed nuclei the coherence length
corresponding to the pairing tensor has a pattern similar to what we have found
previously in spherical nuclei, i.e., it is maximal in the interior of the
nucleus and then it is decreasing rather fast in the surface region where it
reaches a minimal value of about 2 fm. This minimal value of the coherence
length in the surface is essentially determined by the finite size properties
of single-particle states in the vicinity of the chemical potential and has
little to do with enhanced pairing correlations in the nuclear surface. It is
shown that in nuclei the coherence length is not a good indicator of the
intensity of pairing correlations. This feature is contrasted with the
situation in infinite matter.Comment: 14 pages, 17 figures, submitted to PR
Description of nuclear systems with a self-consistent configuration-mixing approach. I: Theory, algorithm, and application to the C test nucleus
Although self-consistent multi-configuration methods have been used for
decades to address the description of atomic and molecular many-body systems,
only a few trials have been made in the context of nuclear structure. This work
aims at the development of such an approach to describe in a unified way
various types of correlations in nuclei, in a self-consistent manner where the
mean-field is improved as correlations are introduced. The goal is to reconcile
the usually set apart Shell-Model and Self-Consistent Mean-Field methods. This
approach is referred as "variational multiparticle-multihole configuration
mixing method". It is based on a double variational principle which yields a
set of two coupled equations that determine at the same time the expansion
coefficients of the many-body wave function and the single particle states. The
formalism is derived and discussed in a general context, starting from a
three-body Hamiltonian. Links to existing many-body techniques such as the
formalism of Green's functions are established. First applications are done
using the two-body D1S Gogny effective force. The numerical procedure is tested
on the C nucleus in order to study the convergence features of the
algorithm in different contexts. Ground state properties as well as
single-particle quantities are analyzed, and the description of the first
state is examined. This study allows to validate our numerical algorithm and
leads to encouraging results. In order to test the method further, we will
realize in the second article of this series, a systematic description of more
nuclei and observables obtained by applying the newly-developed numerical
procedure with the same Gogny force. As raised in the present work,
applications of the variational multiparticle-multihole configuration mixing
method will however ultimately require the use of an extended and more
constrained Gogny force.Comment: 22 pages, 18 figures, accepted for publication in Phys. Rev. C. v2:
minor corrections and references adde
Convergence of Particle-Hole Expansions for the Description of Nuclear Correlations
The convergence properties of a multiparticle-multihole (mp-mh) configuration
mixing approach whose purpose is to describe ground state correlations in
nuclei without particle number and Pauli violations is investigated in the case
of an exactly solvable pairing hamiltonian. Two different truncation schemes
are tested by looking at quantities as correlation energies and single-particle
occupation probabilities. Results show that pairing correlations present in
usual superfluid nuclei can be accurately described using up to 6 particle-6
hole excitations, a convergence fast enought for envisaging extensions to fully
microscopic calculations.Comment: 8 pages, 4 figure
- …