980 research outputs found
Equilibration within a semiclassical off-shell transport approach
Equilibration times for nuclear matter configurations -- modelling
intermediate and high energy nucleus-nucleus collisions -- are evaluated within
the semiclassical off-shell transport approach developed recently. The
transport equations are solved for a finite box in coordinate space employing
periodic boundary conditions. The off-shell transport model is shown to give
proper off-shell equilibrium distributions in the limit for the
nucleon and -resonance spectral functions. We find that equilibration
times within the off-shell approach are only slightly enhanced as compared to
the on-shell limit for the momentum configurations considered.Comment: 19 pages, LaTeX, including 4 postscript figures, submitted to Nucl.
Phys.
Scattering of Two Spinless Particles in 3D Formulation with Coulomb Admixtures
Scattering of two spinless charge particles for simple forces including
coulomb admixtures is calculated without partial wave decomposition. The
coulomb interaction being taken is of the type of screened coulomb potential.
For the forces range are not infinite, the standard scattering theory is
applied. The differential and total cross section is calculated and coulomb
effects are shown.Comment: 4 pages, 2 figure
Electromagnetic break-up of nuclei with A = 3 - 7
This talk contains a short review of some of the progresses made in the last
three years in the calculations of electromagnetic cross sections of light
nuclei up to A=7. Since many of them have been possible thanks to the use of
the Lorentz Integral Transform (LIT) method, both for inclusive and exclusive
reactions, I will first make a few remarks on the method, stressing its
essential points and then show results for different nuclei. One of the
interesting outcomes is e.g. the appearing of typical collective motion
features from ab initio six-body calculations. When a comparison with available
experimental data is attempted, it is rather disappointing to realize that
low-energy data are old, incomplete and not accurate enough to disantangle
interesting effects, showing the need of a major experimental program in this
direction, together with more theoretical efforts to implement modern realistic
forces in continuum calculations of systems.Comment: 4 pages, 7 figures, invited talk at the FB17 - Durham (N.C) June 5-10
200
Low-momentum effective theory for nucleons
Starting from a precise two-nucleon potential, we use the method of unitary
transformations to construct an effective potential that involves only momenta
less than a given maximal value. We describe this method for an S-wave
potential of the Malfliet-Tjon type. It is demonstrated that the bound and
scattering state spectrum calculated within the effective theory agrees exactly
with the one based on the original potential. This might open an avenue for the
construction of effective chiral few-nucleon forces and for a systematic
treatment of relativistic effects in few-body systems.Comment: 10 pp, LaTeX file, 4 figures (uses epsf), extended version, accepted
for publiaction in Phys.Lett.
Does conservative treatment change the brain in patients with chronic musculoskeletal pain? : a systematic review
Background: Chronic musculoskeletal pain is characterized by maladaptive central neuroplastic changes. Many observational studies have demonstrated that chronic pain states are associated with brain alterations regarding structure and/or function. Rehabilitation of patients with chronic musculoskeletal pain may include cognitive, exercise, or multimodal therapies.
Objective: The current review aims to provide a constructive overview of the existing literature reporting neural correlates, based on brain magnetic resonance imaging (MRI) techniques, following conservative treatment in chronic musculoskeletal pain patients.
Study Design: Systematic review of the literature.
Methods: The current review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Literature was searched from 3 databases and screened for eligibility. Methodological quality across studies was assessed with Cochrane Collaboration's tool for assessing risk of bias and quality of evidence was determined applying the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach.
Results: A total of 9 eligible studies were identified with a predominant high risk of bias. Cognitive behavioral therapy induced several structural and functional changes predominantly in prefrontal cortical regions and a shift from affective to sensory-discriminative brain activity after behavioral extinction training. Multidisciplinary treatment in pediatric complex regional pain syndrome facilitated normalization of functional connectivity of resting-state networks and the amygdala, and increased gray matter in prefrontal and specific subcortical areas. Exercise therapy led to specific for resting-state functional connectivity and a trend towards pressure-induced brain activity changes.
Limitations: A very small number of studies was available, which furthermore exhibited small study samples. Moreover, only 2 of the included studies were randomized controlled trials.
Conclusions: It is likely that conservative treatments may induce mainly functional and structural brain changes in prefrontal regions in patients with chronic musculoskeletal pain. Due to the relatively high risk of bias across the included studies, future studies with randomized designs are needed to confirm the current findings. In addition, more research evaluating
Correlations and Equilibration in Relativistic Quantum Systems
In this article we study the time evolution of an interacting field
theoretical system, i.e. \phi^4-field theory in 2+1 space-time dimensions, on
the basis of the Kadanoff-Baym equations for a spatially homogeneous system
including the self-consistent tadpole and sunset self-energies. We find that
equilibration is achieved only by inclusion of the sunset self-energy.
Simultaneously, the time evolution of the scalar particle spectral function is
studied for various initial states. We also compare associated solutions of the
corresponding Boltzmann equation to the full Kadanoff-Baym theory. This
comparison shows that a consistent inclusion of the spectral function has a
significant impact on the equilibration rates only if the width of the spectral
function becomes larger than 1/3 of the particle mass. Furthermore, based on
these findings, the conventional transport of particles in the on-shell
quasiparticle limit is extended to particles of finite life time by means of a
dynamical spectral function A(X,\vec{p},M^2). The off-shell propagation is
implemented in the Hadron-String-Dynamics (HSD) transport code and applied to
the dynamics of nucleus-nucleus collisions.Comment: 20 pages, 7 figures to appear in "Nonequilibrium at short time scales
- Formation of correlations", edited by K. Morawetz, Springer, Berlin (2003),
p16
Solutions of the Wick-Cutkosky model in the Light-Front Dynamics
We study relativistic effects in a system of two scalar particles interacting
via a scalar exchange in the Light Front Dynamcis framework. The results are
compared to those provided by Bethe-Salpeter and non relativistic equations. It
is found in particular that for massive exchange, the relativistic description
is of crucial importance even in the limit of zero binding energy.
PACS: 11.10, 03.70, 03.65P Keywords: Light-Front Dynamics, Relativistic
equations, Quantum Field TheoryComment: 12 pages, 11 figures, Latex.tar.gz file Accepted in Phys. Lett.
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