2,748 research outputs found
The Ellis semigroup of a nonautonomous discrete dynamical system
We introduce the {\it Ellis semigroup} of a nonautonomous discrete dynamical
system when is a metric compact space. The underlying
set of this semigroup is the pointwise closure of \{f\sp{n}_1 \, |\, n\in
\mathbb{N}\} in the space X\sp{X}.
By using the convergence of a sequence of points with respect to an
ultrafilter it is possible to give a precise description of the semigroup and
its operation. This notion extends the classical Ellis semigroup of a discrete
dynamical system. We show several properties that connect this semigroup and
the topological properties of the nonautonomous discrete dynamical system
Pion cloud effects on baryon masses
In this work we explore the effect of pion cloud contributions to the mass of
the nucleon and the delta baryon. To this end we solve a coupled system of
Dyson-Schwinger equations for the quark propagator, a Bethe-Salpeter equation
for the pion and a three-body Faddeev equation for the baryons. In the
quark-gluon interaction we explicitly resolve the term responsible for the
back-coupling of the pion onto the quark, representing rainbow-ladder like pion
cloud effects in bound states. We study the dependence of the resulting baryon
masses on the current quark mass and discuss the internal structure of the
baryons in terms of a partial wave decomposition. We furthermore determine
values for the nucleon and delta sigma-terms.Comment: 9 pages, 4 figures, 2 tables. v2: Numerics corrected; results
updated; discussion extended. Version accepted for publication in Phys.Lett.
Beyond Rainbow-Ladder in a covariant three-body Bethe-Salpeter approach: Baryons
We report on recent results of a calculation of the nucleon and delta masses
in a covariant bound-state approach, where to the simple rainbow-ladder
gluon-exchange interaction kernel we add a pion-exchange contribution to
account for pion cloud effects. We observe good agreement with lattice data at
large pion masses. At the physical point our masses are too large by about five
percent, signaling the need for more structure in the gluon part of the
interaction.Comment: 4 pages, 3 figures, Proceedings of The 13th International Conference
on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2013), Rom
Development and initial validation of a sensory threshold examination protocol (STEP) for phenotyping canine pain syndromes
Objective
To study feasibility and test-retest repeatability of a sensory threshold examination protocol (STEP) and report quantitative sensory threshold distributions in healthy dogs.
Study design
Prospective, observational, cohort study.
Animals
Twenty-five healthy client-owned dogs.
Methods
Tactile sensitivity (TST) (von Frey filaments), mechanical thresholds (MT with 2, 4 and 8 mm probes), heat thresholds (HT) and responsiveness to cold stimulus (CT at 0 °C) were quantitatively assessed for five body areas (BA: tibias, humeri, neck, thoracolumbar region and abdomen) in a randomized order on three different occasions. Linear Mixed Model and Generalised Linear Mixed models were used to evaluate the effects of body weight category, age, sex, BA, occasion, feasibility score and investigator experience. Test-retest repeatability was evaluated with the Intra-class Correlation Coefficient (ICC).
Results
The STEP lasted 90 minutes without side effects. The BA affected most tests (p = 0.001). Higher thresholds and longer cold latencies were scored in the neck (p = 0.024) compared to other BAs. Weight category affected all thresholds (p = 0.037). Small dogs had lower MT (~1.4 N mean difference) and HT (1.1 0C mean difference) than other dogs (p = 0.029). Young dogs had higher HT than adults (2.2 0C mean difference) (p = 0.035). Gender also affected TST, MT and HT (p < 0.05) (females versus males: TST OR= 0.5, MT= 1.3 N mean difference, HT= 2.2 0C mean difference). Repeatability was substantial to moderate for all tests, but poor for TST. There was no difference in thresholds between occasions, except for CT. Test-retest repeatability was slightly better with the 2 mm MT probe compared to other diameters and improved with operator experience.
Conclusions
and clinical relevance The STEP was feasible, well tolerated and showed substantial test-retest repeatability in healthy dogs. Further validation is needed in dogs suffering pain
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