12,858 research outputs found
On the structure of the scalar mesons and
We investigate the structure of the scalar mesons and
within realistic meson-exchange models of the and
interactions. Starting from a modified version of the J\"ulich model for
scattering we perform an analysis of the pole structure of the
resulting scattering amplitude and find, in contrast to existing models, a
somewhat large mass for the ( MeV,
MeV). It is shown that our model provides a description of
data comparable in quality with those of
alternative models. Furthermore, the formalism developed for the
system is consistently extended to the interaction leading to a
description of the as a dynamically generated threshold effect
(which is therefore neither a conventional state nor a
bound state). Exploring the corresponding pole position the
is found to be rather broad ( MeV,
MeV). The experimentally observed smaller width results from the influence of
the nearby threshold on this pole.Comment: 25 pages, 15 Postscript figure
The use of preferred social stimuli as rewards for rhesus macaques in behavioural neuroscience
Macaques are often motivated to perform in neuroscientific experiments by implementing fluid restriction protocols. Daily access to water is controlled and the monkeys are rewarded with droplets of fluid for performing correct trials in the laboratory. Although these protocols are widely used and highly effective, it is important from a 3Rs perspective to investigate refinements that may help to lessen the severity of the fluid restriction applied. We assessed the use of social stimuli (images of conspecifics) as rewards for four rhesus macaques performing simple cognitive tasks. We found that individual preferences for images of male faces, female perinea and control stimuli could be identified in each monkey. However, using preferred images did not translate into effective motivators on a trial-by-trial basis: animals preferred fluid rewards, even when fluid restriction was relaxed. There was no difference in the monkeysâ performance of a task when using greyscale versus colour images. Based on our findings, we cannot recommend the use of social stimuli, in this form, as a refinement to current fluid restriction protocols. We discuss the potential alternatives and possibilities for future research
Direct measurements of the polarization of terrestrial kilometric radiation from Voyagers 1 and 2
Terrestrial radiation measurements obtained with planetary radio astronomy experiments on Voyager-1 and 2 during the early portions of each flight show the signals to be predominantly left-hand circularly polarized. Since these emissions were most probably generated above the Northern Hemisphere auroral zone, it is concluded that the radiation is emitted primarily in the extraordinary mode
Simulation of associative learning with the replaced elements model
Associative learning theories can be categorised according to whether they treat the representation of stimulus compounds in an elemental or configural manner. Since it is clear that a simple elemental approach to stimulus representation is inadequate there have been several attempts to produce more elaborate elemental models. One recent approach, the Replaced Elements Model (Wagner, 2003), reproduces many results that have until recently been uniquely predicted by Pearceâs Configural Theory (Pearce, 1994). Although it is possible to simulate the Replaced Elements Model using âstandardâ simulation programs the generation of the correct stimulus representation is complex. The current paper describes a method for simulation of the Replaced Elements Model and presents the results of two example simulations that show differential predictions of Replaced Elements and Pearceâs Configural Theor
A dynamical model for correlated two-pion-exchange in the pion-nucleon interaction
A microscopic model for the process is presented in the
meson exchange framework, which in the pseudophysical region agrees with
available quasiempirical information. The scalar () and vector ()
piece of correlated two--pion exchange in the pion--nucleon interaction is then
derived via dispersion integrals over the unitarity cut. Inherent ambiguities
in the method and implications for the description of pion--nucleon scattering
data are discussed.Comment: 20 pages, 11 postscript figure
Mitochondrial respiratory capacity is a critical regulator of CD8<sup>+</sup> T cell memory development
CD8+ T cells undergo major metabolic changes upon activation, but how metabolism influences the establishment of long-lived memory T cells after infection remains a key question. We have shown here that CD8+ memory T cells, but not CD8+ T effector (Teff) cells, possessed substantial mitochondrial spare respiratory capacity (SRC). SRC is the extra capacity available in cells to produce energy in response to increased stress or work and as such is associated with cellular survival. We found that interleukin-15 (IL-15), a cytokine critical for CD8+ memory T cells, regulated SRC and oxidative metabolism by promoting mitochondrial biogenesis and expression of carnitine palmitoyl transferase (CPT1a), a metabolic enzyme that controls the rate-limiting step to mitochondrial fatty acid oxidation (FAO). These results show how cytokines control the bioenergetic stability of memory T cells after infection by regulating mitochondrial metabolism
Effect of Seed Pellet Modification on Spiral Root Formation of Tobacco Seedlings
Tobacco seeds are often pelleted to facilitate precision seeding into float trays. Pelleting consists of the application of solid particles, such as clay, to seeds with a binder in a coating pan or tumbling drum to form spherically shaped dispersal units. One of the several advantages of pelleting is to provide seeds with a vastly enlarged bulk size to ensure proper placement of the seed at the surface of the growing medium
- âŠ