5,764 research outputs found
Resonance Contributions to Photoproduction on Protons Found Using Dispersion Relations and an Isobar Model
The contributions of the resonances , ,
, , , , ,
to are found from the data on cross
sections, beam and target asymmetries using two approaches: fixed-t dispersion
relations and an isobar model. Utilization of the two approaches and comparison
of the results obtained with different parametrizations of the resonance
contributions allowed us to make conclusions about the model-dependence of
these contributions. We conclude that the results for the contributions of the
resonances , , to corresponding
multipole amplitudes are stable. With this the results for and
, combined with their PDG photoexcitation helicity amplitudes,
allowed us to find the branching ratios , which have significantly
better accuracy than the PDG data. The total Breit-Wigner width of the
is model-dependent, we have obtained and using dispersion relations and the isobar model,
respectively. The results for the , ,
, are model dependent, only the signs and orders
of magnitude of their contributions to multipole amplitudes are determined. The
results for the are strongly model-dependent.Comment: 26 pages, 6 figure
Functionally dissociating aspects of event memory: the effects of combined perirhinal and postrhinal cortex lesions on object and place memory in the rat.
Reciprocal interactions between the hippocampus and the perirhinal and parahippocampal cortices form core components of a proposed temporal lobe memory system. For this reason, the involvement of the hippocampus in event memory is thought to depend on its connections with these cortical areas. Contrary to these predictions, we found that NMDA-induced lesions of the putative rat homologs of these cortical areas (perirhinal plus postrhinal cortices) did not impair performance on two allocentric spatial tasks highly sensitive to hippocampal dysfunction. Remarkably, for one of the tasks there was evidence of a facilitation of performance. The same cortical lesions did, however, disrupt spontaneous object recognition and object discrimination reversal learning but spared initial acquisition of the discrimination. This pattern of results reveals important dissociations between different aspects of memory within the temporal lobe. Furthermore, it shows that the perirhinal-postrhinal cortex is not a necessary route for spatial information reaching the hippocampus and that object familiarity-novelty detection depends on different neural substrates than do other aspects of event memory
Discrimination of computer-graphic stimuli by mice: a method for the behavioral characterization of transgenic and gene-knockout models.
An automated method is described for the behavioral testing of mice in an apparatus that allows computer-graphic stimulus material to be presented. Mice responded to these stimuli by making a nose-poke toward a computer monitor that was equipped with a touchscreen attachment for detecting responses. It was found that C57BL/6 mice were able to solve single-pair visual discriminations as well as 3-pair concurrent visual discriminations. The finding that mice are capable of complex visual discriminations introduces the possibility of testing mice on nonspatial tasks that are similar to those used with rats, monkeys, and humans. Furthermore, the method seems particularly well suited to the comprehensive behavioral assessment of transgenic and gene-knockout models
Triple dissociation of anterior cingulate, posterior cingulate, and medial frontal cortices on visual discrimination tasks using a touchscreen testing procedure for the rat.
Four experiments examined effects of quinolinic acid-induced lesions of the anterior cingulate, posterior cingulate, and medial frontal cortices on tests of visual discrimination learning, using a new touchscreen testing method for rats. Anterior cingulate cortex lesions impaired acquisition of an 8-pair concurrent discrimination task, whereas posterior cingulate cortex lesions facilitated learning but selectively impaired the late stages of acquisition of a visuospatial conditional discrimination. Medial frontal cortex lesions selectively impaired reversal learning when stimuli were difficult to discriminate; lesions of anterior and posterior cingulate cortex had no effect. These results suggest roles for the anterior cingulate, posterior cingulate, and medial frontal cortex in stimulus-reward learning, stimulus-response learning or response generation, and attention during learning, respectively
Research Information Systems – fit for the future? A report on the situation and plans of the University of Sheffield Library
This article discusses the University of Sheffield’s rationale for joining, and the experience of participating in, the Development Partner Programme for Ex Libris’ Esploro product. It should be noted that the article expresses the opinions of the University of Sheffield Library staff writing the article, and not the Ex Libris company
Fornix lesions can facilitate acquisition of the transverse patterning task: a challenge for configural theories of hippocampal function.
Configural theories of hippocampal function predict that hippocampal dysfunction should impair acquisition of the transverse patterning task, which involves the concurrent solution of three discrimination problems: A+ versus B-; B+ versus C-; and C+ versus A-. The present study tested this prediction in rats using computer-graphic stimuli presented on a touchscreen. Experiment 1 assessed the effects of fornix lesions when the three problems were introduced sequentially (phase 1: A+ vs B-; phase 2: A+ vs B-, B+ vs C-; phase 3: A+ vs B-, B+ vs C-, C+ vs A-). Fornix lesions significantly facilitated acquisition of the complete transverse patterning task (phase 3) but had no effect on the number of sessions or errors required to attain criterion during phase 1 or phase 2. In experiment 2, in which all three problems were presented concurrently from the outset of training, fornix-lesioned animals outperformed control animals during the seventh block of acquisition trials and were not impaired during any stage of acquisition. Importantly, these same animals were significantly impaired on two allocentric spatial tasks: T-maze alternation (experiments 1 and 2) and the Morris Swim Task (experiment 1). These results contradict the predictions of configural theories of hippocampal function and cast doubt on the popular notion that spatial learning is a special case of configural learning
Backward-angle photoproduction of mesons on the proton at = 1.5--2.4 GeV
Differential cross sections and photon beam asymmetries for
photoproduction have been measured at = 1.5--2.4 GeV and at the
scattering angles, --1 cos --0.6. The
energy-dependent slope of differential cross sections for -channel
production has been determined. An enhancement at backward angles is found
above = 2.0 GeV. This is inferred to be due to the -channel
contribution and/or resonances. Photon beam asymmetries have been obtained for
the first time at backward angles. A strong angular dependence has been found
at 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL
Central exclusive production of longlived gluinos at the LHC
We examine the possibility of producing gluino pairs at the LHC via the
exclusive reaction pp -> p+gluino+gluino+p in the case where the gluinos are
long lived. Such long lived gluinos are possible if the scalar super-partners
have large enough masses. We show that it may be possible to observe the
gluinos via their conversion to R-hadron jets and measure their mass to better
than 1% accuracy for masses below 350 GeV with 300/fb of data.Comment: 13 pages, 9 figures. Minor corrections to version
Primakoff effect in eta-photoproduction off protons
We analyse data on forward eta-meson photoproduction off a proton target and
extract the eta to gamma gamma decay width utilizing the Primakoff effect. The
hadronic amplitude that enters into our analysis is strongly constrained
because it is fixed from a global fit to available gamma p to p eta data for
differential cross sections and polarizations. We compare our results with
present information on the two-photon eta-decay from the literature. We provide
predictions for future PrimEx experiments at Jefferson Laboratory in order to
motivate further studies.Comment: 5 pages, 6 figures, gamma-gamma*-eta form factor included, version to
appear in Eur. Phys. J. A
Functionally dissociating aspects of event memory: The effects of combined perirhinal and postrhinal lesions on object and place memory in the rat
Reciprocal interactions between the hippocampus and the perirhinal and parahippocampal cortices form core components of a proposed temporal lobe memory system. For this reason, the involvement of the hippocampus in event memory is thought to depend on its connections with these cortical areas. Contrary to these predictions, we found that NMDA-induced lesions of the putative rat homologs of these cortical areas (perirhinal plus postrhinal cortices) did not impair performance on two allocentric spatial tasks highly sensitive to hippocampal dysfunction. Remarkably, for one of the tasks there was evidence of a facilitation of performance. The same cortical lesions did, however, disrupt spontaneous object recognition and object discrimination reversal learning but spared initial acquisition of the discrimination. This pattern of results reveals important dissociations between different aspects of memory within the temporal lobe. Furthermore, it shows that the perirhinal–postrhinal cortex is not a necessary route for spatial information reaching the hippocampus and that object familiarity–novelty detection depends on different neural substrates than do other aspects of event memory
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