5,754 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
Photoelastic Analysis of Three-dimensional Stress Systems Using Scattered Light
A method has been developed for making photoelastic analyses of three-dimensional stress systems by utilizing the polarization phenomena associated with the scattering of light. By this method, the maximum shear and the directions of the three principal stresses at any point within a model can be determined, and the two principal stresses at a free-bounding surface can be separately evaluated. Polarized light is projected into the model through a slit so that it illuminates a plane section. The light is continuously analyzed along its path by scattering and the state of stress in the illuminated section is obtained. By means of a series of such sections, the entire stress field may be explored. The method was used to analyze the stress system of a simple beam in bending. The results were found to be in good agreement with those expected from elementary theory
Ultrasonic Communication in Rats: Can Playback of 50-kHz Calls Induce Approach Behavior?
Rats emit distinct types of ultrasonic vocalizations, which differ depending on age, the subject's current state and environmental factors. Since it was shown that 50-kHz calls can serve as indices of the animal's positive subjective state, they have received increasing experimental attention, and have successfully been used to study neurobiological mechanisms of positive affect. However, it is likely that such calls do not only reflect a positive affective state, but that they also serve a communicative purpose. Actually, rats emit the highest rates of 50-kHz calls typically during social interactions, like reproductive behavior, juvenile play and tickling. Furthermore, it was recently shown that rats emit 50-kHz calls after separation from conspecifics. The aim of the present study was to test the communicative value of such 50-kHz calls. In a first experiment, conducted in juvenile rats situated singly on a radial maze apparatus, we showed that 50-kHz calls can induce behavioral activation and approach responses, which were selective to 50-kHz signals, since presentation of 22-kHz calls, considered to be aversive or threat signals, led to behavioral inhibition. In two other experiments, we used either natural 50-kHz calls, which had been previously recorded from other rats, or artificial sine wave stimuli, which were identical to these calls with respect to peak frequency, call length and temporal appearance. These signals were presented to either juvenile (Exp. 2) or adult (Exp. 3) male rats. Our data clearly show that 50-kHz signals can induce approach behavior, an effect, which was more pronounced in juvenile rats and which was not selective to natural calls, especially in adult rats. The recipient rats also emitted some 50-kHz calls in response to call presentation, but this effect was observed only in adult subjects. Together, our data show that 50-kHz calls can serve communicative purposes, namely as a social signal, which increases the likelihood of approach in the recipient conspecific
The representation of abstract task rules in the human prefrontal cortex
We have previously reported sustained activation in the ventral
prefrontal cortex while participants prepared to perform 1 of 2 tasks
as instructed. But there are studies that have reported activation
reflecting task rules elsewhere in prefrontal cortex, and this is true in
particular when it was left to the participants to decide which rule to
obey. The aim of the present experiment was to use functional
magnetic resonance imaging (fMRI) to find whether there was
activation in common, irrespective of the way that the task rules
were established. On each trial, we presented a word after a variable
delay, and participants had to decide either whether the word was
abstract or concrete or whether it had 2 syllables. The participants
either decided before the delay which task they would perform or
were instructed by written cues. Comparing the self-generated with
the instructed trials, there was early task set activation during the
delay in the middle frontal gyrus. On the other hand, a conjunction
analysis revealed sustained activation in the ventral prefrontal and
polar cortex for both conditions. We argue that the ventral prefrontal
cortex is specialized for handling conditional rules regardless of how
the task rules were established
Sparticle masses in deflected mirage mediation
We discuss the sparticle mass patterns that can be realized in deflected
mirage mediation scenario of supersymmetry breaking, in which the moduli,
anomaly, and gauge mediations all contribute to the MSSM soft parameters.
Analytic expression of low energy soft parameters and also the sfermion mass
sum rules are derived, which can be used to interpret the experimentally
measured sparticle masses within the framework of the most general mixed
moduli-gauge-anomaly mediation. Phenomenological aspects of some specific
examples are also discussed.Comment: 43 pages, 17 figures, references adde
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Diabetes and disordered eating behaviours in a community-based sample of australian adolescents
Background:People with diabetes have been shown to be at risk for disordered eating compared to their non-diabetic peers. However, the majority of studies have been conducted in relatively small samples drawn from clinical diabetes settings or registries. Community-based samples are required to better understand disordered eating behaviours in this population. In a large community-based population sample of Australian adolescents, this study aimed to (1) investigate disordered eating behaviours in adolescents reporting a diagnosis of diabetes compared to their non-diabetic peers and (2) test associations between disordered eating behaviours and insulin restriction.Methods:Secondary school students (n = 4854; mean (SD) age 14.4 (1.6) years; 47% boys) completed an online survey, including self-reported presence of diabetes, demographics, weight status, substance use, insulin restriction and disordered eating behaviours. Clinically meaningful cut-offs for disordered eating behaviours were generated for analysis.Results:Disordered eating behaviours, specifically self-induced vomiting (diabetes 19.2%, no diabetes 3.3%; p p p p Conclusion:There was a high rate of disordered eating behaviours in adolescents with diabetes compared to their peers without diabetes. The findings of this study may have the potential to inform future health promotion, prevention, and early intervention approaches for those with comorbid diabetes and disordered eating behaviours. Future longitudinal studies are required to evaluate disordered eating behaviours in those with diabetes over time in community-based samples
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
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
Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
Masses, widths and photocouplings of baryon resonances are determined in a
coupled-channel partial wave analysis of a large variety of data. The
Bonn-Gatchina partial wave formalism is extended to include a decomposition of
t- and u-exchange amplitudes into individual partial waves. The multipole
transition amplitudes for and are
given and compared to results from other analyses.Comment: 18 pages, 14 figure
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
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