2,324 research outputs found
Induced Nucleon Polarization and Meson-Exchange Currents in (e,e'p) Reactions
Nucleon recoil polarization observables in reactions are
investigated using a semi-relativistic distorted-wave model which includes one-
and two-body currents with relativistic corrections. Results for the induced
polarization asymmetry are shown for closed-shell nuclei and a comparison with
available experimental data for C is provided. A careful analysis of
meson exchange currents shows that they may affect significantly the induced
polarization for high missing momentum.Comment: 7 pages, 9 figures. Revised version with small changes, new curve in
Fig. 3. To be published in PR
Meson Exchange Currents in (e,e'p) recoil polarization observables
A study of the effects of meson-exchange currents and isobar configurations
in reactions is presented. We use a distorted wave
impulse approximation (DWIA) model where final-state interactions are treated
through a phenomenological optical potential. The model includes relativistic
corrections in the kinematics and in the electromagnetic one- and two-body
currents. The full set of polarized response functions is analyzed, as well as
the transferred polarization asymmetry. Results are presented for proton
knock-out from closed-shell nuclei, for moderate to high momentum transfer.Comment: 44 pages, 18 figures. Added physical arguments explaining the
dominance of OB over MEC, and a summary of differences with previous MEC
calculations. To be published in PR
Quantized form factor shift in the presence of free electron laser radiation
In electron scattering, the target form factors contribute significantly to
the diffraction pattern and carry information on the target electromagnetic
charge distribution. Here we show that the presence of electromagnetic
radiation, as intense as currently available in Free Electron Lasers, shifts
the dependence of the target form factors by a quantity that depends on the
number of photons absorbed or emitted by the electron as well as on the
parameters of the electromagnetic radiation. As example, we show the impact of
intense ultraviolet and soft X-ray radiation on elastic electron scattering by
Ne-like Argon ion and by Xenon atom. We find that the shift brought by the
radiation to the form factor is in the order of some percent. Our results may
open up a new avenue to explore matter with the assistance of laser
Chimpanzees and bonobos use social leverage in an ultimatum game
The ultimatum game (UG) is widely used to investigate our sense of fairness, a key characteristic that differentiates us from our closest living relatives, bonobos and chimpanzees. Previous studies found that, in general, great apes behave as rational maximizers in the UG. Proposers tend to choose self-maximizing offers, while responders accept most non-zero offers. These studies do not rule out the possibility that apes can behave prosocially to improve the returns for themselves and others. However, this has never been well studied. In this study, we offer chimpanzee and bonobo proposers the possibility of taking into account the leverage of responders over the offers they receive. This leverage takes the form of access to alternatives for responders. We find that proposers tend to propose fairer offers when responders have the option to access alternatives. Furthermore, we find that both species use their leverage to reject unequal offers. Our results suggest that great apes mostly act as rational maximizers in an UG, yet access to alternatives can lead them to change their strategies such as not choosing the self-maximizing offer as proposers and not accepting every offer higher than zero as responders
Children’s participation in early childhood education: a theoretical overview
Children’s right to participate in all matters and decisions affecting them has gained recognition in society. Its promotion is recommended from an early age – namely, in early childhood education settings – and it is described as benefiting children, adults and the community in general. Given the complex and polysemic meaning of participation, different conceptualizations, models and perspectives have emerged. In this article, the authors provide a theoretical overview, describing relevant models, concepts and contributions from distinct perspectives and fields of knowledge – sociological, educational, developmental and sociocultural – as well as contributions from social policy. This overview is particularly relevant to inform research and practice about children’s participation in early childhood education.info:eu-repo/semantics/acceptedVersio
Análise financeira de sistemas produtivos integrados.
bitstream/item/123060/1/Doc.-274-ArcoVerde.pd
Superscaling of non-quasielastic electron-nucleus scattering
The present study is focused on the superscaling behavior of electron-nucleus
cross sections in the region lying above the quasielastic peak, especially the
region dominated by electroexcitation of the Delta. Non-quasielastic cross
sections are obtained from all available high-quality data for Carbon 12 by
subtracting effective quasielastic cross sections based on the superscaling
hypothesis. These residuals are then compared with results obtained within a
scaling-based extension of the relativistic Fermi gas model, including an
investigation of violations of scaling of the first kind in the region above
the quasielastic peak. A way potentially to isolate effects related to
meson-exchange currents by subtracting both impulsive quasielastic and
impulsive inelastic contributions from the experimental cross sections is also
presented.Comment: RevTeX, 34 pages including 11 figure
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