3,836 research outputs found
Lepton-nucleus scattering in the impulse approximation regime
We discuss theoretical calculations of electron- and neutrino-nucleus
scattering, carried out using realistic nuclear spectral functions and
including the effect of final state interactions. Comparison between electron
scattering data and the calculated inclusive cross sections off oxygen shows
that the Fermi gas model fails to provide a satisfactory description of the
measured cross sections, and inclusion of nuclear dynamics is needed. The role
of Pauli blocking in charged-current neutrino induced reactions at low is
also analyzed.Comment: To be published in the Proceedings of NUFACT05 (Nucl. Phys. B,
Proceedings Supplements
Using the past to estimate sensory uncertainty
To form a more reliable percept of the environment, the brain needs to estimate its own sensory uncertainty. Current theories of perceptual inference assume that the brain computes sensory uncertainty instantaneously and independently for each stimulus. We evaluated this assumption in four psychophysical experiments, in which human observers localized auditory signals that were presented synchronously with spatially disparate visual signals. Critically, the visual noise changed dynamically over time continuously or with intermittent jumps. Our results show that observers integrate audiovisual inputs weighted by sensory uncertainty estimates that combine information from past and current signals consistent with an optimal Bayesian learner that can be approximated by exponential discounting. Our results challenge leading models of perceptual inference where sensory uncertainty estimates depend only on the current stimulus. They demonstrate that the brain capitalizes on the temporal dynamics of the external world and estimates sensory uncertainty by combining past experiences with new incoming sensory signals
SORLA regulates calpain-dependent degradation of synapsin
Introduction: Sorting-related receptor with A-type repeats (SORLA) is an intracellular sorting receptor in neurons and a major risk factor for Alzheimer disease. Methods: Here, we performed global proteome analyses in the brain of SORLA-deficient mice followed by biochemical and histopathologic studies to identify novel neuronal pathways affected by receptor dysfunction. Results: We demonstrate that the lack of SORLA results in accumulation of phosphorylated synapsins in cortex and hippocampus. We propose an underlying molecular mechanism by demonstrating that SORLA interacts with phosphorylated synapsins through 14-3-3 adaptor proteins to deliver synapsins to calpain-mediated proteolytic degradation. Discussion: Our results suggest a novel function for SORLA which is in control of synapsin degradation, potentially impacting on synaptic vesicle endocytosis and/or exocytosis
Saturation of nuclear matter and short-range correlations
A fully self-consistent treatment of short-range correlations in nuclear
matter is presented. Different implementations of the determination of the
nucleon spectral functions for different interactions are shown to be
consistent with each other. The resulting saturation densities are closer to
the empirical result when compared with (continuous-choice)
Brueckner-Hartree-Fock values. Arguments for the dominance of short-range
correlations in determining the nuclear-matter saturation density are
presented. A further survey of the role of long-range correlations suggests
that the inclusion of pionic contributions to ring diagrams in nuclear matter
leads to higher saturation densities than empirically observed. A possible
resolution of the nuclear-matter saturation problem is suggested.Comment: 5 pages, 1 figure, to be published in Phys.Rev.Let
Extraction of electromagnetic neutron form factors through inclusive and exclusive polarized electron scattering on polarized 3He target
Inclusive 3He(e,e') and exclusive 3He(e,e'n) processes with polarized
electrons and 3He have been theoretically analyzed and values for the magnetic
and electric neutron form factors have been extracted. In both cases the form
factor values agree well with the ones extracted from processes on the
deuteron. Our results are based on Faddeev solutions, modern NN forces and
partially on the incorporation of mesonic exchange currents.Comment: 28 pages, 29 Postscript figure
Correlated Strength in Nuclear Spectral Function
We have carried out an (e,e'p) experiment at high momentum transfer and in
parallel kinematics to measure the strength of the nuclear spectral function
S(k,E) at high nucleon momenta k and large removal energies E. This strength is
related to the presence of short-range and tensor correlations, and was known
hitherto only indirectly and with considerable uncertainty from the lack of
strength in the independent-particle region. This experiment confirms by direct
measurement the correlated strength predicted by theory.Comment: 4 pages, 2 figures, accepted by Phys. Rev. Let
Spectral functions of isoscalar scalar and isovector electromagnetic form factors of the nucleon at two-loop order
We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
and Im at the two-pion threshold
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at . In the
case of the scalar spectral function Im one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological -meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.Comment: 10 pages, 6 figures, submitted to Physical Review
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Planning and Leveraging Event Portfolios: Towards a Holistic Theory
This conceptual paper seeks to advance the discourse on the leveraging and legacies of events by examining the planning, management, and leveraging of event portfolios. This examination shifts the common focus from analyzing single events towards multiple events and purposes that can enable cross-leveraging among different events in pursuit of attainment and magnification of specific ends. The following frameworks are proposed: (1) event portfolio planning and leveraging, and (2) analyzing events networks and inter-organizational linkages. These frameworks are intended to provide, at this infancy stage of event portfolios research, a solid ground for building theory on the management of different types and scales of events within the context of a portfolio aimed to obtain, optimize and sustain tourism, as well as broader community benefits
Logarithmic corrections and soft photon phenomenology in the multipole model of the nucleon form factors
We analyzed the presently available experimental data on nucleon
electromagnetic form factors within a multipole model based on dispersion
relations. A good fit of the data is achieved by considering the coefficients
of the multipole expansions as logarithmic functions of the momentum transfer
squared. The superconvergence relations, applied to this coefficients, makes
the model agree with unitary constraints and pQCD asymptotics for the Dirac and
Pauli form factors. The soft photon emission is proposed as a mechanism
responsible for the difference between the Rosenbluth, polarization and
beam--target--asymmetry data. It is shown, that the experimentally measured
cross sections depend not only on the Dirac and Pauli form factors, but also on
the average number of the photons emitted. For proton this number is shown to
be different for different types of experimental measurements and then
estimated phenomenologically. For neutron the same mechanism predicts, that the
data form different types of experiments must coincide with high accuracy. A
joint fit of all the experimental data reproduce the dependence with the
accuracy . Predictions of the model, that 1) the ratios of the
proton form factors are different for Rosenbluth, polarization and
beam--target--asymmetry experiments and 2) similar ratios are nearly the same
for neutron, can be used for experimental verification of the model.Comment: 14 pages in 2-column format, 4 figures, references added, typos
corrected, minor changes in the text, accepted in Eur. Phys. Journal
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