1,280 research outputs found
The Pion-Nucleon coupling constant from np charge exchange scattering
A novel extrapolation method has been used to deduce the charged Pion-Nucleon
coupling constant from backward differential scattering cross sections. We
applied it to new measurements performed at 162 MeV at the The Svedberg
Laboratory in Uppsala. In the angular range , the
carefully normalized data are steeper than those of most previous measurements.
The extracted value, , in good agreement with
the classical value, is higher than those determined in recent nucleon-nucleon
partial-wave analyses.Comment: 6 pages, 3 encapsulated figures, epsfig, menu97.cls (included
When planning fails: Individual differences and error-related brain activity in problem solving.
The neuronal processes underlying correct and erroneous problem solving were studied in strong and weak problem-solvers using functional magnetic resonance imaging (fMRI). During planning, the right dorsolateral prefrontal cortex was activated, and showed a linear relationship with the participants' performance level. A similar pattern emerged in right inferior parietal regions for all trials, and in anterior cingulate cortex for erroneously solved trials only. In the performance phase, when the pre-planned moves had to be executed by means of an fMRI-compatible computer mouse, the right dorsolateral prefrontal cortex was again activated jointly with right parahippocampal cortex, and displayed a similar positive relationship with the participants' performance level. Incorrectly solved problems elicited stronger bilateral prefrontal and left inferior parietal activations than correctly solved trials. For both individual ability and trial-specific performance, our results thus demonstrate the crucial involvement of right prefrontal cortex in efficient visuospatial planning
Precise strength of th piNN coupling constant
We report here a preliminary value for the piNN coupling constant deduced
from the GMO sumrule for forward piN scattering. As in our previous
determination from np backward differential scattering cross sections we give a
critical discussion of the analysis with careful attention not only to the
statistical, but also to the systematic uncertainties. Our preliminary
evaluation gives (GMO) = 13.99(24).Comment: 4 pages, 1 figure, contribution to INPC/98, to be published in
Conference Proceedings, Nuclear Physics A (Conference Proceedings
Zeta Determinant for Laplace Operators on Riemann Caps
The goal of this paper is to compute the zeta function determinant for the
massive Laplacian on Riemann caps (or spherical suspensions). These manifolds
are defined as compact and boundaryless dimensional manifolds deformed by a
singular Riemannian structure. The deformed spheres, considered previously in
the literature, belong to this class. After presenting the geometry and
discussing the spectrum of the Laplacian, we illustrate a method to compute its
zeta regularized determinant. The special case of the deformed sphere is
recovered as a limit of our general formulas.Comment: 19 pages, 1 figur
Optical design of reflectionless complex media by finite embedded coordinate transformations
Transformation optics offers an unconventional approach to the control of
electromagnetic fields. A transformation optical structure is designed by first
applying a form-invariant coordinate transform to Maxwell's equations, in which
part of free space is distorted in some desired manner. The coordinate
transformation is then applied to the permittivity and permeability tensors to
yield the specification for a complex medium with desired functionality. The
transformation optical structures proposed to date, such as electromagnetic
"invisibility" cloaks and concentrators, are inherently reflectionless and
leave the transmitted wave undisturbed. Here we expand the class of
transformation optical structures by introducing finite, embedded coordinate
transformations, which allow the electromagnetic waves to be steered or
focused. We apply the method to the design of several devices, including a
parallel beam shifter and a beam splitter, both of which exhibit unusual
electromagnetic behavior as confirmed by 2D full-wave simulations. The devices
are designed to be reflectionless, in accordance with a straightforward
topological criterion.Comment: submitted to the journal on Sep 10 2007, abstract changed to make it
more accessible, keywords adde
Transformation Optics for Plasmonics
A new strategy to control the flow of surface plasmon polaritons at metallic
surfaces is presented. It is based on the application of the concept of
Transformation Optics to devise the optical parameters of the dielectric medium
placed on top of the metal surface. We describe the general methodology for the
design of Transformation-Optical devices for surface plasmons and analyze, for
proof-of-principle purposes, three representative examples with different
functionalities: a beam shifter, a cylindrical cloak and a ground-plane cloak.Comment: 15 pages, 3 figure
Precise strength of the NN coupling constant
We report here a preliminary value for the piNN coupling constant deduced from the GMO sumrule for forward piN scattering. As in our previous determination from np backward differential scattering cross sections we give a critical discussion of the analysis with careful attention not only to the statistical, but also to the systematic uncertainties. Our preliminary evaluation gives (GMO) = 13.99(24)
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