24,623 research outputs found
The Two-Nucleon 1S0 Amplitude Zero in Chiral Effective Field Theory
We present a new rearrangement of short-range interactions in the
nucleon-nucleon channel within Chiral Effective Field Theory. This is intended
to reproduce the amplitude zero (scattering momentum 340 MeV) at
leading order, and it includes subleading corrections perturbatively in a way
that is consistent with renormalization-group invariance. Systematic
improvement is shown at next-to-leading order, and we obtain results that fit
empirical phase shifts remarkably well all the way up to the pion-production
threshold. An approach in which pions have been integrated out is included,
which allows us to derive analytic results that also fit phenomenology
surprisingly well.Comment: 34 pages, 7 figure
Empirical likelihood based testing for regression
Consider a random vector and let . We are interested
in testing for some known function , some compact set
IR and some function set of real valued
functions. Specific examples of this general hypothesis include testing for a
parametric regression model, a generalized linear model, a partial linear
model, a single index model, but also the selection of explanatory variables
can be considered as a special case of this hypothesis. To test this null
hypothesis, we make use of the so-called marked empirical process introduced by
\citeD and studied by \citeSt for the particular case of parametric regression,
in combination with the modern technique of empirical likelihood theory in
order to obtain a powerful testing procedure. The asymptotic validity of the
proposed test is established, and its finite sample performance is compared
with other existing tests by means of a simulation study.Comment: Published in at http://dx.doi.org/10.1214/07-EJS152 the Electronic
Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The Airy fibre: an optical fibre that guides light diffracted by a circular aperture
We have designed and made an optical fibre that guides an approximate Airy
pattern as one of its guided modes. The fibre's attenuation was 11.0 dB/km at
1550 nm wavelength, the match between the fibre's mode and the ideal infinite
Airy pattern was 93.7%, and the far field resembled a top-hat beam. The
guidance mechanism has strong similarities to photonic bandgap guidance.Comment: 11 page
Trapping Dynamics with Gated Traps: Stochastic Resonance-Like Phenomenon
We present a simple one-dimensional trapping model prompted by the problem of
ion current across biological membranes. The trap is modeled mimicking the
ionic channel membrane behaviour. Such voltage-sensitive channels are open or
closed depending on the value taken by a potential. Here we have assumed that
the external potential has two contributions: a determinist periodic and a
stochastic one. Our model shows a resonant-like maximum when we plot the
amplitude of the oscillations in the absorption current vs. noise intensity.
The model was solved both numerically and using an analytic approximation and
was found to be in good accord with numerical simulations.Comment: RevTex, 5 pgs, 3 figure
Magnetic bright points in the quiet Sun
We present a visual determination of the number of bright points (BPs)
existing in the quiet Sun, which are structures though to trace intense kG
magnetic concentrations. The measurement is based on a 0.1 arcsec angular
resolution G-band movie obtained with the Swedish Solar Telescope at the solar
disk center. We find 0.97 BPs/Mm^2, which is a factor three larger than any
previous estimate. It corresponds to 1.2 BPs per solar granule. Depending on
the details of the segmentation, the BPs cover between 0.9% and 2.2% of the
solar surface. Assuming their field strength to be 1.5 kG, the detected BPs
contribute to the solar magnetic flux with an unsigned flux density between 13
G and 33 G. If network and inter-network regions are counted separately, they
contain 2.2 BPs/Mm^2 and 0.85 BPs/Mm^2, respectively.Comment: Accepted for publication in ApJL. 2 figs
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