1,398 research outputs found
Precision determination of the pi-N scattering lengths and the charged pi-NN coupling constant
We critically evaluate the isovector GMO sumrule for the charged
coupling constant using recent precision data from p and d atoms
and with careful attention to systematic errors. From the d scattering
length we deduce the pion-proton scattering lengths (statistic) (systematic))~ and . From this a direct evaluation gives (statistic)(systematic) or .Comment: 4 pages, 1 figure, latex and postscript; invited talk at PANIC99; to
appear in Nucl. Phys. A; changed notation: g^2 and f^2 replaced by
conventional g^2/4\pi and f^2/4\p
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
Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1
We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and
G352.7-0.1, to understand the causes of such morphology. The research was
carried out based on new and reprocessed archival VLA observations and
XMM-Newton archival data. The surrounding was investigated based on data
extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring
Survey and the HI Southern Galactic Plane Survey. The present study revealed
that the overall morphology of both SNRs is the result of the mass-loss history
of their respective progenitor stars. Kes79 would be the product of the
gravitational collapse of a massive O9 star evolving near a molecular cloud and
within the precursor's wind-driven bubble, while G352.7-0.1 would be the result
of interactions of the SNR with an asymmetric wind from the progenitor together
with projection effects. No radio point source or pulsar wind nebula was found
associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray
study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray
radiation completely fills in the interior of the remnant and originates in
heated ejecta. Characteristic parameters, like radio flux, radio spectral
index, age, distance, shock velocity, initial energy and luminosity, were
estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and
Astrophysic
The most complete and detailed X-ray view of the SNR Puppis A
With the purpose of producing the first detailed full view of Puppis A in
X-rays, we carried out new XMM-Newton observations covering the missing regions
in the southern half of the supernova remnant (SNR) and combined them with
existing XMM-Newton and Chandra data. The new images were produced in the
0.3-0.7, 0.7-1.0 and 1.0-8.0 energy bands. We investigated the SNR morphology
in detail, carried out a multi-wavelength analysis and estimated the flux
density and luminosity of the whole SNR. The complex structure observed across
the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty
interstellar medium. The southwestern corner includes filaments that perfectly
correlate with radio features suggested to be associated with shock/cloud
interaction. In the northern half of Puppis A the comparison with Spitzer
infrared images shows an excellent correspondence between X-rays and 24 and 70
microns emission features, while to the south there are some matched and other
unmatched features. X-ray flux densities of 12.6 X 10^-9, 6.2 X 10^-9, and 2.8
X 10^-9 erg cm^-2 s^-1 were derived for the 0.3-0.7, 0.7-1.0 and 1.0-8.0 keV
bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray
luminosity between 0.3 and 8.0 keV is 1.2 X 10^37 erg s^-1. We also collected
and updated the broad-band data of Puppis A between radio and GeV gamma-ray
range, producing its spectral energy distribution. To provide constraints to
the high-energy emission models, we re-analyzed radio data, estimating the
energy content in accelerated particles to be Umin=4.8 X 10^49 erg and the
magnetic field strength B=26 muG.Comment: Article accepted to be published in the Astronomy and Astrophysics
Main Journa
The Effect of Particle Strength on the Ballistic Resistance of Shear Thickening Fluids
The response of shear thickening fluids (STFs) under ballistic impact has
received considerable attention due to its field-responsive nature. While
efforts have primarily focused on the response of traditional ballistic fabrics
impregnated with fluids, the response of pure STFs to penetration has received
limited attention. In the present study, the ballistic response of pure STFs is
investigated and the effect of fluid density and particle strength on ballistic
performance is isolated. The loss of ballistic resistance of STFs at higher
impact velocities is governed by particle strength, indicating the range of
velocities over which they may provide effective armor solutions.Comment: 4 pages, 4 figure
How precisely can we determine the pion-nucleon coupling constant from the isovector GMO sum rule?
The isovector GMO sum rule for zero energy forward pion-nucleon scattering is
critically studied to obtain the charged pion-nucleon coupling constant using
the precise negatively charged pion-proton and pion-deuteron scattering lengths
deduced recently from pionic atom experiments. This direct determination leads
to a pseudoscalar charged pion-nucleon coupling constant of 14.23 +- 0.09
(statistic) +- 0.17 (systematic). We obtain also accurate values for the
pion-nucleon scattering lengths.Comment: Talk given at the Eighth International Symposium on Meson-Nucleon
Physics and the Structure of the Nucleon, Zuoz, Switzerland, August 15-21,
1999, 5 pages, 2 figures, file menu.cls include
Cooling Tests of the NectarCAM camera for the Cherenkov Telescope Array
The NectarCAM is a camera proposed for the medium-sized telescopes in the
framework of the Cherenkov Telescope Array (CTA), the next-generation
observatory for very-high-energy gamma-ray astronomy. The cameras are designed
to operate in an open environment and their mechanics must provide protection
for all their components under the conditions defined for the CTA observatory.
In order to operate in a stable environment and ensure the best physics
performance, each NectarCAM will be enclosed in a slightly overpressurized,
nearly air-tight, camera body, to prevent dust and water from entering. The
total power dissipation will be ~7.7 kW for a 1855-pixel camera. The largest
fraction is dissipated by the readout electronics in the modules. We present
the design and implementation of the cooling system together with the test
bench results obtained on the NectarCAM thermal demonstrator.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Nuclear symmetry energy and the r-mode instability of neutron stars
We analyze the role of the symmetry energy slope parameter on the {\it
r}-mode instability of neutron stars. Our study is performed using both
microscopic and phenomenological approaches of the nuclear equation of state.
The microscopic ones include the Brueckner--Hartree--Fock approximation, the
well known variational equation of state of Akmal, Pandharipande and Ravenhall,
and a parametrization of recent Auxiliary Field Diffusion Monte Carlo
calculations. For the phenomenological approaches, we use several Skyrme forces
and relativisic mean field models. Our results show that the {\it r}-mode
instability region is smaller for those models which give larger values of .
The reason is that both bulk () and shear () viscosities increase
with and, therefore, the damping of the mode is more efficient for the
models with larger . We show also that the dependence of both viscosities on
can be described at each density by simple power-laws of the type
and . Using the measured spin
frequency and the estimated core temperature of the pulsar in the low-mass
X-ray binary 4U 1608-52, we conclude that observational data seem to favor
values of larger than MeV if this object is assumed to be outside
the instability region, its radius is in the range () km, and
its mass (). Outside this range it is not possible to
draw any conclusion on from this pulsar.Comment: 10 pages, 6 figures. Version published in Physical Review
Paris nucleon-antinucleon potential constrained by recent antiprotonic-atom data and antineutron-proton total cross sections
We report on an updated Paris nucleon-antinucleon optical potential. The
long- and intermediate-range real parts are obtained by G-parity transformation
of the Paris nucleon-nucleon potential based on a theoretical
dispersion-relation treatment of the correlated and uncorrelated two-pion
exchange. The short-range imaginary potential parametrization results from the
calculation of the nucleon-antinucleon annihilation box diagram into two mesons
with a nucleon-antinucleon intermediate state in the crossed channel. The
parametrized real and imaginary short range parts are determined by fitting not
only the existing experimental data included in the 1999 version of the Paris
nucleon-antinucleon potential, but also the recent antiprotonic-hydrogen data
and antineutron-proton total cross sections. The description of these new
observables is improved. Only this readjusted potential generates an isospin
zero 1S0, 52 MeV broad quasibound state at 4.8 MeV below the threshold. Recent
BES data on J/psi decays could support the existence of such a state.Comment: 10 pages, 20 figures, expanded version with more detail
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