3,718 research outputs found
Advances in Atomic Data for Neutron-Capture Elements
Neutron(n)-capture elements (atomic number Z>30), which can be produced in
planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been
detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a
potentially powerful tool for studying the production and chemical evolution of
trans-iron elements. However, significant challenges must be addressed before
this goal can be achieved. One of the most substantial hurdles is the lack of
atomic data for n-capture elements, particularly that needed to solve for their
ionization equilibrium (and hence to convert ionic abundances to elemental
abundances). To address this need, we have computed photoionization cross
sections and radiative and dielectronic recombination rate coefficients for the
first six ions of Se and Kr. The calculations were benchmarked against
experimental photoionization cross section measurements. In addition, we
computed charge transfer (CT) rate coefficients for ions of six n-capture
elements. These efforts will enable the accurate determination of nebular Se
and Kr abundances, allowing robust investigations of s-process enrichments in
PNe.Comment: To be published in IAU Symp. 283: Planetary Nebulae, an Eye to the
Future; 2 page
Physical properties of solar polar jets: A statistical study with Hinode XRT data
The target of this work is to investigate the physical nature of polar jets
in the solar corona and their possible contribution to coronal heating and
solar wind flow based on the analysis of X-ray images acquired by the Hinode
XRT telescope. We estimate the different forms of energy associated with many
of these small-scale eruptions, in particular the kinetic energy and enthalpy.
Two Hinode XRT campaign datasets focusing on the two polar coronal holes were
selected to analyze the physical properties of coronal jets; the analyzed data
were acquired using a series of three XRT filters. Typical kinematical
properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of
18 jets are evaluated from the observed sequences, thus providing information
on their possible contribution to the fast solar wind flux escaping from
coronal holes. Electron temperatures and densities of polar-jet plasmas are
also estimated using ratios of the intensities observed in different filters.
We find that the largest amount of energy eventually provided to the corona
is thermal. The energy due to waves may also be significant, but its value is
comparatively uncertain. The kinetic energy is lower than thermal energy, while
other forms of energy are comparatively low. Lesser and fainter events seem to
be hotter, thus the total contribution by polar jets to the coronal heating
could have been underestimated so far. The kinetic energy flux is usually
around three times smaller than the enthalpy counterpart, implying that this
energy is converted into plasma heating more than in plasma acceleration. This
result suggests that the majority of polar jets are most likely not escaping
from the Sun and that only cooler ejections could possibly have enough kinetic
energy to contribute to the total solar wind flow.Comment: 21 pages, 10 figures, Submitted and accepted for publishing in
Astronomy and Astrophysics journa
Single parameter testing
Frequency response testing of ac and dc amplifiers, and single parameter testing of X-Y PLOTTE
Single parameter testing Quarterly report
Single parameter testing of ac and dc amplifier
Single parameter testing Quarterly report
Test signals, AC analysis, transfer function determination, and nonlinear components for single parameter testing of amplifie
Single parameter testing, phase D Final report
Single parameter testing techniques for electronic measuring equipment and other component
U.S. Radio in the 21st Century: Staying the Course in Unknown Territory
This essay examines the development of the radio industry in the United States as it makes its way into the 21st century. Issues of regulation, technology, commerce, and culture are addressed
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