5,520 research outputs found
Distinguishing coherent atomic processes using wave mixing
We are able to clearly distinguish the processes responsible for enhanced
low-intensity atomic Kerr nonlinearity, namely coherent population trapping and
coherent population oscillations in experiments performed on the Rb D1 line,
where one or the other process dominates under appropriate conditions. The
potential of this new approach based on wave mixing for probing coherent atomic
media is discussed. It allows the new spectral components to be detected with
sub-kHz resolution, which is well below the laser linewidth limit. Spatial
selectivity and enhanced sensitivity make this method useful for testing dilute
cold atomic samples.Comment: 9 pages, 5 figure
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
A Review of Recent Developments in Atomic Processes for Divertors and Edge Plasmas
The most promising concepts for power and particle control in tokamaks and
other fusion experiments rely upon atomic processes to transfer the power and
momentum from the edge plasma to the plasma chamber walls. This places a new
emphasis on processes at low temperatures (1-200 eV) and high densities
(10^20-10^22 m^-3). The most important atomic processes are impurity and
hydrogen radiation, ionization, excitation, recombination, charge exchange,
radiation transport, molecular collisions, and elastic scattering of atoms,
molecules and ions. Important new developments have occurred in each of these
areas. The best available data for these processes and an assessment of their
role in plasma wall interactions are summarized, and the major areas where
improved data are needed are reviewed.Comment: Preprint for the 11th PSI meeting, postscript with 22 figures, 40
page
OWL-S Atomic services composition with SWRL rules
This paper presents a method for encoding OWL-S atomic processes by means of SWRL rules and composing them using a backward search planning algorithm. A description of the preliminary prototype implementation and a grounding in BPEL are also presented
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Atomic processes in bicircular fields
We investigate laser-assisted electron-ion recombination (LAR), high-order harmonic generation (HHG) and above-threshold ionization (ATI) of argon atoms by a bicircular laser field, which consists of two coplanar counter-rotating circularly polarized fields of frequencies rω and sω. The energy of soft x rays generated in the LAR process is analyzed as a function of the incident electron angle and numerical results of direct recombination of electrons with Ar+ ions are presented. We also present the results of HHG by a bicircular field and confirm the selection rules derived earlier for inert-gas atoms in a p ground state. We show that the photoelectron spectra in the ATI process, presented in the momentum plane, as well as the LAR spectra exhibit the same discrete rotational symmetry as the applied field
The Present and Future of Planetary Nebula Research. A White Paper by the IAU Planetary Nebula Working Group
We present a summary of current research on planetary nebulae and their
central stars, and related subjects such as atomic processes in ionized
nebulae, AGB and post-AGB evolution. Future advances are discussed that will be
essential to substantial improvements in our knowledge in the field.Comment: accepted for publication in RMxAA; 37 page
Hydrogen Recombination with Multilevel atoms
Hydrogen recombination is one of the most important atomic processes
in many astrophysical objects such as Type II supernova (SN~II)
atmospheres, the high redshift universe during the cosmological recombination
era, and H II regions in the interstellar medium. Accurate predictions of
the ionization fraction can be quite different from those given by a
simple solution
if one takes into account many angular momentum sub-states,
non-resonant processes, and calculates the rates of all atomic
processes from the solution of the radiative transfer equation
instead of using a Planck function under the assumption of thermal
equilibrium. We use the general
purpose model atmosphere code PHOENIX 1D to
compare how the fundamental probabilities such as the photo-ionization
probability, the escape probability, and the collisional de-excitation
probability are affected by the presence of other metals in the
environment, multiple angular momentum sub-states, and
non-resonant processes. Our comparisons are based on a model of SN
1999em, a SNe Type II, 20 days after its explosion.Comment: 29 pages, 12 figures, MNRAS, in pres
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