37 research outputs found
Strong Magnetic Field Effects and Molecular Processes with Applications to White Dwarfs
Radiative transitions of hydrogenlike atoms in external magnetic fields of strength applicable to magnetic white dwarfs, i.e. B \u3c 103 megagauss, have been investigated for field-free principal quantum numbers n \u3c 6. Finite proton mass corrections are included. Relativistic corrections are also investigated. Transition probabilities are determined using the length, velocity, and acceleration forms of the electric dipole operator. Discrepancies between previous calculations and magnetic white dwarf observations of low-lying boundbound transitions have been studied. New results for high-lying transitions are also obtained.
The transition probability for the hydrogenlike 2s two-photon decay has been investigated and shown to increase substantially with field strength. The computed two-photon spectra show resonances and interference minima. Anomalous Zeeman depolarization features are found in computed two-photon polarization spectra of alkali atoms in laboratory strength magnetic fields. A previously observed fine structure depolarization feature is shown to decay with decreasing field strength
Cosmological Recombination of Lithium and its Effect on the Microwave Background Anisotropies
The cosmological recombination history of lithium, produced during Big--Bang
nucleosynthesis, is presented using updated chemistry and cosmological
parameters consistent with recent cosmic microwave background (CMB)
measurements. For the popular set of cosmological parameters, about a fifth of
the lithium ions recombine into neutral atoms by a redshift . The
neutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort its
intensity and polarization anisotropies at observed wavelengths around m, as originally suggested by Loeb (2001). The modified anistropies
resulting from the lithium recombination history are calculated for a variety
of cosmological models and found to result primarily in a suppression of the
power spectrum amplitude. Significant modification of the power spectrum occurs
for models which assume a large primordial abundance of lithium. While
detection of the lithium signal might prove difficult, if offers the
possibility of inferring the lithium primordial abundance and is the only probe
proposed to date of the large-scale structure of the Universe for .Comment: 20 pages, 7 figure
Molecular properties of polymeric materials for space applications
This cooperative agreement was intended to investigate the effects of a space environment on the properties of polymeric materials. In addition, efforts have been made to understand and investigate environment simulation techniques and test methodology. The results identified the changes in the properties of six aerospace structural adhesives, three neat high polymers, and two fiber-reinforced polymers, as caused by exposure to four simulated space environmental conditions. Significant property changes occurred for several of the systems as a result of one or more of the exposures. A summary of the research follows a list of related publications and presentations