Title: Polarization of Absorption Lines as a Diagnostics of Circumstellar, Interstellar, and Intergalactic Magnetic Fields: Fine-Structure Atoms

Measurements were made of the absorption spectrum of hydrogen atoms to levels near the ionization threshold in a strong magnetic field. Taking advantage of a classical scaling law, we varied the photon energy and the magnetic-field strength simultaneously, and measured absorption versus [ital B][sup [minus]1/3] at fixed scaled energy, [var epsilon]=[ital E]/([ital B]/[ital B][sub o])[sup 2/3]. The absorption rate has sinusoidal fluctuations which are correlated with closed classical orbits of the electron. Fourier transformation of this signal gives peaks, which we interpret as recurrence strength,'' as a function of the classical action of the closed orbit. Closed-orbit theory gives formulasmore » for these recurrence strengths. We find that the formulas are in good agreement with the measurements. As the scaled energy is increased, observed recurrences proliferate, consistent with a change from orderly to chaotic motion of the electron. Bifurcation theory provides organizing principles for understanding this proliferation and for interpreting the data. New exotic'' orbits suddenly appear through saddle-node bifurcations. The main sequence'' of orbits is produced from an orbit parallel to [ital B] through a sequence of pitchfork and period-doubling bifurcations. Other recurrences are created by period-tripling and higher-order bifurcations of existing orbits. These bifurcations can have generic'' structure, or sometimes the structures are modified by symmetries of the system. Focusing effects associated with these bifurcations cause some recurrences to be particularly strong.« less

In extended x-ray aborption fine structure (EXAFS) study of local environment of Bi{sup 3+} and Pb{sup 2+} ions incorporated in Ba{sub 4.5}Nd{sub 9}Ti{sub 18}O{sub 54} actual sites of Bi- and Pb-incorporated are determined. Evidences are given that dopant ions are not distributed randomly on all theoretically possible sites: Bi{sup 3+} selectively enters one out of three posible channels, corresponding to the sites x=0.9484, y=0.2500, z=0.2939, and/or x=0.0455, y=0.2500, z=0.6928 previously occupied by Nd{sup 3+}, while Pb{sup 2+} selectively enters site x=0.4940, y=0.2500, z=0.4993 previously shared by Ba{sup 2+} and Nd{sup 3+}. {copyright} {ital 1997 Materials Research Society.}