Birefringence in nonlinear anisotropic dielectric media

Light propagation is investigated in the context of local anisotropic nonlinear dielectric media at rest with the dielectric coefficients $\epsilon^\mu{}_\nu = \epsilon^\mu{}_\nu (\vec{E},\vec{B})$ and constant $\mu$, in the limit of geometrical optics. Birefringence was examined and the general conditions for its occurrence were presented. A toy model is exhibited, in which uniaxial birefringent media with nonlinear dielectric properties could be driven by external fields in such way that birefringence may be artificially controlled. The effective geometry interpretation is also addressed.Comment: 5 pages, 1 figur

Analog black holes in flowing dielectrics

We show that a flowing dielectric medium with a linear response to an external electric field can be used to generate an analog geometry that has many of the formal properties of a Schwarzschild black hole for light rays, in spite of birefringence. We also discuss the possibility of generating these analog black holes in the laboratory.Comment: Revtex4 file, 7 pages, 4 eps figures, a few changes in presentation, some references added, conclusions unchange

Geometrical aspects of light propagation in nonlinear electrodynamics

We analyze the propagation of light in the context of nonlinear electrodynamics, as it occurs in modified QED vacua. We show that the corresponding characteristic equation can be described in terms of a modification of the effective geometry of the underlying spacetime structure. We present the general form for this effective geometry and exhibit some new consequences that result from such approach.Comment: LaTex, 11 pages, accepted for publication in Phys. Rev.

EXAFS studies of sodium silicate glasses containing dissolved actinides

Sodium silicate glasses containing dissolved Th, U, Np, and Pu have been studied using the EXAFS technique. Th/sup 4 +/, U/sup 4 +/, Np/sup 4 +/, and Pu/sup 4 +/ ions in the silicate glasses are 8-fold coordinated to oxygen neighbors. The higher valent U/sup 6 +/ and Np/sup 5 +/ ions have complex local symmetries. The U/sup 6 +/ ions appear in a uranyl configuration with 2 oxygen atoms at 1.85A and 4 at 2.25A from the U ion. The Np/sup 5 +/ local symmetry is more complex and difficult to determine uniquely. The U/sup 6 +/ glasses show substantial clustering of the uranium atoms. A structural model, with nearly planar uranyl sheets sandwiched between alkali and silica layers, is used to explain the U/sup 6 +/ EXAFS data. This model allows us to understand why U/sup 6 +/ ions are much more soluble in the glasses than the actinide 4/sup +/ ions. 4 references, 2 figures