40 research outputs found
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
and constant ,
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.
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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