5,781 research outputs found
Boson-fermion mapping of collective fermion-pair algebras
We construct finite Dyson boson-fermion mappings of general collective
algebras extended by single-fermion operators. A key element in the
construction is the implementation of a similarity transformation which
transforms boson-fermion images obtained directly from the supercoherent state
method. In addition to the general construction, we give detailed applications
to SO(2N), SU(l+1), SO(5), and SO(8) algebras.Comment: 22 pages, latex, no figure
SDG fermion-pair algebraic SO(12) and Sp(10) models and their boson realizations
It is shown how the boson mapping formalism may be applied as a useful
many-body tool to solve a fermion problem. This is done in the context of
generalized Ginocchio models for which we introduce S-, D-, and G-pairs of
fermions and subsequently construct the sdg-boson realizations of the
generalized Dyson type. The constructed SO(12) and Sp(10) fermion models are
solved beyond the explicit symmetry limits. Phase transitions to rotational
structures are obtained, also in situations where there is no underlying SU(3)
symmetry.Comment: 25 LaTeX pages, 4 uuencoded postscript figures included, Preprint
IFT/8/94 & STPHY-TH/94-
Composition-induced structural transitions in mixed rare-gas clusters
The low-energy structures of mixed Ar--Xe and Kr--Xe Lennard-Jones clusters
are investigated using a newly developed parallel Monte Carlo minimization
algorithm with specific exchange moves between particles or trajectories. Tests
on the 13- and 19- atom clusters show a significant improvement over the
conventional basin-hopping method, the average search length being reduced by
more than one order of magnitude. The method is applied to the more difficult
case of the 38-atom cluster, for which the homogeneous clusters have a
truncated octahedral shape. It is found that alloys of dissimilar elements
(Ar--Xe) favor polytetrahedral geometries over octahedra due to the reduced
strain penalty. Conversely, octahedra are even more stable in Kr--Xe alloys
than in Kr_38 or Xe_38, and they show a core-surface phase separation behavior.
These trends are indeed also observed and further analysed on the 55-atom
cluster. Finally, we correlate the relative stability of cubic structures in
these clusters to the glassforming character of the bulk mixtures.Comment: 14 pages, 8 figures, 5 tables PRB vol 70, in pres
Observations of comet Levy 1990c in the (OI) 6300-A line with an imaging Fabry-Perot
We have observed the comet Levy 1990c during 16-25 August 1990 using the MPAE focal reducer system based Fabry-Perot etalon coupled with the 1 meter telescope of the Observatory of Hoher List. The free spectral range and resolution limit of the interferometer was approximately 2.18 A and approximately 0.171 A respectively. Classical Fabry-Perot fringes were recorded on a CCD in the cometary (OI) 6300 A line. They are well resolved from telluric air glow and cometary NH2 emission. Our observations indicate that the (OI) is distributed asymmetrically with respect to the center of the comet. In this paper we report the spatial distribution of (OI) emission and its line width in the coma of comet Levy
Doppler velocities in the ion tail of comet Levy 1990c
We have obtained time alternating sequences of column density maps and Doppler velocity fields in the plasma tail of comet Levy 1990c. We describe the observing technique and data analysis, and we present first results
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