3,866 research outputs found
R and D evaluation of a lightweight, high strength magnesium alloy Quarterly report, 1 Nov. 1967 - 1 Feb. 1968
High strength properties of magnesium-scandium alloys with selected additive
R and D evaluation of a lightweight, high strength magnesium alloy Quarterly report, 1 May - 1 Aug. 1969
Lightweight, high strength magnesium alloy development with magnesium-scandium-lithium selectio
R and D and evaluation of a lightweight, high strength magnesium alloy Quarterly report, 1 Feb. - 1 May 1969
Light weight high strength magnesium scandium allo
The two-site Bose--Hubbard model
The two-site Bose--Hubbard model is a simple model used to study Josephson
tunneling between two Bose--Einstein condensates. In this work we give an
overview of some mathematical aspects of this model. Using a classical
analysis, we study the equations of motion and the level curves of the
Hamiltonian. Then, the quantum dynamics of the model is investigated using
direct diagonalisation of the Hamiltonian. In both of these analyses, the
existence of a threshold coupling between a delocalised and a self-trapped
phase is evident, in qualitative agreement with experiments. We end with a
discussion of the exact solvability of the model via the algebraic Bethe
ansatz.Comment: 10 pages, 5 figures, submitted for publication in Annales Henri
Poincar
Bethe ansatz solution of the closed anisotropic supersymmetric U model with quantum supersymmetry
The nested algebraic Bethe ansatz is presented for the anisotropic
supersymmetric model maintaining quantum supersymmetry. The Bethe ansatz
equations of the model are obtained on a one-dimensional closed lattice and an
expression for the energy is given.Comment: 7 pages (revtex), minor modifications. To appear in Mod. Phys. Lett.
A planar extrapolation of the correlation problem that permits pairing
It was observed previously that an SU(N) extension of the Hubbard model is
dominated, at large N, by planar diagrams in the sense of 't Hooft, but the
possibility of superconducting pairing got lost in this extrapolation. To allow
for this possibility, we replace SU(N) by U(N,q), the unitary group in a vector
space of quaternions. At the level of the free energy, the difference between
the SU(N)and U(N,q) extrapolations appears only to first nonleading order in N.Comment: 8 pages, 2 figure
Classical and quantum dynamics of a model for atomic-molecular Bose--Einstein condensates
We study a model for a two-mode atomic-molecular Bose--Einstein condensate.
Starting with a classical analysis we determine the phase space fixed points of
the system. It is found that bifurcations of the fixed points naturally
separate the coupling parameter space into four regions. The different regions
give rise to qualitatively different dynamics. We then show that this
classification holds true for the quantum dynamics.Comment: 13 pages, 7 eps figure
Completeness of ``Good'' Bethe Ansatz Solutions of a Quantum Group Invariant Heisenberg Model
The -quantum group invariant spin 1/2 XXZ-Heisenberg model with open
boundary conditions is investigated by means of the Bethe ansatz. As is well
known, quantum groups for equal to a root of unity possess a finite number
of ``good'' representations with non-zero q-dimension and ``bad'' ones with
vanishing q-dimension. Correspondingly, the state space of an invariant
Heisenberg chain decomposes into ``good'' and ``bad'' states. A ``good'' state
may be described by a path of only ``good'' representations. It is shown that
the ``good'' states are given by all ``good'' Bethe ansatz solutions with roots
restricted to the first periodicity strip, i.e. only positive parity strings
(in the language of Takahashi) are allowed. Applying Bethe's string counting
technique completeness of the ``good'' Bethe states is proven, i.e. the same
number of states is found as the number of all restricted path's on the
-Bratteli diagram. It is the first time that a ``completeness" proof
for an anisotropic quantum invariant reduced Heisenberg model is performed.Comment: LaTeX file with LaTeX figures, 24 pages, 1 PiCTeX figur
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