The ground-state phase diagram of the one-dimensional asymmetric Hubbard model at half-filling is studied by means of a perturbation expansion in the large-U limit and White s density matrix renormalization-group method for various values of the couplings. We argue that the introduction of asymmetry in the hopping parameters is a relevant perturbation for any repulsive U and drives the system into an ordered Neel antiferromagnet. The transition belongs to the Kosterlitz-Thouless universality class.
Ground-state properties of the asymmetric Hubbard model are studied on one-dimensional clusters (rings) with N = 6, 6, and 10 sites. The ground-state energy, correlation functions, and phase diagrams are determined for various sets of model parameters. Computations are performed both by exact diagonalization (for N = 6) and by an approximate method by which correlation efiect's can be examined on larger clusters than exact diagonalization allows. In the limiting cases (one limit corresponds to the spinless Falicov-Kimball model and the other to the Hubbard model) our results agree quite well with those obtained analytically for in6nite systems.
The paper presents the method to analyse the thermal processes occurring in the cast composite solidification. The cast is formed by a bundle of parallel fibres randomly immersed in a host metal matrix. The heat is transferred from the metal matrix and absorbed by the fibres. The objective of this paper is to evaluate the volumetric fraction of the fibres for which the solidification of the metal matrix occurs only due to the presence of fibres playing a role of internal chills. Our method is to compute Voronoi diagrams with Voronoi regions representing the geometric location of the fibres in the metal matrix and to use these regions as control volumes within a variant of the Control Volume Method.
We study a quantum generalization of the infinite-range
Sherrington-Kirkpatrick spin-glass model with biaxial crystal-field
effects described by two uniaxial anisotropy parameters Dx and
Dy. For spin dimensionality S = 1 we report an analytical and
numerical analysis in the (T, Dx, Dy) parameter space (with T
being the temperature). For D ≡ Dx = Dy the model effectively
becomes classical and identical with the crystal-field-split spin-glass
Ising model (introduced by Ghatak and Sherrington) showing
a discontinuous phase transition to the spin-glass phase on a portion
of the T-D line.
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