9 research outputs found
Exact results for the optical absorption of strongly correlated electrons in a half-filled Peierls-distorted chain
In this second of three articles on the optical absorption of electrons in a
half-filled Peierls-distorted chain we present exact results for strongly
correlated tight-binding electrons. In the limit of a strong on-site
interaction we map the Hubbard model onto the Harris-Lange model which can
be solved exactly in one dimension in terms of spinless fermions for the charge
excitations. The exact solution allows for an interpretation of the charge
dynamics in terms of parallel Hubbard bands with a free-electron dispersion of
band-width , separated by the Hubbard interaction . The spin degrees of
freedom enter the expressions for the optical absorption only via a momentum
dependent but static ground state expectation value. The remaining spin problem
can be traced out exactly since the eigenstates of the Harris-Lange model are
spin-degenerate. This corresponds to the Hubbard model at temperatures large
compared to the spin exchange energy. Explicit results are given for the
optical absorption in the presence of a lattice distortion and a
nearest-neighbor interaction . We find that the optical absorption for
is dominated by a peak at and broad but weak absorption bands for . For an appreciable nearest-neighbor interaction, ,
almost all spectral weight is transferred to Simpson's exciton band which is
eventually Peierls-split.Comment: 50 pages REVTEX 3.0, 6 postscript figures; hardcopy versions before
May 96 are obsolete; accepted for publication in The Philosophical Magazine
Economic potential and development prospects of small businesses in rural areas
The article examines the role of small business in the development of rural areas by the example of bakery production. Moreover, it demonstrates the need for the interaction of small bakery businesses with large enterprises of the industry and grain processors.
The article reveals the development trends of small bakery production in rural areas. The conditions for the participation of small bakery businesses in rural areas in the development of the production of functional and specialized bread are substantiated.
The article proposes the directions and mechanisms of support for small bakery production at the level of rural territories. The development of modern methods of redistribution of bakery production in proportion to the living population, measures of state support for small bakery production and expansion of the range of bread products that contribute to improving the health of the population of Russia, is the theme of this study.
The object of the research is the development of small bakery production as a condition for improving the quality of life of the population in rural areas. The subject of the research is production and management relations that ensure the development of small bakery production and its impact on the quality of life of the population in rural areas.peer-reviewe
Parameters of the Effective Singlet-Triplet Model for Band Structure of High- Cuprates by Different Approaches
The present paper covers the problem of parameters determination for
High- superconductive copper oxides. Different approaches, {\it ab initio}
LDA and LDA+U calculations and Generalized Tight-Binding (GTB) method for
strongly correlated electron systems, are used to calculate hopping and
exchange parameters of the effective singlet-triplet model for -layer.
The resulting parameters are in remarkably good agreement with each other and
with parameters extracted from experiment. This set of parameters is proposed
for proper quantitative description of physics of hole doped High-
cuprates in the framework of effective models.Comment: PACS 74.72.h; 74.20.z; 74.25.Jb; 31.15.A