186 research outputs found
Quasi Regular Polyhedra and Their Duals with Coxeter Symmetries Represented by Quaternions I
In two series of papers we construct quasi regular polyhedra and their duals
which are similar to the Catalan solids. The group elements as well as the
vertices of the polyhedra are represented in terms of quaternions. In the
present paper we discuss the quasi regular polygons (isogonal and isotoxal
polygons) using 2D Coxeter diagrams. In particular, we discuss the isogonal
hexagons, octagons and decagons derived from 2D Coxeter diagrams and obtain
aperiodic tilings of the plane with the isogonal polygons along with the
regular polygons. We point out that one type of aperiodic tiling of the plane
with regular and isogonal hexagons may represent a state of graphene where one
carbon atom is bound to three neighboring carbons with two single bonds and one
double bond. We also show how the plane can be tiled with two tiles; one of
them is the isotoxal polygon, dual of the isogonal polygon. A general method is
employed for the constructions of the quasi regular prisms and their duals in
3D dimensions with the use of 3D Coxeter diagrams.Comment: 22 pages, 16 figure
Inter-site Coulomb interaction and Heisenberg exchange
Based on exact diagonalization results for small clusters we discuss the
effect of inter-site Coulomb repulsion in Mott-Hubbard or charge transfer
insulators. Whereas the exchange constant J for direct exchange is
substantially enhanced by inter-site Coulomb interaction, that for
superexchange is suppressed. The enhancement of J in the single-band models
holds up to the critical value for the charge density wave (CDW) instability,
thus opening the way for large values of J. Single-band Hubbard models with
sufficiently strong inter-site repulsion to be near a CDW instability thus may
provide `physical' realizations of t-J like models with the `unphysical'
parameter ratio J/t=1.Comment: Revtex file, 4 PRB pages, with 5 embedded ps-files. To appear in PRB,
rapid communications. Hardcopies of figures or the entire manuscript may also
be obtained by e-mail request to: [email protected]
Estudo da curva de crescimento de bubalinos da raça Murrah criados no estado do Rio Grande do Sul.
Objetivou-se identificar um modelo, dentre oito citados na literatura, que melhor descreva a curva de crescimento de bubalinos da raça Murrah criados no estado de Rio Grande do Sul. Foram utilizadas informações de 42 machos e 48 fêmeas da raça Murrah, nascidos entre 2009 e 2011, totalizando 624 pares de registros peso-idade do nascimento até 750 dias de idades. Os parâmetros dos modelos foram estimados por meio de regressão não-linear pelo procedimento NLIN (SAS system), utilizando-se o método de Gauss Newton. Os critérios para a escolha do melhor ajuste foram: o quadrado médio dos resíduos (QMR), o desvio médio absoluto (DMA), o índice e a avaliação visual do gráfico dos valores observados e estimados. Com base no do QMR, DMA e o índice, constatou-se que o modelo Richards (1959) apresentou melhor ajuste, seguido pelo modelo Von Bertalanffy (1957). Com isto, o modelo Richards (1959) dentre os testados foi capaz de descrever o crescimento de búfalos da raça Murrah criados no estado do Rio Grande do Sul
Theory of Superconducting of doped fullerenes
We develop the nonadiabatic polaron theory of superconductivity of
taking into account the polaron band narrowing and realistic
electron-phonon and Coulomb interactions. We argue that the crossover from the
BCS weak-coupling superconductivity to the strong-coupling polaronic and
bipolaronic superconductivity occurs at the BCS coupling constant independent of the adiabatic ratio, and there is nothing ``beyond'' Migdal's
theorem except small polarons for any realistic electron-phonon interaction. By
the use of the polaronic-type function and the ``exact'' diagonalization in the
truncated Hilbert space of vibrons (``phonons'') we calculate the ground state
energy and the electron spectral density of the molecule. This
allows us to describe the photoemission spectrum of in a wide
energy region and determine the electron-phonon interaction. The strongest
coupling is found with the high-frequency pinch mode and with the
Frenkel exciton. We clarify the crucial role of high-frequency bosonic
excitations in doped fullerenes which reduce the bare bandwidth and the Coulomb
repulsion allowing the intermediate and low-frequency phonons to couple two
small polarons in a Cooper pair. The Eliashberg-type equations are solved for
low-frequency phonons. The value of the superconducting , its pressure
dependence and the isotope effect are found to be in a remarkable agreement
with the available experimental data.Comment: 20 pages, Latex, 4 figures available upon reques
Fourier-Space Crystallography as Group Cohomology
We reformulate Fourier-space crystallography in the language of cohomology of
groups. Once the problem is understood as a classification of linear functions
on the lattice, restricted by a particular group relation, and identified by
gauge transformation, the cohomological description becomes natural. We review
Fourier-space crystallography and group cohomology, quote the fact that
cohomology is dual to homology, and exhibit several results, previously
established for special cases or by intricate calculation, that fall
immediately out of the formalism. In particular, we prove that {\it two phase
functions are gauge equivalent if and only if they agree on all their
gauge-invariant integral linear combinations} and show how to find all these
linear combinations systematically.Comment: plain tex, 14 pages (replaced 5/8/01 to include archive preprint
number for reference 22
Modeling Data Containing Outliers using ARIMA Additive Outlier (ARIMA-AO)
The aim this study is discussed on the detection and correction of data
containing the additive outlier (AO) on the model ARIMA (p, d, q). The process
of detection and correction of data using an iterative procedure popularized by
Box, Jenkins, and Reinsel (1994). By using this method we obtained an ARIMA
models were fit to the data containing AO, this model is added to the original
model of ARIMA coefficients obtained from the iteration process using
regression methods. This shows that there is an improvement of forecasting
error rate data.Comment: 13 page
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