107 research outputs found
Critical properties of the XXZ model with long-range interactions on the double chain
The model in a transverse field on a double chain with a
uniform long-range interaction among the components of the spins is
considered. The nearest-neighbour interactions are restricted to the components
in the plane and to the spins within the same chain leg, such that the
Hamiltonian is given by , where is the number of sites of the lattice and
label the chain legs. The model is solved exactly by
introducing the Jordan-Wigner and integral Gaussian transformations, which map
the Hamiltonian in a non-interacting fermion system and corresponds to an
extension of the model recently studied by the authors for a single chain. The
equation of state is obtained in closed form, and the critical classical (at ) and quantum (at ) behaviours can be determined exactly. The
quantum critical surface is determined in the space generated by the transverse
field and interaction parameters, and the crossover lines separating the
different critical regimes are also obtained. It is also shown that,
differently from the results obtained for the single chain, the system can
present multiple quantum transitions.Comment: 02 pages, 02 figures, to appear in JMMM (Proceedings of ICM2006
The XY model on the one-dimensional superlattice: static properties
The XY model (s=1/2) on the one-dimensional alternating superlattice (closed
chain) is solved exactly by using a generalized Jordan-Wigner transformation
and the Green function method. Closed expressions are obtained for the
excitation spectrum, the internal energy, the specific heat, the average
magnetization per site, the static transverse susceptibility and the two-spin
correlation function in the field direction at arbitrary temperature. At T=0 it
is shown that the system presents multiple second order phase transitions
induced by the transverse field, which are associated to the zero energy mode
with wave number equal to 0 or . It is also shown that the average
magnetization as a function of the field presents, alternately, regions of
plateaux (disordered phases) and regions of variable magnetization (ordered
phases). The static correlation function presents an oscillating behaviour in
the ordered phase and its period goes to infinity at the critical point.Comment: 16 pages, 16 figure
Fractal Power Law in Literary English
We present in this paper a numerical investigation of literary texts by
various well-known English writers, covering the first half of the twentieth
century, based upon the results obtained through corpus analysis of the texts.
A fractal power law is obtained for the lexical wealth defined as the ratio
between the number of different words and the total number of words of a given
text. By considering as a signature of each author the exponent and the
amplitude of the power law, and the standard deviation of the lexical wealth,
it is possible to discriminate works of different genres and writers and show
that each writer has a very distinct signature, either considered among other
literary writers or compared with writers of non-literary texts. It is also
shown that, for a given author, the signature is able to discriminate between
short stories and novels.Comment: 27 pages, 10 tables,15 figures. Revised version accepted in Physica
The one-dimensional XXZ model with long-range interactions
The one-dimensional XXZ model (s=1/2, N sites) with uniform long-range
interactions among the transverse components of the spins is considered. The
Hamiltonian of the model is explicitly given by
where the
are half the Pauli spin matrices. The model is exactly solved by
applying the Jordan-Wigner fermionization, followed by a Gaussian
transformation. In the absence of the long-range interactions (I=0), the model,
which reduces to the isotropic XY model, is known to exhibit a second-order
quantum phase transition driven by the field at zero temperature. It is shown
that in the presence of the long-range interactions (I different from 0) the
nature of the transition is strongly affected. For I>0, which favours the
ordering of the transverse components of the spins, the transition is changed
from second- to first-order, due to the competition between transverse and xy
couplings. On the other hand, for I<0, which induces complete frustration of
the spins, a second-order transition is still present, although the system is
driven out of its usual universality class, and its critical exponents assume
typical mean-field values.Comment: 5 pages, 1 figure, presented at ICM2000, to be published in the
Proceedings (Journal of Magnetism & Magnetic Materials
Project Proof: Internet Enabled Process Reengineering at J.D. Edwards & Company
J.D. Edwards is a provider of the new generation of ERP and collaborative commerce solutions. This case study describes the challenges faced internally by the company to upgrade to the latest enterprise software it would sell to the world. Dubbed Project PROOF, the project started in June 2001 and was completed in November 2002. The perspectives of the CIO, the program manager, and other key personnel are presented. The case study highlights the issues that arise in an enterprise software implementation project. In addition, the case touches upon issues of project management, process redesign, and marketing. The case study uses a multimedia format to add richness and detail. Although J.D. Edwards was acquired in 2003, the issues discussed are relevant to current business practices
Economic injury level for sugarcane caused by the spittlebug Mahanarva fimbriolata (Stål) (Hemiptera:Cercopidae)
EDUCAÇÃO A DISTÂNCIA E OLIMPÍADA NACIONAL DE HISTÓRIA DO BRASIL: O ÊXITO DA MODALIDADE EM UM PROGRAMA INOVADOR
The tools of distance education have been used in numerous teaching, research and extension experiences, corroborating with the quality of teaching that can be achieved with this modality. This study aims to analyze the National History Olimpic of Brazil (NHOB), an extension program maintained at the State University of Campinas, as a successful experiment in use of educational technologies to promote innovation in teaching and the possibility of research. The methodology adopted is a case study, with a qualitative approach, in a historicist perspective. We conclude that the NHOB program has reached thousands of students across the country, encouraging study and research in history, because it increases the possibilities of information and communication technologies, making them efficient means of knowledge.As ferramentas da educação a distância vêm sendo utilizadas em inúmeras experiências de ensino, pesquisa e extensão, corroborando a qualidade de ensino que se pode atingir com essa modalidade. Este estudo tem como objetivo analisar a Olimpíada Nacional de História do Brasil (ONHB), programa de extensão mantido pela Universidade Estadual de Campinas, como experiência exitosa no uso de tecnologias educacionais para promover inovação no ensino e possibilidade de pesquisa. A metodologia adotada é o estudo de caso, de abordagem qualitativa, numa perspectiva historicista. Concluímos que o programa ONHB alcançou a milhares de estudantes por todo o país, incentivando o estudo e a pesquisa em história, porque valeu-se das possibilidades das tecnologias de informação e comunicação, tornando-as meios de aprendizagem eficientes
Autonomous multispecies reaction-diffusion systems with more-than-two-site interactions
Autonomous multispecies systems with more-than-two-neighbor interactions are
studied. Conditions necessary and sufficient for closedness of the evolution
equations of the -point functions are obtained. The average number of the
particles at each site for one species and three-site interactions, and its
generalization to the more-than-three-site interactions is explicitly obtained.
Generalizations of the Glauber model in different directions, using generalized
rates, generalized number of states at each site, and generalized number of
interacting sites, are also investigated.Comment: 9 pages, LaTeX2
Urinary Estrogen Metabolites and Self-Reported Infertility in Women Infected with Schistosoma haematobium
Schistosomiasis is a neglected tropical disease, endemic in 76 countries, that afflicts more than 240 million people. The impact of schistosomiasis on infertility may be underestimated according to recent literature. Extracts of Schistosoma haematobium include estrogen-like metabolites termed catechol-estrogens that down regulate estrogen receptors alpha and beta in estrogen responsive cells. In addition, schistosome derived catechol-estrogens induce genotoxicity that result in estrogen-DNA adducts. These catechol estrogens and the catechol-estrogen-DNA adducts can be isolated from sera of people infected with S. haematobium. The aim of this study was to study infertility in females infected with S. haematobium and its association with the presence of schistosome-derived catechol-estrogens
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