46 research outputs found
Energy of bond defects in quantum spin chains obtained from local approximations and from exact diagonalization
We study the influence of ferromagnetic and antiferromagnetic bond defects on
the ground-state energy of antiferromagnetic spin chains. In the absence of
translational invariance, the energy spectrum of the full Hamiltonian is
obtained numerically, by an iterative modification of the power algorithm. In
parallel, approximate analytical energies are obtained from a local-bond
approximation, proposed here. This approximation results in significant
improvement upon the mean-field approximation, at negligible extra
computational effort.Comment: 3 pages, 2 figures. Manuscript accepted by Journal of Magnetism and
Magnetic Materials, special issue for LAWMMM 2007 conferenc
A interpretação quântica do mundo
A interpretação científica do mundo, embora sempre pautada em observações criteriosas dos fenômenos naturais, depende do estágio de evolução ou do nível cultural em que vivemos. O desenvolvimento da Mecânica Quântica é o mais belo exemplo disso, em que uma boa dose de criatividade foi necessária frente às dificuldades que a Física Clássica apresentava no final do século XIX. Os novos conceitos criados, como a universalidade da dualidade onda-partícula ou o princípio de incerteza norteando processos de medida, regem toda a matéria e não tem análogos na Física Clássica. Embora reinante em escalas subatômicas, recentemente tem-se evidenciado traços de propriedades quânticas fundamentais mesmo no mundo macroscópico.The scientific interpretation of the world, although based on natural phenomena, depends upon our evolutionary stage or cultural level. The development of Quantum Mechanics is one of the most beautiful example of that, in which a great deal of creativity was necessary to overcome the difficulties encountered by the Classical Physics in the end of the 19th century. The new concepts, like the universality of the wave-particle duality or the uncertainty principle in the measuring process, which govern the behavior of all matter, have no analogous in the Classical Physics. Although essential in the subatomic scales, traces of fundamental quantum properties are recently found even in the macroscopic world
Transição de fase num antiferromagneto compressível com acoplamento biquadrático
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Curso de Pós-Graduação em Físico-Químic
Impurity and boundary effects in one and two-dimensional inhomogeneous Heisenberg antiferromagnets
We calculate the ground-state energy of one and two-dimensional spatially
inhomogeneous antiferromagnetic Heisenberg models for spins 1/2, 1, 3/2 and 2.
Our calculations become possible as a consequence of the recent formulation of
density-functional theory for Heisenberg models. The method is similar to
spin-density-functional theory, but employs a local-density-type approximation
designed specifically for the Heisenberg model, allowing us to explore
parameter regimes that are hard to access by traditional methods, and to
consider complications that are important specifically for nanomagnetic
devices, such as the effects of impurities, finite-size, and boundary geometry,
in chains, ladders, and higher-dimensional systems.Comment: 4 pages, 4 figures, accepted by Phys. Rev.
Educação do campo : alternativas metodológicas para uma prática educacional de qualidade
Orientador : Luiz Fernando de Carli LautetArtigo apresentado como Trabalho de Conclusão de CursoArtigo (Especialização) - Universidade Federal do Paraná, Setor Litoral, Curso de Especialização em Educação do CampoInclui referênciasResumo: O referido trabalho está voltado para a análise e estudos sobre as metodologias aplicadas na modalidade educacional da Educação do Campo, bem como se sua prática está contribuindo para uma educação inclusiva e de qualidade. Também, busca-se direcionar os trabalhos práticos dos educadores que, hoje atuam na educação do campo de forma mais consciente, buscando a partir do conhecimento sobre seu surgimento, valorizá-la e acima de tudo, permitir que o homem atuante no campo possa continuar com suas atividades rurais, não sendo prejudicado na busca da aprendizagem, visto que esta valorização e necessária, e com ela, a revisão das metodologias que até então só visavam atender o estudante urban
Morbach, o poeta do nankim!
Neste artigo – publicado originalmente na revista Terra Imatura, em 1940 – Líbero Luxardo (Sorocaba/SP, 1908 – Belém/PA, 1980) tece uma crônica sobre a cidade de Marabá e sobre o artista Augusto Morbach (Itaguatins/GO, 1911 – Belém/PA, 1981), acompanhada de três ilustrações que são possivelmente de autoria de Morbach. Luxardo compila, também, comentários de outros intelectuais a respeito do artista. O artigo é aqui acompanhado por Nota Explicativa de Gil Vieira Costa (ILLA/Unifesspa), responsável pela transcrição e adaptação ortográfica do texto original
Spin-density-functional theory: some open problems and application to inhomogeneous Heisenberg models
Spin-density-functional theory (SDFT) is the most widely implemented and
applied formulation of density-functional theory. However, it is still finding
novel applications, and occasionally encounters unexpected problems. In this
paper we first briefly describe a few of the latter, related to issues such as
nonuniqueness, noncollinearity, and currents. In the main part we then turn to
an example of the former, namely SDFT for the Heisenberg model. It is shown
that time-honored concepts of Coulomb DFT, such as the local-density
approximation, can be applied to this (and other) model Hamiltonians, too, once
the concept of 'density' has been suitably reinterpreted. Local-density-type
approximations for the inhomogeneous Heisenberg model are constructed.
Numerical applications to finite-size and impurity systems demonstrate that DFT
is a computationally efficient and reasonably accurate alternative to
conventional methods of statistical mechanics for the Heisenberg model.Comment: 15 pages, 1 figure, 1 tabl
Numerical renormalization group computation of temperature dependent specific heat for a two-channel Anderson model
The Numerical Renormalization Group (NRG) is applied to diagonalize a two-channel Anderson model describing a local magnetic impurity embedded in a fermionic bath. In spite of the difficulty in computing the specific heat using NRG, the interleaving discretization and multi-step iterative transformation virtually eliminate the numerical oscillations introduced by the logarithmic discretization of the conduction band. These allow to cover uniformly a large range of temperature, from the top of the band to a very small fraction of the bandwidth. This is relevant in describing, for instance, the presence of a low temperature Kondo resonance together with a high temperature Schottky peak, as well to cover Fermi and non-Fermi liquid regimes, like in the recent studied Ce1−xLaxNi9Ge4Ce1−xLaxNi9Ge4 family. We highlight the importance in describing the Schottky peak to define the number of degrees of freedom of the local levels, in order to correctly define the model to describe a given compound.CNPqCAPESFUNDECT-M