Superconductivity and incommensurate spin fluctuations in a generalized t-J model for the cuprates

We consider the slave-fermion Schwinger-boson decomposition of an effective model obtained through a systematic low-energy reduction of the three-band Hubbard Hamiltonian. The model includes a three-site term t'' similar to that obtained in the large-U limit of the Hubbard model but of opposite sign for realistic or large O-O hopping. For parameters close to the most realistic ones for the cuprates, the mean-field solution exhibits d+s superconductivity (predominantly d_{x^2-y^2}) with a dependence on doping x very similar to the experimentally observed. We also obtained incommensurate peaks at wave vectors near $\pi (1,1 +(-) 2x)$ in the spin structure factor, which also agree with experiment.Comment: 9 pages, latex, 2 figures, to appear in Europhys. Let

Fractal Descriptors in the Fourier Domain Applied to Color Texture Analysis

The present work proposes the development of a novel method to provide descriptors for colored texture images. The method consists in two steps. In the first, we apply a linear transform in the color space of the image aiming at highlighting spatial structuring relations among the color of pixels. In a second moment, we apply a multiscale approach to the calculus of fractal dimension based on Fourier transform. From this multiscale operation, we extract the descriptors used to discriminate the texture represented in digital images. The accuracy of the method is verified in the classification of two color texture datasets, by comparing the performance of the proposed technique to other classical and state-of-the-art methods for color texture analysis. The results showed an advantage of almost 3% of the proposed technique over the second best approach.Comment: Chaos, Volume 21, Issue 4, 201

Quantum Phase Diagram of the t-Jz Chain Model

We present the quantum phase diagram of the one-dimensional $t$-$J_z$ model for arbitrary spin (integer or half-integer) and sign of the spin-spin interaction $J_z$, using an {\it exact} mapping to a spinless fermion model that can be solved {\it exactly} using the Bethe ansatz. We discuss its superconducting phase as a function of hole doping $\nu$. Motivated by the new paradigm of high temperature superconductivity, the stripe phase, we also consider the effect the antiferromagnetic background has on the $t$-$J_z$ chain intended to mimic the stripe segments.Comment: 4 pages, 2 figure

Práticas de letramentos: cartilhas das minibibliotecas na formação de educadores kalungas, na licenciatura em educação do campo, da Universidade de Brasilia.

Este estudo apresenta o uso das Cartilhas de Boas Práticas de Manejo para o Extrativismo Sustentável de: Buriti, Mangaba, Umbu, Pequi e Coquinho Azedo, das Minibibliotecas da Embrapa, na formação em letramentos múltiplos de educandos da Turma V, da licenciatura em Educação do Campo (LEdoC), do Campus da Faculdade de Planaltina (FUP), da Universidade de Brasília - UnB, especialmente, os educandos com origem em comunidades Kalungas do nordeste goiano. A formação em letramentos múltiplos representa uma importante estratégia na formação integral, contribuindo com a autonomia e autoria desses educandos, na perspectiva de formar intelectuais orgânicos conforme preconizado por Gramsci. As Minibibliotecas se constituem em uma iniciativa da Embrapa Informação Tecnológica que pretende contribuir com as dinâmicas de escolarização e incentivo à leitura no meio rural, por meio do uso de mídia impressa (livros e cartilhas) e mídia eletrônica (cds e dvds). A intencionalidade de acrescentar as dinâmicas de uso dessas Cartilhas da Minibibliotecas nas estratégias de formação em letramentos múltiplos da LEdoC, aponta a perspectiva de analisar criticamente esses conteúdos, no contexto da Educação do Campo e das comunidades Kalungas e de contribuir com os letramentos múltiplos desses educandos, especialmente na produção e sistematização crítica de conhecimentos. A base teórica que fundamenta a experiência está ancorada nos conceitos de autoria e autonomia de Gramsci (2009); na constituição de um sujeito questionador de FREIRE (1996); letramentos múltiplos de ROJO (2009). Esta é uma pesquisa qualitativa sob a perspectiva da Etnografia Colaborativa, que permitiu realizar uma análise mais integrada, considerando a diversidade e complexidade social existente no ambiente pedagógico da LEdoC e nas comunidades Kalungas de origem dos educandos. As análises evidenciam a vinculação forte desses educandos com a identidade Kalunga; a perspectiva positiva do uso das Cartilhas nas atividades de produção textual (resenhas e narrativas) e, especialmente, o papel preponderante da Licenciatura em Educação do Campo na formação integral desses educandos.Dissertação (Mestrado em Educação) - Faculdade de Educação, Universidade de Brasília, Brasília, DF

Quantum Cosmology of Fab Four John Theory with Conformable Fractional Derivative

We study a quantization via fractional derivative of a nonminimal derivative coupling cosmological theory, namely, the Fab Four John theory. Its Hamiltonian version presents the issue of fractional powers in the momenta. That problem is solved here by the application of the so-called conformable fractional derivative. This leads to a Wheeler\u2013DeWitt equation of second order, showing that a Bohm\u2013de Broglie interpretation can be constructed. That combination of fractional quantization and Bohmian interpretation provides us a new quantization method, in which the quantum potential is the criterion to say if a quantum solution is acceptable or not to be further studied. We show that a wide range of solutions for the scale factor is possible. Among all of those, a bouncing solution analogous to the perfect fluid cosmology seems to deserve special attention

The dimerized phase of ionic Hubbard models

We derive an effective Hamiltonian for the ionic Hubbard model at half filling, extended to include nearest-neighbor repulsion. Using a spin-particle transformation, the effective model is mapped onto simple spin-1 models in two particular cases. Using another spin-particle transformation, a slightly modified model is mapped into an SU(3) antiferromagnetic Heisenberg model whose exact ground state is known to be spontaneously dimerized. From the effective models several properties of the dimerized phase are discussed, like ferroelectricity and fractional charge excitations. Using bosonization and recent developments in the theory of macroscopic polarization, we show that the polarization is proportional to the charge of the elementary excitations