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Comportamento multicrítico no modelo de Heisenberg frustrado: transições de fases clássica e quântica
(Universidade Federal de São Carlos, 2011-09-01) Nunes, Wagner Antonio da Silva; Souza, José Ricardo de; https://lattes.cnpq.br/0253265789709463
In this work we study the critical behavior of systems described by the Anysotropic- Heisenberg model of spin 1/2 with competitive interactions (J1-J2 Model) on planes, and interplane nearest-neighbor interactions. We applied Effective-Field techniques for finite clusters with two (EFT2) and four (EFT4) central sites, as well as Linear Spin-Waves Theory (LSWT). We define α=J2/J1, as the frustration parameter, which together with the the anysotropy exchange and the spatial one lambda, we obtain the respective phase diagrams. Classic phase transitions are studied at finite temperatures, as well as the quantum ones at T=0. We observed the presence of two ferromagnetic (antiferromagnetic) states, a quantum paramagnetic, colinear ferromagnetic (CF) and antiferromagnetic (CAF) at T=0 for J1 < 0 and J1 > 0. We characterized the type of transition (continuous or discontinuous) existing in them. For T > 0, the same phases are found, with the exception of the quantum and the normal paramagnetic ones. The CAF a CF states are characterized in three dimensions in the following way: spin lines with the same orientation adjacent to lines in the opposite sense, and spin planes with the same orientation adjacent to spin planes with opposite sense. In the two dimensions these two states are equivalent. We analyze the classical and quantum limits of the model through the phase destruction of PQ in the ferromagnetic and antiferromagnetic case under the influence of anisotropies. We also applied to the frustated model in the plane and the λ interaction between planes the Theory of Linear Spin Waves and compared their results with those found for the Effective Field Theory.
O ensino de análise combinatória no ensino médio por meio de atividades orientadoras em uma escola estadual do interior paulista
(Universidade Federal de São Carlos, 2011-09-01) Vazquez, Cristiane Maria Roque; Malagutti, Pedro Luiz Aparecido; https://lattes.cnpq.br/5462523657624050; https://lattes.cnpq.br/7759375964594345
This paper has the aim to describe the design, development and application of guiding teaching activities in an area that is usually little explored, the Combinatorics. The study was developed through an intervention that consisted of three activities applied to guiding students in four classes of second grade high school of a state school in São Paulo. The activities were designed with the goal of putting students in a position of action and decision making to facilitate the understanding and the process of knowledge construction and were developed in groups of four or five students. The research classified as naturalist, by the fact that data collection was carried out directly on the site where the problem, is the central issue is to verify whether the teaching of Combinatorics, without the excessive use of formulas, through tutoring activities and use of multiplicative principle, can improve the teaching and understanding of that content. The results were obtained by analyzing the activities addressed by the students who were recorded, by observation, by notes taken by the researchers and also by the evaluation at the end of the research. It was found that the activities were essential for guiding a better performance of students who felt more secure and confident to carry out new activities. These activities represent the final product of this work and it is expected that constitute reference material for teachers who tirelessly seek for new methodologies.