Made available in DSpace on 2015-03-03T15:15:29Z (GMT). No. of bitstreams: 1 FranciscoBLJ_DISSERT.pdf: 1340368 bytes, checksum: 23cf640d31d17bdd88ad96134433ceb1 (MD5) Previous issue date: 2013-11-29 / We studied the Ising model ferromagnetic as spin-1/2 and the Blume-Capel model as spin-1, > 0 on small world network, using computer simulation through the Metropolis algorithm. We calculated macroscopic quantities of the system, such as internal energy, magnetization, specific heat, magnetic susceptibility and Binder cumulant. We found for the Ising model the same result obtained by Koreans H. Hong, Beom Jun Kim and M. Y. Choi [6] and critical behavior similar Blume-Capel model / ?Neste trabalho estudamos o modelo de Ising ferromagn?tico com spin-1/2 e o modelo Blume-Capel com spin-1, ? > 0 em rede mundo pequeno, usando simula??o computacional atrav?s do algoritmo de Metropolis. Calculamos grandezas macrosc?picas do sistema, tais como a energia interna, a magnetiza??o, o calor espec?fico, a susceptibilidade magn?tica e o cumulante de Binder. Encontramos para o modelo de Ising o mesmo resultado obtido pelos Coreanos H. Hong, Beom Jun Kim e M. Y. Choi [6] e um comportamento cr?tico similar o modelo Blume-Capel.

The thesis deals with technologies of goods protection. It is focused on electronic technologies of goods protection, which call EAS (electronic article surveillance) in foreign literature. The goal of this thesis is support for instruction in electronic surveillance of goods. This document systematically describes principle and technical solution recent electronic technologies of goods protection. There are mentioned advantages and disadvantages too. The other chapter deals with basic operating mode and configuration parameters of loop systems, acoustic-magnetic system and radio system. On the basis of this was suggested laboratory task. This task is use for better understanding of principles electronic surveillance of goods. Some possible attacks of electronic surveillance of goods are described at the last chapter of this thesis. This attacks was also realized.

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Dois modelos descrevendo sistemas magnéticos modulados são estudados na presença de um campo magnético. Na primeira parte consideramos um modelo de Ising com interações competitivas numa única direção espacial (modelo ANNNI). A superfície crítica, a linha tricrítica, a estrutura das fases moduladas, e os diagramas de fases são determinados na aproximação de campo médio. O comportamento crítico e tricrítico é analisado através do método de Grupo de Renormalização. Na segunda parte estudamos um modelo adequado à descrição do composto MnP. Cálculos realizados na aproximação de campo médio e através do método de Grupo de Renormalização contribuem para esclarecer os resultados experimentais acerca do ponto de Lifshitz observado neste composto. / Two models describing modulated magnetic systems are studied in the presence of a magnetic field. The first part is dedicated to the study of an Ising model with competing interactions along one of the spatial directions (ANNNI model). The critical surface, the tricritical line, the structure of the modulated phases, and the phase diagrams are determined in the mean field approximation. The critical and the tricritical behaviour is analised by the Renormalization Group method. The second part is concerned with a model suitable for the description of the compound MnP. Calculations carried out in the mean field approximation and through the Renormalization Group method provide a better understanding of the experimental results on the Lifshitz point observed in this compound.

Dois modelos descrevendo sistemas magnéticos modulados são estudados na presença de um campo magnético. Na primeira parte consideramos um modelo de Ising com interações competitivas numa única direção espacial (modelo ANNNI). A superfície crítica, a linha tricrítica, a estrutura das fases moduladas, e os diagramas de fases são determinados na aproximação de campo médio. O comportamento crítico e tricrítico é analisado através do método de Grupo de Renormalização. Na segunda parte estudamos um modelo adequado à descrição do composto MnP. Cálculos realizados na aproximação de campo médio e através do método de Grupo de Renormalização contribuem para esclarecer os resultados experimentais acerca do ponto de Lifshitz observado neste composto. / Two models describing modulated magnetic systems are studied in the presence of a magnetic field. The first part is dedicated to the study of an Ising model with competing interactions along one of the spatial directions (ANNNI model). The critical surface, the tricritical line, the structure of the modulated phases, and the phase diagrams are determined in the mean field approximation. The critical and the tricritical behaviour is analised by the Renormalization Group method. The second part is concerned with a model suitable for the description of the compound MnP. Calculations carried out in the mean field approximation and through the Renormalization Group method provide a better understanding of the experimental results on the Lifshitz point observed in this compound.