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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modelo de Ashkin-Teller anisotr?pico: uma abordagem por grupo de renormaliza??o

Bezerra, Claudionor Gomes 24 May 1994 (has links)
Made available in DSpace on 2014-12-17T15:14:59Z (GMT). No. of bitstreams: 1 ClaudionorGB_DISSERT.pdf: 2304268 bytes, checksum: 610cbceb61cd582290dc8b795fa3a210 (MD5) Previous issue date: 1994-05-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Estudamos as propriedades cr?ticas (diagrama de fases e classes de universalidade) do modelo de Ashkin-Teller anisotr?pico ferromagn?tico, cujo hamiltoniano ? dado por: H = -&#8721;_(<ij>)&#9618;&#12310;{J1TiTj+J2&#963;i&#963;j+J4&#963;i&#963;jTiTj}&#12311; com: J1 + J2 &#8805; 0, J1 + J4 &#8805; 0 , J2 + J4 &#8805; 0, ( &#963;, r = ? 1 ). Utilizamos o m?todo do Grupo de Renormaliza??o no espa?o real, aplicado a uma rede hier?rquica que serve como aproxima??o para a rede quadrada. Observamos a exist?ncia de 5 fases : (i) Paramagn?tica ( P : < &#963; > =< &#428; > =< &#963;&#428; >= 0) ; (ii) Intermedi?ria ( I : < &#963; > =< &#428; >= 0, < &#963;&#428; > &#8800; 0) ; (iii) Ferromagn?tica ( F : < &#963; > &#8800; 0, < &#428; > &#8800; 0, < &#963;&#428; > &#8800; 0) ; (iv) Ferro &#963; ( F&#963; : < &#963; > &#8800; 0, < &#428; >=< &#963;&#428; >= 0 ) ; (v) Ferro &#963; ( F&#428; : < &#428; > &#8800; 0, < &#963; >=< &#963;&#428; >= 0 ). As fronteiras cr?ticas obtidas reproduzem todos os valores exatos conhecidos (em pontos especiais) para a rede quadrada
2

Modelo de ashkin-teller de tr?s cores na rede ponte de wheatstone

Oliveira, Roberto Teodoro Gurgel de 22 February 2010 (has links)
Made available in DSpace on 2014-12-17T15:14:51Z (GMT). No. of bitstreams: 1 RobertoTGO_DISSERT.pdf: 394069 bytes, checksum: fbb8faf7e24cc92335302e442b92ec43 (MD5) Previous issue date: 2010-02-22 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / In this work we study the phase transitions of the ferromagnetic three-color Ashkin-Teller Model in the hierarquical lattice generated by the Wheatstone bridge using real space renormalization group approach. With such technique we obtain the phase diagram and its critical points with respective critical exponents v. This model presents four phases: ferromagnetic, paramagnetic and two intermediates. Nine critical points were found, three of which are of Ising model type, three are of four states Potts model type, one is of eight states Potts model type and the last two which do not correspond to any Potts model with integer number of states. iv / Neste trabalho estudamos as transi??es de fase do modelo de Ashkin-Teller de tr?s cores ferromagn?tico na rede hier?rquica ponte de Wheatstone utilizando o m?todo de grupo de renormaliza??o no espa?o real. Com a utiliza??o desta t?cnica obtemos o diagrama de fases e seus pontos cr?&#305;ticos com respectivos expoentes cr?ticos v. O modelo apresenta quatro fases: ferromagn?tica, paramagn?tica e duas intermedi?rias. Nove pontos cr?&#305;ticos foram encontrados, sendo tr?s de classe de universalidade Ising, tr?s Potts de quatro estados, um Potts de oito estados e dois com classe de universalidade n?o correspondente a nenhum Potts com n?mero inteiro de estados

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