String Theory
Mostrando 13-24 de 32 artigos, teses e dissertações.
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13. A simple theory for vibration of MRI gradient coils
Vibrations of a string can provide a model for vibrations of MRI coil assemblies. The string model for the vibrations of MRI coils is presented, and compared with experimental results. Gradient coils exhibit resonant modes because of the finite coil length, l, and the elasticity of materials that comprise the assembly. The resonance frequencies depend on l a
Brazilian Journal of Physics. Publicado em: 2006-03
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14. "Branas em supergravidade" / Branes in supergravity
This work intends to review the brane solutions of supergravity and contains a datailed deduction of the extremal and black solutions. In order to provide some motivations to the choices through the calculation, this work includes a brief review of some concepts from string theory and supersymmetry. This review will enable us to relate the supergravity solut
Publicado em: 2006
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15. Aplicação de autômatos finitos nebulosos no reconhecimento aproximado de cadeias. / The approximate string matching using fuzzy finite automata.
The approximate string matching problem is recurring in many applications where computer is used to process imprecise, fuzzy or spurious data. An uncountable number of methods, techniques and metrics to solve this class of problem are available, but many of them are inflexible at least in one of following: architecture, metric or application specifics. This
Publicado em: 2006
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16. On current-carrying cosmic strings and the generalized rainich algebra in scalar-tensor gravities
We obtain exact solutions for a static and charged cosmic string in a Einstein-Maxwell-Dilaton theory of a scalar-tensor type in (3+1)-Dimensions. This theory is specified by the dilaton field phi, the graviton field gµn and the electromagnetic field Fµn, and one post-Newtonian parameter alpha(phi). It contains three different cases, each of them correspon
Brazilian Journal of Physics. Publicado em: 2005-12
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17. Classification of energy momentum tensors in n > 5 dimensional space-times: a review
Recent developments in string theory suggest that there might exist extra spatial dimensions, which are not small nor compact. The framework of a great number of brane cosmological models is that in which the matter fields are confined on a brane-world embedded in five dimensions (the bulk). Motivated by this we review the main results on the algebraic class
Brazilian Journal of Physics. Publicado em: 2004-06
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18. Comments on resolution of nonassociativity in SFT: an example from axioms of BCFT
It is known that the associativity of the star product of the open string field theory may be broken in the presence of the nontrivial closed string background. We give an argument that such an anomaly may be resolved by including Chan-Paton factors starting from the axioms of the rational conformal field theory.
Brazilian Journal of Physics. Publicado em: 2002-12
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19. Sewing string tree vertices with ghosts
It is shown how to sew string vertices with ghosts at tree level in order to produce new tree vertices using the Group Theoretic approach to String Theory. It is then verified the BRST invariance of the sewn vertex and shown that it has the correct ghost number.
Brazilian Journal of Physics. Publicado em: 2002-03
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20. Circular cosmic string loop in Brans-Dicke theory
The gravitational field of a stationary circular cosmic string loop, externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding
Braz. J. Phys.. Publicado em: 2001-09
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21. Remarks on Topological Models and Fractional Statistics
One of the most intriguing aspects of Chern-Simons-type topological models is the fractional statistics of point particles which has been shown essential for our understanding of the fractional quantum Hall effects. Furthermore these ideas are applied to the study of high Tc superconductivity. We present here an recently proposed model for fractional spin wi
Brazilian Journal of Physics. Publicado em: 2001-06
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22. Simulação numerica do comportamento mecanico do sal em poços de petroleo
Drilling incidents such as stuck pipe and collapsed casing string take place when some type of salt formations are drilled because of the high pronounced plastic behavior of the salt and the creep behavior as a function of time of this type of rock. The creep behavior becomes faster and more severe if temperature and/or pressure acting on the salt go up. The
Publicado em: 1997
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23. Cordas cosmicas e vortices em relatividade geral : pertubações radiais de soluções estaticas e estacionarias
A linearized theory of the dynamics of small perturbations of certain cylindrically symmetric systems in general relativity is presented. Firstly, we deal with straight, static cosmic strings of finite thickness in the U(l) gauge theory coupled to the Einstein equations. Taking into account the asymptotic behavior of the solution and certain integral ide
Publicado em: 1994
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24. Reconhecimento de caracteres alfanumericos atraves de tecnicas de logica nebulosa
The Pattern Recognition problem is divided into classification and description of the patterns, in which are used Fuzzy Logic techniques, giving flexibility 1n the recogn1t1on process and a tolerance capability to the system. From the var10us dist1ncts mathematical techniques used in the solution of the pattern recogn1t10n problem, there 1s the so called lin
Publicado em: 1990