Hamiltonian Systems
Mostrando 49-60 de 82 artigos, teses e dissertações.
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49. Bose mott-insulators as closed shells
Properties of the ground-state, zero temperature 'phase diagram' of the Bose-Hubbard hamiltonian as understood by Fisher et al. [5] are studied using simple tools in the case of nite systems. The results obtained provide a transparent picture of the thermodynamic limit and reveal features reminiscent of shell structure in many-fermion systems. Independent si
Brazilian Journal of Physics. Publicado em: 2005-03
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50. Carbon nanotube structures: Y-junctions and nanorings
The possibility of coupling two Y-junctions of carbon nanotubes, forming a type of nanotube ring is addressed here. Recent experimental evidences of growing carbon nanotube structures forming basically Y-kind junctions give support to this theoretical proposition. A single-band tight-binding Hamiltonian is considered and local electronic properties are inves
Brazilian Journal of Physics. Publicado em: 2004-06
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51. PHYSICS OF STRONGLY CORRELATED AND DISORDERED SYSTEMS / FÍSICA DE SISTEMAS FORTEMENTE CORRELACIONADOS E DESORDENADOS
In this thesis we study the properties of strongly correlated and disordered materials, using model Hamiltonians to describe them. The thesis is divided in two parts. The first one studies the periodic Anderson model used to describe the properties of a Kondo insulator. In particular we take Ce3Bi4Pt3 as a paradigmatic compound, characterized by a small gap(
Publicado em: 2004
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52. Estudo de portas lógicas quânticas de dois qubits definidas em um subespaço livre de decoerência para um sistema de quatro qubits acoplado ao resto do universo por um agente degenerado / A study of two-qubit quantum logic gates defined in a decoherence free subspaces for a four-qubit system coupled to the rest of the universe via a degenerate agent
In this dissertation we studied theoretical aspects of some recent proposals of passive quantum information processing, that is, discarding error correction protocols. Falling back upon the creation of decoherence-free subspaces through a physical system of four spins coupled to the rest of the universe by a degenerate agent, we showed to be possible to buil
Publicado em: 2004
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53. ELECTRONIC CORRELATION IN QUANTUM DOTS SYSTEMS / CORRELAÇÃO ELETRÔNICA EM SISTEMAS DE PONTOS QUÂNTICOS
In this thesis we investigate the effects of the eletron- eletron interaction on the transport properties of nanosystems. In particular, we study systems constituted by two quantum dots conected to leads, in different topologies. Our main interest is to study the effects of the Kondo regime and the electronic phase on the conductance. In the configuration wh
Publicado em: 2004
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54. Symplectic integrators revisited
This paper is a survey on Symplectic Integrator Algorithms (SIA): numerical integrators designed for Hamiltonian systems. As it is well known, n degrees of freedom Hamiltonian systems have an important property: their ows preserve not only the total volume of the phase space, which is only one of the Poincaré invariants, but also the volume of sub-spaces le
Brazilian Journal of Physics. Publicado em: 2002-12
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55. Dinamica de sistemas quanticos : atomos em cavidades de ions aprisionados
In this thesis we studied the dynamics of two quantum systems: atoms in a cavity and trapped ions. For atoms in a cavity ( QED ) , we studied the dynamics of field prepared in a superposition of coherent states and a statistical mixture. In this system, using a Intensity-Dependence Jaynes-Cummings model (DNJCM) we discuss some aspects of the dynamics of atom
Publicado em: 2002
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56. New method for obtaining complex roots in the semiclassical coherent-state propagator formula
A semiclassical formula for the coherent-state propagator requires the determination of specific classical paths inhabiting a complex phase-space and governed by a Hamiltonian flux. Such trajectories are constrained to special boundary conditions which render their determination difficult by common methods. In this paper we present a new method based on Rung
Braz. J. Phys.. Publicado em: 2001-09
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57. Lagrangian multipliers for coast-arcs of optimum space trajectories
Some properties of generalized canonical systems - special dynamical systems described by a Hamiltonian function linear in the adjoint variables - are applied in determining the solution of the two-dimensional coast-arc problem in an inverse-square gravity field. A complete closed-form solution for Lagrangian multipliers - adjoint variables - is obtained by
Journal of the Brazilian Society of Mechanical Sciences. Publicado em: 2001
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58. Estudo da espectroscopia de massas de mesons segundo um modelo de potencial inspirado em cromodinamica quantica
Since the discovery of QCD (Quantum Chromodynamics), there have been remarkable technical achievements in perturbative calculations applied to hadrons. However, it is difficult to use QCD directly to compute hadronic properties. In this context, phenomenological potential models have provided extremely satisfactory results on description of ordinary hadrons,
Publicado em: 2001
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59. Hamiltonian dynamics of the Landau-Ginzburg model for the phase transition in (NH4)2BeF4
We present a Hamiltonian treatment of the Landau-Ginzburg theory of phase transitions in the case of incommensurate ferroelectric systems like (NH4)2BeF4. This formulation has the advantage of treating the system as an example of a nonlinear dynamical system.
Brazilian Journal of Physics. Publicado em: 2000
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60. Fronteiras fractais em sistemas hamiltonianos e em relatividade geral
We study the dynamics of test particles in Hamiltonian systems with escapes, including Newtonian systems (the Hénon-Heiles system for energies above the escape energy) and general-relativistic systems corresponding to static axisymmetric mass distributions, which could be used to model galactic cores; in particular, we study the motion of test particles in
Publicado em: 2000