Sıddıki, Afif2016-01-082016-01-081999http://hdl.handle.net/11693/18130Ankara : The Department of Physics and the Institute of Engineering and Sciences of Bilkent Univ., 1999.Thesis (Master's) -- Bilkent University, 1999.Includes bibliographical references leaves 58-61.I.' this work we examined a quartic Hamiltonian using two different approaches. We first introduced a mean-field Gaussian approximation in order to handle this Hamiltonian analytically and observed that this approximation is insufficient for all coupling strengths. Hence we applied second and third order non-degenerate time-independent perturbation and obtained third or- ■ ler correcHo[x], 61 leavesEnglishinfo:eu-repo/semantics/openAccessAnharmonicityhigh temperature superconductorsmeanfield approximationdiscrete-finite systemsBose-Einstein condensationQC174.85.H35 S53 1999Hamiltonian systems.Quantum theory.Approximation theory.Thesis