Browsing by Author "Theodorakis, Stavros"

Now showing items 1-20 of 43

    • Article  

      Analytic Q ball solutions in a parabolic-type potential 

      Theodorakis, Stavros (2000)
      We introduce a piecewise parabolic potential for a complex scalar field and we show that it admits stable Q ball solutions. These solutions can be found analytically, unlike the case of polynomial potentials. We find stable ...
    • Article  

      Analytic solutions for the evolution of domain walls 

      Theodorakis, Stavros (1999)
      We introduce an unusual asymmetric double well potential, a piecewise parabolic one, and we show that the solutions for the evolution of its domain walls can be found analytically, in contrast with the case of the standard ...
    • Article  

      Analytic vortex solutions in an unusual Mexican-hat potential 

      Theodorakis, Stavros (1997)
      We introduce an unusual Mexican-hat potential, a piecewise parabolic one, and we show that its vortex solutions can be found analytically, in contrast to the case of the standard |Ψ|4 field theory.
    • Article  

      Bound states in a nonlinear Kronig-Penney model 

      Theodorakis, Stavros; Leontidis, Epameinondas (1997)
      We study the bound states of a Kronig Penney potential for a nonlinear one-dimensional Schrödinger equation. This potential consists of a large, but not necessarily infinite, number of equidistant δ-function wells. We show ...
    • Article  

      Bound states in a nonlinear Kronig-Penney model 

      Theodorakis, Stavros; Leontidis, Epameinondas (1997)
      We study the bound states of a Kronig Penney potential for a nonlinear one-dimensional Schrödinger equation. This potential consists of a large, but not necessarily infinite, number of equidistant δ-function wells. We show ...
    • Article  

      Certain similarities between the evolution of cooperation and phase transitions in physics 

      Theodorakis, Stavros (2001)
      The theory of evolution of cooperation presents a number of striking similarities to the theory of phase transitions in physics. A system that is in a higher energy phase P+ will make a transition to a lower energy phase ...
    • Article  

      Comment on "vortices with ferromagnetic superfluid core in He3-B" 

      Fetter, A. L.; Theodorakis, Stavros (1984)
    • Article  

      Emulation of the evolution of a Bose-Einstein condensate in a time-dependent harmonic trap 

      Theodorakis, Stavros; Constantinou, Y. (2007)
      We emulate the ground state of a Bose-Einstein condensate in a time-dependent isotropic harmonic trap by constructing analytic simulacra of a transformed wavefunction in the regions around the origin and far from the origin. ...
    • Article  

      Evolution of a Bose-Einstein condensate in a rapidly expanding circular box 

      Theodorakis, Stavros; Constantinou, Y. (2007)
      We examine the evolution of the ground state of a Bose-Einstein condensate in a two-dimensional circular box, the wall of which is initially at rest and then recedes with large and constant speed. The final state of the ...
    • Article  

      Field-independent anisotropy in layered superconductors 

      Theodorakis, Stavros; Feinberg, D. (1992)
      Multilayered superconducting SW structures with inequivalent layers are considered, where superconductivity in W (weakly superconducting) layers is induced through their proximity with the S (strongly superconducting) ...
    • Article  

      Fronts in a piecewise linear Schrödinger equation 

      Theodorakis, Stavros (2002)
      We examine the conditions that are necessary for the appearance of fronts as solutions of nonlinear Schrödinger-like equations. We show that fronts can appear even when the potential in these equations has only one minimum. ...
    • Article  

      Ginzburg-Landau modelisation of superconducting multilayers with proximity effect 

      Ettouhami, A. M.; Feinberg, D.; Theodorakis, Stavros (1994)
      A phenomenological modelisation of superlattices made of alternating superconducting (S) and normal (N) layers coupled by proximity effect is presented. It is shown that the anisotropy of such superconductors is not a ...
    • Article  

      Heavy family masses: Analytic results 

      Dimopoulos, Savas; Theodorakis, Stavros (1985)
      We solve analytically the one-loop renormalization group equations for the fermion mass matrices and the quartic coupling, assuming a perturbative SU(3)×SU(2)×U(1) desert, one elementary Higgs boson and any number of ...
    • Article  

      Hierarchy of Tc's in the thallium high-Tc superconductors 

      Theodorakis, Stavros (1988)
      We present a phenomenological formalism determining the critical temperatures of the various superconducting phases in the newly discovered thallium high-Tc superconductors. Tc cannot exceed 146 K (164 K) for the compounds ...
    • Article  

      Inequivalent layers can cause flux-lattice melting in layered superconductors 

      Theodorakis, Stavros (1990)
      The high-Tc superconductors consist typically of superconducting (S) and nonsuperconducting (W) layers. The latter layers acquire actually a nonzero order parameter through a proximity effect. We show that the vortices ...
    • Article  

      Inequivalent layers in the phenomenology of high Tc superconductors 

      Theodorakis, Stavros; Tešanović, Z. (1988)
      We present a phenomenological model describing the high Tc superconductors. The model accounts for the observed positive curvature in the temperature dependence of the H⊥ c2, in terms of a proximity effect between the ...
    • Article  

      Lagrangian of superfluid He3 

      Theodorakis, Stavros (1988)
      This paper presents a phenomenological Lagrangian that fully describes the dynamics of any homogeneous phase of superfluid He3, unitary or not, omitting relaxation. This Lagrangian is built by using the concept of a local ...
    • Article  

      Local pinning of trial wave functions: An optimization method without integrals for finding approximate solutions of field equations 

      Theodorakis, Stavros; Kindyni, N. (2010)
      We present an optimization method that requires no integrations for obtaining approximate solutions of field equations of the form F(Ψ(r{combining right arrow above}))=0. The expression F(Ψ(r{combining right arrow above})) ...
    • Article  

      Lopsided vortex cells in rotating Bose-Einstein condensates 

      Theodorakis, Stavros (2015)
      The amplitude |Ψ| of the wavefunction of a repulsive Bose-Einstein condensate in a two-dimensional axisymmetric harmonic trap decreases as we go from the center of the condensate towards its edge. Consequently the wavefunction ...
    • Article  

      Magnetic-field inversion in vortices in multilayers 

      Theodorakis, Stavros; Leontidis, Epameinondas (1997)
      We present a description of very dense vortex lattices in highly anisotropic multilayers, for high fields parallel to the layers. We show that a magnetic-field inversion can occur away from the center of a vortex, provided ...