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This paper concerns the propagation of particles through a quenched random medium. In the one-and two-dimensional models considered, the local dynamics is given by expanding circle maps and hyperbolic toral automorphisms, respectively. The particle motion in both models is chaotic and found to fluctuate about a linear drift. In the proper scaling limit, the… (More)

- Tapio Simula, Mikko Stenlund
- Physical review. E, Statistical, nonlinear, and…
- 2010

We have studied a model of a random walk in a quenched random environment. In addition to featuring anomalous diffusion and localization, for special regimes of disorder parameters the particle density decomposes into multi-Gaussian structure while its cumulative distribution is normal. We explain the observed fine structure of the density and point out its… (More)

- S M Virtanen, T P Simula, M M Salomaa
- Physical review letters
- 2001

We compute the structure of a quantized vortex line in a harmonically trapped dilute atomic Bose-Einstein condensate using the Popov version of the Hartree-Fock-Bogoliubov mean-field theory. The vortex is shown to be (meta)stable in a nonrotating trap even in the zero-temperature limit, thus confirming that weak particle interactions induce for the… (More)

- Tapio Simula, Matthew J Davis, Kristian Helmerson
- Physical review letters
- 2014

We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent "Onsager vortex" clusters that are stable… (More)

The formation of quantized vortices in trapped, gaseous Bose-Einstein con-densates is considered. The thermodynamic stability of vortex states and the essential role of the surface excitations as a route for vortex penetration into the condensate are discussed. Special focus is on finite-temperature effects of the vortex nucleation process. It is concluded… (More)

- Tapio Simula
- Journal of physics. Condensed matter : an…
- 2013

We have calculated low-lying quasiparticle excitation spectra of rotating three-dimensional Bose-Einstein condensates. We find, as opposed to the prediction of hydrodynamic continuum theories, a minimum in the Tkachenko mode spectrum at intermediate rotation frequencies of the harmonic trap. Such a minimum can harbour a Tkachenko quasiparticle with zero… (More)

- Tapio Simula
- 2002

Teknillinen korkeakoulu Teknillisen fysiikan ja matematiikan osasto Materiaalifysiikan laboratorio Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 10 th of January, 2003, at 12 o'clock noon. ABSTRACT OF… (More)

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