Confinement of two-dimensional excitons in a non-homogeneous magnetic field

The effective Hamiltonian describing the motion of an exciton in an external non-homogeneous magnetic field is derived. The magnetic field plays the role of an effective potential for the exciton motion, results into an increment of the exciton mass and modifies the exciton kinetic energy operator. In contrast to the homogeneous field case, the exciton in a non-homogeneous magnetic field can also be trapped in the low field region and the field gradient increases the exciton confinement. The trapping energy and wave function of the exciton in a GaAs two-dimensional electron gas for specific circular magnetic field configurations are calculated. The results show than excitons can be trapped by non-homogeneous magnetic fields, and that the trapping energy is strongly correlated with the shape and strength of the non-homogeneous magnetic field profile.Comment: 9 pages, 12 figure

Exciton trapping in magnetic wire structures

The lateral magnetic confinement of quasi two-dimensional excitons into wire like structures is studied. Spin effects are take into account and two different magnetic field profiles are considered, which experimentally can be created by the deposition of a ferromagnetic stripe on a semiconductor quantum well with magnetization parallel or perpendicular to the grown direction of the well. We find that it is possible to confine excitons into one-dimensional (1D) traps. We show that the dependence of the confinement energy on the exciton wave vector, which is related to its free direction of motion along the wire direction, is very small. Through the application of a background magnetic field it is possible to move the position of the trapping region towards the edge of the ferromagnetic stripe or even underneath the stripe. The exact position of this 1D exciton channel depends on the strength of the background magnetic field and on the magnetic polarisation direction of the ferromagnetic film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte

Potential use of split-beam echosounder angular information for bivalve banks cartography: a critical evaluation

Peer Reviewe

Universal patterns in sound amplitudes of songs and music genres

We report a statistical analysis over more than eight thousand songs. Specifically, we investigate the probability distribution of the normalized sound amplitudes. Our findings seems to suggest a universal form of distribution which presents a good agreement with a one-parameter stretched Gaussian. We also argue that this parameter can give information on music complexity, and consequently it goes towards classifying songs as well as music genres. Additionally, we present statistical evidences that correlation aspects of the songs are directly related with the non-Gaussian nature of their sound amplitude distributions.Comment: Accepted for publication as a Brief Report in Physical Review

Small bowel pseudomelanosis and oral iron therapy

Small bowel pseudomelanosis is a rarely reported clinical entity characterized by brown pigmentation of small bowel mucosa. The authors describe two cases, both with iron deficiency anemia, one of an 81-year-old female patient submitted for capsule endoscopy that revealed a brown pigmentation of all small bowel mucosa and another of an 81-year-old male whose retrograde double-balloon enteroscopy revealed a diffuse brown pattern of small bowel mucosa. Ileal biopsies confirmed intense iron deposition in the macrophages of the lamina propria. Both patients were on oral iron therapy and the second one had a previous double-balloon enteroscopy, 2 years earlier, which revealed only ileal angiodysplasias. These two cases demonstrate the importance of two new endoscopic methods for diagnosis of small bowel pseudomelanosis, the rarity of such an entity and its close relation with oral iron therapy