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      Infinite potential barrier and hydrostatic pressure effects on impurity-related optical absorption spectra in GaAs double quantum wells

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          Abstract

          Using the effective-mass approximation and the variational method, we have calculated the effects of hydrostatic pressure on the donor- and acceptor-related optical absorption spectra in symmetrical GaAs double quantum well structures. A central finite potential barrier and two infinite external barriers constitute the profile of the potential barrier considered for the wells. Our results are presented as a function of the well and barrier widths and hydrostatic pressure. For the pressure dependence we consider the gamma-X mixing in the central barrier layer. For symmetrical and infinite-external-barrier quantum wells, and depending on the sizes of the structure and the hydrostatic pressure, the donor-related spectra show three special structures, whereas for the acceptor one only two structures appear.

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          Magnetic field induced confinement-deconfinement transition in graphene quantum dots

          Massless Dirac particles cannot be confined by an electrostatic potential. This is a problem for making graphene quantum dots but confinement can be achieved with a magnetic field and here, general conditions for confined and deconfined states are derived. There is a class of potentials for which the character of the state can be controlled at will. Then a confinement-deconfinement transition occurs which allows the Klein paradox to be probed experimentally in graphene dots.
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            Cooling of a suspended nanowire by an AC Josephson current flow

            We consider a nanoelectromechanical Josephson junction, where a suspended nanowire serves as a superconducting weak link, and show that an applied DC bias voltage an result in suppression of the flexural vibrations of the wire. This cooling effect is achieved through the transfer of vibronic energy quanta first to voltage driven Andreev states and then to extended quasiparticle electronic states. Our analysis, which is performed for a nanowire in the form of a metallic carbon nanotube and in the framework of the density matrix formalism, shows that such self-cooling is possible down to a level where the average occupation number of the lowest flexural vibration mode of the nanowire is \(\sim 0.1\).
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              Determination of the positions and orientations of concentrated rod-like colloids from 3D microscopy data

              Confocal microscopy in combination with real-space particle tracking has proven to be a powerful tool in scientific fields such as soft matter physics, materials science and cell biology. However, 3D tracking of anisotropic particles in concentrated phases remains not as optimized compared to algorithms for spherical particles. To address this problem, we developed a new particle-fitting algorithm that can extract the positions and orientations of fluorescent rod-like particles from three dimensional confocal microscopy data stacks, even when the fluorescent signals of the particles overlap considerably. We demonstrate that our algorithm correctly identifies all five coordinates of uniaxial particles in both a concentrated disordered phase and a liquid-crystalline smectic-B phase. Apart from confocal microscopy images, we also demonstrate that the algorithm can be used to identify nanorods in 3D electron tomography reconstructions. Lastly, we determined the accuracy of the algorithm using both simulated and experimental confocal microscopy data-stacks of diffusing silica rods in a dilute suspension. This novel particle-fitting algorithm allows for the study of structure and dynamics in both dilute and dense liquid-crystalline phases (such as nematic, smectic and crystalline phases) as well as the study of the glass transition of rod-like particles in three dimensions on the single particle level.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                bjp
                Brazilian Journal of Physics
                Braz. J. Phys.
                Sociedade Brasileira de Física (São Paulo )
                1678-4448
                June 2006
                : 36
                : 2a
                : 350-353
                Affiliations
                [1 ] Universidad de Antioquia Colombia
                Article
                S0103-97332006000300031
                10.1590/S0103-97332006000300031
                8cf2bded-d327-4cb1-85f9-8fba269b9bb9

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0103-9733&lng=en
                Categories
                PHYSICS, MULTIDISCIPLINARY

                General physics
                GaAs Double Quantum Wells,Effective-mass approximation,Hydrostatic pressure

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