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External Electric (external + electric)

Distribution by Scientific Domains
Physics and Astronomy75%

Terms modified by External Electric

  • external electric field
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    Selected Abstracts

    The dependence of the electrophoretic mobility of small organic ions on ionic strength and complex formation

    ELECTROPHORESIS, Issue 5 2010
    Stuart A. Allison
    Abstract The ionic strength dependence of the electrophoretic mobility of small organic anions with valencies up to ,3 is investigated in this study. Provided the anions are not too aspherical, it is argued that shape and charge distribution have little influence on mobility. To a good approximation, the electrophoretic mobility of a small particle should be equal to that of a model sphere with the same hydrodynamic radius and same net charge. For small ions, the relaxation effect (distortion of the ion atmosphere from equilibrium due to external electric and flow fields) is significant even for monovalent ions. Alternative procedures of accounting for the relaxation effect are examined. In order to account for the ionic strength dependence of a specific set of nonaromatic and aromatic anions in aqueous solution, it is necessary to include complex formation between the anion with species in the BGE. A number of possible complexes are considered. When the BGE is Tris-acetate, the most important of these involves the complex formed between anion and Tris, the principle cation in the BGE. When the BGE is sodium borate, an anion,anion (borate) complex appears to be important, at least when the organic anion is monovalent. An algorithm is developed to analyze the ionic strength dependence of the electrophoretic mobility. This algorithm is applied to two sets of organic anions from two independent research groups. [source]

    Interwell exciton dispersion engineering, coherent phonons generation and optical detectionof exciton condensate

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
    Yu. E. Lozovik
    This issue's Editor's Choice [1] discusses interwell excitons in coupled quantum wells as a candidate for observation of different phases in an exciton system, including the very interesting phenomenon of Bose condensation. The cover picture shows schematically how the generation of coherent phonons and the angular distribution of the exciton photoluminescence (PL) from the quantum well system can be controlled by the external electric and magnetic fields. The first author, Yurii E. Lozovik, is head of the Laboratory of Spectroscopy of Nanostructures at the Institute of Spectroscopy and also Professor of Physics at the Moscow Physical and Technical Institute. His main interests are electron and electron,hole systems in nanostructures, cluster physics, quantum electrodynamics in a cavity, matter in strong magnetic fields, nanotechnology, ultrafast and near field optics, and computer simulations. [source]

    Interwell exciton dispersion engineering, coherent phonons generation and optical detection of exciton condensate

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
    Yu. E. Lozovik
    Abstract We propose to use dispersion engineering of interwell excitons in coupled quantum wells with external electric and magnetic fields in order to generate coherent phonons and to detect exciton condensate. A parallel magnetic field moves the dispersion minimum of interwell excitons away from the radiative zone and thus reduces their recombination rate. Normal electric field moves an interwell excitons dispersion minimum on the energy scale. These two fields effect can be used to tune the resonance condition of the interwell excitons recombination process via an in-well excitons level, which results in acoustic phonon emission. We show, that one can change recombination rate as well as intensity and angular distribution of the interwell excitons photoluminescence in the wide range by controlling the external fields. Based on this principle we propose and theoretically evaluate a procedure to detect the condensate of interwell excitons, as well as a scheme to obtain a coherent and monochromatic phonon beam (saser). The statistics of the phonon emission from the condensate of interwell excitons is studied. Numerical estimate for GaAs/AlGaAs coupled quantum wells is provided. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    A new look at the quantum mechanics of the harmonic oscillator

    ANNALEN DER PHYSIK, Issue 7-8 2007
    H.A. Kastrup
    Abstract In classical mechanics the harmonic oscillator (HO) provides the generic example for the use of angle and action variables and I > 0 which played a prominent role in the "old" Bohr-Sommerfeld quantum theory. However, already classically there is a problem which has essential implications for the quantum mechanics of the (,,I)-model for the HO: the transformation is only locally symplectic and singular for (q,p) = (0,0). Globally the phase space {(q,p)} has the topological structure of the plane ,2, whereas the phase space {(,,I)} corresponds globally to the punctured plane ,2 -(0,0) or to a simple cone with the tip deleted. From the properties of the symplectic transformations on that phase space one can derive the functions h0 = I, h1 = Icos , and h2 = - Isin , as the basic coordinates on {(,,I)}, where their Poisson brackets obey the Lie algebra of the symplectic group of the plane. This implies a qualitative difference as to the quantum theory of the phase space {(,,I)} compared to the usual one for {(q,p)}: In the quantum mechanics for the (,,I)-model of the HO the three hj correspond to the self-adjoint generators Kj, j = 0,1,2, of certain irreducible unitary representations of the symplectic group or one of its infinitely many covering groups, the representations being parametrized by a (Bargmann) index k > 0. This index k determines the ground state energy of the (,,I)-Hamiltonian . For an m -fold covering the lowest possible value for k is k = 1/m, which can be made arbitrarily small by choosing m accordingly! This is not in contradiction to the usual approach in terms of the operators Q and P which are now expressed as functions of the Kj, but keep their usual properties. The richer structure of the Kj quantum model of the HO is "erased" when passing to the simpler (Q,P)-model! This more refined approach to the quantum theory of the HO implies many experimental tests: Mulliken-type experiments for isotopic diatomic molecules, experiments with harmonic traps for atoms, ions and BE-condensates, with charged HOs in external electric fields and the (Landau) levels of charged particles in external magnetic fields, with the propagation of light in vacuum, passing through strong external electric or magnetic fields. Finally it may lead to a new theoretical estimate for the quantum vacuum energy of fields and its relation to the cosmological constant. [source]