71,990 research outputs found

    Kinematic dynamos in precession-driven cavities

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    A simple variational principle for classical spinning particle with anomalous magnetic momentum

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    We obtain Bargmann-Michel-Telegdi equations of motion of classical spinning particle using Lagrangian variational principle with Grassmann variables.Comment: 3 pages, late

    On direction of spontaneous magnetization in a "cubic" ferromagnet

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    The magnetic properties of anisotropic films have been studied using 3D-neutron polarization analysis. The experimental facts refer to essential distinction of the sample states, magnetized in opposite directions. For an explanation of asymmetrical effects the model is offered, in which the fundamental theoretical principles of structural phase transitions are used.Comment: 4 pages LaTeX (phbauth) and 4 figures (epsfig

    Comparison of C═C bond hydrogenation in C-4 unsaturated nitriles over Pt/alumina

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    The hydrogenation of allyl cyanide (but-1-ene-4-nitrile, AC), trans- and cis-crotononitrile (E- and Z-but-2-ene nitrile, TCN and CCN), and methacrylonitrile (2-cyano-1-propene, MCN) were studied, both singly and competitively, over a Pt/alumina catalyst in the liquid phase. Each unsaturated nitrile only underwent C═C bond hydrogenation: no evidence was found for the formation of the saturated or unsaturated amine. The nonconjugated allyl cyanide was found to be the most reactive unsaturated nitrile. Activation energies for the hydrogenation of the C═C bond in AC and MCN were determined giving values of 64 ± 7 kJ mol–1 for AC and 37 ± 4 kJ mol–1 for MCN. The reaction was zero order for both nitriles. Competitive hydrogenations revealed that not only does allyl cyanide react preferentially over the other isomers but also it inhibits the hydrogenation of the other isomers. When all four nitriles were simultaneously hydrogenated, inhibition effects were easily seen suggesting that in terms of strength of bonding to the surface an order of AC > CCN > TCN ∌ MN can be generated

    Oscillations of a Bose-Einstein condensate rotating in a harmonic plus quartic trap

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    We study the normal modes of a two-dimensional rotating Bose-Einstein condensate confined in a quadratic plus quartic trap. Hydrodynamic theory and sum rules are used to derive analytical predictions for the collective frequencies in the limit of high angular velocities, Ω\Omega, where the vortex lattice produced by the rotation exhibits an annular structure. We predict a class of excitations with frequency 6Ω\sqrt{6} \Omega in the rotating frame, irrespective of the mode multipolarity mm, as well as a class of low energy modes with frequency proportional to ∣m∣/Ω|m|/\Omega. The predictions are in good agreement with results of numerical simulations based on the 2D Gross-Pitaevskii equation. The same analysis is also carried out at even higher angular velocities, where the system enters the giant vortex regime.Comment: 4 pages, 2 figure
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