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27 Jul 1998

Volume 73, Issue 4, pp. 423-552

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Bond-orientational order in sheared dense flows of inelastic hard spheres

Piroz Zamankhan, William Polashenski, Hooman Vahedi Tafreshi, Pertti J. Sarkomaa, and Caroline L. Hyndman

Appl. Phys. Lett. 73, 450 (1998); http://dx.doi.org/10.1063/1.121896 (3 pages) | Cited 3 times

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Three-dimensional bond-orientational order is studied using computer simulations with 4296 hard, monodisperse inelastic spheres flowing in a Couette geometry at a high shear rate. At an average volume fraction close to 0.6, a state with extended correlations in the orientations of particle clusters starts to develop for rough particles after sufficiently long run times. However, no clear evidence of crystallization is found in the system. Further tests of a sheared system comprised of smooth, inelastic spheres reveal crystallization consistent with the previous experimental observations. © 1998 American Institute of Physics.
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47.15.Fe Stability of laminar flows
47.27.-i Turbulent flows
61.20.Ja Computer simulation of liquid structure

High-frequency electron beam modulation in a diode with an active plasma cathode

Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner

Appl. Phys. Lett. 73, 453 (1998); http://dx.doi.org/10.1063/1.121897 (3 pages) | Cited 9 times

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We have carried out experiments with an active plasma cathode showing the possibility to generate a modulated electron beam with a repetition rate of 2 Hz without the use of a high-frequency power supply. The modulation of the beam current amplitude reaches values ≥ 30%. This modulation is found to have a frequency of 325±5 MHz for a discharge capacitor of 1 nF and a duration ≥ 1 μs. In addition, the modulated electron beam is accompanied by electromagnetic radiation with the same frequency. We suggest that this high-frequency modulation is caused by electron oscillations within the potential well which is created inside the cathode structure by the positive potential of the plasma. © 1998 American Institute of Physics.
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41.75.Fr Electron and positron beams
07.77.Ka Charged-particle beam sources and detectors
52.59.Mv High-voltage diodes

Precise control of atomic nitrogen production in an electron cyclotron resonance plasma using N2/noble gas mixtures

Z. Y. Fan and N. Newman

Appl. Phys. Lett. 73, 456 (1998); http://dx.doi.org/10.1063/1.121898 (3 pages) | Cited 13 times

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The atomic nitrogen flux and impacting ion kinetic energy are two important parameters which influence the quality of deposited nitride films using reactive growth. In this letter, a method is described to control the flux and kinetic energy of atomic and molecular nitrogen ions using an electron cyclotron resonance plasma with N2/Ar and N2/Ne gas mixtures. The results clearly show that the addition of neon to nitrogen plasma can remarkably enhance the production rate of atomic nitrogen due to Penning ionization involving the metastable state of Ne. In contrast, the addition of argon significantly decreases the rate. © 1998 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
31.50.Df Potential energy surfaces for excited electronic states
52.50.Dg Plasma sources
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Destruction of ozone-depleting substances in a thermal plasma reactor

A. B. Murphy and T. McAllister

Appl. Phys. Lett. 73, 459 (1998); http://dx.doi.org/10.1063/1.121899 (3 pages) | Cited 9 times

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A two-dimensional numerical model of the PLASCON™ plasma reactor is used to investigate the destruction of ozone-depleting substances in the reactor. The model includes electromagnetic, fluid dynamic and chemical kinetic phenomena. Calculated temperature, flow and species concentration fields within the plasma torch, the injection manifold and the reaction tube are presented for the case of the destruction of CFC-12 (CF2Cl2). Conversion of CFC-12 to CFC-13 (CF3Cl), a more stable ozone-depleting substance, is found to occur in the region close to the injection manifold, and to be unaffected by reaction tube geometry. CFC-13 is predicted to be the dominant ozone-depleting substance in the exhaust gas. The predictions of the model are found to be in good agreement with measurements of the exhaust gas composition. © 1998 American Institute of Physics.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.65.-y Plasma simulation
52.75.Hn Plasma torches
52.30.-q Plasma dynamics and flow
82.20.Wt Computational modeling; simulation
52.25.-b Plasma properties
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