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  • 1
    Electronic Resource
    Electronic Resource
    Erratum: "Effects of local reactant concentration perturbations in oscillatory catalysis" [J. Chem. Phys. 108, 5565 (1998)] (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1619-1619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480659
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  • 2
    Electronic Resource
    Electronic Resource
    Spatio-temporal dynamics of oscillatory heterogeneous catalysis: CO oxidation on platinum (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8614-8625 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reaction-rate oscillations in the oxidation of carbon monoxide on the surface of platinum catalysts are studied in a continuous flow reactor at atmospheric pressure using infrared imaging. Small-amplitude temperature oscillations (0.2–8 K) result in approximately isothermal conditions, where changes in rate constants, for typical activation energies and temperatures, are small. The catalysts are in the form of platinum thin films on quartz substrates and provide highly repeatable oscillatory behavior. The platinum films are fabricated in the form of annular rings which provide a quasi-one-dimensional geometry in order to simplify comparison to theoretical models. Time-series measurements by means of thermocouples are used to characterize the oscillations. The infrared images show that most oscillations are spatially synchronized to within the 0.25 s time resolution of the experiment. The images also show that "fine structure'' oscillations (i.e., small-amplitude, high frequency oscillations superimposed on larger-amplitude waveforms) are associated with spatially desynchronized patterns. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468963
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  • 3
    Electronic Resource
    Electronic Resource
    An electron–positron beam–plasma instability (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4982-4994 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a new technique to generate cold electron beams, an electron-beam positron-plasma experiment was performed in a previously unexplored range of energies. An electron beam, formed from a thermalized room-temperature electron plasma, is transmitted through a positron plasma stored in a quadrupole Penning trap geometry. The transit-time instability, which is excited by the beam, was previously studied using a hot-cathode electron gun. The large beam energies produced by the cathode did not permit an investigation of the instability in the interesting range of energies near its onset. Using a new 0.1 eV energy width electron beam, we have reinvestigated the system. The experimental data are compared with the results of a theoretical model, also described in this paper. The theory employs a linearized cold fluid and Vlasov approach to model the plasma and beam dynamics, respectively. The data and predictions are in good agreement over the broad range of energies and beam currents studied. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407284
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  • 4
    Electronic Resource
    Electronic Resource
    Spatial coupling in heterogeneous catalysis (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8209-8215 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spatial coupling mechanisms are studied in the heterogeneous catalytic oxidation of carbon monoxide over platinum at atmospheric pressure under oscillatory conditions. Experiments are conducted in a continuous flow reactor, and the reaction rate is monitored using both infrared imaging and thermocouples. The catalysts are in the form of platinum annular thin films on washer-shaped quartz substrates, and they provide highly repeatable oscillatory behavior. Oscillations are typically spatially synchronized with the entire catalyst "flashing'' on and off uniformly. Spatial coupling is investigated by introducing various barriers which split the annular ring in half. Infrared images show that coupling through the gas phase dominates coupling via the diffusion of CO on the surface or heat diffusion through the substrate. The introduction of a localized heat perturbation to the catalyst surface does not induce a transition in the reaction rate. Thus, it is likely that the primary mode of communication is through the gas-phase diffusion of reactants. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470185
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of local reactant concentration perturbations in oscillatory catalysis (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5565-5570 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reaction-rate oscillations in CO oxidation over heterogeneous platinum thin-film catalysts were studied at atmospheric pressure where spatial coupling is due to gas-phase diffusion of reactant concentration gradients. The catalyst was perturbed locally by the introduction of CO directly above the surface, while the resulting spatiotemporal behavior was monitored using infrared imaging. The transient response of the system was studied in both the steady-state and oscillatory regimes, and comparisons are made between the observed behavior and predictions from models for the oscillations. Using these perturbations, global behavior was initiated using a localized effect. Similarities and differences between the induced oscillations and those occurring naturally are discussed, as are tests to vary the phase of the oscillatory cycle. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475946
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  • 6
    Electronic Resource
    Electronic Resource
    Antimatter plasmas and antihydrogen : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1528-1543 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent successes in confining antimatter in the form of positron and antiproton plasmas have created new scientific and technological opportunities. Plasma techniques have been the cornerstone of experimental work in this area, and this is likely to be true for the foreseeable future. Work by a number of groups on trapping antimatter plasmas is summarized, and an overview of the promises and challenges in this field is presented. Topics relating to positron plasmas include the use of positrons to study the unique properties of electron–positron plasmas, the interaction between positrons and ordinary matter, and the laboratory modeling of positron-annihilation processes in interstellar media. The availability of cold, trapped antiprotons and positrons makes possible the production of neutral antimatter in the form of antihydrogen. This is expected to enable precise comparisons of the properties of matter and antimatter, including tests of fundamental symmetries and the measurement of the interaction of antimatter with gravity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872284
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  • 7
    Electronic Resource
    Electronic Resource
    Modes of spheroidal ion plasmas at the Brillouin limit (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 749-758 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement properties and collective modes of single-component plasmas are investigated in a quadrupole Penning trap. Brillouin-density pure ion plasmas are generated by electron-beam ionization of a low-pressure gas. Large, spheroidal, steady-state plasmas are produced, extending out to contact one or more of the trap electrodes. With the density fixed at the Brillouin limit by the high ion production rate, the electrode potentials determine the plasma shape. The frequencies of azimuthally propagating cyclotron and diocotron modes are found to vary significantly with the plasma aspect ratio. For oblate plasmas, the frequencies are in good agreement with a simple fluid model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871809
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  • 8
    Electronic Resource
    Electronic Resource
    Low-order longitudinal modes of single-component plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2880-2894 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-order modes of spheroidal, pure electron plasmas have been studied experimentally, both in a cylindrical electrode structure and in a quadrupole trap. Comparison is made between measurements of mode frequencies, recent analytical theories, and numerical simulations. Effects considered include trap anharmonicity, image charges, and temperature. Quantitative agreement is obtained between the predictions and these measurements for spheroidal plasmas in the quadrupole trap. In many experiments on single-component plasmas, including antimatter plasmas, the standard diagnostic techniques used to measure the density and temperature are not appropriate. A new method is presented for determining the size, shape, average density, and temperature of a plasma confined in a Penning trap from measurements of the mode frequencies. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871188
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  • 9
    Electronic Resource
    Electronic Resource
    Creation and uses of positron plasmasf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1439-1446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Advances in positron trapping techniques have led to room-temperature plasmas of 107 positrons with lifetimes of 103 s. Improvements in plasma manipulation and diagnostic methods make possible a variety of new experiments, including studies just being initiated of electron–positron plasmas. The large numbers of confined positrons have also opened up a new area of positron annihilation research, in which the annihilation cross sections for positrons with a variety of molecules have been measured, as well as the energy spread of the resulting gamma rays. Such measurements are of interest for fundamental physics and for the modeling of astrophysical plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870693
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  • 10
    Electronic Resource
    Electronic Resource
    The role of mixing in traveling-wave convection (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1468-1468 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In binary fluid mixtures with negative separation ratio, the conduction state has a vertical concentration gradient, due to the Soret effect, which opposes the destabilizing effect of the vertical temperature gradient. The first convective states are traveling waves (TW) with a phase velocity which is much lower than that of the linear instability. Recent perturbation theory calculations and numerical simulations of this nonlinear, traveling-wave state predict that the linear concentration gradient in the conduction state is eliminated in the interior of the fluid by convective mixing, and the concentration gradient remains only in the boundary layers. It is the persistence of the concentration gradient in these boundary layers which leads to the small but nonzero wave speed. As the Rayleigh number R is increased, convective stirring of the mixture decreases the concentration boundary layers, and the TW phase speed goes continuously to zero. We report experimental studies of these nonlinear, traveling-wave states in ethanol/water mixtures in an annular geometry. The measured TW phase speed as a function of R is in excellent agreement with the theoretical predictions over the entire TW branch. The experiments also confirm that this transition to stationary convection is not hysteretic. The role of mixing and the transport of concentration in the dynamics of nonlinear fronts and pulses observed in this system will also be discussed. [Work supported by DARPA URI Contract No. N00014-86-K-0758.]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858002
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