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  • 1
    Electronic Resource
    Electronic Resource
    Direct simulation Monte Carlo study of H/H2 and H/H2/CO mixtures for diamond chemical vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6474-6488 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One-dimensional direct simulation Monte Carlo calculations have been carried out on H/H2 and H/H2/CO mixtures under operating conditions typical of diffusion-dominated diamond chemical vapor deposition processes. Mechanisms have been included in the model for the adsorption and recombination of hydrogen atoms on the diamond surface and the dissociation of molecular hydrogen at the interior of the reactor. Hydrogen atom fluxes and recombinative and conductive heat fluxes to the diamond surface are calculated as a function of pressure, gas composition, hydrogen dissociation and surface reaction probabilities, reactor temperature, and distance between the activating source and substrate. The numerical calculations are shown to be in excellent agreement with analytical results in the limiting regimes of free-streaming particles at low pressures and continuum hydrodynamics at high pressures. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363667
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  • 2
    Electronic Resource
    Electronic Resource
    The stability of imploding detonations: Results of numerical simulations (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 369-380 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relative stability of cylindrically imploding shock and detonation waves has been examined using a two-dimensional numerical model. A sequence of increasingly realistic chemistry models is used to explore the effect of model selection on the results. Comparisons with the predictions of Chester–Chisnell–Whitham (CCW) theory for the acceleration of nonreactive shocks and detonations show quantitative agreement between theory and simulation for symmetrically imploding waves. The influence of structural supports in laboratory experiments on the symmetry of imploding waves is simulated by placing an obstacle in the path of the converging flow. Changes in the convergence time, reductions of the peak pressure at implosion, and deviations from symmetry during the implosion induced by the obstacle are greater for detonations than for the corresponding nonreactive shocks, in qualitative agreement with the linearized CCW theory for shocks and Chapman–Jouguet detonations. These conclusions continue to hold when more sophisticated Zel'dovich–von Neumann–Doering or finite-rate chemistry models are assumed. For these models, a substantial amount of new asymmetrical, dynamical structure is evident in the reaction zone behind the leading shock. The results concur with and extend previous theoretical work suggesting that imploding detonation waves are relatively more unstable than nonreactive shocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868092
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  • 3
    Electronic Resource
    Electronic Resource
    The stability of imploding detonations in the geometrical shock dynamics (CCW) model (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 835-844 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of cylindrically and spherically imploding detonations is examined within the theoretical framework of geometrical shock dynamics. The linearized Chester–Chisnell–Whitham (CCW) equations describing the accelerating detonation wave are solved both analytically and numerically to track the evolution of the distorted wave front. As is the case for the corresponding nonreactive shock problem, for harmonic mode numbers greater than unity the perturbation amplitudes decrease as the implosion proceeds, but not as rapidly as the implosion radius itself. Thus, the detonation is relatively unstable in this model, and indeed is more unstable than the imploding shock of the same initial strength. The latter result is due primarily to the slower acceleration of the detonation wave as it implodes, relative to the nonreactive shock wave.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858300
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  • 4
    Electronic Resource
    Electronic Resource
    Simulations of the sun's polar magnetic fields during sunspot cycle 21 (1987)
    Springer
    Solar physics 108 (1987), S. 47-59 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Regarding new bipolar magnetic regions as sources of flux, we have simulated the evolution of the radial component of the solar photospheric magnetic field during 1976–1984 and derived the corresponding evolution of the line-of-sight polar fields as seen from Earth. The observed timing and strength of the polar-field reversal during cycle 21 can be accounted for by supergranular diffusion alone, for a diffusion coefficient of 800 km2 s-1. For an assumed 300 km2 s-1 rate of diffusion, on the other hand, a poleward meridional flow with a moderately broad profile and a peak speed of 10 m s-1 reached at about 5° latitude is required to obtain agreement between the simulated and observed fields. Such a flow accelerates the transport of following-polarity flux to the polar caps, but also inhibits the diffusion of leading-polarity flux across the equator. For flows faster than about 10 m s-1 the latter effect dominates, and the simulated polar fields reverse increasingly later and more weakly than the observed fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152076
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  • 5
    Electronic Resource
    Electronic Resource
    The decay of the large-scale solar magnetic field (1987)
    Springer
    Solar physics 112 (1987), S. 17-35 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In the absence of new bipolar sources of flux, the large-scale magnetic field at the solar photosphere decays due to differential rotation, meridional flow, and supergranular diffusion. The rotational shear quickly winds up the nonaxisymmetric components of the field, increasing their latitudinal gradients and thus the rates of diffusive mixing of their flux. This process is particularly effective at mid latitudes, where the rotational shear is largest, so that eventually low- and high-latitude remnants of the initial, nonaxisymmetric field pattern survive. In this paper I solve analytically the transport equation describing the evolution of the large-scale photospheric field, to study its time-asymptotic behavior. The solutions are rigidly rotating, uniformly decaying distributions of flux, wound up by differential rotation and localized near either the equator or the poles. A balance between azimuthal transport of flux by the rotational shear and meridional transport by the diffusion gives rise to the rigidly rotating field patterns. The time-scale on which this balance is achieved, and also on which the nonaxisymmetric flux decays away, is the geometric mean of the short time-scale for shearing by differential rotation and the long time-scale for dispersal by supergranular diffusion. A poleward meridional flow alters this balance on its own, intermediate time-scale, accelerating the decay of the nonaxisymmetric flux at low latitudes. Such a flow also hastens the relaxation of the axisymmetric field to a modified dipolar configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148484
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  • 6
    Electronic Resource
    Electronic Resource
    Simulations of the gross solar magnetic field during sunspot cycle 21 (1986)
    Springer
    Solar physics 106 (1986), S. 251-268 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Regarding new bipolar magnetic regions as sources of flux, we have simulated the evolution of the radial component of the solar photospheric magnetic field during 1976–1984 with a spatial resolution of about 34 000 km, and have derived the corresponding evolution of its absolute value averaged over the visible disk. For nominal values of the transport parameters, this simulated gross field is in close, though imperfect, agreement with the observed gross field and its associated indices of solar activity. By analyzing the response of the simulated gross field to variations in the transport parameters and the source properties, we find that the simulated field originates in newly erupted bipolar regions. The lifetimes of these regions are almost always less than 3 mo. Consequently, the strength of the simulated gross field is a measure of the current level of solar activity, and any recurrent patterns with lifetimes in excess of 6 mo must reflect the continuing eruption of new flux at ‘active longitudes’ rather than the persistence of old flux in long-lived magnetic structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00158496
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  • 7
    Electronic Resource
    Electronic Resource
    The origin of the 28- to 29-day recurrent patterns of the solar magnetic field (1986)
    Springer
    Solar physics 104 (1986), S. 425-429 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Numerical simulations of the Sun's mean line-of-sight magnetic field suggest an origin for the 28-to 29-day recurrent patterns of the field and its associated interplanetary phenomena. The patterns are caused by longitudinal fluctuations in the eruption of new magnetic flux, the transport of this flux to mid latitudes by supergranular diffusion and meridional flow, and the slow rotation of the resulting flux distributions at the 28- to 29-day periods characteristic of those latitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00159092
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  • 8
    Electronic Resource
    Electronic Resource
    The decay of the mean solar magnetic field (1986)
    Springer
    Solar physics 103 (1986), S. 203-224 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have analyzed the effects that differential rotation and a hypothetical meridional flow would have on the evolution of the Sun's mean line-of-sight magnetic field as seen from Earth. By winding the large-scale field into strips of alternating positive and negative polarity, differential rotation causes the mean-field amplitude to decay and the mean-field rotation period to acquire the value corresponding to the latitude of the surviving unwound magnetic flux. For a latitudinally broad two-sector initial field such as a horizontal dipole, the decay is rapid for about 5 rotations and slow with a t −1/2 dependence thereafter. If a poleward meridional flow is present, it will accelerate the decay by carrying the residual flux to high latitudes where the line-of-sight components are small. The resulting decay is exponential with an e-folding time of 0.75 yr (10 rotations) for an assumed 15 m s−1 peak meridional flow speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00147824
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  • 9
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    Simulations of the sun's polar magnetic fields during sunspot cycle 21 (1987)
    Springer
    Details
    Publication Date: 1987-03-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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  • 10
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    Simulations of the gross solar magnetic field during sunspot cycle 21 (1986)
    Springer
    Details
    Publication Date: 1986-08-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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