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  • American Institute of Physics (AIP)  (5)
  • 1985-1989  (5)
  • 1950-1954
  • 1930-1934
  • 1
    Digitale Medien
    Digitale Medien
    Amplification of acoustic waves in piezoelectric semiconductors: Effect of nonlinearity in electron effective mass and collision frequency (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 267-271 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper essentially seeks to provide a theoretical construct to the experimental studies on the acoustoelectric amplification in piezoelectric semiconductors showing that the attenuation of an acoustic wave crosses over to its amplification when electron drift velocity exceeds the acoustic wave velocity. In this paper, first, a phenomenological theory is developed to study the relative change in electron mass and collision frequency when an acoustic wave propagates through piezoelectric semiconductors. Then, analytically, we have shown that this nonlinearity in electron mass and collision frequency arising due to the electric vector of the field associated with the wave can also explain this behavior. Numerical computations are made for a typical case of n-InSb at 77 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.337693
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Raman instability in n-type piezoelectric semiconducting plasmas (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3133-3140 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The paper aims at the detailed analytical investigation of Raman instability in a magnetoactive n-type cubic piezoelectric semiconducting crystal belonging to class 4¯3m under a geometrical configuration which can also be employed in analyzing the phenomenon under either Voigt or Faraday orientation. The electric vector E0 of the spatially uniform pump electromagnetic wave (applied along the y axis) is normal to the magnetostatic field B0 (along the z axis) as well as to the plane of propagation (x-z plane) of the scattered waves (Ω,k) and (Ω1,k1). The propagation vectors k, k1 (antiparallel to each other) are in the x-z plane making an angle θ with the x axis. The dispersion relation has been obtained by using a hydrodynamic model of the homogeneous, piezoelectric, one-component (electron) semiconducting plasma; and the threshold value of the pump electric field (necessary to achieve physically reasonable growth of the unstable mode) and the growth rate of the unstable Raman mode well above the threshold field have been obtained for isotropic (B0=0) and magnetoactive (B0≠0) plasmas. We have applied our analysis to a specific semiconductor, n-InSb at 77 K, duly irradiated by a pulsed 10.6-μm CO2 laser for numerical estimation. The phase velocity of the growing unstable mode is found to be constant over the whole range of system parameters and equal to the electromagnetic wave velocity in the crystal. The magnitude of threshold electric field decreases with increasing magnetostatic field and decreasing wave vector. The growth rate increases and attains a maximum value at a certain value of the pump intensity, magnetostatic field, and θ; and if these are raised further, growth rate starts decreasing. When the analysis is extended to Voigt and Faraday configurations, the results are not very encouraging.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.336297
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Reply to comments of Mjølhus (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2724-2725 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A reply to the comments of Mjølhus on a recent paper [Phys. Fluids 30, 1371 (1987)] is presented. It is shown that although some of the criticism is valid, other points cited by Mjølhus do not appear to be mistakes on our part.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866553
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    The evolution of cross helicity in driven/dissipative two-dimensional magnetohydrodynamics (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2171-2184 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A numerical study of the evolution of cross helicity in driven/dissipative magnetohydrodynamics (MHD) is presented. The magnetofluid is incompressible and a two-dimensional (2-D) periodic geometry is considered. Cross helicity, a measure of the correlation between fluctuations in the magnetic field and the velocity field, is injected by use of correlated Gaussian forcing over a finite bandwidth in wavenumber. Numerical experiments include the driving of initially uncorrelated spectra with highly correlated forcing and the driving of correlated spectra with anticorrelated forcing. A recurring and persistent feature of the simulations is the appearance of oppositely signed cross helicity at small scales relative to large scales. A simple argument based on the Elsässer variables and used previously in the context of decaying turbulence explains many of the observed features. The effect of a uniform external magnetic field is considered and the relation to purely decaying 2-D MHD turbulence is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866617
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    The onset of Alfvénic turbulence (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1371-1387 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An investigation is conducted on how low-frequency, ω〈Ωi, magnetohydrodynamic oscillations in a warm plasma may undergo a transition from a coherent state to one of turbulence. A driven/dissipative derivative nonlinear Schrödinger (DNLS) equation is derived from the fluid equations. The time evolution of an arbitrary spectrum of waves is analyzed in the case where one k-mode is unstable, with the rest damped. It is found that the transition from order to chaos in the driven/dissipative system is correlated with the existence or absence of "breathing'' solitons in the associated conservative system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866252
    Standort Signatur Erwartet Verfügbarkeit
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