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  • American Institute of Physics (AIP)  (5)
  • Blackwell Publishing Ltd  (2)
  • 1985-1989  (7)
  • 1950-1954
  • 1930-1934
  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337693
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336297
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866553
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866617
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866252
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  • 6
    Electronic Resource
    Electronic Resource
    Symptom remission in spiked sandal trees by infusion of tetracycline antibiotics (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 36 (1987), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Spike disease of sandal has recently been recorded in Kerala. For chemotherapy of the diseased trees a gravity-flow infusion technique was used to compare tetracycline compounds. All the compounds, including doxycycline and oxytetracycline, were effective when 500 mg per tree was infused in 500 ml water, but disease remission lasted for 4 months only. Repeated infusions failed to give complete remission. Increasing the concentration of tetracycline to 4–8 g per tree gave remission for 7–8 months; at 12 g per tree, phototoxicity was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1987.tb02211.x
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  • 7
    Electronic Resource
    Electronic Resource
    Calculation of Atomic Charges in Large Molecules (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 482 (1986), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1986.tb20939.x
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