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  • 1
    Electronic Resource
    Electronic Resource
    A new telemetry system for a balloon-borne far-infrared astronomical telescope (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 281-288 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new telemetry system (NTS) is described here, which has been developed for a balloon-borne far-infrared astronomical telescope. The NTS includes two space borne encoders (TEs) and the ground station decoder and display subsystems. The design of the TEs uses several novel ideas which simplify on-board hardware implementation. The NTS has shown satisfactory in-flight performance and is now a standard package for regular balloon flight experiments. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150194
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  • 2
    Electronic Resource
    Electronic Resource
    Optical parameters of a magnetized semiconductor plasma with nonparabolic band structure (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4741-4746 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical parameters (linear and nonlinear) and dispersion characteristics of a III–V compound semiconductor plasma subjected to a strong transverse magnetic field have been investigated theoretically. The nonlinearity induced in the medium has been attributed to heating of the carriers by the pump that results in modification of the electron effective mass in a nonparabolic conduction band and the momentum transfer collision frequency of electrons. The external magnetic field is found to have two consequences: (a) increasing the nonlinearity of the medium and (b) modifying the dispersion characteristics and determining the direction of energy flow between the pump and the generated waves. The plasma frequency ωp is found to enhance the magnitude of the optical parameters as usual. For a typical n-InSb semiconductor, linear refractive index and nonlinear refractive index coefficients are found maximum (nl=5.3, nnl=2×10−10 m2 V−2) whereas absorption coefficients al (linear) and anl (nonlinear) are found to vanish when ωo resonates with ωc(=1.138×1014 s−1). The present study once again establishes the device potentials of n-InSb. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1358315
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  • 3
    Electronic Resource
    Electronic Resource
    Scattering of laser beam by acoustohelicon waves in magnetoactive noncentrosymmetric semiconducting crystals (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1689-1695 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the coupled mode theory, an analytical investigation of scattering of laser beam by an acoustohelicon wave and the consequent amplification of the scattered modes and the acoustohelicon wave is carried out in a longitudinally magnetized semiconductor of a noncentrosymmetric nature. We have assumed the origin of nonlinear interaction to be the second order optical susceptibility arising from the nonlinear induced current density. The numerical estimations are made for n-InSb crystal at 77 K. The threshold pump electric field E0th is found to decrease with increasing wave number and decreasing scattering angle. The nonlinear dispersion characteristics for a right hand circularly polarized mode become positive for E0〈E0th and negative for E0(approximately-greater-than)E0th. The nature of a left hand circularly polarized mode is found to be just the reverse. The steady state gain constants for piezoelectric (gp), deformation (gd), and both cases (gb) are also obtained. The influence of the doping level on nonlinear dispersion characteristics and gain constants has also been considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351692
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  • 4
    Electronic Resource
    Electronic Resource
    Parametric dispersion and amplification of acoustohelicon waves in piezoelectric semiconductors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 61-66 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Assuming that the origin of the nonlinear interaction lies in the second-order optical susceptibility arising from the nonlinear induced current density and using the coupled-mode theory, the parametric dispersion and amplification of acoustohelicon waves is analytically investigated in a longitudinally magnetized piezoelectric semiconductor of noncentrosymmetric nature. The relevant experiments have not been reported. The threshold value of the pump electric field E0th and its corresponding excitation intensity is obtained. The longitudinal magnetic field decreases the required magnitude of E0th for the excitation of parametric amplification. The phenomenon of self-defocusing of the signal in the prevailing case is found to be a consequence of the negative dispersive characteristics exhibited by the acoustohelicon waves. Numerical analyses are performed for an InSb crystal at 77 K, duly irradiated by frequency-doubled pulsed 10.6-μm CO2 lasers. The parametric gain constant is observed to be maximum when the cyclotron frequency ωc attains the magnitude equal to that of ω0, the incident laser frequency (=1.78×1014 s−1 ).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347657
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  • 5
    Electronic Resource
    Electronic Resource
    Large Mach number ion acoustic rarefactive solitary waves for a two electron temperature warm ion plasma (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3939-3946 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An exact analytical form of Sagdeev pseudopotential has been derived for a two electron temperature warm ion plasma, from which ion acoustic rarefactive solitary wave solutions could be investigated for a wide range of different plasma parameters, viz., ion temperature (σ), cold to hot electron temperature ratio (β), and initial cold electron concentration (μ). Explicitly large Mach numbers have been obtained for increasing hot to cold electron temperature ratios, and an analytical condition for the upper bound of the Mach number has been derived for such a rarefactive solitary wave. It is found that the width of these waves obey Korteweg–de Vries soliton-type behavior only for small amplitudes (i.e., eφ/Teff〈1) while for large amplitudes, the width of the rarefactive solitary waves increases with increasing amplitude. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871567
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  • 6
    Electronic Resource
    Electronic Resource
    Forbidden regions in ion temperatures for ion acoustic compressive solitary waves for a plasma with two electron temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2139-2145 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is observed that, there exist certain forbidden regions in ion temperatures, for a compressive solitary wave, which do not have any solitary wave solution. These regions exist for a two- as well as a single-electron temperature plasma. A physical model is proposed to explain this phenomenon on the basis of the energy relation. It is revealed that a one-dimensional single warm ion fluid consists of two distinct energy components. A simple algebraic condition has been derived which expresses the balance between nonlinearity and dispersion for a fully nonlinear solitary wave. It shows that both the nonlinearity and dispersion decrease with increasing ion temperature and that the balance condition is well maintained for the whole spectrum of solitary wave solutions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872378
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  • 7
    Electronic Resource
    Electronic Resource
    Anomalous width variations for ion acoustic rarefactive solitary waves in a warm ion plasma with two electron temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3204-3210 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalous width–amplitude variations were observed in large amplitude rarefactive solitary waves which show increasing width with increasing amplitude, contrasting the usual reciprocal relation between the square of the width and the amplitude, beyond a certain value of the plasma parameters [S. S. Ghosh, K. K. Ghosh, and A. N. Sekar Iyengar, Phys. Plasmas, 3, 3939 (1996)]. For the limiting maximum amplitude, the "increasing width" solitary wave tends to a double layer-like solution. The overall variation was found to depend crucially on the specific parameter space. From a detailed investigation of the above behavior, a plausible physical explanation has been presented for such increases in the width. It is found that the ions' initial kinetic energies and the cold electron concentration within the perturbed region play a significant role in determining the observed width–amplitude variation. This contradicts the investigation of Sayal, Yadav, and Sharma [Phys. Scr. 47, 576 (1993)]. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872461
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  • 8
    Electronic Resource
    Electronic Resource
    Nonlinear entropy production operators for magnetohydrodynamic plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1480-1493 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for constructing closure relations based on the invariants of the tensors representing nonequilibrium thermodynamic forcing within the plasma is presented. This approach leads to closure relations that describe all higher-order forcing effects contained within the continuum description. Nonlinear convective-momentum transport and nonlinear momentum-exchange operators are constructed as applications of the method. Closure is achieved by relating the pressure tensor to invariants of the rate of strain tensor, and the momentum-exchange operator to invariants of the gradient of magnetic field tensor. These operators lead to positive definite viscous and Joule entropy production and enhance high wave number dissipative couplings over all other dissipative couplings. The nonlinear dissipative action is localized in physical space, where velocity and magnetic gradients are large, while allowing nearly ideal behavior elsewhere. The operators are computationally tested against the standard magnetohydrodynamic (MHD) operators using three-dimensional configurations that lead to vortex street formation and magnetic reconnection. The nonlinear operators allow greater spatial structure and have flatter modal energy spectra than the standard MHD dissipation operators. Closures that describe the plasma response to nonequilibrium thermodynamic forcing of all orders can be constructed using this approach. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871363
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  • 9
    Electronic Resource
    Electronic Resource
    Relaxation processes in a turbulent compressible magnetofluid (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1520-1534 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The compressible extensions of time asymptotic relaxation states of incompressible two-dimensional magnetohydrodynamic turbulence are studied. A polytropic equation of state is used with viscous and resistive dissipation. The incompressible case is known to allow three distinct time asymptotic types of behavior: magnetic energy dominated relaxation, kinetic energy dominated relaxation, and cross helicity dominated relaxation. At low Mach numbers the incompressible scenario is reproducible from the compressible simulations, and compressibility plays only a secondary role. At moderate, but still subsonic, Mach numbers the distinct incompressible processes are still recognizable, but strong compressibility features dominate the high-wave-number regime of several simulations. In particular, the magnetic and kinetic energy dominated simulations display regions of strong acoustic turbulence near the dissipation scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859477
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  • 10
    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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