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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Activities of enzyme markers of subcellular organelles have been measured in brain tissue from subjects with Alzheimer-type dementia (ATD) and Huntington's disease (HD). Significant increases in the activity of the lysosomal enzyme β-glucuronidase were observed in both ATD temporal cortex and HD putamen. It is suggested that β-glucuronidase activity may be a useful biochemical indicator of cellular damage in the CNS. A significant reduction in neutral α-glucosidase activity was observed in ATD temporal cortex and HD putamen. This change may reflect an alteration in glycoconjugate processing and may relate to the susceptibility of neurones to the degenerative processes of ATD and HD.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using x-ray diffraction techniques, we measure the root-mean-square width of the buried crystalline/amorphous Si(001)/SiO2 interface, as a function of oxide thickness. We find that the interface width decreases with increasing oxide thickness; the oxide growth process kinetically smoothens the buried interface. We also find a difference between the rate of smoothing for wet and dry oxides. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 516-526 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper numerical solutions of Zakharov-type equations for lower-hybrid (LH) waves, including pumping at the long wavelengths and dissipation at short wavelengths in the form of dissipative cavitons are described. The caviton is a quasistationary structure undergoing many sequences of collapse due to dissipation, created by ion–wave interactions, which is compensated for by constant pump action. The possibility of trapping of short-wavelength LH oscillations by much broader density cavitons is investigated both analytically and numerically. Analytic self-similar solutions corresponding to collapse of such cavitons are constructed and demonstrate cascading to shorter wavelengths, which develops faster than the three-dimensional (3-D) quasiclassical cavity contraction. Numerical solutions show the development of deep caviton modulation due to the instability of quasiclassical collapse. Results of the numerical and analytical investigation are used to explain the recent observations of cavity formation in the auroral ionosphere, and show that the measured structures could indeed arise from quasiclassical LH collapse. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Electric Tokamak (ET), currently under construction at the University of California–Los Angeles, is designed to rotate poloidally via a radial current induced by fast wave rf heating fast enough to bifurcate the plasma into a global "H mode" ("high confinement mode"). A global gyrokinetic code is used to explore and illustrate some of the effects on ion temperature gradient turbulence. The realistic radial electric field required to completely suppress these modes for ET parameters is demonstrated to be 〈−30 V/cm at its maximum near the half radius. The effects of both a poloidally supersonic bulk rotation threshold and the shear in this rotation near that supersonic threshold were shown to be important in reducing these modes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1001-1010 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Acceleration of both electrons and ions to relativistic energy by large amplitude magnetosonic waves is investigated by use of numerical simulation. Nonlinear effects are shown to form the saturation mechanism and limit the amplitude below the level where a particle specie can undergo unlimited acceleration, which is expected theoretically. Spiky structures appear both in density and field waveforms that are characteristics of the relativistic regime. Both electrons and ions are strongly accelerated by Elx×Bz drift and Ety field, but their resonance features versus fields are strongly different. Around the trapping time, relativistic electron solitonlike wavelets are triggered from the main wave ramp; a few mechanisms are proposed for their interpretation. Both electrons and ions are strongly heated at the expense of the wave energy. This damping in association with the large space charge effects resulting from the spiky structures is the origin of some observed saturation level in the field energy.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1767-1788 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particle dynamics and field behavior associated with a perpendicular collisionless supercritical and viscous shock are investigated by use of numerical simulation. A one-dimensional, relativistic, fully electromagnetic and nonperiodic particle simulation code (for both electrons and ions) is used where self-consistent space-charge effects and induced effects are totally included. The principal field patterns of the shock (trailing wave train, ramp, and foot region) are studied in detail and are shown to have scale lengths mainly dictated by ion dynamics; the behavior of the corresponding plasma currents associated with the different field components is also presented. Ions are shown to suffer successive "acceleration–trapping–detrapping'' at the shock front, and locally in the trailing wave train of the downstream region through combined effects of the electrostatic and magnetic fields. While detrapped, the reflected ions describe very large Larmor orbits and cause a ring distribution; a large rapid nonstochastic ion heating results from this ion gyration. This heating (resistivity-free) is the main source of dissipation and is responsible for large field damping. Competitive effects such as particle stochasticity, particle trapping, wave damping, wave overtaking, and dispersion effects are shown to interact with each other and to affect the overall dissipation mechanism. Comparison with previous works is also discussed. Various Mach number situations are considered, leading to the definition of a transitory regime between subcritical and supercritical regimes and of a corresponding critical threshold of the electrostatic field. In contrast with the supercritical regime, the subcritical regime is characterized by a low density of trapped-reflected ions, a broad ion distribution function with a weak tail, and a weak adiabatic bulk ion heating.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1110-1114 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron and ion dynamics are investigated through particle simulation of a supercritical oblique collisionless shock. As θ deviates from 90°, ions are accelerated and trapped in the electrostatic wells and later become detrapped; this results in strong ion heating perpendicular to B0. Below a critical angle θte electrons are strongly energized along B0, and heated. A large parallel electron current builds up and induces new transverse electromagnetic components in the ramp of the shock. For weaker angles, ion heating vanishes below a second critical angle θti.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3237-3244 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The parametric dependence of the growth rate of the low-frequency hot-electron interchange mode is studied with a two-and-a-half-dimensional relativistic electromagnetic particle code that models the geometry of a bumpy torus. The simulation results are compared in detail with finite-Larmor-radius theory, as well as zero-Larmor-radius theory. For the long-wavelength modes, the growth rates measured in the simulations tend to agree with those predicted from zero-Larmor-radius theory. For short-wavelength modes, the stabilizing effects of finite Larmor radius are significant.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 821-836 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of strong magnetosonic waves propagating perpendicular to a static field B0 is investigated within the frequency range ωci〈ω〈ωlh; ωci,ω, and ωlh are, respectively, the ion cyclotron, the pump wave, and the lower-hybrid frequencies. A one-dimensional, relativistic, fully electromagnetic, particle simulation code (for both electrons and ions) is used, where self-consistent effects are totally included. During the buildup phase, a longitudinal electric field develops and attains a nonlinear level which strongly distorts its shape so that many harmonics are produced. This is followed shortly by ion trapping, which simultaneously enhances the wave overtaking (the wave crests overtaking the wave troughs) and produced a strong wave damping. A very large ion acceleration accompanied by a strong heating (mainly nonstochastic) perpendicular to B0 results; the electrons exhibit only poor heating associated with their adiabatic compression. The dynamics of both particle species, the consequences of the wave–particle energy transfer and the particle viscosities, are studied in detail. Competitive and self-consistent effects such as space-charge effects, wave overtaking, ion trapping, and wave damping are investigated and compared with previous models; the mechanisms by which these various phenomena interact on each other are analyzed. Characteristics of nonstochastic and stochastic ion heating are also discussed. Our computations show that if sufficient intensity is reached, one is not constrained to use lower-hybrid waves or cyclotron harmonic waves to heat a plasma efficiently and that any frequency below ωlh can be used.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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