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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentiometric titration curves of oxidized and reduced horse heart cytochrome c in 0.15M KCl at 20°C have been obtained by timed titration (0.125-0.500 μmol/sec) from the isoionic points (pH 10.2-10.4) to pH 3 and back to the isoionic point. Computer-assisted (PROPHET) data acquisition and blank corrections give curves with good precision with a maximum standard deviation of 0.3 groups for an average error of 1%. The potentiometric titration curve of reduced cytochrome c is reversible within the precision of the method and for the pH range studied. The potentiometric curves for oxidized cytochrome c titrated upscale (pH 3-10) and downscale (pH 10-3) are not reversible. However, they show the same ionization behavior after the initial downscale titration. This is probably the result of a conformational change. Comparison of the data herein reported with the titration curves of oxidized cytochrome c already published by others indicates good agreement on the basis of a normalization of the concentration of protein or on the basis of 25 titrable groups between the acid end point and the isoionic pH.Titration of the 2 μmol imidazole in the upscale or downscale direction gives the correct analytical concentration and pK′ after correction for the solvent titration. Titration of reduced cytochrome c in the presence and absence of an additional equivalent of imidazole gave a difference titration curve, which indicates that a group on the protein shifts from pK′ 5.8 to pK′ 5.3 in the presence of imidazole. The pK′ of imidazole, in the presence of the protein, remains at a nearly normal value of 7.34.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Supersonic, counterstreaming plasmas were produced by ablating plasma from the inside surfaces of two parallel disks made of aluminum and magnesium, respectively, with a 0.53 μm laser at an intensity of 1014 W/cm2 for 1.3 nsec. Diagnostics included holographic interferometry, a time-integrated x-ray pinhole camera and a gated x-ray crystal spectrograph with imaging slits. The plasmas interpenetrate for the first half of the laser pulse but stagnate once the electron density exceeds 5×1020 cm−3. Spectroscopic measurements suggest a coronal electron temperature of ∼800 eV and an ion temperature of ∼15 keV in the stagnated plasma. The observations are in good agreement with a two ion fluid model of interpenetrating plasmas in which the dominant slowing down process is ion–ion collisions.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interpenetration of two supersonically moving plasmas is affected by both collective modes of oscillation and Coulomb collisions. Two potentially important plasma instabilities, an electrostatic ion two stream and an electromagnetic ion Weibel, are considered and shown to be stabilized if only a small fraction of ion kinetic energy is converted to heat. For low-density, highly supersonic flows, the mean free path for slowing down (dominated in most cases of interest by ion–ion collisions) can be larger than or comparable to the system size. To develop an understanding of these plasmas, a unique hydrodynamic model has been developed that allows interpenetration but explicitly converts kinetic energy into heat as the ions slow down. The model is applied to the collision of two plasmas created by heating two parallel foils.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The (3)/(2) ω0 harmonic emission has been observed from a laser-produced plasma using exploding foil targets illuminated by 1.053 μm laser light with a 300 psec square pulse. The shift of the measured wavelength from (2)/(3) λ0 is found to depend markedly on the target thickness. Variation of the flow velocity and thus the Doppler shifts of the wave frequency with target thickness is found to be more important than variation of the electron temperature. Adjusting the measured wavelength by Doppler shifts calculated with flow velocities from simulations brings the measurements from different target thicknesses into agreement. These results indicate that previous predictions of electron temperatures from analyses of half-harmonic spectra from inertial confinement fusion plasmas are up to a factor of 2 too small.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3109-3115 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stimulated Brillouin scattering spectrum from a plasma is determined by the ion acoustic normal mode frequencies, which are dependent on the ion temperature and flow velocity. Thus these quantities are indirectly measured by the scattered light. The frequencies of ion acoustic normal modes and stimulated Brillouin scattered light are calculated for a model plasma formed by collisionlessly interpenetrating ion beams by assuming the ion–ion two-stream instability is marginally stable. The spectrum differs measurably from the spectrum expected from the hot, stationary plasma created by collisional stagnation. Comparison of the scattered light spectra for these two limiting cases suggests that careful observation of the scattered light near the laser frequency is a potentially useful diagnostic of the collisionality of interpenetrating ion beams.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated Raman scattering (SRS) was studied in experiments with laser-irradiated Au disk targets. Typically the laser energy was 150 J in a 1.0 nsec pulse at a wavelength of 526 nm. Laser intensity at the target was ∼7×1014 W/cm2. The spectrum, angular distribution, onset time, duration, and intensity of the Raman light were measured. In addition the electron density distribution was determined by holographic interferometry and images of the Raman emission were obtained. These data show that the Raman light is primarily backscattered and that scattering occurs at electron plasma densities 0.01 nc ≤n≤0.15nc. SRS occurred at laser intensities which are below theoretical thresholds, given the plasma conditions. Otherwise, most of the data support the present understanding of Raman scattering.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2895-2909 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calculations have been made of the spectrum of light emitted at half-integer harmonics of the laser light frequency ω0. The emitted light results from either the Raman scattering of laser light by Langmuir waves or by the direct conversion of Langmuir waves to light. The Langmuir wave amplitude is calculated from convective instability theory for two-plasmon decay in an inhomogeneous, plane-stratified medium. The Raman scattering process generates harmonics at (n/2) ω0 where n=1,3,5 ...; however, only for n=1 and 3 is the emission level significant. The conversion process produces (1/2) ω0 light with a comparable efficiency to the Raman scattering process near the two-plasmon instability threshold. Results of the calculation are in agreement with the general features of measured emission spectra.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2419-2431 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of the convective two-plasmon decay instability is studied using a kinetic theory formulation which is applicable to high-temperature plasmas. Theoretical values for the Langmuir wave amplification are obtained in several limits. The temperature-dependent effects of Landau damping and kinetic theory corrections to the coupling coefficients are studied. Landau damping significantly reduces the spectrum of unstable modes for T〉1 keV, while kinetic corrections become important for T〉10 keV. The nonresonant scattering of Langmuir waves by thermal electrons is calculated and is found to be comparable to the resonant convective process for T〉20 keV.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser beam smoothing by spectral dispersion and by polarization smoothing has been observed to significantly reduce the scattering losses by stimulated Brillouin and stimulated Raman scattering from inertial confinement fusion hohlraums. For these measurements, the laser beam smoothing and the high-Z hohlraum wall plasma parameters approach the conditions of future inertial confinement fusion experiments. The simultaneous application of the smoothing techniques has reduced the scattering losses by almost one order of magnitude down to the 1% level. The experimental scaling of the stimulated Brillouin reflectivity compares well to modeling assuming nonlinear damping on the ion acoustic waves in three-dimensional nonlinear wave simulations and calculated hohlraum plasma conditions from radiation-hydrodynamic modeling. © 2001 American Institute of Physics.
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  • 10
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that the measured laser power transmission through a large scale length, high temperature plasma (which emulates an indirect drive ignition-scale plasma) is in approximate agreement with the simulated transmission provided the simulations account for the power loss due to scattering from laser-plasma instabilities. Detailed accounting of the incident, transmitted, scattered, and absorbed powers is used to infer the likely location in the target where most of the scattering occurs along the incident beam trajectory. This location is near the incident laser side of the target at peak electron temperatures for a range of laser intensities. As a result, the backscattered light measurements at peak electron temperature do not require significant adjustment to account for attenuation of the backscattered light as it propagates out through the plasma. © 2000 American Institute of Physics.
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