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  • 1990-1994  (16)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 153 (1994), S. 337-345 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A critical examination of the components of the recent impulsive loop flare model of Takakura is made. It is found that his analysis of the stability of the electron distribution resulting from anomalous heat conduction is in error and electron plasma waves would not be excited. Rather, in the regions where the electron/proton temperature ratioT e/T i ≲ 10, electrostatic ion-cyclotron waves would be excited and in the regions whereT e ≳ 10, ion-acoustic waves would be excited. Ratios ofT e/T i ≳ 10 occur only in the late time development behind the conduction fronts. Since the anomalous resistivity due to electrostatic ion-cyclotron waves is fortuitously about 70% of the one used by Takakura, the general development will follow closely the one calculated by him. Because the anomalous resistivity due to ion-acoustic waves is about 95 times the one used by Takakura, the development in the parts of the loop whereT e/T i ≳ 10 for late times would be altered considerably.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 143 (1993), S. 247-258 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Vector magnetogram, Hα, and hard X-ray observations of flares are reviewed which show that nonthermal electron signatures in Hα are never cospatial with regions of maximum current density for the small number of flares analyzed, but lie to the sides of these regions. By considering electron acceleration and transport requirements, four conditions are found that must be fulfilled to observe nonthermal electron signatures in Hα: (1) The plasma betaβ ≤ 0.3 in the acceleration region. (2) The energy flux of electrons above 20 keV is greater than 1010 erg cm−2 s−1. (3) The column densityN ≤ 1020 cm−2 between the electron source and the chromosphere. (4) The coronal pressure in the flux tube connecting to the Hα layerp ≤ 100 dyne cm−2. Condition 2 can be most easily met in the initial stages of flares. In contrast, the only condition for a high-pressure Hα signature isp ≥ 1000 dyne cm−2, which is most easily met in a region of maximum current density or heating and far enough into the flare for significant heating to have occurred. Thus, high-pressure signatures should be expected to occur more frequently than nonthermal electron signatures and to occur generally later in time.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 131 (1991), S. 351-361 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gamma-ray observations are discussed to determine the density of protons of about 1 MeV precipitating to the photosphere. It is shown that Coulomb collisions will produce a positive slope in the proton distribution for energies less than 0.1 MeV for traversed column depths greater than 1018 cm −2. This could lead to plasma wave emission and radiation near the plasma frequency for densities ∼ 3.1 × 1010 cm−3 and temperatures ∼ 4.0 × 104 K where collisional and collisionless damping of the plasma waves is sufficiently weak. It is expected that these conditions will only be satisfied sporadically which leads to stationary radio emission limited in frequency and time. Recent radio observations of impulsive phase non-drifting patches in the 1–3 GHz range with duration 2–4 s are presented which could be produced by this mechanism.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 137 (1992), S. 317-328 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An analysis is made of the Martens-Kuin filament eruption model in relation to observations of coronal mass ejections (CMEs). The field lines of this model are plotted in the vacuum or infinite resistivity approximation with two background fields. The first is the dipole background field of the model and the second is the potential streamer model of Low. The assumption is made that magnetic field evolution dominates compression or other effects which is appropriate for a low-β coronal plasma. The Martens-Kuin model predicts that, as the filament erupts, the overlying coronal magnetic field lines rise in a manner inconsistent with observations of CMEs associated with eruptive filaments. Initially, the bright arc of a CME broadens in time much more slowly than the dark cavity between it and the filament, whereas in the model they broaden at the same rate or the bright arc broadens more rapidly than the dark cavity, depending on the background field. Thus, this model and, by generalization the whole class of so-called Kuperus-Raadu configurations in which a neutral point occurs below the filament, are of questionable utility for CME modeling. An alternate case is considered in which the directions of currents in the Martens-Kuin model are reversed resulting in a so-called normal polarity configuration of the filament magnetic field. In this case, a neutral line occurs above the current-carrying filament. The background field lines now distort to support the filament and help eject it. While the vacuum field results make this configuration appear very promising, a full two- or more-dimensional MHD simulation is required to properly analyze the dynamics resulting from this configuration.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 199-215 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10-12 cm3 molecule-1 s-1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10-13 cm3 molecule-1 s-1 at 298 K.The primary products and molar yields for the OH reaction with ETBE in the presence of NOx were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 23 (1991), S. 907-924 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl tertiary butyl ether (MTBE) has been proposed and is being used as an additive to increase the octane of gasoline without the use of tetraethyl lead and alkylbenzenes. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of MTBE. The kinetics of the reaction of OH with MTBE was examined by using a relative rate technique in which photolysis of methyl nitrite was used as the source of OH. With n-butane as the reference compound a value of (2.99 ± 0.12) × 10-12 cm3 molecule-1 s-1 at a temperature of 298 K was obtained for the rate constant. The products (and product yields) for the OH reaction with MTBE in the presence of NOx were also determined and found to be t-butyl formate (0.68 ± 0.05), methyl acetate (0.14 ± 0.02), acetone (0.026 ± 0.003), t-butanol (0.062 ± 0.009), and formaldehyde (0.48 ± 0.05) in mols/mol MTBE converted. The OH rate constant for the major product formed, t-butyl formate was also measured and found to be (7.37 ± 0.05) × 10-13 cm3 molecule-1 s-1. Mechanisms to rationalize the formation of the products are presented.
    Additional Material: 5 Ill.
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  • 7
    Publication Date: 1992-02-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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  • 8
    Publication Date: 1991-02-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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  • 9
    Publication Date: 1994-08-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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  • 10
    Publication Date: 1993-02-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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