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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2383-2385 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the first direct experimental observation of the coalescence of two shocks induced by a shaped laser pulse. Optical streak photography of the rear surface of aluminum multiple step targets was used to study the breakout of these shocks and observe their behavior. The experimental results are compared with simulations by a one-dimensional Lagrangian hydrodynamic code.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 40 (1991), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A screening programme was used to search for biocontrol agents against Gaeumannomyces graminis causing take-all disease of wheat. Of the 1800 rhizosphere microorganisms tested, 10% controlled the disease in a secondary screen. The 30 most effective isolates were further investigated for mode of action. Although 72% of the sites sampled for antagonistic microbes were planted to continuous cereals, they yielded only 23% of the most effective isolates. Of all the isolates selected, 63% belonged to the genera Bacillus, Pseudomonas and Penicillium; Beauveria and Rhodococcus were also antagonistic. Fluorescent pseudomonads, all producing siderophores in low-iron medium, accounted for 23% of the isolates. Over 50% of strains produced β-glucanases and chitinases. Less than 50% of the strains selected by the in vivo screen inhibited G. graminis in agar plate tests. In the gnotobiotic system used, the Pseudomonas strains were faster in colonizing the wheat roots than the majority of the Bacillus and fungal strains.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4781-4787 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of the negative glow of a low-pressure Hg-Ar discharge is described. The model contains a number of important physical processes (in particular noble-gas excitation and multiple-step ionization) that have not been included in earlier models. The model has also been coupled to a simple description of the Faraday dark space to enable predictions to be made of the axial density and potential profiles across the whole negative-glow Faraday dark-space positive-column region. Results of a number of numerical computations are presented and in general these have been found to be in agreement with experimental observations. The effect of varying the various input parameters to the model on its predictions has also been studied and the results of this will also be presented.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis is presented of K-shell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 μm) at 1018–1019 W/cm2. Stark broadening measurements of He-like and Li-like lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce x-ray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest x-ray pulse at a given wavelength is relatively narrow. Lower intensity produces a short x-ray pulse but low brightness. The x-ray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximately 6% of the laser energy is coupled to the target at 1018 W/cm2 (1% in thermal electrons with Te≈0.6 keV and 5% in suprathermal electrons with Th≈25 keV). At Iλ2=1018 W μm2/cm2 (no prepulse) around 1010 photons are emitted per laser shot, in 2π srd in cold Kα radiation (2–9 A(ring), depending on the target material) and up to 2×1011 photons are obtained in 2π srd with the unresolved transition array (UTA) emission from the Ta target. © 1995 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 2 (1990), S. 1318-1324 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results are presented for the interaction of an intense laser beam in large preformed, homogeneous underdense plasmas. Parametric instabilities, including filamentation, stimulated Raman (SRS) and stimulated Brillouin scattering (SBS), have been extensively studied. In this paper comparisons are made between coherent and smoothed laser interaction beams for their effectiveness in suppressing these instabilities. Direct observations of the enhanced breakup of the coherent interaction beam due to filamentation are presented. Measurements of the transverse scale lengths of the hot spots, and the level of the intensity modulations of the filamentary structures are given. Further, direct experimental observations of SRS and SBS generated in filaments are presented. These provided conclusive evidence that this instability provides the primary mechanism for the generation of SRS and SBS under such plasma conditions. With the smoothed laser interaction beams, using random phase plates (RPP) and induced spatial incoherence (ISI), the level of filamention was significantly reduced. The backscattered fractions of SRS and SBS with respect to the irradiance of the interaction beam were measured for coherent, RPP and ISI. Reduction of typically a factor of 20 and 500 were recorded using RPP and ISI, respectively, in the backscattering levels of SRS and SBS when compared with the coherent interaction beam. The reductions are attributed primarily to the effectiveness of the beam-smoothing techniques in suppressing the filamentation instability.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1301-1322 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A time-resolved study is presented of stimulated Raman backscatter (B-SRS) produced in a large-scale-length preformed plasma in an intense laser pulse. The first direct experimental results are presented to (i) show that the B-SRS is generated predominantly in laser filaments and (ii) provide a direct correlation between the spectral and spatial emission profiles of the B-SRS as a function of interaction irradiance. The "anomalous'' B-SRS spectral features so commonly reported in time-resolved studies are shown to be the characteristic emission of B-SRS from filaments. The B-SRS fraction was also measured as a function of interaction irradiance. The B-SRS intensity "threshold'' and "saturating'' behavior recorded can be well described for the present interaction conditions. The onset of B-SRS is shown to be strongly correlated with the intensity threshold of the filamentation instability. The effect of laser beam "smoothing'' techniques on the B-SRS emission have also been investigated, using either a random phase plate (RPP) or induced spatial incoherence (ISI). The results suggest that their effectiveness in suppressing B-SRS is strongly associated with their ability to reduce the level of filamentation while still producing a high level of plasma perturbation which can effectively destroy the phase-matching conditions necessary for B-SRS.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2676-2681 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved spectroscopy (with a 2 psec temporal resolution) of plasmas produced by the interaction between solid targets and a high contrast subpicosecond table top terawatt (T3) laser at 1016 W/cm2, is used to study the basic processes which control the x-ray pulse duration. Short x-ray pulses have been obtained by spectral selection or by plasma gradient scalelength control. Time-dependent calculations of the atomic physics [Phys. Fluids B 4, 2007, 1992] coupled to a Fokker–Planck code [Phys. Rev. Lett. 53, 1461, 1984] indicate that it is essential to take into account the non-Maxwellian character of the electron distribution for a quantitative analysis of the experimental results.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Optics Communications 92 (1992), S. 73-78 
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Optics Communications 105 (1994), S. 63-66 
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Optics Communications 84 (1991), S. 67-70 
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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