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  • 1
    Electronic Resource
    Electronic Resource
    First experimental observation of the ignition of a "superdense glow'' before the glow-to-arc transition in a pseudospark discharge (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 631-636 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The presented results are the first experimental indication for the existence of a homogeneous superdense glow in the bore hole of the cathode in a pseudospark discharge. The start of this mechanism is leading to the low-impedance high-current phase and starts before the glow-to-arc transition in the pseudospark discharge. It is assumed that the high-current density is carried mainly by metal ions which originate from a self-sustained self-sputtering mechanism, or by a large number of, on a macroscopic scale, homogeneously distributed Schottky emitters. It is shown that the geometric features of the bore hole cause an enhancement of this effect. These results and the theoretical assumptions can also explain very effectively the current quenching of the pseudospark discharge. Current quenching is only occurring during the superdense glow when no cathode spots are ignited. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360805
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  • 2
    Electronic Resource
    Electronic Resource
    The use of carbides as electrode material in a pseudospark switch (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4299-4302 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the following, we report tests of a semiconductor as electrode material in a pseudospark switch, which is a low pressure gas discharge switch. Polycrystalline SiC or BC disks with central apertures were embedded in molybdenum outer electrodes in a typical single stage pseudospark geometry. The maximum voltage applied was 15 kV. Tests were done with peak currents from 50 up to 500 kA at pulse lengths of a few microseconds. We found no difference in the voltage breakdown or the rise in current when compared to conventional metal electrodes such as molybdenum or tungsten. Fast shutter photographs showed that the discharge burns in an intense column at the center and is distributed very homogeneously over the SiC surfaces. Neither cathode nor anode spots were observed. Small sparks occurred at the metal–carbide interface after current zero, which led to a reignition in the second current half-wave. An estimation after the tests showed an erosion rate of about 5 μg/C approximately one order of magnitude lower than in metals. We assume that the current is transported in a thin surface layer. Ion bombardment in the pseudospark discharge heats this layer to more than 2000 K, lowering the specific resistance. The negative temperature–resistance characteristic means that cathode spots are avoided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363377
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  • 3
    Electronic Resource
    Electronic Resource
    The bottleneck in pseudospark discharges (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 625-630 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Physical mechanisms during early phases of pseudospark discharges are still under discussion. Experiments at low rates of current rise (dI/dt〈109 A/s) were performed to investigate these phenomena, using filtered fast shutter photography of the discharge plasma in the visible wavelength region. Additionally temporally resolved measurements of line emission of the filling gas (hydrogen and helium) and cathode material (copper) were performed. These experiments revealed a discharge phase where the cathode surface involved in the discharge is restricted mainly to the inside of the cathode aperture. The voltage drop during that phase is about 200–400 V and the current density exceeds 1 kA/cm2. A possible explanation of the discharge mechanisms during that discharge phase is self-sputtering of cathode material from the cathode surface inside the cathode aperture. The described mechanisms might be fundamental for the transition from the transient hollow cathode phase to the high current phase in pseudospark discharges. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362663
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  • 4
    Electronic Resource
    Electronic Resource
    Acceleration of electrons to 〉0.5 MeV during space–charge neutralization of a 20 keV transient electron beam (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1424-1426 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of high fields produced during space–charge neutralization of an electron beam is demonstrated by production of relativistic electrons (≈0.6 MeV) from a simple, small hollow cathode source operated at 20 kV. Acceleration occurs during a well-characterized, repeatable, glow-type transient plasma phase. The accelerating electron beam is produced within the device, and the total number of (approximately-greater-than)0.5 MeV electrons is estimated to be ≤1010. A model correlating time dependence of the transient plasma with energetic electron production is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116101
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  • 5
    Electronic Resource
    Electronic Resource
    Fe and Mo EXAFS of Azotobacter vinelandii Nitrogenase in Partially Oxidized and Singly Reduced Forms (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 10017-10024 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00145a012
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of nitrogen on competition between cereals and their natural weed populations (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 36 (1996), S. 0 
    Details
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of nitrogen fertilizer on the growth and density of natural weed populations in spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) were investigated in the absence of herbicide. An increased level of applied nitrogen did not enhance: weed germination, tended to decrease the total weed biomass and had a differential effect upon the biomass of individual weed species in both wheat and barky. In competition with barley, Chenopodium album L. and Lamium spp. had lower nitrogen optima than the crop, while Urtica urens L. had a higher nitrogen optimum. In competition with wheat, Stellaria media (L.) Vill., Lamium spp. and Veronica spp. had lower nitrogen optima than the crop. The systematic changes in nitrogen effect with time were analysed by fitting orthogonal polynomials to the growth and density curves. The methodology could be recommended for other studies in which time or other systematic factors are included, as it supplies information which a traditional analysis of variance cannot provide. Since seed production is positively correlated with biomass, so nitrogen level affects seed production and, hence, the seed pool and future weed population, suggesting that fertilizer usage can be exploited in an integrated programme of crop: weed management. A trend towards lower N fertilizer application owing to concerns about the environment willfavour most of the weed species investigated in these experiments and change the composition of weed populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3180.1996.tb01675.x
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  • 7
    Electronic Resource
    Electronic Resource
    Sex differences in ionoregulatory responses to dietary oil exposure in polar cod (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 57 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Serum osmolalities and chloride concentrations were examined in polar cod. When exposed to oil male and female fish responded differently. Ingestion of food contaminated with oil led to a significant decrease in osmolality (from 503 to 492 mOsm kg−1) in males. There was no significant effect of oil ingestion on serum osmolality in females, but chloride concentrations were increased (from 196 to 203 mmol kg−1). Gender related responses should, therefore, be considered when assessing the possible effects of environmental pollutants on fish physiology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02253.x
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  • 8
    Electronic Resource
    Electronic Resource
    Monitoring voluntary feed intake under practical conditions, methods and applications (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of applied ichthyology 11 (1995), S. 0 
    Details
    ISSN: 1439-0426
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0426.1995.tb00025.x
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  • 9
    Electronic Resource
    Electronic Resource
    Disposition and cellular binding of 3H-benzo(a)pyrene at subzero temperatures: studies in an aglomerular arctic teleost fish – the polar cod (Boreogadus saida) (2000)
    Springer
    Polar biology 23 (2000), S. 503-509 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Autoradiography at different levels of resolution was used to study the disposition of the polycyclic aromatic hydrocarbon benzo(a)pyrene (3H-BaP) in juvenile and sexually mature polar cod (Boreogadus saida). Exposure took place via the water or after intragastric administration at subzero temperatures. In water-exposed fish, high total tissue levels were found in the gills, olfactory organ, anterior kidney, liver, skin and intestinal wall. Only traces of radioactivity were present in the muscle, brain and gonads. No major differences in tissue levels or in general distribution pattern between males, females or juvenile fish were observed. The gills appeared to be the absorption site for exposure via water. After oral administration, tissue levels of 3H-BaP-derived radioactivity were negligible. Following both administration routes, levels of radioactivity were highest in the bile and intestinal contents while only traces were observed in the urine, indicating biliary excretion as the major excretory pathway in this aglomerular species. Tape-section autoradiography of fish exposed via water revealed tissue-bound residues of 3H-BaP in the olfactory organs, gills, kidney, liver, skin and intestinal mucosa. Light-microscopy autoradiography demonstrated that the bound residues in the olfactory organ, gills and anterior kidney were localized in epithelial cells, while those in liver and intestinal mucosa were evenly distributed. In conclusion, the present study shows that BaP is absorbed from the water via the gills at subzero temperatures, that tissue levels are considerably higher after water exposure than after dietary exposure, that biliary excretion is predominant and, finally, that site-specific tissue binding in the olfactory organs, gills and anterior kidney is confined to epithelial cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003000000112
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  • 10
    Electronic Resource
    Electronic Resource
    The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants (1998)
    Springer
    Potato research 41 (1998), S. 109-116 
    Details
    ISSN: 1871-4528
    Keywords: fertilization ; starch quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha−1. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)−1 whereas starch from plants grown with 30 kg P ha−1 contained 20.6 nmol P (mg starch)−1. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l−1, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02358433
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