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  • Digitale Medien  (3)
  • South Africa  (2)
  • 78.70B  (1)
Materialart
  • Digitale Medien  (3)
Erscheinungszeitraum
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 43 (1987), S. 283-285 
    ISSN: 1432-0630
    Schlagwort(e): 78.70B
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A cryostat system incorporating a low-energy positron beam for surface measurements down to Temperatures below 2 K is currently under construction at the Royal Holloway and Bedford New College. The positron beam has recently been brought into operation and its operating characteristics have been evaluated. Positrons from a22Na source are converted with an efficiency of ε=2×10−4 and transported magnetically at 1.5 V above the work function to a target at the bottom of a cryostat. The transmission of a 7 mm diameter beam is found to be constant over a range of axial field strengths from 40 to 50 G.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 218 (1991), S. 177-192 
    ISSN: 1573-5117
    Schlagwort(e): fire ; South Africa ; fynbos ; stream chemistry ; water yield ; nitrate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effects of a late-summer prescribed burn on the chemistry of a second-order mountain stream in the south-western Cape, South Africa, were investigated. Nitrate concentrations in stream water were significantly higher during the winter of the post-burn year. Increased concentrations of chloride, bicarbonate, polyphenols and potassium and decreased sodium concentrations were also recorded. Concentrations of ammonium, phosphate, calcium, magnesium, total dissolved solids and hydrogen ions were not significantly affected by the burn. Ionic export from the catchment was generally greater in the post-burn year. Apart from nitrate, however, values probably lie within the natural range of year-to-year variation. It is predicted that enhanced losses of nitrate will decrease progressively with the recovery of the vegetation and the re-establishment of soil/plant nutrient cycles. Atmospheric losses of nutrients in smoke were unquantified, but may be of more significance to site productivity than losses through surface runoff, which, in the case of nitrogen, appear to be compensated by precipitation inputs.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    ISSN: 1573-5117
    Schlagwort(e): storms ; stream chemistry ; antecedent conditions ; fire ; South Africa
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The influence of different antecedent conditions on hydrochemical response during storm events was investigated in a small, south-western Cape mountain catchment. Winter and summer storms (four in total) were sampled both before and after the catchment was deliberately burnt. During winter storms, discharge responded rapidly to rainfall, and direct runoff represented the major component of streamflow. Marked lags were observed between rainfall and discharge peaks during the summer storms, and streamflow was dominated by delayed interflow. Chloride, PO inf4 sup3− -P and NO inf3 sup− -N exhibited variable response to discharge according to seasonal variations in soil-moisture levels, whereas the response of HCO inf3 sup− , H+ and NH inf4 sup+ -N was not influenced by season. The movement of ions appears to be affected more by geochemical processes operating within the soil than by plant-uptake dynamics, as the prescribed burn appeared to have little effect on relationships between ionic concentration and discharge. The findings of the study highlight the complexity of relationships between solute concentration and discharge.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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