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  • 2010-2014  (2)
  • 1970-1974  (3)
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  • 1
    Publication Date: 2013-08-17
    Description: [1]  Avalanches maintain the slipface of aeolian dunes, which alters their air flow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel (DSWT) under wind velocities of 8-11 m s −1 . Changes in slipface topography were observed photographically and measured utilizing a 3D laser scanner with 1 mm 2 spatial resolution. Avalanches in non-cohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32°) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of windspeed over the range of velocities observed. This independence provides the potential to significantly simplify the modelling of grainflow as a function of only the total cross brink sediment transport.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2013-08-17
    Description: [1]  In order to detail the governing conditions through which a slipface matures to the point of failure, dry sand avalanches were observed in the Dune Simulation Wind Tunnel (DSWT) on a 1:1 replica transverse dune with a crest height of approximately 1.2 m. Areal distributions of grainfall and reptation were measured using traps. Changes in the slipface elevation were observed using 3D laser scanning with a vertical accuracy of 0.096 mm for approximately every 1 mm 2 of surface area. Grainfall decayed exponentially from the brink with a constant rate across all wind velocities. Reptation removed sediment from areas close to the brink, and deposited it downslope, creating low amplitude, cross-slope ripples on the slipface. A critical length scale separating grainscale and bulk sediment behaviour is identified, and it defines the lower limit to the validity of angle of repose measurements. Avalanche initiation occurred in an area of steep surface slope below a sediment bulge, with distance from the brink independent of wind velocity. The time between avalanches was found to be constant for constant wind velocity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2019-06-27
    Description: The collection of data on the response of the skeletal and muscular systems to 14-day space flights was evaluated for loss of calcium, nitrogen, and other metabolically related elements. Considerable interindividual variability was demonstrated in all experimental factors that were measured. Calcium balance became less positive and urinary phosphate excretion increased substantially in flight despite a reduction in phosphate intake. Patterns of excretion of magnesium, sodium, potassium, and chloride were different for each subject, and, in part, could be correlated with changes in adrenocortical steroid production. The principal hormonal change was a striking decrease during flight in the urinary excretion of 17-hydroxycortocosteroids. Dermal losses of calcium, magnesium, sulfate, and phosphate were insignificant during all three phases.
    Keywords: BIOSCIENCES
    Type: EXPT-M007 , NASA. Manned Spacecraft Center The Gemini Program Biomed. Sci. Expt. Sum.; p 87-110
    Format: text
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 6 (1970), S. 70-76 
    ISSN: 1432-0827
    Keywords: Bone ; Soft tissue ; Sodium 22 ; Exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Des groupes de jeunes rats sont injectés par voie intraveineuse avec du22Na. Après divers intervalles de temps courts, du sérum et des fragments de foie, de muscle squelettique, de rein et d'os compact soigneusement isolé sont prélevés et étudiés en ce qui concerne les concentrations en sodium stable et isotopique radioactif. La pénétration du22Na dans les tissus mous examinés est très rapide et, après 10 minutes, seule une faible proportion de sodium tissulaire reste relativement inaccessible à la circulation. La vitesse d'absorption de22Na par l'os compact tibial peut être divisée en deux phases: a) une phase rapide qui semble uniquement limitée par la circulation sanguine de l'os et qui est compatible avec la théorie des cycles et b) une phase bien plus lente qui peut s'effectuer par diffusion de l'état solide, recristallisation et remaniement physiologique et qui peut se définir de façon correcte par une formule de fonction de puissance.
    Abstract: Zusammenfassung Gruppen von jungen Ratten erhielten22Na intravenös injiziert. Anschließend wurden nach verschiedenen kurzen Zeitintervallen Proben von Leber, Skelettmuskel, Niere, Serum und saubergereinigten kompakten Knochen entnommen und die Konzentrationen des beständigen und des radioaktiven Natriums gemessen. 22Na drang sehr rasch in die untersuchten Gewebe ein, und nach 10 min blieb nur eine kleine Menge nicht-austauschbares Natrium im Gewebe zurück. Die Geschwindigkeit der22Na-Aufnahme im kompakten Knochengewebe der Tibia konnte in zwei Komponenten aufgeteilt werden: a) Ein rascher Vorgang, der einzig durch die Blutzirkulation im Knochen begrenzt zu sein scheint und der mit dem „cycling concept” vereinbar ist. b) Ein viel langsamerer Vorgang, der eine Diffusion im festen Zustand, eine Rekristallisation und einen physiologischen Umbau einschließen kann und der entsprechend durch eine Potenzfunktion ausgedrückt wird.
    Notes: Abstract Groups of young rats were intravenously injected with22Na. At various short time intervals thereafter samples of liver, skeletal muscle, kidney, serum and thoroughly-cleaned compact bone were removed and assayed for both stable and radioisotopic concentrations of sodium. Penetration of22Na into the analysed soft tissues was very rapid and after 10 minutes only a small amount of tissue sodium remained relatively unavailable to the circulation. The rate of22Na-uptake by the tibial compact bone could be divided into two components: (a) a fast process which appears to be limited only by the blood circulation in bone and is compatible with the cycling concept and (b) a much slower process which may involve solid state diffusion, recrystallisation and physiological remodelling and which is adequately defined by a power function expression.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 7 (1971), S. 133-138 
    ISSN: 1432-0827
    Keywords: Hydroxyapatite ; Magnesium ; Crystals ; Isotopes ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Des cristaux d'apatite sont synthétisés dans des conditions physiological approximatives et en présence d'ions de magnésium. Après vieillissement de 4 à 21 jours, les cristaux sont analysés et l'échange du magnésium incorporé est étudié à l'aide de28Mg. A la fois, l'étude cinétique et l'ampleur des échanges indiquent que les ions de magnésium sont nettement rejetés de la maille de l'apatite. Au niveau de vieux cristaux, près de 90% du magnésium est situé dans des positions (de surface) échangeables. Ces résultats confirment la théorie qui admet que le magnésium de l'apatite est surtout un ion de surface. Ils expliquent la grande labilité du magnésium squelettique chez des animaux soumis à des régimes pauvres en magnésium.
    Abstract: Zusammenfassung Apatitkristalle wurden unter annähernd physiologischen Bedingungen und in Anwesenheit von Magnesiumionen synthetisiert. Nach einer Ausreifungszeit von 4–21 Tagen wurden die Kristalle und der Austausch des eingebauten Magnesiums mittels28Mg untersucht. Sowohl die Kinetik als auch das Ausmaß des Austausches zeigten, daß die Magnesiumionen vom Apatitgitter heftig abgestoßen werden. bie ausgereiften Kristallen waren nahezu 90% des Magnesiums leicht austauschbar an der Oberfläche gelagert. Durch diese Befunde wird ein Konzept unterstützt, wonach das im Apatit vorkommende Magnesium hauptsächlich ein oberflächengebundenes Ion ist. Ferner läßt sich dadurch erklären, weshalb bei magnesiumarm ernährten Tieren so leicht Magnesium aus dem Skelet verfügbar ist.
    Notes: Abstract Apatite crystals were synthesized under approximately physiological conditions and in the presence of magnesium ions. After ageing from 4 to 21 days, the crystals were analyzed and their exchange of incorporated magnesium studied with the use of28Mg. Both the kinetics and the extent of the exchange showed that magnesium ions were strongly rejected by the apatite lattice. In aged crystals, nearly 90% of the magnesium was located in readily exchangeable (surface) positions. These findings support one concept that apatitic magnesium is essentially a surface-limited ion and help to explain the ready availability of skeletal magnesium in animals on magnesium deficient diets.
    Type of Medium: Electronic Resource
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