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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 6 (1970), S. 120-132 
    ISSN: 1432-0827
    Keywords: Vitamin A ; Bone ; Physiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Une comparaison du remainiement osseux de la mandibule, du présphénoide et du fémur de veaux, recevant des quantités variables de vitamin A (2 doses carentielles et 2 doses de contrôle) pendant une durée de 16 semaines, a été réalisée. La croissance enchondrale a également été étudiée. Les résultats indiquent une altération du remaniement des os carencés, liée à une déficience de la résorption sous-périostée, cette dernière étant souvent remplacée par de l'apposition. Le traitement eut peu ou pas d'effet au niveau des surfaces périostées, où le remaniement normal ne nécessite pas de résorption. Etant donné que les osteéoclastes ne sont plus visibles au niveau des surfaces périostées au cours de l'état de carence, il semble que la vitamine A soit susceptible d'agir sur la differenciation de la cellule ostéogénique périostée en ostéoclaste.
    Abstract: Zusammenfassung Der Knochenumbau wurde in Unterkiefer, Präsphenoid und Femur von 4 Gruppen von Kälbern verglichen. Diese erhielten während einer Zeitspanne von 16 Wochen verschiedene Vitamin A-Mengen (2 Vitamin A-Mangel- und 2 Kontrollgruppen). Ferner wurde das endochondrale Wachstum grob gemessen. Die Resultate ergaben eine Veränderung des Umbaus von defizienten Knochen wegen der mangelhaften subperiostalen Resorption, die oft durch Wachstum ersetzt wurde. Jene periostalen Oberflächen, wo die Resorption für einen normalen Umbau nicht erforderlicht ist, wurden durch den Vitamin A-Mangel nur wenig beeinflußt. Die Tatsache, daß die Osteoklasten bei Vitamin A-Mangel von den periostalen Oberflächen verschwinden, läßt vermuten, daß Vitamin A die Fähigkeit der periostalen Stammzellen, sich zu Osteoklasten zu differenzieren, beeinflußt.
    Notes: Abstract The drift patterns of the mandible, presphenoid, and femur were compared in calves fed graded levels (2 deficient, 2 control) of vitamin A for 16 weeks. In addition, gross measurements of endochondral growth were recorded. The results indicated that drift of deficient bones was altered because subperiosteal resorption failed and was often replaced by growth. On those periosteal surfaces where resorption was not required for normal modeling, little effect was found due to treatment. In light of the evidence that osteoclasts disappear from the periosteal surfaces during deficiency, it is suggested that vitamin A affects the ability of the periosteal progenitor cell to differentiate as an osteoclast.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1634
    Keywords: surfactant ; dodecylamine ; capillary pressure ; interfacial tension ; wettability ; NAPL ; organic base
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The presence of surfactants may have profound effects on the transport of organic contaminants in multiphase systems. It is a common practice, however, to model the subsurface migration of liquids independently of the aqueous phase composition. As such, transport in these systems may not be adequately characterized. This study investigates the impact of pH on interfacial tension, wettability, and the drainage capillary pressure–saturation relationship in air–water–quartz and o‐xylene–water–quartz systems containing dodecylamine, an organic base. In these systems, three mechanisms, speciation, partitioning, and sorption, are important in determining the interfacial tension and contact angle, and consequently, important in determining the capillary pressure. By adjusting the pH above and below, the pKa of the base, the relative importance of these mechanisms was altered. Below dodecylamine's pKa of 10.6, the base was primarily in a cationic form resulting in minimal partitioning into the nonaqueous liquid and greater sorption at the quartz surface. Above the pKa, the base was primarily in a neutral form which did not sorb to the quartz, and, furthermore, partitioned into the organic liquid phase where its surface activity was minimized. The combination of these processes caused the capillary pressure to change in a manner consistent with pore‐scale theory of capillarity. The utility in this approach lies in the possibility of predicting transport properties in multiphase systems while incorporating the direct effects of solution chemistry.
    Type of Medium: Electronic Resource
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