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  • 1
    Electronic Resource
    Electronic Resource
    A scanning electron microscopic study of the growth of hydroxyapatite crystals (1972)
    Springer
    Calcified tissue international 10 (1972), S. 91-102 
    Details
    ISSN: 1432-0827
    Keywords: Hydroxyapatite ; Calcification ; Phases ; Growth ; Microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé La croissance cristalline de l'hydroxyleapatite à 25° et à pH constant de 7.4 a été étudiée à l'aide du microscope électronique à balayage. La technique reproductible de croissance par ensemencement à partir de solutions stables sursaturées est utilisée efficacement pour produire des échantillons de minéral à divers stades distincts de croissance. Des changements de phase sont observés avec le progrès de la croissance; ils correspondent dans le temps avec les résultats cinétiques obtenus antérieurement. Un essai de rationalisation est tenté à la lumière des mécanismes proposés pour la formation d'hydroxyleapatite dans des conditionsin vivo.
    Abstract: Zusammenfassung Das Kristallwachstum von Hydroxyapatit bei 25° und einem konstanten pH von 7,4 wurde mit Hilfe eines Raster-Elektronenmikroskopes studiert. Die reproduzierbare Technik des Keimwachstums aus stabilen übersättigten Lösungen wurde mit Erfolg verwendet, um Mineralproben in verschiedenen bestimmten Stadien des Wachstums zu erhalten. Phasenveränderungen wurden beim fortschreitenden Wachstum beobachtet, und diese stimmten zeitlich gut überein mit kinetischen Resultaten, über welche früher berichtet wurde. Es wurde versucht, diese Beobachtungen zu erklären in Anbetracht von Mechanismen, welche für die Bildung von Hydroxyapatit unterin vivo-Bedingungen vorgeschlagen wurden.
    Notes: Abstract The crystal growth of hydroxyapatite at 25° and at a constant pH of 7.4 has been studied with the aid of a scanning electron microscope. The reproducible technique of seeded growth from stable supersaturated solutions was used effectively to produce samples of the mineral at various distinct stages of growth. Phase changes were observed as the growth proceeded and these corresponded favorably in time with kinetic results reported earlier. An attempt was made to rationalize the observations in light of mechanisms proposed for the formation of hydroxyapatite under conditions foundin vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012539
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  • 2
    Electronic Resource
    Electronic Resource
    Performance of two Picea abies (L.) Karst. stands at different stages of decline (1988)
    Springer
    Oecologia 77 (1988), S. 163-173 
    Details
    ISSN: 1432-1939
    Keywords: Forest decline ; Spruce (Picea abies) ; Nutrients ; Growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A declining, closed-canopy Picea abies (L.) Karst. stand produced as much crown biomass as a healthy stand, although some trees were chlorotic due to magnesium deficiency. The production of wood per unit of leaf area in both stands was related to the foliar magnesium concentration. Although leaf area index and climate were similar at both sites, stemwood production was 35% lower in the declining than in the healthy stand. Nutritional disharmony, rather than a deficiency in a single element, was identified as the mechanism for reduced tree vigor. The role of nutrient stress in forest decline was detected by partitioning the season into three periods reflecting different phenological stages: a canopy growth period in spring, a stem growth period in summer, and a recharge period during the non-growing season. Needle growth was associated with nitrogen supply. Most of the magnesium supply required to meet the demand for foliage growth was retranslocated from mature needles. Magnesium retranslocation was related to concentration of nitrogen and magnesium in those needles before bud break. Retranslocation from mature needles during the phase of canopy production resulted in chlorosis in initially green needles if the magnesium concentration before bud break was low. Nitrogen concentration in 0-year-old needles generally remained constant with increasing supply, indicating that foliage growth was restricted by the supply of nitrogen. In contrast, magnesium concentration generally increased with supply, indicating that magnesium supply for needle growth was sufficient. Much of the magnesium required for wood production was taken up from the soil because stored magnesium was largely used for canopy growth. Uptake at the declining site was probably limited because of restricted root expansion and lower soil magnesium compared to the healthy site. For this reason only wood growth was reduced at the declining site. Because the recharge of magnesium during the non-growing period is dependent on uptake from the soil, it was more limited at the declining that at the healthy stand. However, as nitrogen uptake from the atmosphere may account for an appreciable proportion of the total uptake, and as its supply in the soil at both sites was similar, an unbalanced recharge of nitrogen and magnesium may have occurred at the declining site. If mature needles are unable to recharge with magnesium in proportion to the uptake of nitrogen, chlorosis is likely to occur during the next canopy growth period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379182
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Performance of two Picea abies (L.) Karst. stands at different stages of decline (1988)
    Springer
    Oecologia 75 (1988), S. 25-37 
    Details
    ISSN: 1432-1939
    Keywords: Forest decline ; Carbohydrates ; Picea abies ; Growth ; Leaf area index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This is the first in a series of papers on the growth, photosynthetic rate, water and nutrient relations, root distribution and mycorrhizal frequency of two Norway spruce forests at different stages of decline. One of the stands was composed of green trees only while the other included trees ranging in appearance from full green crowns to thin crowns with yellow needles. In this paper we compare the growth and carbohydrate relations of the two stands and examine relationships among growth variables in ten plots. The declining stand produced 65 percent of the wood per ground area compared with the stand in which all trees were green because its foliage produced less wood at any level of leaf area index. The difference in foliage efficiency between the sites could not be explained by differeneces in climate, competition or stand structure. The declining stand appeared to have lower carbon gain as indicated by a smaller increase in reserve carbohydrates before bud break, and weaker sinks for carbohydrates as indicated by less use of the stored carbohydrates than the healthy stand. Thus, growth reduction was probably related to factors which affect both photosynthesis and, even more, the sinks for carbohydrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378810
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    Paper (German National Licenses)
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