Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Computed tomography  (3)
  • Growth  (3)
  • Thermodynamics  (3)
  • genes  (3)
  • 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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    A thermodynamic analysis of the secondary transition in the spontaneous precipitation of calcium phosphate (1978)
    Springer
    Calcified tissue international 25 (1978), S. 209-216 
    Details
    ISSN: 1432-0827
    Keywords: Thermodynamics ; Kinetics ; Apatite ; Octacalcium phosphate ; Tricalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A thermodynamic analysis has been made of the secondary transition stage in the spontaneous precipitation of calcium phosphate following the amorphous-crystalline transformation. The first formed crystalline material has a solubility similar to that of octacalcium phosphate (OCP) and the computed thermodynamic solubility product remains invariant in the pH range 7.00–8.60. The duration of the secondary stage is sensitive to pH and the transition appears to occur by hydrolysis of the first formed OCP-like phase to a more basic apatitic phase with a tricalcium phosphate (TCP) stoichiometry. The crystalline material at the end of this transition has an invariant solubility product, in the pH range 7.00 to 8.60, when the TCP-like molecular formula is assumed. Changes in the solution chemistry which accompany the solid-tosolid transitions are consistent with the above conclusions. The results of this study are also consistent with those of a previous study which suggest that the stability of the amorphous calcium phosphate phase is dependent upon the instability of the solution phase with respect to OCP formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010771
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    A thermodynamic analysis of the amorphous to crystalline calcium phosphate transformation (1978)
    Springer
    Calcified tissue international 25 (1978), S. 59-68 
    Details
    ISSN: 1432-0827
    Keywords: Amorphous calcium phosphate ; Thermodynamics ; Apatite ; Octacalcium phosphate ; Tricalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A thermodynamic analysis of the precipitation of amorphous calcium phosphate (ACP) and its transformation to crystalline apatite has been made. A nearly constant ion product, over a wide variety of conditions, was obtained for a tricalcium phosphate (TCP)-like phase suggesting that the molecular unit which governs the solubility of ACP may be similar in composition to TCP. The introduction of 10% acid phosphate into the formula for the TCP ion product improves the fit of experimental data and results in an invariant ion product. The stability of ACP in solution was found to be dependent upon its thermodynamic instability with respect to an octacalcium phosphate (OCP)-like phase. The dependence of the induction period for the amorphous to crystalline transformation upon the pH and the Ca/P ratio of the solution is best explained by the assumption that an OCP-like phase is initially nucleated on the surfaces of the ACP particles. The events that occur in the immediate post-transition period suggest the hydrolysis of this OCP-like material to an apatitic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010752
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Hydroxyl content of solution-precipitated calcium phosphates (1979)
    Springer
    Calcified tissue international 27 (1979), S. 153-160 
    Details
    ISSN: 1432-0827
    Keywords: Hydroxide ; Hydroxyapatite ; Titration ; Precipitation ; Thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A method is described for determination of the titratable hydroxide ion in calcium phosphate precipitates. The procedure requires accurate analysis of the other titratable species in the crystal lattice but is unaffected by the presence of other lattice constituents or impurities. The method was applied to precipitates that had been previously analyzed by solution thermodynamic techniques, and the results were consistent with the earlier observations. The hydroxide content of the precipitates increased with crystal maturity and with increasing pH of the precipitation medium. The hydroxide content of the amorphous phase and the immediate post-amorphous-crystalline transformation phase was shown to be nearly zero. After 3 to 4 days' maturation, the hydroxide content of precipitates prepared at pH values of 7, 8, and 9 was shown to increase to approximately 23, 40, 56% of that required for pure hydroxyapatite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441178
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Imaging local cerebral blood flow by Xenon-enhanced computed tomography — Technical optimization procedures (1988)
    Springer
    Neuroradiology 30 (1988), S. 283-292 
    Details
    ISSN: 1432-1920
    Keywords: Cerebral blood flow ; Computed tomography ; Partition coefficients ; Xenon contrast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Methods are described for non-invasive, computer-assisted serial scanning throghout the human brain during eight minutes of inhalation of 27%–30% Xenon gas in order to measure local cerebral blood flow (LCBF). Optimized Xenonenhanced computed tomography (XeCT) was achieved by 5-second scanning at one-minute intervals utilizing a state-of-the-art CT scanner and rapid delivery of Xenon gas via a face mask. Values for local brain-blood partition coefficients (Lλ) measured in vivo were utilized to calculate LCBF values. Previous methods assumed Lλ values to be normal, introducing the risk of systematic errors, because Lλ values differ throughout normal brain and may be altered by disease. Color-coded maps of Lλ and LCBF values were formatted directly onto CT images for exact correlation of function with anatomic and pathologic observations (spatial resolution: 26.5 cubic mm). Results were compared among eight normal volunteers, aged between 50 and 88 years. Mean cortical gray matter blood flow was 46.3±7.7, for subcortical gray matter was 50.3±13.2 and for white matter was 18.8±3.2. Modern CT scanners provide stability, improved signal to noise ratio and minimal radiation scatter. Combining these advantages with rapid Xenon saturation of the blood provides correlations of Lλ and LCBF with images of normal and abnormal brain in a safe, useful and non-invasive manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328177
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Potential of a new laser target system for percutaneous CT-guided nerve blocks: technical note (2000)
    Springer
    Neuroradiology 42 (2000), S. 838-841 
    Details
    ISSN: 1432-1920
    Keywords: Key words Nerve block ; technology ; Computed tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A prototype of a laser target device was used for CT-guided nerve blocks in a preliminary series of nine interventions. The system provides guidance from any possible approach. High accuracy of needle insertion was achieved; the average deviation of the planned from the actual angle was 1.4°. The target device is valuable for facilitating minimally invasive therapy and can decrease the time required for the procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002340000433
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    LCBF values decline while Lλ values increase during normal human aging measured by stable xenon-enhanced computed tomography (1988)
    Springer
    Neuroradiology 30 (1988), S. 463-472 
    Details
    ISSN: 1432-1920
    Keywords: Cerebral blood flow ; Partition coefficient ; Computed tomography ; Stable xenon ; Aging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Results of measurements of LCBF and Lλ values utilizing optimal CT-CBF methods under resting conditions are reported among thirty-two neurologically normal volunteers aged between 20 and 88 years. Measurements were made during inhalation of 26–30% stable xenon gas for 8 min and serial scanning utilizing a state-of the-art CT scanner with both eyes closed and ears unplugged. LCBF values for cortical gray matter were lowest in occipital cortex and highest in frontal cortex. Gray matter flow values were also high in subcortical structures with highest values measured in the thalamus. For white matter, highest flow values were measured in the internal capsule. Changes in LCBF and Lλ values were analyzed with respect to advancing age. Significant age-related declines in LCBF values were observed in occipital cortex and frontal white matter. Significant age-related increases in Lλ values were measured in frontal and temporal cortex, caudate nucleus and thalamus. Possible explanations are offered for these age-related increases in Lλ values for gray matter, such as accumulation of lipofuscin in neurons and relative compacting of gray matter with advancing age. The latter increases the numbers of nerve cells sampled per volume of gray matter measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00339684
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Resolving causes of developmental continuity or “tracking.” I. Longitudinal twin studies during growth (1988)
    Springer
    Behavior genetics 18 (1988), S. 133-151 
    Details
    ISSN: 1573-3297
    Keywords: genes ; environment ; development ; growth ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Models of developmental continuity and change in quantitative phenotypes may be tested using longitudinal data from twins. We illustrate a procedure for establishing the power and required sample sizes for detecting developmental transmission against an alternative common-factor hypothesis. We explore the general effects of different heritabilities, different fidelities of environmental and genetic developmental transmission, and varying numbers of occasions of measurement. In addition, a constraint of wide application is postulated for the action of the environment; either environmental effects are transmitted (learned) and occasion specific or they exert a constant influence which is not transmitted (learned). While the situations we examine are necessarily restricted here, our explorations of power show that, providing that we measure on at least four occasions, it is easy to detect developmental transmission with workable sample sizes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01067836
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...