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  • 1
    Publication Date: 1970-09-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 227 (1970), S. 1259-1260 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The first value for the molar absorbance of cattle rhodopsin was reported by Wald and Brown3. They illuminated a rhodopsin sample of known absorbance in the presence of hydroxylamine to obtain quantitatively the all-trans retinaldehyde in the form of its oxime. Having determined the molar ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0827
    Keywords: Calcium phosphates ; Composition ; Dissolution ; Precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Variations in the composition of bone and tooth mineral are consistent with the model that the constituents are a mixed microcrystalline apatite (AP)-octocalcium phosphate (OCP) like phase and an amorphous or submicrocrystalline calcium phosphate (ACP) like phase whereby these phases can occur in different proportions. An appropriate model for a description of the variable composition and the solubility behavior of the apatite phase is given by the formula $$\begin{array}{*{20}c} {\begin{array}{*{20}c} {Ca_{5 - x - y - u} Na_{\frac{2}{3} y} } \\ {\{ (PO_4 )_{3 - x - y } (CO)_{x + y} \} (H_2 O)_{y + z} OH_{1 - x - \frac{1}{3} y - 2u} } \\\end{array}} \\\end{array}$$ in which the compositional parameters x, y, z, and u each account for one type of defect mechanism. Other point defects are formed as well by incorporation of minority amounts of ions such as Cl−, K+, and F−; a number of trace elements can substitute for Ca2+ ions under in vivo conditions. It is suggested that the incorporation of ions in or loss from the crystals in contact with aqueous solutions is reversible. Literature data are used to show the direction in which the solubility product of the apatite phase shifts by incorporation of the different physiologically relevant ions. A quantitative evaluation of the available literature data revealed that Na+ and CO3 = incorporation is the main cause for shifts in the solubility product of biological apatites.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 20 (1982), S. 578-584 
    ISSN: 1741-0444
    Keywords: Caries ; Dental enamel ; Impedance ; Permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The permeability of dental enamel membranes can be estimated by means of diffusion-measurements with radio-isotopes. Because of the low intrinsic permeability of these membranes, determination via this route generally takes two weeks. In this paper a much faster electrochemical method is presented, in which the real and imaginary part of the membrane impedance are measured at discrete intervals in the frequency range 10 Hz–300 kHz. From the parameters that describe these electrochemical data, some were found to correlate closely with the permeability of enamel as determined with radio-isotopes on the same enamel sample. From these results it was concluded that especiallyv max, the frequency where the imaginary part of the membrane impedance is maximal, and Z1 at 100 Hz, the imaginary part of the membrane impedance at 100 Hz, are of practical value as predictor for the permeability of enamel.
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