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  • 1
    ISSN: 1045-4861
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Hydroxyapatite induction by a synthesized pure silica hydrogel was examined in various simulated body fluids (SBFs) having different magnesium, calcium, and phosphate ion concentrations as well as pH values. The silica hydrogel generated biologically active apatite on its surface by taking up calcium and phosphorous ionic groups from a surrounding SBF that was prepared to emulate the human plasma in inorganic composition. The induction period for apatite nucleation on the surface of the silica was largely decreased with the addition of a small amount of the calcium or phosphate ions to the SBF and with an increase in pH, but increased with the addition of magnesium ion. Bioactivity of bioactive materials like Bioglass® and glass-ceramic A-W was well interpreted in terms of the rate of apatite formation reflected in these results. Moreover, the results provide the basic knowledge for designing new bioactive materials. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A measure of the severity of a pipeline failure is the minimum reduction in load in the network necessary to ensure that no node falls below its minimum pressure. The expected loss of sales is calculated as the product of the minimum reduction in load and the expected duration of the period during which the pipeline will be in the inoperable state, and thus reflects both the severity and the frequency of the failure. Consequently, this index, whose evaluation involves network theory, optimization and probability theory, serves as a measure of the insecurity of the gas network.The security index can be evaluated for all points within a system, providing a basis of comparison between the relative vulnerability of different parts. The relative level of security of different design proposals can also be assessed using this index.
    Additional Material: 2 Ill.
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  • 3
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper considers the question of reduction of loads on a pipe network, which may be necessary as a result of failure in supply or interruption of a pipe. The non-linear relationship between pressure loss and flow along a pipe makes the problem of minimizing the reduction of loads also non-linear. An iterative linear approximation technique is therefore adopted. When the question is formulated as a problem in linear programming, the constraints include nodal pressures as well as loads. It is shown how the number of these constraints may be reduced.
    Additional Material: 1 Ill.
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The bone-bonding polymer known as Polyactive® is a block copolymer composed of a polyethylene oxide (PEO) soft segment and a polybutylene terephthalate (PBT) hard segment. This study focuses on the in vitro induction of hydroxyapatite by Polyactive®. Our results show that Polyactive® is capable of inducing hydroxycarbonate apatite (HCAp) formation from a metastable calcium phosphate solution analogous to a physiological solution. In a 4-day incubation, the HCAp formation extended approximately 100 μm deep from the surface. A great number of globules about 1 μm large were found in the calcified Polyactive®. These globules were composed of HCAp crystals embedded in the polymer matrix. There were so many globules in the surface that they connected with each other and formed a calcified layer. Next to the calcified layer was a zone where the globules were scattered. The calcified surface may have acted to promote HCAp growth from the solution, bringing about the formation of a HCAp layer on top of the calcified layer. The transition of solid Polyactive® into a Polyactive® hydro-gel in calcium phosphate solution permitted HCAp formation within the polymer. It is proposed that the COOH groups produced during hydrolysis of Polyactive® play an important role in nucleating hydroxyapatite. A remarkable affinity of the PEO segment of the polymer for calcium ions may facilitate moving calcium and phosphate from the solution into the polymer for the growth of HCAp. © 1997 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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