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  • 1
    Electronic Resource
    Electronic Resource
    Calcaneal ultrasound attenuation in older African-American and Caucasian-American women (1997)
    Springer
    Osteoporosis international 7 (1997), S. 100-104 
    Details
    ISSN: 1433-2965
    Keywords: Bone ultrasound ; Osteoporosis fractures ; Race ; Ethnicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The lower fracture rates among African-American women relative to Caucasian women may reflect their higher bone mass. However, bone mass is not the only determinant of bone strength: the quality and microarchitecture of the bone are also important. Quantitative ultrasound is believed to measure properties of bone strength that are independent of bone mass. To test the hypothesis that there are racial differences in quantitative ultrasound measures of bone, we recruited 154 African-American women age ⩾65 years. A random sample of 300 Caucasian women participating in the Study of Osteoporotic Fractures in Pittsburgh, Pennsylvania, was chosen for comparison. The Walker Sonix UBA 575+ was used to measure calcaneal broadband ultrasonic attenuation (BUA). Duplicate BUA measurements were obtained with a reproducibility of 5%. We measured bone mineral density (BMD) of the hip and calcaneus using single (calcaneus) or dual (hip) energy X-ray absorptiometry. The correlation between BUA and calcaneal BMD was similar in Caucasians (r=0.66,p〈0.001) and African-Americans (r=0.58,p〈0.001). Age-adjusted BUA (dB/MHz) was higher among the African-American women than Caucasian women (69.1 and 66.2, respectively), but these differences were not statistically significant, (p=0.12). Adjustment for calcaneal BMD completely attenuated the racial differences in BUA. BMD at the femoral neck and calcaneus was higher among the African-American women, even after adjusting for age, height and weight. In conclusion, our results suggest that racial differences in rates of fracture cannot be explained by differences in bone quality as assessed by ultrasound attenuation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01623683
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  • 2
    Electronic Resource
    Electronic Resource
    Crosslinking chemistry and network structure in organic coatings. II. Effect of catalysts on cure of melamine formaldehyde/acrylic copolymer films (1980)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 18 (1980), S. 2015-2025 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a previous paper, the extents of reaction of various functional groups in different acrylic copolymer melamine-formaldehyde crosslinked formulations were measured by infrared spectroscopy. From these data and a statistical model, various network structure parameters could be calculated. One of these, effective crosslink density, was found to correlate well with film solvent resistance. In this paper the effects of the addition of strong acid catalysts on cure chemistry and network structure are determined. Both solvent-based and water-based formulations have been studied. In the solvent-based formulations studied, the addition of acid catalysts greatly enhanced the crosslinking reactions at low temperatures and dramatically lowered the cure temperature. Acid catalysts also lowered the cure temperature of a water-based formulation based on a high (180°C) cure temperature melamine. In contrast, the addition of acid catalysts had a negligible effect on the cure chemistry of a water-based formulation crosslinked with a low (130°C) cure temperature melamine. For this case the rate limiting process was found to be the rate of removal of neutralizing amine from the film. Cure temperatures in this system could only be lowered by replacing the amine used with a more volatile amine.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1980.180181002
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  • 3
    Electronic Resource
    Electronic Resource
    Magic-angle 13C-NMR of cured and degraded acrylic copolymer/melamine formaldehyde coatings (1984)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 22 (1984), S. 2009-2020 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Magic-angle carbon-13 NMR has been used to probe the structure and dynamics of acrylic copolymer melamine formaldehyde crosslinked coatings. Changes in chemical composition that occur in conventional accelerated weathering tests were found to be dominated by hydrolysis of acrylic-melamine crosslinks and subsequent formation of melamine-melamine crosslinks. Evidence for photo-oxidation was also observed. These results are in substantial agreement with infrared measurements also made on these coatings. Gated high-power decoupling experiments were used to determine relative mobilities of the different carbon resonances as a function of acrylic copolymer composition and as a function of degradation. It was found that motion of the side-chain carbons on the acrylic copolymer was not sensitive either to the chemical composition of the coating or to the extent of degradation. Mobilities of the main-chain carbons of the acrylic copolymer decrease with increasing glass transition temperature of the acrylic copolymer. For acrylic copolymers containing styrene, it is found that the main-chain carbon mobilities decrease with weathering. The melamine triazine ring becomes very rigid after degradation consistent with the formation of short melamine-melamine crosslinks.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1984.180221202
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  • 4
    Electronic Resource
    Electronic Resource
    Crosslinking chemistry and network structure in organic coatings. I. Cure of melamine formaldehyde/acrylic copolymer films (1980)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 18 (1980), S. 1997-2014 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crosslinking chemistry and network formation in hydroxy and carboxy functional acrylic copolymer resins cured with representative melamine-formaldehyde crosslinking agents have been studied by infrared spectroscopy. Network formation in these systems is dominated by two reactions, the condensation of the hydroxy (or carboxy) functionality of the acrylic resin with melamine alkoxy groups to form acrylic-melamine crosslinks, and the condensation of melamine hydroxy groups to form melamine-melamine crosslinks. The extents of these reactions have been studied as functions of acrylic resin composition, melamine type and concentration, and cure time and temperature. For melamines with just methoxy functionality, the extent of formation of acrylic-melamine crosslinks increased steadily with cure temperature. For melamines with substantial hydroxy functionality, the extent of formation of acrylic-melamine crosslinks increased rapidly then leveled off with increasing cure temperature. The formation of melamine-melamine crosslinks increased slowly with increasing cure temperature. From these data and a statistical model, effective crosslink densities were calculated. The crosslink densities correlated well with solvent resistance.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1980.180181001
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    Paper (German National Licenses)
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