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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 27 (1999), S. 627-640 
    ISSN: 1573-9686
    Keywords: Hemodynamics ; Aorto–iliac bifurcation ; MRI ; Rabbits ; In Vivo ; Wall shear stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Study of the relationship between hemodynamics and atherogenesis requires accurate three-dimensional descriptions of in vivo arterial geometries. Common methods for obtaining such geometries include in vivo medical imaging and postmortem preparations (vessel casts, pressure-fixed vessels). We sought to determine the relative accuracy of these methods. The aorto–iliac (A/I) region of six rabbits was imaged in vivo using contrast-enhanced magnetic resonance imaging (MRI). After sacrifice, the geometry of the A/I region was preserved via vascular casts in four animals, and ex situ pressure fixation (while preserving dimensions) in the remaining two animals. The MR images and postmortem preparations were used to build computer representations of the A/I bifurcations, which were then used as input for computational blood flow analyses. Substantial differences were seen between MRI-based models and postmortem preparations. Bifurcation angles were consistently larger in postmortem specimens, and vessel dimensions were consistently smaller in pressure-fixed specimens. In vivo MRI-based models underpredicted aortic dimensions immediately proximal to the bifurcation, causing appreciable variation in the aorto–iliac parent/child area ratio. This had an important effect on wall shear stress and separation patterns on the “hips” of the bifurcation, with mean wall shear stress differences ranging from 15% to 35%, depending on the model. The above results, as well as consideration of known and probable sources of error, suggests that in vivo MRI best replicates overall vessel geometry (vessel paths and bifurcation angle). However, vascular casting seems to better capture detailed vessel cross-sectional dimensions and shape. It is important to accurately characterize the local aorto–iliac area ratio when studying in vivo bifurcation hemodynamics. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8761Lh
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1642-1645 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cyclobutane tetracarboxylic acid dianhydrides, which were prepared via photodimerization of maleic anhydride or methylmaleic anhydride, gave high molecular weight film-forming polyimides with oxydianiline. The resulting polyimides were found to be photosensitive, presumably because of retrocyclization of the cyclobutane ring. Despite the presence of the cyclobutane ring, the polyimides show good thermal stability. In an effort to enhance the thermal stability and lower the dielectric constant of these polyimides, an approach was made to prepare the fluorinated analogs of the cyclobutane dianhydride monomers via the preparation and photodimerization of fluorinated maleic anhydride derivatives. Thus, both fluoromaleic and difluoromaleic anhydrides were photolyzed to give the target monomers. The proposed application of these monomers, however, has yielded disappointing results due to complications in their synthesis and attempted polymerization.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß der Konzentration von Natriumhydrid als Katalysator und N-Benzoylcaprolactam als Cokatalysator auf die Polymerisation von ε-Caprolactam wurde untersucht. Dazu wurde die Änderung der Grenzviskositätszahl der entstandenen Polymeren in m-Kresol bei 25°C bestimmt. Auch der Einfluß der Polymerisationstemperatur wurde bei konstanter Konzentration von Katalysator und Cokatalysator auf die gleiche Weise untersucht.Obwohl die Reproduzierbarkeit der mittleren Molekulargewichte schwankte, kann man die folgenden Aussagen machen: Der höchste Wert der Viskositätszahl wurde für die niedrigste Konzentration des Cokatalysators erhalten. Die Viskositätszahl der Polymeren erreichte einen Maximalwert bei einer Katalysatorkonzentration von 1,8 mol-% für Cokatalysatorkonzentrationen von 1 und 2 mol-%, jedoch ergab sich bei höheren Konzentrationen an Cokatalysator kein klares Maximum. Im Bereich von 120-200°C ergab sich die höchste Viskositätszahl für die niedrigste Polymerisationstemperatur.
    Notes: The effects of changes in concentration of sodium hydride as catalyst, and N-benzoyl caprolactam as cocatalyst upon the polymerization of ε-caprolactam were studied. The effects were monitored as changes in the intrinsic viscosity of the resultant polymer determined in m-cresol at 25°C. Effects of changes in polymerization temperature at constant catalyst and cocatalyst concentration were also studied.Reproducibility of a given average molecular weight was variable. The highest value of intrinsic viscosity resulted from the lowest cocatalyst concentration studied. Intrinsic viscosity of the product reached a peak at 1.8 mol-% catalyst for 1 and 2 mol-% cocatalyst, but no clear peak occurred at the higher cocatalyst concentrations studied. The highest intrinsic viscosity resulted from the lowest polymerization temperature in the range from 120-200°C.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 28 (1990), S. 439-446 
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 23 (1994), S. 155-159 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An energy-dispersive x-ray fluorescence (EDXRF) apparatus using a radioisotope source with a secondary target (241 Am-Mo) and a Si(Li) x-ray spectrometer was used to measure the Cu, Sr and Bi contents of thin (100 μg cm-2) films sputtered on to MgO. The results were found to be in excellent agreement with those obtained from MeV Rutherford backscattering (RBS) analysis of the same films. The calibration of the EDXRF apparatus was done by measuring x-ray intensities excited in thin sol-gel films of known Cu, Sr and Bi content, as given by the accurately known chemical solutions from which the sol-gel films were prepared. The experimental calibration constants were in excellent agreement with the theoretical values calculated using a thin-film equation, which assumes that characteristic x-ray absorption and secondary excitation are negligible, and the published atomic x-ray data.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 20 (1982), S. 521-523 
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 13 (1975), S. 333-336 
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 16 (1978), S. 115-117 
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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