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  • Polymer and Materials Science  (31)
  • Physics  (5)
  • Cardiac muscle  (3)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 421 (1992), S. 343-349 
    ISSN: 1432-2013
    Schlagwort(e): Cardiac muscle ; Rigor tension ; Ca2+ ; Caffeine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Ventricular trabeculae from rat heart were chemically skinned with Triton-X100, which disrupts all cellular membranes including the sarcoplasmic reticulum. Trabeculae developed a maintained rigor contracture when adenosine triphosphate was withdrawn from the bathing medium. In all preparations, the final level of rigor force developed in the presence of caffeine (10–40 mM) was greater than under control conditions. However, caffeine failed to increase rigor tension when applied after contracture had fully developed. The effect of caffeine on rigor was maximal at about 15 mM; concentrations greater or less than 15 mM were less effective. On average, caffeine decreased the time required to develop half-maximum rigor force. The caffeine-induced potentiation of rigor force occurred in the effective absence of Ca2+ (10−9 M), in solutions strongly Ca2+-buffered with [ethylenebis(oxonitrilo)]tetraaceticacid (10–50 mM). In all preparations, rigor force was found to be independent of [Ca2+] over the range 10−10 M to about 10−7 M. These results suggest that caffeine affects rigor force by a direct effect on the myofilaments via a mechanism that is independent of Ca2+.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1432-2013
    Schlagwort(e): Cardiac muscle ; butanedione monoxime ; heat production ; aequorin luminescence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract At low concentrations (up to 5 mM) the compound 2,3-butanedione monoxime (BDM) was found to reduce twitch tension and initial heat production in isolated papillary muscles without significantly affecting the size of the intracellular Ca transient measured with aequorin luminescence. Higher concentrations of BDM caused further inhibition of twitch tension and heat production with a fall in the size of the Ca+ transient. The size of the aequorin transient was 50% of the control value at 15 mM BDM while twitch tension was negligible. These results suggest that BDM selectively inhibits Ca2+ activated force in cardiac muscle at low concentrations with additional effects on intracellular calcium at concentrations above 5 mM.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Basic research in cardiology 88 (1993), S. 421-429 
    ISSN: 1435-1803
    Schlagwort(e): Cardiac muscle ; hypoxia ; pH ; lactate ; ischaemia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary During hypoxia cardiac contraction declines and there is an intracellular acidosis. We find that, if this acidosis is abolished by decreasing pCO2 there is little restoration of force. Therefore the acidosis is not the major cause of the decline of force. The acidosis may partly result from the generation of lactic acid. No acidosis, is however, seen in isolated cardiac cells. Furthermore a theoretical model shows that lactic acid production would be expected to produce a transient acidosis. We suggest that the observed maintained acidosis may be a consequence of extracellular lactic acid accumulation affecting intracellular pH.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 14 (1970), S. 777-787 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The preparation of isotactic and syndiotactic 1,4-polypentadienes with a cis content of at least 70%-75% using i-Bu2AlH/Ti(i-OPr)4 and AlEtCl2/thiophene/Co(acetylacetonate)2 catalysts, respectively, is reported. Physical characterization of the vulcanizates, prepared by a common recipe, involving infrared analysis, DTA, simple stress-strain and swelling measurements, and dynamic mechanical measurements over a frequency range of 2 decades and temperature range of -60°C to +20°C indicated that no isomerization had taken place during vulcanization and that stereoregularity of the polymer chains affected the resultant cure: the isotactic form was found to have a greater crosslink density than the syndiotactic form. Master curves covering an extended frequency range were constructed from the reduced dynamic mechanical data and the calculated quantities - thermal expansion coefficients of free volume and the fractional free volumes at the glass transition temperatures - agree with the accepted values. Glass transition temperatures of the isotactic and syndiotactic polymers are -37°C and -42°C, respectively, and for their vulcanizates, -33°C and -40°C, respectively.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 1167-1177 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Blends of aromatic/aliphatic polyamides of varying compositions were extrusion compounded with an impact modifying reactive elastomer and injection molded. The effect of two different twin-screw blending configurations on the physical and mechanical properties of the blends was evaluated. Effects of processing conditions on blend morphology were also examined. The experimental results indicate that the extrusion sequence affects the extent of polyamide matrix-elastomer reaction as well as the morphology. The relationship between blend morphology, blend components structure and reactivity, and processing conditions with ultimate properties is discussed. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 26 (1981), S. 159-170 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Carbon dioxide sorption isotherms in poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) are reported for pressures up to 20 atm. Temperatures between 35 and 80°C were studied for PMMA and temperatures between 30 and 55°C were studied for PEMA. Typical dual mode sorption isotherms concave to the pressure axis were observed in all cases. The measured Langmuir sorption capacities of both polymers extrapolated to zero at the glass transition (Tg) consistent with the behavior of other glassy polymer/gas systems. Sorption enthalpies for CO2 in the Henry's law mode for PMMA and PEMA are in the same range (-2 to -4 kcal/mole) as has been reported for a variety of other glassy polymers such as poly(ethylene terephthalate), polycarbonate, and polyacrylonitrile. Some of the data suggest that postcasting treatment of the PEMA films left a small amount of residual solvent in the film. the presence of the trace residual solvent during quenching from the rubbery to the glassy state after annealing appears to cause a dilation of the Langmuir capacity and an alteration in the apparent Langmuir affinity constant of the PEMA film. These results suggest the possibility of tailoring physical properties of glassy polymers such as sorptivity, permeability, impact strength, and craze resistance by doping small amounts of selected residuals into polymers prior to quenching to the glassy state from the rubbery state.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 4099-4111 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A polyamide-epichlorohydrin resin used to shrink-resist wool [Hercosett 125 (Hercules Inc.)] was separated by ultrafiltration into fractions A, B, and C (in the approximate proportions 60, 40, and 2 by weight), which correspond to the three peaks in size exclusion chromatograms (SEC). Viscosity, spectra, and SEC results as well as results of experiments on the reaction of the parent polyamino-polyamide (PAA) with epichlorohydrin indicated that fraction A was high-molecular-weight crosslinked material whereas fraction B was essentially uncrosslinked. Fraction C was minor impurity, possibly a mixture containing a triazine, and it was also found in the PAA from which the original resin was prepared. High-resolution proton NMR spectra of the Hercosett 125 indicated that chlorohydrin or epoxy groups were absent, and thus confirmed an earlier 13C-NMR study that only azetidinium reactive groups were present. Two reactions are believed to occur in Hercosett 125 on storage: hydrolysis of azetidinium to dihydroxypropyl groups and hydrolysis of backbone amides. The small differences in the properties of wool treated with either A or B fractions, and those of wool treated with unfractionated Hercosett 125, were related to the extent of crosslinking before and after curing. As the extent of crosslinking increased, the amount of staining by an anionic dye decreased, and the shrink resistance improved slightly.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 8
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A series of prepolymers containing terminal blocked isocyanate groups was prepared by reaction of isocyanate-terminated prepolymers [derived from a poly(propylene oxide) diol (MW = 2000) or a triol (MW = 3000) and different diisocyanates] with various blocking agents. Their curing rates with a polyepoxide crosslinking agent were measured to assess their suitability for a delayed-cure durable-press treatment for wool. The curing rates varied over a wide range, but commonly used blocking groups such as phenols, caprolactam, β-diketones, and alcohols were not sufficiently reactive for the intended application, although others, e.g., oximes and certain blocking agents containing a basic center such as N,N-diethylhydroxylamine, hydroxypyridines, and hydroxyquinolines, had the required reactivity. Blocking by 1,3-dipolar cycloaddition of nitrones was examined, but the reactivities were too low. Prepolymers containing blocked aromatic isocyanates were more reactive than those containing blocked aliphatic isocyanates. Difunctional butanone oxime-blocked pre-polymers cured slightly more slowly than analogous trifunctional prepolymers.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 9
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Acrylate esters of seven n-1,1-dihydroperfluoroalkanols have been synthesized. The esters are: 1,1-dihydroperfluoroethyl-; 1,1-dihydroperfluoropropyl-; 1,1-dihydroperfluorobutyl-; 1,1-dihydroperfluoropentyl-; 1,1-dihydroperfluorohexyl-; 1,1-dihydroperfluorooctyl-; and 1,1-dihydroperfluorodecyl acrylates. Since these alcohols were difficult to esterify using conventional procedures, acrylyl chloride or acrylic acid plus perfluoroacetic anhydride have been empolyed in this work.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 441-445 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Different hexameric forms of insulin have been crystallized from a variety of conditions. In the presence of 1% phenol, 1.0 M sodium chloride, and at a pH of 8.5, a rhombohedral form is produced with two monomers in the asymmetric unit, space group R3, a = 79.92 Å and c = 40.39 Å. The structure has been solved and refined, using data between 8.0 and 2.5 Å resolution, to a residual of 0.157. Each of the monomers adopts an R conformation, that is residues B1-B8 are α-helical. As a result of the T to R transition, an elliptical cavity is created between symmetry-related monomers and is occupied by a phenol molecule. A region of density within bonding distance to one of the zinc ions has been interpreted as an additional phenol molecule.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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