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  • 1
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    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
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    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
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1042-7147
    Keywords: emulsion ; copolymerization ; tribromophenyl maleimide ; styrene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Emulsion copolymerization of Tribromophenyl Maleimide (TBPMI) and styrene was conducted by semi-batch and batch processes. The effects of monomer composition and copolymerization method on copolymerization rate, molecular weight and molecular weight distribution, latex particle size and size distribution, glass transition temperature (Tg), thermal stability and mechanical properties were investigated. A kinetic study has shown that the rate of copolymerization in the batch process increased with increasing TBPMI content in the monomer feed. For the semi-batch polymerized samples, molecular weight decreased and molecular weight distribution increased with increasing TBPMI content in the monomer feed. For the batch polymerized samples, molecular weight also decreased but no obvious tendency was observed for the molecular weight distribution when TBPMI content increased. Compared with the batch copolymers, the semi-batch copolymers have a higher molecular weight at the same initial monomer mixture composition. Latex particle size decreased, while particle size distribution slightly increased with increasing TBPMI content in both semi-batch and batch latices. The semi-batch samples exhibit only a single Tg, the value of which increses linearly with increasing TBPMI content. For the batch copolymers, two Tgs were found, reflecting a mixture of styrene-rich and TBPMI-rich copolymer chains. TGA results indicate that the thermal stability of the semi-batch copolymers increased with increasing TBPMI concentration. Young's and flexural moduli increased, while tensile and flexural strengths decreased by increasing the TBPMI content for both the semi-batch and batch specimens. The semi-batch specimens have higher tensile and flexural strenghts than the batch ones.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0721-3115
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A threshold particle velocity criteria derived by E.R. Fitzgerald for the beginning of crystal lattice breakup and disintegration has been applied to shocked explosives and an inert material. In shocked explosives, reactions leading to detonation occur above a certain “threshold” magnitude. The computed crystal lattice breakup shock pressures compare rather well with observed experimental “threshold” shock pressures for six high explosives. The six explosives are: Comp-B3, Comp-B, TNT, PBX-9404, Tetryl, and H-6.In addition, the crystal lattice breakup criteria provides an explanation for the observed lowering of the detonation “threshold” shock pressure as the explosives are made more porous or less dense.Finally, the shock pressures, at which output from thermocouples embedded in shocked materials (PBX-9404 and Plexiglass) increases dramatically, compare favorably with predictions based on crystal lattice disintegration criteria.Consequently, it is tentatively concluded that crystal lattice breakup, or self-sustained phonon fission as Fitzgerald calls it, is responsible for the initiation of detonation in shocked explosives and enhanced thermocouple output in shocked materials. It is also postulated that the lattice breakup phenomena is also responsible for phase changes, increased chemical reactivity, and anomalous electrical activity which are observed in certain inert materials under relatively low level shock loading.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 395 (1982), S. 75-77 
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Vascular smooth muscle ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Phenylephrine ; Angiotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequor in was successfully loaded into vascular smooth muscle cells ofAmphiuma tridactylum by either microinjection or a new method which makes the cells reversibly hyperpermeable. Both gave similar results; however, the latter method produced larger signals. Vasoconstrictors produced a sustained contraction and a light (calcium) response consisting of two component: a large transient followed by a smaller, sustained response. Electrical stimulation produced a light transient that was much briefer than the contraction. These results suggest that tension can be maintained in smooth muscle in the presence of lower calcium levels than those present during force development.
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  • 6
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Mammalian cardiac muscles ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Isoproterenol ; Caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequorin was successfully loaded into mammalian working myocardium of ferrets by a chemical procedure which makes the cells reversibly hyperpermeable through exposure to Ethylenebis-(oxyethylenenitrilo) tetraacetic acid (EGTA). After undergoing the loading procedure, developed tension at Lmax was 103±26% of the control, which indicates that the muscles regained normal function. The configurations of the aequorin signals (i.e., calcium transients) and their responses to drugs were the same as reported after microinjection of aequorin. The peak of the Ca++ transient determined by the method of fractional luminescence at 3s intervals of stimulation, 2.5mM [Ca++]o, 22.5°C was 1.1μM; this value is similar to that reported for microinjection. These results indicate that the chemical loading procedure is a useful alternative to microinjection for loading aequorin into mammalian working myocardium.
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  • 7
    ISSN: 1432-2013
    Keywords: Aequorin ; Calcium indicators ; Cyanide ; Hypoxia ; Ferret ; Oxidative phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We used the bioluminescent Ca2+ indicator, aequorin to record intracellular calcium transients during reoxygenation of hypoxic ferret ventricular muscle in order to determine whether alterations in the amplitude and time course of isometric contraction are emdiated by changes in [Ca2+]i. Papillary muscles ≤1 mm in diameter were removed from the hearts of male ferrets and perfused with a bicarbonate-buffered physiologic salt solution at 30°C. Muscles were stimulated to contract isometrically at 0.33 Hz and were loaded with aequorin by a chemical procedure. Hypoxia was induced by changing the gas mixture bubbling the perfusate to 95% N2, 5% CO2; reoxygenation was accomplished by switching the gas mixture to 95% O2, 5% CO2. Hypoxia produced a decrease in peak Ca2+ and tension that was reversed by reoxygenation. However, the effects on tension of changes in oxygenation were greater than expected from the degree of change in [Ca2+]i. The time courses of the Ca2+ transient and isometric twitch moved in opposite directions and were respectively prolonged/abbreviated by hypoxia and abbreviated/prolonged by reoxygenation. These results indicate that changes in the amplitude and time course of the isometric twitch induced by hypoxia and reoxygenation cannot be attributed alone to changes in intracellular Ca2+ availability and are caused in part by a significant decrease in the calcium sensitivity of the contractile apparatus.
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  • 8
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: poly(N-substituted maleimide-co-styrene) copolymer films were electropolymerized onto copper substrates as possible candidates for electronic applications. The N-substituted moieties that were investigated include phenyi, 3-carboxyphenyl, and 4-carboxyphenyl. Uniform coatings of 25 μm or more thickness were successfully applied using each of the three N-substituted maleimides. The thickness was controlled by manipulating the monomer concentration, current density, and reaction time. Not only did the 3- and 4-carboxyphenylmaleimide (CMI)/styrene copolymers have high glass transition temperatures (220°C) and fairly good thermal stability (≈ 430°C), but they also have rather low dielectric constants (2.55 for 4-CMI/styrene), comparable to those of polyimides. Polymerization of the coatings was observed by in-situ Fourier transform infrared spectroscopy (FTIRS), using a special cell that made the observation of the polymer structure development possible. It was found by FTIRS that all three monomers, when used with styrene, produced alternating copolymers. © 1993 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 9
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: 2- or 4-carboxyphenyl methacrylamide (2- or 4-CPM) was successfully electrocopolymerized with either methylmethacrylate (MMA) or N-phenylmaleimide (NPMI) to form a thick thermoplastic matrix with high glass-transition temperature (200-300°C), on Hercules AS-4 graphite fibers. The dependence of the diffusion of active species through the coating upon the solvent/water ratio in the cell was estimated from the electrochemical diffusion behavior of hexacyanoferrate (III) ions. A higher solvent/water ratio helped to increase polymer weight gain by increasing the solvent swelling and increasing the diffusion coefficient of active species. A highly solvent-swollen polymer layer promoted the rate of polymer weight gain. The copolymer composition of 4-CPM/MMA and 4-CPM/NPMI polymers was random, and the effects of variables were consistent with free-radical polymerization kinetics. The electropolymerization rates of 4-CPM/MMA and 4-CPM/NPMI were increased by increasing current density and monomer concentration. For a slight temperature increase (from 28-45°), electropolymerization rate and polymer weight gain increased dramatically for the 4-CPM/NPMI system. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 10
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: A new in situ polymerization method is discussed wherein monomers of the major component are polymerized in the presence of a preformed thermotropic liquid crystalline polymer (LCP). Poly(p-oxybenzoate-co-p-phenyleneisophthalate) (HIQ) was chosen for this study. HIQ is well known to have a narrow process window and to be difficult to process reproducibly, both drawbacks for a commercial product. An in situ polymerization of the HIQ monomers in the presence of a fully polymerized LCP, such as poly(4-oxybenzoate-co-6-oxy-2-naphthoate) (CO) results in the “CO-HIQ” in situ blend. The in situ blend exhibited reduced biphasic morphology and was more homogeneous than was HIQ. The glass fiber-filled CO-HIQ resin also featured improved melt flow and more reproducible mechanical properties than those of HIQ. The in situ blends were characterized by optical microscopy, 1H-NMR, and melt rheology. The effect of the LCP level on the morphology of the in situ blend is discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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