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  • Polymer and Materials Science  (12)
  • Dirichlet form  (1)
  • 1990-1994  (13)
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Potential analysis 2 (1993), S. 219-243 
    ISSN: 1572-929X
    Schlagwort(e): Primary 60J65 ; secondary 60J60, 60J55, 49Q15, 31C25 ; Brownian motion ; reflecting symmetric diffusion ; Dirichlet form ; Caccioppoli set ; set of finite perimeter ; quasimartingale ; Skorokhod decomposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A notion ofstrong Caccioppoli set is defined for bounded Euclidean domains. It is shown that stationary (normally) reflecting Brownian motion on the closure of a bounded Euclidean domain is a quasimartingale on each compact time interval if and only if the domain is a strong Caccioppoli set. A similar result is shown to hold for symmetric reflecting diffusion processes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 293-304 
    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 mechanical properties of a system consisting of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Fracture toughness (KIc) and fracture energy (GIc) were increased, while Young's modulus and yield strength decreased slightly with increasing volume fraction of the dispersed phase. We show that there is no significant influence of the precure schedule and of the various observed particle diameters on the mechanical properties for a constant rubber volume fraction. In our case, the main deformation process in the rubber-modified epoxy networks is shear yielding while cavitation is negligible.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 607-610 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Citric acid (CA)-diethylenetriamine (DETA) salts (CADETA) were prepared by using a 4.5 : 1 molar ratio of DETA-CA and removing the DETA excess. The structure of CADETA was analyzed by 13C-NMR, IR, and DSC associated with weight loss. One-step formulations consisted on dispersions of CADETA (variable amounts) in an epoxy resin based on diglycidylether of bisphenol A (DGEBA, EEW = 185.5 g/eq). The cure was followed in the pressure cell of a DSC (N2 at 2.5 MPa), to avoid volatilization of DETA in the temperature range where decomposition of CADETA and beginning of reaction took place (T 〉 175°C). A very small heat of reaction was observed, (-ΔH) ∼ 10 kJ/eq, resulting from the simultaneous endothermic salt decomposition and exothermic network formation. A stoichiometric formulation showed a Tg = 180°C, i.e., some 60°C higher than the one observed for the usual DGEBA/DETA system.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    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 bisphenol-A diglycidylether (DGEBA) based epoxy was cured with a cycloaliphatic diamine (4,4′-diamino-3,3′-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy terminated butadiene-acrylonitrile random copolymer (ETBN). Results showed that vitrification is slightly delayed with the rubber addition. With ETBN the auto-catalytic mechanism by [OH]0 is predominant at the beginning of the reaction, and on the contrary dilution is the dominant factor after x = 0.15. Phase separation takes place completely, well before gelation and vitrification; the conversion at the onset of phase separation decreases with the rubber amount but does not depend significantly on the temperature. The maximum Tg of the rubber-modified matrix does not depend on the cure temperature but decreases with the initial rubber concentration. This implies that a significant amount of rubber remains in solution in the continuous phase. This explains the delay in vitrification.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 701-716 
    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 morphology of a system consisting of a bisphenol A diglycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3′-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadience-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Scanning (SEM) and transmission (TEM) electron microscopy, differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to characterize the generated morphology. SEM results were not affected by the type of mechanical test and strain rate. Trends observed for the particle size distribution, the volume fraction of dispersed phase, the concentration of dispersed phase particles and the composition of both phases as a function of polymerization temperature and rubber concentration, were discussed. A correlation between the viscosity at the cloud point and the average size of dispersed phase particles was found for different systems, independently of the cure temperature and the initial rubber amount.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 717-735 
    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 phase separation model was used to simulate the morphologies obtained in a system consisting of a diepoxide based on bisphenol-A diglycidylether cured with a cycloaliphatic diamine, in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN). A detailed analysis of experimental factors affecting resulting morphologies was previously reported. The model, based on a thermodynamic description through a Flory-Huggins equation, and constitutive equations for polymerization and phase separation rates, could explain most of the observed trends. A nucleation-growth mechanism was believed to take place because of the very low values of interfacial tensions for this type of systems. Conditions which would lead to spinodal demixing are also discussed.
    Zusätzliches Material: 27 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 967-976 
    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 cure of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA), with benzyldimethylamine (BDMA), was investigated using differential scanning calorimetry. The kinetics showed a first-order behavior with respect to both epoxy and tertiary amine concentrations and a non-Arrhenius dependence on temperature. An activation energy could be defined only in the low-temperature range, i.e., from 80 to 120°C. Its value (E = 24.2 kJ/mol = 5.8 kcal/mol) indicates a very slight dependence on temperature. The glass transition temperature of epoxy networks decreased with an increase in both the tertiary amine concentration and the cure temperature. These effects are attributed to plastification by the free amine and to the decrease in the average length of polyether chains, which, in turn, increases the number of network defects.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1361-1371 
    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 cure reaction of a commercial epoxidized novolac with 4,4' diaminodiphenylsulfone (DDS) was studied at constant cure temperatures in the range 120-270°C, as well as at constant heating rates (differential scanning calorimetry, DSC). Stoichiometric formulations did not attain complete conversion due to the presence of topological restrictions. The limiting conversion was xmax = 0.8. Samples containing an amine excess (≥ 20%) could be completely reacted, whereas this was not possible for formulations containing an epoxy excess. Samples containing a 20% amine excess showed the maximum value of the glass transition temperature (Tg230°C). Cure took place by epoxy-amine hydrogen reactions catalyzed by (OH) groups. A reactivity ratio of secondary to primary amine hydrogens equal to 0.2 was found. The activation energy was E = 61 kJ/mol, as arising from Tg versus time shift factors and time to gel measurements. A unique relationship between Tg and x could be obtained. Gelation took place at xgel = 0.45 and the maximum Tg for the stoichiometric system was Tgmax = 215°C for x = 0.8. A conversion versus temperature transformation diagram was used to represent conditions where gelation, vitrification, degradation, and topological limitations took place. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1373-1379 
    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 buildup of the network arising from the reaction of an epoxy novolac (derived from a phenol - formaldehyde novolac resin), with 4,4'diaminodiphenylsulfone (DDS), was modeled using a kinetic-statistical procedure that takes into account (i) the complex structure of the starting novolac, (ii) the actual polymerization kinetics including the different reactivity of primary and secondary amine hydrogens, and (iii) the formation of intramolecular cycles. Predictions of gel conversion and sol fraction were in excellent agreement with experimental results. Glass transition temperatures Tg's of networks prepared at different stoichiometries were predicted using Nielsen's equation (J. Macromol. Sci.-Rev. Macromol. Chem., C3, 69, 1969) and the concentration of elastic chains arising from the model. Theoretical predictions explained the presence of a maximum in the experimental Tg for formulations containing a 20% amine excess. Experimental values of Tg as a function of conversion, for stoichiometric samples, were correlated using a model proposed in the literature. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 1039-1046 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: This study reports the effects of Simplex bone cement powder (BC) on the proliferation and production of bone resorbing factors in vitro by human adherent monocytes/macrophages. Adherent peripheral blood cells were isolated from seven healthy individuals and exposed to a dispersion of BC powder (1 mg/mL), phytohemagglutinin (PHA, 40 μg/mL), or medium alone at different periods of cell incubation (days 0-2, 0-7, 5-7, or 10-12). Cell proliferation was quantified by incorporation of 3H-thymidine uptake. Culture supernatants were evaluated for levels of interleukin 1-like activity (IL-1) by murine thymocyte proliferation assay, prostaglandin E2 (PGE2) by radioimmunoassay, lysosomal enzyme activity (N-acetyl-β-D-glucosaminidase and β-glucuronidase) using fluorometry, and collagen and casein degrading activity using radioactive substrates. Human adherent peripheral blood cells showed a proliferative response to PHA that coincided with cell maturation; BC did not inhibit PHA-induced cell proliferation of either adherent or nonadherent blood cells, indicating the non-toxic nature of these particles at the concentrations tested. BC stimulated increased release of the lysosomal enzyme N-acetyl-β-D-glucosaminidase; the levels of PGE2, IL-1, collagenase, and caseinase were unchanged. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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