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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 24 (1989), S. 833-839 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The variation of erosion rate with particle flux was studied for five elastomers (natural rubber and epoxidized natural rubber, both with and without antioxidant, and butyl rubber) whilst subject to erosion by 120μm silica particles at 50 m sec−1. Th.e erosion rate was found to increase at low particle fluxes, for the elastomers without antioxidant. Infrared spectroscopy showed that there was a considerable degree of oxygen incorporation into the elastomer surface during erosion. Studies with an intermittent erosion stream suggest that a transient reaction occurs on impact causing degradation of the elastomer surface, which can account for the variation of erosion rate with particle flux. Studies with a range of erodent particles (silica, alumina, silicon carbide and soda-lime glass beads) showed that the degradation is more pronounced for hydrophilic particles.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 12
    ISSN: 1573-2576
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Pig alveolar macrophages are a heterogeneous population of cells. Three subpopulations or bands exist when the whole population is separated according to density. Band 1 cells are the least dense cells and constitute 9% of the total population. Bands 2 and 3 represent 44 and 47% of the total population. The three subpopulations generate superoxide anions, although to varying degrees. Band 3 cells are the most active, while band 1 cells are the least active. The amount of superoxide anions released in a mixed population of bands 1, 2, and 3 cells was less than the sum of that produced from each band assayed separately. Band 1 cells were found to inhibit by 47% the production of superoxide anions by band 3 cells. Conditioned medium from band 1 cells contains a heat-sensitive, nondialyzable, soluble factor responsible for this inhibition.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Psychometrika 40 (1975), S. 153-161 
    ISSN: 1860-0980
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Psychologie
    Notizen: Abstract McNemar's problem concerns the hypothesis of equal probabilities for the unlike pairs of correlated binary variables. We consider four different extensions to this problem, each for testing simultaneous equality of proportions of unlike pairs inc independent populations of correlated binary variables, but each under different assumptions and/or additional hypotheses. For each extension both the likelihood ratio test and the goodness-of-fit chi-square test are given. Whenc=1, all cases reduce to McNemar's problem. Forc ≥ 2, however, the tests are quite different, depending on exactly how the hypothesis and alternatives of McNemar are extended. An example illustrates how widely the results may differ, depending on which extended framework is appropriate.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 165-169 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1451-1458 
    ISSN: 0887-6266
    Schlagwort(e): polystyrene ; postannealing aging time ; brittle fracture behavior ; creep rupture ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The effects of postannealing aging time on the brittle fracture behavior of polystyrene were studied. A combination of mechanical properties, including creep and creep rupture under constant load and the behavior under constant extension rate deformation were examined for polystyrene samples of different prior aging times (from 1h to 2 months). The specimens and fracture surfaces were examined by optical microscopy and SEM to observe any change in the fracture behavior. It was found that longer aging times caused not only a change in the time-dependent modulus of the material but also a significant decrease in the creep rupture life and a decrease in strain to failure. It was found that the reasons for this are that although aging delays craze formation, craze breakdown and ultimate failure are accelerated by aging. The importance of these findings are discussed, particularly in relation to failure criteria involving the use of critical strains. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 665-670 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The use of bend testers for the determination of critical strains in the study of environmental stress cracking has been assessed. Using the combination of polystyrene in ethanol, various factors affecting the measurement of critical strains were investigated, including the strain applied during the bend testing, the time of immersion in the liquid prior to straining, the surface finish, and the extent of physical aging. It was concluded that the best determination of critical strain is the strain at which a sample just shows signs of crazing, rather than the strain at the outer edge of a band of crazes. The measured value of critical strain increases with increased prior immersion time, decreased surface roughness, and decreased physical aging time. Reasons for these variations are discussed. It is concluded that although the use of bend testers is valuable for qualitative testing, careful testing methodologies need to be adopted for it to be a useful quantitative test.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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