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William A. Levinson Anthony Arnold Ofelia Dehodgins 《Polymer Engineering and Science》1993,33(15):980-988
Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: in which . 相似文献
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Curtis Scott Mary Kaliszewski Charles Greskovich Lionel Levinson 《Journal of the American Ceramic Society》2002,85(5):1275-1280
In a given batch more than 30%–40% of polycrystalline, MgO-doped Al2 O3 tubes were converted into single crystals of sapphire by abnormal grain growth (AGG) in the solid state at 1880°C. Most crystals grew 4–10-cm in length in tubes with wall thicknesses of 1/2 and 3/4 mm and outer diameters of 5 and 7 mm, respectively, and had their c -axes oriented ∼ 90° and 45° to the tube axis. Initiation of AGG was associated with low values of bulk MgO concentration near 50 ppm. The unconverted tubes did not develop centimeter-size crystals but instead exhibited millimeter-size grains. The different grain structures in converted and unconverted tubes may be related to nonuniform concentration of MgO in the extruded tubes. The growth front of the migrating crystal boundary was typically nonuniformly shaped, and the interface between the single crystal and the polycrystalline matrix was composed of many "curved" boundary segments indicative of classical AGG in a single-phase material. The average velocities of many migrating crystal boundaries were quite high and reached ∼1.5 cm/h. The average grain boundary mobility at 1880°C was calculated as 2 × 10−10 m3 /(N·s), representing the highest value reported so far in Al2 O3 and within a factor of 2.5 of the calculated intrinsic mobility. Under similar experimental conditions sapphire crystals did not grow when a codopant of CaO, La2 O3 , or ZrO2 was added in concentrations of several hundred ppm. 相似文献
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Deletion of Saccharomyces cerevisiae BIG1 causes an approximately 95% reduction in cell wall beta-1,6-glucan, an essential polymer involved in the cell wall attachment of many surface mannoproteins. The big1 deletion mutant grows very slowly, but growth can be enhanced if cells are given osmotic support. We have begun a cell biological and genetic analysis of its product. We demonstrate, using a Big1p-GFP fusion construct, that Big1p is an N-glycosylated integral membrane protein with a Type I topology that is located in the endoplasmic reticulum (ER). Some phenotypes of a big1Delta mutant resemble those of strains disrupted for KRE5, which encodes another ER protein affecting beta-l,6-glucan levels to a similar extent. In a big1Deltakre5Delta double mutant, both the growth and alkali-soluble beta-l,6-glucan levels were reduced as compared to either single mutant. Thus, while Big1p and Kre5p may have similar effects on beta-l,6-glucan synthesis, these effects are at least partially distinct. Residual beta-l,6-glucan levels in the big1Deltakre5Delta double mutant indicate that these gene products are unlikely to be beta-l,6-glucan synthase subunits, but rather may play some ancillary roles in beta-l,6-glucan synthase assembly or function, or in modifying proteins for attachment of beta-l,6-glucan. 相似文献
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The art and science of speech recognition have been advanced to the state where it is now possible to communicate reliably with a computer by speaking to it in a disciplined manner using a vocabulary of moderate size. It is the purpose of this paper to outline two aspects of speech-recognition research. First, we discuss word recognition as a classical pattern-recognition problem and show how some fundamental concepts of signal processing, information theory, and computer science can be combined to give us the capability of robust recognition of isolated words and simple connected word sequences. We then describe methods whereby these principles, augmented by modern theories of formal language and semantic analysis, can be used to study some of the more general problems in speech recognition. It is anticipated that these methods will ultimately lead to accurate mechanical recognition of fluent speech under certain controlled conditions. 相似文献
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