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排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
Finite element analyses (FEA) of thermosets are often performed on the basis of rheological data for fully cured resin. For the FEA of thermosets during curing, a material model is established and a technique is demonstrated, which allows the rheological data of the linear viscoelastic material to be derived. As the moduli are sensitive to conversion, all measured properties are related to temperature and conversion. Therefore the basis for the rheological data has to be a suitable reaction kinetic. Based on the kinetics shear and compression properties are measured independently and modeled mathematically with the focus to gain a formulation, which is suitable for FEA. The considered time constants are in the range between one second and one month as these times are relevant for the investigated relaxation times. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1868–1872, 2003 相似文献
992.
Manoj Raama Varma N. D. Kataria 《Journal of Materials Science: Materials in Electronics》2007,18(4):441-446
Ba(Zn1/3Ta2/3)O3 has been prepared with different dopants that gave best microwave dielectric properties at room temperature. Effects of different
dopants on the low temperature microwave dielectric properties of BZT were investigated. With decrease in temperature, loss
tangent was found to decrease marginally and then increase at temperatures lower than 100 K. Increase in loss factor at lower
temperatures were found to be less for dopants with smaller ionic radii. Dielectric constant was found to be almost independent
of temperature. Temperature coefficient of resonant frequency slowly decreased from a positive value to negative value when
temperature was lowered. Temperature at which τf becomes zero was found to vary for different dopants. There is a temperature stable region for tanδ, ɛr and τf which varies for different dopants. 相似文献
993.
L. V. Krylov Yu. N. Melent'ev V. I. Yatsenko V. V. Nikitin L. V. Maksimova I. N. Knyazeva 《Metallurgist》1991,35(2):32-32
Magnitogorsk Metallurgical Combine. Translated from Metallurg, No. 2, p. 37, February, 1991. 相似文献
994.
Patients with ulcerative colitis are usually non- or ex-smokers in contrast to Crohn's disease where smoking is common. Abnormalities of quantity and quality of intestinal mucus have been postulated in the pathogenesis of these diseases. It is possible that smoking habit may exert its effects via changes in mucus in inflammatory bowel disease. We have therefore studied incorporation of N-acetylglucosamine into synthesized colonic mucin in explants from 85 controls with normal colonoscopic appearances and histology, including 27 smokers and 58 nonsmokers, 36 patients with ulcerative colitis and 19 with ileocolonic Crohn's disease over 24 h in tissue culture. Incorporation of N-acetylglucosamine into normal explants was 31.3 +/- (SD) 7.1 dpm/microgram biopsy protein, incorporation was increased in patients with active Crohn's disease (mean 41.2 +/- (SD) 10.4 dpm/microgram biopsy protein, p = 0.003), decreased in inactive ulcerative colitis (mean 24.1 +/- 7.8 dpm/microgram biopsy protein, p = 0.0006) but normal in active ulcerative colitis (mean 35.0 +/- 13.8 dpm/microgram biopsy protein, p = 0.44). No significant relationship was found between cigarette smoking habits and mucus synthesis in controls with normal mucosa (nonsmokers, n = 58, mean 31.0 +/- (SD) 7.52 dpm/microgram biopsy protein; smokers, n = 27, mean 31.8 +/- (SD) 6.1 dpm/microgram biopsy protein, p = 0.9). This study shows that mucus glycoprotein synthesis is reduced in inactive ulcerative colitis, rising to normal levels in active disease and that synthesis is increased in Crohn's disease. There is no effect of smoking on mucus synthesis by control biopsies suggesting that the differences seen in inflammatory bowel disease are not related to cigarette smoking. 相似文献
995.
Y Paltieli A Weichselbaum N Hoffman I Eibschitz Z Kam 《Canadian Metallurgical Quarterly》1995,10(7):1638-1641
Based on a laser light scattering technique and fibre optic probe, we have developed and tested a simple and practical device for real time measurements of ciliary activity in human Fallopian tubes during laparoscopy and laparotomy. A further aim was to investigate the relationship between the ciliary beat frequency (CBF) and the morphology of the ciliary epithelium. The mean +/- SE of CBF in the fimbria and in the ampulla were 5.4 +/- 0.3 Hz and 5.0 +/- 0.1 Hz respectively. Small pieces of fimbria and ampulla epithelium were taken from the same sites at which the CBF was measured, and the percentage of ciliary cells was determined by scanning electron microscopy. A high positive correlation was found between CBF and the percentage of ciliary cells in the fimbria (r = 0.84) and in the ampulla (r = 0.88). The instrument presented in this study provided, for the first time, a quantitative examination of the CBF in intact human Fallopian tubes and may be used for the investigation of ciliary activity in patients with infertility. 相似文献
996.
Gubin M.A. Kireev A.N. Koval'chuk E.V. Tyurikov D.A. Depatie D. 《Photonics Technology Letters, IEEE》1995,7(7):745-747
CW operation of a RbCl:Li-FA(II) laser has been obtained under pumping by a red laser diode. Pump power at threshold is 90 mW. Single frequency operation of the color center laser has been achieved. The intensity noise generated by two pump sources (laser diode and Kr-ion laser) is compared 相似文献
997.
Synthesis of oleyl oleate as a jojoba oil analog 总被引:2,自引:0,他引:2
N. Sánchez M. Martinez J. Aracil A. Corma 《Journal of the American Oil Chemists' Society》1992,69(11):1150-1153
Synthesis of a wax ester analog of jojoba oil was accomplished from oleic acid and oleyl alcohol with a zeolite as catalyst.
A full 23 factorial design at two levels has been used in the synthesis. The variables selected were temperature, reduced pressure
and initial catalyst concentration. The most important variable within the range studied was temperature. Reduced pressure
had a negative influence, and initial catalyst concentration showed a positive influence on the process. A response equation
has been determined for the yield of ester. The properties of the synthesized product are similar to those of natural jojoba
oil. 相似文献
998.
Summary Sedimentation experiments and X-ray photoelectron spectroscopy (XPS or ESCA) analyses have been used to study the effect of poly(methylmethacrylate) (PMMA) tacticity on aluminum oxide powder dispersion stability in a common solvent medium. The relative trends from sedimentation densities, and from surface analyses after solvent washing show that (PMMA) adsorption is greatest with isotactic polymer, where isotactic>atactic>syndiotactic adsorption. These results suggest that surface adsorption and hence dispersion stability can be influenced by polymer chain configuration as well as by chain conformation. 相似文献
999.
1000.
G. T. Vigant A. B. Énglin N. N. Zakharova I. V. Klimyuk 《Chemistry and Technology of Fuels and Oils》1991,27(5):244-248
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, 11–13, May, 1991. 相似文献