排序方式: 共有57条查询结果,搜索用时 31 毫秒
21.
A.E. Bekheet N.A. Hegab M.A. Afifi H.E. Atyia E.R. Sharaf 《Applied Surface Science》2009,255(8):4590-4594
Se90Te10−xAgx (0 ≤ x ≤ 6) compositions were prepared by quenching technique. Thin films with different thicknesses of the obtained compositions were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, the refractive index n and the absorption index k, have been calculated from transmittance T and reflectance R through the spectral range of 400-2500 nm for the studied films with different thicknesses (165-711 nm). From the analysis of refractive index n data, high frequency dielectric constant ?∞ was determined. Both ?∞ and n are found to decrease with the increase of Ag content. The optical band gap is calculated for all compositions from the absorption coefficient analysis. The effect of the Ag addition on the obtained optical parameters has been discussed. The analysis of absorption index k data, revealed the existence of allowed indirect transitions for all compositions. It is indicated also that increase with increasing Ag content. 相似文献
22.
Mohamed A. Farag Eman M. Kabbash Ahmed Mediani Stefanie Dll Tuba Esatbeyoglu Sherif M. Afifi 《Molecules (Basel, Switzerland)》2022,27(9)
The present study aimed to assess metabolites heterogeneity among four major Cinnamomum species, including true cinnamon (Cinnamomum verum) and less explored species (C. cassia, C. iners, and C. tamala). UPLC-MS led to the annotation of 74 secondary metabolites belonging to different classes, including phenolic acids, tannins, flavonoids, and lignans. A new proanthocyanidin was identified for the first time in C. tamala, along with several glycosylated flavonoid and dicarboxylic fatty acids reported for the first time in cinnamon. Multivariate data analyses revealed, for cinnamates, an abundance in C. verum versus procyandins, dihydro-coumaroylglycosides, and coumarin in C. cassia. A total of 51 primary metabolites were detected using GC-MS analysis encompassing different classes, viz. sugars, fatty acids, and sugar alcohols, with true cinnamon from Malaysia suggested as a good sugar source for diabetic patients. Glycerol in C. tamala, erythritol in C. iners, and glucose and fructose in C. verum from Malaysia were major metabolites contributing to the discrimination among species. 相似文献
23.
A. S. Abdel-Halim Y. K. Afifi N. Afify 《Journal of Thermal Analysis and Calorimetry》1987,32(4):1071-1079
The effects of the drying conditions on the thermal behaviour of UO3 gel microspheres were studied by TG, DTA and X-ray examination. The effects of drying with air, steam or alcohol on the crystal structure and crystallite size were also studied. The results indicate that the thermal decomposition of UO3 gel microspheres involves five steps: the first two for dehydration, the third for ammonia release, the fourth for ammonia oxidation, and the last one for UO3 recrystallization. It was also found that the crystal growth varied from 110 Å after air drying to 512 Å and 496 Å after steam and alcohol treatment, respectively.
Zusammenfassung Die Effekte der Trocknungsbedingungen auf das thermische Verhalten von UO3-Gelmikrokugeln wurden mittels TG, DTA und Röntgenanalyse untersucht. Ebenfalls wurden die Auswirkungen der Trocknung mit Luft, Dampf und Alkohol auf die Kristallstruktur und die Kristallitgröße untersucht. Die Ergebnisse deuten darauf hin, daß die thermische Zersetzung der UO3-Gelmikrokugeln in 5 Schritten verläuft: die ersten zwei sind Dehydratisierungsprozessen, der dritte der Freisetzung und der vierte der Oxydation von Ammoniak und der letzte der Rekristallisation des UO3 zuzuschreiben. Die Kristallitgröße variiert zwischen 110 Å nach Lufttrocknung und 512 bzw. 496 Å nach Trocknung mit Dampf bzw. Alkohol.
, UO3 . , UO3. , UO3 : — , — , — — UO3. , 110 Å 512 496 Å , , .相似文献
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Chemical screening of the leaves and flowers of Crataegus aronia resulted in the isolation of hyperoside, quercetin, rutin and beta-sitosterol for the first time from this plant. The effects of the hydroethanolic extract of C. aronia (CAHE) on hypercholesterolemic rats were investigated. The rats, treated orally for four weeks with 400 mg/kg/day CAHE, exhibited significant decreases in serum total cholesterol (TC) and low-density lipoprotein (LDL). The results were compared with those obtained after oral administration of atorvastatin (10 mg/kg/day). Furthermore, 10-week daily co-administration of a high cholesterol diet and CAHE (200 mg/kg/day) prevented the increase in TC and LDL. These observations indicate that CAHE has a hypocholesterolemic effect. 相似文献
26.
Karim F. Hirji Stein E. Vollset Isildinha M. Reis Abdelmonem A. Afifi 《Journal of computational and graphical statistics》2013,22(3):209-224
Abstract The investigation of interaction in a series of 2 × 2 tables is warranted in a variety of research endeavors. Though many large-sample approaches for such investigations are available, the exact analysis of the problem has been formulated for the probability statistic only. We present several alternative statistics applicable in this context. We also give an efficient polynomial multiplication algorithm to compute exact distributions and tail areas for the family of stratum-additive statistics. Besides the probability statistic, these include the score, likelihood ratio, and other statistics. In addition to comparing, in empirical terms, the diverse computational strategies for exact interaction analysis, we also explore the theoretical linkages between them. Data from published papers are used for illustration. 相似文献
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In this paper, we present a new method to digitally add a high-frequency spatial carrier in order to use the wavelet phase extraction algorithm, which leads directly to the phase without the unwrapping process. The method needs a fringe pattern and its π/2 shifted version. The application is performed with two shifted fringe patterns obtained from the phase shifting images of the thermomechanical study of an MOS power transistor. A comparison with the phase shifting results is made. 相似文献
28.
Eutypine, 4-hydroxy-3-(3-methyl-3-butene-1-ynyl) benzaldehyde, is a toxin produced by Eutypa lata, the causal agent of eutypa dieback of grapevine. The tolerance of some grapevine cultivars to the disease has been ascribed to the potential reduction of eutypine into its corresponding non-toxic alcohol, eutypinol. In the present study, eutypine biotransformation in different tissues of grapevine was investigated by HPLC and LC-MS. Grape callus tissues were able to biotransform eutypine into eutypinol within the first 3 h of culture. The grape plantlets cultured in vitro can also transform eutypine into eutypinol. Grape plantlet leaves do not have any effect on the uptake of eutypine, which goes through the tissues following a concentration gradient. Results revealed that the toxicity of eutypine in grape tissues is an active process showing that eutypinol is rapidly metabolised into other compounds. The use of micro-cuttings and in vitro plants showed that eutypine strongly accumulates in the bottom part of the diseased plant stems. 相似文献
29.
Tatiana Dyblenko Andrei Chtchemelinine Ryan Reiter Ruhul Q. Chowdhury Alexander Enaya Hanan Afifi Rene Fournier Gabriela Mladenova Alfred Barry P. Lever Edward Lee‐Ruff 《Photochemistry and photobiology》2014,90(2):470-475
A series of 9‐substituted fluorenols and 9,9′‐disubstituted‐9,9′‐bifluorenyls were irradiated to give products derived from fluorenyl radicals. Product distribution was solvent dependent. A TEMPO adduct was isolated from the photoexcitation of 9‐fluorenol. An unusual unsymmetrical 3,9′‐bifluorenyl was observed from the photolysis of 9‐trifluoromethylfluorenol and 9,9′‐di(trifluoromethyl)‐9,9′‐bifluorenyl in more polar or hydrogen‐bonding solvents. The electronic nature of 9‐substituted fluorenyl radicals was probed using theoretical calculations showing the dipolar character of species with electron‐deficient groups. These constitute the first examples of “doubly destabilized” radicals. 相似文献
30.
Ethyl 2-{2-[4-(2,3-dimethyl-5-oxo-1-phenyl-3-(pyrazolin-4-yl)]-2-cyano-1-(phenylamino)vinylthio}-acetate, 2-[4-(2,3-dimethyl-5-oxo-1-phenyl-(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]2-(4-oxo-3-phenyl-(1,3-thiazoilidin-2-ylidene))ethanenitrile, 2-[4-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]-2-(4-methyl-3-phenyl(1,3-thiazolin-2-ylidene))ethanenitrile, 2-(5-acetyl-4-methyl-3-phenyl(1,3-thiazolin-2-ylidene))-2-[4-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]ethanenitrile, and ethyl 2-(cyano(4-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)methylene)-2,3-dihydro-4-methyl-3-phenylthiazole-5-carboxylate were synthesized by treatment of 2-(4-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)-3-mercapto-3-(phenylamino)-acrylonitrile with appropriate halo ketones or halo esters. Also, 4-{2-[5,7-dimethyl-2-(phenylamino)(7a-hydropyrazolo[1,5-a]pyrimidin-3-yl](1,-thiazol-4-yl)}-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one derivatives were synthesized via reaction of 4-{2-[5-amino-3-(phenylamino)pyrazolin-4-yl](1,3-thiazol-2-yl)}-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one with β-diketone or β-keto ester. All synthesized compound were established by elemental analysis, spectral data, and alternative synthesis whenever possible. 相似文献