排序方式: 共有72条查询结果,搜索用时 46 毫秒
31.
Spatially resolved ultrasonic attenuation in resistance spot welds: implications for nondestructive testing 总被引:1,自引:0,他引:1
Spatial variation of ultrasonic attenuation and velocity has been measured in plane parallel specimens extracted from resistance spot welds. In a strong weld, attenuation is larger in the nugget than in the parent material, and the region of increased attenuation is surrounded by a ring of decreased attenuation. In the center of a stick weld, attenuation is even larger than in a strong weld, and the low-attenuation ring is absent. These spatial variations are interpreted in terms of differences in grain size and martensite formation. Measured frequency dependences indicate the presence of an additional attenuation mechanism besides grain scattering. The observed attenuations do not vary as commonly presumed with weld quality, suggesting that the common practice of using ultrasonic attenuation to indicate weld quality is not a reliable methodology. 相似文献
32.
Faramarz Rostami-Charati Zinatossadat Hossaini Bita Mohtat Mehdi Shahraki Mohammad R.Hosseini-Tabatabaei 《中国化学快报》2011,22(10):1143-1146
An efficient synthesis of 1,3-oxathiolane-2-imin derivatives is described via one-pot reaction between arylisothiocyanats, asymmetrically substituted oxiranes and catalytic amount of methanol.The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of this method. 相似文献
33.
Dr. Majid M. Heravi Mariam Hosseini Hossein A. Oskooie Bita Baghernejad F. Farzaneh 《中国化学》2010,28(10):2045-2048
A simple and convenient protocol is described for the preparation of polyhydroquinolines via one‐pot, multi component reaction of an aromatic aldehyde, ethylacetoacetate, ammonium acetate and dimedone using iron loaded mesoporous materials as an efficient catalyst in good yields. 相似文献
34.
o‐Phenylenediamine derivatives readily react with benzoyl chloride derivatives in the presence of MCM‐41 as catalyst to yield 2‐substituted benzimidazoles in very good yields. 相似文献
35.
36.
HClO4‐SiO2, efficiently catalyzed the condensation of o‐aminophenols and 2‐bromo‐1‐aryl‐ethanones to yield 3‐aryl‐2H‐benzo[1,4]oxazines in good yields. 相似文献
37.
38.
39.
Davood Nori‐Shargh Bita Soltani Nasrin Saroogh‐Farahani Farzad Deyhimi 《国际化学动力学杂志》2006,38(2):144-151
The kinetics of the addition reaction of aniline to ethyl propiolate in dimethylsulfoxide (DMSO) as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants, and pseudo‐first‐order method was used to calculate the rate constant. This reaction was monitored by UV–Vis spectrophotometer at 399 nm by the variable time method. On the basis of the experimental results, the Arrhenius equation for this reaction was obtained as log k = 6.07 ‐ (12.96/2.303 RT). The activation parameters, Ea, ΔH#, ΔG#, and ΔS# at 300 K were 12.96, 13.55, 23.31 kcal mol?1 and ?32.76 cal mol?1 K?1, respectively. The results revealed a first‐order reaction with respect to both aniline and ethyl propiolate. In addition, based on the experimental results and using also density functional theory (DFT) at B3LYP/6‐31G* level, a mechanism for this reaction was proposed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 144–151, 2006 相似文献
40.
Bita Baghernejad Majid M. Heravi Hossein A. Oskooie Nargess Poormohammad Maliheh Khorshidi Yahia Sh. Beheshtiha 《Molecular diversity》2011,15(1):245-248