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261.
A sub-solidus phase evolution study was done in CeO2-Sc2O3 and CeO2-Lu2O3 systems under slow-cooled conditions from 1400 °C. Long-range order probing of X-ray diffraction technique is utilized in conjunction with the ability of Raman spectroscopy to detect the changes in local co-ordination. Lu2O3 showed solubility of 30 mol% in CeO2, thus forming an anion deficient fluorite-type (F-type) solid solution, whereas Sc2O3 did not show any discernible solubility. A biphasic region (F+C) was unequivocally detected by Raman spectroscopy in Ce1−xLuxO2−x/2 (0.4?x?0.9) and in Ce1−xScxO2−x/2 (0.1?x?0.9) systems. Raman spectroscopy was valuable in studying these systems since oxygen vacancies are created on doping RE2O3 into ceria and Raman spectroscopy is very much sensitive to oxygen polarizability and local coordination. Back scattered images collected on representative compositions support the above-mentioned results. 相似文献
262.
263.
Optical vortex coronagraph 总被引:1,自引:0,他引:1
We describe a method to observe dim exoplanets that eliminates light from the parent star across the entire exit pupil without sacrificing light from the planet by use of a vortex mask of topological charge m = 2. 相似文献
264.
Wilkinson HS Grover PT Vandenbossche CP Bakale RP Bhongle NN Wald SA Senanayake CH 《Organic letters》2001,3(4):553-556
[reaction: see text] A remarkably general lithium heteroatom assisted TMSCN or TBSCN addition to aldehydes and ketones has been discovered. The process provides excellent selectivities and high rates. Conformationally constrained ketones such as camphor, fenchone, and nopinone give excellent diastereoselectivities with TMSCN. Reduction of 2 provided diastereopure amino alcohol 3 in good yield. alpha- and beta-Methyl cyclohexanones with TBSCN-LiOR afford high diastereoselectivities and yields. 相似文献
265.
The dark core of an optical vortex was used to detect on-axis, forward-scattered light from a colloidal solution in the single and multiple scattering regimes. Using no adjustable parameters we obtain good agreement with a concentration-dependent scattering model. 相似文献
266.
267.
We have studied the hysteresis loops of RBa2Cu3O7 (R=Gd, Ho and Y) and detected anomalies in some of them. The observed anomalies support a recent prediction by Ravi Kumar
and Chaddah based on an extension of Bean’s model. The anomalies indicate lowH
c1 values and we have confirmed this by studying the onset of low-field hysteresis in less than 10 Oe at 77 K for these highT
c superconductors. 相似文献
268.
An electrochemically labile protecting group for alcohols and amines is reported. It can be removed under acidic or basic conditions and at low temperatures. 相似文献
269.
270.
P. S. Grover 《Applied physics. B, Lasers and optics》1979,18(1):109-111
Annihilation and momentum transfer rates of slow positrons in argon gas have been determined by an iterative computer-based
analysis. Agreement of calculated positron annihilation decay constant with experimental measurements at various electric
and temperature fields is very good. 相似文献