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51.
We report infrared absorption of Y1Ba2Cu3O7−δ as a function of oxygen stoichiometry (0<δ<1) and copper substitution by iron in the spectral range of 450–700 cm−1. The strong bands associated with Cu-O vibrations undergo significant changes in their frequencies and intensities asδ is varied across the orthorhombic to tetragonal phase. These changes coupled with those arising as a result of doping with iron has helped in identifying the nature of the vibrational modes.  相似文献   
52.
Let Gn,k denote the oriented grassmann manifold of orientedk-planes in ℝn. It is shown that for any continuous mapf: Gn,k → Gn,k, dim Gn,k = dim Gm,l = l(m −l), the Brouwer’s degree is zero, providedl > 1,n ≠ m. Similar results for continuous mapsg: ℂGm,l → ℂGn,k,h: ℍGm,l → ℍGn,k, 1 ≤ l < k ≤ n/2, k(n — k) = l(m — l) are also obtained.  相似文献   
53.
Vanadia supported on praseodymia (2, 6 and 10 wt.% V2O5) were prepared by wet impregnation and characterized by energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), TGA/DTA and BET surface area measurements. Decomposition of cyclohexanol was conducted over these catalysts in the vapor phase. Acidity of the catalysts was measured by temperature programmed desorption using ammonia as a probe molecule. The structural and acidic properties were correlated to the total conversion and cyclohexene selectivity.  相似文献   
54.
The surface acidity/basicity of perovskite-type mixed oxides (LaCrO3, PrCrO3, SmCrO3, LaMnO3, PrMnO3, SmMnO3, LaFeO3, PrFeO3, SmFeO3, LaCoO3, PrCoO3, SmCoO3, LaNiO3, PrNiO3 and SmNiO3) are reported. These properties have been correlated with the catalytic activity of these oxides towards esterification of acetic acid usingn-butanol.  相似文献   
55.
Several new CuII complexes, having positive reduction potentials in an in situmanner, were synthesized by reaction of the Knoevenagel condensate, 4-salicylidene-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (from curcumin) with 4-X-anilines and CuCl2. The solution electronic spectra of these complexes show intense absorption around 530 nm with unusual high extinction values (, 1600--3600 m-1 cm-1) due to the low symmetry L--d (Cu) LMCT transition. The e.s.r. spectral features with g || > g || > 2.0 having four g || values and a broadening of the g ||component with moderately low A || (110 × 10-4 cm-1) also suggest a lower symmetry around CuII. The cyclic voltammetric studies of the CuII complexes in MeCN show a positive reduction potential (E pc=502--138 mV) with high peak-to-peak separation (E p=87--335 mV). The higher and low A ||values together with positive reduction potentials for these CuII complexes suggest that they can mimic the functional properties of blue copper proteins, but have poor redox stability.  相似文献   
56.
New Processable Polyaromatic amides were prepared from 2,2′-diiododiphenyl-4,4′-dicarbonyl dichloride (I) and several aromatic diamines. Phenylethynyl groups were introduced in these polymides by replacing the iodine groups with copper phenyl acetylide. On thermal curing, 2,2′-di(phenylethynyl)biphenyl group undergoes intramolecular cyclization to form 9-phenyl dibenzanthracene derivative. The cured polymers showed increased heat and chemical stabilities. No melting points were observed for all the polymers below 500°C. The viscosity of the polymers was decreased on substitution of the iodine by phenylethynyl groups.  相似文献   
57.
Summary Cumene is prepared selectively through an eco-friendly route using naturally available montmorillonite clay as the green catalyst. Pillaring of montmorillonite is done to improve the structural stability for long-term use. Alumina pillaring and the influence of mixed pillaring with zirconia and chromia on the structural as well as textural properties are characterized. Montmorillonite shows very high conversion, selectivity and regenerability upon pillaring towards isopropylation of benzene.  相似文献   
58.
Mixing of binary mixtures of nanopowders afforded by rapid expansion of high pressure and supercritical suspensions (REHPS) is investigated to examine the roles of two previously reported deagglomeration mechanisms. The quality of mixing was characterized through intensity and scale of segregation using concentration data obtained through energy dispersive X-ray spectroscopy; the corresponding deagglomeration was quantified using differential mobility and image analyses in conjunction with electron microscopy. Increasing the pressure from which expansion was carried out, and decreasing the nozzle diameter led to improved deagglomeration. However, increased pressure alone did not influence the mixture quality, which was found to also depend on the scale of mixedness of the constituents before transport through the nozzle, establishing that the REHPS mixing is significantly improved by improving the quality of the premix. The scale of segregation correlated with the size of the most energetic eddies present during flow through the nozzle, both of which increased with nozzle diameter, corroborating the importance of previously reported shear-induced deagglomeration mechanism. Finally, REHPS was also shown to be capable of deagglomerating carbon nanotube bundles and mix them well with alumina, silica, and titania at submicron scale.  相似文献   
59.
In combination with abasic site (AP site)-containing DNAs, potential use of a biotic fluorescence compound, Vitamin B2 (riboflavin), is demonstrated for the fluorescence detection of the thymine (T)-related single-nucleotide polymorphisms. Our method is based on construction of the AP site in DNA duplexes, which allows small ligands to bind to target nucleotides accompanied by fluorescence signaling: an AP site-containing probe DNA is hybridized with a target DNA so as to place the AP site toward a target nucleobase, by which hydrophobic microenvironments are provided for ligands to recognize target nucleotides through stacking and hydrogen-bonding interactions. In 10 mM sodium cacodylate buffer solutions (pH 7.0) containing 100 mM NaCl and 1.0 mM EDTA, Vitamin B2 is found to selectively bind to T (K11 = 1.8 × 106 M−1 at 5 °C) over other nucleobases, and this is accompanied by significant quenching of its fluorescence. While the sensing functions depend on the flanking sequences to the AP site, Vitamin B2 is applicable to the detection of T/C (cytosine), T/G (guanine) and T/A (adenine) mutation sequences of the CYP2A6 gene, where the flanking nucleobases are guanines in both positions (-GXG-, X = AP site).  相似文献   
60.
We show that the group of piecewise-linear homeomorphisms of having bounded slopes surjects onto the group of all quasi-isometries of . We prove that the following groups can be imbedded in : the group of compactly supported piecewise-linear homeomorphisms of , the Richard Thompson group , and the free group of continuous rank.

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