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71.
H. P. S. Bhandari G. Lal N. P. S. Sidhu V. K. Mittal H. S. Sahota 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(5):379-385
Unlike previously reported Zn and Se levels were found to be the same in the hair of mentally retarded children and controls. Non-essential toxic Ag concentration was low whereas that of Hg, Au and Sc rather high in mentally retarded children. 相似文献
72.
Guliants VV Bhandari R Swaminathan B Vasudevan VK Brongersma HH Knoester A Gaffney AM Han S 《The journal of physical chemistry. B》2005,109(50):24046-24055
The outermost surfaces and subsurface layers of the orthorhombic (M1) Mo-V-O catalysts promoted with Te, Nb, and Sb oxide species at submonolayer surface coverage were examined by low-energy ion scattering (LEIS). This study indicated that the Nb oxide species was preferentially located at the topmost surface, while the subsurface Te and Sb concentrations declined gradually into the bulk. Although the original Mo-V-O catalyst was essentially unselective in propane oxidation to acrylic acid, significant improvement in the selectivity to acrylic acid was observed when Te, Nb, and Sb oxides were present as the surface species at submonolayer coverage. These findings further suggested that the formation of the surface V-O-M bonds (M = Nb, Te, or Sb) was highly beneficial for both the activity and selectivity of the orthorhombic Mo-V-O catalysts in propane oxidation to acrylic acid. The highest selectivity was observed when both Nb and Te (or Sb) oxide species were present at the surface. The selectivity trends established for the surface-promoted Mo-V-O catalyst parallel those found previously for the corresponding bulk Mo-V-M-O catalysts. These results further indicated that the introduction of surface metal oxide species is a highly promising method to prepare well-defined model catalysts for studies of the structure-activity/selectivity relationships as well as optimize the catalytic performance of the bulk mixed Mo-V-M-O catalysts for selective (amm)oxidation of propane. 相似文献
73.
Guliants VV Bhandari R Brongersma HH Knoester A Gaffney AM Han S 《The journal of physical chemistry. B》2005,109(20):10234-10242
The bulk mixed Mo-V-Te oxides possess high activity and selectivity in propane oxidation to acrylic acid and represent well-defined model catalysts for studies of the surface molecular structure-activity/selectivity relationships in this selective oxidation reaction. The elemental compositions, metal oxidation states, and catalytic functions of V, Mo, and Te in the surface region of the model Mo-V-Te-O system were examined employing low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). This study indicated that the surfaces of these catalysts are terminated with a monolayer, which possesses a different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration, whereas no dependence of these reaction rates on either the surface Mo or Te concentrations was observed. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid. 相似文献
74.
Chip-scale integration of optoelectronic devices such as lasers, waveguides, and modulators on silicon is prevailing as a promising approach to realize future ultrahigh speed optical interconnects. We review recent progress of the direct epitaxy and fabrication of quantum dot (QD) lasers and integrated guided-wave devices on silicon. This approach involves the development of molecular beam epitaxial growth of selforganized QD lasers directly on silicon substrates and their monolithic integration with amorphous silicon waveguides and quantum well electroabsorption modulators. Additionally, we report a preliminary study of long-wavelength (> 1.3 μm) QD lasers grown on silicon and integrated crystalline silicon waveguides using membrane transfer technology. 相似文献
75.
76.
The theory of the continuous flow electrical method for the determination of specific heat of liquids has been extended to the measurements of effective specific heat of packed bed materials consisting of solid-liquid phase systems. Experimental data are reported showing the variation of effective specific heat with mass porosity and saturating liquid specific heat. The weighted arithmetic mean equation of constituent specific heats is in fair agreement with the measured values. 相似文献
77.
78.
Summary Ln(C5H3SO2)3, Ln(C5H3SO2)2(OR) and Ln(C5H3SO2)(OR)2 (where Ln=La, Pr, Nd, Sm, Tb, Gd and Dy; C5H3SO2=2-thenoate anion, and OR=OPr-i or OBu-t) were prepared and characterized by elemental analysis, electronic and i.r. spectral measurements. Electronic absorption spectra show that chelates have a certain degree of covalency compared to the aquo ion. The i.r. spectra indicate interaction of ring sulphur to the metal atom in these carboxylates. Small v values suggest symmetrically bonded bidentate carboxylate groups. 相似文献
79.
80.
On the generators of subgroups of unit groups of group rings 总被引:1,自引:0,他引:1
Ashwani K. Bhandari 《Bulletin of the Brazilian Mathematical Society》1990,20(2):87-93
In this paper we find the generators of a subgroup of finite index in the unit group of the integral group ring of the metacyclic
group of orderpq given byG=(a,x:a
p=1=x
q
,xax
−1=a
f
), wherep is an odd prime,q>2 a divisor ofp-1, andf belongs to the exponentq modulop. 相似文献