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101.
Neutron diffraction has been used to study the variation of antiferromagnetic order in the antimony isomorphous MnSb2O4 (TN ~ 60 K) and NiSb2O4 (TN ~ 46 K). The magnetic moments have been related to the Mn2+ and Ni2+ spins and magnetostrictive effects have been interpreted. The influence of the method of synthesis is mentioned: polycrystalline MnSb2O4 has been obtained from hydrothermal synthesis. Orthorhombic distortions are not connected with magnetic interactions but with structural defects. 相似文献
102.
W. A. SUMMERS JR. C. ENWALL J. G. BURR R. L. LETSINGER 《Photochemistry and photobiology》1973,17(5):295-301
Abstract— Quantum yields for 254 nm ultraviolet photoaddition of the nucleophiles hydrazine, HCN, HSO3 - , methyl amine, and BH4 - to uracil have been measured; the quantum yields for hydrazine, HCN, and HSO3 - additions are pH-dependent. The nucleophiles sulfide, azide, chloride, bromide, iodide, nitrite and thiocyanate failed to photo–add under similar conditions. These reactions are interpreted as 1,4-additions to the conjugated enone system of the anti-aromatic compound, uracil; as suggested by S. Y. Wang (Wang and Nnadi, 1968). The nuclear magnetic resonance (NMR) spectrum of the photohydrate of uracil-5-d-showed that the proton was added to the 5-position in a stereochemically random manner. The photoaddition of HSO3 - takes place at much lower concentrations than required for the thermal addition of this anion and is also stereochemically random. 相似文献
103.
C. T. LIN Y. G. CHYAN G. C. KRESHECK HERBERT C. BITTING JR M. A. EL-SAYED 《Photochemistry and photobiology》1989,49(5):641-648
Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism. 相似文献
104.
Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2392-2395
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Electrical behaviour of catalytic nanostructured CeO2/CuOx composites under air-methane gas impulses
Sébastien Saitzek Sylvie Villain Jean Raymond Gavarri 《Applied Surface Science》2007,253(18):7490-7496
Nanostructured composites based on copper oxide and cerium dioxide phases [CuO-CeO2] were elaborated from sol-gel route, with weight fractions of CuO phase ranging between 0 and 0.4. They are interesting potential catalysts allowing conversion of CH4 and CO into CO2 and H2O and might be used in miniaturized gas sensors. An electrical study of this nanostructured system was carried out to determine catalytic behaviours under air-methane impulses at 350 °C. The electrical analysis was based on a specific homemade electronic device. Time dependent interactions between gas pulses and solid catalyst (CuO/CeO2) were analyzed from a frequency modification of the electronic device. Kinetic parameters were determined from a model describing adsorption and desorption of gases adapted to short interaction time between gas and solid. These time dependent electrical behaviours were then correlated with infrared spectroscopy analyses allowing time dependent analysis of methane conversion into CO2 gas, for long interaction time between gas and solid. 相似文献
110.
Abstract Humic substances are the major organic constituents of soils and sediments. They also occur in small concentrations in natural surface waters and groundwaters. They form through the breakdown of plant and animal tissues by chemical and biological processes that tend to produce complex chemical structures that are more stable than the original material from which they were derived. One of the more important characteristics of humic substances is their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and various organic compounds such as alkanes, fatty acids, and toxic organic substances such as pesticides. 相似文献