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221.
K. Strijckmans N. De Brucker C. Vandecasteele 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(4):389-397
A method for the determination of sulphur in fly ash by instrumental proton activation analysis using the34S/p,n/34mCl reaction was developed. The 2128.5 keV and 3305.0 keV -rays of34mCl /t=32.0 min/ were measured on a Ge/Li/ -spectrometer, shielded with a lead absorber to attenuate low energy -rays. Irradiation and measuring conditions were optimized. The detection limit for instrumental analysis is 0.3 to 1 mg g–1 and the standard deviation is cca. 4% for a typical sample. 相似文献
222.
F.D. De Körösy 《Journal of Electroanalytical Chemistry》1982,141(4):391-417
Biological cell membranes are compared to artificially produced permselective membranes. In spite of the difference in their thickness and electric resistance it is shown that they are similar in many important aspects, and the behaviour of synthetic membranes can explain very many points in the behaviour of cell membranes, especially axons. It is stressed that it is seldom necessary to assume unproven channels in biological membranes which are specific in the transport of a single ion species. Most of the phenomena of selectivity, opening and closing of such membranes can be explained by the influence of pH on membrane sites, by their poisoning with higly charged and/or large counter-ions. The borderline between two oppositely charged regions of a mosaic membrane opens up because it can be traversed by both positive and negative ions and permselectively is lost. Bipolar membranes rectify the current. Amphoteric membranes undergo very complex changes in conducting properties and permselectively with pH, especially when allowance is made for the weakly dissociated sites contained within these membranes. It is suggested that black lipid membranes made in the laboratory could be used to elucidate new points of similarity if they were used under similar conditions to our technical membranes. 相似文献
223.
Natural rubber is reinforced with a novel type of grass fiber (Cyperus Tegetum Rox b). The effects of fiber loading of different mesh sizes on curing characteristics and mechanical properties of grass fiber filled natural rubber composite are studied. Since 400 mesh grass fiber loaded natural rubber composite shows superior mechanical properties, therefore the effect of silane coupling agent was studied for this particular composite. Here composites were prepared by using water leached grass fiber. Optimum cure time increases with the increase in fiber loading but the change in scorch time is less. The same trend of increase in optimum cure time is observed in the presence of Si69. But the value is higher compared to that of rubber composite without Si69. With increase in the fiber loading, modulus and hardness of the composite increases but tensile strength decreases. The mechanical properties of the composite, namely moduli at 200 and 300% elongation and hardness increase in the presence of Si69 but tensile strength is less compared to that of the composite without Si69. Elongation at break is not much affected due to the presence of Si69. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
224.
John F. Callan A. P. De Silva R. C. Mulrooney B. Mc Caughan 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(3-4):257-262
Summary This review highlights recent advances in the use of quantum dots (QD’s) as luminescent sensors. The bulk of the study concentrates
on systems that possess organic ligands bound to the surface of QD’s. These ligands vary from low molecular weight thiols
to larger molecules such as maltose binding protein. All have one thing in common: when a target analyte binds to the ligand/receptor,
a perturbation of the system occurs, that registers itself as a change in the luminescence intensity of the QD. Two main mechanisms
are prevalent in controlling the luminescent intensity in such systems. The first is Photoinduced Electron Transfer (PET)
and the second energy transfer. This review looks at current sensors that operate by using these mechanisms. Two component
systems are also investigated where a quencher is first added to a solution of the QD, followed by addition of the target
analyte that interacts with the quencher to influence the luminescence intensity. 相似文献
225.
XinZHANG DeHuaHE QiJiangZHANG BoQingXU QiMingZHU 《中国化学快报》2003,14(10):1066-1069
Comparatively high CH3OH selectivity (60.0%) and yield (6.7%) were obtained on MoOx/(LaCoO3 Co3O4) catalysts in selective oxidation of methane to methanol using molecular oxygen as oxidant. The interaction between MoOx and La-Co-oxide modified the molecular structure of molybdenum oxide and the ratio of O^-/O^2- on the catalyst surface, which controlled the catalytic performance of MoOx/(LaCoO3 Co3O4) catalysts. 相似文献
226.
José M. Bartoloméa Jesús AlcázarJ.Ignacio Andrés Marcel De BruynJavier Fernández Encarna MatesanzKristof Van Emelen 《Tetrahedron letters》2003,44(47):8545-8548
The synthesis of a series of novel analogues of the 3-substituted-2,3-dihydro-1,4-dioxino[2,3-b]pyridine core, modified in the non-aromatic ring, is described. Due to the presence of a versatile hydroxymethyl group in their structure, these novel scaffolds are attractive intermediates for the preparation of potential new therapeutic agents. 相似文献
227.
P. R. N. De Souza D. A. G. Aranda J. W. De M. Carneiro C. Da S. B. De Oliveira O. A. C. Antunes F. B. Passos 《International journal of quantum chemistry》2003,92(4):400-411
B3 LYP hybrid functional with LACVP* pseudopotential was applied for the optimization of geometries of complexes resulting from interaction of benzene, pyridine, naphthalene, and quinoline with Ptn (n = 4, 7) clusters. For benzene‐containing complexes, the most stable form corresponds to a bridge adsorption, with benzene undergoing considerable geometric distortions, assuming a boat‐like conformation. C? H bonds are bended upward from the plane of the cluster. C? C bonds stretch, especially when they form π‐complexes with low coordinated Pt atoms. Some arrangements for pyridine complexes involving the N atom of the organic moiety undergo further distortions, apparently preserving a formal C? N π bond. Except for that distortion, the behavior of any heteroaromatic complex is similar to that of benzene in the same arrangement. The quinoline–Pt7 complex can suitably be used for simulation of the cinchonidine (CD) anchorage over Pt. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
228.
Arie van Der Kaaden Johan Haverkamp Jaap J. Boon Jan W. De Leeuw 《Journal of Analytical and Applied Pyrolysis》1983,5(3):199-220
Inorganic additives, viz. Na2CO3, NaOH, HCl, ZnC2, NaH2PO4, Na2HPO4, NaCl. MgSO4 and sea salt, to the pyrolysis matrix change the pyrolysis-mass spectrum of amylose significantly. Carbonyl compounds, acids and their lactones, furans, pyranones anhydrosugars and aromatic substances are found in different ratios under the various conditions, as determined by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS).Carbonyl compounds, acids and lactones are released from alkaline and neutral matrices. Furans and anhydrohexoses are particularly formed under neutral and acidic conditions. Pyranones are specific for phosphate matrices. Unsaturated hydrocarbons and aromatic substances arise from strongly alkaline or dehydrating matrices. Degradation pathways are proposed for various compound categories.The results of pyrolysis-mass spectrometry and Py-GC-MS are highly compatible. 相似文献
229.
The uncatalyzed 1,4-addition of phenylmagnesium bromide and furylmagnesium iodide to methyl 5-methoxy-1,5-cyclohexadienylcarboxylate (), directly followed by alkylation and hydrolysis leads to the corresponding cyclohexanones of type (R1 and R2 trans) in moderate to high yield. 相似文献
230.
The systematic preparation of partially fluorinated pentafluorosulfur alkanes containing no additional halogens is reported. Thus, the indirect addition of “HF” (via KF/formamide) to SF5CH=CF2, SF5CFCF2, and SF5C(CF3)CF2 produces SF5CH(in2)CF3, SF5CHFCF3, and SF5C(CF3)2H respectively. The monohydryl-pentafluorosulfur-F- alkanes react readily with S2O6F2 to form the corresponding fluorosulfates by oxidative displacement of hydrogen, while the dihydryl derivative undergoes cleavage to produce F-acetyl fluoride. Efforts to convert some of the new materials to the important but unknown pentafluorosulfur “ketone,” SF5C(O)CF3, were unsuccessful. 相似文献