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21.
The epithermal neutron spectrum shape parameter in nuclear reactors is explained from a theoretical point of view in terms of the neutron slowing down density function. The latter is approximated by Fermi's age theory. Values for are calculated for a simple approximation of a nuclear reactor: a disk shaped fission neutron source in an infinite graphite moderator. The model produces -values with the correct sign and magnitude, compared to experimental values from the literature, determined in a real reactor. It is shown that varies strongly with distance to the neutron source and less strongly with neutron energy. The inappropriateness of average -values, obtained from the slope of quasi-straight lines produced by log-log plots of E versus E, for the correction of non-ideal epithermal neutron activation is discussed. Conclusions are formulated concerning the impact of an energy dependent on comparator type NAA.  相似文献   
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The spectrokinetic indices of the triplet states of nitroaromatic amides were established. The quenching of triplet states by tertiary aromatic amines in apolar solvents leads to the formation of triplet exciplexes. A charge transfer state makes the major contribution to the structure of these exciplexes. Hydrogen atom transfer proceeds efficiently in the case of secondary aromatic amines, leading to the formation of the corresponding neutral radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1912–1915, August, 1989.  相似文献   
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A rapid, sensitive and selective method for the determination of carbamazepine and its major metabolite in plasma has been developed. Other commonly used anticonvulsants can be determined in the same procedure without interference. After extraction with dichloromethane, the components are separated by high-pressure liquid chromatography without further clean-up or concentration on a column packed with small-particle silica gel. The mean recovery from plasma is 98.6% with a relative standard deviation of 1.6%. The detection limit for carbamazepine is approximately 2 ng/ml, requiring 1 ml of plasma.  相似文献   
27.
Abstract— The pH dependence of the apparent reactivity of thiazine dyes in their triplet states has been studied in aqueous solutions, using as electron donor HY-3, the trianionic species of ethylene diamine tetraacetic acid (EDTA), in the pH range 4–8. The pH dependence is found to be related to a change in the degree of protonation of the triplet excited dye. The apparent reactivity and lifetime of two differently protonated forms of thionine, azur B and methylene blue were determined by classical and dye-laser flash techniques, making it possible to evaluate the rate constant for electron abstraction of these molecules in their triplet states. It is found that: (a) protonation on the ring nitrogen increases the electron-abstraction rate constant of the triplet-state species about twenty-fold, and (b) methylation on the side amino groups decreases it.  相似文献   
28.
Excitation functions have been measured for yields of In isotopes in the reactions107Ag(, xn)111–xIn and109Ag(, xn)113–xIn for x=1–5. The alpha particle bombardment of natural silver, the stacked foil technique for irradiation and semiconductor gamma-spectrometry for measurements were used.This work has been sponsored by the Subsecretaría de Ciencia y Tecnología, Argentina.  相似文献   
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The equilibrium of the heterogeneous reaction between dissolved sodium sulfide and biologically produced sulfur particles has been studied. Biologically produced sulfur was obtained from a bioreactor of a hydrogen sulfide removal process in which the dominating organism is Thiobacillus sp. W5. Detailed knowledge of this reaction is essential to understand its effect on the process. The results were compared with the equilibrium of the reaction of sulfide with ‘inorganic’ elemental sulfur. The equilibrium between dissolved sodium sulfide and biologically produced sulfur particles can be described by an equilibrium constant, Kx, which consists of a weighted sum of constants for polysulfide ions of different chain length, rather than a true single equilibrium constant. For biologically produced sulfur pKx = 9.10 ± 0.08 (21 °C) and 9.17 ± 0.09 (35 °C) with an average polysulfide chain length x = 4.91 ± 0.32 (21 °C) and 4.59 ± 0.31 (35 °C). The pKx value for biologically produced sulfur is significantly higher than for reaction of dissolved sodium sulfide with inorganic sulfur (pKx = 8.82; 21 °C). This difference is probably caused by the negatively charged polymeric organic layer, which is present on biologically produced sulfur but absent with “inorganic” sulfur. Specific binding of polysulfide ions to the organic layer results in a higher polysulfide concentration at the reaction site compared to the bulk concentration. This results in an apparent decrease of the measured equilibrium constant, Kx.  相似文献   
30.
Reaction conditions and structure of the starting enamines (cyclic or open-chain) determine greatly the final products of the title reactions. Whereas in benzene and acetonitrile, DMAD and 1 give a mixture of the diastereoisomeric dienamines 5, in methanol they afford pirrolizine 3. Enaminofuranones 2 and 10 furnish the corresponding “Michael adducts” 7a,b,c and 11a,b,c but fail to yield pirrolizines. It has been demonstrated that above b and c adducts differ exclusively on the arrangement of groups around a chiral axis.  相似文献   
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