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1.
M. Zürcher und Gisela Hoepe 《Fresenius' Journal of Analytical Chemistry》1940,119(3-4):134-136
Ohne Zusammenfassung 相似文献
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J. Merino J. A. Sanchez-Cabeza L. Pujol K. Leonard D. McCubbin 《Journal of Radioanalytical and Nuclear Chemistry》2000,243(2):517-524
The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, 241Pu and 239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the 241Pu/239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and 241Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The 241Pu/239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea. 相似文献
4.
Eckhard Herrmann Moein Nouaman Zdirad
k Gisbert Großmann Gisela Ohms 《无机化学与普通化学杂志》1994,620(11):1879-1888
Tetraarylesters of μ-Imido-Diphosphoric Acid and its Thio Derivatives — Structure Investigations New O,O′,O″,O?-tetratolyl- and ditolyl-diphenylesters of the μ-imido-diphosphoric acid and its mono and dithio derivatives were synthesized, compared with the corresponding tetraphenylesters and investigated by 1H, 13C, and 31P NMR spectroscopy and X-ray crystal structure analysis. Structures of the O,O′,O″,O?-tetrakis-(2-methyl-phenyl)-μ-imidodiphosphate, 1b , as well as of the corresponding ortho-, meta- and para-tolylesters of the μ-imido-monothiodiphosphoric acid ( 2a , 2b , 2c ) were determined. All the compounds form dimers via N? H…?O hydrogen bonds in the crystal as well as in nonpolar solvents. The distances around the phosphorus atoms rise with decreasing electronegativity of the phosphorus substituents. Signs of the 2JP? N? P coupling constants were determined by 13C{1H, 31P} triple resonance experiments for some compounds. These constants become more negative owing to substitution of a phosphoryl by a thiophosphoryl group. 相似文献
5.
Bernard Chantegrel Christian Deshayes Bernard Pujol Zhong Jia Wei 《Journal of heterocyclic chemistry》1990,27(4):927-934
The title compounds were prepared from ethyl 5-acyl- or 5-(1-hydroxyethenyl)isoxazole-4-carboxylates which in turn were prepared from ethyl 3-methylamino-2-butenoate or 3(2H)-furanones. 相似文献
6.
Hegedus LS Geisler L Riches AG Salman SS Umbricht G 《The Journal of organic chemistry》2002,67(22):7649-7655
Butenolides 5a and 13 were used as optically active templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine (7). The cis-dihydroxylation of a variety of butenolides occurred with the major product formed from oxidation of the beta-face. 相似文献
7.
Gisela Bodrogai 《Mikrochimica acta》1979,71(1-2):47-51
Zusammenfassung Verschiedene schwefelhaltige Verbindungen ergeben zu hohe Kohlenstoffwerte. Dieser Fehler kann behoben werden, indem die Einwaage im Verbrennungsschiffchen mit vorbehandeltem Cerdioxid abgedeckt oder vermischt wird.
CH determination in containing compounds sulfur
Summary Various sulfur-containing compounds yield carbon values which are too high. This error can be eliminated by covering or mixing the aliquot in combustion boats with pretreated cerium dioxide.相似文献
8.
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Application of the LCAO-MO-SCF- method to conjugated hydrocarbons leads with the effective nuclear Slater's charges, Zeff = Zeff = 3.25 to electronic transitions higher than experimental ones by about 50%.We show that in the case of all trans linear polyenes and fulvene, one may obtain satisfying results by the same method, without any reference to experience, by taking Zeff = 3.0 Zeff = 3.55. There the effective nuclear charges are near of these of the valence state of carbon V
41s2t1t2t32ptz:Zeff = 2.971 Zeff = 3.382 [10]. 相似文献
10.
M. Soukri S. LazarM.D. Pujol M. AkssiraJ.M. Leger C. JarryG. Guillaumet 《Tetrahedron》2003,59(20):3665-3672
2,3-Dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,3′-pyrrolidine (8A) and 2,3-dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,4′-piperidine (9A) have been synthesized from 2-chloro-3-pyridinol. The corresponding 2,3′ (8B) and 2,4′ (9B) isomers were obtained via the Smiles rearrangement, while 9B was also selectively synthesized from 2-nitro-3-pyridinol. The separation of the isomers A and B under the sulfamide form was carried out by flash column chromatography. Subsequent transformations of the corresponding dioxinopyridine derivatives were described. 相似文献