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161.
P. Harting 《Isotopes in environmental and health studies》2013,49(8):347-348
Es wird eine weiterentwickeltes, isotopenanalytisches Verfahren zur probenchemischen Umsetzung von Kohlenwasserstoffen mit Chromium zu Wasserstoff bei 1300 K vorgestellt. Die erzielten Testergebnisse zeigen anhand der gemessenen δD-Werte, daβ Quarzöfen bei diesen Temperaturen noch keine die Isotopenmeβwerte beeinflussende Diffusion von Wasserstoff durch die Wandung zulassen. Auβerdem erfolgte die Reaktion nahezu spontan und vollständig, was die Methode zeitlich sehr effektiv macht. A modified isotope analytical method is presented for the chemical reaction of hydrocarbons with chromium at 1300 K to form hydrogen. The test results obtained (i.e. the measured δD-values) show that at this temperature quartz heating tubes do not allow hydrogen to diffuse through the wail, which fact would influence the isotopic composition. Furthermore the reaction proceeds nearly spontaneously and quantitatively, which yields an effective method, especially with respect to time. 相似文献
162.
H. Koch 《Isotopes in environmental and health studies》2013,49(7):233-238
Die Ausnutzung von Quanten- und Teilchenstrahlung zur Analyse von Stoiffverteilungen und Stoffzusammensetzungen hat im vergangenen Jahrzehnt einen beträctlichen und fast unübersehbaren Umfang angenommen. Es werden mögliche Schicerpunkie der zukünftigen Anforderungen an solche Analysenverfahren — die sich aus der modernen Forschung und Entvicklung ergeben — aufgezeichnet und die Anwendungsmöglichkeiten und der Entwicklungsstand spezieller Verfahren besprochen. Insbesondere werden Mönlichkeiten der Gesamtbilddurstellung, der Scanning-Verfahren und der Oberflächenuntersuchungen dünnster Schichten und Fragen der Strukluraufklärung, der chemischen Bindungen bzw. Bindungskonfigurationen diskutiert. 相似文献
163.
Klaus D. Wutzke Kerstin V. Schmidek 《Isotopes in environmental and health studies》2017,53(6):553-562
A resistant starch (RS) mixture (MIX) consisting of fibre of potatoes (FP) and wrinkled pea starch (WPS), and high amylose maize starch (HAMS) were supplemented in adults to evaluate their effects on fat oxidation by means of a 13CO2-breath test. Sixteen subjects received a regular diet either without or with the supplementation of MIX and HAMS in randomised order. After administration of a [U-13C]algal lipid mixture, exhaled air was collected over 14?h in 0.5- and 1-h intervals. The 13C abundances were measured by nondispersive infrared spectroscopy. In comparison to the dry run (DR), supplementation with MIX and with HAMS increased the cumulative percentage dose recovery: (DR: 16.7?%, MIX: 16.9?%, HAMS: 18.0?%), but without statistical significance. The colonic degradation of MIX and HAMS to short-chain fatty acids tends to lower the formation of carbohydrate-derived acetyl-CoA and contributes to a postprandial lipid oxidation increase by using fat-derived acetyl-CoA as a compensatory fuel source. 相似文献
164.
165.
Philippe Négrel Emmanuelle Petelet-Giraud 《Trends in analytical chemistry : TRAC》2011,30(8):1279-1290
Isotopes of the water molecule (δ18O and δ2H) are a well-used tool for investigating groundwater origin and history (i.e. tracing the recharge conditions over time, processes occurring during infiltration of rainwater towards aquifers and those involved in the water-rock interaction, and mixing of different waters).This review covers several large European aquifers (Portugal, France, UK, Switzerland, Germany, Hungary, and Poland), which were investigated in terms of their recharge conditions, and the story of the groundwater at a large scale, involving recent, Holocene and Pleistocene components and their eventual mixing. 相似文献
166.
Roy E. Hoffman Noach Treitel Mordecai Rabinovitz 《Magnetic resonance in chemistry : MRC》2001,39(8):489-494
Isotope shifts are a well-established tool for structural analysis by NMR. The substitution of a protium with a deuterium is the most widely studied of these effects. However, such studies call for specific deuteration that requires complex synthetic techniques owing to the low natural abundance of deuterium. 13C occurs at a higher natural abundance and couples strongly with its attached proton. We have developed and refined a method to reliably observe these much smaller shifts without needing to resort to chemical synthesis. We show that carbon induced isotope shifts reflect structural features. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
167.
Yu. Yu. Morzherin M. Yu. Kolobov V. S. Mokrushin M. Brauer E. Anders V. A. Bakulev 《Chemistry of Heterocyclic Compounds》2000,36(1):22-36
A series of N-alkyl- and N-aryl-2-cyano-2-diazoacetamides was synthesized by the reaction of 2-amino-2-cyanoacetamides with sodium nitrite in hydrochloric acid. The mechanism of their heteroclectrocyclization to 5-hydroxy-1,2,3-triazoles was investigated kinetically and theoretically by the B3LYP/6-31+G* method. The conclusion was made on the basis of the determined activation energy of the cyclization process. reaction parameters , and kinetic isotope effects, that there is a difference between the mechanisms of cyclization of the N-alkyl and N-aryl derivatives of 2-cyano-2-diazoacetamide; cyclization of the N-alkyl derivatives takes place by a monorotatory mechanism, while cyclization of the N-aryl derivatives takes place by a mechanism where one of the stages is heteroelectrocyclization of 2-diazoacetimidates.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 26–41, January, 2000. 相似文献
168.
Influence of ion-molecular reactions on μ-capture in hydrogen and on fusion in 3Hedμ muonic molecule
The de-excitation processes (J=1)→ (J=0) in muonic molecular ions (ppμ)+ and (3Hedμ)+ are studied. It is shown that the rate of such transitions substantially depends on the chain of ion-molecular reactions
initiated by positively charged muonic ions.
The probabilities of ortho-para transition in the [(ppμ)+H2] and [(ppμ)+e] complexes formed as a result of chemical reactions in the pure hydrogen were estimated.
Taking into account the ion-molecular processes in D2 + He mixtures, the evaluation of the observed rate λf of nuclear fusion in the 3Hedμ muonic molecules was performed. The expected yield of fusion reactions per muon at the mixture density φ=0.1 and concentration
C
He
=0.05 was obtained to be equal to
.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
169.
T. Matsuo T. Maekawa A. Inaba O. Yamamuro M. Ohama M. Ichikawa T. Tsuchida 《Journal of Molecular Structure》2006,790(1-3):129
The heat capacities of HCrO2 and DCrO2 have been measured at temperatures between 5 and 360 K. A lambda anomaly occurred at 320 K for DCrO2 but not for HCrO2. Infrared spectra were recorded at temperatures between 5 and 405 K. The spectrum of DCrO2 changed at 320 K with respect to the peak wave-number and splitting of some of the vibrations, while those of HCrO2 depended smoothly on temperature. These experimental results are discussed in terms of a deuteration-induced phase transition. 相似文献
170.