摘要:

The protocols for13C and15NH. pyloritests stipulate that the diagnostic agent should be taken on an empty stomach. It is presumed that food intake prior to the tests leads to less reliable test results due to a prolongation of the gastric residence time of the diagnostic agent urea. This might allow the bacteria to split a higher proportion of urea, resulting in an increased number of false positives. 12 probands received 150mg [15N]urea and 75 mg sodium [13C]acetate in 75 ml orange juice as a test drink. [15N]Urea served as an agent to diagnose gastricH. pyloricolonization. The15N tests were evaluated using a urine sample of the second hour after test start. [13C]Acetate served as a marker of the gastric emptying of water-soluble food including the urea under the influence of food intake. Breath air samples were taken to calculate the gastric emptying half life (EHL) and the apparent resorption time (RT) of the urea. The double tests were carried out four times within four weeks using identical test protocols but different

ISSN:1025-6016    

DOI:10.1080/10256010008032936

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Investigations were carried out onVigna unguiculataL. Walp. to estimate the distribution and utilization of15N in different organs after stem injection during vegetative, flowering and pod filling stage. During flowering effects of water deficit were also examined. In well watered plants, within 4 days after injection, 65% of15N accumulated in leaves. This was drastically reduced to 42% by water deficit.15N accumulation in stems increased under water deficit. The translocation of15N from the stem base to roots were not altered by water deficit. During pod filling 62% of recovered15N in the plants had accumulated in seeds, 24% in leaves and 11% in stems within 4 days, whereas the uptake of nitrogen in pod walls and roots remained low (2%). These results demonstrate that the method of injecting very small quantities (1 mg/plant) of15N into the stem base allows an exact and detailed quantitative assessment of N translocation/distribution with regard to different organs, different growth stages and different treatments.

ISSN:1025-6016    

DOI:10.1080/10256010008032937

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Although molybdenum is considered to be an essential trace metal for humans, the knowledge about its metabolism is rather limited. The present study was aimed at the assessment of biokinetics following intravenous injection of trace amounts of95Mo or96Mo into five healthy volunteers. In a total of 11 investigations, the plasma clearance up to eight hours and the urinary excretion for at least three days after the injection were evaluated. The tracer concentrations were determined by proton nuclear activation analysis in blood plasma and by thermal ionization mass spectrometry in urine samples respectively. In all subjects, the plasma clearance is much faster than expected from the literature. The data obtained for the plasma clearance of the tracer can reasonably be fitted by a two exponential equation. The half times of the fast component range between 4 and 70 minutes and for the slow component between 3 and 30 hours. The urinary excretion of the injected tracer seems also to be faster than expected and the fractions lost are higher for larger doses administered. For the smallest dose given, 34% of the injected tracer were excreted within one day whereas for the four times larger dose about 60% were lost. These findings on urinary excretion are in agreement with recently published results.

ISSN:1025-6016    

DOI:10.1080/10256010008032938

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Equilibration technique suitable for a large amount ofsamples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-Smass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equliibration technique for small water samples size of between 0.05 and 5 ml was checked. For water samples smaller than 1ml, corresponding to a molar ratio [H2O]/[H2] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calcultion of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for smaples with large differences in δ18O and δD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.

ISSN:1025-6016    

DOI:10.1080/10256010008032939

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Much uncertainty still exists regarding spatial and temporal variability of stable isotope ratios (13C/12C and D/H) in different CH4-emission sources. Such variability is especially prevalent in freshwater wetlands where a range of processes can influence stable isotope compositions, resulting in variations of up to ∼50‰ for δ13C-CH4and ∼150‰ for δD-CH4values. Within a temperate-zone bog and marsh situated in southwestern Ontario, Canada, gas bubbles in pond sediments exhibit only minor seasonal and spatial variation in δ13C-CH4, δD-CH4and δ13C-CO2values. In pond sediments, CO2appears to be the main source of carbon during methanogenesis either directlyviaCO2reduction or indirectly through dissimilation of autotrophic acetate. In contrast, CH4production occurs primarilyviaacetate fermentation at shallow depths in peat soils adjacent to ponds at each wetland. At greater depths within soils, σCO2and H2O increasingly exert an influence on δ13C- and δD-CH4values. Secondary alteration processes (e.g., methanotrophy or diffusive transport) are unlikely to be responsible for depth-related changes in stable isotope values of CH4. Recent models that attempt to predict δD-CH4values in freshwater environments from D/H ratios in local precipitation do not adequately account for such changes with depth. Subenvironments (i.e., soil-forming and open water areas) in wetlands should be considered separately with respect to stable isotope signatures in CH4emission models.

ISSN:1025-6016    

DOI:10.1080/10256010008032940

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A sufficiently stable rate of13CO2exhalation is necessary when the diagnostic13CO2breath tests are performed in healthy subjects and patients. The aim of the research was to define prerequisite conditions for kinetic breath tests in order to ensure a stable13CO2background. A 3-part protocol was developed. Part I: a study of the one-day variation of13CO2abundance in expired CO2confirmed that shifts of the basal13C abundance in breath are inherent in nature. Part II: a study of the variations of13C enrichment after the ingestion of different meals and beverages showed that ingestion of food items containing C4plant sugars, such as maize, induces a significant increase in isotopic abundance. Part III: a new test breakfast containing rice grain cereal, milk and orange juice was tested. This test meal induces no significant change on the basal13CO2abundance in healthy subjects. This new finding allows to avoid the fasting period normally required prior to a breath test which is sometimes difficult for children and pregnant women.

ISSN:1025-6016    

DOI:10.1080/10256010008032941

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1025-6016    

DOI:10.1080/10256010008032935

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor