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1.
Various laboratory techniques have been utilized worldwide for measuring lead-210 in sub-recent deposits through its grand-daughter product polonium-210. Isotope dilution alpha spectrometry proved a suitable tool for absolute determination of lead-210 for the dating of aquatic deposits. Moreover, isotope dilution alpha spectrometry along with speciation experiments can be used to resolve depositional anomalies arising from supported lead-210/Ra-226 disequilibrium levels and unsupported lead-210 mobile fractions. Isotope dilution alpha spectrometry of sub-recent sediment and peat deposits has been critically evaluated for more than ten years. Our results show that type, size and composition of deposits analyzed as well as radiochemical procedures used, together with alpha counting techniques, are important factors influencing lead-210 determinations and tailing corrections using its granddaughter product polonium-210. Optimization of these parameters is of prime importance to achieve economic and accurate analyses, especially at low lead-210 concentrations and small sample sizes. 相似文献
2.
Photosynthetic characteristics, specific leaf mass, chlorophyll and total leaf nitrogen concentrations of four herbaceous
plants (Dicranopteris linearis, Hanguana malayana, Pentaphragma ellipticum, Tacca integrifolia) from nutrient-poor tropical
forests showed that all these plants were well-adapted to their natural growth environments. No photoinhibition was observed
even in the understorey plants.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
4.
《Journal of biomechanics》2014,47(16):3862-3867
The aim of this study was to test the hypothesis that running at fixed fractions of Froude (Nfr) and Strouhal (Str) dimensionless numbers combinations induce dynamic similarity between humans of different sizes. Nineteen subjects ran in three experimental conditions, (i) constant speed, (ii) similar speed (Nfr) and (iii) similar speed and similar step frequency (Nfr and Str combination). In addition to anthropometric data, temporal, kinematic and kinetic parameters were assessed at each stage to measure dynamic similarity informed by dimensional scale factors and by the decrease of dimensionless mechanical parameter variability. Over a total of 54 dynamic parameters, dynamic similarity from scale factors was met for 16 (mean r=0.51), 32 (mean r=0.49) and 52 (mean r=0.60) parameters in the first, the second and the third experimental conditions, respectively. The variability of the dimensionless preceding parameters was lower in the third condition than in the others. This study shows that the combination of Nfr and Str, computed from the dimensionless energy ratio at the center of gravity (Modela-r) ensures dynamic similarity between different-sized subjects. The relevance of using similar experimental conditions to compare mechanical dimensionless parameters is also proved and will highlight the study of running techniques, or equipment, and will allow the identification of abnormal and pathogenic running patterns. Modela-r may be adapted to study other abilities requiring bounces in human or animal locomotion or to conduct investigations in comparative biomechanics. 相似文献
5.
6.
A. Lapolla C. Gerhardinger L. Baldo D. Fedele A. Keane R. Seraglia S. Catinella P. Traldi 《生物化学与生物物理学报:疾病的分子基础》1993,1225(1):33-38
The number of glucose molecules condensed on glycated bovine serum albumin have been easily determined by means of matrix-assisted laser desorption/ionization mass spectrometry. Measurements were carried out on samples from incubation of the proteins with glucose at different concentrations (0.02 M, 0.2 M, 2 M and 5 M). A clear increase in molecular mass of BSA with respect to incubation time is detected. In contrast to what is observed with fluorescence, the plots of molecular mass increase vs. incubation time show tha occurrence of a steady state, corresponding to the complete saturation of all the protein sites against glucose. Comparison of fluorescence and molecular mass data reveals that some further reactions, different from condensation, must take place, which could be in principle either intramolecular or originated by reactivity of modified condensed gluocse moieties vs. free glucose. 相似文献
7.
E. S. Jensen 《Plant and Soil》1991,133(1):83-92
Simultaneous determination of 15N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of 15N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated 15N analysis showed that the recovery of inorganic N in the NH3 trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO3
- and the NH4
+ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO3
- or NH4
+ alone, but can be used for combined diffusion of the two ions. 相似文献
8.
Mass and energy exchange between the atmosphere and leaf influence gas pressurization in aquatic plants 总被引:1,自引:0,他引:1
S. L. STEINBERG 《The New phytologist》1996,134(4):587-599
9.
Cation export from Alaskan arctic watersheds 总被引:1,自引:1,他引:0
Jeffrey C. Cornwell 《Hydrobiologia》1992,240(1-3):15-22
The concentrations and stream fluxes of Na, K, Ca and Mg were determined in 1978, 1980 and 1981 in the Toolik Lake watershed
and in 1978 in the upper Kuparuk River watershed. The annual export of K was strongly influenced by high K concentrations
at the initiation of spring melt. Potassium concentrations were positively correlated with concentrations of particulate and
dissolved organic carbon, particulate and dissolved phosphorus, and particulate, dissolved organic and ammonium nitrogen,
suggesting a common origin in the decomposition of tundra plants. Calcium and Mg stream concentrations were generally highest
in July and August when the depth of the soil active layer reached a maximum of ∼ 0.5 m. Precipitation-derived Na and K accounted
for up to half of the Na and K stream export while chemical weathering supplied > 85 % of exported Ca and Mg. Cation export
rates in these arctic foothill watersheds are among the lowest recorded. 相似文献
10.