Search results for "Natural abundance"
showing 10 items of 16 documents
MATHEMATICAL MODELLING OF THE SPECTRAL LINE PROFILES IN THE HIGH-FREQUENCY DISCHARGE
1999
Abstract The paper is devoted to an estimation of the true profiles of spectral lines and equipment influence based on complex experimental line shape profiles in high-frequency discharge by means of a non-linear multiparameter chi-square fit. The self-absorption and energy transfer effects are taken into consideration. A good agreement with interferometric data from Hg and Hg–Cd high-frequency electrodeless lamps of both natural and isotopic abundance are achieved. The temperature of radiating atoms and the optical density for several lines are obtained as a function of the high-frequency oscillator working regime. The confidence regions, standard deviations and correlations of parameters …
Effect of cactus pear cultivation after Mediterranean maquis on soil carbon stock, δ13C spatial distribution and root turnover
2014
Abstract Mediterranean ecosystems are characterized by nearly complete replacement of natural vegetation by intensive croplands and orchards leading to strong soil degradation. Organic carbon is usually accumulated in soils under maquis leading to partial regeneration of fertility for future agricultural use. The aim of this work was to investigate the effect of land use change from maquis to agriculture on soil organic carbon (SOC) stock and its spatial distribution in a Mediterranean system. Three Mediterranean land use systems (seminatural vegetation, cactus pear crop and olive grove) were selected in Sicily and analysed for soil C stocks and their δ13C. Total SOC and δ13C were measured …
Turnover and availability of soil organic carbon under different Mediterranean land-uses as estimated by 13C natural abundance
2013
Summary Soil organic matter (SOM) is an important factor in ecosystem stability and productivity. This is especially the case for Mediterranean soils suffering from the impact of humans and degradation as well as harsh climatic conditions. We used the carbon (C) exchange resulting from C3-C4 and C4-C3 vegetation change under field conditions combined with incubations under controlled conditions to evaluate the turnover and availability of soil organic C under different land-uses. The 40-year succession of Hyparrenia hirta L. (C4 photosynthesis) after more than 85 years of olive (Olea europaea L.) tree (C3 photosynthesis) growth led to the exchange of 54% of soil organic C from C3 to C4 form…
2015
Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes (2H, 13C, 15N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea th…
Counting IndividualCa41Atoms with a Magneto-Optical Trap
2004
Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of $^{41}\mathrm{Ca}$ present in biomedical samples with isotopic abundance levels between ${10}^{\ensuremath{-}8}$ and ${10}^{\ensuremath{-}10}$. The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$. Within 1 h of observation time, its $3\mathrm{\text{\ensuremath{-}}}\ensuremath{\sigma}$ detection limit on the isotopic abundance of $^{41}\mathrm{Ca}$ reaches $4.5\ifmmode\times\else\texttimes\fi{}{10…
Competition for resources is ameliorated by niche differentiation between Solidago virgaurea life-history stages in the Arctic
2016
Aims Competition has been shown to modify the niche breadth of coexisting species, but within-species interactions have received little attention. Establishing small juvenile individuals and established, larger, sexually reproducing adult individuals represent two life-history stages within species. We investigated the nitrogen and carbon resource use of adult and juvenile individuals and similarity of symbiotic fungal community composition in these two plant life stages. We used the plant Solidago virgaurea growing in a simplified system in the low Arctic as model species. Methods Isotopic signatures (foliar δ15N and foliar δ13C) were analysed to characterize nitrogen acquisition and water…
Understanding the role of soil erosion on co2-c loss using (13)c isotopic signatures in abandoned Mediterranean agricultural land.
2016
Understanding soil water erosion processes is essential to evaluate the redistribution of soil organic carbon (SOC) within a landscape and is fundamental to assess the role of soil erosion in the global carbon (C) budget. The main aim of this study was to estimate the C redistribution and losses using (13)C natural abundance. Carbon losses in soil sediment, dissolved organic carbon (DOC) and CO2 emission were determined. Four bounded parallel plots were installed on a 10% slope. In the upper part of the plots, C3soil was replaced with C4soil. The SOC and δ(13)C were measured after 145.2mm rainfall in the upper (2m far from C4strip), middle (4m far from C4strip) lower (6m far from C4strip) t…
Approach to quantitative spectroscopy of atomic vapor in optical nanocells
2019
We present a method for recovery of narrow homogeneous spectral features out of a broad inhomogeneous overlapped profile based on second-derivative processing of the absorption spectra of alkali metal atomic vapor nanocells. The method is shown to preserve the frequency positions and amplitudes of spectral transitions, thus being applicable for quantitative spectroscopy. The proposed technique was successfully applied and tested for measurements of hyperfine splitting and atomic transition probabilities, development of an atomic frequency reference, determination of isotopic abundance, study of atom-surface interaction, and determination of magnetic-field-induced modification of atomic tran…
Ultratrace analysis of calcium with high isotopic selectivity by diodelaser resonance ionisation mass spectrometry
1997
A resonance ionisation mass spectrometer for the ultratrace determination of calcium isotopes is presented. It achieves high overall efficiency, ultra-high isotopic abundance sensitivity of more than 1010 and complete suppression of isobars. The system can be used for isotope ratio studies on stable and long-lived trace isotopes with the final goal of radiodating via 41Ca-determination. For the different applications optical one-, two- or three-step resonance excitation and subsequent ionisation is applied using simple and inexpensive diodelasers. Additional mass analysis is accomplished in a commercial quadrupole mass spectrometer. The experimental set-up and first results on synthetical a…
High-Resolution Stimulated Raman Spectroscopy and Analysis of the ν1 Stretching Band of GeD4
2007
The high-resolution stimulated Raman spectrum of the ν1 band of GeD4 with natural isotopic abundance germanium has been recorded. It has been analyzed as part of the ν1/ν3 stretching dyad. The ν1 and ν3 band centers have been deduced for all the isotopologues. Copyright © 2006 John Wiley & Sons, Ltd.