By using updated stellar low-mass stars models, we systematically investigate the nucleosynthesis processes occurring in asymptotic giant branch (AGB) stars. In this paper, we present a database ...dedicated to the nucleosynthesis of AGB stars: FRANEC Repository of Updated Isotopic Tables & Yields (FRUITY). An interactive Web-based interface allows users to freely download the full (from H to Bi) isotopic composition, as it changes after each third dredge-up (TDU) episode and the stellar yields the models produce. A first set of AGB models, having masses in the range 1.5 <=M/M <= 3.0 and metallicities 1 X 10--3 <= Z <= 2 X 10--2, is discussed. For each model, a detailed description of the physical and the chemical evolution is provided. In particular, we illustrate the details of the s-process and we evaluate the theoretical uncertainties due to the parameterization adopted to model convection and mass loss. The resulting nucleosynthesis scenario is checked by comparing the theoretical hs/ls and Pb/hs ratios to those obtained from the available abundance analysis of s-enhanced stars. On the average, the variation with the metallicity of these spectroscopic indexes is well reproduced by theoretical models, although the predicted spread at a given metallicity is substantially smaller than the observed one. Possible explanations for such a difference are briefly discussed. An independent check of the TDU efficiency is provided by the C-stars luminosity function. Consequently, theoretical C-stars luminosity functions for the Galactic disk and the Magellanic Clouds have been derived. We generally find good agreement with observations.
The idea that solar system materials were irradiated by solar cosmic rays from the early Sun has long been suggested, but is still questionable. In this study, Sr, Ba, Ce, Nd, Sm, and Gd isotopic ...compositions of sequential acid leachates from the Kapoeta meteorite (howardite) were determined to find systematic and correlated variations in their isotopic abundances of proton-rich nuclei, leading to an understanding of the irradiation condition by cosmic rays. Significantly large excesses of proton-rich isotopes (p-isotopes), super(84)Sr, super(130)Ba, super(132)Ba, super(136)Ce, super(138)Ce, and super(144)Sm, were observed, particularly in the first chemical separate, which possibly leached out of the very shallow layer within a few mu m from the surface of regolith grains in the sample. The results reveal the production of p-isotopes through the interaction of solar cosmic rays with the superficial region of the regolith grains before the formation of the Kapoeta meteorite parent body, suggesting strong activity in the early Sun.
•First successful authenticating tea with different formulations based on multi-elemental stable isotope ratios.•The clustering results of HCA and PCA were worse than that of PLS-DA, BP-ANN.•LDA ...showed superior predictive ability than PLS-DA and BP-ANN models.•δ2H, δ18O, 98Mo/95Mo, 96Mo/95Mo, and 98Mo/96Mo were the markers.
In this work, the potential of C, N, H, O and mineral element stable isotope ratios and chemometric methods as a tool to first authenticate Chinese tea according to their blend raw materials was examined. Forty-four multi-elemental stable isotope ratios of four batches of Chongqing tuo tea (n = 27 for each batch) were determined by the EA-IRMS and ICP-MS methods. The clustering results of HCA and PCA were worse than that of PLS-DA, BP-ANN, and LDA. The PLS-DA model displayed good model performance (R2X = 0.57, R2Y = 0.74, and Q2 = 0.653). By BP-ANN, the total correct authentication rates for model training and external validation were 100% and 91.2%, respectively. The best performance was obtained by LDA, the total correct authentication rates for model training, cross-validation and external validation were 100%, 100% and 96.9%, respectively. δ2H, δ18O, 98Mo/95Mo, 96Mo/95Mo, and 98Mo/96Mo were markers for enabling the accurate authentication of Chongqing tuo tea according to formulas. This study has contributed toward generalizing the use of multi-elemental stable isotope ratio fingerprinting as a promising tool for testing the authenticity of tea worldwide.
We report the major element as well as the oxygen, magnesium, and silicon isotope composition of a unique presolar silicate grain found in the fine-grained fraction of the Antarctic CR2 chondrite ...Graves Nunataks 95229. The grain is characterized by an extremely high super(17)O/ super(16)O ratio (6.3 + or - 0.2 x 10 super(-3) relative to solar values, whereas its super(18)O/ super(16)O ratio is solar within measurement uncertainty. It also shows enrichments in super(25,26)Mg and a significant excess in super(30)Si relative to solar system compositions, with delta super(25)Mg = 79 + or - 21perthousand, delta super(26)Mg = 70 + or - 20perthousand, and delta super(30)Si = 379 + or - 92perthousand. This isotopic composition is consistent with an origin in the ejecta of a ~1.3-1.4 M sub(middot in center) ONe nova with large contributions of material from a main-sequence companion star of roughly solar metallicity. However, many details of the stellar source remain undetermined, owing to the uncertainties of current nova nucleosynthesis models. Auger electron spectroscopic analyses identify O, Mg, Si, and Fe as the grain's major constituents. Its (Mg + Fe)/Si atomic ratios are lower than that of olivine and correspond on average to Fe-Mg-pyroxene. A complex texture and heterogeneous major element distribution within the grain attest to condensation under non-equilibrium conditions, which is consistent with the proposed nova origin.
The ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change. However, relatively little is known about the spatiotemporal variability in the oceanic ...carbon cycle due to the lack of long-term, high-resolution dissolved inorganic carbon isotope (δ13CDIC) data, especially for the temperate North Atlantic, which is the major oceanic sink for anthropogenic CO2. Here, we report shell carbon isotope values (δ13Cshell), a potential proxy for δ13CDIC, of old-grown specimens of the long-lived bivalve mollusk, Arctica islandica. This paper presents the first absolutely dated, annually resolved δ13Cshell record from surface waters of the North Atlantic (Iceland, Gulf of Maine) covering the time interval between 1753 and 2003. According to our results, the δ13Cshell data were unaffected by trends related to ontogenetic age. However, the shell carbonate was precipitated with a constant offset from expected equilibrium by − 1.54 to − 2.7 ± 0.2‰ corresponding to a 6.2 to 10.8 ± 0.8% contribution of respiratory CO2 (− 25‰). The offset did not appear to vary through the lifetime of individual specimens and among specimens. Therefore, the δ13Cshell data of this species can very likely be used as a measure of δ13CDIC. Furthermore, shell stable carbon isotope chronologies exhibited habitat-specific differences and a significant inter-annual and decadal variability related to the natural carbon cycle. In addition, a distinct negative δ13Cshell shift was found reflecting the oceanic Suess effect, i.e. the admixture of anthropogenic CO2. However, this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic Polar Front in the Nordic Seas and a large-scale reorganization of atmospheric and oceanic currents in the North Atlantic. This likely resulted in a reduced admixture of cold Polar water onto the North Icelandic shelf (through the East Iceland Current) and the Gulf of Maine (through the Labrador Current) with an increased volume of warmer, isotopically well-equilibrated Atlantic waters. Our shell-based δ13CDIC proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the North Atlantic.
This study aims to characterize soil chemical properties and microbial biomass, greenhouse gas production, and organic matter dynamics in upland rice field as affected by the long-term fertilizer ...managements in Uganda. Soil total C (TC) and N (TN) contents were in the relatively smaller range under different fertilizer treatments, even after 20 crop seasons. However, available phosphate contents showed positive correlation with average yield of upland rice. Incubation experiments were conducted under aerobic or under flooding conditions to measure CO
2
, methane, and nitrous oxide productions. After the incubation, soil samples were extracted to quantify nitrification rate for aerobic condition and ammonification rate for flooding condition. Soil microbial biomass carbon (MBC) and nitrogen were measured. Stable isotope ratio of
13
C and
15
N were also determined for the soil samples. CO
2
production potential under aerobic condition was higher than the flooding condition. The qCO
2
(CO
2
/MBC) in the treatment applied with compost tended to be higher than the other treatments. Positive correlation between nitrous oxide production and nitrification was found. The delta
13
C values of the soil samples indicated that the effect of C4 plants before rice cultivation still remained, while the contribution of biological N
2
fixation was little according to delta
15
N values. These results indicate that soil microbial biomass in upland rice field of the long-term fertilizer experiment in Uganda was characterized with higher qCO
2
. Greenhouse gas production was affected by fertilizer management, while soil organic C before the long-term experiment still remained in the experiment.
The radical ion HCl+, a key intermediate in the chlorine chemistry of the interstellar gas, has been identified for the first time in the interstellar medium with the Herschel Space Observatory's ...Heterodyne Instrument for the Far-Infrared. The ground-state rotational transition of H super(35)Cl+, super(2)Pi sub(3/2)J = 5/2-3/2, showing Lambda-doubling and hyperfine structure, is detected in absorption toward the Galactic star-forming regions W31C (G10.6-0.4) and W49N. The complex interstellar absorption features are modeled by convolving in velocity space the opacity profiles of other molecular tracers toward the same sources with the fine and hyperfine structure of HCl+. This structure is derived from a combined analysis of optical data from the literature and new laboratory measurements of pure rotational transitions, reported in the accompanying Letter by Gupta et al. The models reproduce well the interstellar absorption, and the frequencies inferred from the astronomical observations are in exact agreement with those calculated using spectroscopic constants derived from the laboratory data. The detection of H super(37)Cl+ toward W31C, with a column density consistent with the expected super(35)Cl/ super(37)Cl isotopic ratio, provides additional evidence for the identification. A comparison with the chemically related molecules HCl and H sub(2)Cl+ yields an abundance ratio of unity with both species (HCl+ : H sub(2)Cl+ : HCl ~ 1). These observations also yield the unexpected result that HCl+ accounts for 3%-5% of the gas-phase chlorine toward W49N and W31C, values several times larger than the maximum fraction (~1%) predicted by chemical models.
We report the discovery of two supernova silica (SiO sub(2)) grains in the primitive carbonaceous chondrites LaPaZ 031117 and Grove Mountains 021710. Only five presolar silica grains have been ...previously reported from laboratory measurements but they all exhibit enrichments in super(17)O relative to solar, indicating origins in the envelopes of asymptotic giant branch stars. The two SiO sub(2) grains identified in this study are characterized by moderate enrichments in super(18)O relative to solar, indicating that they originated in Type II supernova ejecta. If compared to theoretical models, the oxygen isotopic compositions of these grains can be reproduced by mixing of different supernova zones. While both theoretical models of grain condensation and recent NASA Spitzer Space Telescope observations have suggested the presence of silica in supernova ejecta, no such grains had been identified, until now, in meteorites. The discovery of these two silica grains provides definitive evidence of the condensation of silica dust in supernova ejecta.
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