Oxygen isotope effect on the superconductivity and stripe phase in La1.6−x_{1.6-x}Nd0.4_{0.4}Srx_{x}CuO4_4

The oxygen isotope effect on the superconductivity, stripe phase and structure transition is systematically investigated in La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_4$ with static stripe phase. Substitution of $^{16}$O by $^{18}$O leads to a decrease in superconducting transition temperature T$_C$, while enhances the temperature of the structural transition from low-temperature-orthorhombic (LTO) phase to low-temperature-tetragonal (LTT) phase. Compared to the Nd free sample, a larger isotope effect on $T_C$ is observed in La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_4$. These results indicate that the distortion of CuO$_2$ plane suppresses the superconductivity, giving a direct evidence for the competing of stripe phase and superconductivity because the distortion of CuO$_2$ plane enhances the stripe phase.Comment: 4 pages, 5 figure

Isotopes in hydrology and hydrogeology

The structure, status, and processes of the groundwater system, which can only be acquired through scientific research efforts, are critical aspects of water resource management. Isotope hydrology and hydrogeology is a genuinely interdisciplinary science. It developed from the application of methods evolved in physics (analytical techniques) to problems of Earth and the environmental sciences since around the 1950s. In this regard, starting from hydrogeochemical data, stable and radioactive isotope data provide essential tools in support of water resource management. The inventory of stable isotopes, which has significant implications for water resources management, has grown in recent years. Methodologies based on the use of isotopes in a full spectrum of hydrological problems encountered in water resource assessment, development, and management activities are already scientifically established and are an integral part of many water resource investigations and environmental studies. The driving force behind this Special Issue was the need to point the hydrological and water resource management societies in the direction of up-to-date research and best practices

Stable isotopic labeling in proteomics

Labeling of proteins and peptides with stable heavy isotopes (deuterium, carbon-13, nitrogen-15, and oxygen-18) is widely used in quantitative proteomics. These are either incorporated metabolically in cells and small organisms, or postmetabolically in proteins and peptides by chemical or enzymatic reactions. Only upon measurement with mass spectrometers holding sufficient resolution, light, and heavy labeled peptide ions or reporter peptide fragment ions segregate and their intensity values are subsequently used for quantification. Targeted use of these labels or mass tags further leads to specific monitoring of diverse aspects of dynamic proteomes. In this review article, commonly used isotope labeling strategies are described, both for quantitative differential protein profiling and for targeted analysis of protein modifications

Isotope analysis of water by means of near-infrared dual-wavelength diode laser spectroscopy

A novel diode laser spectrometer was developed using dual-wavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water. A 1.4-µm diode laser probed a H16OH/HO2H line pair near 7198 cm-1, while a similar laser observed H16OH, H17OH, and H18OH ro-vibrational lines around 7183 cm-1, or a H16OH/H18OH line pair near 7200 cm–1. The 1-σ standard deviation is 0.2‰ for 18O/16O, and 0.5‰ for the 2H/1H and 17O/16O isotope ratios. Preliminary experiments with repeated injections of a natural abundance sample point to an accuracy of about 1‰ for all three isotope ratios in natural samples.

Stable and Clumped Isotope Characterization of Authigenic Carbonates in Methane Cold Seep Environments

Cold seep environments are characterized by methane-rich fluid migration and discharge at the seafloor. These environments are also intimately linked to microbial communities, which oxidize methane anaerobically, increase alkalinity and promote authigenic carbonate precipitation. We have analyzed a suite of methane-derived authigenic carbonate (MDAC) crusts from the North and Barents Sea using stable and clumped isotopes (δ¹³C, δ¹⁸O, δ⁴⁴Ca, and Δ₄₇) to characterize the sources of fluids as well as the environment of carbonate authigenesis. We additionally assess the potential of MDACs as a Δ₄₇-based paleotemperature archive. The MDACs occur as three main textural-mineralogic types: micritic Mg-calcite cements, micritic aragonite cements and cavity filling aragonite cements. We find that micritic Mg-calcite cements have low δ¹³C_(VPDB) values (−30 to −47‰), high δ⁴⁴Ca_(SW) values (−0.4 to −0.8‰), and Δ₄₇-temperatures (0–6 °C) consistent with shallow sub-seafloor precipitation in isotopic equilibrium. Micritic aragonite cements and cavity filling aragonite cements both have a wider range in δ¹³C_(VPDB) values (−18 to −58‰), lower δ⁴⁴Ca_(SW) values (−0.8 to −1.6‰) and a larger range in Δ₄₇-based apparent temperatures (–2 – 25 °C) with samples displaying equilibrium and disequilibrium clumped isotope values. The range in apparent temperatures as well as δ⁴⁴Ca_(SW) values seen in the aragonite MDACs suggest two kinetic processes: a kinetic isotope effect (KIE) due to the incomplete equilibration of carbon and oxygen isotopes among DIC species from the different sources of DIC (i.e., seawater, methane-sourced DIC and DIC residual to CO₂ degassing or diffusion) and a KIE due to a fast, irreversible precipitation affecting the cations, particularly Ca, bound to carbonate mineral. Our results improve the understanding of kinetic effects on clumped isotope temperatures in MDACs and demonstrate how the multi-isotopic approach combined with textural-mineralogic criteria can be used to identify MDACs for accurate paleotemperature reconstructions

Surface enhancement of oxygen exchange and diffusion in the ionic conductor La2Mo2O9

Isotopic surface oxygen exchange and its subsequent diffusion have been measured using secondary ion mass spectrometry in the fast ionic conductor La2Mo2O9. A silver coating was applied to the sample surface to enhance the surface exchange process for dry oxygen. Contrary to previous studies performed using a wet atmosphere, no grain boundary diffusion tail was observed under these optimized dry exchange conditions. The activation energy for oxygen diffusion was found to be 0.66(+/- 0.09) eV at high temperature (>570 degrees C), and 1.25(+/- 0.01)eV at low temperature (<570 degrees C). Time-of-Flight secondary ion mass spectrometry was employed to investigate the correlation between the silver coating and the O-18 concentration on the sample surface. A close correlation between the presence of silver and oxygen incorporation on the surface was observed. (C) 2010 Elsevier B.V. All rights reserved

Mass transport and electrochemical properties of La2Mo2O9 as a fast ionic conductor

La2Mo2O9, as a new fast ionic conductor, has been investigated widely due to its high ionic conductivity which is comparable to those of the commercialized materials. However, little work has been reported on the oxygen transport and diffusion in this candidate electrolyte material. The main purpose of this project was to investigate oxide ion diffusion in La2Mo2O9 and also the factors which could affect oxygen transport properties. Oxygen isotope exchange followed by Secondary Ion Mass Spectrometry (SIMS) measurements were employed to obtain oxygen diffusion profiles. A correlation between oxygen ion transport and the electrochemical properties such as ionic conductivity was built upon the Nernst Einstein equation relating the diffusivity to electrical conductivity. In-situ neutron diffraction and AC impedance measurements were designed and conducted to investigate the correlation between crystal structure and oxygen transport in the bulk materials. Other techniques, such as synthesis, microstructure studies, and thermal analysis were also adopted to study the electrochemical properties of La2Mo2O9. The results of the study on the effects of microstructure on oxygen diffusion in La2Mo2O9 revealed that the grain boundary component played a significant role in electrochemical performance, although the grain size seemed to have little influence on oxygen transport. The oxygen isotope exchange in 18O2 was successfully carried out by introducing a silver coating on the sample surface, which solved the main difficulty in applying oxygen isotope exchange on pure ionic conductors. The ionic conductivity obtained from the diffusion coefficients was consistent with the result from AC impedance spectroscopy. The number of mobile oxygen ions was estimated to be 5 per unit cell. There was a difference of oxygen self diffusion coefficient when the isotope exchange was conducted in 18O2 and H2 18O. The activation energy of oxygen diffusion in humidified atmosphere was higher than that measured in dry atmosphere. It indicated that the humidified atmosphere had affected oxygen transport in the material. The studies on hydroxyl incorporation and transport explained the decreased oxygen diffusion coefficients in wet atmosphere and also suggested proton conductivity in La2Mo2O9, which leads to further investigation on applications of La2Mo2O9 as a proton conductor. In-situ neutron diffraction and AC impedance measurement revealed a close relationship between crystal structure and ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future

Ocean acidification in the aftermath of the Marinoan glaciation

Boron isotope patterns preserved in cap carbonates deposited in the aftermath of the younger Cryogenian (Marinoan, ca. 635 Ma) glaciation confirm a temporary ocean acidification event on the continental margin of the southern Congo craton, Namibia. To test the significance of this acidification event and reconstruct Earth’s global seawater pH states at the Cryogenian-Ediacaran transition, we present a new boron isotope data set recorded in cap carbonates deposited on the Yangtze Platform in south China and on the Karatau microcontinent in Kazakhstan. Our compiled δ11B data reveal similar ocean pH patterns for all investigated cratons and confirm the presence of a global and synchronous ocean acidification event during the Marinoan deglacial period, compatible with elevated postglacial pCO2 concentrations. Differences in the details of the ocean acidification event point to regional distinctions in the buffering capacity of Ediacaran seawater