Search results for "ISOTOPE"
showing 10 items of 2232 documents
Extensive Evaluation of a Diffusion Denuder Technique for the Quantification of Atmospheric Stable and Radioactive Molecular Iodine
2010
In this paper we present the evaluation and optimization of a new approach for the quantification of gaseous molecular iodine (I(2)) for laboratory- and field-based studies and its novel application for the measurement of radioactive molecular iodine. alpha-Cyclodextrin (alpha-CD) in combination with (129)I(-) is shown to be an effective denuder coating for the sampling of gaseous I(2) by the formation of an inclusion complex. The entrapped (127)I(2) together with the (129)I(-) spike in the coating is then released and derivatized to 4-iodo-N,N-dimethylaniline (4-I-DMA) for gas chromatography-mass spectrometry (GC-MS) analysis. The (127)I(2) collected can be differentiated from the (129)I(-…
Plasticity in the trophic niche of an invasive ant explains establishment success and long‐term coexistence
2021
Invasive species are one of the main threats to biodiversity worldwide and the processes enabling their establishment and persistence remain poorly understood. In generalist consumers, plasticity in diet and trophic niche may play a crucial role in invasion success. There is growing evidence that invasive ants, in particular, occupy lower trophic levels in their introduced range compared to the native one, but evidences remain fragmented. We conducted stable isotope analysis at five locations distributed on two continents to infer the trophic position of the invasive ant Formica paralugubris in the native and introduced part of the range. This species forms large colonies and can be a vorac…
First determination of β-delayed multiple neutron emission beyond A = 100 through direct neutron measurement : The P2n value of 136Sb
2018
Background: β-delayed multiple neutron emission has been observed for some nuclei with A≤100, being the Rb100 the heaviest β2n emitter measured to date. So far, only 25P2n values have been determined for the ≈300 nuclei that may decay in this way. Accordingly, it is of interest to measure P2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A>100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of a…
The Origins of Northern European Autographa Gamma Individuals Evaluated Using Hydrogen Stable Isotopes
2018
1. Many insect species are migratory. As the spring progresses, adults gradually depart from their over‐wintering habitats and arrive in northern zones where they reproduce during the summer. Understanding this transgenerational and highly adaptive migratory behaviour is crucial when interpreting life cycle dynamics of many insect pests. 2. Origins of migratory silver Y moths, Autographa gamma (Linnaeus, 1758), captured from Finland, were studied with stable hydrogen analysis of their wings (δ2Hw). 3. The difference between spring and autumn generation δ2Hw values indicate different geographical natal origins. The probability surface map shows that the spring generation probably emerged in …
Trophic role of marbled crayfish in a lentic freshwater ecosystem
2019
Species’ introductions may cause severe adverse effects on freshwater ecosystems and their biota. The marbled crayfish, Procambarus virginalis Lyko, 2017, is an invasive parthenogenetically reproducing crayfish with rapid reproduction, maturation and tolerance to a wide range of environmental conditions, which was introduced to many sites across Europe during the last decade. Due to its recent speciation and limited number of field studies, the knowledge of trophic interactions of the marbled crayfish in freshwater food webs is scarce. An invaded area located in Central Europe was studied to identify the marbled crayfish food web interactions using analysis of carbon 13 C and nitrogen 15N i…
Invasive catfish in northern Italy and their impacts on waterbirds
2022
Predatory fish have occasionally been observed preying on birds, sometimes repeatedly, but few studies were able to unravel the overall significance of avian prey in fish diet and the predation impacts on bird populations. We used a control/impact study setup, using a Nature Reserve in northern Italy and a nearby control area, to determine: 1) the contribution of waterbirds to wels catfish diet in the Reserve, 2) the population density of wels catfish in the Reserve and control area and 3) the potential impacts of waterbird depredation by wels catfish on waterbird population trends. Our stable isotope Bayesian mixing model indicated that birds contributed 12.2% (5–27.9%, 50% confidence inte…
Gulf of Maine shells reveal changes in seawater temperature seasonality during the Medieval Climate Anomaly and the Little Ice Age
2011
article i nfo In this study, we use subannually resolved oxygen isotope values of fossil (dead-collected) and modern (live- caught) bivalve shells (Arctica islandica L.) from the northwestern Atlantic (Gulf of Maine, USA) to reconstruct past seasonal changes in seawater temperature. Our results indicate decreased seasonal temperature amplitude of about 1.6 °C (or ∼21%) during Medieval times (ca. AD 1033-1062) compared to shells from the early Little Ice Age (ca. AD 1321-1391) and during the late 19th century (AD 1864-1886). Additionally, seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the Gulf of Maine during the 11th century compared to summers and …
Biotic methylation of mercury by intestinal and sulfate-reducing bacteria and their potential role in mercury accumulation in the tissue of the soil-…
2014
Abstract Monomethylmercury as one of the most toxic mercury species influences the health and development of higher organisms and tends to accumulate in the tissue of animals and humans. The aim of this study was to explore the mercury methylating capability of (1) intestinal microbiota of the soil-living earthworm Eisenia foetida (E. foetida) and (2) intestinal sulfate reducing-bacteria in pure cultures. After exposing animals to inorganic mercury chloride (4 mg kg−1 Hg2+) in soil and sterile soil for ten days, the amount of methylmercury in tissue was measured. Despite sterilization of soil, the accumulation of the organic mercury species in tissue was 51 ng g−1. To elucidate the potentia…
Sclerochronology and geochemical variation in limpet shells (Patella vulgata): A new archive to reconstruct coastal sea surface temperature
2007
[1] Climate archives contained in shells of the European limpet, Patella vulgata, accumulated in archaeological deposits can potentially provide much needed information about Holocene environmental change in midlatitude coastal areas. Before reconstructing climate information preserved in these zooarchaeological records, we studied the controls on oxygen and carbon isotope ratios (δ18O and δ13C, respectively) in modern specimens. We tested the hypothesis that P. vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing δ18OSHELL with predicted values. Predicted δ18OSHELL was constructed using observed sea surface temperature (SST) records and the equilibrium…
On Transition Structures for Hydride Transfer Step: A Theoretical Study of the Reaction Catalyzed by Dihydrofolate Reductase Enzyme
1996
Abstract A theoretical study is presented of the catalytic mechanism of dihydrofolate reductase (DHFR) enzyme based upon the characterization of the transition structure (TS) for the hydride transfer step. Analytical gradients at AM1 and PM3 semiempirical levels have been used to characterize the saddle point of index one (SPi-1) on global energy hypersurface for the hydride transfer in the active site of DHFR enzyme. The geometry, stereochemistry, electronic structure, and transition vector (TV) components associated to SPi-1 are qualitatively computational level independent. The TV amplitudes show primary and secondary isotope effects to be strongly coupled. The geometrical arrangement of…