Search results for "ISOTOPE"

Determination of Trace Elements and Elemental Species Using Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

2012

Development of accurate mass spectrometric routine and reference methods for the determination of trace amounts of iridium and rhodium in photographi…

1999

For the determination of trace amounts of iridium and rhodium in photographic emulsions different sample treatment procedures were coupled with inductively coupled plasma mass spectrometry (ICP-MS) and, for iridium, also with negative thermal ionisation isotope dilution mass spectrometry (NTI-IDMS) and ICP-IDMS. IDMS determinations of iridium were carried out using an enriched 191Ir spike solution. Elimination of the silver matrix was established for both mass spectrometric methods, which prevents corresponding memory effects in the ICP-MS system and is essential for the formation of IrO2 - thermal ions, respectively. For NTI-MS measurements, the gelatine matrix of the emulsion must also be…

A penning trap for studying cluster ions

2008

We propose to use a Penning trap for spectroscopy of stored cluster ions. A similar device has been built for the purpose of mass measurements of short-lived nuclei produced at the on-line isotope separator ISOLDE/CERN. A resolving power of 500,000 in a mass measurement of39K and an accuracy of 2 × 10−7 for the85Rb/39K mass ratio were obtained. An efficiency for in-flight capture as high as 70% was achieved. The method provides very high sensitivity since typically only 10 to 100 ions are stored in the trap. We intend to perform laser spectroscopy on trapped Na clusters as a first application of the trap technique.

Acidification processes in a peritidal carbonate succession across the Triassic/Jurassic boundary (Sicily)

2017

For the first time, a correlation between biostratigraphic events and δ13C curve was attempted along an UpperTriassic-Lower Jurassic peritidal limestone succession cropping out in westernmost Sicily. The peritidal carbonates are organized in shallowing upward cycles characterized by subtidal skeletal mudstone to grainstone, intertidal microbial mats and supratidal paleosoils. About 300 meters of this succession covering the Triassic-Jurassic interval were studied in details. On the base of the macro- and microfossil assemblages from the subtidal facies, four informal units have been recognized along the studied section. Unit R1 (at the base, 111 m thick) is dominated by large megalodonts, r…

Solvent-trap reaction of triazolinediones with simple alkenes: An experimental/theoretical study of thermodynamic and kinetic parameters This work is…

2015

The reaction of N-phenyltriazolinedione with simple alkyl-substituted alkenes in a series of simple alcohols as nucleophilic solvents affords two products: a solvent-addition product (trap) and the ene adduct. Herein we present different experimental data which allow the estimation of different kinetic parameters (ΔΔH ≠ene,trap and ΔΔS ≠ene,trap ). The values of those parameters are found to be lower with a longer nucleophile-solvent molecule. Solvent isotope effects are also estimated and found in favour of the heavier (and smaller) deuterated compounds. Results from competition experiments in equimolar binary mixtures of different alcohols as solvents also point to the prevalence of the s…

Suppression of intestinal microbiota-dependent production of pro-atherogenic trimethylamine N-oxide by shifting L-carnitine microbial degradation.

2014

Abstract Aims Trimethylamine-N-oxide (TMAO) is produced in host liver from trimethylamine (TMA). TMAO and TMA share common dietary quaternary amine precursors, carnitine and choline, which are metabolized by the intestinal microbiota. TMAO recently has been linked to the pathogenesis of atherosclerosis and severity of cardiovascular diseases. We examined the effects of anti-atherosclerotic compound meldonium, an aza-analogue of carnitine bioprecursor gamma-butyrobetaine (GBB), on the availability of TMA and TMAO. Main methods Wistar rats received L-carnitine, GBB or choline alone or in combination with meldonium. Plasma, urine and rat small intestine perfusate samples were assayed for L-car…

Nitrogen stable isotopes as tracers of biodeposition from a tuna farm in the Western Mediterranean

2007

Regional variations in the chemical and helium–carbon isotope composition of geothermal fluids across Tunisia

2011

Abstract Tunisia has numerous thermo-mineral springs. Previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology. However little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations. Here, we report on the results of an extensive survey of both natural hot springs and production wells across Tunisia, aimed at investigating the spatial distribution of thermal fluids' geochemical characteristics and He–C isotopic composition. The chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in Tunisia, as a consequence of th…

Anthropogenic travertine between History, Archaeology and Environment: a geoarchaeological study of the Roman site of Jebel Oust, Tunisia.

2013

Travertine, known as lapis tiburtinus during Roman times, are continental limestones precipitated in calcareous environments from thermal waters of hot springs (travertine) or cool waters of karstic springs (calcareous tufa). This phenomenon is well-known during Classical Antiquity and had been described by several ancient authors (Strabo, Pliny the Elder, Vitruvius) who depicted a stone that forms extremely rapidly, a stone that outlines the landscape and which is largely used for construction (e.g. The Colosseum in Roma, the Greek temple at Segesta in Sicily). These deposits are widespread on Earth’s surface showing various morphologies and are great sedimentary records of climatic and hy…

Environmental and depositional controls on laminated freshwater carbonates: An example from the Roman aqueduct of Patara, Turkey

2013

Carbonate deposits in aqueducts are a new high-resolution data source for environmental changes during the time of the Roman Empire, notably in the fields of palaeoclimate and spring hydrology. In order to distinguish environmental effects from those related to depositional setting, laminated carbonate deposits were compared along the entire length of an ancient aqueduct channel at Patara, Turkey. The carbonate deposits, up to 80mm in thickness, are composed of lamina couplets up to 1mm thick of alternating porous microspar and dense, columnar sparite. The former formed in the dry, warm season and the latter in the wet, cool season. The presence of biofilms seems to play a role in the devel…