Search results for "ISOTOPES"
showing 10 items of 1216 documents
Preservation of successive diagenetic stages in Middle Triassic bonebeds: Evidence from in situ trace element and strontium isotope analysis of verte…
2015
Abstract Bonebeds comprise reworked and time averaged constituents of different phosphatic vertebrate remains and, hence, provide an ideal substrate for the study of long and short term diagenetic processes. To test whether trace elements (U, Sr, REE) and 87 Sr/ 86 Sr ratios can be used for distinguishing between successive diagenetic signals, we performed geochemical analyses on vertebrate remains (bones, teeth, scales and coprolites) from two Triassic bonebeds located near Palzem (Germany). Trace element analysis was done on 170 vertebrate remains by LA-ICP-MS while 87 Sr/ 86 Sr ratios were determined for 39 bioclasts using LA-MC-ICP-MS. Although a low inter- and intra-bioclast REE variab…
MRI using hyperpolarized noble gases.
1998
The aim of this study was to review the physical basis of MRI using hyperpolarized noble gases as well as the present status of preclinical and clinical applications. Non-radioactive noble gases with a nuclear spin 1/2 (He-3, Xe-129) can be hyperpolarized by optical pumping. Polarization is transferred from circularly polarized laser light to the noble-gas atoms via alkali-metal vapors (spin exchange) or metastable atoms (metastability exchange). Hyperpolarization results in a non-equilibrium polarization five orders of magnitude higher than the Boltzmann equilibrium compensating for the several 1000 times lower density of noble gases as compared with liquid state hydrogen concentrations in…
A standard calculation methodology for human doubly labeled water studies.
2021
Summary The doubly labeled water (DLW) method measures total energy expenditure (TEE) in free-living subjects. Several equations are used to convert isotopic data into TEE. Using the International Atomic Energy Agency (IAEA) DLW database (5,756 measurements of adults and children), we show considerable variability is introduced by different equations. The estimated rCO2 is sensitive to the dilution space ratio (DSR) of the two isotopes. Based on performance in validation studies, we propose a new equation based on a new estimate of the mean DSR. The DSR is lower at low body masses (<10 kg). Using data for 1,021 babies and infants, we show that the DSR varies non-linearly with body mass betw…
Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI.
2006
Purpose: To study the influence of admixing inert buffer gases to laser-polarized 3 He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods: The diffusion coefficient of 3 He was altered by admixing buffer gases of various molecular weights ( 4 He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laserpolarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted …
Late Turonian climate variability in the Bohemian Cretaceous Basin – A sclerochronological study of Inoceramus hercules shells from the Úpohlavy quar…
2020
Abstract The δ18O record of well-preserved shells of the inoceramid Inoceramus hercules from the Upohlavy working quarry (Czech Republic) provides an insight into the climate variability in the late Turonian benthic environment of the Bohemian Cretaceous Basin. Similar to modern bivalves, this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water. Due to the nearly year-round shell growth, sequentially sampled δ18O values allowed to estimate the narrowest sub-annual temperatures fluctuations that prevailed during lifetime of the organisms. In accordance with previous studies, reconstructed temperatures suggest colder water conditions (19.0 ± …
Screening for Bacillus thuringiensis Crystal Proteins Active against the Cabbage Looper, Trichoplusia ni
2000
Abstract Toxicity tests were performed to find among Cry1 and Cry2 Bacillus thuringiensis crystal proteins those with high activity against the cabbage looper. Tests were performed with neonate larvae on surface-contaminated artificial diet. The crystal proteins found to be toxic were, from higher to lower toxicity: Cry1Ac, Cry1Ab, Cry1C, Cry2Aa, Cry1J, and Cry1F (LC50 of 1.1–4.1, 3.4–4.4, 12, 34, 87, and 250 ng/cm2, respectively). Cry1B, Cry1D, and Cry1E can be considered nontoxic (LC50 higher than 2500 ng/cm2). Cry1Aa was moderately toxic to nontoxic, depending on the source (LC50 of 420 ng/cm2 from PGS and 8100 ng/cm2 from Ecogen). In vitro binding assays with trypsin-activated 125I-labe…
Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale.
2000
Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld corresponds to the Middle Eocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (European Land Mammal Age) Geiseltalian. In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By 40Ar/39Ar dating of the basalt, for the first time a direct numerical calibration mark for an Eocene European mammal locality has been established. The Eckfeld basalt inverse isochron date of 44.3 +/- 0.4 Ma suggests an age for the Geiseltalian/Robiacian boundary at 44 Ma and, together with the 1995 time scale of Berggren et al., a time…
230Th/U-dating of carbonate deposits from ancient aqueducts
2016
Abstract Carbonate deposits in aqueducts, known as calcareous sinter, can reach a considerable thickness and are commonly annually laminated. Environmental and palaeoclimate proxies measured in calcareous sinter samples, such as stable oxygen and carbon isotopes and trace elements, can provide important high-resolution information on hydrological conditions, temperature, and local precipitation in the catchment area of an aqueduct. In order to utilize the proxy data for palaeoclimate reconstruction, the sinter deposits must be dated by annual laminae counting and more precisely by 230 Th/U-dating. The major problem of 230 Th/U-dating of calcareous sinter in aqueducts is the relatively large…
CO2 degassing at La Solfatara volcano (Phlegrean Fields): Processes affecting and of soil CO2
2010
Abstract The soil CO2 degassing is affected by processes of isotope exchange and fractionation during transport across the soil, which can deeply modify the pristine isotope composition. This has been observed in the Solfatara volcano, upon a field survey of 110 points, where the CO2 flux was measured, together with temperature, CO2 concentration and oxygen and carbon isotopes within the soil. Furthermore, in some selected sites, the measurements were made at different depths, in order to analyze vertical gradients. Oxygen isotope composition appears controlled by exchange with soil water (either meteoric or fumarolic condensate), due to the fast kinetic of the isotopic equilibrium between …
Isotope shifts and hyperfine structure in the transitions of stable calcium isotopes and calcium-41
1998
Isotope shifts and hyperfine structure in the 4s2 1S0 → 4s4p 1P1 and 4s2 1S0 → 4s4d 1D2 transitions of calcium have been measured with high-precision laser spectroscopy. Calcium atoms in an atomic beam were excited with single-frequency cw dye and titanium sapphire lasers and then photoionized with the 363.8 nm or 514.5 nm line of an argon ion laser. The resulting ions were analyzed and detected with a quadrupole mass spectrometer. Isotope shifts for all stable calcium isotopes and the radionuclide 41Ca have been measured in both transitions. The corresponding field shift and specific mass shift coefficients as well as hyperfine structure constants for the isotopes 41, 43Ca have been derive…