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Juvenile coho salmon, Onchorynchus kisutch, were exposed to 95mTc in both saltwater and freshwater to study the biokinetic behavior of this element in an anadromous fish. In freshwater, equilibrium whole-body concentration factors (CF5) ranged from 28 to 32 in two separate experiments, in sharp contrast to an equilibriumCF of < 5 in saltwater. While the uptake kinetics were unimodal in saltwater, in freshwater, biomodal uptake kinetics were observed.Technetium-95m retention was biphasic in freshwater depuration experiments, an initial rapid loss of 21% to 26% of the steady-state activity with an elimination half-life of 3 to 5 days was followed by a slower loss rate, with a whole-body elimination half-life ranging from 23 to 33 days. In saltwater, retention was monophasic with an elimination half-life of 5–16 days. Dramatic decreases in 95mTc body burdens when freshwater-labeled fish are transferred to Tc-labeled saltwater indicate that the changes in physiology accompanying saltwater acclimation lead to the loss of 95mTc. 相似文献
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Kevin L. Shelton Justin M. Beasley Jay M. Gregg Martin S. Appold Stephen F. Crowley James P. Hendry Ian D. Somerville 《Mineralium Deposita》2011,46(8):859-880
A newly discovered, extensive sphalerite-bearing breccia (~7.5 wt.% Zn) is hosted in dolomitised Carboniferous limestones
overlying Ordovician–Silurian metasedimentary rocks on the Isle of Man. Although base metal sulphide deposits have been mined
historically on the island, they are nearly all quartz vein deposits in the metamorphic basement. This study investigates
the origin of the unusual sphalerite breccia and its relationship to basement-hosted deposits, through a combination of petrographic,
cathodoluminescence, fluid inclusion, stable isotope and hydrogeologic modelling techniques. Breccia mineralisation comprises
four stages, marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry. In stage
I, high-temperature (T
h > 300°C), high-salinity (20–45 wt.% equiv. NaCl) fluid of likely basement origin deposited a discontinuous quartz vein. This
vein was subsequently dismembered during a major brecciation event. Stages II–IV are dominated by open-space filling sphalerite,
quartz and dolomite, respectively. Fluid inclusions in these minerals record temperatures of ~105–180°C and salinities of
~15–20 wt.% equiv. NaCl. The δ34S values of sphalerite (6.5–6.9‰ Vienna-Canyon Diablo troilite) are nearly identical to those of ore sulphides from mines
in the Lower Palaeozoic metamorphic rocks. The δ18O values for quartz and dolomite indicate two main fluid sources in the breccia’s hydrothermal system, local Carboniferous-hosted
brines (~0.5–6.0‰ Vienna standard mean ocean water) and basement-involved fluids (~5.5–11.5‰). Ore sulphide deposition in
the breccia is compatible with the introduction and cooling of a hot, basement-derived fluid that interacted with local sedimentary
brines. 相似文献
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M. A. Beasley R. M. Sharples T. J. Bridges D. A. Hanes S. E. Zepf K. M. Ashman D. Geisler 《Monthly notices of the Royal Astronomical Society》2000,318(4):1249-1263
We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately −1.6≤[Fe/H]≤0 dex. There is evidence of a radial metallicity gradient in the globular cluster system which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters has an age of 14.5±4 Gyr and the metal-rich population is 13.8±6 Gyr old. Monte Carlo simulations indicate that the globular cluster populations present in these data are older than 6 Gyr at the 95 per cent confidence level. We find that within the uncertainties, the globular clusters are old and coeval, implying that the bimodality seen in the broadband colours primarily reflects metallicity and not age differences. 相似文献
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An earlier work based on atmospheric input of 210Po to oceanic surface waters, in situ production from its radioactive precursors and its measured equilibrium concentration has shown that 210Po is removed from the upper mixed layer at a rapid rate, expressible by a turnover (or mean residence) time of 0.6 years. Since 210Po is known to be highly concentrated in numerous marine species, a method was devised to assess the importance of marine zooplankton in removing this radio-nuclide from the surface waters. Measurements of 210Po losses from living zooplankton lead to a rapid turnover time of the order of 0.9 years due to zooplankton metabolic activity alone. It is shown experimentally that fecal pellet deposition constitutes a major mechanism in transporting the radionuclide from surface to deeper waters. 相似文献
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Huib Jan Van Langevelde Ylva PihlstrÖm Anthony Beasley 《Astrophysics and Space Science》2005,295(1-2):249-255
Centaurus A, the nearest AGN shows molecular absorption in the millimeter and radio regime. By observing the absorption with VLBI, we try to constrain the distribution of the gas, in particular whether it resides in the circumnuclear region. Analysis of VLBA observations in four OH and two H2CO transitions is presented here, as well as molecular excitation models parameterized with distance from the AGN. We conclude that the gas is most likely associated with the tilted molecular ring structure observed before in molecular emission and IR continuum. The formaldehyde absorption shows small-scale absorption which requires a different distribution than the hydroxyl. 相似文献