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31.
32.
Drew E. Latta Maxim I. Boyanov Kenneth M. Kemner Edward J. O’Loughlin Michelle M. Scherer 《Applied Geochemistry》2012
Structural Fe(II) has been shown to reduce several oxidized environmental contaminants, including NO3, chlorinated solvents, Cr(VI), and U(VI). Studies investigating reduction of U(VI) by soils and sediments, however, suggest that abiotic reduction of U(VI) by Fe(II) is not significant, and that direct enzymatic reduction of U(VI) by metal-reducing bacteria is required for U(VI) immobilization as U(IV). Here evidence is presented for abiotic reduction and immobilization of U(VI) by structural Fe(II) in a redoximorphic soil collected from a hillside spring in Iowa. Oxidation of Fe(II) in the soil after reaction with U(VI) was demonstrated by Mössbauer spectroscopy and reduction of U(VI) by the pasteurized soil using U LIII-edge X-ray absorption spectroscopy (XAS). XAS indicates that both reduced U(IV) and oxidized U(VI) or U(V) are present after U(VI) interaction with the Fe(II) containing soil. The EXAFS data show the presence of a non-uraninite U(IV) phase and evidence of the oxidized U(V) or U(VI) fraction being present as a non-uranyl species. Little U(VI) reduction is observed by soil that has been exposed to air and oxidation of Fe(II) to goethite has occurred. Soil characterization based on chemical extractions, Mössbauer spectroscopy, and Fe K-edge XAS indicate that the majority of Fe(II) in the soil is structural in nature, existing in clay minerals and possibly a green rust-like phase. These data provide compelling evidence for abiotic reduction of U(VI) by structural Fe(II) from soil near Fe-rich oxic–anoxic boundaries in natural environments. The work highlights the potential for abiotic reduction of U(VI) by Fe(II) in reduced, Fe-rich environments. 相似文献
33.
Forced imbibition was performed in reservoir sandstone by injecting water into a dry sample. The injection was monitored with X‐ray computed tomography and acoustic acquisition to simultaneously visualize the displacement of the fluid and quantify its presence by calculating saturation and P‐wave velocities. We observed a strong influence when changing the injection rates on the acoustic response. Upon decreasing the injection rate from 5 mL/h to 0.1 mL/h, P‐wave velocities decreased sharply: 100 m/s in 1 h. This behaviour is related to the partially saturated conditions of the sample (76% of saturation) before decreasing the injection rate. The air that is still trapped is free to move due to a decrease of pore pressure that is no longer forced by the higher injection rate. After 1 hour, P‐wave velocities started increasing with small changes in saturation. Stopping injection for 16 hrs decreased saturation by 8% and P‐wave velocities by 100 m/s. Restarting injection at 5 mL/h increased saturation to 76% while P‐wave velocities fluctuated considerably for 2 hrs until they stabilized at 2253 m/s. Through the computed tomography scans we observed a water front advancing through the sample and how its shape changed from a plane to a curve after decreasing the injection rate. 相似文献
34.
Calorific content was measured in 28 species of New Zealand macroalgae. Values ranged from 1.04 to 3.34 kcal g‐1 dry weight (wt), 3.03–5.18 kcal g‐1 ash‐free dry wt, and 0.13–1.75 kcal g‐1 wet wt. Seasonal variation in calorific content was measured in two of these species, Macrocystis pyrifera and Ulva lactuca, both of which showed clear changes in energy content over a 1‐year period. Factors affecting variation in calorific content between species and during the year are discussed, and the application of the current findings to ecological and aquacultural research on New Zealand seaweeds are considered. 相似文献
35.
The aim of this study was to investigate the effects of supercritical CO2 (scCO2) injection on the elastic and anelastic properties of sandstone at seismic and ultrasonic frequencies. We present the results of the low‐frequency and ultrasonic experiments conducted on water‐saturated sandstone (Donnybrook, Western Australia) flooded with scCO2. The sandstone was cut in the direction perpendicular to a formation bedding plane and tested in a Hoek triaxial pressure cell. During the experiments with scCO2, the low‐frequency and ultrasonic systems and the pump dispensing scCO2 were held at a temperature of 42°C. The elastic parameters obtained for the sandstone with scCO2 at seismic (0.1 Hz–100 Hz) and ultrasonic (~0.5 MHz) frequencies are very close to those for the dry rock. The extensional attenuation was also measured at seismic frequencies for the dry, water‐saturated, and scCO2‐injected sandstones. The applicability of Gassmann's fluid substitution theory to obtained results was also tested during the experiments. 相似文献
36.
Roman?Golowin Maxim?PortnyaginEmail author Kaj?Hoernle Alexander?Sobolev Dimitry?Kuzmin Reinhard?Werner 《Contributions to Mineralogy and Petrology》2017,172(11-12):104
High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20–25% of total melting with 8–10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb < 0.8, Zr/Y < 2, Ti/V < 12) and high-Cr-spinel compositions (Cr# > 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H2O contents (< 0.2 vs. > 2 wt% in boninites), ~ 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO2 (ΔQFM < + 0.2 vs. ΔQFM > + 0.2) and originated from deeper and hotter mantle (1.4–1.7 GPa, ~ 1440 °C vs. 0.8–1.0 GPa, ~ 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior. 相似文献
37.
Sara Auer Ilya Bindeman Paul Wallace Vera Ponomareva Maxim Portnyagin 《Contributions to Mineralogy and Petrology》2009,157(2):209-230
Klyuchevskoy volcano, in Kamchatka’s subduction zone, is one of the most active arc volcanoes in the world and contains some
of the highest δ18O values for olivines and basalts. We present an oxygen isotope and melt inclusion study of olivine phenocrysts in conjunction
with major and trace element analyses of 14C- and tephrochronologically-dated tephra layers and lavas spanning the eruptive history of Klyuchevskoy. Whole-rock and groundmass
analyses of tephra layers and lava samples demonstrate that both high-Mg (7–12.5 wt% MgO) and high-Al (17–19 wt% Al2O3, 3–6.5 wt% MgO) basalt and basaltic andesite erupted coevally from the central vent and flank cones. Individual and bulk
olivine δ18O range from normal MORB values of 5.1‰ to values as high as 7.6‰. Likewise, tephra and lava matrix glass have high-δ18O values of 5.8–8.1‰. High-Al basalts dominate volumetrically in Klyuchevskoy’s volcanic record and are mostly high in δ18O. High-δ18O olivines and more normal-δ18O olivines occur in both high-Mg and high-Al samples. Most olivines in either high-Al or high-Mg basalts are not in oxygen
isotopic equilibrium with their host glasses, and Δ18Oolivine–glass values are out of equilibrium by up to 1.5‰. Olivines are also out of Fe–Mg equilibrium with the host glasses, but to a lesser
extent. Water concentrations in olivine-hosted melt inclusions from five tephra samples range from 0.4 to 7.1 wt%. Melt inclusion
CO2 concentrations vary from below detection (<50 ppm) to 1,900 ppm. These values indicate depths of crystallization up to ~17
km (5 kbar). The variable H2O and CO2 concentrations likely reflect crystallization of olivine and entrapment of inclusions in ascending and degassing magma. Oxygen
isotope and Fe–Mg disequilibria together with melt inclusion data indicate that olivine was mixed and recycled between high-Al
and high-Mg basaltic melts and cumulates, and Fe–Mg and δ18O re-equilibration processes were incomplete. Major and trace elements in the variably high-δ18O olivines suggest a peridotite source for the parental magmas. Voluminous, highest in the world with respect to δ18O, and hydrous basic volcanism in Klyuchevskoy and other Central Kamchatka depression volcanoes is explained by a model in
which the ascending primitive melts that resulted from the hydrous melt fluxing of mantle wedge peridotite, interacted with
the shallow high-δ18O lithospheric mantle that had been extensively hydrated during earlier times when it was part of the Kamchatka forearc. Following
accretion of the Eastern Peninsula terrains several million years ago, a trench jump eastward caused the old forearc mantle
to be beneath the presently active arc. Variable interaction of ascending flux-melting-derived melts with this older, high-δ18O lithospheric mantle has produced mafic parental magmas with a spectrum of δ18O values. Differentiation of the higher δ18O parental magmas has created the volumetrically dominant high-Al basalt series. Both basalt types incessantly rise and mix
between themselves and with variable in δ18O cumulates within dynamic Klyuchevskoy magma plumbing system, causing biannual eruptions and heterogeneous magma products.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
38.
Fluid inclusion microthermometric data are often reported as homogenization temperature frequency histograms. Interpretation
of such histograms for a single fluid inclusion assemblage (FIA) of non-reequilibrated fluid inclusions is usually straightforward
and provides an accurate determination of the original density (Th) of that FIA. However, interpretation of such histograms for reequilibrated inclusions is more problematic. Decompression
experiments using synthetic inclusions in natural quartz and conducted at 2–5 kbar and 600–700 °C with a maximum internal
overpressure of 2 kbar indicate that histogram shape reflects the sample's P-T history. Our results further indicate that the mean, mode, range, standard deviation, extreme values, etc., all have a significance
with respect to the P-T history of the sample. Thus, a mound-shaped, unimodal histogram with low range is indicative of a nearly isochoric cooling
P-T path. A unimodal histogram that is slightly skewed to the right, and with a low standard deviation but high range, results
from inclusion deformation in the plastic regime (high temperature/low strain rates). Fluid inclusions deformed plastically
show no correlation between size and density. Histogram outliers should not be ignored and may be used to determine an isochore
that passes close to the conditions of entrapment (minimum Th) or close to the final reequilibration conditions (maximum Th). The histogram mean Th value corresponds to an isochore that represents the internal overpressure (about 1 kbar) that can be maintained over geologic
time by a majority of reequilibrated fluid inclusions. A multimodal histogram with high range and high standard deviation
indicates inclusion brittle deformation (low temperature/high strain environments). Fluid inclusions deformed in a brittle
manner show strong positive correlation between size and density. Histograms produced in the laboratory show many similarities
to histograms for natural samples, offering the hope that laboratory results may be used to interpret P-T histories of natural samples.
Received: 20 May 1997 / Accepted: 3 April 1998 相似文献
39.
Maxim Lyutikov 《Astrophysics and Space Science》1998,264(1-4):411-421
A theory of pulsar radio emission generation, in which the observed waves are produced directly by the maser-type plasma instabilities
on the anomalous cyclotron-Cherenkov resonance
and the Cherenkov-drift resonance
, is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the
interaction of the fast particles of the primary beam and from the tail of the distribution with the normal modes of a strongly
magnetized one-dimensional electron-positron plasma. The waves emitted at these resonances are vacuum-like electromagnetic
waves that may leave the magnetosphere directly. The cyclotron-Cherenkov instability is responsible for core emission pattern
and the Cherenkov-drift instability produces conal emission. The conditions for the development of the cyclotron-Cherenkov
instability are satisfied for the both typical and millisecond pulsars provided that the streaming energy of the bulk plasma
is not very high γ
p
= 5 ÷ 10. In a typical pulsar the cyclotron-Cherenkov and Cherenkov-drift resonances occur in the outer parts of magnetosphere
at r
res
≈ 109cm. This theory can account for various aspects of pulsar phenomenology including the morphology of the pulses, their polarization
properties and spectral behavior.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
40.
Maxim Lyutikov 《Monthly notices of the Royal Astronomical Society》1998,293(4):447-468
Normal modes of a one-dimensional relativistically streaming electron–positron plasma in a superstrong magnetic field are considered, taking into account possible different bulk velocities and thermal effects. This physical picture corresponds to the plasma present on the open field lines of rotating neutron stars where the observed radio emission is generated. Various cases are considered: relativistic and non-relativistic relative streaming of cold components, and relativistically hot distributions. A distinction between superluminous and subluminous waves (which can be excited by the Cherenkov effect) is clearly stated. In the low-frequency regime the Cherenkov and cyclotron two-stream instabilities occur. Polarization of the quasi-transverse modes changes from circular for the propagation along magnetic field lines to linear for angles of propagation larger than some critical angle that depends on the relative velocity of the plasma components. 相似文献