The role of surface heterogeneity in modelling the stable boundary layer     

A. McCabe  A. R. Brown 《Boundary-Layer Meteorology》2007,122(3):517-534

High-resolution numerical simulations are performed for three nights for each of two areas of the United Kingdom. Area-averaging techniques are then used to calculate effective stability functions for turbulence parametrizations in models using typical mesoscale and global spatial resolutions. Comparisons are made with parametrizations commonly used in numerical weather prediction models. The present results do not suggest that significant enhancement of the stability functions above 50 m is justified. Closer to the surface, more significant enhancement is observed in some regions. It is shown that the amount of enhancement is related to the variability of the orography.  相似文献   

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide   总被引：1，自引：0，他引：1  

Aaron J. Slowey  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2007,71(4):877-894

Methylmercury can accumulate in fish to concentrations unhealthy for humans and other predatory mammals. Most sources of mercury (Hg) emit inorganic species to the environment. Therefore, ecological harm occurs when inorganic Hg is converted to methylmercury. Sulfate- and iron-reducing bacteria (SRB and FeRB) methylate Hg, but the effects of processes involving oxidized and reduced forms of sulfur and iron on the reactivity of Hg, including the propensity of inorganic Hg to be methylated, are poorly understood. Under abiotic conditions, using a laboratory flow reactor, bisulfide (HS⁻) was added at 40 to 250 μM h⁻¹ to 5 g L⁻¹ goethite (α-FeOOH) suspensions to which Hg(II) was adsorbed (30-100 nmol m⁻²) at pH 7.5. Dissolved Hg initially decreased from 10³ or 10⁴ nM (depending on initial conditions) to 10⁻¹ nM, during which the concentration of Hg(II) adsorbed to goethite decreased by 80% and metacinnabar (β-HgS_(s)) formed, based on identification using Hg L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The apparent coordination of oxygens surrounding Hg(II), measured with EXAFS spectroscopy, increased during one flow experiment, suggesting desorption of monodentate-bound Hg(II) while bidentate-bound Hg(II) persisted on the goethite surface. Further sulfidation increased dissolved Hg concentrations by one to two orders of magnitude (0.5 to 10 nM or 30 nM), suggesting that byproducts of bisulfide oxidation and Fe(III) reduction, primarily polysulfide and potentially Fe(II), enhanced the dissolution of β-HgS_(s) and/or desorption of Hg(II). Rapid accumulation of Fe(II) in the solid phase (up to 40 μmol g⁻¹) coincided with faster elevation of dissolved Hg concentrations. Fe(II) served as a proxy for elemental sulfur [S(0)], as S(0) was the dominant bisulfide oxidation product coupled to Fe(III) reduction, based on sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In one experiment, dissolved Hg concentrations tracked those of all sulfide species [S(-II)]. These results suggest that S(-II) reacted with S(0) to form polysulfide, which then caused the dissolution of β-HgS_(s). A secondary Fe-bearing phase resembling poorly formed green rust was observed in sulfidized solids with scanning electron microscopy, although there was no clear evidence that either surface-bound or mineralized Fe(II) strongly affected Hg speciation. Examination of interrelated processes involving S(-II) and Fe(III) revealed new modes of Hg solubilization previously not considered in Hg reactivity models.  相似文献   

Analysis of I in groundwater samples: Direct and quantitative results below the drinking water standard     

Christopher F. Brown  Keith N. GeiszlerMichael J. Lindberg 《Applied Geochemistry》2007

This paper highlights an analytical method based on mass measurement that can be used to directly quantify ¹²⁹I in groundwater samples at concentrations below the maximum contaminant level (MCL) without the need for sample pre-concentration or extraction. Samples were analyzed on a Perkin Elmer ELAN DRC II ICP-MS after minimal dilution using O₂ as the reaction gas. Analysis of continuing calibration verification standards indicated that the dynamic reaction cell (DRC) mode could be used for quantitative analysis of ¹²⁹I in samples below the MCL (0.0057 ng/mL or 1 pCi/L). The low analytical detection limit of ¹²⁹I analysis in the DRC mode coupled with minimal sample dilution (1.02x) resulted in a final estimated quantification limit of 0.0051 ng/mL. Subsequent analysis of three groundwater samples containing ¹²⁹I resulted in fully quantitative results in the DRC mode, and spike recovery analyses performed on all three samples confirmed that the groundwater matrix did not adversely impact the analysis of ¹²⁹I in the DRC mode. This analytical approach has been proven to be a cost-effective, high-throughput technique for the direct, quantitative analysis of ¹²⁹I in groundwater samples at environmentally relevant concentrations that reach below the current MCL.  相似文献   

Elasticity of an upper mantle clinopyroxene     

M. D. Collins  J. M. Brown 《Physics and Chemistry of Minerals》1998,26(1):7-13

The ambient pressure elastic properties of a natural clinopyroxene (C2/c symmetry) from Kilbourne Hole, NM have been determined. In terms of end-members, diopside (CaMgSi₂O₆), hedenbergite (CaFeSi₂O₆), jadeite (NaAlSi₂O₆), cosmochlor (NaCrSi₂O₆), and Mg-Tschermak (MgAl(AlSi)O₆), its composition is Di₇₂He₉Jd₃Cr₃Ts₁₂. The analytic density, based on chemistry and cell parameters is 3.327 (0.003) g/cm³. The elastic constants [c₁₁, c₁₂, c₁₃, c₁₅, c₂₂, c₂₃, c₂₅, c₃₃, c₃₅, c₄₄, c₄₆, c₅₅, c₆₆] are [273.8 (0.9), 83.5 (1.3), 80.0 (1.1), 9.0 (0.6), 183.6 (0.9), 59.9 (1.6), 9.5 (1.0), 229.5 (0.9), 48.1 (0.6), 76.5 (0.9), 8.4 (0.8), 73.0 (0.4), 81.6 (1.0)] GPa where uncertainties are reported at the 95% confidence level. The aggregate (mean of Hashin-Strikman bounds) adiabatic bulk modulus is 117.2 (0.7) GPa, and the shear modulus is 72.2 (0.2) GPa. Although measured moduli are broadly consistent with trends in elasticity versus atomic volume, deviations from the systematics would produce significant (percent level) changes in calculated velocities for candidate mantle mineral assemblages. The compositional dependence of elasticity for several clinopyroxenes is explored on the basis of just the Di+He and Jd+Ts mole fractions. The bulk modulus lies within experimental uncertainties of the linear mixture of end-member properties while the shear modulus deviates by 3%. Received: 29 September 1997 / Revised, accepted: 4 March 1998  相似文献   

Data handbook for clay materials and other non-metallic minerals: Edited by H. van Olphen and J. J. Fripiat. Pergamon Press, 1979, 346 + XIV pp. 124 illustrations (ISBN 0 08 022850 X) U.S. $76.00, £33.00     

G. Brown 《Geochimica et cosmochimica acta》1981,45(4):595-596

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Hydrocarbons in the water and sediment of wilderness lake II     

R.A. Brown  P.K. Starnes 《Marine pollution bulletin》1978,9(6):162-165

Hydrocarbons are reported for another wilderness lake including polynuclear aromatics. All hydrocarbons appear to be of natural origin.  相似文献   

A rapid field method for detecting oil in sediments     

Lewis R. Brown  Gerard S. Pabst  Melvin Light 《Marine pollution bulletin》1978,9(3):81-82

A rapid thin-layer chromatographic technique for estimating the relative concentration of crude oil in sediments has been developed. The limit of detection on the chromatogram is 2 μg of Empire Mix or Saudi Arabian crude oil. The technique has been tested on 335 sediment samples collected from 67 stations in the Gulf of Mexico and has been utilized in assessing the location of oil entering the sediments from the Argo Merchant spill incident.  相似文献   

Solar activity obervations and predictions: P.S. McIntosh and M. Dryer (Editors), 1972. MIT Press,London, 444 pp., £ 7.90     

Geoffrey M. Brown 《Earth》1975,11(3):260-261

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Phase relations of pyroxene and amphibole in greenstone,blueschist and eclogite of the Franciscan Complex,California     

E. H. Brown  J. Y. Bradshaw 《Contributions to Mineralogy and Petrology》1979,71(1):67-83

The phase relations of pyroxenes, amphiboles and associated minerals in metamorphic rocks of the Franciscan Complex can be graphically depicted on a ternary diagram which has at its apices the metamorphic clinopyroxene end members, viz NaAl-NaFe³⁺-Ca(Fe²⁺, Mg). Phases are plotted by projection from a constant subassemblage of minerals. This analysis allows interpretation of the effects of pressure, temperature, bulk rock composition and fluid composition on stability of minerals within the Franciscan.Pyroxenes in meta-igneous rocks and metagraywackes have a limited compositional range and fall into two groups: the omphacites, with 50±5% diopside +hedenbergite component; and the jadeitic pyroxenes with 10±5% diopside+hedenbergite. Pyroxenes intermediate between these two groups are unstable relative to assemblages containing Na-amphibole+other minerals.Coexisting pyroxenes and amphiboles in eclogites and associated coarse blueschists comprise equilibrium assemblages, and the proportion of pyroxene to amphibole is a function of rock composition. Eclogites are stable at higher temperature than regionally developed fine-grained greenstones and blueschists in the Franciscan, and at higher pressure than amphibolites. X _H2O ^fluid is not an important factor in the stability of Franciscan eclogite relative to amphibolite.  相似文献   

Structure energies of the alkali feldspars     

Gordon E. Brown  Philip M. Fenn 《Physics and Chemistry of Minerals》1979,4(1):83-100

Structural energetics of the alkali feldspars have been studied using a “lattice” or structure energy model. Electrostatic energies, U _e,for 20 well-refined, non-intergrown alkali feldspars were calculated using Bertaut's (1952) summation procedure and average about ?13,400 kcal/mol; the repulsive energies of the alkali site in each structure (～15 kcal/mol) were calculated using repulsive parameters for K-O and Na-O interactions estimated from bulk modulus data for NaF and KF and the exponential form of the repulsive potential. Using a procedure in which the position of the alkali cation was varied while the oxygen cage was kept fixed, structure energy gradients for the alkali sites of high albite and a hypersolvus Ab₄₂Or₅₈ structure were computed. In both cases, a broad structure energy well, elongated approximately parallel to c and subparallel to the observed split Na positions, was found. In both structures there is a single energy minimum corresponding closely with the observed single alkali positions. Comparison of U _e values for the alkali feldspars with different K/Na ratios shows that intermediate compositions are predicted to be less “stable” than either endmember and that the potassic end-member is predicted to be less “stable” than the sodic one, assuming that all other factors contributiong to the free energies of each phase are approximately the same. Comparison of U _e values for the high albite and low sanidine structures with different Al/Si distributions and a fixed tetrahedral framework indicates that the ordered charge distributions are 63.0 and 54.8 kcal/mol, respectively, more “stable” than the disordered distributions. Smaller, more realistic energy differences were obtained by using U _evalues averaged from four separate calculations with a +3 charge on a different T site in each and with +4 charges on the other T sites. If, in addition, the charges on cations and oxygen are reduced to half their nominal formal charges, in agreement with Pauling's electroneutrality principle and the results of recent molecular orbital calculations on silicates, the predicted electrostatic energy differences are reduced to 3.6 and 1.6 kcal/mol, respectively. These calculations also indicate that the T₁O site in the high albite structure energetically favors Al and that the Al/Si distribution determines the Na position within the alkali site.  相似文献