From the Workshop Organizers     

Allan Treiman 《Meteoritics & planetary science》2003,38(12):1711-1712

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Atomistic simulation of the mechanisms of noble gas incorporation in minerals     

Z. Du  N.L. Allan  J.A. Purton 《Geochimica et cosmochimica acta》2008,72(2):554-573

Atomistic simulations have been carried out to investigate the mechanisms of noble gas incorporation in minerals using both the traditional two-region approach and the “supercell” method. The traditional two-region approach has been used to calculate defect energies for Ne, Ar, Kr and Xe incorporation in MgO, CaO, diopside and forsterite in the static limit and at one atmosphere pressure. The possibilities of noble gas incorporation via both substitution and interstitial mechanisms are studied. The favored mechanism varies from mineral to mineral and from noble gas to noble gas. In all minerals studied, the variation of the solution energies of noble gas substitution with atomic radius appears approximately parabolic, analogous to those for 1⁺, 2⁺, 3⁺ and 4⁺ trace element incorporation on crystal lattice sites. Noble gas solution energies thus also fall on a curve, similar to those previously observed for cations with different charges, but with much lower curvature.The “supercell” method has been used to investigate the pressure dependence of noble gas incorporation in the same systems. Results indicate a large variation of the solubility of the larger noble gases, Kr and Xe with pressure. In addition, explicit simulation of incorporation at the (0 0 1) surface of MgO shows that the solubility of the heavier noble gases may be considerably enhanced by the presence of interfaces.  相似文献   

Characterization and cycling of atmospheric mercury along the central US Gulf Coast     

Mark A. Engle  Michael T. Tate  David P. Krabbenhoft  Allan Kolker  Mark L. Olson  Eric S. Edgerton  John F. DeWild  Ann K. McPherson 《Applied Geochemistry》2008

Concentrations of atmospheric Hg species, elemental Hg (Hg^°), reactive gaseous Hg (RGM), and fine particulate Hg (Hg-PM_2.5) were measured at a coastal site near Weeks Bay, Alabama from April to August, 2005 and January to May, 2006. Mean concentrations of the species were 1.6 ± 0.3 ng m⁻³, 4.0 ± 7.5 pg m⁻³ and 2.7 ± 3.4 pg m⁻³, respectively. A strong diel pattern was observed for RGM (midday maximum concentrations were up to 92.7 pg m⁻³), but not for Hg^° or Hg-PM_2.5. Elevated RGM concentrations (>25 pg m⁻³) in April and May of 2005 correlated with elevated average daytime O₃ concentrations (>55 ppbv) and high light intensity (>500 W m⁻²). These conditions generally corresponded with mixed continental-Gulf and exclusively continental air mass trajectories. Generally lower, but still elevated, RGM peaks observed in August, 2005 and January–March, 2006 correlated significantly (p < 0.05) with peaks in SO₂ concentration and corresponded to periods of high light intensity and lower average daytime O₃ concentrations. During these times air masses were dominated by trajectories that originated over the continent. Elevated RGM concentrations likely resulted from photochemical oxidation of Hg^° by atmospheric oxidants. This process may have been enhanced in and by the near-shore environment relative to inland sites. The marine boundary layer itself was not found to be a significant source of RGM.  相似文献   

Instrument calibration of ocean bottom seismographs   总被引：1，自引：0，他引：1  

Allan M. Sauter  Leroy M. Dorman 《Marine Geophysical Researches》1986,8(3):265-275

To increase the accuracy of measuring sea floor motion with ocean bottom seismometers, we calibrate the seismometer system on the ocean floor. Data from the sea floor calibration, augmented with electronic and land calibration data, enables us to find the OBS transfer function to an accuracy of 0.5% in the frequency range of 0.1 to 32 Hz. We are able to distinguish between temperature, instrument and OBS ground coupling effects, all of which alter the transfer function. This paper reviews our method of calibration and discusses the effects of temperature and some of the instrument design features on the vertical seismometer transfer function.  相似文献   

An interview with Paul Witherspoon, distinguished hydrogeologist from the USA     

R. Allan Freeze  Iraj Javandel 《Hydrogeology Journal》2008,16(5):811-815

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Semi-Analytic Stereological Analysis of Waste Package/Fracture Intersections in a Granitic Rock Nuclear Waste Repository   总被引：1，自引：0，他引：1  

Allan Hedin 《Mathematical Geosciences》2008,40(6):619-637

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A dipole field model for axisymmetric alfvén waves with finite ionosphere conductivities     

W. Allan  F.B. Knox 《Planetary and Space Science》1979,27(1):79-85

An axisymmetric model for approximate solution of the magnetospheric Alfvén wave problem at latitudes above the plasmapause is proposed, in which a realistic dipole geometry is combined with finite anisotropic ionosphere conductivities, thus bringing together various ideas of previous authors. It is confirmed that the axisymmetric toroidal and poloidal modes interact via the ionospheric Hall effect, and an approximate method of solution is suggested using previously derived closed solutions of the uncoupled wave equations.A solution for zero Hall conductivity is obtained, which consists of sets of independent shell oscillations, regardless of the magnitude of the Pedersen conductivity. One set reduces to the classical solutions for infinite Pedersen conductivity, while another predicts a new set of harmonics of a quarter-wave fundamental, with longer eigenperiods than the classical solutions for a given L-shell.  相似文献   

Conceptual models in exploration geochemistry: The Canadian cordillera and Canadian shield: P.M.D. Bradshaw (compiler and editor). Association of Exploration Geochemists special publication,no. 3, Elsevier Scientific Publishing Co., Amsterdam—Oxford—New York,N.Y., 1975, 223 pp., Dfl. 39.00/US $ 16.25     

R.J. Allan 《Chemical Geology》1976,18(3):245-250

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Carbon isotope fractionation in wood during carbonization   总被引：1，自引：0，他引：1  

C.S.M. Turney  D. Wheeler  Allan R. Chivas 《Geochimica et cosmochimica acta》2006,70(4):960-964

A significant uncertainty exists as to whether δ¹³C values in charcoal meaningfully represent the stable isotopic content of the original material, with studies suggesting variable responses to both natural and laboratory heating. An extensive study was undertaken using fully homogenised samples of wood taken from Eucalyptus spp., Quercus robur and Pinus radiata. The results demonstrate that the duration of heating had no tangible effect on the final composition of the charred material, with the δ¹³C and carbon content of wood fixed after 30 min of heating. Furthermore, all three wood types become progressively depleted in ¹³C with increasing temperature. The results demonstrate that even at temperatures commonly reached in natural fires (<450 °C) isotopic fractionation of up to 1.3‰ can take place indicating that the absolute values obtained from charcoal extracted for paleoenvironmental reconstruction must be interpreted with caution.  相似文献   

Evolved mare basalt magmatism, high Mg/Fe feldspathic crust, chondritic impactors, and the petrogenesis of Antarctic lunar breccia meteorites Meteorite Hills 01210 and Pecora Escarpment 02007     

James M.D. Day  Christine Floss  Lawrence A. Taylor  Mahesh Anand  Allan D. Patchen 《Geochimica et cosmochimica acta》2006,70(24):5957-5989

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