First-order asymptotics for the eigenfrequencies of the Earth and application to the retrieval of large-scale lateral variations of structure     

Barbara Romanowicz  Geneviève Roult 《Geophysical Journal International》1986,87(1):209-239

Summary . We present a variety of examples, showing systematic fluctuations as a function of angular order of measured eigenfrequencies for given normal modes of the Earth. The data are single station measurements from the GEOSCOPE network. Such fluctuations are attributed to departures from the lowest order asymptotic expression of the geometrical optics approximation. We derive first-order asymptotic expressions for the location parameter for all three components of the Earth's motion, by a method based on the stationary phase approximation and geometric relations on the unit sphere.
We illustrate the sensitivity of the fluctuations to the different parameters involved (source parameters, epicentral distance, laterally heterogeneous earth model) with synthetic examples corresponding to GEOSCOPE observations. Finally, we show the results of first attempts at inversion, which indicate that, when the fluctuations are taken into account, more accurate estimates of the great circle average eigenfrequencies can be obtained, and additional constraints put on the structure in the neighbourhood of the great circle.  相似文献   

Resources in Antarctica: Potential for conflict     

Barbara Mitchell 《Marine Policy》1977,1(2):91-101

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A simple method for calculating growth rates of petroleum hydrocarbon plumes   总被引：3，自引：0，他引：3  

Bekins BA  Cozzarelli IM  Curtis GP 《Ground water》2005,43(6):817-826

Consumption of aquifer Fe(III) during biodegradation of ground water contaminants may result in expansion of a contaminant plume, changing the outlook for monitored natural attenuation. Data from two research sites contaminated with petroleum hydrocarbons show that toluene and xylenes degrade under methanogenic conditions, but the benzene and ethylbenzene plumes grow as aquifer Fe(III) supplies are depleted. By considering a one-dimensional reaction front in a constant unidirectional flow field, it is possible to derive a simple expression for the growth rate of a benzene plume. The method balances the mass flux of benzene with the Fe(III) content of the aquifer, assuming that the biodegradation reaction is instantaneous. The resulting expression shows that the benzene front migration is retarded relative to the ground water velocity by a factor that depends on the concentrations of hydrocarbon and bioavailable Fe(III). The method provides good agreement with benzene plumes at a crude oil study site in Minnesota and a gasoline site in South Carolina. Compared to the South Carolina site, the Minnesota site has 25% higher benzene flux but eight times the Fe(III), leading to about one-sixth the expansion rate. Although it was developed for benzene, toluene, ethylbenzene, and xylenes, the growth-rate estimation method may have applications to contaminant plumes from other persistent contaminant sources.  相似文献   

The yield and isotopic composition of radiolytic H₂, a potential energy source for the deep subsurface biosphere     

Li-Hung Lin  Greg F. Slater  Barbara Sherwood Lollar  T.C. Onstott 《Geochimica et cosmochimica acta》2005,69(4):893-903

The production rate and isotopic composition of H₂ derived from radiolytic reactions in H₂O were measured to assess the importance of radiolytic H₂ in subsurface environments and to determine whether its isotopic signature can be used as a diagnostic tool. Saline and pure, aerobic and anaerobic water samples with pH values of 4, 7, and 10 were irradiated in sealed vials at room temperature with an artificial γ source, and the H₂ abundance in the headspace and its isotopic composition were measured. The H₂ concentrations were observed to increase linearly with dosage at a rate of 0.40 ± 0.04 molecules (100 eV)⁻¹ within the dosage range of 900 to 3500 Gray (Gy; Gy = 1 J Kg⁻¹) with no indication of a maximum limit on H₂ concentration. At ∼2000 Gy, the H₂ concentration varied only by 16% across the experimental range of pH, salinity, and O₂. Based upon this measured yield and H₂ yields for α and β particles, a radiolytic H₂ production rate of 10⁻⁹ to 10⁻⁴ nM s⁻¹ was estimated for the range of radioactive element concentrations and porosities typical of crustal rocks. The δD of H₂ was independent of the dosage, pH (except for pH 4), salinity, and O₂ and yielded an αD_H2O-H2 of 2.05 ± 0.07 (αD_H2O-H2 = (D/H)_H2O to (D/H)_H2), slightly less than predicted radiolytic models. Although this radiolytic fractionation value is significantly heavier than that of equilibrium isotopic exchange between H₂ and H₂O, the isotopic exchange rate between H₂ and H₂O will erase the heavy δD of radiolytic H₂ if the age of the groundwater is greater than ∼10³ to 10⁴ yr. The millimolar concentrations of H₂ observed in the groundwater of several Precambrian Shields are consistent with radiolysis of water that has resided in the subsurface for a few million years. These concentrations are well above those required to support H₂-utilizing microorganisms and to inhibit H₂-producing, fermentative microorganisms.  相似文献   

Geomagnetic secular variation since 1901   总被引：3，自引：0，他引：3  

Barbara M. Hodder 《Geophysical Journal International》1981,65(3):763-776

Summary. All available annual means, from the world-wide network of magnetic observatories, of north intensity ( X ), east intensity ( Y ) and vertical intensity (Z) from 1901 to 1977 are subjected to spherical harmonic analysis to obtain 38 models of the Earth's geomagnetic field at two-year intervals. These models are differenced to give 37 models of secular variation at two-year intervals from 1903.5 to 1975.5. The results show the decreasing trend of the dipole moment and are analysed for possible information on the westward drift of the magnetic field.  相似文献   

“WOMEN IN GEOGRAPHY” REVISITED: PRESENT STATUS,NEW OPTIONS     

Barbara Rubin 《The Professional geographer》1979,31(2):125-134

The representation of women on geography faculties did not increase appreciably between 1971 and 1977, but women in other academic disciplines have fared somewhat better. The latter have improved their status primarily as a result of actions taken by professional associations representing their fields. When a professional association ignores its female constituency or refuses to commit itself to improving their circumstances, federal agencies now offer alternative channels for obtaining redress.  相似文献   

Depth-related influences on biodegradation rates of phenanthrene in polluted marine sediments of Puget Sound, WA     

Tang YJ  Carpenter SD  Deming JW  Krieger-Brockett B 《Marine pollution bulletin》2006,52(11):1431-1440

A whole-core injection method was used to determine depth-related rates of microbial mineralization of (14)C-phenanthrene added to both contaminated and clean marine sediments of Puget Sound, WA. For 26-day incubations under micro-aerobic conditions, conversions of (14)C-phenanthrene to (14)CO(2) in heavily PAH-contaminated sediments from two sites in Eagle Harbor were much higher (up to 30%) than those in clean sediments from nearby Blakely Harbor (<3%). The averaged (14)C-phenanthrene degradation rates in the surface sediment horizons (0-3 cm) were more rapid (2-3 times) than in the deeper sediment horizons examined (>6 cm), especially in the most PAH polluted EH9 site. Differences in mineralization were associated with properties of the sediments as a function of sediment depth, including grain-size distribution, PAH concentration, total organic matter and total bacterial abundance. When strictly anaerobic incubations (in N(2)/H(2)/CO(2) atmosphere) were used, the phenanthrene biodegradation rates at all sediment depths were two times slower than under micro-aerobic conditions, with methanogenesis observed after 24 days. The main rate-limiting factor for phenanthrene degradation under anaerobic conditions appeared to be the availability of suitable electron acceptors. Addition of calcium sulfate enhanced the first order rate coefficient (k(1) increased from 0.003 to 0.006 day(-1)), whereas addition of soluble nitrate, even at very low concentration (<0.5 mM), inhibited mineralization. Long-term storage of heavily polluted Eagle Harbor sediment as intact cores under micro-aerobic conditions also appeared to enhance anaerobic biodegradation rates (k(1) up to 0.11 day(-1)).  相似文献   

Chemical characterization of fine particulate matter during peak PM10 episodes in Apulia (South Italy)     

Martino Amodio  Paolo Bruno  Maurizio Caselli  Gianluigi de Gennaro  Paolo Rosario Dambruoso  Barbara Elisabetta Daresta  Pieirna Ielpo  Francesco Gungolo  Claudia Marcella Placentino  Vincenzo Paolillo  Maria Tutino 《Atmospheric Research》2008,90(2-4):313-ICNAA07

Some peak PM10 episodes, occurred during PM monitoring campaigns performed on October 2005 and February and June 2006 in Bari town, have been characterized. Moreover back trajectories of air masses and Principal Component Analyses were applied. Three of the peak PM10 episodes investigated were related to local emissions of primary pollutants during poor atmospheric dispersion conditions. The other two peak PM10 episodes considered are related with long range transport air masses toward Apulia region: in one case the chemical characterization and the back trajectories analysis indicate that high PM10 value detected is due to the Saharan dust advection in the Apulia region; in the other case air masses with different origin give rise to high PM10 value.Moreover PM10 daily mean concentrations, presented in this paper collected from January 2005 to August 2007 and obtained by automatic device in six stations of air quality monitoring networks in Bari territory, do not show a seasonal trend for PM10 concentrations, contrary to the PM10 trend shown in the towns of North Italy. This can be explained mostly considering that our region presents generally meteo-climatic conditions that favour pollutants dispersion.  相似文献   

Towards molecular-level understanding of geochemical processes in mineral exploration     

Joël Brugger  Allan Pring  Frank Reith  Barbara Etschmann  Weihua Liu 《Journal of Geochemical Exploration》2009

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A synchrotron X-ray absorption spectroscopic study of copper solubility and speciation in supercritical water     

Weihua Liu  Joël Brugger  Barbara Etschmann  Denis Testemale  Jean-Louis Hazemann 《Journal of Geochemical Exploration》2009

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