Transient marine electromagnetics: the 2.5-D forward problem   总被引：3，自引：0，他引：3  

M. E. Everett  R. N. Edwards 《Geophysical Journal International》1993,113(3):545-561

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The Leonard Medal     

Everett K. Gibson 《Geochimica et cosmochimica acta》1979,43(12):1995

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Stratified flow over non-uniform surfaces: Turbulent energy model     

Chin-Hua Huang  Everett C. Nickerson 《Boundary-Layer Meteorology》1974,7(1):107-123

A turbulent energy model is developed to simulate the response of a neutrally stratified atmospheric boundary layer to sudden changes in surface roughness. A mechanism of turbulent energy transfer is proposed, based upon the results of numerical experiments, that explains the distribution of shear stress and hence the distribution of velocity profiles in the atmospheric surface layer. Two length scales associated with the turbulent energy equation are obtained from experimental data and the law of the wall. Turbulent energy is also predicted.The predicted growth of the internal boundary layer is slower than that obtained from mixing-length models. Also, the predicted surface shear stress obtained from the turbulent energy model is in better agreement with field data than that obtained from mixing-length models.  相似文献   

The distribution of total nitrogen in iron meteorites     

Everett K. Gibson Jr  Carleton B. Moore 《Geochimica et cosmochimica acta》1971

Total nitrogen abundances in 123 iron meteorites have been determined by inert carrier-gas fusion extraction-gas chromatography. The median value for the iron meteorites was found to be 18 ppm N. The N contents of Sulfide inclusions are greater, in nine cases out of ten, than the corresponding metallic phase. The N content of the iron meteorites is positively correlated with germanium content. The effects of terrestrial weathering and heat treatment by man are discussed in relation to the N contents measured for certain specimens. A correlation between N and cooling rates was found, with lower cooling rates associated with greater N abundances.  相似文献   

The transition to microbial photosynthesis in hot spring ecosystems     

Alysia Cox  Everett L. Shock  Jeff R. Havig 《Chemical Geology》2011,280(3-4):344-351

Even casual observations of continental hot springs reveal that photosynthesis has its limits. In an effort to explore the transition to photosynthesis, field measurements of temperature and pH were made at 996 hot spring locations at Yellowstone National Park ranging from 14° to 94 °C and pH from 0.8 to 9.7. In addition, sulfide measurements were made in 426 of these locations showing concentrations up to 8820 μg L^? 1 total sulfide. These data indicate that the previously established upper temperature (73–75 °C) for the transition to photosynthesis is reached in many basic hot springs, but that the transition occurs at lower temperature with decreasing pH below ~ 6.5. As an example, no strong evidence for photosynthesis was found above 45 °C at pH ~ 2. In several locations, photosynthesis appears to be suppressed despite temperatures and pH values that permit photosynthesis elsewhere. Sulfide concentrations may be responsible for the suppression of photosynthesis at these sites. Total sulfide concentrations were observed to decrease downstream in hot spring outflow channels. Abiotic processes (degassing, oxidation, mineral precipitation, etc.) are too slow to account for these decreases, suggesting an explanation from microbial sulfide oxidation that is supported by field experiments. Microbial sulfide oxidation may determine the ultimate suitability of some hot springs for microbial photosynthesis.  相似文献   

Thermodynamic constraints on fayalite formation on parent bodies of chondrites     

Mikhail Yu. Zolotov  Mikhail V. Mironenko  Everett L. Shock 《Meteoritics & planetary science》2006,41(11):1775-1796

Abstract— Thermochemical equilibria are calculated in the multicomponent gas‐solution‐rock system in order to evaluate the formation conditions of fayalite, (Fe_0.88–1.0Mg_0.12–0)₂SiO₄, Fa_88–100, in unequilibrated chondrites. Effects of temperature, pressure, water/rock ratio, rock composition, and progress of alteration are evaluated. The modeling shows that fayalite can form as a minor secondary and transient phase with and without aqueous solution. Fayalite can form at temperatures below ?350 °C, but only in a narrow range of water/rock ratios that designates a transition between aqueous and metamorphic conditions. Pure fayalite forms at lower temperatures, higher water/rock ratios, and elevated pressures that correspond to higher H₂/H₂O ratios. Lower pressure and water/rock ratios and higher temperatures favor higher Mg content in olivine. In equilibrium assemblages, fayalite usually coexists with troilite, kamacite, magnetite, chromite, Ca‐Fe pyroxene, and phyllosilicates. Formation of fayalite can be driven by changes in temperature, pressure, H₂/H₂O, and water/rock ratios. However, in fayalite‐bearing ordinary and CV3 carbonaceous chondrites, the mineral could have formed during the aqueous‐to‐metamorphic transition. Dissolution of amorphous silicates in matrices and/or silica grains, as well as low activities of Mg solutes, favored aqueous precipitation of fayalite. During subsequent metamorphism, fayalite could have formed through the reduction of magnetite and/or dehydration of ferrous serpentine. Further metamorphism should have caused reductive transformation of fayalite to Ca‐Fe pyroxene and secondary metal, which is consistent with observations in metamorphosed chondrites. Although bulk compositions of matrices/chondrites have only a minor effect on fayalite stability, specific alteration paths led to different occurrences, quantities, and compositions of fayalite in chondrites.  相似文献   

Does the Milky Way launch a large-scale wind?     

John E. Everett  Ellen G. Zweibel  Robert A. Benjamin  Dan McCammon  Lindsay Rocks  Donald P. Cox  John S. Gallagher 《Astrophysics and Space Science》2007,311(1-3):105-110

The ROSAT All-Sky Survey revealed soft X-ray emission on kiloparsec scales towards the Galactic center. Separately, it has also been observed that the cosmic ray intensity (measured via γ-ray emission) rises only very slowly towards the center of the Galaxy, counter to expectations based on the greater number of cosmic ray sources there. A thermal and cosmic-ray driven wind could potentially explain both of these observations. We find that a cosmic-ray and thermally driven wind fits the X-ray observations well; in fact, a wind fits significantly better than an earlier-proposed static-polytrope gas model.  相似文献   

Outflows from AGNs: a brief overview of observations and models     

John E. Everett 《Astrophysics and Space Science》2007,311(1-3):269-273

Recent observations show that outflows from Active Galactic Nuclei are much more common than previously thought, with such outflows seen in various wavebands. I review the recent advances in observations of wind signatures and the progress in modelling various wind launching mechanisms.  相似文献   

A qualitative risk assessment for the impacts of climate change on nationally and internationally important geoheritage sites in Scotland     

Rachel M.L. Wignall  John E. Gordon  Vanessa Brazier  Colin C.J. MacFadyen  Nick S. Everett 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):120-134

Climate change is a significant concern for nature conservation in the 21?st century. One of the goals of the 2014 Scottish Climate Change Adaptation Programme is to identify the consequences of climate change for protected areas and to put in place adaptation or mitigation measures. As a contribution to the process, this paper develops a methodology to identify the relative level of risk to nationally and internationally important geological and geomorphological sites in Scotland from the impacts of climate change. The methodology is based on existing understanding of the likely responses of different types of geosite to specific aspects of climate change, such as changes in rainfall, rising sea levels or increased storminess, and is applied to assess the likelihood of damaging impacts on groups of similar geoheritage features in sites with similar characteristics. The results indicate that 80 (8.8%) of the ～900 nationally and internationally important geoheritage sites in Scotland are at ‘high’ risk from climate change. These include active soft-sediment coastal and fluvial features, finite Quaternary sediment exposures and landforms in coastal and river locations, active periglacial features, sites with palaeoenvironmental records, finite or restricted rock exposures and fossils. Using this risk-based assessment, development of indicative geoheritage climate-change actions have been prioritised for these sites. Depending on the characteristics of the sites, management options may range from ‘do nothing’ to rescue excavations and posterity recording. Monitoring is an essential part of the management process to trigger evidence-based interventions.  相似文献   

Lunar Beagle and Lunar Astrobiology     

Everett K. Gibson  Colin T. Pillinger  Lester J. Waugh 《Earth, Moon, and Planets》2010,107(1):25-42

The study of the elements and molecules of astrobiological interest on the Moon can be made with the Gas Analysis Package (GAP) and associated instruments developed for the Beagle 2 Mars Express Payload. The permanently shadowed polar regions of the Moon may offer a unique location for the “cold-trapping” of the light elements (i.e. H, C, N, O, etc.) and their simple compounds. Studies of the returned lunar samples have shown that lunar materials have undergone irradiation with the solar wind and adsorb volatiles from possible cometary and micrometeoroid impacts. The Beagle 2’s analytical instrument package including the sample processing facility and the GAP mass spectrometer can provide vital isotopic information that can distinguish whether the lunar volatiles are indigenous to the moon, solar wind derived, cometary in origin or from meteoroids impacting on the Moon. As future Lunar Landers are being considered, the suite of instruments developed for the Mars Beagle 2 lander can be consider as the baseline for any lunar volatile or resource instrument package.  相似文献