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101.
Simon A. Hunt Alex Lindsay-Scott Ian G. Wood Michael W. Ammann Takashi Taniguchi 《Physics and Chemistry of Minerals》2013,40(1):73-80
Orthorhombic post-perovskite CaPtO3 is isostructural with post-perovskite MgSiO3, a deep-Earth phase stable only above 100 GPa. Energy-dispersive X-ray diffraction data (to 9.4 GPa and 1,024 K) for CaPtO3 have been combined with published isothermal and isobaric measurements to determine its P–V–T equation of state (EoS). A third-order Birch–Murnaghan EoS was used, with the volumetric thermal expansion coefficient (at atmospheric pressure) represented by α(T) = α0 + α1(T). The fitted parameters had values: isothermal incompressibility, $ K_{{T_{0} }} $ = 168.4(3) GPa; $ K_{{T_{0} }}^{\prime } $ = 4.48(3) (both at 298 K); $ \partial K_{{T_{0} }} /\partial T $ = ?0.032(3) GPa K?1; α0 = 2.32(2) × 10?5 K?1; α1 = 5.7(4) × 10?9 K?2. The volumetric isothermal Anderson–Grüneisen parameter, δ T , is 7.6(7) at 298 K. $ \partial K_{{T_{0} }} /\partial T $ for CaPtO3 is similar to that recently reported for CaIrO3, differing significantly from values found at high pressure for MgSiO3 post-perovskite (?0.0085(11) to ?0.024 GPa K?1). We also report axial P–V–T EoS of similar form, the first for any post-perovskite. Fitted to the cubes of the axes, these gave $ \partial K_{{aT_{0} }} /\partial T $ = ?0.038(4) GPa K?1; $ \partial K_{{bT_{0} }} /\partial T $ = ?0.021(2) GPa K?1; $ \partial K_{{cT_{0} }} /\partial T $ = ?0.026(5) GPa K?1, with δ T = 8.9(9), 7.4(7) and 4.6(9) for a, b and c, respectively. Although $ K_{{T_{0} }} $ is lowest for the b-axis, its incompressibility is the least temperature dependent. 相似文献
102.
The age of formation of the Lapstone Monocline has been long considered to be late Pliocene/early Pleistocene (the Kosciusko Uplift) but it is now generally thought to be much older. Palaeomagnetic data from haematite‐rich beds within the Hawkesbury Sandstone on and about the monocline indicate that it formed before the oldest haematite was introduced to these beds. The age of this oldest haematite is 15 ± 7 Ma. On the basis of these data, the age of the monocline is unlikely to be less than 8 Ma, probably exceeds 15 Ma, and could be older than 22 Ma. 相似文献
103.
104.
Regions with Mediterranean climates are seasonally arid and provide a niche for ephemeral species which germinate following discrete and variable rainfall during summer. These species must be able to detect when conditions are suitable for completion of their life cycle. Common heliotrope (Heliotropium europaeum) is one such species. It is considered a weed in its naturalised habitat in southern Australia as it uses resources that could be used by ensuing crops, and is toxic to livestock.We examined common heliotrope's germination responses to temperature and water potential, the effect of simulated rainfall on seedling emergence and plant growth in lysimeters.Fresh seeds of common heliotrope have relatively high optimum temperatures and water potentials for germination (around 35 °C and 0 MPa). Germination percentage of seeds extracted from the soil seed bank varies seasonally. In the soil types and climate of the study area, 24.2 mm is the minimum amount of rainfall resulting in emergence. Evapotranspiration required to reach minimal reproductive output was 19.4 mm.Common heliotrope's germination requirements have been selected to ensure that it will only germinate after sufficient rainfall to allow reproductive output. This is the mechanism through which common heliotrope detects its temporal niche. 相似文献
105.
Understanding the nature of communication between aquifers can be challenging when using traditional physical and geochemical groundwater sampling approaches. This study uses two multiport wells completed within Edwards and Trinity aquifers in central Texas to determine the degree of groundwater inter‐flow between adjacent aquifers. Potentiometric surfaces, hydraulic conductivities, and groundwater major ion concentrations and Sr isotope values were measured from multiple zones within three hydrostratigraphic units (Edwards and Upper and Middle Trinity aquifers). Physical and geochemical data from the multiport wells were combined with historical measurements of groundwater levels and geochemical compositions from the region to characterize groundwater flow and identify controls on the geochemical compositions of the Edwards and Trinity aquifers. Our results suggest that vertical groundwater flow between Edwards and Middle Trinity aquifers is likely limited by low permeability, evaporite‐rich units within the Upper and Middle Trinity. Potentiometric surface levels in both aquifers vary with changes in wet vs. dry conditions, indicating that recharge to both aquifers occurs through distinct recharge areas. Geochemical compositions in the Edwards, Upper, and Middle Trinity aquifers are distinct and likely reflect groundwater interaction with different lithologies (e.g., carbonates, evaporites, and siliceous sediments) as opposed to mixing of groundwater between the aquifers. These results have implications for the management of these aquifers as they indicate that, under current conditions, pumping of either aquifer will likely not induce vertical cross‐formational flow between the aquifers. Inter‐flow between the Trinity and the Edwards aquifers, however, should be reevaluated as pumping patterns and hydrogeologic conditions change. 相似文献
106.
Viruses as Groundwater Tracers: Using Ecohydrology to Characterize Short Travel Times in Aquifers 总被引:1,自引:0,他引:1
Viruses are attractive tracers of short (<3 year) travel times in aquifers because they have unique genetic signatures, are detectable in trace quantities, and are mobile in groundwater. Virus “snaphots” result from infection and disappearance in a population over time; therefore, the virus snapshot shed in the fecal wastes of an infected population at a specific point in time can serve as a marker for tracking virus and groundwater movement. The virus tracing approach and an example application are described to illustrate their ability to characterize travel times in high‐groundwater velocity settings, and provide insight unavailable from standard hydrogeologic approaches. Although characterization of preferential flowpaths does not usually characterize the majority of other travel times occurring in the groundwater system (e.g., center of plume mass; tail of the breakthrough curve), virus approaches can trace very short times of transport, and thus can fill an important gap in our current hydrogeology toolbox. 相似文献
107.
Diffuse CO2 efflux near the Ukinrek Maars, two small volcanic craters that formed in 1977 in a remote part of the Alaska Peninsula, was investigated using accumulation chamber measurements. High CO2 efflux, in many places exceeding 1000 g m−2 d−1, was found in conspicuous zones of plant damage or kill that cover 30,000–50,000 m2 in area. Total diffuse CO2 emission was estimated at 21–44 t d−1. Gas vents 3-km away at The Gas Rocks produce 0.5 t d−1 of CO2 that probably derives from the Ukinrek Maars basalt based on similar δ13C values (∼−6‰), 3He/4He ratios (5.9–7.2 RA), and CO2/3He ratios (1–2 × 109) in the two areas. A lower 3He/4He ratio (2.7 RA) and much higher CO2/3He ratio (9 × 1010) in gas from the nearest arc-front volcanic center (Mount Peulik/Ugashik) provide a useful comparison. The large diffuse CO2 emission at Ukinrek has important implications for magmatic degassing, subsurface gas transport, and local toxicity hazards. Gas–water–rock interactions play a major role in the location, magnitude and chemistry of the emissions. 相似文献
108.
Randall J. Hunt Joseph Luchette Willem A. Schreuder James O. Rumbaugh John Doherty Matthew J. Tonkin Douglas B. Rumbaugh 《Ground water》2010,48(3):360-365
Groundwater models can be improved by introduction of additional parameter flexibility and simultaneous use of soft-knowledge. However, these sophisticated approaches have high computational requirements. Cloud computing provides unprecedented access to computing power via the Internet to facilitate the use of these techniques. A modeler can create, launch, and terminate “virtual” computers as needed, paying by the hour, and save machine images for future use. Such cost-effective and flexible computing power empowers groundwater modelers to routinely perform model calibration and uncertainty analysis in ways not previously possible. 相似文献
109.
S. Mondal J.D.A. Piper L. Hunt G. Bandyopadhyay S. Basu Mallik 《Journal of Asian Earth Sciences》2009,34(4):493-506
Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ~2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ~2400 and ~2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana. 相似文献
110.
Unsteady Stream Depletion from Ground Water Pumping 总被引:20,自引:0,他引:20
Bruce Hunt 《Ground water》1999,37(1):98-102