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21.
Art F. White Marjorie S. Schulz Davison V. Vivit Alex E. Blum David A. Stonestrom 《Journal of Geochemical Exploration》2006,88(1-3):363
Spatial and temporal variations in pore water compositions are characterized for a deep regolith profile developed on a marine terrace chronosequence near Santa Cruz California. Variations are resolved in terms of the dominance of either a lithogenic process, i.e. chemical weathering, or a biogenic process, i.e. plant nutrient cycling. The concept of elemental fractionation is introduced describing the extent that specific elements are mobilized and cycled as a result of these processes. 相似文献
22.
Arūnas Kučinskas Vladas Vansevičius Toshihiko Tanabé 《Astrophysics and Space Science》2002,280(1-2):151-157
We discuss a possible use of the asymptotic giant branch (AGB) stars for tracing star formation histories on the Galactic
and extragalactic distance scales with the ESA's astrometric space mission GAIA. Extensive numerical simulations demonstrate
that metallicities (Δ [M/H] ≲ 0.3) can be obtained for the AGB stars with GAIA up to the distances of ∼ 200 kpc, if no interstellar
extinction is present. Reliable population ages can be also obtained from the AGB stars if their T
eff are constrained precisely. We show that precise effective temperatures can be obtained by fitting observed spectral energy
distributions of the AGB stars with theoretical fluxes calculated from the synthetic spectra. A combination of the derived
effective temperatures with the bolometric luminosities allows to derive precise population ages for a wide range of ages
and metallicities over the large distance scales. This demonstrates that AGB stars can be employed very effectively for tracing
star formation histories with GAIA, allowing to refine the global evolutionary scenarios of stellar populations in the Milky
Way and the galaxies beyond.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
23.
Marjorie Schulz David Stonestrom Guntram Von Kiparski Corey Lawrence Carrie Masiello Art White John Fitzpatrick 《Applied Geochemistry》2011
Concentrations of CO2 in soil atmosphere and CO2 efflux were measured across a marine terrace soil chronosequence near Santa Cruz, California. Soil development, specifically the formation of an argillic horizon, has created a two-tier soil gas profile in the older terrace soils. The soil above the argillic horizon has seasonal variations in soil CO2 associated with plant respiration. The older soils with dense argillic horizons maintain a year round ~1%CO2 below the argillic horizon. The CO2efflux during the growing season is higher on the older terraces. 相似文献
24.
Jokūbas Sūdžius Saulius Raudeliūnas Arūnas Kučinskas Audrius Bridžius Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):109-114
We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis
is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter
in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, E
B-V = 0.06) will be easily traced with GAIA up to the distances of ∼ 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, E
B-V = 0.13) will be located up to the distances of ∼ 2.5 kpc. This holds for the reddening tracers of spectral types O – K2 brighter
than V = 17. Inmost cases, due to their low spatial density, the early type stars (O– A2) cannot provide reliable information about
the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification
of the individual interstellar clouds beyond the distances of ∼ 3 kpc. Therefore, we conclude that the information available
from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar
matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information,
including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA
itself (parallaxes, E
B-V etc.).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
The solubility of neodymium (III) fluoride was investigated at temperatures of 150, 200 and 250 °C, saturated water vapor pressure, and a total fluoride concentration (HF°aq + F−) ranging from 2.0 × 10−3 to 0.23 mol/l. The results of the experiments show that Nd3+ and NdF2+ are the dominant species in solution at the temperatures investigated and were used to derive formation constants for NdF2+ and a solubility product for NdF3. The solubility product of NdF3(logKsp=logaNd3++3logaF-) is −24.4 ± 0.2, −22.8 ± 0.1, and −21.5 ± 0.2 at 250, 200 and 150 °C, respectively, and the formation constant of NdF2+(logβ=logaNdF2+-logaNd3+-logaF-) is 6.8 ± 0.1, 6.2 ± 0.1, and 5.5 ± 0.2 at 250, 200 and 150 °C, respectively. The results of this study show that published theoretical predictions significantly overestimate the stability of NdF2+ and the solubility of NdF3.The potential impact of the results on natural systems was evaluated for a hypothetical fluid with a composition similar to that responsible for REE mineralization in the Capitan pluton, New Mexico. In contrast to results obtained using the theoretical predictions of Haas [Haas J. R., Shock E. L., and Sassani D. C. (1995) Rare earth elements in hydrothermal systems: estimates of standard partial molal thermodynamic properties of aqueous complexes of the rare earth elements at high pressures and temperatures. Geochim. Cosmochim. Acta59, 4329-4350.], which indicate that NdF2+ is the dominant species in solution, calculations employing the data presented in this paper and previously published experimental data for chloride and sulfate species [Migdisov A. A., and Williams-Jones A. E. (2002) A spectrophotometric study of neodymium(III) complexation in chloride solutions. Geochim. Cosmochim. Acta66, 4311-4323; Migdisov A. A., Reukov V. V., and Williams-Jones A. E. (2006) A spectrophotometric study of neodymium(III) complexation in sulfate solutions at elevated temperatures. Geochim. Cosmochim. Acta70, 983-992.] show that neodymium chloride species predominate and that neodymium fluoride species are relatively unimportant. This suggests that accepted models for REE deposits that invoke fluoride complexation as the method of hydrothermal REE transport may need to be re-evaluated. 相似文献
26.
Arūnas Kučinskas Audrius Bridžius Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):159-163
The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the
Large Magellanic Cloud with ESA's astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual
stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective
temperatures (Δ T
eff<10%) can be obtained from GAIA photometry down to V ∼ 18 for stars in populations within the studied metallicity range ([M/H] = -0.4 ... -1.7). GAIA will also provide photometric
metallicities (Δ [M/H] ≲ 0.3 dex) for the cluster giants brighter than V ∼ 17.5. The knowledge of the effective temperature sand metallicities will allow to obtain accurate ages of stellar populations
younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations
(≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will
provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better
understanding of stellar and galactic evolution in different astrophysical environments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
27.
O. Nikodemus G. Brūmelis G. Tabors L. Lapia S. Pope 《Journal of Atmospheric Chemistry》2004,49(1-3):521-531
The concentrations of heavy metals (Cd, Cr, Cu, Pb, Ni, V, Zn) in feather moss were estimated in national surveys in Latvia in 1990, 1995 and 2000. Hylocomium splendens was used as a biomonitor in 1990 and Pleurozium schreberi in the latter two years. Maps of the distributions of the metals in Latvia have been produced. The paper discusses the reasons underlying the distributions and also the temporal trends during the last ten years. 相似文献
28.
Art Raiche 《Surveys in Geophysics》1994,15(2):159-207
Researchers in the field of electromagnetic modelling and inversion have taken advantage of the impressive improvements of new computer hardware to explore exciting new initiatives and solid extensions of older ideas. Finite-difference time-stepping methods have been successfully applied to full-domain 3D models. Another new method combines time-stepping with spatial frequency solutions. The 2D model 3D source (2.5D) problem is also receiving fresh attention both for continental and sea floor applications.The 3D inversion problem is being attacked by several researchers using distorted Born approximation methods. Q-domain inversions using transformation to pseudo-wave field and travel time tomography have also been successfully tested for low contrast problems. Subspace methods have been successful in dramatically reducing the computational burden of the under-determined style of inversion. Static magnetic field interpretation methods are proving useful for delineating the position of closely-spaced multiple targets.Novel (appeals to nature) methods are also being investigated. Neural net algorithms have been tested for determining the depth and offset of buried pipes from EM ellipticity data. Genetic algorithms and simulated annealing have been tested for extremal model construction.The failure of researchers to take adequate account of the properties of the mathematical transformation from algorithms to the number domain represented by the computing process remains a major stumbling block. Structured programming, functional languages, and other software tools and methods are presented as an essential part of the serial process leading from EM theory to geological interpretation. 相似文献
29.
The speciation of samarium (III) in chloride-bearing solutions was investigated spectrophotometrically at temperatures of 100-250 °C and a pressure of 100 bars. The simple hydrated ion, Sm3+, is predominant at ambient temperature, but chloride complexes are the dominant species at elevated temperatures. Cumulative formation constants for samarium chloride species were calculated for the following reactions:
30.
Katharine Hayhoe Cameron P. Wake Thomas G. Huntington Lifeng Luo Mark D. Schwartz Justin Sheffield Eric Wood Bruce Anderson James Bradbury Art DeGaetano Tara J. Troy David Wolfe 《Climate Dynamics》2007,28(4):381-407
To assess the influence of global climate change at the regional scale, we examine past and future changes in key climate,
hydrological, and biophysical indicators across the US Northeast (NE). We first consider the extent to which simulations of
twentieth century climate from nine atmosphere-ocean general circulation models (AOGCMs) are able to reproduce observed changes
in these indicators. We then evaluate projected future trends in primary climate characteristics and indicators of change,
including seasonal temperatures, rainfall and drought, snow cover, soil moisture, streamflow, and changes in biometeorological
indicators that depend on threshold or accumulated temperatures such as growing season, frost days, and Spring Indices (SI).
Changes in indicators for which temperature-related signals have already been observed (seasonal warming patterns, advances
in high-spring streamflow, decreases in snow depth, extended growing seasons, earlier bloom dates) are generally reproduced
by past model simulations and are projected to continue in the future. Other indicators for which trends have not yet been
observed also show projected future changes consistent with a warmer climate (shrinking snow cover, more frequent droughts,
and extended low-flow periods in summer). The magnitude of temperature-driven trends in the future are generally projected
to be higher under the Special Report on Emission Scenarios (SRES) mid-high (A2) and higher (A1FI) emissions scenarios than
under the lower (B1) scenario. These results provide confidence regarding the direction of many regional climate trends, and
highlight the fundamental role of future emissions in determining the potential magnitude of changes we can expect over the
coming century.
相似文献
Katharine HayhoeEmail: |