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161.
Seismic velocity analysis is a crucial part of seismic data processing and interpretation which has been practiced using different
methods. In contrast to time consuming and complicated numerical methods, artificial neural networks (ANNs) are found to be
of potential applicability. ANN ability to establish a relationship between an input and output space is considered to be
appropriate for mapping seismic velocity corresponding to travel times picked from seismograms. Accordingly a preliminary
attempt is made to evaluate the applicability of ANNs to determine velocity and dips of dipping layered earth models corresponding
to travel time data. The study is based on synthetic data generated using inverse modeling approach for three earth models.
The models include a three-layer structure with same dips and same directions, a three-layer model with different dips and
same directions, as well as a two-layer model with different dips and directions. An ANN structure is designed in three layers,
namely, input, output, and hidden ones. The training and testing process of the ANN is successfully accomplished using the
synthetic data. The evaluation of the applicability of the trained ANN to unknown data sets indicates that the ANN can satisfactorily
compute velocity and dips corresponding to travel times. The error intervals between the desired and calculated velocity and
dips are shown to be acceptably small in all cases. The applicability of the trained ANN in extrapolating is also evaluated
using a number of data outside of the range already known to ANN. The results indicate that the trained ANN acceptably approximates
the velocity and dips. Furthermore, the trained ANN is also evaluated in terms of capability of handling deficiency in input
data where acceptable results were also achieved in velocity and dip calculations. Generally, this study shows that velocity
analysis using ANNs can promisingly tackle the challenge of retrieving an initial velocity model from the travel time hyperbolas
of seismic data. 相似文献
162.
Eleven incubation experiments were conducted in the South Atlantic sector of the Southern Ocean to investigate the relationship between new production (ρNO–3), regenerated production (ρNH+4), and total carbon production (ρC) as a function of varying light. The results show substantial variability in the photosynthesis–irradiance (P vs E) parameters, with phytoplankton communities at stations that were considered iron (Fe)-limited showing low maximum photosynthetic capacity (PBmax) and low quantum efficiency of photosynthesis (αB) for ρNO3, but high PBmax and αB for ρNH4, with consequently low export efficiency. Results at stations likely relieved of Fe stress (associated with shallow bathymetry and the marginal ice zone) showed the highest rates of PBmax and αB for ρNO3 and ρC. To establish the key factors influencing the variability of the photosynthetic parameters, a principal components analysis was performed on P vs E parameters, using surface temperature, chlorophyll-a concentration, ambient nutrients, and an index for community size structure. Strong covariance between ambient nitrate (NO3) and αB for ρNO3 suggests that Fe and possibly light co-limitation affects the ability of phytoplankton in the region to access the surplus NO3 reservoir. However, the observed relationships between community structure and the P vs E parameters suggest superior performance by smaller-sized cells, in terms of resource acquisition and Fe limitation, as the probable driver of smaller-celled phytoplankton communities that have reduced photosynthetic efficiency and which require higher light intensities to saturate uptake. A noticeable absence in covariances between chlorophyll-a and αB, between PBmax and αB, and between temperature and αB may have important implications for primary-production models, although the absence of some expected relationships may be a consequence of the small dataset and low range of variability. However, significant relationships were observed between ambient NO3 and αB for ρNO3, and between the light-saturation parameter Ek for ρNO3 and the phytoplankton community’s size structure, which imply that Fe and light co-limitation drives access to the surplus NO3 reservoir and that larger-celled communities are more efficient at fixing NO3 in low light conditions. Although the mean PBmax results for ρC were consistent with estimates of global production from satellite chlorophyll measurements, the range of variability was large. These results highlight the need for more-advanced primary-production models that take into account a diverse range of environmental and seasonal drivers of photosynthetic responses. 相似文献
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164.
Concentrations of contaminants in surface water samples collected in west-central Indiana impacted by acidic mine drainage 总被引:1,自引:0,他引:1
The results of analyses of surface waters collected from a variety of locations in west-central Indiana indicate extensive contamination by acidic mine drainage. These samples had pH values as low as 2.1 and total iron concentrations as high as 1200 mg1–1. The speciation of iron, expressed as the ratio [Fe(II)]/[Fe(III)] ranged from 0.08 to 8.27. Measured lead concentrations were as high as 811 mgl–1. In addition, the concentrations of nitrate and sulfate ions were as high as 359 and 624 mgl–1, respectively. 相似文献
165.
A. E. Lucas 《GeoJournal》1996,39(2):133-142
Geographic information systems can provide easy access to large quantities of geographically-referenced data for monitoring, planning and environmental decision support for coastal applications. The dynamic and variable nature of the coastal ocean environment gives rise to data issues different than those associated with land-based GIS. This paper investigates, in particular, the use of different data, including those produced by numerical simulations or ocean models, for coastal management and is illustrated with examples from a Baltic Sea GIS implementation. Implications for the use of these data in environmental management are discussed. 相似文献
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167.
W. van Westrenen N. L. Allan J. D. Blundy M. Yu Lavrentiev B. R. Lucas J. A. Purton 《Physics and Chemistry of Minerals》2003,30(4):217-229
We have performed atomistic computer simulations on trace element incorporation into the divalent dodecahedral X-sites of
pyrope (Py — Mg3Al2Si3O12) – grossular (Gr — Ca3Al2Si3O12) solid solutions. An ionic model and the Mott–Littleton two-region approach to defect energies were used to calculate the
energetics of substitution by a range of divalent trace-elements and of charge-balanced substitution by trivalent ions in
the static limit. Results are compared with experimental high-temperature, high-pressure garnet-melt trace element partitioning
data obtained for the same garnet solid solution to refine our understanding of the factors controlling element partitioning
into solid solutions. Defect energies (U
def,f), relaxation (lattice strain) energies (U
rel), and solution energies (U
sol) were derived using two different approaches. One approach assumes the presence of one type of hybrid X-site with properties
intermediate between pure Mg and Ca sites, and the other assumes discrete Mg and Ca X-sites, and thus two distinct cation
sublattices. The hybrid model is shown to be inadequate, since it averages out local distortions in the garnet structure.
The discrete model results suggest trace elements are more soluble in Py50Gy50 than in either end-member compound. Physically this is due to small changes in size of the X-sites and the removal of unfavourable
interactions between third nearest neighbours of the same size. Surprisingly, depending on the local order, large trace element
cations may substitute for Mg2+ and small trace elements for Ca2+ in Py50Gr50. These solubilities provide an explanation for the anomalous trace-element partitioning behaviour along the pyrope–grossular
join observed experimentally.
Received: 27 January 2000 / Accepted: 14 February 2003 相似文献
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