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201.
Conclusion A simple method of estimating fracture porosity and permeability based on empirical relations between fracture aperture andJRC andJCS can be developed. This shows very close correlation with existing data, using simple discontinuity models. There is quite a good correlation between fracture porosity and permeability and depth for larger initial apertures. 相似文献
202.
Instrumental Neutron Activation Analysis by Collecting Only One Spectrum: Results For International Geochemical Reference Samples 总被引:1,自引:0,他引:1
Instrumental neutron activation analysis of rocks and minerals is currently done on basis of collecting 2 or 3 energy spectra. We have found that, by collecting one spectrum one week after irradiation, satisfactory results for the USGS and CRPG geochemical reference samples can be obtained. 相似文献
203.
The vibrational properties of metastable Ca-GeO3 perovskite are investigated as a function of temperature using Raman scattering. Mode-assignments are derived from polarized spectra of optically oriented single crystals. Neither symmetry-breaking structural transformations nor soft-mode behavior is revealed in the Raman spectra between room temperature and 650° C. Only a small decrease in the local static octahedral tilt angles can be inferred from the Raman data over this temperature range. A Landau extrapolation of the lowest frequency Ag modes suggests that these modes become critical near 2000° C, a temperature that is above the extrapolated zero pressure melting point. 相似文献
204.
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207.
Samples of three dolerite dykes from South-West Greenland give a pooled weighted mean Rb-Sr whole-rock isochron age of 2,130±65
Ma. Initial 87Sr/86Sr ratios are 0.70155±0.00018 for one of the dykes (Naujat) and 0.70277±0.00012 for the other two (Torssut and Akinaq). A
fourth dyke (Qaqarssuaq) did not yield an isochron. Torssut samples have significantly lower initial 207Pb/204Pb ratios than samples from the Naujat dyke, indicating that the Torssut dyke has been affected by crustal contamination.
Samples of the dykes vary widely in chemical composition because of an uneven distribution of different primocryst phases
throughout the dykes, and because of variable degrees of fractionation of the magma. For two of the dykes some constraints
on the composition of the parent magma have been inferred from trace element data. Higher concentrations of K, Rb, Ba, Sr,
Ce and perhaps Nb (at comparable levels of magmatic fractionation) in the dykes with higher Sri are probably related to crustal contamination of their parent magmas.
Two of the dykes probably intruded from zoned magma chambers. The marginal zones of these dykes crystallised from a strongly
fractionated magma, whereas the centres of the dykes consist of more primitive material with large proportions of olivine
and plagioclase primocrysts. The central part of Torssut is less strongly contaminated with crustal Pb than the border zones.
A more detailed analysis of the Pb-isotopic composition in the Torssut dyke shows that contaminant lead must have been derived
from rocks in the deeper crust considerably older than the late Archaean gneisses which occur at the surface. 相似文献
208.
In the Thames Estuary at the eastern end of Long Island Sound, most mussels achieve maximal gonadal development during the summer and larval settlement occurs primarily during the fall. The timing of reproductive events is several months later than has been reported for other populations of mussels in Long Island Sound but corresponds to that of mussels inhabiting the south shore of Long Island. The data support the growing body of evidence which indicates that temperature is not a major factor determining the reproductive period of this bivalve. 相似文献
209.
We used a reproducible seeded growth technique with a pH-stat to study the kinetics of calcite precipitation at 25°C. We performed different experiments at initial Ca2+ and HCO3? concentrations ranging from 0.7–2 and 4–7 mmol L?1, pH values ranging from 8.25 to 8.70, values ranging from 0.0006 to 0.01 atm, and ionic strengths ranging from 0.015 to 0.10 mol L?1. With this experimental data set, we used initial rate measurements and integral methods to test several precipitation rate equations. Rate equations that possess a disequilibrium functional dependence, such as the BURTON et al. (1951) dislocation model, forms of the Davies and Jones (1955) model, and the model used by Reddy and Nancollas (1973), did not adequately describe the kinetics of calcite precipitation at pH greater than 8 and less than 0.01 atm. Rate equations that describe independent dissolution and precipitation mechanisms with elementary reactions, such as the equation presented by Plummeret al. (1978), and nancollas and Reddy (1971) were more successful. However, Plummer's model did not adequately describe the rate of all experiments due to the presence of an OH? surface term in the precipitation rate equation. The elementary reaction of the Nancollas and Reddy model is written in terms of bulk Ca2+ and CO3? concentrations, and appears to be the most successful model which describes calcite precipitation at pH > 8 and atm. The Nancollas and Reddy model, altered to account for varying ionic strengths, adequately described the rate of all experiments and yielded a precipitation rate constant of dm6 mol?1 m?2 s?1, with an apparent Arrhenius activation energy of 48.1 kJ mol?1. 相似文献
210.
Modern social science is concerned with policing the ‘boundary’ between nature and culture, with limiting and excluding phenomena which threaten to challenge its account of the social determination of the attributes of human beings. The paper argues that this boundary defence is an unusually touchy and difficult matter because social science has inherited an Enlightenment conception of man as ‘unique’. Human culture is regarded as different in quality from any possible form of animal association or attainment. At the same time as supporting this ontology it supposes the ‘boundary’ is in some sense a matter of empirical science, capable of specification by reference to evidence. We try to show the confusions these two contradictory circumstances produce by considering two debates: those concerning the possibility of ‘feral’ children and those concerning the uniqueness of language to human beings. It is demonstrated that the modern debates develop theories, issues and lines of dispute which appeared in the eighteenth century. 相似文献