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91.
Philippe Gillet François Guyot Geoffrey D. Price Benoit Tournerie Andrée Le Cleach 《Physics and Chemistry of Minerals》1993,20(3):159-170
The effect of pressure (up to 21 GPa at room temperature) and temperature (up to 1570 K at room pressure) on the Raman spectrum of CaTiO3 is presented. No significant changes, which could be attributed to a major structural change, are observed in the spectra up to 22 GPa. The pressure shifts of the Raman modes can be related to a significant compression of the Ti-O bond. Discontinuous changes in the spectra upon heating may be related to phase changes observed by calorimetry and X-ray diffraction. The important temperature shifts of some low-frequency modes can be related to an increase in the Ti-O-Ti angle in agreement with the X-ray data showing a decrease of the structural distortion with increasing temperature. These data are compared to those available for MgSiO3-perovskite and show that CaTiO3 is a good structural analogue for MgSiO3-perovskite. The present spectroscopic data are used to calculate the specific heat and entropy of CaTiO3. The role of the low frequency modes in the calculations is emphasized. Good agreement is observed between calculated and experimentally determined values in the 0–1300 K temperature range. A similarly defined model is proposed for MgSiO3-perovskite. It is found that the entropy lies between 57 and 64 J/mol/K at 298 K and between 190 and 200 J/mol/K at 1000 K in agreement with the values inferred from experimental equilibrium data. Finally we briefly discuss the values of the Grüneisen parameters of both perovskites inferred from macroscopic and microscopic data. 相似文献
92.
P. Thierry C. Chatillon-Colinet J. C. Mathieu J. R. Regnard J. Amossé 《Physics and Chemistry of Minerals》1981,7(1):43-46
A high temperature calorimetric solution method involving the use of a sodium and lithium metaborate (NaBO2+LiBO2) molten bath at 1,180 K, has been developed in order to measure the enthalpy of formation of the forsterite-fayalite (Mg2SiO4-Fe2SiO4) system. The samples used for these measurements have been obtained by synthesis. They have been carefully controlled by chemical and X-ray analysis and Mössbauer spectroscopy. The results obtained for forsterite and fayalite agree closely with the data commonly found in the literature. Owing to the uncertainty of the experimental results, it is not possible to determine conclusively whether an enthalpy of mixing exists in this system. 相似文献
93.
Jack Dymond Richard Cobler Louis Gordon Pierre Biscaye Guy Mathieu 《Earth and Planetary Science Letters》1983,64(3):417-429
Hydrothermal waters collected by “Alvin” from the Galapagos Spreading Center are enriched in222Rn by factors of 50–200 over bottom waters. The226Ra in the same samples, however, is enriched by less than a factor of four over bottom waters. Enrichments of222Rn result primarily from α-recoil from rock surfaces while226Ra enrichments are dominantly produced by high-temperature alteration of cooling ridge volcanics. The abundances of both nuclides exhibit positive correlations with temperature. The data extrapolate to bottom water temperatures and compositions, demonstrating the importance of seawater mixing. Different vents, however, have different mixing lines, and vents with high222Rn have low226Ra. We propose these patterns result from variations in the extent of low-temperature crustal interaction with the hydrothermal fluids. Low-temperature crustal waters can maintain high steady state222Rn contents due to the α-recoil additions to the fluids. The226Ra, however, is strongly adsorbed at low-temperatures resulting in low concentrations of this nuclide in low-temperature crustal waters. Thus, physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and222Rn/226Ra values of the hot springs.The222Rn/226Ra value appears to be a sensitive indicator of low-temperature crustal interaction. Values > 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow. Values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust. Values of222Rn/226Ra between 103 and 104 are indicative of interaction of the hydrothermal fluids with sediments. Such values are observed in water samples from the Galapagos hydrothermal mounds. 相似文献
94.
95.
Experimental calibration of lake-sediment spectral reflectance to chlorophyll a concentrations: methodology and paleolimnological validation 总被引:1,自引:0,他引:1
Alexander P. Wolfe Rolf D. Vinebrooke Neal Michelutti Benoit Rivard Biplob Das 《Journal of Paleolimnology》2006,36(1):91-100
Chlorophyll a preserved in lake sediments reflects, in part, past primary production. This study assesses the spectral properties of sedimentary
chlorophyll a using visible-near infrared reflectance (VNIR) spectroscopy, with the objective of establishing a new, non-destructive paleolimnological
proxy. Reflectance spectra were determined from a dilution series (n = 10) involving incremental additions of pulverized modern algae to a lake sediment matrix of low organic content. This enabled
an assessment of the development of sediment reflectance spectra in relation to different sediment chlorophyll a concentrations, and subsequent regression of spectral features against measured concentrations of chlorophyll a and derivatives obtained by high performance liquid chromatography (HPLC). The experiment demonstrates that ubiquitous troughs
in sediment reflectance near 675 nm are attributable to chlorophyll a and derivative compounds. A significant correlation (r
2 = 0.98, P < 0.01) was obtained between the area of the reflectance trough in the 650–700 nm interval and summed concentrations of chlorophyll
a, all derivative isomers, and degradational pheopigments. A simple linear inference model derived from this experiment was
applied to a down-core sequence of VNIR spectra from a productive prairie lake (Alberta, Canada), where it produced inferred
sediment chlorophyll a concentrations in concordance with HPLC measurements. Although a larger training set is desirable to further refine the inference
model, the analyses reported here demonstrate that reflectance spectroscopy provides a rapid, semi-quantitative method for
assessing the chlorophyll a content of lake sediments. 相似文献
96.
97.
Lithospheric controls on the formation of provinces hosting giant orogenic gold deposits 总被引:10,自引:0,他引:10
Frank P. Bierlein David I. Groves Richard J. Goldfarb Benoit Dubé 《Mineralium Deposita》2006,40(8):874-886
Ages of giant gold systems (>500 t gold) cluster within well-defined periods of lithospheric growth at continental margins, and it is the orogen-scale processes during these mainly Late Archaean, Palaeoproterozoic and Phanerozoic times that ultimately determine gold endowment of a province in an orogen. A critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle (SCLM) beneath a province at the time of gold mineralisation, as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere. A proxy for the latter is a short pre-mineralisation crustal history such that thick SCLM was not developed before gold deposition. In constrast, orogens with protracted pre-mineralisation crustal histories are more likely to be characterised by a thick SCLM that is difficult to delaminate, and hence, such provinces will normally be poorly endowed. The nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks, with back-arc basalts, transitional basalts and basanites enriched in gold relative to other rock sequences. Thus, segments of orogens with thin lithosphere may enjoy the conjunction of giant-scale fluid flux through gold-enriched sequences. Although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits, the precise siting of those giants depends on the critical conjunction of a number of province-scale factors. Such features control plumbing systems, traps and seals in tectonically and lithospherically suitable terranes within orogens. 相似文献
98.
A non-local parameterisation of shear turbulence is proposed, which includes a dimensionless multiplicative constant as the
sole tunable parameter. Analytical and numerical solutions in the case of plane Couette flow exhibit sheared velocity profiles
with logarithmic behaviour near the boundaries, and the classical logarithmic flow profile is reproduced for a semi-infinite
domain. We also prove that the families of analytical solutions obtained are locally unique: if the velocity is a strictly-increasing
function of the distance from the boundary, a small perturbation of the velocity profile must be of the same functional form
as the basic flow. 相似文献
99.
F.-X. Désert A. Benoit S. Gaertner J.-P. Bernard N. Coron J. Delabrouille P. de Marcillac M. Giard J.-M. Lamarre B. Lefloch J.-L. Puget A. Sirbi 《New Astronomy》1998,3(8):1073-669
We report on the first observation of the Sunyaev–Zel'dovich (SZ) effect, a distortion of the Cosmic Microwave Background radiation (CMB) by hot electrons in clusters of galaxies, with the Diabolo experiment at the IRAM 30 m telescope. Diabolo is a dual-channel 0.1 K bolometer photometer dedicated to the observation of CMB anisotropies at 2.1 and 1.2 mm. A significant brightness decrement in the 2.1 mm channel is detected in the direction of three clusters (Abell 665, Abell 2163 and CL0016+16). With a 30 arcsec beam and 3 arcmin beamthrow, this is the highest angular resolution observation to date of the SZ effect. Interleaving integrations on targets and on nearby blank fields have been performed in order to check and correct for systematic effects. Gas masses can be directly inferred from these observations. 相似文献
100.
Jacques Mathieu Fabrice Jeannerod Frédéric Hervant Thomas C. Kane 《Aquatic Sciences - Research Across Boundaries》1997,59(1):39-47
Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus. 相似文献