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41.
D.K. Paul P. Kresten T. Ray Barman R.H. McNutt A.O. Brunfelt 《Journal of Volcanology and Geothermal Research》1984,21(1-2)
Petrographic and geochemical data are given for some basaltic rocks from the Koynaghat, Ambaghat and Panvel sections of the western Deccan volcanic province. This study confirms geochemical features established earlier for the Deccan basalts but brings out minor additional characters. Mineralogical and major-element compositions of the basaltic flows from the Koyna and Panvel sections indicate tholeiitic affinity; the Ambaghat flows exhibit a slight affinity towards alkali basalt. Rare earth element (REE) distribution patterns and trace-element abundances suggest minor fractionation of olivine and plagioclase during the evolution of the flows. The general similarity of chemical and mineralogical features over a wide area and the lack of conspicuous inter-element relationships suggest that the flows reflect the combined effects of partial melting, minor mineral fractionation and selective crustal contamination. 相似文献
42.
Durga Ray 《Boundary-Layer Meteorology》1986,36(1-2):117-131
Using variable atmospheric eddy diffusivities, it is possible to obtain a theoretical explanation of observations concerning the increase of cell flatness in cellular cloud patterns. The inclusion of a horizontal variation of eddy size as proposed by Ray (1965) and supported by Agee (1973) has a large influence on theoretical Rayleigh number and cell shape, the degree of cell flatness being principally controlled by the degree of horizontal variation of the eddies. It is also shown that observations regarding the reversal of the circulation pattern could be interpreted on the basis of eddy diffusivities that change sign along the reference directions. This suggests that it may be useful to rethink our ideas about the existence of spatial variations in the eddy transfer coefficients in atmospheric convection. 相似文献
43.
Gas is extracted from large (6–31 kg) Antarctic ice samples to obtain sufficient CO2 for14C measurements with small low-level proportional counters. The14C ages of Byrd core ice are in accord with glaciological estimates ranging from (2.2−1.1+1.4)×103 yr at 271 m depth to more than 8 × 103 yr at 1071 m depth. The CO2 abundances in gas extracted from Byrd core ice range from 0.0216 to 0.051%, with below present-day atmosphere CO2 abundances for ice from 1068 and 1469 m depths. The CO2 abundance in gas from Allan Hills surface ice samples ranges between four and six times the atmospheric value and the CO2 had a specific activity three times that of contemporary carbon. A possible explanation for the anomalously high specific activity is surface melting with the incorporation into CO2 of14C produced by cosmic ray spallation of oxygen in ice. The CO2 abundance in gas extracted from subsurface Allan Hills ice ranged from 0.030 to 0.065%, and the specific activities are below contemporary carbon, indicating ages greater than 5×103 yr. The18O/16O ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18O/16O ratio in the ice. The O2, N2, and Ar abundances and isotopic compositions are similar to those in contemporary air, except for positive15N/14N ratios in a few samples. 相似文献
44.
Various models have been suggested concerning the origin and evolution of the earth's atmosphere. An estimate of the nitrogen content of the mantle could further constrain atmospheric models. Total nitrogen content was determined by thermal neutron activation analysis via 14N(n,p)14C. The 14C was converted to carbon dioxide and counted in miniature low level proportional counters. The total nitrogen content of U.S.G.S. standards BCR-1 and G-2 as determined by different laboratories is variable, probably due to atmospheric adsorption by the finely ground samples. Total nitrogen content was determined in deep sea basalt glasses from three regions: East Pacific Rise (, and ), Mid-Atlantic Rift (FAMOUS Region:, and ) and the Juan de Fuca Ridge (). Matrix material from the same samples as the glasses was available from the East Pacific Rise (, and ) and the Mid-Atlantic Rift () which are about 50 to 100% greater than the associated glasses. The increased matrix abundance may be due to incorporation of chemically bound nitrogen from sea water rather than dissolved molecular nitrogen. The nitrogen content of the FAMOUS samples are inconsistent with the model of Langmuir et al. (1977) for petrogenesis based on trace element data. Factors which can affect the observed nitrogen content in the basalts and the interpretation in terms of the mantle nitrogen abundance are discussed (e.g. partial melting and degassing of the basalts). A lower limit of about 2 ppm N in the mantle can be estimated. 相似文献
45.
A dynamic response analysis procedure for an x-braced tubular steel offshore platform frame is described, including details of the mathematical model adopted to represent the dynamic buckling behaviour of the brace member. Results obtained with this mathematical technique are compared with experimental data measured during shaking table tests of a 5/48 scale model frame. The agreement between experiment and analysis is excellent for different levels of response, ranging from linearly elastic to cyclic brace buckling. 相似文献
46.
On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofML = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ ML ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·1020 resp. 4·1018dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant. 相似文献
47.
Progress in Carrier Phase Time Transfer 总被引:1,自引:0,他引:1
Jim Ray Felicitas Arias Gérard Petit Tim Springer Thomas Schildknecht Jon Clarke Jan Johansson 《GPS Solutions》2001,4(4):47-54
The progress of the joint Pilot Project for time transfer, formed by the International GPS Service (IGS) and the Bureal International
des Poids et Mesures (BIPM), was recently reviewed. Three notable milestones were set. (1) The IGS will implement, at least
in a test mode, an internally realized time scale based on an integration of combined frequency standards within the IGS network.
This will eventually become the reference time scale for all IGS clock products (instead of the current GPS broadcast time).
(2) A new procedure for combined receiver and satellite clock products will be implemented officially in November 2000. Receiver
clocks are an entirely new product of the IGS. (3) The BIPM will coordinate an effort to calibrate all Ashtech Z12-T (and
possibly other) receivers suitable for time transfer applications, either differentially or absolutely. Progress reports will
be presented publicly in the spring 2001. ? 2001 John Wiley & Sons, Inc. 相似文献
48.
We have inferred the temperature sensitivity of Dorne Margolin choke ring antennas by direct estimation from differential
clock estimates for two GPS sites separated by 2400 km. At each site, the cable and receiver systems are very well isolated
from environmental variations. By direct comparison of the observed clock variations between these sites with local temperature
measurements, empirical temperature coefficients for each system have been estimated. These thermal coefficients most likely
apply to the only uncontrolled components of the systems, the Dorne Margolin choke ring antennas. Based on these results,
the short-term (diurnal) stability of the antennas appears to be better than 2 ps/°C. The possibility that longer-term effects
exist due to sensitivity in the daily average of the pseudorange observations has not been tested and cannot be excluded.
? 2001 John Wiley & Sons, Inc. 相似文献
49.
40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite carbonatites from the Sung Valley
carbonatite-alkaline complex, which is believed to be a part of the Rajmahal-Bengal-Sylhet (RBS) flood basalt province, yielded
indistinguishable plateau ages of 108.8 ± 2.0Ma, 106.4 ± 1.3Ma and 107.5 ± 1.4Ma, respectively. The weighted mean of these
ages, 107.2 ± 0.8 Ma, is the time of emplacement of this complex. This implies that Sung Valley complex and probably other
such complexes in the Assam-Meghalaya Plateau postdate the main flood basalt event (i.e., the eruption of tholeiites) in the
RBS province by ∼10Ma. 相似文献
50.
P. N. Shukla N. Bhandari Anirban Das A. D. Shukla J. S. Ray 《Journal of Earth System Science》2001,110(2):103-110
We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having
an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western
periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated
with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more
than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance
of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution
to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in
fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in
hydrothermal activity. 相似文献