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41.
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
42.
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
43.
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
44.
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
45.
Comparability of Large-Scale Studies of Agricultural Chemical Contamination of Rural Private Wells 总被引:1,自引:0,他引:1
Detection of agricultural chemicals in ground water has prompted numerous studies. Federal, state, and regional studies were conducted in the last 10 years in order to assess the occurrence of agricultural chemicals in ground water. The results of the studies present the number or percentage of samples with agricultural chemicals above the drinking water standard or health advisory levels as well as samples with detections of one or more compounds. Data comparison from one state or region to another are frequently referred to by regulatory and agency personnel involved in water quality and agriculture issues. Unless the history of pesticide use, method of chemical analyses, detection limits, statistical design of the sampling plan, well type, well depth, geology of the formation material, and typical land use around the wellhead are known, such comparisons can be misleading. Reporting the limitations or presenting a disclaimer should be a key element for a study so that "apples and oranges" are not compared. 相似文献
46.
The metamorphic rocks of the Jutogh Series around Simla, structurally overlying the less metamorphosed rock groups along a thrust contact, have been involved in three phases of deformation and two episodes of metamorphism. The first metamorphism is in the albite-epidote-amphibolite facies in a major part of the area, reaching the amphibolite facies locally in the central part. This metamorphism is late-to post-kinematic with reference to the F
1 movement, the thermal peak having been reached in a post-F
1 pre-F
2 static phase. The second metamorphism, syn-to post-tectonic with respect to F
2 but preceding F
3, is generally in the greenschist facies, and only locally in the albite-epidote-amphibolite facies in the higher structural levels. Metamorphic overprinting has caused widespread retrogression and disequilibrium assemblages. As the large scale recumbent folding and thrusting of F
1 and F
2 phases belong to the Tertiary Himalayan orogeny, the metamorphism in the Jutogh Series could not have been Precambrian in age. 相似文献
47.
A.L. AlbeeA.A. Chodos A.J. GancarzE.L. Haines D.A. PapanastassiouL. Ray F. TeraG.J. Wasserburg T. Wen 《Earth and Planetary Science Letters》1972
Luna 16 sample B-1 was the largest fragment (62 mg) obtained in the sample exchange with the USSR. Petrologic, mineralogic, and chemical investigations have been made on this fragment in conjunction with Rb-Sr and40Ar/39Ar investigations by our colleagues. Sample B-1 is a fine-grained ophitic basalt but is distinguished from the Apollo samples by containing a single pyroxene, predominantly pigeonitic, an ilmenite content (7%) intermediate to that of the Apollo 11 and 12 samples, and subequal amounts of pyroxene (50%) and plagioclase (40%). Chemically it is distinguished by a high Sr content (437 ppm) and a high K/U value (4700). The K-content (1396 ppm) is higher than that of Luna 16 soil sample A-2. 相似文献
48.
49.
Amygdaloidal tholeiitic flows, locally pillowed, have been mapped at intervals over a distance of 280 km along the margins of the North Savannas Rift Valley in southern Guyana and Brazil. The combined chemical and petrological evidence suggests that the formation represents an originally uniform continental tholeiitic sequence that has undergone variable secondary alteration involving increasing oxidation and ingress of soda, potash and water. The lavas are both spatially and temporally related to the rift faulting; field observations and K∶Ar age determinations on eleven samples from different localities indicate that the flows were erupted during the Early to Middle Jurassic (180-150 m. y.). It is shown that this tectono-magmatic event is synchronous with the initiation of the southern North Atlantic rift and the pan-Antarctic rift which resulted in fragmentation of the continents according to the scheme ofDietz &Holden (1970). 相似文献
50.