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41.
The growth of Glasgow from a small town into a heavily industrialised conurbation depended greatly on its local geological riches. Extensive mining and quarrying of a range of minerals took place from the 18th century onwards. The early underground stoop and room (pillar and stall) workings, and the backfilled quarries, together with variably consolidated natural superficial deposits, have bequeathed to the city a heritage of unwanted engineering problems which cannot easily be quantified. Recent work by the British Geological Survey (BGS) illustrates the scale of both geological and man-made problems. 相似文献
42.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
43.
44.
Summary. Asymptotic ray theory (ART) fails in transition regions near critically reflected, bottom glancing or caustic-forming rays in a vertically inhomogeneous layered earth. These deficiencies are repaired here by replacing the transitional ray fields with guided modes plus truncation remainders. Exact ray-mode equivalences and their high-frequency asymptotic approximations are formulated, and their validity and efficiency are verified by numerical comparisons for SH motion in a two-layer earth model comprised of an inhomogeneous sediment above an homogeneous semi-infinite bedrock. 相似文献
45.
46.
Transverse secondary circulations involving surface convergence, observed in a well-mixed estuary in North Wales, are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary. The circulation and axial convergence, however, are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase.Convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross-section, produced by non-uniform advection of the longitudinal gradient through the channel. A diagnostic model, using measured mean distributions of cross-sectional density, indicates surface transverse velocities (~0.1 ms?1) similar to those observed in the estuary. The model further predicts appreciable transverse divergent currents at a fractional depth of 0.75: a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators. 相似文献
47.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
48.
Transport by southeastern rivers has insignificant influence on the lead concentration of southeastern shelf waters. If the rate of mobilization and transport of lead by these rivers is representative of uncontaminated fluvial transport during the Pleistocene, only about 5% of the prehistoric output of lead to the North Atlantic can be accounted for by river input.Lead concentrations in southeastern shelf waters are similar to those of North Atlantic Water from the upper 1000 m, which is probably similar to the intrusion source water for the shelf. Atmospheric inputs to the shelf of the same magnitude as observed for the Western North Atlantic are difficult to reconcile given the residence time of shelf waters and their lead concentration unless the rate of loss of lead to shelf sediments is about the same as the atmospheric flux. 相似文献
49.
Y.-B. WU S. GAO H.-J. GONG H. XIANG W.-F. JIAO S.-H. YANG Y.-S. LIU H.-L. YUAN 《Journal of Metamorphic Geology》2009,27(6):461-477
U–Pb age, trace element and Hf isotope compositions of zircon were analysed for a metasedimentary rock and two amphibolites from the Kongling terrane in the northern part of the Yangtze Craton. The zircon shows distinct morphological and chemical characteristics. Most zircon in an amphibolite shows oscillatory zoning, high Th/U and 176 Lu/177 Hf ratios, high formation temperature, high trace element contents, clear negative Eu anomaly, as well as HREE-enriched patterns, suggesting that it is igneous. The zircon yields a weighted mean 207 Pb/206 Pb age of 2857 ± 8 Ma, representing the age of the magmatic protolith. The zircon in the other two samples is metamorphic. It has low Th/U ratios, low trace element concentrations, variable HREE contents (33.8 ≥ LuN ≥2213; 14.7 ≤ LuN /SmN ≤ 354) and 176 Lu/177 Hf ratios (0.000030–0.001168). The data indicate that the zircon formed in the presence of garnet and under upper amphibolite facies conditions. The metamorphic zircon yields a weighted mean 207 Pb/206 Pb age of 2010 ± 13 Ma. These results combined with previously obtained Palaeoproterozoic metamorphic ages suggest a c. 2.0 Ga Palaeoproterozoic collisional event in the Yangtze Craton, which may result from the assembly of the supercontinent Columbia. The zircon in two samples yields weighted mean two-stage Hf model ( T DM2 ) ages of 3217 ± 110 and 2943 ± 50 Ma, respectively, indicating that their protoliths were mainly derived from Archean crust. 相似文献
50.
R. PALMERI M. L. FREZZOTTI G. GODARD R. J. DAVIES 《Journal of Metamorphic Geology》2009,27(9):685-705
Monocrystalline quartz inclusions in garnet and omphacite from various eclogite samples from the Lanterman Range (Northern Victoria Land, Antarctica) have been investigated by cathodoluminescence (CL), Raman spectroscopy and imaging, and in situ X‐ray (XR) microdiffraction using the synchrotron. A few inclusions, with a clear‐to‐opalescent lustre, show ‘anomalous’ Raman spectra characterized by weak α‐quartz modes, the broadening of the main α‐quartz peak at 465 cm?1, and additional vibrations at 480–485, 520–523 and 608 cm?1. CL and Raman imaging indicate that this ‘anomalous’α‐quartz occurs as relicts within ordinary α‐quartz, and that it was preserved in the internal parts of small quartz inclusions. XR diffraction circular patterns display irregular and broad α‐quartz spots, some of which show an anomalous d‐spacing tightening of ~2%. They also show some very weak, hazy clouds that have d‐spacing compatible with coesite but not with α‐quartz. Raman spectrometry and XR microdiffraction characterize the anomalies with respect to α‐quartz as (i) a pressure‐induced disordering and incipient amorphization, mainly revealed by the 480–485 and 608‐cm?1 Raman bands, together with (ii) a lattice densification, evidenced by d‐spacing tightening; (iii) the cryptic development of coesite, 520–523 cm?1 being the main Raman peak of coesite and (iv) Brazil micro‐twinning. This ‘anomalous’α‐quartz represents the first example of pressure‐induced incipient amorphization of a metastable phase in a crustal rock. This issue is really surprising because pressure‐induced amorphization of metastable α‐quartz, observed in impactites and known to occur between 15 and 32 GPa during ultrahigh‐pressure (UHP) experiments at room temperature, is in principle irrelevant under normal geological P–T conditions. A shock (due to a seism?) or a local overpressure at the inclusion scale (due to expansion mismatch between quartz and its host mineral) seem the only geological mechanisms that can produce such incipient amorphization in crustal rocks. This discovery throws new light on the modality of the quartz‐coesite transition and on the pressure regimes (non‐lithostatic v. lithostatic) during high‐pressure/UHP metamorphism. In particular, incipient amorphization of quartz could favour the quartz‐coesite transition, or allow the growth of metastable coesite, as already experimentally observed. 相似文献