排序方式： 共有35条查询结果，搜索用时 15 毫秒
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dr. phil. N. KINGO JACOBSEN CHR. BAY B. FREDSKILD B. GRøNNOW B. HOLM JAKOBSEN M. MELDGAARD 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):29-44
Jacobsen, N. Kingo, et.al. Report of activities at Tugtuligssuaq, Melville Bugt, 1978–79. Geografisk Tidsskrift 80: 29–44. Copenhagen, June 1980. A joint cooperative Greenland/Danish expedition to the Melville Bugt area, Tugtuligssuaq/Kap Seddon to throw light on the Eskimos' immigration routes to Greenland seen in relation to climatic fluctuations. Studies of geography, botany, zoology, archaeology, and ethnohistory have been carried out. 相似文献
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Nicholas E. TIMMS Steven M. REDDY David HEALY Alexander A. NEMCHIN Marion L. GRANGE Robert T. PIDGEON Robert HART 《Meteoritics & planetary science》2012,47(1):120-141
Abstract– The microstructures of lunar zircon grains from breccia samples 72215, 73215, 73235, and 76295 collected during the Apollo 17 mission have been characterized via optical microscopy, cathodoluminescence imaging, and electron backscatter diffraction mapping. These zircon grains preserve deformation microstructures that show a wide range in style and complexity. Planar deformation features (PDFs) are documented in lunar zircon for the first time, and occur along {001}, {110}, and {112}, typically with 0.1–25 μm spacing. The widest PDFs associated with {112} contain microtwin lamellae with 65°/<110> misorientation relationships. Deformation bands parallel to {100} planes and irregular low‐angle (<10°) boundaries most commonly have <001> misorientation axes. This geometry is consistent with a dislocation glide system with <100>{010} during dislocation creep. Nonplanar fractures, recrystallized domains with sharp, irregular interfaces, and localized annealing textures along fractures are also observed. No occurrences of reidite were detected. Shock‐deformation microstructures in zircon are explained in terms of elastic anisotropy of zircon. PDFs form along a limited number of specific {hkl} planes that are perpendicular to directions of high Young’s modulus, suggesting that PDFs are likely to be planes of longitudinal lattice damage. Twinned {112} PDFs also contain directions of high shear modulus. A conceptual model is proposed for the development of different deformation microstructures during an impact event. This “shock‐deformation mechanism map” is used to explain the relative timing, conditions, and complexity relationships between impact‐related deformation microstructures in zircon. 相似文献
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The delayed fission neutron counting method has been used for the analysis of thirty-three international geochemical reference samples for their uranium contents in the range of 0.2 to 1500 ppm. These include three from the Canada Centre for Mineral and Energy Technology, three from Atomic Energy Commission, USA, New Brunswick Laboratory, two from Bhabha Atomic Research Centre, India, fourteen from Centre de Recherches Pétrographiques et Géochimiques and eleven from US Geological Survey. The experimental set up has a detection limit of 0.08 μg and a determination limit of 0.15 μg U. At the lower limit the precision of determination is about 20 percent while at concentrations higher than 1 ppm it is better than 10 percent. 相似文献
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NICHOLSON HUGH; CONDOMINES MICHEL; FITTON J. GODFREY; FALLICK ANTHONY E.; GR?NVOLD KARL; ROGERS GRAEME 《Journal of Petrology》1991,32(5):1005-1020
The Krafla volcanic system consists of a central volcano andassociated fissure swarm in the NE axial rift zone of Iceland.Lavas spanning the whole of Krafla's exposed volcanic history(estimated to be 0-> 300 ka) have been analysed and rangein composition from olivine tholeiite to rhyolite. Major-elementcompositions suggest that fractional crystallization exertsthe main control over the differentiation process. However,K2O and the very incompatible trace elements, Rb, Th, and U,are all enriched beyond the extent expected by closed-systemfractional crystallization. Fractionation coupled with periodicreplenishment and tapping of the reservoir is unlikely to beresponsible for this enrichment, despite the geophysical evidencesuggesting a large number of inflations and deflations of ashallow magma reservoir (Tryggvason, 1986). Th- and O-isotope results confirm the work of previous authorsthat crustal assimilation is operating on a local scale beneathKrafla. A model is suggested, fitting both the Th- and O-isotopicdata, which involves the partial melting and incorporation ofa hydrothermally altered wall-rock contaminant during fractionalcrystallization (i. e., AFC processes). This process of partialmelting is likely to enhance the most highly incompatible elementconcentrations (e. g., increasing Rb/Zr) more than expectedby closed-system fractional crystallization. 相似文献
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Reddy , I. K., D. Rankin , 1971, Magnetotelluric Effect of Dipping Anisotropies, Geophysical Prospecting 19, 84–97. A solution is obtained for the magnetotelluric effect in the case of multi-layered earth, each layer containing dipping anisotropy, with the strike of anisotropy oriented at an arbitrary angle to the measuring directions. A technique to compute tensor impedances and tensor apparent resistivities is presented and the importance of anisotropies in magnetotelluric interpretation is discussed. 相似文献
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B VENKATESH LAKSHMAN NANDAGIRI B K PURANDARA V B REDDY 《Journal of Earth System Science》2011,120(3):387-398
The objective of this study is to apply and test a simple parametric water balance model for prediction of soil moisture regime
in the presence of vegetation. The intention was to evaluate the differences in model parameterization and performance when
applied to small watersheds under three different types of land covers (Acacia, degraded forest and natural forest). The watersheds selected for this purpose are located in the sub-humid climate within
the Western Ghats, Karnataka, India. Model calibration and validation were performed using a dataset comprising depth-averaged
soil moisture content measurements made at weekly time steps from October 2004 to December 2008. In addition to this, a sensitivity
analysis was carried out with respect to the water-holding capacity of the soils with the aim of explaining the suitability
and adaptation of exotic vegetation types under the prevailing climatic conditions. Results indicated reasonably good performance
of the model in simulating the pattern and magnitude of weekly average soil moisture content in 150 cm deep soil layer under
all three land covers. This study demonstrates that a simple, robust and parametrically parsimonious model is capable of simulating
the temporal dynamics of soil moisture content under distinctly different land covers. Also, results of sensitivity analysis
revealed that exotic plant species such as Acacia have adapted themselves effectively to the local climate. 相似文献
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M SHRAVAN KUMAR V K ANANDAN AMIT KESARKAR P NARASIMHA REDDY 《Journal of Earth System Science》2011,120(1):65-72
Doppler SODAR (Sound Detection and Ranging) measurements over a tropical Indian station at National Atmospheric Research Laboratory
(NARL), Gadanki (13.5°N, 79.2°E) during two consecutive monsoon seasons, 2007 and 2008, are investigated to study the influence
of mechanically generated turbulence on temperature structure parameter (CT2)_{\rm T}^{2}) in the convective boundary layer. Increase in the CT2_{\rm T}^{2} is observed after the arrival of monsoon for both seasons. Contribution of vertical wind shear in horizontal wind component
to CT2_{\rm T}^{2} due to zonal winds is responsible for the increase observed in the temperature structure parameter which is inferred from
the results obtained. CT2_{\rm T}^{2} is found to be increased by an order of 2 in both the lower and upper altitudes, respectively. Magnitude of wind speed is
reported to be doubled with the arrival of monsoon. It is also observed that, southwest monsoon wind modulates the day-to-day
variations of wind pattern over this station during the onset phase of monsoon season. The lower variability observed at lower
height is attributed to the complex topography surrounding this region. 相似文献
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