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91.
Abstract— Ovoid grains consisting of glass of stoichiometric (Mg, Fe)SiO3 composition that is intimately associated with majorite were identified in the shock veins of the Suizhou meteorite. The glass is surrounded by a thick rim of polycrystalline majorite and is identical in composition to the parental low‐Ca pyroxene and majorite. These ovoid grains are surrounded by a fine‐grained matrix composed of majorite‐pyrope garnet, ringwoodite, magnesiowüstite, metal, and troilite. This study strongly suggests that some precursor pyroxene grains inside the shock veins were transformed to perovskite within the pyroxene due to a relatively low temperature, while at the rim region pyroxene grains transformed to majorite due to a higher temperature. After pressure release, perovskite vitrified at post‐shock temperature. The existence of vitrified perovskite indicates that the peak pressure in the shock veins exceeds 23 GPa. The post‐shock temperature in the meteorite could have been above 477 °C. This study indicates that the occurrence of high‐pressure minerals in the shock veins could not be used as a ubiquitous criterion for evaluating the shock stage of meteorites. 相似文献
92.
Characterizing spatial variability of soil properties in salt affected coastal India using geostatistics and kriging 总被引:2,自引:0,他引:2
93.
A. Raja Bayanna Shibu K. Mathew P. Venkatakrishnan N. Srivastava 《Solar physics》2014,289(10):4007-4019
The Multi-application Solar Telescope is a 50 cm off-axis Gregorian telescope that has been installed at the lake site of Udaipur Solar Observatory. For quasi-simultaneous photospheric and chromospheric observations, a narrow-band imager has been developed as one of the back-end instruments for this telescope. Narrow-band imaging is achieved using two lithium niobate Fabry–Perot etalons working in tandem as a filter. This filter can be tuned to different wavelengths by changing either voltage, tilt, or temperature of the etalons. To characterize the etalons, a Littrow spectrograph was set up in conjunction with a 15 cm Carl Zeiss Coudé solar telescope. The etalons were calibrated for the solar spectral lines Fe i 6173 Å, and Ca ii 8542 Å. In this work, we discuss the characterization of the Fabry–Perot etalons, specifically, the temperature and voltage tuning of the system for the spectral lines proposed for observations. We present the details of the calibration set-up and various tuning parameters. We also present solar images obtained using the system. 相似文献
94.
We present G-band and Ca ii H filtergrams of two sunspot light bridges in NOAA AR 10953 taken from the 50-cm Solar Optical Telescope onboard the Japanese
space satellite Hinode on 1 May 2007. The two light bridges differ in structure, with one of them resembling the filamentary penumbra and the other
possessing a dark central lane running along the axis of the bridge having a width of 170 km, which is close to the diffraction
limit of the telescope. Velocity measurements of the light bridges using proper motion displacements of inhomogeneities, averaged
over the entire time series, show a nonuniform flow with velocities peaking at 250 and 180 m s−1 for the two bridges, respectively. We report observations of an archlike structure over one of the light bridges in the Ca
images. Brightness enhancements are seen traveling along this arch as well as along the light bridge. Observations suggest
that these enhancements over light bridges could possibly be a signature of lower chromospheric heating. 相似文献
95.
在泡沫钻进过程中,现有的消泡器往往不能很好地达到消泡的目的。笔者建立了消泡器室内试验台,进行了消泡压力对消泡器消泡能力的影响试验,通过测试不同压力与不同泵转速确定了消泡压力与消泡率的关系,同时借助FLUENT软件对消泡器的扩散管和消泡管内部的压力分布,进行了数值模拟与分析。根据分析结果对消泡器进行了优化设计,将消泡管的长度从15cm增加至65cm。对改进后的消泡器进行室内试验,其消泡率达到80%左右。 相似文献
96.
Spatial Scale Effects of Climate Scenarios on Simulated Cotton Production in the Southeastern U.S.A.
Ruth M. Doherty Linda O. Mearns K. Raja Reddy Mary W. Downton Larry McDaniel 《Climatic change》2003,60(1-2):99-129
We examine the effect of climate scenarios generated using results from climate models of different spatial resolution on yields simulated by the deterministic cotton model GOSSYM for the southeastern U.S.A. Two related climate change scenarios were used: a coarse-scale scenario produced from results of a general circulation model (GCM) which also provided the boundary conditions to a regional climate model (RCM), from which a fine-scale scenario was constructed. Cotton model simulations were performed for three cases: climate change alone; climate change and elevatedCO2; climate change, elevated CO2 and adaptations to climate change. In general, significant differences in state-average projected yield changes between the coarse and fine-scale scenarios are found for these three cases. In the first two cases, different directions of change are found in some sub-regions. With adaptation, yields substantially increase for both climate scenarios, but more so for the coarse-scale scenario (30%domain-average increase). Under irrigation, yield change differences between the two climate scenarios are small in all three cases, and yields are higher under irrigation ( 35% domain-average increase with adaptation case) compared to dryland conditions. For the climate change alone case, differences in summer water-stress levels explain the contrasts in dryland yield patterns between the coarse and fine-scale climate scenarios. 相似文献
97.
Gehad M. Saleh 《中国地球化学学报》2006,(2)
Tungsten-bearing hydrothermal veins range from tensional veinlets to lodes containing multiple injections of hydrothermal quartz veins. Major composite lodes display greisen alteration envelopes characterized by enrichments in volatiles, K2O, Al2O3, Rb, L… 相似文献
98.
Raja CHAIRI Zohra EL ASMI DJELLOULI 《中国地球化学学报》2005,24(4):345-351
The geochemistry data show that the total organic carbon (TOC) contents are high in the surface sediments in the eastern part of the Moknine' s Sebkha. Low decreasing of organic matter ( OM ) with increasing depth indicates the good preservation of OM in modern sediments. "Lignite levels" inserted in the sand sequence and deposited at the edge and in the intermediate zone are considered as lithologic and organic markers. It is characterized by high TOC and poor hydrogen index (HI) , indicating a higher plant origin and good preservation of OM in thin beds under anoxic condition. In all samples low values of HI are typical for strong terrigenous input in the Sebkha. Gas chromatography (GC) of saturate fraction showed that OM in the border zone is provided from plants but in the central zone OM is a mixture of terrestrial fraction and little fraction from microalgae. The study of free lipids indicated that this environment was influenced by intense bacterial and microbial activities, as evidenced by the abundance of n-alkanes and nC18-nC22. 相似文献
99.
100.
Results of a paleomagnetic study carried out on the exposed volcanic rocks on the western side of the South Kenya Rift Valley are presented. Nine stratigraphic groups ranging in age from Miocene to Pleistocene were sampled. The rocks consist of basalts, trachytes, nephelinites, melanephelinites, olivine melanephelinites and ignimbrites. Paleomagnetic poles obtained for different age ranges are as follows: Period I (0.64–0.72 Ma), 116°E, 85°N (A95 = 6°); Period II (1.6–6.9 Ma), 297°E, 84°N (A95 = 4°); Period III (12.0–15.0 Ma), 34°E, 80°N (A95 = 9°). The results for Period II show large secular variations which are in disagreement with the model predictions for near-equatorial sites. 相似文献