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121.
Michio Hashizume Kiyoshi Ito Toshikatsu Yoshii 《Geophysical Journal International》1981,66(1):157-168
Summary. Two record sections have been prepared for a series of explosions near Lake Biwa, south-western Honshu, Japan. The record sections cover both the array stations and the network of microearthquake stations that are distributed throughout the area. This enabled us to detect for the first time in the Japanese islands the phase reflected at the Mohorovicić discontinuity. Until now the weakness and obscurity of the phase has made it difficult to detect. We were able to overcome this problem by processing the seismograms to enhance the phase. Our work leads us to propose that the surface of the Mohorović discontinuity may be divided into pieces by a number of deep faults, while a thin layer of ultrabasic rock in the lower crust may account for the weakness of the signal. 相似文献
122.
Mn-carbonates are documented in the late-glacial varved sediments from Big Watab Lake, Minnesota, USA. The Mn-carbonate is authigenic and forms rims around contemporaneous epilimnetic calcite. Although such carbonates are found in minor amounts throughout the entire late-glacial sequence, significant quantities of Mn-carbonate are associated mainly with laminated intervals.Because of the suspected difference in isotopic fractionation between different carbonate minerals, the stable-isotopic compositions of bulk carbonate samples are used as a proxy for relative amounts of the Mn-carbonate in the sediment. High 18O and low 13C values are associated with abundant Mn-carbonates. Low 18O and high 13C values are associated with only minor concentrations of Mn-carbonates.The oxygen-18 record is correlated with fluctuations in the vegetation assemblage based on pollen spectra using a multiple regression model with backward elimination. The proposed link between the sedimentary archive and local vegetation is the mediation of advective mixing in the lake by forest composition. In this model, periods of forest closure resulted in a well-stratified water column that was anoxic at the sediment/water interface, permitting the formation of authigenic Mn-carbonates. Openings of Artemisia in the forest allowed wind shear to mix oxygen to depth, causing bioturbation of the laminations and preventing the formation of Mn-carbonate. 相似文献
123.
S. Ono E. Ito T. Katsura A. Yoneda M. J. Walter S. Urakawa W. Utsumi K. Funakoshi 《Physics and Chemistry of Minerals》2000,27(9):618-622
In situ synchrotron X-ray experiments in the system SnO2 were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure
apparatus. Orthorhombic phase (α-PbO2 structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the
isothermal bulk modulus of cubic phase K
0 = 252(28) GPa and its pressure derivative K
′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the
P-V-T data obtained, and is 1.7(±0.7) × 10−5 K−1 at 25 GPa.
Received: 7 December 1999 / Accepted: 27 April 2000 相似文献
124.
Impacts of regional warming on long‐term hypolimnetic anoxia and dissolved oxygen concentration in a deep lake
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Although few reports have described long‐term continuous anoxia in aquatic systems, Lake Ikeda in Japan experienced such conditions in the hypolimnion from 1990 to 2010. The present study aimed to assess temporal fluctuations in the lake's thermal stability from 1978 to 2011 to understand the influence of regional climate change on hypolimnetic anoxia in this lake. Because complete vertical mixing, which supplies dissolved oxygen (DO) to the hypolimnion, potentially occurs on February, we calculated the Schmidt stability index (S) in February and compared it with hypolimnetic DO dynamics. Vertical water temperature profiles were calculated using a one‐dimensional model, and calculated temperatures and meteorological data were used to analyse annual fluctuations in water temperatures, thermocline depth, meteorological variables and S. We estimated that mean annual air and volume‐weighted water temperatures increased by 0.028 and 0.033 °C year?1, respectively, from 1978 to 2011. Between 1986 and 1990, S and water temperature increased abruptly, probably due to a large upwards trend in air temperature (+0.239 °C year?1). We hypothesize that a mixing regime that lacked overturn took effect at this time and that this regime lasted until 2011, when S was particularly small. These results demonstrate that abrupt climate warming in the late 1980s likely triggered the termination of complete mixing and caused the 21‐year period of successive anoxia in Lake Ikeda. We conclude that the lake response to a rapid shift in regional climate conditions was a key factor in changing the hypolimnetic water environment and that thermal stability in winter is a critical environmental factor controlling the mixing regime and anoxic conditions in deep lakes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
125.
The tried and tested multianvil apparatus has been widely used for high-pressure and high-temperature experimental studies in Earth science. As a result, many important results have been obtained for a better understanding of the components, structure and evolution of the Earth. Due to the strength limitation of materials, the attainable multianvil pressure is generally limited to about 30 GPa (corresponding to about 900 km of the depth in the Earth) when tungsten carbide cubes are adopted as second-stage anvils. Compared with tungsten carbide, the sintered diamond is a much harder material. The sintered diamond cubes were introduced as second-stage anvils in a 6–8 type multianvil apparatus in the 1980s, which largely enhanced the capacity of pressure generation in a large volume press. With the development of material synthesis and processing techniques, a large sintered diamond cube (14 mm) is now available. Recently, maximum attainable pressures reaching higher than 90 GPa (corresponding to about 2700 km of the depth in the Earth) have been generated at room temperature by adopting 14-mm sintered diamond anvils. Using this technique, a few researches have been carried out by the quenched method or combined with synchrotron radiation in situ observation. In this paper we review the properties of sintered diamond and the evolution of pressure generation using sintered diamond anvils. As-yet unsolved problems and perspectives for uses in Earth Science are also discussed. 相似文献
126.
Regional long-term production modeling from a single well test, Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope 总被引:1,自引:0,他引:1
127.
Yasuhiro Oba Takeshi Chigai Yoshihiro Osamura Naoki Watanabe Akira Kouchi 《Meteoritics & planetary science》2014,49(1):117-132
We experimentally studied hydrogen (H)–deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H–D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18 kJ mol?1, CH3NH2 reacted with D atoms to yield deuterated methylamines at 10 K, suggesting that the H–D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine. 相似文献
128.
129.
130.
Fractal structure of spatial distribution of microfracturing in rock 总被引:10,自引:0,他引:10