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31.
32.
Mechanistic model development and numerical analyses were carried out on coupled thermo-hydraulic-mechanical processes in bentonite-based buffer material for the geological disposal of high-level radioactive waste with small-scale laboratory experiments and a full-scale test. The mechanism of water movement in compacted bentonite was identified by applying theoretical equations to the experimental results. The application clearly explained the observed results of the temperature dependence of the hydraulic conductivity in the saturated state and the water diffusivity in the unsaturated state for the compacted bentonite and the dry density dependence of the diffusivity. The full-scale coupled test, BIG-BEN, was conducted at PNC (Power Reactor and Nuclear Fuel Development Corporation) Tokai Works. The results of the numerical analyses for the full-scale test which are based on the present knowledge of coupled processes and our small-scale experiments were in good agreement with the measured results except for mechanical phenomena. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
33.
Hitoshi Hasegawa Suvapak Imsamut Punya Charusiri Ryuji Tada Yu Horiuchi Ken‐Ichiro Hisada 《Island Arc》2010,19(4):605-621
The Tibetan Plateau is a key factor in controlling the present‐day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high‐pressure belt, and the prevailing surface‐wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high‐pressure belt in low‐latitude Asia during the Cretaceous. Spatio‐temporal changes in the paleo‐wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high‐pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid‐Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo‐wind direction data, suggest the development of low‐latitude desert and an equatorward shift of the subtropical high‐pressure belt (relative to the present‐day) in Asia during the mid‐Cretaceous. 相似文献
34.
Heterogeneity in supraglacial debris thickness and its role in glacier mass changes of the Mount Gongga 总被引:3,自引:0,他引:3
In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, it accelerates ice melting on ~10.2% of total ablation zone and produces rapid wastage of ~25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the importance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world. 相似文献
35.
Blair Thornton Seiki Ohnishi Tamaki Ura Naoteru Odano Shun Sasaki Tsuneo Fujita Tomowo Watanabe Kaoru Nakata Tsuneo Ono Daisuke Ambe 《Marine pollution bulletin》2013
An estimated 3.5 ± 0.7 × 1015 Bq of 137Cs is thought to have been discharged into the ocean following the melt down at Fukushima Dai-ichi Nuclear Power Plant (F1NPP). While efforts have been made to monitor seafloor radiation levels, the sampling techniques used cannot capture the continuous distribution of radionuclides. In this work, we apply in situ measurement techniques using a towed gamma ray spectrometer to map the continuous distribution of 137Cs on the seafloor within 20 km of the F1NPP. The results reveal the existence of local 137Cs anomalies, with levels of 137Cs an order of magnitude higher than the surrounding seafloors. The sizes of the anomalies mapped in this work range from a few meters to a few hundreds of meters in length, and it is demonstrated that the distribution of these anomalies is strongly influenced by meter scale features of the terrain. 相似文献
36.
We performed stable carbon and nitrogen-guided analyses of biomagnification profiles of arsenic (As) species, including total As, lipid-soluble As, eight water-soluble As compounds (arsenobetaine (AB), arsenocholine (AC), tetramethylarsonium ion (TETRA), trimethylarsine oxide (TMAO), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), arsenate (As[V]), and arsenite (As[III])), and non-extracted As in a tropical mangrove ecosystem in the Ba Ria Vung Tau, South Vietnam. Arsenobetaine was the predominant As species (65-96% of water-soluble As). Simple linear regression slopes of log-transformed concentrations of total As, As fractions or individual As compounds on stable nitrogen isotopic ratio (δ15N) values are regarded as indices of biomagnification. In this ecosystem, lipid-soluble As (slope, 0.130) and AB (slope, 0.108) were significantly biomagnified through the food web; total As and other water-soluble As compounds were not. To our knowledge, this is one of the first reports on biomagnification profiles of As compounds from a tropical mangrove ecosystem. 相似文献
37.
Background
Induced precipitation of phosphate minerals to scavenge trace elements from groundwater is a potential remediation approach for contaminated aquifers. The success of engineered precipitation schemes depends on the particular phases generated, their rates of formation, and their long term stability. The purpose of this study was to examine the precipitation of calcium phosphate minerals under conditions representative of a natural groundwater. Because microorganisms are present in groundwater, and because some proposed schemes for phosphate mineral precipitation rely on stimulation of native microbial populations, we also tested the effect of bacterial cells (initial densities of 105 and 107 mL-1) added to the precipitation medium. In addition, we tested the effect of a trace mixture of propionic, isovaleric, formic and butyric acids (total concentration 0.035 mM).Results
The general progression of mineral precipitation was similar under all of the study conditions, with initial formation of amorphous calcium phosphate, and transformation to poorly crystalline hydroxylapatite (HAP) within one week. The presence of the bacterial cells appeared to delay precipitation, although by the end of the experiments the overall extent of precipitation was similar for all treatments. The stoichiometry of the final precipitates as well as Rietveld structure refinement using x-ray diffraction data indicated that the presence of organic acids and bacterial cells resulted in an increasing a and decreasing c lattice parameter, with the higher concentration of cells resulting in the greatest distortion. Uptake of Sr into the solids was decreased in the treatments with cells and organic acids, compared to the control.Conclusions
Our results suggest that the minerals formed initially during an engineered precipitation application for trace element sequestration may not be the ones that control long-term immobilization of the contaminants. In addition, the presence of bacterial cells appears to be associated with delayed HAP precipitation, changes in the lattice parameters, and reduced incorporation of trace elements as compared to cell-free systems. Schemes to remediate groundwater contaminated with trace metals that are based on enhanced phosphate mineral precipitation may need to account for these phenomena, particularly if the remediation approach relies on enhancement of in situ microbial populations. 相似文献38.
Koji Sugie Kenshi Kuma Satoshi Fujita Satomi Ushizaka Koji Suzuki Tsutomu Ikeda 《Journal of Oceanography》2011,67(2):183-196
We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal
centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates
and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore
desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions
with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies
were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from
high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions
could often occur in surface waters of the Oyashio region from spring to summer. 相似文献
39.
Transport of oceanic nitrate from the continental shelf to the coastal basin in relation to the path of the Kuroshio 总被引:1,自引:0,他引:1
Ryo Sugimoto Akihide Kasai Toshihiro Miyajima Kouichi Fujita 《Continental Shelf Research》2009,29(14):1678-1688
Hydrographic and biogeochemical observations were conducted along the longitudinal section from Ise Bay to the continental margin (southern coast of Japan) to investigate changes according to the Kuroshio path variations during the summer. The strength of the uplift of the cold deep water was influenced by the surface intrusion of the Kuroshio water to the shelf region. When the intrusion of the Kuroshio surface water to the shelf region was weak in 2006, the cold and NO3−-rich shelf water intruded into the bottom layer in the bay from the shelf. This bottom intrusion was intensified by the large river discharge. The nitrogen isotope ratio (δ15N) of NO3− (4–5‰) in the bottom bay water was same as that in the deeper NO3− over the shelf, indicating the supply of new nitrogen to the bay. The warm and NO3−-poor shelf water intruded into the middle layer via the mixing region at the bay mouth when the Kuroshio water distributed in the coastal areas off Ise Bay in 2005. The regenerated NO3− with isotopically light nitrogen (δ15N=−1‰) was supplied from the shelf to the bay. This NO3− is regenerated by the nitrification in the upper layer over the shelf. The contribution rate of regenerated NO3− over the shelf to the total NO3− in the subsurface chlorophyll maximum layer in the bay was estimated at 56% by a two-source mixing model coupled with the Rayleigh equation. 相似文献
40.