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911.
912.
不同环剪方式下滑带土残余强度试验研究 总被引:9,自引:0,他引:9
以三峡库区黄土坡滑坡滑带土为研究对象,利用环剪仪研究了黄土坡滑坡滑带土在单级剪、预剪以及多级剪3种环剪方式下的残余强度特征。试验结果表明:不同环剪试验下剪切带的形成与剪切位移相关;残余强度随有效法向应力的增大而增大,对于已经存在剪切带的滑带土,环剪时能很快达到残余强度状态;滑带土环剪轴向压缩分初始剪胀、颗粒运移压密和稳定压密3个阶段,且每个阶段剪应力变化趋势不同;预剪试验和多级剪切试验得到的残余强度偏大,应该首选单级剪切试验测试滑带土残余强度指标。 相似文献
913.
Diel tuning of photosynthetic systems in ice algae at Saroma-ko Lagoon, Hokkaido, Japan 总被引:1,自引:0,他引:1
Shimpei Aikawa Hiroshi Hattori Yasushi Gomi Kentaro Watanabe Sakae Kudoh Yasuhiro Kashino Kazuhiko Satoh 《Polar Science》2009,3(1):57-72
Ice algae are the major primary producers in seasonally ice-covered oceans during the cold season. Diurnal change in solar radiation is inevitable for ice algae, even beneath seasonal sea ice in lower-latitude regions. In this work, we focused on the photosynthetic response of ice algae under diurnally changing irradiance in Saroma-ko Lagoon, Japan. Photosynthetic properties were assessed by pulse-amplitude modulation (PAM) fluorometry. The species composition remained almost the same throughout the investigation. The maximum electron transport rate (rETRmax), which indicates the capacity of photosynthetic electron transport, increased from sunrise until around noon and decreased toward sunset, with no sign of the afternoon depression commonly observed in other photosynthetic organisms. The level of non-photochemical quenching, which indicates photoprotection activity by dissipating excess light energy via thermal processes, changed with diurnal variations in irradiance. The pigment composition appeared constant, except for xanthophyll cycle pigments, which changed irrespective of irradiance. These results indicate that ice algae tune their photosynthetic system harmonically to achieve efficient photosynthesis under diurnally changing irradiance, while avoiding damage to photosystems. This regulation system may be essential for productive photosynthesis in ice algae. 相似文献
914.
基于ARMA模型的隧道位移时间序列分析 总被引:7,自引:0,他引:7
在新奥法隧道施工中,隧道位移监测对于评价围岩稳定性和支护结构合理性起重要作用。目前大都采用AR模型对隧道位移进行时间序列分析,避开了非线性估计,致使拟合精度和模型实用性较差。为此,介绍了具有较高预测精度和较好适用条件的ARMA模型及其常用参数估计方法,基于其参数非线性估计带来的不便性,提出一种ARMA模型参数估计近似线性方法,把残差用Taylor级数一阶展开,将非线性估计线性化,用线性最小二乘法估计参数最终值。用该方法对重庆市大足县南环二路南山隧道位移监测数据进行时间序列建模分析,预测与实测值吻合较好,证明了该方法的实用性。 相似文献
915.
通过岩心和测井资料分析,系统地研究了松辽盆地中央坳陷滨北地区上白垩统青山口组的沉积特征;采用单因素分析多因素综合作图法,编制出了研究区上白垩统青山口组各亚段的砂岩含量、暗色泥岩含量和紫红色泥岩含量等单因素图件,在此基础上做出沉积相图,深入分析了研究区沉积演化规律。研究表明,青山口组主要发育三角洲和湖泊2种沉积相,进一步分为三角洲平原、三角洲前缘、滨浅湖和半深湖-深湖4种沉积亚相。从研究区边缘到中心,沉积相类型由三角洲平原亚相渐变为三角洲前缘、滨浅湖和半深湖-深湖亚相;自下而上由半深湖-深湖亚相逐渐变为滨浅湖、三角洲前缘、三角洲平原亚相。青山口组沉积时期可划分为青山口组沉积早期、青山口组沉积中期和青山口组沉积晚期。不同时期、不同构造单元的沉积特征表现各异,从青山口组沉积早期到青山口组沉积晚期,研究区湖盆发育总体表现出规模由大到小的特点。 相似文献
916.
Neoproterozoic Attunga Eclogite in Eastern Australia Margin 总被引:1,自引:0,他引:1
917.
918.
Nutrient concentrations (nitrate + nitrite, phosphate and silicate) in deep seawater (321 m depth) of Toyama Bay, Japan, were measured from August 1996 to July 1997 to determine the magnitude of daily variations. Significant daily variations were observed; concentrations ranged from 4.42 to 22.4 µM for nitrate + nitrite, from 0.86 to 1.98 µM for phosphate, and from 9.91 to 47.7 µM for silicate, respectively. However, there were not significant relationships between nutrient concentrations and water temperature, or between nutrients and salinity. Since temperature and salinity in the >300 m depth layer were constant through the year, the results suggest that there may be water masses with different nutrient concentrations in the deep layers (at about 320 m depth) of the bay, and a horizontal advection of these water masses may be responsible for the observed daily variations. 相似文献
919.
920.
Yumiko Watanabe Shun'ichi Nakai Akihiro Hiruta Ryo Matsumoto Kunio Yoshida 《Earth and Planetary Science Letters》2008,272(1-2):89-96
We performed U–Th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off Joetsu, of the eastern margin of Japan Sea, to decipher the active period of the methane seep. The carbonates contain 230Th, part of which is located in detritus such as silicate and organics, at the time of precipitation. The initial 230Th renders accurate dating with U–Th radioactive disequilibrium method difficult. We assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty. A (230Th/232Th)–(234U/232Th) isochron drawn by three chips divided from a carbonate nodule (PC05-04-50) passed through data points of local sediments. We conclude that the problem of initial 230Th can be resolved by measurements of local sediments. Results show that carbonate nodules include local sediment as impurities. Furthermore, the results of trace element analyses such as Rb, Zr, Nb, REE, Pb, and Th also support the idea.In all, 18 carbonate samples were dated with correction of initial 230Th using the mean value of local sediment in this study. The U–Th correction ages show 12–35ka with an isochron age of 26 ± 3ka. Results indicate that during the time interval of U–Th ages, from 12ka to 35ka, environmental conditions must have been favorable for enhanced methane flux through sediment. The extensive methane flow period at 20ka accords with the lowest-stand sea level during the last glacial age. Results of this study also suggest that U–Th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation. In order to acquire U–Th ages of carbonate at methane seep sites, however, it is important to evaluate the amount of initial 230Th accurately using the value of sediment. 相似文献