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201.
The Changbai Mountains (2749 m a.s.l.) in northeastern China are one of the typical mountain regions with glaciation since late Pleistocene as evidenced by well-preserved erosive and accumulative landforms at elevations above 2000 m a.s.l, formed by glaciers around the crater lake, Tianchi Lake. Cirque glaciers developed on both the inner and outer sides of the volcanic cone. Well-preserved cirques, glacial trough valleys, glacial threholds, polished surfaces of the glacial erratics and the moraine ridges indicate that several glaciation processes took place during the last glacial period in this region. Resuits of optically stimulated luminescence (OSL) dating on the moraine sediments, and the K/Ar, thermal ionization mass spectrometry (TIMS), electronic spinning resonance (ESR) dating on the volcanic rocks suggest two periods of glacier advances. One is named the Black Wind Mouth glacier advance taking place on the west and north slopes of the volcanic cone at an elevation of 2000-2100 m a.s.l., which is dated to about 20 ka, being the result of the Last Glacial Maximum (LGM). The other is named the Meteorological Station glacier advance at the elevation of 2400-2600 m a.s.l., dated to 11 ka during the late glacial period, and is tentatively correlated to the Younger Dryas stage. The scope of the former glacier advance is larger than that of the latter. Regional comparisons showed that the glacial sequences in the Changbai Mountains are similar to other glaciated areas in eastern Asia during the later part of the last glacial cycle. 相似文献
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203.
在股票价格、公司价值均服从分数布朗运动,公司负债为常数的条件下,讨论脆弱欧式股票看涨期权的风险价值(value at risk,VaR)和条件风险价值(conditional value at risk,CVaR)的计算问题,并推导了该期权的VaR和CVaR的计算公式. 相似文献
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205.
针对三峡水利枢纽拦河大坝泄洪流量大、孔口多、泄洪消能结构复杂,岸坡厂房坝段基岩长大缓倾角结构面因坝后厂房深挖临空危及坝基稳定,坝体混凝土耐久性要求高且温控防裂困难;茅坪溪防护土石坝沥青混凝土心墙设计施工尚缺乏实践经验;电站运行水头高、变幅大,引水压力管道及进水口选型和蜗壳埋设方式技术复杂,地下电站采用变顶高尾水洞替代常规的尾水调压室;双线五级船闸运行水头高、输水水力条件复杂,且在山体深挖岩槽中修建,全衬砌船闸结构、高水头输水系统和大型人字闸门及启闭机设计难度大等关键技术问题,文章重点介绍了各建筑物设计研究解决问题的途径、采用的优选方案及技术措施和通过实践检验的创新成果。 相似文献
206.
利用1951年9月~2010年8月宜昌站逐日气象资料,采用气候趋势系数、5a滑动平均法、累积距平和一元线性回归法对宜昌市近59年来的气候变化趋势特征进行了诊断分析,结果表明:宜昌市的年平均气温呈现上升趋势,年平均最低气温的上升速率高于年平均最高气温的上升速率,导致年平均日较差呈现下降的趋势;在季节变化上,除了夏季,其他季节都呈升高趋势,其中春季的上升趋势最为显著.年降水量呈现略微增加的趋势,冬季增加趋势较为显著.该成果对进一步研究和预测宜昌市的气候变化有着重要意义. 相似文献
207.
针对常规偏振发生器中机械转动带来系统误差大的问题,提出了基于双液晶相位延迟器调制的偏振光发生系统,该系统由偏振片结合两片液晶相位可变延迟器(Liquid Crystal Variable Retarder,LCVR)组成.利用液晶相位可变延迟器的电控作用,计算机控制双LCVR延迟量的不同组合,实现对入射光波偏振态的调制.通过对Stokes参数定义中的6种特定偏振态的测定,验证了此方案的可行性,偏振度的精度可达千分之一,可为系统定标和测试提供更加精确的偏振光源,并能大幅提高偏振测量系统的精度、节省实验时间. 相似文献
208.
采用光还原沉积法制备了SO_4~(2-)/Au-TiO_2催化剂,考察了其在丙二醇单甲醚乙酸酯合成反应中的催化活性。用XRD对催化剂结构进行了表征,结果显示催化剂经过酸化后的晶体结构并没有发生改变,Au颗粒均匀地分散在TiO_2表面。使用SO_4~(2-)/Au-TiO_2催化剂,以合成丙二醇单甲醚乙酸酯为探针反应,研究了反应温度、酸醚物质的量比、催化剂用量对反应平衡转化率的影响。实验结果表明,其最佳反应条件为反应温度413 K,酸醚物质的量比3:1,催化剂用量3%(w)。 相似文献
209.
To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870℃ for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850℃, where grains with a diameter ≤ 500 nm accounted for 30% and those with a diameter >0.5 μm accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%. 相似文献
210.
Slip rate along the Lijiang-Ninglang fault zone estimated from repeating microearthquakes 总被引:2,自引:0,他引:2
Seismicity and slip rates along the Lijiang-Ninglang fault zone between 1999 and 2006 were investigated with the waveform
data recorded by the Yunnan digital Seismic Network. The relocated seismicity by the double difference method clearly exhibits
different features between the northern and southern segments. More than 76% earthquakes occurred in the southern segment
of the fault near the Lijiang area. The relocated seismicity appears to reflect the crustal velocity structure of the study
area. Using cross-correlation analysis, we identified a total of 92 doublets and 70 multiplets that show high waveform similarity.
Most of these sequences are aperiodic with recurrence intervals varying from a few minutes to hundreds of days. Using two
sequences that occurred regularly over the study period, we obtained a fault slip rate of approximately 5 mm/a at ∼23 km,
in good agreement with geologic and surface GPS measurement.
Supported by National Basic Research Program of China (Grant No. 2004CB418405) and National Natural Science Foundation of
China (Grant No. 40174014) 相似文献