马四剖面揭示的共和盆地12 ka以来的环境演变

以共和盆地东部风成沉积剖面(MS剖面)磁化率为依据,运用四次回归方程重建了剖面形成时的年均气温和降水量,确定近12 ka以来共和盆地年均温度–0.37℃～5.09℃,多年平均温度为2.5℃,降水量267.91～550.77 mm,多年平均降水量为418.62 mm。对常量元素氧化物(SiO_2、Al_2O_3和Fe_2O_3)含量进行分析,结果表明:1)古土壤层SiO_2含量均低于风成砂层, Al_2O_3和Fe_2O_3含量均高于风成砂层; 2)风成砂层SiO_2含量S3>S5>S1,Al_2O_3和Fe_2O_3含量S5>S3>S1,揭示S3层形成时期冷干, S5层次之, S1层干旱程度较弱;土壤层SiO_2含量S4>S2>S6, Al_2O_3和Fe_2O_3含量为S6>S2>S4,表明S6形成时期气候温湿, S2层次之, S4层温湿程度较低; 3)分层氧化物变异系数大小表明S2和S6层形成时气候波动剧烈, S1和S3层形成时期气候较稳定。以常量元素氧化物含量、温度和降水为依据,结合14C测年,重建了近12 ka以来共和盆地环境演变过程:11.9 ka BP以前为凉干期,11.9～9.7 ka BP为温湿期, 9.7～8.0 ka BP为冷干期, 8.0～4.8 ka BP为暖湿期, 4.8～2.9 ka BP为凉干期, 2.9 ka BP以来为温润期。马四剖面记录的环境演变过程与青藏高原其他区域环境演变过程具有相似性,表明共和盆地环境演变与区域环境变化具有同步性。     

关于“冰臼”问题与韩同林先生商榷

跨世纪的“冰臼”与“壶穴”之争,尘埃未定,缘于尚无定论．“发现冰臼”却常见于报道．本文根据国内研究冰川的成果就韩同林先生《发现冰臼》书中“冰臼”的定义、表现、成因、分布、“冰臼”遗迹的保存机理、“冰说”理论以及模拟“冰臼”的实验设计的合理性等问题提出质疑．从而阐明了：天坑、天井、冰洞、冰湖不是“冰臼”;闽、粤无“冰臼”;“冰说”理论不成立的观点．     

循环荷载下砂土液化特性颗粒流数值模拟

利用PFC2D常体积循环双轴试验条件,对砂土在不排水循环荷载作用下的液化特性进行了颗粒流数值模拟,数值模拟按等应力幅加荷方式进行。颗粒流数值模拟的优点在于得到试样液化宏观力学表现的同时,通过不同循环加荷时刻试样内细观组构参量（包括配位数、接触法向分布、粒间法向接触力、粒间切向接触力）的演化规律,分析砂土液化过程中细观组构变化与宏观力学响应之间的内在联系,从而可进一步探讨砂土液化的细观力学机制。数值模拟研究结果表明,砂土液化现象在宏观力学表现上反映为超静孔隙水压力的累积上升和平均有效主应力的不断减小,在细观组构上对应于配位数的累积损失和粒间接触力的不断减小。砂土液化细观机制分析表明,试样配位数的减少与循环加荷过程中组构各向异性滞后于应力各向异性有关。     

土石坝变形计算中的应力路径问题

通过试验资料,说明了应力路径对砂土的应力-应变关系的影响;从实测资料及有限元法计算的结果,分析了土石坝中应力路径的特点;然后介绍了部分现有在土石坝变形计算中考虑应力路径影响的方法;最后,通过砂土的等应力比及变应力比路径试验资料的分析,揭示了二者之间具有良好的相关关系,推导了变应力比路径下非线性弹性模型参数的计算方法,提出了在土石坝变形计算中考虑应力路径影响的分析方法。     

HP-2型滑坡遥测系统

以自行研制的恒流式静态应变仪(中国专利号:88212764.0)为主机的HP-2型滑坡遥测系统,用作测值远传和分散设点集中遥测数据。本系统配接PC-1500A或IBM PC/XT计算机,可构成滑坡监测系统;它既能控制多点巡回检测、定点检测和通道号显示,亦可控制应变仪作半桥或全桥测量,又能控制采样时间等。1987—1990年运行结果表明,本遥测系统相当稳定可靠。     

Comparison Between Eddy-Correlation and Inertial Dissipation Methods in the Marine Atmospheric Surface Layer

A comparison of momentum fluxes determined by the eddy-correlation method(ECM) and the inertial dissipation method (IDM) has been performed using longterm measurements over the sea. The measurements were made on the island ofÖstergarnsholm in the middle of the Baltic Sea. The results show that a`classical' form of the inertial dissipation method, i.e., assuming that the transportterms are negligible, and using an effective value for the Kolmogorov constant of0.55, can be used with a mean relative difference between the two methods of about15% for -1 < z/L < 0.5 (z being height and L the Obukhov length). The IDMmethod works best for high wind speeds and neutral conditions. For low windspeeds (U < 6 m s^-1) the relation between the two methods is morecomplex. IDM then gives higher values than ECM on the average (about 20%),especially for swell conditions, indicating the need for an imbalance function inthe turbulent kinetic energy budget. Calculations of the effective Kolmogorovconstant, _a, suggest a dependence upon the wave age, _a increasing with increasing wave age, where the value 0.59 fits the data well for saturated waves.     

非零宇宙常数Global Monopole的引力场

本文讨论了膨涨宇宙处于宇宙常数不为零时ＧｌｏｂａｌＭｏｎｏｐｏｌｅ存在的可能性、稳定性及求其引力场的解。最后分析了ＧｌｏｂａｌＭｏｎｏｐｏｌｅ的宇宙演化。     

土壤水分常数测定之我见

通过对土壤容重、田间持水量、凋萎湿度测定方法的研究,提出了土壤水分常数测定规范中存在和应注意的问题,以利做好当前的土壤水分常数测定工作。     

On the estimation of hysteretic energy demands for SDOF systems

Based on a statistical study of the dynamic response of single degree of freedom (SDOF) systems subjected to earthquake ground motions, a rule to estimate hysteretic energy demands is proposed. Expressions for elastic–perfectly plastic, stiffness degrading and pinching SDOF systems were obtained. The proposed rule does not explicitly depend on the period of the system; instead, it depends on the elastic pseudo‐acceleration and elastic velocity spectra. It is shown that the proposed rule can be applied to compute hysteretic energy demands for systems located at different soil conditions. In addition, information about scatter and bias of the proposed rule is also presented. Copyright © 2007 John Wiley & Sons, Ltd.