精密三角高程测量法在武咸城际铁路勘测中的应用

水准测量传递高程适合在地势平坦的地区,如果地形复杂通视条件差,水准法就会受到限制。在武咸铁路勘测中,采用全站仪精密三角高程测量法,通过同时对向观测,消除或减弱了大气折光、仪器高量取误等误差的影响,达到了二等水准测量的精度要求,证明用精密三角高程测量法代替二等水准测量是可行的。     

Numerically obtained vortices in granular media

With our meshfree numerical code SPARC (Soft PARticle Code), which is based on strong solutions of the equations of equilibrium, we were able to derive vortex patterns ("turbulence") in deformations hitherto believed to be homogeneous. The formation of such vortices demonstrates the nonuniqueness of the corresponding boundary value problem. We present some evidence that such vortices can be related with ptygmatic folds, which are observed in rock.     

地震观测传递函数的精度问题

数字地震观测的传递函数由反馈地震计和地震数据采集器的传递函数合成。地震数据采集器的传递函数主要用数字算法生成,其精度可以做得很高。反馈地震计是机电一体化的模拟传感部件,其传递函数的精度和稳定性均欠佳。尤其是由反馈地震计生成的主导二阶极点,对应传统地震观测的周期和阻尼两个重要参数,其精度和稳定性往往较低,不利于地震学研究深入发展的需要。以四川地震观测的标定数据为例,说明数字地震观测传递函数的精度和稳定性急待改进。     

Biases and accuracy of, and an alternative to, discrete nonlinear filters

The biases and accuracy of the extended Kalman filter (EKF) and a second-order nonlinear filter (SONF) are discussed from the point of view of a frequentist; these are often derived by applying the relevant conditional quantities to the linear Kalman algorithm under the Bayesian framework. The EKF and the SONF are biased, although the SONF has been derived in the hope of improving first-order filters. Unfortunately the biases of the SONF may be magnified further, because the second-order terms of the relevant Bayesian conditional quantities have never been properly used to derive the SONF from the frequentist point of view. The variance–covariance matrix of the SONF given in the literature is proven to be incorrect up to the second-order approximation, and the correct one is derived. Finally, also from the point of view of a frequentist, an alternative, almost unbiased SONF is proposed, if the randomness of partials is neglected. Received: 12 July 1997 / Accepted: 5 October 1998     

一种二阶锥线性化方法在上限有限元中的应用研究

对于平面应变条件下岩土稳定性分析,基于线性规划的上限有限元需对常用的摩尔-库仑屈服准则形成的二阶锥约束进行线性化,直接地处理方法是以外接多边形替代锥体投影形成的圆域。为了提高线性化精度往往需直接增加外接多边形边数,从而造成线性规划模型中决策变量包含大量的塑性乘子变量,使计算难度大为增加甚至变得不可行。为此,引入Ben-Tal和Nemirovsky提出的一种二阶锥线性化方法,并将其嵌入到自编的上限有限元程序。经算例分析发现,该法与外接多边形线性化方法所获计算结果相互印证,且其通过适量的增加决策变量和等式约束数目,能保证摩尔-库仑屈服准则线性化精度,同时形成的线性规划规模更小,可望应用于基于线性规划模型的上限有限元中。     

松辽盆地坳陷期湖盆层序地层研究

以横跨松辽盆地北部东西向大剖面为例,综合应用钻井岩芯、测井曲线、古生物和地震资料,进行松辽盆地北部坳陷期(早白垩世晚期—晚白垩世)湖盆层序地层学研究,共识别出2个二级层序界面和13个三级层序界面,划分出2个二级层序和13个三级层序。2个二级层序以姚家组底界不整合面为界,自下而上命名为SSI、SSII。     

An analytical study on the second-order resonance system of tide in an ideal partially-enclosed bay

In the numerical studies of a real tide M4 resonance system, the Xiangshan Port which is a partially-closed bay, Dong et al. [1999. Acta Oceanologica Sinica, 21 （3）： 1-6] found the interesting phenomenon that the advection plays an important role in inhibiting the growth of the amplitude of the tidal second-order resonance response （M4）. This result is contrary to the general traditional ideas for a non-resonance system. How this phenomenon is interpreted and what internal mechanism is behind the phenomenon are the main focuses of this study. The followings are examined： （1） the dynamic features of a second-order resonance system of tide; （2） the dominating factors on the second-order resonance responses; （3） the effects of both the friction and the advection on the second-order resonance responses; and （4） their roles in dominating the second-order resonance response and internal mechanisms by using the analytical methods. The respective results show that： （1） Both the bottom friction and the advection play significant roles in dominating the magnitude of the amplitude of the second-order resonance responses; （2） the effect of the friction on the second-order resonance response depends on the distribution ratio of the work-done of the system to friction force exhausted into between the damping of the first-order system and the inner excitation of the second-order system; （3） the advection plays a positive role in increasing the amplitude of the second-order non-resonance response in the second order non-resonance of tide; （4） in a second-order resonance system of tide, the effect of the advection may be either to increase or to decrease the amplitudes of the second-order resonance responses of tide, which depends on the distribution ratio mentioned above.     

Prediction of hydrological drought durations based on Markov chains: case of the Canadian prairies

Abstract

Hydrological drought durations (lengths) in the Canadian prairies were modelled using the standardized hydrological index (SHI) sequences derived from the streamflow series at annual, monthly and weekly time scales. The rivers chosen for the study present high levels of persistence (as indicated by values exceeding 0.95 for lag-1 autocorrelation in weekly SHI sequences), because they encompass large catchment areas (2210–119 000 km²) and traverse, or originate in, lakes. For such rivers, Markov chain models were found to be simple and efficient tools for predicting the drought duration (year, month, or week) based on annual, monthly and weekly SHI sequences. The prediction of drought durations was accomplished at threshold levels corresponding to median flow (Q50) (drought probability, q?=?0.5) to Q95 (drought probability, q?=?0.05) exceedence levels in the SHI sequences. The first-order Markov chain or the random model was found to be acceptable for the prediction of annual drought lengths, based on the Hazen plotting position formula for exceedence probability, because of the small sample size of annual streamflows. On monthly and weekly time scales, the second-order Markov chain model was found to be satisfactory using the Weibull plotting position formula for exceedence probability. The crucial element in modelling drought lengths is the reliable estimation of parameters (conditional probabilities) of the first- and second-order persistence, which were estimated using the notions implicit in the discrete autoregressive moving average class of models. The variance of drought durations is of particular significance, because it plays a crucial role in the accurate estimation of persistence parameters. Although, the counting method of the estimation of persistence parameters was found to be unsatisfactory, it proved useful in setting the initial values and also in subsequent adjustment of the variance-based estimates of persistence parameters. At low threshold levels corresponding to q < 0.20, even the first-order Markov chain can be construed as a satisfactory model for predicting drought durations based on monthly and weekly SHI sequences.

Editor D. Koutsoyiannis; Associate editor C. Onof

Citation Sharma, T.C. and Panu, U.S., 2012. Prediction of hydrological drought durations based on Markov chains in the Canadian prairies. Hydrological Sciences Journal, 57 (4), 705–722.     

电离层二阶项模型的构建及其变化规律分析研究

在高精度大地测量GPS数据处理研究和应用领域,电离层二阶项延迟影响不容忽视。采用带有三角级数的曲面拟合模型构建电离层延迟二阶项模型,并结合西安市高精度GPS地面沉降监测数据,分析近五年来该区域电离层总电子含量、一阶项、二阶项延迟的半年与年变化规律及其对定位结果的影响,在电离层二阶项的研究方面获得了一些有意义的结论。     

泉州市中心规划区似大地水准面精化实践研究

本文主要介绍了利用GPS测量结合二等水准测量技术,按照统一规划、整体设计的原则,建立泉州市中心规划区厘米级区域似大地水准面精化的实践经验.