初论地洼学说的进展与前景     

孙希贤  龙昱 《大地构造与成矿学》1992,16(4):405-409

笔者在研究有关文献和参加一些学术会议后发现.地洼学说近十余年来进展显著,科研成果累累.被称为当代最有生命力的学科之一,但系统地研究其成长过程尚欠缺.为了促进地球科学的不断发展。总结经验与教训。扩大学科间的交流.本文重点论述了地洼学说产生的历史背景:进展阶段与特点;发展总体趋势;学说的前景和展望等问题.  相似文献   

遥感影像反立体纠正方法研究     

周爱霞  高连峰 《国土资源遥感》2007,18(2):20-22

以四川省广元市某区遥感影像为例，尝试了一种基于DEM和IHS变换的遥感影像反立体纠正方法。该方法首先对IHS变换得到的亮度分量I进行滤波处理，将反映地物反射率差异的亮度信息与地形因子信息分离，然后用DEM制作的地形阴影图替换原图像中的地形因子信息，最后进行IHS反变换。试验结果表明，该方法能有效纠正遥感图像上的反立体现象，并基本保持与原图像色彩一致。  相似文献   

建立天空场景的模拟算法   总被引：1，自引：0，他引：1  

顾大权  范茵  许屏  龚琳 《气象科技》2007,35(2):292-294

建立真实感的天空场景,在环境仿真和气象现象模拟中,有着极其重要的应用价值,也是计算机可视化研究中的难题。首先通过确定色彩层次模型,改进基于中点的变位方法生成基本云图,然后使用基于图像的方法进行云图映射,最后融合气象信息要素等过程生成天空背景,并采用光照叠加、背景合成及色彩调整等方法,产生千姿百态、形象逼真的天空场景图。可在多种气象现象的模拟仿真,纹理贴图的产生以及气象信息可视化系统的开发等方面发挥重要的作用。  相似文献   

复杂应力条件下长江口原状饱和软黏土门槛循环应力比试验研究     

刘功勋  栾茂田  郭莹  王忠涛  贺林  张俊峰 《岩土力学》2010,31(4):1123-1129

针对取自于长江口的海洋原状饱和软黏土,利用土工静力-动力液压三轴-扭转多功能剪切仪,在控制不同初始固结参数的三向非均等固结状态和不排水条件下,分别进行了轴向和扭转双向耦合循环剪切以及循环扭剪等多种复杂循环剪切试验。分别研究了初始大主应力方向角、初始偏应力比、初始中主应力系数以及循环剪切应力模式等因素对门槛循环应力比的影响。试验结果表明,在三向非均等固结条件下,初始大主应力方向角、初始偏应力比对门槛循环应力比影响显著,门槛循环应力比随着初始大主应力方向角与初始偏应力比的增大而明显减小;而初始中主应力系数对门槛循环应力比基本没有影响。循环剪切应力模式对门槛循环应力比具有显著影响,在相同的初始固结应力条件下,循环耦合剪切试验确定的门槛循环应力比明显小于循环扭剪试验所确定的门槛循环应力比。  相似文献   

黄土高原半干旱区异常能量闭合率特征分析   总被引：1，自引：0，他引：1  

朱岩  左洪超  郭阳  武建军 《干旱气象》2014,(5):719-726

以兰州大学半干旱气候与环境观测站（简称SACOL站）4 a的陆面通量数据为基础,利用普通最小二乘法（OLS）和能量平衡比率（EBR）方法,对能量平衡的异常闭合特征及其与相对垂直湍强（RIw）的关系进行了研究,并进行了能量滞后分析。结果表明,能量过闭合和负闭合现象分别主要发生在白天和夜间,大小遵从正态分布;较大异常闭合产生的原因主要是日出日落时净辐射与地表热通量接近以及降水影响造成湍流通量出现异常大值。一般来说,垂直湍流运动越强,异常闭合越少,闭合度越向1收敛,反之亦然。强湍流或极弱湍流都不利于产生异常闭合,过闭合、负闭合的最适相对垂直湍强RIw约为0.11、0.14。另外,能量支出项的相对滞后也是造成包括负闭合在内的异常闭合的原因之一。剔除湍强较弱的点或将地表热通量G0、感热H、潜热LE相位相对净辐射Rn提前30 min后,异常闭合所占比重减少;月平均EBR法过闭合度降低,OLS法闭合度提高。  相似文献   

On the possibility of investigation of the magnetic field structure in subphotospheric layers of the Sun according to observations of sunspot torsional oscillations     

O. S. Gopasyuk  S. I. Gopasyuk 《Bulletin of the Crimean Astrophysical Observatory》2008,104(1):52-58

A method of investigation of the magnetic field structure in subphotospheric layers of the Sun has been developed. The method is based on observations of the torisonal oscillations of single sunspots. Characteristics of the torsional oscillations have been obtained from observations of the longitudinal magnetic field and radial velocities of seven single sunspots in the photospheric line Fe I λ5253 Å. The parameters of the torsional oscillations and magnetic tubes in the deep layers have been determined. The radius of the cross section of a magnetic flux tube forming a sunspot is greatest near the Sun’s surface and is approximately equal to the radius of a sunspot umbra. Down to the deeper layers, it decreases quite quickly. The longitudinal electric current appearing in the magnetic tube changes direction. The typical time of the current changes is determined by the period of the torsional oscillations. The intensity of the longitudinal magnetic field in the tube increases with depth. The Alfven wave velocity averaged over the length of a magnetic tube is tens or hundreds of times less than this velocity in a sunspot umbra. It decreases with an increase in the period of oscillations. A decrease in the Alfven wave velocity leads to an increase in the twisting angle of magnetic field lines.  相似文献   

Inelastic torsional response of buildings to the 1985 Mexican earthquake: a parametric study     

A. M. Chandler

G. L. Hutchinson  W. Jiang 《Soil Dynamics and Earthquake Engineering》1991,10(8):429-439

This study aims to determine the influence of torsional coupling on the inelastic response of a series of models representing typical structural configurations in real buildings. The lake bed (SCT) east-west component of the 1985 Mexico City earthquake was employed in the analysis, and is representative of a severe ground motion known to have induced large inelastic structural deformations in a high proportion of those buildings having asymmetrical distributions of stiffness and/or strength. Material non-linearity in lateral load-resisting elements has been defined using a hysteretic Ramberg-Osgood model. Structural eccentricities have been introduced into the building models by (i) asymmetrical distributions of stiffness and/or strength, (ii) asymmetrical configuration of lateral load-resisting elements, or (iii) varying post-elastic material behaviour in the resisting elements. The dynamic inelastic response of these models has been obtained by a numerical integration of the relevant equations of motion, expressed in a non-dimensional incremental form.

In the elastic range, the results correlate well with those of previous studies. In the inelastic range, it is concluded that the peak ductility demand of the worst-affected element increases with the ground excitation level across the range of building periods considered, and that the influence of torsional coupling on the key response parameters is model dependent. Most significantly, the strength eccentricity relative to the centre of mass has been shown to influence the peak edge displacement response more than conventionally employed stiffness eccentricity.  相似文献   

Theory of Basin Scale Dynamics of a Stratified Rotating Fluid     

Leo R. M. Maas 《Surveys in Geophysics》2004,25(3-4):249-279

The dynamics of a stratified fluid contained in a rotating rectangular box is described in terms of the evolution of the lowest moments of its density and momentum fields. The first moment of the density field also gives the position of the fluids centre-of-mass. The resulting low-order model allows for fast assessment both of adopted parameterisations, as well as of particular values of parameters. In the ideal fluid limit (neglect of viscous and diffusive effects), in the absence of wind, the equations have a Hamiltonian structure that is integrable (non-integrable) in the absence (presence) of differential heating. In a non-rotating convective regime, dynamically rich behaviour and strong dependence on the single (lumped) parameter are established. For small values of this parameter, in a self-similar regime, further reduction to an explicit map is discussed in an Appendix. Introducing rotation in a nearly geostrophic regime leads through a Hopf bifurcation to a limit cycle, and under the influence of wind and salt to multiple equilibria and chaos, respectively.  相似文献   

利用常熟地震台同场地形变仪记录检测对比地球自由振荡信号     

钱文杰  狄樑  刘冬冬  陆德明  丁建国 《地震地磁观测与研究》2021,42(4):110-118

利用常熟地震台同场地观测的洞体应变仪、体应变仪、水管倾斜仪、垂直摆倾斜仪记录数据,采用小波变换与功率谱密度估计方法,检测2011年3月11日日本9.0级大地震激发的地球自由振荡信号,其中检测到47个球型基频振型（₀S₃—₀S₄₉）、15个环型基频振型（₀T₅—0T₂₅）以及部分球型谐频振型,与地球初步参考模型（PREM）理论频率值基本符合,表明检测结果较好。对比结果显示：水管倾斜仪检测球型振荡振型能力最强,垂直摆倾斜仪检测环型振荡振型能力最强;体应变仪可检测到清晰的环型基频振型,且信噪比较高;倾斜仪对自由振荡信号的检测能力优于应变仪。  相似文献   

东海南部黑潮区春季温盐度垂直分布类型及其逆现象成因的初步分析   总被引：3，自引：1，他引：2  

沈雪龙 《海洋学研究》1999,17(1):8-12

用１９８８～１９９６年在东海南部黑潮区共５个航次的春季水文观测资料,分析了该海区温、盐度垂直分布类型的地理分布,讨论了春季温、盐度逆转现象的形成原因。这主要是春季季风已转变为南风,在南风的驱动下,迫使表层水离岸向东向外海扩张,台湾暖流向北伸展,黑潮次表层水的向岸入侵的结果  相似文献