Minimal Energy and Gravitation     

Corrado Massa 《Astrophysics and Space Science》2006,305(4):377-384

Quantum theory in Robertson – Walker spacetime suggests the existence of a minimal energy ε of the order of 10⁻⁴⁵ erg. Reasonable forms for ε give the expansion factor R=R(t)(t= the cosmic time) with no need of gravitational field equations.Einstein's theory should be modified in gravitational fields of strength less than ε c/ħ ∼ 10⁻⁸ cm/s² where c is the speed of light and ħ is the reduced Planck constant. The cosmological term λ is expected to decrease as the universe expands.In the Appendix, ε is derived from a big bang – big crunch Newtonian cosmology.  相似文献   

Damage identification method using harmonic excitation force considering both modelling and measurement errors     

Aiko Furukawa  Junji Kiyono  Hirokazu Iemura  Hisanori Otsuka 《地震工程与结构动力学》2005,34(10):1285-1304

A method of structural damage identification using harmonic excitation force is presented. It considers the effects of both measurement and modelling errors in the baseline finite element model. Damage that accompanies changes in structural parameters can be estimated for a damaged structure from the change between measured vibration responses and ones calculated from the analytical model of the intact structure. In practice, modelling errors exist in the analytical model due to material and geometric uncertainties and a reduction in the degrees of freedom as well as measurement errors, making identification difficult. To surmount these problems, bootstrap hypothesis testing, which enables statistical judgment without information about these errors, was introduced. The method was validated by numerical simulation using a three‐dimensional frame structure and real vibration data for a three‐storey steel frame structure. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

大地构造和海陆起源的内波假说（Ⅱ）──建立假说的大地构造学与运动学基础     

池顺良  鍾荣融  骆鸣津  杨洪之 《大地测量与地球动力学》1996,(2)

介绍建立大地构造内波假说的根据，即：（１）全球海陆分布的低阶球谐特征；（２）全球大洋中脊体系的存在；（３）大陆永存及生长的事实；（４）地壳均衡及莫霍面的化学分界面性质；（５）地槽活动的现象、规律等。在分析以在事实的基础上，研究了大地构造运动中主要的物质运动过程，认为从薄地壳底部向厚地壳底部迁移的地壳物质流，引起地壳厚度的自激波动，推动地槽运动和大陆生长。  相似文献   

The log-normal distribution for hydraulic conductivity of compacted clays: Two or three parameters?     

Huaming Zhai  Craig H. Benson 《Geotechnical and Geological Engineering》2006,24(5):1149-1162

Risk and uncertainty assessments for waste containment systems employing clay barriers often include spatial variability in the hydraulic conductivity as part of the analysis. The two-parameter log-normal distribution is often used to describe the spatial variability, but for compacted clays the three-parameter form can be more appropriate. A statistical hypothesis test was developed that can be used to determine if the two- or three-parameter form of the log-normal distribution is more appropriate. The test is based on a likelihood ratio, comparing likelihood functions for the two- and three-parameter forms at their maximums. Likelihood functions are used assuming that a data set can be segregated into a set of distinct groups of hydraulic conductivities. A step-by-step calculation procedure is described and the test is applied to data collected from 45 sites.  相似文献   

Townsend's Hypothesis, Coherent Structures And Monin–Obukhov Similarity     

K. G. McNaughton  Yves Brunet 《Boundary-Layer Meteorology》2002,102(2):161-175

Townsend's hypothesis states that turbulence near a wall can be divided into an activepart that transports momentum, and an inactive part that does not, and that these twokinds of turbulence do not interact. Active turbulence is generated by wind shear and has properties that scale on local parameters of the flow, while inactive turbulence isthe product of energetic processes remote from the surface and scales on outer-layerparameters. Both kinds of motion can be observed in the atmospheric surface layer, soMonin–Obukhov similarity theory, which is framed in terms of local parameters only,can apply only to active motions. If Townsend's hypothesis were wrong, so that activeand inactive motions do interact in some significant way, then transport processes nearthe ground would be sensitive to outer-layer parameters such as boundary-layer depth,and Monin–Obukhov theory would fail.Experimental results have shown that heat transport near the ground does depend onprocesses in the outer layer. We propose a mechanism for this whereby inactive motionsinitiate active, coherent ejection/sweep structures that carry much of the momentum andheat. We give evidence that the inactive motions take the form of streak patterns of fasterand slower air, and argue that these are induced by the pressure effects of large eddiespassing overhead. The streak pattern includes regions where faster streams of air overtakeand engulf slower-moving streaks. Transverse vortices form across the spines of the streaksat these places and some of them develop into horseshoe vortices. These horseshoe vorticesgrow rapidly and are rotated forward in the sheared flow so they soon contact the ground,squirting the air confined between the legs of the horseshoe vortex outwards as a forcefulejection. This model is consistent with a wide range of results from the field and laboratoryexperiments. Heat transport is significantly affected, so undermining the dimensionalassumptions of Monin–Obukhov similarity theory.  相似文献   

中国大陆及其邻区强震活动与活动地块关系研究   总被引：16，自引：0，他引：16  

马宏生  张国民  刘杰  李丽  陈化然 《地学前缘》2003,10(Z1):74-80

从活动地块假说出发 ,在活动地块研究的基础上 ,探讨了中国大陆及邻区活动地块与强震活动的关系。研究指出 ,主要构造变形和强烈地震大都发生在活动地块边界。在占总面积 17%的活动地块边界上 ,集中了全部的 8级以上巨大地震和 86 %的 7级以上大地震 ,其释放能量占全部总能量的 95 %以上 ,表明中国大陆及其邻区活动地块边界带控制了绝大部分的强地震。从活动地块的整体来看 ,强震活动不仅显示出显著的韵律性特征 ,而且其高、低起伏基本上与中国大陆地区一致 ,只是强震活跃时段有时稍长于中国大陆。各轮回强震活动都有各自活动的主体地区 ,反映了不同活跃期内地块的不同活动方式。文中还从现今地壳运动角度 ,讨论了活动地块运动速率与强地震活动水平之间的可能联系。  相似文献   

1966年以来华北地区一系列七级大震破裂过程的数值模拟   总被引：9，自引：5，他引：9       下载免费PDF全文

陈祖安  白武明  林邦慧  王新华  许国凯  张瑞清  黄为清 《地球物理学报》2003,46(3):373-381

用非连续变形分析方法(DDA+FEM)数值模拟，在华北地区各地块相互制约的块体系统环境中，地块边界断层上发生1966年邢台地震、 1969年渤海地震、 1975年海城地震、 1976年唐山地震等不同类型破裂模式大震的破裂过程. 数值模拟结果给出每个大震释放的主应力场，最大剪应力变化等值线图，地震前后位移变化矢量图，发震断层滑移随时间变化以及走滑错距和应力降等震源参数. 这些结果与地震的震源机制，用地震波资料研究得到的震源参数,宏观等震线,地表观测的水平位移矢量图基本一致. 其中1969年渤海地震正交破裂模式的结果与宏观等震线及小震分布图像更接近. 1976年唐山地震复杂震源模式与该震早期余震分布图像更相符. 表明用DDA+FEM方法进行数值模拟研究，能较好地模拟地震破裂过程.  相似文献   

Testing an earthquake prediction algorithm   总被引：1，自引：0，他引：1  

Vladimir G. Kossobokov  John H. Healy  James W. Dewey 《Pure and Applied Geophysics》1997,149(1):219-232

A test to evaluate earthquake prediction algorithms is being applied to a Russian algorithm known asM8 TheM8 algorithm makes intermediate term predictions for earthquakes to occur in a large circle, based on integral counts of transient seismicity in the circle. In a retroactive prediction for the period January 1, 1985 to July 1, 1991 the algorithm as configured for the forward test would have predicted eight of ten strong earthquakes in the test area. A null hypothesis, based on random assignment of predictions, predicts eight earthquakes in 2.87% of the trials. The forward test began July 1, 1991 and will run through December 31, 1997. As of July 1, 1995, the algorithm had forward predicted five out of nine earthquakes in the test area, which success ratio would have been achieved in 53% of random trials with the null hypothesis.  相似文献   

Determining the maximum degree of harmonic coefficients in geopotential models by Monte Carlo methods   总被引：1，自引：0，他引：1  

K. R. Koch r 《Studia Geophysica et Geodaetica》2005,49(3):259-275

Random errors for the harmonic coefficients of a geopotential model are generated from the matrix of normal equations by a parallel computer applying the Gibbs sampler. This leads to random values for the harmonic coefficients. They are transformed by nonlinear, quadratic transformations to random values for the square roots of degree variances, of mean squares of geoid undulations and gravity anomalies. The expected values of these quantities are not equal to the values of these quantities computed by the estimated harmonic coefficients, due to correlations and errors in the estimation. By hypothesis tests estimated harmonic coefficients distorted by correlations and errors are detected. Applying the tests to the geopotential model ITG-CHAMP01 of the Institute of Theoretical Geodesy in Bonn it is concluded that above the degree 62 the harmonic coefficients cannot add any information to the geopotential model.  相似文献   

Bound and mobile soil water isotope ratios are affected by soil texture and mineralogy,whereas extraction method influences their measurement     

Rachel E. Adams  Ayumi Hyodo  Toby SantaMaria  Cynthia L. Wright  Thomas W. Boutton  Jason B. West 《水文研究》2020,34(4):991-1003

Questions persist about interpreting isotope ratios of bound and mobile soil water pools, particularly relative to clay content and extraction conditions. Interactions between pools and resulting extracted water isotope composition are presumably related to soil texture, yet few studies have manipulated the bound pool to understand its influence on soil water processes. Using a series of drying and spiking experiments, we effectively labelled bound and mobile water pools in soils with varying clay content. Soils were first vacuum dried to remove residual water, which was then replaced with heavy isotope-enriched water prior to oven drying and spiking with heavy isotope-depleted water. Water was extracted via centrifugation or cryogenic vacuum distillation (at four temperatures) and analysed for oxygen and hydrogen isotope ratios via isotope ratio mass spectrometry. Water from centrifuged samples fell along a mixing line between the two added waters but was more enriched in heavy isotopes than the depleted label, demonstrating that despite oven drying, a residual pool remains and mixes with the mobile water. Soils with higher clay + silt content appeared to have a larger bound pool. Water from vacuum distillation samples have a significant temperature effect, with high temperature extractions yielding progressively more heavy isotope-enriched values, suggesting that Rayleigh fractionation occurred at low temperatures in the vacuum line. By distinctly labelling bound and mobile soil water pools, we detected interactions between the two that were dependent on soil texture. Although neither extraction method appeared to completely extract the combined bound and mobile (total water) pool, centrifugation and high temperature cryogenic vacuum distillations were comparable for both δ²H and δ¹⁸O of soil water isotope ratios.  相似文献