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511.
512.
A lot of researches onb value have been made in seismology. Since the 1960’s Mogi, Scholz and others have studied AE of rock specimens in laboratory
and discovered that it is related to natural earthquakes. All former researchers used integral specimens to studyb value in the laboratory. However a major earthquake is usually related to a existing seismic-fault in that area. For this
reason, a series of fracture experiments with rock and glass specimens having pre-existing crack or notch is performed in
order to examine the effect of preexisting crack tob value. The experimental results show that theb value begins to decrease as soon as the initiation of the crack and finally drop to a very low value when the specimen breaks
unstably. Based on these, a brief discussion on the possible mechanism ofb value change for natural earthquakes is given.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,9, 393–400, 1987.
Projects sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
513.
In order to reduce the size of problems involving analysis of the dynamic response of structural systems, a transformatio based on appropriately selected Ritz shapes is commonly employed. The lower mode shapes may at times serve a effective Ritz shapes. However, the computation of mode shapes is a time consuming task; in addition, the mode shapes may not form the best basis for representing the spatial distribution of loads. The recently developed load dependent vectors, which are derived from a static solution for the applied loads, address some of the problems inherent in the use of mode shapes. However, both the natural mode shapes and the load dependent vectors fail to account for the frequency content of the loading, a parameter that may influence strongly the response, particularly for loading with a high frequency content. A procedure is presented here for the generation of frequency dependent vectors. A combination of load dependent and frequency dependent vectors will often form a very efficient basis for the representation of the response, as illustrated by several examples presented here. 相似文献
514.
拉萨近地层风廓线模拟 总被引:1,自引:0,他引:1
本文利用1986年中美联合青藏高原大气科学试验期间的考察资料,研究了拉萨近郊风廊线的特征。从莫宁——奥布赫夫相似理论出发,建立了青藏高原近地层风廓线模拟的模式。 相似文献
515.
煤古植物学:历史、现状与展望 总被引:2,自引:0,他引:2
据对50年来的文献分析,简要评述了煤古植物学这一分支学科的产生背景,研究现状和未来发展趋势;并指出,煤古植物学尽管有广泛的应用前景,但由于受研究方法和研究手段的限制,它仍处于发展的初级阶段。 相似文献
516.
全球冻融地区土壤是重要的N20释放源的综合分析 总被引:3,自引:0,他引:3
N2O是重要的温室气体之一,它是微生物硝化作用和脱氮化作用过程的产物。有多种释放源,其中土壤圈是重要的释放源之一。在影响N2O释放通量的诸多因素中温度是关键因素之一。本文根据土壤冻融加强有机质矿化作用,以及对微生物群体产生非生物应力的性质,结合冻融地区土壤和冻土带湿地所具有的特征,进行综合分析,论述冻融地区土壤是重要的N2O释放源。 相似文献
517.
Hong Hao 《地震工程与结构动力学》1993,22(5):389-404
This paper analyses the in-plane stochastic responses of incompressible circular arches to spatially correlated multiple excitations. The dynamic, quasi-static and total structural displacements, moments, shear and axial forces are calculated. The results are compared with those obtained by various simplified excitations. The effects of the ground motion spatial variations on arch responses are examined. The results indicate that the responses may be underestimated or overestimated by neglecting the ground motion spatial variations, depending upon the structure and ground motion properties, the locations where the responses are evaluated, and the response quantity under consideration. 相似文献
518.
1997年4-6月云南省地震局对滇西南重点监视区做了短临预报,但这期间未发生所预期的地震。而滇西南地区6级地震的背景和省内的前兆异常变化是明显的。为此,认为前兆异常是区域应力场增强的结果。异常与地震是相互伴生的兄弟关系,不是父子间因果关系,是造成地震虚报的主要原因。 相似文献
519.
Nans Addor Hong X. Do Camila Alvarez-Garreton Gemma Coxon Keirnan Fowler Pablo A. Mendoza 《水文科学杂志》2020,65(5):712-725
ABSTRACTLarge-sample hydrology (LSH) relies on data from large sets (tens to thousands) of catchments to go beyond individual case studies and derive robust conclusions on hydrological processes and models. Numerous LSH datasets have recently been released, covering a wide range of regions and relying on increasingly diverse data sources to characterize catchment behaviour. These datasets offer novel opportunities, yet they are also limited by their lack of comparability, uncertainty estimates and characterization of human impacts. This article (i) underscores the key role of LSH datasets in hydrological studies, (ii) provides a review of currently available LSH datasets, (iii) highlights current limitations of LSH datasets and (iv) proposes guidelines and coordinated actions to overcome these limitations. These guidelines and actions aim to standardize and automatize the creation of LSH datasets worldwide, and to enhance the reproducibility and comparability of hydrological studies. 相似文献
520.
Chen Hong-Fei Xu Wen-Yao Chen Geng-Xiong Hong Ming-Hua Peng Feng-Lin 《Solar physics》2001,204(1-2):339-349
In this paper geomagnetic disturbances at middle and low latitudes are discussed by using geomagnetic data of the magnetic
storm of 15–16 July 2000. This storm is a response to the solar Bastille Day flare on 14 July. Generally, the geomagnetic
disturbances at middle and low latitudes during a storm are mainly caused by three magnetospheric–ionospheric current systems,
such as the ring current system (RC), the partial ring current and its associated region II field-aligned currents (PR), and
the region I field-aligned currents (FA). Our results show that: (1) The northward turning of IMF-Bz started the sudden commencement of the storm, and its southward turning caused the main phase of the storm. (2) The PR- and
FA-currents varied violently in the main phase. In general, the field of the FA-current was stronger than that of the PR-current.
(3) In the first stage of the recovery phase, the RC-field gradually turned anti-parallel to the geomagnetic axis from a 15°
deviation, and the local time (Λ) pointed by the RC-field stayed at 16:00. After that, Λ rotated with the stations, and the
RC-field was not anti-parallel to the geomagnetic axis, but 5°–10° deviated. These facts suggest that the warped tailward
part of the ring current decays faster than the symmetric ring current. 相似文献