Hybrid seismic modeling based on discrete-wave number and finite-difference methods     

Jiří Zahradník  Peter Moczo 《Pure and Applied Geophysics》1996,148(1-2):21-38

Any calculation of seismic wave propagation comprising the seismic source, the travel path, and the receiver site in a single finite-difference (FD) model requires a considerable amount of computer time and memory. Moreover, the methods currently available for including point sources in the 2D FD calculations are far-field approximations only. Therefore we have developed a new hybrid method for treating the seismic wave fields at localized 2D near-surface structures embedded in a 1D background medium, and excited by a point source. The source radiation and propagation in the background model is solved by the discrete-wave number (DW) method, while the propagation in the local 2D structure is calculated by the FD method. The coupling between the two sets of calculations is performed on a rectangular excitation box surrounding the local structure. We show the usefulness of the method in ground-motion studies where both near-field source effects and local site effects are important. Technical problems connected with the inconsistency between the 3D source radiation and the 2D FD calculation are minor for the relatively distant in-plane point explosive sources, but are more serious for the in-plane dislocation sources.  相似文献   

A robust-symmetric mean: A new way of mean calculation for environmental data   总被引：4，自引：0，他引：4  

Chaosheng Zhang  Shen Zhang 《GeoJournal》1996,40(1-2):209-212

Environmental data seldom follow normal distributions, so how to calculate their means is a very important problem. Commonly used methods for mean calculation, such as arithmetic mean, geometric mean, and median, were evaluated. Arithmetic means should only be used when datasets follow normal distributions. Geometric means are suitable for datasets which follow log-normal distributions. Medians are a kind of robust treatment. However, their efficiency is very low. Based on the methods described, two new ideas are developed: robust and symmetric, for calculating means. As far as the symmetric feature is concerned, Box-Cox power transformation is better than logarithmic transformation. Robust statistics and Box-Cox transformation are combined to produce the robust-symmetric mean. As environmental data often follow log-normal or skewed distributions, this method is better than the previous ones and also is appropriate.  相似文献   

不均匀植被分布对地表面和大气边界层影响的数值试验   总被引：9，自引：0，他引：9  

季劲钧  苗曼倩 《大气科学》1994,18(3):293-302

研究陆地与大气间相互作用的方法之一是建立联系地表面层与大气间各种过程的数值模式进行模拟。本文是建立一个陆面过程与二维大气边界层相耦合的模式,耦合模式中包含了发生在大气边界层、植被冠层和土壤表层各种动力、热力和水文过程。运用这一模式模拟了荒漠环境中一片绿洲的不均匀地表面形成的局地气候。由于绿洲植被与周围荒漠有着显著不同的水份与能量平衡关系,使绿洲表面与边界层较四周荒漠冷而湿,并形成了相应的局地环流,即所谓“绿洲效应”。试验结果表明,模拟的气候状况与观测现象是一致的。模式可以用于陆气相互作用的研究。  相似文献   

Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere     

J. Bošková  F. Jiříček  J. Šmilauer  P. Tříska 《Studia Geophysica et Geodaetica》1994,38(1):82-92

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P  相似文献   

Densities of Huanghe River estuary and Bohai Bay waters     

陈国华  季荣  谢式南  张力军 《中国海洋湖沼学报》1994,12(2):130-135

The densities of 36 water samples from the Huanghe River estuary and Bohai Bay were determinedby a magnetic float densimcter under three temperatures from 15℃ to 25℃.All the measured densities ofsamples were greater than that of the values calculated from the International Equation of State of Seawater.The differences between the measured and calculated densities increased with the decrease of salinities.The dif-ferences appeared exponentially correlated with[Ca~(2+)]/s,[Mg~(2+)]/s and[SO_4~(2-)]/s,and had"s"type curverelationship with the alkalinity in all salinity range.But in the salinity ranging from 25.72 to 31.57,therelationships were all linear.The density difference can be estimated from the equation △ρ（10~3kg·m~(-3)）=（-2.79+236.5([Ca~(2+)]/s)/(-9.7464×10~（-3）+[Ca~(2+)]/s).It was the high alkalinity and[Ca~(2+)]/s that resulted in the measured densi-ties of seawaters being higher than the calculated densities in the Huanghe estuary and Bohai Bay.  相似文献   

Magnetic properties,self-reversal remanence and thermal alteration products of smythite     

Miroslav Krs  František Novák  Marta Krsová  Petr Pruner  Jiří Jansa 《Studia Geophysica et Geodaetica》1993,37(4):382-400

Summary This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Kruné hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe³⁺ sulphate with a composition of Fe₂(SO₄)₃, oxidation of these sulphides gives rise to -Fe₂O₃. The result of the subsequent decomposition of the mentioned sulphate is the formation of -Fe₂O₃, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is -Fe₂O₃. In the smythite concentrate the conversion to Fe³⁺ sulphate and -Fe₂O₃ is about twice as intensive as in greigite. No direct conversion to -Fe₂O₃ was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10^–2 down to 10^–3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10^–4 down to 10^–6 in the temperature interval of Fe-oxides origin (above 400°C).Presented at the 3rd Conference on New Trends in Geomagnetism, Castle of Smolenice, Czechoslovakia, June 22–29, 1992  相似文献   

The effect of an optically thin region on stability of an accretion disk around a supermassive black hole     

B. F. Liu  G. Z. Xie  K. F. Ji 《Astrophysics and Space Science》1995,225(2):299-314

We analyse conditions of the innermost portion of an accretion disk and establish a set of equations for this region. A stable innermost region may exist, which can probably explain the observed UV and X-ray spectra, avoiding the unstable emission. We then discuss the detailed radial structure of a disk around a black hole for typical AGN parameters and obtain different kinds of- relationships for different regions of a disk. On the basis of this, we discuss the stability. A new type of cycle is present, which we call a double S shaped cycle. In this cycle, the extent of accretion rate variability is much larger than that in dwarf nova cycles. This probably solves the problem of violent variability of AGN. In the meantime, the very high accretion rate at the hottest state in limit cycles in the unstable region may provide continuous injection of matter to the jet and power the relativistic motion of the jet.  相似文献   

坡地农林复合系统的结构类型与效益分析─以长江三峡库区坡地农业为例   总被引：4，自引：0，他引：4  

申元村  彭业轩 《地理研究》1995,14(3):43-51

本义认为现代术语的农林复合系统来源于生产实践,体现了农业与林业的有机结合、品种生态和经济的有机结合、产品多样化以及管理科学化4个方面相统一的特点。文章在分析三峡库区农林复合系统的类型结构基础上,提出了农林复合系统可以进行层次结构划分的观点。最后,以典型案例研究方法入手,对1种农林结构类型进行效益分析,结果表明,采用植物篱农林复合坡地系统,是现阶段生产力水平下实现坡地生态经济协调发展的有效途径,值得广泛推广。  相似文献   

黑龙江省与呼伦贝尔盟土地类型的划分及其分布规律   总被引：1，自引：0，他引：1  

赵松乔  戴旭  申元村  杨柳林 《地理研究》1982,1(1):49-57

本文就土地研究的几个主要概念,即土地、土地分类、土地分级作了简要讨论,并结合黑龙江省及呼伦贝尔盟的具体条件,对为农、林、牧业服务的土地分类原则进行了初步探讨,还拟订了该区土地分级系统——土地类和土地型,及适合于大比例尺制图的土地组。在此基础上,将全区分为18个土地类、71个土地型。文章还从水平带性、垂直带性和土地结构三个方面,介绍了该区土地类型分布的一般规律。  相似文献   

论Eppley PIR精密红外辐射仪的测量精度   总被引：1，自引：0，他引：1  

江灏  沈志宝 《高原气象》1992,(4)

本文依据红外辐射表(PIR)的结构、性能和工作原理讨论了测量精度及有关影响因素,比较了粗测和精测两种方法的特点,在此基础上提出了各测量方法的适用范围和精度范围以及提高测量精度的措施,同时也给出了一些特定场合下的测量实例及提高测量精度的具体方法。分析表明:精测方法具有很好的测量精度以及很强的环境适应性。粗测在限定的温度范围内具有测量简单、换算方便、易于实现自动化等优点,精度尚能满足一般要求,但在限定的温度范围以外,测量精度急剧恶化。在影响测量精度的各因素中以温度响应中表体热辐射测量的影响最大,在粗测方法中表内电池的性能与测量精度关系重大。强烈日射对测量精度有一定影响,经订正后可基本消除。  相似文献