Asteroid motion near the 3 : 1 resonance     

John D. Hadjidemetriou 《Celestial Mechanics and Dynamical Astronomy》1993,56(4):563-599

A mapping model is constructed to describe asteroid motion near the 3 : 1 mean motion resonance with Jupiter, in the plane. The topology of the phase space of this mapping coincides with that of the real system, which is considered to be the elliptic restricted three body problem with the Sun and Jupiter as primaries. This model is valid for all values of the eccentricity. This is achieved by the introduction of a correcting term to the averaged Hamiltonian which is valid for small values of the ecentricity.We start with a two dimensional mapping which represents the circular restricted three body problem. This provides the basic framework for the complete model, but cannot explain the generation of a gap in the distribution of the asteroids at this resonance. The next approximation is a four dimensional mapping, corresponding to the elliptic restricted problem. It is found that chaotic regions exist near the 3 : 1 resonance, due to the interaction between the two degrees of freedom, for initial conditions close to a critical curve of the circular model. As a consequence of the chaotic motion, the eccentricity of the asteroid jumps to high values and close encounters with Mars and even Earth may occur, thus generating a gap. It is found that the generation of chaos depends also on the phase (i.e. the angles andv) and as a consequence, there exist islands of ordered motion inside the sea of chaotic motion near the 3 : 1 resonance. Thus, the model of the elliptic restricted three body problem cannot explain completely the generation of a gap, although the density in the distribution of the asteroids will be much less than far from the resonance. Finally, we take into account the effect of the gravitational attraction of Saturn on Jupiter's orbit, and in particular the variation of the eccentricity and the argument of perihelion. This generates a mixing of the phases and as a consequence the whole phase space near the 3 : 1 resonance becomes chaotic. This chaotic zone is in good agreement with the observations.  相似文献   

Transmission and reflection of Rayleigh waves at a thin low velocity vertical layer: A laboratory and theoretical study     

P. F. Biagi  T. S. Gegechkory  E. N. Its  P. Manjgaladze  V. Sgrigna  D. Zilpimiani 《Pure and Applied Geophysics》1990,133(2):317-327

A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling.  相似文献   

Thermal evolution of the orogenic lower crust during exhumation within a thickened Moldanubian root of the Variscan belt of Central Europe   总被引：4，自引：5，他引：4  

L. TAJ&#;MANOVá  J. KONOPÁSEK  K. SCHULMANN 《Journal of Metamorphic Geology》2006,24(2):119-134

At the eastern margin of the Bohemian Massif (Variscan belt of Central Europe), large bodies of felsic granulite preserve mineral assemblages and structures developed during the early stages of exhumation of the orogenic lower continental crust within the Moldanubian orogenic root. The development of an early steep fabric is associated with east–west-oriented compression and vertical extrusion of the high-grade rocks into higher crustal levels. The high-pressure mineral assemblage Grt-Ky-Kfs-Pl-Qtz-Liq corresponds to metamorphic pressures of ∼18 kbar at ∼850 °C, which are minimum estimates, whereas crystallization of biotite occurred at 13 kbar and ∼790 °C during decompression with slight cooling. The late stages of the granulite exhumation were associated with lateral spreading of associated high-grade rocks over a middle crustal unit at ∼4 kbar and ∼700 °C, as estimated from accompanying cordierite-bearing gneisses. The internal structure of a contemporaneously intruded syenite is coherent with late structures developed in felsic granulites and surrounding gneisses, and the magma only locally explored the early subvertical fabric of the felsic granulite during emplacement. Consequently, the emplacement age of the syenite provides an independent constraint on the timing of the final stages of exhumation and allows calculation of exhumation and cooling rates, which for this part of the Variscan orogenic root are 2.9–3.5 mm yr⁻¹ and 7–9.4 °C Myr⁻¹, respectively. The final part of the temperature evolution shows very rapid cooling, which is interpreted as the result of juxtaposition of hot high-grade rocks with a cold upper-crustal lid.  相似文献   

Site Effects Study in the Serravalle Village (NE Italy) by Means of Spectral Ratios Analyses Relatively to Multiple Reference Sites     

Andrea Restivo  Carla Barnaba  Alberto Michelini 《Natural Hazards》2006,39(1):31-49

The area of Serravalle, sited in the northern part of the town of Vittorio Veneto (TV), NE Italy, has been the target of a seismic microzonation campaign. 10 seismic stations have been deployed for a 7 months period to record in continuous mode. Three stations were installed on bedrock outcrops and seven on sedimentary sites with variable cover thickness. Spectral analyses have been performed on the collected data-set using the Generalized Inversion Technique (GIT, e.g. Andrews, 1986). In particular, spectral ratios have been calculated for each station relatively to the average of the three reference, bedrock sites. The spectral ratios provide quantitative estimates of the seismic motion amplifications which occur in each of the monitored sites. Two sites show high values of amplification, 5 times larger than signal amplitude at the reference sites, in correspondence of well discernible peak frequencies of 5 Hz. Results for the other stations show smaller amounts of site amplification spreading over a broad range of frequencies. Sites where the highest amplifications were recorded all lie on the left bank of the Meschio River and in areas farther away from its outlet into the plain correlating with the presence of thick layers of Quaternary deposits.  相似文献   

Assessment of Marine Clay Improvement Under Reclamation Fills by in-situ Testing Methods     

A. Arulrajah  H. Nikraz  M. W. Bo 《Geotechnical and Geological Engineering》2006,24(2):219-226

In ground improvement projects with prefabricated vertical drains, the duration of the preloading period is set in advance based on the predetermined time rate of consolidation of the compressible layer. If prediction is accurately done, the required degree of consolidation is met at the pre-determined preloading time. As such, there is a requirement for in-situ tests to be carried out just prior to the removal of surcharge to assess the degree of consolidation of the improved ground. In-situ tests were carried out after 23 months of surcharge loading at the In-Situ Test Site within the Changi East Reclamation Project in the Republic of Singapore. In-situ testing works in this research study comprises the use of field vane shear, piezocone, flat dilatometer and self-boring pressuremeter. The in-situ tests were carried out to determine the shear strength and degree of consolidation of the Singapore marine clay at Changi after 23 months of surcharge loading. The In-Situ Test Site consisted of a Vertical Drain Area as well as an untreated Control Area. Both areas were located adjacent to each other and were surcharged simultaneously to the same level and surcharge left in place for a period of 23 months. Comparison was made between the in-situ test results of the Vertical Drain Area and the untreated Control Area.  相似文献   

紫色丘陵区不同土地利用方式下土壤活性有机碳垂直分布特征     

《山地学报》2006,24(B10):21-26

  相似文献   

山西霍山植物群落主要层LAI垂直分布规律     

杨志芳刘任涛  毕润成 《山地学报》2006,24(B10):307-312

在山西霍山七里峪林场，采用间接的光学测量方法对沿着海拔分布的植物群落主要层叶面积指数（LAI）进行了测量，从不同的角度对LAI的垂直分布规律进行分析。结果表明：1．海拔不同，LAI表现出很大的差异，海拔1750m左右的LAI值大于较高与较低海拔的；对LAI和海拔之间的关系进行回归，得到LAI分布的拟合方程：y=b0＋b1x＋b2x^2＋b3x^3（R=0．712，P〈0．01）。2．同一海拔样带，阴坡LAI均大于阳坡，但对同种种群来说，阴坡树种平均胸径并不一定均大于阳坡。3．植被类型LAI比较表现为：低山针叶林〈低山灌丛〈落叶阔叶林〈落叶针叶林〈常绿针叶林；而主要群系LAI比较表现为：油松林（0．38）〈落叶松林（0．78）〈山杨林及其混交林（1．09）〈白桦林（2．00）〈辽东栎林及其混交林（3．73）。4．典型群落LAI值变化分析和人工林与天然林以，比较表明，LAI值在一定海拔达到最大值，这对于山西霍山人工林栽培和丰产林培育等具有重要意义。  相似文献   

Ground motion scaling in the Marmara region, Turkey   总被引：1，自引：0，他引：1  

A. Akinci  L. Malagnini  R. B. Herrmann  R. Gok  M. B. Sørensen 《Geophysical Journal International》2006,166(2):635-651

  相似文献   

Seismotectonics of the Cyprian Arc   总被引：1，自引：0，他引：1  

Shimon Wdowinski  Zvi Ben-Avraham  Ronald Arvidsson  Goran Ekström 《Geophysical Journal International》2006,164(1):176-181

  相似文献   

Retrieval of stratospheric O3 and NO2 vertical profiles using zenith scattered light observations     

G. S. Meena  C. S. Bhosale  D. B. Jadhav 《Journal of Earth System Science》2006,115(3):333-347

Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to retrieve vertical profiles of ozone (O₃) and nitrogen dioxide (NO₂) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured and recalculated slant column densities (SCDs) and they are found to be well matching. O₃ and NO₂ vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡ SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities (TCDs) of O₃ and NO₂ along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003. The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer and minimum in the winter season. Increasing trend is found in column density of NO₂ in stratospheric, tropospheric and surface layers, but no trend is observed in O₃ columns for above layers during the period 2000–2003  相似文献