基于小波变换的信号突变检测滤波和瞬态谱研究

该文简述了小波理论产生的背景和发展过程,详细介绍了小波变换的概念、基本特性以及基于小波变换的信号突变检测、滤波及基于小波包变换的瞬态谱研究方法和结果。文后对小波变换在地震信号处理中的应用前景进行了讨论。     

地面大回线源在地下形成的瞬变电磁场的反演研究

本文研究了地面大回线源在地下形成的瞬变电磁场的反演方法。其反演计算采用改进的阻尼最小二乘可行方向法,理论计算表明,反演计算效果好。     

辽西地区中生代义县旋回火山活动特征分析

辽西地区广泛发育中生代火山岩,其中以义县旋回火山岩最为发育。本文在对辽西地区义县旋回火山岩微量元素地球化学特征研究的基础上,认为义县旋回火山岩具有同源性质,由壳幔混溶物质作用于统一的火山活动过程中产生。     

Transient creep and semibrittle behavior of crystalline rocks

We review transient creep and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing deformation in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient creep data for crystalline rocks at elevated temperatures are analyzed but are poorly understood because of lack of information on the deformation processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient creep at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the creep rate. Empirical transient creep equations are extrapolated at 200° to 600°C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17×10² to 3.17×10⁸ years. At the higher temperatures, appreciable transient creep strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic.     

涡度规则分布与非规则分布的转换

用一个β平面准地转正压模式积分１２个模式日,研究涡旋相互作用问题。初始场上有一个台风涡旋和一对涡旋偶极子,它们的等值线均为光滑、规则的分布。规则分布的涡旋之间的相互作用,可以激发出一个非规则的貌似混乱的涡度分布区域。随着时间的演化,在这个非规则分布的区域,一个相对有序的反气旋环流又逐渐显示出来。     

A deeper look at the colors of the saturnian irregular satellites

We have performed broadband color photometry of the twelve brightest irregular satellites of Saturn with the goal of understanding their surface composition, as well as their physical relationship. We find that the satellites have a wide variety of different surface colors, from the negative spectral slopes of the two retrograde satellites S IX Phoebe (S^′=−2.5±0.4) and S XXV Mundilfari (S^′=−5.0±1.9) to the fairly red slope of S XXII Ijiraq (S^′=19.5±0.9). We further find that there exist a correlation between dynamical families and spectral slope, with the prograde clusters, the Gallic and Inuit, showing tight clustering in colors among most of their members. The retrograde objects are dynamically and physically more dispersed, but some internal structure is apparent.     

Irregular Satellites of Jupiter: a study of the capture direction

The irregular satellites of Jupiter are believed to be captured asteroids or planetesimals. In the present work is studied the direction of capture of these objects as a function of their orbital inclination. We performed numerical simulations of the restricted three-body problem, Sun-Jupiter-particle, taking into account the growth of Jupiter. The integration was made backward in time. Initially, the particles have orbits as satellites of Jupiter, which has its present mass. Then, the system evolved with Jupiter losing mass and the satellites escaping from the planet. The reverse of the escape direction corresponds to the capture direction. The results show that the Lagrangian points L1 and L2 mainly guide the direction of capture. Prograde satellites are captured through these two gates with very narrow amplitude angles. In the case of retrograde satellites, these two gates are wider. The capture region increases as the orbital inclination increases. In the case of planar retrograde satellites the directions of capture cover the whole 360° around Jupiter. We also verified that prograde satellites are captured earlier in actual time than retrograde ones. This paper was presented at the Asteriods, Comets and Meteors meeting held at Búzios, Rio de Janeiro, Brazil in August 2005 and could not be included in the special issue related to that conference.     

新四面体理论与磁极倒转

本文以最新修正了的新四面体理论模型来解释地球磁极倒转现象及其规律性。文章简要回顾了依附于收缩说的地球四面体理论的兴衰,接着简述了应归属于脉动说范畴的新四面体理论研究的最新进展——地球多级驻波(式)脉动演化模型。新模型可概括为:地球的形态在演化过程中呈“准球体→负准四面体→准球体→正准四面体→准球体→…”的驻波脉动;在呈每种形体的大阶段中,又包含着次级、更次级的驻波脉动。然后论述了地磁极性倒转的规律性(即多变→固定[正向]→多变→固定[反向] →多变→…)以及新模型对其所做的解释(即固定正向和固定反向阶段分别为负和正准四面体阶段,多变阶段为准球体阶段)。     

Power capture performance of an oscillating-body WEC with nonlinear snap through PTO systems in irregular waves

Compared with solar and wind energy, wave energy is a kind of renewable resource which is enormous and still under development. In order to utilize the wave energy, various types of wave energy converters (WECs) have been proposed and studied. And oscillating-body WEC is widely used for offshore deployment. For this type of WEC, the oscillating motion of the floater is converted into electricity by the power take off (PTO) system, which is usually mathematically simplified as a linear spring and a damper. The linear PTO system is characteristic of frequency-dependent response and the energy absorption is less powerful for off resonance conditions. Thus a nonlinear snap through PTO system consisting of two symmetrically oblique springs and a linear damper is applied. A nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two oblique springs to the original length of both springs. JONSWAP spectrum is utilized to generate the time series of irregular waves. Time domain method is used to establish the motion equation of the oscillating-body WEC in irregular waves. And state space model is applied to replace the convolution term in the time domain motion equation. Based on the established motion equation, the motion response of both the linear and nonlinear WEC is numerically calculated using 4th Runge–Kutta method, after which the captured power can be obtained. Then the influences of wave parameters such as peak frequency, significant wave height, damping coefficient of the PTO system and the nonlinear parameter γ on the power capture performance of the nonlinear WEC is discussed in detail. Results show that compared with linear PTO system, the nonlinear snap through PTO system can increase the power captured by the oscillating body WEC in irregular waves.     

Three-body capture of irregular satellites: Application to Jupiter

We investigate a new theory of the origin of the irregular satellites of the giant planets: capture of one member of a ∼100-km binary asteroid after tidal disruption. The energy loss from disruption is sufficient for capture, but it cannot deliver the bodies directly to the observed orbits of the irregular satellites. Instead, the long-lived capture orbits subsequently evolve inward due to interactions with a tenuous circumplanetary gas disk.We focus on the capture by Jupiter, which, due to its large mass, provides a stringent test of our model. We investigate the possible fates of disrupted bodies, the differences between prograde and retrograde captures, and the effects of Callisto on captured objects. We make an impulse approximation and discuss how it allows us to generalize capture results from equal-mass binaries to binaries with arbitrary mass ratios.We find that at Jupiter, binaries offer an increase of a factor of ∼10 in the capture rate of 100-km objects as compared to single bodies, for objects separated by tens of radii that approach the planet on relatively low-energy trajectories. These bodies are at risk of collision with Callisto, but may be preserved by gas drag if their pericenters are raised quickly enough. We conclude that our mechanism is as capable of producing large irregular satellites as previous suggestions, and it avoids several problems faced by alternative models.