地震信号随机噪声压制的双树复小波域双变量方法

有效地压制地震信号中的噪声是地震信号解释和后续处理的重要环节之一.本文建立两种双树复小波域双变量模型对地震信号中的随机噪声进行压制.地震信号经双树复小波变换后,同一方向实部与虚部系数、实部(或虚部)系数与对应的模之间存在较强的相关性.鉴于此,对同一方向实部与虚部小波系数建立双变量模型,从含噪地震信号小波系数中估计原始信号的小波系数,再基于双树复小波逆变换重构得到降噪后的地震信号.进一步对同一方向实部(或虚部)系数与对应的模建立双变量模型,得到地震信号随机噪声压制的第二种双树复小波域双变量方法.最后对合成地震记录和实际地震资料中的随机噪声进行压制的实验结果证实本文两种方法都能够有效地压制地震信号中的随机噪声.     

湖南锡矿山土壤重金属污染评价

在前人工作的基础上,运用地质累积指数等环境地球化学研究的方法,对锡矿山土壤及其农作物中重金属污染进行了分析与评价.结果表明: (1)土壤中以Sb、Hg、Cd污染最为严重,其污染程度达强度以上;Zn、Cu、As、Pb次之,Cr未受到污染. (2)萝卜中元素的生物吸收系数顺序为Zn＞Cd＞Pb=As＞Cu＞Sb＞Hg＞Cr,其吸收程度与土壤污染程度并不一致,除与土壤中元素的浓度有关外,且受元素的生物吸收能力的控制.     

冻融循环作用下黄土基本物理性质变异性研究

以陕西富平重塑黄土为研究对象, 引入有关变异性分析的变化量和变异系数两个参数, 对历经不同冻融循环次数后黄土的物理性质指标进行清晰全面的描述. 结果表明:土样的密度和孔隙比的变化量呈现"共轭"变化, 水理性质指标的变化量均随冻融次数的增加而变小; 各项指标的变异系数均随冻融次数逐渐减小, 即土样内部形成新的结构, 并趋于稳定. 在分析黄土基本物理性质变异性的基础上, 可进一步探讨其内部颗粒排列、粒度成分及矿物成分等的发展转变, 为解决该地区冻融黄土的土工问题提供了参考, 同时, 也是判断其工程性质最基本的依据之一.     

Computation of elliptic Hansen coefficients and their derivatives

The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74.     

低频天波信号的变化与地磁活动关系的分析

基于临潼（34°22＇N，109°13＇E）对来自冲绳（26°36＇N，128°09＇E）的100kHz低频一跳天波的时延及场强的实测，并利用相应的地磁扰动等资料、进行了有关低频天波信号变化与地磁活动的关系的分析研究。结果表明：（1）当地磁扰动的日平均指数较高时，低频天波信号的时延、场强的变化也较为明显;（2）磁暴达主相的当日，低频天波信号的时延、场强大多有明显变化，并且对延、场强的变化还与低频天线反射点处于白天还是夜晚有关，若处于夜晚，天演变化较大。若处于白天，变化较小；（3）在磁暴初相时，低频天波信号的时延、场强无明显的变化；（4）低频一跳天渡时延变化值与磁暴主相最大变幅H值有较好的正相关。     

Polarization and amplitude attributes of reflected plane and spherical waves

The characteristics of a reflected spherical wave at a free surface are investigated by numerical methods; in particular, the polarization angles and amplitude coefficients of a reflected spherical wave are studied. The classical case of the reflection of a plane P wave from a free surface is revisited in order to establish our terminology, and the classical results are recast in a way which is more suited for the study undertaken. The polarization angle of a plane P wave, for a given angle of incidence, is shown to be 90° minus twice the angle of reflection of the reflected S wave. For a Poisson's ratio less than 1/3, there is a non-normal incident angle for which both amplification coefficients are 2 precisely; for this incident angle the direction of the particle motion at the free surface is also the direction of the incident wave. For a wave emanating from a spherical source, the polarization angle, for all angles of incidence, is always less than, or equal to, the polarization angle of a plane P wave. The vector amplification coefficient of a spherical wave, for all angles of incidence, is always greater than the vector amplification coefficient of a plane P wave. As expected, the results for a spherical wave approach the results for a plane P wave in the far field. Furthermore, there was a good agreement between the theoretical modelling and the numerical modelling using the dynamic finite element method (DFEM).     

Gas Chromatographic Determination of Extractable Compounds Composition and Emission Rate of Volatile Terpenes from Larch Needle Litter

A combination of solid-phase microextraction (SPME) and gas chromatography can be successfully used both for establishing the qualitative composition of volatile organic compounds (VOC) emitted by leaf litter and for determining their emission rates. Taking as an example European larch litter, it is shown that dead plant material contains considerable amounts of volatile components as well as non-volatile compounds that can be VOC precursors formed as a result of enzymatic reactions. It is proposed to include the determination of extractable compounds into the methodology of studying litter as a source of atmospheric VOC. Some data on litter mass are reported and it is concluded that this data may be included into special models for emission evaluation. In this work the distribution coefficients of monoterpene hydrocarbons between the gas phase and polydimethylsiloxane fiber coating necessary for quantitative determinations in SPME were estimated.     

A New Method to Determine the Derivatives of the Laplace Coefficients

The determination of the secular variations of the orbital elements of objects in N-body systems is based on the literal development of the perturbing function. The development makes use of the Laplace coefficients and their derivatives. In this paper a new method is described for the analytical computation of the derivatives of the Laplace coefficients. It is an explicit formula in the sense that it only contains the Laplace coefficients and the parameter on which the Laplace coefficients depend. The advantage of this method is that it is unnecessary to calculate all the derivatives up to the desired order. It is enough to calculate the Laplace coefficients. Easy coding is a further benefit of the method and it provides more accurate numerical results. The paper describes in detail the application of the method through an example and gives comparison with former methods.This revised version was published online in October 2005 with corrections to the Cover Date.     

Hydrodynamic Coefficients and Wave Excitation Forces for A Ship near A Quay

In this paper,the effects of a quay or a solid jetty on hydrodynamic coefficients and vertical wave excitation forces on a ship woth or without forward speed are discussed.A modified simple Green function technique is used to calculate the 2D coefficients while the strip theory is used to calculate the 3D coefficients. Wave excitation forces are also calculated with the strip theory. Numerical results are provided for hydrodynamic coefficients and vertical wave excitation forces on a 200000 DWT tanker ship. It is found that the quay has a considerable effect on the hydrodynamic coefficients and wave excitation forces for a ship.     

Hydrodynamic coefficients of a submerged pulsating sphere in finite depth

By extending the work of Linton (Linton, C.M., 1991. Radiation and diffraction of waver waves by a submerged sphere in finite depth. Ocean Engineering 18 (1/2), 61–74), the problem of radiation of water waves by a submerged pulsating sphere in finite depth is formulated using the multipole method. As in Linton (1991), this leads to an infinite system of linear equations, which are easily solved numerically. Simple expressions are derived for the hydrodynamic characteristics of such a body. Results showing the effect of varying both the immersion depth and the water depth on the hydrodynamic coefficients of the pulsating sphere are given. The paper resumes the work presented in Lopes (Lopes, D.B.S., 1999. On the study of the Archimedes wave swing device for wave energy utilization (in Portuguese). MSc on the Management and Modelling of the Marine Environment, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa.).