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

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.     

Fitting matrix-valued variogram models by simultaneous diagonalization (Part I: Theory)

Suppose that ¯(x₁),...,¯Z(x_n). are observations of vector-valued random function ¯(x). In the isotropic situation, the sample variogram γ^*(h) for a given lag h is $$\bar \gamma ^ * (h) = \frac{1}{{2N(h)}}\mathop \sum \limits_{s(h)} (\overline Z (x_1 ) - \overline Z (x_1 )) \overline {(Z} (x_1 ) - \overline Z (x_1 ))^T $$ where s(h) is a set of paired points with distance h and N(h) is the number of pairs in s(h).. For a selection of lags h₁, h₂, .... h_k such that N (h₁) > O. we obtain a ktuple of (semi) positive definite matrices $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ . We want to determine an orthonormal matrix B which simultaneously diagonalizes the $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ or nearly diagonalizes them in the sense that the sum of squares of offdiagonal elements is small compared to the sum of squares of diagonal elements. If such a B exists, we linearly transform $\overline Z (x)$ by $\overline Y (x) = B\overline Z (x)$ . Then, the resulting vector function $\overline Y (x)$ has less spatial correlation among its components than $\overline Z (x)$ does. The components of $\overline Y (x)$ with little contribution to the variogram structure may be dropped, and small crossvariograms fitted by straightlines. Variogram models obtained by this scheme preserve the negative definiteness property of variograms (in the matrix-valued function sense). A simplified analysis and computation in cokriging can be carried out. The principles of this scheme arc presented in this paper.     

Diploptene: an indicator of terrigenous organic carbon in Washington coastal sediments

The pentacyclic triterpene 17 beta(H),21 beta(H)-hop-22(29)-ene (diploptene) occurs in sediments throughout the Columbia River drainage basin and off the southern coast of Washington state in concentrations comparable to long-chain plantwax n-alkanes. The same relationship is evident for diploptene and long-chain n-alkanes in soils from the Willamette Valley. Microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process, respectively, for diploptene in coastal sediments. Similarity between the stable carbon isotopic composition (delta 13CPDB) of diploptene isolated from soil in the Willamette Valley (-31.2 +/- 0.3%) and from sediments deposited throughout the Washington coastal environment (-31.2 +/- 0.5%) supports this argument. Values of delta for diploptene in river sediments are variable and 8-17% lighter, indicating that an additional biological source such as methane-oxidizing bacteria makes a significant contribution to the diploptene record in river sediments. Selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more-13C-depleted form of diploptene in Washington coastal sediments, but this mechanism remains unproven.     

基于微电子系统（MEMS）加速度地震勘探三分量数字检波器简介

基于微电子机械系统（MEMS）制成的微加速度三分量数字地震检波器。集数据采集、处理及传输功能干一体，在结构模型、工作原理、性能指标控制等方面不同于常规检波器，其信号幅值在低于自然频率范围内没有衰减。因其独特的制造技术，MEMS检波器具有超低噪声，大动态范围和极高的向量保真度性能。     

Zircon LA-ICP-MS U-Pb age, Ce^4＋/Ce^3＋ ratios and the geochemical features of the Machangqing complex associated with copper deposit

1IntroductionQuite a number of porphyry copper deposits havebeen found in the Cenozoic alkali-intrusions along theJinshajiang-Ailaoshan-Red River fault zone,whichconstitute the Cenozoic ore belt in China.The Cenozo-ic alkali-intrusive rocks are similar in…     

地震地质灾害空间预警评估定量化方法研究初探

建立“发育度”、“潜势度”、“危险度”、“危害度”等概念来描述地震地质灾害各影响因子、要素及可能的灾害危害程度,进而建立构成地震地质灾害层次分析的概念体系及地震地质灾害空间预警评估模型,将定性评估转化为定量评估进行初步研究。     

用CC的方法分析和解决一个常见的网络安全问题

CC导出PP的过程是一种安全评估通用语言到某类产品的具体应用过程,需要经过需求分析、得出安全目的、提出安全功能要求与安全保证要求等几个阶段。本文利用这些过程的基本方法和思想全面分析一个常见的网络安全问题,并按照保护轮廓的模式给出该网络的安全要求。     

基于复小波变换的SAR图像斑点滤波方法

斑点噪声的存在使得SAR图像的应用受到较大的限制.文中首先介绍了SAR图像斑点噪声模型以及几种常用的SAR斑点噪声抑制方法;然后对小波变换斑点噪声滤波方法进行分析,提出了基于二元树复小波变换的SAR图像滤波方法.实验比较表明,二元树复小波变换抑制SAR斑点噪声效果明显,较小波变换更具有优越性.     

H-90B微机γ能谱比活度测量仪

本介绍了H-90B微机γ能谱比活度测量仪的研制方案、仪器组成特点及主要技术指标；简述了仪器的工作原理，工作条件及测量方法；最后，介绍了其在现场检测建筑材料放射性比活度方面的应用情况。     

长江下游一次大暴雨的中尺度模拟分析

运用中尺度数值模式（MM5V3.6）对2004年6月25日长江下游地区一次大暴雨天气过程进行了数值模拟,结合天气形势和卫星云图对此次过程进行了分析.结果表明：在东北冷涡和西太平洋副热带高压两大天气尺度系统的作用下,西南低空急流的再次加强和中低层切变线共同作用是此次大暴雨过程的主要原因.螺旋度分析表明,在不均匀的强上升气流的作用下,涡旋的水平分量向垂直分量转化是此次强降水的可能机制之一.