Vertical dynamic response of a disk on a saturated poroelastic half-space

This paper considers the vertical dynamic response of a disk on a saturated poroelastic half-space. Firstly the pressure-solid displacement form of the harmonic equations of motion for a poroelastic solid are developed from the form of the equations originally presented by Biot. These equations are solved by a new method. Then the mixed boundary value problem for the vertical harmonic vibration of a disk on a poroelastic half-space is studied. The two types of drainage conditions at the surface of the poroelastic half-space are considered: (a) the surface of the poroelastic half-space is assumed to be completely pervious both within and exterior to the plate; (b) The interface between the plate and the poroelastic half-space is assumed to be impervious and the exterior region is assumed to be pervious. By using the Hankel transform techniques, the paper develops the governing dual integral equations. These governing integral equations are further reduced to systems of standard Fredholm integral equations of the second kind by Abel transform.     

Dust in the disk winds from young stars as a source of the circumstellar extinction

We consider the problem of dust grain survival in the disk winds from T Tauri and Herbig Ae stars. For our analysis, we have chosen a disk wind model in which the gas component of the wind is heated through ambipolar diffusion to a temperature of ～10⁴ K. We show that the heating of dust grains through their collisions with gas atoms is inefficient compared to their heating by stellar radiation and, hence, the grains survive even in the hot wind component. As a result, the disk wind can be opaque to the ultraviolet and optical stellar radiation and is capable of absorbing an appreciable fraction of it. Calculations show that the fraction of the wind-absorbed radiation for T Tauri stars can be from 20 to 40% of the total stellar luminosity at an accretion rate ? _a = 10^?8-10^?6 M _⊙yr^?1. This means that the disk winds from T Tauri stars can play the same role as the puffed-up inner rim in current accretion disk models. In Herbig Ae stars, the inner layers of the disk wind (r ≤ 0.5 AU) are dust-free, since the dust in this region sublimates under the effect of stellar radiation. Therefore, the fraction of the radiation absorbed by the disk wind in this case is considerably smaller and can be comparable to the effect from the puffed-up inner rim only at an accretion rate of the order of or higher than 10^?6 M _⊙yr^?1. Since the disk wind is structurally inhomogeneous, its optical depth toward the observer can be variable, which should be reflected in the photometric activity of young stars. For the same reason, moving shadows from gas and dust streams with a spiral-like shape can be observed in high-angular-resolution circumstellar disk images.     

应用MODIS遥感数据监测巢湖水质

以巢湖为研究对象,对MODIS的各个波段辐射率与水质参数叶绿素a浓度、悬浮物浓度和透明度进行拟合,分析了MODIS各个波段辐射率的拟合在监测大型内陆湖泊水质中的可行性.结果表明:MODIS波段辐射率的组合能与巢湖水质参数进行较好的匹配,MODIS波段1—4和10—11对于监测巢湖中叶绿素a浓度、悬浮物浓度和透明度有重要意义.     

四种海水透明度现场测量方法的对比分析及发展趋势研究

随着海洋探测的不断发展,海水透明度作为海水光学性质的一个重要参量,也越来越受到人们的关注。文章对比分析了4种海水透明度现场测量方法:透明度盘法~([1])、光纤式高光谱剖面测量法~([2])、激光衰减测量法~([3])和基于双光路原理的海水IOPs高光谱测量法~([4]),主要分析了4种方法的测量原理,对比各自的优缺点,并提出了海水透明度测量未来发展设想。     

平台巴西圆盘复合型加载下T应力计算法

平台巴西圆盘(CFBD)具有避免加载点处应力集中、保证破坏由预制裂纹尖端处起始的优点,成为研究脆性材料断裂性能的常用试件之一。最近的研究发现,T应力也会影响材料断裂性能,但平台巴西圆盘并没有计算T应力的解析公式。使用解析分析与有限元数值分析相结合的方法,对复合型加载条件下平台巴西圆盘试件的T应力进行了计算,并对误差进行了系统的分析。结果表明,在一定载荷分布角内相对裂纹长度 时,不管是纯I、纯II还是复合型加载条件下平台巴西圆盘计算的T应力都可以用中心裂纹巴西圆盘均布载荷下T应力计算公式来计算;T应力相对误差随着相对裂纹长度的增加而增加。     

太阳系外行星研究进展

过去的二十年间,利用多种技术（如脉冲时间、径向速度、天文学观测、穿越光度计、反射光度计、微透镜和直接图像）发现了405个太阳系外行星。对这些太阳系外行星的研究首次提供了有关行星生长的信息,诸如星盘结构和演化,星盘性质和大小等。2009年4月对GJ581d行星的观测表明,这个行星处于＂宜居区域＂内,意味着它有液态水,因此可能有生命存在。     

颈椎间盘病变的CT表现及临床意义

目的 探讨颈椎间盘病变的CT平扫诊断与临床的价值。材料与方法，对80例颈椎间盘病变的CT表现按节段，类型，程度进行分析。结果：外伤是导致椎间盘病变的主要因素；颈椎间盘膨出和脱出均较少见，以突出为主；单节段发生较少，多节段发生常见，以C5／6，C4／T，C6／7多见；突出程度多在2－5mm之间。结论：CT检查能显示颈椎间盘病变的节段，类型以及与脊髓和神经根的关系，为临床制定治疗方案提供影像学依据。     

数据库系统研制中的几个实用技术

本文根据几个数据系统开发发的实践经验,针对距平台数据导入,无ＤＳＮ连接、动态结账,软、硬盘备份恢复,控件优化等方面提出了几种简洁有效的实用技术。     

Horizontal vibrations of a disk on a poroelastic half-space

This paper analytically examines the horizontal vibration of a rigid disk on a saturated poroelastic half-space. The pressure-solid displacement form of the harmonic equations of motion for asymmetric dynamic problem are developed from the form of the equations originally presented by Biot. Making use of a new method the solution of the above equations is obtained. According to the mixed boundary -value conditions, the dual integral equations of the horizontal vibration of a rigid disk on a saturated poroelastic half-space are established. By appropriate transforms, it is shown that the dual integral equations can be reduced to a pair of Fredholm integral equations of the second kind, whose solutions are then computed. Numerical results for the horizontal dynamic compliance coefficient are given at the end of this paper.