基于LS-RSGFD方法优化的横向各向同性(TI)介质一阶qP波高精度数值模拟

为克服各向异性介质弹性波数值模拟中存在着计算量大和波场分离困难等局限,研究了声学近似的VTI介质和TTI介质一阶qP波数值模拟方法.首先对VTI介质弹性波方程进行声学近似,推导了VTI介质一阶qP波方程;然后基于精确的TTI介质频散关系,引入一个包含各向异性控制参数σ的新辅助波场,推导了稳定的TTI介质二阶耦合qP波波动方程,并通过引入波场的伪速度分量,推导了等价的一阶应力-速度形式.结合旋转交错网格有限差分(RSGFD)和基于最小二乘优化的有限差分(LS-FD)两种各具优势的方法,研究了最小二乘旋转交错网格有限差分(LS-RSGFD)方法,并用其数值求解VTI和TTI介质一阶qP波方程,然后通过构造其LS-RSGFD格式,实现了高精度的各向异性介质qP波波场数值模拟.数值模拟结果表明:TI介质一阶qP波方程能够准确地模拟各向异性介质中qP波的运动学特征,引入控制参数σ能够有效地减弱不稳定性问题,保证非均匀TTI介质中qP波场的稳定传播;利用优化的LS-RSGFD方法可以得到高精度的合成地震记录,同时还可以相对地提高计算效率.     

Hot Subdwarfs in Precataclysmic Binaries

We present a brief review of the recent results in modeling physical processes in strongly irradiated atmospheres of unevolved companions in precataclysmic binary systems (PCB) and their light curves. Constraints on physical parameters of the hot sdws primaries, thermal instability in upper irradiated atmosphere, monochromatic albedos, the deficit of the total emergent flux compared to the incoming flux from hot sdw primary are briefly discussed.     

On the peak level of tearing instability in an ion-scale current sheet: The effects of ion temperature anisotropy

We have systematically surveyed the effects of the ion temperature anisotropy on the peak reconnected flux level of the tearing instability excited in a thick current sheet (its half-thickness D equal to the ion inertial length). A series of two- and three-dimensional (2-D and 3-D) simulations have been performed for a magnetotail-like situation, where the ion perpendicular temperature is fixed to balance the magnetic pressure of the lobe while the ion parallel temperature can be varied to give rise to the temperature anisotropy α_i=T_i,perp/T_i,para. Focusing on the behavior of the fastest growing mode (wavelength λ=12D), the results are summarized as follows: (1) The peak levels are larger when the initial α_i is larger and lobe reconnection is obtained only when α_i>1.5. (2) 3-D effects do speed-up the reconnection process but do not change the peak level substantially. (3) The time-scale of gas pressure build-up at the center of magnetic islands relative to the time-scale of reconnected flux growth is identified to be the key issue in determining the peak level. Based on these results for the fastest growing mode with λ=12D, discussion is given on the larger-scale development, that is, what happens when longer wavelength modes are allowed to develop.     

The typical seismic behavior in the vicinity of a large earthquake

The Global Centroid Moment Tensor catalog (GCMT) was used to construct the spatio-temporal generalized vicinity of a large earthquake (GVLE) and to investigate the behavior of seismicity in GVLE. The vicinity is made of earthquakes falling into the zone of influence of a large number (100, 300, or 1000) of largest earthquakes. The GVLE construction aims at enlarging the available statistics, diminishing a strong random component, and revealing typical features of pre- and post-shock seismic activity in more detail. As a result of the GVLE construction, the character of fore- and aftershock cascades was examined in more detail than was possible without of the use of the GVLE approach. As well, several anomalies in the behavior exhibited by a variety of earthquake parameters were identified. The amplitudes of all these anomalies increase with the approaching time of the generalized large earthquake (GLE) as the logarithm of the time interval from the GLE occurrence. Most of the discussed anomalies agree with common features well expected in the evolution of instability. In addition to these common type precursors, one earthquake-specific precursor was found. The decrease in mean earthquake depth presumably occurring in a smaller GVLE probably provides evidence of a deep fluid being involved in the process. The typical features in the evolution of shear instability as revealed in GVLE agree with results obtained in laboratory studies of acoustic emission (AE). The majority of the anomalies in earthquake parameters appear to have a secondary character, largely connected with an increase in mean magnitude and decreasing fraction of moderate size events (mw5.0–6.0) in the immediate GLE vicinity. This deficit of moderate size events could hardly be caused entirely by their incomplete reporting and can presumably reflect some features in the evolution of seismic instability.     

GIS analysis to assess landslide susceptibility in a fluvial basin of NW Sicily (Italy)

Landslide hazard assessment, effected by means of geostatistical methods, is based on the analysis of the relationships between landslides and the spatial distributions of some instability factors. Frequently such analyses are based on landslide inventories in which each record represents the entire unstable area and is managed as a single instability landform. In this research, landslide susceptibility is evaluated through the study of a variety of instability landforms: landslides, scarps and areas uphill from crown. The instability factors selected were: bedrock lithology, steepness, topographic wetness index and stream power index. The instability landform densities computed for all the factors, which were arranged in Unique Condition Unit, allowed us to derive a total of three prediction images for each landslide typology. The role of the instability factors and the effects generated by the use of different landforms were analyzed by means of: a) bivariate analysis of the relationships between factors and landslide density; b) predictive power validations of the prediction images, based on a random partition strategy.The test area was the Iato River Basin (North-Western Sicily), whose slopes are moderately involved in flow and rotational slide landslides (219 and 28, respectively). The area is mainly made up of the following complexes: Numidian Flysch clays (19%, 1%), Terravecchia sandy clays (5%, 1%), Terravecchia clayey sands (3%, 0.3%) and San Cipirello marly clays (9%, 0%). The steepness parameter shows the highest landslide density in the [11–19°] class for both the typologies (8%, 1%), even if the density distributions for rotational slides are right-asymmetric and right-shifted. We obtained significant differences in shape when we used different instability landforms. Unlike scarps and areas uphill from crowns, landslide areas produce left-asymmetric and left-shifted density distributions for both the typologies. As far as the topographic wetness index is concerned, much more pronounced differences were detected among the instability landforms of rotational slides. In contrast, the flow landslides produce normal-like density distributions. The latter and the rotational slide landslide areas produce the highest density values in the class [5.5–6.7], despite an abrupt decreasing trend starting from the first class [3.2–4.4], which is generated by the density values of the rotational slide scarps and areas uphill from crowns. The stream power index at the foot of the slopes, which was automatically derived using a GIS-procedure, shows a positive correlation with the landslide densities marked by the maximum classes: [4.8–6.0] for flows, and [6.0–7.2] for rotational slides. The validation procedure results confirmed that the choice of instability landform influences the results of the susceptibility analysis. Furthermore, the validation procedure indicates that: a) the predictive models are generally satisfactory; b) scarps and zones uphill from crown areas are the most diagnostically unstable landforms, for flow and rotational slide landslides respectively.     

Improved bounds on linear instability of barotropic zonal flow within the shallow water equations

Here we develop mathematical results to describe the location of linear instability of a parallel mean flow within the framework of the shallow water equations; growth estimates of near neutral modes (for disturbances subcritical with respect to gravity wave speed) in the cases of non-rotating and rotating shallow water. The bottom topography is taken to be one-dimensional and the isobaths are parallel to the mean flow. In the case of a rotating fluid, the isobaths and the mean flow are assumed to be zonal. The flow is front-like: there is a monotonic increase of mean flow velocity. Our results show that for barotropic flows the location of instabilities will be a semi-ellipse region in the complex wave velocity plane, that is based on the wave-number, Froude number, and depth of the fluid layer. We also explore the instability region for the case of spatially unbounded mean velocity profiles for non-rotating shallow water.     

修正的粘滞律及有磁吸积盘的稳定性研究

本文采用修正的粘滞定律及磁流体力学研究了薄吸积盘内区及外区的稳定性问题。运用微扰方法导出了色散方程，分析了四种情况下吸积盘的不稳定性，结果表明：在同时考虑磁场和修正的粘滞律时，吸积盘中存在着三种振荡模式，其中粘滞模式总是稳定的，磁声速模式（包括向里、向外传播两种模式）通常是不稳定的。这些结果为解释ＢＬ Ｌａｃ天体、Ｓｅｙｆｅｒｔ星系、类星体等活动星系核的光变现象提供了理论依据。     

Analysis of cyclogenesis parameter for developing and nondeveloping low-pressure systems over the Indian Sea

A cyclone genesis parameter, termed the genesis potential parameter (GPP), for the Indian Sea is proposed. The parameter is defined as the product of four variables, namely vorticity at 850 hPa, middle tropospheric relative humidity, middle tropospheric instability, and the inverse of vertical wind shear. The variables are calculated using the National Centers for Environmental Prediction (NCEP), USA, reanalysis data, averaged within a circle of 2.5° radius around the centre of cyclonic system. The parameter is tested with a sample dataset of 35 nondeveloping and developing low-pressure systems that formed over the Indian Sea during the period 1995–2005. The result shows that there is a distinction between GPP values for nondeveloping and developing systems in more than 85% cases. The composite GPP value is found to be around three to five times greater for developing systems than for nondeveloping systems. The analysis of the parameter at early development stage of a cyclonic storm appears to provide a useful predictive signal for intensification of the system.     

滑动方向相反的含障碍体平行断层失稳破坏应变场变化特征的研究

通过对滑动方向相反的含障碍体平行断层失稳破坏岩石破裂实验的应变场时空分布特征的分析,探讨了岩石破坏过程和破坏方式。并且通过对平行断层和障碍体破坏所产生的相互作用和影响的分析,进一步研究了这种滑动方向相反的含障碍体平行断层失稳破坏的增、减震机制,结果表明是一种互为增震机制。最后通过数值模拟技术对实验的破坏过程进行了模拟,证明了实验结果与数值模拟结果一致,说明实验结果具有可靠性。     

高陡层状土质边坡风蚀失稳过程及机理研究

吐鲁番交河故城台地高陡层状土质边坡的失稳过程受风蚀控制和影响非常典型;在土层组合特征和抗风蚀能力差异以及当地终年多大风的气候特征的共同作用下,坡体土层形成风蚀空腔并在空腔的控制下发生变形破坏.以工程地质定性分析、风洞实验、物理模拟为主要手段,结合数值模拟,分析了该边坡在自然风蚀改造过程中表现出具有特殊性、多样性和阶段性...