On the Structure of Symplectic Mappings. The Fast Lyapunov Indicator: a Very Sensitive Tool

It is already known (Froeschlé, Lega and Gonczi, 1997) that the Fast Lyapunov Indicator (FLI), that is the computation on a relatively short time of the largest Lyapunov indicator, allows to discriminate between ordered and weak chaotic motion. We have found that, under certain conditions, the FLI also discriminates between resonant and non-resonant orbits, not only for two-dimensional symplectic mappings but also for higher dimensional ones. Using this indicator, we present an example of the Arnold web detection for four and six-dimensional symplectic maps. We show that this method allows to detect the global transition of the system from an exponentially stable Nekhoroshevs like regime to the diffusive Chirikovs one.     

Chromothermal oscillations and collapse of strange stars to black holes: astrophysical implications

We study the effects of temperature on strange stars. It is found that the maximum mass of the star decreases with the increase of temperature, as at high temperatures the equations of state become softer. Moreover, if the temperature of a strange star increases, keeping its baryon number fixed, its gravitational mass increases and its radius decreases. This leads to a limiting temperature, where it turns into a black hole. These features are the result of a combined effect of the change of gluon mass and the quark distribution with temperature. We report on a new type of radial oscillation of strange stars, driven by what we call 'chromothermal' instability. We also discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma-ray bursts.     

A sequential sparse polynomial chaos expansion using Bayesian regression for geotechnical reliability estimations

Polynomial chaos expansions (PCEs) have been widely employed to estimate failure probabilities in geotechnical engineering. However, PCEs suffer from two deficiencies: (a) PCE coefficients are solved by the least-square minimization method which easily causes overfitting issues; (b) building a high order PCE is often computationally expensive. In order to overcome the aforementioned drawbacks, the Bayesian regression technique is employed to evaluate PCE coefficients, which not only provides a sparse solution but also avoids overfitting. With the aid of the predictive means and variances given by Bayesian analysis, a learning function is proposed to sequentially select the most informative samples that are critical to build a PCE. This sequential learning scheme can highly enhance the computational efficiency of PCEs. Besides, importance sampling (IS) is incorporated into the sequential learning (SL)-PCEs to deal with geotechnical problems with small failure probabilities. The proposed method of SL-PCE-IS is applied to three illustrative examples, which shows that the improved PCE method is more effective and efficient than the common PCEs method, leading to accurate estimations of small failure probabilities using fewer training samples.     

面向土地利用调查的时空数据库构建技术

为了满足"一调""二调"等不同时期土地利用变化数据管理与分析的需要,文章在分析时态数据库构建中存在的问题的基础上,引入变更事件、重建事件和多基态,建立了基于事件组的多基态修正模型,实现了"一调""二调"土地利用数据一体化存储;针对"一调""二调"空间数据不一致的几何重建和语义转换问题,提出通过重建事件表实现重建前后要素归档及查询;同时,针对土地利用数据管理的现状以及数据形态,提出了土地利用变更增量提取、时态拓扑关系构建的方法,实现了土地利用时空数据库的构建。最后,以武汉市汉南区数据为例开发了原型系统,实验结果表明本文提出的模型、方法具有较强的实用性。     

Na-K-Mg三角图修正与Na-K温标选取

Na-K-Mg三角图作为水-岩平衡状态初步判定的方法,未考虑具体温标公式和矿物成分对平衡状态的影响,因此通过基于不同Na-K温标公式修正后的Na-K-Mg三角图判断水岩平衡状态,并利用适合的Na-K温标公式计算地下热储温度,对划分地热系统成因类型和开发利用地热资源具有重要意义。研究发现,修正后的Na-K-Mg三角图中任意一点,对某种温标公式确定的曲线处于平衡状态,对另一温标公式确定的曲线则有可能处于部分平衡状态;且温度越低,这种现象越显著。最贫Mg上边界和最富Mg下边界是由不同的温标公式确定的,随温度具有明显的分段性。利用各Na-K温标公式作出T-lg（Na/K）曲线图,绘制曲线交点对应的基于各\     

A mathematical model for steady‐state regolith production at constant erosion rate

It has been hypothesized that many soil profiles reach a steady‐state thickness. In this work, such profiles were simulated using a one‐dimensional model of reaction with advective and diffusive solute transport. A model ‘rock’ is considered, consisting of albite that weathers to kaolinite in the presence of chemically inert quartz. The model yields three different steady‐state regimes of weathering. At the lowest erosion rates, a local‐equilibrium regime is established where albite is completely depleted in the weathering zone. This regime is equivalent to the transport‐limited regime described in the literature. With an increase in erosion rate, transition and kinetic regimes are established. In the transition regime, both albite and kaolinite are present in the weathering zone, but albite does not persist to the soil–air interface. In the weathering‐limited regime, here called the kinetic regime, albite persists to the soil–air interface. The steady‐state thickness of regolith decreases with increasing erosion rate in the local equilibrium and transition regimes, but in the kinetic regime, this thickness is independent of erosion rate. Analytical expressions derived from the model are used to show that regolith production rates decrease exponentially with regolith thickness. The steady‐state regolith thickness increases with the Darcy velocity of the pore fluid, and in the local equilibrium regime may vary markedly with small variations in this velocity and erosion rate. In the weathering‐limited regime, the temperature dependences for chemical weathering rates are related to the activation energy for the rate constant for mineral reaction and to the ΔH of dissolution, while for local equilibrium regimes they are related to the ΔH only. The model illustrates how geochemical and geomorphological observations are related for a simple compositional system. The insights provided will be useful in interpreting natural regolith profiles. Copyright © 2010 John Wiley & Sons, Ltd.     

Biaxial test simulations using a packing of polygonal particles

The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd.     

地震波形分类技术在地质异常体解释中的应用

地震波形分类技术具有统计地震信号总体变化和反映这种变化分布规律的特点,是地震属性分析技术的重要延伸,在地质异常体解释方面具有良好的应用效果。高密度三维地震资料具有高信噪比,高分辨率和高保真度的特点,尝试利用波形分类技术对高密度三维地震资料反映的煤层赋存状态、岩浆岩侵入区进行预测,并对陷落柱解释方法进行了研究。井下巷道实际揭露和钻孔验证结果表明：波形分类方法解释的地质异常体精度高、圈定范围准确,可以为煤矿安全开采提供精准的地质资料。     

东亚地区天气吸引子特征的研究

利用东亚地区１１个有代表性测站（１９７９－１９８８年）连续１０年的５００ｈＰａ逐日位势高度时间序列，全面计算了它们的浑沌特征量。结果表明，各测站相应的关联维数都是分数；完整的Ｌｙａｐｕｎｏｖ指数谱中，不仅都有正值、零和负值，而且Ｌｙａｐｕｎｏｖ指数之和都小于零。因此，从整体来看，相应于东亚地区天气尺度的吸引子是由一个有限窨支撑起来的。东亚地区的天气吸引子所显示的系统平均Ｋｏｌｍｏｇｏｌｏｖ熵约为０     

多因素复杂系统最佳因素权重确定的一种新思路——以深港西部通道工程深圳湾公路大桥为例

为了客观地反映各因素对目标问题的影响程度,本文首次提出了最佳因素权重概念。定义最佳因素权重为研究区域内系统质量处于极限状态时的各因素权重之组合。结合深港西部通道工程深圳湾公路大桥桥址比选方案,详细说明了本方法的研究思路及其确定方法。通过最佳因素权重方法,能客观地、定量地确定出多因素复杂系统中的最优场址。