Rotation and dilation deformation mechanisms for auxetic behaviour in the α-cristobalite tetrahedral framework structure

 Analytical expressions are derived for the Poisson's ratios associated with a three-dimensional network of regular, corner-sharing tetrahedra in which: (1) the tetrahedra are assumed to be rigid and free to rotate relative to each other; (2) the tetrahedra are assumed to maintain shape and orientation but are free to change size (dilate); (3) tetrahedral rotation and dilation are assumed to act concurrently. The structure has a primitive unit cell containing four tetrahedra and is analogous to the molecular structure of α-cristobalite. Strain-dependent variations in Poisson's ratio are also predicted by the models. For deformation due to tetrahedral rotation the network is found to exhibit negative Poisson's ratios in each of the three principal directions, with the magnitude of the Poisson's ratio being dependent on the angle of rotation of the tetrahedra. The behaviour of the Poisson's ratio is isotropic in the transverse plane, but anisotropic elsewhere. In the dilation model negative Poisson's ratios equal to −1 are observed for uniaxial loading in any of the principal directions, with the value being constant irrespective of tetrahedral size. The model for concurrent tetrahedral rotation and dilation allows positive as well as negative Poisson's ratios, with the values determined by the framework geometry and relative strengths of the two mechanisms. The concurrent model also offers a design route to materials and structures having ultrahigh Young's moduli. Received: 15 February 2000 / Accepted: 1 October 2000     

湖南洞庭坳陷大地电磁测深研究

介绍了大地电磁测深在湖南洞庭坳陷的主要研究成果。详细分析、推断了洞庭地区的区域构造格局，深部电性结构及壳、幔高导层的分布特点     

松潘地区岩金统计成矿予测中泛克立格法的应用

川西北地区是国内重要的岩金普查靶区。本文对松潘地区的地质特征,泛克立格法原理,及在本区的应用情况作了介绍,对主要计算步骤,给出基本结果,对计算获得的有意义异常区,进行地质解释,并将此方法与趋势面分析进行对比。     

When are relative variograms useful in geostatistics?

The relative variogram has been employed as a tool for correcting a simple kind of nonstationarity, namely that in which local variance is proportional to local mean squared. In the past, this has been linked in a vague way to the lognormal distribution, although if {Z_t; t D}is strongly stationary and normal over a domain D,then clearly {exp (Z_t); t D}will stillbe stationary, but lognormal. The appropriate link is made in this article through a universal transformation principle. More general situations are considered, leading to the use of a scaled variogram.     

海洋沉积物动力学的示踪物方法

本文的论题是示踪物方法在海洋物源追踪和沉积物输运率计算中的应用 ,以及示踪物方法的普适性理论框架。定量的物源追踪需要适当的示踪标记和物质混合模型 ,有必要根据沉积动力过程的研究来确定示踪标记的变换函数 ,从而将改进的示踪标记用于混合模型分析。人工示踪物实验的现有方法以空间积分法最为常用 ,其关键是示踪物质心运动和沉积物活动层的界定。天然示踪物的质心位置是无法定义的 ,因此不能借用传统人工示踪物方法来估算物质输运率 ;在某些特殊情形下 ,可以利用天然示踪物的质量守衡原理来获得物质输运信息。今后 ,以示踪物质的连续方程为基础 ,有可能建立一种同时适用于人工和天然示踪物的普适理论框架。其中需解决的问题包括示踪物与现场物质的差异、沉积速率和活动层厚度的时间尺度、沉积物扩散过程等。     

Observational manifestations of prerecombination protoobjects

We consider the image formation for an extremely distant source in an optically dense, homogeneous, and isotropic medium. We show that the angular size of the image would presently be θ₀ ≈ 10′, irrespective of the initial redshift z. Parameters of the inhomogeneities capable of producing the observed effect were estimated. We note that this effect should be taken into account for the baryon density fluctuations that were damped according to Silk at the prerecombination epoch. The spot radiation spectrum is shown to be a diluted Planckian spectrum with a dilution factor much larger than unity. We also point out the presence of peculiar tangential polarization in the spot, which reaches several tens of percent at the spot edge. All these observational features clearly distinguish the fluctuations under consideration from the standard fluctuations.     

A difference method of searching for spectral-spatial fluctuations of the cosmic microwave background radiation

We consider methods of searching for the spectral-spatial fluctuations of the cosmic microwave background radiation that were formed in the early Universe. Based on the narrow-band spatial-frequency properties of these fluctuations, we suggest a difference method of their search. We describe the method and present our simulation results. This technique is shown to have a significant advantage over the existing methods. We give recommendations to optimize the observing and reduction procedures.     

陆相坳陷盆地层序地层格架下岩性地层圈闭/油藏类型与分布规律——以松辽盆地白垩系泉头组—嫩江组为例

本文在圈闭组成和形成条件分析的基础上对坳陷盆地层序地层格架下岩性地层圈闭/油藏类型与分布规律进行了初步分析和总结,探讨了层序地层格架下不同体系域中圈闭/油藏类型的纵向分布、盆地中不同构造部位圈闭/油藏类型的横向分布规律。系统解剖了松辽坳陷盆地白垩系二级层序格架内低位、湖侵和高位体系域中圈闭/油藏类型的纵向分布和变化特征;对比分析了坳陷盆地从凹陷带(近凹中心)、过渡带(凹陷边缘)到斜坡带(环凹斜坡)圈闭/油藏类型的横向分布和变化规律。圈闭/油藏类型的纵、横向分布和变化规律表明:岩性地层圈闭/油藏的形成及类型具有纵向“层控”、横向“相控”的规律性,即纵向上受控于层序格架(体系域),横向上受控于一定构造背景下特定的沉积相带。     

基于Java的系统开发中MVC架构的应用

论述了如何在Java应用开发领域中使用设计模式和MVC(Model-View-Controller)架构。介绍了设计模式的概念和特点,以及MVC架构的设计思想,并分析了MVC架构中包含的几种主要模式,采用MVC架构作为开发的基本架构,可以使开发的项目耦合度降低,提高程序的可扩展性。根据Java应用系统的特点,在实际的“数值预报业务监控系统”的应用开发中如何采用MVC架构提出了一些自己的想法。     

东天山觉罗塔格地区夹白山一带晚古生代构造格局及演化

研究区早石炭世经历了中天山古陆北缘被动陆缘向活动陆缘沟弧盆体系演化的全过程.阿齐山-雅满苏岛弧带于维宪期发育在广宽陆棚海之上.岛弧为大型背形结构,雅满苏断裂带为火山喷发的主要通道,弧前盆地生成于弧沟间隙部位.晚石炭世早期,弧后区发生扩张作用而塌陷形成向形的边缘盆地.晚石炭世末,北侧康古尔洋区以弧弧对接方式关闭,弧区伴有深成花岗岩浆侵位.早二叠世早期进入松弛阶段,在弧间及弧后南缘产生上叠断陷盆地.晚二叠世右旋走滑变动席卷全区,最后大型造山带与地块之间发生块体右旋滑移错位,由此奠定了现今的盆山构造格局初貌.