线性时滞系统的近似变结构控制

为了回避时延现象的存在给变结构控制方案中滑动模态的恰当定义及保证其渐近稳定的切换函数参数矩阵的确定带来的诸多不便和困难,对于线性时滞系统,首先根据帕德近似公式对其模型作近似处理,然后再采用变结构控制。该控制方案具有一定的应用价值。     

基于韦伯-费希纳定律的营养状态普适韦伯指数公式

在适当设定各营养状态指标"参照值"Cj0的基础上,用相应于"参照值"Cj0的指标"规范值"xj作为基于韦伯-费希纳定律的营养状态指数公式中的刺激量.由于各项指标的同级营养状态标准的"规范值"xjl差异不大,从而可认为各指标的营养状态韦伯指数公式都具有一个共同适用的韦伯常数α,并采用智能解域搜索算法优化α,得出对所有14项营养指标皆适用的营养状态普适韦伯指数公式.将营养状态韦伯指数公式应用于数十个湖泊的富营养化评价,并与其它多种方法的评价结果进行比较,结果表明该公式不但理论依据充分,而且具有简单、适用的特点.     

Evolution-EM signals before earthquakes in terms of mesomechanics and complexity

MHz-to-kHz electromagnetic (EM) anomalies have been detected worldwide over time intervals ranging from a few days to a few hours prior to near-surface earthquakes (EQs) that have occurred on land with magnitude approximately six or larger. The MHz radiation systematically appears earlier than the kHz. Laboratory experiments on rock samples reveal a similar change in the frequency content during progressive deformation, i.e. the emissions exhibit a frequency shift from MHz to kHz just before failure of the samples. Herein, we attempt to associate these consecutively emerging MHz and kHz modes of the pre-fracture EM emission with successive distinct stages of the fracture preparation process and the associated fracture mechanisms. We base our approach on synergetic principles of physical mesomechanics. A universal principle of physical mesomechanics is that the plastic deformation of a solid is related to its loss of shear stability at the micro-, meso-, and macroscale levels. Global fracture is determined by the mechanism controlling the development of macroscale bands of localized deformation associated with meso- and microscale relaxation processes. The major result we obtain is that the shift from MHz to kHz EM activity may signal the transition of plastic flow localization from the mesoscale to the macroscale, culminating in global fracture. A complexity measure (Approximate Entropy) and a persistency–anti-persistency measure (Hurst exponent) also give evidence of a two stage-model of EQ preparation process: significant complexity decrease and accession of persistency can be confirmed in the strong kHz EM activity that emerges in the tail of the pre-seismic EM activity. Laboratory experiments on rock samples reveal similar symptoms of an imminent global instability.     

空间直角坐标计算大地坐标的抛物线逼近法

采用抛物线逼近法求解大地纬度和大地高,先计算空间点在椭球面上的子午面坐标,然后求解点的大地纬度和大地高。     

汶川8.0级地震对鄂尔多斯块体西南缘断裂体系影响的数值模拟

利用有限元方法及静态位移解理论,采用前人反演的汶川8.0级地震破裂过程时空参数,定量计算分析汶川地震对鄂尔多斯块体西南缘断裂体系的影响.数值计算表明,具逆冲右旋性质的汶川地震,在汶川-宝鸡-线以东产生顺时针的位移扰动场,以西产生逆时针的位移扰动场,这与该分界两侧附近的活断层整体走滑方向相一致.水平剪切应力场的局部极值区...     

红土型金矿中痕量金分析应用研究

总结红土型金矿运用痕量金分析的理论基础,对不同金标样样品进行准确度、精密度检查,表明痕量金分析可以满足矿点的检查、异常查证的基本要求。与室内法相比,本法有方便、快捷、低成本、高效率及易掌握等特点。     

Numerical Investigation of the Galactic Problem by Computing Families of Periodic Solutions

The galactic dynamical system expressed by a third-order axisymmetric polynomial potential is investigated numerically by computing periodic solutions. We define as Sthe compact set of initial conditions generating bounded motions, and as S ^p , with S ^p ? S, the countable set of all initial conditions generating periodic solutions. Then, we consider the subsets S _s ^p and S _a ^p of S ^p , where S _s ^p ∪ S _a ^p = S ^p , S _s ^p S _a ^p = Ø, the first of which corresponds to symmetric periodic solutions, and the second to asymmetric solutions. Then, we approximate the set S _s ^p , leaving treatment of the set S _a ^p of asymmetric solutions for a future publication. The set S _s ^p is known to be dense in S (‘Last Geometric Theorem of Poincar;’, Birkhoff, 1913). Using a computer programme capable to locate all elements of the set S _s ^p that generate symmetric periodic solutions that re-enter after intersecting the axis of symmetry from 1 to ntimes. The results of the approximation of S _s ^p in the total domain and in the sample sub-domains of zooming, we present in graphical form as family curves in the (x, C) plane. The solutions located with the largest periods re-enter after 440 galaxy revolutions while the families calculated fully (initial conditions, period, energy, stability co-efficient) include solutions that re-enter after 340 galaxy revolutions. To advance further the approximation of the set S _s ^p thus obtained, we applied the same procedure inside eight sub-domains of the domain Sinto which we ‘zoomed’ through selection of finer search steps and double maximum periods. The family curves thus calculated presented in the (x, C) plane do not intersect anywhere in some sub-domains and their pattern resembles that of laminar flow. In other sub-domains, however, we found family curves from which branching families emanate. The concepts of completeand non-completeapproximation of S _s ^p in sub-domains of laminar and sub-domains with branching family curves, respectively, is introduced. Also, the concept of basic family of order1, 2, ..., n, are defined. The morphology of individual periodic solutions of all families is investigated, and the types of envelopes found are described. The approximate set S _s ^p was also checked by computing Poincar; sections for energy values corresponding to the mean energy range of the eight sub-domains of zooming mentioned above. These sections show that most parts of the compact domain in Sgenerating non-periodic but bounded solutions correspond to with well-shaped tori that intersect the x-axis, a fact that implies that dominant to exclusive type of periodic solutions are the symmetric ones with two normal crossings of this axis. The presence of non-symmetric periodic solutions as well as of chaotic regions is encountered. All calculations reported here were performed using the variable step R-K 8th-order direct integration and setting the allowable energy variation Δ C= |C _start? C _end| < 10^?13. The output, consisting of many thousands of families and their properties (initial conditions, morphology, stability, etc.), is stored in a directory entitled ‘Atlas of the Symmetric Periodic Solution of the Galactic Motion Problem’.     

Evolution of the General Solution of the Restricted Problem Covering Symmetric and Escape Solutions

The work presented in paper I (Papadakis, K.E., Goudas, C.L.: Astrophys. Space Sci. (2006)) is expanded here to cover the evolution of the approximate general solution of the restricted problem covering symmetric and escape solutions for values of μ in the interval [0, 0.5]. The work is purely numerical, although the available rich theoretical background permits the assertions that most of the theoretical issues related to the numerical treatment of the problem are known. The prime objective of this work is to apply the ‘Last Geometric Theorem of Poincaré’ (Birkhoff, G.D.: Trans. Amer. Math. Soc. 14, 14 (1913); Poincaré, H.: Rend. Cir. Mat. Palermo 33, 375 (1912)) and compute dense sets of axisymmetric periodic family curves covering the initial conditions space of bounded motions for a discrete set of values of the basic parameter μ spread along the entire interval of permissible values. The results obtained for each value of μ, tested for completeness, constitute an approximation of the general solution of the problem related to symmetric motions. The approximate general solution of the same problem related to asymmetric solutions, also computable by application of the same theorem (Poincaré-Birkhoff) is left for a future paper. A secondary objective is identification-computation of the compact space of escape motions of the problem also for selected values of the mass parameter μ. We first present the approximate general solution for the integrable case μ = 0 and then the approximate solution for the nonintegrable case μ = 10⁻³. We then proceed to presenting the approximate general solutions for the cases μ = 0.1, 0.2, 0.3, 0.4, and 0.5, in all cases building them in four phases, namely, presenting for each value of μ, first all family curves of symmetric periodic solutions that re-enter after 1 oscillation, then adding to it successively, the family curves that re-enter after 2 to 10 oscillations, after 11 to 30 oscillations, after 31 to 50 oscillations and, finally, after 51 to 100 oscillations. We identify in these solutions, considered as functions of the mass parameter μ, and at μ = 0 two failures of continuity, namely: 1. Integrals of motion, exempting the energy one, cease to exist for any infinitesimal positive value of μ. 2. Appearance of a split into two separate sub-domains in the originally (for μ = 0) unique space of bounded motions. The computed approximations of the general solution for all values of μ appear to fulfill the ‘completeness’ criterion inside properly selected sub-domains of the domain of bounded motions in the (x, C) plane, which means that these sub-domains are filled countably densely by periodic family curves, which form a laminar flow-line pattern. The family curves in this pattern may, or may not, be intersected by a ‘basic’ family curve segment of order from 1 up to 3. The isolated points generating asymptotic solutions resemble ‘sink’ points toward which dense sets of periodic family curves spiral. The points in the compact domain in the (x, C) plane resting outside the domain of bounded motions (μ = 0), including the gap between the two large sub-domains (μ > 0) created by the aforementioned split, generate escape motions. The gap between the two large sub-domains of bounded motions grows wider for growing μ. Also, a number of compact gaps that generate escape motions exist within the body of the two sub-domains of bounded motions. The approximate general solutions computed include symmetric, heteroclinic, asymptotic, collision and escape solutions, thus constituting one component of the full approximate general solution of the problem, the second and final component being that of asymmetric solutions.     

《盐湖研究》合订本征订启事

<正>《盐湖研究》是原国家科委批准的学术类自然科学期刊,由中国科学院青海盐湖研究所主办,科学出版社出版,1993年创刊并在国内外公开发行。《盐湖研究》自公开发行以来,深受广大读者的厚爱,为了便于我刊读者和文献情报服务单位系统收藏,编辑部藏有94-95年、96-97年、98-     

地壳现代形变的近似动力学模型

为计算不同时刻介质中的形变位移,提出用近似模型代替有一定流变和给定作用力系的介质某一边缘问题解.最优化反演问题解带有近似模型的自由参数,为求出模型自由参数系,将反演问题解分解为形变锋族运动学问题解和模型振幅参数的测定.