Changes in crop type distribution in Zhangye City of the Heihe River Basin,China

With rapid economic development in China, crops have undergone remarkable changes in both their type and spatial pattern. Timely and accurate information of crop type distribution will help government and agricultural producers quickly understand regional agricultural production conditions to better facilitate appropriate adjustments in planting patterns and policies. Another benefit of acquiring such knowledge of crops is that it should enhance regional agricultural competitiveness, optimize resource allocations, and further guarantee national food security. Towards this end, and using the Zhangye City in the Heihe River Basin as a study area, the present research elaborated upon a methodology to classify crop type distribution based on multi-temporal Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM+) images. Using this methodology we achieved the spatial distributions of crop types in Zhangye City in 2007 and 2012, and analyzed changes in their distributions over this period. In addition, some landscape indices were calculated to clarify the landscape pattern of crops. The crop conversion potentials in 2017 were modeled using four conversion sub-models of the Multi-Layer Perceptron (MLP) neural network. Generally, the overall accuracy of crop classification in Zhangye was high, at 89.38%. From 2007 to 2012, the cultivated land area in Zhangye increased from 463.81 × 10³ ha to 493.89 × 10³ ha. The sowing area of corn and oilseed rape increased by 39.21 × 10³ ha and 5.99 × 10³ ha, respectively, while for wheat and barley the sowing area decreased by 3.61 × 10³ ha and 9.14 × 10³ ha, respectively. Considering other crop types as a group, their sowing area decreased by only 2.37 × 10³ ha. The increase in corn sowing area mainly came from the conversion of other crops to corn, which accounted for 43.09% of its total sowing area in 2012. Furthermore, corn and oilseed rape showed a tendency of intensive sowing, whereas for wheat and barley the tendency was towards scattered sowing. For the future, corn has high conversion potential in Linze and Gaotai counties of Zhangye, while wheat, barley and oilseed rape have high conversion potentials in Minle and Shandan counties.     

A rigorous Hamiltonian approach to the rotation of elastic bodies

When the problem of the rotation of a non-rigid body is studied, the usual procedure consists of adding perturbations to the Hamiltonian of the rigid solid. In some cases, as occurs with the centrifugal deformation, the new perturbations contains potentials which depend on the velocity, but usually one alter neither the definition of the canonical variables nor the method for obtaining the Hamiltonian. Although this procedure gives good estimates and its formulation is simpler, it is incorrect from a theoretical point of view.In this paper we rigorously develop a Hamiltonian formulation of the problem, considering potentials that depend on the velocity. Thus the differences between the two procedures are clearly shown, giving special emphasis to the case of the elastic Earth, for which we show that the differences obtained cannot be ignored within the accuracy limits at present required.     

浅析松辽盆地北部油气成藏规律及资源勘探前景

通过对松辽盆地北部50年来的石油地质勘探理论、勘探技术以及油气资源储量现状的深入分析研究,指出松辽盆地北部日前及以后时期的石油勘探仍以松辽盆地北部中央坳陷为丰,其次为西部斜坡及滨北地区.剩余资源十分丰富,平面上主要分布在中央坳陷,纵向上主要分布在中部含油组合（萨尔图、葡萄花和高台子油层）和下部含油组合（扶杨油层）.深层的天然气勘探仍以徐家围子断陷为书要勘探领域,其次为古龙断陷和双城断陷.同时应积极探索浅层气、油页岩等非常规资源的开发,为实现“百年油田”的宏伟目标提供资源保障.     

Piezomagnetic fields produced by dislocation sources

Tectonomagnetic modeling based on the linear piezomagnetic effect is reviewed with special attention to dislocation models. Stacey's scheme was the prototype for such modeling, as proposed in his first seismomagnetic calculations in 1964. The linear piezomagnetic law is presented, in which the stress-induced magnetization is expressed as a linear combination of stress components. The Gauss law for magnetic field and the Cauchy-Navier equation for static elastic equilibrium are combined through linear piezomagnetism and the Hooke law to yield the basic equation for piezomagnetic potential. A representation theorem for its solution is given by surface integrals of the displacement and its normal derivative over the strained body.A Green's function method is developed to compute the piezomagnetic field produced by a dislocation surface in an elastic half-space. Volterra's formula for piezomagnetic potential is derived by modifying Stacey's scheme for tectonomagnetic modeling. The Green's functions for the problem are called elementary piezomagnetic potentials, which are defined as potentials produced by elementary dislocations. Special consideration is required to construct the elementary piezomagnetic potentials, because the stress field around a point dislocation has a singularity of orderr ^–3. The integral representing elementary piezomagnetic potentials is not uniformly convergent. Owing to inappropriate convergency, the Green's functions obtained in an earlier study led to a puzzling outcome. Revised Green's functions give consistent results with those obtained so far by numerical integrations. Generally the piezomagnetic field produced by dislocation sources is weak in the case of a homogeneous earth model. Two enhancement effects for piezomagnetic signals are suggested: one due to inhomogeneous magnetization and the other via bore-hole observations.     

建筑物上侧击雷电的三维数值模拟

基于三维近地面闪电先导发展随机模式,通过改变先导初始电位和建筑物几何特性,分析各种情况下的侧击雷电发生概率,探讨侧击雷电产生原因及影响因素。结果发现:建筑物尖端电场畸变值是影响侧击雷电产生的重要参量,当下行先导靠近建筑物且传播位置低于建筑物的高度时,建筑侧面电场畸变值达到触发阈值,侧击雷电易产生;下行先导的初始电位以及建筑物几何特性（高度和宽度）是影响侧击雷电发生概率的重要因素,当下行先导初始电位在-9~-3 MV范围内,侧击雷电发生概率呈先增加后降低的趋势,当初始电位为-4.5 MV时,侧击雷电的发生概率达到峰值;当建筑物高度在50~150 m范围内,侧击雷电发生概率随着高度增加呈先增加后减少的趋势;当建筑物高度为100 m时,侧击雷电发生概率达到峰值;当建筑物宽度在30~70 m范围内,侧击雷电发生概率随建筑物宽度呈递减趋势;当建筑物宽度为30 m时,侧击雷电的发生概率达到峰值。     

新疆北部哈拉阿拉特山走滑-冲断复合构造特征与油气勘探方向

位于准噶尔盆地西北缘前陆冲断带北段的哈拉阿拉特山,以往认为是一个典型的逆冲推覆构造带。笔者通过野外地质调查和对地震与大地电磁测深(MT)资料的综合解释研究,发现该区总体表现出走滑—冲断复合构造特征。其形成受控于达尔布特断裂在不同时期不同性质的活动,主要经历了两个阶段:二叠-三叠纪是以逆冲推覆为主兼具走滑的斜向冲断,形成该区以逆冲推覆构造为主要特征的走滑—冲断构造;侏罗纪以来主要以左行压扭走滑变形为主,沿达尔布特断裂变形强烈,形成花状构造,并在一定程度上改造了前期形成的逆冲推覆构造,但强度较弱。因此,目前在哈拉阿拉特山地区所见到的构造现象实际上是二叠纪至三叠纪斜向冲断和侏罗纪以来的压扭走滑两期构造变形的叠加样式,总体构成走滑—冲断复合构造。这一地质构造模型的建立对地震解释具有指导作用,同时指出逆冲推覆构造下盘的隐伏背斜未经后期走滑改造,是油气勘探的重要方向。     

Bounds on Rotation Periods of Disrupted Binaries in the Full 2-Body Problem

Constraints on the final rotation rates of a Hill unstable binary in the full 2-body problem are derived and analyzed. Application of these constraints are made to the problem of a constant density body spun to disruption. This analysis has relevance to the evolution of asteroid spin rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the adelphic potentials compatible with a set of planar orbits

Given a planar potentialB=B(x, y), compatible with a monoparametric family of planar orbitsf(x, y)=c, we face the problem of producing potentialsA=A(x, y), adelphic toB(x, y), i.e. nontrivial potentials which have in common withB(x, y) the given set of orbits. We establish a linear, second order partial differential equation for a functionP(x, y) and we prove that, to any definite positive solution of this equation, there corresponds a potentialA(x, y) adelphic toB(x, y).     

Linear Stability of the Lagrangian Triangle Solutions for Quasihomogeneous Potentials

In this paper, we study the linear stability of the relative equilibria for homogeneous and quasihomogeneous potentials. First, in the case the potential is a homogeneous function of degree −a, we find that any relative equilibrium of the n-body problem with a>2 is spectrally unstable. We also find a similar condition in the quasihomogeneous case. Then we consider the case of three bodies and we study the stability of the equilateral triangle relative equilibria. In the case of homogeneous potentials we recover the classical result obtained by Routh in a simpler way. In the case of quasihomogeneous potentials we find a generalization of Routh inequality and we show that, for certain values of the masses, the stability of the relative equilibria depends on the size of the configuration.     

基于二次耦合势的广域电磁法有限体积三维正演计算

与可控源音频大地电磁（CSAMT）相比,广域电磁法通过采用全区视电阻率定义,突破了卡尼亚视电阻率所需的远区条件限制,极大拓展了可控源电磁观测区域和探测深度.考虑到电偶源激发场的三维特征以及地下复杂三维结构,为提高广域电磁数据解释精度,本文实现了基于二次耦合势的广域电磁法三维正演计算.该算法利用Helmholtz定理将麦克斯韦方程转化为库伦规范下的磁矢势和电标势耦合方程,有效改善了离散所得大型线性方程组的谱性质,并通过强加散度条件来消除电场伪解的影响.此外,采用散射场方法,其中一次场使用准解析法求解,二次场使用有限体积法求解,克服了局部激发场源奇异性问题.通过与一维层状模型下电偶源产生的电磁场准解析解对比,验证了本文算法的正确性.在此基础上,利用本文的正演算法对比分析了广域电磁法与CSAMT对典型三维目标体的探测能力,结果表明在相同的观测条件下,广域电磁法能够更准确地反映地下目标体信息,拥有更优的分辨能力.