瞬态弹性波散射的变换域积分方程法

针对瞬态弹性波散射的问题,从弹性动力学问题的积分表示定理出发,采用Laplace变换的方法,得到了变换域内均质体位移场的积分方程表示;在此基础上推导了适合瞬态弹性波对异质体散射求解的变换域位移场积分方程。     

不规则网土壤测量在水系沉积物异常查证中的应用

在大兴安岭森林沼泽景观区,植被茂盛、土壤表层腐殖质发育,且通视条件差,运用传统的规则网土壤测量方法进行1/5万水系沉积物异常查证,工作周期长、劳动强度大;采用不规则网土壤测量方法进行异常查证,取得了快速评价异常、追踪异常源,缩短找矿周期的效果。     

平面不规则基础隔震结构抗扭设计研究

针对平面不规则结构在水平地震作用下的振动特性,通过调整隔震层隔震支座的布置,得到3种不同工况的隔震层刚心与上部结构质心、刚心相对位置关系,分别以楼层位移和层间位移为指标的扭转位移比,作为平面不规则基础隔震结构扭转响应指标,利用弹塑性时程分析方法,通过对3种不同工况的扭转指标对比分析研究,提出适用于平面不规则基础隔震结构的抗扭设计方法。结果表明：对于平面不规则结构,应在保证隔震层扭转位移比小于1.2的基础上,使隔震层的刚心和上部结构的刚心分别位于上部结构质心的两侧,可有效控制上部结构的扭转。     

近岸波浪破碎区不规则波浪的数值模拟

基于近岸不规则波浪传播的抛物型缓坡方程和两类波浪破碎能量损耗因子,对近岸波浪破碎区不规则波浪的波高分布进行了数值模拟,并结合实验结果对数值模拟结果进行了验证分析,结果表明采用两类波浪破碎能量损耗因子所模拟的破碎区波高与实测值均吻合良好,波浪破碎能量损耗因子及波浪破碎指标对破碎区波浪波高分布影响较明显。     

Regular and irregular periodic orbits

We distinguish between regular orbits, that bifurcate from the main families of periodic orbits (those that exist also in the unperturbed case) and irregular periodic orbits, that are independent of the above. The genuine irregular families cannot be made to join the regular families by changing some parameters. We present evidence that all irregular families appear inside lobes formed by the asymptotic curves of the unstable periodic orbits. We study in particular a dynamical system of two degrees of freedom, that is symmetric with respect to the x-axis, and has also a triple resonance in its unperturbed form. The distribution of the periodic orbits (points on a Poincaré surface of section) shows some conspicuous lines composed of points of different multiplicities. The regular periodic orbits along these lines belong to Farey trees. But there are also lines composed mainly of irregular orbits. These are images of the x-axis in the map defined on the Poincaré surface of section. Higher order iterations of this map , close to the unstable triple periodic orbit, produce lines that are close to the asymptotic curves of this unstable orbit. The homoclinic tangle, formed by these asymptotic curves, contains many regular orbits, that were generated by bifurcation from the central orbit, but were trapped inside the tangle as the perturbation increased. We found some stable periodic orbits inside the homoclinic tangle, both regular and irregular. This proves that the homoclinic tangle is not completely chaotic, but contains gaps (islands of stability) filled with KAM curves.     

GIS专业基于面向对象程序设计的DEM生成教学实验设计

数字高程模型是地理信息科学专业的必修课,DEM生成方法是该课程的核心知识点之一。通常以GIS软件为实验操作平台构建DEM,GIS软件提供良好的操作界面且简化教学过程,但软件同时会弱化学生对DEM生成过程的理解,而面向对象程序设计课程往往开设在数字高程模型课程之前。文中融合面向对象程序设计和数字高程模型课程知识点,采用面向对象程序设计思想对DEM课程中的DEM生成实验进行设计并实现,为GIS专业的DEM生成实验提供新的教学思路,提升DEM课程教学实践的品质和效果。     

Delaunay三角网的并行构网算法

针对传统的Delaunay三角网的并行构建算法负载均衡性不高、运行效率较低等问题,该文在综合逐点插入算法和分治算法各自优点的基础上,提出了一种Delaunay三角网并行构建算法。该算法首先使用动态格网剖分点要素集,从而得到若干点要素子集;然后根据点要素子集数量初始化线程池,每个点要素子集由一个线程按照插入点法构建Delaunay子网;当所有线程完成子三角网构建,最后使用逐点插入法合并所有子网,从而实现所有点要素的Delaunay三角网构建。分析与实验结果表明,相对于传统的并行算法,该并行算法的负载均衡性好、运行时间少、加速比高,具有较好的构建效率,而且构建结果满足Delaunay规则。     

Calibrating a Land Parcel Cellular Automaton (LP-CA) for urban growth simulation based on ensemble learning

The reliability of raster cellular automaton (CA) models for fine-scale land change simulations has been increasingly questioned, because regular pixels/grids cannot precisely represent irregular geographical entities and their interactions. Vector CA models can address these deficiencies due to the ability of the vector data structure to represent realistic urban entities. This study presents a new land parcel cellular automaton (LP-CA) model for simulating urban land changes. The innovation of this model is the use of ensemble learning method for automatic calibration. The proposed model is applied in Shenzhen, China. The experimental results indicate that bagging-Naïve Bayes yields the highest calibration accuracy among a set of selected classifiers. The assessment of neighborhood sensitivity suggests that the LP-CA model achieves the highest simulation accuracy with neighbor radius r = 2. The calibrated LP-CA is used to project future urban land use changes in Shenzhen, and the results are found to be consistent with those specified in the official city plan.     

不规则伊/蒙混层粘土矿物成因类型及晶体化学分类

不规则伊/蒙混层粘土矿物(I/S)分布极为广泛,根据大量资料,提出了I/S的成因及晶体化学分类。按其成因分为三类:成岩型、风化型、火山热液型;按其晶体化学性质分为完全无序型、部分有序型及准晶态型。讨论了各成因类型I/S的晶体化学特点,认为产出于P/T界线层粘土中的I/S具二维晶格一维准晶格。探讨了I/S与烃类形成的关系。     

Isoprenoid alkanes with irregular “head-to-head” linkages

A lightly biodegraded crude oil from the Tolkinsk field (Upper Jurassic), situated in north-west Siberia, was found to contain a series of C₂₈–C₃₉ isoprenoid alkanes. Most of these components contain a pristane unit linked head-to-head with other isoprenoid units. The structures of these components were elucidated by mass spectral interpretations, comparisons with a synthesised standard and by reference to data published previously in the literature. These results extend the carbon number range, the variety of structural types, and the number of reported occurrences of these compounds in geological samples. These results provide further evidence for a contribution of bacterial cell-wall lipids to crude oils.