Note on estimates of the glacial-isostatic decay spectrum for Fennoscandia

For more than 30 years, Sauramo's (1958) shoreline diagram of the Fennoscandian uplift has been used in geophysical studies for estimates of the glacial-isostatic decay spectrum in order to infer from it the viscosity stratification in the Earth's mantle below Fennoscandia. The intent of the present note is to point out that more recent geological studies suggest that Sauramo's shoreline diagram is an incorrect representation of the Fennoscandian uplift. Geophysical interpretations based on the diagram may therefore require revision.     

Mapping multiple tree species classes using a hierarchical procedure with optimized node variables and thresholds based on high spatial resolution satellite data

ABSTRACT

Tree species distribution mapping using remotely sensed data has long been an important research area. However, previous studies have rarely established a comprehensive and efficient classification procedure to obtain an accurate result. This study proposes a hierarchical classification procedure with optimized node variables and thresholds to classify tree species based on high spatial resolution satellite imagery. A classification tree structure consisting of parent and leaf nodes was designed based on user experience and visual interpretation. Spectral, textural, and topographic variables were extracted based on pre-segmented images. The random forest algorithm was used to select variables by ranking the impact of all variables. An iterating approach was used to optimize variables and thresholds in each loop by comprehensively considering the test accuracy and selected variables. The threshold range for each selected variable was determined by a statistical method considering the mean and standard deviation for two subnode types at each parent node. Classification of tree species was implemented using the optimized variables and thresholds. The results show that (1) the proposed procedure can accurately map the tree species distribution, with an overall accuracy of over 86% for both training and test stages; (2) critical variables for each class can be identified using this proposed procedure, and optimal variables of most tree plantation nodes are spectra related; (3) the overall forest classification accuracy using the proposed method is more accurate than that using the random forest (RF) and classification and regression tree (CART). The proposed approach provides results with 3.21% and 7.56% higher overall land cover classification accuracy and 4.68% and 10.28% higher overall forest classification accuracy than RF and CART, respectively.     

地幔对流环型场的激发(Ⅰ)

讨论了地幔内部的粘滞度及施加在地表和CMB 的边界条件对地幔对流环型场的激发分析表明,当粘滞度侧向均匀时,环型场与极型场自然解耦,且环型场不影响重力位,当粘滞度侧向不均时,环型场与极型场耦合在一起.两者共同影响重力位.当引入板块运动速度时,边界条件非零,也能激发环型场;对侧向均匀粘滞度地幔,零边界条件不能激发环型场     

均匀介质中散射过程的奇性分析

本文比较详细地讨论和分析了均匀介质中零偏移距散射曲面拓扑奇性和相应回波解析奇性之间的关系和分类.其基础是衍射理论的Kirchhoff积分,原理是通过曲面几何函数的解析奇性和距离函数的拓扑奇性之间的联系.基本的数学工具是Morse理论和突变理论.     

ENERGY EQUATION AND SYMMETRIC INSTABILITY CRITERION

In this paper,by using generalized normal mode method the symmetric instability criterion which can be used not only in the constant parameters but also in the variable parameters was derived from the energy equation on the symmetric disturbance.If the thermal wind was in balance or quasi-balance,the criterion was consistent with that obtained by Emanuel with parcel method and Hoskins with normal mode method.It is shown that in the generating stage of disturbance,the symmetrically instable development of disturbance is associated with the energy transformation by which the energy of the basic field is transferred into the energy of the disturbance field.     

凤凰─茶陵地学断面重力异常机制分析

对凤凰─茶陵地学断面重力异常,根据爆炸地震测深资料,确定密度分层,用变密度水平梯形体构制剖面密度模型,计算理论重力异常和实测布格重力异常吻合较好。根据剖面密度模型,可以合理地解释布格重力异常。并将地壳划分为沉积盖层、变质岩层、麻粒岩层三层结构,分别计算三层的重力效应曲线及上地幔低密度体重力效应曲线。还计算了莫霍面起伏引起的重力异常曲线,分析了引起地壳重力异常的各种因素及特点。     

Ｅ网格变量分布下差分格式的性质

本文用线性化的浅水波方程系统地分析、讨论了Ｅ网格变量分布下差分计算的性质；指出了目前有关讨论Ｅ网格差分性质在方法上存在的问题；给出了一种解决Ｅ网格中两个Ｃ网格分离的方法；提出了一种Ｅ网格用于海洋计算时，海洋侧边界条件的处理方法。初步的数值试验证明了这些方法对抑制Ｅ网格中的计算躁声是有效的。     

岩浆物理性质和流体动力学研究

本文评述了岩浆物理性质和流体动力学应用于火成岩岩石学研究的新进展，并强调了其地质成果。岩浆的密度和粘度是岩浆两个最重要的物理性质，岩浆密度和粘度的变化对岩浆流体动力学习性以及产生火成岩的多样性起了重要作用。岩浆房中的双扩散对流、岩浆房的再充填以及边界作用等是岩浆流体动力学的重要机制，对它们的研究，使人们对火成岩的成因和演化以及地球动力学产生了新的认识。本文还概述了流体动力学机制的主要地质结果，如：地幔对流、成矿作用、带状岩浆房、层状侵入体以及火山岩中的流体动力学等。但直到目前，岩浆流体动力学机制及其应用仍是一个崭新的研究领域。     

预应力约束下装配式剪力墙结构减震性能研究

为了应对中国在新时期提出的“经济,适用,绿色,美观”的建筑政策,装配式结构逐渐成为近年来关注的焦点.对比传统现浇结构,装配式结构更符合节能、节材、环保等要求.因此,进一步研究装配式结构的抗震性能是非常重要的.考虑现有装配式剪力墙结构节点连接部位存在湿作业、施工难度大,常常出现强构件弱节点,抗震性能有待进一步深入研究等情况.为此我们提出一种新的结构形式———预应力约束下装配式剪力墙结构,该结构通过预应力筋连接结构的墙、板,使结构形成一个整体,减少施工现场湿作业,施工质量得以提高.当地震发生时结构通过改变自身的刚度,使其自震周期增大,达到减小地震应力的目的,同时很多提高延性因素的条件也无需考虑,避免钢材的浪费.通过对现浇剪力墙结构模型和预应力约束下装配式剪力墙结构模型进行时程分析,计算结果表明:与现浇剪力墙结构相比,预应力约束下装配式剪力墙结构可减小90%的地震作用,减震效果显著.     

Spectral and photometric evolution of the symbiotic nova HM Sagittae in 1986–2002

We present the results of our photometric and spectroscopic observations of the symbiotic nova HM Sge in 1994–2002. After its outburst in 1975, the star was shown to fade in the U, B, V bands at a rate of about \(0\mathop m\limits_. 05\) per year. The behavior of the B-V and U-B color indices reflects the variations of emission lines and, in part, the fading of the erupted component. We have studied the evolution of the emission spectrum in the range from Hδ to λ7751 Å over the period 1986–2002. The absolute fluxes in the hydrogen lines decreased by half, the ionization of the gaseous envelope continued to increase, and the Raman O VI lines appeared and strengthened. The significant (threefold) decrease in the ratio of the auroral and nebular O III lines is interpreted as a drop in the electron temperature of the envelope as its density decreased by a factor of about 1.5. We have measured the absolute intensity of the near-infrared continuum up to 10 000 Å and show that the infrared continuum follows the pulsations of the Mira star in the system HM Sge. We conclude that the dust envelope around the cool component became noticeably transparent in the 1990s.