基于土地利用格局的浙中城市群区域景观稳定性研究

土地利用/覆盖变化不仅影响城市生态系统的平衡, 而且会引发很多复杂的社会问题, 成为地理学人地关系综合研究热点领域. 本文运用1990、2000和2014年的遥感影像数据, 在标准假彩色分类基础上, 计算景观指数并构建景观稳定性模型, 解析土地利用视角下浙中城市群区域的景观稳定性变化. 研究发现: (1)1990~2014年的24a间, 林地占土地总面积的百分比逐年递增, 其中1990~2000年增长较少, 2000~2014年增长较多; 水域占比逐年下降, 1990~2000年从4.94%降到2.90%; 随着建设用地的逐年上涨, 耕地和未利用地的占比逐年下降; 浙中城市群东北方向微量的湿地, 24a间面积占比下降了近一半, 从0.31%降到0.16%. (2)景观结构及其变化表明, 城市的斑块形状从简单化向复杂化发展, 这与城市的发展由无序到有序, 低级到高级的过程相一致; 耕地、林地和湿地受人类活动的影响逐渐加剧, 抗干扰能力减弱. (3)浙中城市群的景观稳定性从1990年到2000年大幅度下降, 2000年到2014年增强; 类型尺度上, 除未利用地外的其他5类景观的稳定性都经历了先降低后增强的过程, 而未利用地的稳定性从1990年开始持续增强, 2000年到2014年间虽有所下降但下降幅度不大.     

A note on the edge cover chromatic index of multigraphs

Let G be a multigraph with vertex set V(G). An edge coloring C of G is called an edge-cover-coloring if each color appears at least once at each vertex v∈V(G). The maximum positive integer k such that G has a k-edge-cover-coloring is called the edge cover chromatic index of G and is denoted by . It is well known that , where μ(v) is the multiplicity of v and δ(G) is the minimum degree of G. We improve this lower bound to δ(G)−1 when 2≤δ(G)≤5. Furthermore we show that this lower bound is best possible.     

On the rings whose injective hulls are flat

Let be a commutative Noetherian ring with nonzero identity and let the injective envelope of be flat. We characterize these kinds of rings and obtain some results about modules with nonzero injective cover over these rings.

     

A note on finite abelian covers

We prove that any abelian cover over a smooth variety is defined by some cyclic equations. From the defining equations, we compute explicitly the normalization, branch locus, ramification indices, global invariants, and the resolution of singularities. As an application, we construct a new algebraic surface which is the quotient of ball.     

A majorization principle forp-valent functions

A theorem augmenting the well-known Lindelöf principle (concerning Green functions) and the Mityuk inequality forp-valent maps is proved. Applications of this theorem and of the symmetrization method to the geometric theory of functions of a complex variable are given.     

Lω-空间的ωδ-紧性

在Lω-空间中借助βα-ωδ-开覆盖,定义了Lω-空间的ωδ-紧性,ωδ-基与ωδ-子基,并证明了ωδ-紧性被连续的Zadeh型函数所保持,Tychonoff乘积定理也成立.     

Nearly tight approximation bounds for vertex cover on dense k-uniform k-partite hypergraphs

We establish almost tight upper and lower approximation bounds for the Vertex Cover problem on dense k-uniform k-partite hypergraphs.     

基于时序Sentinel-2A影像的玉米秸秆覆盖区智能识别研究

秸秆还田是减少土壤侵蚀、增加土壤有机碳的重要措施,对黑土地保护具有重要意义。区域范围内玉米秸秆覆盖区的准确、快速识别,对监测保护性耕作实施、农业补贴政策的制定具有重要作用。以实施保护性耕作的典型区吉林省四平市为研究区,基于GEE(google earth engine)云平台,结合2020年5月—11月的Sentinel-2时序遥感影像,依据玉米生长季和收获后的秸秆状态构建光谱特征和指数特征,指数特征包括归一化差值植被指数(NDVI)和归一化差值秸秆指数(NDRI)。为避免数据冗余,对时序特征值按大小排序,同时利用分位法以0%,25%,50%,75%,100%分位选取分位(QT)特征,进而构建数据集。应用参数优化后的随机森林方法对按照7∶3划分的样本集进行训练和验证,然后对数据集分类,结合连通域标定法去除分类过程中产生的细小连通域,进一步优化全局结果。通过Kappa和整体精度(OA)定量和定性评价,实验结果表明：(1) 基于不同特征集组成数据集的分类模型(M1/M2/M3/M4/M5)定量评价结果均优于90%,其中所设计数据集的分类模型M5效果最好,Kappa和OA分别为97.41%和97.91%,相比于未加入QT特征集的分类模型M2的Kappa和OA分别提升4.52%和3.64%,同时M5识别结果可以有效保留边缘细节信息;(2)针对不同时间尺度的QT特征集,利用5月—11月时序遥感影像的QT特征集分类模型M5_6/M5可以极大地抑制其他作物秸秆的影响,相比仅利用11月时序影像QT特征的M5_1模型分类结果的Kappa和OA分别提升了3.9%和3.12%;(3) 基于M5模型,结合连通域标定法的分类模型M6的Kappa和OA分别为96.76%和97.36%,仅次于M5模型识别结果,模型M6在保证较高精度的同时避免了细碎图斑,优化了分类可视化效果。该研究提出的M6模型适用于识别研究区玉米秸秆覆盖区,该方法能够在GEE云平台环境下快速执行,适合推广应用于东北地区秸秆覆盖区。     

Electromagnetic Characteristics and Corrosion Resistance of New Magnetosoft Materials Based on Capsulated Iron Powders

A new method of depositing an insulating multifunctional oxide coating on metal particles was developed. Such coatings increase corrosion resistance and insulate metal particles from each other. On base of capsulated by oxide coating water-atomized iron powder ASC100.29, new composite soft magnetic materials were synthesized, which are able of replacing electrical steel in devices. Structural, electromagnetic properties and corrosion characte-ristics of the obtained composites were studied. It was found that the synthesized composite materials have low electromagnetic losses, high values of magnetic induction(up to 2.1 T) and good corrosion resistance. The results demonstrate that the use of such materials in power supplies, chokes, transformers, stators and rotors of electric machines and other products ensures their stable operation under various conditions.