光滑质点流体动力学(SPH)方法(综述)

综合介绍了一种新的纯(Lagrangian方法——光滑质点流体动力学(SPH)方法,由于它计算空间导数时不需要使用网格,从而避免了高维拉氏差分网格法中的网格缠结和扭曲的麻烦,它对非对称的和内含真空区域的三维问题特别有效。重点介绍了该方法的理论基础,流体动力学方程组的推导,人为粘性和热传导,自引力、汇和磁场,光滑核的选取,以及SPH执行过程等有关问题     

随机删失数据下核密度估计的Berry-Esseen界

本文在随机删失数据下研究了概率密度函数的核估计,获得了此核估计的一个Berry－Esseen界.     

关于部分变换半群

证明了集上部分变换半群的幂等元分离同态像为弱逆半群,给出了有限集上部分变换半群的Ｒ类、Ｌ类、Ｄ类和幂等元个数计数公式     

WKICA算法在多光谱遥感特征提取中的应用研究

多光谱遥感图像具有高度冗余、非线性化的特点。对其进行有效的特征提取是完成精确目标分类的前提。基于核方法强大的非线性映射能力,提出一种小波核独立成分分析WKICA算法。WKICA算法结合小波核函数近似正交,能够对复杂非线性信号进行逐步逼近的优势,有效提高了核独立成分分析KICA算法的求解精度。将其应用在多光谱遥感图像特征提取中,并对预处理条件下的图像采用不同的监督分类方法进行分类实验。实验结果表明,在WKICA算法预处理条件下,能够更有效的滤除图像噪声,相比较传统的特征提取算法,能够获取更加精确的图像分类效果。     

在SDSS DR8恒星光谱中自动搜寻稀有天体

SDSS DR8海量光谱中包含许多有研究价值的稀有天体,如特殊白矮星(DZ,DQ,DC)、碳星、白矮主序双星、激变变星等,如何在海量光谱中自动搜寻稀有天体有着极其重要的意义。提出一种基于核密度估计和K-近邻(K-nearest neighbor, KNN)相结合的方法在SDSS DR8 信噪比大于5的546 383个恒星光谱中搜寻稀有天体。首先对光谱进行高斯核密度估计,选取概率最小的5 000个光谱作为稀有类,概率最大的300 000个光谱作为普通类,然后进行KNN分类,同时也将5 000个稀有光谱的K个最近邻也作为稀有的天体,结果共有21 193条光谱。为了方便分析,对这些光谱聚类后进行人工检查。这些光谱主要包括由于数据缺失、红化、流量定标不准引起的问题光谱、行星状星云、没有物理联系的光谱双星、类星体、特殊白矮星(DZ,DQ,DC)、碳星、白矮主序双星、激变变星等。通过和SIMBAD,NED,ADS及一些主要的文献交叉验证,我们新发现了3个DZ白矮星、1个白矮主序双星、2个伴星为G型星的激变变星,3个激变变星的候选体、6个DC白矮星,1个DC白矮星候选体和1个 BL Lacertae(BL lac)候选体。还发现了1个有CaⅡ三重发射线和MgⅠ发射线的DA白矮星和1个光谱上表现出发射线的晚M恒星但测光图上像是一个星云或星系。     

板栗仁衣的挥发性成分

板栗仁衣经水蒸汽蒸馏 ,乙醚萃取挥发性成分 ,通过气相色谱与质谱联用法测定 ,发现板栗的仁衣中含 2 9个组分 ,确定了其中 17个组分的结构     

P-stable models of strong kernel programs

The research community has long recognized the study of non-monotonic reasoning (NMR) as a promising approach to model features of commonsense reasoning. We study one of the semantics that are useful to formalize NMR, called the p-stable semantics. We introduce three different formats for normal programs: negative normal programs, restricted negative normal programs and strong kernel programs. These forms help to simplify the search of p-stable models of the original program. One of the main results of this paper indicates that the p-stable semantics for strong kernel programs is the same as the stable semantics. This way, all the applications based on stable semantics for those kernel programs (defined in [S. Costantini, A. Provetti, Normal forms for answer set programming, J. Theory Pract. Log. Program. 5 (2005) 747-760]) that are strong kernel programs can also be based on the p-stable semantics.     

求解一类二阶非线性偏微分方程的新算法

在再生核空间中给出一类二阶非线性偏微分方程的一个新的求解方法,近似解un(x)是通过在再生核空间中截断精确解u(x)而得到的,最后,通过一个数值算例来说明该方法是有效的.     

Some sufficient conditions for the existence of kernels in infinite digraphs

A kernel N of a digraph D is an independent set of vertices of D such that for every w∈V(D)−N there exists an arc from w to N. If every induced subdigraph of D has a kernel, D is said to be a kernel perfect digraph. D is called a critical kernel imperfect digraph when D has no kernel but every proper induced subdigraph of D has a kernel. If F is a set of arcs of D, a semikernel modulo F of D is an independent set of vertices S of D such that for every z∈V(D)−S for which there exists an (S,z)-arc of D−F, there also exists an (z,S)-arc in D. In this work we show sufficient conditions for an infinite digraph to be a kernel perfect digraph, in terms of semikernel modulo F. As a consequence it is proved that symmetric infinite digraphs and bipartite infinite digraphs are kernel perfect digraphs. Also we give sufficient conditions for the following classes of infinite digraphs to be kernel perfect digraphs: transitive digraphs, quasi-transitive digraphs, right (or left)-pretransitive digraphs, the union of two right (or left)-pretransitive digraphs, the union of a right-pretransitive digraph with a left-pretransitive digraph, the union of two transitive digraphs, locally semicomplete digraphs and outward locally finite digraphs.     

Vertex- and edge-minimal and locally minimal graphs

Given a family of graphs , a graph is called edge-minimal (vertex-minimal) if for every subgraph (induced subgraph) G^′ of G; furthermore, G is called locally edge-minimal (locally vertex-minimal) if whenever G^′ is obtained from G by deleting an edge (a vertex). Similarly, the concepts of minimality and local minimality are introduced for directed graphs (digraphs) and, more generally, for partially ordered sets.For example, by the Strong Perfect Graph Theorem, the only vertex-minimal graphs with χ>ω are odd holes and anti-holes. In contrast, the only locally vertex-minimal graphs with χ>ω are partitionable graphs. Somewhat surprisingly, there are infinitely many non-trivial perfect graphs that are locally edge-minimal and -maximal simultaneously. In other words, such a graph is perfect but it becomes imperfect after any edge is deleted from or added to it.In this paper we consider vertex- and edge-minimal and locally minimal graphs in the following families: (i) perfect and imperfect graphs, (ii) graphs with χ=ω and with χ>ω, (iii) digraphs that have a kernel and kernel-free digraphs, and finally, (iv) vertex-minimal complementary connected d-graphs.