Active Contours Under Topology Control—Genus Preserving Level Sets

We present a novel framework to exert topology control over a level set evolution. Level set methods offer several advantages over parametric active contours, in particular automated topological changes. In some applications, where some a priori knowledge of the target topology is available, topological changes may not be desirable. This is typically the case in biomedical image segmentation, where the topology of the target shape is prescribed by anatomical knowledge. However, topologically constrained evolutions often generate topological barriers that lead to large geometric inconsistencies. We introduce a topologically controlled level set framework that greatly alleviates this problem. Unlike existing work, our method allows connected components to merge, split or vanish under some specific conditions that ensure that the genus of the initial active contour (i.e. its number of handles) is preserved. We demonstrate the strength of our method on a wide range of numerical experiments and illustrate its performance on the segmentation of cortical surfaces and blood vessels. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Isogenies and the Discrete Logarithm Problem in Jacobians of Genus 3 Hyperelliptic Curves,

We describe the use of explicit isogenies to translate instances of the Discrete Logarithm Problem (DLP) from Jacobians of hyperelliptic genus 3 curves to Jacobians of non-hyperelliptic genus 3 curves, where they are vulnerable to faster index calculus attacks. We provide explicit formulae for isogenies with kernel isomorphic to (ℤ/2ℤ)³ (over an algebraic closure of the base field) for any hyperelliptic genus 3 curve over a field of characteristic not 2 or 3. These isogenies are rational for a positive fraction of all hyperelliptic genus 3 curves defined over a finite field of characteristic p>3. Subject to reasonable assumptions, our constructions give an explicit and efficient reduction of instances of the DLP from hyperelliptic to non-hyperelliptic Jacobians for around 18.57% of all hyperelliptic genus 3 curves over a given finite field. We conclude with a discussion on extending these ideas to isogenies with more general kernels. This paper was solicted by the Editors-in-Chief as one of the best papers from EUROCRYPT 2008, based on the recommendation of the program committee. A condensed version of this work appeared in the proceedings of the EUROCRYPT 2008 conference.     

A note on cyclic groups,finite fields,and the discrete logarithm problem

We show how the discrete logarithm problem in some finite cyclic groups can easily be reduced to the discrete logarithm problem in a finite field. The cyclic groups that we consider are the set of points on a singular elliptic curve over a finite field, the set of points on a genus 0 curve over a finite field given by the Pell equation, and certain subgroups of the general linear group.     

亏格为3的超椭圆曲线除子加法的并行算法

本文给出了求超椭圆曲线除子加法并行算法的一个易于实现的一般性方法,使用该方法得到的并行算法的并行轮数是最小的.将该方法应用于亏格为3的超椭圆曲线除子加法运算中,得到分别使用9和7个乘法处理器,可在15轮运算中实现除子加法和倍点运算的一个并行算法.     

奥陶纪肿笔石类笔石的研究

首次研究了采自江西玉山下奥陶统宁国组的一个半立体状保存的肿笔石标本(新种)Cardiograptus angustus Zone.研究表明,其发育型式为等称笔石式,始部最初几对胞管(th11除外)向外弯曲,与Cardiograptus angustus(Jin)特征一致.据此对Oncograptus属的属征作了重新厘定和种的归并.     

Faster pairing computation on genus 2 hyperelliptic curves

In this paper, new efficient pairings on genus 2 hyperelliptic curves of the form C:y²=x⁵+ax with embedding degree k satisfying 4|k are constructed, that is an improvement for the results of Fan et al. (2008) [10]. Then a variant of Miller?s algorithm is given to compute our pairings. In this algorithm, we just need to evaluate the Miller function at two divisors for each loop iteration. However, Fan et al. had to compute the Miller function at four divisors. Moreover, compared with Fan et al.?s algorithm, the exponentiation calculation is simplified. We finally analyze the computational complexity of our pairings, which shows that our algorithm can save 2036m operations in the base field or be 34.1% faster than Fan et al.?s algorithm. The experimental result shows that our pairing can achieve a better performance.     

一株具有纤维蛋白溶解活性的海单胞菌的分离和鉴定

目的对从双齿围沙蚕消化道内分离的菌株Y5进行纤维蛋白溶解活性检测及系统分类鉴定。方法用纤维蛋白平板法检测Y5的纤维蛋白溶解活性,并从形态、生理、生化、DNA(G+C)含量、脂肪酸成分、16S rRNA基因序列及系统发生分析等方面进行分类鉴定。结果菌株Y5为革兰阴性杆菌;DNA(G+C)含量为47.5%;主要脂肪酸成分为C_(18:1)ω7c,C_(16:1)ω7c,C_(16:0),C_(10:0)3-OH;16S rRNA基因序列与9种已确定的海单胞菌一致性为93%～97%;在系统发生树中与其他海单胞菌位于同一类群中;该菌株在纤维蛋白平板上显示出明显的纤维蛋白溶解活性。结论菌株Y5属于海单胞菌属。该菌株具有纤维蛋白溶解活性,有望为开发溶栓药物提供又一重要资源。     

Parallel Computation of the Topology of Level Sets

This paper introduces two efficient algorithms that compute the Contour Tree of a three-dimensional scalar field F and its augmented version with the Betti numbers of each isosurface. The Contour Tree is a fundamental data structure in scientific visualization that is used to pre-process the domain mesh to allow optimal computation of isosurfaces with minimal overhead storage. The Contour Tree can also be used to build user interfaces reporting the complete topological characterization of a scalar field, as shown in Figure~\ref{fig:top}. Data exploration time is reduced since the user understands the evolution of level set components with changing isovalue. The Augmented Contour Tree provides even more accurate information segmenting the range space of the scalar field into regions of invariant topology. The exploration time for a single isosurface is also improved since its genus is known in advance. Our first new algorithm augments any given Contour Tree with the Betti numbers of all possible corresponding isocontours in linear time with the size of the tree. Moreover, we show how to extend the scheme introduced in [3] with the Betti number computation without increasing its complexity. Thus, we improve on the time complexity in our previous approach from O(m log m) to O(n log n + m), where m is the number of cells and n is the number of vertices in the domain of F. Our second contribution is a new divide-and-conquer algorithm that computes the Augmented Contour Tree with improved efficiency. The approach computes the output Contour Tree by merging two intermediate Contour Trees and is independent of the interpolant. In this way we confine any knowledge regarding a specific interpolant to an independent function that computes the tree for a single cell. We have implemented this function for the trilinear interpolant and plan to replace it with higher-order interpolants when needed. The time complexity is O(n + t log n), where t is the number of critical points of F. For the first time we can compute the Contour Tree in linear time in many practical cases where t = O(n^1–). We report the running times for a parallel implementation, showing good scalability with the number of processors.     

王府井商业街综合景观评价

伴随当前城市建设的迅速发展,商业街作为最富有活力的街道开放空间,已经成为城市景观设计中最基本的构成要素之一.作为城市景观设计的一部分,商业街以它自身特有的功能在城市中发挥着越来越大的作用.商业街的兴起,反映了人们对那种充满生机与活力的街道生活的内心向往.鲜明的视觉形象,良好的绿化环境,足够的活动场所成为景观设计的基本出发点.王府井商业街要遵循设计的基本出发点,呈现场所精神,以创造一个可读性强的商业街,营造公众心中意象的王府井.     

PIXE ANALYSIS OF TRACE ELEMENTS IN GENUS HIPPOPHAE L

Trace elements in four kinds of the Genus Hippophae L pulps were analysed byPIXE. Optimization of the system performance was done by carefully selecting the absorbers, Analytical sensitivities of the PIXE system were obtained by means of "external standard method".