科研进展
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(高蒙蒙、芮和兵、宋林亮)A basis theorem for the affine Kauffman category and its cyclotomic quotients论文题目:A basis theorem for the affine Kauffman category and its cyclotomic quotients论文作者:Mengmeng Gao, Hebing Rui, Linliang Song发表刊物:Journal of Algebra成果介绍:The affine Kauffman category is a strict monoidal category and can be considered as a $q$-analogue of the affine Brauer category in (Rui and Song in Math.Zeit.293,503-550,2019).In this paper,we prove a basis theorem for the...2022-09-30
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(金方舟)Fundamental classes in motivic homotopy theory成果介绍:We develop the theory of fundamental classes in the setting of motivic homotopy theory. Using this we construct, for any motivic spectrum, an associated twisted bivariant theory, extending the formalism of Fulton and MacPherson. We import the tools of Fulton’s intersection theory into this setting: (refined) Gysin maps, specialization maps, and formulas for excess of intersection, self-intersections, and blow-ups. We also develop a theory of Euler classes of vector bundles in this setting. For the Milnor–Witt spectrum recently constructed by Déglise–Fasel, we get a bivariant theory extending the Chow–Witt groups of Barge–Morel, in the same way the higher Chow groups extend the classical Chow groups. As another application we prove a motivic Gauss–Bonnet formula, computing Euler characteristics in the motivic homotopy category.2021-11-16
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(熊革)Sharp affine isoperimetric inequalities for the volume decomposition functionals of polytopes成果介绍:在这篇文章中,我们有一个基本的发现:利用代数学中线性无关(linear independence)的概念和数学中维数(dimension)的概念,把n维空间中多面体的体积(volume)这个基本的几何量分解成了n个n次齐次多项式。其中第n个齐次多项式恰好是纽约大学的Erwin Lutwak, Deane Yang 和 Gaoyong Zhang三位教授于2001年引入的仿射不变量(Transactions of AMS,353 (2001), 1767-1779),而前(n-1)个齐次多项式是首次发现的。这n个n次齐次多项式叫做多面体的体积分解泛函。 本文利用锥体积测度的子空间集中条件(subspace concentration condition)和变分的办法,完全解决了3维空间中体积分解泛函的极值问题,建立了严格的仿射反向等周不等式。2021-11-16
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(舒杰)Generalized Birch lemma and the 2-part of the Birch and Swinnerton-Dyer conjecture for certain elliptic curves成果介绍:In the present paper, we generalize the celebrated classical lemma of Birch and Heegner on quadratic twists of elliptic curves over We prove the existence of explicit infinite families of quadratic twists with analytic ranks 0 and 1 for a large class of elliptic curves, and use Heegner points to explicitly construct rational points of infinite order on the twists of rank 1. In addition, we show that these families of quadratic twists satisfy the 2-part of the Birch and Swinnerton-Dyer conjecture when the original curve does. We also prove a new result in the direction of the Goldfeld conjecture. All these results apply to a large class of elliptic curves, especially for elliptic curves without CM. As applications, we present examples of elliptic curves of small conductors, of Newmann-Setzer curves and also examples of elliptic curves without CM for which the full Birch and Swinnerton-Dyer conjecture holds.2021-11-16
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(芮和兵、宋林亮)Affine Brauer category and parabolic category O in types B, C, D成果介绍:oA strict monoidal category referred to as affine Brauer category AB is introduced over a commutative ring κ containing multiplicative identity 1 and invertible element 2. We prove that morphism spaces in AB are free over κ. The cyclotmic (or level k) Brauer category CBf(ω) is a quotient category of AB. We prove that any morphism space in CBf(ω) is free over κ with maximal rank if and only if the u-admissible condition holds in the sense of (1.32). Affine Nazarov–Wenzl algebras (Nazarov in J Algebra 182(3):664–693, 1996) and cyclotomic Nazarov–Wenzl algebras (Ariki et al. in Nagoya Math J 182:47–134, 2006) will be realized as certain endomorphism algebras in AB and CBf(ω),respectively.2018-12-13
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(姜立建)A two-stage ensemble Kalman filter based on multiscale model reduction for inverse problems in time fractional diffusion-wa成果介绍: 集合卡尔曼滤波广泛应用于动态系统的状态和参数估计,其观测数据是依据时间序列获得的。对高维或者非线性问题,需要的集合样本很多,反复计算正问题是非常耗时的。大多数贝叶斯反问题的后验通常只集中在先验支集的一小部分。因此,我们提出了两阶段的集合卡尔曼滤波,其核心是构造新先验并基于该先验构造有效的替代模型。该方法对集合卡尔曼滤波序列后验进行了改进,显著提高同化和反演效率。在第一阶段,我们基于广义多尺度有限元的粗化模型构造新先验,该先验只由一部分观测数据得到并剔除了后验的不重要区域。同时广义多尺度有限元可提粗网格上一组分层多尺度基函数, 对于构造降维模型自由度的选取给予了很大的灵活性。在第二阶段,我们将广义多尺度有限元和多项式混沌展开相结合在新先验上建立替代模型。为减少计算正问题的次数,我们采用稀疏多项式混沌展开。基于数据的动态特性,替代模型将会同步数据的更新。与标准的集合卡尔曼滤波相比较,该方法可获得更精确的估计并显著提高了探索后验的效率。我们还将其应用到非高斯模型和分层模型,进一步扩展了该方法在贝叶斯反问题中的适用性。2018-12-05
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(姜立建)Adaptive least-squares mixed Generalized multiscale finite element methods成果介绍:最小二乘混合多尺度有限元方法可以同时精确求解复杂多孔介质中达西流问题中的速度与压力。此方法不需要满足速度与压力的多尺度空间的相容性条件,从而可以更加自由的选取速度和压力的多尺度解空间。 为了更高效的求解此类问题,我们构造了离线自适应的和在线自适应的方法。本文研究了两种可以有效求解高对比多孔介质单相达西流问题的自适应最小二乘混合多尺度有限元方法。离线自适应方法根据残差指标用迭代的方式增加局部速度多尺度基函数和压力基函数。这种方法可以根据高对比系数来得到更好的逼近空间。而在线自适应方法通过构造一系列新的在线速度和压力基函数来更快地降低解的误差。同时这种逼近空间的构造也考虑了源项的信息。两种自适应方法都能得到相比均匀增加自由度更精确的解,并且用较少的基函数达到了更高的精度。我们也给出了自适应最小二乘混合多尺度有限元的收敛性分析。数值结果显示当我们选取合适个数的初始基函数,在线自适应方法比离线自适应方法以及均匀增加法的收敛速度都要快。2018-12-05
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(郑恺)Geodesics in the space of Kähler cone metrics, II. Uniqueness of constant scalar curvature Kähler cone metrics成果介绍: In this article, we give a complete construction of geodesics in the space of Kähler cone metrics (cone geodesics) and we address the problem on the uniqueness of constant scalar curvature Kähler (cscK) cone metrics, when the cone angle stays in the whole interval (0,1). The part when the angle in [1/2,1) requires new weighted function spaces and new analytic techniques. We determine the asymptotic behaviour of both cone geodesics and cscK cone metrics, prove the reductivity of the automorphism group and establish the linear theory for the Lichnerowicz operator, which immediately implies the openness of the path deforming the cone angles of cscK cone metrics.2018-12-03
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(王琤)A Posteriori Error Estimates of Two-Grid Finite Element Methods for Nonlinear Elliptic Probl...成果介绍: 自适应算法是一种根据后验误差估计,并按照特定自适应策略进行自动调整以改进求解过程的数值方法,其核心是后验误差估计与自适应策略。将自适应算法与有限元、有限体或间断有限元等离散方法结合,可构造一类求解具有不光滑解的微分方程的高效算法。两重网格算法是求解非线性微分方程的一类有效数值算法。该方法仅在粗网格上求解非线性问题,而在细网格上求解相应的线性化问题。适当地选择粗细网格,可在数值解收敛阶不降低的同时,显著地减少计算量,从而提高算法效率。本文研究了求解二阶非线性椭圆边值问题的两重网格算法的残量型后验误差估计,构造了其范数误差的可计算的上下界估计,数值实验验证了所提出的后验误差估计子的有效性。2018-04-19
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(周海港)Counting zeros in quaternion algebras using Jacobi forms成果介绍: 本文利用Jacobi形式理论研究有理数域上四元代数的极大order中一些元素的个数p(n,r),这些元素的特征多项式等于任意给定的二次多项式x2-rx+n=0。令N是无平方因子正整数,QN是在N的素因子处分歧的正定四元代数。我们新定义的类数HN(n) 推广了经典的Hurwitz类数H(n), 证明了这些个数p(n,r)的加权均值等于HN(4n-r2), 特别在N=2,3,5,7,13 的时候,p(n,r)就等于HN(4n-r2)的倍数。在证明过程中,我们构造出level为N的权为2的Jacobi Eisenstein级数,并明确地计算出其傅里叶系数,还研究了Hecke算子在由四元代数极大order得到的theta级数上的特征形式。我们推广了Deuring,Eichler,Gross和Pizer等人相关的工作, 作为推论,我们给出著名的Eichler迹公式一个新的证明,还给出四元代数理想类数和简洁的型数公式,而Eichler和Pizer都曾给出形式比较复杂的型数公式。2018-04-13