An action of subgroups of mapping class groups on polynomial algebras

We study a certain subgroup of the mapping class group of a surface with boundary by obtaining an action of this subgroup on a polynomial algebra. This action comes from a lift of the action of the subgroup on a trace algebra, Magnus having done a similar thing for the braid groups. We then investigate the invariant theory for this action and various representations that this action affords. In particular, we obtain finite permutation representations and infinite linear representations of these subgroups that are non-trivial on subgroups of the Torelli group.     

n-Marked黎曼球面的对称性

本文讨论了n-marked黎曼球面模空间上自然的对称群作用,计算出其全部的不动点及n-marked黎曼球面的对称类型,同时讨论了黎曼球面上SL(2,C)作用的动力系统特征,得出其周期性的一个描述,并在这些基础上给出n-punctured黎曼球面模空间的奇性刻画．     

Braid Action on Derived Category Nakayama Algebras

We construct an action of a braid group associated to a complete graph on the derived category of a certain symmetric Nakayama algebra which is also a Brauer star algebra with no exceptional vertex. We connect this action with the affine braid group action on Brauer star algebras defined by Schaps and Zakay–Illouz. We show that for Brauer star algebras with no exceptional vertex, the action is faithful.     

The adic realization of the Morse transformation and the extension of its action to the solenoid

We consider the adic realization of the Morse transformation on the additive group of integer dyadic numbers. We discuss the arithmetic properties of this action. Then we extend this action to an action of the group of rational dyadic numbers on the solenoid. Bibliography: 14 titles. To the memory of Alexander Livshits Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 360, 2008, pp. 70–90.     

群在von Neumann代数上作用的自由和遍历性注记

本文研究了群在von Neumann代数上作用的自由性和遍历性问题.利用投影和群SL2(R)的Iwasawa分解,得到了可数离散群在交换von Neumann代数上作用的自由性的等价刻画,证明了SL2(R)在上半平面H上有理作用导出的SL2(R)在极大交换von Neumann代数A={Mf:f∈L2(H,dxdy/y2)}上的作用α是遍历的,但不是自由的.     

Torsion in equivariant cohomology and Cohen-Macaulay G-actions

We show that the well-known fact that the equivariant cohomology (with real coefficients) of a torus action is a torsion-free module if and only if the map induced by the inclusion of the fixed point set is injective generalises to actions of arbitrary compact connected Lie groups if one replaces the fixed point set by the set of points with isotropy rank equal to the rank of the acting group. This is true essentially because the action on this set is always equivariantly formal. In case this set is empty we show that the induced action on the set of points with highest occuring isotropy rank is Cohen-Macaulay. It turns out that just as equivariant formality of an action is equivalent to equivariant formality of the action of a maximal torus, the same holds true for equivariant injectivity and the Cohen-Macaulay property. In addition, we find a topological criterion for equivariant injectivity in terms of orbit spaces.     

The Partition Algebra as a Centralizer Algebra of the Alternating Group

ABSTRACT

In this article, we focus on the result of V.F.R. Jones which says that the partition algebra is the algebra of all transformations commuting with the action of the symmetric group on tensor products of its permutation representation. In particular, we restrict the action of the symmetric group to the action of the alternating group. In this context, we compute a basis for the centralizer algebra and show when the centralizer is isomorphic to the partition algebra.     

Learning About Science,Technology, and Society (STS) Through an Action Research Project: Co-Constructing an Issues-Based Model for STS Education

This article describes the experiences of six science teachers and a facilitator (the author) involved in an action research group in science, technology and society (STS) education. Two strands of research have informed the evolution of this action research project. The first strand comes from an interest in science, technology and society education, while the second strand emerges from the literature on action research as a possible means of accomplishing some of the goals articulated by STS advocates. Therefore, the purposes of this paper are two-fold. First, the paper explores the genesis of an issues-based model for STS education and curriculum development created by the teachers and facilitator of the action research group, and briefly highlights applications of this model in a classroom context. Second, action research is examined as a potential tool for professional development in the context of science education.     

Convexity of Multi-valued Momentum Maps

A famous theorem of Atiyah, Guillemin and Sternberg states that, given a Hamiltonian torus action, the image of the momentum map is a convex polytope. We prove that this result can be extended to the case in which the action is non-Hamiltonian. Our generalization of the theorem states that, given a symplectic torus action, the momentum map can be defined on an appropriate covering of the manifold and its image is the product of a convex polytope along a rational subspace times the orthogonal vector space. We also prove that this decomposition in direct product is stable under small equivariant perturbations of the symplectic structure; this, in particular, means that the property of being Hamiltonian is locally stable. The technique developed allows us to extend the result to any compact group action and also to deduce that any symplectic n-torus action, with fixed points, on a compact 2n-dimensional manifold, is Hamiltonian.     

Perturbations of Smooth Actions with Nontrivial Cohomology

We prove a general perturbation result for smooth Lie group actions with nontrivial finite‐dimensional cohomology. It describes sufficient conditions on cohomology over an action which imply that the action lies in a finite‐dimensional family of actions such that any small perturbation of the family intersects the smooth conjugacy class of the given action. We cast the classical KAM result on perturbations of Diophantine vector fields on tori into this general setup, and we address a few applications and potential applications of this result to homogeneous Lie group actions with finite‐dimensional first cohomology. © 2014 Wiley Periodicals, Inc.     

HOPF代数的右伴随作用构造的上循环模(英文)

本文研究了上循环模,对于特征为O的域k上满足S~2=id_H的Hopf代数H,和左H-模代数A,利用日的右伴随作用以及H在A上的模作用,构造了上循环模(C)_H~#(A),并且证明了由H的右伴随作用和左伴随作用分别诱导的上循环模(C)_H~(#)(A)和(C)_H~(#)(A)足同构的.     

The spherical part of the local and global Springer actions

The affine Weyl group acts on the cohomology (with compact support) of affine Springer fibers (local Springer theory) and of parabolic Hitchin fibers (global Springer theory). In this paper, we show that in both situations, the action of the center of the group algebra of the affine Weyl group (the spherical part) factors through the action of the component group of the relevant centralizers. In the situation of affine Springer fibers, this partially verifies a conjecture of Goresky–Kottwitz–MacPherson and Bezrukavnikov–Varshavsky. We first prove this result for the global Springer action, and then deduce from it the result for the local Springer action. This gives an application of global Springer theory to more classical problems.     

A Galois correspondence for compact group actions on C-algebras

In this paper, we prove a Galois correspondence for compact group actions on C^?-algebras in the presence of a commuting minimal action. Namely, we show that there is a one-to-one correspondence between the C^?-subalgebras that are globally invariant under the compact action and the commuting minimal action, that in addition contain the fixed point algebra of the compact action and the closed, normal subgroups of the compact group.     

Skew-products of higher-rank graphs and crossed products by semigroups

We consider a free action of an Ore semigroup on a higher-rank graph, and the induced action by endomorphisms of the C ^?-algebra of the graph. We show that the crossed product by this action is stably isomorphic to the C ^?-algebra of a quotient graph. Our main tool is Laca’s dilation theory for endomorphic actions of Ore semigroups on C ^?-algebras, which embeds such an action in an automorphic action of the enveloping group on a larger C ^?-algebra.     

On the Action of a Groupoid on a Manifold

In this paper,some properties of reduction for symplectic F-spaces are discussed.The properties of stable subgroups are discussed.We find that the symplectic action of a symplectic groupoid on a symplectic manifold can induce a symplectic map between reduced symplectic manifolds.This symplectic action can be characterized by the action of its induced symplectic groupoid on a symplectic manifold.Lastly,we shall discuss Poisson reduction and give a Poisson reduction theorem.     

关于群胚作用和李双代数胚态射

在这篇文章中，我们讨论了李双代数胚之间的态射，得到了一些李双代数胚之间态射的性质．研究了泊松群胚在泊松流形上的泊松作用，以及这个泊松作用与被作用流形的切李双代数胚到作用泊松群胚的切李双代数胚之间的态射的关系，得到了一些有用的结论。     

博弈方的行动集合变化的博弈运动研究——以稀土出口贸易为例

文章以稀土出口贸易为背景,分析了博弈方的行动集合随时间变化的博弈运动。首先定义了行动集合的三种变化情形:集合变大、集合变小和集合变化不确定。然后针对单个博弈方行动集合的三种变化情形,分别讨论了均衡解的运动轨迹,分析表明:在行动集合变大和变小两种情形下,均衡解的轨迹呈现互逆的运动特性;在行动集合变化不确定的情形下,保守和冒险策略等价,固定策略严格优于保守、冒险策略。在此基础上,将模型推广到博弈双方的行动集合均发生变化的博弈运动模型,分析表明上述结论仍然成立。最后,以中国同马来西亚在2012年6月到2013年3月间的稀土出口贸易为例,验证了本文模型和求解方法的合理性与可行性。     

On the Orbit Sizes of Permutation Groups on the Power Set

We study the action of finite permutation groups of odd order on the power set of a set on which they act naturally, and establish a theorem that guarantees the existence of a lot of distinct orbit sizes in this action. 1991 Mathematics Subject Classification: 20B05     

Partial Skew Polynomial Rings: Prime and Maximal Ideals

In this article, we consider rings R with a partial action α of a cyclic infinite group G on R. We define partial skew polynomial rings as natural subrings of the partial skew group ring R ?_α G. We study prime and maximal ideals of a partial skew polynomial ring when the given partial action α has an enveloping action.     

关于有限群的Γ_K类和半惯性子群的一些注记(英文)

本文研究了一个有限群和它的特征标的Galois共轭类.利用群作用和Galois作用,得到了关于相应Γ_K类和半惯性子群的一些结果,推广了一些著名定理.