AR-箭图的构造和矩阵双模问题

本文简要介绍了Artin代数表示理论中的下述内容:Auslander-Reiten箭图(简称AR-箭图)稳定分支的结构,野型遗传代数稳定分支的性质,代数闭域上有限维代数Λ引出的矩阵双模问题、对偶的余双模问题及其相伴的具有余代数结构的双模(简称box), modΛ、P_1(Λ)及相伴box的表示范畴之间几乎可列序列的几乎一一对应,驯顺代数Λ上任意两个模之间态射集的维数和性质;最后介绍了代数的驯顺性与其模范畴的齐性.     

AR箭图,例外序列与导出Hall代数中的算法

如果半单Lie代数g和有限维遗传代数Λ对应于相同的Dynkin图,则有量子群U_q(g)的正部分U~+典范地同构于Hall代数H(Λ).一个自然的问题是:如何将U+中的根向量分解为Chevalley生成元的单项式的线性组合?Chen和Xiao给出的两种算法分别利用了Λ-模的例外序列上的辫子群作用以及Λ的Auslander-Reiten箭图的结构.对于To(e|¨)n定义的导出Hall代数,本文提出了类似的问题.并得到了相应的两种算法.这两种算法也同样适用于Kapranov定义的格代数和Heisenberg double.而且,所有新的递归公式都具有和量子Serre关系相似的形式.     

项链李代数的结构

研究项链李代数的结构,定义了箭图Q的重箭图Q循环上的映射σ,证明了这是一个李运算.引入左右指标数组概念,利用它们把项链李代数N_Q的基分成了5类,并构造了项链李代数的一些有趣的子代数.     

rep(A_3,I,A)中的Gorenstein投射模

设A是域k上的有限维代数,(Q,I)是带关系的箭图,令Λ=AkkQ/I.Λ的模范畴Λ-Mod及有限生成模范畴Λ-mod分别与(Q,I)在A上的表示范畴Rep(Q,I,A)及有限维表示范畴rep(Q,I,A)等价.给出了范畴rep(A_3,I,A)中Gorenstein投射模的具体构造,其中(A_3,I)=3α→2β→1,I=βα.在此基础上,给出了代数A是自入射代数的一个充分必要条件.     

含重边星形箭图偏周期预投射代数的希尔伯特级数

设△是一个有限无圈的箭图.引入了由△所决定的偏周期预投射代数,它是一个定义在周期为p的稳定平移箭图Z△/(r^p)上的代数,记为Π_(Q(△,p),J).推广了Eting和Eu的方法并得到无圈的连通星形箭图△所决定的偏周期预投射代数Π_((Q(△,p)),J)的希尔伯特级数的计算公式.     

rep(A_3,I,A)中的Gorenstein投射模北大核心CSCD

设A是域k上的有限维代数,(Q,I)是带关系的箭图,令Λ=AkkQ/I.Λ的模范畴Λ-Mod及有限生成模范畴Λ-mod分别与(Q,I)在A上的表示范畴Rep(Q,I,A)及有限维表示范畴rep(Q,I,A)等价.给出了范畴rep(A_3,I,A)中Gorenstein投射模的具体构造,其中(A_3,I)=3α→2β→1,I=<βα>.在此基础上,给出了代数A是自入射代数的一个充分必要条件.     

截面代数的Hochschild上同调群

用代数表示论中方法给出了截面代数的Hochschild上同调群与其Gabriel箭图的组合性质之间的关系。     

一般箭图偏周期预投射代数的Hilbert级数

设△是一个有限无圈的箭图,引入了由△所决定的偏周期预投射代数,它是一个定义在周期为p的稳定平移箭图Z△/(T~p)上的代数,记为∏_(Q(Δ,p),J).当周期p=1时,偏周期预投射代数就是偏预投射代数.推广了Eting和Eu的方法并得到无圈箭图△所决定的偏周期预投射代数∏_((Q(Δ,p)),J)的Hilbert级数的计算公式.     

星形箭图偏周期预投射代数的Hilbert级数

设△是一个有限无圈的箭图.引入了由Δ所决定的偏周期预投射代数,它是一个定义在周期为p的稳定平移箭图Z△/(τ~p)上的代数,记为Π_(Q(Δ,p),J).当周期p=1时,偏周期预投射代数就是偏预投射代数.我们推广了Eting和Eu的方法并得到无圈的星形箭图△所决定的偏周期预投射代数Π_((Q(Δ,p)),J)的Hilbert级数的计算公式.     

关于项链李代数的结构

Le Bruyn和V．Ginzbrug最近引入了项链李代数。它是定义在箭图上的一种无限堆李代数，在非交换几何研究中起了重要作用。本研究项链李代数结构，证明了当箭图中有长度大于1的循环时，其项链李代数不是幂零李代数，我们还给出了没有圈的箭图上项链李代数的分解。     

THE RAMSEY NUMBERS FOR STARS AND STRIPES

Let Σ=Σ_{i=1}^{t}(n_i-1) and Λ=Σ_{j=1}^s(m_j-1). This paper considers the generalized Ramsey number R(K_{1,n_1},…, K_{1,n_t},m_1K_2,…, m_sK_2) for any Σ and Λ. And the authors get their exact values if 1<=Λ<=Σ and their upper bounds if Λ>= Σ     

Hochschild （Co）homology of Galois Coverings of Grassmann Algebras

Let ∧ be the Z2-Galois covering of the Grassmann algebra A over a field k of characteristic not equal to 2. In this paper, the dimensional formulae of Hochschild homology and cohomology groups of ∧ are calculated explicitly. And the cyclic homology of∧ can also be calculated when the underlying field is of characteristic zero. As a result, we prove that there is an isomorphism from i≥1 HH^i（∧） to i≥1 HH^i（∧）.     

Density of weighted wavelet frames

If ψ ∈ L²(R), Λ is a discrete subset of the affine groupA =R ⁺ ×R, and w: Λ →R ⁺ is a weight function, then the weighted wavelet system generated by ψ, Λ, and w is . In this article we define lower and upper weighted densities D _w ⁻ (Λ) and D _w ⁺ (Λ) of Λ with respect to the geometry of the affine group, and prove that there exist necessary conditions on a weighted wavelet system in order that it possesses frame bounds. Specifically, we prove that if W(ψ, Λ, w) possesses an upper frame bound, then the upper weighted density is finite. Furthermore, for the unweighted case w = 1, we prove that if W(ψ, Λ, 1) possesses a lower frame bound and D _w ⁺ (Λ⁻¹) < ∞, then the lower density is strictly positive. We apply these results to oversampled affine systems (which include the classical affine and the quasi-affine systems as special cases), to co-affine wavelet systems, and to systems consisting only of dilations, obtaining some new results relating density to the frame properties of these systems.     

The C*-algebra of the N-dimensional harmonic oscillator

In this paper we study the Fredholm thoery of a C*-algebraOl of o-order pseudo-differential operators on L²(ⁿ). IfK denotes the ideal of all compact operators of L², the algebraOl will be generated by (i) the idealK, (ii) a function algebra CS(ⁿ) and (iii) by the bounded operators x_j, D_j, j=1,...,n, = H^–1/2, H=1+¦x¦²–. We show thatOl/K is a commutative C*-algebra with identity and obtain its Gelfany space M. This provides Fredholm criterion and index formula for a graded algebra of partial differential operators including all oeprators with polynomial coefficients. We also give Fredholm criterion and index formula for systems of such operators.     

Dimension Theory and Nonstable K1 of Quadratic Modules

Employing Bak's dimension theory, we investigate the nonstable quadratic K-group K _1,2n (A, ) = G _2n (A, )/E _2n (A, ), n 3, where G _2n (A, ) denotes the general quadratic group of rank n over a form ring (A, ) and E _2n (A, ) its elementary subgroup. Considering form rings as a category with dimension in the sense of Bak, we obtain a dimension filtration G _2n (A, ) G _2n ⁰(A, ) ; G _2n ¹(A, ) ... E _2n (A, ) of the general quadratic group G _2n (A, ) such that G _2n (A, )/G _2n ⁰(A, ) is Abelian, G _2n ⁰(A, ) G _2n ¹(A, ) ... is a descending central series, and G _2n ^d(A)(A, ) = E _2n (A, ) whenever d(A) = (Bass–Serre dimension of A) is finite. In particular K _1,2n (A, ) is solvable when d(A) < .     

On Series of Translates of Positive Functions

For , a discrete infinite set of nonnegative real numbers, and a nonnegative measurable function f: R R ⁺, consider . The sets naturally break into two types. Type 1 consists of such that either C = R almost everywhere or else C = Ø a.e., for every f. Type 2 consists of all the other . We introduce a notion of asymptotic density for and the complementary notion of asymptotic lacunarity. We demonstrate that is of type 2 if it is asymptotically lacunary or else is asymptotically dense and exhibits asymptotically large Q-independent sets. We also give some examples of sets of both types.     

Gradings and Derived Categories

Let G{{\mathcal G}} be a group, Λ a G{{\mathcal G}}-graded Artin algebra and gr(Λ) denote the category of finitely generated G{{\mathcal G}}-graded Λ-modules. This paper provides a framework that allows an extension of tilting theory to D^b(gr(L)){{\mathcal D}}^b(\rm gr(\Lambda)) and to study connections between the tilting theories of D^b(L){{\mathcal D}}^b(\Lambda) and D^b(gr(L)){{\mathcal D}}^b(\rm gr(\Lambda)). In particular, using that if T is a gradable Λ-module, then a grading of T induces a G{{\mathcal G}}-grading on End_Λ(T), we obtain conditions under which a derived equivalence induced by a gradable Λ-tilting module T can be lifted to a derived equivalence between the derived categories D^b(gr(L)){{\mathcal D}}^b(\rm gr(\Lambda)) and D^b(gr(End_L(T))){{\mathcal D}}^b(\rm gr(\rm End_{\Lambda}(\textit T))).     

Varieties for Modules of Quantum Elementary Abelian Groups

We define a rank variety for a module of a noncocommutative Hopf algebra A = L \rtimes GA = \Lambda \rtimes G where L = k[X₁, ..., X_m]/(X₁^l, ..., X_m^l), G = (\mathbbZ/l\mathbbZ)^m\Lambda = k[X_1, \dots, X_m]/(X_1^{\ell}, \dots, X_m^{\ell}), G = (\mathbb{Z}/\ell\mathbb{Z})^m and char k does not divide ℓ, in terms of certain subalgebras of A playing the role of “cyclic shifted subgroups”. We show that the rank variety of a finitely generated module M is homeomorphic to the support variety of M defined in terms of the action of the cohomology algebra of A. As an application we derive a theory of rank varieties for the algebra Λ. When ℓ=2, rank varieties for Λ-modules were constructed by Erdmann and Holloway using the representation theory of the Clifford algebra. We show that the rank varieties we obtain for Λ-modules coincide with those of Erdmann and Holloway.     

A Martingale Approach in the Study of Percolation Clusters on the Z d Lattice

Consider percolation on Z ^d with parameter p. Let K _n be the number of occupied clusters in [–n, n] ^d . Here we use a martingale method to show that if p0, 1, K _n satisfies the CLT for all d>1. Furthermore, we investigate the large deviations and concentration property for K _n . Besides K _n , we also consider the distribution of the number _n of such vertices connected by the infinite occupied cluster in a large box [–n, n] ^d . We show that _n satisfies the CLT and investigate the concentration property for _n , by using the martingale method in the supercritical phase.