Poincaré series and Coxeter functors for Fuchsian singularities

We consider Fuchsian singularities of arbitrary genus and prove, in a conceptual manner, a formula for their Poincaré series. This uses Coxeter elements involving Eichler-Siegel transformations. We give geometrical interpretations for the lattices and isometries involved, lifting them to triangulated categories.     

Symmetries and apparent singularities for the simplest Fuchsian equations

We consider the simplest Fuchsian second-order equations with particular attention to the role of apparent singularities. We show the relation to the Painlevé equation and follow the matrix formulation of the problem.     

Semi-invariants of canonical algebras

We describe the algebras of semi-invariants on the varieties of regular representations of canonical algebras. In particular, we show that these algebras are polynomial algebras or complete intersections. Received: 29 March 1999     

On q-asymptotics for linear q-difference-differential equations with Fuchsian and irregular singularities

We consider a Cauchy problem for some family of linear q-difference-differential equations with Fuchsian and irregular singularities, that admit a unique formal power series solution in two variables $\stackrel{?}{X}(t,z)$ for given formal power series initial conditions. Under suitable conditions and by the application of certain q-Borel and Laplace transforms (introduced by J.-P. Ramis and C. Zhang), we are able to deal with the small divisors phenomenon caused by the Fuchsian singularity, and to construct actual holomorphic solutions of the Cauchy problem whose q-asymptotic expansion in t, uniformly for z in the compact sets of $\mathbb{C}$, is $\stackrel{?}{X}(t,z)$. The small divisors? effect is an increase in the order of q-exponential growth and the appearance of a power of the factorial in the corresponding q-Gevrey bounds in the asymptotics.     

The canonical sheaf of Du Bois singularities

We prove that a Cohen-Macaulay normal variety X has Du Bois singularities if and only if π_∗ωX^′(G)?ωX for a log resolution π:X^′→X, where G is the reduced exceptional divisor of π. Many basic theorems about Du Bois singularities become transparent using this characterization (including the fact that Cohen-Macaulay log canonical singularities are Du Bois). We also give a straightforward and self-contained proof that (generalizations of) semi-log-canonical singularities are Du Bois, in the Cohen-Macaulay case. It also follows that the Kodaira vanishing theorem holds for semi-log-canonical varieties and that Cohen-Macaulay semi-log-canonical singularities are cohomologically insignificant in the sense of Dolgachev.     

Moduli algebras of some non-semiquasihomogeneous singularities

Under some additional restrictions we find dimensions and bases of moduli algebras of isolated singularities of polynomials in n variables that are sums of n monomials of equal weighted degrees and one monomial of lower degree.     

Indecomposable modules for domestic canonical algebras

We show that-up to precisely one-each exceptional module over a domestic canonical algebra of quiver type over a field k can be represented by matrices whose entries are just 0 and 1. In the case we calculate the matrices of these representations explicitly.     

Extended dyer-lashof algebras and modular coinvariants

Given an increasing sequence of integersN=(0,n ₁,n ₂,...), a functorG _N is constructed from the category of based spaces of the homotopy type ofCW compleces and based maps to a subcategory of in analogy to May's approximation modelC. A family of homology operationsRN is associated toG _N and its algebraic structure is described in terms of modular coinvariants of parabolic subgroups.     

Extended Rees algebras and mixed multiplicities

Partially supported by the general research fund at the University of Kansas     

Derived equivalences of selfinjective algebras preserve singularities

We prove that the derived equivalences (more generally the stable equivalences of Morita type) of finite dimensional selfinjective algebras over algebraically closed fields preserve the types of singularities in the orbit closures of module varieties. As an application, we obtain that the orbit closures in the module varieties of the Brauer tree algebras are normal and Cohen-Macaulay. Mathematics Subject Classification (2000):14B05, 14L30, 16D50, 16G20     

Deformation of isolated hypersurface singularities and their moduli algebras

By the using of determinantal varieties from moduli algebras of hypersurface singularites the relation of the deformation of hypersurface singularities and the deformation of their moduli algebras is studied. For a type of hypersurface singularities a weak Torelli type result is proved. This weak Torelli type result showes that for families of hypersurface singularities the moduli algebras can be used to distinguish the complex structures of singularities at least in some weak sence. Research supported by NNSF     

Construction of a linear Pfaff system of Fuchsian type with algebraic manifold of singularities

We present a constructive proof of the existence of a two-dimensional completely integrable Fuchsian Pfaff system on CP ⁿ with four singular surfaces forming a pencil, with 2-step solvable monodromy group, and with fundamental solution matrix realizing a given homomorphism.     

格蕴涵代数的扩展LI-理想

LI-理想是研究格蕴涵代数结构特征的一个重要的工具性概念.综合运用代数学与逻辑学的方法和原理对格蕴涵代数的LI-理想理论作进一步深入研究.首先,引入格蕴涵代数L的LI-理想A关于L的子集M的扩展LI-理想及稳定LI-理想概念并考察它们的基本性质.其次,讨论了L的几类扩展LI-理想集的格论特征.证明了L的关于一个给定子集M?L的稳定LI-理想全体之集S(M)与L的一个LI-理想A关于任意子集M?L的扩展LI-理想全体之集EA均构成完备Heyting代数的结论.再次,给出了商格蕴涵代数和乘积格蕴涵代数的扩展LI-理想的若干性质.最后,借助于L的扩展LI-理想之特性获得了L的ILI-理想的若干等价刻画.