A converse to a theorem of Oka and Sakamoto for complex line arrangements

Let C_1 and C_2 be algebraic plane curves in the complex plane such that the curves intersect in d_1\cdot d_2 points where d_1,d_2 are the degrees of the curves respectively. Oka and Sakamoto proved that the fundamental group of the complement of C_1 \cup C_2 is isomorphic to the direct of product of the fundamental group of the complement of C_1 and the fundamental group of the complement of C_2. In this paper we prove the converse of Oka and Sakamoto's result for line arrangements. Let A_1 and A_2 be non-empty arrangements of lines in complex plane such that the fundamental group of the complement of A_1 \cup A_2 is isomorphic to the direct product of the complements of the arrangements A_1 and A_2. Then, the intersection of A_1 and A_2 consists of |A_1| \cdot |A_2| points of multiplicity two.Comment: 15 pages, 3 figure

On Extensions of generalized Steinberg Representations

Let F be a local non-archimedean field and let G be the group of F-valued points of a reductive algebraic group over F. In this paper we compute the Ext-groups of generalized Steinberg representations in the category of smooth G-representations with coefficients in a certain self-injective ring.Comment: 22 pages, LaTe

Critical points and resonance of hyperplane arrangements

If F is a master function corresponding to a hyperplane arrangement A and a collection of weights y, we investigate the relationship between the critical set of F, the variety defined by the vanishing of the one-form w = d log F, and the resonance of y. For arrangements satisfying certain conditions, we show that if y is resonant in dimension p, then the critical set of F has codimension at most p. These include all free arrangements and all rank 3 arrangements.Comment: revised version, Canadian Journal of Mathematics, to appea

Homogenization in integral viscoelasticity

A multi-phase periodic composite subjected to inhomogeneous shrinkage and mechanical loads including prescribed interface jumps of displacements and tractions is considered. The composite components are anisotropic linear viscoelastic and aging (described by the non-convolution Volterra integral operators). The paper presents some results about asymptotic homogenization and 2-scale convergence in appropriate function spaces