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Unless stated otherwise, the seminar meets Tuesdays in room WH-100E at 2:50 p.m. There will be refreshments served at 4:00 in room WH-102.
Organizers: Alex Feingold and Hung Tong-Viet
To receive announcements of seminar talks by email, please join the seminar's mailing list.
Abstract: Please come or contact the organizers if you are interested in giving a talk this semester or want to invite someone.
Abstract: A semigroup is a set S equipped with an associative operation. The covering number of a semigroup S is the minimum number of proper subsemigroups whose union is S. In this talk, I will introduce basic semigroup theory and some fundamental examples while proving the following theorem: If S is a finite semigroup that is not a group nor generated by a single element, then the covering number of S is 2. Similar questions have been studied for groups and loops. (Joint work with Luise-Charlotte Kappe and Marcin Mazur.)
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Abstract: A mode A is an algebra which is idempotent and in which every operation is a homomorphism from the appropriate power of A to A. We will explore some results on a particular class of modes which are constructed from semilattices. In particular, we will look at the question of when is a semilattice mode subdirectly irreducible, both in general and in the particular case of when the mode has a single binary operation.
Abstract: BCK-algebras are algebraic structures arising from non-classical logic. This talk will focus primarily on the classes of commutative BCK-algebras and commutative involutory BCK-algebras. Particularly, I will discuss some basic ideal theory and spectral properties of such algebras, looking at differences between the bounded and unbounded cases.
Abstract: In this talk we consider the centers of the centralizers of elements in finite groups. We will then obtain a lower bound on the order of a maximal abelian subgroup in terms of the indices of the centralizers of elements and the orders of the centers of the centralizers of elements. We will use this to obtain a lower bound for maximal abelian subgroups of semi-extraspecial groups.
Abstract: We explore the question of when does a polynomial with integer coefficients induce an automorphism of the infinite regular d-ary tree. This is well-known for d=2, and there are some partial results for d prime. We extend the results to the case when d is square-free.
Abstract: The Chermak-Delgado measure of a subgroup H of a finite group G is defined as the product of the order of H with the order of the centralizer of H in G, |H||CG(H)|, and the set of all subgroups with maximal Chermak-Delgado measure forms a dual sublattice of the subgroup lattice of G. In this talk we step back from centralizers and consider four types of centralizer-like subgroups, defined using general words in the alphabet {x,y,x−1,y−1} instead of the specific commutator word. We show that this generalization results in four sublattices of the subgroup lattice of a finite group, some of which may be equal to one another depending on the word. We consider which properties of the Chermak-Delgado lattice generalize to the new lattices, and which properties are specialized in the Chermak-Delgado lattice. (This work is joint with Elizabeth Wilcox.)
Abstract: This talk will consist of a (quick) introduction to universal algebra where we focus on three topics: the definability of principal congruences, classifying subdirectly irreducibles, and determining the clone of term operations. We will attempt to understand these topics by focusing on two examples: the two-element semilattice and the three-element non-transitive tournament (a.k.a. the triangle).
Abstract: The complex irreducible characters Irr(G) of a finite group G contain a lot of information about G itself. Recently, it has been realized that some of this information can still be captured if, instead of considering the entire set Irr(G), one only considers those irreducible characters taking values in some suitable subfield of C. This motivates the following definitions: IrrF(G) is the subset of irreducible characters taking values in the subfield F⊆C; and ClF(G) is the set of conjugacy classes of G whose elements, when evaluated at every character of G, take values in F. A result of Isaacs & Navarro says that |IrrF(G)|=|IrrF(G/N)| and |ClF(G)|=|ClF(G/N)| whenever N⊴ contains no non-trivial \mathbb{F}-elements.
For a prime p, the p-Brauer characters of G arise from representations of G over \overline{\mathbb{F}}_p. They provide a link between the representation theory of G in characteristic 0 and in characteristic p. Whenever one has a relationship involving characters and conjugacy classes G, it is natural to wonder if there is an analogous relationship between the p-Brauer characters and p-regular conjugacy classes.
I will give some examples of the sorts of \mathbb{F}-generalizations alluded to in the first paragraph; introduce the basic notions of Brauer characters; and discuss a Brauer analogue of the Isaacs-Navarro result mentioned above.
Abstract: I will continue my exploration of covering numbers of semigroups by considering specific classes of semigroups. A monoid is a semigroup with an identity. An inverse semigroup I is a semigroup such that for each element a\in I there exists a unique element a^{-1}\in I such that aa^{-1}a=a and a^{-1}aa^{-1}=a. I will give a complete description of the covering number of monoids and inverse semigroups with respect to submonoids and inverse subsemigroups respectively (modulo the covering numbers of groups and semigroups). I will use Green's relations and other results to describe the structure of such semigroups.
Abstract: Often, we think of fractals as subsets of \mathbb{R}^n. Many definitions in fractal geometry can be generalized to any metric space, including groups equipped with a metric. In particular, the Hausdorff dimension and Box counting dimension can be defined on any metric space. Profinite groups can be equipped with a natural metric, under which we can discuss fractal properties. This will be an expository talk in which I define fractal dimensions and profinite groups. My goal is to set up the following question: Given two fractal subgroups of the automorphism group of the rooted infinite n-ary tree, what is the dimension of their intersection?
Abstract: The commuting probability d(G) of a finite G (introduced by Erdős and Turán in 1968), is defined to be the probability that two randomly chosen elements of G commute. The commuting probability d(G) is also called the commutativity degree of G. Erdős and Turán showed that d(G)=k(G)/|G|, where k(G) is number of conjugacy classes of G. In 1973, W. H. Gustafson proved that d(G)\leq 5/8 for any non-abelian group G. Since then, there are numerous results concerning the structure of finite groups using various bounds on the commuting probability. In this talk, I will consider a p-local version of the commuting probability. Specifically, for a prime p, we define d_p(G) to be the ratio k_p(G)/|P|, where k_p(G) is the number of conjugacy classes of p-elements of G and P is a Sylow p-subgroup of G. Using the invariant d_p(G), we obtain some new criteria for the existence of normal p-complements in finite groups.
Abstract: For a subgroup H of a finite group G, the Chermak-Delgado measure of H is defined as m_{G}(H) := |H||C_{G}(H)|. The subgroups of G with maximum Chermak-Delgado measure form a dual sublattice of the subgroup lattice of G. In this talk I will discuss some properties of such maximum-measure subgroups and calculate the Chermak-Delgado lattice for some classes of finite groups.
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