METU Mathematics Seminars
Fall 2016

Previous Seminars: Spring 2016, Fall 2015, Spring 2015, Fall 2014, Spring 2014, Fall 2013, Spring 2013, Fall 2012, Spring 2012, Fall 2011, Spring 2011.

The seminars will be held in Gündüz İkeda Room at 15:40 unless otherwise stated.

October 13
Rutgers University
How difficult is it to classify the minimal homeomorphisms of the Cantor set?
In this talk, we will analyze the topological conjugacy problem for minimal homeomorphisms of the Cantor space from the point of view of descriptive set theory. We shall not assume any prior knowledge on the topic and the first half of the talk will be devoted to the mathematical framework provided by descriptive set theory to analyze the relative complexity of classification problems. In the second half of the talk, we shall focus on the topological conjugacy relation on the space of minimal homeomorphisms of the Cantor space and show that the Friedman-Stanley jump of the identity relation on reals is a lower bound for the Borel complexity of this relation.

October 20
The Bebutov-Kakutani Representation Theorem
Famously investigated by M. V. Bebutov, there is a natural flow on the set of real valued functions on the real line with the metric of uniform convergence on compact sets. This flow is universal in the sense that each flow on a compact metric space can be imbedded as its subflow. A weaker version of this fact was first proven by V. V. Nemytskii in a paper which remained mostly unnoticed until S. Kakutani provided a brief and natural demonstration.

October 27
Bilkent University
Lines in quartic surfaces

November 3
İstanbul University
On extended Legendrian dualities and their applications

November 10
Marmara University
All Separable Infinite Dimensional FrechetSpaces are Homeomorphic

November 17
METU Department of Chemical Engineering
The dynamics of the rise and fall of empires

November 24
METU Department of Physics
The right-hand side of Einstein's equation
It is well-known that Einstein's equation has two sides. About these two sides, Einstein wrote "it is similar to a building, one wing of which is made of fine marble(left part of the equation), but the other wing of which is built of low grade wood (right side of equation). What he called "marble" is the geometry side and "wood" the matter side. The wood part is really still problematic. I will explain this and also talk about the recent observation of binary black hole mergers and the sound they produced.

December 1
Bilkent University
Orthogonal polynomials for continuous singular measures
First we recall some results about asymptotic behaviour of orthogonal polynomials for finite gap sets and then discuss the case of continuous singular measures.

December 8
Atılım University
Disconjugacy via Lyapunov and Vallee-Poussin type inequalities for forced differential equations
In this talk, in the case of oscillatory potentials, we present some new Lyapunov and Vall´ee-Poussin type inequalities for second-order forced differential equations. No sign restriction is imposed on the forcing term. The obtained inequalities generalize and complement the existing results in the literature. This is joint work with Ravi P. Agarwal.

December 15
Intermediate Growth in Finitely Presented Algebras
Let A be an (not necessarily associative) algebra over a field k generated by a finite set X. The growth function of A with respect to X is defined as the dimension of the subspace of A spanned by all monomials on X of length at most n. The asymptotic behavior of this function does not depend on the generating set X and it is called the growth of A. The growth rate is a widely studied invariant for finitely generated algebraic structures such as algebras, groups, semigroups. This talk will be a survey of history, open problems and some new results around this notion. The main focus will be on finitely presented algebras whose growth is intermediate between polynomial and exponential.

December 22
Doguş University
A subgroup H of a group G is called a TI-subgroup if H intersects trivially with any conjugate of H different from H and H is called an STI subgroup of G if for any normal subgroup N of G the subgroup HN/N is TI in G/N. In this talk the following result will be proven: If A is of prime order and acts coprimely on a finite group G in such a way that the group F of fixed points of A is an STI-subgroup of G, then F is solvable if and only if G is solvable.

December 29
Bilkent University Department of Physics
Topological Effects in Non-relativistic Quantum Mechanics:An overview of the 2016 Nobel Prize
The 2016 Nobel Prize in Physics has been awarded to J. Michael Kosterlitz, Duncan Haldane, and David J. Thouless, for “theoretical discoveries of topological phase transitions and topological phases of matter”. In this talk I will try to explain why Topology, a branch of geometry which studies properties which do not change with continuous changes in size or shape, becomes important in determining the physical properties of a system and phase transitions between different states of matter. Without presenting any mathematical details, I will motivate the order parameter concept and its connection to topological defects. I will try to review some of the concepts regarding Kosterlitz Thouless phase transitions, Thouless charge pumps, Thouless-Kohmoto-Nightingale-den Nijs conductance formula, Haldane gap in spin chains and the Haldane model. Finally I would like to review current status of the field, including our recent work[1]. The talk is aimed at a broad audience with minimal background in mathematics and physics, and should be accessible to undergraduate students. [1]F. Nur Ünal, Erich J. Mueller, and M. Ö. Oktel PHYSICAL REVIEW A 94, 053604 (2016) “Nonequilibrium fractional Hall response after a topological quench.”

January 5
Galatasaray University
Arithmetic of the étale co-site of the modular curve
The central question of studying the absolute Galois group (together with the theorem of Belyi) has been the key ingredients of (so-called) geometric Galois actions which was outlined in a research proposal entitled "Esquisse d’un Program” by Grothendieck. This theory, although focusses on the étale site of the modular curve, can be used for "non-étale" covers, too. We will exemplify related arithmetic questions by discussing covers that arise from annuli, which apparently were quite well-known to Gauss! If time permits, we explain a generalisation that arises by replacing the modular group by Hecke groups. This is joint work with M.Uludag. This research is funded by TUBITAK 1001 grant 114R073.