Thời gian: 9h, Thứ 4, ngày 19/2/2014

Địa điểm: Phòng số 4, nhà A14, Viện Toán học, 18 Hoàng Quốc Việt, Hà Nội

Tóm tắt:  We study the problem of covering Euclidean space R^d by possibly overlapping translates of a convex body P, such that almost every point is covered exactly k times, for a fixed integer k.  Such a covering of Euclidean space by translations of P is called a k-tiling.   We will first give a historical survey that includes the investigations of classical tilings by translations (which we call 1-tilings in this context).  They began with the work of the famous crystallographer Fedorov and with the work of Minkowski, who founded the Geometry of Numbers.   Some 50 years later Venkov and McMullen gave a complete characterization of all convex objects that 1-tile Euclidean space.

Today we know that k-tilings can be tackled by methods from Fourier analysis, though some of their aspects can also be studied using purely combinatorial means.  For many of our results, there is both a combinatorial proof and a Harmonic analysis proof.  For k  larger than 1, the collection of convex objects that k-tile is much wider than the collection of objects that 1-tile;  there is currently no complete knowledge of the polytopes that k-tile in dimension 3 or larger, and even in 2 dimensions it is quite challenging.  We will cover both ``ancient'', as well as very recent, results concerning 1-tilings and other k-tilings.  This is joint work with Nick Gravin, Dmitry Shiryaev, and Mihalis Kolountzakis.