报告人：Pertti Mattila教授（University of Helsinki, Finland）
报告题目：Hausdorff dimension, projections and the Kakeya problem
报告摘要：Hausdorff dimension is a parameter measuring metric size of general sets. Marstrand proved in 1954 that if A is a Borel set in plane of Hausdorff dimension s, then its almost all projections on lines have dimension s, if s is not greater than 1, and they have positive one-dimensional measure,
if s > 1. I shall discuss some recent developments related to this. A Kakeya (or Besicovitch) set is a set of Lebesgue measure zero containing a unit line segment in every direction. They exist in the Euclidean n-space if n >1, and their Hausdorff dimension is 2 in the plane. It is not known if their Hausdorff dimension is n in every n-space when n > 1. I discuss some relations of this problem to projections.
报告人简介：Pertti Mattila为芬兰赫尔辛基大学教授，国际知名的几何测度论和调和分析专家，ICM45分钟报告人，曾在国际顶级数学期刊“Annals. of Math.”和“Acta Math”发表多篇学术论文，并曾担任“Acta Math”杂志编委。