Stock Photo - 22 August 2020, Saxony, Leipzig: Franziska Brauer (l) and Doreen Linke, test persons from Saxony and Saxony-Anhalt, show so-called ""tracers"", which are used in the large-scale experiment of the University Medical Center Halle/Saale and can trace paths. Around 2200 visitors take part in the experiment entitled ""Restart-19"", in which the pop singer Tim Bendzko will perform. The scientists want to use sensors and other aids to monitor walking paths, and fluorescent disinfectant is to make visible which surfaces are often touched. They also want to trace the flight of aerosols - the smallest mixtures of particles that could carry the virus. The aim is to develop a mathematical model with which the risk of a corona outbreak after a major event in a hall can be assessed. Photo: Hendrik Schmidt/dpa-Zentralbild/dpa. - Leipzig/Saxony/Germany