Abstract:

Bloodstain Pattern Analysis is a forensic discipline in which, among others, the position of victims can be determined at crime scenes on which blood has been shed. To determine where the blood source was investigators use a straight-line approximation for the trajectory, ignoring effects of gravity and drag and thus overestimating the height of the source. To include gravity and air drag into the models, the maximum diameter a droplet that impacts on a surface needs to be determined. However for a long time this was subject of controversy, notably for high-velocity impacts of low-viscosity liquids such as water or blood.

I will present our work on the drop impact for simple and complex liquids and show that the controversy can be resolved by understanding that the spreading behavior cannot simply be predicted by equating the inertial to either capillary or viscous forces, since, for most situations of practical interest, all three forces are important. We determine the correct scaling behaviors for the viscous and capillary regimes and, by interpolating between the two, find a universal rescaling. This allows to include gravity and drag in the trajectory calculation of blood drops on the crime scene also; the origin’s location can be determined roughly four times more accurately than with the straight-line approximation.

Bio:

Prof. dr. Daniel Bonn, is professor of physics and director of the van der Waals-Zeeman Institute at the University of Amsterdam. He heads the ‘Soft Matter’ research priority area of the Faculty of Science, an interdisciplinary virtual institute that brings together physicists, engineers, chemists, biologists and informatics researchers. He published more than 300 papers and over 30 PhD students have graduated under his supervision. Bonn is also co-founder of the start-up company GreenA that just received a Round A investment from a venture capital firm.

Pizza will be ordered at 12:30 !!