Abstract:  Granular materials consist of an unconsolidated ensemble of solid particles that interact and collide with each other. In engineering and the geosciences a large variety of problems exist where granular materials play a critical role. As a result there is a significant need to develop our understanding of the physical behavior of these materials. In this presentation I will highlight my research on granular materials by focusing on two different topics: booming sand dunes and granular segregation.   “Booming” sand dunes are able to produce a persistent, low-frequency sound that resembles a pure note from a music instrument. The sound has a dominant audible frequency (70 - 105 Hz) and several higher harmonics that may be heard from distances far away. A natural or induced avalanche from a slip face of the booming dune triggers an emission that may last for several minutes. I will introduce our model for the sound propagation in booming dunes and provide validation with quantitative field research done in the Mojave Desert and Death Valley National Park in California, USA.  Segregation is the separation of grains with different size or density due to a variety of physical processes. Intuitively, one may think that size sieving is simply due to the smaller particles falling into the holes between the larger particles. The majority of the existing experimental work is centred on rotating geometries, which have significant limitations and shortcomings when scaling to practical avalanching applications and chute flows. For this part of the presentation, I am outlining the effects of segregation on natural large-scale flows, such as the Blackhawk Slide in California, USA and snow avalanches in Switzerland and I am introducing the fundamental experiments on segregation I am currently running in the laboratory.  Biosketch:  Dr. Nathalie Vriend currently holds a prestigious NERC postdoctoral research fellowship at the University of Cambridge, UK and moves to an independent Royal Society Research Fellowship in January 2014 at the same institution. Her current research topics include laboratory research on the avalanching and segregation of granular materials and field research on snow avalanches in Switzerland. She finished her PhD in mechanical engineering and geophysics at the California Institute of Technology in Pasadena in 2010, and focused on desert dune migration and wave propagation in sand by researching the mystifying problem of booming sand dunes. Her PhD was awarded with the Centennial Prize for best thesis in Mechanical Engineering.  Home Page:  http://www.damtp.cam.ac.uk/user/nv253/ Host:  Prof. Eckart Meiburg