Hu, David L.
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ItemEntangled granular media(Georgia Institute of Technology, 2012-05-17) Gravish, Nick ; Franklin, Scott V. ; Hu, David L. ; Goldman, Daniel I. ; Georgia Institute of Technology. School of Physics ; Rochester Institute of Technology. Dept. of Physics ; Georgia Institute of Technology. School of Mechanical EngineeringWe study the geometrically induced cohesion of ensembles of granular“u particles” that mechanically entangle through particle interpenetration. We vary the length-to-width ratio l/w of the u particles and form them into freestanding vertical columns. In a laboratory experiment, we monitor the response of the columns to sinusoidal vibration (with peak acceleration Γ). Column collapse occurs in a characteristic time τ which follows the relationτ∝exp(Γ/Δ). Δ resembles an activation energy and is maximal at intermediate l/w. A simulation reveals that optimal strength results from competition between packing and entanglement
ItemFrom Urination to Georgia Tech's First Ig Nobel Prize(Georgia Institute of Technology, 2015-10-19) Hu, David L. ; Georgia Institute of Technology. School of Physics ; Georgia Institute of Technology. School of Mechanical EngineeringHow long does an elephant urinate? How quickly does a dog shake? How many eyelashes does a camel have? Asking a new and sometimes strange question is arguably the most important step in advancing science, and not any less so if you study animal movement, a field at least as old as Leonardo da Vinci’s pioneering observations. Asking questions is not only fun, but can also lead to unexpected scientific discoveries. In this talk, I will discuss my journey with wacky science, how it led me from being peed on while changing a diaper, to this year’s Ig Nobel Prize.
ItemAnt Rafts and Other Water Repellent Systems(Georgia Institute of Technology, 2012-04-10) Hu, David L. ; Georgia Institute of Technology. Institute for Bioengineering and Bioscience ; Georgia Institute of Technology. School of Mechanical EngineeringWe present a series of experiments demonstrating the water-repellent adaptations of a range of animals, from insects to mammals. These adaptations are necessary for survival in rain and other wet environments. During flash floods, fire ants weave hydrophobic rafts with their own bodies in order to keep their colonies dry. We discuss their method of self-assembly and present a model that predicts their construction rate. To survive raindrop impacts, flying insects take advantage of their low mass, which prevents drops from splashing on them. The resulting impact force on flying mosquitoes is 100-300 gravities, quite possibly the largest in the natural world. For such small insects, small size is advantageous in rain. If an animals is large, active mechanisms must be employed to shed water. Mammals of all sizes can shake off 70% of the water on their bodies in fractions of a second. We show that wet mammals shake at tuned frequencies to dry and present a scaling law relating animal size and frequencies required to dry. In this talk, the audience will learn the basics of modeling and experimentation with surface-tension phenomena.
ItemCube-Shaped Poo and Georgia Tech's Second Ig Nobel Prize(Georgia Institute of Technology, 2019-10-08) Hu, David L. ; Georgia Institute of Technology. School of Physics ; Georgia Institute of Technology. School of Mechanical EngineeringHow does a wombat produce cube-shaped feces? How long does it take an elephant to urinate? Answering these two questions have landed David Hu two Ig Nobel Prizes, awards given at Harvard University for research that makes people laugh, and then think. Hu will talk about his lab's latest adventures catching elephant pee in trash cans, inflating wombat intestines with clown balloons, and dressing up as a gigantic piece of cubed poo at this year's Ig Nobel Ceremony.