At a low density, crowds of people can behave like a fluid, which has led to numerous hydrodynamically-based crowd models. At higher densities, though, crowds are more like a soft solid, and researchers are adapting models developed for granular materials like sand to describe these crowds. In granular materials, these models help scientists identify how vibrations move through the complex network of grains and what circumstances might cause sudden reorganizations. In a large crowd, this could tell scientists the difference between the innocuous shuffle at a rock concert and the trigger for a deadly stampede. Getting real-world data for comparison is tough – obviously, it’s unethical to intentionally cause a crowd to panic – so thus far the models remain relatively untested. (Image credit: M. Lebrun; research credit: A. Bottinelli and J. Silverberg)
Month: October 2019
Getting Cold
Just as some chemical reactions produce heat, many chemical combinations absorb heat. In “Getting Cold,” the Beauty of Science team demonstrates this by showing endothermic processes in both visible and infrared light. Combinations that appear humdrum from our normal perspective suddenly become vibrant and interesting when we see the temperature variations accompanying them.
Evaporation is a good example. As humans, we sweat so that when our sweat evaporates off our skin, it takes heat away with it. Water (the main ingredient in sweat) isn’t the fastest evaporating liquid, however. Here it’s shown alongside ethyl acetate, a common ingredient in nail polish remover. And anyone who’s used nail polish remover is familiar with the chill it leaves behind as it evaporates. Just look how much colder and darker it is when evaporating! (Video and image credit: Beauty of Science)
Explosive Flame Fronts
Though they look like jellyfish or space creatures, these images from photographer Linden Gledhill are actually explosions. What you’re seeing is the detonation of hydrogen gas with oxygen. The teal sphere with its wavy surface marks the flame front, and the crisp, stringy edges seen here and there in the foreground are the remains of a soap bubble that held the hydrogen before it sparked. You can see a similar set-up (using methane rather than hydrogen) in action here, and you can see other artistic takes on combustion in previous posts like this one. (Image credit: L. Gledhill, Flickr)
Calimero’s Uprising!
Here on FYFD posts often focus on research results, with animations and images showing only a tiny portion of the apparatus necessary to conduct that work. But in this timelapse, we get to see a glimpse of what it takes to make the research happen. The video covers a 12-week period in which student Sietze Oostveen sets up, modifies, and takes measurements with a rotating tank apparatus called Calimero.
The video captions give you a sense of all the little tasks that go into experimental work, from installing thermal control and measurement systems (in this case, laser Doppler velocimetry, or LDV) to making sure that the rotating table is balanced correctly. In experimental work, it’s worth remembering that you’ll likely spend as much or more time preparing to take data than you will actually doing measurements! (Video credit: S. Oostveen/UCLA Spinlab)
