In this month’s FYFD/JFM video, we explore some intersections between the animal kingdom and our own lives. Learn about designing better buildings with inspiration from termites; see the fascinating superpower of the star-nosed mole; and learn what goes into products like the toothpaste you (hopefully) use daily. All this and more in the latest video! Missed one of our previous ones? Good news: we’ve got you covered. (Image and video credit: N. Sharp and T. Crawford)
In the latest JFM/FYFD video, we tackle some of the less pleasant aspects of summer weather: stopping invasive insects, understanding how plants dispense poison, and looking at the physics behind jellyfish stings. And if you’ve missed any of our previous videos, we’ve got you covered. (Image and video credit: T. Crawford and N. Sharp)
Many species of kelp change their blade shape depending on the current they experience. In fast-moving waters, the kelp grows flat blades, but when the water around them is slower, the same plant will grow ruffled edges on its blades. In a slow current, the ruffled version’s extra drag causes it to flutter up and down with a large amplitude. That helps spread the blades out to catch more sunlight and increase photosynthesis, but it comes at the cost of higher drag, which could tear the plant from its holdfast.
In contrast, the flat-bladed kelp collapses into a more hydrodynamic shape. This clumps the flat blades together, making photosynthesis harder, but it streamlines the kelp, making it easier to resist getting ripped out by fast-moving tides. (Image credit: J. Hildering; research credit: M. Koehl et al.; submission by Marc A.)
Have you ever wondered why it is that fish in a pond or lake don’t freeze during the winter? The secret is due to a peculiarity of water that’s vital for life here on Earth. In general, cold things are denser than warmer ones. This is why, for the most part, cold fluids tend to sink and warmer ones rise here on Earth. So as fall moves into winter and water near the surface of a pond cools, it sinks. But only to a point.
Water is at its densest at 4 degrees Celsius. Any colder and the water will actually expand and become less dense. This is why you can’t fill ice cube trays to the very top before putting them in the freezer. In the pond it means that buoyant convection shuts down at 4 degrees Celsius. When the water at the top keeps cooling down to the freezing point, it doesn’t sink. Instead, the fish and other pond life get to spend the winter at a chill – but not freezing – 4 degrees. (Video credit: A. Fillo)
Harbor seals and their brethren have a superpower that lets them track their prey even without sight or sound. It’s their whiskers, which are sensitive enough to follow the trail left by a single fish thirty seconds earlier. The secret to the whisker’s sensitivity lies in its shape. Instead of a uniform, circular cross-section, the seal’s whisker is oval-shaped and its width varies along the length in a wavy pattern. So unlike a straight cylinder, which vibrates when towed through water, the seal’s whiskers are unperturbed by their own movement. They shed only weak vortices and do not vibrate as a result.
But, if you expose the whiskers to any external turbulence, like the vortices trailing a fish, the whisker ‘slaloms’ back-and-forth in time with the wake. That motion gets transmitted to the nerves in the seal’s cheek, carrying potential information about both the size and speed of the wake’s originator. Researchers hope similar bio-inspired whiskers could help underwater vehicles track schools of fish or locate underwater drilling leaks. (Image credit: M. Richter; video credit: MIT; research credit: H. Beem and M. Triantafyllou; via the Economist; submitted by Russ A. and Kam-Yung Soh)
Conventional wisdom – and the Second Law of Thermodynamics – require all fluids to have viscosity, with the noted and bizarre exception of superfluids, which can flow with zero viscosity. In essence, you cannot have work (i.e. flow) for free. Some effort has to be lost to resistance.
But scientists have discovered, bizarrely, that adding bacteria to water can result in zero or even negative viscosities – meaning that effort is required to keep the flow from accelerating. Before you ask, no, this is not a recipe for a perpetual motion machine. What happens when the bacteria-filled fluid is sheared is that the bacteria align and start collectively swimming. The local effects of each bacteria combine en masse to create a fluid that seemingly flows on its own. In the end, though, it’s the bacteria that are supplying that work. It certainly raises interesting prospects, though, for harnessing the power of bacterial superfluids. See the links below for more. (Image credit: M. Copeland, source; research credit: S. Guo et al., A. Loisy et al.; via Quanta; submitted by Kam-Yung Soh)
Every summer, as the ice melts, the waters of the Chukchi Sea off the Alaskan coast come alive with phytoplankton blooms. In satellite images like this one, they can look like abstract paintings formed from swirling colors. In the Chukchi Sea, two main currents collide. One, water from the Bering Sea, is cold, salty, and nutrient-rich. This is the preferred home to phytoplankton known as diatoms, which are responsible for some of the greenish hues seen here.
Coccolithophores, another variety of phytoplankton, prefer the warmer, less salty Alaskan coastal waters. Despite a relative lack of nutrients, the coccolithophores thrive, creating the milky turquoise color seen in the image. Knowing these characteristics of the phytoplankton, observing the growth of blooms over time may tell scientists about how the flows in these areas shift and change from year to year. (Image credit: NASA; via NASA Earth Observatory)
For some people, a musical tone is enough to induce vertigo and feelings of being drunk. These individuals often have a small hole or defect in the bone that surrounds the canals of the inner ear. Normally, the fluid inside these canals reacts when we rotate our heads, triggering a counterrotation of our eyes that helps stabilize the image on our retinas. But when there’s a defect in the bone surrounding the canal, certain acoustic tones may pump that fluid directly. The patient’s eyes then try to correct for a rotation that’s not occurring, thereby inducing dizziness and vertigo. (Image credit: M. Moiner; research credit: M. Iversen et al.; submitted by Marc A.)
Spend a summer afternoon floating in a kayak and chances are you’ll see some impressive aerial acrobatics from dragonflies. One of the dragonfly’s superpowers is its ability to fly backwards, which helps it evade predators and take-off from almost any orientation. To do this, the dragonfly rotates its body so that it is nearly vertical, thereby changing the direction it generates lift. In engineering terms, this is “force-vectoring,” similar to the techniques used by helicopters and vertical-take-off jets.
Scientists found that backwards-flying dragonflies could generate forces two to three times their body weight, in part due to the strong leading-edge vortices (bottom image) formed on the forewings. They also found that the hind wings are timed so that their lift is enhanced by catching the trailing vortex of the first pair of wings. Engineers hope to use what they’re learning from insect flight to build more capable flying robots. (Image and research credit: A. Bode-Oke et al., source; via Science)
Blocking blood vessels by creating embolisms is, under most circumstances, very bad. But researchers are exploring ways to fight cancer by intentionally and strategically creating these blockages. In gas embolotherapy, researchers inject fluid droplets, which can carry chemotherapy drugs, into the bloodstream. Once they circulate into a cancerous tumor, they use ultrasound to vaporize the droplet and create a gas bubble. Those bubbles lodge inside the capillaries of the tumor, starving it of fresh blood and trapping the chemotherapy drugs inside. It’s a one-two punch to the cancer. Without blood flow, the cancer cells die, and, since the cancer-killing drugs get mostly trapped inside the tumor, patients may require lower dosages and endure fewer side effects. The technique is currently in animal testing, but hopefully it will be a valuable therapy for human patients in the future. (Image credit: Chemical & Engineering News; research credit: Y. Feng et al.; via AIP)