In many ways, smell is a strange sense. The very act of sniffing – pulling air and odor molecules into our noses – changes what remains behind in a way that sight and sound do not. Humans aren’t great sniffers, but dogs have an exquisite sense of smell, and in this video, Deep Look describes how and why that is. From special scent organs to their experimental protocols, dogs are well-adapted to reading the world by smell. (Image and video credit: Deep Look)
The skinny, freshwater alligator gar can grow to more than 2 meters in length, giving it a distinct resemblance to its namesake. But this fish’s history traces back more than a hundred million years to the Early Cretaceous. And a new (pre-printed) study, combining live observations and numerical models built from CT-scans, is shedding new light on how the gar and its prehistoric ancestors feed.
The gar uses a lateral strike (top) to come at its prey from the side. But hydrodynamically speaking, that’s a tough way to catch dinner. As soon as the gar’s snout accelerates toward its prey, it pushes a bow wave ahead of it, like an early warning signal. To counter that disadvantage, the gar has a complex bone structure in its skull (bottom) that helps it generate suction. Note how the gar’s jaw and throat open sequentially from front to back. Each expansion sucks in water, and by timing them just right, the gar produces suction throughout its entire attack. The bow wave warning does its prey no good if both are already getting sucked into the gar’s mouth! (Image and research credit: J. Lemberg et al., bioRxiv pre-print; via Science; submitted by Kam-Yung Soh)
Hagfish – an eel-like species – are known for their prodigious slime production, which helps them escape predators (and, in some cases, seriously muck up highways). Part of the hagfish’s slime consists of ~10 cm fibers that the creature deploys in tiny skeins (bottom) only a hundred microns across. To form the viscoelastic slime that thwarts its predators, those skeins of fiber have to unravel and do so in only tenths of a second. A new study shows that viscous drag plays a major role in that unraveling.
Most fish use a suction method to catch prey. In the hagfish’s case, that does the predator more harm than good because the very flow it creates to try and catch the hagfish pulls the slime skein apart and helps the slime expand 10,000 times in volume, creating a mess that chokes the gills of the attacking fish. (Image credit: top – L. Böni et al.; bottom – G. Choudhary et al., source; research credit: G. Choudhary et al.; via Ars Technica; submitted by Kam Yung Soh)
As pilots can tell you, flying near the ground (or an open expanse of water) gives one an aerodynamic boost. Essentially, the surface acts like a mirror, reflecting and dissipating the wingtip vortices that create downwash. That reduces the power necessary to fly, as long as you’re flying within about a wingspan of the surface.
Theoretically, flapping fliers like bats and birds should also benefit from this ground effect, but measurements have been hard to come by. A new study using bats trained to fly in a wind tunnel provides some of the first detailed measurements of ground effect for flapping animals. The researchers found a 29% reduction in the power necessary for flight when in ground effect compared to being out of it! That’s twice the savings predicted by modeling, meaning we still have a ways to go to accurately capture the physics of flapping flight under these circumstances.
Such a substantial savings also strengthens arguments for flight developing from the ground up. Using ground effect, surface-dwelling animals could have evolved flight gradually, taking advantage of the energy savings offered by sticking close to the surface. (Image and research credit: L. Johansson et al.; submitted by Marc A.)
The sharpshooter is a small, sap-sucking insect capable of consuming more than 300 times its body weight in fluid each day. To sustain that level of intake, the insect also has to have a robust mechanism for expelling excess fluid, and that particular talent has earned the insect the nickname of the “pissing fly”. Together a group of sharpshooters can expel enough fluid to imitate rain (top).
Individually, the insects form a droplet on hydrophobic hairs near their anus. Once the droplet is large enough, those hairs bend like a spring, and the droplet gets catapulted off the insect with an acceleration greater than 20g. That makes it among the fastest reactions in the natural world – more than twenty times the acceleration of a cheetah. Understanding this mechanism is valuable for engineers building robotics as well as for finding ways to counter the agricultural menace the sharpshooters present when it comes to spreading diseases among infected crops. (Image and video credit: E. Challita et al.; via WashPo; submitted by Marc A.)
Few flows are more integral to our well-being than blood flow through the heart. Over the course of our lives, our hearts develop from a few cells pushing viscous blood through tiny arteries to the muscular center of a vast circulatory network, capable of powering us through incredible physical feats. What’s most astonishing about all this is that the heart goes through all these changes and adaptations without ever pausing.
Peering into the heart to see it in action is difficult, but researchers today are combining imaging techniques like CT and MRI with computational fluid dynamics to build patient-specific heart models. Not only does this help us understand hearts in general; it’s paving the way toward predicting how a specific treatment may affect a patient. Imagine, for example, being able to simulate and compare different models of an artificial heart valve to see which will work best for a particular patient. We’re not to the point of doing so yet, but it’s a very real possibility in the future.
To see some examples of predicted and measured heart flows, check out this video by J. Lantz. In the meantime, happy Valentine’s Day! (Image credits: Linköping University Cardiovascular Magnetic Resonance Group, video source; via Another Fine Mesh)
Swallowing – whether of food, beverage, or medication – is an important process for humans, but it’s one many struggle with, especially as they age. To help study the physics behind swallowing, one research group has built an artificial mouth and throat model, shown in the bottom row of images. The model uses rollers to imitate the wave-like motion of swallowing.
In our mouths, chewed food typically combines with saliva to form a soft ball we can move from our tongue and down our throat with a series of reflex actions. How easily we swallow something depends on its flow properties, our saliva, shape, and more.
In their early studies of model swallowing, researchers have focused on what it takes to swallow pills (suspended in liquid). What they found is probably consistent with your own experience: smaller pills are easier to swallow than large ones, and elongated pills are easier to swallow than round ones of the same volume. That seems to be a function of elongated pills’ smaller cross-section when aligned with flow going down the throat. As the research continues, scientists hope to explore what can be done to make food easier to swallow for those who struggle with it. (Image credits: meal – D. Shevtsova; model – M. Marconati; via APS Physics; submitted by Kam-Yung Soh)
We often imagine that collective motion creates an advantage – that the schooling fish and flocks of birds gain something from this behavior – but that’s not always the case. Above, you see nematodes moving through a thin liquid layer. Random collisions occasionally bring the nematodes into contact, and once that happens, surface tension holds them together with a force that exceeds what their muscles can supply. Essentially, they move together for the same reason that Cheerios clump together in your cereal bowl. But despite being stuck alongside one another, there’s no change in how the nematode moves. It sees neither an advantage nor a disadvantage from being attached to its neighbor. (Image and research credit: S. Gart et al., source)
This post completes our series on collective motion. Check out the previous posts about honeybee waves, how crowds are like sand, the fluid properties of worms, and why a lack of randomness makes predicting group behaviors hard.
Giant honeybees live in huge open nests. To protect themselves, they’ve developed a mesmerizing wave-like defense known as shimmering. When shimmering, the bees in a hive, beginning from a distinct spot, will flip over to expose their abdomens. Taken together, this creates large-scale patterns like those seen above.
Scientists have connected the behavior to the presence of wasps that prey on the bees. It seems that shimmering helps to repel the wasps without putting individual bees in danger. If shimmering doesn’t ward off the wasps, the bees can also use their flight muscles to heat the area around the intruder to a wasp-lethal temperature – or, individuals bees can sacrifice themselves by stinging the wasp. (Image credit: Beekeeping International, source; research credit: G. Kastberger et al.; via Gizmodo)
This post is part of our series on collective motion. Check out our previous posts about how crowds are like sand, the fluid properties of worms, and why a lack of randomness makes predicting group behaviors hard.
Although most animals are more solid than fluid, what happens when you put many of them together can be strikingly fluidic. Above you see the black aquatic worm, Lumbriculus variegatus, which must keep moist to stay alive. An individual worm will die within an hour of being removed from the water, but, in a group, the worms can survive far longer. They do so, in part, by acting like a viscoelastic fluid, a material with both solid (elastic) and fluid (viscous) properties.
In small groups, the worms squirm tightly together to minimize their collective surface area and prevent themselves from drying out. But in larger groups, the worm blobs begin sending out feelers, searching for more advantageous circumstances. In the top image, you can see this causes three of the blobs to ultimately merge into an even bigger one. The worm collective can also “liquify”, allowing the blob to change shape and tackle obstacles like flowing through a pipe. (Image and research credit: Y. Ozkan-Aydin et al.; via Science)
This is the second post in our series on collective motion. Check out the first post here.