FYFD

Tag: biology

  • Escaping the Limits of Viscosity

    Escaping the Limits of Viscosity

    For large creatures, it’s not hard to feel the evidence of someone else swimming nearby. But to tiny swimmers water is incredibly viscous and hard to move. These creatures have to swim very differently than their larger cousins, and evidence of their motion dies out quickly. But at least one microorganism,  Spirostomum ambiguum, has discovered a method for overcoming the limits of size and viscosity.

    The single-celled swimmer, when threatened, contracts its body in milliseconds, generating accelerations greater than those seen by fighter pilots. That acceleration is strong enough that it generates a burst of turbulence powerful enough to overcome the natural damping of its viscous surroundings. Within their colonies, S. ambiguum seem to use contraction to send out hydrodynamic signals to neighbors, who pass on the call to arms. To see the colonies in action, check out this previous article. (Image and research credit: A. Mathijssen et al.; via Physics Today; submitted by Kam-Yung Soh)

  • If You Teach a Goose to Fly

    If You Teach a Goose to Fly

    Scientists do all manner of odd things in the name of science. To teach bar-headed geese – birds capable of flying at the altitude of Everest – to fly in a wind tunnel, one group of researchers fostered a group of geese from the moment they hatched. They taught them to fly, first by chasing their bicycling parent and then following her on a motor scooter. Only then could they train the geese to fly in a wind tunnel designed to test how these birds manage to keep flying with only 30% of the oxygen found at sea level*.

    The birds’ secret, it turns out, is metabolic. As the oxygen dropped, so did the temperature of the geese’s blood. Hemoglobin, which binds oxygen in blood cells, is more efficient at lower temperatures, allowing the birds to get more oxygen. At the same time, though, their overall metabolism slowed down, meaning that they required less oxygen overall to function. Taken together, these adaptations make the geese excellent fliers in conditions most animals cannot tolerate. (Image and research credit: J. Meir et al.; via WashPo; submitted by Marc A.)

    * Occasionally I get comments pointing out that drag decreases with altitude, thereby making it easier to cut through the air. While this is true, I can say from my own experience of living and exercising at altitude that, for most of us, the effects of low oxygen levels far outweigh the savings in drag. It’s hard to appreciate a tiny drop in drag when your heart rate is sky high!

  • The Impressive Take-Off of Pigeons

    The Impressive Take-Off of Pigeons

    One reason that peregrine falcons are such amazing fliers is that their prey, pigeons, are no slouches in flight, either. Able to take off vertically and accelerate to 100 kph in two seconds, pigeons are pint-sized powerhouses. With this high-speed video, BBC Earth highlights the mechanics of this vertical take-off. Pigeons begin by bending their legs and jumping high enough that their first downstroke can extend fully and still clear the ground. That gives them a headstart on generating the force they need to propel themselves upward. 

    Note the way the pigeon’s wings move, sweeping from directly behind the bird’s back to a full extension in front of it. With the bird moving vertically, this motion tells us that it’s thrust – not aerodynamic lift – from the wingstroke that’s powering this take-off. In that sense, the pigeon is something like a Harrier jet, using the thrust of air downward to take off vertically. (Image and video credit: BBC Earth)

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    Feathered Fighter Jets

    Peregrine falcons are built for speed. They’ve been clocked at more than 380 kilometers per hour when diving. This video from Deep Look examines some of the features that make these birds of prey so fast, from the shape of their eyes to the tubercles in their nostrils that help them breathe during high-pressure dives. 

    Part of the falcon’s speed comes from its signature stoop, where it pulls in its wings to form a tight, streamlined shape. This reduces drag forces on the falcon, letting gravity pull it toward a high terminal velocity. But even with its wings extended, the falcon exudes speed and agility. Its wings form a sharp leading edge to cut through the air, with stiff, overlapping feathers that slice the flow. Compare this to the feathers of an owl, which specializes in silence rather than speed for catching its prey. (Video and image credit: Deep Look)

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    How Ant Stingers Work

    Anyone who’s felt the sting of a fire ant knows it only takes an instant for this species to deliver a painful blow. Scientists are uncovering why that is using some of the first-ever high-speed footage of ant stingers in action. Stingers are actually made up of multiple separate pieces, including a central stylet and a pair of lancets that move up and down along the stylet. This lancet motion pulls the stinger deeper and helps form and deliver droplets of venom. The back-and-forth motion helps ants release up to 13 venom droplets per second, a level of speed that’s key for some of its high-speed, small-scale battles. (Image and video credit: Ant Lab; research credit: A. Smith)

  • Testing Vesicles

    Testing Vesicles

    In biology, vesicles contain a liquid surrounded by a lipid membrane. The characteristics of that membrane – like its stiffness – can change over time in ways that indicate other changes. For example, vesicles carrying HIV become stiffer as they grow more infectious. In the past, to observe these properties scientists used atomic force microscopes, which require removing the vesicles from the liquid in which they naturally reside. That’s problematic because it potentially changes how the vesicle responds. 

    Now researchers have developed a new method: a microfluidic system that subjects vesicles to electric fields in order to deform them and measures their properties without removing them from their carrier fluid. This provides a faster and more reliable method of testing a vesicle’s deformation, capable of testing hundreds of samples at a time. (Image credit: Wikimedia; research credit: A. Morshed et al.; submitted by Eric S.)

  • Seeing the Song

    Seeing the Song

    We can’t always see the flows around us, but that doesn’t mean they’re not there. Audobon Photography Award winner Kathrin Swaboda waited for a cold morning to catch this spectacular photo of a red-winged blackbird’s song. In the morning chill, moisture from the bird’s breath condensed inside the vortex rings it emitted, giving us a glimpse of its sound. (Image credit: K. Swaboda; via Gizmodo; submitted by Joseph S and Stuart H)

  • Catching Fire

    Catching Fire

    Citrus fruits like oranges house tiny pockets of oil in their peels. When squeezed, the oils jet out in tiny micro-jets that are about the width of a human hair. Despite their small size, the jets reach speeds of about 30 m/s and quickly break into a stream of droplets. When exposed to the flame of a lighter, like in the animation above, those microdroplets combust easily, creating a momentary fireball used to augment some cocktails. For more on how the citrus peel generates these jets, check out this previous post. (Image credit: Warped Perception, source; research credit: N. Smith et al.)

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    Doing the Wave

    Not everything that behaves like a fluid is a liquid or a gas. In particular, groups of organisms can behave in a collective manner that is remarkably flow-like. From schools of fish to fire-ant rafts, nature is full of examples of groups with fluid-like properties. 

    One of the most mesmerizing examples are these giant honeybee colonies, which essentially do “the wave” to frighten away predators like wasps. Researchers are still trying to understand and mimic the way these groups coordinate such behaviors. Can even complicated patterns be generated by a simple set of rules an individual animal follows? That’s the sort of question active matter researchers investigate. Check out the video above to see a whole cliff’s worth of bee colonies shimmering. (Image and video credit: BBC Earth)

  • Dandelion Flight, Continued

    Dandelion Flight, Continued

    Not long ago, we learned for the first time that dandelion seeds fly thanks to a stable separated vortex ring that sits behind their bristly pappus. Building on that work, researchers have now published a mathematical analysis of flow around a simplified dandelion pappus. Despite their simplifications, the model captures the flow observed in the previous experiments (bottom image: experiments on left; model on right). 

    The model also allowed researchers to test various features – like the number of filaments in the pappus – and see how they affected the flow. Interestingly, they found that dandelion flight was most stable with about 100 filaments, which is right around the number of a typical pappus! (Image credits: dandelion – Pixabay, figure – P. Ledda et al.; research credit: P. Ledda et al.; via APS Physics; submitted by Kam-Yung Soh and Marc A.)