FYFD

Tag: biology

  • Sharkskin Fluid Dynamics

    Sharkskin Fluid Dynamics

    Sharks have evolved some incredible fluid dynamical abilities. Instead of scales, their skin is covered in microscopic structures called denticles. To give you a sense of size, each denticle in the black and white image above is about 100 microns across. Denticles are asymmetric and overlap one another, creating a preferential flow direction along the shark. When water tries to move opposite the preferred direction, the denticles will bristle, like in the animation above. The bristled denticles form an obstacle for the reversed flow without any effort on the shark’s part. Since local flow reversal is an early sign of separation, researchers theorize that this bristling tendency prevents flow along the shark’s skin from separating. Keeping flow attached, especially along the shark’s tail, is vital not only to the shark’s agility but to keeping its drag low. Researchers have even begun 3D printing artificial shark skin to try and harness the animal’s hydrodynamic prowess. For much more shark-themed science, be sure to check out this week’s “Several Consecutive Calendar Days Dedicated to Predatory Cartilaginous Fishes” video series by SciShow, It’s Okay to be Smart, The Brain Scoop, Smarter Every Day, and Minute Physics. (Image credits: J. Oeffner and G. Lauder; A. Lang et al.; original video; jidanchaomian)

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    Why Do Joints Pop?

    Joint popping is one of those things some people revel in and others detest. What you may not have realized, though, is that fluid dynamics are responsible for the sound. Joints contain a non-Newtonian liquid called synovial fluid to lubricate them. When you manipulate the joint to stretch it, pressure in the fluid drops and gases dissolved in the synovial fluid are released, forming a cavitation bubble. The creation and collapse of this bubble are what cause the audible popping. (Video credit: SciShow)

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    Catching Prey

    Over at Smarter Every Day, Destin has a new video, this time about how fish eat, which involves some pretty awesome physics. Instead of accelerating their entire body to close the distance to prey, fish thrust their jaws forward. As they do, they open their mouth, expanding the volume there and lowering the pressure. This causes water to flow into their mouth, pulling the prey with it. But the water has momentum, which would push the fish backward. To prevent this, the fish then opens its gills, allowing the water to rush back out while trapping the prey in its mouth. Be sure to check out Destin’s video so that you can see the process in high-speed. (Video credit: Smarter Every Day)

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    Blood Flow Simulations

    Though we may not often consider it, our bodies are full of fluid dynamics. Blood flow is a prime example, and, in this video, researchers describe their simulations of flow through the left side of the heart. Beginning with 3D medical imaging of a patient’s heart, they construct a computational domain – a meshed virtual heart that imitates the shape and movements of the real heart. Then, after solving the governing equations with an additional model for turbulence, the researchers can observe flow inside a beating heart. Each cycle consists of two phases. In the first, oxygenated blood fills the ventricle from the atrium. This injection of fresh blood generates a vortex ring. Near the end of this phase, the blood mixes strongly and appears to be mildly turbulent. In the second phase, the ventricle contracts, ejecting the blood out into the body and drawing freshly oxygenated blood into the atrium. (Video credit: C. Chnafa et al.)

  • Tear Films

    Tear Films

    The human eye has a thin tear film over its surface to maintain moisture and provide a smooth optical surface. The film consists of multiple layers: a lipid layer at the air interface to decrease surface tension and delay evaporation; an aqueous middle layer; and an inner layer of hydrophilic mucins that keep the film attached to the eye. The entire film is a few microns thick, with the lipid layer estimated to be only 50-100 nm thick and the mucin layer just a few tenths of a micron. The aqueous portion of the tear film is supplied from the lacrimal gland in the corner of the eye. In the animation above, the fresh aqueous fluid is fluorescent. It gathers in the corner of the eye several seconds after a blink due to reflex tearing. The tear fluid then flows around the outer edges of the eye until the subject blinks and the fresh tear gets distributed throughout the film. (Research credit: L. Li et al.; original video)

  • Pitcher Plant Fluid Dynamics

    Pitcher Plant Fluid Dynamics

    Carnivorous pitcher plants owe much of their efficacy to the viscoelasticity of their digestive fluid. A viscoelastic fluid’s resistance to deformation has two components: the usual viscous component that resists shearing and an elastic component, often derived from the presence of polymers, that resists stretching – kind of like a liquid rubber band. It’s the latter effect that’s important when it comes to the pitcher plant trapping insects. When a fly or ant falls into the liquid within the plant, it will flail and try to swim, thereby straining the fluid. In part © of the image above, you can see how long fluid filaments stretch as the fly moves; this is because the digestive fluid’s extensional viscosity, the elastic component, is 10,000 times larger than its shear viscosity, the usual viscous component, for motions like the fly’s. This viscoelastic fluid is so effective at trapping insects that, as seen in part (b) above, it has to be diluted by more than 95% before insects can escape it! (Image credit: L. Gaume and Y. Forterre)

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    Mushrooms Make Their Own Breeze

    Mushrooms don’t rely on a stray breeze to spread their spores; they generate their own air currents instead. The key is evaporation. The mushroom cap contains large amounts of water, and, as this water evaporates, it cools the mushroom and the air next to it. This cool air is denser than the surrounding air, and so tends to spread out and convect. At the same time, though, the water vapor that evaporated from the mushroom is less dense than nearby air, which helps it rise. This combination of spreading and rising air carries spores away from the mushroom cap and, as seen in the video above, can combine to form beautiful and complex currents that spread the spores. (Video credit: E. Dressaire et al.)

  • Fluids Round-up – 20 October 2013

    Fluids Round-up – 20 October 2013

    Some very cool fluids applications in this week’s fluids round-up. On to the links!

    ETA: I somehow forgot to include the first of the upcoming APS presentations to get wide media recognition: Law of Urination, which has shown up all over the place.

    (Photo credit: San Diego Air and Space Museum Archive/In Focus)

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    Studying Coughs

    Bioaerosols–tiny airborne fluid droplets generated by coughing or sneezing–are a major concern for the spread of contagions like influenza. It may be possible, however, to mitigate some of these effects by manipulating biological fluid properties. The video above shows an experimental model of a cough, complete with the generation of bioaerosols from some fake human lung mucus. Contrast this with a cough where the model’s mucus has been treated to increase its viscoelasticity. The treated mucus generates substantially fewer droplets during a cough. The results suggest that drugs that increase viscoselasticity of biofluids may help stem the spread of disease. (Video credit: K. Argue et al.; research credit: M. D. A. Hasan et al.)

  • Seed-Ejection via Raindrop

    [original media no longer available]

    We don’t often think of plants as using fluid dynamics aside from capillary action drawing water from their roots, but many plants also use fluid dynamics to disperse reproductive materials.  This high-speed video explores the efficacy of splashing raindrops at ejecting seeds from different blossoms. (Video credit: G. Amador et al)