FYFD

Tag: biology

  • Fluids Round-Up

    Fluids Round-Up

    New year, new (or renewed) experiments. This is the fluids round-up, where I collect cool fluids-related links, articles, etc. that deserve a look. Without further ado:

    (Video credit and submission: Julia Set Collection/S. Bocci; image credit: IRPI LLC, source)

  • Inside APS DFD 2015

    Inside APS DFD 2015

    What do shark scales, underwater robots, blood flow, and art have in common? They’re all a part of the latest FYFD video! Check out my behind-the-scenes look at the latest American Physical Society Division of Fluid Dynamics meeting. Meet the researchers and find out about the science everyone was talking about! (Image/video credit: N. Sharp)

  • Collecting Water in the Desert

    Collecting Water in the Desert

    Desert-dwelling plants like cactuses have to be efficient collectors of water. Many types of cactus are particularly good at gathering water from fog that condenses on their spines. Droplets that form near a spine’s tip move slowly but inexorably toward the base of the spine so that the cactus can absorb them. The secret to this clever transport lies in the microstructure of the spine’s surface. The

    Gymnocalycium baldianum cactus, for example, has splayed scales along its spines. Capillary interactions with the scales result in differences in curvature on either side of the droplet. Curved fluid surfaces generate what’s known as Laplace pressure, with a tighter radius of curvature causing a larger Laplace pressure. Because the curvature of the droplet varies from the base side to the tip side of the spine, the difference in Laplace pressures across the droplet creates a force that drives the droplet toward the spine’s base. (Image credit: C. Liu et al., source)

  • Nectar-Eating Bats

    Nectar-Eating Bats

    Nectar-eating bats have evolved to use several methods to drink. Some bats, like the Pallas’ long-tongued bat (top), use a lapping method. Hair-like papillae on the bat’s tongue increase the contact area with the nectar, helping to draw the fluid up in viscous globs as the bat repeatedly dips its tongue into the nectar. The orange nectar bat (middle and bottom), in contrast, has a tongue with a long central groove. This bat’s tongue stays submerged as it drinks. Researchers hypothesize that muscle action along the tongue, combined with capillary action in the narrow groove, allow the bat to actively pump nectar up to its mouth. It’s worth noting that the edges of the bat’s tongue do not curl around to touch, so the bat is definitely not using suction as one would with a straw. (Image credit: M. Tschapka et al., source)

  • How Plants Move

    How Plants Move

    Though most plants don’t move at speeds that we humans notice, many plants are remarkably active, as seen in the timelapse animations above. Much of this motion is driven by water flow inside the plant. The two plants above are phototropic–they move in response to light. The motion is actuated via a specialized motor cell called the pulvinus, which is located at the base of the leaf where it meets the stem. Unlike animal cells, plant cells have stiff outer walls that allow them to maintain an internal pressure–or turgor pressure–that differs from the outside environment. In fact, it’s not unusual for a plant’s cell to hold a pressure equivalent to 5 atmospheres! The plant manipulates this turgor pressure by controlling the transport of ions across cell membranes. Pump more ions into a cell, and osmosis will cause water to flow into the area of high solute (ion) concentration. This causes the cell to swell and raises the turgor pressure, resulting in the plant’s leaf moving. (Image credit: L. Miller and A. Hoover, source; additional research credit: J. Dumais and Y. Forterre)

  • Controlling Droplet Bounce

    Controlling Droplet Bounce

    Water repellent, or hydrophobic, surfaces are common in nature, including lotus leaves, many insects, and even some geckos. These hydrophobic surfaces typically gain their water-repelling ability from extremely tiny nanoscale structures in the form of tiny hairs or specially textured surfaces. But, while the nanoscale structures impart superhydrophobicity, researchers have found that larger macroscale structures can improve water-repellent characteristics by reducing a drop’s time of contact with the surface. A smaller contact time means less chance of contamination on self-cleaning surfaces. It’s also helpful in preventing water from freezing on contact to cold surfaces – valuable, for example, in protecting airplane wings’ leading edges from icing over. This combination of nanoscale and macroscale, water-repelling structures can be found in nature, too, such as on the wings of butterflies, which must quickly shed water in order to fly. (Image credits: K. Hounsell et al.; A. Gauthier et al., source video)

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    Leaping Mobulas

    Mobula rays engage in some pretty incredible aerial acrobatics. This species of ray, second only to manta rays in size, can jump up to 2 meters into the air. Large groups of mobula rays will engage in this behavior, including both males and females, but it remains unclear to scientists exactly what purpose the jumping serves. It may be a form of communication, which might explain the rays’ apparent preference for belly flopping. By striking the water surface with as much of their body as possible simultaneously, the rays generate both a large splash and a concussive clap that carries through the water. (Video credit: BBC; via J. Hertzberg)

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    The Upside-Down Jellyfish

    The upside-down jellyfish Cassiopea lives along the sea bottom in coastal regions. As its name suggests, the jellyfish rests upside-down with its bell against the sea floor and its frilly oral arms pointed upward. This jellyfish is a filter feeder, and it draws water up and through its arms by pulsing its bell. The video above visualizes this flow using dye. Each pulse propels fluid up through the arms and draws in fresh water from the surroundings. The frilly arms break up any large vortices from the pulsed flow and diffuse the filtered water as it moves upward. (Video credit: Applied Fluid Mechanics Laboratory at Oklahoma State University)

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    Rain-spread Pathogens

    Like humans, plants can spread pathogens to one another. Although scientists had observed correlations between rainfall and the spread of diseases among plants, this study is one of the first to look at the fluid dynamics of leaf and rainfall interaction. When a raindrop hits a leaf, it doesn’t simply splash as it would against an immobile surface. The impact of the drop deforms the leaf, and the plant’s rebound significantly affects the trajectory and size of the resulting droplets. Depending on factors like the leaf’s stiffness, a large drop, carrying many pathogens, may rebound and splatter onto a neighboring leaf. Other leaves tend to catapult out many smaller droplets, which may fly farther afield but carry fewer pathogens. For more, check out the press release or the original research paper. (Video credit: Massachusetts Institute of Technology; research credit: Bourouiba Research Group)

  • Why Joints Pop

    Why Joints Pop

    Joints like our knuckles are lubricated with liquid called the synovial fluid. When manipulated, these joints can pop or crack audibly. For half a century, researchers have thought the cracking sound joints under tension make was the result of bubbles in the synovial fluid collapsing. But a new cine magnetic resonance imaging (MRI) study shows that the sound is generated during bubble inception and that the cavity persists after the sound. When the bones of the joint are pulled, viscous forces resist their separation. With enough force, the joints separate suddenly, causing a pressure drop in the synovial fluid that forms a vapor-filled cavity in the joint. According to the real-time MRI observations, this is when the sound is generated. The cavity does eventually dissipate, they found, but only well after the pop. The whole joint-cracking process is consistent with the tribonucleation mechanism seen in machinery.  (Image credit: G. Kawchuk et al.; GIF via skunkbear, source video)