FYFD

Tag: science

  • Wet Masks Block Droplets Better

    Wet Masks Block Droplets Better

    As wearing face masks for long periods has become more typical, you may have wondered whether a soggy mask offers less protection. All masks — cloth, surgical, and N-95s — get moist from their wearer’s breath. A recent study indicates this isn’t a cause for alarm, though.

    Researchers looked at how relatively high-speed droplets (like those from a cough or sneeze) impact dry and wet masks. These high-speed droplets can break into smaller droplets upon impact with a mask layer. The more layers a mask has, the fewer droplets make it through. But even for single-layer masks*, a moistened mask layer lets fewer droplets through. So you don’t have to worry if it’s a little humid in there. Your mask is still working! (Image credit: top – V. Davidova, other – S. Bagchi et al.; research credit: S. Bagchi et al.; via APS Physics)

    * To be clear, you should be wearing masks that are more than a single layer thick. Personally, I’m still only going into indoor public spaces in an N-95 at this point.

    Droplet penetration through a mask. Top row: dry, single layer mask. Middle row: wet, single layer mask. Bottom row: wet, triple layer mask.
    Droplet penetration through a mask. Top row: dry, single layer mask. Middle row: wet, single layer mask. Bottom row: wet, triple layer mask. When wet, masks permit fewer droplets through.
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    Breaking Compound Ligaments

    When pulled, viscous liquids stretch into ligaments that thin and then break into droplets. In this video, researchers investigate how these ligaments break up, depending on their composition. The initial views show the break-up of a water-glycerol ligament (Image 1) and an oil ligament (Image 2). By placing a water droplet inside oil, the researchers got quite different results, including oil-encapsulated droplets (Image 3). The technique could be useful for making compound droplets, even with more than two components. (Image and video credit: V. Thiévenaz and A. Sauret)

  • “In Flight”

    “In Flight”

    Photographer Mark Harvey captured these stunning portraits of birds in flight. From acrobatic songbirds to soaring raptors, the images show the incredible morphology of a bird’s wing during flight. Most birds are constantly changing their wing shape to generate lift, change trajectory, and stabilize their flight. Note the separation between the flight feathers in all of these birds. Those gaps are thought help break up the birds’ wingtip vortices, thereby reducing their induced drag. You may also notice that the owls in Harvey’s photos have feathers that look a bit different from the other birds; owls have adaptations in their feathers that help damp out turbulence, which makes them quieter in flight. Prints of Harvey’s images are available on his website. (Image credit: M. Harvey; via Colossal 1, 2)

  • Triple Leidenfrost Effect

    Triple Leidenfrost Effect

    Droplets can skitter across a hot surface on a layer of their own vapor, thanks to the Leidenfrost effect. If two Leidenfrost droplets of the same liquid collide, they merge immediately. But that doesn’t always happen with two dissimilar liquids. A new study looks at how dissimilar Leidenfrost droplets collide. The researchers found that these drops can bounce off one another repeatedly before their eventual merger (Image 1).

    Just as a vapor layer prevents the drops from touching the hot plate, a vapor layer forms between them when they collide, preventing contact (Image 2). Because of these three distinct areas of Leidenfrost vapor (one beneath each drop and one between the drops), the researchers call this the triple Leidenfrost effect.

    Eventually, the more volatile (in other words, easily evaporated) drop shrinks to a size similar to its capillary length, at which point the drops merge. If the boiling points of the two liquids are vastly different, the merger can be explosive (Image 3). (Image and research credit: F. Pacheco-Vázquez et al.; via APS Physics)

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    Insects Taking Flight

    As awkward as they look sometimes, insects are amazing fliers. In this video from Ant Lab, we see all kinds of insects taking flight. Some, like the mantis, execute flying leaps to get in the air, whereas weevils begin flapping from a tripod stance. Watching these videos I’m always struck by how flexible insect wings are. They flex far more than I would imagine. And these insects have a lot of excess lift. Just check out that carrion beetle taking off despite being covered in mites! (Image and video credit: Ant Lab)

  • Jovian Circulation

    Jovian Circulation

    Jupiter‘s atmosphere remains quite mysterious, due to our limited ability to measure the depths of the gas giant’s clouds. But measurements from the Juno spacecraft are continuing to shape researchers’ understanding of our massive neighbor. By tracking ammonia distributions in Jupiter’s belts and zones, a team has found a series of circulation cells similar to the Ferrel cells of Earth’s midlatitudes.

    Unlike the stronger Hadley cells and polar cells, Earth’s Ferrel cells are relatively weak. They’re driven by turbulence and the motion of the circulation cells to the north and south. The Northern and Southern hemispheres each have one Ferrel cell. In contrast, Jupiter — with its larger size and higher rotation rate — boasts eight Ferrel-like cells in each hemisphere! (Image and research credit: K. Duer et al.; via Universe Today; submitted by Kam-Yung Soh)

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    Filming the Brinicle

    It may have been 10 years since the BBC filmed the first timelapse of a growing brinicle, but the footage is just as amazing now as it was then! This video gives you the behind-the-scenes story of what it took to capture this natural wonder under the Antarctic ice. It’s incredible to see the shots of sinking brine streaming off the brinicles, too. The difference in density (and thus refractive index) of the brine and the ocean water is substantial enough that your eye can actually pick them out as separate fluids. I once went snorkeling in an area with similarly varied salinity and it was completely bizarre watching everything suddenly go wavy and blurry as I swam. (Image and video credit: BBC)

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    “The Green Reapers”

    This short film from artist Thomas Blanchard focuses on carnivorous plants and their prey. These plants — including Venus fly traps, sundews, and pitcher plants — rely on fluids both to attract and capture their prey. Plants like the Venus fly trap build turgor pressure in their cells to move and prop open their leaves. Once triggered, a mechanical release allows the fluid pressure to snap the trap closed. Sweet-smelling fluids invite insects in, only to become nightmarishly difficult to escape once prey try to unstick themselves from the highly viscoelastic liquids. (Video and image credit: T. Blanchard; via Colossal)

  • Driven From Equilibrium

    Driven From Equilibrium

    With the right application of force, liquids can take on shapes that defy our intuition. Here researchers sandwiched two immiscible oils between glass slides and applied an electric field. Because the two oils have different electrical responses, charges build along the interface between them. These charges lead to non-trivial electrohydrodynamic flows and a multitude of bizarre shapes. They observed polygonal droplets, streaming droplet lattices, and spinning filaments among others. As long as the electric field remains on, the wild behaviors continue; once the field is turned off, the oils relax back to typical, rounded drops. (Image, video, and research credit: G. Raju et al.; via Physics World)

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    The Bubbly Escape

    Sometimes experiments don’t work as planned and, instead of answers, they lead to more questions. In this video, we see an experiment looking at an air bubble trapped beneath a cone. It’s the same situation you get by holding a mug upside-down in a sink full of water but with inclined walls. As the cone moves downward, it squeezes the trapped air bubble. A film of air gets pushed along the walls of the cone, eventually forming finger-like bubbles that wrap around the edge of the cone and get entrained into the vortex ring outside the cone.

    Clearly, there is some kind of instability that drives the air bubble to form these fingers rather than spreading uniformly. But the big question is which one? Is this a density-driven Rayleigh-Taylor instability caused by air getting pushed into water? Or is it a Saffman-Taylor instability causes by the less viscous air forcing its way into the more viscous water? What do you think? (Image and submission credit: U. Jain)

    A bubble trapped beneath a cone gets distorted and squeezed as the cone accelerates downward.