FYFD

Category: Research

  • Pluto’s Subsurface Ocean

    Pluto’s Subsurface Ocean

    Since the New Horizons probe visited Pluto in 2015, scientists have suspected that Sputnik Planitia (a.k.a. Pluto’s Heart), shown above, may hide a subsurface ocean. But it’s tough to explain how that ocean could stay warm enough to be liquid while the surface ice remains cold and viscous enough to support the variations in thickness we see. One theory cites the possibility of ammonia in the ocean, essentially serving as anti-freeze, but that would require much higher concentrations of ammonia than have been observed in comets – which, like Pluto, spend most of their time in the icy, frigid regions of the Kuiper Belt.

    A new study suggests another theory: a layer of gas-trapping hydrates between the liquid ocean and its icy cap. A thin layer of clathrate hydrates, as proposed by the authors, would trap gases like methane and create a thermally-insulating layer between a warm ocean and much colder ice cap. Because heat would struggle to cross the insulation layer, the water beneath would stay above the freezing point without the cold ice above leeching all of its warmth away.

    It would likely require future missions to Pluto or other potential ocean worlds to confirm the presence of such a hydrate layer, but, for now, the theory provides a possible new explanation for how icy objects like Pluto maintain liquids. (Image credit: NASA/JHU Applied Physics Laboratory/SwRI; research credit: S. Kamata et al.; via Gizmodo)

  • Guiding Particles with Chladni Patterns

    Guiding Particles with Chladni Patterns

    During the 19th century, Ernst Chladni and Michael Faraday independently explored the patterns formed by particles of different sizes placed on a vibrating plate. Faraday found that large particles accumulated at nodes of the plate, where there was no vertical vibration, whereas smaller particles moved toward anti-nodes, where air currents caused by the large vibration amplitude lifted them up.

    The situation becomes a little different if you submerge the vibrating plate in water. Then large, heavy particles gather at the anti-nodes. Drag keeps the particles on the plate, while acoustic forces and gravity conspire to move the particles horizontally toward the anti-nodes (top). Because anti-node patterns change with frequency, this actually provides a way to manipulate particle’s trajectories. The researchers demonstrated this by steering a particle through a maze (bottom) as well as by manipulating an entire swarm of beads. (Image and research credit: K. Latifi et al.; via Physics World; submitted by Kam-Yung Soh)

  • Giving Chocolate that Smooth Finish

    Giving Chocolate that Smooth Finish

    Anyone who’s tried to make chocolate confections at home can tell you that achieving that perfect smooth consistency isn’t easy. It was only after Rodolphe Lindt invented the process of conching in 1879 that anyone enjoyed smooth chocolate. Conching is what allows granular solids like sugar, milk and cocoa powders to mix with liquid cocoa butter into a smooth, homogeneous liquid. Although the process has been known for more than a century, it’s only recently that researchers have unraveled the underlying physics that enables it.

    One of the key parameters to conching is the a mixture’s jamming volume fraction; in other words, the point where the fraction of solid particles in the mixture is too high for it to flow freely. In the first stage of conching, the solid particulates and a small amount of liquid are stirred and slowly heated. The mechanical action of stirring breaks up aggregates and raises the jamming volume fraction. By the end of the dry conche, the mixture could flow, in theory, except that it fractures at a lower stress than what’s necessary to flow.

    At this point, chocolatiers add the remainder of the liquid ingredients. That infusion of moisture decreases the friction between solid particles and further raises the jamming volume fraction. With the system now far below that jamming point, the mixture transforms into a freely-flowing, smooth fluid. By understanding the intricacies of the process, scientists hope to reduce the energy necessary in chocolate production and similar industrial processes.  (Image credit: A. Stein; research credit: E. Blanco et al.; via Physics World; submitted by Kam-Yung Soh)

  • The Leidenfrost Crack

    The Leidenfrost Crack

    In 1756, Leidenfrost reported on the peculiar behaviors of droplets on surface much hotter than the liquid’s boiling point. Such droplets were highly mobile, surfing on a thin layer of their own vapor and were prone to loud cracking noises.

    More recently, scientists have observed that drops with an initially small radius eventually rocket off the hot surface whereas larger drops end their lives in an explosion (above) – the source of Leidenfrost’s crack. Now researchers have explained why drops of different sizes have such different fates. The key is their level of contamination.

    To reach the take-off radius, the drop has to evaporate a significant portion of its volume. For an initially-large drop, that’s tough because any solid contaminants in the drop will build up along the surface of the drop as it shrinks. Eventually, they restrict the liquid from evaporating, which thins the vapor layer the drop sits on. It sinks until a part of it touches the surface. The sudden influx of heat from the surface explosively destroys whatever remains of the drop. (Image and research credit: S. Lyu et al.; via Brown University; submitted by gdurey)

  • Wrapping Rivulets

    Wrapping Rivulets

    Tea lovers have long been frustrated by the tendency of liquid jets to adhere to solid surfaces – the so-called teapot effect that makes the last vestiges of every pour drip down the spout. By investigating the effect with vertical rods, researchers found that, at low enough flow rates, a liquid jet is able to adhere completely, forming a liquid helix that coils around the rod. The authors were also able to construct a mathematical model to capture the behavior. They concluded that both the wettability of a surface and the curvature of the solid are critical to determining whether or not a liquid jet will stick. (Image and research credit: E. Jambon-Puillet et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Inside an Evaporating Drop

    Inside an Evaporating Drop

    The evaporation of a simple droplet holds far more complexity than one would expect. If you look closely at the edge of the drop, there’s a tiny, beautiful display at work. It begins with small variations in surface tension at the contact line where solid, liquid, and gas meet. These could be caused by local temperature or concentration differences; either way, the gradient in surface tension creates a flow. It starts out as a series of microjets spaced evenly around the contact line (left). 

    As the microjets strengthen, they merge into larger and larger vortical structures (right). This kind of feature – large structures emerging from smaller ones – is known as an inverse cascade. Fluid dynamicists have traditionally studied the classic (turbulent) energy cascade, where kinetic energy moves from large scales into smaller ones, but researchers are beginning to recognize more situations where the inverse cascade occurs, such as in the storms of Jupiter. (Image and research credit: A. Ghasemi et al., source)

  • How Rain Can Spread Pathogens

    How Rain Can Spread Pathogens

    Rainfall can help spread pathogens from an infected plant to healthy ones. This transfer can happen both through droplets and by dry-dispersal of pathogen spores (top). When a raindrop hits a leaf, its initial spread triggers a vortex ring of air that can lift thousands of dry spores into a swirling trajectory (bottom). That boost in height carries spores beyond the slower wind speeds of the plant’s boundary layer and into faster air streams that disperse it toward healthy plants. (Image and research credit: S. Kim et al.)

  • Plant Week: Bunchberry Dogwood

    Plant Week: Bunchberry Dogwood

    The bunchberry dogwood, unlike its taller relatives, is a low-lying subshrub that spreads along the ground. But it sports some of the fastest action of any plant, requiring 10,000 frames per second to capture! When young buds form in the bunchberry flower, their four petals are fused, completely hiding the stamens. As the plant matures, the pollen-carrying stamens grow faster than the petals, causing them to peek out the sides of the bud. But the petals stay attached at the tip, holding the stamens in while pressure inside the stamens creates a store of elastic energy.

    When disturbed, the petals break loose and the stamens spring up and out. The anthers at their tips hold the pollen in place until the stamen reaches its maximum vertical velocity, at which point the anthers swing out to release the pollen upward. In essence, the flower works in the same manner as a trebuchet, flinging pollen with an acceleration 2,400 times greater than gravity. That’s enough to coat pollen onto nearby insects and to launch the remainder high enough for the wind to catch it. (Image and research credit: D. Whitaker et al., source; via Science News; submitted by Kam-Yung Soh)

    And with that, FYFD’s Plant Week is a wrap! Missed one of the previous posts? You can catch up with them here.

  • Plant Week: Citrus Jets

    Plant Week: Citrus Jets

    Bartenders and citrus lovers the world over are familiar with the mist of oil that bursts from a bent citrus peel. These microjets are about the width of a human hair, but they can spray at nearly 30 m/s in some citrus species. That’s an acceleration g-force of more 5,100, comparable to a bullet fired from a gun!

    The key to the jets is the structure of the fruit’s peel. Citrus fruits have a relatively thick, soft inner material, known as the albedo, which houses the oil reservoirs. The thin, stiff outer layer of the peel, called the flavedo or zest, covers that. When the peel is bent, the albedo compresses, increasing the pressure inside the oil reservoirs up to an additional atmosphere’s worth. Meanwhile, the flavedo is stretched. When that outer layer fails, it releases the oil pressure and a jet spurts out. For more on this work, including some awesome high-speed videos, check out my interview (starting at 2:59) with one of the authors in the video below. (Image and research credit: N. Smith et al.; video credit: N. Sharp and T. Crawford)

    FYFD is celebrating Plant Week all this week. Check out our previous posts on how moisture lets horsetail plant spores walk and jump, the incredible aerodynamics of dandelion seeds, and the ultra-fast suction bladderworts use to hunt.

  • Plant Week: Jumping Spores

    Plant Week: Jumping Spores

    You might think that plants are pretty stationary, but they have evolved a myriad of ways of moving, especially when it comes to spreading their seeds and spores. Shown above is the spore of the horsetail plant, a spherical pod with four, ribbon-like elators that are moisture-sensitive. When exposed to water, the elators curl around the spore, but as they dry out, they unfurl (top). Repeated cycles of this allows the spores to “walk” short distances (middle). And, if the elators deploy quickly, the spore can even “jump” (bottom). Researchers recorded jumps high enough for the spores to catch a breeze and disperse further. For similar moisture-driven plant action, check out this seed that buries itself! (Image and research credit: P. Marmonttant et al., source; via Science News; submitted by Kam-Yung Soh)

    We’re celebrating botanically-based physics all this week with Plant Week. Check out our previous posts on the ultra-fast suction of carnivorous bladderworts and the incredible flight of dandelion seeds.