FYFD

Category: Research

  • The Great Red Spot’s Cycle

    The Great Red Spot’s Cycle

    First spotted by humanity in 1664, Jupiter‘s Great Red Spot is a seemingly endless storm. Strictly speaking, there is debate as to whether observations prior to 1831 were of the same storm, but there’s no denying that the storm has raged unabated since regular observations began in the first half of the nineteenth century. Despite its longevity, the Great Red Spot is not unchanging. Overall, its major axis is shrinking, making the storm more circular over time. The storm also has a 90-day cycle in which its size, shape, and brightness vary, as seen below. Researchers note that the changes are relatively subtle — at least to the eye — but now that they’ve been identified, it may be possible to use amateur astronomers’ data to track these variations more closely. (Image credits: GRS – K. Gill/NASA, snapshots – A. Simon et al.; research credit: A. Simon et al.; via Gizmodo)

    Over a 90 day cycle, Jupiter's Great Red Spot oscillates in size, shape, and other characteristics.
    Over a 90 day cycle, Jupiter’s Great Red Spot oscillates in size, shape, and other characteristics.
  • Self-Cleaning With Salt Critters

    Self-Cleaning With Salt Critters

    Even freshwater contains trace salts and minerals that cause scaly buildups as they evaporate. Getting rid of the scale usually requires toxic chemicals and/or lots of scrubbing, neither of which are desirable at the industrial level. At the same time, we’re extremely limited in the amount of freshwater that we have available; only about 1% of Earth’s water is liquid and fresh. If we could use salt water in more industrial processes, that would preserve freshwater for drinking and agriculture. But how do we tackle the scaly buildup?

    (A) On microtextured surfaces, salt from evaporating drops can work its way into the gaps, destroying the superhydrophobicity of the surface. (B) In contrast, nanotextured surfaces give the salt nowhere to adhere, resulting in "salt critters" that grow upward and detach.
    (A) On microtextured surfaces, salt from evaporating drops can work its way into the gaps, destroying the superhydrophobicity of the surface. (B) In contrast, nanotextured surfaces give the salt nowhere to adhere, resulting in “salt critters” that grow upward and detach.

    Enter “salt critters.” Researchers found that when salt water evaporated from microtextured surfaces designed to shed water, salt would eventually build up in the gaps, breaking the hydrophobic effect and allowing scale to build up. In contrast, a nanotextured surface left nowhere for the salt to adhere. On these surfaces, evaporating salt water built jellyfish-like salt critters that rose from the surface and, eventually, broke off and rolled away, leaving the surface pristine. (Image credit: S. McBride; research credit: S. McBride et al.; via Physics Today)

  • Waves Break Up Floating Rafts

    Waves Break Up Floating Rafts

    Small particles can float on a liquid, held together as a raft through capillary action. But those rafts — like the tea skin below — break up when waves jostle them. In this study, researchers looked at how standing waves broke up a raft of graphite powder. Although the raft’s break-up resembles fields of sea ice breaking apart, the researchers found that different mechanisms were responsible. In their experiment, waves pushed and pulled horizontally at the raft, causing it to fracture. But that push-and-pull is negligible in sea ice, where sheets instead break from the up-and-down motion of waves vertically bending the ice. Nevertheless, the new insights are valuable for various biofilms and some ice floes. (Image and research credit: L. Saddier et al.; via APS Physics)

    The skin atop a cup of tea breaks up into polygons after stirring with a spoon.
    The skin atop a cup of tea breaks up into polygons after stirring with a spoon. Although the effect resembles sea ice breakup, the specific wave mechanism differs.
  • Breaking in Rogue Seas

    Breaking in Rogue Seas

    Many models for forecasting ocean waves simplify the physics by assuming that waves are essentially two-dimensional, like a long breaker heading toward shore. But in the open ocean, waves often come from more than one direction; crossing seas are a good example. When waves from different directions combine, a recent study shows, the resulting wave can grow far larger and steeper than expected. These monstrous rogue waves are especially dangerous for offshore infrastructure like oil rigs and wind turbines, which must be built to withstand rare but extreme waves. (Image credit: O. Мороз; research credit: M. McAllister et al.; via Gizmodo)

  • “Immersion”

    “Immersion”

    Some seabirds, including gannets and boobies, feed by plunge diving. From high in the air, they fold their wings and dive like darts into the water, impacting at speeds around 24 m/s to help them reach the depths where their prey swim. With their narrow beaks and necks, the critical moments in this feat come when the bird’s head is submerged but its body remains out of the water. At this point, the bird’s head is decelerating quickly and its body is still moving at full speed; if the neck cannot withstand this combination of forces, it will buckle.

    But plunge divers, it turns out, have a secret weapon that helps them handle impact: their head shape. A study of water entry dynamics using 3D-printed models of birds’ heads found that plunge divers have a shape that increases the amount of time it takes to enter the water. The impact forces stretch out over that longer period of contact, which also stretches out the time it takes for the bird to reach its maximum deceleration. The end result? That extended contact time protects birds from unsafe levels of deceleration, just like a crumple-zone in a crashing car keeps its occupants from experiencing the worst decelerations. (Image credit: K. Zhou/BPOTY; research credit: S. Sharker et al.; via Colossal)

  • Slushy Snow Affects Antarctic Ice Melt

    Slushy Snow Affects Antarctic Ice Melt

    More than a tenth of Antarctica’s ice projects out over the sea; this ice shelf preserves glacial ice that would otherwise fall into the Southern Ocean and raise global sea levels. But austral summers eat away at the ice, leaving meltwater collected in ponds (visible above in bright blue) and in harder-to-spot slush. Researchers taught a machine-learning algorithm to identify slush and ponds in satellite images, then used the algorithm to analyze nine years’ worth of imagery.

    The group found that slush makes up about 57% of the overall meltwater. It is also darker than pure snow, absorbing more sunlight and leading to more melting. Many climate models currently neglect slush, and the authors warn that, without it, models will underestimate how much the ice is melting and predict that the ice is more stable than it truly is. (Image credit: Copernicus Sentinel/R. Dell; research credit: R. Dell et al.; via Physics Today)

  • Peering Inside Viscous Fingering

    Peering Inside Viscous Fingering

    Viscous fingers form when a low-viscosity fluid is pumped into a narrow, viscous-fluid-filled gap. The branching pattern that forms depends on the ratio of the two viscosities, among other factors. To better understand what goes on inside these fingers, researchers carefully alternated injecting dyed and undyed fluid. This creates a pattern of concentric rings that deform as the fingers spread.

    In this particular study, the initial fluid and injected fluids are miscible, meaning that they can mix into one another. In modeling their experiments, the team found that this mixing created stratification — i.e., layers of fluids with different densities — in the narrow gap between their plates. The stratification’s effects were large enough that the model required a correction term for them; that’s a bit surprising because we’d usually expect that the tiny third-dimension of the gap would be too small to matter! (Image and research credit: S. Gowan et al.)

  • Underground Convection Thaws Permafrost Faster

    Underground Convection Thaws Permafrost Faster

    In recent years, Arctic permafrost has thawed at a surprisingly fast pace. Much of that is, of course, due to the rapid warming caused by climate change. But some of that phenomenon lives underground, where water’s unusual properties cause convection in gaps between rocks, sediment, and soil.

    Water is densest not as ice but as water. This is why ice cubes float in your glass. Water’s densest form is actually a liquid at 4 degrees Celsius. For water-logged Arctic soils, this means that the densest layer is not at the frozen depth but at a higher, shallower depth. This places a dense liquid-infused layer over a lighter one, a recipe for unstable convection.

    Illustration of underground convection and permafrost thaw. On the left: temperature and density of the water in Arctic soil varies with depth. The temperature decreases with depth, but because water is densest at 4 degrees Celsius, the density is greatest at a shallower depth than the freezing interface. As a result of this unstable configuration (dense water over less dense water), convection can occur (right side).
    Illustration of underground convection and permafrost thaw. On the left: temperature and density of the water in Arctic soil varies with depth. The temperature gets colder the deeper you go, but because water is densest at 4 degrees Celsius, the density is greatest at a shallower depth than the freezing interface. As a result of this unstable configuration (dense water over less dense water), convection can occur (right).

    In a recent numerical simulation, researchers found that this underground convection caused permafrost to thaw much more quickly than it would due to heat conduction alone. In fact, the effects appeared in as little as one month, so in a single summer, this convection could have a big effect on the thaw depth. (Image credit: top – Florence D., figure – M. Magnani et al.; research credit: M. Magnani et al.)

  • Pterosaur Tail Vanes

    Pterosaur Tail Vanes

    Among vertebrates, pterosaurs were the first to achieve powered flight. Early pterosaurs have tail vanes — similar in appearance to the frills seen on some lizards — but later species lost this feature. Whether the tail vanes helped in flight or served a display purpose is an open question among paleontologists. One group, in a recent pre-print, studied the vanes’ fossilized interior structure and found a cross-linked lattice that provided internal tension to the vanes. That means the vanes could potentially be held stiff, even in the face of aerodynamic forces that would cause untensioned surfaces to flutter. The result suggests that the tail vanes could have helped early fliers steer, even if evolution later moved that function (along with display) to other parts of the body. (Image credit: Sviatoslav-SciFi; research credit: N. Jagielska et al.; via jshoer)

  • Jamming Soft Grains

    Jamming Soft Grains

    Hard granular materials — sand, gravel, glass beads, and so on — can flow, but, in narrow regions or under large forces, they can also jam up, essentially turning into a solid. Soft particles can also flow and jam, but do so under different conditions than hard particles. One group of researchers used a custom-built rheometer to measure jamming in soft particles like the hydrogel beads pictured here. They found that they could extend existing models for jamming in hard particles, but they had to rescale the mathematics to account for the way soft particles change their shape under pressure. (Image credit: Girl with red hat; research credit: F. Tapia et al.; via APS Physics)