FYFD

Category: Research

  • Watch Hagfish Slime Unfurl

    Watch Hagfish Slime Unfurl

    The eel-like hagfish has one of the best defenses in the ocean. When threatened, it releases a slime that clogs the gills of its predator but allows the hagfish itself to slough off the slime and escape. The hagfish slime’s secret weapon is long protein threads, which are initially rolled into bundles called skeins. Seen above, these skeins resemble the yarn skeins knitters and crocheters buy, but a hagfish’s skeins are only as big as the width of a human hair.

    When water flows by quickly enough, the thread in a skein begins to unwind and stretch out. With enough threads unwound, the slime gets stretchy and viscous. Researchers found that it takes relatively little flow to begin this unwinding because the adhesion between threads and the surrounding fluid is higher than the thread-to-thread sticking power. (Research and image credit: M. Hossain et al., video)

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  • Tracing the Origins of Ocean Waters

    Tracing the Origins of Ocean Waters

    The Sub-Antarctic Mode Waters (SAMW) lie in the southern Indian Ocean and the east and central Pacific Ocean, where they serve as an important sink for both heat and carbon dioxide. Scientists have long debated the origins of the SAMW’s waters, and a new study may have an answer.

    Researchers combined data from ocean observations with a model of the Southern Ocean to essentially trace the SAMW’s ingredients back to their respective origins. The results showed that about 70% of the Indian Ocean’s SAMWs came from subtropical waters, but those waters contributed to only about 40% of the Pacific’s SAMWs. Pacific SAMWs had their largest contributions from upwelling circumpolar waters.

    Understanding where a SAMW’s waters came from helps scientists predict how those waters will mix and how much heat and carbon they can absorb. (Image credit: NASA; research credit: B. Fernández Castro et al.; via Eos)

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  • Ice Discs Surf on Herringbones

    Ice Discs Surf on Herringbones

    Inspired by the roaming rocks of Death Valley, researchers went looking for ways to make ice discs self-propel. Leidenfrost droplets can self-propel on herringbone-etched surfaces, so the team used them here, as well. On hydrophilic herringbones, they found that meltwater from the ice disc would fill the channels and drag the ice along with it.

    But on hydrophobic herringbone surfaces, the ice disc instead attached to the crest of the ridges and stayed in place–until enough of the ice melted. Then the disc would detach and slingshot (as shown above) along the herringbones. This self-propulsion, they discovered, came from the asymmetry of the meltwater; because different parts of the puddle had different curvature, it changed the amount of force surface tension exerted on the ice. Thus, when freed, the ice disc tried to re-center itself on the puddle.

    The team is especially interested in how effects like this could make ice remove itself from a surface. After all, it requires much less energy to partially melt some ice than it does to completely melt it. (Image and research credit: J. Tapochik et al.; via Ars Technica)

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  • Flipping Icebergs

    Flipping Icebergs

    When an iceberg flips, it creates waves that can endanger ships nearby, but the move can also trigger further melting. In the ocean, many factors, including wind and waves, can contribute to an iceberg flipping, so researchers studied small, lab-scale versions to see how melting–alone–affects an iceberg’s likelihood of flipping.

    The results showed that melting alone was enough to destabilize icebergs and make them flip, as seen in the timelapse above. These mini-icebergs melted faster underwater, changing the berg’s overall shape and eventually triggering a flip. Corners developed at the waterline where the different melt rates above- and below-the-water met. Whenever a flip occurred, one of these corners would always settle at the new water line, causing the lab iceberg to change from a circular cylinder to a polygon as melting continued. (Image credit: M. Whiston; research and video credit: B. Johnson et al.; via APS)

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  • Striations on the Sun

    Striations on the Sun

    One of the perpetual challenges for fluid dynamicists is the large range of scales we often have to consider. For something like a cloud, that means tracking not only the kilometer-size scale of the cloud, but the large eddies that are about 100 meters across and smaller ones all the way down to the scale of millimeters. In turbulent flows, all of these scales matter. That problem is even harder for something like the Sun, where the sizes range from hundreds of thousands of kilometers down to only a few kilometers.

    It’s those fine-scale features that we see captured here. This colorized image shows light and dark striations on solar granules. Scientists estimate that each one is between 20 and 50 kilometers wide. They’re reflections of the small-scale structure of the Sun’s magnetic field as it shapes the star’s hot, conductive plasma. (Image credit: NSF/NSO/AURA; research credit: D. Kuridze et al.; via Gizmodo)

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  • Dusty Clouds Make More Ice

    Dusty Clouds Make More Ice

    Even when colder than its freezing point, water droplets have trouble freezing–unless there’s an impurity like dust that they can cling to. It’s been long understood in the lab that adding dust allows water to freeze at warmer temperatures, but proving that at atmospheric scales has been harder. But a new analysis of decades’ worth of satellite imagery has done just that. The team showed that a tenfold increase in dust doubled the likelihood of cloud tops freezing.

    Since ice-topped clouds reflect sunlight and trap heat differently than water-topped ones, this connection between dust and icy clouds has important climate implications. (Image and research credit: D. Villanueva et al.; via Eos)

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  • Biodegradable PIV Particles

    Biodegradable PIV Particles

    Particle image velocimetry–PIV, for short–is used to visualize fluid flows. The technique introduces small, neutrally-buoyant particles into the flow and illuminates them with laser light. By comparing images of the illuminated particles, computer algorithms can work out the velocity (and other variables) of a flow. Typical methods use hollow glass spheres or polystyrene beads as the particles that follow the flow, but these options have many downsides. They’re expensive–as much as $200/pound–and they can potentially harm test subjects, like animals whose swimming researchers are studying. Instead, researchers are now looking at biodegradable options for PIV particles.

    One study found that corn and arrowroot starches were good candidates, at least for applications using artificial seawater. The powders were close to neutrally-buoyant, had uniform particle sizes, and accurately captured the flow around an airfoil, live brine shrimp, and free-swimming moon jellyfish. (Image credit: M. Kovalets; research credit: Y. Su et al.; via Ars Technica)

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  • Compressing Jupiter’s Magnetosphere

    Compressing Jupiter’s Magnetosphere

    Shaped by its strong internal magnetic field and the incoming solar wind, Jupiter has the largest magnetosphere in the solar system. It also has highly active aurorae at its poles, though they are most visible in ultraviolet wavelengths. A new analysis of Juno’s data shows that on 6-7 December 2022, Jupiter’s magnetosphere got compressed, coinciding with aurorae six times brighter than usual. The compression itself came from a shock wave in the incoming solar wind. (Image credit: NASA/JPL; research credit: R. Giles et al.; via Eos)

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  • Aboard a Hurricane Hunter

    Aboard a Hurricane Hunter

    For decades, NOAA has relied on two WP-3D Orion aircraft–nicknamed Kermit and Miss Piggy–to carry crews into the heart of hurricanes, collecting data all the while. Every ride aboard a Hurricane Hunter is a bumpy one, but some flights are notorious for the level of turbulence they see. In a recent analysis, researchers used flight data since 2004 (as well as a couple of infamous historic flights) to determine a “bumpiness index” that people aboard each flight would experience, based on the plane’s accelerations and changes in acceleration (i.e., jerk).

    The analysis confirmed that a 1989 flight into Hurricane Hugo was the bumpiest of all-time, followed by a 2022 flight into Hurricane Ian, which was notable for its side-to-side (rather than up-and-down) motions. Overall, they found that the most turbulent flights occurred in strong storms that would weaken in the next 12 hours, and that the bumpiest spot in a hurricane was on the inner edge of the eyewall. That especially turbulent region, they found, is associated with a large gradient in radar reflectivity, which could help future Hurricane Hunter pilots avoid such dangers. (Image credit: NOAA; research credit: J. Wadler et al.; via Eos)

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  • Tides Widen Ice Cracks

    Tides Widen Ice Cracks

    When icebergs calve off of Arctic and Antarctic coastlines, it affects glacial flows upstream as well as local mixing between fresh- and seawater. A recent study points to ocean tides as a major factor in widening the ice cracks that lead to calving. The team built a simplified mathematical model of an ice shelf, taking into account the ice’s viscoelasticity, local tides, and winds. Then they compared the model’s predictions with satellite, GPS, and radar data of Antarctica’s Brunt Ice Shelf, where an iceberg the size of Greater London broke off in 2023.

    Between their model and the observation data, the team was able to show that the crack that preceded calving consistently grew during the spring tides, when tidal forces were at their strongest. The work gives us one more clue for refining our predictions of when major calving events are likely. (Image and research credit: O. Marsh et al.; via Gizmodo)

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