FYFD

Category: Research

  • 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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  • Oil-Slicked Bubble Bursts

    Oil-Slicked Bubble Bursts

    When bubbles at the surface of the ocean pop, they can send up a spray of tiny droplets that carry salt, biomass, microplastics, and other contaminants into the atmosphere. Teratons of such materials enter the atmosphere from the ocean each year. To better understand how contaminants can cross from the ocean to the atmosphere, researchers studied what happens when a oil-coated water bubble pops.

    The team looked at bubbles about 2 millimeters across, coated in varying amounts of oil, and observed their demise via high-speed video. When the bubble pops, capillary waves ripple down into its crater-like cavity and meet at the bottom. That collision creates a rebounding Worthington jet, like the one above, which can eject droplets from its tip.

    The team found that the oil layer’s thickness affected the capillary waves and changed the width of the resulting jet. They were able to build a mathematical model that predicts how wide a jet will be, though a prediction of the jet’s velocity is still a work-in-progress. (Image credit: Р. Морозов; research credit: Z. Yang et al.; via APS)

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  • A New Plasma Wave for Jupiter

    A New Plasma Wave for Jupiter

    Jupiter‘s North Pole has a powerful magnetic field combined with plasma that has unusually low electron densities. This combination, researchers found, gives rise to a new type of plasma wave.

    Ions in a magnetic field typically move parallel to magnetic field lines in Langmuir waves and perpendicularly to the field lines in Alfvén waves — with each wave carrying a distinctive frequency signature. But in Jupiter’s strong magnetosphere, low-density plasma does something quite different: it creates what the team is calling an Alfvén-Langmuir wave — a wave that transitions from Alfvén-like to Langmuir-like, depending on wave number and excitation from local beams of electrons.

    Although this is the first time such plasma behavior has been observed, the team suggests that other strongly-magnetized giant planets — or even stars — could also form these waves near their poles. (Image credit: NASA / JPL-Caltech / SwR I/ MSSS/G. Eason; research credit: R. Lysak et al.; via APS)

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  • Earth’s Core is Leaking

    Earth’s Core is Leaking

    In Earth’s primordial days, liquid iron fell through the ball of magma that was our planet, collecting elements–like ruthenium-100–that are attracted to iron. All of that material ended up in Earth’s outer core, a dense sea of liquid metal that geoscientists assumed was unable to cross into the lighter mantle. But recent observations suggest instead that core material is making its way to the surface.

    Measurements from volcanic rocks in the Galapagos Islands, Hawai’i, and Canada’s Baffin Island all contain ruthenium isotopes associated with that primordial core material, indicating that that magma came from the core, not the mantle. Separately, seismic analyses suggest that this material could be crossing through continent-sized blobs of warm, large-grained crystals caught deep below Africa and the Pacific, at the boundary between the mantle and the outer core. For more, check out this Quanta Magazine article. (Image credit: B. Andersen; research credit: N. Messling et al. and S. Talavera-Soza et al.; via Quanta)

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  • Double Detonation in Type 1a Supernovae

    Double Detonation in Type 1a Supernovae

    Type 1a supernovae are agreed to be explosions of white dwarf stars, the remains of stars similar in mass to our Sun. They’re thought to be triggered when extra mass — from a nearby companion star, for example — triggers a runaway fusion reaction in their carbon and oxygen, elements that white dwarfs generally don’t have enough mass to successfully fuse. The runaway fusion then blows the star apart.

    But there’s another theory — demonstrated through numerical simulations — that suggests an alternate mechanism: a small explosion on the star’s surface could compress the interior enough to trigger fusion of the heavier elements there, thereby triggering a second detonation. The two explosions would happen in quick succession, making them difficult to detect, but astronomers predicted that each explosion could create a shell of calcium; given enough time, those two shells could drift apart, allowing astronomers to see a shell of sulfur between them.

    The team looked to a supernova remnant about 300 years old, and using a spectrograph from the Very Large Telescope, they were able to image — as predicted — a two shells of calcium, separated by sulfur, supporting the double-detonation hypothesis.

    The impact of double-detonation in Type 1a supernovae could be far-reaching. Right now, the intensity of these objects seems to be consistent enough that astronomers use their brightness to estimate their distance. Over the years, those distance estimates have been used to measure the universe’s expansion and provide evidence for the existence of dark matter. But if Type 1a supernovae are not all the same intensity, we may need to reevaluate their use as a universal yardstick. (Image credit: ESO/P. Das et al.; research credit: P. Das et al.; via Ars Technica)

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  • Studying Hydroelastic Turbulence

    Studying Hydroelastic Turbulence

    Can energy at the small-scales of a turbulent flow work its way up to larger scales? That’s a question at the heart of today’s study. Here, researchers are studying hydroelastic waves — created by stretching a thin elastic membrane over a water tank. The membrane gets vibrated up and down in just one location with an amplitude of about 1 millimeter. The resulting waves depend both on the movement of the water and the elasticity of the membrane, mimicking situations like ice-covered seas.

    Rather than simply dying away, the local fluctuations introduced at the membrane spread, coalescing into larger-scale hydroelastic waves. How energy flows between these scales could have implications for weather forecasting, climate modeling, and other turbulent systems. (Image and research credit: M. Vernet and E. Falcon; via APS)

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  • Roll Waves in Debris Flows

    Roll Waves in Debris Flows

    When a fluid flows downslope, small disturbances in the underlying surface can trigger roll waves, seen above. Rather than moving downstream at the normal wave speed, roll waves surge forward — much like a shock wave — and gobble up every wave in their way.

    Such roll waves are fairly innocuous when flowing down a drainage ditch but far more problematic in the muddy debris flows of a landslide. Debris flows are harder to predict, too, thanks to their combined ingredients of water, small grains, and large debris.

    A new numerical model has shed some light on such debris flows, after showing good agreement with a documented landslide in Switzerland. The model suggests that roll waves get triggered in muddy flows at a higher flow speed than in a dry granular flow but a lower flow speed than is needed in pure water.

    For a great overview of roll waves, complete with videos, check out this post by Mirjam Glessner. (Image credit: M. Malaska; research credit: X. Meng et al.; see also M. Glessmer; via APS)

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