FYFD

Category: Research

  • Snapping When Swollen

    Snapping When Swollen

    The Venus flytrap snaps shut on its hapless prey by swelling cells in its leaves with water. Under the added pressure of a fly’s footstep, the leaves’ snapping instability triggers, trapping the insect. Researchers are using similar physics to create jumping and snapping polymer gels, like the one seen below.

    This jumping polymer shell exploits snapping that occurs as it dries out.

    To trigger the behavior, researchers soaked their polymer-based gel strips and shells in a solvent of n-hexane, which easily permeated the material and made it swell up. As the solvent evaporates from the swollen gel, the polymer material changes shape, sometimes in smooth bends and sometimes in abrupt snaps. The group was able to harness those snaps to have their materials descend slopes and climb ladders — all without motors, batteries, or external sources of energy. (Image credit: plant – A. Dénes, shell – Y. Kim et al.; research credit: Y. Kim et al.; via Physics World)

  • Predicting Meteotsunamis

    Predicting Meteotsunamis

    Meteotsunamis, or meteorological tsunamis, are large waves driven by weather rather than seismic energy. Although they occur along shorelines throughout the world, forecasters have very little infrastructure in place to predict or detect them. But a new study of an April 2018 meteotsunami on Lake Michigan (pictured above) has provided evidence that existing models may be able to forecast these events.

    The Lake Michigan meteotsunami was driven by an atmospheric gravity wave, which carried with it a substantial pressure drop. Most of the time such waves travel faster or slower than water waves, and there is little to no interaction. But on this day, the atmospheric wave and the water waves were traveling at the same speed in the same direction, creating a resonance that strengthened the water wave.

    Using existing National Oceanic and Atmospheric Administration (NOAA) models, researchers were able to reconstruct the event digitally, with results that agreed well with observations. That success means that forecasters may be able to predict the events ahead of time, potentially saving lives. (Image credit: D. Maglothin; research credit: E. Anderson and G. Mann; via Gizmodo)

  • Jovian Auroras

    Jovian Auroras

    Like Earth, Jupiter is home to polar auroras that light the sky as charged particles interact with the planet’s magnetosphere. A recent paper identifies interesting features in the aurora that appear similar to expanding vortex rings (see inset below). Although the researchers cannot yet identify the origin of the rings, they hypothesize that the process begins at the far edges of Jupiter’s magnetosphere where it interacts with the incoming solar wind. One theory posits that shear flows and Kelvin-Helmholtz instabilities where the magnetosphere and solar wind meet drive the phenomenon. (Image credit: Jupiter – NASA, ESA, and J. Nichols, aurora features – NASA/SWRI/JPL-Caltech/SwRI/V. Hue/G. R. Gladstone/B. Bonfond; research credit: V. Hue et al.; via Gizmodo)

    Diagram showing an inset of Jupiter's northern aurora, with further insets showing the expanding ring features.
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    Flying Spiders Use Electric Fields

    Many species of spider fly with a technique calling ballooning. We’ve touched on spider flight before, but more recent research adds a new dimension to the phenomenon. Researchers showed that spiders can actually use electrical fields in their flight. When isolated from flow or outside electrical fields, researchers found that spiders would still begin ballooning behaviors when subjected to electrical fields similar to those found in nature. The spiders were even able to take off in the artificial environment, using the electrostatic force between the surrounding fields and their negatively charged silk strands. While electrical fields alone were enough to get spiders aloft, the team thinks spiders in nature likely still use a combination of electrostatic force and aerodynamic drag in order to travel the vast distances spiders have been known to cover. (Video and image credit: BBC; research credit: E. Morley and D. Robert)

  • Airborne Aerosol Transmission of COVID-19

    Airborne Aerosol Transmission of COVID-19

    Early in the COVID-19 pandemic health officials resisted the idea that the novel coronavirus was transmissible through tiny aerosol droplets rather than larger, non-buoyant droplets. One case that made headlines and helped shift opinion was that of an outbreak among patrons of a Guangzhou restaurant traced to a single, pre-symptomatic patient zero. The pattern of who became sick at the carrier’s table and those nearby made little sense unless the restaurant’s air flow played a role in spreading the virus.

    https://www.youtube.com/watch?v=WaZiCqQmO4g

    This paper studies the incident in detail, using an in-house computational fluid dynamics (CFD) code to simulate both airflow in the restaurant and the paths aerosol droplets would follow in that environment. It takes into account flow from the air conditioner and the warm air rising from customers. The study’s predictions of which areas would have the highest concentrations of virus-laden aerosols matches well with the actual pattern of the outbreak. The authors hope that tools like theirs can help prevent future outbreaks by indicating the most dangerous paths for transmission and measures that can block those. (Image credit: Center for Disease Control; video, research, and submission credit: H. Liu et al.)

  • Oil-Coated Bubbles

    Oil-Coated Bubbles

    Bubbles in industrial applications are often more complicated than a simple pocket of air surrounded by water. Here researchers investigate the formation of an air bubble coated in oil before it rises through water. The photo above shows a series of snapshots as the bubble forms. Initially, a droplet of oil sits pinned on the surface. As air gets injected, the oil stretches around the growing bubble. Eventually, buoyancy pulls the bubble off the injector, creating a rising air bubble coated in oil. The team found that oil-coated bubbles could grow much larger than those in water alone. (Image and research credit: B. Ji et al.)

  • How the Hummingbird Got Its Hum

    How the Hummingbird Got Its Hum

    Summer hikes in the Rocky Mountains are frequently pierced by a hum that can deepen to a bomber-like buzz as hummingbirds flit by. They’re so small and fast that they’re hard to see, but they’re never hard to hear. A new study pins down just where that telltale hum comes from.

    To determine the specific origin of the hummingbird’s sound, researchers observed hovering hummingbirds with an array of over 2,000 microphones and multiple high-speed cameras. With this set-up, they could create a 3D acoustic map of the bird’s sounds, correlated with its motions. They found that the bird’s sounds come primarily from aerodynamic forces generated during their distinctive wingstroke – not from vortices or the fluttering of their feathers.

    They also found that the hummingbird’s fast wingstroke — about 40 times per second — fed into sounds at 40 and 80 Hz, as well as higher frequency overtones. Since these sounds are well within human hearing range, they make up most of what we hear from the birds. (Image credit: P. Bonnar; research credit: B. Hightower; via The Guardian; submitted by Kam-Yung Soh)

  • Loopy Networks and Bird Lungs

    Loopy Networks and Bird Lungs

    When mammals breathe, air flows back and forth inside our lungs. But in birds that inhale and exhale get transformed into one-directional flow inside their lungs. To figure out how, researchers built loopy networks of pipes that turn oscillating flow into unidirectional flow.

    The simplest structure that does this is shown above. The main loop is driven by a pump that oscillates back and forth. A second loop connects through two T-junctions, oriented at 90-degrees to one another. Watch the particles in each loop carefully. Those in the bottom loop move back and forth, driven by the oscillating pump. But the particles in the upper loop only move in one direction! The key to this, the researchers found, are vortices that form at the T-junctions (last image). When the flow in the main loop changes direction, it creates vortices that block flow along one arm of the T-junction, thereby isolating the upper loop. (Image credit: bird – A. Mckie, others – Q. Nguyen et al.; research credit: Q. Nguyen et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Viscoelastic Coiling

    Viscoelastic Coiling

    Drizzle honey or syrup from high enough, and you’ll see it coil like a liquid rope. This feature of viscous fluids also extends to polymer-filled viscoelastic fluids. But recent work shows that the elasticity of these fluids delays the onset of coiling; put differently, if you pour two fluids of comparable viscosity, the viscoelastic one will have to fall farther before it will start coiling. The authors also found that the coiling frequency for a viscoelastic fluid is smaller than a viscous one, given the same experimental conditions. (Image credit: flo222; research credit: Y. Su et al.)

  • Iceberg Melting Depends on Shape

    Iceberg Melting Depends on Shape

    Not all icebergs melt equally. Through a combination of experiment and numerical simulation, researchers have shown that an iceberg’s shape underwater strongly affects how it melts. Specifically, icebergs in a flow melt more quickly on the front and side surfaces and slower on the underside. This means that narrow icebergs that project deep into the water will melt faster than wider, shallow ones. Currently, climate models don’t account for this variation, but the researchers hope their work will help build more accurate models for future studies. (Image credit: iceberg – C. Matias, experiment – E. Hester et al.; research credit: E. Hester et al.; see also APS Physics)

    Snapshots of a model iceberg as it melts.