FYFD

Category: Research

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    Little Surfer

    Here’s another look at SurferBot, a low-cost, vibration-based robot capable of traversing both water and land. SurferBot’s vibration creates asymmetric ripples on the water surface. Because the waves are bigger at the rear of the robot, it gets propelled forward. But there doesn’t have to be water for SurferBot to get around! It’s actually amphibious, moving on both land and water. It can even transition from land to water on its own. (Image and video credit: E. Rhee et al.; research credit: E. Rhee et al.)

  • To Fizz or Not to Fizz

    To Fizz or Not to Fizz

    Place a drop of carbonated water on a superhydrophobic surface and it will slide almost frictionlessly, much the way Leidenfrost drops do. The drop behaves this way thanks to the self-produced layer of carbon dioxide vapor that it levitates on. As the gas escapes, the drop eventually settles back into contact with its surface. But until then, its levitation makes for some fun.

    On the treated half of the glass (left), bubbles form a continuous film against the glass. On the untreated side (right), bubbles nucleate, grow, and rise as expected for a fizzy drink.
    On the treated half of the glass (left), bubbles form a continuous film against the glass. On the untreated side (right), bubbles nucleate, grow, and rise as expected for a fizzy drink.

    Single droplets aren’t the only source of fun, however. In the images above, researchers coated the left half of a wine glass with a superhydrophobic treatment, while leaving the right half of the glass untouched. Once (dyed) carbonated water is poured into the glass, we see a bizarre dichotomy. In the right, untreated half of the glass, carbon dioxide bubbles nucleate, grow, and rise through the glass. But on the left side, the liquid appears still and bubble-less. In fact, the carbon dioxide gas on the left side is forming a continuous bubble film by the surface of the glass! (Image, video, and research credit: P. Bourrianne et al., see also)

  • Squeeze or Splatter?

    Squeeze or Splatter?

    Many a white shirt has met the disaster of a nearly-empty condiment bottle. One moment, you’re carefully squeezing out ketchup, and the next — sppplltlttt — you’re covered in red splatters. This messy phenomenon of gas displacing a liquid is widespread, showing up in condiments, some volcanic eruptions, and even the reinflation of a collapsed lung. Researchers have now constructed a mathematical model to fully capture and explain the process.

    When you squeeze a container with both air and a liquid — like ketchup — in it, the air is easily compressed but the liquid is not. The extra pressure of the air creates a driving force that pushes the liquid out, despite its viscous resistance. Most of the time, these two forces are balanced, and the ketchup flows smoothly out of the container. But when the volume of ketchup is small compared to the air, squeezing can overpressurize the air, driving the ketchup out in an uncontrolled burst.

    Luckily, the mathematics also suggest a solution to this problem: squeeze more slowly and double the size of the nozzle. You can also, they note, simply remove the top to avoid splatter. (Image credit: Rodnae Productions; research credit: C. Cuttle and C. MacMinn; via Ars Technica; submitted by Kam-Yung Soh)

  • Nanoconfined Water

    Nanoconfined Water

    Water is a decidedly weird substance. It’s densest above its freezing point; it has a slippery liquid-like layer on its solid form; and, in the right form, it can bend like a wire. So it’s not surprising that water demonstrates some odd behaviors when it’s confined inside a space so narrow it’s only one molecule thick.

    A new, simulation-based study finds that this nanoscale-confined water flows with a wide variety of behaviors, depending on the temperature and pressure. In some conditions, the water ceases to act molecularly, with hydrogen atoms flowing through a lattice of oxygen atoms. These superionic forms were thought only to exist in the extreme conditions of a gas giant’s interior, but these simulations suggest we can find them under far milder circumstances. (Image and research credit: V. Kapil et al.; via Physics World; submitted by Kam-Yung Soh)

  • Soapy Solutions

    Soapy Solutions

    When a drop of soap falls into a pool of water, its surface-loving molecules spread out on the water’s surface. Exactly how the soap spreads depends on the local concentration of its surfactant molecules, which create areas with different surface tensions that cause flow. All in all, it’s a tough process to predict because it varies in time at every point on the pool. But a recent paper offers a new class of exact solutions for the problem.

    The paper considers a surfactant-laden droplet spreading over a (relatively speaking) deep pool. Other researchers showed recently that this situation can be described with a complex version of the Burgers’s equation, which was originally developed to describe turbulent flows. The authors solved the equation for a variety of initial conditions and found that the time-dependent spread of the surfactants was sensitive to the initial surface distribution. The higher the initial surface concentration, the faster the surfactants spread. (Image credit: T. Despeyroux; research credit: T. Bickel and F. Detcheverry; via APS Physics; submitted by Kam-Yung Soh)

  • Waves in Liquid Crystals

    Waves in Liquid Crystals

    Liquid crystals are now ubiquitous in displays, but scientists are still discovering new properties for this state of matter. Here, a team explores nematic liquid crystals, whose rod-like shape rotates in three dimensions as they apply a voltage. The layer of liquid crystals is held between polarizing filters, creating regions of light and dark that depend on the liquid crystals’ orientations.

    Traveling waves and other wave patterns form in this liquid crystal as the voltage applied to it increases.
    Traveling waves and other wave patterns form in this liquid crystal as the voltage applied to it increases.

    As the researchers increase the voltage, traveling waves form. With higher voltages, the waves appear to slow a stop. The slowing waves result from the molecules tilting far from a vertical orientation, which makes it harder for individual molecules to rotate since they experience greater resistance from their neighbors. (Image, video, and research credit: V. Panov et al.; via APS Physics)

  • Airflow in the Opera

    Airflow in the Opera

    Like so many other performers, the singers and musicians of New York’s Metropolitan Opera House were left without a way to safely perform when the SARS-CoV-2 pandemic began in early 2020. In search of safe ways to perform and rehearse, the Met turned to researchers at nearby Princeton University, who worked directly with the performers to explore aerosol production and airflow in the context of professional opera.

    Through visualization and other experiments, the team found that the highly-controlled breathing of opera singers actually posed a lower risk for spreading pathogens than typical speaking and breathing. Most of a singer’s voiced sounds are sustained vowels, which produce a slow, buoyant jet that remains close to a singer. The exception are consonants, which created rapid, forward-projected jets.

    In the orchestra, the researchers found that placing a mask over the bell of wind instruments like the trombone reduced the speed and spread of air. One of the highest risk instruments they found was the oboe. Playing the oboe requires a long, slow release of air, but between musical phrases, oboists rapidly exhale any remaining air from their lungs and take a fresh breath. That rapid exhale creates a fast, forceful jet of air that necessitates placing the oboist further from others. (Image credit: top – P. Chiabrando, others – P. Bourrianne et al.; research credit: P. Bourrianne et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Why Moths Are Slow Fliers

    Why Moths Are Slow Fliers

    Hawkmoths and other insects are slow fliers compared to birds, even ones that can hover. To understand why these insects top out at 5 m/s, researchers simulated their flight from hovering to forward flight at 4 m/s. They analyzed real hawkmoths flying in wind tunnels to build their simulated insects, then studied their digital moths with computational fluid dynamics.

    During hovering flight, they found that hawkmoths generate equal amounts of lift with their upstroke and downstroke. As the moth transitions into forward flight, though, its wing orientation shifts to reduce drag, and the upstroke stops being so helpful. Instead, the upstroke generates a downward lift that the downstroke has to counter in addition to the insect’s weight. At higher forward speeds, this trend gets even worse.

    The final verdict? Hawkmoths don’t have the flexibility to twist their wings on the upstroke the way birds do to avoid that large downward lift. Since they can’t mitigate that negative lift, the insects have a slower top speed overall. (Image and research credit: S. Lionetti et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Never Break the Chain

    Never Break the Chain

    Pour water out of a bottle, and you’ll see a jet with a shape that resembles chain links. Sometimes known as a “liquid chain,” this phenomenon occurs when water pours through a non-circular hole. It’s quite a complex behavior, as shown in this recent study of the nonlinear effect. Even so, the authors found that the amplitude and wavelength of the chain’s sections are tied directly to the shape of the opening. Current models of the effect don’t account for the viscosity of the liquid, though, so future experiments will have to explore how fluids other than water behave. (Image and research credit: D. Jordan et al.; via APS Physics; submitted by Kam-Yung Soh)

    A comparison of oscillating jet shapes and metal chains.
    A comparison of an oscillating jet’s shape and metal chains. Each view is rotated 45 degrees from the one before.
  • Stabilizing Jupiter’s Polar Storms

    Stabilizing Jupiter’s Polar Storms

    Four years ago, Juno discovered an octagon of eight cyclones at Jupiter’s northern pole and a similar five cyclone structure at its southern pole. Since then, both polygons have remained intact. What keeps the storm systems so stable is still an open question, but a recent observational study using Juno measurements found that an anticyclonic ring sits between the central and outer cyclones. In line with a previous theoretical study, this ring structure helps shield and stabilize the storm system.

    The underlying convective mechanisms of the storm remain a mystery, though, as the current study is limited in resolution to a scale of about 200 kilometers. (Image credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM; research credit: A. Ingersoll et al.; via Gizmodo)