FYFD

Category: Research

  • Snoozing Sperm Whales Blow Bubbles

    Snoozing Sperm Whales Blow Bubbles

    Sperm whales like to nap under the water and away from the waves. They seem to do this in a vertical, head-up orientation. That makes sense, given that their enormous heads, which take up a third of their bodies, are full of oil, wax, and air–all buoyant materials. What’s less obvious is how the whales maintain their depth while sleeping. Why don’t they just bob right up to the surface with all that buoyancy?

    In a recent study, scientists attached devices to the whales that recorded their orientation, depth, and the sound of any bubbles the whale released. The team found that, over the course of a typical nap, whales let out 11 or so bubble bursts. This behavior appears to help them regulate their buoyancy so that they can maintain depth while they snooze. (Image credit: S. Granzotto; research credit: N. Freymond et al.; via Ars Technica)

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  • Freezing Via Ice Bridge

    Freezing Via Ice Bridge

    For frost to spread on a surface, individual water droplets freeze and then spread the freezing front to a nearby droplet. Frequently that happens through an ice bridge that connects one droplet to the next. On hydrophilic surfaces, the bridge grows along the surface, slowly connected one droplet to the next and the next until the entire surface is covered in frost. On superhydrophobic surfaces, frost still spreads via ice bridge, but those ice bridges are suspended in the air, cantilevered out from the frozen droplet. You can watch the process in the image below.

    The researchers found that frost was later to form and slower to spread on these superhydrophobic surfaces, which could be valuable for applications like the heat exchanger found in heat pumps. Once a heat exchanger’s finned surface is frost-covered, its efficiency plummets. The team suggests that coating these surfaces to be superhydrophobic could help keep them operating efficiently longer in cold and humid conditions. (Image credit: frost – K. Shimizu, experiment – S. Yang et al.; research credit: S. Yang et al.; via Physics World)

    Animation of a suspended ice bridge growing between water droplets on a superhydrophobic surface.
    Animation of a suspended ice bridge growing between water droplets on a superhydrophobic surface.
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  • Representing Rain’s Microphysics

    Representing Rain’s Microphysics

    Realistically modeling rainfall remains an extremely difficult problem. To be practical, results have to be on the scale of kilometers; no one is looking to find out whether rain will fall from one specific cloud over their head. But making that prediction depends on physics that happens at the microscale, where droplets tens of microns in size are condensing, colliding, and eventually growing large enough to fall as rain. A new study takes a look at three machine-learning models that could help describe those microscale physics with less computational overhead.

    The researchers used three different algorithms, all trained on high-quality simulations of microdroplet physics. The goal here was to represent the complex, nonlinear physics reflected in those results with an algorithm that’s less complicated and less computationally expensive than the methods used to create the training data. The team then tested the trained algorithms to see how they performed in conditions that were different than their training data.

    They found that the model with the best performance–in terms of giving more accurate predictions in the test cases–was actually the simplest of the three models. So it may be possible to get reasonable results for rain microphysics from simpler, easier-to-compute algorithms. The team does warn, though, that all of the models need more work before they’d be ready to add to commercial-grade weather prediction software. (Image credit: J. Fowler; research credit: E. de Jong et al.; via Eos)

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  • Stripping Mars’ Atmosphere

    Stripping Mars’ Atmosphere

    Mars was once a warmer, wetter place, swathed in a thick and protective atmosphere. Unlike Earth, Mars lacks a strong global magnetic field, which allows the solar wind to strip its atmosphere, but the exact mechanisms of that process have been unclear. But a new study has caught the process in action.

    Illustration of the Kelvin-Helmholtz instability occurring as the solar wind and Mars' electric field interact.
    Illustration of the Kelvin-Helmholtz instability occurring as the solar wind and Mars’ electric field interact.

    By combining simultaneous measurements from two spacecraft–NASA’s MAVEN and China’s Tianwen-1–the team was able to monitor the upstream solar wind conditions and the atmospheric ions escaping. They found that previously-observed “plasma clouds” in the Martian atmosphere result from a Kelvin-Helmholtz instability between the solar wind and Mars’ electric field. Within these clouds, the ion flux is ten to a hundred times greater than at steady-state conditions.

    This mechanism directly couples ion escape from Mars’ atmosphere to the solar wind, and it’s likely that this process plays out for other unmagnetized planets as well. (Image credit: Mars – NASA, illustration – C. Zhang et al.; research credit: C. Zhang et al.; via Gizmodo)

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  • Capillary Slinkies

    Capillary Slinkies

    Nature is full of helical fibers, including in plants and bird feathers. In this study, researchers explore how these soft springs react to droplets. When the pitch of the spring (roughly speaking, the spacing between coils) is small, droplets can flow down in a plug (not shown). But as the pitch increases, droplets can take on a caterpillar-like (or, eruciform) shape. These drops descend quickly, in part, the team found, because internal flows within the droplet help it along.

    A caterpillar-shaped droplet slides down a soft spring.
    A caterpillar-shaped droplet slides down a soft spring.

    Other drops maintain a spherical shape as they descend the widely-spaced coils of the spring. These drops tend to spin around the coil as they go, with their center of mass actually moving side-to-side as they descend. (Image and research credit: B. Bhatt and A. Carlson)

    A sphere-shaped droplet slides down a soft spring.
    A sphere-shaped droplet slides down a soft spring.
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  • Dragonfly Dogfights

    Dragonfly Dogfights

    Like fighter pilots of old, male dragonflies engage in aerial combat where each tries to outmaneuver the other to keep a sight on their rival’s tail. A recent study observed this combat in the field and uncovered some surprising similarities to dogfighting. Like pilots, dragonflies used spiraling turns and other high-g moves to gain an advantageous position behind the other. In human combat, that position favors the forward-facing weapons of the pilot in back; for dragonflies, it keeps their rival in the part of their vision that best detects movement.

    Interestingly, the team found that–even in the midst of combat–dragonflies spent at least a third of their time gliding. It’s unclear whether they glide to conserve energy or because it’s easier to track a rival when gliding.

    The authors dig into the control rules needed for dragonflies to execute these chases and found that even relatively simple control schemes–constrained by the dragonfly’s physical limits–result in complex flight contests. (Image and research credit: S. Fabian et al.; via Ars Technica)

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  • How Corals Stir

    How Corals Stir

    Reef-building coral polyps constantly stir the water around them with dense carpets of microscopic hair-like cilia. The beating of the cilia helps polyps feed while also pushing away sediment and debris. Their stirring increases nutrient and gas exchange with seawater, too. A new study combines experimental measurements with a simple mathematical model to recreate the three-dimensional flows corals make. The model’s efficiency means it should be useful for future studies of how corals and other cilia-covered systems interact with bacteria or other active particles. (Image and research credit: S. Selvan et al.; via APS)

    Particle tracks showing stirring created by coral cilia.
  • Screening for Sleep Apnea

    Screening for Sleep Apnea

    Snoring and sleep apnea–a condition where aeroelastic flutter obstructs the airway and stops breathing during sleep–often go hand-in-hand. But diagnosing sleep apnea involves an expensive and time-consuming screening in which the patient has to sleep while monitored by various sensors. To make the process easier, researchers are developing a screening method based only on audio recording.

    They started with a pre-trained audio model designed for speech recognition and stripped back computationally-expensive layers that weren’t relevant to snoring. Then they trained the new model using labeled audio data taken from standard clinical testing for sleep apnea. That means the model was told which audio recordings corresponded to “normal” snoring and which showed signs of sleep apnea. From there, the model was able to correctly identify apnea-related audio from fresh recordings just under 74% of the time. While that accuracy isn’t high enough to use the tool for diagnosis, it could help patients pre-screen for sleep apnea at home to decide whether the more invasive testing is warranted. (Image credit: L. Cline; research credit: H. Li et al.; via Physics World)

  • Ice Giant or Magma Ocean World?

    Ice Giant or Magma Ocean World?

    Uranus and Neptune–known as our system’s ice giants–are our least explored planets. Both have received exactly one flyby, from the Voyager 2 spacecraft. The data from those flybys remain our primary source of knowledge about each planet. The traditional model for each planet’s interior (dating back to before the flybys) consists of three layers: a rocky core; an icy mantle made up of water, ammonia, and methane; and a hydrogen/helium-rich atmosphere. That structure is one way to match the limited measurements we have from these planets, but, as today’s preprint study points out, it’s not the only way.

    The authors suggest an alternative structure, in which a hydrogen-rich atmosphere overlays a supercritical magma ocean capable of dissolving hydrogen into heavier, metallic elements. Their suggestion is motivated by several factors. First, objects in the outer solar system–including Kuiper Belt objects–have less icy material than originally assumed, which suggests that Uranus and Neptune’s progenitors wouldn’t have been so ice-rich, either. Second, our understanding of how “rocky” materials respond at the temperatures and pressures found in these planet interiors has evolved. In particular, silicate, hydrogen, and iron are actually miscible at these conditions. That means that discrete sub-layers separated by material type are not as likely.

    Using the magma ocean model, the team found compositions for both Uranus and Neptune that conformed well to our limited data about their gravitational and magnetic field properties. Time–and more data–will tell as to which interior model best describes these enigmatic giants. (Image credit: NASA; research credit: E. Young et al. (preprint); via Gizmodo)

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  • Inside an Espresso Bed

    Inside an Espresso Bed

    When pulling a shot of espresso, there are complicated physics at play. The ground coffee is tamped into a puck-like bed of grains, through which high-temperature, high-pressure water is forced. Here, researchers used X-ray tomography to visualize how and when water moves through the bed, which affects how flavors extract.

    Composite images of water penetrating a bed of finely ground coffee (left) and a bed of coarsely ground coffee (right).
    Composite images of water penetrating a bed of finely ground coffee (left) and a bed of coarsely ground coffee (right).

    In a finely ground bed, water is relatively slow to penetrate the bed, but moves in fairly uniformly. Water can get into the coarse grind a little faster but does so less uniformly. With the new experimental technique in place, the team is interested in seeing how water temperature affects infiltration and what solids get extracted. (Image credit: top – R. Wicks, experiment – J. Foster et al.; research credit: J. Foster et al.; via Physics World)