FYFD

Category: Research

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    Visualizing Unstable Flames

    Inside a combustion chamber, temperature fluctuations can cause sound waves that also disrupt the flow, in turn. This is called a thermoacoustic instability. In this video, researchers explore this process by watching how flames move down a tube. The flame fronts begin in an even curve that flattens out and then develops waves like those on a vibrating pool. Those waves grow bigger and bigger until the flame goes completely turbulent. Visually, it’s mesmerizing. Mathematically, it’s a lovely example of parametric resonance, where the flame’s instability is fed by system’s natural harmonics. (Video and image credit: J. Delfin et al.; research credit: J. Delfin et al. 1, 2)

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  • Predicting Landslide Speeds

    Predicting Landslide Speeds

    Knowing what speed a landslide will reach helps us predict how much damage they can cause. That speed depends on many factors: the steepness of the terrain, the sliding distance, the thickness of the flowing layer, and the type of grains making up the flow. Researchers found that predictions from previous studies often underestimated the speeds reached by thicker flows. Through laboratory experiments with grains of different shapes, a team found that those models mistakenly assumed a fully-developed flow — in other words, one where the grains have reached a constant final speed. While spherical grains reach that state over a short sliding distance, that’s not the case for other grains.

    Instead, the team used their results to build a new predictive model for landslide speeds. This one still depends on incline angle and flow thickness, but it also uses a dynamical friction coefficient to describe the granular material and capture how the flow’s speed varies with distance down the incline. (Image credit: W. Hasselmann; research credit: Y. Wu et al.; via APS News)

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  • Quick-Drying, Fast-Cracking

    Quick-Drying, Fast-Cracking

    Water droplets filled with nanoparticles leave behind deposits as they evaporate. Like a coffee ring, particles in the evaporating droplet tend to gather at the drop’s edge (left). As the water evaporates, the deposit grows inward (center) and cracks start to form radially. After just a couple minutes, the solid deposit covers the entire area of the original droplet and is shot through with cracks (right).

    Researchers found that the cracks’ patterns and propagation are predictable through a model that balances the local elastic energy and and the energy cost of fracture. They also found that the spacing between radial cracks depends on the deposit’s local thickness. Besides explaining the patterns seen here, these cracking models could help analyze old paintings, where cracks could hide information about the artist’s methods and the artwork’s condition. (Image and research credit: P. Lilit et al.; via Physics Today)

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  • An Exoplanet’s Supersonic Jet Stream

    An Exoplanet’s Supersonic Jet Stream

    WASP-127b is a hot Jupiter-type exoplanet located about 520 light-years from us. A new study of the planet’s atmosphere reveals a supersonic jet stream whipping around its equatorial region at 9 kilometers per second. For comparison, our Solar System’s fastest winds, on Neptune, are a comparatively paltry 0.5 kilometers per second. The team estimates the speed of sound — which depends on temperature and the atmosphere’s chemical make-up — on WASP-127b as about 3 kilometers per second, far below the measured wind speed. The planet’s poles, in contrast, are much colder and have far lower wind speeds.

    Of course, these measurements can only give us a snapshot of what the exoplanet’s atmosphere is like; we don’t have altitude data, for example, to see how the wind speed varies with height. Nevertheless, it shows that exoplanets beyond our planetary system can have some unimaginably wild weather. (Video and image credit: ESO/L. Calçada; research credit: L. Nortmann et al.; via Gizmodo)

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    Explosively Jetting

    Dropping water from a plastic pipette onto a pool of oil electrically charges the drop. Then, as it evaporates, it shrinks and concentrates the charges closer and closer. Eventually, the strength of the electrical charge overcomes surface tension, making the drop form a cone-shaped edge that jets out tiny, highly-charged microdrops. Afterward, the drop returns to its spherical shape… until shrinkage builds up the charge density again. This microjetting behavior can carry on for hours! (Video and image credit: M. Lin et al.; research preprint: M. Lin et al.)

  • Flushing the Brain During Sleep

    Flushing the Brain During Sleep

    When we sleep, our brains flush out waste that builds up during our waking hours, but how this happens has been something of a mystery. A new study of sleeping mice has visualized and tracked the flow for the first time. The researchers found that, during a specific sleep phase (the non-rapid eye movement portion), the mice released pulses of norepinephrine — a cousin to adrenaline — that periodically contracted blood vessels in the rodents’ brains. As these blood vessels contract and relax, it forces the nearby cerebrospinal fluid to flow. In short, the pulsing of the blood vessels pumps the fluid bathing the brain, flushing it.

    The team also found that certain medications — like the sleep aid Ambien — disrupted this flow in mice by suppressing the blood vessels’ oscillations. It’s not known yet whether our brains operate on the same pumping principle or whether medications could affect that, but it does suggest that a similar study in humans is worthwhile. (Image credit: K. Howard; research credit: N. Hauglund et al.; via Science)

  • Peering Inside a Hailstone

    Peering Inside a Hailstone

    In spring and summer, major thunderstorms can include dangerous and destructive hailstones. In Catalonia, a group of scientists collected hailstones after a record-breaking 2022 storm, finding some as large as 12 centimeters across. Using a dentist’s CT scanner, they looked at the interior of the hailstones, uncovering layers that reveal how the hail grew. In the past, researchers have studied hail by slicing the ice; that method gives them only a single cross-section through the hailstone, which gets destroyed in the process. In contrast, a CT scan revealed the full interior of the ice.

    The scientists found that, even though hail often appears spherical, the nucleus of the hail is not always located in the center. They saw that the hail grew in uneven layers that varied in density, depending on the storm conditions the hail experienced. To get to the enormous sizes seen here, hailstones have to travel up and down repeatedly through a storm, building up layer by layer. From the hail’s interior structure, the team could also tell what orientation the hail took its final fall in; the ice along the bottom of the hailstone was bubble-free, indicating that it collected as water drops hit the surface and froze. (Image credit: T. Ribas; research credit: C. Barqué et al.; via New Scientist)

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  • Flow Behind Viscous Fingers

    Flow Behind Viscous Fingers

    Nature is full of branching patterns: trees, lighting, rivers, and more. In fluid dynamics, our prototypical branching pattern is the Saffman-Taylor instability, created when a less viscous fluid is injected into a more viscous one in an confined space. Most attention in this problem has gone to the branching interface where the two fluids meet, but recently, a team has examined the flow away from the fingers by alternately injecting dyed and undyed fluid to visualize what goes on. That’s what we see here. Notice how the central dye rings, far from the branching fingers, still appear circular. Yet, even a few centimeters away from the fingers, the dye is starting to show ripples that correspond to the fingers. That’s an indication that the pressure gradient generated at the tips of the fingers is pretty far-reaching! (Image and research credit: S. Gowen et al.)

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  • Tracking Meltwater Through Flex

    Tracking Meltwater Through Flex

    Greenland’s ice sheet holds enough water to raise global sea levels by several meters. Each year meltwater from the sheet percolates through the ice, filling hidden pools and crevasses on its way to draining into the sea. Monitoring this journey directly is virtually impossible; too much goes on deep below the surface and the ice sheet is a precarious place for scientists to operate. So, instead, they’re monitoring the bedrock nearby.

    Researchers used a network of Global Navigation Satellite System (GNSS) stations like the one above to track how the ground shifted and flexed as meltwater collected and moved. They found that the bedrock moved as much as 5 millimeters during the height of the summer melt. How quickly the ground relaxed back to its normal state depended on where the water went and how quickly it moved. Their results indicate that the water’s journey is not a short one: meltwater spends months collecting in subterranean pools on its way to the ocean — something that current climate models don’t account for. Overall, the team’s results indicate that there’s much more hidden meltwater than models predict and it spends a few months under the ice on its way to the sea. (Image credit: T. Nylen; research credit: J. Ran et al.; via Eos)

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  • Swimming Like a Ray

    Swimming Like a Ray

    Manta rays are amazing and efficient swimmers — a necessity for any large animal that survives on tiny plankton. Researchers have built a new soft robot inspired by swimming mantas. Like its biological inspiration, the robot flaps its pectoral fins much as bird flaps its wings; this motion creates vortices that push water behind the robot, propelling it forward. For a downstroke, air inflates the robot’s body cavity, pushing the fins downward. When that air is released, its fins snap back up. With this simple and energy efficient stroke, researchers are able to control the robot’s swimming speed and depth, allowing it to maneuver around obstacles. Flapping faster helps the robot surface, and slower flapping allows it to sink. (Living manta rays also sink if they slow down.) Check out the robot in action below. (Image credit: J. Lanoy; video and research credit: H. Qing et al.; via Ars Technica)