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  • Wobbling Plasma Could Help Planets Grow

    Wobbling Plasma Could Help Planets Grow

    To form planets, the dust and gas around a star has to start clumping up. While there are many theories as to how this could happen, it’s a difficult process to observe. A recent study shows that a magnetorotational (MR) instability could do the job.

    The team used a Taylor-Couette set-up (where an inner cylinder rotates inside an outer cylinder) filled with a liquid metal alloy. With the cylinders moving relative to one another at over 2,000 rotations per minute, the team measured how the magnetic field changed in the churning fluid. Parts of the liquid metal formed free shear layers, and within these, the MR instability occurred, causing some regions to slow down and others to speed up.

    The experiments suggest that triggering a MR instability is easier to achieve than once thought, which supports the possibility that it occurs in protoplanetary disks, helping to drive dust together into planets. (Image credit: ALMA/ESO/NAOJ/NRAO; research credit: Y. Wang et al.; via Eos)

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    Draining Topography is Hard

    At first glance, draining an ocean seems simple like a simple problem: just put a drain at the lowest point. But, as shown in this Minute Physics video, the problem is harder than it sounds because drainage depends not just on a point’s elevation but also on the path that leads to the drain. Fortunately, Henry has some clever methods for figuring out which areas would drain and how. (Video and image credit: Minute Physics)

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  • Wave Energy Through the Meniscus

    Wave Energy Through the Meniscus

    Even small changes to a meniscus can change how much wave energy passes through it. A new study systemically tests how meniscus size and shape affects the transmission of incoming waves.

    As seen above, the meniscus was formed on a suspended barrier. By changing the barrier size and wettability as well as the characteristics of incoming waves, researchers were able to map out how the meniscus affected waves that made it past the barrier.

    Oblique view of meniscus experiment showing incoming waves (moving from right to left) passing through a barrier and meniscus. Upper view shows 15Hz waves; lower one shows 5 Hz waves.

    In particular, they found that drawing the meniscus upward by raising the barrier would, at first, enhance wave transmission but then suppressed wave energy as the barrier moved higher. They attributed the change in behavior to an interplay between water column height and meniscus inclination. (Research and image credit: Z. Wang et al.; via Physics World)

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  • Fluids at the Angstrom-Scale

    Fluids at the Angstrom-Scale

    We spend our lives dealing with fluids at a scale where the motion of individual molecules is beneath our notice. There’s no reason to track every molecule of water moving through a municipal pipe; it’s effectively impossible, anyhow! But once you are dealing with pipes that are small enough–below about 1 nanometer in diameter–fluids have to be considered molecule-by-molecule. At this scale, so-called angstrofluidics behave very differently.

    Intuition suggests that flow through such tiny channels would be extremely slow, however researchers have observed protein channels that allow a single water molecule through at a time while still processing a billion molecules each second. Combine this throughput with charged channel walls that can sort molecules by polarity, and angstrofluidics offers the possibility for unprecedented control for filtering, desalination, and drug testing. (Image credit: T. Miroshnichenko; see also R. Boya et al.)

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  • Why Sharper Knives Mean Fewer Onion Tears

    Why Sharper Knives Mean Fewer Onion Tears

    Onions are a well-known source of tears for many a cook. And while the chemical source of their power–onions release a chemical that reacts in our eyes to produce tears–has been known for years, no one has looked at the fluid dynamics in the process until now.

    Video of droplets sprayed as a knife cuts into an onion.

    As seen above, a knife piercing the onion’s surface releases a mist of high-speed droplets, followed by a slower spray. Much like a citrus fruit’s microsprays, the onion’s fountain depends on both solid and fluid mechanics. As the knife presses into the onion’s stiffer outer layer, pressure builds in the softer layer underneath, which contains pores of fluid. Once the knife breaks the epidermis, that pressurized fluid sprays out.

    The good news is that the team also confirmed a common culinary wisdom: using a sharper knife and a slower, gentler cut will reduce the spray and its speed, resulting in fewer tears. (Image credit: M. Stone; research credit: Z. Wu et al.)

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    Floating Bridges

    For most of history, floating bridges have been temporary structures, often used by militaries crossing water, but over the course of the twentieth century, engineers learned to build more permanent floating bridges. These structures require very particular conditions–calm waters, minimal ice, and so on–but they can be great options for crossing lakes where the traditional anchoring options for a bridge just don’t exist. In this Practical Engineering video, Grady discusses some of the challenges and innovations of these unusual bridges. (Video and image credit: Practical Engineering)

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  • Oceans Could “Burp” Out Absorbed Heat

    Oceans Could “Burp” Out Absorbed Heat

    Earth’s atmosphere and oceans form a complicated and interconnected system. Water, carbon, nutrients, and heat move back and forth between them. As humanity pumps more carbon and heat into the atmosphere, the oceans–and particularly the Southern Ocean–have been absorbing both. A new study looks ahead at what the long-term consequences of that could be.

    The team modeled a scenario where, after decades of carbon emissions, the world instead sees a net decrease in carbon–which could be achieved by combining green energy production with carbon uptake technologies. They found that, after centuries of carbon reduction and gradual cooling, the Southern Ocean could release some of its pent-up heat in a “burp” that would raise global temperatures by tenths of a degree for decades to a century. The burp would not raise carbon levels, though.

    The research suggests that we should continue working to understand the complex balance between the atmosphere and oceans–and how our changes will affect that balance not only now but in the future. (Image credit: J. Owens; research credit: I. Frenger et al.; via Eos)

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  • Our Best Look Yet at a Solar Flare

    Our Best Look Yet at a Solar Flare

    Scientists have unveiled the sharpest images ever captured of a solar flare. Taken by the Inouye Solar Telescope, the image includes coronal loop strands as small as 48 kilometers wide and 21 kilometers thick–the smallest ones ever imaged. The width of the overall image is about 4 Earth diameters. The captured flare belongs to the most powerful class of flares, the X class. Catching such a strong flare under the perfect observation conditions is a wonderful stroke of luck.

    Although astronomers had theorized that coronal loops included this fine-scale structure, the Inouye Solar Telescope is the first instrument with the resolution to directly observe structures of this size. Confirming their existence is a big step forward for those working to understand the details of our Sun. (Video and image credit: NSF/NSO/AURA; research credit: C. Tamburri et al.; via Gizmodo)

  • Buccaneer Archipelago

    Buccaneer Archipelago

    Off western Australian, hundreds of low-lying islands and coral reefs jut into the ocean as part of the Buccaneer Archipelago. Tides here have a range of nearly 12 meters, so water rips through the narrow channels as the tide ebbs and flows. These fast flows lift sediment that dyes the water a bright turquoise. (Image credit: M. Garrison; via NASA Earth Observatory)

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  • Salt and Sea Ice Aging

    Salt and Sea Ice Aging

    Sea ice’s high reflectivity allows it to bounce solar rays away rather than absorb them, but melting ice exposes open waters, which are better at absorbing heat and thus lead to even more melting. To understand how changing sea ice affects climate, researchers need to tease out the mechanisms that affect sea ice over its lifetime. A new study does just that, showing that sea ice loses salt as it ages, in a process that makes it less porous.

    Researchers built a tank that mimicked sea ice by holding one wall at a temperature below freezing and the opposite wall at a constant, above-freezing temperature. Over the first three days, ice formed rapidly on the cold wall. But it did not simply sit there, once formed. Instead, the researchers noticed the ice changing shape while maintaining the same average thickness. The ice got more transparent over time, too, indicating that it was losing its pores.

    Looking closer, the team realized that the aging ice was slowly losing its salt. As the water froze, it pushed salt into liquid-filled pores in the ice. One wall of the pore was always colder than the others, causing ice to continue freezing there, while the opposite wall melted. Over time, this meant that every pore slowly migrated toward the warm side of the ice. Once the pore reached the surface, the briny liquid inside was released into the water and the ice left behind had one fewer pores. Repeated over and over, the ice eventually lost all its pores. (Image credit: T. Haaja; research credit and illustration: Y. Du et al.; via APS)

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