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Search results for: “transition”

  • A New Mantle Viscosity Shift

    A New Mantle Viscosity Shift

    The rough picture of Earth’s interior — a crust, mantle, and core — is well-known, but the details of its inner structure are more difficult to pin down. A recent study analyzed seismic wave data with a machine learning algorithm to identify regions of the mantle where waves slowed down. These shifts in seismic wave speed occur in areas where the mantle’s viscosity changes; a higher viscosity makes waves travel slower.

    The team found seismic wave speed shifts at depths of 400 and 650 kilometers, corresponding to known viscosity changes. But they found shifts at 1050 and 1500 kilometers, as well — the first time anyone has shown a global viscosity shift at those depths. Their analysis suggests a higher viscosity in this mid-mantle transition zone, which could affect how tectonic plates, which rely on these slow mantle flows, move. (Image credit: NASA; research credit: K. O’Farrell and Y. Wang; via Eos)

  • Herding Sheep

    Herding Sheep

    Flocks of birds, schools of fish, and herds of sheep all resemble fluids at times, and physicists have been trying to recreate their collective motion for decades. Many of these models simplify the animals into particles that follow simple rules based on the direction and speed of their neighbors. Over time, the models have grown more complex; for example, some might differentiate a “sheepdog” particle from “sheep” particles. And some models even tweak the “sheep” to account for the personality traits that real sheep show, like how skittish they behave toward a sheepdog. Physics World has a neat overview of several studies in this vein. (Image credit: E. Osmanoglu; via Physics World)

  • Junggar Basin Aglow

    Junggar Basin Aglow

    The low sun angle in this astronaut photo of Junggar Basin shows off the wind- and water-carved landscape. Located in northwestern China, this region is covered in dune fields, appearing along the top and bottom of the image. The uplifted area in the top half of the image is separated by sedimentary layers that lie above the reddish stripe in the center of the photo. Look closely in this middle area, and you’ll find the meandering banks of an ephemeral stream. Then the landscape transitions back into sandy wind-shaped dunes. (Image credit: NASA; via NASA Earth Observatory)

  • Searching for Stability in Cleaner Flames

    Searching for Stability in Cleaner Flames

    Spiking natural gas power plants with hydrogen could help them burn cleaner as we transition away from carbon power. But burners in power plants and jet engines can be extremely finicky, thanks to thermoacoustic instabilities. As a flame burns, it can sputter and fluctuate in its heat output. That creates pressure oscillations (which we sometimes hear as sound waves) that reflect off the burner’s walls and return toward the flame, causing further fluctuations. This feedback loop can be destructive enough to explode combustion chambers.

    Adding hydrogen to a burner designed purely for natural gas can trigger these instabilities (above image), but researchers hope that by exploring fuel-mixtures and their effect at lab-scale, they can help designers find safe ways to adapt industrial burners for the cleaner fuel mixture. (Image and research credit: B. Ahn et al.; via APS Physics)

  • Tornadoes in a Bucket

    Tornadoes in a Bucket

    In nature, some powerful tornadoes form additional tornadoes within their shear layer. These subvortices revolve around the main tornado, causing massive destruction in their wake. In the laboratory, researchers create a similar multi-tornado system with a spinning disk at the bottom of a shallow, cylindrical layer of water. Depending on how fast the disk spins, different numbers of subvortices form around the main vortex.

    In this poster, researchers show the transition from a 3-subvortex system to a 2-subvortex one. Starting at the 12 o’clock position and moving clockwise, we see 3 subvortices arranged in a triangle. A sudden change in the disk’s rotation speed destabilizes the system, causing the subvortices to break down and shift into a new 2-subvortex configuration. As this happens, material that was isolated in each subvortex (darker blue regions) is suddenly able to mix. That suggests that a real-world multiple vortex tornado might suddenly shed debris if it lost enough angular momentum. Back in the lab, though, the shift to a stable 2-subvortex system once again isolates material in individual subvortices and prevents it from mixing with the rest of the flow. (Image and research credit: G. Di Labbio et al. 1, 2)

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    Serpents and Ouroboros

    Beads of condensation on a cooling, oil-slicked surface have a dance all their own in this video. Large droplets gobble up their fellows as they follow serpentine paths; each new droplet donates its interfacial energy to feed the larger drop’s kinetic energy. Eventually, the big drops switch to a circular path, like an ouroboros, the tail-eating serpent of mythology. This transition happens due to the oil shifted by the dancing droplets. You can recreate the effect at home by rubbing a thin layer of oil over glass and setting it atop a hot mug of your favorite beverage. (Video and image credit: M. Lin et al.; research credit: M. Lin et al.)

  • Staying Cool in the Sun

    Staying Cool in the Sun

    For humans, staying cool in the summer heat often means expending energy on air conditioners, fans, and other cooling devices. But scientists are exploring other, less energy-intense options for beating the heat. At a conference, researchers recently unveiled a plant-based bi-layer film that’s able to stay about 7 degrees Fahrenheit cooler than its surroundings while illuminated by the sun.

    The film uses passive daytime radiative cooling, which means that it emits its heat into space (without getting absorbed by the air nearby) without any external power source. A square meter of the film generates over 120 watts of cooling power, comparable to many residential air conditioners. Even better, the films are built from layered cellulose, a sustainable and renewable resource, and can be made in a variety of colors.

    The team hopes to transition their films to commercial manufacturing, where they can be incorporated into buildings and automobiles to provide some passive cooling, thereby limiting reliance on air conditioners. (Image and research credit: Q. Shen et al.; via Ars Technica)

  • How a Leak Can Stop Itself

    How a Leak Can Stop Itself

    Some leaks can actually stop themselves, and a new analysis shows how. When a vertical pipe has a small hole, water initially spouts out of it, then dribbles, and, finally, drips as the water level in the pipe falls, decreasing the driving pressure of the flow. But the pipe doesn’t have to empty to a level below the hole for the leak to stop. Instead, a final droplet can form a cap over the hole, with its shape providing enough pressure to balance the remaining pressure from fluid in the pipe.

    Water leaking from a vertical pipe transitions from continuous flow to discrete drops (left). Dripping continues until the final droplet forms at t = 0 seconds.
    Water leaking from a vertical pipe transitions from continuous flow to discrete drops (left). Dripping continues until the final droplet forms at t = 0 seconds.

    The researchers found that the final drop’s kinetic energy (as well as its potential energy) was critical to determining which drop would stop the flow. The last drop behaves like a lightly-damped harmonic oscillator; it needs enough potential energy to counter the flow and a small enough inertia that it doesn’t slip away down the pipe. (Image credit: top – G. Crofte, experiment – C. Tally et al.; research credit: C. Tally et al.; via APS Physics)

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    Twisted Fibers

    A drop sliding down a fiber can do so asymmetrically or symmetrically. The asymmetric configuration is unstable and will spontaneously shift to a symmetric one. Adding a second, parallel fiber stabilizes an asymmetric drop, letting it slide without shifting. And twisting the two fibers together gives even more control, allowing researchers to tweak drop shape, speed, and orientation independent of properties like the drop’s volume or viscosity. (Image and video credit: V. Kern and A. Carlson)

  • Where Fresh and Salty Meet

    Where Fresh and Salty Meet

    Waterways twist through the wetlands of Adair Bay in this astronaut-captured image of northwestern Mexico. The estuary marks the transition between the Great Altar Desert and the Gulf of California. Fresh and salt water mix in the sediment-rich waterways. Mangroves and other salt-tolerant vegetation flourish in the coastal marsh. During low tides, evaporating water leaves behind salt flats, seen here in gray and white. High tides flood the area with nutrients that support both the vegetation and abundant aquatic life. (Image credit: NASA; via NASA Earth Observatory)

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