FYFD

Category: Research

  • Convection Inside the Mantle

    Convection Inside the Mantle

    Most of what we know about Earth’s interior comes from observing how seismic waves–mostly from earthquakes–bounce around. As our observations have gotten better–more seisometers, better imaging techniques–scientists have identified two large anomalies sitting near the bottom of the mantle. Known as large low-velocity provinces, or LLVPs, these zones take up continent-sized areas beneath parts of Africa and the Pacific.

    Seismic waves show lower speeds in large, continent-sized zones that sit beneath Africa and the Pacific. These large low-velocity provinces (LLVPs) are outlined in red.
    Seismic waves show lower speeds in large, continent-sized zones that sit beneath Africa and the Pacific. These large low-velocity provinces (LLVPs) are outlined in red.

    The LLVPs are hot, which would normally make them buoyant, but their stationary nature suggests they are made up of extremely dense material. Narrow plumes of hot material make their way up from the LLVPs to form volcanic hotspots like those that made the Hawaiian and Galapagos Islands. Balancing that upward convection is the downward convection of former tectonic material carried into the mantle at subduction zones.

    What the LLVPs are made of remains an active research question. One suggestion is that they contain remnants of Theia, the planet thought to have impacted the proto-Earth to form our Moon. (Image credits: E. Garnero and C. Richardson; see also Physics Today)

    Illustration showing convection in the Earth's inner mantle. Former tectonic material subducts downward in dark blue zones. The large low-velocity provinces (LLVPs) are shown in orange. Hot-spot volcanic activity is seen at the surface (black triangles) above narrow plumes that lift material from the LLVPs toward the surface.
    Illustration showing convection in the Earth’s inner mantle. Former tectonic material subducts downward in dark blue zones. The large low-velocity provinces (LLVPs) are shown in orange. Hot-spot volcanic activity is seen at the surface (black triangles) above narrow plumes that lift material from the LLVPs toward the surface.
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  • Where Waves Carry Plastics

    Where Waves Carry Plastics

    The classic theory of steady wave motion predicts a phenomenon called Stokes drift, in which particles spread horizontally in the direction of wave travel. That means that something like microplastics will drift in the direction that waves are traveling. But in the real world, ocean waves aren’t quite so neat and unchanging. A new study looks at what happens when waves are decaying in strength–in other words, what happens in our world when the wind dies down.

    In those circumstances, the researchers found that particles did not just drift horizontally–they drifted vertically, too. Further, how much a particle drifts vertically depends on its initial depth. Since plastics vary in their buoyancy–and can be found in varying numbers and sizes throughout the upper layer of the ocean–this mechanism could significantly affect how waves mix and transport pollution. (Image credit: N. Jensen; research credit: T. Izawa et al.; via Physics World)

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  • A Fluidic Space Telescope

    A Fluidic Space Telescope

    A telescope’s resolution is set by the size of its reflective surface. Our largest space telescope, JWST, has a 6.5-meter reflector, the largest we could manage given manufacturing constraints and the need to launch it in a rocket. To reach even larger sizes, researchers are considering a new type of reflector: one made of liquid.

    A fluidic telescope has some obvious advantages: surface tension makes it atomically smooth, and liquids can be packed into any convenient shape for launch. But there are challenges, also. Like, what happens to the reflector when you point it in an new direction?

    That’s what this study looks at, mathematically. Using a mathematical model of a 50-meter-wide, millimeter-thick fluid, the researchers analyzed how different maneuvers over the telescope’s lifetime would affect the image quality.

    Shifting the reflector creates perturbations in the surface, initially at the mirror’s edges. Over time, those perturbations move toward the center of the mirror and, at the same time, decay. The team found that, while typical space telescope operations distorted parts of the mirror beyond the limits of good optical quality, the inner 80% of the mirror could remain undisturbed for twenty or more years. That would be like having a 40-meter telescope in orbit with more than 6x the resolution of JWST. (Image credit: NASA; research credit: I. Gabay et al.)

    An artist's conception of a fluidic space telescope, made with a liquid reflecting surface tens of meters wide.
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  • Droplets Can Climb Sugar Fibers

    Droplets Can Climb Sugar Fibers

    In nature, droplets and fibers can meet on a spider’s web, on fur, or on a dew-gathering cactus. Here, researchers explore what happens when the droplet can dissolve the fiber it’s suspended on. As the authors note, a lumberjack who cuts the branch they sit on makes a fatal choice. The droplet sees a different outcome.

    As the droplet hangs on the fiber, it dissolves the fiber’s sugar. Dense, sugar-laden water flows downward along the fiber and a replenishing upward flow goes along the droplet’s exterior. Because the sugar concentration is lower near the top of the drop, the fiber thins most quickly there.

    A droplet at the end of a sugar fiber dissolves the fiber, then "jumps" up to the next intact section.
    A droplet hanging at the end of a sugar fiber dissolves the fiber and then “jumps” upward to the next intact portion.

    The droplet has capillary forces along its top and bottom, where it meets the fiber. At the top, the droplet is free to expand, wetting more fiber, but the bottom of the drop is pinned to the fiber. The excess capillary force there goes into compressing the fiber.

    As soon as the fiber breaks, the capillary force is no longer balanced, and the droplet jumps upward. If the drop and fiber are sized just right, the drop will jump upward enough to stay attached to the fiber instead of falling off. (Image and research credit: S. Dorbolo et al.)

  • Burning Oil Spills With Fire Whirls

    Burning Oil Spills With Fire Whirls

    Though they are relatively infrequent, large marine oil spills, like 2010’s Deepwater Horizon, are devastating and incredibly difficult to clean up. In many locations, the “best” option for responding to such disasters is burning off the oil before it can absorb enough water to sink. But these floating fires leave behind unburned oil and produce soot. To enhance the burn, researchers are looking at the possibility of triggering large-scale fire whirls.

    Often seen in wildfires, these fire vortices are intense and localized. Researchers made a more than 5-meter tall version in these experiments by arranging three walls that spun up the in-flowing air. The fire whirl sat above a pool of water topped in a layer of oil that served as the whirl’s fuel.

    Within the whirl, the fire’s burn rate was 40% higher than a typical pool fire, and soot production was 40% lower–showing that fire whirls can burn cleaner. But the whirls are more finicky to start and maintain. It’s not yet clear whether such intense whirls are possible in the chaotic conditions on the ocean. (Research and image credit: W. Cui et al.; via Eos)

    View of a large-scale fire whirl experiment built around an oil spill on a pool.
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  • The Disappearing Great Salt Lake

    The Disappearing Great Salt Lake

    Since 1989, Utah’s Great Salt Lake has lost some 70% of its surface area. The exposed lakebed left behind is a source of toxic dust that gets lifted into the air. Researchers are trying to understand what water sources exist beneath the lake and whether they might save the saline lake and its ecosystem from disappearing entirely.

    A recent study pinpoints underground water by measuring the electrical resistance between electrodes placed meters apart in the ground (photo above). Because salty water is more electrically conductive than fresh water, the researchers can distinguish between them. So far, they’ve found quite a lot of fresh water, sometimes only a couple meters below the surface. But those patches are often quite close to saline water, too.

    The group also described to Eos that they found mounds of invasive reeds lying atop concentrations of fresh water. The invasive species seems to be sucking up water that would otherwise feed back into the lake or support native plants that provide habitat to native birds. (Image credit: M. Thorne; research credit: M. Jacketta et al.; via Eos)

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  • Closing a Venus Fly Trap

    Closing a Venus Fly Trap

    The Venus fly trap has long fascinated scientists with its ability to catch fast-moving prey. Just how the plant closes its “trap” leaf so quickly is a matter of debate. A new study gives us more detail–but not complete clarity–about what’s going on.

    One way that plants move rapidly is by moving water into or out of cells, changing their internal pressure. The new experiments showed that this is not what the fly trap does. Specifically, by watching the speed at which individual Venus fly trap cells take up water, the team concluded that closing the leaf would take 30-150 seconds–far more than the 1 second observed.

    Instead, the team showed that the trap’s rapid closure happens because the plant’s cell walls rapidly soften, making the leaf unable to stay open against previously-stored elastic energy. Instead, the trap snaps closed. The physical mechanism behind the softening is still unclear, though, so the charismatic plant still has mysteries for us to discover. (Image credit: N. Suzuki; research credit: J. Ryu et al.; via Nature and Gizmodo)

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  • Dropping Oobleck

    Dropping Oobleck

    Oobleck is a peculiar substance. Formed from a suspension of cornstarch particles in water, it can flow like a liquid at low shear rates or jam into a solid under impact. Here, researchers explore what happens to a droplet of oobleck impacting a surface. As they expected, the team found that dilute drops could spread like a normal liquid during impact (top), and denser suspensions could impact like a solid would (below). But at the right conditions, they found that cornstarch-rich droplets could show liquid-like behavior at high shear rates and transition to solid-like behavior once the shear rate slowed down. (Image and research credit: A. Mobaseri et al.; via APS)

    An oobleck drop impacts and acts mostly solid.
  • Oyster Reefs Sequester Nitrogen

    Oyster Reefs Sequester Nitrogen

    The US eastern seaboard was once blanketed with oyster beds, but overharvesting, pollution, and habitat destruction decimated the population. As filter-feeders, oysters are naturally good at cleaning intertidal zones, and the reefs they build by cementing themselves to one another provide valuable habitat for many species of fish. A new study shows that oysters are even more economically valuable than we knew, thanks to their ability to sequester nitrogen.

    Agricultural and industrial run-off carries nitrates into the ocean in high concentrations that trigger deadly phytoplankton blooms, which choke off oxygen levels for larger species like fish. One way to reduce nitrogen levels in the water is denitrification, a process where microbes break down the nitrate into, among other things, inert nitrogen gas. The surface of oyster reefs is one place where this happens. But nitrates that evade these microbes can also get trapped and buried by a growing oyster reef.

    To understand how much nitrogen an oyster reef can bury, researchers studied cores removed from restored oyster beds. Below the top ten centimeters (where microbes do their denitrification), nitrogen levels in the oysters increased, with a square meter of oyster reef, on average, sequestering 6 grams of nitrogen per year, comparable to the amount that microbes removed. But some oyster reefs outperformed others. In particular, intertidal flat reefs–which grow faster–buried more than twice the nitrogen of subtidal reefs.

    The team estimated that, in North Carolina’s Carteret County, oyster reefs sequester some 120,000 kilograms of nitrogen annually, at an economic value of over $3 million. (Image credit: J. Andrews/UNC-Chapel Hill; research credit: A. Smiley et al.; via Eos)

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  • Featured Video Play Icon

    Why Unpaved Roads Washboard

    As anyone who has regularly traveled unpaved roads knows, they have a tendency to develop regularly spaced corrugations, otherwise known as washboarding. In addition to shaking cars and passengers, these uneven surfaces make cars harder to control, sicne the wheels can lose contact with the ground entirely at times.

    Unfortunately, this phenomenon is fairly unavoidable. Once you have a wheel moving across a granular surface above a critical speed, you get these self-reinforcing patterns. It’s similar to the way that tidal ripples and sand dunes form, and it’s how you get moguls on a ski run, too!

    Although they’re somewhat inevitable, as Grady describes, engineers are hard at work figuring out how to keep them from forming too quickly. (Video and image credit: Practical Engineering; research credit: N. Taberlet et al. and I. Hewitt et al.)

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