FYFD

Tag: biology

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    Understanding Fish and Turbines

    Fish detect turbulence in the water around them; among other things, this helps them avoid colliding with objects. Here, researchers are looking to understand how fish interact with underwater turbines. Experiments give them a set of trajectories that actual fish follow when dealing with the experimental turbine. But to understand what the fish is detecting, the researchers build a digital facsimile of the turbine and use Large Eddy Simulation (LES) to calculate the turbine’s wake.

    By overlaying the fish trajectories onto the simulated flow structures, they can better understand what flows the fish is and is not comfortable with. That knowledge helps engineers design turbines with smaller ecological impact. (Video and image credit: H. Seyedzadeh et al.)

  • A Fungus That Freezes Water

    A Fungus That Freezes Water

    Although water can freeze below 0 degrees Celsius, it requires a little help–in the form of a nucleation site–to do so. Often temperatures must dip well below 0 degrees Celsius for droplets to become ice. But a new study shows that at least one fungus forms proteins that help the process along.

    The proteins come from the Mortierellaceae  fungal family, by way of a bacterial species some hundreds of thousands of years ago or more. In experiments, adding the fungal protein helped water freeze 10 or more degrees Celsius sooner than it otherwise would.

    The authors note that there are many possible applications for this freezing additive; it could help preserve food or cells without requiring lower freezing temperatures that could damage delicate tissues. It could also serve as a cloud seeding chemical in place of toxic silver iodide particles. (Image and research credit: R. Eufemio et al.; via Gizmodo; see also V. Tech)

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  • Insect Wings in Extreme Macro

    Insect Wings in Extreme Macro

    Photographer Chris Perani is fascinated by the microstructures of insect wings, which he captures in “extreme macro” through focus stacking–letting us see wings in glorious micron-scale detail. In addition to giving insects their brilliant colors and irridescence, these structures serve another key role: they help insects stay dry. In a world where contact with water is unavoidable, insects have instead evolved to trap air in the gaps of their wings, letting water slide off instead of sticking. (Image credit: C. Perani; via Colossal)

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    Schooling at Scale

    Relatively simple visual and hydrodynamic signals are enough to make digital fish school in ways that resemble living ones. Here, researchers look at what happens when well-behaved schools of fish get too big. The researchers first demonstrate that their schools behave reasonably at one hundred members, either in a schooling configuration or a group milling around a central region.

    At one thousand fish, the schools are still reasonably coherent and sensible. But at fifty thousand fish, the picture is drastically different. Neither schooling nor milling groups are able to remain together. They fracture and scatter into smaller groupings. (Video and image credit: H. Hang et al.)

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  • Frog Kick

    Frog Kick

    A toad swims across a pond in this award-winning image from photographer Paul Hobson. The shot was actually captured from below the water, with the camera kept dry in a glass housing. Although the frog appears to be mid-leap, the light-distorting ripples around its feet hint at the flow its kick generated. It’s reminiscent of the vortices left by water striders as they move. (Image credit: P. Hobson/BWPA; via Colossal)

    “A Toad Swims Across Its Woodland Pond” by Paul Hobson
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  • Fluid Flows Break Up Microswimmer Clumps

    Fluid Flows Break Up Microswimmer Clumps

    The field of active matter looks at the collective motion of particles and organisms–how birds flock and fish school. In systems of “dry” squirmers–those that have no hydrodynamic interactions with one another–clumps of squirmers can form with empty spaces in between them. This is known as motility-induced phase separation, or MIPS. Researchers wondered whether microswimmers in a fluid–which do produce hydrodynamic forces that can affect one another–would also show MIPS.

    In a new study, researchers show, instead, that hydrodynamic interactions between swimmers will prevent (or destroy) these clumps. Through a combination of theoretical work and simulation, the authors found that translational flows between swimmers swept the swimmers out of clumps as they formed. Rotational flows between swimmers made them able to change direction faster, which also kept stable clumps from forming. (Image and research credit: T. Zhou and J. Brady; via APS)

    Hydrodynamic interactions destroy clumps of microswimmers. This simulation shows microswimmers that are initially in a clumped formation before hydrodynamic interactions are "turned on". Once the swimmers can affect one another through the flows their motion creates, the clumps quickly break apart.
    Hydrodynamic interactions destroy clumps of microswimmers. This simulation shows microswimmers that are initially in a clumped formation before hydrodynamic interactions are “turned on”. Once the swimmers can affect one another through the flows their motion creates, the clumps quickly break apart.
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    Bioconvection

    Convection isn’t always driven by temperature. Here, researchers explore the convective patterns formed by Thiovulum bacteria. These bacteria are negatively buoyant, meaning they will sink if they aren’t swimming. They also have an asymmetric moment of inertia, so any flow moving past them tends to affect their swimming direction.

    When let loose in a Hele-Shaw cell with a oxygen levels that decrease with depth, the bacteria create complex convection-like patterns. They swim slowly upward in wide, slow plumes and sink in denser, narrow plumes. In other areas, they form large-scale rotating vortices. (Video and image credit: O. Kodio et al.)

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  • Turbulence and Bioluminescence

    Turbulence and Bioluminescence

    If you’ve ever seen crashing waves glowing blue, you’ve been treated to bioluminescence. Although many creatures can bioluminesce, tiny dinoflagellates–a type of marine phytoplankton–are one of the easiest to spot. These microscopic organisms create a flash of light in response to viscous stresses. Their response to flow-induced stresses is so robust that they can be used to visualize stress fields.

    In a new study, researchers explored how turbulence affects the dinoflagellate’s luminescence. They mathematically modeled the dinoflagellate as an elastic dumbbell that emitted light based on its extent and rate of deformation. Then they explored how this model dinoflagellate behaved in different types of turbulent flows. They found that the fluctuations and intermittency of turbulent flows both encouraged the radiant displays. (Image credit: T. McKinnon; research credit: P. Kumar and J. Picardo)

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  • Thunderstorms Make Trees Glow

    Thunderstorms Make Trees Glow

    Scientists have long hypothesized that the high electrical charge of thunderstorms could produce an opposite charge in the ground that would discharge from the forest canopy. But this phenomenon, known as a corona, had never been observed on actual trees. A new study, however, has observed this ghostly ultraviolet (UV) glow from the tips of sweetgum leaves and loblolly pine needles during thunderstorms.

    Catching these coronae in action required a new kind of UV detector that was ultra-sensitive to the particular band of UV-light emitted by coronas, hot fires, or mercury lamps. Since the latter two weren’t present during the team’s field observations, they were able to conclude that the light they detected came from coronae.

    The group observed that corona discharges were transient, jumping from leaf to leaf and branch to branch across the forest canopy. For any creature capable of detecting that glow by eye, it must be incredible to watch the treetops lit by their own ever-shifting auroras during every thunderstorm. (Image credit: W. Brune; research credit: P. McFarland et al.; via SciAm)

    A UV corona forms on tree leaves beneath a thunderstorm.
  • “Frozen”

    “Frozen”

    For tiny invertebrates like this one, water is a very different substance than we’re used to. At this scale, surface tension is a force as powerful–or more so–than gravity. Droplets remain spherical, caught on long, spike-like hairs. Even the surface of a pond is different, forming a trampoline creatures can skim but that requires special techniques to escape. (Image credit: N. Baumgartner/CUPOTY; via Colossal)