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Tag: biology

  • 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)

  • Gliding Like a Grasshopper

    Gliding Like a Grasshopper

    Many biorobots are built after flies and bees–insects that rely heavily on flapping flight. For small robots, this means carrying heavy batteries or remaining tethered in order to power their motors. Instead, researchers have turned to grasshoppers for a lesson in small-scale gliding.

    Grasshoppers have two sets of wings. The forward set provide protection and camouflage, while the hindwings are used to fly. The team studied the corrugated, foldable hindwings of the American grasshopper, then 3D-printed model wing designs and attached them to gliders. They found that the corrugated wings performed well at low angles of attack, but that non-corrugated wings–which still shared the outline and camber of the insect’s wings–were more efficient gliders over a range of conditions.

    The team hopes that their grasshopper-inspired gliders give insect-like biorobots more efficient flying options. (Image credit: Princeton/S. Khan/Fotobuddy; research credit: K. Lee et al.; via Physics World)

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  • Caught in a Spider’s Web

    Caught in a Spider’s Web

    Grains of pollen are caught amid droplets on a spider’s web in this award-winning image by John-Oliver Dum. How droplets behave on fibers has been a popular topic in recent years with research on how droplets nestle into corners, how they slide on straight or twisted wires, the patterns formed by streams of falling drops, and what happens to a droplet on a plucked string. (Image credit: J. Dum; via Ars Technica)

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  • Necroprinting By Mosquito

    Necroprinting By Mosquito

    Engineers have been adapting biological materials into robotics in recent years. One of the latest versions of this trend is “necroprinting,” in which researchers built a microscale 3D printer around a mosquito’s proboscis. Made to pierce thick skin to reach blood, the mosquito proboscis offered the kind of size, geometry, and stiffness needed for small-scale printing. The team found that their necroprinter performed well at the ~20 micron scale, with the mosquito-based nozzle costing only a fraction of what a conventional human-made nozzle would. (Image credit: NIAID; research credit: J. Puma et al.; via Ars Technica)

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  • A Drop of Algae

    A Drop of Algae

    Spheres of a Volvox colonial algae glow green inside a droplet in this award-winning microphotograph by Jan Rosenboom. Pinned on an inclined surface, the droplet is frozen in a balance between gravity and surface tension that keeps its shape–and its contact angles–asymmetric. Droplets will also take on a shape similar to this when air is blowing past them. (Image credit: J. Rosenboom; via Ars Technica)

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  • Marangoni Effect in Biology

    Marangoni Effect in Biology

    For decades, biologists have focused on genetics as the key determiner for biological processes, but genetic signals alone do not explain every process. Instead, researchers are beginning to see an interplay between genetics and mechanics as key to what goes on in living bodies.

    For example, scientists have long tried to unravel how an undifferentiated blob of cells develops a clear head-to-tail axis that then defines the growing organism. Researchers have found that, rather than being guided purely by genetic signals, this stage relies on mechanical forces–specifically, the Marangoni effect.

    The image above shows a mouse gastruloid, a bundle of stem cells that mimic embryo growth. As they develop, cells flow up the sides of the gastruloid, with a returning downward flow down the center. This is the same flow that happens in a droplet with higher surface tension in one region; the Marangoni effect pulls fluid from the lower surface tension region to the higher one, with a returning flow that completes the recirculation circuit.

    The same thing, it turns out, happens in the gastruloid. Genes in the cells trigger a higher concentration of proteins in one region of the bundle, creating a lower surface tension that causes tissue to flow away, helping define the head-to-tail axis. (Image credit: S. Tlili/CNRS; research credit: S. Gsell et al.; via Wired)

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