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Search results for: “art”

  • How the Hagfish Deploys Its Slime

    How the Hagfish Deploys Its Slime

    Hagfish – an eel-like species – are known for their prodigious slime production, which helps them escape predators (and, in some cases, seriously muck up highways). Part of the hagfish’s slime consists of ~10 cm fibers that the creature deploys in tiny skeins (bottom) only a hundred microns across. To form the viscoelastic slime that thwarts its predators, those skeins of fiber have to unravel and do so in only tenths of a second. A new study shows that viscous drag plays a major role in that unraveling. 

    Most fish use a suction method to catch prey. In the hagfish’s case, that does the predator more harm than good because the very flow it creates to try and catch the hagfish pulls the slime skein apart and helps the slime expand 10,000 times in volume, creating a mess that chokes the gills of the attacking fish. (Image credit: top – L. Böni et al.; bottom – G. Choudhary et al., source; research credit: G. Choudhary et al.; via Ars Technica; submitted by Kam Yung Soh)

  • Viscoelasticity and Liquid Armor

    Viscoelasticity and Liquid Armor

    One proposed method for improving bulletproof armor is adding a layer of non-Newtonian fluid that can help absorb and dissipate the kinetic energy of impact. Thus far researchers have focused on shear-thickening fluids – like cornstarch-based oobleck – filled with particles that jam together if anything tries to deform them quickly. But is it really the shear-thickening properties that matter for high-speed impacts?

    To test this, researchers studied projectile impact on three fluids: water (left), a cornstarch mixture (not shown), and a shear-thinning polymer mixture (right). Water is Newtonian, and it slows down the projectile but doesn’t stop it. Both the shear-thickening cornstarch and the shear-thinning polymer mixture do stop the projectile. And by modeling the impacts, researchers concluded that the key to that energy dissipation isn’t their shear-related behaviors: it’s the fact that both fluids are viscoelastic.

    That means that these fluids show both viscous (fluid-like) and elastic (solid-like) responses depending on the timescale of an impact. The high speed of the impact triggered a strong viscous response in both fluids, bringing the projectile to a halt. And if, as the researchers suggest, it’s a fluid’s viscoelasticity that matters most, that widens the field of candidates when it comes to developing a fluid-based armor. (Image and research credit: T. de Goede et al.)

  • Sorting Blood Cells

    Sorting Blood Cells

    Many diseases – like sickle-cell anemia and malaria – are accompanied by changes in the stiffness of red blood cells. And while microfluidic devices capable of sorting blood cells by size exist, few have made microfluidic devices capable of sorting blood cells by their deformability. But a new set of simulations suggests we could do so relatively easily.

    Existing devices sort blood cells by size using an array of tiny posts – kind of like a cellular pachinko machine. Through simulation, researchers found that by changing the shape of these posts – specifically by turning them from circles into sharper triangles –  they could sort the red blood cells by their stiffness. Because the sharp corners create large local stresses in the fluid, the blood cells get deformed when passing the corner. That ends up deflecting stiffer cells into a different stream. Build a whole array of posts and you can sort the blood cells by their degree of stiffness – ideally allowing you to isolate the most diseased cells. (Image and research credit: Z. Zhang et al.; via APS Physics)

    ETA: Added a clarification: some researchers, like Beech et al., have investigated deformability-based sorting devices.

  • Landslide Lubrication

    Landslide Lubrication

    In 2008, an 8.2 magnitude earthquake in China caused the enormous Daguangbao landslide, which loosed over one cubic kilometer of rocks and debris. That material rushed down the mountainside, running more than 4 kilometers before coming to a stop. A new study uses field measurements and laboratory experiments to explain how the landslide could run so far from its source.

    The researchers found that friction between the sliding material and the stable rock heated that layer to over 850 degrees Celsius, hot enough to start decomposing the dolomite in the fall. That vaporized carbon dioxide out of the rock, which helped lower the friction. Simultaneously, the high temperatures and high pressures within in the landslide caused recrystallization in the falling rocks; this created a viscous layer that helped lubricate the slide. The team estimated that the two mechanisms working in tandem enabled the landslide to reach an estimated 60 m/s. (Image and research credit: W. Hu et al.; via Nature; submitted by Kam-Yung Soh)

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    “The World Below”

    Since the first cosmonauts and astronauts entered orbit around our planet, they’ve held a unique perspective. Thanks to the timelapse photography of recent astronauts aboard the ISS and the editing skills of photographer Bruce W. Berry, Jr, the rest of us can enjoy a taste of that viewpoint. Turn up the volume, fire up the big screen, and enjoy.

    I particularly like how several of the sequences show off the depth of the atmosphere. Earth’s atmosphere is incredibly thin compared to the size of our planet – less than one percent of Earth’s radius – but thanks to the shadows that clouds cast on one another, you can really appreciate their height in sequences like the one at 2:26. (Video credit: B. Berry, Jr. using NASA footage)

  • Patterns of Flame

    Patterns of Flame

    In nature, the way a system behaves often depends on multiple competing factors. This is particularly apparent for chemical reactions, some of of which can oscillate in wild patterns as different forces compete. Similar patterns can occur in combustion, as shown above.

    What you see here are patterns formed on a flame propagating down a tube. They’re a result of what’s known as a thermal-diffusive instability. Flames like these typically propagate by conducting heat into the fuel-air mixture ahead of the flame front, thereby raising its temperature, while, simultaneously, fuel and air diffuse into the flame to sustain the chemical reactions. If the rates of heat transfer and chemical diffusion are balanced, the flame moves steadily. But if there’s an imbalance between those factors, instabilities occur.

    In this case, the temperature rises much faster than the time needed for fresh fuel to move into the flame. As the temperature goes up, the reaction rate increases exponentially, and the flame surges forward. But the slow resupply of fuel makes the reaction rate drop, causing the flame’s progress to stall. This interplay results in the complex, pulsating instabilities we see here. (Image and submission credit: H. Pearlman; research credit: H. Pearlman and D. Ronney)

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    The Sharpshooter Insect

    The sharpshooter is a small, sap-sucking insect capable of consuming more than 300 times its body weight in fluid each day. To sustain that level of intake, the insect also has to have a robust mechanism for expelling excess fluid, and that particular talent has earned the insect the nickname of the “pissing fly”. Together a group of sharpshooters can expel enough fluid to imitate rain (top).

    Individually, the insects form a droplet on hydrophobic hairs near their anus. Once the droplet is large enough, those hairs bend like a spring, and the droplet gets catapulted off the insect with an acceleration greater than 20g. That makes it among the fastest reactions in the natural world – more than twenty times the acceleration of a cheetah. Understanding this mechanism is valuable for engineers building robotics as well as for finding ways to counter the agricultural menace the sharpshooters present when it comes to spreading diseases among infected crops. (Image and video credit: E. Challita et al.; via WashPo; submitted by Marc A.)

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    Massive Worthington Jet

    The FloWave facility in Scotland is one of the coolest ocean simulators out there. Equipped with 168 individual wave makers and 28 submerged flow-drive units, it’s capable of recreating almost any ocean conditions imaginable. So naturally the Slow Mo Guys used it to create a giant spike wave.

    Essentially, this is an oversized Worthington jet, the same as the ones you see after a droplet hits the surface. But with several thousand tonnes of crystalline clear water, the effect of that wave focusing is pretty spectacular. When you’re watching the high-speed footage, be sure to pay attention to the details, like the glassy surface of the collapsing jet, or the way holes open and expand as the splash curtain comes down around Dan’s head (above). Longtime readers will recognize many familiar features. (Image and video credit: The Slow Mo Guys)

  • Forming an Oxbow

    Forming an Oxbow

    Without human intervention, meandering rivers become more sinuous over time. This is driven by the flow around a river bend, which tends to push sediment from the outer bank of the curve to the inner, making the bend more pronounced. Eventually, loops in the river can pinch off and form a separate oxbow lake, as seen in the animation above and video below.

    By studying many photo sequences like this one, researchers have concluded that how quickly a river bend meanders depends on its curvature. In general, the higher the curvature, the faster the river bend will migrate. When rivers deviate from this rule of thumb, it’s typically because part of a river bank is tougher to erode than other sections. (Image and video credit: Z. Sylvester/Geolounge; research credit: Z. Sylvester; via Landsat; submitted by Aatish B.)

  • Swallowing Physics

    Swallowing Physics

    Swallowing – whether of food, beverage, or medication – is an important process for humans, but it’s one many struggle with, especially as they age. To help study the physics behind swallowing, one research group has built an artificial mouth and throat model, shown in the bottom row of images. The model uses rollers to imitate the wave-like motion of swallowing. 

    In our mouths, chewed food typically combines with saliva to form a soft ball we can move from our tongue and down our throat with a series of reflex actions. How easily we swallow something depends on its flow properties, our saliva, shape, and more. 

    In their early studies of model swallowing, researchers have focused on what it takes to swallow pills (suspended in liquid). What they found is probably consistent with your own experience: smaller pills are easier to swallow than large ones, and elongated pills are easier to swallow than round ones of the same volume. That seems to be a function of elongated pills’ smaller cross-section when aligned with flow going down the throat. As the research continues, scientists hope to explore what can be done to make food easier to swallow for those who struggle with it. (Image credits: meal – D. Shevtsova; model – M. Marconati; via APS Physics; submitted by Kam-Yung Soh)

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