FYFD

Tag: biology

  • Featured Video Play Icon

    A Primer on Blood Pressure

    Some of the most important fluid dynamics goes on every moment inside our bodies. After only a few weeks of gestation, the human heart begins its lifelong task of pumping blood throughout tens of thousands of kilometers’ worth of blood vessels. One of our simplest methods for tracking the health of this critical system is a person’s blood pressure, which measures the forces exerted on our blood vessels as our hearts pump. This video gives a brief primer on blood pressure as well as some of the problems that arise when extended bouts of high blood pressure damage our blood vessels. (Image and video credit: TED-Ed)

  • Bacterial Turbulence

    Bacterial Turbulence

    Conventional fluid dynamical wisdom posits that any flows at the microscale should be laminar. Tiny swimmers like microorganisms live in a world dominated by viscosity, therefore, there can be no turbulence. But experiments with bacterial colonies have shown that’s not entirely true. With enough micro-swimmers moving around, even these viscous, small-scale flows become turbulent.

    That’s what is shown in Image 2, where tracer particles show the complex motion of fluid around a bacterial swarm. By tracking both the bacteria motion and the fluid motion, researchers were able to describe the flow using statistical methods similar to those used for conventional turbulence. The characteristics of this bacterial turbulence are not identical to larger-scale turbulence, but they are certainly more turbulent than laminar. (Image credits: bacterium – A. Weiner, bacterial turbulence – J. Dunkel et al.; research credit: J. Dunkel et al.; submitted by Jeff M.)

  • Featured Video Play Icon

    Why Aren’t Trees Taller?

    Trees are incredible organisms, with some species capable of growing more than 100 meters in height. But how do trees get so big and why don’t they grow even taller? The limit, it turns out, is how far fluid forces can win over gravity.

    To live and grow, trees must be able to transport nutrients between their roots and their highest branches. As explained in the video, there are three forces that enable this transport inside trees: transpiration, capillary action, and root pressure. Of these, you are probably most familiar with capillary action, where intermolecular forces help liquids climb up the inside of narrow spaces, like the straw in your drink. Capillary action can’t lift liquids more than a few centimeters against gravity, though.

    Similarly, root pressure is limited in how far it can raise liquids. Functionally, it’s pretty similar to the way a column of water or mercury can be held up by atmospheric pressure acting at the base of a barometer. But atmospheric pressure can only hold up 10.3 meters of water, so what’s a tree to do?

    This is where transpiration — the most important force for sap transport in the tree — comes in. As water evaporates out of the tree’s leaves, it creates negative pressure that — along with water’s natural cohesion — literally drags sap up from the roots. It’s this massive pull that drives the flow and enables most of a tree’s height. (Image and video credit: TED-Ed)

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    Sundews Weaponize Viscoelasticity

    In nutrient-poor soils, carnivorous plants like the cape sundew supplement their diets by eating insects. To entice their prey, the cape sundew secretes droplets of sugary water. But unwary insects who land to feed soon find themselves unable to pull away from this viscoelastic liquid. Complex molecules in the fluid grant it elasticity, so when insects pull against it, the liquid stretches and pulls back instead of breaking up. Other carnivorous plants, like the pitcher plant, use similar non-Newtonian tricks to trap insects. (Video and image credit: Deep Look)

  • Fungal Fluid Dynamics

    Fungal Fluid Dynamics

    Many plants gain the soil-bound nutrients they need by trading with symbiotic fungi. Underground, these fungi spread networks that gather and store phosphorus, which they then trade with host plants to get the carbon they need. Research shows that the fungi can be shrewd traders, moving phosphorus from nutrient-rich areas to poorer ones in order to maximize their trade gains.

    What you see above are snapshots of some of this transport within the fungal network. Notice how flow within the branching network changes direction. The fungus can force these flow reversals in a matter of seconds, allowing it to move nutrients to wherever the best returns are found. (Image and research credit: M. Whiteside et al.)

  • The Power of a Penguin’s Rectum

    The Power of a Penguin’s Rectum

    When brooding their eggs, penguins can rarely leave the nest, but answering nature’s call is still necessary. To keep the nest clean, Adélie penguins project their feces up to more than a meter away. A new study refines previous calculations on this subject and finds that the penguin’s rectum develops far higher pressures than that of humans.

    In one hypothetical calculation, the authors estimate that a human of average height, capable of developing penguin-like rectal pressures, would project excrement more than 3 meters. In the authors’ words, “He/she should not use usual rest rooms.”

    Knowing the likely range of contact for penguins is important primarily for zookeepers, who understandably would like to avoid such projectiles. (Image credit: H. Neufeld; research credit: H. Tajima and F. Fujisawa; via phys.org)

  • Undulating Keeps Flying Snakes Steady

    Undulating Keeps Flying Snakes Steady

    Flying snakes undulate through the air as they glide. But, unlike on land, these wiggles aren’t for propulsion. A new study shows instead that they are key to the snake staying stable in flight.

    Upon take-off, a flying snake flattens its body, forming a wing-like shape that helps them generate lift and control drag. But while they glide, they also slither and pitch their tail.

    Researchers recorded more than 150 flights by live snakes, then used that data to construct their own digital snake. The model could fly like a real snake or be tested without undulations to see what would happen. The researchers discovered that, without that mid-air slithering, the snake quickly lost control and rolled to the side. (Image and research credit: I. Yeaton et al.; via NYTimes; submitted by Kam-Yung Soh)

  • Quantifying Bioluminescence

    Quantifying Bioluminescence

    Some single-celled organisms, like dinoflagellates, light up when disturbed. This bioluminescence is considered a defense mechanism, triggered by threats to the organism. Now researchers are quantifying just what it takes to light up a single dinoflagellate.

    Dinoflagellates respond both to stress caused by the fluid flow around them and to mechanical deformation — in other words, getting poked. Both methods involve bending and stretching the dinoflagellate’s cell wall, which stretches calcium-ion channels connected to bioluminescence. The researchers found that the intensity of the light produced depended both on the amount and speed of cell wall deformation.

    The model built from their observations should help scientists better understand what forces cause a specific response. That means dinoflagellates could be used as a non-invasive means of understanding fluid flow around swimmers like dolphins or sea lions! (Image and research credit: M. Jalaal et al.; via APS Physics)

  • The Challenges of Being Small

    The Challenges of Being Small

    For juvenile fish, feeding is a challenge. Their small size — often less than 5 mm in length — makes hydrodynamically capturing prey much harder because of viscosity’s relatively larger effect on them. But size may not be the only factor in determining their success, as a new study shows.

    Researchers studied feeding behaviors of two, equally-sized species’ larvae: zebrafish and guppies. The biggest difference between these two species is their developmental time prior to beginning to hunt on their own. Guppies develop five times longer than zebrafish larvae before they start feeding.

    Both fish have the same hydrodynamic limitations to overcome. If you look closely at the first image, you’ll see fluid being pushed ahead of the fish as it swims. The researchers refer to this as a bow wave, and it effectively announces to any prey that the fish is approaching. To sneak up on prey, the fish has to be able to generate enough suction force to pull its food in from beyond the bow wave’s reach. The experiments showed that guppies were able to do this reliably, while zebrafish could not. The subsequent difference in their feeding success was stark: the guppies’ success rate was almost five times that of the zebrafish! (Image and research credit: T. Dial and G. Lauder, source; via G. Lauder)

  • Shake It!

    Shake It!

    Vibrate a pool of water, and you’ll get Faraday waves, ripple-like excitations that form their own distinctive pattern compared to the driving vibration. But you don’t have to vibrate a pure liquid to see Faraday waves. A recent study observed them in vibrated earthworms!

    Odd as this may sound, the results make sense. When anesthetized (as they were in the experiments), earthworms are essentially a liquid wrapped in an elastic membrane, which is not so different from a droplet held together by surface tension.

    But why vibrate earthworms in the first place? It turns out earthworms are a good model organism for studies of vertebrate neural systems, so observing how vibrations propagate through them can provide insight into how our own nervous systems transmit information. (Image, research, and submission credit: I. Maksymov and A. Pototsky)