FYFD

Tag: science

  • In Search of a Better Espresso

    In Search of a Better Espresso

    Of specialty coffee drinks, espresso has the most cup-to-cup variation in quality. For those who are not coffee aficionados — such as yours truly — espresso is made by forcing hot water through a packed bed of coffee grains. Many factors can affect the final output, including the amount of dry coffee used, the fineness of the grind, water temperature and pressure, and how tightly packed the granular bed is.

    Conventional wisdom suggests that a fine grind is best since it increases the exposed surface area of coffee, but researchers found this is not, in fact, ideal. At very fine grinds, the bed of coffee becomes so tightly packed that water cannot pass through some sections, meaning that the coffee there is completely wasted since nothing is extracted.

    Instead, a slightly coarser grind provided better and more consistent extraction because water passed through the entire bed of grains. The researchers point out that this not only produces a good, consistent cup of espresso, but it does so with less waste, something that is becoming more and more important as the climate crisis affects coffee growers. (Image credit: K. Butz; research credit: M. Cameron et al.; via Cosmos; submitted by Kam-Yung Soh)

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    The World in a Droplet

    Capturing refracted images in a droplet is a popular pastime among high-speed photographers, and in this solo Slow Mo Guy outing, we get to see that process in video. Physically, the subject is a simple drop of water, which on impact with a pool, rebounds into a Worthington jet and ejects one or more droplets from its tip. Despite hundreds of years of study, it’s still a joy to watch, especially at 12,000 frames per second.

    It’s also not the easiest image to capture, and one thing I rather enjoy about this video is how it gives you a sense of the trial and error involved in capturing just the right view. Even without having to worry about the timing issues, there is a lot of fiddling with lenses, focus, lights, and positioning — something familiar not just to photographers and videographers but to many researchers as well! (Image and video credit: The Slow Mo Guys)

  • Perfecting Giant Bubbles

    Perfecting Giant Bubbles

    Whether young or old, everyone enjoys blowing soap bubbles, and the bigger the bubble, the more impressive it is. Researchers have been on a quest to discover how bubbles can survive with volumes measured in the tens of meters and thicknesses of mere microns.

    The key to these behemoth bubbles are the polymer chains inside them. The long molecules of polymers get entangled with one another and resist further stretching, which strengthens the soap film. The researchers found that a mixture of polymer lengths are even better for long-lasting bubbles because they entangle more fully than polymers that are all the same size.

    But if what you really want are practical results, I have good news for you: the researchers have released their recommended recipe for making the best giant soap bubbles. It’s included in the video below, but I’ve also reproduced it in text for easier recreation (with thanks to Ars Technica):

    Giant Soap Bubble Solution
    From the Burton Lab, via Ars Technica

    Ingredients
    1 liter of water (about 2 pints)
    50 milliliters of Dawn Professional Detergent (a little over 3 TBSP)
    2-3 grams of guar powder, a food thickener (about 1/2 heaping TSP)
    50 milliliters of rubbing alcohol (a little more than 3 TBSP)
    2 grams of baking powder (about 1/2 TSP)

    Directions
    Mix the guar powder with the alcohol and stir until there are no clumps.

    Combine the alcohol/guar slurry with the water and mix gently for 10 minutes. Let it sit for a bit so the guar hydrates. Then mix again. The water should thicken slightly, like thin soup or unset gelatin.

    Add the baking powder and stir.

    Add the Dawn Professional Detergent and stir gently to avoid causing the mixture to foam.

    Dip a giant bubble wand with a fibrous string into the mixture until it isf fully immersed and slowly pull the string out. Wave the wand slowly or blow on it to create giant soap bubbles.

    Happy bubble making! (Image credit: Burton Lab; video credit: Emory University; research credit: S. Frazier et al.; via Ars Technica; submitted by Kam-Yung Soh)

  • Where are Titan’s Deltas?

    Where are Titan’s Deltas?

    Saturn’s moon Titan is the only other planetary body in our solar system known to have bodies of liquid on its surface. But where Earth has lakes and seas of water, Titan’s are hydrocarbon-based, primarily ethane and methane. As on Earth, these liquids rain from skies and run down rivers and streams into larger bodies. What they do not do, as far as scientists can tell, is form deltas.

    On Earth (and ancient Mars), rivers tend to slow and branch out as they run into larger, still bodies. Many of these river deltas — like the Nile, Ganges, and Mississippi — are visible from space. But so far we’ve seen no equivalent formations on Titan, even though the radar resolution of Cassini should have allowed for it.

    There are currently two hypotheses to explain this absence. One posits that density differences between hydrocarbon rivers and lakes mean that deltas do not form. On Titan, the larger bodies are warmer and do not absorb as much atmospheric nitrogen, making them lighter overall. That means a cold, dense river might just sink immediately beneath the lake without slowing to deposit sediment.

    Another hypothesis is that deltas do form but that the shifting shorelines of Titan’s seas wash them out and make them unrecognizable. There’s evidence that Titan’s northern and southern hemispheres can swap their liquid hydrocarbons back and forth on a 100,000 year timescale. If that’s true, those shifts could obscure any evidence of deltas.

    Experiments are underway to test the first hypothesis, but the final answers may have to wait until NASA’s Dragonfly mission reaches Titan in 2034. (Image credit: Titan – NASA/JPL-Caltech/ASI/Cornell, Alaska – NOAA; via AGU Eos; submitted by Kam-Yung Soh)

  • Wild Gray Seals Clap Back

    Wild Gray Seals Clap Back

    Here’s a paper that cries out for fluid dynamical/acoustical follow-up: wild gray seals have been observed signaling underwater by clapping their forefins. As you can hear in the video, the sound is quite loud and carries well underwater. The biologists who observed the behavior postulate that it’s used by males during breeding season to ward one another off and to signal strength to nearby females.

    Although many species (including humans) slap against the water surface to generate noise, we don’t know of other species producing such a loud clap entirely underwater. The clap resembles the motions used by seals for propulsion, though the results are obviously quite different. I know plenty of researchers already looking into seal propulsion — here’s your future work! (Image and video credit: B. Burville; research credit: D. Hocking et al.; via Gizmodo)

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    Collective Catfish Convection

    Gather many birds, fish, or humans together and you often get collective motion that’s remarkably fluid-like in appearance. This video shows a group of juvenile striped eel catfish, an (eventually) venomous species that uses strength in numbers for protection while young. Their movement is rather mesmerizing, and if you watch individual catfish, you’ll see a sort of convective motion inside the blob. There’s a general downward trend near the front of the school and a rising one on the backside. Perhaps they’re taking turns feeding near the bottom of the pack? (Image and video credit: Abyss Dive Center; via Colossal)

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    Coalescence in Heavy Metal Droplets

    When a drop of water falls into a pool, it doesn’t always coalesce immediately. Instead, it can go through a coalescence cascade in which the drop partially coalesces, a daughter drop bounces off the surface, settles, and itself partially coalesces. We’ve seen this many times before, but today’s video shows something a little different: here the drop and pool in question are made of a gallium alloy immersed in a background of sodium hydroxide. This means that the drop has very high surface tension (and density) but does not form an oxidation layer on its surface that could inhibit coalescence. And just like the water droplet, the gallium alloy undergoes a series of partial coalescences.

    A heavy metal droplet undergoes partial coalescence with a pool of the same liquid.

    There’s one key difference, though. Did you notice that the water droplets bounce higher as the drops get smaller, but the gallium droplets do the opposite? Previous research suggested that the droplet rebound height is driven by capillary forces, but the high surface tension of both of these liquids means that capillary forces should be large for both of them. Perhaps there’s much more viscous drag in the gallium and sodium hydroxide case? (Image, video, and research credit: R. McGuan et al.)

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    “Otherworld, Vol. 1”

    Roman De Giuli’s “Otherworld, Volume 1” is a beautiful exploration of color and flow. Glittery particulates act as tracers in the flow, reminiscent of the way rheoscopic fluids do. In many sequences, the glitter lends a sense of texture to the flow. Without context, I cannot say whether those are true flow features, but they certainly remind me of instabilities like Tollmien-Schlichting waves. (Image and video credit: R. De Giuli)

  • Holding Fast in the Flow

    Holding Fast in the Flow

    Many tiny creatures in the natural world face living in fast flows. The larvae of the net-winged midge, for example, forage their way through fast-flowing Alpine springs with speeds of 3 m/s or more. You or I would find standing in such water a challenge, but these larvae are unbothered, thanks to the clever suction-cup-like appendages that help anchor them to rough rocks.

    The larvae generate their strong attachment with an outer rim flexible enough to conform to uneven surfaces. When they activate the central piston of the suction cup, this creates a seal strong enough to withstand forces up to 600 times the larvae’s body weight. But holding on to one spot forever is hardly useful, so the larvae also have a V-shaped notch in the cup controlled by dedicated muscles. When activated, this quickly breaks the seal, allowing the larvae to relocate. (Image and research credit: V. Kang et al.; via The Engineer; submitted by Marc A.)

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    Superwalking Droplets

    Vibrate a pool of silicone oil and you can generate walking droplets. Drive the vibration at two simultaneous frequencies and you can support much larger droplets, known as superwalkers. These superwalkers have their own intriguing dynamics, a few of which are featured in this video.

    Superwalkers can create promenading pairs, chase one another, orbit, and even form ordered and disordered crystals. They can even generate stop-and-go traffic patterns. As with regular walkers, these complex behaviors come from the interaction of bouncing droplets with their ripples and those of their neighbors. (Image, video, and research credit: R. Valani et al.)