FYFD

Category: Research

  • Blowing Smoke

    Blowing Smoke

    It’s unusual – but not entirely unheard of – to see volcanoes blowing smoke rings during inactive periods. But given their unpredictability, scientists had not studied this phenomenon in much depth. In a recent presentation, though, a group unveiled results from numerical studies of volcanic vortex rings. They found that the decreasing pressure on rising magma allows dissolved gases to emerge as bubbles. If the magma has the right viscosity, those bubbles can merge into one big pocket that depressurizes explosively in the vent. As the hot gases burst upward, the walls of the vent cause them to curl up into a vortex ring, provided the vent is fairly circular and uniform. That sends the roiling vortex up into the atmosphere, where it cools, condenses, and becomes visible.

    The need for a circular vent matches observations of volcanic vortex rings in nature, like the infrared image shown above. Volcano watchers find that vortex rings only form from some vents, and the more circular the vent, the more likely it can produce vortex rings. (Image credit: B. Simons; research credit: F. Pulvirenti et al.; via Nat Geo; submitted by Kam-Yung Soh)

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    How Ant Stingers Work

    Anyone who’s felt the sting of a fire ant knows it only takes an instant for this species to deliver a painful blow. Scientists are uncovering why that is using some of the first-ever high-speed footage of ant stingers in action. Stingers are actually made up of multiple separate pieces, including a central stylet and a pair of lancets that move up and down along the stylet. This lancet motion pulls the stinger deeper and helps form and deliver droplets of venom. The back-and-forth motion helps ants release up to 13 venom droplets per second, a level of speed that’s key for some of its high-speed, small-scale battles. (Image and video credit: Ant Lab; research credit: A. Smith)

  • Plasma Shock Waves

    Plasma Shock Waves

    Solar flares and coronal mass ejections send out shock waves that reverberate through our solar system. But shock waves through plasma – the ionized, high-energy particles making up the solar wind – do not behave like our typical terrestrial ones. Instead of traveling through collisions between particles, these astrophysical shock waves are driven by interactions between moving, charged particles and magnetic fields. 

    A driving burst of plasma accelerated into ambient plasma creates electromagnetic forces that accelerate ambient ions to supersonic speeds, pushing the shock wave onward even without particles directly colliding. Thus far, piecing together the physics of these interactions has been a challenge because spacecraft are limited in what and where they can measure. But a group here on Earth has now recreated and observed some of this process in the lab. (Image credit: NASA Solar Dynamics Observatory; research credit: D. Schaeffer et al.; via phys.org)

  • Collecting Dew

    Collecting Dew

    In areas of the world where fresh water is scarce, one potential source is dew collection. Scientists have been working in recent years on making overnight dew collection more efficient. The challenge is that drops won’t begin to slide down an inclined surface until they are large enough for gravity to overcome the surface tension forces that pin the drop. Most efforts have focused on reducing the critical size where drops begin to slide through surface treatments and chemical coatings. 

    A recent study, however, uses a different tactic. Instead of aiming to reduce the critical drop size, these researchers built a grooved surface designed to encourage drops to grow faster. By helping the droplets coalesce quickly, their surface (right side) is able to start shedding droplets much faster than a smooth surface (left side). Under test conditions, the grooved surface was shedding droplets after only 30 minutes, whereas the smooth surface shed its first drops after 2 hours. (Image and research credit: P. Bintein et al.; see also APS Physics)

  • Testing Vesicles

    Testing Vesicles

    In biology, vesicles contain a liquid surrounded by a lipid membrane. The characteristics of that membrane – like its stiffness – can change over time in ways that indicate other changes. For example, vesicles carrying HIV become stiffer as they grow more infectious. In the past, to observe these properties scientists used atomic force microscopes, which require removing the vesicles from the liquid in which they naturally reside. That’s problematic because it potentially changes how the vesicle responds. 

    Now researchers have developed a new method: a microfluidic system that subjects vesicles to electric fields in order to deform them and measures their properties without removing them from their carrier fluid. This provides a faster and more reliable method of testing a vesicle’s deformation, capable of testing hundreds of samples at a time. (Image credit: Wikimedia; research credit: A. Morshed et al.; submitted by Eric S.)

  • Liquid Magnets

    Liquid Magnets

    Ferrofluids – those distinctively spiky liquids – are made up of magnetically sensitive nanoparticles in a carrier liquid, and although they respond to applied magnetic fields, they retain no magnetism outside of that field. But researchers have now succeeded in making actual liquid magnets. Shown above, these drops also contain ferromagnetic nanoparticles. But unlike traditional ferrofluids, in these drops the nanoparticles are not entirely free to move. They’re jammed together at the interface, so when a magnetic field is applied, the nanoparticles will align like tiny bar magnets. When that magnetic field is removed, though, the nanoparticles cannot easily reconfigure, so they remain aligned and the drops continue being magnetic. 

    Researchers hope these ultrasoft magnets, which can be manipulated remotely through magnetic fields, will be useful in the future for applications like targeted drug delivery. In theory one could introduce, say, chemotherapy drugs into one of these liquid magnets, then use magnetic fields to guide it directly to a cancerous tumor. (Image and research credit: X. Liu et al.; via Science News; submitted by Kam-Yung Soh)

  • Entraining Bubbles

    Entraining Bubbles

    If you stand on a bridge and watch the current flow past pylons below, you’ll see disturbances marking the wakes. Dragging a rod – or an oar – at a high enough speed through the water creates something similar: a wavy cavity in the fluid surface that surfs along behind the rod. The faster you pull the rod, the harder you’ll have to work, until that wake becomes so turbulent that it begins entraining air bubbles, like the tiny ones seen above. Once entrainment starts, the drag coefficient drops somewhat, presumably due to changes in the pressure distribution around the rod. The characteristics of air entrainment change with object size as well. Larger rods can entrain air through the cavity and not just in the wake. (Image and research credit: V. Ageorges et al.)

  • The Snowy Salt of the Dead Sea

    The Snowy Salt of the Dead Sea

    At nearly 10 times saltier than the ocean, the Dead Sea is one of the saltiest places on Earth, and since 1979, scientists have observed it growing even saltier as snow-like salt precipitates to the bottom of the lake. Numerical simulations have now confirmed that this salt-fall is the result of double-diffusive salt fingers.

    Here’s how the mechanism works: the upper layer of the lake is made up of warmer, saltier water covering deeper, colder waters. As the sun evaporates water near the surface, what’s left behind becomes saltier and heavier. Tiny pockets of this warm, salty water sink into colder regions and rapidly cool. The heat can move a lot more quickly than the salt, though, and since cold water cannot hold as much salt as warmer water, some of the salt precipitates out. That forms the falling crystals scientists observe sinking to the bottom of the lake. (Image and research credit: R. Ouillon et al., source; via Physics World; submitted by Kam-Yung Soh)

  • Superwalkers

    Superwalkers

    Walking droplets – drops that bounce their way across a pool of the same liquid without coalescing – have fascinated researchers in recent years with their unusual behaviors, some of which mimic quantum phenomena. In a new experiment, researchers vibrate the pool at two frequencies simultaneously, which helps support much larger droplets, known as superwalkers. When the two driving frequencies are close to a harmonic match – like at 80 Hz and just under half that at 39.5 Hz – the droplets will walk, then come to a stop, and then begin walking again. (Image and research credit: R. Valani et al.; via APS Physics; submitted by Justin B and Kam-Yung Soh)

  • Jets from Lasers

    Jets from Lasers

    Laser-induced forward transfer (LIFT) is an industrial printing technique where a laser pulse aimed at a thin layer of ink creates a tiny jet that deposits the ink on a surface. In practice, the technique is plagued with reproducibility issues, in part because it’s difficult to produce only a single cavitation bubble when aiming a laser at the liquid layer. This is what we see above. 

    The laser pulse creates its initial bubble just above the middle of the liquid layer. Shock waves expand from that first bubble and quickly reflect off the liquid surface (top) and wall (bottom). When reflected, the shock waves become rarefaction waves, which reduce the pressure rather than increasing it. This helps trigger the clouds of tiny bubbles we see above and below the main bubble. 

    The effect is worst along the path of the laser pulse because that part of the liquid has been weakened by pre-heating, but impurities and dissolved gases in the liquid layer are also prone to bubble formation, as seen far from the bubble. The trouble with all these unintended bubbles is that they can easily rise to the surface, burst, and cause additional jets of ink that splatter where users don’t intend. (Image and research credit: M. Jalaal et al.; submitted by Maziyar J.)