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Blueberry pancake

Researchers explain the unique movement of Pancake when swirled

When a glass filled with wine is swirled clockwise, the wine will also spin in the clockwise direction, however, while making a blueberry pancake, if it is swirled in the clockwise direction, the pancake spins in an anticlockwise direction.

The same is the case with a glass of beads. A few beads will rotate clockwise when the glass is swirled clockwise. However, a lot of beads in a glass when swirled clockwise will rotate counterclockwise.

Lisa Lee, a graduate student of Applied Physics at School of Engineering and Applied Sciences, Harvard said she was surprised at the behaviour of these exact same objects under the same situations.

The research team set about to understand the physics behind these actions and it turns out that friction is responsible for this. Beads are a part of a class of material called granular media, which means a collection of macroscopic particles such as sand or snow. The work appears in the Physical Review E journal.

Wine rotates clockwise when moved clockwise due to wine being a liquid-like granular media in low friction, while pancakes rotate in an anticlockwise direction when rotated clockwise which is similar to granular media under high friction.

Macroscopic particles are very interesting as they can move like a liquid or a solid depending on the conditions. Sand flows like a liquid in an hourglass but acts like a solid to support your weight on beaches. The object transition from liquid to solid has been an open question for decades.

Lee and the researchers found out that smaller groups of beads will have lower effective friction than larger pairs of beads which results in the transition from liquid to solid. When one particle rolls in one direction it experiences little friction however if many particles which are in contact with each other roll in the same direction, then they experience a large amount of friction which causes the group to solidify and thus change the behavior.

Using computer simulations, Lee and co-authors, John Paul Ryan and Miranda Holmes-Cerfon showed that in the absence of friction, the particles never solidified, no matter the quantity in which they were present. The rougher the particles were, the quicker was the transition from liquid to solid.

Shmuel Rubinstein, Associate Professor of Applied Physics at SEAS and senior author of the study said that this is an interesting case of system-size behaviors emerging from local interactions. The emergence of coherent circulations is an exciting subject for study like the case of 2D turbulence and active spinners. It is quite interesting that daily objects such as marbles and dishes can demonstrate similar physics.

Journal Reference: Physical Review E.

The newly described stone eating shipworm, known as Lithoredo abatanica.

Researchers discover stone eating creatures in Philippines

Researchers associated with numerous institutions across the U.S. have discovered a rare species of shipworms named Lithoredo abatanica that feeds on rocks and stones instead of woods. They published a paper in the Proceedings of the Royal Society B and described their study and the discovery.

The shipworms are water-dwelling mollusks which are known due to their ability to chew the wood and digest it. They are also popular for creating holes in wooden structures present in water and now, the researchers claim to have discovered a species of these shipworms that do not feed on wood at all but eats the limestone instead.

After breaking through the rocks to get a specimen of these worms, they reported their small size of 150mm and their close resemblance to worms than other mollusks. Unlike the wood-eating shipworms, these worms have large, flat teeth that could scrape away rocks unlike, sharp invisible teeth of the wood eater ship worms which could cover the shells and lacked the sac which was used to digest these woods. In addition to this, these shipworms were also found to excrete sand. Researchers, however, cannot determine any motive behind their rock eating nature but say that it does not impart any nutritional value.

These ship worms which eat rocks have the tendency to change the course of rivers as well. These shipworms have extremely shrunken shells, two in number which is modified into drill like heads.

The regular wood eating marine ship worms store the wood that they eat in a very special digestive sac which they ingest and scrape away to make a protective burrow for itself. The rock-eating ship worms do the same except that they differ from the usual ones in the fact that they lack the sac.

The rock-eating ship worms rely on the bacteria that reside in their gills to produce nutrients and food which is sucked in by this newly existing shipworms from the hind end for nourishment. The gills found in the stone-eating shipworms are quite larger than normal, which shows that they are important for their survival. Researchers are working on how their metabolism works.

rayleigh taylor instability

Researchers demonstrate gravitational instability in granular materials for the first time

Natural phenomenon such as volcanoes and mudslides can be explained by the movement of granular particles like sand. This time engineers illustrated how bubbles are formed in the sand of lighter grain as same as other liquids even though powder materials move towards each other when mixed. Though grains present in the sand are solid when the huge volume is mixed it behaves like a liquid. Falling sand dunes or sand flowing through an hourglass are known as granular materials and the science of how they flow is still unknown.

Rayleigh-Taylor instability a mechanism in fluid dynamics explains the reason that it happens between two fluids having different densities and the light fluid thrusts the heavy fluids just like oil comes up when mixed with water. Engineers of Columbia University and ETH Zurich had discovered something likely. Chris Boyce of Columbia University, a chemical engineer said that they think their discovery can be transformed. The group discovered that upwards gas flow between granular material and vibration both produces a process alike RT instability. The study has been published in the Proceedings of the National Academy of Sciences In this process, the lighter grain starts to move upwards in between heavier grains forming fingers and bubbles. 

This works just like oil and water but they never mix whereas sand mixes. The bubbles are formed because the group of lighter grain allows the gas to flow through it easier than the heavier grains which rise the tension of the upward drag force and downward contact forces created by gas flow which creates RT instability making the results similar to that of RT instabilities in liquid but the process is different.

The researchers also noticed captivating things like the cascade branch of a descending granular droplet as mentioned in their paper. The weight of the droplets moving downwards of the heavier grains create a chain of force downwards thus not letting the drops to pass through. So the droplets break into branches while moving downwards creating somewhat similar to lightning. Another discovery was the instability similar to RT can occur when there is a huge range of flow of gas and conditions of vibration which can be used as a help in understanding the role of subterranean processes at the time of earth tremors.

Boyce said that their discovery can not only be used to describe the process of the formation of mineral deposits and geological formations but also in technologies of powder-processing in the energy, pharmaceuticals industries, and constructions. Thus we can conclude that the study of bubbles is helping to find out new things behind geological factors.