It turns out that if you keep turning a tube containing tens of thousands of small dice from side to side, the dice will become tightly packed.
If you roughly put dice with a side of 5 mm into a cylinder and keep turning them left and right with a constant force, almost all the dice will be neatly lined up in about 3 hours to 1 day and packed tightly together without any gaps. has been revealed in research. This technology is expected to be applied to industrial fields where it is necessary to align particulate matter, and to processing technology in zero gravity space in space.
Physics - Focus: Dice Become Ordered When Stirred, Not Shaken
The act of aligning fine particles is widely used in a variety of cases, including the construction industry, where sand and pebbles are mixed to make cement, and the pharmaceutical field, where materials are mixed uniformly to make medicines. In a gravitational environment, by applying vibration to a container containing particulate material or hitting it gently from the outside, it is possible to create 'looseness' in the overlap of the particles inside, and remove the excess space left inside. You can reduce the overall volume by compressing it tightly.
A research team led by Diego Maza of the University of Navarra in Spain has been searching for a different method, and has found that it is possible to put particulate matter in a cylindrical container and then rotate the tube to tightly gather the material. We investigated.
In the experiment, 25,000 5mm square dice were poured into a cylinder that was set upward. In this state, we continued to twist the tube clockwise and counterclockwise with a constant force when looking at the tube from above, and examined changes in the particles. Then, as shown below, the dice were initially stacked apart, but after a certain period of time, they changed to a state where they were aligned as if they had been laid out precisely by a machine.
by K. Asencio et al., Phys. Rev. Lett. (2017)
This phenomenon is thought to occur because both the force that presses the dice against the wall of the cylinder due to the centrifugal force generated by the rotation of the cylinder, and the acceleration force of the vibrations generated when the rotation is reversed are applied to the dice. Masu. In particular, the acceleration force when reversing has a large effect on the results, and when the acceleration force exceeds ``0.5G'', the time required for alignment is significantly reduced. If you continue to apply acceleration of 0.5G with the cylinder's reversal period being about 1 second, it will take about 10,000 cycles to reach the final state, which is 10,000 seconds if you calculate that 1 cycle = 1 second. This means that the alignment was completed in about 2 hours and 46 minutes.
On the other hand, when the acceleration fell below 0.5G, the pace of alignment suddenly stagnated, and even after 100,000 cycles, the dice in the center of the tube continued to be disjointed. Mr. Maza, who has witnessed the current situation, believes that it will take more than 10 years for everything to be aligned.
Looking at the arrangement of the dice from above, when the acceleration is weak (a), the arrangement is random, whereas when the acceleration is strong (b), almost all the dice draw concentric circles, and You can see that they are arranged radially from the center.
Matthias Schröter of the Max Planck Institute's Dynamics and Self-Organization Institute explains this phenomenon, which occurs when colloidal particles contained in a liquid come together. He points out that the same mechanism as ``crystalline order'' occurs when the dice touch the wall. Due to the centrifugal force and acceleration force, the outermost dice first come into contact with the wall surface without any gaps, creating another new 'wall surface.' Then, the dice located one step inside create a wall surface in the same way... It is thought that by continuing to occur inward, a state in which all the dice are lined up in an orderly manner is created. .
Mr. Maza believes that this method can be applied to handling materials that could not be aligned using conventional methods. He also talks about the prospect of being able to perform alignment in the same way as on the ground in outer space, where there is no gravity.
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