The Mystery of the Hourglass: Understanding Solid-Fluid Transition in Granular Materials

Granular materials such as sand have mysterious properties that continue to baffle scientists; For example, Imagine sand in an hourglass, sometimes it can behave like a solid and sometimes it can flow freely like a liquid. Experts Onuttom Narayan of the University of California and Harsh Mathur of Case Western Reserve University in Ohio say they have found a way to describe this behavior.

In a paper published in the scientific journal European Physical Journal E, researchers describe how they have found a way to identify this point of interference between the flow and solid states of granular materials. It is important to understand the problem to prevent solid blockages, especially where smooth flow is required for many materials used in the pharmaceutical, construction and agricultural industries.

For example, in the production of some drugs in pill format, a process must be carried out that compresses the granules and turns them into tablets, so that the material turns from liquid to solid. Data from the study can also be used to predict the behavior of terrestrial sedimentary zones where buildings will be constructed.

“The vibration spectrum of granular packings can be used as a signature of the interference transition, as the density of states at zero frequency becomes nonzero in the transition. It has previously been suggested that the vibration spectrum of granular packings can be obtained approximately from random matrix theory,” the study explains.

Interference point: liquid and solid

To understand this point of interference, the researchers ran computer simulations with information gathered by other scientists by studying frictionless polystyrene spheres. From here, The simulations were compared to random matrix theory, a compilation of mathematical predictions developed in the mid-1950s.

The result allowed scientists to develop A model describing the static and vibrational properties of granular materials. The observation also made it possible to understand that the granules compress and retract like springs as they collide with each other; This shows that even a small collision can generate a large force due to the behavior of the granules.

The ultimate goal of scientists The aim was to study the evolution of the distribution of these granular materials near the point of interference when particles collide before becoming trapped. – like a pill compressed until it solidifies.

“In this paper, we show that the random matrix approach can be used successfully to calculate correlations between vibrational frequencies in a granular system close to the interference transition, if the matrix set is chosen correctly. The vibrational properties of granular matter also show that this may be possible. The paper aims to provide a unified understanding of the physics of granular matter.” “It can be applied more broadly,” he said.

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