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Posts Tagged ‘Interface structure’


The Music of the Elements

Larry H. Bernstein, MD, FCAP, Curator

LPBI

 

A Scientist is Creating Music from the Periodic Table

Mon, 02/29/2016 –   Suzanne Tracy, Editor-in-Chief, Scientific Computing and HPC Source
When researchers ran computer simulations to study vibrations, they noticed that some of the polymers didn’t behave as expected. If they tweaked the starting parameters, the system evolved normally up to a point, but then it diverged into a patterned series of vibrations that were not random. The simulated polymer becomes thermally superconductive — that is, capable of transporting heat with no resistance, much like the existing class of superconducting materials that conduct electricity without resistance.
When researchers ran computer simulations to study vibrations, they noticed that some of the polymers didn’t behave as expected. If they tweaked the starting parameters, the system evolved normally up to a point, but then it diverged into a patterned series of vibrations that were not random. The simulated polymer becomes thermally superconductive — that is, capable of transporting heat with no resistance, much like the existing class of superconducting materials that conduct electricity without resistance.

A researcher at Georgia Institute of Technology has applied for a National Science Foundation grant to create an educational app that would catalog a unique musical signature for each element in the periodic table so that scientists would have a new tool to use in identifying the differences between the molecular structures of solids, liquids and gases. Asegun Henry, Director of the Atomistic Simulation & Energy (ASE) Research Group, and an Assistant Professor in the George W. Woodruff School of Mechanical Engineering, is also in the process of setting all of the elements in the table to music.

“My hope is that it will be an interesting tool to teach the periodic table, but also to give people some notion about the idea that the entire universe is moving around and making noise,” Henry told Gizmodo. “You just can’t hear it.”

As Gizmodo’s Jennifer Ouellette explains, it’s more than just a fun exercise. “Henry and his graduate student, Wei Lv, were interested in a peculiar feature of polymers, long chains of molecules all strung together, with thousands upon thousands of different modes of vibration that interact with each other. Polymers are much more complicated than the simple toy models, so it’s harder to describe their interactions mathematically. Scientists must rely on computer simulations to study the vibrations.”

“How the energy of the interaction changes with respect to the distance between the molecules dictates a lot of the physics,” says Henry. “We have to slow down the vibrations of the atoms so you can hear them, because they’re too fast, and at too high frequencies. But you’ll be able to hear the difference between something low on the periodic table and something like carbon that’s very high. One will sound high-pitched, and one will sound low.”

However, when Henry and Lv ran their computer simulations, they noticed that some of the polymers they were modeling didn’t behave as expected, Ouellette reports. If they tweaked the starting parameters a bit, the system evolved normally up to a point, but then it diverged into a patterned series of vibrations that were not random. The simulated polymer becomes thermally superconductive — that is, capable of transporting heat with no resistance, much like the existing class of superconducting materials that conduct electricity without resistance (albeit at very low temperatures).

“Toy models are fictitious and designed to be really simple and plain so that you can analyze them easily,” said Henry. “We did this with a real system, and the [effect] actually persisted.”

Henry and Lv successfully identified three vibrational modes out of several thousand responsible for the phenomenon. However, traditional analysis techniques — like plotting the amplitudes of the modes over time in a visual graph — didn’t reveal anything significant. It wasn’t until the researchers decided to sonify the data that they pinpointed what was going on. This involved mapping pitch, timbre and amplitude onto the data to translate it into a kind of molecular music. The three modes faded in and out over time and eventually synchronized, creating a kind of sonic feedback loop until the simulated material became thermally superconductive.

“As soon as you play it, your ears pick up on it immediately,” said Henry. So, it’s solid proof-of-principle of sonification as an analytical tool for materials science.

Henry is attempting to identify the underlying mechanism behind the phenomenon in order to understand why it manifests in some polymer systems, but not others. This information could help to actually construct physical thermal superconducting materials. “It would change the world,” said Henry. “Conceptually you’d be able to run a thermal superconducting pipe from the Sahara desert and provide heat to the rest of the world.”

 

Phonon transport at interfaces: Determining the correct modes of vibration

Kiarash Gordiz1 and Asegun Henry1,2,a)

J. Appl. Phys. 119, 015101 (2016); http://dx.doi.org/10.1063/1.4939207

For many decades, phonon transport at interfaces has been interpreted in terms of phonons impinging on an interface and subsequently transmitting a certain fraction of their energy into the other material. It has also been largely assumed that when one joins two bulk materials,interfacialphonon transport can be described in terms of the modes that exist in each material separately. However, a new formalism for calculating the modal contributions to thermal interface conductance with full inclusion of anharmonicity has been recently developed, which now offers a means for checking the validity of this assumption. Here, we examine the assumption of using the bulk materials’ modes to describe the interfacial transport. The results indicate that when two materials are joined, a new set of vibrational modes are required to correctly describe the transport. As the modes are analyzed, certain classifications emerge and some of the most important modes are localized at the interface and can exhibit large conductance contributions that cannot be explained by the current physical picture based on transmission probability.

Article outline:
I. INTRODUCTION

II. ICMA FORMALISM

III. MODAL BASIS SETS

  A. EMD simulations

  B. Wave-packet simulations

IV. CLASSIFICATION OF THE MODES OF VIBRATION

V. CORRELATION MAPPING

VI. CONCLUSION

 

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