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Yeonsu Jung from Harvard University will be presenting at this week's Physics Colloquium. The seminar will be presented in person at 4 p.m., Thursday, September 28 in Fisher 139.

Entanglement Transition in Random Packing of Rods

ABSTRACT:

Random packings of stiff rods can form a cohesive structure by virtue of entanglements driven by frictional and steric effects even in the absence of local cohesive interactions; a common example is seen in bird’s nests made of twigs. But how does entanglement lead to a disordered yet cohesive material?

To address this, we experimentally probe the jammed state of stiff rods on microscopic and intermediate scale using a combination of imaging and mechanical testing. X-ray Computerized Tomography (X-ray CT) allows us to observe the configuration in a tangled rod network. The resulting 3D volume imge was segmented to locate centerlines of the rods and their contacts.

We adopt the average crossing number (ACN) as a measure of pairwise entanglement. We define local entanglement as the sum of ACN between all possible pairs within a mesoscale neighborhood. This measure of local entanglement effectively illustrates shifts in the internal configuration of a rod packing—specifically, the positions and orientations of the rods—and its correlation with mechanical stability. Moreover, we analyzed entanglement concerning compressive strain and aspect ratio. Our findings indicate that a highly entangled state consistently forms when the aspect ratio exceeds 100, but compressive strain exhibits minimal impact.

BIO:

Dr. Yeonsu Jung is a postdoctoral fellow in the School of Engineering and Applied Sciences at Harvard University. He received his PhD in Mechanical Engineering at Seoul National University. His research interest is to investigate a variety of complex phenomena emerging from geometric and topological interactions.