S1E10
Episode 10 (September 13, 2020)
Yongquan Liu
Xi'an Jiaotong University
Aniruddh Vashisth
University of Washington
Kok Zhi Lee
Purdue University
Compact Wave Controllers Based on Elastic Metasurfaces
Abstract:
The manipulation of elastic waves has been of special interest for a long period of time, owing to their wide applications in structural health monitoring, aseismic design of structures, and medical ultrasonography, etc. Elastic metasurfaces have been recently developed to offer a preferable possibility to manipulate elastic waves, showing the compact and simple-to-implement features. Herein, by artificially tuning the phase and amplitude of certain interfaces, we propose and experimentally demonstrate some examples to manipulate guided elastic waves using metasurfaces, such as source illusions, asymmetric wave propagation, metacages and metaguides. This work may underlie the design of compact devices with complete control over guided elastic waves, and may be potentially useful for applications in elastodynamics like nondestructive testing, high-resolution ultrasonography and analog signal processing.
Using Molecular Dynamics and Experimental Mechanics to Understand Thermo-mechanical Behavior of Polymers
Abstract:
Thermo-mechanical properties of polymers are dependent on the material chemistry of the base materials. Various methods have been developed to perform atomistic-scale simulations for the cross-linking of polymers. Most of these methods involve connecting the reactive sites of the monomers, but these typically do not capture the entire reaction process from the reactants to final products through transition states. Experimental time scales for cross-linking reactions in polymers range from minutes to hours, which are time scales that are inaccessible to atomistic scale simulations. Because simulating reactions on realistic time scales is computationally expensive, in this investigation, an accelerated simulation method was developed within the ReaxFF reactive force field framework. This new method allows simulation of cross-linking at realistic, low temperatures, which helps to mimic chemical reactions and avoids unwanted high-temperature side reactions and still allows us to reject high-barrier events. This new method - Accelerated ReaxFF - can be used to correctly simulate the molecular structures of thermosetting polymers and polymer derived ceramics, and shows good agreement with experimental results.
A Novel Mechanism Controls Neurite Outgrowth Inhibition by A Glycolytic Enzyme
Abstract:
Neurite outgrowth inhibition by NogoA via receptors has been a hurdle for therapeutic intervention in neurodegenerative diseases and spinal cord injury. Although NogoA knockout exhibits enhanced neuron regeneration in spinal cord injured mice, inhibition of Nogo receptors does not recover to the extent observed in NogoA knockout mice, suggesting the presence of other pathways. Here, we identified a novel pathway by NogoA, which inhibits neurite outgrowth via decreasing a glycolytic enzyme, Pgk1. Pgk1 stimulates neurite outgrowth independent from its glycolytic role, while depletion of secreted Pgk1 inhibits neurite outgrowth in cell line and zebrafish without activating known NogoA-dependent pathway. We revealed that extracellular Pgk1 inhibits neurite outgrowth by triggering a reduction of p-Cofilin-S3, a growth cone collapse marker, through decreasing a novel Rac1-GTP/p-Pak1-T423/p-P38-T180/p-MK2-T334/p-Limk1-S323/p-Cofilin-S3 molecular pathway. Not only did supplementary Pgk1 enhance neurite outgrowth in a cell line, but injection of Pgk1 also rescued denervation in muscle-specific NogoA-overexpression of zebrafish and an Amyotrophic Lateral Sclerosis mouse model. Collectively, our results provided insight into NogoA-mediated neurite outgrowth inhibition and shed new light on potential therapeutic in NogoA-mediated neurodegenerative diseases and spinal cord injury.