Molecular dynamics of nanodroplet impact: The effect of the projectile’s molecular mass on sputtering

The impact of electrosprayed nanodroplets on ceramics at several km/s alters the atomic order of the target, causing sputtering, surface amorphization and cratering. The molecular mass of the projectile is known to have a strong effect on the impact phenomenology, and this article aims to rationalize this dependency using molecular dynamics. To achieve this goal, the article models the impact of four projectiles with molecular masses between 45 and 391 amu, and identical diameters and kinetic energies, 10 nm and 63 keV, striking a silicon target. In agreement with experiments, the simulations show that the number of sputtered atoms strongly increases with molecular mass. This is due to the increasing intensity of collision cascades with molecular mass: when the fixed kinetic energy of the projectile is distributed among fewer, more massive molecules, their collisions with the target produce knock-on atoms with higher energies, which in turn generate more energetic and larger numbers of secondary and tertiary knock-on atoms. The more energetic collision cascades intensify both knock-on sputtering and, upon thermalization, thermal sputtering. Besides enhancing sputtering, heavier molecules also increase the fraction of the projectile’s energy that is transferred to the target, as well as the fraction of this energy that is dissipated

Switching of +/-360deg domain wall states in a nanoring by an azimuthal Oersted field

We demonstrate magnetic switching between two $360^\circ$ domain wall vortex states in cobalt nanorings, which are candidate magnetic states for robust and low power MRAM devices. These $360^\circ$ domain wall (DW) or "twisted onion" states can have clockwise or counterclockwise circulation, the two states for data storage. Reliable switching between the states is necessary for any realistic device. We accomplish this switching by applying a circular Oersted field created by passing current through a metal atomic force microscope tip placed at the center of the ring. After initializing in an onion state, we rotate the DWs to one side of the ring by passing a current through the center, and can switch between the two twisted states by reversing the current, causing the DWs to split and meet again on the opposite side of the ring. A larger current will annihilate the DWs and create a perfect vortex state in the rings.Comment: 5 pages, 5 figure

Framing Friction: A Content Analysis Investigating How the CDC Framed Social Media Communication with the Public During the COVID-19 Pandemic

The novel coronavirus was first discovered in Wuhan, China in December 2019. This zoonotic disease quickly spread through over 100 countries, including the U.S. The World Health Organization (WHO) declared a global health emergency by the end of January 2020. Soon after, many U.S. states issued mandatory stay-at-home orders, which caused adverse effects for agricultural businesses and food supply chains. During this crisis, the Centers for Disease Control and Prevention (CDC) shared information through social media platforms such as Facebook. This study sought to understand how the CDC framed direct communication to the public about issues related to COVID-19 using Facebook videos. Five videos directly related to COVID-19 were selected from the CDC’s Facebook page for analysis. A content and framing analysis was used to determine emergent frames and the use of organization-public relationship (OPR) indicators to better understand how a public entity communicates with the public during a pandemic. Emergent frames were community, protecting yourself, encouragement to take action, understanding, and fear. A conversational tone of voice was used in four out of the five videos, and each video demonstrated the use of at least one OPR indicator. Implications from this work reinforce that Facebook videos can be used to communicate the importance of scientific information using conversational voice and OPR indicators. It is recommended that agricultural communicators include OPR indicators in social media videos during other similar zoonotic disease crises. Future research should seek to understand the public’s response to this type of scientific communication