An official website of the United States government
Abstract Artificial self‐propelled colloidal particles have recently served as effective building blocks for investigating many dynamic behaviors exhibited by nonequilibrium systems. However, most studies have relied upon excluded volume interactions between the active particles. Experimental systems in which the mobile entities interact over long distances in a well‐defined and controllable manner are valuable so that new modes of multiparticle dynamics can be studied systematically in the laboratory. Here, a system of self‐propelled microscale Janus particles is engineered to have contactless particle–particle interactions that lead to long‐range attraction, short‐range repulsion, and mutual alignment between adjacent swimmers. The unique modes of motion that arise can be tuned by modulating the system's parameters.
more »
« less
Three-dimensional particle shape characterizations from half particle geometries
- Award ID(s):
- 1917332
- PAR ID:
- 10213182
- Date Published:
- Journal Name:
- Powder Technology
- Volume:
- 367
- Issue:
- C
- ISSN:
- 0032-5910
- Page Range / eLocation ID:
- 122 to 132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Single-particle electrochemistry has become an important area of research with the potential to determine the rules of electrochemical reactivity at the nanoscale. These techniques involve addressing one entity at the time, as opposed to the conventional electrochemical experiment where a large number of molecules interact with an electrode surface. These experiments have been made feasible through the utilization of ultramicroelectrode (UMEs), i.e., electrodes with at least one dimension, e.g., diameter of 30 μm or less. This paper provides a theoretical and practical introduction to single entity electrochemistry (SEE), with emphasis on collision experiments between suspended NPs and UMEs to introduce concepts and techniques that are used in several SEE experimental modes. We discuss the intrinsically small currents, below 1 nA, that result from the electroactive area of single entities in the nanometer scale. Individual nanoparticles can be detected using the difference in electrochemical reactivity between a substrate and a nanoparticle (NP). These experiments show steady-state behavior of single NPs that result in discrete current changes or steps. Likewise, the NP can have transient interactions with the substrate electrode that result in current blips. We review the effect of diffusion, the main mass transport process that limits NP/electrode interactions. Also, we pointed out the implications of aggregation and tunneling in the experiments. Finally, we provid a perspective on the possible applications of single-element electrochemistry of electrocatalyst.more » « less
-
Abstract Magnetic reconnection in the relativistic regime has been proposed as an important process for the efficient production of nonthermal particles and high-energy emission. Using fully kinetic particle-in-cell simulations, we investigate how the guide-field strength and domain size affect the characteristic spectral features and acceleration processes. We study two stages of acceleration: energization up until the injection energyγinjand further acceleration that generates a power-law spectrum. Stronger guide fields increase the power-law index andγinj, which suppresses acceleration efficiency. These quantities seemingly converge with increasing domain size, suggesting that our findings can be extended to large-scale systems. We find that three distinct mechanisms contribute to acceleration during injection: particle streaming along the parallel electric field, Fermi reflection, and the pickup process. The Fermi and pickup processes, related to the electric field perpendicular to the magnetic field, govern the injection for weak guide fields and larger domains. Meanwhile, parallel electric fields are important for injection in the strong guide-field regime. In the post-injection stage, we find that perpendicular electric fields dominate particle acceleration in the weak guide-field regime, whereas parallel electric fields control acceleration for strong guide fields. These findings will help explain the nonthermal acceleration and emission in high-energy astrophysics, including black hole jets and pulsar wind nebulae.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.powtec.2020.03.046
