Multiscaling at Point J: Jamming is a Critical Phenomenon

We analyze the jamming transition that occurs as a function of increasing packing density in a disordered two-dimensional assembly of disks at zero temperature for ``Point J'' of the recently proposed jamming phase diagram. We measure the total number of moving disks and the transverse length of the moving region, and find a power law divergence as the packing density increases toward a critical jamming density. This provides evidence that the T = 0 jamming transition as a function of packing density is a {\it second order} phase transition. Additionally we find evidence for multiscaling, indicating the importance of long tails in the velocity fluctuations.Comment: 4 pages, 5 figures; extensive new numerical data; final version in press at PR

Static and Dynamic Phases for Vortex Matter with Attractive Interactions

Exotic vortex states with long range attraction and short range repulsion have recently been proposed to arise in superconducting hybrid structures and multi-band superconductors. Using large scale simulations we examine the static and dynamic properties of such vortex states interacting with random and periodic pinning. In the absence of pinning this system does not form patterns but instead completely phase separates. When pinning is present there is a transition from inhomogeneous to homogeneous vortex configurations similar to a wetting phenomenon. Under an applied drive, a dynamical dewetting process can occur from a strongly pinned homogeneous state into pattern forming states. We show that a signature of the exotic vortex interactions under transport measurements is a robust double peak feature in the differential conductivity curves.Comment: 5 pages, 4 postscript figure

Bidirectional Sorting of Flocking Particles in the Presence of Asymmetric Barriers

We numerically demonstrate bidirectional sorting of flocking particles interacting with an array of asymmetric barriers. Each particle aligns with the average swimming direction of its neighbors according to the Vicsek model and experiences additional steric interactions as well as repulsion from the fixed barriers. We show that particles preferentially localize to one side of the barrier array over time, and that the direction of this rectification can be reversed by adjusting the particle-particle exclusion radius or the noise term in the equations of motion. These results provide a conceptual basis for isolation and sorting of single- and multi-cellular organisms which move collectively according to flocking-type interaction rules.Comment: 5 pages, 7 postscript figure

Structure and Melting of Two-Species Charged Clusters in a Parabolic Trap

We consider a system of charged particles interacting with an unscreened Coulomb repulsion in a two-dimensional parabolic confining trap. The static charge on a portion of the particles is twice as large as the charge on the remaining particles. The particles separate into a shell structure with those of greater charge situated farther from the center of the trap. As we vary the ratio of the number of particles of the two species, we find that for certain configurations, the symmetry of the arrangement of the inner cluster of singly-charged particles matches the symmetry of the outer ring of doubly-charged particles. These matching configurations have a higher melting temperature and a higher thermal threshold for intershell rotation between the species than the nonmatching configurations.Comment: 4 pages, 6 postscript figure

A collaborative VR Murder Mystery using Photorealistic User Representations

The VRTogether project has developed a Social VR platform for remote communication and collaboration. The hyper-realistic representation of users, as volumetric video, allows for natural interaction in a virtual environment with others. This video shows one of the use cases, an escape room style, where remote users need to collaboratively resolve a murder mystery. The experience takes place in the victim’s apartment where the police team (avatars) together with up to four real-time captured users (point clouds), work as a team to find clues and come up with a conclusion about what happened to the victim and who was the criminal. This experience includes a layer of interaction, enabling the users to interact with the environment, by touching objects, and to talk to the characters. It also allows for navigating between the rooms of the apartment. The experience provides immersion and social connectedness, where users are protagonists of the story, sharing the virtual environment and following the narrative. The combination of virtual reality environments (space and characters) with novel technologies for real-time volumetric video conferencing enables unique new experiences in a number of areas such as healthcare, broadcasting, and gaming. The video can be watched here: https://youtu.be/Hsj1YWo55k

Characterizing plastic depinning dynamics with the fluctuation theorem

We demonstrate that the fluctuation theorem can be used to characterize plastic flow phases in collectively interacting particle assemblies driven over quenched disorder when strong fluctuations and crackling noise with 1/f α character occur. By measuring the frequency of entropy-destroying trajectories and the diffusivity near the threshold for motion, we map out the different dynamic phases and demonstrate that the fluctuation theorem holds in the strongly fluctuating plastic flow regime which was previously shown to be chaotic. For different driving rates and disorder strength, we find that it is possible to define an effective temperature which decreases with increasing drive, as expected for this type of system. When the size of the pinning sites is large, we identify specific regimes where the fluctuation theorem holds only at long times due to an excess of negative entropy events that occur when particles undergo circular motions within the traps. We discuss how the fluctuation theorem could be applied to plastic flow in other driven nonthermal systems with quenched disorder such as superconducting vortices, magnetic domain walls, Coulomb glasses, and earthquake models

Measuring Biological Aptitude Omics QA/QC Rubrics

Sequencing, Proteomics, and Metabolomics QA/QC Scoring Rubrics for the DARPA Measuring Biological Aptitude Program, associated with "Efforts to enhance reproducibility in a human performance research project" by J.A. Drocco, et al. (2023).</p