Yunker, Peter J.

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Now showing 1 - 5 of 5
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    Experimental Data for "Spatial constraints and stochastic seeding subvert microbial arms race"
    (Georgia Institute of Technology, 2024-01) Copeland, Raymond ; Zhang, Christopher ; Hammer, Brian K. ; Yunker, Peter J.
    Surface attached communities of microbes grow in a wide variety of environments. Often, the size of these microbial community is constrained by their physical surroundings. However, little is known about how size constraints of a colony impact the outcome of microbial competitions. Here, we use individual-based models to simulate contact killing between two bacterial strains with different killing rates in a wide range of community sizes. We found that community size has a substantial impact on outcomes; in fact, in some competitions the identity of the most fit strain differs in large and small environments. Specifically, when at a numerical disadvantage, the strain with the slow killing rate is more successful in smaller environments than in large environments. The improved performance in small spaces comes from finite size effects; stochastic fluctuations in the initial relative abundance of each strain in small environments lead to dramatically different outcomes. However, when the slow killing strain has a numerical advantage, it performs better in large spaces than in small spaces, where stochastic fluctuations now aid the fast killing strain in small communities. Finally, we experimentally validate these results by confining contact killing strains of Vibrio cholerae in transmission electron microscopy grids. The outcomes of these experiments are consistent with our simulations. When rare, the slow killing strain does better in small environments; when common, the slow killing strain does better in large environments. Together, this work demonstrates that finite size effects can substantially modify antagonistic competitions, suggesting that colony size may, at least in part, subvert the microbial arms race.
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    Why is Structural Hierarchy So Prevalent in Biological Materials?
    (Georgia Institute of Technology, 2018-04-19) Michel, Jonathan ; Yunker, Peter J.
    Structural hierarchy, in which materials possess distinct features on multiple length scales, is ubiquitous in nature. Many biological materials, such as bone, cellulose, and muscle, have as many as ten hierarchical levels. While structural hierarchy confers many mechanical advantages, including improved toughness and economy of material, it also presents a problem as each hierarchical level substantially increases the amount of information necessary for proper assembly. This seems to conflict with the broad prevalence of naturally occurring hierarchical structures. At the present, there is no general framework for understanding the interplay between structures on disparate length scales; such a framework is a critical tool for accounting for the robustness of hierarchical materials to defects. Here, we use simulations and experiments to validate a generalized model for the tensile stiffness of hierarchical, stretching-stabilized networks with a nested, dilute hexagonal lattice structure, and demonstrate that the stiffness of such networks becomes less sensitive to errors in assembly with additional levels of hierarchy. Following seminal work by Maxwell and others on criteria for stiff frames, we extend the concept of connectivity in network mechanics, and find a similar dependence of material stiffness upon each hierarchical level. More broadly, this work helps account for the success of hierarchical, filamentous materials in biology and materials design, and offers a heuristic for ensuring that desired material properties are achieved within the required tolerance.
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    Cellular Packing, Mechanical Stress and the Evolution of Multicellularity
    (Georgia Institute of Technology, 2018-04-19) Jacobeen, Shane ; Brandys, Colin G. ; Graba, Elyes C. ; Pentz, Jennifer T. ; Ratcliff, William C. ; Yunker, Peter J.
    The evolution of multicellularity set the stage for sustained increases in organismal complexity. However, a fundamental aspect of this transition remains largely unknown: how do simple clusters of cells evolve increased size when confronted by forces capable of breaking intracellular bonds? Here we show that multicellular snowflake yeast clusters fracture due to crowding-induced mechanical stress. Over seven weeks (~291 generations) of daily selection for large size, snowflake clusters evolve to increase their radius 1.7-fold by reducing the accumulation of internal stress. During this period, cells within the clusters evolve to be more elongated, concomitant with a decrease in the cellular volume fraction of the clusters. The associated increase in free space reduces the internal stress caused by cellular growth, thus delaying fracture and increasing cluster size. This work demonstrates how readily natural selection finds simple, physical solutions to spatial constraints that limit the evolution of group size—a fundamental step in the evolution of multicellularity.
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    Symposium on Soft Matter Forefronts - Welcome
    (Georgia Institute of Technology, 2018-04-18) Alexeev, Alexander ; Brettmann, Blair ; Fernandez-Nieves, Alberto ; Matsumoto, Elisabetta A. ; Rocklin, D. Zeb ; Yunker, Peter J.
    The symposium aims to familiarize attendees with the soft-matter research and expertise at Georgia Tech and to demonstrate the role Georgia Tech plays in influencing and advancing the field.
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    The Coffee-Ring Effect and the Physics of Breakfast
    (Georgia Institute of Technology, 2015-11-30) Yunker, Peter J.
    As anyone who has ever spilled coffee knows, liquids that contain suspended particles tend to leave ring-shaped stains when they dry. This ubiquitous phenomenon has been observed for thousands of years, but the physics behind it has only become clear over the past 20 years. In a related vein, while finishing a bowl of cereal, you may have noticed that the final few pieces tend to clump together on the surface of the milk. I will explain the physics underlying these, and other related effects. Further, though they may sound silly, these discoveries have many industrial applications, thus demonstrating value of understanding the basic physics of seemingly simple systems.