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1. Simulated surface diffusion in nanoporous gold and its dependence on surface curvature

   https://doi.org/10.1016/j.commatsci.2023.112430  

   Winkeljohn, Conner Marie; Shahriar, Sadi; Seker, Erkin; Mason, Jeremy K (October 2023, Computational Materials Science)

   The morphological evolution of nanoporous gold is generally believed to be governed by surface diffusion. This work specifically explores the dependence of mass transport by surface diffusion on the curvature of a gold surface. The surface diffusivity is estimated by molecular dynamics simulations for a variety of surfaces of constant mean curvature, eliminating any chemical potential gradients and allowing the possible dependence of the surface diffusivity on mean curvature to be isolated. The apparent surface diffusivity is found to have an activation energy of ~0.74 eV with a weak dependence on curvature, but is consistent with the values reported in the literature. The apparent concentration of mobile surface atoms is found to be highly variable, having an Arrhenius dependence on temperature with an activation energy that also has a weak curvature dependence. These activation energies depend on curvature in such a way that the rate of mass transport by surface diffusion is nearly independent of curvature, but with a higher activation energy of ~1.01 eV. The curvature dependencies of the apparent surface diffusivity and concentration of mobile surface atoms is believed to be related to the expected lifetime of a mobile surface atom, and has the practical consequence that a simulation study that does not account for this finite lifetime could underestimate the activation energy for mass transport via surface diffusion by ~0.27 eV. 

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2. NASA's surface biology and geology designated observable: A perspective on surface imaging algorithms

   https://doi.org/10.1016/j.rse.2021.112349  

   Cawse-Nicholson, Kerry; Townsend, Philip A.; Schimel, David; Assiri, Ali M.; Blake, Pamela L.; Buongiorno, Maria Fabrizia; Campbell, Petya; Carmon, Nimrod; Casey, Kimberly A.; Correa-Pabón, Rosa Elvira; et al (May 2021, Remote Sensing of Environment)
3. Inertial effects on free surface pumping with an undulating surface

   https://doi.org/10.1017/jfm.2024.888  

   Chen, Zih-Yin; Pandey, Anupam; Takagi, Daisuke; Jung, Sunghwan; Lee, Sungyon (November 2024, Journal of Fluid Mechanics)

   Free surface flows driven by boundary undulations are observed in many biological phenomena, including the feeding and locomotion of water snails. To simulate the feeding strategy of apple snails, we develop a centimetric robotic undulator that drives a thin viscous film of liquid with the wave speed$$V_w$$. Our experimental results demonstrate that the behaviour of the net fluid flux$$Q$$strongly depends on the Reynolds number$$Re$$. Specifically, in the limit of vanishing$$Re$$, we observe that$$Q$$varies non-monotonically with$$V_w$$, which has been successfully rationalised by Pandeyet al.(Nat. Commun., vol. 14, no. 1, 2023, p. 7735) with the lubrication model. By contrast, in the regime of finite inertia ($${Re} \sim O(1)$$), the fluid flux continues to increase with$$V_w$$and completely deviates from the prediction of lubrication theory. To explain the inertia-enhanced pumping rate, we build a thin-film, two-dimensional model via the asymptotic expansion in which we linearise the effects of inertia. Our model results match the experimental data with no fitting parameters and also show the connection to the corresponding free surface shapes$$h_2$$. Going beyond the experimental data, we derive analytical expressions of$$Q$$and$$h_2$$, which allow us to decouple the effects of inertia, gravity, viscosity and surface tension on free surface pumping over a wide range of parameter space. 

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4. Programming and simulating chemical reaction networks on a surface

   https://doi.org/10.1098/rsif.2019.0790  

   Clamons, Samuel; Qian, Lulu; Winfree, Erik (May 2020, Journal of The Royal Society Interface)

   Models of well-mixed chemical reaction networks (CRNs) have provided a solid foundation for the study of programmable molecular systems, but the importance of spatial organization in such systems has increasingly been recognized. In this paper, we explore an alternative chemical computing model introduced by Qian & Winfree in 2014, the surface CRN, which uses molecules attached to a surface such that each molecule only interacts with its immediate neighbours. Expanding on the constructions in that work, we first demonstrate that surface CRNs can emulate asynchronous and synchronous deterministic cellular automata and implement continuously active Boolean logic circuits. We introduce three new techniques for enforcing synchronization within local regions, each with a different trade-off in spatial and chemical complexity. We also demonstrate that surface CRNs can manufacture complex spatial patterns from simple initial conditions and implement interesting swarm robotic behaviours using simple local rules. Throughout all example constructions of surface CRNs, we highlight the trade-off between the ability to precisely place molecules and the ability to precisely control molecular interactions. Finally, we provide a Python simulator for surface CRNs with an easy-to-use web interface, so that readers may follow along with our examples or create their own surface CRN designs. 

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5. Crowder and surface effects on self-organization of microtubules

   https://doi.org/10.1103/PhysRevE.103.062408  

   Sahu, Sumon; Herbst, Lena; Quinn, Ryan; Ross, Jennifer L. (June 2021, Physical Review E)

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