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1. Non‐Flat Universes and Black Holes in Asymptotically Free Mimetic Gravity

   https://doi.org/10.1002/prop.201900103  

   Chamseddine, Ali H.; Mukhanov, Viatcheslav; Russ, Tobias B. (December 2019, Fortschritte der Physik)

   Abstract The recently proposed theory of “Asymptotically Free Mimetic Gravity” is extended to the general non‐homogeneous, spatially non‐flat case. We present a modified theory of gravity which is free of higher derivatives of the metric. In this theory asymptotic freedom of gravity implies the existence of a minimal black hole with vanishing Hawking temperature. Introducing a spatial curvature dependent potential, we moreover obtain non‐singular, bouncing modifications of spatially non‐flat Friedmann and Bianchi universes. 

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2. Mechanisms of soil bacterial and fungal community assembly differ among and within islands

   https://doi.org/10.1111/1462-2920.14864  

   Wang, Pandeng; Li, Shao‐Peng; Yang, Xian; Zhou, Jizhong; Shu, Wensheng; Jiang, Lin (December 2019, Environmental Microbiology)

   Summary The study of islands has made substantial contributions to the development of evolutionary and ecological theory. However, we know little about microbial community assembly on islands. Using soil microbial data collected from 29 lake islands and nearby mainland, we examined the assembly mechanisms of soil bacterial and fungal communities among and within islands. We found that deterministic processes, especially homogeneous selection, tended to be more important in shaping the assembly of soil bacterial communities among islands, while stochastic processes tended to be more important within islands. Moreover, increasing island area increased the importance of homogeneous selection, but reduced the importance of variable selection, for soil bacterial community assembly within islands. By contrast, stochastic processes tended to dominate soil fungal community assembly both among and within islands, with dispersal limitation playing a more important role within than among islands. Our results highlight the scale‐ and taxon‐dependence of insular soil microbial community assembly, suggesting that spatial scale should be explicitly considered when evaluating the influences of habitat fragmentation on soil microbial communities. 

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3. Universality of noise-induced resilience restoration in spatially-extended ecological systems

   https://doi.org/10.1038/s42005-021-00758-2  

   Ma, Cheng; Korniss, Gyorgy; Szymanski, Boleslaw K.; Gao, Jianxi (December 2021, Communications Physics)

   Abstract Many systems may switch to an undesired state due to internal failures or external perturbations, of which critical transitions toward degraded ecosystem states are prominent examples. Resilience restoration focuses on the ability of spatially-extended systems and the required time to recover to their desired states under stochastic environmental conditions. The difficulty is rooted in the lack of mathematical tools to analyze systems with high dimensionality, nonlinearity, and stochastic effects. Here we show that nucleation theory can be employed to advance resilience restoration in spatially-embedded ecological systems. We find that systems may exhibit single-cluster or multi-cluster phases depending on their sizes and noise strengths. We also discover a scaling law governing the restoration time for arbitrary system sizes and noise strengths in two-dimensional systems. This approach is not limited to ecosystems and has applications in various dynamical systems, from biology to infrastructural systems. 

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4. Turing Bifurcation in the Swift–Hohenberg Equation on Deterministic and Random Graphs

   https://doi.org/10.1007/s00332-024-10054-2  

   Medvedev, Georgi S; Pelinovsky, Dmitry E (October 2024, Journal of Nonlinear Science)

   Abstract The Swift–Hohenberg equation (SHE) is a partial differential equation that explains how patterns emerge from a spatially homogeneous state. It has been widely used in the theory of pattern formation. Following a recent study by Bramburger and Holzer (SIAM J Math Anal 55(3):2150–2185, 2023), we consider discrete SHE on deterministic and random graphs. The two families of the discrete models share the same continuum limit in the form of a nonlocal SHE on a circle. The analysis of the continuous system, parallel to the analysis of the classical SHE, shows bifurcations of spatially periodic solutions at critical values of the control parameters. However, the proximity of the discrete models to the continuum limit does not guarantee that the same bifurcations take place in the discrete setting in general, because some of the symmetries of the continuous model do not survive discretization. We use the center manifold reduction and normal forms to obtain precise information about the number and stability of solutions bifurcating from the homogeneous state in the discrete models on deterministic and sparse random graphs. Moreover, we present detailed numerical results for the discrete SHE on the nearest-neighbor and small-world graphs. 

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5. Can Stochastic Slip Rupture Modeling Produce Realistic M 9+ Events?

   https://doi.org/10.1029/2022jb025716  

   Small, David T.; Melgar, Diego (March 2023, Journal of Geophysical Research: Solid Earth)

   Abstract Stochastic slip rupture modeling is a computationally efficient, reduced‐physics approximation that has the capability to create large numbers of unique ruptures based only on a few statistical assumptions. Yet one fundamental question pertaining to this approach is whether the slip distributions calculated in this way are “realistic.” Rather, can stochastic modeling reproduce slip distributions that match what is seen inM9+ events recorded in instrumental time? We focus here on testing the ability of the von Karman ACF method for stochastic slip modeling to reproduceM9+ events. We start with the 2011M9.1 Tohoku‐Oki earthquake and tsunami where we test both a stochastic method with a homogeneous background mean model and a method where slip is informed by an additional interseismic coupling constraint. We test two coupling constraints with varying assumptions of either trench‐locking or ‐creeping and assess their influence on the calculated ruptures. We quantify the dissimilarity between the 12,000 modeled ruptures and a slip inversion for the Tohoku earthquake. We also model tsunami inundation for over 300 ruptures and compare the results to an inundation survey along the eastern coastline of Japan. We conclude that stochastic slip modeling produces ruptures that can be considered “Tohoku‐like,” and inclusion of coupling can both positively and negatively influence the ability to create realistic ruptures. We then expand our study to show that for the 1960M9.4–9.6 Chile, 1964M9.2 Alaska, and 2004M9.1–9.3 Sumatra events, stochastic slip modeling has the capability to produce ruptures that compare favorably to those events. 

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