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1. Fundamental competition of smooth and non-smooth bifurcations and their ghosts in vibro-impact pairs

   https://doi.org/10.1007/s11071-022-08152-5  

   Serdukova, Larissa; Kuske, Rachel; Yurchenko, Daniil (December 2022, Nonlinear Dynamics)

   Abstract A combined analysis of smooth and non-smooth bifurcations captures the interplay of different qualitative transitions in a canonical model of an impact pair, a forced capsule in which a ball moves freely between impacts on either end of the capsule. The analysis, generic for the impact pair context, is also relevant for applications. It is applied to a model of an inclined vibro-impact energy harvester device, where the energy is generated via impacts of the ball with a dielectric polymer on the capsule ends. While sequences of bifurcations have been studied extensively in single- degree-of-freedom impacting models, there are limited results for two-degree-of-freedom impacting systems such as the impact pair. Using an analytical characterization of impacting solutions and their stability based on the maps between impacts, we obtain sequences of period doubling and fold bifurcations together with grazing bifurcations, a particular focus here. Grazing occurs when a sequence of impacts on either end of the capsule are augmented by a zero-velocity impact, a transition that is fundamentally different from the smooth bifurcations that are instead characterized by eigenvalues of the local behavior. The combined analyses allow identification of bifurcations also on unstable or unphysical solutions branches, which we term ghost bifurcations. While these ghost bifurcations are not observed experimentally or via simple numerical integration of the model, nevertheless they can influence the birth or death of complex behaviors and additional grazing transitions, as confirmed by comparisons with the numerical results. The competition between the different bifurcations and their ghosts influences the parameter ranges for favorable energy output; thus, the analyses of bifurcation sequences yield important design information. 

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2. Bifurcating vector fields driven by time-scale separated motivational dynamics

   https://doi.org/10.1016/j.ifacol.2023.10.1842  

   Baxevani, Kleio; Tanner, Herbert G (January 2023, IFAC-PapersOnLine)

   Dynamical systems can be designed to exhibit a range of distinct behaviors, which all arise from the same set of continuous dynamics when the latter bifurcates, triggered by a switch in one of its scalar parameters. Building on recent advances that introduce motivation and value dynamics as an efficient way to design multi-behavioral systems, this paper lifts some of the existing restrictions on what kind of planar vector fields can be combined to produce bifurcations. This relaxation enriches the class of dynamical systems that such an approach applies, and gives rise to new behaviors. The paper identifies new analytical conditions under which this new set of planar vector fields can undergo Hopf bifurcations and result in a multi-behavioral system. Numerical simulations and experimental results confirm the theoretical predictions for the existence of the Hopf bifurcations and the applicability of the theory in real systems. 

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3. Antibody binding reports spatial heterogeneities in cell membrane organization

   https://doi.org/10.1038/s41467-023-38525-2  

   Arnold, Daniel P.; Xu, Yaxin; Takatori, Sho C. (May 2023, Nature Communications)

   Abstract The spatial organization of cell membrane glycoproteins and glycolipids is critical for mediating the binding of ligands, receptors, and macromolecules on the plasma membrane. However, we currently do not have the methods to quantify the spatial heterogeneities of macromolecular crowding on live cell surfaces. In this work, we combine experiment and simulation to report crowding heterogeneities on reconstituted membranes and live cell membranes with nanometer spatial resolution. By quantifying the effective binding affinity of IgG monoclonal antibodies to engineered antigen sensors, we discover sharp gradients in crowding within a few nanometers of the crowded membrane surface. Our measurements on human cancer cells support the hypothesis that raft-like membrane domains exclude bulky membrane proteins and glycoproteins. Our facile and high-throughput method to quantify spatial crowding heterogeneities on live cell membranes may facilitate monoclonal antibody design and provide a mechanistic understanding of plasma membrane biophysical organization. 

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4. Influence of Soil Moisture on the Development of Organized Convective Systems in South America

   https://doi.org/10.1029/2024JD042108  

   Paccini, Laura; Schiro, Kathleen_A (May 2025, Journal of Geophysical Research: Atmospheres)

   Abstract This study investigates the role of soil moisture (SM) on the initiation and organization of convective systems using the convection‐permitting ICOsahedral Non‐hydrostatic (ICON) model. We conduct two sets of experiments: a Control experiment with interactive SM and a fixed SM experiment (FixedSM) with invariable SM conditions. We focus on two regions in South America: the Amazon and southeastern South America (SESA). Larger organized convective systems are associated with greater SM heterogeneity in both regions, though other large‐scale synoptic influences affect the robustness of this relationship in SESA. These results remain largely unaffected by disabling the effects of precipitation on SM in the FixedSM experiment, and complementary analyses using satellite‐based estimates of SM and precipitation support these findings. Spatial compositing of mesoscale environments in the Amazon shows the presence of well‐defined SM gradients, at a length scale of a few hundred kilometers, many hours before convective system detection. Larger SM gradients correspond to larger gradients in thermodynamic variables, particularly surface temperature and sensible heat flux, and are associated with larger convective systems. Overall, our findings suggest that surface heterogeneities such as SM gradients not only affect deep convection initiation, as previously suggested, but they can also encourage the growth and organization of convective systems into larger clusters, particularly in the absence of significant synoptic influences. 

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5. Physicochemical Hydrodynamics of Particle Diffusiophoresis Driven by Chemical Gradients

   https://doi.org/10.1146/annurev-fluid-030424-110950  

   Ault, Jesse T; Shin, Sangwoo (January 2025, Annual Review of Fluid Mechanics)

   Chemical gradients, the spatial variations in chemical concentrations and components, are omnipresent in environments ranging from biological and environmental systems to industrial processes. These thermodynamic forces often play a central role in driving transport processes taking place in such systems. This review focuses on diffusiophoresis, a phoretic transport phenomenon driven by chemical gradients. We begin by revisiting the fundamental physicochemical hydrodynamics governing the transport. Then we discuss diffusiophoresis arising in flow systems found in natural and artificial settings. By exploring various scenarios where chemical gradients are encountered and exploited, we aim to demonstrate the significance of diffusiophoresis and its state-of-the-art development in technological applications. 

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