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1. On the motion of a pendulum with a cavity filled with a compressible fluid

   https://doi.org/10.1063/5.0143910  

   Galdi, G P; Mácha, V; Nečasová, Š; She, B (November 2023, Journal of Mathematical Physics)

   We study the motion of the coupled system, S, constituted by a physical pendulum, B, with an interior cavity entirely filled with a viscous, compressible fluid, F. The system is constrained to rotate about a horizontal axis. The presence of the fluid may strongly affect the motion of B. In fact, we prove that, under appropriate assumptions, the fluid acts as a damper, namely, S must eventually reach a rest-state. Such a state is characterized by a suitable time-independent density distribution of F and a corresponding equilibrium position of the center of mass of S. These results are proved in the very general class of weak solutions and do not require any restriction on the initial data, other than having a finite energy. We complement our findings with some numerical tests. The latter show, among other things, the interesting property that “large” compressibility favors the damping effect, since it drastically reduces the time that S takes to go to rest. 

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2. Interaction of a Supernova with a Circumstellar Disk

   https://doi.org/10.3847/1538-4357/aaa96e  

   McDowell, Austin T.; Duffell, Paul C.; Kasen, Daniel (March 2018, The Astrophysical Journal)
3. A Game of Life with dormancy

   https://doi.org/10.1098/rspb.2024.2543  

   Nevermann, Daniel Henrik; Gros, Claudius; Lennon, Jay T (January 2025, Proceedings of the Royal Society B: Biological Sciences)

   The factors contributing to the persistence and stability of life are fundamental for understanding complex living systems. Organisms are commonly challenged by harsh and fluctuating environments that are suboptimal for growth and reproduction, which can lead to extinction. Many species contend with unfavourable and noisy conditions by entering a reversible state of reduced metabolic activity, a phenomenon known as dormancy. Here, we develop Spore Life, a model to investigate the effects of dormancy on population dynamics. It is based on Conway’s Game of Life (GoL), a deterministic cellular automaton where simple rules govern the metabolic state of an individual based on the metabolic state of its neighbours. For individuals that would otherwise die, Spore Life provides a refuge in the form of an inactive state. These dormant individuals (spores) can resuscitate when local conditions improve. The model includes a parameter $\alpha \in \left[\mathrm{0,1}\right]$that controls the survival probability of spores, interpolating between GoL ( $\alpha =0$) and Spore Life ( $\alpha =1$), while capturing stochastic dynamics in the intermediate regime ( $0<\alpha <1$). In addition to identifying the emergence of unique periodic configurations, we find that spore survival increases the average number of active individuals and buffers populations from extinction. Contrary to expectations, stabilization of the population is not the result of a large and long-lived seed bank. Instead, the demographic patterns in Spore Life only require a small number of resuscitation events. Our approach yields novel insight into what is minimally required for the origins of complex behaviours associated with dormancy and the seed banks that they generate. 

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4. Interaction of a free surface with a vortex patch

   https://doi.org/10.1016/j.wavemoti.2019.04.006  

   Curtis, Christopher W.; Kalisch, Henrik (August 2019, Wave Motion)
5. Dynamics of a circular cylinder with a passive degree of freedom interacting with an inviscid fluid containing a point vortex

   https://doi.org/10.1115/DSCC2017-5153  

   Tallapragada, Phanindra; Pollard, Beau; Fedonyuk, Vitaliy (October 2017, ASME Dynamic Systems and Control Conference)

   In the recent past the design of many aquatic robots has been inspired by the motion of fish. Actuated internal rotors or moving masses have been frequently used either for propulsion and or the control of such robots. However the effect of internal passive degrees of freedom or passive appendages on the motion of such robots is poorly understood. In this paper we present a minimal model that demonstrates the influence of passive degrees of freedom on an aquatic robot. The model is of a circular cylinder with a passive internal rotor, immersed in an inviscid fluid interacting with point vortices. We show through numerics that the motion of the cylinder containing a passive degree of freedom is significantly different than one without. These results show that the mechanical feedback via passive degrees of freedom could be a useful way to control the motion of aquatic robots. 

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