# gst: substrate friction and geometric confinement could act as transitional control parms (in active nematics).

<< Using a minimal continuum model, (AA) investigate the interplay between circular confinement and substrate friction in active nematics. Upon increasing the friction from low to high, (They) observe a dynamical phase transition from a circulating flow phase to an anisotropic flow phase in which the flow tends to align perpendicular to the nematic director at the boundary. (AA) demonstrate that both the flow structure and dynamic correlations in the latter phase differ from those of an unconfined, active turbulent system and may be controlled by the prescribed nematic boundary conditions. (AA) results show that substrate friction and geometric confinement act as valuable control parameters in active nematics. >> 

Cody D. Schimming, C. J. O. Reichhardt, C. Reichhardt. Friction-mediated phase transition in confined active nematics. Phys. Rev. E 108, L012602. Jul 27, 2023. 

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.108.L012602 

https://twitter.com/PhysRevE/status/1684921441651691520

Also: transition, in https://www.inkgmr.net/kwrds.html

Keywords: gst, transition, friction, friction-mediated phase transition, confinement, nematics

# behav: use of social information in flight (among ‘griffon’ vultures Gyps fulvus and G. rueppellii)

 <<Animals rely on a balance of personal and social information to decide when and where to move next in order to access a desired resource, such as food. The benefits from cueing on conspecifics to reduce uncertainty about resources availability can be rapidly overcome by the risks of within-group competition, often exacerbated toward low-ranked individuals. Being obligate soarers, relying on thermal updrafts to search for carcasses around which competition can be fierce, vultures represent ideal models to investigate the balance between personal and social information during foraging movements. Linking dominance hierarchy, social affinities and meteorological conditions to movement decisions of eight captive vultures, Gyps spp., released for free flights in natural-like soaring conditions,  (AA) found that they relied on social information (i.e. other vultures using/having used the thermals) to find the next thermal updraft, especially in unfavourable flight conditions. Low-ranked individuals were more likely to disregard social cues when deciding where to go next, possibly to minimise the competitive risk of social aggregation. These results exemplify the architecture of decision-making during flight in social birds. It suggests that the environmental context, the context of risk and the social system as a whole calibrate the balance between personal and social information use. >> 

Sassi Yohan, Nouzieres Basile, Scacco Martina, et al. The use of social information in vulture flight decisions. bioRxiv. doi: 10.1101/ 2023.07.26.550671. Jul 28, 2023.

https://www.biorxiv.org/content/10.1101/2023.07.26.550671v1

Also: behav, in https://www.inkgmr.net/kwrds.html

# gst: tipping in a low-dimensional model of a (tropical) cyclone.

 <<Tipping is the rapid, and often irreversible, change in the state of a system [Ashwin P. et al (2017)] >> 

AA << present a case study of both rate and noise-induced tipping between the stable states, relating to the destabilization or formation of a tropical cyclone. While the stochastic system exhibits transitions both to and from the non-storm state, noise-induced tipping is more likely to form a storm, whereas rate-induced tipping is more likely to be the way a storm is destabilized, and in fact, rate-induced tipping can never lead to the formation of a storm when acting alone. For rate-induced tipping acting as a destabilizer of the storm, a striking result is that both wind shear and maximal potential velocity have to increase, at a substantial rate, in order to effect tipping away from the active hurricane state. For storm formation through noise-induced tipping, (AA) identify a specific direction along which the non-storm state is most likely to get activated. >> 

Katherine Slyman, John A. Gemmer, et al. Tipping in a Low-Dimensional Model of a Tropical Cyclone. arXiv: 2307.15583v1 [math.DS]. Jul 28, 2023.

https://arxiv.org/abs/2307.15583

 

Also: vortex, instability, noise, in https://www.inkgmr.net/kwrds.html

Keywords: gst, climate, storm, cyclone, vortex, noise, tipping, noise-induced tipping

# gst: dynamics and interactions of multiple bright droplets and bubbles, and interactions of kinks with droplets and with antikinks.

<< Droplets bearing different chemical potentials experience mass-exchange phenomena. Individual bubbles exhibit core expansion and mutual attraction prior to their destabilization. Droplets interacting with kinks are absorbed by them, a process accompanied by the emission of dispersive shock waves and gray solitons. Kink-antikink interactions are repulsive, generating counter-propagating shock waves. >> 

 

G. C. Katsimiga, S. I. Mistakidis, et al. Interactions and dynamics of one-dimensional droplets, bubbles and kinks. arXiv: 2306.07055v2 [cond-mat.quant-gas]. Jul 26, 2023.

https://arxiv.org/abs/2306.07055

Also: drop, bubble, waves, soliton, in https://www.inkgmr.net/kwrds.html

Keywords: gst, drop, bubble, kink, wave, soliton, homoclinic orbits

# gst: transitions by coupled instabilities

AA << present an experimental study of quasiperiodic transitions between a highly ordered square-lattice pattern and a disordered, defect-riddled state, in a circular Faraday system. (They)  show that the transition is driven initially by a long-wave amplitude modulation instability, which excites the oscillatory transition phase instability, leading to the formation of dislocations in the Faraday lattice. The appearance of dislocations dampens amplitude modulations, which prevents further defects from being created and allows the system to relax back to its ordered state. The process then repeats itself in a quasiperiodic manner. >>

Valeri Frumkin, Shreyas Gokhale. Coupled instabilities drive quasiperiodic order-disorder transitions in Faraday waves. Phys. Rev. E 108, L012601. July 17, 2023. 

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.108.L012601

Also: parrondo, tit-for-tat, game, transition, chaos, in https://www.inkgmr.net/kwrds.html

Keywords: parrondo, tit-for-tat, game,  transition, chaos

# gst: inertial particles within co-rotating dusty vortices

 << dispersed particles with moderate inertia cause the vortex pair to push apart to a separation nearly twice as large as the initial separation. >>

 

 << antisymmetric vorticity generated by particles flung out of the rotational cores causes the vortex pair repulsion. Eventually, the two dusty vortices merge into a single vortex with most particles accumulating outside the core similar to the dusty Lamb-Oseen vortex described in Shuai & Kasbaoui (2022) >>

 

 << For weakly inertial particles, (AA) find that the merger dynamics follow the same mechanics as those of a single-phase flow, albeit with a density that must be adjusted to match the mixture density. >>

 

<< Lastly, highly inertial particles tend to fragment the vortex cores leading to murky merger dynamics. >>

Shuai Shuai, Anubhab Roy, M. Houssem Kasbaoui. The merger of co-rotating vortices in dusty flows. arXiv: 2307.05413v1 [physics.flu-dyn]. Jul 11, 2023. 

https://arxiv.org/abs/2307.05413

Also: particle, vortex, in https://www.inkgmr.net/kwrds.html

Keywords: gst, particle, vortex 

# gst: evolution of survivors compared to discrete vs continuous noise

<< Environmental variations can significantly influence how populations compete for resources, and hence shape their evolution. Here, (AA) study population dynamics subject to a fluctuating environment modeled by a varying carrying capacity changing continuously in time according to either binary random switches, or by being driven by a noise of continuous range. >>

<< the slow strain fixation probability can be greatly enhanced for a continuously varying environment compared to binary switches, even when the first two moments of the carrying capacity coincide. >>️

Ami Taitelbaum, Robert West, et al. Evolutionary dynamics in a varying environment: Continuous versus discrete noise. Phys. Rev. Research 5, L022004. April 4, 2023. 

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L022004

Also: noise, in https://www.inkgmr.net/kwrds.html

Keywords: gst, evolution, noise, discrete vs continuous noise