# gst: instability triggered by mixed convection in a thin fluid layer.

<< ️(AA) investigate the convective stability of a thin, infinite fluid layer with a rectangular cross-section, subject to imposed heat fluxes at the top and bottom and fixed temperature along the vertical sides. The instability threshold depends on the Prandtl number as well as the normalized flux difference (f) and decreases with the aspect ratio (ϵ), following a ϵf^−1 power law. >>

<< ️Using 3D initial value and 2D eigenvalue calculations, (They) identify a dominant 3D mode characterized by two transverse standing waves attached to the domain edges. (They) characterize the dominant mode’s frequency and transverse wave number as functions of the Rayleigh number and aspect ratio. An analytical asymptotic solution for the base state in the bulk is obtained, valid over most of the domain and increasingly accurate for lower aspect ratios. >>

<< A local stability analysis, based on the analytical base state, reveals oscillatory transverse instabilities consistent with the global instability characteristics. The source term for this most unstable mode appears to be interactions between vertical shear and horizontal temperature gradients. >>

Florian Rein, Keaton J. Burns, Stefan G. Llewellyn Smith, et al. Instability triggered by mixed convection in a thin fluid layer. arXiv: 2512.02331v1 [physics.flu-dyn]. Dec 2, 2025.

https://arxiv.org/abs/2512.02331

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

Keywords: gst, waves, instability, transitions, convection, vertical shear, horizontal temperature gradients.

# gst: two instabilities in one liquid sheet.

<< ️Two cylindrical liquid jets (dia = 1 mm) of a glycerol-water mixture (80/20) impinge at 90º to one another, creating a thin liquid sheet bordered by a thick rim. Classical fish-bone shapes (sheet-thread-droplet) are formed where the rim instability is driven by Rayleigh-Plateau type mechanisms. >>

<< ️Here (AA) also see fish-bone shapes occurring for similar reasons. However, the waves on the sheet are formed by small imbalances between the two jet velocities (natural pipe driven oscillation), rather than the traditional Kelvin-Helmholtz instability. (They) stroboscopic photograph of the sheet reveals that both of these instabilities can coexist within a narrow range of operating conditions. >>

<< ️The breakup of the liquid sheet (lower down) is caused by the combined instability of spatially growing waves. The liquid sheet breaks down mainly through the growth of bounded waves. These waves eventually break, forming long threads at the bottom of the sheet, which further disintegrate into droplets due to the Rayleigh-Plateau instability of threads. >>

Sandip Dighe, Hrishikesh Gadgil, Tadd Truscott. Two instabilities in one liquid sheet. Phys. Rev. Fluids 10, 110501. Nov 20, 2025

https://journals.aps.org/prfluids/abstract/10.1103/nvkn-hk4g

77th Annual Meeting of the APS Division of Fluid Dynamics (Nov 24 — 26, 2024). P2692828: Two instabilities in one liquid. 

https://gfm.aps.org/meetings/dfd-2024/673f8914d88f37002bbe76d8

Also: waves, instability, transitions, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, waves, instability, transitions.

# gst: symmetries at the origin of hierarchical emergence.

<< ️Many systems of interest exhibit nested emergent layers with their own rules and regularities, and our knowledge about them seems naturally organised around these levels. This (AA) paper proposes that this type of hierarchical emergence arises as a result of underlying symmetries. By combining principles from information theory, group theory, and statistical mechanics, one finds that dynamical processes that are equivariant with respect to a symmetry group give rise to emergent macroscopic levels organised into a hierarchy determined by the subgroups of the symmetry. >>

<< ️The same symmetries happen to also shape Bayesian beliefs, yielding hierarchies of abstract belief states that can be updated autonomously at different levels of resolution. These results are illustrated in Hopfield networks and Ehrenfest diffusion, showing that familiar macroscopic quantities emerge naturally from their symmetries. Together, these results suggest that symmetries provide a fundamental mechanism for emergence and support a structural correspondence between objective and epistemic processes, making feasible inferential problems that would otherwise be computationally intractable. >>

Fernando E. Rosas. Symmetries at the origin of hierarchical emergence. arXiv: 2512.00984v1 [q-bio.NC]. Nov 30, 2025.

https://arxiv.org/abs/2512.00984

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

Keywords: gst, networks, transitions, nested emergent layers, hierarchical emergences, subgroup symmetry, Bayesian beliefs, Hopfield networks, Ehrenfest diffusion.

# gst: atypical chimera states in an ensemble of partially mobile particles.

<< ️(AA) study the influence of nonuniform motion of oscillators in a ring chain with nonlocal coupling on their collective dynamics and reveal the mechanism behind the emergence of an atypical chimera state in such systems. >>

<< ️The mechanism relies on regular spatially inhomogeneous motion of oscillators, which breaks the symmetry of the effective interaction kernel. This symmetry breaking induces spatial phase correlations in the asynchronous part of the system, giving rise to nonuniformly twisted and previously unobserved coherent-incoherent-twisted states. >>

Pavel A. Shcherbakov, Lev A. Smirnov, Vasily A. Kostin, et al. Atypical Chimera States in an Ensemble of Partially Mobile Particles. arXiv: 2512.00876v1 [nlin.PS]. Nov 30, 2025. 

https://arxiv.org/abs/2512.00876

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

Keywords: gst, chimera, phase oscillators, nonlocal coupling, active particles, twisted state, alternating chimera state, cross-correlation.

# gst: degrees of universality in wave turbulence

<< ️Turbulence of weakly interacting waves displays a great deal of universality: independence of the details of the interaction and of the pumping and dissipation scales. Here (AA) study how inverse turbulent cascades (from small to large scales) transition from weak to strong. (They) find that while one-loop corrections can be dependent on excitation and dissipation scales, new types of universality appear in strong turbulence. (They) contrast turbulence of spin waves in ferromagnets with turbulent cascades in the Nonlinear Schrödinger Equation (NSE) and in an MMT-like (Majda-McLaughlin-Tabak) model in higher dimensions having a multiplicative interaction vertex: vertex renormalization gives rise to dependence on the pumping (UV scale) in the former but not in the latter. >>

<< ️As a result of this spectral nonlocality, spin-wave turbulence stops being weak if one is sufficiently far from the pumping scale, even when the interaction of waves with comparable wavenumbers is weak. (AA) paraphrase this as: nonlocality enhances nonlinearity. >>

<< ️(AA) then describe strong turbulence in a multi-component version of these models with a large number of components. (They) argue that strong spin-wave turbulence is similar to turbulence of the focusing NSE, as it realizes a critical-balance state. However, UV nonlocality causes the level of spin-wave turbulence at large scales to decrease with increasing pumping level, culminating in a state that is independent of the level of pumping. >>

Jiasheng Liu, Vladimir Rosenhaus, Gregory Falkovich. Degrees of universality in wave turbulence. arXiv: 2512.04866v1 [cond-mat.stat-mech]. Dec 4, 2025.

https://arxiv.org/abs/2512.04866

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

Keywords: gst, waves, turbulence, transitions.

# gst: apropos of escape, qualitatively distinct mechanisms of noise-induced escape in diffusively coupled bistable elements.

<< ️The analysis of noise-induced escape in ensembles of bistable elements is challenging, because nonlinearity, coupling, and noise all play essential roles. (AA) show that the interplay of these three factors yields three qualitatively distinct escape mechanisms in diffusively coupled bistable elements, depending on the coupling strength. >> 

<< ️To clarify the relation between coupling strength and mean escape time, (They) derive effective one-dimensional dynamics: nonlinear mean-field Fokker-Planck equation in the weak-coupling regime, stochastic mean-field dynamics in the strong-coupling regime, and deterministic mean-field dynamics in the intermediate regime. >>

<< ️(AA) validate these reduced descriptions by comparing predictions with numerical simulations. (They) identify a distinct dominant driving factor of escape processes in each regime. Notably, the three escape mechanisms emerge through the interplay of nonlinearity, diffusive coupling, and dynamical noise -- rather than bifurcations of the noise-free system. >>

<< ️(AA) approach serves as a framework applicable to other diffusively coupled stochastic nonlinear systems, motivating a further search for similar synergistic phenomena. >>

Hidemasa Ishii, Hiroshi Kori. Qualitatively distinct mechanisms of noise-induced escape in diffusively coupled bistable elements. arXiv: 2512.01388v1 [nlin.AO]. Dec 1, 2025.

https://arxiv.org/abs/2512.01388

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

Keywords: gst, noise, escape, noise-induced escape, bistable elements, weak- mean- strong- regimes, stochasticity.

# gst: finding information in the randomness of living matter.

<< ️In recent research, (AA) succeeded in developing a theoretical description that can rigorously characterize the role of fluctuations in systems. "It is mathematically challenging to predict the behavior of such systems if using traditional tools from statistical mechanics," (Martin Kjøllesdal Johnsrud) >>.

<< ️The physicists thus developed a suitable mathematical tool to extend the existing field theories, and they are now able to make predictions about systems out of equilibrium, such as active matter. "With our formalism, we are able to define measurable quantities that can help to characterize nonequilibrium dynamics of living matter and enable experimental design of artificial active systems," (Ramin Golestanian) >>. 

Manuel Maidorn. Finding information in the randomness of living matter. Phys.org. Nov 28, 2025.

https://phys.org/news/2025-11-randomness.html

Martin Kjøllesdal Johnsrud, Ramin Golestanian. Phys. Rev. Research 7, L032053. Sep 9, 2025.

https://journals.aps.org/prresearch/abstract/10.1103/xx4z-lj5c

Martin Kjøllesdal Johnsrud, Ramin Golestanian. Phys. Rev. Research 7, L032054. Sep 9, 2025.

https://journals.aps.org/prresearch/abstract/10.1103/flzv-lq7x

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

Keywords: gst, active matter, complex systems, microscopic fluctuations, noise, nonequilibrium dynamics, stochastic field theories, statistical mechanics.