# gst: apropos of drift surfaces, e.g., banana orbits, perturbed toroidal vortices display internal simply connected topology.

<< ️This (AA) work shows that the interiors of perturbed zero-helicity vortices display simply connected topology with a crescent-shaped boundary. Flux surfaces in fluid and magnetic vortices were explored analytically, while particle trajectories in the context of plasma confinement were examined numerically, demonstrating the existence of both toroidal and simply connected topologies. >>

<< ️Numerical simulations of particle trajectories were conducted in the context of fusion confinement to calculate particle trajectories in a perturbed Soloviev equilibrium where simply connected flux surfaces were observed. The orbits often displayed crescent shapes, yet showed several marked differences from the flux surfaces, e.g., gyro-radii of size comparable to the crescent diameter, asymmetric crescents, connections between well-separated crescent tips, and possibly toroidal shapes, with an inversion of the roles played by the major and minor axes. >>

<< ️This new topology appears for perturbations in a broad class, with amplitudes and spatial variance allowed to be arbitrarily small. A corollary of this work proves the closedness of field lines under odd-parity perturbations of zero-helicity vortices. >>

Taosif Ahsan, Samuel A. Cohen, Alan H. Glasser. Perturbed Toroidal Vortices Display Internal Simply Connected Topology. arXiv: 2507.04596v1 [math-ph]. Jul 7, 2025. 

https://arxiv.org/abs/2507.04596

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

Keywords: gst, vortex, particle, transition, foliated torus, toroidal vortices, banana orbits. 

# gst: noise reinstates collapsed populations; stochastic reversal of deterministic extinction.

<< ️Conventional wisdom suggests that environmental noise drives populations toward extinction. In contrast, (AA) report a paradoxical phenomenon in which stochasticity reverses a deterministic tipping point, thereby preventing collapse. Using a hybrid model that integrates logistic growth with a density-triggered sigmoidal collapse, (They) uncover a striking reversal: deterministic fragility on one side, and stochastic rescue under weak noise on the other. >>

AA << analysis demonstrates that noise disrupts the convergence of deterministic trajectories toward extinction by altering the phase space topology, enabling back-transitions to viable states. This mechanism gives rise to noise-induced metastability and reveals a form of stochastic robustness not captured by deterministic models. >>

<< ️These findings suggest that natural fluctuations can serve as a stabilizing force in complex systems, offering a compelling counter-narrative to classical models in ecology, epidemiology, and beyond. (AA) advocate for a re-evaluation of stabilization strategies, emphasizing the constructive role of stochasticity in averting population collapse. >>

Vinesh Vijayan, B Priyadharshini, et al. Noise reinstates collapsed populations: stochastic reversal of deterministic extinction. arXiv:2507.03954v1 [q-bio.PE]. Jul 5, 2025.

https://arxiv.org/abs/2507.03954

Also:  noise, weak, disorder & fluctuations, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, noise, weakness, disorder,  

fluctuations, tipping point, transitions, stochasticity, stochastic reversal, stochastic rescue. 

# gst: apropos of ghost entities, criticality governs response dynamics and entrainment of periodically forced ghost cycles.

<< ️Many natural and engineered systems display oscillations that are characterized by multiple timescales. Typically, such systems are described as slow-fast systems, where the slow dynamics result from a hyperbolic slow manifold that guides the movement of the system's trajectories. Recently, (AA) have provided an alternative description in which the slow timescale results from Lyapunov-unstable transient dynamics of connected dynamical ghosts that form a closed orbit termed ghost cycle. >>

Here, AA << investigate the response properties of both types of systems to external forcing. Using the classical Van der Pol oscillator and modified versions of this model that correspond to a one-ghost and a two-ghost cycle, respectively, (They) find significant differences in the responses of slow-fast systems and ghost cycles, including increased entrainment regions of the latter. Nonautonomous model analysis reveals that the differences stem from a continuous remodeling of the attractor landscape of the ghost cycle models, enabled by being organized close to saddle-node on invariant cycle bifurcations, in contrast to a qualitatively unaltered attractor landscape of the slow-fast system. >>

(AA) << ️further demonstrate that the observed features occur in various systems with ghost cycles regardless of the exact mathematical model formulation leading to those ghost cycles, making them likely to apply to many other models with ghost cycles across different disciplines and contexts. (They) thus propose that systems containing ghost cycles display increased flexibility and responsiveness to continuous environmental changes. >>

Daniel Koch, Ulrike Feudel, Aneta Koseska. Criticality governs response dynamics and entrainment of periodically forced ghost cycles. Phys. Rev. E 112, 014205. Jul 8, 2025.

https://journals.aps.org/pre/abstract/10.1103/3d9z-qrb1

Also: transition, attractor, self-assembly, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, transition, attractor, self-assembly, bifurcations, saddle-node, synchronization, criticality, self-organized criticality.

# gst: wave-kinetic dynamics of forced-dissipated turbulent internal gravity waves

<< Internal gravity waves are an essential feature of stratified media, such as oceans and atmospheres. >>

<< To investigate their dynamics, (AA) perform simulations of the forced-dissipated kinetic equation describing the evolution of the energy spectrum of weakly nonlinear internal gravity waves. >>

<< During the early evolution, three well-known nonlocal interactions, the elastic scattering, the induced diffusion, and the parametric subharmonic instability, together with a superharmonic resonance play a prominent role. >>

<< In contrast, local interactions are responsible for anisotropic energy cascade on longer timescales. >>

AA << reveal emergence of a condensate at small horizontal wave vectors that can be interpreted as a pure wave-wave interaction-mediated layering process. >>

Vincent Labarre, Giorgio Krstulovic, Sergey Nazarenko. Wave-Kinetic Dynamics of Forced-Dissipated Turbulent Internal Gravity Waves. Phys. Rev. Lett. 135, 014101. Jul 1, 2025.

https://journals.aps.org/prl/abstract/10.1103/b82h-z21n

arXiv:2407.11469v3 [physics.flu-dyn]. Mar 28, 2025.

https://arxiv.org/abs/2407.11469

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

Keywords: gst, waves, weakness, turbulence, transitions, stratified turbulence, wave-turbulence interactions, weak turbulence.

# gst: self-organization to multicriticality; when a system can self-organize to a new type of phase transition while staying on the verge of another.

<< Self-organized criticality is a well-established phenomenon, where a system dynamically tunes its structure to operate on the verge of a phase transition. Here, (AA) show that the dynamics inside the self-organized critical state are fundamentally far more versatile than previously recognized, to the extent that a system can self-organize to a new type of phase transition while staying on the verge of another. >>

<< In this first demonstration of self-organization to multicriticality, (AA) investigate a model of coupled oscillators on a random network, where the network topology evolves in response to the oscillator dynamics. (They) 

 show that the system first self-organizes to the onset of oscillations, after which it drifts to the onset of pattern formation while still remaining at the onset of oscillations, thus becoming critical in two different ways at once. >>

 

<< The observed evolution to multicriticality is robust generic behavior that (AA) expect to be widespread in self-organizing systems. Overall, these results offer a unifying framework for studying systems, such as the brain, where multiple phase transitions may be relevant for proper functioning.>>

Silja Sormunen, Thilo Gross, Jari Saramäki. Self-organization to multicriticality. arXiv: 2506.04275v1 [nlin.AO]. Jun 4, 2025. 

https://arxiv.org/abs/2506.04275

Also: network, random, self-assembly, transition, brain, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, network, random, self-assembly, transition, phase transition, multiple phase transitions, self-organizing systems, self-organized criticality, multicriticality, brain.

# life: the pervasive "soft power" of ancient India.

<< One of the big contentions of popular historian William Dalrymple’s latest book “The Golden Road: How Ancient India Transformed the World,” which came out in the United States a few weeks ago, is that the Indian subcontinent’s connections to the West, especially via the Roman Empire, were far richer than those of China (i.e. the “Silk Road” cited). Once the might of Rome reached Egypt and the maritime routes of the Red Sea, it brought the customers of the Mediterranean to India’s doorstep. It also saw Indian philosophy and mathematics travel west and east. >>

<< Once their economic links to the West thinned with the collapse of the Roman Empire, South Indian merchant guilds turned east, embarking on trade and contacts that spread Indian religion and ideas across a wide expanse of Asia and underlay the grandeur of centuries-old temple complexes like Angkor Wat in Cambodia or Borubudur in Indonesia. >>

<< it’s one of the great soft power miracles of world history, because unlike Islam and unlike quite a lot of Christianity, no one took Buddhism at the point of a sword. No one imposed Buddhism at any point. It was the sophistication of its ideas and particularly its attractiveness to the merchant classes, bizarrely. The Buddhist monasteries act as banks, as factories and as caravanserais. >>

Ishaan Tharoor with Rachel Pannett. How ancient India changed the world. WorldView (by mail). washingtonpost.com. May 19, 2025.

https://s2.washingtonpost.com/camp-rw/?trackId=660de34bb906a33aae6b8103&s=682aadf6f062960b82a2f3e6

Also:  forms of power, waves, attractor, Zen, compassion, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: life, forms of power, soft power, waves, attractors, Zen, compassion, transition.

# gst: period-doubling route to chaos in viscoelastic flows

<< Polymer solutions can develop chaotic flows, even at low inertia. This purely elastic turbulence is well studied, but little is known about the transition to chaos. In two-dimensional (2D) channel flow and parallel shear flow, traveling wave solutions involving coherent structures are present for sufficiently large fluid elasticity. >>

AA << numerically study 2D periodic parallel shear flow in viscoelastic fluids, and (They) show that these traveling waves become oscillatory and undergo a series of period-doubling bifurcations en-route to chaos. >>

Jeffrey Nichols, Robert D. Guy, Becca Thomases. Period-doubling route to chaos in viscoelastic Kolmogorov flow. Phys. Rev. Fluids 10, L041301. Apr 17, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.L041301

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

Keywords: gst, chaos, waves, traveling waves, elasticity, viscoelastic fluids, turbulence, elastic turbulence, period-doubling bifurcations, transitions

# gst: elastic instability of wormlike micelle solution flow in serpentine channels

AA << investigated the flow behavior of a highly elastic, shear-thinning, semi-dilute (Wormlike micelle) WLM solution in serpentine channels at low Reynolds number and moderate Weissenberg numbers. >>

Their << flow visualization experiments revealed three key phenomena: >>

1. << At low Wi, the base flow is steady and laminar but exhibits spatial asymmetry with wall slip, reflecting the shear-thinning and shear banding properties of the WLM solution. Above a critical Wi (..) the flow undergoes an elastic instability and transitions to a 3D unsteady flow state characterized by pronounced spatiotemporal velocity fluctuations. (..). >>

2. << Alongside this unstable bulk flow, dead zones of stagnant fluid form in the downstream portion of halfloops—reflecting the ability of the WLM solution to support shear localization, complementing reports of dead zone formation for other types of complex fluids (..). Due to coupling to the velocity fluctuations in the bulk flow, these dead zones fluctuate in their size; however, they are bounded by a maximalsize that minimizes the fluid streamline curvature, and therefore the generation of elastic stresses. Dead zones also exhibit multistable behavior—forming and persisting in some half-loops, not forming in other half-loops, and randomly switching between these two states. (..). >>

3. << The unstable flow state also features intermittent, 3D “twisting” velocity inversion events amid the spatiotemporally-fluctuating bulk flow. These twisting events reduce the hydrodynamic tortuosity compared to the base flow state, and their geometric structure can also be rationalized as minimizing the fluid streamline curvature, and therefore the generation of elastic stresses. >>

Emily Y. Chen, Sujit S. Datta. Elastic instability of wormlike micelle solution flow in serpentine channels. arXiv: 2504.02951v1 [physics.flu-dyn]. 

https://arxiv.org/abs/2504.02951

Also: elastic, instability, disorder & fluctuations, transition, behav, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, elasticity, instability, disorder & fluctuations, transition, behavior, multistable behavior, randomly switch, twisting events, dead zone

# gst: apropos of drift-waves, their coherent puff and slugs in transitional turbulence.

<< The long-term development of the transitional regime of drift-wave turbulence is studied in a magnetized plasma column by means of the conditional-average technique. >>

<< In the transitional regime, small changes in the magnetic-field strength as control parameter lead to large changes in the correlation times, indicating the existence of a critical point of an underlying nonequilibrium continuous phase transition. >>

<< This and the spatiotemporal dynamics shows similarities to puff splitting, slug-gap splitting, and puff jamming. >>️

P. Manz, S. Knauer, et al. Coherent puff and slugs in transitional drift-wave turbulence. Phys. Rev. E 111, 045203. April 8, 2025.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.045203

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

Keywords: gst, waves, drift-waves, turbulence, jamming, transition, puff splitting, slug-gap splitting, puff jamming 

# gst: conventional and anomalous mobility edges in a quasiperiodic chain.

<< Mobility edges (MEs) constitute the energies separating the localized states from the extended ones in disordered systems. Going beyond this conventional definition, recent proposal suggests for an ME which separates the localized and multifractal states in certain quasiperiodic systems - dubbed as the anomalous mobility edges (AMEs). >>

<< In this study, (AA) propose an exactly solvable quasiperiodic system that hosts both the conventional and anomalous mobility edges under proper conditions. (They) show that with increase in quasiperiodic disorder strength, the system first undergoes a delocalization to localization transition through an ME of conventional type. >>

<< Surprisingly, with further increase in disorder, (They) obtain that a major fraction of the localized states at the middle of the spectrum turn multifractal in nature. Such unconventional behavior in the spectrum results in two AMEs, which continue to exist even for stronger quasiperiodic disorder. >>

AA << numerically obtain the signatures of the coexisting MEs complement it through analytical derivation using Avila's global theory. In the end (They) provide important signatures from the wavepacket dynamics. >>️

Sanchayan Banerjee, Soumya Ranjan Padhi, Tapan Mishra. Emergence of distinct exact mobility edges in a quasiperiodic chain. arXiv: 2503.19834v1 [cond-mat.quant-gas]. Mar 25, 2025.️

https://arxiv.org/abs/2503.19834

Also: edge, order, disorder, waves, transition,  in https://www.inkgmr.net/kwrds.html 

Keywords: gst, edge, order, disorder, waves, transition 

# gst: apropos of bubble rearrangements, transition from slip to scraping as critical-like behavior in foam dynamics.

<< Jamming systems, including colloids, emulsions, foams, and biological tissues, undergo significant deformation during processes like material scraping or wound self-healing. To adequately spread a foam or cream over a surface, external force must be applied to artificially scrape it. Notably, the transition from slip to scraping when foam is manipulated using a rigid plate remains poorly understood. >>

<< Systematic observations of the internal foam structure during scraping were conducted, and the scraping length was qualitatively analyzed by varying the scraping velocity. (AA) study reveals that the transition from slip to scraping is driven by the sequential propagation of bubble rearrangements. Furthermore, the scraping length diverges towards the transition point, with a critical exponent of approximately 0.61. >>

<< These findings align with directional percolation theory, underscoring the robustness of the theoretical framework. >>

Masaya Endo, Rei Kurita. Critical-like behavior in foam dynamics: Transition from slip to scraping. Phys. Rev. Research 7, 023013. Apr 3, 2025.

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.023013

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

Keywords: gst, bubble, bubble rearrangements, foam, jamming, transition, criticality, scraping,  percolation

# gst: noise as endogenous control

<< Systems biology faces the monumental task of synthesizing vast amounts of molecular facts into a cohesive whole. While it is recognized that stochasticity is ubiquitous in the cell, with noise playing a role in gene expression, differentiation, and switching (..), it is still commonly argued that the cell functions in spite of the noisy cellular environment. >>️

<< Stochastic systems have a control-theoretic interpretation in which noise plays the role of endogenous control. In the weak-noise limit, relevant at low temperatures or in large populations, control is optimal and an exact mathematical mapping from noise to control is described, where the maximizing the probability of a state becomes the control objective. >>

<< In Langevin dynamics noise is identified directly with control, while in general Markov jump processes, which include chemical reaction networks and electronic circuits, (AA) use the Doi-Zel'dovich-Grassberger-Goldenfeld-Peliti path integral to identify the `response' or `tilt' field π as control, which is proportional to the noise in the semiclassical limit. This solves the longstanding problem of interpreting π. >>

AA << illustrate the mapping on multistable chemical reaction networks and systems with unstable fixed points. The noise-control mapping builds intuition for otherwise puzzling phenomena of stochastic systems: why the probability is generically a non-smooth function of state out of thermal equilibrium; why biological mechanisms can work better in the presence of noise; and how agentic behavior emerges naturally without recourse to mysticism. >>

Eric De Giuli. Noise equals endogenous control. arXiv: 2503.15670v2 [q-bio.MN]. Mar 24, 2025.

https://arxiv.org/abs/2503.15670

Also: noise, disorder & fluctuations, transition, dance, jazz, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, noise, disorder, transition, ethno, crosstalk, gossip, misinformation, fake news, dance, jazz

# gst: apropos of transitions to turbulence, pulsatility delays the transition to sustained turbulence in quasi-2D shear flows

<< Two-dimensional disturbances require high Reynolds numbers to incite transition from a steady base flow, as transient growth is modest. With the addition of an oscillatory base flow component, (AA) work shows that the transient growth experienced by two-dimensional initial perturbations is often well above that provided by the steady component. >>

<< However, as has been shown for three-dimensional flows [B. Pier and P. J. Schmid, J. Fluid Mech. 926, A11 (2021)], the transient growth is almost entirely composed of modal intracyclic growth, rather than a transient mechanism which takes advantage of non-normality. This lack of transient growth, relative to the severe decay induced by the favorable pressure gradient during the acceleration phase of the oscillatory base flow, only ever delays the transition to sustained turbulence. >>

<< Thus, a nonoscillatory driving force remains the most efficient strategy for sustained turbulence in quasi-two-dimensional shear flows. The only benefit provided by pulsatility is that the amplitude of the initial condition required to trigger intermittent turbulence is orders of magnitude smaller. >>️

Christopher J. Camobreco, Alban Pothérat, Gregory J. Sheard. Pulsatility delays the transition to sustained turbulence in quasi-two-dimensional shear flows. Phys. Rev. Fluids 10, 023905. Feb 25, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.023905

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

Keywords: gst, pause, transition, turbulence, vortex

# behav: locomotion-dependent auditory gating to the parietal cortex guides multisensory decisions

<< Decision-making in mammals fundamentally relies on integrating multiple sensory inputs, with conflicting information resolved flexibly based on a dominant sensory modality. However, the neural mechanisms underlying state-dependent changes in sensory dominance remain poorly understood. >>

 AA << study demonstrates that locomotion in mice shifts auditory-dominant decisions toward visual dominance during audiovisual conflicts. Using circuit-specific calcium imaging and optogenetic manipulations, (They) found that weakened visual representation in the posterior parietal cortex (PPC) leads to auditory-dominant decisions in stationary mice. >>

<< Prolonged locomotion, however, promotes visual dominance by inhibiting auditory cortical neurons projecting to the PPC (ACPPC). This shift is mediated by secondary motor cortical neurons projecting to the auditory cortex (M2AC), which specifically inhibit ACPPC neurons without affecting auditory cortical projections to the striatum (ACSTR). >>

AA << findings reveal the neural circuit mechanisms underlying auditory gating to the association cortex depending on locomotion states, providing insights into the state-dependent changes in sensory dominance during multisensory decision-making. >>️

Ilsong Choi, Seung-Hee Lee. Locomotion-dependent auditory gating to the parietal cortex guides multisensory decisions. biorxiv. doi: 10.1101/ 2024.02.14.580296. Jan 24, 2025.

https://www.biorxiv.org/content/10.1101/2024.02.14.580296v2

Also: Inchingolo G. Cultural transitions and epidemiology. Proceedings of the 13th Scientific Meeting of the International Epidemiological Association - IEA, Sydney, Australia, Sept 26--29, 1993: 129. Med Hypotheses 1994; 43(4): 201-206. https://pubmed.ncbi.nlm.nih.gov/7838001/     Inchingolo G. Placebo effects via deterministic chaos during traditional dances. Genova, 7 Marzo 1995: abstract. Proceedings of the 6th Congress of the International Association of Biomedical Gerontology - IABG, (Part 1, Oriental Medicine), Makuhari, Japan, August 20-26, 1995. INRCA, Technical Report, Genova, 18 August 1995: 1-26. https://www.inkgmr.net/papers.html 

Also: behav, dance, transition, brain, sound, ethno, in https://www.inkgmr.net/kwrds.html 

Keywords: behavior, dance, transition, brain, sound, ethno

# gst: apropos of the impact of noise, stochastic Kuramoto oscillators with inertia and higher-order interactions.

<< The impact of noise in coupled oscillators with pairwise interactions has been extensively explored. Here, (AA) study stochastic second-order coupled Kuramoto oscillators with higher-order interactions and show that as noise strength increases, the critical points associated with synchronization transitions shift toward higher coupling values. By employing the perturbation analysis, (They) obtain an expression for the forward critical point as a function of inertia and noise strength. Further, for overdamped systems, (AA) show that as noise strength increases, the first-order transition switches to second-order even for higher-order couplings. >>

️

Priyanka Rajwani, Sarika Jalan. Stochastic Kuramoto oscillators with inertia and higher-order interactions. Phys. Rev. E 111, L012202. Jan 13, 2025.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.L012202   arXiv: 2407.14874v1 [nlin.AO]. Jul 20, 2024. https://arxiv.org/abs/2407.14874 

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

Keywords: gst, noise, transition, coupled oscillators, synchronization transition

# gst: route from avalanches with random fields to stochastic branching events

<< Many complex systems with discrete symmetry breaking exhibit avalanche dynamics. Under quasistatically slow external driving, the temporal evolution v(t) of physical observables appears to be split between long periods of quiescence and well-delimited fast transformation events, the so-called avalanches. >>

<< Due to their fast nature, such avalanches can be regarded as instantaneous and labeled as point events k in time with a branching parameter. (..) Many physical systems exhibit criticality in the form of scale-free avalanches rendering power-law distributions of sizes and durations. >>️

<< Avalanches in mean-field models can be mapped to memoryless branching processes defining a universality class. (AA) present a reduced expression mapping a broad family of critical and subcriticial avalanches in mean-field models at the thermodynamic limit to rooted trees in a memoryless Poisson branching processes with random occurrence times. (They) derive the exact mapping for the athermal random field Ising model and the democratic fiber bundle model, where avalanche statistics progress towards criticality, and as an approximation for the self-organized criticality in slip mean-field theory. Avalanche dynamics and statistics in the three models differ only on the evolution of the field density, interaction strength, and the product of both terms determining the branching number. >>

️

Jordi Baró, Álvaro Corral. A universal route from avalanches in mean-field models with random fields to stochastic Poisson branching events. arXiv: 2502.08526v3 [cond-mat.dis-nn]. Feb 15, 2025. 

https://arxiv.org/abs/2502.08526

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

Keywords: gst, waves, instability, transition

# gst: criticality and multistability in quasi-2D turbulence

       Fig. 1(a) Helmholtz resonators

<< Two-dimensional (2D) turbulence, despite being an idealization of real flows, is of fundamental interest as a model of the spontaneous emergence of order from chaotic flows. The emergence of order often displays critical behavior, whose study is hindered by the long spatial and temporal scales involved. >>

Here AA << experimentally study turbulence in periodically driven nanofluidic channels with a high aspect ratio using superfluid helium. (They) find a multistable transition behavior resulting from cascading bifurcations of large-scale vorticity and critical behavior at the transition to quasi-2D turbulence consistent with phase transitions in periodically driven many-body systems. >>

AA << demonstrate that quasi-2D turbulent systems can undergo an abrupt change in response to a small change in a control parameter, consistent with predictions for large-scale atmospheric or oceanic flows. >>️

Filip Novotny, Marek Talir, et al. Critical behavior and multistability in quasi-two-dimensional turbulence. arXiv: 2406.08566v1 [physics.flu-dyn]. Jun 12, 2024.

https://arxiv.org/abs/2406.08566

Also: order, disorder, disorder & fluctuations, turbulence, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, order, disorder, disorder & fluctuations, criticality, turbulence, transition 

# gst: discontinuous transitions to active nematic turbulence.

<< Active fluids exhibit chaotic flows at low Reynolds number known as active turbulence. Whereas the statistical properties of the chaotic flows are increasingly well understood, the nature of the transition from laminar to turbulent flows as activity increases remains unclear. Here, through simulations of a minimal model of unbounded active nematics, (AA) find that the transition to active turbulence is discontinuous. (They) show that the transition features a jump in the mean-squared velocity, as well as bistability and hysteresis between laminar and chaotic flows. >>

<< From distributions of finite-time Lyapunov exponents, (AA) identify the transition at a value A∗≈4900 of the dimensionless activity number. Below the transition to chaos, (They) find subcritical bifurcations that feature bistability of different laminar patterns. These bifurcations give rise to oscillations and to chaotic transients, which become very long close to the transition to turbulence. Overall, (Their) findings contrast with the continuous transition to turbulence in channel confinement, where turbulent puffs emerge within a laminar background. >>

AA << propose that, without confinement, the long-range hydrodynamic interactions of Stokes flow suppress the spatial coexistence of different flow states, and thus render the transition discontinuous. >>️

Malcolm Hillebrand, Ricard Alert. Discontinuous Transition to Active Nematic Turbulence. arXiv: 2501.06085v1 [cond-mat.soft]. Jan 10, 2025.

https://arxiv.org/abs/2501.06085

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

Keywords: gst, chaos, transition, turbulence, jumps, active nematics

# gst: quadrupolar stress drives collapse of nematic order on frictional substrates.

<< The field of active nematics has traditionally employed descriptions based on dipolar activity, with interactions that align along a single axis. However, it has been theoretically predicted that interactions with a substrate, prevalent in most biological systems, would require novel forms of activity, such as quadrupolar activity, that are governed by hydrodynamic screening. >>

<< Here, by combining experiments and numerical simulations, (AA) show that upon light-induced solidification of the underlying medium, microtubule-kinesin mixtures undergo a transformation that leads to a biphasic active suspension. Using an active lyotropic model, (They) prove that the transition is governed by screening effects that alter the dominant form of active stress. Specifically, the combined effect of friction and quadrupolar activity leads to a hierarchical folding that follows the intrinsic bend instability of the active nematic layer. >>

AA << results demonstrate the dynamics of the collapse of orientational order in active nematics and present a new route for controlling active matter by modifying the activity through changing the surrounding environment. >>️

Aleksandra Ardaseva, Ignasi Velez-Ceron, et al. Beyond Dipolar Activity: Quadrupolar Stress Drives Collapse of Nematic Order on Frictional Substrates. arXiv: 2407.03723v3 [cond-mat.soft]. Jan 14, 2025. 

https://arxiv.org/abs/2407.03723

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

Keywords: gst, transition, collapse, active nematics, stress 

# gst: traveling strings of active dipolar colloids.

AA << study an intriguing new type of self-assembled active colloidal polymer system in 3D. It is obtained from a suspension of Janus particles in an electric field that induces parallel dipoles in the particles as well as self-propulsion in the plane perpendicular to the field. >>

<< At low volume fractions, in experiment, the particles self-assemble into 3D columns that are self-propelled in 2D. Explicit numerical simulations combining dipolar interactions and active self-propulsion find an activity dependent transition to a string phase by increasing dipole strength. >>

AA << classify the collective dynamics of strings as a function of rotational and translational diffusion. (..) (They) also discover long range correlations of the fluctuations along the string contour that grow with the active persistence time, a purely active effect that disappears in the thermal limit. >>

Xichen Chao, Katherine Skipper, et al. Traveling Strings of Active Dipolar Colloids. Phys. Rev. Lett. 134, 018302. Jan 6, 2025. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.018302

Also: particle, colloids, self-assembly, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particle, colloids, self-assembly, Janus, polymers, strings, transition