# gst: chaos creates and destroys branched flows.

<< Electrons, lasers, tsunamis, and ants have at least one thing in common: they all display branched flow. Whenever a wave propagates through a weakly refracting medium, flow is expected to accumulate along certain directions, forming structures called branches. >>️

AA << explore the laws governing the evolution of the branches in periodic potentials. On one hand, (They) observe that branch formation follows a similar pattern in all non-integrable potentials, no matter whether the potentials are periodic or completely irregular. Chaotic dynamics ultimately drives the birth of the branches. On the other hand, (AA) results reveal that for periodic potentials the decay of the branches exhibits new characteristics due to the presence of infinitely stable branches known as superwires.  >>️

Alexandre Wagemakers, Aleksi Hartikainen, et al. Chaotic dynamics creates and destroys branched flow. arXiv: 2406.12922v1 [nlin.PS]. Jun 14, 2024. 

https://arxiv.org/abs/2406.12922

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

Keywords: gst, chaos, transition, branched flows, superwires 

# ai: apropos of Black Box in Generative Artificial Intelligence, the scientific XAI.

<< The scientific method is the cornerstone of human progress across all branches of the natural and applied sciences, from understanding the human body to explaining how the universe works. The scientific method is based on identifying systematic rules or principles that describe the phenomenon of interest in a reproducible way that can be validated through experimental evidence. In the era of artificial intelligence (AI), there are discussions on how AI systems may discover new knowledge. >>

<< More specifically, knowing what data AI systems used to make decisions can be a point of contact with domain experts and scientists, that can lead to divergent or convergent views on a given scientific problem. Divergent views may spark further scientific investigations leading to new scientific knowledge. Convergent views may instead reassure that the AI system is operating within bounds deemed reasonable to humans. >>️

<< The perspective (AA) present here was inspired by several authors that published on the topic of AI for science in the past few years, but perhaps one contribution stands out: the inspiring New York Times editorial by Steven Strogatz (Strogatz, S. One giant step for a chess-playing machine. New York Times 26 (2018)) covering the winning of AlphaZero against Stockfish. In that piece, Strogatz states: “What is frustrating about machine learning, however, is that the algorithms can’t articulate what they’re thinking. We don’t know why they work, so we don’t know if they can be trusted. AlphaZero gives every appearance of having discovered some important principles about chess, but it can’t share that understanding with us.”. He additionally cites Garry Kasparov (the former world chess champion) that stated: “we would say that its [AlphaZero] style reflects the truth. This superior understanding allowed it to outclass the world’s top traditional program despite calculating far fewer positions per second.” >>️

AA highlights the importance of three aspects regarding scientific XAI (explainable Artificial Intelligence): accuracy, reproducibility, understandability, ️

Apropos of 'understandability', << The machine view should be understandable to scientists and domain experts. (..) If we want a scientist to make sense of the data used by a machine, this data should contain viable features that allow a scientist to tap into its existing corpus of knowledge. >>

<< XAI may also alleviate some of the risks that we may face when using AI for scientific discovery, that we share with Messeri and Crockett (‘adopting AI in scientific research can bind to our cognitive limitations and impede scientific understanding despite promising to improve it’). >>

️

Gianmarco Mengaldo. Explain the Black Box for the Sake of Science: Revisiting the Scientific Method in the Era of Generative Artificial Intelligence. arXiv: 2406.10557v1 [cs.AI]. Jun 15, 2024.

https://arxiv.org/abs/2406.10557

Also: ai (artificial intell), in https://www.inkgmr.net/kwrds.html 

Keywords: AI, XAI, Artificial Intelligence

# gst: buckling instability in a chain of sticky bubbles

<< A slender object undergoing an axial compression will buckle to alleviate the stress. Typically the morphology of the deformed object depends on the bending stiffness for solids, or the viscoelastic properties for liquid threads. >>️

AA << study a chain of uniform sticky air bubbles that rise due to buoyancy through an aqueous bath. A buckling instability of the bubble chain with a characteristic wavelength is observed.  >>️

<< If a chain of bubbles is produced faster than it is able to rise, the dominance of viscous drag over buoyancy results in a compressive stress that is alleviated by buckling the bubble chain. >>️

<< Unlike other systems, in which buckling arises from a cost associ­ated with bending, to our knowledge this is the first study of drag-induced buckling with no intrinsic cost to bending—a buckling instability with a characteristic lengthscale emerges as a result of hydrodynamics. >>

️

Carmen L. Lee and Kari Dalnoki-Veress. Buckling instability in a chain of sticky bubbles. Phys. Rev. Research 6, L022062. Jun 14, 2024. 

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.L022062

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

Keywords: gst, bubble, instability, drop, droplet, droploid, transition 

# gst: a knitted weaving that paints distances, dissimilarities, divergences, diversities, discrepancies, discriminations, displacements, deviations, ...

Frank Nielsen. Distances, dissimilarities, divergences, diversities, discrepancies, discriminations, displacements, deviations, etc. Sep 15th 2023. 

https://franknielsen.github.io/Divergence/index.html

https://x.com/FrnkNlsn

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

Keywords: gst, transition, distances, dissimilarities, divergences, diversities, discrepancies, discriminations, displacements, deviations

# gst: elasticity of fibres prefers the chaos of turbulence.

FIG. 4. Maximal Lyapunov exponents λ1 associated with the flow regions sampled by the fibre centre of masses in a 3D turbulent flow. 

<< Turbulent flows are ubiquitous in nature and are responsible for numerous transport phenomena that help sustain life on earth. >>️

AA << have shown that the stretching of fibres is due only to elasticity and their inertia playing a minimal role as they are advected by a turbulent carrier flow. A highly elastic fibre is much more likely to be stretched out and as a result prefers a “straighter” configuration rather than a coiled one. >>️

<< These inertial, elastic fibres then exhibit non-trivial preferential sampling of a 3D turbulent flow in a manner qualitatively similar to 2D turbulence (..). Inertia leads fibres away from vortical regions while their elasticity pulls them inside the vortices. Upto a moderate inertia (St ∼ O(1)), fibres increasingly prefer the straining regions of the flow, while at much larger inertia (St ≫ 1) they decorrelate from the flow and preference for straining regions begins to diminish again. >>️

<< However, owing to a large elasticity, fibres get trapped in vortical regions (at small St), as well as are unable able to exit the straining regions quickly. A more elastic and extensible fibre is, thus, more likely to spend longer times in both vortical and the straining regions of the flow. >>️

<< This picture of preferential sampling of a 3D turbulent flow by elastic, inertial fibres is also confirmed by alternately studying the chaoticity of the sampled flow regions via Lyapunov Exponents. Less elastic fibres prefer less chaotic (vortical) regions of the flow while more chaotic (straining) regions are preferred at large Wi. LEs also confirm that preferential sampling has a non-monotonic dependence on St for small elasticity but which is lost when Wi becomes very large.  >>

<< It would (..) be even more interesting to see how chaotic the fibre trajectories themselves are and what that has to say about fibre dynamics in turbulent flows. >>️

️

Rahul K. Singh. Elasticity of fibres prefers the chaos of turbulence. arXiv: 2406.06033v1. Jun 10, 2024.

https://doi.org/10.48550/arXiv.2406.06033

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

Keywords: gst, elastic, chaos, turbulence

# gst: approaching uncertainty among many-body real-time dynamics

<< Analog quantum simulation is emerging as a powerful tool for uncovering classically unreachable physics such as many-body real-time dynamics. >>️

AA << examines the interplay of errors arising from simulation of approximate time evolution with those due to practical, real-world device constraints. >>️

Nikita A. Zemlevskiy, Henry F. Froland, Stephan Caspar. Optimization of algorithmic errors in analog quantum simulations. Phys. Rev. A 109, 052425. May 15, 2024. 

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.052425

<< The new technique focuses on two sources of error that arise from the approximations used to map the quantum system of interest to the analog quantum simulator. In a real-world simulator, these error sources are linked in a complex way, and individually minimizing each error can increase the overall uncertainty of a simulation. (AA) tackled this problem by first isolating the two error sources and then carefully studying their interplay. This analysis enabled the researchers to finely tune a simulation’s parameters to minimize its overall uncertainty and to maximize its precision. >>️

Ryan Wilkinson. Quantifying Uncertainties in Quantum Simulations. 

Physics 17, s51. May 15, 2024. 

https://physics.aps.org/articles/v17/s51

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

Keywords: gst, uncertainty, error, noise

# gst: breakup of Janus droplet in a bifurcating microchannel

<< Droplet breakup is frequently observed in natural and industrial processes (..)  Although valuable insights on the breakup mechanisms of single-phase droplets in microchannels have been provided over the past decades, the breakup physics of complex emulsions is still poorly understood. >>️

<< Spatially asymmetric Janus microdroplets, distinct from single-phase or double emulsion droplets possessing one uniform interface with the ambient phase, are anticipated to show unique breakup behaviors, which has not been explored.  >>️

AA << conduct both microfluidic experiments and three-dimensional lattice Boltzmann simulations to investigate the dynamic breakup of ionic liquid (IL)-water Janus droplets in an assembled 3D-printed microchannel with a bifurcation. >>️

<< Three different flow regimes are identified: (i) division into two daughter Janus droplets, (ii) breakup into a single-phase droplet and a smaller Janus droplet, and (iii) nonbreakup.  >>️

AA << find that the strong constraint effect of the main channel and large Ca_av (average capillary numbers) values are essential to the symmetrical breakup of Janus droplets. The tunnel between the mother droplet and the wall of the main channel, which allows the lateral shift of the Janus droplet, and moderate flow rates facilitate the breakup of the IL single-phase portion of Janus droplets.  >>

<< Through 90° rotation of the splitting microchannel, (AA) elucidate the distinctions in Janus droplet behaviors under two baffle orientations. Potential impacts of the oblique flow characteristic of [bmim]⁢Fe⁢Cl4-water Janus droplets on the droplet breakup are discussed. >>️

️

Hao Wang, Shiteng Wang, et al. Dynamic breakup of Janus droplet in a bifurcating microchannel. Phys. Rev. Fluids 9, 064203. Jun 11, 2024. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.9.064203 

Also: 'Janus' in FonT https://flashontrack.blogspot.com/search?q=janus

Also: 'drop', 'droplet', 'droploid', in https://www.inkgmr.net/kwrds.html 

Keywords: gst, Janus, drop, droplet, droploid

# gst: helical instabilities from mixed mode transitions in boundary layers

<< Recent (..) direct numerical simulations (DNS) of adverse- and zero-pressure-gradient boundary layers beneath moderate levels of free stream turbulence (𝑇⁢𝑢≤2%) revealed a mixed mode transition regime, intermediate between orderly and bypass routes. >>️

<< In this regime, the amplitudes of the Klebanoff streaks and instability waves are similar, and both can contribute significantly as these interact. Three-dimensional visualizations of transitional eddies revealed a helical pattern, quite distinct from the sinuous and varicose forms seen in pure bypass transition. This raises the fundamental question of whether the helical pattern could be attributed to a previously unknown instability mode. >>️

In AA work << based on stability analyses, (they) show that it is indeed the case. Two-dimensional stability analyses are performed herein for base flows extracted from DNS flow fields. >>️

Rikhi Bose, Paul A. Durbin. Mixed mode transition in boundary layers: Helical instability. Phys. Rev. Fluids 9, 063905. Jun 12, 2024. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.9.063905

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

Keywords: gst, instability, transition, turbulence, waves

# gst: chaos controlled and disorder driven phase transitions by breaking permutation symmetry

<< Introducing disorder in a system typically breaks symmetries and can introduce dramatic changes in its properties such as localization. At the same time, the clean system can have distinct many-body features depending on how chaotic it is. >>

<< In this work the effect of permutation symmetry breaking by disorder is studied in a system which has a controllable and deterministic regular to chaotic transition. >>

<< Results indicate a continuous phase transition from an area-law to a volume-law entangled phase irrespective of whether there is chaos or not, as the strength of the disorder is increased. The critical disorder strength obtained by finite size scaling, indicate a strong dependence on whether the clean system is regular or chaotic to begin with. >>

<< Additionally, (AA) find that a relatively small disorder is seen to be sufficient to delocalize a chaotic system. >>

Manju C, Arul Lakshminarayan, Uma Divakaran. Chaos controlled and disorder driven phase transitions by breaking permutation symmetry. arXiv: 2406.00521v1 [quant-ph]. Jun 1, 2024. 

https://arxiv.org/abs/2406.00521

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

Keywords: gst, transition, chaos, disorder 

FonT: who is Manju C?

# gst: defects around obstacles, active nematic ratchet in asymmetric arrays

AA << numerically investigate the effect of an asymmetric periodic obstacle array in a two-dimensional active nematic. (They) find that activity in conjunction with the asymmetry leads to a ratchet effect or unidirectional flow of the fluid along the asymmetry direction. The directional flow is still present even in the active turbulent phase when the gap between obstacles is sufficiently small. >>️

AA << demonstrate that the dynamics of the topological defects transition from flow mirroring to smectic-like as the gap between obstacles is made smaller, and explain this transition in terms of the pinning of negative winding number defects between obstacles. >>

️

Cody D. Schimming, C. J. O. Reichhardt, C. Reichhardt. Active nematic ratchet in asymmetric obstacle arrays. Phys. Rev. E 109, 064602. Jun 3, 2024. 

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.064602 

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

Keywords: gst, nematic ratchet,  transition, turbulence, defect, error

# gst: controlled creation of point defects in 3D colloidal crystals

<< Crystal defects crucially influence the properties of crystalline materials and have been extensively studied. Even for the simplest type of defect—the point defect—however, basic properties such as their diffusive behavior, and their interactions, remain elusive on the atomic scale. >>️

Here AA << demonstrate in situ control over the creation of isolated point defects in a three-dimensional (3D) colloidal crystal allowing insight on a single-particle level. >>

AA << experimental model system provides a unique opportunity to shed light on the interplay between point defects, on the mechanisms of their diffusion, on their interactions, and on collective dynamics. >>️

Max P. M. Schelling, Janne-Mieke Meijer. Controlled creation of point defects in three-dimensional colloidal crystals. Phys. Rev. E 109, L062601. Jun 4, 2024.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.L062601

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

Keywords: gst, colloids, defect, error, transition

# gst: periodic defect braiding in active nematics confined to a cardioid.

AA' paper << examines self-mixing in active nematics, a class of fluids in which mobile topological defects drive chaotic flows in a system comprised of biological filaments and molecular motors. (They) present experiments that demonstrate how geometrical confinement can influence the braiding dynamics of the defects. >>️

<< Notably, (AA) show that confinement in cardioid-shaped wells leads to realization of the golden braid, a maximally efficient mixing state of exactly three defects with no defect creation or annihilation. >>

<< Increasing the size of the confining cardioid produces a transition from the golden braid, to the fully chaotic active turbulent state. >>️️

Fereshteh L. Memarian, Derek Hammar, et al. Controlling Chaos: Periodic Defect Braiding in Active Nematics Confined to a Cardioid. Phys. Rev. Lett. 132, 228301. May 28, 2024. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.228301

https://x.com/PhysRevLett/status/1796622457303876000

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

Keywords: gst, chaos, turbulence, active nematics, cardioid