# gst: from alternating stripes to alternating labyrinths, the Belousov−Zhabotinsky transition

<< Alternating (temporally period-2) stripes and labyrinths have been observed in media of chemical and biochemical reactions; however, the mechanisms underlying the formation of these spatiotemporal patterns remain unclear. >>

AA << conduct computer simulation using a modified model of Belousov−Zhabotinsky reaction that incorporates a global feedback loop with a spatial strength profile of Gaussian distribution. The simulation results demonstrate that the transition from alternating stripes to alternating labyrinths occurs when the feedback is negative with a certain width of the Gaussian function. (AA) add the same Gaussian-weighted feedback loop to an amplitude equation to describe the amplitude dynamics of the period-2 oscillation and show that the pattern dynamics of the Belousov−Zhabotinsky reaction can be well captured by this amplitude equation. >>

<< Analyses of the amplitude equation demonstrate that the transition from stripes to labyrinths arises from the transverse instabilities of bistable fronts caused by the Gaussian-weighted negative global feedback. >>️

Chunli Huang, Zhen Song, Zhilin Qu. Transition from alternating stripes to alternating labyrinths in oscillatory media. Phys. Rev. E 111, L032201. Mar 13, 2025.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.L032201

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

Also: Orologio chimico. Notes (quasi-stochastic poetry). Apr 08, 2005.

https://inkpi.blogspot.com/2005/04/1558-orologio-chimico.html  

Keywords: gst, transitions, BZ reaction, labyrinths, alternating labyrinths

# gst: dynamics of fluid-driven fractures across material heterogeneities.

<< Fracture propagation is highly sensitive to the conditions at the crack tip. In heterogeneous materials, microscale obstacles can cause propagation instabilities. Macroscopic heterogeneities modify the stress field over scales larger than the tip region. >>

 Here AA << experimentally investigate the propagation of fluid-driven fractures through multilayered materials. (They) focus on analyzing fracture profiles formed upon injection of a low-viscosity fluid into a two-layer hydrogel block. >>

<< Experimental observations highlight the influence of the originating layer on fracture dynamics. Fractures that form in the softer layer are confined, with no penetration in the stiffer layer. Conversely, fractures initiated within the stiffer layer experience rapid fluid transfer into the softer layer when reaching the interface. >>

AA << report the propagation dynamics and show that it is controlled by the toughness contrast between neighboring layers, which drives fluid flow. (They) model the coupling between elastic deformation, material toughness, and volume conservation. After a short transient regime, scaling arguments capture the dependence of the fracture geometry on material properties, injection parameters, and time. These results show that stiffness contrast can modify fracture propagation over large length scales and demonstrate the importance of macroscopic scale heterogeneities on fracture dynamics. >>

Sri Savya Tanikella, Marie C. Sigallon, Emilie Dressaire. Dynamics of fluid-driven fractures across material heterogeneities. Phys. Rev. E 111, 025504. Feb 28, 2025.   https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.025504     arXiv: 2407.10298v1 [physics.flu-dyn]. Jul 14, 2024.  https://arxiv.org/abs/2407.10298

Also: fracture, crack, elastic, 

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

Keywords: gst, fracture, crack, elasticity, instability, disorder, transitions

# gst: tuning to the edge of instability (in the cochlea)

<< Sound produces surface waves along the cochlea's basilar membrane. To achieve the ear's astonishing frequency resolution and sensitivity to faint sounds, dissipation in the cochlea must be canceled via active processes in hair cells, effectively bringing the cochlea to the edge of instability. But how can the cochlea be globally tuned to the edge of instability with only local feedback? >>

<< Surprisingly, (AA) find the basilar membrane supports two qualitatively distinct sets of modes: a continuum of localized modes and a small number of collective extended modes. Localized modes sharply peak at their resonant position and are largely uncoupled. As a result, they can be amplified almost independently from each other by local hair cells via feedback reminiscent of self-organized criticality. >>

<< However, this amplification can destabilize the collective extended modes; avoiding such instabilities places limits on possible molecular mechanisms for active feedback in hair cells. >>

AA << work illuminates how and under what conditions individual hair cells can collectively create a critical cochlea. >>️

Asheesh S. Momi, Michael C. Abbott, et al. Hair Cells in the Cochlea Must Tune Resonant Modes to the Edge of Instability without Destabilizing Collective Modes. PRX Life 3, 013001. Jan 2, 2025.

https://journals.aps.org/prxlife/abstract/10.1103/PRXLife.3.013001 

Also: sound, music, pause, silence, instability, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, acoustics, bifurcations, sensory processes, sound detection, auditory system, ear, criticality, self-organized criticality, sound, music, pause, silence, instability

# gst: apropos of viscoelastic flow instabilities, uncertainty in elastic turbulence.

<< Elastic turbulence can lead to increased flow resistance, mixing and heat transfer. Its control - either suppression or promotion - has significant potential, and there is a concerted ongoing effort by the community to improve our understanding. >>

AA << identify four regimes of uncertainty evolution, characterised by I) rapid transfer to large scales, with large scale growth rates of τ6 (where τ represents time), II) a dissipative reduction of uncertainty, III) exponential growth at all scales, and IV) saturation. These regimes are governed by the interplay between advective and polymeric contributions (which tend to amplify uncertainty), viscous, relaxation and dissipation effects (which reduce uncertainty), and inertial contributions. >>

<< In elastic turbulence, reducing Reynolds number increases uncertainty at short times, but does not significantly influence the growth of uncertainty at later times. At late times, the growth of uncertainty increases with Weissenberg number, with decreasing polymeric diffusivity, and with the logarithm of the maximum length scale, as large flow features adjust the balance of advective and relaxation effects. >>

Jack R. C. King, Robert J. Poole, et al. Uncertainty in Elastic Turbulence. arXiv: 2501.09421v1 [physics.flu-dyn]. Jan 16, 2025. 

https://arxiv.org/abs/2501.09421

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

Keywords: gst, uncertainty, elastic, elasticity, turbulence 

# gst: apropos of transverse instabilities, from chimeras to extensive chaos

<< Populations of coupled oscillators can exhibit a wide range of complex dynamical behavior, from complete synchronization to chimera and chaotic states. We can thus expect complex dynamics to arise in networks of such populations. >>️

Here AA << analyze the dynamics of networks of populations of heterogeneous mean-field coupled Kuramoto-Sakaguchi oscillators, and show that the instability that leads to chimera states in a simple two-population model also leads to extensive chaos in large networks of coupled populations. >>️

Pol Floriach, Jordi Garcia-Ojalvo, Pau Clusella. From chimeras to extensive chaos in networks of heterogeneous Kuramoto oscillator populations. arXiv: 2407.20408v2 [nlin.CD]. Oct 11, 2024.

https://arxiv.org/abs/2407.20408

Also: chimera, instability, chaos, network, in 

https://www.inkgmr.net/kwrds.html 

Keywords: gst, chimera, instability, chaos, network

# gst: spontaneous bouncing, trampolining, and hovering behaviors of a levitating water droplet without constraints.

<< The levitating Leidenfrost (LF) state of a droplet on a heated substrate is often accompanied by fascinating behaviors such as star-shaped deformations, self-propulsion, bouncing, and trampolining. These behaviors arise due to the vapor flow instabilities at the liquid-vapor interface beneath the droplet at sizes typically comparable to the capillary length scale of the liquid. >>

AA << report on the spontaneous bouncing, trampolining, and hovering behavior of an unconstrained LF water droplet. (..) the water droplet exhibits an increase in bouncing height at specific radii with intermittent reduction in the height of bounce leading to a quiescent LF state. The reemergence of the trampolining behavior from the quiescent hovering state without any external forcing is observed at sizes as low as 0.1 times the capillary length. (AA) attribute the droplet bouncing behavior to the dynamics of vapor flow beneath the LF droplet. >>

AA << propose that the trampolining behavior of the droplet at specific radii is triggered by harmonic and subharmonic resonance between the natural frequency of the vapor layer and Rayleigh frequency of the droplet. This proposed mechanism of resonance-driven trampolining of LF droplets is observed to be applicable for different liquids irrespective of the initial volume and substrate temperatures, thus indicating a universality of the behavior. (AA) attribute the intermittent trampolining events to the change in the natural frequency of the droplet and the vapor layer due to evaporative mass loss. >>

Pranjal Agrawal, Susmita Dash. Reemergence of Trampolining in a Leidenfrost Droplet. arXiv: 2408.02335v1 [physics.flu-dyn]. Aug 5, 2024. 

https://arxiv.org/abs/2408.02335

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

Keywords: gst, drop, droplet, droploid, behav, behaviour

# 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: analogy between quasi-2D and 3D liquid drops.

<< Liquid drops are everywhere around us and important in numerous technological applications. Here, (AA) demonstrate a quasi-two-dimensional (Q2D) analogy to the regular, often close to axisymmetric, three-dimensional (3D) drops. >>️

<< The Q2D drops are created by confining liquids between vertical walls, leading to formation of low aspect ratio capillary bridges that are deformed by gravity. When stationary, the Q2D drops adopt projected shapes that are analogous to 3D sessile drops, ranging from circular drops to puddles. >>️

<< When moving, the Q2D drops exhibit capillary and fluid mechanical behaviours analogous to 3D drops, including impacts and sliding on pseudo-surfaces. The Q2D drops also exhibit considerably more complex phenomena such as levitation, instabilities and pattern formation when subjected to external electric, magnetic and flow fields -- all seen also in regular 3D drops. >>️

<< 3D-Q2D analogy suggests that the diverse and often complicated phenomena observed in 3D drops can be studied in the Q2D geometry, >>

️

Tytti Kärki, Into Pääkkönen, et al. Quasi-Two-Dimensional Drops. arXiv: 2401.11845v1 [physics.flu-dyn]. Jan 22, 2024.

https://arxiv.org/abs/2401.11845

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

Keywords: gst, drop, droplet, droploid, analogy

# gst: kirigami exposed to external flows.

<< Kirigami patterned materials have found several applications in recent years due to their ability to assume complicated shapes and exhibit emergent physical properties when exposed to external forces. >>️

<< Consisting of an array of cuts in a thin material, fabrication of these patterns can be quite simple. Here (AA) show that when they are placed in fluid flow, kirigami cut sheets with various patterns produce a verity of flow patterns in the wake. Through several sets of experiments, (AA) show that the kirigami sheets placed in flow can undergo static or dynamic flow-induced instabilities as a result of which they can buckle or undergo limit cycle oscillations, or they can remain stable while undergoing very large elongations. >>️

<< The ability to create controlled small-scale vortex shedding, induce desired flow-induced instabilities on structures, and form specifically-angled jets will enable several future applications in flow mixing (e.g., by producing small vortices in uniform flow at low Reynolds numbers), flow control (e.g., by controlling the direction and the number of jets that are produced downstream), and underwater soft robotics (e.g., by imposing desired flow-induced oscillations on structures). >>

️

Adrian G. Carleton, Yahya Modarres-Sadeghi. Kirigami Sheets in Fluid Flow.  arXiv: 2311.09381v1 [physics.flu-dyn]. Nov 15, 2023. 

https://arxiv.org/abs/2311.09381

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

Keywords: gst, kirigami, origami, fluid flows, vortex

# gst: apropos of transitions, three distinct new families of long-wave instabilities and potential new pathways to turbulence.

AA << reveal three previously unknown instabilities, distinct from the well-known Kelvin-Helmholtz Instability (KHI) and Holmboe Wave Instability (HWI), in that they have longer wavelengths (..) and often slower growth rates. >>

<< The circumstances under which turbulence can persist in strongly stratified flows remains a fascinating debate within the community. [AA] demonstrated that weakly unstable (very) long waves may trigger turbulence and mixing after long periods of time, even under initially very strongly stratified conditions. >>

Lu Zhu, Amir Atoufi, Adrien Lefauve, Rich R. Kerswell, P. F. Linden. Long-wave instabilities of sloping stratified exchange flows. arXiv:2309.10056v1 [physics.flu-dyn]. Sep 18, 2023.

https://doi.org/10.48550/arXiv.2309.10056

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

Keywords: gst, waves, instability, long-wave instability, transition, turbulence, chaos

# 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: myriad of complex dynamics from the atomization of acoustically levitated droplets

AA << report the dynamics of a droplet levitated in a single-axis acoustic levitator. The deformation and atomization behavior of the droplet in the acoustic field exhibits a myriad of complex phenomena, in sequences of steps. These include the primary breakup of the droplet through stable levitation, deformation, sheet formation, and equatorial atomization, followed by secondary breakup which could be umbrella breakup, bag breakup, bubble breakup or multistage breakup depending on the initial size of the droplet. >>

<< Both the primary and the secondary breakup of the droplet admit interfacial instabilities such as Faraday instability, Kelvin Helmholtz (KH) instability, RT instability, and RP instability and are well described with visual evidence. >>️

Sunil K. Saroj, Rochish M. Thaokar. Atomisation of an acoustically levitated droplet: Experimental observations of a myriad of complex phenomenon. arXiv: 2307.00400v1 [physics.flu-dyn]. Jul 1, 2023.

https://arxiv.org/abs/2307.00400

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

Keywords: gst, drop, droplet, transition, instability

# gst: apropos of modulational instabilities, the case of vortex-ring quantum droplets in a radially-periodic potential.

FIG. 11: (Color online) Typical examples of stable nested patterns with soliton and vortex QDs (quantum droplets)  which were created in adjacent radial troughs. In panels (a1-b4) the pattern was created from the initial dynamical states with parameters (N,S,On) = (46,0,2) and (N,S,On) = (35,1,1) in the outer and inner troughs, respectively. In panels (c1-d4) the input was taken with parameter sets (N,S,On) = (120,1,3) and (N,S,On) = (46,0,2) in the outer and inner troughs.

AA << establish stability and characteristics of two-dimensional (2D) vortex ring-shaped quantum droplets (QDs) formed by binary Bose-Einstein condensates. >>️

<< another noteworthy option is to construct a two-ring complex in which one vortex-ring component is subject to the MI  (modulational instability), hence it is replaced by an azimuthal soliton (or maybe several solitons), (..), while the vortex component trapped in another potential trough avoids the azimuthal MI and remains essentially axisymmetric. >>️

<< Examples of such heterogeneous robust states, produced by simulations of Eq. (3), are displayed in Fig. 11. Panels 11(a1-b4) show a complex in which the MI takes place in the outer circular trough, producing an azimuthal soliton which performs rotary motion, while the inner vortex ring is  modulationally stable. An opposite example is produced in Figs. 11(c1-d4), where the outer vortex ring remains stable against azimuthal perturbations, while the MI creates a soliton exhibiting the rotary motion in the embedded (inner) circular trough. The rotation direction of the soliton is driven by the vorticity sign of the underlying QD (quantum droplet). It is relevant to mention that the multi-ring potential considered here holds different vortex-ring or azimuthal-soliton states nearly isolating them from each other. (..) An additional problem, which is left for subsequent analysis, is interplay between adjacent radial modes in the case when the separation between the adjacent rings is essentially smaller. >>️

Bin Liu, Yi xi Chen, et al. Vortex-ring quantum droplets in a radially-periodic potential. arXiv: 2212.05838v1 [nlin.PS]. Dec 12, 2022.

https://arxiv.org/abs/2212.05838

Also

keyword 'drop' | 'droplet' | 'droploids' in FonT

https://flashontrack.blogspot.com/search?q=drop

https://flashontrack.blogspot.com/search?q=droplet

https://flashontrack.blogspot.com/search?q=droploids

keyword 'goccia' in Notes 

(quasi-stochastic poetry): 

https://inkpi.blogspot.com/search?q=goccia

keyword 'instability' | 'instabilities' in FonT

https://flashontrack.blogspot.com/search?q=instability

https://flashontrack.blogspot.com/search?q=instabilities

keyword 'instabile' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=instabile

Keywords: gst, drop, droplet, vortex, vortices, vortexes, vorticity, instability,  modulational instabilities

# gst: self-buckling and self-writhing of semi-flexible Entities (among P. mirabilis)

<< Multi-flagellated microorganisms can buckle and writhe under their own activity as they swim through a viscous fluid. New equilibrium configurations and steady-state dynamics then emerge which depend on the organism's mechanical properties and on the oriented distribution of flagella along its surface. Modeling the cell body as a semi-flexible Kirchhoff rod and coupling the mechanics to a dynamically evolving flagellar orientation field, (AA) derive the Euler-Poincaré equations governing dynamics of the system, and rationalize experimental observations of buckling and writhing of elongated swarmer P. mirabilis cells. >>

<< A sequence of bifurcations is identified as the body is made more compliant, due to both buckling and torsional instabilities. The results suggest that swarmer cells invest no more resources in maintaining membrane integrity than is necessary to prevent self-buckling. >>

️

Wilson Lough, Douglas B. Weibel, et al. Self-buckling and self-writhing of semi-flexible microorganisms. arXiv: 2211.04381v1 [cond-mat.soft]. Nov 8, 2022. 

https://arxiv.org/abs/2211.04381

Also 

keyword 'swimming' in FonT

https://flashontrack.blogspot.com/search?q=swimming

Keywords: gst, motility, swarm, swarming, swarmer, swim, swimming, swimmer, buckling, writhing. 

# gst: apropos of vibrating pivots, driving a damped coplanar double pendulum.

AA << present results of linear and nonlinear motions of a parametrically driven coplanar double pendulum with velocity-dependent damping. The equations of motion of a damped double pendulum of unequal masses with its pivot vibrated vertically are different from those obtained under gravity modulation. 

Linear stability analysis shows that tongue-shaped marginal stability curves divide the plane of driving parameters into multiple regions of subharmonic and harmonic instabilities. The instability zones for one normal mode overlap with those for the other. 

The double pendulum may oscillate or rotate about its pivot harmonically or subharmonically. The limit cycles corresponding to the normal mode oscillations of a double pendulum of equal masses are squeezed into a line in its configuration space. 

For unequal masses, two marginal curves for subharmonic instabilities merge to form a double-well shaped curve in the presence of damping, which is qualitatively new. The pendulum shows driving amplitude sensitive multi-period complex oscillations for driving parameters near the extrema of the merged instability zones and boundaries of the overlapping zones. 

For larger driving amplitude, the pendulum shows subharmonic, harmonic or chaotic rotations. >>

️

Rebeka Sarkar, Krishna Kumar, Sugata Pratik Khastgir. Parametrically driven damped coplanar double pendulum. arXiv:2208.03292v1 [physics.class-ph]. Aug 2, 2022. 

https://arxiv.org/abs/2208.03292

Also

keyword 'pendulum' in FonT

https://flashontrack.blogspot.com/search?q=pendulum

keyword 'pendolo' | 'pendola' in Notes

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=pendolo

https://inkpi.blogspot.com/search?q=pendola

Keywords: gst, pendulum, double pendulum, instability, chaos, chaotic rotations

# gst: when turbulence is driven by a strongly compressive guide

<< it is not fully understood how shocks drive turbulence, in particular whether shock driving is a more solenoidal (rotational, divergence-free) or a more compressive (potential, curl-free) mode of driving turbulence. >>️

<< Here, (AA) use hydrodynamical simulations of a shock inducing turbulent motions in a structured, multi-phase medium. >>️

<< Using simulations in which a shock is driven into a multi-phase medium with structures of different sizes and Γ<1, (AA) find b∼1 for all cases, showing that shock-driven turbulence is consistent with strongly compressive driving. >>️

Saee Dhawalikar, Christoph Federrath,  et al. The driving mode of shock-driven turbulence. arXiv:2205.14417v1 [astro-ph.GA]. May 28, 2022. 

https://arxiv.org/abs/2205.14417

Also

keywords 'turbulence' in FonT

https://flashontrack.blogspot.com/search?q=turbulence

keywords 'turbolento' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=turbolento

keyword 'waves' in FonT

https://flashontrack.blogspot.com/search?q=waves

keyword 'onda' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=onda

keyword 'instability' | 'instabilities' in FonT

https://flashontrack.blogspot.com/search?q=instability

https://flashontrack.blogspot.com/search?q=instabilities

keyword 'instabile' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=instabile

Keywords: gst, turbulence, instability, waves, shock waves

# gst: apropos of instabilities, viscoelastic liquid bridges can be destabilized by torsion.

<< Liquid bridges are formed when liquids are constrained between two (or more) surfaces via the capillary force. They appear in a wide range of contexts including biology, medicine, and engineering. In the context of biology, liquid bridges enable animals like geckos to adhere to vertical walls (..) >>

<< By experiment and simulation, (AA) report that viscoelastic liquid bridges made of constant viscosity elastic liquids, a.k.a. Boger fluids, can be effectively destabilized by torsion. Under torsion, the deformation of the liquid bridge depends on the competition between elastocapillarity and torsion-induced normal stress effects. When the elastocapillary effect dominates, the liquid bridge undergoes elastocapillary instability and thins into a cylindrical thread, whose length increases and whose radius decays exponentially over time. When the torsion-induced normal stress effect dominates, the liquid bridge deforms in a way similar to edge fracture, a flow instability characterized by the sudden indentation of the fluid's free surface when a viscoelastic fluid is sheared at above a critical deformation rate. The vertical component of the normal stress causes the upper and lower portions of the liquid bridge to approach each other, and the radial component of the normal stress results in the liquid bridge thinning more quickly than under elastocapillarity. Whether such quick thinning continues until the bridge breaks depends on both the liquid bridge configuration and the level of torsion applied. >>️

San To Chan, Stylianos Varchanis, et al. Torsional instability of constant viscosity elastic liquid bridges. Soft Matter, 2022,18, 1965-1977. doi: 10.1039/ D1SM01804C. Feb 7, 2022. 

https://pubs.rsc.org/en/content/articlelanding/2022/SM/D1SM01804C

image: https://twitter.com/softmatter/status/1504473129074126851

Also

keyword 'instability' | 'instabilities' in FonT

https://flashontrack.blogspot.com/search?q=instability

https://flashontrack.blogspot.com/search?q=instabilities

keyword 'instabile' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=instabile

keyword 'torsione' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=torsione

keywords: instability, torsion, torsional instability, viscoelastic liquid, bridge

# gst: apropos of transitions, perspectives on viscoelastic flow instabilities; the 'porous individualism'

<< given the observation that disorder can suppress the transition to elastic turbulence in 2D porous media (..), it has been unclear whether and how this transition manifests in disordered 3D media — though elastic turbulence has been speculated to underlie the long-standing observation that the macroscopic flow resistance of an injected polymer solution can abruptly increase above a threshold flow rate in a porous medium, but not in bulk solution >>️

AA << found that the transition to unstable flow in each pore is continuous, arising due to the increased persistence of discrete bursts of instability above a critical value of the characteristic (Weissenberg no.) Wi; however, the onset value varies from pore to pore. This observation that single pores exposed to the same macroscopic flow rate become unstable in different ways provides a fascinating pore-scale analog of “molecular individualism” [P.  De Gennes, Molecular individualism. Science 276, 1999–2000 (1997)], in which single polymers exposed to the same extensional flow elongate in different ways; the authors therefore termed it “porous individualism”, although it is important to note that here, this effect is still at the continuum (not molecular) scale. Thus, unstable flow is spatially heterogeneous across the different pores of the medium, with unstable and laminar regions coexisting >>

AA << quantitatively established that the energy dissipated by unstable pore-scale fluctuations generates an anomalous increase in flow resistance through the entire medium that agrees well with macroscopic pressure drop measurements. >>

Sujit S. Datta, Arezoo M. Ardekani, et al. Perspectives on viscoelastic flow instabilities and elastic turbulence. arXiv: 2108.09841v1 [physics.flu-dyn]. Aug 22, 2021. 

https://arxiv.org/abs/2108.09841

Also

keyword 'transition' | 'transitional' in FonT

https://flashontrack.blogspot.com/search?q=transition

https://flashontrack.blogspot.com/search?q=transitional

keyword 'transition' | 'transizion*' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=transition

https://inkpi.blogspot.com/search?q=transizione

https://inkpi.blogspot.com/search?q=transizioni

keywords: gst, droplet, fluctuations, disorder, instability, viscoelastic flow instability, turbulence, elastic turbulence, individualism, porous individualism, transition

# gst: streak-vortex instabilities in heterogeneous turbulent boundary layers

AA << re-examine the turbulent boundary layers developing over surfaces with spanwise heterogeneous roughness of various roughness wavelengths 0.32≤S/δ¯¯≤3.63, where S is the width of the roughness strips and δ¯¯ is the spanwise-averaged boundary-layer thickness. >>

<< The heterogeneous cases induce counter-rotating secondary flows, and these are compared to the large-scale turbulent structures that occur naturally over the smooth wall. Both appear as meandering elongated high- and low-momentum streaks in the instantaneous flow field. >>

<< Results suggest that the secondary flows might be spanwise-locked turbulent structures, with S/δ¯¯ governing the strength of the turbulent structures and possibly the efficacy of the surface in locking the structures in place (most effective when S/δ¯¯≈1). >>

<< Conditional averages of the fluctuating velocity fields of both spanwise heterogeneous and smooth wall cases result in structures that are strongly reminiscent of the streak-vortex instability model. (proposed in Jeong et al.,1997) >>

<< One outstanding question that remains unanswered in the present study is the cause of the prominent meandering of the turbulent structures, which is only observed when S/δ¯¯≈1 >>️️

️

Dea Daniella Wangsawijaya, Nicholas Hutchins. Investigation of unsteady secondary flows and large-scale turbulence in heterogeneous turbulent boundary layers. arXiv: 2110.02268v1 [physics.flu-dyn]. Oct 5, 2021.

https://arxiv.org/abs/2110.02268

keywords: gst, fluid dynamics, vortices, vortex instability, streak-vortex instability,  roughness, heterogeneous roughness, turbulence, turbulent boundary layers.

# gst: intermittent large-intensity pulses (LIE) due to instabilities in quasiperiodic motion (in Zeeman laser)

AA << report intermittent large-intensity pulses that originate in Zeeman laser due to instabilities in quasiperiodic motion, >>

<< one route follows torus-doubling to chaos and another goes via quasiperiodic intermittency in response to variation in system parameters. >>

<< During quasiperiodic intermittency, the temporal evolution of the laser shows intermittent chaotic bursting episodes intermediate to the quasiperiodic motion instead of periodic motion >>

<< The intermittent bursting appears as occasional large-intensity events (LIE). In particular, this quasiperiodic intermittency has not been given much attention so far from the dynamical system perspective, in general. >>

S. Leo Kingston, Arindam Mishra, Marek Balcerzak, Tomasz Kapitaniak, Syamal K. Dana. Instabilities in quasiperiodic motion lead to intermittent large-intensity events in Zeeman laser. arXiv: 2109.11847v1 [nlin.CD]. Sep 24, 2021. 

https://arxiv.org/abs/2109.11847

keywords: gst, quasiperiodic motion, intermittency, quasiperiodic intermittency, instability, chaos.