# gst: ️apropos of spontaneous active matter, the active droploids.

<< Active matter comprises self-driven units, such as bacteria and synthetic microswimmers, that can spontaneously form complex patterns and assemble into functional microdevices. These processes are possible thanks to the out-of-equilibrium nature of active-matter systems, fueled by a one-way free-energy flow from the environment into the system. Here, (AA) take the next step in the evolution of active matter by realizing a two-way coupling between active particles and their environment, where active particles act back on the environment giving rise to the formation of superstructures. >>️

<< These structures hinge on mutually coupled structure formation processes of the colloids, which form an engine, and the surrounding solvent, which phase separates in regions of high colloidal density and encapsulates the engine within a droplet shell.  >>

️

Jens Grauer, Falko Schmidt, et al. Active droploids. arXiv:2109.10677v1 [cond-mat.soft]. Sep 22, 2021.

https://arxiv.org/abs/2109.10677

Also

keyword 'drop' | 'droplet' in FonT

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

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

keyword 'goccia' in Notes (quasi-stochastic poetry): 

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

keywords: gst, drops, droplets, colloids, active matter, active droploids, self-assembly, solitons.

# gst: stagnation points controlling the onset and strength of chaotic fluctuations (in viscoelastic porous media flows)

<< Viscoelastic porous media flows become chaotic beyond critical flow conditions, impacting processes including enhanced oil recovery and targeted drug delivery. Understanding how geometric details of the porous medium affect the onset and strength of the chaotic flows can lead to fundamental insights and potential optimization of such processes. Recently, it has been argued that geometric disorder in the medium suppresses chaotic fluctuations. In contrast, (AA) demonstrate that disorder can also significantly enhance fluctuations given a different originally ordered configuration. (AA) show that the occurrence of stagnation points in the flow field is the vital factor controlling the onset and strength of fluctuation, providing a general and intuitive understanding of how pore geometry affects this important class of complex viscoelastic flows. >>

Simon J. Haward, Cameron C. Hopkins, Amy Q. Shen. Stagnation points control chaotic fluctuations in viscoelastic porous media flow. PNAS. 118 (38)  e2111651118. doi: 10.1073/ pnas.2111651118. Sep 21, 2021. 

https://www.pnas.org/content/118/38/e2111651118

https://twitter.com/ShenU_OIST/status/1438306244998033408

Also

keyword 'elastic' | 'turbulence' | 'disorder' in FonT

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

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

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

keyword 'elastico' | 'turbolento' | 'disordine' in Notes

(quasi-stochastic poetry)

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

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

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

keywords: viscoelastic flows, porous media, stagnation, elastic turbulence, chaos, chaotic fluctuations, geometric disorder.

# gst: approaching the complex mechanics of crumpled sheets

<< Crumpling an ordinary thin sheet transforms it into a structure with unusual mechanical behaviors, such as logarithmic relaxation, emission of crackling noise, and memory retention. >>️

<< the response of crumpled sheets to cyclic strain is intermittent, hysteretic, and encodes a memory of the largest applied compression. (..) these behaviours emerge due to an interplay between localized and interacting geometric instabilities in the sheet. >>

<< after training multiple memories can be encoded, a phenomenon known as return point memory. >>

AA << study lays the foundation for understanding the complex mechanics of crumpled sheets, and presents an experimental and theoretical framework for the study of memory formation in systems of interacting instabilities. >>️️

Dor Shohat, Daniel Hexner, Yoav Lahini. Memory from coupled instabilities in crumpled sheets. arXiv: 2109.05212v1 [cond-mat.soft]. Sep 11, 2021.

https://arxiv.org/abs/2109.05212

keywords: gst, sheet, crumpled sheets, instability, bistability, memory, return point memory

# gst: apropos of transitions: effects of random waves interacting with a coherent structure

<< Solitary waves interacting with random (..) waves (..) are studied. Two opposing types of dynamics are identified: First, the random thermal waves can erode the solitary wave; second, this structure can grow as a result of this interaction. These two types of behavior depend on a dynamical property of the solitary wave (its angular frequency), and on a statistical property of the thermal waves (the chemical potential). >>

<< Either process leads to an increase of the wave entropy. >>

Yuanting Chen, Benno Rumpf. Growth or decay of a coherent structure interacting with random waves. Phys. Rev. E 104, 034213. Sep 15, 2021.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.104.034213

Also

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

# poe: an anonymous short "stressed poetry", already in use in the 2nd Century CE, resonates like the rhythms of Chuck Berry's "Johnny B. Goode"

<< they say what they like; let them say it; I don't care. >>️

This << little-known text written in ancient Greek shows that "stressed poetry," the ancestor of all modern poetry and song, was already in use in the 2nd Century CE, 300 years earlier than previously thought. >>

<< The experimental verse became popular across the eastern Roman Empire and survives because, as well as presumably being shared orally, it has been found inscribed on twenty gemstones and as a graffito in Cartagena, Spain. >>️

<< the poem used a different form of meter to that usually found in ancient Greek poetry. As well as showing signs of the long and short syllables characteristic of traditional "quantitative" verse, this text employed stressed and unstressed syllables. Until now, "stressed poetry" of this kind has been unknown before the fifth century, when it began to be used in Byzantine Christian hymns. >>️

<< You didn't need specialist poets to create this kind of musicalized language, and the diction is very simple, so this was a clearly a democratizing form of literature. We're getting an exciting glimpse of a form of oral pop culture that lay under the surface of classical culture. >> Tim Whitmarsh. ️

<< this poem could represent a "missing link" between the lost world of ancient Mediterranean oral poetry and song, and the more modern forms that we know today. >>

️

Tom Almeroth-Williams. Ancient Greek 'pop culture' discovery rewrites history of poetry and song. University of Cambridge. Sep 09, 2021.

https://phys.org/news/2021-09-ancient-greek-culture-discovery-rewrites.html

Tim Whitmarsh. Less care, more stress: a rhythmic  poem from the roman empire. The Cambridge Classical Journal, 1-29. doi: 10.1017/ S1750270521000051. Aug 25, 2021.

https://www.cambridge.org/core/journals/cambridge-classical-journal/article/less-care-more-stress-a-rhythmic-poem-from-the-roman-empire/B5A03C3981F21E885228D3C3184109E9

# gst: shape-shifting architecture inspired by metamorphosis, the metamorphosis kirigami system.

<< Kirigami is a variation of origami that involves cutting and folding paper. But while kirigami traditionally uses two-dimensional materials, Yin (Jie Yin) applies the same principles to three-dimensional materials. The metamorphosis system starts with a single unit of 3D kirigami. Each unit can form multiple shapes in itself. But these units are also modular—they can be connected to form increasingly complex structures. Because the individual units themselves can form multiple shapes, and can connect to other units in multiple ways, the overall system is capable of forming a wide variety of architectures. >>

<< The system we've developed was inspired by metamorphosis, (..) With metamorphosis in nature, animals change their fundamental shape. We've created a class of materials that can be used to create structures that change their fundamental architecture. (..) Think of what you can build with conventional materials, (..) Now imagine what you can build when each basic building block is capable of transforming in multiple ways.  (..) The metamorphosis kirigami system does not allow you to disassemble a structure, (..) And because the sides of each cubic unit are rigid and fixed at 90-degree angles, the assembled structure does not bend or flex very much. However, the finished structure is capable of transforming into different architectures.>> Jie Yin.️

Matt Shipman. Inspired by metamorphosis, researchers create materials for shape-shifting architecture. North Carolina State University. Sep 08, 2021. 

https://phys.org/news/2021-09-metamorphosis-materials-shape-shifting-architecture.html  

Yanbin Li, Jie Yin. Metamorphosis of three-dimensional kirigami-inspired reconfigurable and reprogrammable architected matter. Materials Today Physics, 21, 100511. doi: 10.1016/ j.mtphys.2021.100511.

https://www.sciencedirect.com/science/article/abs/pii/S2542529321001723

Also

keyword 'origami' in FonT

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

Keywords: gst, origami, kirigami, architecture, bifurcation, metamorphosis,  reconfigurability, reprogrammability.

# gst: apropos of unexpected thresholds, the minimum temperature for levitating a droplet

<< During the Leidenfrost effect, a thin insulating vapor layer separates an evaporating liquid from a hot solid. (AA) demonstrate that Leidenfrost vapor layers can be sustained at much lower temperatures than those required for formation. >>

<< the explosive failure point is nearly independent of material and fluid properties, suggesting a purely hydrodynamic mechanism determines this threshold. >>️

Dana Harvey, Joshua Mendez Harper, Justin C. Burton. Minimum Leidenfrost Temperature on Smooth Surfaces. Phys. Rev. Lett. 127, 104501. Sep 1, 2021.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.104501

Christopher Crockett. The Minimum Temperature for Levitating Droplets. Physics 14, s107. Sep 1, 2021.

https://physics.aps.org/articles/v14/s107

Also

keyword 'drop' | 'droplet' in FonT

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

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

keywords: gst, drop, droplet, waves, buckling, lubrication, convection, interfacial flows, threshold, levitation, bubble.

# gst: drift motion of two-core spiral chimeras (grouped into 3 main classes, symmetrical, asymmetrical, and meandering spiral)

AA << consider a two-dimensional array of heterogeneous nonlocally coupled phase oscillators on a flat torus and study the bound states of two counter-rotating spiral chimeras, shortly two-core spiral chimeras, observed in this system. In contrast to other known spiral chimeras with motionless incoherent cores, the two-core spiral chimeras typically show a drift motion. Due to this drift, their incoherent cores become spatially modulated and develop specific fingerprint patterns of varying synchrony levels. >>

Numerical analysis of Ott-Antonsen equation allows << to reveal the stability region of different spiral chimeras, which (AA) group into three main classes—symmetric, asymmetric, and meandering spiral chimeras. >>️

Martin Bataille-Gonzalez, Marcel G. Clerc, Oleh E. Omel'chenko. Moving spiral wave chimeras. Phys. Rev. E 104, L022203 (Letter). Aug 20, 2021.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.104.L022203

Also (Ott-Antonsen equation)

<< Synchronization in Nature. 

Generic behavior involving a large  ensemble of nearly identical oscillators that are weakly coupled. 

- Cellular clocks in the brain.

- Pacemaker cells in the heart.

- Flashing fire flies.

- Deep Brain Stimulation (DBS) treatment for  Parkinson’s. 

- Pedestrians on a bridge.

- Many more. 

>>

Steven  Strogatz

Thomas M. Antonsen Jr. and Edward Ott. Synchronization: What can a plasma physicis say about generic collective behavior? (Happy Birthday Nat!) (Presentation). In: Solved and Unsolved Problems In Plasma Physics. Symposium. Princeton, New Jersey. Mar 28-30, 2016. 

https://fisch-fest2016.pppl.gov/presentations/1-10-Antonsen.pdf

# gst: apropos of transitions, when a liquid droplet takes a turn (as a swimming behavior of amoebas)

Masatoshi Ichikawa and coll.  << have analyzed the conditions that cause self-propelling droplets to take linear or curved trajectories. The team studied water droplets between 60 and 800 μm across as they moved through oil that contained a surfactant. The droplets moved as a result of the Marangoni effect, in which an unequal distribution of surfactant molecules on the surface of each droplet creates a surface-tension gradient. (They) found that larger droplets tended to follow more tightly curved paths than smaller droplets. To understand the cause of this difference, Ichikawa and coll.  created a 3D model describing the concentration of surfactant on the surface of the droplets. They also studied the droplets’ internal flow, by observing the paths of small tracer particles. They characterized this flow as the sum of multiple patterns of fluid motion present in each droplet, including radial, dipolar, and quadrupolar motion. These patterns of motion were determined by the surface-tension gradients created by the uneven surfactant distribution on each droplet. In turn, such patterns controlled how the droplets moved. In particular, the team found that the angular difference between the dipolar and quadrupolar flows within droplets was strongly correlated with more curved droplet trajectories. In larger droplets, this angle changed more easily, causing the tightly curved trajectories. The researchers say that this fundamental mechanism may also influence the swimming behavior of amoebas.  >>️

Sophia Chen. When Liquid Droplets Take a Turn. Physics 14, s109. Aug 19, 2021.

https://physics.aps.org/articles/v14/s109

Saori Suda, Tomoharu Suda, et al. Straight-to-Curvilinear Motion Transition of a Swimming Droplet Caused by the Susceptibility to Fluctuations. Phys. Rev. Lett. 127, 088005. Aug 19, 2021.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.088005

Also

keyword 'drop' | 'droplet' in FonT

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

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

# gst: when randomly-timed external impulses can synchronize

<< Random perturbations applied in tandem to an ensemble of objects can synchronize their motion. (AA) study multiple copies of an object in periodic motion such as a firing neuron, each with an arbitrary phase. Randomly-timed external impulses can synchronize these phases. For impulses slightly too strong to synchronize, (they) find remarkable erratic synchronization, with stochastic fluctuations from near-perfect to more random synchronization. The sampled entropies of these phase distributions themselves form a steady-state ensemble. A stochastic dynamics model for the entropy's evolution accounts for the observed exponential distribution of entropies and the stochastic synchronization. >>

<< One general virtue of noise-induced synchronization is that one may use it to induce synchronization without

specific knowledge about the limit cycle being synchronized, such as the phase map function or the cycle time.(..) As noted in the Introduction, synchronization of a remote oscillator enables transmission of information.

Stochastic synchronization appears to have comparable ability, potentially useable by technology or biology. >>️

<< The stochastic synchronization phenomenon explored above seems to be a distinctive mode of organization. It can be produced via broad classes of driving, and creates striking fluctuations of randomness. This model may aid understanding of other puzzling systems showing erratic fluctuations, such as strong turbulence. >>️

️

Yunxiang Song, Thomas A. Witten. Stochastic synchronization induced by noise. arXiv:2108.13172v1 [cond-mat.stat-mech]. Aug 16, 2021.

https://arxiv.org/abs/2108.13172

Also

<< stabilizzare il volo del fascio di aquiloni  >> in: ️2149 - onda di predazione (to knock seals off the ice).  Notes. Dec 17, 2007. (quasi-stochastic poetry)

https://inkpi.blogspot.com/2007/12/2149-onda-di-predazione-to-knock-seals.html

keyword 'noise' | 'fuzzy' in FonT

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

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