# 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

# gst: compression and fracture of ordered and disordered droplet rafts

AA << simulate a two-dimensional array of droplets being compressed between two walls. The droplets are adhesive due to an attractive depletion force. As one wall moves toward the other, the droplet array is compressed and eventually induced to rearrange. The rearrangement occurs via a fracture, where depletion bonds are quickly broken between a subset of droplets. >>

<< For monodisperse, hexagonally ordered droplet arrays, this fracture is preceded by a maximum force exerted on the walls, which drops rapidly after the fracture occurs. >>

<< In small droplet arrays a fracture is a single well-defined event, but for larger droplet arrays, competing fractures can be observed. These are fractures nucleated nearly simultaneously in different locations. >>

AA << also study the compression of bidisperse droplet arrays. The addition of a second droplet size further disrupts fracture events, showing differences between ideal crystalline arrays, crystalline arrays with a small number of defects, and fully amorphous arrays. >>

️

Pablo Eduardo Illing, Jean-Christophe Ono-dit-Biot, et al. Compression and fracture of ordered and disordered droplet rafts. Phys. Rev. E 109, 014610. Jan 17, 2024.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.014610

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

Also:  raft   https://flashontrack.blogspot.com/search?q=raft  

zattera (quasi-stochastic poetry) https://inkpi.blogspot.com/2005/04/1864-onda-di-liberazione.html  

randa (quasi-stochastic poetry) https://inkpi.blogspot.com/search?q=randa

Keywords: gst, drop, droplet, raft, defect, fracture, crack

# gst: pulsating active matter.

<< the mechanical pulsation of locally synchronized particles is a generic route to propagate deformation waves. >>

️

AA << consider a model of dense repulsive particles whose activity drives periodic change in size of each individual. >>️

They << show that the competition between repulsion and synchronization triggers an instability which promotes a wealth of dynamical patterns, ranging from spiral waves to defect turbulence. >>️

Yiwei Zhang, Etienne Fodor. Pulsating Active Matter. Phys. Rev. Lett. 131, 238302. Dec 8, 2023. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.238302

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

Keywords: gst, waves, particle, transition, instability, turbulence

# gst: apropos of collisions of a vortex dipoles, vortex unbinding, vortex pinning to the edge, and emission of rarefaction pulses.

<< Vortices and dark solitons are fundamental defects that appear in nonlinear physics at all scales, from nonlinear optics to cosmic fluids. In two or three dimensions, dark solitons are fundamentally connected to highly ordered vortex states through an intrinsic modulation instability in the surrounding matter. >>️

<< Here, [AA] report an experimental realization of ring dark soliton (RDS)  generation in a two-dimensional atomic superfluid trapped in a circular box. By quenching the confining box potential, [they] observe an RDS emitted from the edge and its peculiar signature in the radial motion. As an RDS evolves, [they] observe transverse modulations at discrete azimuthal angles, which clearly result in a patterned formation of a circular vortex dipole array. Through collisions of the vortex dipoles with the box trap, [they] observe vortex unbinding, vortex pinning to the edge, and emission of rarefaction pulses. >>

Hikaru Tamura, Cheng-An Chen, Chen-Lung Hung. Observation of Self-Patterned Defect Formation in Atomic Superfluids–from Ring Dark Solitons to Vortex Dipole Necklaces. Phys. Rev. X 13, 031029. Sep 14, 2023. 

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.13.031029

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

Keywords: gst, soliton, dark soliton, vortex, turbulence, waves. 

# 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: nematic order condensation and topological defects in inertial active nematics

<< Living materials at different length scales manifest active nematic features such as orientational order, nematic topological defects, and active nematic turbulence. Using numerical simulations (AA) investigate the impact of fluid inertia on the collective pattern formation in active nematics. >>️

<< an incremental increase in inertial effects due to reduced viscosity results in gradual melting of nematic order with an increase in topological defect density before a discontinuous transition to a vortex-condensate state. The emergent vortex-condensate state at low enough viscosities coincides with nematic order condensation within the giant vortices and the drop in the density of topological defects. (AA) further show flow field around topological defects is substantially affected by inertial effects. (..) no evidence of universal scaling at higher viscosities. >>

️

Roozbeh Saghatchi, Mehmet Yildiz, Amin Doostmohammadi. Nematic order condensation and topological defects in inertial active nematics. Phys. Rev. E 106, 014705. July 25, 2022.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.106.014705

Also: 'turbulence', 'vortex', 'defect', 'drop' in https://www.inkgmr.net/kwrds.html

Keywords: gst, behavior, collective behavior, patterns, turbulence, nematic turbulence, viscosity, vortex, defect, drop

# gst: intentional defects to trap confined acoustic modes that are protected from perturbation

AA << has discovered how to exploit certain defects to protect confined energy in acoustics systems. Their experimental approach provides a versatile platform to create at-will defects for further theoretical validation and to improve control of waves in other systems, such as light >>

<< We set to understand whether topological defects, such as disclinations, can be created to trap highly confined acoustic modes that are protected from perturbation, (..) Our core insight was that, if we consider the point group symmetry of the disclination, a pair of disclinations modes are prevented from pairing away from zero frequency. This protection mechanism results from the interplay of the symmetry-protected topological phase of the crystalline lattice and the topological charge and symmetry of the disclination. >> Wladimir A. Benalcazar.

<< This is the first work experimentally validating that such protected states exist in the disclination core, >> Yun Jing. 

️

Ashley J. Wennersherron. Researchers find imperfections provide protection for system symmetry. Penn State College of Engineering. May 20, 2022.

https://phys.org/news/2022-05-imperfections-symmetry.html

Sarah Wells. Symmetrical Binding for Topological States. Physics 15, s56. Apr 26, 2022. 

https://physics.aps.org/articles/v15/s56

Yuanchen Deng, Wladimir A. Benalcazar, et al. Observation of Degenerate Zero-Energy Topological States at Disclinations in an Acoustic Lattice. Phys. Rev. Lett. 128, 174301. Apr 26, 2022. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.174301

Also

keyword 'acoustic' in FonT

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

Keywords: gst, acoustics, acoustic metamaterials, symmetry, system symmetry, imperfection, defect, topological defects, disclination

# gst: weird nature: the generation of complex (frilly, flexible, and functional) wrinkling patterns by 'defects'

<< A ubiquitous motif in nature is the self-similar hierarchical buckling of a thin lamina near its margins. This is seen in leaves, flowers, fungi, corals and marine invertebrates. We investigate this morphology from the perspective of non-Euclidean plate theory. We identify a novel type of defect, a branch-point of the normal map, that allows for the generation of such complex wrinkling patterns in thin elastic hyperbolic surfaces, even in the absence of stretching. We argue that branch points are the natural defects in hyperbolic sheets, they carry a topological charge which gives them a degree of robustness, and they can influence the overall morphology of a hyperbolic surface without concentrating elastic energy. >>️

Kenneth K. Yamamoto, Toby L. Shearman, et al. Nature's forms are frilly, flexible, and functional. arXiv: 2103.10509v1. Mar 18, 2021.

https://arxiv.org/abs/2103.10509

Also

keyword 'error' | 'fuzzy' | 'noise'  in FonT 

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

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

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

keywords 'errore' | 'errori' in Notes (quasi-stochastic poetry)

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

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

# gst: predicting the exact force needed to crumple a dented can

<< Dent an aluminum can and it will be easier to crush from top to bottom. But predicting the exact force needed to crumple a dented can is notoriously difficult, requiring knowledge of the exact dimensions and position of the flaw >>

Katherine Wright. Synopsis: Crumpling Coke Cans. Nov 28, 2017

https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.119.224101

AA << measure the response of cylindrical shells to poking and identify a stability landscape, which fully characterizes the stability of perfect shells and imperfect ones in the case where a single defect dominates >>

Emmanuel Virot, Tobias Kreilos, et al.  Stability Landscape of Shell Buckling. Phys. Rev. Lett. 119, 224101. doi: 10.1103/PhysRevLett.119.224101.  Nov 28,  2017

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.224101  

# s-epidem: diurnal mosquitoes with Zika virus inside

<< Experts are concerned that the illness, which is increasingly linked to a disorder that causes paralysis, may become a problem in the U.S. >>

Dina Fine Maron. Zika Disease: Another Reason to Hate Mosquitoes.  October 8, 2015

http://www.scientificamerican.com/article/zika-disease-another-reason-to-hate-mosquitoes/

A new global map highlights places #Zika could spread

https://twitter.com/ScienceNews/status/690677908927598593

Meghan Rosen. Rapid spread of Zika virus in the Americas raises alarm. Mosquito-borne disease linked to birth defect is pushing northward from Brazil. 3:08PM, January 22, 2016

https://www.sciencenews.org/article/rapid-spread-zika-virus-americas-raises-alarm