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Visualizzazione dei post in ordine di pertinenza per la query gst. Ordina per data Mostra tutti i post
Visualizzazione dei post in ordine di pertinenza per la query gst. Ordina per data Mostra tutti i post

lunedì 17 ottobre 2022

# life: a proposito di bizzarri scenari, qui un ipotetico scenario22 dipinto dal reale ...

img: Congo Square, New Orleans, Louisiana (wikipedia.org)

In definitiva qui si configurerebbe un - intrigante assai - scenario che, grosso modo, si potrebbe sinteticamente 'dipingere' in questi termini: 

(i) entità tre palle destrogire, animate aciclicamente da interazioni attrattive- repulsive a causa di già a suo tempo disvelate pulsioni neuro cognitive arcaiche, riconducibili a visioni neuro predatorie CTZ estreme, perciò ipoteticamente (si fa per dire) a-priori ad esiti immediati e in prospettiva drammaticamente lesivi- autolesivi; 

(ii) entità tre palle levogire, animate da analoghe pulsività, purtuttavia in.forme  tenui, in modalità sottotraccia, frenate da feed-back a modalità allosterica, ombreggiate, stemperate, diluite, discrete, timidamente celate, talvolta fantasmatiche perfino, quasi ma non del tutto mai silenti, perciò anch'esse a tutti gli effetti operative, sebbene a dinamiche più fluide, lente, meno dirompenti rispetto alle destrogire; 

(iii) entrambe l'Entità destrogire e levogire animat(t)rici,  generat(t)rici di dinamiche bi-multi-forcate, transeunti, con picchi di improvvisi aciclici burst ad effetti RAG-time diretti e inversi;

(iv) lo scenario al contorno e forse anche all'interno, nei vari specifici contesti, riconducibile grosso modo alla formazione aciclica di ipotetici buchi neri non inerti, caratterizzati da aciclicità in compressione e dilatazione - come fossero fisarmoniche - animati (in perpetuo?) da multi vortici in ingresso e in uscita;

Non so se basti compulsare un manuale delle funzioni speciali per formalizzare in qualche adatto topo-modo questo pulsatile multi scenario, purtuttavia assolutamente intrigante ... 

Qui una AI operativa nella formalizzazione di analogie potrebbe modellizzare, forse ... (e.g. https://flashontrack.blogspot.com/2021/08/aibot-mechanism-of-analogy-could-be.html )

Quello che appare evidente è la complessità d'insieme, un bizzarro dipinto, uno scenario dinamico che, al confronto, le storiche danze in Congo Square potrebbero sembrare semplici, ordinate coreografie ... queste, rispetto a quelle, delle topo-forme  'primitive', per dire ed anzicheforse.

In sintesi, i riferimenti (ovviamente generici) del bizzarro scenario: 

(:) buco nero con vortici 

(:) scenari generati da 3 palle 
(a)
(b)

(:) effetti RAG-time (RAG: Ralph, Al, George) 
(a) (quasi-stochastic poetry)
(b)

(:) pulsioni predatorie supportate / giustificate da visioni neuro- post- CTZ nelle modalità arcaiche oppure friendly 

(:) Congo Square, jazz 
(a)
(b)
(c) (quasi-stochastic poetry)

(:) approccio Bertalanffy 

(:) un bizzarro tracciatore 

Anche

"Amico, qualunque cosa suonerai ... "
(a) (quasi-stochastic poetry)
(b)

Keywords: life, gst, Congo Square, jazz, Jelly Roll, transition, three-body, RAG, CTZ, black hole, bizarre tracker




lunedì 15 marzo 2021

# gst: an atomic imaging of a (slow) crack

AA << successfully imaged the snapping of individual atomic bonds in a one-atom-thick sheet of rhenium disulfide ( ReS2) using scanning transmission electron microscopy. (STEM) >>

<< Because of its unusual chemistry, Re forms a 2D lattice with "lanes" that guide cracks, allowing the cracks to propagate with ease. The heavy element also efficiently deflects electrons, providing the signal needed to gain clear images. The study is a remarkable example of how a specific material can provide insight into the universal behavior of matter. >>

<< Because of its strong scattering, ReS2 provides an ideal target for STEM. (Interestingly, tungsten, the periodic-table neighbor of Re, has just one fewer proton and is routinely used in electron microscopy to stain viruses and bacterial flagella.)  >>

<< By measuring the deformation of the lattice around the crack, the team showed that the tearing stresses were concentrated around the crack tip. The stresses then decayed as the inverse square root of the distance from the tip, a finding that matches predictions for macroscopic materials. Using these measurements, the team defined a stress intensity threshold for cracks to propagate. >>

<< The images taken by Huang and colleagues used seconds-long exposure times, meaning they could only follow the propagation of the slowest crack (those that moved at a few angstroms per second). There is much interest in how faster cracks behave, as these cracks are subject to instabilities, meaning they can deviate from a straight line or form branches, for example. To observe faster cracks, future experiments could use reduced exposure times. >>

Itamar Kolvin. Atomic Imaging of Cracks. Physics 13, 193. Dec 9, 2020. 


Lingli Huang, Fangyuan Zheng, et al. In Situ Scanning Transmission Electron Microscopy Observations of Fracture at the Atomic Scale. Phys. Rev. Lett. 125, 246102. Dec 9, 2020.


Also

(+)  the intriguing dynamics of a crack. Nov 7, 2017. 


(+) multiple cracks, simultaneously ... Oct 23, 2016.


(+) onda criptica. May 22, 2005 (quasi-stochastic poetry)


(+) keyword "fracture" in FonT







martedì 22 febbraio 2022

# gst: apropos of a immaginary transition (with a tipping point), which simulates the chaotic interactions of three black holes.


<< The interactions between three bodies such as stars or planets or black holes cannot be predicted with an elegant formula. Moerman (Arend Moerman) therefore used a computer that calculates what happens for a short period of time and then uses the result for the next period of time. >>

AA << varied the masses of the three interacting black holes. They started with one solar mass and went up to a billion times the mass of the sun. >>

<< Around ten million solar masses, there appeared to be a tipping point. In the simulations, black holes that are lighter than about ten million solar masses mostly eject each other through a gravitational slingshot. Black holes heavier than about ten million solar masses start to merge. First, two black holes merge. The third black hole will follow later. The black holes merge because they lose kinetic energy and that is because they emit gravitational waves. >>

<< Arend's work (..) has led to a new understanding of how black holes become supermassive. In the simulations, we see that heavy black holes no longer endlessly move around each other, but that, if they are heavy enough, they collide pretty much instantly. >> Simon Portegies Zwart. 

Simulating chaotic interactions of three black holes. Netherlands Research School for Astronomy. Oct 20, 2021. 


Tjarda C. N. Boekholt, Arend Moerman, Simon F. Portegies Zwart. Relativistic Pythagorean three-body problem. Phys. Rev. D 104, 083020. 14 Oct 14,  2021. 


Also

more on the three-body problem (695 families of collisionless orbits). FonT. Oct 16, 2017. 


keyword 'black hole' | 'astro' in FonT



keyword 'transition' | 'transitional' in FonT



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




keywords: gst, black hole, three-body problem, transition, chaos, chaotic interaction, tipping point.



mercoledì 14 giugno 2023

# gst: apropos of transitions, droplet trajectories during single and collective bursting bubbles

<< Mechanisms of droplet production from bursting bubbles have been extensively studied for single bubbles, but remain sparsely investigated in more complex collective settings. >>️

<< In the collective bubbling experiment, subsurface quasimonodisperse bubbles are rising up to the surface where, depending on the surfactant concentration, they can either merge or assemble in rafts of monodisperse bubbles. Drop trajectories are recorded, analyzed, and shown to exhibit uniquely distinctive features for the different production mechanisms: centrifuge film drops are ejected sideways, and jet drops are ejected vertically. Different single-burst scalings are finally compared to the experimental size-velocity relationships, and reveal that drops coming from collective bubble bursting appear slower and more scattered than when coming from single bursting bubbles. >>️

B. Neel and L. Deike. Velocity and size quantification of drops in single and collective bursting bubbles experiments. Phys. Rev. Fluids 7, 103603. Oct 5, 2022. 

Also: 'when a superbubble can generate trains of shock waves'. Mar 6, 2019.

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

Keywords: gst, transition, drop, droplet, droploid, bubble, collective dynamics,  fluid dynamics

PS: << they can either merge or assemble in rafts of monodisperse bubbles >> ; this is poetry, without unnecessary adjectives, anzicheforse ... FonT. Wed June 14, 2023 16:58 (cest)


lunedì 27 dicembre 2021

# gst: reshaping Kuramoto model, when a collective dynamics becomes chaotic, with a surprisingly weak coupling.

<< The emergence of collective synchrony from an incoherent state is a phenomenon essentially described by the Kuramoto model (..) Collective synchronization is a phenomenon in which an ensemble of heterogeneous, self-sustained oscillatory units (commonly known as oscillators) spontaneously entrain their rhythms. This is a pervasive phenomenon observed in natural systems and man-made devices, covering a wide range of spatio-temporal scales, from cell aggregates to swarms of fireflies >>

<< However, this is only partly true, (..) Kuramoto’s perturbative phase-reduction approach is valid for weak coupling. Specifically, oscillator heterogeneity and interactions appear at zeroth and linear orders in the coupling constant, respectively. >> 

AA << have introduced the ‘enlarged Kuramoto model’; a population of phase oscillators in which three-body interactions enter in a perturbative way. Remarkably, this makes a world of difference, drastically reshaping the traditional Kuramoto scenario. The ‘enlarged Kuramoto model’ exhibits a variety of unsteady states, including collective chaos and hyperchaos. >>

Ivan Leon, Diego Pazo. Enlarged Kuramoto Model: Secondary Instability and Transition to Collective Chaos. arXiv: 2112.00176v1 [nlin.AO]. Nov 30, 2021.


Also

More on the three-body problem (695 families of collisionless orbits). FonT. Oct 16, 2017. 


Keywords: gst, behav, instability, Kuramoto model, three-body interactions, chaos, collective chaos, hyperchaos.

giovedì 27 aprile 2023

# gst: like the slender body theory, the effect of curvature on the diffusion of colloidal bananas.


<< Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior.  >>️

AA << investigate the two-dimensional diffusion of smoothly curved colloidal rods—also known as colloidal bananas—as a function of their opening angle α >>️

<< the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles. >>️

Justin-Aurel Ulbrich, Carla Fernández-Rico, et al. Effect of curvature on the diffusion of colloidal bananas. Phys. Rev. E 107, L042602. April 21, 2023.


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

Keywords: gst, colloids, particles, behavior




venerdì 17 giugno 2016

# s-gst-game: tit-for-tat and the emergence of morality

<< Ultimately, the results showed that the best strategy was 'tit for tat' – which means that a player starts out cooperating on the first move, and then does whatever it's opponent does >>

<< it's interesting that it emerged – it self-organised – into this state of being that the Old Testament morality ended up winning in this environment >>

<< So in fact what was found in later studies, when they examined prisoner's dilemma in environments where errors occurred with a certain frequency, is that the population tended to evolve to more generous, more like New Testament strategies that will 'turn the other cheek' >>

<< If natural selection leads to morality, that's pretty interesting. And that came from maths! >>.  Steven  Strogatz.

Steven  Strogatz, in: Elena  Holodny. The  mathematical  origins  of  morals.  Business  Insider, 14  Jun  2016

http://www.sciencealert.com/a-professor-explains-how-1980s-game-theory-could-explain-how-morality-evolved

FonT: <<  and then does whatever it's opponent does >> ... approccio senz'altro utile all'interno di scenari di simulazione; in contesti reali un approccio creativo, esplorativo, perturbativo, e per mia opinione anche funzionale, al problema di  decidere sul comportamento cooperativo al successivo "run" e' quello di affidarsi all'esito del lancio di moneta, ovviamente dopo un giudizio (formato da componenti di natura analitica ma anche soggettiva) circa il contesto che ha fatto intravedere la necessita' - per l'attore cooperativo - di una biforcazione, di operare una scelta.

Percio' "tit-for-tat generoso quasistocastico", tutte le volte che un gambler decide di iniziare/ sostenere un gioco "al buio", anche quando sa, oppure sospetta, che il gioco e' "a priori" fondamentalmente truccato, vale a dire deviante dai due vincoli del gioco legale, naturale [1,2,3]

Nelle componenti  "eye for an eye" vs "turn the other cheek" o, se si vuole piu' in generale, nei livelli di "risveglio" in senso buddista degli attori partecipanti tit-for-tat, dipende, anche a breve/ medio termine, la velocita' evolutiva degli esiti del gioco, esiti che riverberano in ambito sociale, anche all'interno di contesti "altri".

[1] - 1809 - strutturanti decisioni. November 26, 2004

http://inkpi.blogspot.it/2004/11/1809-strutturanti-decisioni.html

[2] - 1821 - i due beffardi vincoli. November 26, 2004

http://inkpi.blogspot.it/2004/11/1821-i-due-beffardi-vincoli.html

[3] - s-gst: never boring with chaos and tit-for-tat theories. June 12, 2016

http://flashontrack.blogspot.it/2016/06/s-gst-never-boring-with-chaos-and-tit.html

martedì 10 agosto 2021

# ai.bot: a mechanism of analogy could be the master key to achieving an abstract artificial intelligence

<< It’s understanding the essence of a situation by mapping it to another situation that is already understood, (..) If you tell me a story and I say, ‘Oh, the same thing happened to me,’ literally the same thing did not happen to me that happened to you, but I can make a mapping that makes it seem very analogous. It’s something that we humans do all the time without even realizing we’re doing it. We’re swimming in this sea of analogies constantly. >> Melanie Mitchell.
John Pavlus. The Computer Scientist Training AI to Think With Analogies. QuantaMag. Jul 14, 2021.



Also

here a fuzzy example:  "qui non e' impossibile immaginare ..." (here it is not impossible to imagine ... )
in: Notes. Dec 31, 2015 (quasi-stochastic poetry)


keyword 'gst' (general system theory) in FonT 


keyword 'organoids' in FonT


keyword 'ai' | 'bot' in FonT



keyword 'ia' | 'ai' | 'robota' in Notes (quasi-stochastic poetry)






mercoledì 6 ottobre 2021

# gst: apropos of disorder & fluctuations

a 'synthetic disorder & fluctuations' from these two blogs ... 

keyword 'disorder' in FonT 

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

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



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


keyword 'caos' | 'caotico' in Notes  (quasi-stochastic poetry) 


keyword 'waves' in FonT 

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

keyword 'gst' (General Sistem Theory) in FonT 





lunedì 3 gennaio 2022

# gst: weird but not so weird dynamics, basins with tentacles could be common in high-dimensional systems.


<< Basins of attraction are fundamental to the analysis of dynamical systems (..). Over the years, many remarkable properties of basins have been discovered (..), most notably that their geometry can be wild, as exemplified by Wada basins (..), fractal basin boundaries (..), and riddled or intermingled basins (..). Yet despite these foundational studies, much remains to be learned about basins, especially in systems with many degrees of freedom. >>

AA show that for locally-coupled Kuramoto oscillators << high-dimensional basins tend to have convoluted geometries and cannot be approximated by simple shapes such as hypercubes. Although they are impossible to visualize precisely (because of their high dimensionality), (they) present evidence that these basins have long tentacles that reach far and wide and become tangled with each other. Yet sufficiently close to its own attractor, each basin becomes rounder and more simply structured, somewhat like the head of an octopus. >>

<< In terms of (AA) metaphor, almost all of a basin’s volume is in its tentacles, not its head. This finding is not limited to Kuramoto oscillators. (AA) provide a simple geometrical argument showing that, as long as the number of attractors in a system grows subexponentially with system size, the basins are expected to be octopus-like. As further evidence of their genericity, basins of this type were previously found in simulations of jammed sphere packings (..) where they were described as “branched” and “threadlike” away from a central core (..) and accurate methods were developed for computing their volumes (.,). There is also enticing evidence of octopus-like basins in neuronal networks (..), power grids (..), and photonic couplers (..). >>

<< Figure 4 is a further attempt to visualize the structure of high-dimensional basins, now by examining randomly oriented two-dimensional (2D) slices of state space, either far from a twisted state or close to one. (..) Despite the fact that each basin is connected (..)  the basins look fragmented in this 2D slice. >>

 Fig. 4(a): << Perhaps another metaphor than tentacles—a ball of tangled yarn—better captures the essence of the basin structure in this regime, far from any attractor, in which differently colored threads (representing different basins) are interwoven together in an irregular fashion. >>

Fig. 4(b): << The basin structure near an attractor is strikingly different. (..) the basins near an attractor are organized like an onion. >>

Yuanzhao Zhang, Steven H. Strogatz. Basins with tentacles. arXiv: 2106.05709v3 [nlin.AO]. Nov 2, 2021. 



Also

Reshaping Kuramoto model, when a collective dynamics becomes chaotic, with a surprisingly weak coupling. Dec 27, 2021.


Keywords: gst, dynamical systems, high-dimensional systems, Kuramoto oscillator, attractors, basin of attraction 



martedì 13 settembre 2022

# gst: "birds of a feather flock together", the swarmalators

<< Swarmalators have emerged as a new paradigm for dynamical collective behavior of multi-agent systems due to the interplay of synchronization and swarming that they inherently incorporate. Their dynamics have been explored with different coupling topologies, interaction functions, external forcing, noise, competitive interactions, and from other important viewpoints. Here (AA) take a systematic approach and review the collective dynamics of swarmalators analytically and/or numerically. Long-term states of position aggregation and phase synchronization are revealed in this perspective with some future >>️

Gourab Kumar Sar, Dibakar Ghosh. Dynamics of swarmalators: A pedagogical review. arXiv: 2208.14803v1 [nlin.AO]. Jul 25, 2022. Europhysics Letters 139, 53001. 
doi: 10.1209/ 0295-5075/ac8445. 

Also

Keyword 'swarm' in FonT


Keywords: gst, behavior, collective behavior, self-organization, synchronization, spontaneous synchronization, swarm, swarmalators.


sabato 14 gennaio 2023

# gst: approaching chaotic dynamics to trace the complexity of rough nanostructured surfaces

AA << use the basic ingredients of chaotic dynamics (stretching and folding of phase space points) for the characterization of the complexity of microscopy images of rough surfaces. The key idea is to use an image as the initial condition of a chaotic discrete dynamical system, such as the Arnold cat map, and track its transformations during the first iterations of the map. Since the basic effects of the Arnold map are the stretching and folding of image texture, the application of the map leads to an enhancement of the high frequency content of images along with an increase of discontinuities in pixel intensities. (AA) exploit these effects to quantify the complexity of S type (lying between homogeneity and randomness) of the image texture since the first (enhancement of high frequencies) can be used to quantify the distance of texture from randomness and noise and the second (the proliferation of discontinuities) the distance from order and homogeneity. The method is validated in synthetic images which are generated from computer generated surfaces with controlled correlation length and fractal dimension and it is applied in real images of nanostructured surfaces obtained from a scanning electron microscope with very interesting results. >>️

A. Kondi, V. Constantoudis, P. Sarkiris, K. Ellinas, and E. Gogolides. Using chaotic dynamics to characterize the complexity of rough surfaces. Phys. Rev. E 107, 014206. Jan 11, 2023. 


Also

Able to track changes in noise. 
(quasi-stochastic poetry) 
Notes. Sep 13, 2007. 

Also

keyword 'chaos' | 'chaotic' in Font



keyword 'caos' | 'caotico' in Notes (quasi-stochastic poetry)



Keywords: gst, chaos, chaotic, nano, roughness, wetting, surfaces, etching scanning 


mercoledì 20 settembre 2023

# 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. 

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

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


giovedì 17 marzo 2022

# gst: apropos of weird transitions: from non-equilibrium conditions square droplets and liquid lattices can emerge.


<< Spontaneous emergence of organized states in materials driven by non-equilibrium conditions is of notable fundamental and technological interest. In many cases, the states are complex, and their emergence is challenging to predict. Here, (AA) show that an unexpectedly diverse collection of dissipative organized states emerges in a simple system of two liquids under planar confinement when driven by electrohydrodynamic shearing.

At low shearing, a symmetry breaking at the liquid-liquid interface leads to a one-dimensional corrugation pattern. 

At slightly stronger shearing, topological changes give raise to the emergence of Quincke rolling filaments, filament networks, and two-dimensional bicontinuous fluidic lattices. 

At strong shearing, the system transitions into dissipating polygonal, toroidal, and active droplets that form dilute gas-like states at low densities and complex active emulsions at higher densities. >>

Geet Raju, Nikos Kyriakopoulos, Jaakko V. I. Timonen. Diversity of non-equilibrium patterns and emergence of activity in confined electrohydrodynamically driven liquids. Science  Advances. Vol 7, Issue 38. doi: 10.1126/ sciadv.abh1642. 15 Sep 15, 2021.


<< Things in equilibrium tend to be quite boring, (..) It's fascinating to drive systems out of equilibrium and see if the non-equilibrium structures can be controlled or be useful. Biological life itself is a good example of truly complex behavior in a bunch of molecules that are out of thermodynamic equilibrium. >>  Jaakko Timonen.

Physicists make square droplets and liquid lattices. Aalto University. Sep 15, 2021. 


Also

keyword 'drop' | 'droplet' in FonT



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


keywords: gst, drop, droplet, lattice, transition, out of equilibrium.



lunedì 6 maggio 2024

# gst: random walk model for dual cascades in wave turbulence.

<< Dual cascades in turbulent systems with two conserved quadratic quantities famously arise in both two-dimensional hydrodynamic turbulence and also in wave turbulence based on four-wave interactions. >>

<< in wave turbulence the systematic spectral fluxes observed in a dual cascade do not require an irreversible dynamical mechanism, rather, they arise as the inevitable outcome of blind chance. >>️️

Oliver Bühler. Random walk model for dual cascades in wave turbulence. Phys. Rev. E 109, 055102. May 1, 2024. 

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

Keywords: gst, waves, turbulence, weak turbulence, random, random walks


martedì 28 febbraio 2023

# gst: flocking transitions of unfriendly species.

AA consider << two kinds of self-propelled particles, A and B, that tend to align with particles from the same species and to antialign with the other. The model shows a flocking transition (..) it has a liquid-gas phase transition and displays micro-phase-separation in the coexistence region where multiple dense liquid bands propagate in a gaseous background. >>


<< The interesting features (..) are the existence of two kinds of bands, one composed of mainly A particles and one mainly of B particles, the appearance of two dynamical states in the coexistence region: the PF (parallel flocking) state in which all bands of the two species propagate in the same direction, and the APF (antiparallel flocking) state in which the bands of species A and species B move in opposite directions. When PF and APF states exist in the low-density part of the coexistence region they perform stochastic transitions from one to the other. The system size dependence of the transition frequency and dwell times show a pronounced crossover that is determined by the ratio of the band width and the longitudinal system size. >>

AA << work paves the way for studying multispecies flocking models with heterogeneous alignment interactions. >>

Swarnajit Chatterjee, Matthieu Mangeat, et al. Flocking of two unfriendly species: The two-species Vicsek model. Phys. Rev. E 107, 024607. Feb 14, 2023

Also

keyword 'swimmers' in FonT

Keywords: gst, flocking, particles, self-propelled particles, swimmers,  microswimmers


lunedì 24 aprile 2023

# gst: emergent organization and polarization due to active fluctuations.


AA << introduce and study a model of active Brownian motion with multiplicative noise describing fluctuations in the self-propulsion or activity. (They) find that the standard picture of density accumulation in slow regions is qualitatively modified by active fluctuations, as stationary density profiles are generally not determined only by the mean self-propulsion speed landscape. As a result, activity gradients generically correlate the particle self-propulsion speed and orientation, leading to emergent polarization at interfaces pointing either towards dense or dilute regions depending on the amount of noise in the system.  >>
Benoit Mahault, Prakhar Godara, Ramin Golestanian. Emergent organization and polarization due to active fluctuations. Phys. Rev. Research 5, L022012. April 12, 2023. 

Also: 'particle', 'fluctuations', 'noise', 'self-assembly' in https://www.inkgmr.net/kwrds.html

Keywords: gst, particle, organization, polarization, fluctuations, noise, self-propulsion, self-assembly 



venerdì 9 giugno 2023

# gst: another way for the evaporation of a black hole

<< The quantum fluctuations that pervade empty space spontaneously give birth to pairs of particles and antiparticles. Ordinarily, these pairs annihilate so promptly that their existence is virtual. But a powerful field can pull a pair’s members apart for long enough that their existence becomes real. Now (AA) have proposed that particle pairs can be brought into existence by the immense gravitational tidal forces around a black hole (..).>>

<< If the vacuum is stable, all pairs that are created are also destroyed. But a strong field destabilizes the vacuum, makes some paths more likely than others, and leads to a deficit of pairs that recombine. The deficit is balanced by a net outflow of real particles, which, in the case of a black hole’s gravitational field, leads to the black hole’s eventual evaporation. >>️

Charles Day. Another Way for Black Holes to Evaporate. Physics 16, s77. Jun 2, 2023. 

Michael F. Wondrak, Walter D. van Suijlekom, Heino Falcke. Gravitational Pair Production and Black Hole Evaporation. Phys. Rev. Lett. 130, 221502. Jun 2, 2023. 

Also:  'black hole', in https://www.inkgmr.net/kwrds.html

Keywords: gst, black hole, astrophysics


sabato 20 novembre 2021

# gst: predict the wetting of the wedge; why do the teapots always drip?

<<  The "teapot effect" has been threatening spotless white tablecloths for ages: if a liquid is poured out of a teapot too slowly, then the flow of liquid sometimes does not detach itself from the teapot, finding its way into the cup, but dribbles down at the outside of the teapot. >>

<< This phenomenon has been studied scientifically for decades—now a research team at TU Wien has succeeded in describing the "teapot effect" completely and in detail with an elaborate theoretical analysis and numerous experiments: An interplay of different forces keeps a tiny amount of liquid directly at the edge, and this is sufficient to redirect the flow of liquid under certain conditions. >>

<< Although this is a very common and seemingly simple effect, it is remarkably difficult to explain it exactly within the framework of fluid mechanics,  (..) We have now succeeded for the first time in providing a complete theoretical explanation of why this drop forms and why the underside of the edge always remains wetted, >>  Bernhard Scheichl.

<< The sharp edge on the underside of the teapot beak plays the most important role: a drop forms, the area directly below the edge always remains wet. The size of this drop depends on the speed at which the liquid flows out of the teapot. If the speed is lower than a critical threshold, this drop can direct the entire flow around the edge and dribbles down on the outside wall of the teapot. >>

<< The mathematics behind it is complicated—it is an interplay of inertia, viscous and capillary forces. The inertial force ensures that the fluid tends to maintain its original direction, while the capillary forces slow the fluid down right at the beak. The interaction of these forces is the basis of the teapot effect. However, the capillary forces ensure that the effect only starts at a very specific contact angle between the wall and the liquid surface. The smaller this angle is or the more hydrophilic (i.e. wettable) the material of the teapot is, the more the detachment of the liquid from the teapot is slowed down. >>

<< Interestingly, the strength of gravity in relation to the other forces that occur does not play a decisive role. Gravity merely determines the direction in which the jet is directed, but its strength is not decisive for the teapot effect. The teapot effect would therefore also be observed when drinking tea on a moon base, but not on a space station with no gravity at all. >>️

Why teapots always drip. Vienna University of Technology. Nov 08, 2021


Scheichl, B., Bowles, R., & Pasias, G. (2021). Developed liquid film passing a smoothed and wedge-shaped trailing edge: Small-scale analysis and the ‘teapot effect’ at large Reynolds numbers. Journal of Fluid Mechanics, 926, A25. doi: 10.1017/jfm.2021.612. Sep 8, 2021. 


keywords: gst, teapot effect, interfacial flows, thin films, boundary layers, Reynolds number, viscosity, viscous–inviscid interaction 

mercoledì 17 agosto 2022

# gst: rare transitions in noisy net scenarios


AA << study small white noise perturbations of planar dynamical systems with heteroclinic networks in the limit of vanishing noise. (They)  show that the probabilities of transitions between various cells that the network tessellates the plane into decay as powers of the noise magnitude. (They) show that the most likely scenario for the realization of these rare transition events involves spending atypically long times in the neighborhoods of certain saddle points of the network. >>️

Yuri Bakhtin, Hong-Bin Chen, Zsolt Pajor-Gyulai. Rare transitions in noisy heteroclinic networks. arXiv: 2205.00326v1 [math.PR]. Apr 30, 2022.    https://arxiv.org/abs/2205.00326

Also

keyword 'noise'  in FonT 

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

Keywords: gst, transitions, networks, heteroclinic networks, noise