venerdì 31 dicembre 2021

# behav: unfrequent events under radical uncertainty; rats tend to avoid black swan situations.

AA << present a novel experimental design that aims at measuring the extent to which animal subjects are sensitive to rare and extreme events and, in addition, how rats respond to those very unfrequent events under radical uncertainty. (..) the novelty of (AA) design is that it provides two direct measures that help interpreting (..) behavioral data: Total Sensitivity to Rare and Extreme Events, and One-sided Sensitivity to Rare and Extreme Events with Black-Swan Avoidance/Jackpot-Seeking behaviors as limiting cases. >>️

<< First, most rats (..) can be grouped into a moderate to high Total Sensitivity group. This means that most rats diversify their choices across options in such a way that they more often rely on convex ones than on concave ones overall. Therefore, they tend to seek extreme gains/Jackpots and to avoid extreme losses/ Black Swans. In addition, most rats (..) tend to exhibit Black Swan Avoidance, which indicates that, given Total Sensitivity, they tend to try more often to avoid Black Swans than to seek Jackpots. (AA) interpret such a behavior as significant aversion towards uncertainty about rare and extreme losses.  >>️

<< all rats diversify their choices across a set of options, which is reminiscent of observed behaviors such as, for example, bet-hedging in animals and financial portfolio strategies used by humans >>
️
<< results from similar experiments among different species might be of interest for the analysis of neurobiological substrates involved in decision-making and its evolutionary traits in the context of rare and extreme events. >>️

Mickael Degoulet, Louis-Matis Willem, et al. Decision-Making in Rats is Sensitive to Rare and Extreme Events: the Black Swan Avoidance. bioRxiv 10.1101/2021.11.01.466806v1. Nov 04, 2021. 


 Keywords: behav, game, decision-making, bet-hedging, trading, uncertainty, gain, loss, black swan 


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mercoledì 29 dicembre 2021

# game: in a iterated prisoner's dilemma scenario forgiveness turns out to be an adaptation

<< Prisoner’s dilemma is used to represent a range of real life phenomena such as economics, commerce, nature and wildlife. >>

<< Researchers working on iterated prisoner's dilemma (IPD) with limited memory inspected the outcome of different forgetting strategies in homogeneous environment, within which all agents adopt the same forgetting strategy at a time. In this work, with the intention to represent real life more realistically, (AA) improve existing forgetting strategies, offer new ones, and conduct experiments in heterogeneous environment that contains mixed agents and compare the results with previous research as well as homogeneous environment >>

<< in a more realistic environment consisting of all types of agents, in terms of both cooperation probabilities and forgetting strategies, agents who forget defectors consistently outperform other forgetting strategies for all memory ratio values. Moreover, the best performing defectors are also the ones that forget other defectors. In other words, agents who “forgive” defectors are the best performers. Hence, forgiveness is an adaptation. >>

FMC : Forget most cooperator first 
FMP : Forget most played first 
FMU : Forget most unpredictable first 
FR :  Forget randomly 
FLP : Forget least played first 
FMD : Forget most defector first 

Meliksah Turker, Haluk O. Bingol. Forgiveness is an Adaptation in Iterated Prisoner's Dilemma with Memory. arXiv:2112.07894v1 [cs.GT]. Dec 15, 2021


Also

keyword 'game' | 'tit-for-tat' in FonT



keyword 'game' | 'tit-for-tat' in Notes
(quasi-stochastic poetry)



Keywords: game, iterated prisoner's dilemma, forgiveness, adaptation


alle Nessun commento:

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.

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venerdì 10 dicembre 2021

# life; apropos of #1or2achoos from Wuhan ...

Messrs. A, B, C & D state - between the lines, undertrack, at least a year late -

Commissione DuPre (Dubbio e Precauzione ) live streaming 8/12/2021 


that the official anti covid19 apparatus it appears to be a big, very big mess (i.e. 'un grande pastrokkio') ...

probably Messrs. A, B, C & D could be accused of being thieves, sexual maniacs, they could block their career and make their spouses do twenty years of precariousness ...

their future pensioners' allowance could be taken away or reduced ... 

as well as more ... 

I suppose & anzicheforse ...

luckily for everyone, the 'bushman  variant' of sarscov-2 (Covid-19 B.1.1.529 Omicron) 

Republic of Botswana - new covid 19 variant detected in Botswana -  Presidential covid-19 task force.


could save in short-term, perhaps, the world from this big trouble (i.e.  'grande impiccio').

Here there are three simple questions: 

(a) Why in anticipation of the 'great tea trolley disaster' (after SARS appearance in Nov 2002, Guangdong, China; after MERS in Nov 2012, Gedda, Saudi Arabia) spray forms of antiviral drugs (e.g. remdesivir,  remdesivir like) have not been prepared?


(b) Why in the meantime, hitech reusable anti-viral anti-bacterial fabrics not been studied and tested?

(c) Does it seem serious to propose a vaccine - to treat every six/eight months eight billion people inside a window of 15/30 days - to confine (sic) a mutant virus (one mutation every week) that is transmitted by air? 

Also 

the unmentionable GTTD - Great Tea Trolley Disaster, by Bristow


keyword 'virus' | 'sars-cov-2' | 'sars' in FonT: 




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


keyword 'bosciman*' | 'nomad*' in Notes
(quasi-stochastic poetry)





keyword 'bushmen' | 'nomads' in FonT 



keywords: virus, coronavirus, sars, mers, sars-cov-2, covid-19, 2019ncov, bushman  variant, B.1.1.529, Omicron, 1or2achoos, mask


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sabato 4 dicembre 2021

# life: apropos of 'dancing at a fixed point'

the last interview to Dr Albert Bourla (Pfizer) about the annual (or maybe semi-annual (?)) shot reiteration of the vaccine against #sars-cov-2   remember to me the 'homoclinic dynamics' that I cited at the 13th Meeting of the Internat Epidemiol Associat - IEA (Sydney, 1993) ... after a large trajectories started at zero point (i.e.  the fixed point), the final point of the dynamic returns at the same zero point ...

<< People will be likely to need to have annual Covid vaccinations for many years to come, the head of Pfizer [Dr Albert Bourla ] has told the BBC >>️

Fergus Walsh. Pfizer boss: Annual Covid jabs for years to come. Dec 2, 2021. 


Who knows if there is a convincing reason that explains why to treat a virus with a high frequency of mutations one should prefer a vaccine approach instead of an antiviral drug ...

to find: 'antiviral drugs covid-19'  


Apropos of 'homoclinic orbits' ...

<< the reinjection of the departing trajectories in the vicinity of an unstable fixed point of the saddle-focus type [..] is frequently associated with the emergence of orbits of a rather exceptional type known as 'homoclinic orbits'. These are trajectories that leave the fixed point but come back to it; in other words, they tend to the same limit when time t goes to +∞ as well as to -∞ . [..]. Homoclinic orbits are very sensitive to variation of parameter [parms] values and are generally destroyed if the [parms] do not satisfy a strict equality (in the terminology of [..] they are structurally unstable). However, for nearby values of the [parms] their disappearance leaves a very rich structure of orbit in phase space, some of which behave chaotically. >>️

Nicolis G., Prigogine I. Exploring complexity. Freeman, NY (1989): 130-131.


Apropos of: [+∞ , -∞] plus infinity, minus infinity; 

<< In modern mysticism, the infinity symbol has become identified with a variation of the ouroboros, an ancient image of a snake eating its own tail that has also come to symbolize the infinite, [..] >> 


Also 

Onda omoclina. Notes. Tuesday, Jan  11, 2005 (quasi-stochastic poetry)

<< ed assistere al mutar dell' onda omoclina / (..) >>
️

Also

Inchingolo GM.  Cultural transitions and epidemiology.  Proceedings of the 13th Scientific Meeting of the International Epidemiological Association - IEA, Sydney, Australia, Sept 26-29, 1993: 129.   Med Hypotheses 1994; 43(4): 201-206.


Also

Onda di carambola. Notes. Nov  29, 2004. (quasi-stochastic poetry)


keywords: life, dance, fixed point, homoclinic orbits, instability, chaos,  virus, coronavirus, sars-cov-2,  covid19, 2019ncov, drugs, antiviral drug, vaccine, jabs, Covid jabs.

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mercoledì 1 dicembre 2021

# gst: small-scale random perturbations, Arnold's cat spontaneously stochastic

<< Multi-scale systems (..) may possess a fascinating property of spontaneous stochasticity: a small-scale initial uncertainty develops into a randomly chosen largescale state in a finite time, and this behavior is not sensitive to the nature and magnitude of uncertainty (..). >>

A << intriguing form is the Eulerian spontaneous stochasticity (ESS) of the velocity field itself: an infinitesimal small-scale noise triggers stochastic evolution of velocity field at finite scales and times. >>

AA << prove that a formally deterministic system with scaling symmetry yields a stochastic process with Markovian properties if it is regularized with a vanishing small-scale random perturbation. Besides its significance for understanding turbulence, (their) model extends the phenomenon of ESS beyond the scope of fluid dynamics: (AA) discuss a prototype of a feasible experiment for observing ESS in optics or electronics, as well as potential applications in other physical systems.>>

Alexei A. Mailybaev, Artem Raibekas. Spontaneously stochastic Arnold's cat. arXiv:2111.03666v1 [nlin.CD]. Nov 5,  2021.


keywords: gst, Arnold's cat, randomness, stochasticity, spontaneous stochasticity, small-scale random perturbations, noise, turbulence, chaos 


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sabato 27 novembre 2021

# gst: apropos of hybrid nanostructures, the Kondo cloud effects on 'impurities' (inside superconductors).

<< when a metal contains magnetic impurities, conduction electrons can form a screening cloud, which essentially screens the impurity's spin. This physical phenomenon is known as the Kondo effect; thus, the resulting cloud is referred to as a Kondo cloud. >>

<< While the behavior of the Kondo cloud in normal systems is well-understood, its properties in the presence of superconducting materials have not yet been explored in depth. So far, most physicists have believed that the screening of impurity spins in hybrid nanostructures takes place predominantly in the screened, rather than in the unscreened, quantum phase. >>

<< The system we considered exhibits a quantum phase transition when the ground state changes between the Kondo state and the so-called Shiba state, (..) Up to now, it was believed that the screening occurs in the Kondo phase. Quite strikingly, we have however, demonstrated that the Kondo cloud exists also in the unscreened phase. >>  Ireneusz Weymann.

Ingrid Fadelli. Study predicts the behavior of a Kondo cloud in a superconductor. Phys.org. Nov  23, 2021. 


Catalin Pascu Moca, Ireneusz Weymann, et al. Kondo Cloud in a Superconductor.  Phys. Rev. Lett. 127, 186804. Oct 27, 2021.


keywords: gst, nano, hybrid nanostructure, superconductor, transition, impurity, Kondo cloud, Kondo effect


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martedì 23 novembre 2021

# gst: apropos of transitions, when collisions can induce coherent dynamics.

<< In this paper (AA)  demonstrate a route to develop coherence in a system of non-driven oscillators. Here, the coherence is brought about via physical collisions through which the oscillators exchange energy. While coherence in the classical situations occurs due to sustained coupling terms in the dynamical equations, collision induced coherence is enabled solely through strong interactions that are of intermittent nature! >>

<< Very few studies (..) have attempted to study the contact dynamics during a collision. (AA) have generalized the framework of these experiments to demonstrate the collision-induced development of coherent dynamics in the simple one-dimensional arrangement of balls known as the Newton’s cradle. >>

Ayanesh Maiti, Shankar Ghosh. Collision-induced coherent dynamics. arXiv:2111.08902v1 [nlin.CD]. Nov 17, 2021. 


keywords: gst, transitions, oscillation, collision 



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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 

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venerdì 19 novembre 2021

# gst: apropos of oscillations, viscous streaming around an immersed microfeature (e.g. a bubble)

<< Viscous streaming refers to the rectified, steady flows that emerge when a liquid oscillates around an immersed microfeature, typically a solid body or a bubble. The ability of such features to locally concentrate stresses produces strong inertial effects to which both fluid and immersed particles respond within short length (O(100) microns) and time (milliseconds) scales, rendering viscous streaming arguably the most efficient mechanism to exploit inertia at the microscale. >>️

(AA) << demonstrate that a multi-curvature approach in viscous streaming dramatically extends the range of accessible flow topologies. (They) show that numerically predicted, but never experimentally observed, streaming flows can be physically reproduced, computationally engineered, and in turn used to enhance particle manipulation, filtering and separation in compact, robust, tunable and inexpensive devices. >>️

Yashraj Bhosale, Giridar Vishwanathan, et al. Multi-curvature viscous streaming: flow topology and particle manipulation. arXiv: 2111.07184v1 [physics.flu-dyn]. Nov 13, 2021.


keywords: gst, viscosity, viscous streaming, bubble, oscillations, liquid oscillations, flanking vortex, particle manipulation 

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giovedì 18 novembre 2021

# gst: apropos of Cake-cutting, the Art of dividing a cake by countably many cuts

<< Cake-cutting is a playful name for the fair division of a heterogeneous, divisible good among agents, a well-studied problem at the intersection of mathematics, economics, and artificial intelligence. The cake-cutting literature is rich and edifying. However, different model assumptions are made in its many papers, in particular regarding the set of allowed pieces of cake that are to be distributed among the agents and regarding the agents' valuation functions by which they measure these pieces. >>️

A simple example proposed by AA  <<  shows that a formal mathematical approach to cake-cutting needs to address questions like:

(o) Are (open, closed, half-open) intervals the only possible pieces of cake? 

(o) Do we allow for finitely many or infinitely many cuts (a “cut” being the split of any subset of [0,1] at a single point)? 

(o) Which properties should a valuation function have, and how does it interact with the family of admissible pieces of cake?  >>

<< Among the questions (AA) have tried to answer are: 

(i) Which subsets of [0,1] should be considered as pieces of cake? Only finite unions of intervals or more general sets? 

(ii) If valuation functions are considered as set-functions as studied in measure theory, should they be σ-additive or only finitely additive? 

(iii) more ...
>>️
️
AA << have surveyed the existing rich literature on cake-cutting algorithms and have identified the most commonly used choices of sets consisting of what is allowed as pieces of cake. After showing that these five most commonly used sets are distinct from each other, (they) have discussed them in comparison. >>️

Peter Kern, Daniel Neugebauer, et al. Cutting a Cake Is Not Always a "Piece of Cake": A Closer Look at the Foundations of Cake-Cutting Through the Lens of Measure Theory. arXiv: 2111.05402v1 [cs.GT]. Nov 9, 2021. 


keywords: gst, cake, cake-cutting, math.
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venerdì 12 novembre 2021

# gst: a screw mechanism to separate realistic racemic mixtures by local vorticity

AA developed << an explanatory "screw"  model for predicting the shear-flow separation of enantiomers >>

<< Enantiomers of chiral molecules are non-superposable mirror images with the same structural formula. In achiral environments, enantiomers have identical physical and chemical properties, and this prevents separation by classical methods. >>

<< A screw is a simple chiral object that couples rotation around one axis with displacement along that axis. This displacement is perpendicular to the plane of rotation and is characterized by the screw’s pitch (or lead). Here (it is defined) pitch (P) as the perpendicular distance advanced by a screw in a 2π-revolution. In a lab-fixed frame, left-and right-handed screws have pitches with the same magnitude, but with flipped signs, rotating in opposite directions to do the same task. This concept can be easily extended to chiral molecules by considering the translation-rotation coupling tensor (..). In a medium which induces rotation of molecules (as in a vortex flow), chiral molecules will translate in opposite directions. As a consequence, this asymmetry may enable the resolution of the enantiomers. >>

Thus  a << competition model and continuum drift diffusion equations are developed to predict separation of realistic racemic mixtures. (..) Additionally, (AA) find that certain achiral objects can also exhibit a non-zero molecular pitch. >>

<< Although it has been used << shear flow as the source to rotate the chiral molecules and achieve separation, it may be possible to use external forces to rotate the enantiomers >>️
️
Duraes A, Gezelter JD. Separation of Enantiomers through Local Vorticity: A Screw Model Mechanism. ChemRxiv. Cambridge: Cambridge Open Engage; Vers 1. doi: 10.33774/ chemrxiv-2021-196zw. Oct 04, 2021. 


keywords: gst, vortices, separation, enantiomeric separation, racemic mixture, screw mechanism, translation-rotation coupling, transitions.

alle Nessun commento:

lunedì 8 novembre 2021

# geo: apropos of oscillations, a 'true polar wander' (TPW); Earth tip on its side 84 Ma ago.

<< It has been debated for the past few decades whether the outer, solid shell of the Earth can wobble about, or even tip over relative to the spin axis. Such a shift of Earth is called "true polar wander," (TPW) but the evidence for this process has been contentious. New research (..) provides some of the most convincing evidence to date that such planetary tipping has indeed occurred in Earth's past. >>️

<< The Earth is a stratified ball, with a solid metal inner core, a liquid metal outer core, and a solid mantle and overriding crust at the surface which we live on. All of this is spinning like a top, once per day. Because the Earth's outer core is liquid, the solid mantle and crust are able to slide around on top of it.  >>
️
Did the Earth tip on its side 84 million years ago? Tokyo Institute of Technology. Oct 18, 2021. 


<< a new high-resolution palaeomagnetic record from two overlapping stratigraphic sections in Italy (..) provides evidence for a ~12° TPW oscillation from 86 to 78 Ma. This observation represents the most recent large-scale TPW documented and challenges the notion that the spin axis has been largely stable over the past 100 million years. >>️

Mitchell, R.N., Thissen, C.J.,  et al. A Late Cretaceous true polar wander oscillation. Nat Commun 12, 3629. doi: 10.1038/ s41467-021-23803-8. June 15, 2021. 


keywords: gst, geo, geodynamics, geophysics, palaeomagnetism, oscillations, wobble, true polar wander, tpw

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sabato 30 ottobre 2021

# 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. 



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

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venerdì 22 ottobre 2021

# gst: the effect of noise on the dynamics of microswimmers in externally-driven fluid flows.

AA << have quantified the effect of noise on swimmer dynamics in a steady, two-dimensional hyperbolic fluid flow. In such a flow, swimmers are ultimately forced to escape to the left or the right, with their transient dynamics near the passive unstable fixed point determining which way they go. >>

<< Without noise, a swimmer’s fate is sealed based on its position relative to the SwIM (swimming invariant manifolds) in the xθ phase space. With noise, the swimmer’s motion is a stochastic process. >>

AA << calculated the steady-state orientation distributions of diffusive, run-and-tumble, or mixed swimmers in the hyperbolic flow. The fluctuations give some swimmers greater opportunity to cross the SwIM and exit on the opposite side than they would have without noise. There is however a maximal distance that swimmers can get on either side of the passive fixed point and still be able to swim back to the other side—this is where the stable BIMs (burning invariant manifolds) block inward swimming particles. >>

<< Fluctuations make it increasingly likely that a swimmer close to one of these BIMs does indeed end up crossing it, causing irreversible changes to the fluctuating swimmers’ trajectories (assuming negligible translational diffusion).  >>️

Simon A. Berman, Kevin A. Mitchell. Swimmer dynamics in externally-driven fluid flows: The role of noise. arXiv: 2108.10488v1 [physics.flu-dyn]. Aug 24, 2021.


keywords: gst, swimmer, swimming particle, fluid dynamics, chaotic dynamics, rotational diffusion, random fluctuation, tumbling, noise


alle Nessun commento:

mercoledì 20 ottobre 2021

# 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.


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


alle Nessun commento:

lunedì 11 ottobre 2021

# 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. 


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


alle Nessun commento:

giovedì 7 ottobre 2021

# gst: depicting scenarios between wobblers and kinks; energy transfers and destructive interferences

<< asymmetric scattering between wobblers and kinks (..) is investigated in two different scenarios. First, the collision between wobblers with opposite phase is analyzed. (..) a destructive interference between the shape modes of the colliding wobblers takes place at the impact time. The second scenario involves the scattering between a wobbler and an (unexcited) kink. In this case the energy transfer from the wobbler to the kink can be examined. The dependence of the final velocities and wobbling amplitudes of the scattered wobblers on the collision velocity and on the initial wobbling amplitude is discussed. Both situations lead to very different fractal structures in the velocity diagrams. >>️

<< it is also worthwhile mentioning the results displayed (..) It can be verified that systematically when a scattered wobbler gains more kinetic energy than the other, it obtains less vibrational energy and vice versa. >>️

A. Alonso-Izquierdo, L. M. Nieto, J. Queiroga-Nunes. Asymmetric scattering between kinks and wobblers. arXiv:2109.13904 (hep-th). Sep 28, 2021. 




alle Nessun commento:

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 





alle Nessun commento:

venerdì 1 ottobre 2021

# ai: perpetual nirvana among 'self-addicted', 'self-cracked', 'playful' machines, the wireheading effect.

<< In 1953, a Harvard psychologist thought he discovered pleasure – accidentally – within the cranium of a rat. With an electrode inserted into a specific area of its brain, the rat was allowed to pulse the implant by pulling a lever. It kept returning for more: insatiably, incessantly, lever-pulling. In fact, the rat didn’t seem to want to do anything else. Seemingly, the reward centre of the brain had been located. >>️

<< More than 60 years later, in 2016, a pair of artificial intelligence (AI) researchers were training an AI to play video games. The goal of one game – Coastrunner – was to complete a racetrack. But the AI player was rewarded for picking up collectable items along the track. When the program was run, they witnessed something strange. The AI found a way to skid in an unending circle, picking up an unlimited cycle of collectables. It did this, incessantly, instead of completing the course. >>️

<< What links these seemingly unconnected events is something strangely akin to addiction in humans. Some AI researchers call the phenomenon "wireheading". >>️

Thomas Moynihan, Anders Sandberg. Drugs, robots and the pursuit of pleasure – why experts are worried about AIs becoming addicts. The Conversation. Sep 14, 2021. 


Rock'n Roll Monkey/Unsplash, FAL (img)  


FonT: so one could hypothesize a suitable 'magic string' that mitigates hypothetical autocatalytic pulsatile wireheading effects, even for artificial, bio-artificial entities.

An ethno-drug revisited ... Ayahuasca, prelude of a "magic string" in neuropharmacology. FonT.  July 8, 2018.


Also

"senza finalita' ideologiche, solo per curiosita',  giusto per giocare ..." in: 
Anomalous formation of molecules after vapor deposition. FonT.  Dec 31, 2015. 


A mechanism of analogy could be the master key to achieving an abstract artificial intelligence. FonT. Aug 10, 2021. 


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





keywords: ai, bots, artificial intelligence, wireheading effect, addiction


alle Nessun commento:

sabato 25 settembre 2021

# 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.


Also

keyword 'drop' | 'droplet' in FonT



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


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






alle Nessun commento:

mercoledì 22 settembre 2021

# 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. 



Also

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




keyword 'elastico' | 'turbolento' | 'disordine' in Notes
(quasi-stochastic poetry)





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


alle Nessun commento:

domenica 19 settembre 2021

# 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.


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

alle Nessun commento:

venerdì 17 settembre 2021

# 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.


Also

keyword 'waves' in FonT


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




alle Nessun commento:

mercoledì 15 settembre 2021

# 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.


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.




alle Nessun commento:

venerdì 10 settembre 2021

# 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. 


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.


Also

keyword 'origami' in FonT


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



alle Nessun commento:

giovedì 9 settembre 2021

# 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.


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


Also

keyword 'drop' | 'droplet' in FonT



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

alle Nessun commento:

martedì 7 settembre 2021

# 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.


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. 



alle Nessun commento:

venerdì 3 settembre 2021

# 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.


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.








alle Nessun commento:

giovedì 2 settembre 2021

# 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.


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)


keyword 'noise' | 'fuzzy' in FonT




alle Nessun commento:

lunedì 30 agosto 2021

# gst: apropos of 1or2achoos (e.g. from Wuhan), the dynamics of turbulence in a fluid puff

<< Turbulence is everywhere -- in the movement of the wind, the ocean waves and even magnetic fields in space. It can also be seen in more transient phenomena, like smoke billowing from a chimney, or a cough. (..) Understanding this latter type of turbulence -- called puff turbulence -- is important not only for the advancement of fundamental science, but also for practical health and environmental measures, >>️

<< The very nature of turbulence is chaotic, so it's hard to predict, (..) Puff turbulence, which occurs when the ejection of a gas or liquid into the environment is disrupted, rather than continuous, has more complicated characteristics, so it's even more challenging to study. But it's of vital importance -- especially right now for understanding airborne transmission of viruses like SARS-CoV-2. >>️ Marco Edoardo Rosti. 

<< The new model, (..) includes how minute fluctuations within the puff behave, and how both large-scale and small-scale dynamics are impacted by changes in temperature and humidity. (..) at cooler temperatures (15°C or lower), (AA) model deviated from the classical model for turbulence. >>️

<< In the classical model, turbulence reigns supreme -- determining how all the little swirls and eddies within the flow behave. But once temperatures dipped, buoyancy started to have a greater impact. >>

<< The effect of buoyancy was initially very unexpected. It's a completely new addition to the theory of turbulent puffs,>> Marco Edoardo Rosti. ️

Secrets of COVID-19 transmission revealed in turbulent puffs. Okinawa Institute of Science and Technology (OIST). Aug 26, 2021. 


Andrea Mazzino, Marco Edoardo Rosti. Unraveling the Secrets of Turbulence in a Fluid Puff. Phys. Rev. Lett. 127, 094501. Aug 25, 2021. 


Also

keyword 'drop' | 'droplet' in FonT:



keyword 'turbulence' in FonT:


keyword 'turbolento' | 'turbolenza' in Notes (quasi-stochastic poetry): 



keyword 'virus' | 'sars-cov-2' | 'sars' in FonT: 




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



alle Nessun commento:

sabato 21 agosto 2021

# gst: apropos of transitions, randomness can stabilize edge states in short- lifetime regions of disordered periodically-driven systems

<< lifetimes of the edge states exhibit universal behavior when random potentials exist since the edge- and bulk- dominant eigenstates are mixed, leading to that lifetimes are prolonged by random potentials in the region II (short- lifetime region) and shortened in the region I (long- lifetime region). >>

<<  it is an intriguing phenomenon that random potentials tend to stabilize edge states in the region II (short- lifetime regions). >>

Ken Mochizuki, Kaoru Mizuta, Norio Kawakami. Fate of Topological Edge States in Disordered Periodically-driven Nonlinear Systems. arXiv: 2108.00649 (nlin). Aug 2, 2021.


Also

keyword 'random' in FonT


keyword 'disorder' in FonT


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






alle Nessun commento:

martedì 17 agosto 2021

# brain: like a Zazen entity, mice can spontaneously self-modulate cortical dopamine impulses to reward.

AA << recently set out to investigate less understood aspects related to spontaneous impulses of dopamine. Their results, (..) have shown that mice can willfully manipulate (..) random dopamine pulses. >>

<< Rather than only occurring when presented with pleasurable, or reward-based expectations, (..) the neocortex in mice is flooded with unpredictable impulses of dopamine that occur approximately once per minute. >>️

<< mice on a treadmill received a reward if they showed they were able to control the impromptu dopamine signals. Not only were mice aware of these dopamine impulses, the data revealed, but the results confirmed that they learned to anticipate and volitionally act upon a portion of them. >>️️

<< Critically, mice learned to reliably elicit (dopamine) impulses prior to receiving a reward, (..) These effects reversed when the reward was removed. We posit that spontaneous dopamine impulses may serve as a salient cognitive event in behavioral planning. (..) We further conjecture that an animal's sense of spontaneous dopamine impulses may motivate it to search and forage in the absence of known reward-predictive stimuli, >> the researchers noted.️

'Feel good' brain messenger can be willfully controlled, new study reveals. University of California, San Diego. Jul 23, 2021. 


Conrad Foo, Adrian Lozada, et al. Reinforcement learning links spontaneous cortical dopamine impulses to reward. Current Biology. doi: 10.1016/ j.cub.2021.06.069. Jul 23, 2021. 


Also

keywords 'dopamine' and 'meditation' in PUBMED








alle Nessun commento:

sabato 14 agosto 2021

# gst: asymmetric ferroelectric bi-stability with two unequal stable polarization states by broken inversion symmetry

AA << demonstrated this phenomenon for the first time in engineered two-dimensional crystals. (..) These engineered crystals lead to an asymmetric bi-stability with two unequal stable polarization states in contrast to a natural ferroelectric. >>

New electronic phenomenon discovered. University of North Florida. Aug 11, 2021. 


<< In atomic-layer superlattices constructed using three constituent phases, (..) the stacking sequence of the atomic layers is found to control the symmetry of the high-temperature dielectric response. In such a superlattice when a nanostructured asymmetric strain is programmed into the lattice via the stacking order, the natural symmetry at high temperatures is removed and a polarized sample is obtained in which the polarization increases as the temperature is lowered. In contrast to a ferroelectric characterized by a bistable ground state with two equal and opposite electronic polarizations, (they)  experiments show evidence of asymmetric ferroelectric correlations that set in when such a sample becomes hysteretic below a temperature Tx, with two unequal polarization states. >>

Maitri P. Warusawithana, Caitlin S. Kengle, et al. Asymmetric ferroelectricity by design in atomic-layer superlattices with broken inversion symmetry.  Phys. Rev. B 104, 085103. Aug 4,  2021.





alle Nessun commento:

giovedì 12 agosto 2021

# brain: brain images of silence

<< When imagining music, the musicians' brain activity had the opposite electrical polarity to when they listened to it -- indicating different brain activations -- but the same type of activity as for imagery occurred in silent moments of the songs when people would have expected a note but there wasn't one. >>

<< There is no sensory input during silence and imagined music, so the neural activity we discovered is coming purely from the brain's predictions e.g., the brain's internal model of music. Even though the silent time-intervals do not have an input sound, we found consistent patterns of neural activity in those intervals, indicating that the brain reacts to both notes and silences of music. Ultimately, this underlines that music is more than a sensory experience for the brain as it engages the brain in a continuous attempt of predicting upcoming musical events. Our study has isolated the neural activity produced by that prediction process. And our results suggest that such prediction processes are at the foundation of both music listening and imagery. >> Giovanni Di Liberto. 

The music of silence: Imagining a song triggers similar brain activity to moments of mid-music silence. Trinity College Dublin. Aug 3, 2021. 


Guilhem Marion, Giovanni M. Di Liberto,  Shihab A. Shamma. The Music of Silence. Part I: Responses to Musical Imagery Encode Melodic Expectations and Acoustics. Journal of Neuroscience  JN-RM-0183-21. doi: 10.1523/ JNEUROSCI.0183-21.2021. 2 Aug 2, 2021.


Giovanni M. Di Liberto, Guilhem Marion,  Shihab A. Shamma. The music of silence. Part II: Music Listening Induces Imagery Responses. Journal of Neuroscience JN-RM-0184-21. doi: 10.1523/ JNEUROSCI.0184-21.2021. 
Aug 2, 2021.


Also

2123 - le dislocazioni pausali di Theo. 
(quasi-stochastic poetry). Notes. Feb 26, 2007.


A pause (acyclic pauses?)  approach to enhance and manage creativity. Mar 23, 2019.


We pronounce words more slowly compared with verbs and sometimes pause. May 20, 2018.



alle Nessun commento:

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)






alle Nessun commento:

lunedì 9 agosto 2021

# art: Nomadic masters; Neanderthals created art.

AA << analysed samples of red residues collected from the flowstone surface and compared them with iron oxide-rich deposits in the cave. They concluded that the ochre-based pigment was intentionally applied, i.e. painted -- by Neanderthals, as modern humans had yet to make their appearance on the European continent -- and that, importantly, it had probably been brought to the cave from an external source. >>

<< variations in pigment composition between samples were detected, corresponding to different dates of application, sometimes many thousands of years apart. Thus, it seems that many generations of Neanderthals visited this cave and coloured the draperies of the great flowstone formation with red ochre. >>

<< This behaviour indicates a motivation to return to the cave and symbolically mark the site, and it bears witness to the transmission of a tradition down through the generations. >>

Neanderthals indeed painted Andalusia’s Cueva de Ardales. CNRS. 
Aug 2, 2021. 


Africa Pitarch Marti, Joao Zilhao, et al. The symbolic role of the underground world among Middle Paleolithic Neanderthals. PNAS. 118 (33) e2021495118; doi: 10.1073/ pnas.2021495118. Aug 17, 2021. 








alle Nessun commento:

martedì 3 agosto 2021

# life: Nomadic masters, ancient people ate bread, beer and other carbs, long before domesticated crops

<< it has become clear that early humans were cooking and eating carbs almost as soon as they could light fires. >>

<< These are the best grinding tools ever, and I’ve seen a lot of grindstones, (..) People at Göbekli Tepe knew what they were doing, and what could be done with cereals. They’re beyond the experimentation phase. >> Laura Dietrich.
️
<< The old-fashioned idea that hunter-gatherers didn’t eat starch is nonsense, >> Dorian Fuller.️

Andrew Curry. How ancient people fell in love with bread, beer and other carbs. Well before people domesticated crops, they were grinding grains for hearty stews and other starchy dishes. Nature 594, 488-491. doi: 10.1038/ d41586-021-01681-w. Jun 22, 2021.


Audio long-read: How ancient people learned to love carbs. Nature Podcast 
Jul 26, 2021.







alle Nessun commento:

sabato 31 luglio 2021

# phys: Sir Isaac in the corner? The image of a "Time crystal", as a perpetual chaotic "out-of-equilibrium" phase; order and stability in an excited, evolving state.

<< A time crystal is a new phase of matter that, simplified, would be like having a snowflake that constantly cycled back and forth between two different configurations. It’s a seven-pointed lattice one moment and a ten-pointed lattice the next, or whatever. >>

<< What’s amazing about time crystals is that when they cycle back and forth between two different configurations, they don’t lose or use any energy. >>

<< Time crystals can survive energy processes without falling victim to entropy. The reason they’re called time crystals is because they can have their cake and eat it too. >>

<< They can be in a state of having eaten the whole cake, and then cycle right back to a state of still having the cake – and they can, theoretically, do this forever and ever. >>

<< Most importantly, they can do this inside of an isolated system. That means they can consume the cake and then magically make it reappear over and over again forever, without using any fuel or energy. >>️

Tristan Greene. Google's 'time crystals' could be the greatest scientific achievement of our lifetimes. Jul 30, 2021. 


<< The time crystal is the first “out-of-equilibrium” phase: It has order and perfect stability despite being in an excited and evolving state. >>
️
Natalie Wolchover. Eternal Change for No Energy: A Time Crystal Finally Made Real. Jul 30, 2021. 


Xiao Mi, Matteo Ippoliti, et al. Observation of Time-Crystalline Eigenstate Order on a Quantum Processor. arXiv:2107.13571v1 (quant-ph). Jul 28, 2021.



alle Nessun commento: