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lunedì 16 gennaio 2023

# gst: diffusivity of ordered and freely evolving bubbly suspensions.

AA << investigate the dispersion of a passive scalar such as the concentration of a chemical species, or temperature, in homogeneous bubbly suspensions, by determining an effective diffusivity tensor. Defining the longitudinal and transverse components of this tensor with respect to the direction of averaged bubble rise velocity in a zero mixture velocity frame of reference, (AA) focus on the convective contribution thereof, this being expected to be dominant in commonly encountered bubbly flows. >>

<< In the limits of low and of high Péclet number, including inertial effect of the flow does not affect the scaling of the effective diffusivity with respect to the Péclet number. These results are confirmed by direct numerical simulations performed in different flow regimes, for spherical or very deformed bubbles and from vanishingly small to moderate values of the Reynolds number. Scalar transport in arrays of freely rising bubbles is considered by us subsequently, using numerical simulations. In this case, the dispersion is found to be convectively enhanced at low Péclet number, like in ordered arrays. At high Péclet number, the Taylor dispersion scaling obtained for ordered configurations is replaced by the one characterizing a purely mechanical dispersion, like in random media, even if the level of disorder is very low. >>️

Aurore Loisy, Aurore Naso, Peter D. M. Spelt. The effective diffusivity of ordered and freely evolving bubbly suspensions. arXiv:2301.00028v1 [physics.flu-dyn]. Dec 30, 2022. 

Also

keyword "bubble" in FonT


keyword "bolla" | "bolle" in Notes (quasistochastic-poetry): 



Keywords: gst, bubble, bubbly suspensions, diffusion, fluctuation




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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. 

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keyword 'chaos' | 'chaotic' in Font



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



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


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martedì 10 gennaio 2023

# brain: how the brain says 'Oops!'

AA << have uncovered how signals from a group of neurons in the brain's frontal lobe simultaneously give humans the flexibility to learn new tasks—and the focus to develop highly specific skills. >>

<< The study's key finding is that the brain uses the same group of neurons for performance feedback in many different situations—whether a person is attempting a new task for the first time or working to perfect a specific skill. >>

<< Part of the magic of the human brain is that it is so flexible, (..) We designed our study to decipher how the brain can generalize and specialize at the same time, both of which are critical for helping us pursue a goal. >> Ueli Rutishauser. ️

️
New Study Reveals How the Brain Says 'Oops!'. Cedars-Sinai Medical Center. May 5, 2022. 

AA << recorded the activity of more than 1000 neurons in the medial frontal cortex of human epilepsy patients while they performed complex cognitive tasks. They found that domain-general and domain-specific performance monitoring neurons were intermixed within this brain region. The population activity gave rise to a geometry that allowed domain-general signals to be read out with more than 90% accuracy on single trials while at the same time retaining the ability to separate different conflict conditions. These results show how the human medial frontal cortex resolves the fundamental trade-off between task generalization and specialization, which is critical for cognitive flexibility. >>
️
Zhongzheng Fu, Danielle Beam, et al. The geometry of domain-general performance monitoring in the human medial frontal cortex. Science. Vol 376, Issue 6593. doi: 10.1126/ science.abm9922. May 6, 2022.

Also

keyword 'cervello' | 'brain' in Notes
(quasi-stochastic poetry)



keyword 'brain' in FonT


keyword 'organoids' in FonT


PS: An image of "oops", not completely spanned in the air, could be this:


Keywords: brain, mind, cervello, mente, oops






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lunedì 9 gennaio 2023

# gst: apropos of instability, bubbles may have unexpected chills

<< Bubbles are ubiquitous, existing in everything from the foam on a beer to party toys for children. Despite this pervasiveness, there are open questions on the behavior of bubbles, such as why some bubbles are more resistant to bursting than others. >>️

AA << created a soap bubble from a mixture made of dishwashing liquid, water, and glycerol. They then measured the soap film’s temperature under a variety of environmental conditions. They found that the film could be up to 8 °C colder than the surrounding air. They also found that glycerol content of the soap film impacted this temperature difference, with films containing more glycerol having higher temperatures. Boulogne (Francois Boulogne) says that such a large temperature difference could impact bubble stability.  >>️

Anna Napolitano. Bubbles Have an Unexpected Chill. Physics 15, s173. Dec 19, 2022. 

Francois Boulogne, Frederic Restagno, Emmanuelle Rio. Measurement of the Temperature Decrease in Evaporating Soap Films. Phys. Rev. Lett. 129, 268001. Dec 19, 2022.

Also

keyword "bubble" in FonT


keyword "bolla" | "bolle" in Notes (quasistochastic-poetry): 



Keywords: gst, bubble, stability, evaporation, burst





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venerdì 30 dicembre 2022

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

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

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

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

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

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



Also

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




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


keyword 'instability' | 'instabilities' in FonT



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


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






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giovedì 22 dicembre 2022

# gst: breakthrough in unstable growth processes, shorter branches can revive when a striking transition of the leading branch reaches the boundary of the system.

<< Transport networks, such as vasculature or river networks, provide key functions in organisms and the environment. They often emerge as a result of unstable growth processes, in which growing branches compete for the available flux. This leads to effective repulsion between the branches and screening of the shorter ones. (AA) show that a striking transition in growth dynamics takes place as the leading branch reaches the boundary of the system. The shorter branches revive then and grow toward the leading one forming loops. These effects are observed both in living and inanimate systems. >>

Stanisław Zukowski, Annemiek Johanna Maria Cornelissen, et al. Finger revival and reconnections near breakthrough in unstable growth processes. arXiv: 2212.08878v1 [physics.flu-dyn]. Dec 17, 2022.

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keyword 'transition' in FonT: 

keyword 'transizione' | 'transition' in Notes (quasi-stochastic poetry): 



Keywords: gst, transition, growth, growth dynamics, transport networks, spatial networks







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mercoledì 21 dicembre 2022

# gst: apropos of transitions, rich behaviors from chimeras or solitary states to traveling waves

AA << study numerically the spatiotemporal dynamics of a ring network of nonlocally coupled nonlinear oscillators, each represented by a two-dimensional discrete-time model of the classical van der Pol oscillator. >>
<< It is shown that the discretized oscillator exhibits a richer behavior, combining the peculiarities of both the original system and its own dynamics. Moreover, a large variety of spatiotemporal structures is observed in the network of discrete van der Pol oscillators when the discretization parameter and the coupling strength are varied. Such regimes as the coexistence of multichimera state/traveling wave and solitary state are revealed for the first time and studied in detail. >>
<< It is established that the majority of the observed chimera/solitary states, including the newly found ones, are transient towards the purely traveling wave mode. The peculiarities of the transition process and the lifetime (transient duration) of the chimera structures and the solitary state are analyzed depending on the system parameters, observation time, initial conditions, and influence of external noise. >>

Elena Rybalova, Sishu Muni, Galina Strelkova. Transition from chimera/solitary states to traveling waves. arXiv: 2212.07990v1 [nlin.AO]. Dec 15, 2022. 

Also

keyword 'transition' | 'transitional' in FonT



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




keyword 'waves' in FonT


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


Keywords: gst, behavior, van der Pol oscillator, transition, chimera state, solitons, solitary state, waves, noise









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