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

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

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

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

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

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

Also

keyword 'drop' | 'droplet' in FonT

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

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

# gst: 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. 

https://www.sciencedaily.com/releases/2021/08/210811131503.htm

<< 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.

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.085103  

# gst: weird Nature; randomly arranged nanowire networks seem to behave, at the edge of chaos, like cortical neuronal cultures

<< an artificial network of nanowires can be tuned to respond in a brain-like way when electrically stimulated. >>️

<< If the signal stimulating the network was too low, then the pathways were too predictable and orderly and did not produce complex enough outputs to be useful. If the electrical signal overwhelmed the network, the output was completely chaotic and useless for problem solving. The optimal signal for producing a useful output was at the edge of this chaotic state. >>️

<< Some theories in neuroscience suggest the human mind could operate at this edge of chaos, or what is called the critical state, (..) Some neuroscientists think it is in this state where we achieve maximal brain performance. (..) What's so exciting about this result is that it suggests that these types of nanowire networks can be tuned into regimes with diverse, brain-like collective dynamics, which can be leveraged to optimize information processing. >> Zdenka Kuncic.️

<< In the nanowire network the junctions between the wires allow the system to incorporate memory and operations into a single system. This is unlike standard computers, which separate memory (RAM) and operations (CPUs). >>

<< These junctions act like computer transistors but with the additional property of remembering that signals have traveled that pathway before. As such, they are called 'memristors', >> Joel Hochstetter.

️

'Edge of chaos' opens pathway to artificial intelligence discoveries. University of Sydney. Jun 29, 2021.

https://phys.org/news/2021-06-edge-chaos-pathway-artificial-intelligence.html

Joel Hochstetter, Ruomin Zhu, et al. Avalanches and edge-of-chaos learning in neuromorphic nanowire networks. Nat Commun 12, 4008. doi: 10.1038/ s41467-021-24260-z. Jun 29, 2021.

https://www.nature.com/articles/s41467-021-24260-z

# gst: critical points seem to act behind the complex behavior of collectives.

<< Current experiments support the controversial hypothesis that a well-known concept in physics—a critical point—is behind the striking behavior of collective animal systems. >>

AA << showed that light-controlled microswimming particles can be made to organize into collective states such as swarms and swirls. By studying the particles fluctuating between these states, they provide evidence for critical behavior—and support for a physical principle underlying the complex behavior of collectives.>>

<< What we observed is that the system can make sudden transitions from one state to the other, which demonstrates the flexibility needed to react to an external perturbation like a predator, (..) and provides clear evidence for a critical behavior. >> Clemens Bechinger

<< Through very simple interactions, they have shown that you can tune a physical system to a collective state - criticality - of balance between order and disorder. >> Iain Couzin

Physics principle explains order and disorder of swarms. University of Konstanz. Jun 11, 2020.

https://phys.org/news/2020-06-physics-principle-disorder-swarms.html

Bauerle T., Loffler R.C., Bechinger C. Formation of stable and responsive collective states in suspensions of active colloids. Nat Commun 11, 2547. doi: 10.1038/ s41467-020-16161-4. May 21, 2020.

https://www.nature.com/articles/s41467-020-16161-4

Also 

keyword 'self-assembly' in FonT

https://flashontrack.blogspot.com/search?q=self-assembly

# chem: bizarre phase transitions in tantalum disulfide, it should be a conducting metal, but in the real world, it acts like an insulator

<< It has long been known that  crystalline materials should be good conductors when they have an odd number of electrons in each repeating cell of the structure, but may be poor conductors when the number is even. However, sometimes this formula does not work, with one case being "Mottness," a property based on the work of Sir Nevill Mott. According to that theory, when there is strong repulsion between electrons in the structure, it leads the electrons to become "localized"-paralyzed, in other words-and unable to move around freely to create an electric current. >>

<< For the current study, (..) the research group decided to look at tantalum disulfide, a material with 13 electrons in each repeating structure, which should therefore make it a conductor. However, it is not, and there has been controversy over whether this property is caused by its "Mottness" or by a pairing structure. >>

<< The exact nature of the insulating state and of the phase transitions in tantalum disulfide have been long-standing mysteries, and it was very exciting to find that Mottness is a key player, aside from the pairing of the layers. This is because theorists suspect that a Mott state could set the stage for an interesting phase of matter known as a quantum spin liquid. >> Christopher Butler. 

Jens Wilkinson. 'Tantalizing' clues about why a mysterious material switches from conductor to insulator. 

 RIKEN. May 18, 2020.

https://phys.org/news/2020-05-tantalizing-clues-mysterious-material-conductor.html   

AA << also observe the collapse of Mottness at an extrinsically re-stacked termination, demonstrating that the microscopic mechanism of insulator-metal transitions lies in degrees of freedom of inter-layer stacking. >>

C. J. Butler, M. Yoshida, et al. Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2. Nat Commun 11, 2477. doi: 10.1038/ s41467-020-16132-9. May 18, 2020

https://www.nature.com/articles/s41467-020-16132-9   

Also

Quantum spin liquid. 

https://en.m.wikipedia.org/wiki/Quantum_spin_liquid

# gst: exploring the lifespan of a liquid droplet

<< Current theories state that the droplet's diameter-squared decreases in proportion to time (classical law); however, this period only accounts for a small portion of the drop's evolution. As the diameter approaches the unobservable micro- and nano-scale, molecular dynamics have to be used as virtual experiments and these show a crossover to a new behaviour, with the diameter now reducing in proportion to time (nano-scale law). >>

<< It is fascinating that intuition based on everyday observations are a hindrance when attempting to understand nanoscale flows, so that, as in this research, one has to lean on theory to enlighten us. >>  James Sprittles.

The lifespan of an evaporating liquid drop. University of Warwick. Oct 10, 2019.     https://m.phys.org/news/2019-10-lifespan-evaporating-liquid.html

Rana A.S., Lockerby D.A., Sprittles J.E.  Lifetime of a Nanodroplet: Kinetic Effects and Regime Transitions. Phys. Rev. Lett. 123, 154501 Oct 9, 2019.     https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.154501