📰 Explain waves and vortices in subcritical active matter

Active matter consists of individual entities that convert energy into work, causing it to move, and allowing it to self-regulate due to their mutual interactions. Many living systems can be seen under this corner (In geometry, the general concept of angle comes in several concepts…), but also, increasingly, collections of synthetic, active or cell-derived microparticles. Theoretical approach to issue (Material is the substance that makes any object that has a tangible reality. …) Active does not benefit from general correct results when in balance Thermodynamics (There are two simple ways to define thermodynamics: thermodynamics…)but retains the main themes: symmetries, conservation laws, and transitions Stage (The word phase can have several meanings, it is used in several areas and …) Crucial, but the emerging properties of the active ingredient are often novel, offering new waysself-regulation (Self-regulation is an ascending order phenomenon, and it goes in the opposite direction of…) Moving (The word dynamic is often used to designate or define something related to movement. It is…).

In a recent article in PNASHuggs Chateaux (IRAMIS / SPECIFICATIONS), Xia-qing Shi and the group of Tian Hui Zhang (Suzhou University) have shown that a system of subcritical active colloids (that is, near the threshold of their setting in motion) presents astonishingly new kinds of self-organized collective dynamics, such as isolated self-organizing vortices consisting of thousands of particles.

The active substance systems studied generally consist of organisms (biofilaments, cells, colloidal particles, robots, animals, etc.) that move, even when alone or isolated. Their collective characteristics are fascinating and their study allows us to better understand how they workenergy (In the general sense, energy defines everything that allows you to do work, generate energy, etc.) Injected into the system is converted into action.

The results of his studies Hugo Chatti (IRAMIS / SPECIFICATIONS) and Xia-qing Shi, associated with the group of Tian Hui Zhang (Soochow University) and recently published in PNAS, show that isolated particles that are potentially active but without practically appreciable motion can exhibit properties oforganisation (the organization is) Collectively specific and wonderful because ofinteraction (An interaction is the exchange of information, influences, or energy between two agents within…) with peers. By combining experiences, theory (The word theory comes from the Greek word theorein, which means “to contemplate, observe, …) and numerical simulations, it is clear that such a subcritical active substance can be produced using “Quincke rollers”: with his pioneering work (1896), Georg Hermann Quincke* showed that insulating colloidal particles immersed in liquid (The liquid is a completely deformable medium of matter. We collect under this…) driver and subject to electric field (In physics, an electric field is a field created by particles…) current intensity greater than threshold Eagainst It suffers from instability, which leads to its rotation in the liquid. For denser particles of liquid, the particles begin to roll at the bottom of the container in a random direction.

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This collective dynamic of Quincke rolls* It has already been studied in the supercritical system E > Eagainst. Here it is clear that amazing collective phenomena also appear in a subcritical system, i.e. for a area (The field corresponds to the idea of ​​the given space 🙂 less than E.against. In this system a certain dynamic is possible, because particles that are close to each other can begin to roll even with respect to E c. Reported organized phenomena include waves (A wave is the propagation of a disturbance that results in a reverse change in its path…) FromActivity (The term activity can refer to a profession.) Fast and stable isolated vortices of arbitrary size made up of thousands of particles moving at the same time Speed (distinguish 🙂.

Experimental results: (a) Schematic diagram of the experimental device. (BJ) Various views where the particles are colored according to their speed (according to the color code mentioned on the right). The said spatial scale is 100 µm. The particles are left at rest white (White is the color of an object heated to about 5000°C (see…). The numbers in the top row appear A density (Density or relative density of an object is the ratio of its density to…) of high particles (BE, Φ ≃ 0.4) and are arranged from left to right by increasing the value of E/Ec. Likewise for the bottom row where the particle density is low (FJ, Φ0.2).

Different configurations are obtained depending on the E/E . valuesagainst: Figures B and F show resting clusters with a local hexagonal arrangement 0.65 eagainst. (C) wide mysterious (A wave is an oscillatory movement of the surface of an ocean, sea or lake. …) for activity at E = 0.89 Eagainst. (D) Subcritical flocking in Widely (The grand ladder, also called the aerial ladder or automatic ladder, is…) at E = 0.98 eastagainst. (e) Subcritical flow at E = 0.98 E.against. (G) The localized activity at E = 0.9 E.against. (H) A self-stable tourbillon insulated at E = 0.948 E.against. (i) A free-standing loop insulated at E = 0.968 E.against. (j) snowflake spiral (In mathematics, a helix is ​​a curve that starts at a central point and then exits…) at E = 0.98 eastagainst.

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These fascinating collective dynamics cannot be explained by the simple models that normally apply to such systems. A new type of form must be submitted to calculatetogether (In set theory, a set intuitively identifies a set…) observed phenomena.

Modeling results: (AE) Typical configurations in the 960 µm area with periodic boundary conditions. Disks with a diameter of 10 µm are centered on the particle positions. The stationary particles are white while the moving particles are colored according to their speed with the color code mentioned in (E). (a) The activity waves propagate from left to right in a dense system (mc = 8.9, Φ = 0.33, i.e. ~ 3900 particles). (b) Subcritical flow regime in a dense system with particles (~5530) moving mainly from right to left (mc = 3, Φ = 0.47). (CE) Formation of a vortex and ring structure (Φ = 0.12, 1433 particles). (against) I have seen (Sight is the meaning that allows the observation and analysis of the environment through reception and …) instantaneous in a transient state (mc = 3). (d) The final vortex including most of the system particles (mc = 0.5). (e) Final ring composition including most of the system particles (mc = 0.05).

Figures illustrating the experimental and modeling results Experiment and modeling thus show all the richness of the studied system, in which a description of the collective properties of the considered active particles is obtained, it is necessary, after the interactions between particles is usually considered in simple models of the active substance, to take into account the liquid that surrounds Their and local configs.

This study is currently ongoing withexploration (Exploration is searching with the intention of discovering something unknown.) experimental (In art, these are creative approaches based on questioning dogmas…) And the Digital (Digital information is information…) Several promising methods: the application of a periodically modified field, the simultaneous use of several particle sizes, etc. This makes it possible to differ more than one Adjust (A parameter in a broad sense is an element of information to be taken into account…) From the value of the simple static electric field, revealing more dynamic self-regulation patterns.

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Activity waves and free-standing vortices in subcritical Quincke reel sets.
Zeng Tao Leo (Liu (Chinese: 柳, pinyin: liǔ xiù) is a camel on the moon…)and Yan Shi, Yongfeng Zhao, Hugues Chaté, Xia-qing Shi and Tian Hui Zhang, PNAS 118(40) (2021) e2104724118.

* Quincke rolls: the structures noted in 1896 by Georg Hermann Quincke, brother of Heinrich Quincke, first described in 1882 by angioedema, or angioedema.

Z.T. Liu, Y. Shi, Y. Zhao, H. Chaté, X.-q. Shi, and TH Zhang, Center for Soft Condensed Matter Physics and Interdisciplinary Research, Socho UniversityAnd the Suzhou (Suzhou (simplified Chinese: 苏州; traditional Chinese: …) 215006, China.

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