Active fluids exhibit spontaneous flows with complex spatiotemporal structure, which have been observed in bacterial suspensions, sperm cells, cytoskeletal suspensions, self-propelled colloids, and ...cell tissues. Despite occurring in the absence of inertia, chaotic active flows are reminiscent of inertial turbulence, and hence they are known as active turbulence. Here, we survey the field, providing a unified perspective over different classes of active turbulence. To this end, we divide our review into sections for systems with either polar or nematic order, and with or without momentum conservation (wet or dry). Comparing to inertial turbulence, we highlight the emergence of power-law scaling with either universal or nonuniversal exponents. We also contrast scenarios for the transition from steady to chaotic flows, and we discuss the absence of energy cascades. We link this feature to both the existence of intrinsic length scales and the self-organized nature of energy injection in active turbulence, which are fundamental differences from inertial turbulence. We close by outlining the emerging picture, remaining challenges, and future directions.
This paper is devoted to study the thermodynamic topological defects, Joule–Thomson (J−T) and Maxwell’s equal area law of Phantom RN AdS black holes (BHs). The inversion temperatures and inversion ...curves are obtained and by using the isenthalpic curves in the temperature–pressure (T−P) plane to locate the cooling and heating regions. Using Maxwell’s equal-area law, we select different independent conjugate variables to study the phase transitions of Phantom RN AdS BHs. We find that phase transition rely on the electric potential and horizon radius of the BH when its charge is constant. Phase transition of Phantom RN AdS BH are proportional to the ratio of event horizon to its cosmological constant, where the latter is assumed to be constant. Moreover, we consider the Phantom RN AdS BH as defects with a topological nature within thermodynamic domain and examine the local and global topology by computing the winding numbers at the defects, which concludes that the overall topological charge is either equal to 0 or 1.
•Study of thermodynamic topological defects in Phantom RN AdS black holes (BHs).•Determination of inversion temperatures and curves, locating cooling and heating regions.•Application of Maxwell’s equal-area law to analyze phase transitions using different conjugate variables.•Phase transitions in Phantom RN AdS BHs depend on electric potential and horizon radius under constant charge.•Examination of thermodynamic topology and computation of topological charges for critical points.
Defect dynamics in active nematics Giomi, Luca; Bowick, Mark J; Mishra, Prashant ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
11/2014, Volume:
372, Issue:
2029
Journal Article
Peer reviewed
Open access
Topological defects are distinctive signatures of liquid crystals. They profoundly affect the viscoelastic behaviour of the fluid by constraining the orientational structure in a way that inevitably ...requires global changes not achievable with any set of local deformations. In active nematic liquid crystals, topological defects not only dictate the global structure of the director, but also act as local sources of motion, behaving as self-propelled particles. In this article, we present a detailed analytical and numerical study of the mechanics of topological defects in active nematic liquid crystals.
Topological Soliton Arrays
In article number 2201749, Ivan Smalyukh, Dong Ki Yoon, and co‐workers report a new way to rationalize the real‐time observation of the generation and transformation of ...topological solitons using cholesteric liquid crystals confined in patterned substrates. The line textures are cholesteric fingers of the third kind (CF‐3s), in which 1D topological solitons called twist walls are stabilized by two twist disclination lines, which are nucleated and grown from the air pockets on the top view. This image represents that the CF‐3s array is formed like an infinite maze.
A bifunctional graphene catalyst with abundant topological defects is achieved via the carbonization of natural gelatinized sticky rice to probe the underlying oxygen electrocatalytic mechanism. A ...nitrogen‐free configuration with adjacent pentagon and heptagon carbon rings is revealed to exhibit the lowest overpotential for both oxygen reduction and evolution catalysis. The versatile synthetic strategy and novel insights on the activity origin facilitate the development of advanced metal‐free carbocatalysts for a wide range of electrocatalytic applications.
Electronic states at domain walls in bilayer graphene are studied by analyzing their four- and two-band continuum models, by performing numerical calculations on the lattice, and by using quantum ...geometric arguments. The continuum theories explain the distinct electronic properties of boundary modes localized near domain walls formed by interlayer electric field reversal, by interlayer stacking reversal, and by simultaneous reversal of both quantities. Boundary mode properties are related to topological transitions and gap closures, which occur in the bulk Hamiltonian parameter space. The important role played by intervalley coupling effects not directly captured by the continuum model is addressed using lattice calculations for specific domain wall structures.
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