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Complex and active fluids find broad applications in flows through porous materials. Nontrivial rheology can couple to porous microstructure leading to surprising flow patterns and associated transport properties in geophysical, biological, and industrial systems. Viscoelastic instabilities are highly sensitive to pore geometry and can give rise to chaotic velocity fluctuations. A number of recent studies have begun to untangle how the pore-scale geometry influences the sample-scale flow topology and the resulting dispersive transport properties of these complex systems. Beyond classical rheological properties, active colloids and swimming cells exhibit a range of unique properties, including reduced effective viscosity, collective motion, and random walks, that present novel challenges to understanding their mechanics and transport in porous media flows. This review article aims to provide a brief overview of essential, fundamental concepts followed by an in-depth summary of recent developments in this rapidly evolving field. The chosen topics are motivated by applications, and new opportunities for discovery are highlighted. [ABSTRACT FROM AUTHOR]

The present work demonstrates the effect of the grain size on electrocaloric and pyroelectric properties in BaTiO3-based ceramics prepared by a chemical coating method and then sintered in a reducing atmosphere at different temperatures. In a grain size of 136 ± 50 nm to 529 ± 245 nm, the electrocaloric temperature change increases from 0.30 K to 0.63 K under the electric field of 4 MV/m at the ferroelectric–paraelectric phase transition. The corresponding entropy change, heat extraction capacity, coefficient of performance, and electrocaloric strength exhibit a twofold increase (i.e., 0.31 J/kg K–0.75 J/kg K, 148 J/kg–303 J/kg, 7–14, and 0.0075 K cm/kV–0.016 K cm/kV, respectively). The effects of the grain size on the pyroelectric properties are established from the pyroelectric coefficient and the associated pyroelectric figures of merit (FOMs). The pyroelectric coefficient and pyroelectric FOMs exhibit about a fivefold increase with the increasing grain size. The pyroelectric energy harvesting is calculated for the Olsen cycle. The energy harvesting capabilities enhance from ∼96 kJ/m3 to ∼135 kJ/m3 when the cycle is operated at temperatures between 303 K and 423 K and an electric field between 1 MV/m and 4 MV/m. The results show that the increase in the grain size significantly improves the electrocaloric and pyroelectric properties. Furthermore, it is established that the pyroelectric properties are more sensitive to the grain size as compared to the electrocaloric effect when ceramics are prepared by the chemical coating-cum-sintering route. In summary, the present study suggests that microstructure control in BaTiO3 fabrication with the enhanced grain size can be an effective approach to enhance the pyroelectric and electrocaloric properties. [ABSTRACT FROM AUTHOR]

An analytical formalism of whistler pumped free electron laser (FEL) with tapered magnetic field is developed. The tapering raises the efficiency of the device to 7% for typical parameters. The frequency and power of the FEL can be controlled by tuning the plasma density and/or magnetic field also by increasing the energy of electron beam. The angle of injection of electron beam is very crucial for higher efficiency of FEL. Presence of plasma ensures the space charge and current neutralization and larger power handling capacity of the device. [ABSTRACT FROM AUTHOR]