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Multiferroic ceramic composites are promising multifunctional materials owing to their ability to simultaneously exhibit electric and magnetic control, making them suitable for a wide range of technological applications. This study presents a comprehensive investigation of BaZr0.15Ti0.85O3-ZnFe2O4(BZT-ZF) multiferroic composites using dielectric analysis, impedance spectroscopy, electric modulus studies, and Raman spectroscopy. Composites of BZT1-x-ZFx were prepared using ferroelectric BaZr0.15Ti0.85O3 and ferromagnetic ZnFe2O4 through solid state reaction method with different mol% fractions of x (where x = 0.03, 0.05, 0.07 and 0.10). The results reveal that samples exhibit a tetragonal perovskite structure coexisting with a cubic spinel ferrite phase. The existence of ferroelectric and ferromagnetic phases in the composites is confirmed by Raman spectroscopy. Impedance spectroscopy, analyzed through Cole-Cole plots, reveals a reduction in grain boundary effects with increasing temperature. This behavior is likely attributed to the formation of oxygen vacancies during high-temperature sintering, which influences the impedance at the grain–grain boundary interfaces. 

Abstract The effect of thermal stress on beneficial symbiosis, in the face of rapid climate change, remains poorly understood. We investigate this using the model system, Euprymna scolopes (Es), the Hawaiian bobtail squid, and its bioluminescent symbiont, Vibrio fischeri (Vf), which enables the squid to camouflage itself through counter-illumination. Successful colonization of the squid by Vf must occur hours after hatching and is mediated by fluid flow due to respiration within the squid mantle cavity. To study this process, we develop a mathematical model using the method of regularized stokeslets to simulate the flow and resulting bacterial trajectories within the squid. We explore how thermal stress, mediated by physiological changes in respiration, ciliary dynamics and internal geometry, affects early colonization by analysing the time bacteria spend in regions crucial to the establishment of symbioses in these simulations. A variance-based sensitivity analysis of physiologically relevant parameters on these metrics demonstrated that changes in the breath cycle significantly affect and reduce the time bacteria spend in the critical zone within the squid, hindering colonization. 

Abstract Bacteria often develop distinct phenotypes to adapt to environmental stress. In particular, they can produce biofilms, dense communities of bacteria that live in a complex extracellular matrix. While previous studies have investigated how bacterial biofilms are regulated under laboratory conditions, they have not considered (1) the data requirements necessary to estimate model parameters and (2) how bacteria respond to recurring stressors in their natural habitats. To address (1), we adapted a mechanistic population model to explore the dynamics of biofilm formation in the presence of predator stress, using synthetic data. We used a Maximum Likelihood Estimation framework to measure crucial parameters underpinning the biofilm formation dynamics. We used genetic algorithms to propose an optimal data collection schedule that minimised parameter identifiability confidence interval widths. Our sensitivity analysis revealed that, within the explored regimes, we could simplify the binding dynamics and eliminate biofilm detachment. To address (2), we proposed a structured version of our model to capture the long-term behaviour and evolutionary selection. In our extended model, the subpopulations feature different maximal rates of biofilm formation. We compared the selection under different predator types and amounts and identified key parameters that affected the speed of selection via sensitivity analysis. 

We study the mixing of passive scalars in a velocity field generated by selected-eddy simulations (SES), an approach where only a randomly selected subset of spectrally distributed modes obey Navier–Stokes dynamics. The Taylor Reynolds number varies from 140 to 400 and the Schmidt number ($$Sc$$) varies from 0.25 to 1. By comparing the results with direct numerical simulations (DNS), we show that most statistics are captured with as low as$$0.5\,\%$$of Navier–Stokes modes in the velocity field. This includes scalar gradients, spectra, structure functions and their departures from classical scaling due to intermittency. The results suggest that all modes need not be resolved to accurately capture turbulent mixing for$$Sc\leqslant 1$$scalars. 

A single particle representation of a self-propelled microorganism in a viscous incompressible fluid is derived based on regularised Stokeslets in three dimensions. The formulation is developed from a limiting process in which two regularised Stokeslets of equal and opposite strength but with different size regularisation parameters approach each other. A parameter that captures the size difference in regularisation provides the asymmetry needed for propulsion. We show that the resulting limit is the superposition of a regularised stresslet and a potential dipole. The model framework is then explored relative to the model parameters to provide insight into their selection. The particular case of two identical particles swimming next to each other is presented and their stability is investigated. Additional flow characteristics are incorporated into the modelling framework with in the addition of a rotlet double to characterise rotational flows present during swimming. Lastly, we show the versatility of deriving the model in the method of regularised Stokeslets framework to model wall effects of an infinite plane wall using the method of images. 

AbstractPrevious theoretical and simulation results indicate that anisotropic porous materials have the potential to reduce turbulent skin friction in wall-bounded flows. This study experimentally investigates the influence of anisotropy on the drag response of porous substrates. A family of anisotropic periodic lattices was manufactured using 3D printing. Rod spacing in different directions was varied systematically to achieve different ratios of streamwise, wall-normal, and spanwise bulk permeabilities ($$\kappa _{xx}$$ ${\kappa }_{\mathrm{xx}}$,$$\kappa _{yy}$$ ${\kappa }_{\mathrm{yy}}$, and$$\kappa _{zz}$$ ${\kappa }_{\mathrm{zz}}$). The 3D printed materials were flush-mounted in a benchtop water channel. Pressure drop measurements were taken in the fully developed region of the flow to systematically characterize drag for materials with anisotropy ratios$$\frac{\kappa _{xx}}{\kappa _{yy}} \in [0.035,28.6]$$ $\frac{{\kappa }_{\mathrm{xx}}}{{\kappa }_{\mathrm{yy}}}\in [0.035,28.6]$. Results show that all materials lead to an increase in drag compared to the reference smooth wall case over the range of bulk Reynolds numbers tested ($$\hbox {Re}_b \in [500,4000]$$ ${\text{Re}}_b\in [500,4000]$). However, the relative increase in drag is lower for streamwise-preferential materials. We estimate that the wall-normal permeability for all tested cases exceeded the threshold identified in previous literature ($$\sqrt{\kappa _{yy}}^+> 0.4$$ ${\sqrt{{\kappa }_{\mathrm{yy}}}}^{+}>0.4$) for the emergence of energetic spanwise rollers similar to Kelvin–Helmholtz vortices, which can increase drag. The results also indicate that porous walls exhibit a departure from laminar behavior at different values for bulk Reynolds numbers depending on the geometry. Graphical abstract