Experiments have shown that self-propelled particles can slide along the surface of a circular obstacle without becoming trapped over long times. Using simulations and theory, we study impact boundary conditions on diffusive transport active in an lattice. We find particle dynamics with sliding result large diffusivities even at high density, unlike classical specular reflection. These are very well described by model based Run-and-Tumble microscopically derived reorientation functions...

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions downwelling fluid (gyrotaxis). It is necessary understand how such biases affect algal dispersion natural industrial flows, especially view growing interest photobioreactors. Motivated by this, we here study gyrotactic laminar turbulent channel flows using direct numerical simulation (DNS) analytical theory Bees Croze...

Active propulsion, as performed by bacteria and Janus particles, in combination with hydrodynamic interaction results the accumulation of at a flat wall. However, microfluidic devices cylindrical pillars sufficiently small radius, self-propelled particles can slide along scatter off surface pillar, without becoming trapped over long times. This nonequilibrium scattering process has been predicted to result large diffusivities, even high obstacle density, unlike that undergo classical...

One of the greatest challenges this century is to employ nature's resources address world's energy, food, water and chemical requirements without further unsettling potentially precarious environmental balance in which we live. The recent resurgence interest green algae for biotechnological applications, such as bioenergy, carbon capture pharmaceuticals, means it vital that understand dynamics suspensions living cells. It widely appreciated mathematics can aid optimization production...

Classical Taylor-Aris dispersion theory is extended to describe the transport of suspensions self-propelled dipolar cells in a tubular flow. General expressions for mean drift and effective diffusivity are determined exactly terms axial moments, compared with an approximation la Taylor. As case, skewness finite distribution biased swimming vanishes at long times. The general can be applied particular models microorganisms, thus used predict diffusion bioreactors, elucidate competing...

There is much current interest in modelling suspensions of algae and other micro-organisms for biotechnological exploitation, many bioreactors are tubular design. Using generalized Taylor dispersion theory, we develop a population-level swimming-advection-diffusion model vertical pipe flow. In particular, combination gravitational viscous torques acting on individual cells can affect their swimming behaviour, which termed gyrotaxis. This typically leads to local cell drift diffusion...

Suspensions of microswimmers are a rich source fascinating new fluid mechanics. Recently we predicted the active pipe flow dispersion gyrotactic microalgae, whose orientation is biased by gravity and shear. Analytical theory predicts that these swimmers disperse in markedly distinct manner from passive tracers (Taylor dispersion). Dispersing display non-zero drift effective diffusivity non-monotonic with Péclet number. Such predictions agree numerical simulations, but hitherto have not been...

The recent interest in using microorganisms for biofuels is motivation enough to study bioconvection and cell dispersion tubes subject imposed flow. To optimize light nutrient uptake, many swim directions biased by environmental cues (e.g. phototaxis algae chemotaxis bacteria). Such taxes inevitably lead accumulations of cells, which, as have a density different the fluid, can induce hydrodynamic instabilites. large-scale fluid flow spectacular patterns that arise are termed bioconvection....

The exchange of diffusive metabolites is known to control the spatial patterns formed by microbial populations, as revealed recent studies in laboratory. However, matrices used, such agarose pads, lack structured geometry many natural habitats, including soil or on surfaces plants animals. Here we address important question how may exchanges and interaction. We model mathematically mutualistic interactions within a minimal unit structure: two growing reservoirs linked channel through which...

We explore theoretically the modifications to interactions between charged surfaces across an ionic solution caused by presence of dielectric polymers. Although chains are neutral, polymer physics and electrostatics coupled; intrasurface electric fields polarize any low-permittivity species (e.g., polymer) dissolved in a high-permittivity solvent water). This coupling enhances depletion from increases screening electrostatic with respect model which treats polymeric effects as independent....

Microbial communities are of considerable significance for biogeochemical processes, the health both animals and plants, biotechnological purposes. A key feature microbial interactions is exchange nutrients between cells. Isotope labelling followed by analysis with secondary ion mass spectrometry (SIMS) can identify nutrient fluxes heterogeneity substrate utilisation on a single cell level. Here we present novel approach that combines SIMS experiments mechanistic modelling to reveal...

Researchers experimentally characterize the response of helically swimming alga to oscillatory shear flows and find that algal trajectories orient perpendicular flow-shear plane. Their results have implications for both active suspension rheology design novel cell processing methods.

The experimental characterisation of the swimming statistics populations microorganisms or artificially propelled particles is essential for understanding physics active systems and their exploitation. Here, we construct a theoretical framework to extract information on three-dimensional motion micro-swimmers from Intermediate Scattering Function (ISF) obtained Differential Dynamic Microscopy (DDM). We derive expressions ISF helical oscillatory breaststroke swimmers, test by applying it...

A recent theory by Feigel predicts the finite transfer of momentum from a quantum vacuum to fluid placed in strong perpendicular electrical and magnetic fields. The arises because optically anisotropic magnetoelectric response induced After summarizing Feigel's original assumptions derivation (corrected trivial mistakes), we rederive same result simpler route, validating semiclassical approach. We then derive stress exerted on that, if hypothesis is correct, should induce Poiseuille flow...

Abstract Bacteria can chemotactically migrate up attractant gradients by controlling run-and-tumble motility patterns. In addition to this well-known chemotactic behaviour, several soil and marine bacterial species perform chemokinesis; they adjust their swimming speed according the local concentration of chemoeffector, with higher at concentration. A field then induces a spatially varying speed, which results in drift towards lower concentrations—contrary created chemotaxis. Here, explore...

The light environment controls the swimming of microalgae through a light-seeking and avoiding behaviour, which is known as phototaxis. In this work, we exploit phototaxis to control migration concentration populations soil microalga Chlamydomonas reinhardtii . By imaging suspension these in cuvette illuminated from above by blue light, study how changes stability demonstrate thin, porous layer at top prevents phototaxing sinking, leading up-concentration region layer. We discuss potential...

Abstract Microbial communities are of considerable significance for biogeochemical processes, the health both animals and plants, biotechnological purposes. A key feature interactions between microbes is exchange nutrients cells. Isotope labelling followed by analysis with secondary ion mass spectrometry (SIMS) can identify nutrient fluxes heterogeneity substrate utilisation on a single cell level. Here we present novel approach that combines SIMS mechanistic model to reveal otherwise...

A recent theory posits that the quantum vacuum can transfer momentum to magnetoelectric media (the Feigel effect). Several related theories of have since been proposed. Neither these, nor original observed experimentally, existence a effect remaining highly contentious. Some investigations predict measurable effect; others conclude is not physically possible. Most analyses, including Fiegel theory, do model experimentally realistic geometries and boundary conditions. I recently provided an...