A multiple-relaxation-time lattice-boltzmann model for bacterial chemotaxis: effects of initial concentration, diffusion, and hydrodynamic dispersion on traveling bacterial bands

Modeling the Migration and Growth of Shewanella Oneidensis MR-1 in a Diffusion-Dominated Microfluidic Gradient Chamber Under the Influence of an Antibiotic Concentration Gradient

Motility and chemotaxis allow bacteria to migrate from areas that become depleted in energy yielding substrates to more favorable locations, possibly enhancing the biodegradation of pollutants in soil and groundwater. However, in some cases substrates are co-mingled with one or more toxic solutes that inhibit pollutant degradation and/or microbial growth, and the impacts on motility and chemotaxis represent a knowledge gap. In this study, a one-dimensional diffusion reaction model is developed and used to simulate dissimilatory biological reduction of nitrate to ammonia (DNRA) presented in a previously published microfluidic gradient chamber (MGC) experiment, where spatial abundances of Shewanella oneidensis MR-1 cells were recorded over 5 days in a diffusion limited porous media domain as it degraded nitrate and lactate introduced from opposite boundaries, and at one boundary co-mixed with the antibiotic ciprofloxacin. The model considers S. oneidensis chemotaxis toward nitrate and nitrite, random motility, and growth inhibition by ciprofloxacin. Parameters were adjusted within ranges commonly reported in the literature to obtain results that agreed with the data. Simulation results indicate that motility and not chemotaxis, in combination with inhibition of cell growth by ciprofloxacin, controls the distribution of cells in the toxic region (containing ciprofloxacin) of the MGC. This suggests that cell motility may facilitate nitrate removal in soil and groundwater by enabling microorganisms to migrate toward nitrate contaminated regions with elevated antibiotic concentrations.

A State of the Art Review on Sensible and Latent Heat Thermal Energy Storage Processes in Porous Media: Mesoscopic Simulation

Sharing renewable energies, reducing energy consumption and optimizing energy management in an attempt to limit environmental problems (air pollution, global warming, acid rain, etc.) has today become a genuine concern of scientific engineering research. Furthermore, with the drastic growth of requirements in building and industrial worldwide sectors, the need for proper techniques that allow enhancement in the thermal performance of systems is increasingly being addressed. It is worth noting that using sensible and latent heat storage materials (SHSMs and phase change materials (PCMs)) for thermal energy storage mechanisms can meet requirements such as thermal comfort in buildings when selected correctly. However, as the operating temperature changes, a series of complex technical issues arise, such as heat transfer issues, leaks, corrosion, subcooling, supercooling, etc. This paper reviews the most recent research advances in the area of sensible and latent heat storage through the porous media as potential technology while providing useful information for researchers and engineers in the energy storage domain. To this end, the state and challenges of PCMs incorporation methods are drawn up, and an updated database of various research is provided while discussing the conclusions concerning the sensible and latent heat storage in porous media, their scopes of application and impact on energy consumption. In the light of this non-exhaustive review, it turns out that the adoption of porous matrices improves the thermal performance of systems, mitigates energy consumption and drops CO2 emissions while ensuring thermal comfort within buildings. In addition, at the representative elementary volume (REV) and pore scales, the lattice Boltzmann method (LBM) is examined as an alternative method to the commonly used, traditional numerical methods. These two approaches are compared based on results available in the literature. Through these means, their ability to handle latent and sensible heat storage process in a porous medium is demonstrated. To sum up, to be more complete, perspectives of sensible and latent energy storage technologies are covered.

Tuning chemotactic and diffusiophoretic spreading via hydrodynamic flows

The transport of microorganisms by chemotaxis is described by the same "log-sensing" response as colloids undergoing diffusiophoresis, despite their different mechanistic origins. We employ a recently-developed macrotransport theory to analyze the advective-diffusive transport of a chemotactic or diffusiophoretic colloidal species (both referred to as "colloids") in a circular tube under a steady pressure-driven flow (referred to as hydrodynamic flow) and transient solute gradient. First, we derive an exact solution to the log-sensing chemotactic/diffusiophoretic macrotransport equation. We demonstrate that a strong hydrodynamic flow can reduce spreading of solute-repelled colloids, by eliminating super-diffusion which occurs in an otherwise quiescent system. In contrast, hydrodynamic flows always enhance spreading of solute-attracted colloids. Second, we generalize the exact solution to show that the above tunable spreading phenomena by hydrodynamic flows persist quantitatively for decaying colloids, as may occur with cell death, for example. Third, we examine the spreading of chemotactic colloids by employing a more general model that captures a hallmark of chemotaxis, that log-sensing occurs only over a finite range of solute concentration. Apart from demonstrating for the first time the generality of the macrotransport theory to incorporate an arbitrary chemotactic flow model, we reveal via numerical solutions new regimes of anomalous spreading, which match qualitatively with experiments and are tunable by hydrodynamic flows. The results presented here could be employed to tailor chemotactic/diffusiophoretic colloid transport using hydrodynamic flows, which are central to applications such as oil recovery and bioremediation of aquifers.