A rheological approach to identify efficient biopolymer producing bacteria.

This study investigates the relationship between collective motion and propulsion of bacterial consortia and their biopolymer production efficiency. Rheological tests were conducted for suspensions of two different methanotrophic bacterial consortia obtained after enrichment of sediment samples from mangrove sites in Brazil. We considered the linear viscoelasticity region and analyzed the values of storage and loss moduli as functions of days of cultivation, for different values of the volume fraction. The suspensions' rheological behaviors reflected the bacterial growth stage. We found that the formation of structures over time in some types of consortia can hinder the movement of bacteria in the search for nutrients. The change in complex viscosity of the two consortia followed a different and rich behavior that appears to be closely related to their capacity to capture methane. Our analysis showed a possible correlation between collective motion, viscosity reduction, and biopolymer production. The pieces of evidence from this study suggest that the efficiency of bacterial motion is directly related to biopolymer production, and this could facilitate the process of identifying the best consortium of biopolymer producing bacteria.

Prediction of jet mixing noise with Lighthill's Acoustic Analogy and geometrical acoustics.

A computational aeroacoustics prediction tool based on the application of Lighthill's theory is presented to compute noise from subsonic turbulent jets. The sources of sound are modeled by expressing Lighthill's source term as two-point correlations of the velocity fluctuations and the sound refraction effects are taken into account by a ray tracing methodology. Both the source and refraction models use the flow information collected from a solution of the Reynolds Averaged Navier-Stokes equations with a standard k-epsilon turbulence model. By adopting the ray tracing method to compute the refraction effects a high-frequency approximation is implied, while no assumption about the mean flow is needed, enabling the application of the method to jet noise problems with inherently three-dimensional propagation effects. Predictions show good agreement with narrowband measurements for the overall sound pressure levels and spectrum shape in polar angles between 60° and 110° for isothermal and hot jets with acoustic Mach number ranging from 0.5 to 1.0. The method presented herein can be applied as a relatively low cost and robust engineering tool for industrial optimization purposes.