Africa RISING: Innovation for development highlights

Poster prepared for a share fair, Addis Ababa, May 201

Measurements of the scattering characteristics of sediment suspensions with different mineralogical compositions

Acoustic studies of suspended sediments often assume the dominant mineral in suspension is quartz, the density and intrinsic scattering properties of which are implemented when inverting acoustic backscatter data collected at sea. However, compositional analysis studies of suspended and sea-bed particulate material show a wide range of mineral species contribute to the inorganic fraction of sediments in the marine environment. Whilst no theoretical framework exists to predict the acoustic properties of irregularly shaped sediment grains, the density, compressional, and shear wave velocities of common marine mineral species can vary by up to a factor of two. In this study, we present and compare measurements of the intrinsic scattering parameters, namely the normalized total scattering cross section, χ, and the backscatter form function, f, obtained from homogenous suspensions of irregularly shaped sand sized grains of both magnetite and quartz. Our preliminary measurements suggest that in the geometric scattering regime, χ is enhanced for magnetite sands by ~ 100 % relative to quartz. Similarly, measurements of the form function for magnetite sands are enhanced by ~ 33 % relative to quartz in the geometric regime, though no measurable difference was observed in the Rayleigh regime. The implications of these results for acoustic backscatter data collected at sea are discussed

Measurements of the backscattering characteristics of suspensions having a broad particle size distribution

Acoustic backscatter systems (ABS) can be used to non-intrusively measure profiles of both the concentration and particle size of suspended sediments in the marine environment. Inversion of ABS measurements into sediment size and concentration requires knowledge of two scattering parameters, namely the total normalised scattering cross-section, &chi;, and the form function, f. &chi; quantifies the acoustical scattering by a given particle over all angles, relative to its cross sectional area, and represents attenuation due to particle scattering losses. f describes the backscattering characteristics of a particle relative to its geometrical size. In recent years, a number of studies have presented measurements of f and &chi; for populations of sediments sieved over narrow size ranges, thereby essentially providing values for nominally a single particle size in suspension. In the present study, we extend these works by looking at the impact that a broad particle size distribution has on the form of f and &chi;. Here we model and measure the average form function for a broad size distribution (&sigma; = ±0.35a0, where &sigma; is the standard deviation about the mean particle radius, a0) of suspended glass spheres, whose scattering characteristics are well documented. The model is in close agreement with the provisional measurements, and suggests that for populations of suspended glass spheres with broad size distributions, the form function increases by about 40% in the Rayleigh regime (&lambda; >> 2&pi;a0, where &lambda; is the wavelength of the sound in water), whilst decreasing by a factor of around 25% in the geometric regime (&lambda; << 2&pi;a0), relative to that obtained for populations with a nominally single size in suspension. The output from this work has direct implications for the calculation of particle size and concentration profiles, obtained from acoustic backscatter data collected on suspensions of marine sediments at sea

Environmental Health Impacts of Concentrated Animal Feeding Operations: Anticipating Hazards—Searching for Solutions

A scientific conference and workshop was held March 2004 in Iowa City, Iowa, that brought together environmental scientists from North America and Europe to address major environmental health issues associated with concentrated animal feeding operations (CAFOs) in large, industrialized livestock production facilities. After one and a half days of plenary sessions, five expert workgroups convened to consider the most relevant research areas, including respiratory health effects, modeling and monitoring of air toxics, water quality issues, influenza pandemics and antibiotic resistance, and community health and socioeconomic issues. The workgroup reports that follow outline the state of the science and public health concerns relating to livestock production as they apply to each workgroup topic. The reports also identify areas in which further research is needed and suggest opportunities to translate science to policy initiatives that would effect improvements in public and environmental health. Viable solutions to some of the current environmental health problems associated with CAFOs are outlined. In addition, these reports bring to light several major concerns, including air and water contamination, the rise of antibiotic-resistant bacteria in livestock, and the specter of influenza outbreaks arising from siting industrialized poultry and swine production in proximity to each other and to humans