On observing acoustic backscattering from salinity turbulence.

It has been hypothesized that at sufficiently high levels of oceanic salinity turbulence it should be possible to observe acoustic backscattering. However, there have been limited in situ measurements to confirm this hypothesis. Using an autonomous underwater vehicle equipped with upward and downward looking 1.2 MHz acoustic Doppler current profilers and with turbulence and fine scale sensors, measurements were performed in a region of intense turbulence and a strong salinity gradient. The approach taken was to correlate variations in the backscattered acoustic intensity, I, with a theoretical acoustic backscattering cross section per volume for salinity turbulence, σ(s), to obtain an estimated scattering cross section per volume, σ(e). Results indicated that of order 50% of the observed region was characterized by salinity turbulence induced backscattering.

Synthesis of 18O-labelled alcohols from unlabelled alcohols.

The synthesis of primary, secondary and tertiary 18O-enriched alcohols from readily available 16O-alcohols via a Mitsunobu esterification and hydrolysis is described. The method is further exemplified in the labelling of the active pharmaceutical ingredient, dropropizine and is shown to be tolerant of modern, separation friendly Mitsunobu reagents.

Acoustic scattering from a thermally driven buoyant plume revisited.

Far-field weak scattering theory is applied to the case of high-frequency broad-bandwidth acoustic scattering from a thermally generated buoyant plume in a controlled laboratory environment. To first order, the dominant scattering mechanism is thermally driven sound-speed variations that are related to temperature deviations from ambient. As a result, the received complex acoustic scattering is a measure of the one-component three-dimensional Fourier transform of the temperature difference field measured at the Bragg wave number. The Bragg wave number vector is the difference between the scattered and incident wave vectors. Solving for its magnitude yields the Bragg scattering condition; this is the Fourier component of the plume variability that produces scattering. Results are presented for multistatic scattering from unstable and turbulent plumes using a parallel scattering geometry. The data justify application of the far-field weak scattering theory to the present case of a thermal plume. As a consequence, quantitative results on medium variability can be inferred using high-frequency broad-bandwidth acoustic scattering. Particular attention is given to the role of anisotropy of the variability of the scattering field in determining the validity of far-field Bragg scattering.