Absorption and velocity dispersion due to crystallization and melting of emulsion droplets

The influence of droplet crystallization and melting on the ultrasonic properties of oil-in-water emulsions has been investigated. The ultrasonic velocity and attenuation were measured in a series of 3 wt% n-hexadecane-in-water emulsions as a function of frequency (0.3–4 MHz), droplet diameter (0.4 and 1 μm) and temperature (0–25°C). The emulsified n-hexadecane crystallized at about 5°C due to supercooling effects and melted at about 18°C. As solid and liquid n-hexadecane have significantly different ultrasonic properties, an appreciable change in the velocity and attenuation is observed during the phase transition. This behaviour is modified significantly in systems where the emulsion droplets are partially crystalline because the temperature fluctuations associated with the ultrasonic wave can perturb the phase equilibria solid liquid causing excess attenuation and velocity dispersion. The magnitude of this effect depends on the ultrasonic frequency and the average droplet size.     

Computation of Orientational Averages in Solid-State NMR by Gaussian Spherical Quadrature

We investigate Gaussian spherical quadrature as a method for calculating orientational averages in solid-state NMR. For the case of magic-angle-spinning sideband amplitudes of isolated spins-1/2, we demonstrate the superiority of Gaussian spherical quadrature over other orientational averaging methods. Depending on the shift anisotropy parameters and the desired accuracy, the computation speed is enhanced by a large factor (between two and many hundreds). In addition, a method for improving any present sampling scheme is devised. Such schemes are called SHREWD (Spherical Harmonic Reduction or Elimination by a Weighted Distribution). The role of orientational symmetry in solid-state NMR is explored. We also discuss the limitations of the Gaussian spherical quadrature methods.     

Mobile-ion concentrations and mixed-alkali effects in β-alumina solid electrolytes

A theory of the mixed-alkali effect based on the weak electrolyte model is used in the analysis of conductivity isotherms in the Na/K β-alumina system. This gives mobile interstitialcy concentrations, [Na²⁺₂] or [Na⁺_i], which agree remarkably well with those obtained by Wolf from calculations based on changes in the Haven ratio, H_R. The high conductivity of β-alumina arises apparently from a high “defect mobility” rather than from the existence of quasi-liquid motions. Other consequences of the weak electrolyte theory are discussed.     

Determination and Persistence of Bay 68138 and Two of its Metabolities in Turf Grass

Residues of Bay 68138 (Nemacur P^®) [ethyl 4-(methylthio)-m-tolyl isopropylphosphor-amidate] and its sulfoxide and sulfone were determined in turf grass. The extracts were separated by liquid chromatography on silica gel into two fractions which were concentrated and injected into a gas chromatograph equipped with a flame photometric detector sensitive to phosphorus. Recoveries were 95 to 105 % for all three compounds at the 0.10-ppm level; sensitivity to each compound was 0.01 ppm or better. Retention times for the three compounds on six liquid phases, p-values in seven solvent systems, and conditions for separating the compounds by liquid chromatography were determined. Total residues in turf grass treated with a granular formulation at the rate of 15 lb (active ingredient) per acre, declined from 4930 to 102 ppm (dry basis) during a 49-day period of weathering. Bay 68138 was found to oxidize to its sulfoxide and sulfone.     

Interactive simulation of bushfires in heterogeneous fuels

The program IGNITE, developed by the authors, is a landscape fire modelling system that deals with fires in heterogeneous fuels. Landscapes are represented as cellular automata (grids of pixels) and fire spread is modelled as an epidemic process. An integrated geographic information system permits the importing and editing of maps from compatible sources, such as satellite imagery. Maps, models and other information are organized as scenarios; historical fires can be recorded and replayed. Modules are being developed for application to fire prevention, fire suppression, land-use management, and to training and education. An illustration of using the system to deal with heterogeneous fuel is its application to the problem of percolation in patchy fuel.     

Cyclische Phenyl-carbamate des Miotin-Typs und ihre Wirkung auf die Acetylcholinesterase

Cyclic Phenyl Carbamates and Their Action on Acetylcholinesterase Several six-, seven-, and eight-membered cyclic phenyl carbamates of the miotin type have been synthesised and their in vitro potency as inhibitors of acetylcholinesterase determined. The eight-membered rings were found to be the most potent and are comparable with physostigrnin or miotin. It was concluded that, for maximum potency, the orientation of the carbamate group relative to the aromatic plane has to be close to orthogonal.