Standard small targets for calibrating underwater sonars

Ping-pong balls form convenient reference targets for underwater sonars. Theoretical and experimental studies have confirmed that the acoustic target strength of such a ball can be predicted to within about ±·58 dB over a wide range of frequencies, even down to frequencies at which the wavelength in water exceeds the radius of the ball. Computed and experimental results are compared.     

A bivariate strong law of large numbers

Probability Theory and Related Fields -     

Observation of a free radical during the photolysis of phenyliodoacetylene

An ESR spectrum observed during the photolysis of phenyliodoacetylene indicates the formation of a π-radical. It is suggested that a crossing of α- and π-levels occurs in the phenylethynyl radical.     

Preparation and properties of tetramethyl-dipicrylamine

Tetramethyldipicrylamine has been synthesised. It gives precipitates with ammonium, potassium, rubidium and caesium ions, that vary widely in crystalline form and offer a possibility of qualitative usage in chemical microscopy. The potassium salt is of sufficiently low solubility to be of analytical interest.     

The reduction of camera fan noise in a photoprint room

The noise level produced by a fan was reduced by 21 dB(A) by enclosing it in a ‘soundproof box’. The general problems of designing such a box, and, in particular, that of preventing the enclosed fan from overheating, are discussed. The construction of the box is described in detail and its actual performance compared with that theoretically attainable.     

Green chemical functionalization of single-walled carbon nanotubes in ionic liquids

Single walled carbon nanotubes (SWNTs) are exfoliated and functionalized predominantly as individuals by grinding them for minutes at room temperature with aryldiazonium salts in the presence of ionic liquids (ILs) and K(2)CO(3). This constitutes an extremely rapid and mild green chemical functionalization process for obtaining the individualized nanotube structures. A number of ILs and various reaction conditions were surveyed. Raman, XPS, UV/vis/NIR spectroscopies, thermogravimetric analysis, and atomic force and transmission electron microscopies were used to characterize the products.