The barrier attenuation of garden fences

A study has been undertaken of the barrier attenuation produced by 40 different finite garden fences shielding suburban homes from traffic noise. Two alternative techniques of measuring barrier attenuation were used and an empirical relationship between the results is obtained. The attenuation measured in terms of $\text{L}{}_{\mathrm{<mtext>1</mtext>}}$, $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$ or $\text{L}{}_{\mathrm{eq}}$ generally agrees within ± 1 dB(A) for a given barrier. Similarly constructed fences can produce different attenuations, depending on their surroundings. The effects of unshielded ends, open gates and vegetation are considered. It is postulated that buildings reflect back sound, the effect depending on building size and distance from the fence. A reasonable trend is obtained for brick barriers; however, the wooden fence results may be obscured by sound leakage through the fence.     

Three New Chiral Aminoethers from Tartaric Acid for Improved Asymmetric Syntheses with Organolithium Reactions. Preliminary communication

The chiral aminoethers 1–4 , accessible from tartaric acid, are tested as complexing ligands in organolithium reactions. The tetramine 4 turns out to cause highest inductions [see Table 2 and Equations (1)–(4)].     

Almost-Baer subplanes of free projective planes

We examine Baer subplanes, and subplanes which are almost-Baer subplanes, of any free plane—showing the subplanes are pairwise isomorphic—thus giving further examples of planes investigated by Barlotti.On leave from the University of Tasmania, Hobart, Australia.     

Structure sensitive factors in molecular cluster formation by ion bombardment of single crystal surfaces

The dynamics of molecular cluster formation from a solid bombarded by a 600 eV Ar⁺ ion have been studied classically by computer simulation. The dimers and trimers are found to establish their identity as clusters within interaction range of the solid, but not by a direct ejection of a bound molecule. The Cu₂/Cu and Cu₃/Cu ratios are found to be strongly dependent on crystal orientation. The (111) face is 2–3 times more likely to produce multimers than the (100) face. We find 9 trimers from (111) but none from (110). The relationship between cluster composition and the original arrangement of those atoms on the surface is presented in detail. We find that each multimer forms from atoms that originate within a roughly circular region of area ～70 Ų or less. This region is not necessarily centered on the ion impact point. A consequence of this observation is that dimers can consist of atoms that were several Ångströms apart on the surface but that most trimers contain at least one nearest neighbor pair of atoms. The calculated energy distribution for the dimers matches well with similar experimental studies.     

Green's functions for gravitational multi-instantons

The Green's functions for scalar fields propagating on the self-dual gravitational multi-instantons and multi-Taub-NUT metrics are given explicitly in closed form. The special cases for flat space, Taub-NUT and the Eguchi-Hanson instanton are listed. A construction is described for obtaining the Green's functions for fields of arbitrary spin.