Motion of muonium (hydrogen) in the III-V nitrides

Muon spin relaxation measurements in the III-V nitrides have provided data on the motion of each of the three charge-states of the muonium 'isotope' of hydrogen. Motional parameters are established for Mu(+) in InN, Mu(0) in AlN, and Mu(-) in GaN, with qualitative results in the other materials. Both Mu(+) and Mu(0) show tunneling below 300 K and thermal diffusion at higher temperatures leading to interactions with other impurities or extended defects

Fouling of heat-transfer surfaces in oil-fired boilers for domestic heating

Domestic-heating boilers fired with distillate oil are subject to fouling of the convective section gas-side surfaces, and this fouling leads to a reduction in efficiency and to increased maintenance requirements. A rapid test to enable the composition of fouling deposits and the rates of fouling to be studied has been developed and used at two laboratory sites. It involves special fouling surfaces which can be removed for deposit analysis. Fouling rates are shown to be directly related to the sulphur content of the fuel. Also, operation with reduced excess air in these boilers can lessen fouling rates by reducing the conversion of fuel sulphur to sulphuric acid. Results are compared with those from tests on full-size boilers

Anisotropic muonium centers in aluminum nitride

An atomic-like neutral muonium center with a small anisotropy is inferred from hyperfine decoupling curves and longitudinal relaxation data on AIN. The isotropic contribution of A = 4422 M Hz, 99% of the full vacuum value, is accompanied by a weak dipolar term with D = 144 MHz as average values extracted from complete decoupling curves at a few temperatures. Simulations assuming the four nitrogen antibonding sites well reproduce the decoupling data. The hyperfine constants are consistent with those previously obtained from fitting temperature-dependent longitudinal relaxation rates to a simple model for Mu(0) motion. (c) 2005 Elsevier B.V. All rights reserved