The dipole moment of HNO in its ÃA″ excited state determined using optical—optical double resonance stark spectroscopy

The Stark splittings and rotational asymmetry splittings of a number of levels of the ùA″ excited state of HNO have been measured using the sub-Doppler technique of optical—optical double resonance, μ_a is found to be 1.08 ± 0.01 D for the 100 vibronic state, and 1.05 ± 0.01 D for the 020 vibronic state. These values are to be compared with a recently determined ground state value of μ_a = 0.996 D. The asymmetry splittings of some of the levels studied are considerably larger than predicted from the known rotational constants, indicating minor rotational perturbations.     

Accuracy, latency, and listener-search behavior in localization in the horizontal and vertical planes

Thirty-six listeners localized continuous filtered noise bursts centered on 2.3 or 8.3 kHz under normal listening conditions or while wearing earmuffs. The noise bursts were from any one of 20 loudspeakers, 18 degrees apart, visible to the listeners, and arranged in the horizontal and vertical planes. Listeners were free to move, while remaining seated, throughout all trials. The noise bursts were terminated by the listeners. Measures of accuracy and latency showed that earmuff listening had a significant effect whereas, overall, signal frequency had no significant effect. There was, however, an apparent downward shift of the 2.3-kHz signals presented above the midline in the vertical plane. Analysis of video records of listeners' behavior revealed a strong tendency for initial orientation by head or eye movement to correlate with final response, even when both were inaccurate. The paradigm adopted in this latter aspect of the study illustrates an "ecological" approach to the study of auditory phenomena.     

The mechanism of the Fischer-Hepp rearrangement of aromatic N-nitroso-amines

Rate equations have been deduced for two possible mechanisms for the Fischer-Hepp rearrangement of aromatic N-nitroso-amines in acid solution: (a) for the commonly assumed intermolecular process involving de-nitrosation to the secondary amine and a free nitrosating agent, followed by a direct C-nitrosation of the secondary amine by this nitrosating agent, and (b) for a mechanism whereby rearrangement and de-nitrosation occur concurrently, by two separate reactions of the protonated N-nitroso-amine. All the experimental evidence supports mechanism (b), whilst most of it is incompatible with (a). Particularly diagnostic of the mechanism are (1) the observed rearrangement: de-nitrosation product ratios under certain limiting conditions, (2) the question of halide ion catalysis, and (3) the rate form found under the limiting condition of a large excess of added secondary amine.     

Sound propagation in the vicinity of an isolated building: an experimental investigation

Recently, the study of acoustics in urban terrain has been concerned with the propagation of sound through street canyons typical of residential areas in large cities, while sparsely built suburban and rural areas have received little attention. An isolated building's effect on propagating sound is a fundamental case of suburban acoustics and urban acoustics in general. Its study is a necessity in order to determine the processes that might be required to model the sound field in the building's vicinity, e.g., diffraction and wind effects. The work herein presents the results of an experimental effort to characterize the interaction between propagating sound and a single story, gabled-roof building typical of some North American suburban and rural areas. Recorded data are found to reasonably compare to a common diffraction model in some instances.     

Meson fields, exchange currents and progenitor sum rules

The theory of the integrated photoabsorption cross section and the dipole sum rule is reviewed. A new progenitor sum rule, in which meson fields appear explicitly, is derived from a field theory of interacting pions and nucleons. The relation of this sum rule to previous results obtained in a potential theory is elucidated, and the role of neutron-proton correlations in nuclear ground states is discussed in terms of their effect on the dipole sum rule. The inclusion of ρ-mesons (again in an oversimplified theory) and their contribution to progenitor sum rules is also mentioned.     

Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.