Structural-Properties Of Amorphous Hydrogenated Carbon .1. A High-Resolution Neutron-Diffraction Study

The structure of samples of amorphous hydrogenated carbon, prepared from acetylene and propane precursors, containing 35 and 32 at.% hydrogen, respectively, was investigated by time-of-flight neutron diffraction in the range 0.2-50 angstrom-1 using the ISIS spallation source. The large dynamic range of the data ensures a real-space resolution sufficient to reveal directly the proportions of sp2 and sp3 hybridized carbon. The results show that, in these hard carbon materials, the carbon-atom sites are predominantly sp2 bonded, and the carbon-carbon single bond:carbon-carbon double bond ratio is about 2.5:1. The detailed information on atomic correlations thus provided is used to discuss current structural models, and in particular the data are used to show that these models require significant modification

A spectroscopic study of the structure of amorphous hydrogenated carbon

A range of amorphous hydrogenated carbon (a-C:H) samples have been studied using inelastic neutron spectroscopy (INS) and Fourier transform infrared (FTIR) spectroscopy. Using these complementary techniques, the bonding environments of both carbon and hydrogen can be probed in some detail, with the INS data providing not only qualitative but also quantitative information. By comparing the data from each of the samples we have been able to examine the effects of different deposition conditions, i.e. precursor gas, deposition energy and deposition method, on the atomic-scale structure of a-C:H

Structural properties of amorphous hydrogenated carbon. IV. A molecular-dynamics investigation and comparison to experiments

Hydrogenated amorphous carbon structures, a-C:H, with densities of 1.8 and 2.0 g/cm3, have been generated by semiempirical density-functions (DF) molecular-dynamics (MD) rapid cooling of a liquid phase of 128 carbon and 64 hydrogen atoms within periodically arranged cubic supercells. The electronic bonding properties of the model structures are analyzed within a local-orbital description. The structural properties are compared to relevant statistical and diffraction data obtained by neutron scattering and NMR in order to achieve a fundamental understanding of structure-related properties on the molecular level of chemical bonding

Splitting ‘intervocalic’: Expanding the typology of lenition environments

The basic types of lenition environments (‘initial’, ‘intervocalic’, ‘final’) need to be separately evaluated as they differ along parameters like word position (e.g., pre-consonantal vs. final codas) or stress relations. This paper argues that we need to recognise an additional such parameter: the length of the vowel preceding an intervocalic consonant. We show that a number of phenomena from varieties of English and German show lenition patterns which draw a distinction between reflexes found in post-short (vc) and post-long (vvc) environments. The theoretical consequence of our observations is that phonological theory needs to be able to account for the post-short vs. post-long distinction in the form of a parametrically-determined representational difference

Handbook for geografhy teachers

xii, 525 p.; 21 cm

Structural-Properties Of Amorphous Hydrogenated Carbon .3. NMR Investigations

Our NMR studies give experimental evidence of bonding heterogeneity in samples of a-C:H on the nanometer scale. Two classes of protons were identified with distinctly different spin-lattice-relaxation behavior. The difference in the spin-lattice relaxation provides a means of spectral editing of cross-polarization magic-angle spinning, combined rotation and multiple-pulse spectroscopy, dipolar dephasing spectra, and multiple quantum NMR experiments. This combination of the various NMR techniques allows for a detailed structural investigation of a-C:H, e.g., the sp2:sp3 ratio, the relative amount of hydrogenated and nonhydrogenated carbons, etc. A model incorporating the heterogeneity is established and discussed. The NMR results are compared with neutron spectroscopy and diffraction data

On the same wavelength? Hyperdiverse young people at a community radio station

This paper uses a case study of youth-led community radio station, KCC Live, based in Knowsley, neighbouring Liverpool, UK, to explore which styles of voice belong in the soundscape of KCC Live, and how young people in this ‘ordinary’ social space view the ‘other’. I extend the term hyperdiversity to a discussion of how youth voice on the airwaves can involve the prioritisation of certain local cultural representations, and the silencing of others. I am also interested in young people’s perception towards ‘out-groups’ (people from other towns within Liverpool, and Merseyside more broadly). This notion of out-groups considers identity as a system of categorisation, in which boundaries are used to distinguish localities, creating binary distinctions between ‘us’ and ‘others’. This paper finds that engaging hyperdiverse young people in meaningful interactions around a shared interest, in this case community radio, stimulates the development of relationships across categorical differences

Neutron Compton scattering from amorphous hydrogenated carbon

Neutron Compton scattering (NCS) measurements have been used to determine the kinetic energies of atoms in samples of amorphous hydrogenated carbon (a-C:H), graphite and diamond at momentum transfers between 40 and 300 Angstrom(-1). We find that the kinetic energy of individual carbon atoms is the same within statistical error in a-C:H and graphite but significantly higher in diamond. The kinetic energy of the hydrogen in a-C:H is lower than expected from previous spectroscopic measurements and we infer that the sample contained molecular hydrogen. Observed deviations from the impulse approximation are consistent with theoretical calculations. We discuss future prospects for Ncs measurements on non-crystalline materials