171,534 research outputs found
Heteroatom-doped hydrogenated amorphous carbons, a-C:H:X 'Volatile' silicon, sulphur and nitrogen depletion, blue photoluminescence, diffuse interstellar bands and ferro-magnetic carbon grain connections (Research Note)
Context. Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of
heteroatoms, which can lead to interesting effects. Aims. To investigate the
doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms
within the astrophysical context. Methods. A search of the literature on doped
a-C:H reveals a number of interesting phenomena of relevance to astrophysics.
Results. X dopants in a-C:H:X materials can affect the sp3/sp2 ratio (X = Si, O
and N), lead to blue photoluminescence (undoped or X = N), induce
ferromagnetic-like behaviour (X = N and S) or simply be incorporated (depleted)
into the structure (X = Si, O, N and S). Si and N atoms could also incorporate
into fullerenes, possibly forming colour-centres that could mimic diffuse
interstellar bands. Conclusions. Doped a-C:H grains could explain several
dust-related conundrums, such as: 'volatile' Si in photo-dissociation regions,
S and N depletion in molecular clouds, blue luminescence, some diffuse
interstellar bands and ferromagnetism in carbonaceous grains.Comment: 5 page
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Asian Varieties of Service Capitalism?
There is currently only limited empirical research and theoretical conceptualisation of the role of knowledge-intensive business services (KIBS) in the economies of Asia within economic geography or elsewhere in the wider social scientific literature. This paper argues that existing theoretical understandings of KIBS are inadequate to conceptualise the nature of ongoing KIBS development in Asian economies – both emerging and mature – and seeks to address this absence by developing a theoretical framework that draws on a range of existing theoretical approaches within and beyond economic geography. To do this, it proposes the concept of ‘service capitalism’, developed from work concerned with varieties of capitalism (VoC), variegated capitalism and advanced service industries. The paper elaborates its theoretical argument by presenting research into two forms of Asian service capitalism through two case studies examining respectively the specific nature of Japanese KIBS and the development of KIBS in China. Using the case studies, it demonstrates how service industry development in both these Asian economies exhibits distinctive characteristics that are a consequence of both local institutional, corporate, and socio-cultural contexts but are also interconnected the wider global economy in complex ways. The paper thus presents a significant and disruptive challenge to existing theories of KIBS development as based on the western experience, and contemporary deployments of the varieties of capitalism and variegated capitalism approaches
Grain growth, optical polarisation, and extinction in interstellar clouds
Increases in the wavelength of maximum polarization and the ratio of total to selective extinction are generally assumed to be the result of grain growth in interstellar clouds. Using a grain model in which the interstellar extinction is explained by amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) mantles on silicate cores the effects of these absorbing carbonaceous mantles on the polarizing properties of large (500 to 2500 A radius) silicate grains were theoretically studied. The polarization model of Mathis was adopted and it was shown that carbon-coated silicate grains can explain the relationship between the wavelength of maximum polarization and R observed toward dark clouds
H2 formation via the UV photo-processing of a-C:H nano-particles
Context. The photolysis of hydrogenated amorphous carbon, a-C(:H), dust by UV
photon-irradiation in the laboratory leads to the release of H2 as well as
other molecules and radicals. This same process is also likely to be important
in the interstellar medium. Aims. To investigate molecule formation arising
from the photo-dissociatively-driven, regenerative processing of a-C(:H) dust.
Methods. We explore the mechanism of a-C(:H) grain photolysis leading to the
formation of H2 and other molecules/radicals. Results. The rate constant for
the photon-driven formation of H2 from a-C(:H) grains is estimated to be
2x10^-17 cm^3 s^-1. In intense radiation fields photon-driven grain
decomposition will lead to fragmentation into daughter species rather than H2
formation. Conclusions. The cyclic re-structuring of arophatic a-C(:H)
nano-particles appears to be a viable route to formation of H2 for low to
moderate radiation field intensities (1 < G_0 < 10^2), even when the dust is
warm (T ~ 50 - 100 K).Comment: 7 pages, 2 figures, accepted for publication in A&
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