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41.
Geoffrey D. Bromiley Fiona A. Bromiley David W. Bromiley 《Physics and Chemistry of Minerals》2006,33(8-9):613-621
The solubility and incorporation mechanisms of hydrogen in synthetic stishovite as a function of Al2O3 content have been investigated. Mechanisms for H incorporation in stishovite are more complex than previously thought. Most H in stishovite is incorporated via the Smyth et al. (Am Mineral 80:454–456, 1995) model, where H docks close to one of the shared O–O edges, giving rise to an OH stretching band in infrared (IR) spectra at 3,111–3,117 cm−1. However, careful examination of IR spectra from Al-stishovite reveals the presence of an additional OH band at 3,157–3,170 cm−1. All H is present on one site, with interstitial H both coupled to Al3+ substitutional defects on adjacent octahedral (Si4+) sites, and decoupled from other defects, giving rise to two distinct absorption bands. Trends in IR data as a function of composition are consistent with a change in Al incorporation mechanism in stishovite, with Al3+ substitution for Si4+ charge-balanced by oxygen vacancies at low bulk Al2O3 contents, and coupled substitution of Al3+ onto octahedral (Si4+) and interstitial sites at high bulk Al2O3 contents. Trends in OH stretching frequencies as a function of Al2O3 content suggest that any such change in Al incorporation mechanism could alter the effect that Al incorporation has on the compressibility of stishovite, as noted by Ono et al. (Am Mineral 87:1486–1489, 2002). 相似文献
42.
Organic material in meteorites provides insight into the cosmochemistry of the early solar system. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the Allende and Murchison carbonaceous chondrites was investigated by use of a technique called microprobe laser-desorption laser-ionization mass spectrometry, which permits spatial resolution with approximately a 40-μm spot size. Sharp chemical gradients of PAHs are associated with specific meteorite features. The ratios of various PAH intensities relative to the smallest PAH, naphthalene, are nearly constant across the sample. These findings suggest a common origin for PAHs dating before or during the formation of the parent body, consistent with proposed interstellar formation mechanisms. 相似文献
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Fiona Nunan Dražen Cepić Bwambale Mbilingi Konstantine Odongkara Ernest Yongo Monica Owili 《社会与自然资源》2018,31(3):306-319
Social ties influence access to knowledge and cooperation in natural resource management, with the sharing of certain characteristics thought to be positive for social cohesion and participatory forms of management. In this article, a holistic characterisation of fisherfolk personal networks is developed, disaggregating results by the main occupational groups within the fisheries studied, to provide a more nuanced understanding of the personal networks of types of fisherfolk. Links are then made between the characteristics of personal networks and evidence on how fisherfolk benefit from their networks, interpreted as contributing to social cohesion within the communities. The personal networks of fisherfolk (boat crew, boat owners and traders/processors) of Kenya, Tanzania and Uganda bordering Lake Victoria were investigated using personal network analysis, with fisherfolk asked who they discuss their fisheries activities with. The analysis found that networks based on the same occupation were more characteristic of fish traders/processors networks than those of boat crew and boat owners and that shared ethnicity, gender and location were characteristic of boat owner and boat crew networks, though shared ethnicity may reflect the composition of the communities rather than choice. Social and economic interactions within the networks were based on provision of credit, social support and advice, suggesting that these form the basis of social cohesion and should be taken into consideration in working with fishing communities in both development interventions and designing collaborative management approaches. 相似文献
45.
Fiona A. Harrison Finn E. Christensen William Craig Charles Hailey Wayne Baumgartner C. M. H. Chen James Chonko W. Rick Cook Jason Koglin Kristin-Kruse Madsen Michael Pivavoroff Steven Boggs David Smith 《Experimental Astronomy》2005,20(1-3):131-137
Hard X-ray/soft gamma-ray astrophysics is on the verge of a major advance with the practical realization of technologies capable of efficiently focusing X-rays above 10 keV. Hard X-ray focusing telescopes can achieve orders of magnitude improvements in sensitivity compared to the instruments based on coded apertures and collimated detectors that have traditionally been employed in this energy band. Compact focal planes enable high-performance detectors with good spectral resolution to be employed in efficient, low-background configurations. We have developed multilayer coated grazing incidence optics and solid state Cadmium Zinc Telluride focal plane systems for the High Energy Focusing Telescope (HEFT) balloon-borne experiment, and for the Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer satellite. In this paper we describe the technologies, telescope designs, and performance of both experiments. 相似文献
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Fiona Simpson 《GeoJournal》2000,50(2-3):127-131
Ethnic minorities are facing increasing problems of social exclusion in Central and Eastern Europe. The complex nature of
the transition from socialism means that the institutional framework to support them is still being established. Whilst non-governmental
organisations (NGOs) have a crucial role to play in promoting a more inclusive society, through improving access to local
democratic structures for otherwise excluded groups and acting as fora for improved community participation throughout the
region, their development remains fraught with problems. Examination of the experiences of one such organisation, ETNO Agentura
based in northern Slovakia, provides an insight into the problems and opportunities arising as community representatives work
together to provide social support for ethnic minorities. The paper outlines key issues arising from the case of ETNO Agentura,
including difficulty in gaining access to supporting finance and securing long term financial viability, the lack of institutional
capacity of local authorities to become receptive to their views, and implicit socio-cultural barriers to ethnic minority
representation in community participation processes. Developing a fuller understanding of these problems and the measures
required to overcome them is a central part of establishing a more effective role for NGOs within post socialist societies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
50.
New articulated specimens of the British Ordovician cystoid first mentioned under the name ‘Hemicosmites rugatus Forbes’ in 1848 allow its morphology and systematic affinities to be established for the first time. Despite being based on isolated plates, ‘H. rugatus Forbes’ has been reported from England and Wales, Belgium, France, Spain and Thailand, and has been attributed to four genera. It is characterized by a heteromorphic, circular stem, a theca with four basal, six infra‐lateral and eight lateral plates, all with sharp‐crested ridges running to plate angles, multiple arms in each ambulacrum and an extensive tegmen. These characters indicate it belongs in the family Caryocrinitidae and genus Caryocrinites. Caryocrinites rugatus had arms with lateral brachioles that folded in against the main arm axis, as in the type species C. ornatus Say. It is the first Ordovician species known to possess this character. Isolated plates show sorting and a few may represent other species of Caryocrinites s.l. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献