9,477 research outputs found
Characteristics and classification of A-type supergiants in the Small Magellanic Cloud
We address the relationship between spectral type and physical properties for
A-type supergiants in the SMC. We first construct a self-consistent
classification scheme for A supergiants, employing the calcium K to H epsilon
line ratio as a temperature-sequence discriminant. Following the precepts of
the `MK process', the same morphological criteria are applied to Galactic and
SMC spectra with the understanding there may not be a correspondence in
physical properties between spectral counterparts in different environments. We
then discuss the temperature scale, concluding that A supergiants in the SMC
are systematically cooler than their Galactic counterparts at the same spectral
type, by up to ~10%. Considering the relative line strengths of H gamma and the
CH G-band we extend our study to F and early G-type supergiants, for which
similar effects are found. We note the implications for analyses of
extragalactic luminous supergiants, for the flux-weighted gravity-luminosity
relationship and for population synthesis studies in unresolved stellar
systems.Comment: 14 pages, 14 figures, accepted by MNRAS; minor section removed prior
to final publicatio
Flame resistant elastic elastomeric fibers
Development of materials to improve flame resistance of elastic elastomeric fibers is discussed. Two approaches, synthesis of polyether based urethanes and modification of synthesized urethanes with flame ratardant additives, are described. Specific applications of both techniques are presented
Development of a Flame Resistant Silicone Rubber
Flame resistant silicone rubber using aluminum silicates and aromatic bromide
Does the far-infrared/radio correlation in spiral galaxies extend to the spatial domain
A comparison is made between the spatial distribution of the thermal far-infrared and non-thermal radio emission of nearby spiral galaxies. This is done in an attempt to improve our understanding of the well known correlation between the integrated Infrared Astronomy Satellite (IRAS) far-infrared and radio emission of spiral galaxies, e.g., de Jong et al., 1985, Helou et al., 1986. A physical explanation for this correlation is not straight forward due to the ambiguous nature of the origin of the far-infrared and radio, and the dependence of the non-thermal radio on each galaxies' magnetic field. It is now widely believed that the infrared emission detected in the longer wavelength IRAS wavebands (less than 50 microns) arises from at least two distinct sources, e.g., Cox et al., 1986, Persson and Helou, 1987: (1) a warm (T approx. 40 K) component associated with dense dust clouds heated by embedded O and B type stars; and (2) a cooler (T approx. 20 K) component associated with diffuse dust distributed throughout the interstellar matter (ISM) heated by the interstellar radiation field. A link between the warm component and the radio via electrons originating in Type II supernovae (the ultimate fate of many of the O and B type stars responsible for the warm component) has been suggested by numerous authors. The supporting evidence is scarce and inconclusive. Researchers have attempted to provide some insight into the problem by looking at the spatial distribution of the different components in some nearby spiral galaxies, starting with the face-on spiral M51. The source of the far-infrared data is the IRAS chopped photometric channel (CPC) instrument. Warm and cold far-infrared fluxes integrated over all wavelengths and the radio intensity at two frequencies are plotted against radius. All plots are to a common resolution of 100 arcsec, the radio data originating from the Cambridge Low Frequency Synthesis Telescope (151 MHz) and the VLA (1490 MHz, from Condon, 1987). The warm and cold regions are assumed to be representedby a single galactic wide temperatures of 50 K and 20 K respectively. A dust emissivity of 1 has been assumed. The form of the plots is little effected by varying these assumptions. The radio and cold component curves appear to follow each other most closely, in contradiction to the simple OB star/type II supernovae hypothesis
Discourse Analysis: varieties and methods
This paper presents and analyses six key approaches to discourse analysis, including political discourse theory, rhetorical political analysis, the discourse historical approach in critical discourse analysis, interpretive policy analysis, discursive psychology and Q methodology. It highlights differences and similarities between the approaches along three distinctive dimensions, namely, ontology, focus and purpose. Our analysis reveals the difficulty of arriving at a fundamental matrix of dimensions which would satisfactorily allow one to organize all approaches in a coherent theoretical framework. However, it does not preclude various theoretical articulations between the different approaches, provided one takes a problem-driven approach to social science as one?s starting-point
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