Wolf-Rayet phenomena

The properties of stars showing Wolf-Rayet phenomena are outlined along with the direction of future work. Emphasis is placed on the characteristics of W-R spectra. Specifically the following topics are covered: the absolute visual magnitudes; the heterogeneity of WN spectra; the existence of transition type spectra and compositions the mass loss rates; and the existence of very luminous and possibly very massive W-R stars. Also, a brief overview of current understanding of the theoretical aspects of stellar evolution and stellar winds and the various scenarios that have been proposed to understand W-R spectra are included

How Basic is (Patented) University Research? The Case of GM Crops

One of the main reasons for subsidising university research is the widespread belief that it generates proportionally more positive knowledge externalities than corporate research. Over the last two decades, however, this belief has been shaken by the increasingly aggressive patenting of university-based innovation. This perception was supported by Henderson, Jaffe and Trajtenberg (1998) who found both a sharp increase in university patenting and a decrease in the relative 'importance' of university innovation over the later part of their 1965-1992 sample. In this paper, we have compared the knowledge externalities generated by university and corporate patents related to GM crop research. Our main measure of knowledge externalities is the total number of third party cites generated by a patent. Our main result is that patented university research is not associated with greater knowledge externalities than corresponding corporate patents. If anything, corporate patents appear to generate greater numbers of net citations. This basic conclusion survives when we control for a number of variables that could affect citation counts (e.g. patent examiner effects) and when we break our sample into sub-periods. This does not imply that university patents are similar to corporate patents in every respect. We find two main differences. Firstly, there is some evidence that the shape of the distribution of citations is not identical for the two groups of patents as university patents appear to experience a more sluggish start than their corporate brethren. Secondly, even controlling quite narrowly for areas of specialisation, university patents receive a disproportionate number of cites from other university patents. These two results suggest that there are some fundamental differences in the types of knowledge flows generated by university and corporate patents.

The Stellar Content of Obscured Galactic Giant H II Regions: II. W42

We present near infrared J, H, and K images and K-band spectroscopy in the giant HII region W42. A massive star cluster is revealed; the color-color plot and K-band spectroscopic morphology of two of the brighter objects suggest the presence of young stellar objects. The spectrum of the bright central star is similar to unobscured stars with MK spectral types of O5-O6.5. If this star is on the zero age main sequence, then the derived spectrophotometric distance is considerably smaller than previous estimates. The Lyman continuum luminosity of the cluster is a few times that of the Trapezium. The slope of the K-band luminosity function is similar to that for the Trapezium cluster and significantly steeper than that for the massive star cluster in M17 or the Arches cluster near the Galactic center.Comment: 30 pages, 11 figures, late

Mass-loss rates from early-type stars

The mass loss rates are derived for a number of unevolved O-type stars and a few WN stars from high dispersion IUE spectra of their P Cygni profiles. When combined with other published mass loss rates, it is found that the relationship between log m and M sub BOL is a broad band rather than a linear relation, suggesting that the line radiation driven wind theory may not be sufficient to explain mass loss. The mass loss rates for the WN stars, while more uncertain, confirm that these stars lose mass about 100 times faster than O-stars

Spectroscopic observations of selected stellar systems

Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range

Solvable Lie algebras are not that hypo

We study a type of left-invariant structure on Lie groups, or equivalently on Lie algebras. We introduce obstructions to the existence of a hypo structure, namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain associated cohomology groups, determine a first obstruction. We also construct necessary conditions for the existence of a hypo structure with a fixed almost-contact form. For non-unimodular Lie algebras, we derive an obstruction to the existence of a hypo structure, with no choice involved. We apply these methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational conflicts eliminated. To appear in Transformation Group