Ralph A. Duncan

Learn More
[1] Helium isotopes are a robust geochemical tracer of a primordial mantle component in hot spot volcanism. The high He/He (up to 35 RA, where RA is the atmospheric He/He ratio of 1.39 10 ) of some Hawaiian Island volcanism is perhaps the classic example. New results for picrites and basalts from the Hawaiian-Emperor seamount chain indicate that the hot(More)
Determination of reliable crystallization ages by K-Ar methods for young (<1 Ma), fresh basalts from the seafloor has been frustrated by several effects. The small amounts of radiogenic 4øAr developed over these timescales in such 10w-K rocks are difficult to resolve from predominantly atmospheric 4øAr. An additional concern is that mantle-derived 4øAr may(More)
The development of free electron laser (FEL) sources has provided an unprecedented bridge between the scientific communities working with ultrafast lasers and extreme ultraviolet (XUV) and X-ray radiation. Indeed, in recent years an increasing number of FEL-based applications have exploited methods and concepts typical of advanced optical approaches. In(More)
We present a sensitive radio image of the nebula associated with the Luminous Blue Variable star HR Carinae. This nebula is small and diicult to observe optically due to the presence of the bright star. The radio image shows the laments in the outer regions of the nebula seen in optical coronagraphic images. The core of the nebula is elongated north{south(More)
Placement of a 3-m-wide, black, polyethylene film mulch down rows of peach (Prunus persica 'Red Haven' on 'Lovell' rootstock) and almond (Prunus dulcis 'Nonpareil' on 'Lovell') trees in the San Joaquin Valley of California resulted in irrigation water conservation of 75%, higher soil temperature in the surface 30 cm, a tendency toward greater root mass,(More)
We have used the Australia Telescope Compact Array to image four southern luminous blue variable stars: AG Car, He3-519, HR Car and WRA 751, at wavelengths of 3 and 6 cm, and resolutions of 1 and 2 arcsec respectively. With the partial exception of HR Car, all radio images show an unresolved stellar core surrounded by a large ionized gaseous nebula, and(More)
  • 1