30 research outputs found
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
Molecular control of development in the reef coral, Acropora millepora
A brief overview of the embryonic and larval development of Acropora, including some previously unpublished data, provides the background for this review of our rapidly expanding knowledge of the genes that control early development in corals, with particular emphasis on Hox and Hox-like genes. Since the Phylum Cnidaria is widely accepted to be an ancient group of organisms, genes, and motifs within genes, that are shared by corals and higher metazoans are presumably ancient. Thus, shared genes allow us to study how gene structure and function have changed with time, while genes specific to higher metazoans have, presumably, evolved more recently. Anatomically, corals have many fewer cell types than higher metazoans, but it is not clear that this apparent simplicity will be reflected at the molecular level. We have already found Acropora representatives of structural genes, housekeeping genes, nuclear receptors, Hox-like genes, Pax genes and components of the dpp signalling pathway. However, thus far there is no unequivocal evidence for the cluster of Hox genes, known as the zootype genes, that is otherwise widespread among the Metazoa. As more data become available, the Cnidaria are making an increasing contribution to our knowledge of the evolution of gene structure, function, and regulation. We here illustrate the evolutionary approach that we are taking to the characterisation of coral genes with a review of our work on the Acropora Hox- like gene, cnox2-Am
Molecular control of development in the reef coral, Acropora millepora
A brief overview of the embryonic and larval development of Acropora, including some previously unpublished data, provides the background for this review of our rapidly expanding knowledge of the genes that control early development in corals, with particular emphasis on Hox and Hox-like genes. Since the Phylum Cnidaria is widely accepted to be an ancient group of organisms, genes, and motifs within genes, that are shared by corals and higher metazoans are presumably ancient. Thus, shared genes allow us to study how gene structure and function have changed with time, while genes specific to higher metazoans have, presumably, evolved more recently. Anatomically, corals have many fewer cell types than higher metazoans, but it is not clear that this apparent simplicity will be reflected at the molecular level. We have already found Acropora representatives of structural genes, housekeeping genes, nuclear receptors, Hox-like genes, Pax genes and components of the dpp signalling pathway. However, thus far there is no unequivocal evidence for the cluster of Hox genes, known as the zootype genes, that is otherwise widespread among the Metazoa. As more data become available, the Cnidaria are making an increasing contribution to our knowledge of the evolution of gene structure, function, and regulation. We here illustrate the evolutionary approach that we are taking to the characterisation of coral genes with a review of our work on the Acropora Hox- like gene, cnox2-Am
An investigation of the major and minor constituents of lithium niobate waveguides
5.00SIGLEAvailable from British Library Document Supply Centre- DSC:9091.9F(AERE-R--12026) / BLDSC - British Library Document Supply CentreGBUnited Kingdo
The impact of the sandeel fishery closure in the northwestern North Sea on seabird food consumption, distribution and productivity
In the North Sea, the lesser sandeel (Ammodytes marinus) is the target of an industrial fishery and the principal prey of many top predators. Because of concerns about potential effects on predators, the sandeel fishery off eastern Scotland was closed in 2000, and local sandeel abundance increased subsequently. To examine whether closure benefitted sandeel-dependent seabirds, we compared summer sandeel consumption, at-sea distributions, and breeding success of seven species with fishery removals and abundance of older (1+ group) and young-of-the-year (0 group) sandeels from 1996 to 2003. Breeding success of black-legged kittiwake (Rissa tridactyla), a species that has declined in recent decades, was related to abundance of both 1+ group (the age class targeted by the fishery) and 0 group sandeels. The proportion of 0 group consumed by kittiwakes and proportion of the kittiwake population foraging in the area were linked to 0 group abundance. None of these parameters in the other seabird species were associated with sandeel abundance. Our results suggest that fishery closure can have a beneficial impact on top predators sensitive to variation in abundance of the target species, although environmental conditions before and after closure are also likely to be critically important