12,208 research outputs found
Planetary Nebula Surveys: Past, Present and Future
In this review we cover the detection, identification and astrophysical
importance of planetary nebulae (PN). The legacy of the historic Perek &
Kohoutek and Acker et al. catalogues is briefly covered before highlighting the
more recent but significant progress in PN discoveries in our Galaxy and the
Magellanic Clouds. We place particular emphasis on the major MASH and the IPHAS
catalogues, which, over the last decade alone, have essentially doubled
Galactic and LMC PN numbers. We then discuss the increasing role and importance
that multi-wavelength data is playing in both the detection of candidate PN and
the elimination of PN mimics that have seriously biased previous PN
compilations. The prospects for future surveys and current efforts and
prospects for PN detections in external galaxies are briefly discussed due to
their value both as cosmic distance indicators and as kinematical probes of
galaxies and dark matter properties.Comment: 8 pages, 1 figure, Proceedings of the Asymmetric Planetary Nebula V
Conference (Invited Review, Lake District, England, June 2010
Thermoelectric properties of AgGaTe and related chalcopyrite structure materials
We present an analysis of the potential thermoelectric performance of p-type
AgGaTe, which has already shown a of 0.8 with partial optimization,
and observe that the same band structure features, such as a mixture of light
and heavy bands and isotropic transport, that lead to this good performance are
present in certain other ternary chalcopyrite structure semiconductors. We find
that optimal performance of AgGaTe will be found for hole concentrations
between 4 and 2 cm at 900 K, and 2
and 10 cm at 700 K, and that certain other
chalcopyrite semiconductors might show good thermoelectric performance at
similar doping ranges and temperatures if not for higher lattice thermal
conductivity
Thermoelectric properties of -FeSi
We investigate the thermoelectric properties of -FeSi
using first principles electronic structure and Boltzmann transport
calculations. We report a high thermopower for both \textit{p}- and
\textit{n}-type -FeSi over a wide range of carrier
concentration and in addition find the performance for \textit{n}-type to be
higher than for the \textit{p}-type. Our results indicate that, depending upon
temperature, a doping level of 3 - 2
cm may optimize the thermoelectric performance
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