5,273 research outputs found
Talking about gas generation
Dr Richard Shaw currently dedicates his work to a long-term view of radioactive waste management, specifically trying to understand how its waste gases move in deep geological repositories. Here, he explains the huge scope of the FORGE project, and its heavily collaborative approac
Non-linear Redshift-Space Power Spectra
Distances in cosmology are usually inferred from observed redshifts - an
estimate that is dependent on the local peculiar motion - giving a distorted
view of the three dimensional structure and affecting basic observables such as
the correlation function and power spectrum. We calculate the full non-linear
redshift-space power spectrum for Gaussian fields, giving results for both the
standard flat sky approximation and the directly-observable angular correlation
function and angular power spectrum. Coupling between large and small scale
modes boosts the power on small scales when the perturbations are small. On
larger scales power is slightly suppressed by the velocities perturbations on
smaller scales. The analysis is general, but we comment specifically on the
implications for future high-redshift observations, and show that the
non-linear spectrum has significantly more complicated angular structure than
in linear theory. We comment on the implications for using the angular
structure to separate cosmological and astrophysical components of 21 cm
observations.Comment: 22 pages, 6 figures, changed to version accepted in Physics Review
Extragalactic Planetary Nebulae: Observational Challenges & Future Prospects
The study of extragalactic planetary nebulae (EPN) is a rapidly expanding
field. The advent of powerful new instrumentation such as the PN spectrograph
has led to an avalanche of new EPN discoveries both within and between
galaxies. We now have thousands of EPN detections in a heterogeneous selection
of nearby galaxies and their local environments, dwarfing the combined galactic
detection efforts of the last century. Key scientific motivations driving this
rapid growth in EPN research and discovery have been the use of the PNLF as a
standard candle, as dynamical tracers of their host galaxies and dark matter
and as probes of Galactic evolution. This is coupled with the basic utility of
PN as laboratories of nebula physics and the consequent comparison with theory
where population differences, abundance variations and star formation history
within and between stellar systems informs both stellar and galactic evolution.
Here we pose some of the burning questions, discuss some of the observational
challenges and outline some of the future prospects of this exciting,
relatively new, research area as we strive to go fainter, image finer, see
further and survey faster than ever before and over a wider wavelength regimeComment: 4 pages, no figures, LaTeX, to be published in Proceedings of the ESO
workshop on Planetary Nebulae beyond the Milky Way held at ESO, Garching, May
19-21, 200
Early-life-history profiles, seasonal abundance, and distribution of four species of Clupeid larvae from the northern Gulf of Mexico, 1982 and 1983
We present data on ichthyoplankton distribution, abundance,
and seasonality and supporting environmental information for
four species of coastal pelagics from the family Clupeidae: round herring Etrumeus teres, scaled sardine Harengula jaguana, Atlantic thread herring Opisthonema oglinum, and Spanish sardine Sardinella aurita. Data are from 1982 and 1983 cruises across the northern Gulf of Mexico sponsored by the Southeastern Area Monitoring and Assessment Program (SEAMAP). This is the first such examination for these species on a multiyear and gulfwide scale. Bioproflles on reproductive biology, early life history, meristics, adult distribution, and fisheries characteristics are also presented for these species.
During the summer, larval Atlantic thread herring and scaled
and Spanish sardines were abundant on the inner shelf <40 m
depth), but were rare or absent in deeper waters. Scaled sardine and thread herring were found virtually everywhere inner-shelf waters were sampled, but Spanish sardines were rare in the north-central Gulf. During 1982, larval Atlantic thread herring were the most abundant of the four target c1upeid species, whereas Spanish sardine were the most abundant during 1983. On the west Florida shelf, Spanish sardine dominated larval c1upeid populations both years. Scaled sardine larvae were the least abundant of the four species both years, but were still captured in 25% of inner-shelf bongo net collections. Round herring larvae, collected February-early June (primarily March-April), were abundant on the outer shelf (40-182 m depth) and especially off Louisiana. Over the 2-year period, outer-shelf mean abundance for round herring was 40.2 larvae/10 m2; inner-shelf mean abundances for scaled sardine, Atlantic thread herring, and Spanish sardine were 14.9, 39.2, and 41.9 larvae/l0 m2, respectively. (PDF file contains 66 pages.
PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
Analysis of emission lines in gaseous nebulae yields direct measures of
physical conditions and chemical abundances and is the cornerstone of nebular
astrophysics. Although the physical problem is conceptually simple, its
practical complexity can be overwhelming since the amount of data to be
analyzed steadily increases; furthermore, results depend crucially on the input
atomic data, whose determination also improves each year. To address these
challenges we created PyNeb, an innovative code for analyzing emission lines.
PyNeb computes physical conditions and ionic and elemental abundances, and
produces both theoretical and observational diagnostic plots. It is designed to
be portable, modular, and largely customizable in aspects such as the atomic
data used, the format of the observational data to be analyzed, and the
graphical output. It gives full access to the intermediate quantities of the
calculation, making it possible to write scripts tailored to the specific type
of analysis one wants to carry out. In the case of collisionally excited lines,
PyNeb works by solving the equilibrium equations for an n-level atom; in the
case of recombination lines, it works by interpolation in emissivity tables.
The code offers a choice of extinction laws and ionization correction factors,
which can be complemented by user-provided recipes. It is entirely written in
the python programming language and uses standard python libraries. It is fully
vectorized, making it apt for analyzing huge amounts of data. The code is
stable and has been benchmarked against IRAF/NEBULAR. It is public, fully
documented, and has already been satisfactorily used in a number of published
papers.Comment: 17 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysics. Typos and reference list corrected in this versio
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