246 research outputs found
From Molecular Cores to Planet-forming Disks with SIRTF
The SIRTF mission and the Legacy programs will provide coherent data bases
for extra-galactic and Galactic science that will rapidly become available to
researchers through a public archive. The capabilities of SIRTF and the six
legacy programs are described briefly. Then the cores to disks (c2d) program is
described in more detail. The c2d program will use all three SIRTF instruments
(IRAC, MIPS, and IRS) to observe sources from molecular cores to protoplanetary
disks, with a wide range of cloud masses, stellar masses, and star-forming
environments. The SIRTF data will stimulate many follow-up studies, both with
SIRTF and with other instruments.Comment: 6 pages, from Fourth Cologne-Bonn-Zermatt-Symposium, The Dense
Interstellar Matter in Galaxie
The SKA and "High-Resolution" Science
"High-resolution", or "long-baseline", science with the SKA and its
precursors covers a broad range of topics in astrophysics. In several research
areas, the coupling between improved brightness sensitivity of the SKA and a
sub-arcsecond resolution would uncover truly unique avenues and opportunities
for studying extreme states of matter, vicinity of compact relativistic
objects, and complex processes in astrophysical plasmas. At the same time, long
baselines would secure excellent positional and astrometric measurements with
the SKA and critically enhance SKA image fidelity at all scales. The latter
aspect may also have a substantial impact on the survey speed of the SKA, thus
affecting several key science projects of the instrument.Comment: JENAM-2010: Invited talk at JENAM session S7: The Square Kilometre
Array: Paving the way for the new 21st century radio astronomy paradigm; 9
page
Protracted timescales of lower crustal growth at the fast-spreading East Pacific Rise
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 5 (2012): 275-278, doi:10.1038/ngeo1378.Formation of the oceanic crust at mid-ocean ridges is a fundamental component of
plate tectonics. A majority of the crust at many ridges is composed of plutonic rocks
that form by crystallization of mantle-derived magmas within the crust. Recent
application of U/Pb dating to samples from in-situ oceanic crust has begun to
provide exciting new insight into the timing, duration and distribution of
magmatism during formation of the plutonic crust1-4. Previous studies have focused
on samples from slow-spreading ridges, however, the time scales and processes of
crustal growth are expected to vary with plate spreading rate. Here we present the
first high-precision dates from plutonic crust formed at the fast-spreading East
Pacific Rise (EPR). Individual zircon minerals yielded dates from 1.420–1.271
million years ago, with uncertainties of ± 0.006–0.081 million years. Within
individual samples, zircons record a range of dates of up to ~0.124 million years,
consistent with protracted crystallization or assimilation of older zircons from
adjacent rocks. The variability in dates is comparable to data from the Vema
lithospheric section on the Mid-Atlantic Ridge (MAR)3, suggesting that time scales
of magmatic processes in the lower crust may be similar at slow- and fast-spreading
ridges.This research was partially funded by NSF grant OCE-0727914 (SAB), a Cardiff
University International Collaboration Award (CJL) and NERC grant NE/C509023/1
(CJM).2012-07-2
Influence of climatic variables on crown condition in pine forests of Northern Spain
Producción CientÃficaThe aim of this study was to find relationships between crown condition and
some climatic parameters to identify which are those having a main influence on
crown condition, and how this influence is shown in the tree (crown transparency),
and to contribute to the understanding of how these parameters will affect under
future climate change scenarios
The stellar and sub-stellar IMF of simple and composite populations
The current knowledge on the stellar IMF is documented. It appears to become
top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr
pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing
metallicity and in increasingly massive early-type galaxies. It declines quite
steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars
having their own IMF. The most massive star of mass mmax formed in an embedded
cluster with stellar mass Mecl correlates strongly with Mecl being a result of
gravitation-driven but resource-limited growth and fragmentation induced
starvation. There is no convincing evidence whatsoever that massive stars do
form in isolation. Various methods of discretising a stellar population are
introduced: optimal sampling leads to a mass distribution that perfectly
represents the exact form of the desired IMF and the mmax-to-Mecl relation,
while random sampling results in statistical variations of the shape of the
IMF. The observed mmax-to-Mecl correlation and the small spread of IMF
power-law indices together suggest that optimally sampling the IMF may be the
more realistic description of star formation than random sampling from a
universal IMF with a constant upper mass limit. Composite populations on galaxy
scales, which are formed from many pc scale star formation events, need to be
described by the integrated galactic IMF. This IGIMF varies systematically from
top-light to top-heavy in dependence of galaxy type and star formation rate,
with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and
Galactic Structure, Vol.5, Springer. This revised version is consistent with
the published version and includes additional references and minor additions
to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-
The role of coxI -associated repeated sequences in plant mitochondrial DNA rearrangements and radish cytoplasmic male sterility
The gene coxI , encoding subunit I of mitochondrial cytochrome c oxidase, has been characterized from the normal (fertile) and Ogura (male-sterile) cytoplasms of radish to determine if a previously identified mitochondrial DNA rearrangement, and its associated transcriptional differences, could play a role in Ogura cytoplasmic male sterility (CMS). The normal and Ogura loci are virtually identical for 2.8 kb, including a 527-codon open reading frame whose product is approximately 95% identical to other plant COXI polypeptides. A rearrangement 120 bp 5′ to the coding region results in different 5′ transcript termini for the two genes. A comparison of several crucifer mitochondrial DNAs indicates that this rearrangement also occurs in the normal radish cytoplasm and is, therefore, not involved in Ogura CMS. Sequences present at the coxI locus belong to at least two different dispersed repeat families, members of which are also associated with other rearranged genes in radish.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46974/1/294_2004_Article_BF00336485.pd
The Murchison Widefield Array Transients Survey (MWATS). A search for low-frequency variability in a bright Southern hemisphere sample
We report on a search for low-frequency radio variability in 944 bright (>4 Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for several years with the Murchison Widefield Array. In the majority of sources, we find very low levels of variability with typical modulation indices 2.8 yr) with time-averaged modulation indices M¯¯¯¯¯=3.1−7.1M¯=3.1−7.1 per cent. With 7/15 of these variable sources having peaked spectral energy distributions, and only 5.7 per cent of the overall sample having peaked spectra, we find an increase in the prevalence of variability in this spectral class. We conclude that the variability seen in this survey is most probably a consequence of refractive interstellar scintillation and that these objects must have the majority of their flux density contained within angular diameters less than 50 milliarcsec (which we support with multiwavelength data). At 154 MHz, we demonstrate that interstellar scintillation time-scales become long (∼decades) and have low modulation indices, while synchrotron-driven variability can only produce dynamic changes on time-scales of hundreds of years, with flux density changes less than one milli-jansky (without relativistic boosting). From this work, we infer that the low-frequency extragalactic southern sky, as seen by SKA-Low, will be non-variable on time-scales shorter than 1 yr
Genome-wide association study of depression phenotypes in UK Biobank identifies variants in excitatory synaptic pathways
Depression is a polygenic trait that causes extensive periods of disability. Previous genetic studies have identified common risk variants which have progressively increased in number with increasing sample sizes of the respective studies. Here, we conduct a genome-wide association study in 322,580 UK Biobank participants for three depression-related phenotypes: broad depression, probable major depressive disorder (MDD), and International Classification of Diseases (ICD, version 9 or 10)-coded MDD. We identify 17 independent loci that are significantly associated (P < 5 × 10−8) across the three phenotypes. The direction of effect of these loci is consistently replicated in an independent sample, with 14 loci likely representing novel findings. Gene sets are enriched in excitatory neurotransmission, mechanosensory behaviour, post synapse, neuron spine and dendrite functions. Our findings suggest that broad depression is the most tractable UK Biobank phenotype for discovering genes and gene sets that further our understanding of the biological pathways underlying depression
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