85 research outputs found
Molecular gas in NGC6946
We present imaging of molecular gas emission in the star-forming spiral
galaxy NGC6946. Our CO(1-0) and CO(3-2) images, made at 22" resolution with the
IRAM 30-m and the Heinrich Hertz 10-m radio telescopes, are the most extensive
CO observations of this galaxy and are among the most extensive observations of
molecular gas in any spiral galaxy. The molecular component in NGC6946 is
unusually massive, with a ratio of molecular to atomic Hydrogen of 0.57. A star
formation efficiency image for NGC6946 ranges by over two orders of magnitude
with highest values found in the northeastern spiral arm, and anticorrelates
with the 6cm polarized emission image, which traces the regular part of the
magnetic field. We analyse the ISM in NGC6946's disk by making 1-D and 2-D
comparisons of images made in several wavebands. A point-by-point correlation
technique finds that the molecular gas is closely associated with the
7micron-emitting dust. The high correlation found between the MIR emission and
the radio continuum at 6cm cannot be due to dust heating and gas ionization in
star-forming regions because the thermal radio emission is less correlated with
the MIR than the nonthermal emission. A coupling of magnetic fields to gas
clouds is proposed as a possible scenario.Comment: A&A accepted, 23 pages, 11 figures. Version with high resolution
figures available at: http://cfa-www.harvard.edu/~wwalsh/sp.htm
Diversity, distribution and conservation status of island conifers: a global review
Aim Conifers comprise an ancient and diverse group of plants showing a wide
distribution range. To better understand the general patterns of species successfully
established on islands, this review compiles information about the distribution,
diversity, dispersal potential and conservation status of insular conifers,
with special emphasis on those inhabiting remote oceanic islands.
Location Global.
Methods An exhaustive survey was made of world-wide databases and literature.
We registered information on island distribution (including ocean region,
extension and geological origin of the island), endemism and threat status for
each insular conifer.
Results 285 of the 547 conifer species considered in this review show an insular
distribution (i.e. their distribution encompass insular territories). The family
Podocarpaceae is best represented, with 40% of the insular species. The importance
of endozoochory for long-distance dispersal is clear, because it was the
most frequent dispersal syndrome among oceanic conifers. A high proportion
of the total threatened conifers occur on islands (52%), and many of them are
insular endemics (72%). Among conifer families, Araucariaceae is the most
threatened in insular territories.
Main conclusions Our results highlight the wide diversity of insular conifers,
as well as the key role of oceanic islands in catalysing speciation mechanisms.
Pacific islands in particular harbour the greatest diversity levels, constituting a
major centre of diversification. The wide distribution of conifers reflects their
great potential for dispersal and colonization, endozoochory being the most
favourable dispersal syndrome for reaching remote islands. The general threat
status of insular conifers highlights the fragility of island biota and the urgent
need for policies focused on their preservation.Ministerio de Educación y CienciaOrganismo Autónomo de Parques Nacionale
Patients' age as a determinant of care received following acute stroke: A systematic review
<p>Abstract</p> <p>Background</p> <p>Evidence-based care should improve acute stroke outcomes with the same magnitude of effect for stroke patients of all ages. However, there is evidence to suggest that, in some instances, older stroke patients may receive poorer quality care than younger patients.</p> <p>Our aim was to systematically review evidence of the quality of care provided to patients with acute stroke related to their age. Quality of care was determined by compliance with recommended care processes.</p> <p>Methods</p> <p>We systematically searched MEDLINE, CINAHL, ISI Web of Knowledge, Ageline and the Cochrane Library databases to identify publications (1995-2009) that reported data on acute stroke care process indicators by patient age. Data extracted included patient demographics and process indicator compliance. Included publications were critically appraised by two independent reviewers using the Critical Appraisal Skills Programme tool, and a comparison was made of the risk of bias according to studies' findings. The evidence base for reported process indicators was determined, and meta-analysis was undertaken for studies with sufficient similarity.</p> <p>Results</p> <p>Nine from 163 potential studies met the inclusion criteria. Of the 56 process indicators reported, eleven indicators were evidence-based. Seven of these indicators (64%) showed significantly poorer care for older patients compared to younger ones, while younger patients received comparatively inferior care for only antihypertensive therapy at discharge. Our findings are limited by the variable methodological quality of included studies.</p> <p>Conclusion</p> <p>Patients' age may be a factor in the care they receive after an acute stroke. However, the possible influence of patients' age on clinicians' decision-making must be considered in terms of the many complex issues that surround the provision of optimal care for older patients with acute stroke.</p
Drosophila Duplication Hotspots Are Associated with Late-Replicating Regions of the Genome
Duplications play a significant role in both extremes of the phenotypic spectrum of newly arising mutations: they can have severe deleterious effects (e.g. duplications underlie a variety of diseases) but can also be highly advantageous. The phenotypic potential of newly arisen duplications has stimulated wide interest in both the mutational and selective processes shaping these variants in the genome. Here we take advantage of the Drosophila simulans–Drosophila melanogaster genetic system to further our understanding of both processes. Regarding mutational processes, the study of two closely related species allows investigation of the potential existence of shared duplication hotspots, and the similarities and differences between the two genomes can be used to dissect its underlying causes. Regarding selection, the difference in the effective population size between the two species can be leveraged to ask questions about the strength of selection acting on different classes of duplications. In this study, we conducted a survey of duplication polymorphisms in 14 different lines of D. simulans using tiling microarrays and combined it with an analogous survey for the D. melanogaster genome. By integrating the two datasets, we identified duplication hotspots conserved between the two species. However, unlike the duplication hotspots identified in mammalian genomes, Drosophila duplication hotspots are not associated with sequences of high sequence identity capable of mediating non-allelic homologous recombination. Instead, Drosophila duplication hotspots are associated with late-replicating regions of the genome, suggesting a link between DNA replication and duplication rates. We also found evidence supporting a higher effectiveness of selection on duplications in D. simulans than in D. melanogaster. This is also true for duplications segregating at high frequency, where we find evidence in D. simulans that a sizeable fraction of these mutations is being driven to fixation by positive selection
Population Genomic Inferences from Sparse High-Throughput Sequencing of Two Populations of Drosophila melanogaster
Short-read sequencing techniques provide the opportunity to capture genome-wide sequence data in a single experiment. A current challenge is to identify questions that shallow-depth genomic data can address successfully and to develop corresponding analytical methods that are statistically sound. Here, we apply the Roche/454 platform to survey natural variation in strains of Drosophila melanogaster from an African (n = 3) and a North American (n = 6) population. Reads were aligned to the reference D. melanogaster genomic assembly, single nucleotide polymorphisms were identified, and nucleotide variation was quantified genome wide. Simulations and empirical results suggest that nucleotide diversity can be accurately estimated from sparse data with as little as 0.2× coverage per line. The unbiased genomic sampling provided by random short-read sequencing also allows insight into distributions of transposable elements and copy number polymorphisms found within populations and demonstrates that short-read sequencing methods provide an efficient means to quantify variation in genome organization and content. Continued development of methods for statistical inference of shallow-depth genome-wide sequencing data will allow such sparse, partial data sets to become the norm in the emerging field of population genomics
Influence of Ambient Sound Fluctuations on the Crossing Decisions of Pedestrians who Are Visually Impaired: Implications for Setting a Minimum Sound Level for Quiet Vehicles
Impact of a Braille-Note on Writing: Evaluating the Process, Quality, and Attitudes of Three Students Who are Visually Impaired
- …