37,768 research outputs found
Mathematical morphology and applications in automated sunspot detection
This presentation discusses the mathematical morphology and applications in automated sunspot detection
X-ray Emission from the 3C 273 Jet
We present results from four recent Chandra monitoring observations of the
jet in 3C 273 using the ACIS detector, obtained between November 2003 and July
2004. We find that the X-ray emission comes in two components: unresolved knots
that are smaller than the corresponding optically emitting knots and a broad
channel that is about the same width as the optical interknot region. We
compute the jet speed under the assumption that the X-ray emission is due to
inverse Compton scattering of the cosmic microwave background, finding that the
dimming of the jet X-ray emission to the jet termination relative to the radio
emission may be due to bulk deceleration.Comment: 2 pages, 2 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
Progress toward a Soft X-ray Polarimeter
We are developing instrumentation for a telescope design capable of measuring
linear X-ray polarization over a broad-band using conventional spectroscopic
optics. Multilayer-coated mirrors are key to this approach, being used as Bragg
reflectors at the Brewster angle. By laterally grading the multilayer mirrors
and matching to the dispersion of a spectrometer, one may take advantage of
high multilayer reflectivities and achieve modulation factors over 50% over the
entire 0.2-0.8 keV band. We present progress on laboratory work to demonstrate
the capabilities of an existing laterally graded multilayer coated mirror pair.
We also present plans for a suborbital rocket experiment designed to detect a
polarization level of 12-17% for an active galactic nucleus in the 0.1-1.0 keV
band.Comment: 11 pages, 12 figures, to appear in the proceedings of the SPIE,
volume 8861, on Optics for EUV, X-Ray, and Gamma-Ray Astronom
Militarism and the American Spirit by S. L. A. Marshall, Spring Commencement: June 2, 1963
Text of speech delivered by Brigadier General S. L. A. Marshall at the UND Spring Commencement on June 2, 1963. Marshall was a military historian and writer for the Detroit News in Detroit, MI. He entitled his remarks: Militarism and the American Spirit
Sorted gene genealogies and species- specific nonsynonymous substitutions point to putative postmating prezygotic isolation genes in Allonemobius crickets
Citation: Noh, S., & Marshall, J. L. (2016). Sorted gene genealogies and species- specific nonsynonymous substitutions point to putative postmating prezygotic isolation genes in Allonemobius crickets. Peerj, 4, 29. doi:10.7717/peerj.1678In the Allonemobius socius complex of crickets reproductive isolation is primarily accomplished via postmating prezygotic barriers. We tested seven protein-coding genes expressed in the male ejaculate for patterns of evolution consistent with a putative role as postmating prezygotic isolation genes. Our recently diverged species generally lacked sequence variation. As a result, omega-based tests were only mildly successful. Some of our genes showed evidence of elevated omega values on the internal branches of gene trees. In a couple of genes, these internal branches coincided with both species branching events of the species tree, between A. fasciatus and the other two species, and between A. socius and A. sp. nov. Tex. In comparison, more successful approaches were those that took advantage of the varying degrees of lineage sorting and allele sharing among our young species. These approaches were particularly powerful within the contact zone. Among the genes we tested we found genes with genealogies that indicated relatively advanced degrees of lineage sorting across both allopatric and contact zone alleles. Within a contact zone between two members of the species complex, only a subset of genes maintained allelic segregation despite evidence of ongoing gene flow in other genes. The overlap in these analyses was arginine kinase (AK) and apolipoprotein A-1 binding protein (APBP). These genes represent two of the first examples of sperm maturation, capacitation, and motility proteins with fixed non-synonymous substitutions between species-specific alleles that may lead to postmating prezygotic isolation. Both genes express ejaculate proteins transferred to females during copulation and were previously identified through comparative proteomics. We discuss the potential function of these genes in the context of the specific postmating prezygotic isolation phenotype among, our species, namely conspecific sperm precedence and the superior ability of conspecific males to induce oviposition in females
Optical detection of the Pictor A jet and tidal tail : evidence against an IC/CMB jet
Date of Acceptance: 12/06/2015New images of the FR II radio galaxy Pictor A from the Hubble Space Telescope reveal a previously undiscovered tidal tail, as well as a number of jet knots coinciding with a known X-ray and radio jet. The tidal tail is approximately 5″ wide (3 kpc projected), starting 18″ (12 kpc) from the center of Pictor A, and extends more than 90″ (60 kpc). The knots are part of a jet observed to be about 4′ (160 kpc) long, extending to a bright hotspot. These images are the first optical detections of this jet, and by extracting knot flux densities through three filters, we set constraints on emission models. While the radio and optical flux densities are usually explained by synchrotron emission, there are several emission mechanisms that might be used to explain the X-ray flux densities. Our data rule out Doppler-boosted inverse Compton scattering as a source of the high-energy emission. Instead, we find that the observed emission can be well described by synchrotron emission from electrons with a low-energy index (p ∼ 2) that dominates the radio band, while a high-energy index (p ∼ 3) is needed for the X-ray band and the transition occurs in the optical/infrared band. This model is consistent with a continuous electron injection scenario.Peer reviewedFinal Accepted Versio
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