153 research outputs found
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
Optical constants of magnetron-sputtered magnesium films in the 25-1300 eV energy range
The transmittance of dc magnetron-sputtered Mg thin films was measured in the 25-1300 eV spectral range. Freestanding Mg films protected with Al layers were characterized ex situ. Transmittance measurements were used to obtain the extinction coefficient k of Mg films. The obtained k values along with the data available in the literature, and with interpolations and extrapolations for the rest of the spectrum, were used to obtain the real part of the index of refraction n by the Kramers-Krönig analysis. Sum-rule tests indicated a good consistency of the data. © 2010 American Institute of Physics.Peer Reviewe
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Progress in Large Period Multilayer Coatings for High Harmonic and Solar Applications
Multilayer coatings for normal incidence optics designed for the long wavelength region (25 nm < {lambda} < 50 nm) are particularly challenging due to the few number of layers that can be utilized in the reflection. Recently, Mg/SiC multilayers have been fabricated with normal incidence reflectivity in the vicinity of 40% for wavelengths near the He-II line at 30.4 nm. Motivated by this success we have investigated the use of a tri-band multilayer to increase the bandwidth while maintaining the reflectivity. The multilayers were deposited by conventional magnetron sputtering. Using Mg/SiC bilayers a reflectivity of 45% was achieved at 27 to 32 nm at an angle of 5 deg from normal. The Mg/Sc/SiC multilayer systems have also been investigated. It obtained a near normal incidence reflectivity of 35% while increasing the bandwidth by a factor of 2. These results are very encouraging for the possibility of more widespread applications of normal incidence optics in high harmonic applications
Serological Survey and Pathogen Exposure of Adult Female White-tailed Deer in the Western Dakotas
Establishing baseline values for pathogen exposure and nutritional indices is necessary to monitor population health. However, little is known about white-tailed deer (Odocoileus virginianus) pathogen exposure and nutritional condition in the Northern Great Plains. Our objective was to assess pathogen exposure and establish nutritional indices for female white-tailed deer in Dunn and Grant counties, North Dakota and Perkins County, South Dakota. During 2014, we collected blood serum from 150 adult female white-tailed deer. Pathogens with the highest antibody prevalence included West Nile Virus (WNV; 85%), epizootic hemorrhagic disease (48%), and malignant catarrhal fever (32%). Serum values for creatine kinase, globulin, glucose, potassium, and lactate dehydrogenase in all three study areas were higher than reference ranges while sodium was low in Grant County relative to Dunn and Perkins counties. We speculate that high exposure of WNV and high potassium values combined with low sodium values may affect neonate survival in Grant County. However, regional differences in pathogen exposure, their connection to serum values, and their potential interactive effects on survival are not well understood
Serological Survey and Pathogen Exposure of Adult Female White-tailed Deer in the Western Dakotas
Establishing baseline values for pathogen exposure and nutritional indices is necessary to monitor population health. However, little is known about white-tailed deer (Odocoileus virginianus) pathogen exposure and nutritional condition in the Northern Great Plains. Our objective was to assess pathogen exposure and establish nutritional indices for female white-tailed deer in Dunn and Grant counties, North Dakota and Perkins County, South Dakota. During 2014, we collected blood serum from 150 adult female white-tailed deer. Pathogens with the highest antibody prevalence included West Nile Virus (WNV; 85%), epizootic hemorrhagic disease (48%), and malignant catarrhal fever (32%). Serum values for creatine kinase, globulin, glucose, potassium, and lactate dehydrogenase in all three study areas were higher than reference ranges while sodium was low in Grant County relative to Dunn and Perkins counties. We speculate that high exposure of WNV and high potassium values combined with low sodium values may affect neonate survival in Grant County. However, regional differences in pathogen exposure, their connection to serum values, and their potential interactive effects on survival are not well understood
Habitat Selection of White-tailed Deer Fawns and their Dams in the Northern Great Plains
Habitat availability can affect important life-history traits such as survival; however, little information exists on how microhabitat characteristics found at parturition sites selected by dams and bed sites selected by their offspring differ fromthe surrounding area and from each other. Therefore, we assessed how vegetation affected maternal parturition and offspring bed site selection for white-tailed deer (Odocoileus virginianus) in the Northern Great Plains. Dams selected for sites with decreased vegetation height, potentially improving their visibility, which may increase their ability to escape approaching predators. Conversely, there was no variation between vegetative characteristics at neonate bed sites and their associated random sites, indicating grasslands provide adequate concealment for neonates. Dams possess the ability to flee from approaching predators, thus increasing the importance of visibility while giving birth. Conversely, neonates depend on fear bradycardia as their main antipredator defense, so concealment is more important. Our results suggest that vegetation structure is an important characteristic to white-tailed deer as habitat needs vary between adults and neonates
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Metrologies for the Phase Characterization of Attosecond
EUV optics play a key role in attosecond science since only with higher photon energies is it possible to achieve the wide spectral bandwidth required for ultrashort pulses. Multilayer EUV mirrors have been proposed and are being developed to temporally shape (compress) attosecond pulses. To fully characterize a multilayer optic for pulse applications requires not only knowledge of the reflectivity, as a function of photon energy, but also the reflected phase of the mirror. This work develops the metrologies to determine the reflected phase of an EUV multilayer mirror using the photoelectric effect. The proposed method allows one to determine the optic's impulse response and hence its pulse characteristics
In-situ X-ray-absorption Spectroscopy Study of Hydrogen Absorption by Nickel-Magnesium Thin Films
Structural and electronic properties of co-sputtered Ni-Mg thin films with varying Ni to Mg ratio were studied by in-situ x-ray absorption spectroscopy in the Ni L-edge and Mg K-edge regions. Co-deposition of the metals led to increased disorder and decreased coordination around Ni and Mg compared to pure metal films. Exposure of the metallic films to hydrogen resulted in formation of hydrides and increased disorder. The presence of hydrogen as a near neighbor around Mg caused a drastic reduction in the intensities of multiple scattering resonances at higher energies. The optical switching behavior and changes in the x-ray spectra varied with Ni to Mg atomic ratio. Pure Mg films with Pd overlayers were converted to MgH2: the H atoms occupy regular sites as in bulk MgH2. Although optical switching was slow in the absence of Ni, the amount of H2 absorption was large. Incorporation of Ni in Mg films led to an increase in the speed of optical switching but decreased maximum transparency. Significant shifts in the Ni L3 and L2 peaks are consistent with strong interaction with hydrogen in the mixed films
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