2,093 research outputs found
Three-meter balloon-borne telescope
The Three-Meter Balloon-Borne Telescope is planned as a general purpose facility for making far-infrared and submillimeter astronomical observations from the stratosphere. It will operate throughout the spectral range 30 microns to 1 millimeter which is largely obscurred from the ground. The design is an f/13.5 Cassegrain telescope with an f/1.33 3-meter primary mirror supported with a 3-axis gimbal and stabilization system. The overall structure is 8.0 m high by 5.5 m in width by 4.0 m in depth and weighs 2000 kg. This low weight is achieved through the use of an ultra lightweight primary mirror of composite construction. Pointing and stabilization are achieved with television monitoring of the star field, flex-pivot bearing supports, gyroscopes, and magnetically levitated reaction wheels. Two instruments will be carried on each flight; generally a photometric camera and a spectrometer. A 64-element bolometer array photometric camera operating from 30 to 300 microns is planned as part of the facility. Additional instruments will be derived from KAO and other development programs
Balloon-borne three-meter telescope for far-infrared and submillimeter astronomy
The scientific objectives, engineering analysis and design, results of technology development, and focal-plane instrumentation for a two-meter balloon-borne telescope for far-infrared and submillimeter astronomy are presented. The unique capabilities of balloon-borne observations are discussed. A program summary emphasizes the development of the two-meter design. The relationship of the Large Deployable Reflector (LDR) is also discussed. Detailed treatment is given to scientific objectives, gondola design, the mirror development program, experiment accommodations, ground support equipment requirements, NSBF design drivers and payload support requirements, the implementation phase summary development plan, and a comparison of three-meter and two-meter gondola concepts
Resolved Mid-Infrared Emission Around AB Aur and V892 Tau with Adaptive Optics Nulling Interferometric Observations
We present the results of adaptive optics nulling interferometric
observations of two Herbig Ae stars, AB Aur and V892 Tau. Our observations at
10.3 microns show resolved circumstellar emission from both sources. Further
analysis of the AB Aur emission suggests that there is an inclined disk
surrounding the star. The diameter of the disk is derived to be 24 to 30 AU
with an inclination of 45 to 65 degrees from face-on, and a major-axis PA of 30
+/- 15 degrees (E of N). Differences in the physical characteristics between
the mid-IR emission and emission at other wavelengths (near-IR and millimeter),
found in previous studies, suggest a complex structure for AB Aur's
circumstellar environment, which may not be explained by a disk alone. The
similarity in the observed size of AB Aur's resolved emission and that of
another Herbig Ae star, HD 100546, is likely coincidental, as their respective
evolutionary states and spectral energy distributions suggest significantly
different circumstellar environments.Comment: 11 pages, 1 figure, Accepted for publication in ApJ Letter
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Understanding the Catalytic Active Sites of Crystalline CoSbxOy for Electrochemical Chlorine Evolution
The chlorine evolution reaction (CER) is a key reaction in electrochemical oxidation (EO) of water treatment. Conventional anodes based on platinum group metals can be prohibitively expensive, which hinders further application of EO systems. Crystalline cobalt antimonate (CoSbxOy) was recently identified as a promising alternative to conventional anodes due to its high catalytic activity and stability in acidic media. However, its catalytic sites and reaction mechanism have not yet been elucidated. This study sheds light on the catalytically active sites in crystalline CoSbxOy anodes by using scanning electrochemical microscopy to compare the CER catalytic activities of a series of anode samples with different bulk Sb/Co ratios (from 1.43 to 2.80). The results showed that Sb sites served as more active catalytic sites than the Co sites. The varied Sb/Co ratios were also linked with slightly different electronic states of each element, leading to different CER selectivities in 30 mM chloride solutions under 10 mA cm–2 current density. The high activity of Sb sites toward the CER highlighted the significance of the electronic polarization that changed the oxidation states of Co and Sb
Effects of light and temperature on germination of Pyxidanthera brevifolia Wells (Diapensiaceae)
Pyxidanthera brevifolia is an evergreen semiwoody cushion plant endemic to the Sandhills of North and South Carolina, with the majority of populations occurring on Fort Bragg Military Reservation in North Carolina. Currently the species is listed as Endangered in North Carolina and is designated as a Species at Risk (SAR) by the US Department of Defense. Previous studies have suggested that seeds may not be viable because they failed to germinate under controlled conditions. Our objectives in this study were to attempt germination of Pyxidanthera brevifolia seeds, determine the best temperature conditions for germination, and understand more about germination requirements to aid in future restoration efforts. Using seeds that had been stored at room temperature for six months, we performed a germination experiment at the NCSU Phytotron with six treatments, all combinations of three temperature regimes (low (18 uC day / 14 uC night), medium (22/18 uC), and high (26/ 22 uC)) and two light conditions (light and dark). We monitored the experiment for 13 weeks, recording the number of seeds germinating per dish and the number of days to germination for seeds in each treatment. We found that Pxyidanthera brevifolia produces germinable seeds and that there are significant effects of light and temperature on germination. Highest germination occurred under low temperature and high light conditions (78%); the combination of high temperature and no light produced the lowest germination (6%). Seeds exposed to light germinated significantly earlier at the coolest temperature, compared to medium and high temperatures. These results indicate that it is possible to germinate seeds of this rare plant and suggest that germination of Pyxidanthera brevifolia likely occurs in late fall and is dependent on adequate light availability
From Parasite to Mutualist: Rapid Evolution of Wolbachia in Natural Populations of Drosophila
Wolbachia are maternally inherited bacteria that commonly spread through host populations by causing cytoplasmic incompatibility, often expressed as reduced egg hatch when uninfected females mate with infected males. Infected females are frequently less fecund as a consequence of Wolbachia infection. However, theory predicts that because of maternal transmission, these “parasites” will tend to evolve towards a more mutualistic association with their hosts. Drosophila simulans in California provided the classic case of a Wolbachia infection spreading in nature. Cytoplasmic incompatibility allowed the infection to spread through individual populations within a few years and from southern to northern California (more than 700 km) within a decade, despite reducing the fecundity of infected females by 15%–20% under laboratory conditions. Here we show that the Wolbachia in California D. simulans have changed over the last 20 y so that infected females now exhibit an average 10% fecundity advantage over uninfected females in the laboratory. Our data suggest smaller but qualitatively similar changes in relative fecundity in nature and demonstrate that fecundity-increasing Wolbachia variants are currently polymorphic in natural populations
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