27,126 research outputs found
Using ACIS on the Chandra X-ray Observatory as a particle radiation monitor II
The Advanced CCD Imaging Spectrometer is an instrument on the Chandra X-ray
Observatory. CCDs are vulnerable to radiation damage, particularly by soft
protons in the radiation belts and solar storms. The Chandra team has
implemented procedures to protect ACIS during high-radiation events including
autonomous protection triggered by an on-board radiation monitor. Elevated
temperatures have reduced the effectiveness of the on-board monitor. The ACIS
team has developed an algorithm which uses data from the CCDs themselves to
detect periods of high radiation and a flight software patch to apply this
algorithm is currently active on-board the instrument. In this paper, we
explore the ACIS response to particle radiation through comparisons to a number
of external measures of the radiation environment. We hope to better understand
the efficiency of the algorithm as a function of the flux and spectrum of the
particles and the time-profile of the radiation event.Comment: 10 pages, 5 figures, to be published in Proc. SPIE 8443, "Space
Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray
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Mild acute stress improves response speed without impairing accuracy or interference control in two selective attention tasks: Implications for theories of stress and cognition.
Acute stress is generally thought to impair performance on tasks thought to rely on selective attention. This effect has been well established for moderate to severe stressors, but no study has examined how a mild stressor-the most common type of stressor-influences selective attention. In addition, no study to date has examined how stress influences the component processes involved in overall selective attention task performance, such as controlled attention, automatic attentional activation, decision-making, and motor abilities. To address these issues, we randomly assigned 107 participants to a mild acute stress or control condition. As expected, the mild acute stress condition showed a small but significant increase in cortisol relative to the control condition. Following the stressor, we assessed attention with two separate flanker tasks. One of these tasks was optimized to investigate component attentional processes using computational cognitive modeling, whereas the other task employed mouse-tracking to illustrate how response conflict unfolded over time. The results for both tasks showed that mild acute stress decreased response time (i.e., increased response speed) without influencing accuracy or interference control. Further, computational modeling and mouse-tracking analyses indicated that these effects were due to faster motor action execution time for chosen actions. Intriguingly, however, cortisol responses were unrelated to any of the observed effects of mild stress. These results have implications for theories of stress and cognition, and highlight the importance of considering motor processes in understanding the effects of stress on cognitive task performance
High temperature static strain gage development contract, tasks 1 and 2
Results are presented for the first two tasks to develop resistive strain gage systems for use up to 1250 K on blades and vanes in gas turbine engines under tests. The objective of these two tasks was to further improve and evaluate two static strain gage alloys identified as candidates in a previous program. Improved compositions were not found for either alloy. Further efforts on the Fe-11.9Al-10.6Cr weigth percent alloy were discontinued because of time dependent drift problems at 1250 K in air. When produced as a 6.5 micrometer thick sputtered film, the Pd-13Cr weight percent alloys is not sufficiently stable for this use in air at 1250 K and a protective overcoat system will need to be developed
Evolution from a molecular Rydberg gas to an ultracold plasma in a seeded supersonic expansion of NO
We report the spontaneous formation of a plasma from a gas of cold Rydberg
molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1
K in a seeded supersonic molecular beam, to single Rydberg states extending as
deep as 80 cm below the lowest ionization threshold. The density of
excited molecules in the illuminated volume is as high as 1 x 10
cm. This population evolves to produce prompt free electrons and a
durable cold plasma of electrons and intact NO ions.Comment: 4 pages (two column) 3 figures; smaller figure files, corrected typo
Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation
The role of orbital differentiation on the emergence of superconductivity in
the Fe-based superconductors remains an open question to the scientific
community. In this investigation, we employ a suitable microscopic spin probe
technique, namely Electron Spin Resonance (ESR), to investigate this issue on
selected chemically substituted BaFeAs single crystals. As the
spin-density wave (SDW) phase is suppressed, we observe a clear increase of the
Fe 3 bands anisotropy along with their localization at the FeAs plane. Such
an increase of the planar orbital content interestingly occurs independently on
the chemical substitution responsible for suppressing the SDW phase. As a
consequence, the magnetic fluctuations combined with the resultant particular
symmetry of the Fe 3 bands are propitious ingredients to the emergence of
superconductivity in this class of materials.Comment: 6 pages, 5 figure
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