7,185 research outputs found
Detection of H-alpha emission from the Magellanic Stream: evidence for an extended gaseous Galactic halo
We have detected faint, diffuse H\alpha emission of surface brightness Rayleighs, R, and R respectively,
corresponding to emission measures of 1.0 to 0.5 \cmsixpc. We have observed
several positions near the MS IV concentration, and find that the strongest
emission is on the sharp leading-edge density gradient. There is less emission
at points away from the gradient, and halfway between MS III and MS IV the
H< 0.04\alpha emission at cloud leading edges to heating of the
Stream clouds by ram pressure from ionized gas in the halo of the Galaxy. These
observations suggest that ram pressure from halo gas plays a large role in
stripping the Stream out of the Magellanic Clouds. They also suggest the
presence of a relatively large density of gas, , in the Galactic halo at kpc radius, and far above the
Galactic plane, . This implies that the Galaxy has a very large
baryonic, gaseous extent, and supports models of Lyman-$\alpha and metal-line
QSO absorption lines in which the absorption systems reside in extended
galactic halos.Comment: 15 pages, aaspp latex, + 1 table & 3 figures. Accepted in A.J. Also
available from http://www.physics.rutgers.edu/~bweiner/astro/papers
A Persistent Simulation Environment for Autonomous Systems
The age of Autonomous Unmanned Aircraft Systems (AUAS) is creating new challenges for the accreditation and certification requiring new standards, policies and procedures that sanction whether a UAS is safe to fly. Establishing a basis for certification of autonomous systems via research into trust and trustworthiness is the focus of Autonomy Teaming and TRAjectories for Complex Trusted Operational Reliability (ATTRACTOR), a new NASA Convergent Aeronautics Solution (CAS) project. Simulation Environments to test and evaluate AUAS decision making may be a low-cost solution to help certify that various AUAS systems are trustworthy enough to be allowed to fly in current general and commercial aviation airspace. NASA is working to build a peer-to-peer persistent simulation (P3 Sim) environment. The P3 Sim will be a Massively Multiplayer Online (MMO) environment were AUAS avatars can interact with a complex dynamic environment and each other. The focus of the effort is to provide AUAS researchers a low-cost intuitive testing environment that will aid training for and assessment of decisions made by autonomous systems such as AUAS. This presentation focuses on the design approach and challenges faced in development of the P3 Sim Environment is support of investigating trustworthiness of autonomous systems
MEASURING SQUASH HITTING ACCURACY USING THE âHUNT SQUASH ACCURACY TESTâ
The purpose of this study was to determine the reliability and validity of the Hunt Squash Accuracy Test (HSAT). Reliability: ten male squash players performed the HSAT twice within seven days. Each test consisted of 375 shots across 13 different types of squash strokes on both the forehand and backhand side. Reliability was measured using a typical error (TE) score from consecutive pairs of trials. The overall TE score for the test was 1.82%, demonstrating that the HSAT is very reliable at the 90% confidence limit. Validity: measured using a correlation analysis comparing the results of 8 individualâs HSAT scores against a round-robin tournament ranking where all 8 players played against each other, as well as coach rankings of player ability. Validity was considered high with correlation coefficients of 0.93 for both the round-robin and coach ranking
The soil and plant biogeochemistry sampling design for The National Ecological Observatory Network
Human impacts on biogeochemical cycles are evident around the world, from changes to forest structure and function due to atmospheric deposition, to eutrophication of surface waters from agricultural effluent, and increasing concentrations of carbon dioxide (CO2) in the atmosphere. The National Ecological Observatory Network (NEON) will contribute to understanding human effects on biogeochemical cycles from local to continental scales. The broad NEON biogeochemistry measurement design focuses on measuring atmospheric deposition of reactive mineral compounds and CO2 fluxes, ecosystem carbon (C) and nutrient stocks, and surface water chemistry across 20 ecoâclimatic domains within the United States for 30 yr. Herein, we present the rationale and plan for the groundâbased measurements of C and nutrients in soils and plants based on overarching or âhighâlevelâ requirements agreed upon by the National Science Foundation and NEON. The resulting design incorporates early recommendations by expert review teams, as well as recent input from the larger natural sciences community that went into the formation and interpretation of the requirements, respectively. NEON\u27s efforts will focus on a suite of data streams that will enable endâusers to study and predict changes to biogeochemical cycling and transfers within and across air, land, and water systems at regional to continental scales. At each NEON site, there will be an initial, oneâtime effort to survey soil properties to 1 m (including soil texture, bulk density, pH, baseline chemistry) and vegetation community structure and diversity. A sampling program will follow, focused on capturing longâterm trends in soil C, nitrogen (N), and sulfur stocks, isotopic composition (of C and N), soil N transformation rates, phosphorus pools, and plant tissue chemistry and isotopic composition (of C and N). To this end, NEON will conduct extensive measurements of soils and plants within stratified random plots distributed across each site. The resulting data will be a new resource for members of the scientific community interested in addressing questions about longâterm changes in continentalâscale biogeochemical cycles, and is predicted to inspire further processâbased research
X-ray/Optical/Radio Observations of a Resolved Supernova Remnant in NGC 6822
The supernova remnant (SNR), Ho 12, in the center of the dwarf irregular
galaxy NGC 6822 was previously observed at X-ray, optical, and radio
wavelengths. By using archival Chandra and ground-based optical data, we found
that the SNR is spatially resolved in X-rays and optical. In addition, we
obtained a ~5" resolution radio image of the SNR. These observations provide
the highest spatial resolution imaging of an X-ray/optical/radio SNR in that
galaxy to date. The multi-wavelength morphology, X-ray spectrum and
variability, and narrow-band optical imagings are consistent with a SNR. The
SNR is a shell-shaped object with a diameter of about 10" (24 pc). The
morphology of the SNR is consistent across the wavelengths while the Chandra
spectrum can be well fitted with a nonequilibrium ionization model with an
electron temperature of 2.8 keV and a 0.3-7 keV luminosity of 1.6e37 erg/s. The
age of the SNR is estimated to be 1700-5800 years.Comment: 6 pages, 3 figures, accepted for publication in the Astronomical
Journa
Packet Timescale Wavelength Switching Enabled by Regression Optimisation
A linear regression algorithm is applied to a digital-supermode distributed Bragg reflector laser to optimise wavelength switching times. The algorithm uses the output of a digital coherent receiver as feedback to update the pre-emphasis weights applied to the laser section currents. This permits in-situ calculation without manual weight adjustments. The application of this optimiser to a representative subsection of channels indicates this commercially available laser can rapidly reconfigure over 6.05 THz, supporting 122 channels, in less than 10 ns
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