47,646 research outputs found
LDR structural experiment definition
A system study to develop the definition of a structural flight experiment for a large precision segmented reflector on the Space Station was accomplished by the Boeing Aerospace Company for NASA's Langley Research Center. The objective of the study was to use a Large Deployable Reflector (LDR) baseline configuration as the basis for focusing an experiment definition, so that the resulting accommodation requirements and interface constraints could be used as part of the mission requirements data base for Space Station. The primary objectives of the first experiment are to construct the primary mirror support truss and to determine its structural and thermal characteristics. Addition of an optical bench, thermal shield and primary mirror segments, and alignment of the optical components, would occur on a second experiment. The structure would then be moved to the payload point system for pointing, optical control, and scientific optical measurement for a third experiment. Experiment 1 will deploy the primary support truss while it is attached to the instrument module structure. The ability to adjust the mirror attachment points and to attach several dummy primary mirror segments with a robotic system will also be demonstrated. Experiment 2 will be achieved by adding new components and equipment to experiment one. Experiment 3 will demonstrate advanced control strategies, active adjustment of the primary mirror alignment, and technologies associated with optical sensing
Inside the Bondi radius of M87
Chandra X-ray observations of the nearby brightest cluster galaxy M87 resolve
the hot gas structure across the Bondi accretion radius of the central
supermassive black hole, a measurement possible in only a handful of systems
but complicated by the bright nucleus and jet emission. By stacking only short
frame-time observations to limit pileup, and after subtracting the nuclear PSF,
we analysed the X-ray gas properties within the Bondi radius at 0.12-0.22 kpc
(1.5-2.8 arcsec), depending on the black hole mass. Within 2 kpc radius, we
detect two significant temperature components, which are consistent with
constant values of 2 keV and 0.9 keV down to 0.15 kpc radius. No evidence was
found for the expected temperature increase within ~0.25 kpc due to the
influence of the SMBH. Within the Bondi radius, the density profile is
consistent with . The lack of a temperature increase inside
the Bondi radius suggests that the hot gas structure is not dictated by the
SMBH's potential and, together with the shallow density profile, shows that the
classical Bondi rate may not reflect the accretion rate onto the SMBH. If this
density profile extends in towards the SMBH, the mass accretion rate onto the
SMBH could be at least two orders of magnitude less than the Bondi rate, which
agrees with Faraday rotation measurements for M87. We discuss the evidence for
outflow from the hot gas and the cold gas disk and for cold feedback, where gas
cooling rapidly from the hot atmosphere could feed the cirumnuclear disk and
fuel the SMBH. At 0.2 kpc radius, the cooler X-ray temperature component
represents ~20% of the total X-ray gas mass and, by losing angular momentum to
the hot gas component, could provide a fuel source of cold clouds within the
Bondi radius.Comment: 14 pages, 8 figures, accepted by MNRA
Application of LANDSAT-2 data to the implementation and enforcement of the Pennsylvania Surface Mining Conservation and Reclamation Act
The author has identified the following significant results. Evaluation of LANDSAT imagery indicates severe limitations in its utility for surface mine land studies. Image stripping resulting from unequal detector response on satellite degrades the image quality to the extent that images of scales larger than 1:125,000 are of limited value for manual interpretation. Computer processing of LANDSAT data to improve image quality is essential; the removal of scanline stripping and enhancement of mine land reflectance data combined with color composite printing permits useful photographic enlargements to approximately 1:60,000
Evidence of Program Quality and Youth Outcomes in the DYCD Out-of-School Time Initiative: Report on the Initiative's First Three Years
Examines New York City's progress in improving out-of-school-time program quality and serving more children and youth, participants' and parents' overall satisfaction with quality and accessibility, and links between programming, quality, and benefits
A technology development program for large space antennas
The design and application of the offset wrap rib and the maypole (hoop/column) antenna configurations are described. The NASA mission model that generically categorizes the classes of user requirements, as well as the methods used to determine critical technologies and requirements are discussed. Performance estimates for the mesh deployable antenna selected for development are presented
Evaluation of the Beacon Community Centers Middle School Initiative: Report on the First Year
Evaluates the first year of an initiative to provide structured after-school and summer programs for fifth- through eighth-graders. Examines the centers' adaptation to the new focus, enrollment and participation levels, and implementation of core goals
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Source-specific Fine Particulate Using Spatiotemporal Concentration Fields Developed using Chemical Transport Modelling and Data Assimilation
A range expanding signal conditioner
Telemetry system modifications to improve signal resolution are described. Process uses zero suppression technique which consists of subtracting known voltage from input and amplifying remainder. Schematic diagram of circuit is provided and details of operation are presented
The effect of the quasar H1821+643 on the surrounding intracluster medium: revealing the underlying cooling flow
We present a detailed study of the thermodynamic properties of the
intracluster medium of the only low redshift galaxy cluster to contain a highly
luminous quasar, H1821+643. The cluster is a highly massive, strong cool core
cluster. We find that the ICM entropy around the quasar is significantly lower
than that of other similarly massive strong cool core clusters within the
central 80 kpc, and that the entropy lies significantly below the extrapolated
baseline entropy profile from hierarchical structure formation. By comparing
the scaled temperature profile with those of other strong cool core clusters of
similar total mass, we see that the entropy deficiency is due to the central
temperature being significantly lower. This suggests that the presence of the
quasar in the core of H1821+643 has had a dramatic cooling effect on the
intracluster medium around it. We find that, if the quasar was brighter in the
past, Compton cooling by radiation from the quasar may have caused the low
entropy and temperature levels in the ICM around the quasar. Curiously, the
gradients of the steep central temperature and entropy decline are in
reasonable agreement with the profiles expected for a constant pressure cooling
flow. It is possible that the system has been locked into a Compton cooled
feedback cycle which prevents energy release from the black hole heating the
gas sufficiently to switch it off, leading to the formation of a huge (~3x10^10
solar mass) supermassive black hole.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
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