16,583 research outputs found
NASTRAN level 16 programmer's manual updates for aeroelastic analysis of bladed discs
The programming routines for the NASTRAN Level 16program are presented. Particular emphasis is placed on its application to aeroelastic analyses, mode development, and flutter analysis for turbomachine blades
The prompt energy release of gamma-ray bursts using a cosmological k-correction
The fluences of gamma-ray bursts (GRBs) are measured with a variety of
instruments in different detector energy ranges. A detailed comparison of the
implied energy releases of the GRB sample requires, then, an accurate
accounting of this diversity in fluence measurements which properly corrects
for the redshifting of GRB spectra. Here, we develop a methodology to
``k-correct'' the implied prompt energy release of a GRB to a fixed co-moving
bandpass. This allows us to homogenize the prompt energy release of 17
cosmological GRBs (using published redshifts, fluences, and spectra) to two
common co-moving bandpasses: 20-2000 keV and 0.1 keV-10 MeV (``bolometric'').
While the overall distribution of GRB energy releases does not change
significantly by using a k-correction, we show that uncorrected energy
estimates systematically undercounts the bolometric energy by ~5% to 600%,
depending on the particular GRB. We find that the median bolometric
isotropic-equivalent prompt energy release is 2.2 x 10^{53} erg with an r.m.s.
scatter of 0.80 dex. The typical estimated uncertainty on a given k-corrected
energy measurement is ~20%.Comment: Accepted to the Astronomical Journal. 21 pages (LaTeX) and 4 figure
The Wyoming Survey for H-alpha. I. Initial Results at z ~ 0.16 and 0.24
The Wyoming Survey for H-alpha, or WySH, is a large-area, ground-based,
narrowband imaging survey for H-alpha-emitting galaxies over the latter half of
the age of the Universe. The survey spans several square degrees in a set of
fields of low Galactic cirrus emission. The observing program focuses on
multiple dz~0.02 epochs from z~0.16 to z~0.81 down to a uniform
(continuum+line) luminosity at each epoch of ~10^33 W uncorrected for
extinction (3sigma for a 3" diameter aperture). First results are presented
here for 98+208 galaxies observed over approximately 2 square degrees at
redshifts z~0.16 and 0.24, including preliminary luminosity functions at these
two epochs. These data clearly show an evolution with lookback time in the
volume-averaged cosmic star formation rate. Integrals of Schechter fits to the
extinction-corrected H-alpha luminosity functions indicate star formation rates
per co-moving volume of 0.009 and 0.014 h_70 M_sun/yr/Mpc^3 at z~0.16 and 0.24,
respectively. The formal uncertainties in the Schechter fits, based on this
initial subset of the survey, correspond to uncertainties in the cosmic star
formation rate density at the >~40% level; the tentative uncertainty due to
cosmic variance is 25%, estimated from separately carrying out the analysis on
data from the first two fields with substantial datasets.Comment: To appear in the Astronomical Journa
The Waikato range imager
We are developing a high precision simultaneous full-field acquisition range imager. This device measures range with sub millimetre precision in range simultaneously over a full-field view of the scene. Laser diodes are used to illuminate the scene with amplitude modulation with a frequency of 10MHz up to 100 MHz. The received light is interrupted by a high speed shutter operating in a heterodyne configuration thus producing a low-frequency signal which is sampled with a digital camera. By detecting the phase of the signal at each pixel the range to the scene is determined. We show 3D reconstructions of some viewed objects to demonstrate the capabilities of the ranger
Heterodyne range imaging as an alternative to photogrammetry
Solid-state full-field range imaging technology, capable of determining the distance to objects in a scene simultaneously for every pixel in an image, has recently achieved sub-millimeter distance measurement precision. With this level of precision, it is becoming practical to use this technology for high precision three-dimensional metrology applications. Compared to photogrammetry, range imaging has the advantages of requiring only one viewing angle, a relatively short measurement time, and simplistic fast data processing. In this paper we fist review the range imaging technology, then describe an experiment comparing both photogrammetric and range imaging measurements of a calibration block with attached retro-reflective targets. The results show that the range imaging approach exhibits errors of approximately 0.5 mm in-plane and almost 5 mm out-of-plane; however, these errors appear to be mostly systematic. We then proceed to examine the physical nature and characteristics of the image ranging technology and discuss the possible causes of these systematic errors. Also discussed is the potential for further system characterization and calibration to compensate for the range determination and other errors, which could possibly lead to three-dimensional measurement precision approaching that of photogrammetry
On-Orbit Validation of a Framework for Spacecraft-Initiated Communication Service Requests with NASA's SCaN Testbed
We design, analyze, and experimentally validate a framework for demand-based allocation of high-performance space communication service in which the user spacecraft itself initiates a request for service. Leveraging machine-to-machine communications, the automated process has potential to improve the responsiveness and efficiency of space network operations. We propose an augmented ground station architecture in which a hemispherical-pattern antenna allows for reception of service requests sent from any user spacecraft within view. A suite of ground-based automation software acts upon these direct-to-Earth requests and allocates access to high-performance service through a ground station or relay satellite in response to immediate user demand. A software-defined radio transceiver, optimized for reception of weak signals from the helical antenna, is presented. Design and testing of signal processing equipment and a software framework to handle service requests is discussed. Preliminary results from on-orbit demonstrations with a testbed onboard the International Space Station are presented to verify feasibility of the concept
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