2,788 research outputs found
Flight researh at NASA Ames Research Center: A test pilot's perspective
In 1976 NASA elected to assign responsibility for each of the various flight regimes to individual research centers. The NASA Ames Research Center at Moffett Field, California was designated lead center for vertical and short takeoff and landing, V/STOL research. The three most recent flight research airplanes being flown at the center are discussed from the test pilot's perspective: the Quiet Short Haul Research Aircraft; the XV-15 Tilt Rotor Research Aircraft; and the Rotor Systems Research Aircraft
Development of EM-CCD-based X-ray detector for synchrotron applications
A high speed, low noise camera system for crystallography and X-ray imaging applications is developed and successfully demonstrated. By coupling an electron-multiplying (EM)-CCD to a 3:1 fibre-optic taper and a CsI(Tl) scintillator, it was possible to detect hard X-rays. This novel approach to hard X-ray imaging takes advantage of sub-electron equivalent readout noise performance at high pixel readout frequencies of EM-CCD detectors with the increase in the imaging area that is offered through the use of a fibre-optic taper. Compared with the industry state of the art, based on CCD camera systems, a high frame rate for a full-frame readout (50 ms) and a lower readout noise (<1 electron root mean square) across a range of X-ray energies (6–18 keV) were achieved
Calibration of dimensional change in finite element models using AGR moderator brick measurements
AbstractPhysically based models, resolved using the finite element (FE) method, are often used to model changes in geometry and the associated stress fields of graphite moderator bricks within a reactor. These models require inputs that describe the loading conditions (field variables), and coded relationships describing the behaviour of material properties. Historically, behaviour on material properties have been obtained from Materials Test Reactor (MTR) experiments, however data relating to samples trepanned from operating reactors are increasingly being used to improve models. Geometry measurements from operating reactors offer the potential for improving the coded relationship for dimensional change in FE models. A non-linear mixed-effect model is presented for calibrating the parameters of FE models that are sensitive to mid-brick diameter, using channel geometry measurements obtained from inspection campaigns. The work makes use of a novel technique: the development of a Bayesian emulator, which is a surrogate for the FE model. The use of an emulator allows the influence of the inputs to the finite element model to be evaluated, and delivers a substantial reduction in the computational burden of calibration
AF Ni-Cd cell qualification program
The present status of the USAF NiCd cell qualification program, which is underway at the Naval Surface Warfare Center-Crane Division, is summarized. The following topics are discussed: overview; background; purpose; stress tests; results for super Ni-Cd; results for SAFT cells; GPS stress test; GPS simulated orbit; and results for gates cells. The discussion is presented in viewgraph format
Assessing North American Forest Disturbance from the Landsat Archive
Forest disturbances are thought to play a major role in controlling land-atmosphere fluxes of carbon. Under the auspices of the North American Carbon Program, the LEDAPS (Landsat Ecosystem Disturbance Adaptive Processing System) and NACP-FIA projects have been analyzing the Landsat satellite record to assess rates of forest disturbance across North America. In the LEDAPS project, wall-to-wall Landsat imagery for the period 1975-2000 has been converted to surface reflectance and analyzed for decadal losses (disturbance) or gains (regrowth) in biomass using a spectral "disturbance index". The NACP-FIA project relies on a geographic sample of dense Landsat image time series, allowing both disturbance rates and recovery trends to be characterized. Preliminary results for the 1990's indicate high rates of harvest within the southeastern US, Eastern Canada, and the Pacific Northwest, with spatially averaged (approx.50x50 km) turnover periods as low as 25-40 years. Lower rates of disturbance are found in the Rockies and Northeastern US
The CFHTLS Strong Lensing Legacy Survey: I. Survey overview and T0002 release sample
AIMS: We present data from the CFHTLS Strong Lensing Legacy Survey (SL2S).
Due to the unsurpassed combined depth, area and image quality of the
Canada-France-Hawaii Legacy Survey it is becoming possible to uncover a large,
statistically well-defined sample of strong gravitational lenses which spans
the dark halo mass spectrum predicted by the concordance model from galaxy to
cluster haloes. METHODS: We describe the development of several automated
procedures to find strong lenses of various mass regimes in CFHTLS images.
RESULTS: The preliminary sample of about 40 strong lensing candidates
discovered in the CFHTLS T0002 release, covering an effective field of view of
28 deg is presented. These strong lensing systems were discovered using an
automated search and consist mainly of gravitational arc systems with splitting
angles between 2 and 15 arcsec. This sample shows for the first time that it is
possible to uncover a large population of strong lenses from galaxy groups with
typical halo masses of about . We discuss the future
evolution of the SL2S project and its main scientific aims for the next 3
years, in particular our observational strategy to extract the hundreds of
gravitational rings also present in these fields.Comment: 11 pages, 5 figures, A&A in pres
Quasar candidates selection in the Virtual Observatory era
We present a method for the photometric selection of candidate quasars in
multiband surveys. The method makes use of a priori knowledge derived from a
subsample of spectroscopic confirmed QSOs to map the parameter space. The
disentanglement of QSOs candidates and stars is performed in the colour space
through the combined use of two algorithms, the Probabilistic Principal
Surfaces and the Negative Entropy clustering, which are for the first time used
in an astronomical context. Both methods have been implemented in the VONeural
package on the Astrogrid VO platform. Even though they belong to the class of
the unsupervised clustering tools, the performances of the method are optimized
by using the available sample of confirmed quasars and it is therefore possible
to learn from any improvement in the available "base of knowledge". The method
has been applied and tested on both optical and optical plus near infrared data
extracted from the visible SDSS and infrared UKIDSS-LAS public databases. In
all cases, the experiments lead to high values of both efficiency and
completeness, comparable if not better than the methods already known in the
literature. A catalogue of optical candidate QSOs extracted from the SDSS DR7
Legacy photometric dataset has been produced and is publicly available at the
URL voneural.na.infn.it/qso.html.Comment: 75 pages, 43 figure, 7 tables, accepted for publication in MNRA
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