3,617 research outputs found
Beyond LISA: Exploring Future Gravitational Wave Missions
The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer
(BBO) have been proposed as follow on missions to the Laser Interferometer
Space Antenna (LISA). Here we study the capabilities of these observatories,
and how they relate to the science goals of the missions. We find that the
Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension
to the ALIA mission, will go considerably further toward meeting ALIA's main
scientific goal of studying intermediate mass black holes. We also compare the
capabilities of LISA to a related extension of the LISA mission, the Laser
Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the
initial deployment phase of the BBO would be sufficient to address the BBO's
key scientific goal of detecting the Gravitational Wave Background, while still
providing detailed information about foreground sources.Comment: 9 pages, 10 figures, published versio
On the stability of Poiseuille pipe flow
Numerical analysis of Poiseuille pipe flow stability using Reynolds numbe
Simulated propeller slipstream effects on a supercritical wing
To quantify the installed performance of high speed (M = 0.8) turboprop propulsion systems, an experimental program designed to assess the magnitude of the aerodynamic interference of a propeller slipstream on a supercritical wing has been conducted. The test was conducted in the NASA Ames 14-foot wind tunnel. An ejector-nacelle propeller slipstream simulator was used to produce a slipstream with characteristics typical of advanced propellers presently being investigated. A supercritical wing-body configuration was used to evaluate the interference effects. A traversing total pressure rake was used to make flow field measurements behind the wing and to calibrate the slipstream simulator. The force results indicated that the interference drag amounted to an increase of ten counts or about 3% of the wing-body drag for a two engine configuration at the nominal propeller operating conditions. However, at the higher swirl angles (11 deg vs. 7 deg nominally) the interference drag was favorable by about the same magnitude
Integrating case-based reasoning and hypermedia documentation: an application for the diagnosis of a welding robot at Odense steel shipyard
Reliable and effective maintenance support is a vital consideration for the management within today's manufacturing environment. This paper discusses the development of a maintenance system for the world's largest robot welding facility. The development system combines a case-based reasoning approach for diagnosis with context information, as electronic on-line manuals, linked using open hypermedia technology. The work discussed in this paper delivers not only a maintenance system for the robot stations under consideration, but also a design framework for developing maintenance systems for other similar applications
Darwin Meets Einstein: LISA Data Analysis Using Genetic Algorithms
This work presents the first application of the method of Genetic Algorithms
(GAs) to data analysis for the Laser Interferometer Space Antenna (LISA). In
the low frequency regime of the LISA band there are expected to be tens of
thousands galactic binary systems that will be emitting gravitational waves
detectable by LISA. The challenge of parameter extraction of such a large
number of sources in the LISA data stream requires a search method that can
efficiently explore the large parameter spaces involved. As signals of many of
these sources will overlap, a global search method is desired. GAs represent
such a global search method for parameter extraction of multiple overlapping
sources in the LISA data stream. We find that GAs are able to correctly extract
source parameters for overlapping sources. Several optimizations of a basic GA
are presented with results derived from applications of the GA searches to
simulated LISA data.Comment: 8 pages, 12 figure
LISA Source Confusion
The Laser Interferometer Space Antenna (LISA) will detect thousands of
gravitational wave sources. Many of these sources will be overlapping in the
sense that their signals will have a non-zero cross-correlation. Such overlaps
lead to source confusion, which adversely affects how well we can extract
information about the individual sources. Here we study how source confusion
impacts parameter estimation for galactic compact binaries, with emphasis on
the effects of the number of overlaping sources, the time of observation, the
gravitational wave frequencies of the sources, and the degree of the signal
correlations. Our main findings are that the parameter resolution decays
exponentially with the number of overlapping sources, and super-exponentially
with the degree of cross-correlation. We also find that an extended mission
lifetime is key to disentangling the source confusion as the parameter
resolution for overlapping sources improves much faster than the usual square
root of the observation time.Comment: 8 pages, 14 figure
STOL aircraft transient ground effects. Part 1: Fundamental analytical study
The first phases of a fundamental analytical study of STOL ground effects were presented. Ground effects were studied in two dimensions to establish the importance of nonlinear effects, to examine transient aspects of ascent and descent near the ground, and to study the modelling of the jet impingement on the ground. Powered lift system effects were treated using the jet-flap analogy. The status of a three-dimensional jet-wing ground effect method was presented. It was shown, for two-dimensional unblown airfoils, that the transient effects are small and are primarily due to airfoil/freestream/ground orientation rather than to unsteady effects. The three-dimensional study showed phenomena similar to the two-dimensional results. For unblown wings, the wing/freestream/ground orientation effects were shown to be of the same order of magnitude as for unblown airfoils. This may be used to study the nonplanar, nonlinear, jet-wing ground effect
Impact reactivity of materials at very high oxygen pressure
The requirements for impact testing of materials in an oxygen atmosphere at pressures from 82.7 MPa (12,000 psi) to 172 MPa (25,000 psi) were evaluated. The impact tester system was evaluated for potential pressure increases from 69 MPa (10,000 psi) to 82.7 MPa (12,000 psi). The low pressure oxygen and nitrogen systems, the impact tower, the impact test cell, and the high pressure oxygen system were evaluated individually. Although the structural integrity of the impact test cell and the compressor were sufficient for operation at 82.7 MPa (12,000 psi), studies revealed possible material incompatibility at that pressure and above. It was recommended that if a component should be replaced for 82.7 MPa (12,000 psi) operation the replacement should meet the final objectives of 172 MPa (25,000 psi). Recommended changes in the system include; use of Monel 400 for pressures above 82.7 MPa (12,000 psi), use of bellows to replace the seal in the impact tester, use of a sapphire window attached to a fiber optic for event sensing, and use of a three diaphragm compressor
In-flight propeller flow visualization using fluorescent minitufts
Extension of fluorescent minutuft method to in-flight flow visualization on propellers is described. Extremely thin nylon monofilament for the minitufts, is used in a process of attaching them to the test surface with small drops of lacquer-like adhesive, and the use of fluorescence photography for recording the minituft patterns. Using this method, thousands of minitufts can be applied to small, high speed wind tunnel models without affecting the airflow. The minitufts can remain in place throughout a wind tunnel test, permitting nonintrusive flow visualization data to be acquired at any time
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