518 research outputs found
Investigation of an aircraft trailing vortex using a tuft grid
With the increasing capacity of airport terminal areas, and the use of the new large jet transports, it has become important to understand the turbulent wake created by these aircraft. A study of the trailing vortex of a wing has been made using a tuft grid in a 6 foot wind tunnel. The study included an investigation of the use of mass injection at the wing tip as a means of destroying the vortex. Test results show that a fully developed, stable, vortex exists at least a distance of thirty chord lengths downstream of the wing, and that the swirl of the vortex can be reduced or eliminated by mass injection at the wing tip
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Multiple determinants of the productive use of the regular past tense suffix
We offer evidence that the productive use of English regular
past tense morphology (e.g., drived) results from
competitions among lexical-level features within a single
mechanism associative system. W e present error data
from: (1) on-line elicited productions by adult native
speakers (N = 51), and (2) cormectionist back-propagation
networks trained to map stems and past tenses of 552
English verbs. The frequency of regularizations is
analyzed in terms of item frequency, stem final alveolar
consonant, and similarity in past tense mapping across
"friends" and "enemies" in phonologically defined
neighborhoods. All items were compiled from a lexicon of
1,191 verbs which represents a near-exhaustive listing of
monosyllabic stem-past tense pairs in current American
English. Results revealed striking similarities between the
hiunan and simulation data. Regularizations were
significantly correlated with item frequency, as well as
phonological attributes of the stem. Crucially,
regularization was a function of phonological similarity to
frequent suffixed items, especially for irregulars that
normally undergo a vowel-change. These results are
incompatible with the view that regularization applies by
default, independently of inter-item similarities which
support the acquisition and processing of lexical items in
associative systems
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Token Frequency and Phonological Predictability in a Pattern Association Network: Implications for Child Language Acquisition
The degree to which the behavior of PDP models of pattern associations (Rumelhart &McClelland, 1986; 1987) approximates children's acquisition of inflectional morphology has recently been highlighted in discussions of the applicability of P D P to the study of human cognition and language (Pinker & Mehler, 1988). In this paper, we attempt to eliminate many of the limitations of the R & M model, adopting an empirical approach to the analysis of learning(hit rate and error type) in two sets of simulations in which vocabulary structure (token frequency)and the presence of phonological subregularities are manipulated. A 3-layer back propagation network is used to implement a pattern association task with strings that are analogous to four types of present and past tense English verbs. W e overview resulting"competitions" when strings are randomly assigned to verb classes, in particular, the conditions under which different overgeneralization errors (both " pure" and " blended") are produced.In a second set of simulations, identical type and token frequencies are used, but strings are assigned to the identity and vowel change classes on the basis of phonological shape of the stem. Phonological cues are exploited by the system leading to overall improved performance.However, overgeneralizations continue to be observed in similar conditions. Token frequency works together with phonological subregularities to determine patterns of learning,including the conditions under which " rule-like"behavior will and will not emerge. The results are discussed with reference to behavioral data on children's acquisition of the English past tense
Pressure investigation of NASA leading edge vortex flaps on a 60 deg Delta wing
Pressure distributions on a 60 deg Delta Wing with NASA designed leading edge vortex flaps (LEVF) were found in order to provide more pressure data for LEVF and to help verify NASA computer codes used in designing these flaps. These flaps were intended to be optimized designs based on these computer codes. However, the pressure distributions show that the flaps wre not optimum for the size and deflection specified. A second drag-producing vortex forming over the wing indicated that the flap was too large for the specified deflection. Also, it became apparent that flap thickness has a possible effect on the reattachment location of the vortex. Research is continuing to determine proper flap size and deflection relationships that provide well-behaved flowfields and acceptable hinge-moment characteristics
An experimental study of pressures on 60 deg Delta wings with leading edge vortex flaps
An experimental study was conducted in the Virginia Tech Stability Wind Tunnel to determine surface pressures over a 60 deg sweep delta wing with three vortex flap designs. Extensive pressure data was collected to provide a base data set for comparison with computational design codes and to allow a better understanding of the flow over vortex flaps. The results indicated that vortex flaps can be designed which will contain the leading edge vortex with no spillage onto the wing upper surface. However, the tests also showed that flaps designed without accounting for flap thickness will not be optimum and the result can be oversized flaps, early flap vortex reattachment and a second separation and vortex at the wing/flap hinge line
PyPhi: A toolbox for integrated information theory
Integrated information theory provides a mathematical framework to fully
characterize the cause-effect structure of a physical system. Here, we
introduce PyPhi, a Python software package that implements this framework for
causal analysis and unfolds the full cause-effect structure of discrete
dynamical systems of binary elements. The software allows users to easily study
these structures, serves as an up-to-date reference implementation of the
formalisms of integrated information theory, and has been applied in research
on complexity, emergence, and certain biological questions. We first provide an
overview of the main algorithm and demonstrate PyPhi's functionality in the
course of analyzing an example system, and then describe details of the
algorithm's design and implementation.
PyPhi can be installed with Python's package manager via the command 'pip
install pyphi' on Linux and macOS systems equipped with Python 3.4 or higher.
PyPhi is open-source and licensed under the GPLv3; the source code is hosted on
GitHub at https://github.com/wmayner/pyphi . Comprehensive and
continually-updated documentation is available at https://pyphi.readthedocs.io/
. The pyphi-users mailing list can be joined at
https://groups.google.com/forum/#!forum/pyphi-users . A web-based graphical
interface to the software is available at
http://integratedinformationtheory.org/calculate.html .Comment: 22 pages, 4 figures, 6 pages of appendices. Supporting information
"S1 Calculating Phi" can be found in the ancillary file
Aerodynamics of magnetic levitation (MAGLEV) trains
High-speed (500 kph) trains using magnetic forces for levitation, propulsion and control offer many advantages for the nation and a good opportunity for the aerospace community to apply 'high tech' methods to the domestic sector. One area of many that will need advanced research is the aerodynamics of such MAGLEV (Magnetic Levitation) vehicles. There are important issues with regard to wind tunnel testing and the application of CFD to these devices. This talk will deal with the aerodynamic design of MAGLEV vehicles with emphasis on wind tunnel testing. The moving track facility designed and constructed in the 6 ft. Stability Wind Tunnel at Virginia Tech will be described. Test results for a variety of MAGLEV vehicle configurations will be presented. The last topic to be discussed is a Multi-disciplinary Design approach that is being applied to MAGLEV vehicle configuration design including aerodynamics, structures, manufacturability and life-cycle cost
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