scholarly journals High Frequency Roughness Scattering from Various Rough Surfaces: Theory and Laboratory Experiments

2012 ◽  
Vol 02 (01) ◽  
pp. 50-59
Author(s):  
Virginie Jaud ◽  
Jean-Pierre Sessarego ◽  
Cedric Gervaise ◽  
Yann Stephan
Keyword(s):  
High Frequency ◽  
Laboratory Experiments ◽  
Rough Surfaces

scholarly journals Comparison of velocity and turbulence profiles obtained with a Vectrino Profiler and PIV

2018 ◽  
Vol 40 ◽  
pp. 05070
Author(s):  
Jay Lacey ◽  
Jason Duguay ◽  
Bruce MacVicar
Keyword(s):  
High Frequency ◽  
Laboratory Experiments ◽  
Measurement Techniques ◽  
Measurement Methods ◽  
Doppler Velocity ◽  
Sweet Spot ◽  
Turbulence Statistics ◽  
Significant Bias ◽  
Turbulent Statistics ◽  
Background Turbulence

Laboratory experiments were carried out in a small openchannel hydraulic flume at the Université de Sherbrooke. A PIV and an acoustic Doppler velocity profiler (Vectrino II (VII)) were used to measure high frequency velocities in profiles along the centreline of a small openchannel flume. Two background turbulence levels were tested. Comparisons were made of mean and turbulent statistics obtained with the two measurement techniques. The results show reasonable agreement between mean streamwise and lateral velocities measured with the PIV and VII near the “sweet spot” of the VII. In contrast, mean vertical velocities deviate substantially between the two measurement methods. Turbulence statistics have somewhat similar profile shapes, yet significant bias is observed between the two measurement methods.

scholarly journals The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds

2008 ◽  
Vol 275 (1637) ◽  
pp. 955-962 ◽  
Author(s):  
Christopher James Clark ◽  
Teresa J Feo
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Laboratory Experiments ◽  
Wild Birds ◽  
High Speed Video ◽  
Calypte Anna

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna's hummingbird ( Calypte anna ) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather's fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds.

EXPERIMENTAL VERIFICATION OF HIGH FREQUENCY PERFORMANCE OF FTFN-BASED SIMPLE CHAOTIC CIRCUIT

2005 ◽  
Vol 15 (01) ◽  
pp. 191-205 ◽  
Author(s):  
FATMA YILDIRIM ◽  
ESMA UZUNHİSARCIKLI ◽  
RECAI KILIÇ ◽  
MUSTAFA ALÇI
Keyword(s):  
Experimental Verification ◽  
High Frequency ◽  
Chaotic Dynamics ◽  
Laboratory Experiments ◽  
Reference Model ◽  
Chaotic Circuit ◽  
Circuit Topology ◽  
Pspice Simulations ◽  
Extended Frequency ◽  
High Frequency Performance

In this study, we aimed to improve the VOA-based simple chaotic circuit proposed by Sprott in the literature by using FTFN-based circuit topology. And also, by choosing one of the FTFN-based circuits whose chaotic dynamics are very similar to that of Chua's circuit as a reference model, we tested the performance of this model at different frequencies and its extended frequency performance has been verified by laboratory experiments and PSpice simulations.

scholarly journals Modelling of High-Frequency Roughness Scattering from Various Rough Surfaces through the Small Slope Approximation of First Order

2012 ◽  
Vol 02 (01) ◽  
pp. 1-11 ◽  
Author(s):  
Virginie Jaud ◽  
Cedric Gervaise ◽  
Yann Stephan ◽  
Ali Khenchaf
Keyword(s):  
High Frequency ◽  
Rough Surfaces ◽  
First Order

Transformation of Rice’s small perturbation solution for rough surface scattering into the high frequency reciprocal physical and geometric optics solutions

2012 ◽  
Vol 90 (6) ◽  
pp. 557-564
Author(s):  
Ezekiel Bahar
Keyword(s):  
Small Perturbation ◽  
High Frequency ◽  
Rough Surfaces ◽  
Geometrical Optic ◽  
Low Frequency ◽  
Perturbation Solution ◽  
Physical Optics ◽  
Surface Element ◽  
Scattering Coefficients ◽  
Scatter Coefficient

A step by step transformation of the low frequency small height and slope perturbation solution into the high frequency reciprocal and dual, physical and geometrical optic solutions is presented. The familiar Kirchhoff approximations for the fields impressed by the incident plane wave upon the rough surfaces results in nonreciprocal solutions. It is shown that the surface element scattering coefficients based on the Kirchhoff approximations agree with the corresponding reciprocal physical optics solutions only at the stationary phase, specular points on the rough surfaces. While the Kirchhoff approximations and physical optics approximations are based on the characterization of the surface fields by Fresnel reflection coefficients, the corresponding surface element scatter coefficient derived for the small perturbation solution and the full wave solutions are based on the imposition of boundary conditions for the tangential components of the electric and magnetic fields. A flow graph schematically depicting the relationships between these solutions for the scattered fields is also presented.

AN EXPERIMENTAL STUDY ON CHAOTIC DYNAMICS OF CFOA-BASED SC-CNN CIRCUIT

2005 ◽  
Vol 15 (08) ◽  
pp. 2551-2558 ◽  
Author(s):  
ENIS GÜNAY ◽  
MUSTAFA ALÇI ◽  
FATMA YILDIRIM
Keyword(s):  
Neural Network ◽  
High Frequency ◽  
Chaotic Dynamics ◽  
Laboratory Experiments ◽  
Cellular Neural Network ◽  
Current Feedback ◽  
Op Amp ◽  
Op Amps ◽  
Experimental Implementation ◽  
High Frequency Performance

In this paper, an experimental implementation of State Controlled Cellular Neural Network (SC-CNN) circuit using Current Feedback Op Amp (CFOA) is presented and its chaotic dynamics including high frequency performance are investigated by laboratory experiments. Depending on its significant advantages over the conventional voltage op amps (VOAs), without imposing any restrictions, the CFOAs have been used instead of the VOAs in SC-CNN circuit. Experimental results have shown that the proposed implementation has a capacity of higher frequency operation.

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