The efficacy of audio-visual interactions in speech perception comes from two kinds of factors. First, at the information level, there is some "complementarity" of audition and vision: It seems that some speech features, mainly concerned with manner of articulation, are best transmitted by the audio channel, while some other features, mostly describing place of articulation, are best transmitted by the video channel. Second, at the information processing level, there is some "synergy" between audition and vision: The audio-visual global identification scores in a number of different tasks involving acoustic noise are generally greater than both the auditory-alone and the visual-alone scores. However, these two properties have been generally demonstrated until now in rather global terms. In the present work, audio-visual interactions at the feature level are studied for French oral vowels which contrast three series, namely front unrounded, front rounded, and back rounded vowels. A set of experiments on the auditory, visual, and audio-visual identification of vowels embedded in various amounts of noise demonstrate that complementarity and synergy in bimodal speech appear to hold for a bundle of individual phonetic features describing place contrasts in oral vowels. At the information level (complementarity), in the audio channel the height feature is the most robust, backness the second most robust one, and rounding the least, while in the video channel rounding is better than height, and backness is almost invisible. At the information processing (synergy) level, transmitted information scores show that all individual features are better transmitted with the ear and the eye together than with each sensor individually.

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The results are reported of an experimental investigation of fully developed turbulent ®ow through a square duct of water (as a control) and of two polymers, an aqueous solution of 0.1% carboxymethylcellulose + 0:1% Keltrol TF, a xanthan gum (CMC/XG) and a 0.125% aqueous solution of a polyacrylamide, Separan AP 273 (PAA). The more elastic rheology of PAA leads to drag-reduction levels up to 77%, compared with 65% for CMC/XG. There are also substantial reductions in the levels and changes in the spatial distribution of the transverse turbulence intensities and the Reynolds shear stress, again dependent on the degree of viscoelasticity of the working ®uid. Concomitant changes are evident in the secondary ®ow, which depends upon second derivatives of the Reynolds stresses, and also in the primary axial ®ow due to the redistribution of axial momentum by the secondary ®ow.

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