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Preparation of nanoforms of layered piezoelectric of systems BI2O3-TA(2)O(5)-AO (A=CA,SR,BA)
Štarman, S. ; Matz, V. ; Kváča, Z. ; Mohyla, M. ; Olšák, V. ; Plocek, Jiří ; Vaněk, Přemysl ; Tylš, B.
Based on the known Aurivillius phases types ABi2Ta2O9 and A2BiTaO6 ( A=Ca, Sr, Ba) were supplemented with new compositions of layered tantalates, which resulted the possibility of the existence of a new phase Sr2BiTaO6. Ternary compounds with piezoelectric structure were prepared as nanoforms by solgel reactions of homogeneous acetate Bi, Ta, A and subsequent annealing in a controlled atmosphere. Annealing temperature was determined from DSC curves based on the weight loss and phase transitions. Composition and structure of nanocrystals has been analyzed by X-ray diffraction (XRD), scanning nanomorphology (SEM) and acoustic measurements.
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Computer modeling of effects of vocal exercising with a tube on vocal tract sound power transfer
Horáček, Jaromír ; Vampola, T. ; Laukkanen, A. M. ; Švec, J. G.
Two 3D finite element (FE) models were constructed, based on CT measurements of a subject phonating on [a:] before and after phonation into a tube. Acoustic analysis was performed exciting the models by acoustic flow velocity at the vocal folds. The generated acoustic pressure of the response was computed in front of the mouth and inside the vocal tract for both FE models. Average amplitudes of the pressure oscillations inside the vocal tract and in front of the mouth were compared to display a cost-efficiency of sound energy transfer at different formant frequencies. Comparison of the pressure oscillation inside and outside the vocal tract showed that formants differ in their efficiency, F4 (at about 3.5 kHz, i.e. at the speaker’s or singer’s formant region) being the most effective. The results suggest that exercising on semi-occlusions help in improving the vocal economy.
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Notes on wave and waveguide concepts in AE
Převorovský, Zdeněk
A purpose of this paper is to point out some current problems related with wave concepts and quantitative AE source identification. Main tasks concerning AE detection, localization and source identification are discussed and their advances during the last ten years are mentioned.
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