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Helical Spin Structures in c-Axis Dy/Y Superlattice

100%

Seroczyńska M., Kociński J.

Acta Physica Polonica A

1996

vol. 89

issue 1

99-104

On the basis of Landau's theory of symmetry changes at continuous phase transitions, we have derived the formulae for two incommensurate helical spin structures which are symmetry allowed in Dy/Y superlattice, when the helical axis is parallel to the c-axis of the hexagonal lattice. These structures have different extinction coefficients in their cross-sections for magnetic scattering of neutrons and therefore can be distinguished by experiment. Magnetic satellite peaks around the reciprocal lattice points K + 0 are allowed for only one of these spin structures, namely that inferred from earlier experiments.

Convolutive Blind Signal Separation Spatial Effectiveness in Speech Intelligibility Improvement

81%

Kociński J., Sęk A., Libiszewski P.

Acta Physica Polonica A

2011

vol. 119

issue 6A

996-999

Blind signal separation is one of the latest methods to improve the signal to noise ratio. The main objective of blind source separation is the transformation of mixtures of recorded signals to obtain each source signal at the output of the procedure, assuming that they are statistically independent. For acoustic signals it can be concluded that the correct separation is possible only if the source signals are spatially separated. That finding suggests analogies with the classical spatial filtering (beamforming). In this study we analyzed an effect of the angular separation of two source signals (i.e. speech and babble noise) to improve speech intelligibility. For this purpose, we chose the blind source separation algorithm based on the convolutive separation, based on second order statistics only. As a system of sensors a dummy head was used (one microphone inside each ear canal), which simulated two hearing aids of a hearing impaired person. The speech reception threshold, before and after the blind source separation was determined. The results have shown significant improvement in speech intelligibility after applying blind source separation (speach reception threshold fell even more than a dozen dB) in cases where the source signals were angularly separated. However, in cases where the source signals were coming from the same directions, the improvement was not observed. Moreover, the effectiveness of the blind source separation, to a large extent, depended on the relative positions of signal sources in space.

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2 Acta Physica Polonica A

1 2011

1 1996

2 Kociński J.

1 Libiszewski P.

1 Seroczyńska M.

1 Sęk A.

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Helical Spin Structures in c-Axis Dy/Y Superlattice

Convolutive Blind Signal Separation Spatial Effectiveness in Speech Intelligibility Improvement