The effect of the power amplifier on speech intelligibility in public address systems is often marginalised – i.e. it is assumed that it does not introduce significant signal distortion. This approach is justified when the linear range of the amplifier is used. The large crest factor of the speech signal and economic considerations mean that the amplifier also works in the non-linear range. In this paper, the effect of power amplifier distortion on the speech transmission index for public address systems (STIPA) is presented. In the first step, this influence was evaluated by measurements for Class AB and D amplifiers. Then, a computer model of the public address system based on the direct STIPA method, taking into account the non-linear properties of the amplifier, was proposed. Using the computer model, the optimum amplifier driving values were determined taking into account the reverberation time and interfering noise.

A diagnostic technique based on independent component analysis (ICA), fast Fourier transform (FFT), and support vector machine (SVM) is suggested for effectively extracting signal features in infrasound signal monitoring. Firstly, ICA is proposed to separate the source signals of mixed infrasound sources. Secondly, FFT is used to obtain the feature vectors of infrasound signals. Finally, SVM is used to classify the extracted feature vectors. The approach integrates the advantages of ICA in signal separation and FFT to extract the feature vectors. An experiment is conducted to verify the benefits of the proposed approach. The experiment results demonstrate that the classification accuracy is above 98.52% and the run time is only 2.1 seconds. Therefore, the proposed strategy is beneficial in enhancing geophysical monitoring performance.

This study was conducted to consider the effect of cadmium (Cd) on the liver and serum levels of zinc (Zn) and copper (Cu), and the role of N-acetylcysteine (NAC) in preserving cells against Cd toxicity. Rats were randomly divided into five groups, including G1 (control), G2 (single dose of Cd), G3 (continuous administration of Cd), G4 (single dose of Cd + continu- ous administration of NAC), and G5 (continuous administration of Cd + continuous administra- tion of NAC). Rats in G2 and G4 groups were exposed with single dose of Cd on the first day of study. Continuous administration of Cd and NAC was used every day for 4 weeks. Levels of Zn and Cu were measured by atomic absorption spectroscopy. Expression of matrix metallo- proteinases-2 ( MMP2) and MMP9 genes was evaluated using RT-PCR. The mean level of Cd in serum and liver tissue of G2 group increased significantly by about 26-27%, whereas in G3 group, it increased significantly by about 50-60%. While NAC treatment significantly raised Zn and Cu values, Cd levels significantly decreased in the serum and tissue samples of rats exposed to single or continuous Cd. Exposure to single and continuous administration of Cd caused a significant increase in MMP2 expression by 10.14-fold (P=0.016) and 27.61-fold (P<0.001), respectively. Single and continuous administration of Cd led to a significant increase in MMP9 expression by 3.63-fold (P=0.046) and 43.12-fold (P<0.001), respectively. NAC treatments decreased the expression of MMP2 and MMP9 in rats exposed to single or continuous Cd. Cd exposure was strongly associated with Zn and Cu depletion, and overexpression of MMP2 and MMP9. NAC can protect the liver against Cd toxicity by elevating Zn and Cu contents and down-regulating proteolytic enzymes.