In this paper, we present the methods to detect the channel delay profile and the Doppler spectrum of shallow underwater acoustic channels (SUAC). In our channel sounding methods, a short impulse in form of a sinusoid function is successively sent out from the transmitter to estimated the channel impulse response (CIR). A bandpass filter is applied to eliminate the interference from out-of-band (OOB). A threshould is utilized to obtain the maximum time delay of the CIR. Multipath components of the SUAC are specified by correlating the received signals with the transmitted sounding pulse with its shifted phases from 0 to 2π. We show the measured channel parameters, which have been carried out in some lakes in Hanoi. The measured results illustrate that the channel is frequency selective for a narrow band transmission. The Doppler spectrum can be obtained by taking the Fourier transform of the time correlation of the measured channel transfer function. We have shown that, the theoretical maximum Doppler frequency fits well to that one obtained from measurement results.

Basing on the data of Al2O3 and SiO2 thermodynamic acnvrties in SiO2-containing calcium aluminates of three formulae, CaO · Alz03, I 2CaO · 7Alz03 and 3Ca0 · Alz03 (shortly denoted as C1A" C12A7 and C3A1), at 1873K for the wide range of SiO2 mole fractions [!], we propose their activities expressed as functions of CaO contents provided there is no change in SiO2 mole fraction. The proposed relations allow to follow the change of the inclusions and steel composition during calcium treatment when calcium or calcium-silicon are added. An evolution of inclusion and steel compositions during calcium treatment was investigated starting from the partly modified inclusions C1A1-SiO2 with x;,02 = O.IO and 0.03. It was shown that the change of calcium aluminosilicates composition is slightly different for the pure calcium and calcium-silicon additions. With the calcium treatment the mole fraction of SiO2 in inclusions is decreasing less significant.