A method for frequency-multiplexed multi-sample gas sensing is presented. It enables measuring multiple samples placed simultaneously in the setup, without any optical or mechanical switching. Samples are measured using heterodyne detection and signal from each sensing path is encoded at different carrier frequency. Subsequently, a signal from particular sample is retrieved through heterodyne beatnote demodulation at unique frequency. This technique is particularly suitable for real-time calibration of the sensor through a sequential (or simultaneous) detection of three signals: from unknown sample, reference sample and baseline. Basic setup is demonstrated and proof-of-concept experiments are presented. Very good agreement with spectra measured using standard tunable diode absorption spectroscopy is obtained.

It has been shown in the present paper that exploitation of the experimental potential of a photoacoustic technique can provide information on a type of intermolecular interactions in aqueous mixtures containing organic liquids, when the basic parameters of these mixtures, such as density, ρ, specific heat, cp, or thermal conductivity, λ, are unknown. Earlier investigations of concentration dependence of effusivity in different aqueous solutions of organic liquids demonstrated that the photoacoustics method is a sensitive tool to identify hydrophobic properties of such liquids. In our experiment this suggestion was exploited for a solution of methanol which is known to display much weaker hydrophobicity than other alcohols.

It was confirmed that the location of extreme deviations from linearity for the thermal effusivity, Δe, agrees well with that of characteristic points for the isentropic compressibility coefficient, κS, and the excess molar volume, V_m^E, as a function of the concentration.

Methane explosions are one of the greatest hazards in the coal mining industry and have caused many accidents. On 27 July 2016 at approximately 11:01 a.m., an explosion of methane occurred at the bottom of Zygmunt return shaft at the depth of 411 metres. The explosion resulted in one casualty.
The article presents the results of, and the conclusions from, an in-depth analysis of the changes in the parameters of mine air, especially methane concentration, air flow and the operation of mine fans, recorded by sensors installed in the workings and in Zygmunt ventilation shaft around the time of the accident. The analysis was based on signals recorded by the monitoring system, related to the evolution of methane and fire hazards prior to and after the accident occurred. An attempt was made to identify the cause and the circumstances of the methane explosion at the bottom of the return shaft.