A block bayesian compressive sensing method based on the equivalent source method for near-field acoustic holography

The conventional equivalent source method for near-field acoustic holography is an effective noise diagnosis method using microphone array. However, its performance is limited by microphone spacing, so the effect is unsatisfied when the wave number is high. In this paper, to broaden the frequency suitability and improve the performance of sound source reconstruction with low signal-to-noise ratios, a block Bayesian compressive sensing method based on the equivalent source method is proposed. Numerical results show that this proposed method has a good reconstruction performance and makes wideband reconstruction possible. By changing the frequency, location, and signal-to-noise ratio of the sound source, the reconstruction performance of the proposed method can remain stable. Finally, the validity and practicability of the proposed method are verified by experiments.

Simultaneous determination of gross alpha/beta activities in water by liquid scintillation counting and its applications in the environmental monitoring

Based on the standards of ISO11704-2018 and ASTM D7283-17, a method for simultaneous determination of gross alpha and gross beta activity concentrations in water by liquid scintillation counting (LSC) was established, which can be applied to various types of water samples in routine monitoring, such as drinking water, groundwater, geothermal water, seawater, and radioactive wastewater. The sample’s pH value and concentrated volume must be controlled to avoid quenching as much as possible. The validation tests show that the deviations of gross alpha and gross beta activities can satisfy quality control requirements in a wide range of activity ratios. For the actual samples, the measurement results of the LSC method are in good agreement with those of the thick source method. Moreover, the LSC method performs better in detection limit and a simpler pretreatment process than the thick source method.

Determination of the anisotropic thermal conductivity of an aerogel-based plaster using transient plane source method

Aerogel-based plasters are composite materials with declared thermal conductivities in the range of traditional insulating materials, i.e. 30-50 mW/(m·K). Based on the results from reported field measurements, aerogel-based plasters can significantly reduce the thermal transmittance of uninsulated walls. However, the in-situ measured thermal conductivities have sometimes been higher than the declared values measured in laboratory and in the main direction of the heat flow. Meanwhile, the anisotropic thermal performance of aerogel-based plasters, i.e., deviating thermal performance in the different directions of heat flow, has not been explored yet. The objective of this study is thus to evaluate the anisotropic thermal conductivity of an aerogel-based plaster. This is done in a set of laboratory measurements using the transient plane source method. Six identical and cubic samples with the dimensions of 10×10×10 cm3 were paired two and two, creating three identical sample sets. In total, 360 measurements of thermal conductivity and thermal diffusivity, and 130 measurements for specific heat capacity were conducted. The results indicate a weak anisotropy of less than ±6.5 % between the three directions (x, y, z). Considering the accuracy of the selected measurement technique, better than ±5 %, supplementary measurements using another technique are recommended.