A phase adjuster (PA) is proposed to improve the cooling effect of a loop-tube-type thermoacoustic cooling system. A PA is a device for accelerating the particle velocity. The PA is embedded in the loop tube and narrows the cross-sectional area of the part of the loop tube. The PA creates a strong boundary condition in which the particle velocity is accelerated. It is confirmed that the phases of the sound pressure and particle velocity are adjusted so that the sound generated in the loop tube is resonated with the total tube length at one-wavelength resonance. This results in a great improvement in the cooling effect of the thermoacoustic cooling system.

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In a recent theoretical investigation of positron diffusion in gases, Shizgal and Ness suggest that the results for helium obtained by their method of solution of the diffusion equation differ in a few significant details from the earlier results of Campeanu and Humberston. It is explained here that the apparent discrepancies arise from misunderstandings in the interpretation of the earlier work and that, consequently, the results of the two methods are in good agreement.