Thermoacoustic converters are devices for direct conversion of acoustic energy into thermal energy in the form of temperature difference, or vice versa – for converting thermal energy into an acoustic wave. In the first case, the device is called a thermoacoustic heat pump, in the second – thermoacoustic engine. Thermoacoustic devices can use (or produce) a standing or travelling acoustic wave. This paper describes the construction and properties of a single-stage thermoacoustic engine with a travelling wave. This kind of engine works using the Stirling cycle. It uses gas as a working medium and does not contain any moving parts. The main component of the engine is a regenerator equipped with two heat exchangers. Most commonly, a porous material or a set of metal grids is used as a regenerator. An acoustic wave is created as a result of the temperature difference between a cold and a hot heat exchanger. The influence of working gas, and such parameters as static pressure and temperature at heat exchanger on the thermoacoustic properties of the engine, primarily its efficiency, was investigated. The achieved efficiency was up to 1.4% for air as the working medium, which coincides with the values obtained in other laboratories. The efficiency for argon as working gas is equal to 0.9%.

Additive manufacturing (AM) is a process that joins similar or dissimilar materials into application-oriented objects in a wide range of sizes and shapes. This article presents an overview of two additive manufacturing techniques; namely Laser metal deposition (LMD) and Wire arc additive manufacturing (WAAM). In LMD, metallic powders are contained in one or more chambers, which are then channelled through deposition nozzles. A laser heats the particles to produce metallic beads, which are deposited in layers with the aid of an in-built motion system. In WAAM, a high voltage electric arc functions as the heat source, which helps with ensuring deposition of materials, while materials in wire form are used for the feedstock. This article highlights some of the strengths and challenges that are offered by both processes. As part of the authors’ original research work, ­Ti-6Al-4V, Stainless steel 316L and Al-12Si were prepared using LMD, while the WAAM technique was used to prepare two Al alloys; Al-5356 and CuAl8Ni2. Microstructural analysis will focus on similarity and differences in grains that are formed in layers. This article will also offer an overall comparison on how these samples compare with other materials that have been prepared using LMD and WAAM.

Sparse fish microremains have been found in marine limestones from the Middle Devonian (Givetian) Skały

Formation (Sitka Coral-Crinoid Limestone Member and Sierżawy Member), Świętomarz–Śniadka section,

Bodzentyn Syncline, Łysogóry Region, northern Holy Cross Mountains, associated with conodonts of the

hemiansatus to ansatus zones. Thelodont scales referred here to Australolepis sp. cf. A. seddoni come from near

Śniadka village, from samples dated as hemiansatus to rhenanus/varcus zones. This increases the known range

for the genus from its original find in Western Australia. The presence of a thelodont in the late Middle Devonian

in Poland extends the known distribution of turiniids around the peri-Gondwana shorelines of Palaeotethys.