This paper treats the stability of two superposed gravitating streams rotating about the axis transverse to the horizontal magnetic field. The critical wave number for instability is found to be affected by rotation for propagation perpendicular to the axis about which the system rotates. The critical wave number for instability is not affected by rotation when waves propagate along the axis of rotation. The critical wave number is affected by both the magnetic field and the streaming velocity in both cases. Both the magnetic field and the rotation are stabilizing, while the streaming velocity is destabilizing.
Approximately 1000 specimens representing more than 30 species and strains of the family Steinernematidae, from Australia, North and South America and Europe were investigated by scanning electron microscopy to determine the structure of the lateral field of the infective juveniles. Although fixation and critical point drying may cause distortion of the ridges of the lateral field, three basic types of arrangement could be observed. Six ridges were present on Steinernema affinis and S. intermedia; seven ridges were present in most species and strains from forest-ecosystems (i.e. S. kraussei) and eight ridges were present in species and strains from agroecosystems (i.e. S. bibionis and S. carpocapsae).
The article aims to identify barriers related to developing agricultural biogas plants in Poland. The secondary data was supplemented by primary data from a questionnaire conducted among employees of an enterprise whose biogas production is one of the elements of the circular economy. The results of the research revealed that the majority of respondents indicated external, systemic and developmental obstacles. The largest percentage of responses concerned the lack of stable legal regulations in the scope of renewable energy sources, including biogas plants, and the lack of programs financing the construction of agricultural biogas plants. Moreover, the respondents pointed to the proposals that could improve the development of agricultural biogas plants in the future. The respondents considered updating and ensuring the profitability of investments in the situation of significantly higher expenditures, growing costs of business and debt servicing through the reference price as a significant motivator, as well as inclusion in the support system of tariffs guaranteeing a stable income for at least 15 years. Barriers to developing agricultural biogas plants in Poland remain unchanged, and the awareness of the positive impact of agricultural biogas plants on many levels is still very low.
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