In recent times the areas of application of direct current systems are being expanded. This may lead to increased risk of electric shock. The subject of investigations described in this paper is a non-linear model of the resistance of the human body under the conditions of direct current electric shock. The aim of the study was to determine the approximate model of the human body resistance at a hand-to-hand DC flow, which may be useful for assessing the effects of the electric shock. The investigations were carried out on three subjects using the hand to hand current path. Experimental studies were conducted within a voltage range of up to 80 V, while the analytical form of the identified model enables extrapolation of the obtained results to a wider range of touch voltages. The identified models allow to evaluate the shock hazard within a voltage range of up to 1500 V. The adopted shock hazard criterion was the probability of ventricular fibrillation of 5 %. The result of the studies was a direct correlation between maximum allowable duration of shock and the touch voltage determined for the three subjects on the basis of the relationship between shock duration and the touch current specified in the IEC report, and of non-linear models of resistance identified on the basis of experimental studies. It was demonstrated that for touch voltages of up to 650 V the fibrillation phenomenon should not occur when the shock duration is shorter than 10 seconds.

Natural gas is one of the main energy sources in Poland and accounts for about 15% of the primary energy consumed in the country. Poland covers only 1/5 of its demand from domestic deposits. The rest is imported from Russia, Germany, Norway, the Czech Republic, Ukraine, and Central Asia. An important issue concerning the market of energy resources is the question of the direct impact of the prices of energy resources on the income of exporting and importing countries. It should also be remembered that unexpected and large fluctuations are detrimental to both exporters and importers of primary fuels. The article analyzes natural gas deposits in Poland, raw material trade and proposes a model for forecasting the volume of its consumption, which takes into account historical consumption, prices of energy resources and assumptions of Poland’s energy policy until 2040. A hybrid model was built by combining ARIMA with LSTM artificial neural networks. The validity of the constructed model was assessed using ME, MAE, RMSE and MSE. The average percentage error is 2%, which means that the model largely represents the real gas consumption course. The obtained forecasts indicate an increase in consumption by 2040.

The research presented in the article was aimed at verifying the effectiveness of environmental taxes in reducing the level of greenhouse gas emissions. For this purpose, data provided by Eurostat in the environmental taxes category were used. They were treated as explanatory variables. Data were entered into the ARMAX models built by the authors. The dependent variable was the emission of two greenhouse gases covered by the research, namely carbon dioxide and methane. The research was carried out in Poland, for which the results obtained for Sweden were used as the benchmark. The built models made it possible to verify the relationship between environmental taxes in the categories of energy, transport, pollution, resources, and the level of CO2 and CH4 emissions. The nature of the explanatory variable was also examined. Environmental taxes can fulfill a fiscal, incentive, and redistributive function. The conducted research shows that these taxes, in fact, fulfill mainly a fiscal function, while redistributive and incentive functions are insufficient. It was also observed that the direction and strength of the impact of taxes differ depending on the greenhouse gas.

Wychody produktów wzbogacania oraz ich jakooeae -a zatem równie¿ wartooeae produkcjizale¿¹ od wzbogacalnooeci wêgla surowego, stopnia z³o¿onooeci i konfiguracji uk³adu technologicznego przeróbki wêgla oraz parametrów rozdzia³u operacji przeróbczych. Porównanie efektów wzbogacania wêgla surowego w ró¿nych uk³adach technologicznych, zw³aszcza porównanie wartooeci produkcji o zadanej jakooeci, pozwala oceniae przydatnooeae poszczególnych wariantów wzbogacania (Yagun i in. 2002). Dotychczas w kilku publikacjach wykazane zosta³o (Pielot

The paper presents some issues related to the control of fatigue test machines based on W(t) parameter taking into account the simultaneous interaction of stress and strain. This parameter is defined as a product of these values. Such a research method represents a new approach in fatigue testing with an innovative control system. Because of the W(t) function characteristics, the system presents nonlinear behavior and there is a significant deterioration of the control quality and the controlled signal significantly differs from the reference signal waveform. This problem can be solved by introducing a nonlinear block into the feedback loop. Fatigue tests have been carried out for sinusoidal and randomized reference signal waveforms. These tests have proved that the controlled signal follows reference values with an appropriate control quality.