accuracy точність NTC-thermistor forecasting neural network optimization нейронна мережа оптимізація прогнозування NTC-термистор NTC-термістор R/T-characteristics R/T-характеристика RBF-network RBF-мережа accuracy of approximation calibration core diameter defectiveness level details evolutionary modeling exchange rate genetic algorithm machine learning measuring data neural network approximation neural network model neural network models operating temperature range polynomial model