Pollution caused by plastic materials has a great impact on the environment. The biodegradation process is a good treatment solution for common polymers and biodegradation susceptible ones. The present work introduces new insight into the biodegradation process from a mathematical point of view, as it envisions a new empirical model for this complex process. The model is an exponential function with two different time constants and a time delay, which follows the weight loss profile of the polymer during the biodegradation process. Moreover, this function can be generated as the output variable of a dynamic exogenous system described through state equations. The newly developed models displayed a good fit against the experimental data, as shown by statistical indicators. In addition, the new empirical model was compared to kinetics models available in the literature and the correlation coefficients were closest to 1 for the new empirical model in all discussed cases. The mathematical operations were performed in the MATLAB Simulink environment.

The article focuses on devising solutions for monitoring the condition of the filter capacitors of DC-DC converters. The article introduces two novel DC-DC buck converter designs that monitor the equivalent series resistance (ESR) and the capacitance of capacitors using a parameter observer (PO) and simple variable electrical networks (VEN). For the first scheme, the PO processes in real time the voltage at the capacitor terminals during a discharge-charge cycle. For the second scheme, the filtering is performed with two or more capacitors in parallel, and the PO processes the voltage at the terminals of each capacitor during two discharge processes without interrupting the filtering operation of the converter. The paper presents the principles and theoretical support on which the two schemes of DC-DC buck converters are based, design details regarding PO and VEN, as well as experiments performed with each of the schemes. In the experimental schemes, the PO is implemented with a microcontroller, and the parameters of some aluminum electrolytic filter capacitors are calculated in a real-time manner of about $40 \mathrm{m}\mathrm{s}$. The calculation accuracy of the equivalent capacity is very good. Regarding the calculation accuracy of the ESR, it is shown that it depends on the fulfillment of certain ratios between the VEN resistances, on the one hand, as well as between them and the ESR, on the other hand.

This paper describes the implementation of a parameter observer (PO) intended to estimate the capacitance and equivalent serial resistance of a capacitor (ESR). The implemented observer consists of a dynamic second-order discrete-time system. The input signal of the observer is the voltage at the terminals of the capacitor measured during its discharge across a variable resistance in two steps. The implemented observer can be used in quasi-online or offline mode. The theoretical and experimental supporting materials provide a comprehensive picture of the implementation and conditions of use of the PO. The experimental verification was carried out with a microcontroller with Cortex^®-M7 core architecture. The sampling time of the PO was 20 μs, and the estimation of the parameters was obtained before the end of the discharge of the capacitor. In the cases described in the paper, this means approximately 25 ms. Due to the PO’s capabilities (estimation speed, reduced computational complexity and precision)—proved by the experiments carried out on three electrolytic capacitors of 100 μF, 220 μF and 440 μF—the implementation is of interest for several applications, primarily in the field of power electronic applications.

The remote prognostic, diagnosis, and maintenance of electrolytic capacitors are research topics of interest due to their presence in numerous electronic devices and their increased susceptibility to degradation over time. The authors’ focus in this article is on the proposal of a new diagram for monitoring the parameters of the capacitors that compose the filter bank of a DC–DC buck converter by connecting them in parallel. Each capacitor is modeled by an equivalent series R–C circuit composed of an equivalent capacitance and an equivalent series resistance (ESR). The method used allows successive investigation of the three capacitors that compose the bank by triggering discharge/charge sequences, acquiring the voltages at the capacitor terminals, and estimating the time constants of each capacitor using a parameter observer. During the estimation of the parameters of a capacitor, the converter uses the other two capacitors maintained in operation. The monitoring cycle of all capacitors of the bank lasts less than $40 \mathrm{m}\mathrm{s}$, not significantly affecting the operation of the converter. The study undertaken is correlated with the thermal map of the board on which the converter is made. The dispersion of the measured values of the equivalent capacitances is below $0.25\%$, and of the ESR below $2.6\%$. The major advantage of the method is that the monitoring is performed online and in real time.

In our previous research work, we investigated different methods to mitigate the vortex rope that appears in the draft tube of a Francis turbine when it operates at off-design operating points. The most promising results were obtained for a method involving an axial jet of water. The minor disadvantage of this method was the high value of the flow rate of the water jet. Our present work focuses on another method that decreases the value of the flow rate of the jet. In this sense, a new device has been developed that produces a pulsating water jet, which mitigates the pressure fluctuations associated with the swirling flows. The objective of this paper is to use our experimental test rig to validate the efficiency of a pulsating water jet in mitigating the vortex rope. To perform that, pressure measurements were carried out at four test levels to evaluate the pressure amplitude evolution when the pulsating jet was deployed. From preliminary investigations, the results indicate that this method leads to a decrease of the pressure amplitude of the vortex rope, with a lower value of the flow rate of the jet.