Universitatea Transilvania din Brasov

Open Access Repository

Arhiva digitală instituțională ce oferă acces deschis la rezultatele cercetării științifice și la resurse pentru educație: teze de doctorat, articole științifice, baze de date, studii, rapoarte, lucrări prezentate la conferințe și alte documente relevante.

Universitatea Transilvania din Brasov Open Access Repository

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Universitatea Transilvania din Brasov

Recent Submissions

Fuzzy Logic-Based Control of a Battery Energy Storage System to Mitigate Frequency Excursions in the Cuban Power System Caused by Electric Arc Furnaces
(Springer Science and Business Media LLC, 2026-04-28) Domínguez, Julio Espinosa; Serban, Ioan; Breffe, Orlys Ernesto Torres
This paper proposes an adaptive control for a battery energy storage system (BESS) using a fuzzy logic controller (FLC), specially designed to operate in parallel with an electric arc furnace (EAF) in the Cuban power system. The BESS control system was developed with considerations for the characteristics of the Cuban power system, the typical power demand profile of the EAF, and the battery lifetime. The primary goal is to mitigate the frequency excursions that currently occur during EAF operation, enabling the furnace to complete the smelting process without restrictions. Furthermore, the system aims to reduce battery stress, thereby enhancing their lifetime. For this purpose, the BESS active power is managed by an adaptive compensator, governed by the FLC. Based on information coming from all three components involved - power system frequency, furnace state and battery usage rate, the proposed FLC generates an optimal output to adjust the compensator’s behaviour. The performance of the proposed system was evaluated through simulations and experimental tests. The results demonstrate that using adaptive control applied to BESS can be an effective solution for steelworks connected to weak power systems, such as the current Cuban power system.
Electric Vehicle Integration with Grid-Forming Capability in Renewable-Powered Microgrids: A Survey and Future Perspectives
(Institute of Electrical and Electronics Engineers (IEEE), 2026-04-08) Osman, Mohamed; Serban, Ioan
In recent years, electric vehicles (EVs) are increasingly recognized as flexible energy resources that can provide ancillary services to renewable energy sources-based microgrids (MGs), particularly when operated under grid-forming (GFM) control techniques. However, realizing this potential requires developments across several layers, including EV charger architectures, storage systems coordination, and hierarchical MG control. This paper brings these developments together. It reviews recent advancements in hybrid energy storage systems, converter topologies for on-board and off-board EV chargers, advanced control and energy management systems, vehicle-to-grid implementations, and EV-interactive MG operation. It also provides a comparative assessment of three proposed GFM-based EV-MG integration schemes in terms of GFM resource availability, active power exchange capacity, efficiency, infrastructure cost, and ancillary service potential. Major open research challenges and promising directions are discussed at the end.
Biomechanical Analysis of the Breaststroke Kick in Young Swimmers UsingWearable Inertial Sensors: An Exploratory Pilot Study
(Sensors, 2026-03-07) Brus, Denisa Iulia; Enoiu, Răzvan Sandu; Catana, Dorin
Breaststroke performance is highly dependent on lower-limb biomechanics and the coordination of movement during the kick cycle. Recent advances in wearable inertial sensor technology enable objective analysis of human motion in real training environments. This study presents an exploratory pilot investigation aimed at evaluating the feasibility of using wearable inertial sensors for biomechanical analysis of the breaststroke kick in young swimmers. Five male children (aged 8–10 years) with basic breaststroke proficiency participated in a single-group pre–post exploratory study conducted over a three-month period. Lower-limb motion was monitored using wearable inertial measurement units attached bilaterally to the shanks and feet, allowing real-time kinematic feedback and data recording during training sessions. The intervention consisted of five structured training sessions integrating drill-based breaststroke kick exercises with sensor-assisted feedback. Outcome measures included time-based swimming performance tests (40 m breaststroke kick with kickboard and 40 m breaststroke without kickboard) and qualitative biomechanical evaluations of the passive and active phases of the breaststroke kick. Additionally, selected IMU-derived kinematic variables (peak ankle dorsiflexion and external foot rotation angles) were analyzed to provide quantitative biomechanical insight. Following the intervention, improvements were observed across all outcome measures, including reduced swimming times and increased technique scores assigned by two independent evaluators. These findings support the feasibility of integrating wearable IMUs for technique monitoring and simple kinematic quantification of breaststroke kick mechanics in young swimmers; larger controlled studies are required to assess efficacy.
Removal of a Calcium Silicate-Based Sealer from Oval Root Canals Using Different Irrigation Activation Techniques: A Stereomicroscopic and SEM–EDS Study
(MDPI AG, 2026-04-10) Merfea, Mihai; Cimpean, Sanda Ileana; Pop-Ciutrila, Ioana Sofia; Assaf, Elie; Delean, Ada Gabriela; Badea, Iulia Clara; Cuc, Stanca; Surdu, Vasile Adrian
Calcium silicate-based sealers are widely used in contemporary endodontics, but their strong interaction with dentinal substrates may complicate their removal during nonsurgical retreatment and potentially hinder canal disinfection. This ex vivo study evaluated the effectiveness of different irrigation activation techniques in removing a calcium silicate-based sealer from oval-shaped root canals. Sixty extracted single-rooted teeth were instrumented and obturated using the single-cone technique with NeoSealer Flo, followed by retreatment using a reciprocating system. Specimens were randomly assigned to four final irrigation protocols: conventional needle irrigation (CNI) with NaOCl/EDTA, ultrasonic activation (US), diode laser activation (LI), and Er:YAG laser activation using the SWEEPS mode (SW) (n = 15). Residual filling material was quantified before and after final irrigation using stereomicroscopic imaging and ImageJ (version 1.54) analysis. Dentinal surface morphology and residual sealer were further evaluated using SEM–EDS. Statistical analysis included one-way ANOVA and chi-square tests (p < 0.05). All protocols significantly reduced residual filling material compared with mechanical retreatment alone (US 15.08%, CNI 7.89%, LI 8.01%, SW 7.20%) (p < 0.01). US resulted in significantly greater sealer removal compared with CNI, LI, and SW, with mean differences ranging from 7.08% to 7.88% (p < 0.05). These findings indicate that irrigation activation enhances the removal of NeoSealer Flo calcium silicate-based sealer, with ultrasonic activation demonstrating greater effectiveness among the evaluated techniques, under the conditions of this experimental setup.
Heart Rate Variability and Perceived Recovery as Predictors of Performance in Athletes Competing in Sprint Events Stefan Alecu
(MDPI, 2026-03-17) Alecu Stefan; Onea Gheorghe Adrian
Introduction: This study investigated heart rate variability (HRV) and perceived recovery status (PRS) in relation to sprint performance in competitive athletes involved in sprint events. A secondary aim was to explore potential gender-based differences in these relationships. Methods: Fifty-six sprint-trained athletes (21 males, 35 females; age 16–21) participated in a 5-day in-season microcycle. Daily morning HRV was measured using Polar H10 chest straps and the HRV4Training app, with the root mean square of successive differences (LnRMSSD) used as the primary HRV marker. Perceived recovery was assessed each morning using the PRS scale. On each day, athletes completed 20 m maximal sprint tests. Linear mixed-effects models were used to examine the relationships between LnRMSSD, PRS, gender, and sprint performance while accounting for repeated measurements within athletes. Results: Linear mixed-effects modeling revealed that LnRMSSD was a significant negative predictor of sprint time (β = −0.019, p = 0.003), indicating that higher parasympathetic activity was associated with faster sprint performance. PRS was also a significant negative predictor of sprint performance (β = −0.014, p = 0.008). Conclusions: Daily recovery markers were associated with sprint performance in competitive sprint athletes, with potential gender-specific patterns that should be interpreted cautiously. Both LnRMSSD and PRS were significantly associated with sprint performance, highlighting the relevance of combining physiological and subjective recovery markers in athlete monitoring.