Search Results (18)

The displacement of synchronous machines by inverter-based resources raises critical concerns regarding the stability of future low-inertia power systems. Grid-forming (GFM) inverters offer a pathway to address these challenges by autonomously establishing voltage and frequency while emulating inertia and damping. This paper investigates the feasibility of operating a transmission-scale network with 100% GFM penetration by fully replacing all synchronous generators in the IEEE 39-bus system with a heterogeneous mix of droop, virtual synchronous machine (VSM), and synchronverter controls. System stability is assessed under a severe fault-initiated separation, focusing on frequency and voltage metrics defined through center-of-inertia formulations and standard acceptance envelopes. A systematic parameter sweep of virtual inertia (H) and damping ($D_p$) reveals their distinct and complementary roles: inertia primarily shapes the Rate of Change in Frequency and excursion depth, while damping governs convergence speed and steady-state accuracy. All tested parameter combinations remain within established stability limitations, confirming the robust operability of a fully inverter-dominated grid. These findings demonstrate that properly tuned GFM inverters can enable secure and reliable operation of future power systems without reliance on synchronous machines. Full article

Hybrid learning spaces may be described as physical environments enhanced by digital technologies, which enable learning scenarios involving both in-person and online participation. This article presents a hybrid learning space designed for higher education. The design of the space has been informed by Lefebvre’s design principles: (a) spatial practice enabling flexible usage scenarios, (b) representations of space conveying openness and adaptability, and (c) representational spaces supporting experiences of presence in both physical and digital form. The article describes design characteristics guiding the implementation of the hybrid learning space and explains corresponding design decisions, such as the use of a wall-sized projection. Further, the article introduces affordances and usage scenarios of the hybrid learning space developed. Moreover, an evaluation study of the hybrid learning space is conducted by means of a 360°-based virtual field trip (VFT). The VFT, led by an educator, serves as preparation for a field trip (FT) to a composting plant two weeks later. Participants of both VFT and FT (N = 11) completed a questionnaire addressing psychological constructs related to learning, including motivation, emotion, immersion, presence, and cognitive load. We report the results of the VFT alongside those of the FT as a baseline. Some notable differences, for example in social presence, suggest areas for further development of the hybrid learning space. Overall, the study characterises key features of hybrid learning spaces, identifies their contribution to high-quality teaching and provides inspirations for their further development. Full article

This work presents a high-fidelity simulation of the Peach Bottom turbine trip (PBTT) benchmark using the Virtual Environment for Reactor Applications (VERA), a multiphysics reactor modeling tool developed by the U.S. Department of Energy’s Consortium for Advanced Simulation of Light Water Reactors energy innovation hub. The PBTT benchmark, based on a 1977 transient event at the end of cycle 2 in a General Electric Type-4 boiling water reactor (BWR), is a critical test case for validating core physics models with thermal feedback during rapid reactivity events. VERA was employed to perform end-to-end, pin-resolved simulations from conditions at the beginning of cycle 1 through the turbine-trip transient, incorporating detailed neutron transport, fuel depletion, and subchannel thermal hydraulics. The simulation reproduced key benchmark observables with high accuracy: the peak power excursion occurred at 0.75 s, matching the scram time and closely aligning with the benchmark average of 0.742 s; the simulated maximum power spike was approximately 7600 MW, which is within 3% of the benchmark average of 7400 MW; and void-collapse dynamics were consistent with benchmark expectations. Reactivity predictions during cycles 1 and 2 remained within 1500 pcm and 400 pcm of criticality, respectively. These results confirm VERA’s ability to model complex coupled neutronic and thermal hydraulic behavior in a BWR turbine-trip transient, which will support its use in future studies of modeling dryout, fuel performance, and uncertainty quantification for transients of this type. Full article

Balance control in pirouettes has previously been characterized by constraint of the topple angle. However, there is a paucity of research using the margin of stability (MoS) as a dynamic measure of balance related to pirouettes. Therefore, this study aimed primarily to examine the MoS as a metric of balance during a single-turn en dehors pirouette in healthy female amateur ballet dancers. Four participants performed pirouettes until five successful pirouettes were achieved without hopping or loss of balance. Three-dimensional motion capture was used to record the motion trajectories of anatomical markers based on the Plug-in-Gait and Oxford Foot models. Motion synchronized with ground reaction forces was used to calculate the center of pressure (CoP), base of support (BoS), center of the pivot foot, center of mass (CoM), and extrapolated center of mass (XCoM) throughout the turn phase, using laboratory (LCS) and virtual left foot (LFT) coordinate systems. In the LCS and LFT coordinate system, the excursions and patterns of motion of both the CoM and XCoM relative to the CoP were similar, suggesting a neurological relationship. Two different measures of the margin of stability (MoS) in the LFT coordinate system were tabulated: the distance between the (1) XCoM and CoP and (2) XCoM and BoS center. The magnitude of both versions of the MoS was greatest at turn initiation and toe-touch, which was associated with two foot contacts. The MoS values were at a minimum approximately 50% of the stance during the turn phase: close to zero along the anteroposterior (A/P) axis and approximately 50 mm along the mediolateral (M/L) axis. On average, MoS magnitudes were reduced (mean across participants: approximately 20 mm) along the A/P axis, and larger MoS magnitudes (mean across participants: approximately 50 mm) along the M/L axis throughout the turn phase. Although all turns analyzed were completed successfully, the larger MoS values along the M/L axis suggest a fall potential. The variability between trials within a dancer and across participants and trials was documented and showed moderate inter-trial (16% to 51%) and across-participant CV% (range: 10% to 28%), with generally larger variations along the A/P axis. Although our results are preliminary, they suggest that the MoS may be useful for detecting faults in the control of dynamic balance in dehors pirouette performance, as a part of training and rehabilitation following injury. Full article

During the covid pandemic period of 2019–2020, teaching was carried out via homeschooling, and secondary vocational schools had to deal with the problem of ensuring the implementation of excursions, which were a part of their apprentices’ practical training. In the context of the COVID-19 pandemic, a group of people at Constantine the Philosopher University in Nitra (Slovakia) came up with a plan to develop some virtual excursions to help secondary vocational schools replace field trips with their virtual counterparts. In the paper, the authors describe the results of the stated intention: two virtual excursions aimed at the production and processing of metal products and verification of their applicability in educational practice based on a qualitative analysis of expert opinions collected by means of individually led semi-structured interviews. The conclusions of the analysis confirm the high degree of usability of the created excursions and verify some positive impacts of the implementation of virtual excursions into the teaching practice, e.g., it increased student motivation to learn, increased student interest in lesson content, increased student activity, and intensified study activities overall, including various forms of self-study. Full article

Postural imbalance is a leading cause of injury in older adults. Our study investigated the effectiveness of virtual reality (VR)-based interventions on balance ability in this population. Here, we examined 21 older, healthy adults (75.8 ± 5.2 years old). Participants performed 6 weeks of balance training, twice per week for 30 min; the experimental group donned an Oculus VR headset during the training while control participants did not. To assess balance ability, a force platform measured displacement of the center of pressure (COP) during quiet standing in double-leg, tandem, and single-leg stances with eyes closed pre- and post-assessment. COP measurements included mediolateral (ML) and anterior–posterior (AP) directions for root mean square (RMS), peak-to-peak displacement (MAXD), total excursion (TE), and 95% confidence area ellipse (AE) parameters. Post-training assessments showed improvements (significant decreases) in the COP parameters. Control group COP parameters improved in various stances ranging from a 3% to 40% decrease on average. The VR group improved MAXD, TE, and 95% AE ranging from a 5% to 47% decrease, on average, across various stances post- compared to pre-training. VR-based exercise training programs may encourage older adults to engage in mobility exercises, leading to a reduced risk of falls or injuries. Full article

Inclusive design does not stop at removing physical obstacles such as staircases. It also involves identifying architectural features that impose sensory burdens, such as repetitive visual patterns that are known to potentially cause dizziness or visual discomfort. In order to assess their influence on human gait and its stability, three repetitive patterns—random dots, repetitive stripes, and repetitive waves (Lisbon pattern)—were displayed in a coloured and greyscale variant in a virtual reality (VR) environment. The movements of eight participants were recorded using a motion capture system and electromyography (EMG). During all test conditions, a significant increase in the muscular activity of leg flexor muscles was identified just before touchdown. Further, an increase in the activity of laterally stabilising muscles during the swing phase was observed for all of the test conditions. The lateral and vertical centre of mass (CoM) deviation was statistically evaluated using a linear mixed model (LMM). The patterns did cause a significant increase in the CoM excursion in the vertical direction but not in the lateral direction. These findings are indicative of an inhibited and more cautious gait style and a change in control strategy. Furthermore, we quantified the induced discomfort by using both algorithmic estimates and self-reports. The Fourier-based methods favoured the greyscaled random dots over repetitive stripes. The colour metric favoured the striped pattern over the random dots. The participants reported that the wavey Lisbon pattern was the most disruptive. For architectural and structural design, this study indicates (1) that highly repetitive patterns should be used with care in consideration of their impact on the human visuomotor system and its behavioural effects and (2) that coloured patterns should be used with greater caution than greyscale patterns. Full article

Falls are considered a significant cause of disability, pain, and premature deaths in older adults, often due to sedentary lifestyles and various risk factors. Combining immersive virtual reality (IVR) with physical exercise, or exergames, enhances motivation and personalizes training, effectively preventing falls by improving strength and balance in older people. IVR technology may increase the ecological validity of the assessments. The main goal of our study was to assess the feasibility of using a KAVE-based VR platform combining simulations of Levadas and a cable car to perform a balanced assessment and profiling of the older adult population for high risk of falls and the related user experience. A VR-based platform using a Wii balance board and a CAVE was developed to assess balance and physical fitness. Validated by the Biodex Balance System (BBS), 25 older adults participated in this study. The usability and presence were measured through the System Usability Scale and ITC-SOPI questionnaires, respectively. The IVR system showed a high presence and a good usability score of 75. Significant effects were found in the maximum excursion of the centre of pressure (COP) on the anterior–posterior axis during the cable car simulation (CCS), correlating with BBS metrics. Multiple discriminative analysis models and the support vector machine classified fall risk with moderate to high accuracy, precision, and recall. The system accurately identified all high-risk participants using the leave-one-out method. This study suggests that an IVR-based platform based on simulations with high ecological validity can be used to assess physical fitness and identify individuals at a higher risk of falls. Full article

Considering the variability and heterogeneity of motor impairment in children with Movement Disorders (MDs), the assessment of postural control becomes essential. For its assessment, only a few tools objectively quantify and recognize the difference among children with MDs. In this study, we use the Virtual Reality Rehabilitation System (VRRS) for assessing the postural control in children with MD. Furthermore, 16 children (mean age 10.68 ± 3.62 years, range 4.29–18.22 years) were tested with VRRS by using a stabilometric balance platform. Postural parameters, related to the movements of the Centre of Pressure (COP), were collected and analyzed. Three different MD groups were identified according to the prevalent MD: dystonia, chorea and chorea–dystonia. Statistical analyses tested the differences among MD groups in the VRRS-derived COP variables. The mean distance, root mean square, excursion, velocity and frequency values of the dystonia group showed significant differences (p < 0.05) between the chorea group and the chorea–dystonia group. Technology provides quantitative data to support clinical assessment: in this case, the VRRS detected differences among the MD patterns, identifying specific group features. This tool could be useful also for monitoring the longitudinal trajectories and detecting post-treatment changes. Full article

This study characterizes the effects of a postural training program on balance and muscle control strategies in a virtual reality (VR) environment. The Robotic Upright Stand Trainer (RobUST), which applies perturbative forces on the trunk and assistive forces on the pelvis, was used to deliver perturbation-based balance training (PBT) in a sample of 10 healthy participants. The VR task consisted of catching, aiming, and throwing a ball at a target. All participants received trunk perturbations during the VR task with forces tailored to the participant’s maximum tolerance. A subgroup of these participants additionally received assistive forces at the pelvis during training. Postural kinematics were calculated before and after RobUST training, including (i) maximum perturbation force tolerated, (ii) center of pressure (COP) and pelvic excursions, (iii) postural muscle activations (EMG), and (iv) postural control strategies (the ankle and hip strategies). We observed an improvement in the maximum perturbation force and postural stability area in both groups and decreases in muscle activity. The behavior of the two groups differed for perturbations in the posterior direction where the unassisted group moved towards greater use of the hip strategy. In addition, the assisted group changed towards a lower margin of stability and higher pelvic excursion. We show that training with force assistance leads to a reactive balance strategy that permits pelvic excursion but that is efficient at restoring balance from displaced positions while training without assistance leads to reactive balance strategies that restrain pelvic excursion. Patient populations can benefit from a platform that encourages greater use of their range of motion. Full article

Pre-service teacher education should be underpinned by pedagogies that would enhance self-directed learning. Future teachers need to create contexts in the classrooms that would enable learners to, as self-directed learners, identify individual learning goals for themselves, search for appropriate resources, and monitor and assess their own learning. Self-directed learning is essential to adequately prepare learners for a complex and changing world. This paper focuses on the affordances of a first-year student teacher excursion to scaffold learning and the development of a professional identity, and to address the ‘apprenticeship of observation’ that could prevent optimal learning. Pre-service teachers often enter the Bachelor of Education degree with a naïve understanding of the teaching profession. Furthermore, they come from school contexts that often do not enhance self-directed learning. The faculties of education from three different universities have engaged in excursions for first-year student teachers, where the student teachers, as Homo ludens (the playing human), engage in problem-based and cooperative learning activities, exploring the complexities of the teaching profession. Social constructivism underpins the excursion. Findings over 17 years (2007–2023) across three universities—the University of Johannesburg, North-West University and the University of the Western Cape—show that such immersion pedagogy is a high-impact educational practice, in which student teachers learn from practice. The findings show that the excursion provides pre-service teachers with a more nuanced understanding of the teaching profession, enhanced sensitivity to diversity, social justice and inclusivity, an understanding of the value of reflection, and a sense of belonging as a student in the higher education sector. The findings also highlight the affordances of excursions to enhance self-directed learning, an important attribute to ensure continued professional development. Due to the COVID-19 pandemic, higher education institutions had to rethink teaching and learning, and this article also explores the transformation of face-to-face excursions to virtual online excursions. Full article

Virtual reality systems have been developed primarily for the entertainment sector. However, they are being increasingly considered as high potential tools for use in industry and education. In this context, schools are now facing a challenge to introduce virtual-reality-supported teaching into their processes. With this in mind, the authors, in their paper, focus on the possibility for using virtual excursions as part of vocational education and training. For this purpose, they analyze the suitability and usability of selected virtual reality systems, as well as relevant camera systems, for the creation of virtual reality software products designed for industrial practice in upper secondary vocational schools’ apprenticeships (vocational education and training). The main results of their analyses are summarized in the form of tabularized SWOT parameters. Full article

This work proposes the use of fuzzy-logic-based voltage frequency control (VFC) and adaptive inertia to improve the frequency response of a virtual synchronous generator (VSG)-based isolated microgrid system. The joint VFC and inertial control scheme is proposed to limit frequency deviations in these isolated microgrid systems, mainly caused by the increasing penetration of intermittent distributed energy resources, which lack rotational inertia. The proposed controller uses artificial neural networks (ANN) to estimate the exponent of voltage-dependent loads and modulate the system frequency by adjusting the output voltage of the VSGs, which increases the system’s active power reserves while providing inertial control by adjusting the inertia of VSGs to minimize frequency and VSG DC-link voltage excursions. A genetic algorithm (GA)-based optimization strategy is developed to optimally adjust the parameters of the fuzzy logic controller to diminish the impact of disturbances on the system. In addition, the proposed technique is illustrated through simulations within the framework of a test system based on the CIGRE medium-voltage benchmark under various circumstances. The results of these simulations demonstrate that the proposed control strategy outperforms existing methods. Full article

Background: Changes in the visual environment and thereby, the spatial orientation, can induce postural instability leading to falls. Virtual reality (VR) has been used to expose individuals to virtual environments (VE) that increase postural threats. Claustrophobia is an anxiety disorder categorized under situational phobias and can induce such postural threats in a VE. Purpose: The purpose of the study was to investigate if VR-generated claustrophobic simulation has any impact on postural threats that might lead to postural instability. Methods: Thirty healthy men and women (age: 20.7 ± 1.2 years; height: 166.5 ± 7.3 cm; mass: 71.7 ± 16.2 kg) were tested for postural stability while standing on a force platform, upon exposure to five different testing trials, including a normal stance (NoVR), in stationary VE (VR), and three consecutive, randomly initiated, unexpected claustrophobia trials (VR CP1, VR CP2, VR CP3). The claustrophobia trials involved all four walls closing in towards the center of the room. Center of pressure (COP)-derived postural sway variables were analyzed with a one-way repeated measures analysis of variance at an alpha level of 0.05. Results: Significant main effect differences existed in all but one dependent COP-derived postural sway variables, at p < 0.05. Post-hoc pairwise comparisons with a Bonferroni correction revealed that, predominantly, postural sway excursions were significantly lower in claustrophobia trials compared to NoVR and VR, but only accomplished with significantly increased sway velocity. Conclusion: The VR CP trials induced lower postural sway magnitude, but with increased velocity, suggesting a bracing and co-contraction strategy when exposed to virtual claustrophobic postural threats. Additionally, postural sway decreased with subsequent claustrophobia trials, suggesting potential motor learning effects. Findings from the study offer insights to postural control behavior under virtual claustrophobic simulations and can aid in VR exposure therapy for claustrophobia. Full article

The Middle Eocene Climatic Optimum (MECO; ~40 Ma), which interrupted for ~500–600 kyr the long-term cooling trend culminating at the Eocene/Oligocene boundary, still requires a comprehensive understanding of the biotic resilience. Here we present a high-resolution integrated foraminiferal and calcareous nannofossil study across the MECO from the expanded and continuous Tethyan Baskil section (eastern Turkey) that offers a complete magneto-biostratigraphic and geochemical framework. The five MECO phases identified reveal a transition from oligotrophic (pre-MECO) to eu-mesotrophic conditions, possibly related to accelerated hydrological cycle, during the initial MECO and MECO δ¹³C negative excursion phases. The MECO WARMING PEAK phase, marking the highest carbonate dissolution interval, records the most striking biotic changes, such as peak in warm and eutrophic nannofossils, virtual disappearance of the oligotrophic planktic foraminiferal large Acarinina and Morozovelloides, and peak in eutrophic deep dwellers Subbotina. Benthic foraminifera suggest in this phase an improvement in the quality of organic matter to the seafloor. The post-MECO phase shows only a partial recovery of the pre-event conditions. Large Acarinina and Morozovelloides did not recover their abundance, possibly due to cooler conditions in this phase. Our reconstruction reveals how paleoenvironment and marine biota from the studied Neo-Tethyan setting reacted to the MECO perturbations. Full article