Korea Railroad Research Institute

This study conducted a comparative life cycle assessment (LCA) of three end-of-life scenarios for prestressed concrete railway sleepers (PCRS): landfilling without recycling (S1), recycled concrete aggregate (RCA) recycling (S2), and CO₂ capturing material reprocessing (S3). The system boundary and functional unit were defined in accordance with EN 15,804, and greenhouse gas (GHG) emissions were evaluated using the IPCC 2021 GWP (100-year) method. An avoided burden approach was applied to reflect the environmental benefits of material substitution and CO₂ capture. The results indicate that S2 and S3 achieved net carbon offsets of 44,416 kgCO₂eq and 95,371 kgCO₂eq, respectively, relative to the baseline scenario (S1). These environmental benefits were primarily attributed to the avoided emissions from virgin material substitution and direct CO₂ removal. The study highlights the importance of on-site separation technologies for maximizing resource recovery and provides a circular solution for decarbonizing infrastructure waste management systems.

I propose a deterministic framework for describing water surface dynamics based on the temporal recording of localized force-mass interactions. The surface response is interpreted as a time-ordered execution of local mechanical histories governed by causal accessibility. Numerical simulations constructed from this formulation reproduce structured surface patterns under geometric confinement and show close correspondence with experimentally observed water surface behavior. These results suggest that water surface patterns may be naturally interpreted as geometric records of force transmission over time.

The increasing interconnection of inverter-based resources (IBRs) with low short-circuit current has weakened grid strength, making phase-locked loops (PLLs) susceptible to instability due to accumulated phase-angle error under current limiting. This study defines such instability as IBR instability induced by reduced grid robustness and proposes a root-mean-square (RMS) model-based screening method. After fault clearance, the residual q-axis voltage observed by the PLL is treated as a disturbance signal and, using the PLL synchronization equations, is analyzed with a standard second-order formulation. The maximum phase angle at which synchronization fails is defined as θpeak, and the corresponding q-axis voltage is defined as Vq,crit. This value is then mapped to a screening metric Ppeak suitable for RMS-domain assessment. The proposed methodology is applied to the IEEE 39-bus test system: the stability boundary and Ppeak are obtained in Power System Simulator for Engineering (PSSE), and the results are validated through electromagnetic transient (EMT) simulations in PSCAD. The findings demonstrate that the RMS-based screening can effectively identify operating conditions that are prone to PLL instability in weak grids, providing a practical tool for planning and operation with high IBR penetration. This screening method supports power system planning for high-penetration inverter-based resources by identifying weak-grid locations that require EMT studies to ensure secure operation after grid faults.

This study analyzes the performance of positioning techniques based on configuration changes of 5G New Radio (NR) signals. In 5G networks, a terminal’s position is determined from the Time of Arrival (TOA) of Positioning Reference Signals (PRS) transmitted by base stations. We propose an algorithm that improves TOA accuracy under low sampling-rate constraints and implement 5G PRS for positioning in a software-defined modem. We also examine how flexible time–frequency resource allocation of PRS affects TOA estimation accuracy and discuss optimal PRS configurations for a given signal environment. With the proposed configuration, the terminal can achieve sub-sample TOA accuracy, reaching approximately 0.3 samples.

ABSTRACT Demand responsive transport (DRT) systems have emerged as innovative solutions to address transportation inequality in areas underserved by conventional public transit. However, some recent DRT services have struggled because of a limited understanding of local contexts and user needs. A growing number of studies have investigated successful modal shift cases, the advantages of DRT, and user satisfaction. Nevertheless, studies conducting in-depth analyses of the factors influencing satisfaction and deriving the factors contributing to modal shifts are rare, with most evaluations limited to simple score-based assessments. This study aims to fill this gap by identifying factors affecting the three core characteristics of DRT services: mobility, accessibility, and user convenience. Using survey data from passengers, we analyzed both satisfaction and dissatisfaction using Binary Logistic Regression with a structured dataset. The analysis revealed several pivotal factors that influence user satisfaction. Key findings include the following: satisfaction levels are positively influenced by a ‘stronger intention to continue using DRT’, ‘reduced first-mile walking time’, and ‘lower detour rates’. Satisfaction with mobility and user convenience is particularly enhanced by the ‘experience of travelling to previously inaccessible locations’. Accessibility satisfaction was significantly affected by a ‘stronger intention to continue using DRT’. Furthermore, user convenience satisfaction is notably influenced by ‘female passengers’, ‘booking via phone’, and ‘no experience with call cancellations’. These findings have significant implications for the DRT service design and operational strategies.

This study presents an integrated evaluation framework for textile-based electrical muscle stimulation smartwear electrodes, combining physiological and user-centered assessments to ensure comprehensive performance analysis. Four electrode types—lock stitch, knit, hot stamping, and moss stitch—were examined using a systematic five-step process with nine participants. Quantitative measurements were obtained using electromyography to determine maximum voluntary contraction and tensiomyography to assess muscle contraction velocity. The knit electrode demonstrated a statistically significant reduction in maximum voluntary contraction following stimulation (W = 2.0, p = 0.012, Cohen’s d = 0.58), indicating effective neuromuscular activation and fatigue induction. The moss stitch electrode also showed a notable trend toward reduced muscle activation (W = 6.0, p = 0.055, d = 0.37). In contrast, the lock stitch and hot stamping electrodes exhibited negligible changes. User experience surveys revealed overall high acceptance across all electrode types (4.0–4.5 of mean scores on a 5-point scale), with the moss stitch electrode receiving the highest ratings for perceived safety and minimal skin discomfort, while the hot stamping electrode scored lowest in breathability. The proposed framework enables balanced evaluation of both functional performance and user experience, offering practical design guidance for optimizing textile electrodes across applications ranging from high-intensity athletic training to low-intensity rehabilitation.