Ice thermal energy storage (ITES) systems offer an effective means of shifting peak cooling loads to off-peak periods, but their performance depends strongly on the thermophysical properties of the phase change material (PCM) and on key operating and geometric parameters. This study presents a systematic experimental investigation of the external icing and cold energy storage performance of Al2O3 and multi-walled carbon nanotube (MWCNT) nanofluids as PCMs in a U-tube cold thermal energy storage unit. Nine primary conditions were examined across three coolant inlet temperatures (−5.5, −7.5, and −10 °C) and six nanofluid concentrations, supplemented by parametric studies on heat-transfer-fluid flow rate, initial PCM temperature, and tube outer diameter. Reducing the coolant inlet temperature from −5.5 to −10 °C increased total stored energy by 95%, identifying thermal driving force as the dominant performance lever. Al2O3 nanofluids exhibited a monotonic concentration–performance relationship, with 0.5 vol.% yielding an 18% stored-energy gain, whereas MWCNT nanofluids showed a non-monotonic response, peaking at 0.01 vol.% due to agglomeration at higher loadings. A coefficient-of-performance-based storage-rate index confirmed that lower coolant temperatures remain energy-cost-effective despite reduced refrigeration efficiency. Supplementary studies showed that initial PCM temperature and tube diameter exert moderate but practically significant effects, while flow rate has limited influence once the ice layer thickens. A Buckingham π-based empirical correlation for ice-layer thickness, validated against independent literature data, achieved over 95% of predictions within ±15% deviation. These findings provide quantitative, design-oriented guidance for optimising nanofluid-enhanced ITES systems.
In Korea, Nuclear Power Plants continually prepare and revise the final safety analysis report (FSAR), which is essential for predicting the source-term information of radioactive materials throughout their lifecycle. This report provides detailed information on the source-terms of Chalk River Unidentified Deposits (CRUD). The management of radioactive corrosion products, present on nuclear fuel surfaces and within the primary system, is crucial for ensuring equipment integrity and controlling worker exposure during operation. Unlike earlier studies that focused solely on the radioactive inventory of major components, this study established an integrated evaluation framework by coupling the CRUDTRAN, ORIGEN2, and PHITS codes to quantitatively assess the relative contribution of the CRUD source-term on the core support barrel (CSB) to worker doses, in comparison with the activation source-terms of the reactor pressure vessel (RPV). By calculating these specific source-terms and conducting subsequent radiation exposure assessments, this work underscores the critical significance of the CRUD source-term during the decommissioning phase. The comparative dose assessment revealed that in the absence of system decontamination, the radiation exposure contributed by the CRUD source-term exceeded that from the structural activation of the RPV across the range of deposition-fraction assumptions, from about 1.5 times under the minimum assumption to about 117 times under the maximum assumption. These quantitative findings indicate that CRUD is a major source of worker exposure during the decommissioning phase, which should not be neglected relative to the activation of internal components.
Precise pressure monitoring in rarefied gas environments is essential for process control and system reliability in precision engineering applications. Conventional vacuum gauges, including mechanical deformation-based gauges, ionization gauges, and thermal-conductivity-based Pirani gauges, often require calibration for specific operating conditions or show limited sensitivity in low-pressure ranges. In this study, we propose a suspended microheater-based 3ω sensor designed to suppress substrate heat loss and enhance the contribution of gas-mediated heat transfer to the measured electrothermal response. The low-frequency 3ω response was interpreted using a quasi-steady thermal-resistance framework, in which the inverse temperature amplitude serves as a conductance-like indicator under fixed oscillatory heating. The pressure-dependent gas contribution was described using an effective rarefied-gas thermal-conductivity model with a representative effective length scale. A Pt microheater was fabricated on a SiNx membrane, and 3ω measurements were performed in air over a pressure range of 1.9 × 10–2–7.5 × 102 Torr and a driving-frequency range of 0.1–10 Hz. As the pressure decreased, both the temperature amplitude and phase delay increased, with the largest pressure sensitivity observed at 0.1 Hz. Comparison between the inverse temperature amplitude and the calculated effective thermal conductivity showed close correspondence in the slip and transition regimes, whereas the low-pressure deviation was consistent with the increasing relative importance of residual, weakly pressure-dependent heat-loss pathways as gas-mediated conduction diminished. These results demonstrate that a suspended 3ω microheater can provide a compact electrothermal platform for vacuum-pressure sensing by directly transducing pressure-dependent changes in rarefied gas heat transfer.
While transformational and transactional leadership are key drivers of performance in public organizations, their effects on organizational effectiveness depend on structural conditions. This study examines organizational effectiveness-measured as agencies' reported goal attainment-and analyzes how the span of control, an indicator of the structural distance between leaders and subordinates, moderates the relationship between these leadership styles and effectiveness. Drawing on panel data from U.S. federal agencies, the analysis shows that transformational leadership is positively associated with effectiveness, whereas transactional leadership is negatively associated with it. Moreover, transformational leadership relates more strongly to effectiveness under narrow spans of control, where supervisors provide more personalized attention, whereas transactional leadership is more effective under broader spans that rely on standardized oversight. These findings clarify how leadership approaches can align with organizational structures to enhance public sector effectiveness.
AB5 toxins constitute a major family of bacterial exotoxins. Their pathogenicity depends on the coordinated actions of two components: an enzymatically active A subunit and a pentameric B subunit. The B subunit mediates host cell recognition and intracellular trafficking. Among them, cholera toxin represents a representative model for investigating structure–function relationships governing toxin entry and delivery. While the catalytic activity of the A subunit has been extensively characterized, growing evidence indicates that pathogenic outcomes are critically shaped by trafficking strategies encoded within the B subunit pentamer. This review focuses on the cholera toxin B subunit (CTB) as a model system to elucidate how pentameric organization enables multivalent GM1 recognition, receptor clustering, and efficient intracellular transport. We summarize current knowledge on the molecular basis of CTB pentamerization, its thermodynamic and structural advantages, and the role of multivalency in amplifying delivery efficiency and pathogenicity. In addition, we examine how CTB-mediated intracellular trafficking influences uptake pathway selection and intracellular routing, thereby contributing to consistent and robust toxic outcomes. Beyond pathogenic mechanisms, we briefly discuss the potential implications of CTB-mediated trafficking for translational applications. By integrating structural, cellular, and functional perspectives, this review demonstrates how CTB-mediated mobility governs intracellular routing and uptake pathway selection. This framework provides a basis for understanding AB5 toxin pathogenicity and its broader biological significance.
