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NanoCoating Preparation to Improve Heat Dissipation of a Heat Sink Inside an Enclosure for Power Electronic Devices
No full textHeat sinks dissipate heat from electronic components, and the increase in heat generation owing to technological advancements has prompted researchers to improve heat sink efficiency. The present study aims to improve heat sinks by high-emissivity nanocoating where the coating is prepared using nanoparticles CuO and MWCNT at a rate of 6% in half a liter of Acrylic resin and solvents Xylene and Butyl acetate at a rate of 30%. After coating the heat sink, the emissivity was examined and it was (0.963) while it was before coating (0.202). The heat sink is examined inside a cubic cavity with a right surface containing heaters that give temperature at the same value as the thyristors (58.5°C, 90°C, and 112.5°C) and a cold left surface (30°C). The temperatures at the tip of each fin are measured before and after coating when they change with time and at a steady state. The results showed that the nanocoating significantly reduced the temperature compared to the uncoated condition with the improvement percentage at a heater temperature of 58.5°C ranging from 10% to 15% at 90°C ranging from 24% to 34% and at 112.5°C ranging from 23% to 35%. It is concluded that the nanocoating showed great effectiveness in improving the performance of the heat sink at all temperatures, but the maximum effectiveness was at high thermal loads
Root Exudation Facilitates Water Infiltration and Rewetting of Dry Soil
No full textThe way plant roots facilitate water infiltration in soil may be just as important as the efficiency with which the root system in turn extracts it from the soil. Here we studied the mechanisms through which the root system facilitates water infiltration through a dry soil layer. Dye tracing experiments were conducted in model soil microcosms to characterise how root growth and exudation affect the permeability of dry layers of the model soil. Results showed that the growth of plant roots through the dry layers of an artificial soil increased the water infiltration rate. In the absence of roots, dissolved root exudates had a significant effect on water infiltration but penetration of the dry layer by a needle did not. We conclude that in dry soil, root architecture and root exudation act synergistically to increase soil hydraulic conductivity, and this may help decrease the water lost by evaporation. This mechanism could be used to select root traits that match the soil and climate, thereby improving water use efficiency in agriculture
Investigating the effect of climate-related hazards on claim frequency prediction in motor insurance with incomplete data
No full textA climate-related dataset provided by a Greek insurance company is analysed to quantify the risks that weather-related hazards, driven by climate change, pose to motor insurance. However, accurately modelling the relationship between these hazards and claim frequencies is challenging, largely because the available records are incomplete. Specifically, they capture only those storm events that result in at least one claim while omitting unreported events. To address this limitation, we introduce a novel class of compound frequency models for the joint analysis of storm occurrences and the corresponding claim frequencies with accurate predictive power. These models are specifically designed to recover the joint distribution of actual storm events and underlying claim processes even when faced with incomplete data. Additionally, we incorporate geospatial covariates to evaluate their influence on both storm occurrences and claim frequencies. Given Greece’s vulnerability to extreme weather due to its geographical position, understanding the influence of climate change on insurance risks is critical. Notably, our findings reveal a negative intrinsic dependence between actual storm counts and per-storm claim frequencies, suggesting potential diversification benefits for insurers as climate change leads to more frequent weather-related hazards
A Stochastic Model of Mutual Insurance under Heterogeneous Time Preferences
No full textThis research examines the premium control problem of a mutual insurance company when its policyholders have heterogeneous (or present-biased) time preferences. When decisions are made collectively by policyholders with diverse time preferences, utilitarian aggregation results in time-inconsistent time preferences. To address time inconsistency, we employ an intrapersonal game-theoretic framework and seek a time-consistent equilibrium strategy. The equilibrium strategy recommends collecting premiums at the minimal rate when the mutual insurer’s reserve surpasses a specified threshold and at the maximal rate when it falls below this threshold. We find that higher heterogeneity (or equivalently, the decreasing impatience) of policyholders’ time preferences will lead to lower reserve thresholds. Our model offers insights for mutual insurers to design premium policies when their policyholders have diverse time preferences
Intermolecular sp<sup>3</sup>C‐H Metalation of Non‐Nucleophilic Brønsted Bases Using Simple Lewis Acids
No full text2,6‐Di‐tert‐butyl substituted pyridines (tBu2‐py) are widely used non‐nucleophilic Brønsted bases. Their ubiquity is due to their highly hindered basic site and chemically robust nature. Herein we report that simple M2X6 Lewis acids (M = Al or Ga, X = Cl, Br or I) effect intermolecular sp3C‐H metalation of tBu2‐py bases under mild conditions. The sp3C‐H metalated products can be converted in‐situ into ‐BPin, ‐iodo, ‐bromo and ‐hydroxy derivatives for further elaboration. Mechanistic investigations indicate that: (i) a frustrated Lewis pair effects sp3C‐H heterolysis to form the C‐M bond and a protonated pyridine; (ii) C‐H metalation requires singly halide‐bridged super‐electrophilic M2X6 dimers for sufficiently low barriers. Finally, sp3C‐H metalation using M2X6 is not limited to tBu2‐py bases. Thus, it is important to be aware of this facile sp3C‐H functionalisation when using a range of non‐nucleophilic Brønsted bases
Optimizing SPION Labeling for Single-Cell Magnetic Microscopy
No full textThis study explores the correlation between the iron mass on cell surfaces and the resultant magnetic field. Human colorectal cancer cells (HT29 line) were labeled with varying concentrations of superparamagnetic iron oxide nanoparticles (SPIONs) and imaged via an NV center widefield magnetic microscope. To assess the labeling efficacy, a convolutional neural network trained on simulated magnetic dipole data was utilized to reconstruct key labeling parameters on a cell-by-cell basis, including cell diameter, sensor proximity, and the iron mass associated with surface-bound SPIONs. Our analysis provided quantitative metrics for these parameters across a range of labeling concentrations. The findings indicated that increasing the SPION concentration enhances both the cell-surface iron mass and magnetic field strength, demonstrating a saturation effect. This methodology offers a coherent framework for the quantitative, high-throughput characterization of magnetically labeled cells, presenting significant implications for the fields of cell biology and magnetic sensing applications.</p
Intermolecular sp<sup>3</sup>C‐H Metalation of Non‐Nucleophilic Brønsted Bases Using Simple Lewis Acids
No full text2,6‐Di‐tert‐butyl substituted pyridines (tBu2‐py) are widely used non‐nucleophilic Brønsted bases. Their ubiquity is due to their highly hindered basic site and chemically robust nature. Herein we report that simple M2X6 Lewis acids (M = Al or Ga, X = Cl, Br or I) effect intermolecular sp3C‐H metalation of tBu2‐py bases under mild conditions. The sp3C‐H metalated products can be converted in‐situ into ‐BPin, ‐iodo, ‐bromo and ‐hydroxy derivatives for further elaboration. Mechanistic investigations indicate that: (i) a frustrated Lewis pair effects sp3C‐H heterolysis to form the C‐M bond and a protonated pyridine; (ii) C‐H metalation requires singly halide‐bridged super‐electrophilic M2X6 dimers for sufficiently low barriers. Finally, sp3C‐H metalation using M2X6 is not limited to tBu2‐py bases. Thus, it is important to be aware of this facile sp3C‐H functionalisation when using a range of non‐nucleophilic Brønsted bases
On the use of UAV-thermal imaging for CFD validation of urban thermal microclimate
No full textComputational Fluid Dynamics (CFD) simulations are widely applied to assess urban microclimate processes and adaptation strategies. However, their accuracy and reliability critically depend on high-quality validation data. Although field measurements and reduced-scale wind-tunnel testing are commonly used for validation, the use of remote sensing methods remains limited despite their potential. This study systematically evaluates UAV-based thermal imaging as a tool for validating microscale CFD predictions of urban thermal conditions. The case study focuses on the city centre of Semarang, Indonesia, where ground-truth field measurements and UAV surveys with visible RGB and infrared (IR) imaging are conducted. CFD simulations are performed for the same area using 3D URANS with the realizable k–ε model on a high-resolution computational grid. Results show that (i) UAV-IR data and ground-truth measurements differed by 0.47 °C – 1.40 °C across asphalt, concrete, and soil–grass surfaces ranged from, confirming the accuracy of UAV thermal imaging; and (ii) CFD simulations deviated by 3.88 °C in surface-averaged temperatures for impervious-based areas compared with UAV-IR data. These findings highlight UAV thermal imaging as a practical and data-driven approach for validating CFD models, enabling more robust analyses and design of sustainable urban thermal environments
CFD simulations of running aerodynamics:Impact of computational parameters
No full textRunning is a fundamental discipline in athletics, yet its aerodynamic characteristics have not yet been intensively studied, particularly from a computational perspective. In recent years, Computational Fluid Dynamics (CFD) has become an increasingly valuable tool for advancing research in sports aerodynamics. However, the reliability of CFD predictions depends strongly on the selection of computational parameters which remains insufficiently explored in the context of human running. This paper presents a detailed study on the impact of grid resolution, computational domain size, and turbulence modelling on the computed drag area for a full-scale female runner manikin. The CFD simulations are validated by comparison with wind tunnel measurements performed in a geometrically matched test section. The sensitivity analysis provides practical guidelines for generating grids that balance accuracy and computational economy. The blockage ratio (BR) is found to be a critical parameter: values exceeding 3.5% result in drag overestimations larger than 2.8%. Among the turbulence models tested, transition-sensitive models (γ–SST and T–SST) in pseudo-transient RANS formulation and the hybrid scale-adaptive simulation (SAS) approach showed the best agreement with experimental results. Based on these findings, the study proposes a set of best-practice guidelines for reliable and cost-effective CFD simulations of running aerodynamics
Expat-preneurs navigating the crisis: the wheel of change as a framework for resilience during the COVID-19 pandemic
No full textPurposeThe paper aims to explore the concept of resilience during the extraordinary challenges brought about by the COVID-19 pandemic. Design/methodology/approach The authors conducted semi-structured interviews with 26 expatriate entrepreneurs in Dubai, and explored the challenges faced by small and medium enterprises (SMEs).FindingsThe findings highlight the critical role of resilience in business survival during the pandemic. This study emphasizes action-oriented crisis management strategies—such as leadership roles, readiness for change, organizational culture and financial stability—that expatriate entrepreneurs implement to overcome the crisis.Research limitations/implicationsThis study contributes to international business and international human resource management by introducing the Wheel of Change framework, highlighting how expatriate entrepreneurs in Dubai develop resilience through behavioral and operational strategies. It bridges strategic agility with human-centered adaptability, emphasizing the role of cultural intelligence and leadership during crises. The model addresses a key gap by linking personal resilience with institutional adaptation, offering a dynamic lens to understand entrepreneurial behavior in globalized, high-risk environments. Practical implicationsThe insights derived from how expat-preneurs navigate and rebound from crises can inform the design of policies and support mechanisms for global businesses confronting unforeseen disruptions. The framework offers actionable strategies for cultivating organizational resilience and ensuring long-term sustainability, particularly for SMEs operating in volatile or multicultural contexts. Originality/valueThis study introduces the Wheel of Change framework, developed from the lived experiences of expat-preneurs during COVID-19. The model captures both reactive and forward-looking strategies across crisis phases, integrating behavioral and operational resilience. It offers a novel lens to understand adaptability, stakeholder engagement and strategic agility. The understanding of how expat entrepreneurs experience rebound from the crisis offers insights to inform policies and strategies for supporting global business during unexpected crises and offers practical strategies to cultivate resilience and long-term sustainability
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