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Heat transfer characteristics of flat-plate micro heat pipes with integrated copper foam for aerospace thermal management
No full textThe effective operation of heat pipes is crucial in aerospace thermal management. This study aims to improve the reliability of flat-plate micro heat pipes under varying gravity conditions caused by insufficient capillary force. It combines copper foam structures of different pore diameters and porosities with micro-fin wick structures within flat-plate micro heat pipes to form a composite wick structure. The impact of these structures on the thermal performance of flat-plate micro heat pipe is analyzed to elucidate the principles by which the structures enhance capillary force. Results show that the effective thermal conductivity of sample #1–1 (composite wick structure) at 90°, 0°, and − 10° is 11834.36, 2401.9, and 1046.6 W/(m·K), respectively, which is 3.01, 2.42, and 2.32 times that of sample #2–1 (without micro-fin structure) at the corresponding angles. The effective thermal conductivity of sample #1–1 (composite wick structure) is 11834.36 W/(m·K), which is 4.57 times higher than that of sample #1–4 (without copper foam structure). Furthermore, the copper foam performance is optimal at 0.8 mm pore diameter and 80 % porosity when pore diameter and porosity are the only variables. Overall, sample #1 exhibits significantly superior heat transfer performance under different gravity conditions compared to sample #2. These findings address the limitations of previous studies focused exclusively on the thermal performance of composite wicks under gravitational conditions, as well as expand the applicability of flat-plate micro heat pipes in thermal management technologies across diverse gravitational environments.</p
HypeRL:Parameter-Informed Reinforcement Learning for Parametric PDEs
Get PDFIn this work, we devise a new, general-purpose reinforcement learning strategy for the optimal control of parametric partial differential equations (PDEs). Such problems frequently arise in applied sciences and engineering and entail a significant complexity when control and/or state variables are distributed in high-dimensional space or depend on varying parameters. Traditional numerical methods, relying on either iterative minimization algorithms or dynamic programming, while reliable, often become computationally infeasible. Indeed, in either way, the optimal control problem must be solved for each instance of the parameters, and this is out of reach when dealing with high-dimensional time-dependent and parametric PDEs. In this paper, we propose HypeRL, a deep reinforcement learning (DRL) framework to overcome the limitations shown by traditional methods. HypeRL aims at approximating the optimal control policy directly. Specifically, we employ an actor-critic DRL approach to learn an optimal feedback control strategy that can generalize across the range of variation of the parameters. To effectively learn such optimal control laws, encoding the parameter information into the DRL policy and value function neural networks (NNs) is essential. To do so, HypeRL uses two additional NNs, often called hypernetworks, to learn the weights and biases of the value function and the policy NNs. We validate the proposed approach on two PDE-constrained optimal control benchmarks, namely a 1D Kuramoto-Sivashinsky equation and a 2D Navier-Stokes equations, by showing that the knowledge of the PDE parameters and how this information is encoded, i.e., via a hypernetwork, is an essential ingredient for learning parameter-dependent control policies that can generalize effectively to unseen scenarios and for improving the sample efficiency of such policies
Environmental Performance, Financial Constraints, and Tax Avoidance Practices: Insights from FTSE All-Share Companies
Get PDFThrough its initiative known as the Climate Change Act (2008), the Government of the United Kingdom encourages corporations to enhance their environmental performance with the significant aim of reducing targeted greenhouse gas emissions by the year 2050. Previous research has predominantly assessed this encouragement favourably, suggesting that improved environmental performance bolsters governmental efforts to protect the environment and fosters commendable corporate governance practices among companies. Studies indicate that organisations exhibiting strong corporate social responsibility (CSR), environmental, social, and governance (ESG) criteria, or high levels of environmental performance often engage in lower occurrences of tax avoidance. However, our findings suggest that an increase in environmental performance may paradoxically lead to a rise in tax avoidance activities. Using a sample of 567 firms listed on the FTSE All Share from 2014 to 2022, our study finds that firms associated with higher environmental performance are more likely to avoid taxation. The study further documents that the effect is more pronounced for firms facing financial constraints. Entropy balancing, propensity score matching analysis, the instrumental variable method, and the Heckman test are employed in our study to address potential endogeneity concerns. Collectively, the findings of our study suggest that better environmental performance helps explain the variation in firms’ tax avoidance practices
Case Study Thirteen - The CBL Continuum:A Tool for CBL Implementation
Get PDFThis open access book maps the role of challenge-based learning (CBL) in the transformation of higher education pedagogy, towards being sector-informed as well as student-driven. CBL democratises the process of learning by repositioning students as drivers, who are empowered to make decisions on course content, assess needs in the real world and develop opinions. Teachers monitor student learning and engagement and mentor students to express their needs. Chapters showcase existing CBL practices in different settings, and include case studies which detail the practical application of CBL in multiple contexts. The authors develop an emerging theory of practical learning based on the insights of the curriculum designers, practitioners and students. The book will be of interest to researchers, teacher educators/trainers and research supervisors in higher education.</p
Integrating urban digital twin with cloud-based geospatial dashboard for coastal resilience planning:A Case Study in Florida
No full textCoastal communities are confronted with a growing incidence of climate-induced flooding, necessitating adaptation measures for resilience. In this paper, we introduce a framework that integrates an urban digital twin with a geospatial dashboard to allow visualization of the vulnerabilities within critical infrastructure across a range of spatial and temporal scales. The synergy between these two technologies fosters heightened community awareness about increased flood risks to establish a unified understanding, the foundation for collective decision-making in adaptation plans. The paper also elucidates ethical considerations while developing the platform, including ensuring accessibility, promoting transparency and equity, and safeguarding individual privacy.</p
Towards a Critical Political Economy of Surveillance and Digital Authoritarianism
Get PDFIn this short piece, we suggest some directions for considering the interrelated questions of postcolonial authoritarianism, platfonn capitalism, and surveillance. We first put forward a three-level model of contemporary digital authoritarianism, which argues for a prism of discourses, practices, and infrastructures, before we turn specifically to the political economy of contemporary capitalism. Here, we shift the focus away from only either state and/or the individual and the conventional entities in between, to consider the new platfonn actors driving authoritarianism and digital surveillance in the twenty-first century.</p
Operando synchrotron X-ray analysis of melt pool dynamics in an Al-Sn immiscible alloy
Get PDFThe melt flow in an Al-50vol% Sn immiscible alloy, produced by single-track laser melting of Al and Sn elemental powders, was studied in real time. High-speed synchrotron X-ray imaging was used to track the movements of Al and Sn liquids, and also to examine elemental distributions in the laser tracks, complimented by electron microscopy after solidification. Key aspects, including melt pool geometry, keyhole instability, and flow dynamics (flow pattern and velocity), were examined using digital image analysis. Relatively deeper melt pools formed at 400 W and 300 mm/s exhibited greater stability, with smooth surfaces, consistent outward flow, and minor vortices near the keyhole. In contrast, shallower pools produced at higher scanning speeds (>500 mm/s) demonstrated greater instability with increased surface waviness, and stronger velocity fluctuations, leading to numerous micro-vortices and increased Al-Sn heterogeneity. Velocity scale estimations, supported by experimental observations, examined the roles of vapour pressure, Marangoni effect, buoyancy, inertial, and surface tension forces in the flow. The results revealed that vapour pressure and mechanical waves dominated at high scanning speeds (shallow pools), while Marangoni forces were equally significant in deep pools at lower speeds (300 mm/s). Buoyancy was found to have minimal impact in both cases. Furthermore, the interaction between inertial and surface tension forces played a critical role in determining the degree of waviness of the pools’ surfaces. These findings offer valuable insights into melt pool dynamics during laser processing of immiscible alloys and other metallic systems using elemental powders, and provide guidance for developing high-fidelity computational fluid dynamics models.</p
A Pearson's Random Walk Method of Estimating the Electromagnetic Emissions of N Parallel Connected Power Electronic Converters
No full textThis article presents a Pearson's random walk approach for modelling the electromagnetic emissions of N parallel connected power electronic converters. For the first time, a methodology that enables testing the random walk approach is presented. This methodology is validated in two ways: firstly, via simulations of a simplified setup consisting of 8 half-bridge power electronic converters. Secondly, it is validated with the use of an experimental setup consisting of 3 dc/dc converters. The verification is done in the complex domain, as well as by comparing the magnitude of the common mode current via the theoretical cumulative distribution function and the empirical cumulative distribution function. Finally, the probability of electromagnetic interference reduction at a specific harmonic of the switching frequency is derived.</p
Brands in Transition:Balancing Brand Differentiation and Standardization in Sustainable Packaging
Get PDFIn the changing field of sustainable packaging, companies are confronted with the challenge of balancing sustainability with brand differentiation. The move toward standardized, reusable packaging is beneficial for the environment but restricts the use of custom designs. This study explores how standardized, reusable packaging affects consumer perception in the fast-moving consumer goods (FMCG) sector. It focuses on the evolving role of brands to maintain brand differentiation. This research is centered around two case studies. The first examines 219 tomato products to understand the factors driving packaging diversity. Data was collected from three Dutch supermarket websites to analyze packaging types, materials, and size. The second case study investigates consumer responses to single-use versus standardized reusable packaging across eight brands in both food and non-food categories. An online survey was used to assess perceived quality (PQ), willingness to buy (WTB), and brand perception. The results indicate that standardization has a limited effect on perceived quality (the impression of excellence that a consumer experiences), suggesting that it may encourage more brands to adopt reusable packaging. Willingness to buy findings, indicating whether consumers have theintention to buy a product, were mixed. A decrease was observed in food products and an increase noted in non-food. Brand perception most often showed a decrease, indicating challenges in maintaining brand differentiation. Three strategic approaches for brands to align with a sustainability-driven market while preserving value are presented. These are focusing on visual and verbal differentiation, collaborating with competitors to adopt a common archetypal packaging, or shifting marketing away from physical packagingtowards digital and authentic communication. However, the new role of marketers will need further exploration, with a focus on authentically communicating the real content and its added value
Resolving the W-on-Si interface by non-destructive low energy ion scattering
Get PDFWe present the use of Low Energy Ion Scattering (LEIS) as a non-destructive technique for characterizing the W-on-Si interface. LEIS spectra inherently contain depth-resolved information in the subsurface signal. However, assisting the spectra analysis with simulations is necessary for extracting quantitative information about the sample's depth composition. In this study, we compare measured and simulated LEIS spectra of W thin films on Si. These results prove, for the first time, the applicability of the method to probe a complex interface formed by a thin film of heavier atoms deposited on a film of lighter atoms. W/Si thin-film structures are used in X-ray optics, where precise control over interface composition is essential. Our findings affirm LEIS as a valuable technique for characterizing these interfaces with sub-nanometer accuracy.</p