This paper investigates a hydrogen-electric powerplant in which the fuel cell is the sole source of propulsive power. Roughly half of the hydrogen energy leaves the stack as heat at a temperature only slightly above ambient. With no battery to absorb transient demand, the only way to protect the stack once the cooling system saturates is to reduce power, at the cost of thrust during take-off. Thermal control and aircraft performance are normally studied separately, so this cost has not been quantified.

A closed-loop model of a Dash 8-Q300 retrofit is presented, comprising the fuel cell stacks, an actuator-disk propeller, a lumped thermal model of the stack, a flight dynamics subsystem, and a rule-based thermal supervisor using hysteresis, rate limiting, and blended mode transitions. Take-off was simulated across a range of ambient temperatures and coolant contact areas. The supervisor kept the stack within its temperature limit under every tested condition and maintained full power through rotation and initial climb without thrust discontinuities. The performance penalty is strongly asymmetric about the design point and increases non-linearly with ambient temperature because the temperature difference available for heat rejection decreases as ambient temperature rises. Thermal management therefore determines take-off distance and cannot be sized independently of the aircraft. ... Read more

The fashion industry is among the world's most environmentally damaging sectors, driven by rising production, shortening garment lifetimes, and a linear take-make-dispose model. Clothing repair is widely recognised as a circular economy strategy for extending garment lifetimes, yet its uptake remains limited, and the Dutch consumer context is under-researched.

This study examined the clothing repair options available for consumers in South Holland; consumers' experiences and the motivations and barriers shaping their repair decisions; and the strategies that could upscale repair more effectively. A mixed-methods design combined a market screening of repair services, a consumer survey, and semi-structured interviews with repair stakeholders.

The market screening showed that repair infrastructure in South Holland is widely available: 216 independent repair businesses concentrated in cities with high accessibility and 118 repair cafés distributed across municipalities. However, pricing information is often unclear, repair cafés have limited accessibility, brand and online repair options remain scarce and community initiatives vary per municipality.

The consumer survey found a young (83% below 35 years), predominantly female (66.9%) highly repair-engaged sample: 56% repaired an item themselves, while 39% did so with the help of a friend or a family member and 36% used a repair service. Awareness of independent repair businesses was high, whereas repair cafés were known by roughly half. Brand repair, online platforms and community initiatives were almost unknown. Cost of repair, emotional value, and environmental concerns were the most influential factors affecting repair decisions, with emotional and environmental drivers more pronounced among those already engaged in repair. Majority of people expressed interest in using repair services more in the future. Interviews confirmed these findings and further identified low-quality garments, weak business incentives and fragmented stakeholder collaboration as structural barriers.

When comparing repair groups (formal repairers, informal repairers, attempted repairers and non-repairers) on clothing acquisition behaviour, awareness of repair services, importance of factors affecting repair and future repair intention, formal repairers appeared to be driven more by environmental concerns compared to informal repairers and non-repairers and reported higher interest in using repair services than informal repairers. When comparing students and non-students no significant differences were found. Correlation analysis found mostly weak to moderate correlations with distance and opening hours of the repair service showing highest correlation.

The results indicate that repair infrastructure and consumer interest already exist, but accessible, standardised information does not. The study recommends increasing the visibility of repair services through a centralised information platform and national and regional campaigns; reframing repair as part of maintenance of one's item; strengthening its social dimension through repair cafés and community initiatives; using financial and regulatory instruments such as repair vouchers, reduced VAT on repaired products; further developing extended producer responsibility repair requirements; designing policies to be mutually reinforcing to support repair; and strengthtening the collaboration of Dutch repair actors by the government or a neutral actor.

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Cost–benefit analysis (CBA) remains the dominant framework for the ex ante evaluation of transport policies and infrastructure investments, grounded in welfare economics and aimed at maximizing aggregate social welfare. However, a growing body of literature questions whether CBA adequately captures the multidimensional objectives of contemporary transport policy, including effectiveness, efficiency, and equity. This paper addresses this debate by systematically identifying and structuring criticisms of CBA in transport, drawing on a scoping review of 75 publications and insights from two expert workshops involving 16 specialists from multiple disciplines. The analysis categorizes criticisms into four groups: (1) fundamental limitations of CBA; (2) shortcomings in practical application; (3) issues related to debatable policy questions; and (4) decision-making challenges. Building on these insights, the paper discusses potential avenues for improvement, including better integration of distributional and accessibility effects, refinement of valuation methods, and alternative approaches. The results suggest that many shortcomings attributed to CBA stem from how it is applied within policy processes. The continued use of CBA in transport policy contexts requires an understanding of inherent weaknesses, their improvement, and appropriate use. ... Read more

The oxidation of ultra-high temperature ceramics (UHTCs) remains a central challenge in their deployment in extreme environments. Among UHTCs, zirconium carbide (ZrC) has emerged as a leading candidate for aerospace propulsion, hypersonic flight, and nuclear applications due to its exceptional melting point, outstanding thermal stability, and robust structural stability. However, its susceptibility to oxidation at elevated temperatures fundamentally limits long-term performance. Despite decades of investigation, the oxidation behavior of ZrC remains incompletely understood and inconsistently reported. Reported oxidation rate constants and activation energies vary widely, and the mechanistic pathways particularly the formation, stability, and protective nature of the thermally grown oxide layers are not systematically understood. Crucially, prior studies often confound multiple extrinsic and intrinsic variables, including temperature (T), oxygen pressure (P), exposure time (t), and carbon substoichiometry (x), which result in a fragmented and sometimes contradictory body of knowledge. The lack of a systematic, parameter-resolved framework has prevented the establishment of predictive relationships governing ZrC oxidation.
This dissertation demonstrates a systematic experimental and mechanistic framework to decouple and quantify the intertwined effects of T, P, t, and x on zirconium carbide oxidation. We fabricated high-density (relative density > 98%), high-purity zirconium carbide ceramics with controlled carbon substoichiometry (x = 0.66 to near-stoichiometric) via spark plasma sintering (SPS), enabling precise control of density and defect populations for reproducible evaluation of oxidation behavior. Afterwards, we conducted oxidation experiments across a comprehensive parameter space spanning 400–1000 °C, oxygen pressures from vacuum to 21 % O2, and exposure durations up to 32400 s. A fully integrated, multiscale characterization strategy was implemented, combining thermogravimetric analysis (TGA), quadrupole mass spectrometry (QMS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDX), in-situ and ex-situ X-ray diffraction (XRD), Raman spectroscopy, and elemental analyses using elemental infrared analyzer (EMIA) and elemental gas analyzer (EMGA). This coordinated methodology enabled real-time kinetic tracking, phase identification, interfacial structural analysis, and defect-sensitive compositional quantification within a unified experimental matrix.
The results systematically demonstrate a three-stage oxidation mechanism governing the oxidation behavior of ZrC, consisting of a distinct passivation regime, an intermediate regime in which CO2/CO evolution induces localized cracking, and a long-term linear oxidation regime characterized by complete through-thickness cracking of the oxide scale. The passivation regime is associated with the formation of a single compact oxide layer containing retained carbon. Oxidation behavior exhibits strong coupling within the three-dimensional T–P–t space, with activation energies undergoing nontrivial temperature- and oxygen-pressure-dependent transitions that regulate the evolution between protective and nonprotective oxidation regimes. The transition conditions governing passivation breakdown are shown to depend sensitively on the competition between carbon retention and carbon oxidation, providing insight into variations in previously reported oxidation kinetics, and contributing to a more unified mechanistic understanding of oxidation kinetics and passivation in ZrC.
The results further indicate that oxygen pressure fundamentally governs oxide scale architecture, interfacial evolution, and phase stability during oxidation. Under oxygen-rich conditions, oxidation proceeds through formation of a double-layer oxide scale consisting of an outer porous zirconia layer and an inner compact Zr–C–O region, whereas oxygen-limited environments produce a structurally distinct single-layer scale. The compact Zr–C–O layer is shown to consist predominantly of zirconia enriched with amorphous free carbon, improving the understanding of scale composition. In addition, previously unreported oxidation front stripes are identified at the ZrC/Zr–C–O interface, along which elliptical submicropores preferentially develop. The discovery of these stripe-guided interfacial oxidation features advances the mechanistic picture of carbide oxidation, and reveals a previously unknown mode of localized oxidation front evolution. To quantitatively describe oxide scale development, a phenomenological growth model incorporating compact Zr–C–O layer formation, temperature, and oxygen pressure is developed to predict oxide scale thickness evolution under oxygen-rich conditions. The model successfully reproduces experimentally observed growth behavior across broad oxidation conditions, and offers a predictive framework linking environmental conditions to oxide scale evolution. However, due to significant oxide scale spallation at temperatures exceeding 800 °C, the current formulation is restricted to a maximum operating temperature of approximately 800 °C. Furthermore, in-situ XRD measurements indicate that size- and temperature-dependent phase transformations control the stability of thermally grown zirconia in ZrC under vacuum, demonstrating that oxygen-scarce environments do not fully suppress oxidation processes.
To elucidate the role of an intrinsic compositional parameter, carbon substoichiometry (x), we systematically investigate its influence on oxidation kinetics and reveal a non-monotonic dependence of the parabolic oxidation rate constants on carbon content, reflecting competing defect-mediated oxidation transport mechanisms. The observed behavior arises from the interplay among carbon diffusion barriers, vacancy-assisted oxygen migration, and carbon-oxidation-induced transport pathways. Carbon substoichiometry is therefore shown to strongly influence defect populations, oxygen transport kinetics, interfacial stability, and passivation effectiveness, thereby demonstrating stoichiometric control as a viable defect-engineering strategy for tailoring oxidation resistance in zirconium carbide.
By rigorously decoupling the four governing parameters: temperature, oxygen pressure, exposure time, and carbon substoichiometry, this work establishes one of the first systematic parameter-resolved frameworks for elucidating the oxidation behavior in zirconium carbide ceramic. The study reduces discrepancies in oxidation kinetics, clarifies the mechanistic origin and stability of the compact Zr–C–O layer, introduces the previously unknown oxidation front stripe phenomenon, and develops a predictive oxide scale growth framework for ZrC oxidation. More broadly, this dissertation supports the development of a more predictive mechanistic description grounded in coupled defect chemistry, interfacial evolution, transport-controlled oxide growth, and phase stability.
Beyond advancing the fundamental science of zirconium carbide oxidation, the experimental methodology and mechanistic approach developed herein can be extended to other carbide and ultra-high temperature ceramic systems, such as HfC, TiC, ZrB2, and HfB2. The findings enable improved parameter mapping and support defect-engineering-based strategies for designing oxidation-resistant UHTCs, thereby guiding future research toward more predictive and parameter-resolved materials engineering for extreme environment applications. ... Read more

Offshore wind farms in the North Sea are built in proximity of each other. Close enough that one can block and reduce each other’s incoming wind. This thesis asks whether that coupling can be used on purpose. Curtailing an upwind farm weakens its wake, increasing the incoming wind speed at the downwind farm. The upwind farm gives up energy, and the downwind farm partly recovers it. That is what a transmission line does, but less efficiently.

Whether the trade-off is worth making depends on the wake physics and the electricity market. Efficiency and direction of the trade-off depends on wake and atmospheric physics. Whether the energy is more needed downwind depends on the energy-market conditions.

Combining them in one optimisation problem is difficult, because the wake is non-linear in exactly the quantity being optimised. The Jensen wake model is therefore linearised in two steps. First, the
power curve, the power coefficient curve and the mapping to the axial induction factor are replaced with piecewise linear fits. Second, the remaining dependence on curtailment is removed with a Taylor expansion around two reference points. The result maps a single scalar to the output of every turbine in a two-farm cluster and remains tractable for clusters of 374 turbines.

The cluster is placed in two market settings. In the first, day-ahead prices are fixed, and the operator
maximises cluster revenue. Applied to the Belgian–Dutch cluster on 6 August 2021, curtailing the Belgian farm raises revenue from 81.8 to 96.7 kEUR, an increase of 18 %. Kenis et al. report 21 % for the same hour with a Gaussian wake model and multiplicative superposition. The two studies agree on
direction and order of magnitude, and the difference follows from the wake model that the linearisation permits. Over 2021 as a whole, the control strategy increases revenue in 310 of 8688 hours and raises annual cluster revenue by 1.1 %.

In the second setting, the price is no longer an input. The cluster is embedded in a nodal model of the Dutch and Belgian electricity systems, which minimises total system cost. The question becomes whether curtailment serves the system rather than the wind farm operator. Four cases are examined; IJmuiden Ver with Hollandse Kust West shows no benefit: a detour with spare capacity always remains available, and the system prefers the cable. Borssele with the Belgian zone in the 2020 system shows none either, because neither country holds a surplus of cheap generation. Adding 10 GW of planned Dutch capacity changes that. At windy hours, the Netherlands generates more cheap wind energy than the demand and interconnectors can handle. Curtailing the upwind farm increases the downwind farm’s energy generation, which can displace energy generation from fossil gas. Over a 24 h window 2.2 GW h of gas generation is avoided. Reducing the Belgian nuclear fleet to its 2026 capacity increases the windows when curtailing is useful, because a flexible unit is left on the margin more often. Measured as power gained downwind over power given up upwind, the cluster transports at 29 to 63 % efficiency.

Cluster control is therefore not a substitute for transmission, and the conditions under which it pays are narrow. A congested border, a surplus of cheap generation in the upwind zone, a flexible generator still on the margin downwind, and a wind direction running from one to the other must all hold at the same time. Wherever a route with spare capacity exists, the system takes it instead. In the cases studied
here, those conditions were met in a small share of the year, and only after 10 GW of planned capacity was added to the system. But where they do hold, the effect is not marginal: a single eight-hour period displaced 3.1 GW h of gas generation, and the periods over which the wind allows it can last for days rather than hours. ... Read more