Clausthal University of Technology

When establishing a safety case for a high-level nuclear waste repository, coupled thermal, hydraulic, mechanical and chemical (THMC) processes are modelled to assess radionuclide transport and the integrity of barriers. Modelling these processes requires numerous parameters, which are all subject to uncertainty. However, complex and extensive uncertainty quantification (UQ) methods can come at great computational cost, especially when performed on multi-parametric problems. Therefore, UQ methods are sought with manageable computational effort while still capturing the relevant information to allow a meaningful interpretation of the results. The aim of this study is the comparison of three different UQ methods with different levels of complexity and computational cost in terms of their results. Radionuclide transport and THM-calculations are performed by employing these methods to the French Callovo-Oxfordian claystone as a reference material. The three methods include: (1) a UQ method based on the complete sampling of input parameter distributions by a Monte Carlo approach, (2) a UQ method based on a minimal number of data points, by sampling quantiles of the input parameter distributions, as well as the bounds of the distributions’ intervals, and (3) a UQ method that involves a first-order second-moment reliability approach. The results depict the different limitations and benefits of the UQ methods analysed while highlighting that a comprehensive understanding of parameter sensitivity and modelling approach are key to choosing the appropriate UQ method. • Applicability of UQ methods depends on complexity of problem. • FOSM and quantile method can be appropriate for linear problems and non-coupled processes. • MC approach remains method of choice for complex non-linear analyses.

While studying biofilm formation in industrial settings with a quartz crystal microbalance with dissipation monitoring (QCM-D), it was found that the shift in half bandwidth, ΔΓ, often was much larger than the shift in frequency, Δ f . Also, ΔΓ was almost independent of overtone order. The microbial biofilms were mostly composed of prokaryotic cells, which contact the resonator surface across soft filament like structures at their cell wall called pili. A simple model is proposed, which explains the peculiar QCM response induced by these biofilms. The key element of the model is a coupled dashpot, representing small, dissipative contacts between the sample and the resonator. The dashpot replaces the coupled mass known from gravimetric sensing. The coupled-dashpot model predicts the shift in frequency to be close to zero (Δ f ≈ 0) and the shift in half bandwidth to be about the same on the different overtones (ΔΓ ≈ const ). The value of ΔΓ is proportional to the product of the number density of the contacts and their stiffness. The model – if found to agree with experiment – yields structural information on the sample and can guide data aggregation. The model was substantiated and illustrated with numerical simulations. A side aspect is a simple and economical instrument design, which brings QCM-based biofilm monitoring closer to routine practice. • New inexpensive setup for QCM measurements. • Biofilm formation mainly affects the bandwidth. • Modeling of behavior with a mechanical dashpot.

Sorption in shales is a key process controlling their gas storage capacity. It is, however, a complex phenomenon due to the broad and variable petrophysical characteristics of shales. This complexity is further compounded by the simultaneous occurrence of gas adsorption on mineral and organic surfaces and absorption processes within sedimentary organic matter. In this study, gravimetric sorption experiments were conducted on three geologically distinct shales at 40 °C and pressures ranging from 2 to 15 MPa. We examined both pristine powdered shale samples and their solvent-extracted counterparts to investigate the dominant controls and sorption mechanisms of hydrogen (H 2 ) and carbon dioxide (CO 2 ) - two gases central to energy transition. The sorption capacity of H 2 is shown to be independent of the total organic carbon (TOC) content and is rather governed by the available pore volume in the shale, with thermal maturity exerting a positive influence on porosity development, particularly in samples exhibiting contrasting maturities. Conversely, the CO 2 sorption capacity is controlled by both TOC content and available pore volume. An increase in either parameter enhances the sorption capacity. Comparisons of H 2 and CO 2 sorption capacities among samples possessing relatively similar textural properties and contrasting TOC content indicate that the contribution of H 2 absorption in organic matter becomes increasingly significant at elevated pressures, while CO 2 absorption is shown to increase the total sorption capacity at all investigated pressures. This study provides the first experimental evidence on the role of H 2 and CO 2 absorption in increasing the sorption capacity of immature organic-rich shales. • H 2 retention occurs via adsorption, governed mainly by textural properties. • At high pressure and in TOC-rich shales, absorption enhances H 2 sorption. • CO 2 sorption is enhanced by larger textural properties and/or higher TOC content.

The highly stable metal-organic framework (MOF) composed of [Zr 6 O 4 (μ 3 -OH) 4 (OH) 6 (H 2 O) 6 (BTC) 2 ]·nH 2 O units (MOF-808) was modified by incorporating gold (Au) nanoparticles and functional groups to enhance electrocatalytic activity for the borohydride oxidation reaction (BOR). Three composite materials (Au@MOF-808, Au@MOF-808-NH 2 , and Au@MOF-808-SH) were prepared by the incorporation of Au in structurally related MOFs, MOF-808, MOF-808-NH 2 , and MOF-808-SH, respectively. These composite materials were evaluated as anodic electrocatalysts for BOR in alkaline media using cyclic voltammetry and chronoamperometry. Among the prepared materials, Au@MOF-808-NH 2 exhibited the highest BOR activity, with an apparent activation energy of 15.3 kJ mol −1 , a reaction order of 0.6, an anodic charge transfer coefficient of 0.63, and a number of exchanged electrons of 4.4. The latter was significantly below the theoretical eight-electron value, indicating the presence of alternative reaction pathways. Notably, this material achieved a high mass-specific BOR peak current of 4.23 A μg Au −1 , demonstrating outstanding electrocatalytic efficiency despite the ultralow noble metal loading. These results underscore the potential of Au@MOF-808-NH 2 as a cost-effective and scalable anodic electrocatalyst for high-performance direct borohydride fuel cells. • Ultralow Au-loaded functionalized MOF-808 boosts borohydride oxidation reaction (BOR). • Au@MOF-808-NH 2 shows the highest BOR activity among the prepared composites. • Record-high mass activity of 4.23 A μg Au −1 achieved with Au@MOF-808-NH 2 electrocatalyst. • A low activation energy of 15.3 kJ mol −1 suggests an efficient BOR pathway. • BOR mechanism involves partial BH 4 − hydrolysis, as implied by a 4.4-electron transfer behaviour.

Abstract Regolith-hosted rare earth element (REE) deposits in South China supply most of the world’s heavy REE (HREE), but the parent minerals that liberate HREE during weathering remain uncertain because commonly invoked accessory phases are refractory. Here we recognize that fluorite is the dominant HREE host in the granitic bedrock of the world’s largest deposit (Shitouping; ~174,000 t HREE oxides). Fluorite occurs in the Early Cretaceous syenogranite at a concentration of ~0.8 wt.% and contains 4.7 wt.% REE with a LREE/HREE ratio of 0.3, accounting for 82% of the bulk-rock HREE budget. During supergene weathering, fluorite dissolves almost completely (> 99%), releasing HREE that adsorb onto clay minerals in the overlying saprolite, whereas refractory phases such as xenotime persist. Mass-balance modelling confirms that HREE ions liberated from primary magmatic fluorite constitute the principal source of the economic ore. Extreme magmatic fractionation enriches residual melts in fluorine and HREE, driving fluorite crystallization and preferential HREE incorporation. Our results imply that regolith-hosted HREE deposits require bedrocks enriched in easily weathered HREE phases (notably fluorite) and depleted in refractory HREE hosts (e.g., xenotime and titanite), guiding exploration to F-rich, highly fractionated granites low in P and Ti.

Abstract Laser Doppler Vibrometry (LDV) is a versatile, non-contact measurement technique for precise vibration analysis. It is also commonly applied to the measurement of acoustic and ultrasonic fields. Its capability to capture broadband optical pathlength variations signals is essential for characterizing complex acoustic phenomena. However, the measurement sensitivity of LDV is fundamentally constrained by quantum shot noise. While increasing optical power can enhance the signal-to-noise ratio (SNR), excessive laser intensity may cause undesirable heating of the sample, which alters its true vibration characteristics and compromises measurement accuracy. To overcome this limitation, this work employs squeezed light to suppress shot noise without raising the optical power. The displacement noise floor is reduced by 36% from 0.28pm/ 10 Hz to 0.18pm/ 10 Hz , corresponding to a decrease from 89 fm/ Hz to 57 fm/ Hz . These results demonstrate the significant potential of squeezed light to enhance LDV performance for low-power, high-precision vibration measurements on highly reflective targets.

Abstract This study explores how different instructional formats, such as printed manuals, tablets, and smart glasses, affect training efficiency and sustainability within a procedural assembly task. As industries and educational institutions pursue sustainable digital transformation, traditional printed manuals are increasingly being replaced by digital and wearable systems that offer scalability, adaptability, and reduced material use. Thirty-three participants performed a standardized twelve-step assembly task using one of the three modalities. Results showed that smart glasses yielded the highest task efficiency and lowest error rates, while tablets received the most favorable usability ratings due to participants’ familiarity with touchscreen interfaces. Printed manuals performed the worst, causing frequent workflow interruptions and greater cognitive demand. Qualitative feedback supported these findings, highlighting that hands-free, adaptive digital guidance promotes smoother task flow and less dependence on static, resource-intensive materials. Overall, the study demonstrates that digital and wearable instructional systems not only enhance immediate performance outcomes but also support long-term sustainability goals and alignment with Industry 4.0 practices. The findings provide empirical evidence for the benefits of digital training tools and offer practical guidance for organizations aiming to develop scalable, efficient, and environmentally responsible instructional strategies.

The energy transition is a long-term strategy dedicated to achieving carbon neutrality in Germany by 2045. This process includes the development of renewably generated electricity from wind and solar power. As these energy sources are dependent on weather conditions, imbalances in availability and demand might result in a deficit or excess of renewable energy. In times of excessive availability, hydrogen can be generated and stored in subsurface storage sites from which it can be withdrawn when the demand increases. Using subsurface storage sites is a viable option as those currently store natural gas. Considering the properties of hydrogen, converting existing storage sites poses many challenges, including the total stored energy content and the amount of extractable working gas. Using an exemplary storage formation, a numerical simulation model is set up in an open-source software and used to calculate and compare the stored volumes and energy contents for natural gas and hydrogen. Storage withdrawal and pressure profiles for both cases are developed. A pseudo gas is defined with individually alternating compressibility, density and viscosity behavior to independently assess the influence of these properties on the withdrawal rates. A sensitivity analysis of various storage, bottom-hole flowing pressures and the skin factor on the extraction rates is also performed. The results show that a larger volume of natural gas and a resulting higher energy content can be stored in the storage site compared to hydrogen. Changes in extraction rates occur earlier and pressure decrease is greater for stored hydrogen. The compressibility factor has the largest influence on the extraction behavior of the gas, leading to a steeper decline in hydrogen withdrawal rates and a quicker pressure depletion. The levels of the storage and the bottom-hole flowing pressure impact the slope of the decline and the level of withdrawal rates.