335598 research outputs found
Sort by
Gallia‐ Versus Alumina‐Supported Cu: Dynamics of Ga in Catalysts for Green Methanol Production
No full textThe transformation of CO and green hydrogen into methanol presents a sustainable route for chemical and fuel production. Conventional methanol synthesis catalysts, such as Cu/ZnO/AlO, employ AlO as a structural promoter, while GaO has recently emerged as a promising alternative. This study compares Cu-based catalysts supported on AlO (CA) and GaO (CG), prepared via coprecipitation of layered double hydroxide precursors with identical molar Cu:M (M = Al or Ga) ratio of 70:30. Using in situ and operando X-ray absorption spectroscopy and X-ray powder diffraction, we investigate the structural and redox dynamics of Ga during activation and CO hydrogenation. Gallium from its precursor state undergoes several phase transitions. At elevated temperatures, Ga exhibits redox activity, transitioning from Ga to metallic Ga and forming CuxGay alloys at 480 °C, followed by de-alloying and re-oxidation at even higher temperatures. Our results suggest that the beneficial role of Ga reported in literature arises from metal-oxide interfacial effects rather than bulk alloying. Excess GaO leads to low conversion levels and pronounced deactivation compared to the AlO-supported Cu catalyst and thus should be prevented. These findings highlight the importance of controlling promoter loading and dynamic behavior in catalyst design to optimize activity, stability, and selectivity for CO-to-methanol conversion
Corrosion of Stellite Alloys and WC ‐Based Cemented Ceramics Exposed to Oxygen‐Containing Molten Pb at 600°C and 700°C
No full textLiquid metals such as molten lead (Pb) are attractive heat transfer fluids for high-temperature thermal energy storage systems. Although extensive research is performed on the corrosion behavior of structural steels and Fe-based alloys in liquid Pb, the corrosion resistance of materials with high wear resistance in such environments is less explored. In order to expand the knowledge on the compatibility of wear-resistant materials with molten Pb in a temperature range relevant for high-temperature thermal energy storage systems, the current study investigates for the first time Pb corrosion of the two commercial Co-Cr-based alloys Stellite 21 and Stellite 6 and of two commercial tungsten carbide (WC) ceramics, one with Co binder and the other with Ni/Cr binder, in the temperature range from 600°C to 700°C. Static exposure tests in molten Pb containing 2 × 10 wt.% dissolved oxygen are performed for up to 5000 h. The results reveal the formation of Cr-rich oxides on the surfaces of all materials, though an oxide scale with protective properties is found for Stellite 6 at 700°C only. Here, the scale is composed of an outer Cr-rich oxide layer and an inner Si-rich oxide. In all other cases, dissolution of alloying elements (Co-Cr-based alloys) and of the binder phase (WC-based ceramics) is observed to various extents, which gives first indications for the service life of respective components exposed to liquid Pb environments
Compositional patterns of device-measured movement behaviour in juvenile idiopathic arthritis: results from the multicentre ActiMON study
No full textBackground
Children and adolescents with juvenile idiopathic arthritis (JIA) are at increased risk for long-term physical and psychosocial complications, making physical activity (PA) and sedentary behaviour (SB) key modifiable lifestyle factors. Although increasingly acknowledged as relevant, data on the daily distribution of these behaviours in JIA remain scarce. This study aimed to (1) describe the time-use composition of SB and PA intensities in young people with JIA, (2) identify correlates of greater relative time spent in SB, and (3) compare movement behaviour patterns to matched population controls using a compositional data analysis (CoDA) approach.
Methods
Patients aged 10–20 years with JIA and individually matched population controls wore hip-worn accelerometers (ActiGraph wGT3X-BT) for eight consecutive days. Movement behaviours were categorized into SB, light-intensity PA, and moderate-to-vigorous PA (MVPA) using validated, age-specific cut-points. CoDA with log-ratio transformations was used to model associations and compare groups. Diifferences in movement composition were assessed using adjusted multivariate analysis of variance (MANOVA).
Results
Data from 126 matched pairs (mean age: 15.0 ± 2.1 years; 67% female) were analysed. Patients spent, on average, 86% of waking time in SB, 8% in light-intensity PA, and 6% in MVPA. Overall, 76% did not meet the WHO recommendation of an average of ≥ 60 min of MVPA per day. Among those who did, 87% still spent ≥ 75% of their wear time sedentary. A greater proportion of SB relative to PA was associated with female gender (B = 0.13; p = 0.042), higher age (B = 0.06; p < 0.001), and higher BMI (B = 0.01; p = 0.049). Compared to controls, patients spent more time in SB, less in light-intensity PA, and slightly more in vigorous PA (all p < 0.001). Group differences remained significant after adjustment and were consistent across weekdays and weekends.
Conclusions
Young people with well-controlled JIA show a distinctly unbalanced movement behaviour composition compared to controls, marked by a predominance of sedentary behaviour—even among those meeting PA guidelines. This highlights the limitations of threshold-based definitions and underscores the importance of assessing full daily movement patterns. Promoting light-intensity PA may offer a feasible strategy to reduce sedentary time, particularly in girls, older adolescents, and individuals with higher BMI.
Trial registration
The study was registered in the German Clinical Trials Register (DRKS00022258)
In Situ Investigation of Microstructure Evolution and Stress Generation During Low‐Pressure Carburizing and Quenching by Means of Synchrotron X‐Ray Diffraction
No full textLow-pressure carburizing (LPC) is a thermochemical process that enriches steel surfaces with carbon. While LPC is already used in industry, there are still aspects that offer opportunities for optimization if the necessary basic process understanding is provided. The present study quantifies the effect of LPC process parameters on the material state of different steel grades. For this purpose, in situ carburizing and quenching experiments are performed in a custom-built chamber for synchrotron X-ray diffraction at the German Electron Synchrotron in Hamburg. During carbon enrichment, carbon saturation and carbide formation are observed, slowing acetylene decomposition. Carbides that initially form at the surface dissolve in later diffusion steps. The kinetics of carbide formation and dissolution strongly depend on steel grade and carbide size. Quenching experiments further enable systematic analysis of phase-specific stresses at the surface and subsurface. The influence of transformation temperature across the carbon gradient is tracked, revealing differences in maximum stresses in both austenite and martensite. A direct correlation is identified between the local martensite fraction and the generated stresses within the carburized layer. This work provides new experimental insights into carbon uptake, carbide evolution, and stress development during LPC, offering pathways for process optimization across different steel types
Comprehensive and open model structure for the design of future energy systems with sector coupling
No full text
Numerical Simulations of Suppression Effect of Water Mist on Hydrogen Deflagration in Confined Spaces
No full textHydrogen safety issues are attracting increasing focus as more and more hydrogen-powered vehicles are going to be operated in traffic infrastructures of different kinds such as tunnels. Due to the confinement feature of traffic tunnels, hydrogen deflagration may pose a risk when a hydrogen leak event occurs in a tunnel, e.g., failure of the hydrogen storage system caused by a car accident in a tunnel. A water injection system can be designed in tunnels as a mitigation measure to suppress the pressure and thermal loads of hydrogen combustion in accident scenarios. The COM3D is a fully verified three-dimensional finite-difference turbulent flow combustion code, which models gas mixing, hydrogen combustion, and detonation in nuclear containment with mitigation devices, or other confined facilities like vacuum vessels of fusion and semi-confined hydrogen facilities in industry, such as traffic tunnels, hydrogen refueling stations, etc. Therefore, by supporting the European HyTunnel-CS project, the COM3D is applied to simulate numerically the hydrogen deflagration accident in a tunnel model, being suppressed by water mist injection. The suppression effect of water mist and the suppression mechanism are elaborated and discussed in the study
Charpy impact properties of EUROFER97-3 after neutron irradiation at 330 °C and 540 °C to damage doses of 21–23 dpa
No full texthe reduced activation ferritic-martensitic (RAFM) EUROFER97-3 steel of two heat treatments (EUROFER97-3_1100/700 and EUROFER97-3_980/780) after irradiation in the BOR-60 fast reactor at temperatures of 330 °C and 540 °C, with damage doses ranging from 21.6 to 22.8 dpa showed big differences in the Charpy impact
properties depending on the irradiation temperature. Significant drop in the upper shelf energy (USE) and shift of the ductile-brittle transition temperature (DBTT) occurred after irradiation at 330 °C. However, irradiation at 540°C resulted in only minor changes in the USE and DBTT compared to the unirradiated reference state. Probably, these changes are attributed of the formation of radiation-induced defects and evolution in the phase structure
Characterizing and Evaluating Mental Health Misinformation on Social Media: A Qualitative and Deep Learning-Based Study
No full textSocial media plays a powerful role in accelerating the spread of misinformation, especially in the mental health domain, where misleading content may even cause disasters. Given the extensive coverage and complexity of social media data, manually moderating online misinformation is infeasible. Therefore, the present study proposes an integrated framework that combines qualitative analysis and deep learning to automatically detect and evaluate mental health misinformation. Guided by expert interviews and grounded theory, in the present study, a 21-level, fine-grained credibility assessment framework covering seven dimensions was developed. Using the framework, in this study, 814 Chinese social media posts were manually annotated, and a high-quality dataset was constructed. On this dataset, we trained and evaluated three deep learning models, that is, Gated Recurrent Unit (GRU), Bidirectional Encoder Representations from Transformers (BERT), and Robustly Optimized BERT Approach (RoBERTa), to automatically assess the credibility of mental health content. The results show that BERT, GRU, and RoBERTa models are effective at leveraging a range of clear sentiment-related cues and surface-level patterns to evaluate mental health misinformation on social media, particularly on dimensions such as Inflammatory Expression and One-sidedness of Expression. However, all three models face challenges in evaluating evidence quality and detecting context-dependent misinformation. When dealing with these challenges, BERT and GRU outperform RoBERTa, particularly in dimensions such as Logical Rigor. This study provides a robust, scalable, and expert-informed approach to improve the credibility of mental health information online