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Ignition Indices of Hydrogen Mixtures under Electrolysis Process Conditions
No full textThe formation of hydrogen-oxygen mixtures for example due to cross-over, malfunction or start-up and shut-down processes is a hazard very specific to given electrolysis processes that must be properly addressed. In this work the explosion limits of hydrogen-oxygen-mixtures at conditions up to 30 bar and 300 °C were determined experimentally. It was found that the existing experimental data can be interpolated with good accuracy using empirical approaches. Moreover, explosion limits at atmospheric conditions were also determined with reduced ignition energy, down to 1 mJ. Although in the literature it can be found that the ignition energy of flammable gases increases strongly when the concentration changes from stoichiometric to near the explosion limits, no significant influence on the mixture concentration was found within tested ignition energy range for H2/O2 mixtures. Finally, hot surface ignition for mixtures with 6 mol% hydrogen in oxygen, thus slightly above the explosion limit, were experimentally studied at different pressures up to 30 bara. Similarly, only slight difference from the ignition temperatures determined for stoichiometric mixtures were found. A 0D adiabatic, constant-volume reactor model was used to calculate the ignition temperatures. The model was tested for its prediction of ignition temperatures of hydrogen mixtures at different pressures
Designing microcompression experiments for nanoporous metals via computational plasticity
No full textMicropillar compression testing is essential for understanding bulk metal plasticity at small scales and has emerged as a key technique for evaluating nanoporous metals like nanoporous gold (NPG). To support experimental design, we present a computational plasticity study on single crystal NPG micropillars, systematically examining four extrinsic factors: pillar height-to-diameter ratio, taper angle, friction coefficient, and misalignment angle. The study reveals that NPG exhibits similar trends to its bulk counterpart but is less prone to post-yield buckling in unstable crystal orientations. For optimal NPG pillar stability, an aspect ratio of is recommended and a moderate taper angle to prevent artificial stiffening and yielding. Even minimal friction enhances stability, while buckling is mainly governed by misalignment, requiring to also avoid underestimating the elastic modulus
Datasets for structural and mechanical properties of nanoporous networks from FIB reconstruction
No full textThis dataset paper presents a comprehensive archive of 3D tomographic reconstruction image files, volume mesh files for finite element simulations, and tabulated structural and mechanical properties data of nanoporous gold structures. The base material is nanoporous gold, fabricated using a dealloying process, with a solid fraction of approximately 0.30. The NPG samples with ligament sizes ranging from 20 nm to 400 nm were prepared by dealloying and by controlling the thermal annealing process. The original data consist of tomographic TIFF files acquired through Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) 3D reconstruction, as detailed in Philosophical Magazine 2016 96 (32-34), 3322-3335. At each ligament size, six sets of 3D tomographic images were obtained from different regions of the same sample to ensure representative data. New simulations and analyses were conducted based on the 3D image data. The resulting structural and mechanical property data of nanoporous gold are reported for the first time in this dataset paper. Volume meshing of the 3D reconstructed data was performed using Simpleware software. Structural parameters, including surface area, solid volume, and solid volume fraction of the nanoporous network, were extracted from the meshed volumes. Structural connectivity was assessed from the 3D microstructures. The meshed volumes were then used as input for finite element simulations performed in Abaqus to evaluate mechanical responses under uniaxial compression along all three principal axes respectively. From the resulting stress–strain curves, the Young’s modulus and yield strength of each structure were determined. Both elastic and plastic Poisson’s ratios were analyzed from true strain increments. This dataset includes the 3D tomographic images, corresponding volume mesh files, mechanical behavior data and tables summarizing the structural and mechanical properties. The archived data serve as a database for nanoporous network materials and can be reused for numerical simulations, additive manufacturing, and machine learning applications within the materials science community. All files are openly accessible via the TORE repository at https://doi.org/10.15480/882.1523
Evaluating the reproducibility and consistency of different sample preparation techniques used for ATR-FTIR spectroscopy from the RILEM 295-FBB TG1 round robin test
No full textAttenuated Total Reflection Fourier Transform Infrared spectroscopy has become a popular spectroscopic technique in bituminous binder analysis. However, comparable results are not obtainable yet due to differences in devices, measurement routines, sample preparation procedures, and spectral evaluation. Thus, the Task Group 1 of the RILEM TC 295-FBB: “Fingerprinting bituminous binders using physicochemical analysis” focuses on bringing this method towards pre-standardization. This study evaluates the reproducibility and consistency from round robin test, where 21 participating laboratories performed six different preparation techniques on three different binders in an unaged, short-term, and long-term aged state. A total of 6461 spectra were recorded and evaluated for their mean, standard deviation and coefficient of variation (CV) in the spectral region between 1800 and 600 cm−1. The results show that the solid sample preparation methods provide excellent reproducibility, with a coefficient of variation below 2%. Only the solvent method showed a higher coefficient of variation at 7.18%. Outliers with a high CV were detected and categorized into two groups: one where only one of the four samples differed and the other where all 16 spectra showed slight scattering in the overall absorption. The consistency of the method is significantly influenced by the accuracy of sample preparation, which is crucial for minimizing differences in slope, baseline, and noise in the spectra. These findings show the excellent reproducibility of these sample preparation methods and will be further examined to establish universal indices for evaluating effects such as ageing, bringing the method closer towards standardization
Antibiotic tolerance of biofilms emerging from multicellular effects of antibiotic efflux
No full textEfflux pumps play an important role in the context of antimicrobial resistance, which is the ability to grow in the presence of antimicrobials. Many of these transporters can be categorized into multidrug efflux pumps, extruding various antimicrobials out of the cells, and thereby leading to antimicrobial resistance. It has been shown that efflux pumps can be linked by global regulators that regulate efflux pump expression affecting cell-to-cell-interactions, membrane integrity and biofilm formation. The aim of this study is to investigate the survival of cells in biofilms upon exposure to antimicrobials through the interplay of efflux-mediated spatial interactions . To this end, we generated fluorescently labeled E. coli strains that differ in their levels of AcrAB-TolC efflux pump activity and an acrB knockout-strain. The strains were characterized in terms of their antimicrobial susceptibility of three antibiotics, tetracycline, kanamycin, ampicillin, and the biocide benzalkonium chloride. The knockout strain shows higher susceptibility than the wildtype strain, with highest difference observed upon exposure to benzalkonium chloride. The results were confirmed with an efflux activity assay, which showed decreased efflux for the knockout strain as compared to the wildtype. Interestingly, adding the efflux inhibitor PAβN at intermediate concentrations induced bimodality in efflux activity in the wildtype. To investigate the link between colony structure and spatial patterns of efflux pump gene expression, strains with different fluorescent labels and efflux activity were mixed in a 1:1 ratio and grown on agar supplemented with antimicrobials at sub-inhibitory concentrations. Analysis of the colonies with fluorescence microcopy shows that the absence of the AcrAB efflux pump affects the structure of sector formation and morphology within the colony. We observed relatively large sectors with similar surface area for high efflux and low efflux cells in the absence of antimicrobials and at low concentrations. In contrast, sectors are disappearing due a strong intermixing of high and low efflux strains with increasing antibiotic concentration, specifically upon exposure to tetracycline and kanamycin. As next steps, we will perform quantitative analysis of colony images, to better interpret the results, develop a mathematical model of interacting cell types and investigate efflux-based interactions at the single-cell level. Taken together, out data suggest that efflux shapes cell-to-cell interactions and these interactions affect the spatial arrangement and the morphology of biofilms. Understanding the dynamics can provide insights into the emergence of resistance of bacterial communities to antimicrobial environments, the complex interplay of resistance, efflux, and biofilm formation, which potentially gives information to combat biofilm resistance
Application of the substructure method to assess the fire resistance of thermally restrained columns
No full textUsually, the fire resistance of load-bearing structural elements is determined by single members testing. A mechanical load is applied to the member in a force-controlled manner and is maintained constant throughout the fire test. After applying the mechanical load, the thermal exposure starts according to the ISO 834 fire curve. In this conventional test method, no interaction between the tested member and the entire building structure is considered. In buildings, the surrounding structure can restrain the thermal expansion of a member in case of fire. This may have both positive and negative effects on the fire resistance of this structural element.
Several years ago, the Institute for Sustainability and Innovation in Structural Engineering (ISISE) at the University of Coimbra in Portugal and the Bundesanstalt für Materialforschung und prüfung (BAM) in Germany carried out fire tests on circular and square steel-reinforced concrete columns with restrained thermal expansion. BAM´s column test furnace allows the specimen to be subjected to thermal exposure and mechanical loading simultaneously. In addition, this device has a substructure test module, which can also provide restrained test conditions. In an ongoing research project at BAM and Technische Universität Braunschweig, the effect of restrained test conditions on the behaviour of steel-reinforced columns under fire exposure is further investigated
Pressure-Liquefied Ammonia Jet Dispersion: Multi-Model Intercomparison Using Desert Tortoise and FLADIS Field Data
No full textThis paper presents the findings of an international model inter-comparison exercise that was undertaken in the period 2021-2024 to assess the performance of atmospheric dispersion models for simulating releases of pressure-liquefied ammonia. The exercise used data from ammonia field trials dating from the 1980s and 1990s: the Desert Tortoise and the FLADIS trials. Concentration data from two arcs of sensors in the Desert Tortoise trials and three arcs of sensors in the FLADIS trials were used. Twenty-one independent modelling teams from North America and Europe participated in the exercise and provided in total twenty-seven sets of results from a range of different models, including empirically-based nomograms, integral, Gaussian puff, Lagrangian particle, and Computational Fluid Dynamics (CFD) models. The work is novel in presenting the results from such a large cohort of models, examining specifically the dispersion behaviour of ammonia. This is particularly relevant at the current time, given the growing international interest in using ammonia as a clean energy vector and shipping fuel.
The study found that the agreement between model predictions and measurements (as determined by performance measures such as geometric mean bias and geometric variance) varied between different models. At any downwind distance, the range in predicted plume arc-max concentrations spanned a range of up to one or two orders of magnitude about the measurements. Several modelling teams used the same models and, in most cases, their predictions differed. Given appropriate inputs, most models generally predicted concentrations that agreed with the data within commonly-used model acceptance criteria. There was no single class of model that provided superior predictions to others; predictions from several empirically-based nomograms, integral, Gaussian puff, Lagrangian particle, and CFD models were all in close agreement with the data (as defined by the model acceptance criteria).
The findings of the exercise are being used to help plan a programme of future ammonia experiments in the USA, called the Jack Rabbit III trials. The results are also useful for assessing the performance of models that may be applied to assess risks at ammonia facilities, and for emergency planning and response
TisB enables antibiotic tolerance in Salmonella by preventing prophage induction through ATP depletion
No full textAntibiotic persistence comprises drug-tolerant bacteria that can survive treatment with antibacterial agents, despite lacking classical genetic resistance mechanisms. Therefore, persisters are clinically relevant because they can lead to treatment failures and chronic infections. Additionally, antibiotic persistence facilitates the evolution of resistance through genetic mutations. Persisters are triggered by a lack of nutrients, bacterial toxins, low ATP levels, or other stress responses that shut down bacterial metabolism. However, the involvement of prophages, viruses that integrate into bacterial chromosomes, is less well understood. In this study, we tested a tisAB deletion in Salmonella Typhimurium and examined persister cell formation following treatment with the DNA-damaging drug ciprofloxacin. TisB is a bacterial toxin that increases the influx of protons across the inner bacterial membrane into the cytosol, causing ATP depletion. We demonstrate that the deletion of tisAB increases prophage induction and bacterial killing, leading to a reduced persister cell fraction. The tisAB mutant is unable to down regulate its ATP concentration after exposure to ciprofloxacin, which in turn allows for stronger binding of RecA to single-stranded DNA, the activator of both the SOS response and prophage induction
Gasflaschenzerknall in einer Löschanlage: Ursachen – Schadensanalyse – Prävention
No full textSchadensanalyse an einer mit Inergen gefüllten Gasflasche aus einer Löschanlage aus dem vergütetem Stahl 34CrMo4. Die Durchführung der Schadensanalyse erfolgte nach VDI 3822. Schadensursache war Spannungsrisskorrosion durch Wasserreste in Verbindung mit dem Gasbestandteil Kohlendioxid des eingefüllten Inergen. Die Wasserreste verblieben nach der hydraulischen Druckprüfung unentdeckt in der 1996 hergestellten Gasflasche. Auch bei der Erstbefüllung mit Inergen im Jahr 2003 blieben die Wasserreste unentdeckt. Nach Installation der befüllten Gasflasche in der Löschanlage im Jahr 2004 verblieb diese dort bis zum Schadensereignis im Jahr 2021
Development, Validation and Application of an Accelerated Weathering Protocol for Assessing Bisphenol A Release from Polycarbonate Materials into the environment
No full textBisphenol A (BPA) is under continuous regulatory scrutiny and listed as substance of very high concern (SVHC). Particular concern is related to its frequent detection in surface waters, despite being readily biodegradable. Several studies have been conducted to investigate sources and pathways of BPA in the environment, concluding that its main use as monomer in polycarbonate (PC) contributes only marginally to environmental BPA releases over its life cycle.
To better understand the actual releases of BPA from PC under environmental conditions, a newly developed methodology (Federal Institute for Materials Research and Testing, BAM) was applied, which comprises a novel accelerated weathering protocol for polycarbonate (PC) materials, combined with an advanced analytical setup allowing for improved detection of BPA at trace level concentrations. The weathering protocol achieves a 13.6-fold acceleration compared to Central European outdoor conditions and simulates environmental stressors (global radiation, rain, temperature variations) in a laboratory weathering chamber, with simultaneous BPA release measurements using an organic isotope dilution calibration LC-MS/MS approach. Validation was performed in parallel outdoor exposure tests, by using haze and yellowness index measurements as reference parameters.
PC sample types representative of major polycarbonate applications were examined: Samples with different levels of UV-protection as used in transparent sheets used outdoor in construction or housings in Electro- and Electronic applications as well as samples with a protective coating as used in automotive applications (headlamps, glazing and construction).
Results demonstrated consistently low total BPA releases of around 0.3 mg m⁻² for samples with exposed PC surfaces, while releases from coated samples were significantly reduced by around two orders of magnitude. In all cases examined, the BPA release ceased to zero after a period of four to six weeks, equivalent to approximately 1 to 1.5 years of outdoor exposure. This suggests that potential BPA releases diminish to virtually zero after that timespan. While the newly developed test method is not suitable for routine laboratory implementation, it provides crucial quantitative data on BPA release from PC materials during accelerated environmental weathering