Understanding the diffusion of water and solutes in clay-rich materials is critical for several applications, notably radioactive waste disposal. Most of the available experimental data on tracer diffusion in clay porous media are interpreted using only bulk porosity and, to a lesser extent, on particle orientation, implicitly assuming their homogeneity in the sample. Nevertheless, these parameters can be heterogeneously distributed in both natural and laboratory-made clay samples, and a quantitative assessment of their impact on water diffusion is still lacking. To address this gap, synchrotron two-dimensional micro-X-ray diffraction was used to map the microstructural heterogeneity in porosity and clay particle orientation in two laboratory-made illite porous media obtained by compaction in dry conditions or centrifugation in wet conditions. The resulting maps were coupled with the CrunchODiTi reactive transport code to derive the macroscopic water effective diffusion coefficient by accounting for porosity and the orientation tensor of clay particles at each map pixel. The results indicate that heterogeneity in clay particle orientation has a negligible effect on the water effective diffusion coefficients, such that the use of an average value is sufficient. Conversely, pronounced variations in water diffusion values among different porosity heterogeneity patterns (i.e., homogeneous, bedding, and random) demonstrate that the porosity microstructure can either amplify or attenuate diffusion anisotropy associated with the preferred orientation of clay particles. The methodology developed in this work, which integrates microstructural heterogeneity mapping with diffusion calculations, provides a new framework for incorporating the textural properties of clay-rich rocks into the prediction of water and solute transport.
In recent years, the civil aviation industry has encountered growing pressure from the public and regulators to curb air pollutants and climate emissions. Sustainable aviation fuels (SAFs) produced through the Hydroprocessed Esters and Fatty Acids (HEFA) method have been approved as blends with conventional Jet A-1 under ASTM D7566. However, comparative burner-scale evidence linking composition, gaseous emissions, and emission indices (EI) across lean to rich combustion remains limited, particularly for HEFA-rich blends and SO2 behaviour. This study employs the FAA-certified Next Generation (NexGen) burner-for the first time applied to HEFA-SAF and HEFA-rich blends to measure O2, CO2, CO, NOx and SO2 for Jet A-1 (B0), HEFA-SAF (B100) and their blends (B50J50, B70J30, B90J10) across twelve equivalence ratios (phi = 0.50-1.44), compute fuelnormalised EI-CO, EI-CO2, EI-NOx and EI-SO2, none of which have been reported from this platform for SAF or blends and pair emissions with GC-MS end-member fingerprints. NexGen burner provides a realistic fire conditions, like those encountered in real-life accidents, particularly in areas near aircraft engines. HEFA blending improved key properties (lower density and viscosity, lower freezing point, higher flash point and gravimetric energy density). B100 showed the highest residual O2 and the lowest CO, NOx and SO2; EI-CO peaked at 0.811 g/kg fuel (B0) but plunged to 0.010 g/kg fuel for B100, while EI-NOx decreased from 0.198 g/kg fuel (B0) to 0.014 g/kg fuel for B100. HEFA-rich blends EI-CO decreased and their EI-CO2 increased. However, EI-NOx increased non-linearly with HEFA fraction under lean-to-stoichiometric conditions (phi = 0.50-1.0). Attributed to the higher gravimetric energy density of HEFA-rich blends increasing local flame temperature and amplifying the thermal Zeldovich NOx pathway; an equivalence-ratio-dependent trade-off that reverses at rich conditions where B100 retains its 80.1% NOx advantage over B0. Non-monotonic EI-SO2 across the blend series suggested intra-batch sulphur variability in the HEFA-SAF supply. These results provides a single-platform, composition-aware dataset that supports emissions benchmarking and blend optimization for certification. Future work should evaluate non-volatile particulate matter and complement the results with FTIR or GCxGC analysis to reduce co-elution ambiguity. Also, combine emissions with heat release, and fuel-specific energy conversion metrics.
Doppler broadening positron annihilation spectroscopy is a powerful technique for investigation of neutral and negatively-charged atomic-scale defects in materials. However, it has one important drawback, which is that studies are typically designed to only illuminate relative differences in positron annihilation characteristics in a specific suite of samples. It is difficult and considered ill-advised to compare the data that different laboratories report for apparently similar samples, which limits the scope of applications of the technique. The root of the problem is that the resolution and calibration of the detector used to collect the energy spectra of the positron-electron annihilation radiation affect their shape and the S and W parameters that are used for its characterisation. The present study explores whether this obstacle can be overcome by modelling the differences between the data sets that were obtained via different detectors or the same detector at different times. We were able to reproduce the observed differences between the analyses of UO(2)that were acquired in our laboratory over the past similar to 25 years using the same detector that has changed its properties. However, our attempt to reproduce the differences between our and literature data did not work out as well, which can be pinned in part to a real difference between the samples and in part to the incompleteness of the published descriptions of the methodology. We conclude with recommendations to improve current practices of data acquisition and reporting.
This work proposes to substitute the conventional mortar in the joints of a masonry wall with an unsaturated polyester polymer mortar and to predict accurately (up to numerical errors) the wall's local mechanical behaviour at different states (defect-free and with damage (i.e., containing voids and microcracks)) using the finite element method in order to provide a reference numerical solution useful for further research based either on fracture mechanics or micromechanics (e.g., for the assessment of the accuracy of linearization schemes (Rekik et al., 2007, 2012) for elastoviscoplastic masonry). Under monotonic biaxial compression, the polymer mortar is assumed to follow the Ramberg-Osgood type relation. According to the regular arrangement of masonry, the wall is considered as a succession of periodic cells in both vertical and horizontal directions. Based on the equivalent elliptical crack concept (Lee et al., 1997; Mazars et al., 1996), the localised damage in a UP mortar joint in a periodic masonry cell is converted into a crack approached here by an elliptical void, avoiding infinite stresses at tips of sharp cracks (Dormieux et al., 2006). Based on typical crack patterns available in the literature for masonry walls with conventional mortar, four configurations for the wall joints were explored: defect-free mortar, presence of elliptical voids only at the bed (at bed-head joint intersections) or head joints, or simultaneously at both bed and head joints. These configurations can result from various factors (defects or poor placement in two successive layers, ingress of moisture, hygrothermal effects, ageing mechanisms, acidic environments, influence of aggregate, previous loads, etc.). Under biaxial compressive load, it can be noticed that the risk of failure is higher for a wall with elastic bricks since rigid bricks prevent brick deformation. Results for freedefect wall show a high concentration of stress in the bed joints, mainly at the bed-head mortar joints' intersections and brick/bed joints interfaces. Comparisons between the three configurations of damaged masonry states with the same damage fraction demonstrate that the vertical equivalent voids at head joints highly increase the stress concentration inside the wall, mainly at head-bed mortar joint junctions. Moreover, the state with damage in both head and bed joints is the most risky of all, showing high stress concentration at head-bed joint junctions, around head joints and in the mid-width of bricks, recalling the crack pattern of a brick masonry wall with conventional mortar (Page, 1981; Ren et al., 2017) and concrete masonry with high adhesive mortar (Thamboo and Dhanasekar, 2016; Zahra et al. 2021). The effect of the equivalent void ellipse aspect ratio was also investigated, showing an increase of the failure risk for higher void dimensions: radius or half-height.
Particle deposition and clogging in porous media control the performance of many natural and engineered applications, including groundwater filtration, geothermal injection, and subsurface fluid management. Once deposits form, permeability progressively declines and flow pathways become blocked, making mitigation strategies essential for maintaining long-term operation. Oscillatory injection has been proposed as a potential strategy to delay clogging, yet how its effectiveness depends on physicochemical conditions and complex pore geometries remains poorly understood. Here, we use microfluidic experiments with colloidal suspensions to investigate how oscillatory flow modulates particle transport and clogging in tortuous porous domains. Controlled oscillatory forcing is applied over a range of frequencies while monitoring permeability evolution and deposition dynamics. Under saline conditions, oscillatory flow delays clogging and increases the injected volume before hydraulic failure with increasing frequency, consistent with electrostatic screening that promotes particle aggregation and allows cyclic pressure fluctuations to destabilize growing deposits intermittently. However, the frequency response changes with physicochemical conditions and can even reverse. As ionic strength decreases and electrostatic interactions become stronger, aggregation is suppressed, and clogging becomes increasingly governed by particle crowding and pore bridging, where higher-frequency oscillations can instead accelerate blockage. These findings demonstrate that oscillatory injection does not have a universal effect on clogging, but instead depends on the balance between hydrodynamic forcing and particle interactions. This regime-dependent behavior provides a basis for designing more effective injection strategies in porous media.
