Grain Size Distribution Research Articles

A quantitative assessment of the behavior of metallic elements in urban soils exposed to industrial dusts near Dunkerque (northern France)

Abstract. In urban and industrialized areas, soil contamination and degradation caused by industrial dust deposition may pose significant health and environmental risks. Generally, the mobility and thus bioavailability of potentially toxic elements (PTEs) are key factors in these issues. In the Dunkerque agglomeration, one of the most industrialized regions in France, the soils are periodically exposed to metallurgical dust fallout, rich in PTEs. However, no study has reported on the behavior of these PTEs once integrated into the soils. The aim of this study is therefore to assess the fate of PTEs in the urban soils of Dunkerque in terms of vertical migration and potential bioavailability. Four soil short cores were collected in the city of Gravelines (Dunkerque agglomeration) along a gradient from industrial emitters to deposition sites. Each soil core was cut into discrete 1 cm sections for PTE concentration analyses (ICP-AES/MS). Single HCl extractions were performed to evaluate PTE mobility in soils and their behavior according to the current soil parameters. For this purpose, key soil properties were identified, including grain-size distribution, mineralogy, pH, cation exchange capacity (CEC), TOC (total organic carbon), calcium carbonates and water contents in addition to the soil chemical composition (XRF, ICP-AES/MS). The studied soils revealed globally low absorbent capacities for pollutants (CEC averaging 5.3meq/100g), partially counterbalanced by the buffering effect of calcium carbonates (contents ranging from 8 %–30 %). Near the industrial emitters, minor (1<EF<3) to moderately severe (5<EF<10) enrichment factors (EFs) were highlighted for industrial PTE (Cr, Ni, Mo, Mn, Cd and Zn) in the top 3 cm of soils near the industrial emitters. The contamination profiles of these soils are assigned to atmospheric inputs of metallurgical dust. Using a relatively strong leaching reagent (1 M HCl), we estimated a low vertical mobility for Cr, Ni and Mo (average leached ratios<25 %) in soils, suggesting their association with refractory phases (natural or anthropogenic). In contrast, Mn, Cd and Zn, which are related to industrial and/or urban sources, present a higher mobility (average leached ratios>60 % for Mn and Cd and about 44 % for Zn). Our study points out the stability of industrial PTEs in soils under the current physicochemical conditions (calcareous soils with a slightly basic pH of 7.8). In this context, the monitoring of industrial PTEs in these urban soils is highly recommended, considering (1) the presence of allotment gardens in the vicinity of emitters and (2) the potential evolution of soil conditions due to increasing flood events.

In situ volcanic ash sampling and aerosol–gas analysis based on UAS technologies (AeroVolc)

Abstract. Volcanic degassing and explosive eruptions inject significant amounts of gas and ash into the atmosphere, impacting the local environment and atmospheric dynamics from local to global scales. While ground- and satellite-based remote-sensing systems are key to describing explosive volcanism and assessing associated hazards, direct in situ measurements inside volcanic clouds are not possible with these methods. This study presents an innovative approach using an unoccupied aircraft system (UAS) for (i) airborne ash sampling and (ii) measurements of aerosol and gas concentrations (AeroVolc system). Commercial instruments (DJI™ Matrice 30 UAV, Alphasense™ N3 optical particle counter, and Soarability™ Sniffer4D Mini2 multigas hardware) were combined with custom-built ash collectors and particle counters to enable a more detailed analysis of volcanic clouds. Here, we showcase the deployment of our UAS on Sakurajima (Japan) and Etna (Italy), two volcanoes known for their frequent explosive eruptions and persistent degassing activity, to demonstrate how this approach enables in situ, high-resolution sample and data collection within challenging environments. Results provide grain size distributions (GSDs), information on the occurrence of particle aggregation, and solid aerosol (PM1, PM2.5, and PM10, corresponding to solid aerosol particles with a diameter of less than 1, 2.5, and 10 µm, respectively) and gas (SO2 and CO2) concentrations. Depending on whether the UAS was operated within or below ash- and/or gas-rich clouds, different insights were gained that open up new perspectives for volcanological research. These insights include the composition, concentration, generation, dispersion, and sedimentation patterns of volcanic clouds.

Grain size distribution characteristics of sediments in recreational beaches: a case study of three major beaches in Zhanjiang City of western Guangdong

Recreational beaches are widely distributed in coastal cities. Investigating the coupling mechanisms between anthropogenic interventions and natural coastal processes on sediment grain-size distribution is critical for maintaining and enhancing recreational beach functionality and value. This study examines three major recreational beaches within Zhanjiang Bay, conducting comparative analyses of surface sediment characteristics including representative grain-size metrics, granulometric composition, and statistical parameters. Key findings include: (a) significant variations in mode size (0.87–1.89 φ) and D10 values (-0.80 to -0.09 φ) among the three beaches, contrasted with limited differences in D50 and D90 metrics; (2) dominance of medium sand (26.16–39.14%) and coarse sand (26.75–31.43%) fractions, supplemented by fine and very coarse sand components, with central transects exhibiting higher medium-coarse sand concentrations than southern/northern sections; (3) sorting coefficient gradients (0.90–1.21) ranking central > northern > southern beaches, while mean grain size (0.83–1.21 φ), skewness (-0.12 to -0.02), and kurtosis (0.87–1.18) show no distinct spatial patterns. Sediment grain-size distribution patterns are governed by four primary mechanisms: artificial nourishment inputs, anthropogenic sediment modification (harvesting/excavation), natural sediment supply processes, and hydrodynamic forcing. This research establishes a typical framework for characterizing recreational beach sediments, advancing understanding of multi-factor controlled grain-size distribution patterns and sediment transport dynamics.

Estimating the mass of tephra accumulated on roads to best manage the impact of volcanic eruptions: the example of Mt Etna, Italy

Abstract. Explosive eruptions release significant quantities of tephra, which can spread and settle on the ground, potentially leading to various types of damage and disruption to public infrastructure, including road networks. The quantification of the tephra load is, therefore, of significant interest to evaluate and reduce environmental and socio-economic impact, as well as for managing crises. Tephra dispersal and deposition is a function of multiple factors, including the mass eruption rate (MER), tephra characteristics (size, shape, density), top plume height (HTP), grain size distribution (GSD), and local wind field. In this work, we quantified the tephra mass deposited on the main road network on the east-southeast flanks of Mt Etna (Italy) during lava fountains that occurred in 2021, which reached heights of hundreds of metres. We focused on road connections of municipalities significantly affected by these events such as Milo, Santa Venerina, and Zafferana Etnea. First, we analysed a sequence of 39 short-lasting and intense lava fountains detected by the X-band weather radar, applying a volcanic ash radar retrieval approach that permits us to compute the main eruption source parameters (ESPs), such MER, HTP, and GSD. When radar measurements were unavailable for a specific event, we analysed images acquired both by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) radiometer and by the visible and/or thermal infrared camera of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (Catania), to derive the main ESPs. Second, we used the computed ESPs as inputs to run two different numerical models, Tephra2 and Fall3D, and to reproduce tephra dispersal and accumulation on the road network. Finally, we produce, for the first time, georeferenced estimates of tephra mass deposited on the whole road network of three municipalities, allowing us to identify the main roads which have been mostly impacted by tephra accumulation, as well as to estimate the total mass of primary tephra that has been removed from roads. Such information represents a valuable input for planning and quick management of the short-term tephra load hazard for future explosive events on Mt Etna.

Distributed estimation of surface sediment size in paraglacial and periglacial environments using drone photogrammetry

Abstract Grain‐size analysis offers insights into geological processes and landform dynamics. Traditional grain‐size sampling methods are labour intensive and offer limited spatial coverage, posing challenges in paraglacial and periglacial environments characterized by large spatial variability in sediment sizes. This study introduces a new workflow that combines structure‐from‐motion, image segmentation and texture‐based optical granulometry techniques to estimate surface grain size in paraglacial and periglacial environments efficiently. Utilizing high‐resolution orthomosaics (ground sampling distance 8 mm) and Cellpose, a deep‐learning image segmentation model, the new workflow achieves high‐accuracy grain‐size distributions (GSDs) with low errors. These GSDs, along with lower resolution orthomosaics (ground sampling distance 30 mm), are used to train SediNet—a machine‐learning framework—to predict GSDs accurately from pixel tiles. Tested across six alpine basins in the Canadian Rockies and a rock glacier in Italy, the model demonstrates effectiveness and accuracy, promising advancements in geoscientific research and the understanding of paraglacial and periglacial dynamics.

Gravel bar shielding: A mechanism responsible for bar stability in gravel‐ and cobble‐bedded streams

Abstract The stability of gravel bars and riverbanks is often attributed to the presence of vegetation, yet the conditions controlling the stability of such bars without of a vegetation cover have remained unclear. Here, we propose that such controls are exerted by what we refer to as ‘lateral lag deposits’, which result from the winnowing of gravel bar edges during periods when channels widen. We base this interpretation on an example from the Sense River, Switzerland, a natural wandering‐braided stream with gravel‐cobble bars devoid of vegetation. Through a survey where we measured the size of several thousands of grains along two up to 50 m‐long reaches, we found that the 84th percentile values (D84) of the grain size distributions (GSD) are consistently larger on the eroded bar edges compared to the bar top or the channel between bars. At these bar edges, the coarse grains appear to shield the gravel bar from lateral erosion, thus forming a lag deposit. Orthoimages taken along the studied reaches between 2017 and 2023 reveal that the target lateral lag deposits outlasted several lower‐discharge floods, during which the sedimentological architecture of the investigated reach changed multiple times. We therefore suggest that lateral lag deposits are among the sedimentological structures of braided streams with the highest preservation potential and that they exert the largest threshold to the complete reworking of gravel bars without vegetation.

Different methods of estimating riverbed sediment grain size diverge at the basin scale

IntroductionThe distribution of sediment grain size in streams and rivers is often quantified by the median grain size (D50), a key metric for understanding and predicting hydrologic and biogeochemical function of streams and rivers. Manual D50 measurements are time-consuming and ignore larger grains, while approaches to model D50 based on catchment characteristics may over-generalize and miss site-scale heterogeneity. Machine learning-enabled object detection methods like You Only Look Once (YOLO) provides an alternative that enables estimation of D50 that is faster than manual measurements and more site-specific than predictions based on catchment characteristics.MethodsTo understand the potential role of object detection methods for improving understanding of D50, we compared D50 estimates made manually, predicted from catchment characteristics, and using a YOLO-enabled approach across the Yakima River Basin.ResultsWe found distinct differences between methods for D50 averages and variability, and relationships between D50 estimates and basin characteristics.DiscussionWe discuss the advantages and limitations of object detection methods versus current methods, and explore potential future directions to combine D50 methods to better estimate spatiotemporal variation of D50, and improve incorporation into basin-scale models.

Dataset for Quantifying the Effect of Ultrasonic Scattering from a Distribution of Grain Sizes

Dataset for Quantifying the Effect of Ultrasonic Scattering from a Distribution of Grain Sizes

A Method to Obtain Remotely Sensed Grain Size Distributions From Granular Deposits With Complex Surfaces

Abstract Constraining the grain size distribution of granular deposits with complex surfaces is difficult with existing approaches. Field and laboratory techniques are time consuming and limited by the maximum grain size that laboratories can accommodate. In this study, we present a new method to identify the coarse fraction of the grain size distribution at a debris‐flow fan deposit surveyed with terrestrial laser scanning (TLS) in Glenwood Canyon, Colorado, USA. This method is a novel grain segmentation algorithm developed for application to point cloud data of deposits with complex surfaces and angular grains ranging in size from centimeters to a meter. This approach combines an existing random forest machine learning method with a novel iterative clustering algorithm. We compared the grain size distribution from our algorithm with a Wolman pebble count conducted in the field, and found a root mean squared error of less than 2 cm from the 5th to 95th percentile of the grain size distribution of grains ranging from cobble to boulder sized (6.3–78 cm in our application). Finally, we compared our new algorithm with an existing open‐source grain segregation algorithm, and our method outperformed the selected alternative when applied to the debris‐flow deposit point cloud.

The impact of wide-graded debris flow on sediment-trap dams in the Tibetan Plateau: an experimental study

In the Tibetan Plateau, pronounced topographical relief (steep mountains and deep valleys) coupled with intense weathering processes generates highly fragmented slope surfaces, creating debris-flow source materials with exceptionally heterogeneous grain-size distributions. These conditions frequently produce debris flows that exhibit extraordinary impact forces which cause severe damage to sediment-trap dams. Through 27 sets of flume experiments that systematically varied the particle-size distribution ( d max ), bulk density ( γ ) and flume slope ( θ ), this study investigates the impact mechanisms of wide-graded debris flows on sediment-trap dams. The results demonstrate that debris-flow interactions with sediment-trap dams occur through three distinct phases: (1) impact run-up, (2) rotational backflow and (3) depositional back-silting. Lower bulk-density flows exhibited greater run-up heights and more pronounced phase differentiation. Measured impact forces ( F ) showed an inverse relationship with bulk density ( γ ↑→ F ↓), while displaying positive correlations with both slope gradient ( θ ↑→ F ↑) and maximum particle size ( d max ↑→ F ↑). This occurs because higher- γ flows experience increased internal shear resistance, resulting in a reduction in velocity. Steeper slopes enhance kinematic energy, while larger particles generate more concentrated momentum transfer during impact. Sensitivity analysis revealed that d max exerts dominant control over impact dynamics compared to γ and θ . These findings provide critical insights for sediment-trap dam design in high-altitude debris-flow mitigation systems.

Effect of grain size distribution in non-cohesive spatial dam breach: hydraulic model investigation and systematic calibration of 2D numerical model

The breaching of earthen embankment dams can result in uncontrolled release of immense volumes of water, which can be catastrophic to downstream settlements, infrastructure, and ecosystems. The spatial dam breach process depends on the embankment sediment grain size distribution (GSD), a dependence that is investigated here with an experimental hydraulic model in combination with a numerical model. Experimental results indicate that breach development is faster, and therefore a larger flood discharge is expected, for dams made of sediment with wider GSDs. The numerical model was set up to reproduce the experiments, by applying a single-grain morphodynamic solver that was systematically calibrated to the two dominant morphodynamic processes. The model reproduced the rates of breach growth, breach discharge, and sediment erosion for the uniform-sediment dam, as well as the faster breach growth in dams made of wider-GSD sediment. However, the breach growth rate was overestimated for dams with wider sediment GSDs.

TEXTURAL ANALYSIS AND HYDRAULIC CHARACTERISTICS OF AJALI SANDSTONES OF OBOLLO-AFOR AND ENVIRONS IN ANAMBRA BASIN, SOUTHEASTERN, NIGERIA

The movement and storage of groundwater are determined by the porosity and hydraulic conductivity of the medium, which defines its permeability. Hydraulic conductivity depends on both the properties of the porous material and the fluid, and it has long been linked to the grain-size distribution of granular media. This study highlights the textural characteristics and hydraulic conductivity of Ajali Sandstone in Obollo-Afor area (southeastern Nigeria). The investigation approach involved field sampling and collection of 12 sandstone samples from different outcrop locations followed by laboratory studies such as grain size analysis. Grain size analysis and textural studies show that the sandstones mean range from 0.96-1.87 (av. 1.52). Other parameters such as coefficient of uniformity (Cu) range from 2.133 to 4.263 (av. 0.399), while sorting values of 0.83-1.10 (av. 0.96) imply moderately sorted sediments. The sandstones are mostly platykurtic and coarse skewed indicating sand of fluvial origin ranging from channel floor, point bar to braided rivers. Analysis shows that the sediments were deposited in beach/shallow agitated and fluvial agitated environments. The Ajali Sandstone porosity values range from 36.53%-42.6% (av. 39.9) and the hydraulic conductivity values of 2.579-68.101m/day (av. 43.741m/day). These values of porosity and hydraulic conductivity are indications of high specific yield for the sandstone of the study area.

Evolution of Stratigraphic Sequence and Sedimentary Environment in Northern Yellow River Delta Since MIS5

Quaternary climate has been characterized by pronounced glacial–interglacial cycles, with eustatic sea-level fluctuations directly controlling coastal sedimentary environments. The Yellow River Delta, situated on the southwestern coast of Bohai Bay, bears a distinct stratigraphic imprint of marine–terrestrial environmental transitions. However, critical knowledge gaps persist in reconstructing an integrated continental–marine stratigraphic framework. This study focuses on the nearshore core CB2302, integrating sediment lithology, grain size, foraminiferal assemblages, and geochemical proxies to establish a regional stratigraphic chronology since MIS5. Three depositional units (DU1–DU3) and 12 sedimentary subunits (C1–C12) were identified based on grain-size distributions, geochemical signatures, hydrodynamic, and microfossil assemblages. Integration of AMS 14C dating and sequence stratigraphic analysis establishes a post-MIS 5 stratigraphic framework for the northern Yellow River Delta, revealing sedimentary responses to three transgressive–regressive cycles (MIS 5e, 5c, and 5a) and confirming widespread terrestrial deposition during MIS 4–2, with no detectable marine influence in MIS 3 strata. Furthermore, correlation with representative cores across the Yellow–Bohai Sea coastal system elucidates a unified model of shoreline migration patterns driven by post-MIS5 sea-level oscillations. These findings advance the understanding of Quaternary sediment–landscape interactions in deltaic systems and provide critical stratigraphic benchmarks for petroleum exploration and coastal engineering in active depositional basins.

Thermal damage in crystalline rocks: the role of heterogeneity

Accurately evaluating the impact of microstructural heterogeneity on thermal damage and failure mechanisms in crystalline rocks is crucial for geothermal energy development and the establishment of nuclear waste repositories. However, in thermal damage analyses of crystalline rocks using the discrete element method, most studies fail to account for the reduction in mineral mechanical and thermal properties caused by temperature increases. This study uses a Grain-Based model to simulate the microscopic mineral structure of crystalline rocks, focusing on analyzing the effect of heterogeneity. Thermal damage resulting from the uneven expansion of minerals is simulated by assigning specific thermal properties to each mineral. The temperature-induced degradation of mechanical and thermal properties is incorporated by introducing a temperature-dependent relationship for these characteristics in crystalline rocks. Along with moment tensor inversion theory, the microseismic behavior of crystalline rocks is explored to enhance understanding of rock failure mechanisms. The results indicate the following: (1) Thermal stress depends on the mineral’s size, shape and arrangement. The sharp corners and edges of irregularly shaped minerals are more likely to become stress concentration points under the influence of temperature. (2) Peak strength gradually decreases with increasing heterogeneity and larger grain sizes. A negative correlation between quartz content and peak strength becomes more evident when the temperature exceeds 450 °C. (3) The combined effects of high temperature and heterogeneity lead to a more significant increase in the b value. Smaller grains increase the complexity of crack paths, leading to more frequent branching at grain boundaries and resulting in higher b values. (4) The uneven distribution of grain sizes is the primary factor influencing the mechanical properties of crystalline rocks, while grain size is a secondary factor. At the same temperature, samples with more uniform grain distributions and smaller grain sizes exhibit higher thermal stability.

Multifractal Characteristics of Grain Size Distributions in Braided Delta-Front: A Case of Paleogene Enping Formation in Huilu Low Uplift, Pearl River Mouth Basin, South China Sea

Multifractal analysis has been used in the exploration of soil grain size distributions (GSDs) in environmental and agricultural research. However, multifractal studies regarding the GSDs of sediments in braided delta-front are currently scarce. Open-source software designed for the realization of this technique has not yet been programmed. In this paper, the multifractal parameters of 61 GSDs from braided delta-front in the Paleogene Enping Formation in Huilu Low Uplift, Pearl River Mouth basin, are calculated and compared with traditional parameters. Multifractal generalized dimension spectrum curves are sigmoidal and decrease monotonically. Multifractal singularity spectrum curves are asymmetric, convex, and right-hook unimodal. The entropy dimension and singularity spectrum width ranges of silt-mudstones and gravelly sandstones are wider than those of fine and medium-coarse sandstones. The symmetry degree scopes from different lithologies are concentrated in distinguishing intervals. With the increase of grain sizes, the symmetry degree decreases overall. Both the symmetry degree and mean of GSDs are effective to distinguish the different lithologies from various depositional environments. A flexible and easy-to-use MATLAB (2021b)® GUI (graphic user interface) package, MfGSD (Multifractal of GSD, V1.0), is provided to perform multifractal analysis on sediment GSDs. After raw GSDs imported into MfGSD, multifractal parameters are batch calculated and graphed in the interface. Then, all multifractal parameters can be exported to an Excel file, including entropy dimension, singularity spectrum, correlation dimension, symmetry degree of multifractal spectrum, etc. MfGSD is effective, and the multifractal parameters outputted from MfGSD are helpful to distinguish depositional environments of GSDs. MfGSD is open-source software that can be used to explore GSDs from various kinds of depositional environments, including water or wind deposits.

Spatio-temporal variations on alluvial fan channel width in response to grain size on the channel bed under constant upstream boundary conditions

It has been widely accepted that channel geometry on alluvial fans is predominantly controlled by upstream boundary conditions and remains stable if those conditions do not change. This study challenges that notion by examining how channel width on alluvial fans varies in space and time under constant upstream conditions. Experiments using a sediment mixture (sand and crushed walnut) with constant sediment and water discharge rates reveal distinct patterns in channel width. In lower water discharge runs, total channel width decreases over time, while in higher discharge runs, it increases. Theoretical principles suggest that channel width is inversely proportional to grain size. Sand results in a wider channel width compared to walnut sediment, making its proportion along the channel a key factor in controlling the average channel width. The disproportional advancement of sand reaches relative to the fan margin, which varies across different discharge runs, drives changes in slope and channel width over time. This study highlights that surface grain-size distribution can change as the fan grows, even when external conditions remain constant, leading to variations in channel geometry. Sedimentary records often attribute signal changes to upstream boundary variations. However, our findings highlight the critical role of intrinsic fan width dynamics, underscoring the need to consider this factor in fan evolution studies.

Effects of liquefied beds on the basal layers of turbidity currents

Abstract Controlled laboratory experiments of turbidity currents (TCs) flowing over three types of beds (compacted beds, loose-sand beds, and liquefied beds) reveal that liquefied mobile beds play an important role in driving the denser basal layer of turbidity currents by supporting sediments in suspension more effectively over space and time. Based on measured near-bed concentration and velocity, as well as deposit characterization, a relationship was established between the spatial evolution of the TCs and the presence of liquefied and/or fluidized beds. Velocity and sediment concentration profiles of TCs were measured throughout the 4-m-long flume during 4 min to 6 min runs. Deposit thickness and grain-size distributions were analyzed after each experiment. Results indicate similar values of hydraulic and sedimentological properties for both loose beds and compacted beds. Moreover, TCs flowing over liquefied beds were capable of maintaining higher near-bed concentrations along the entire flume. Additionally, values of median grain size were larger in the deposits generated by TCs that flowed over liquefied beds when compared to loose beds and compacted beds. This indicates the role of liquefied beds on sustaining near-bed sediments in suspension and on increasing the sediment-transport competence of TCs. The observations shed light on the occurrence of long-term turbidity currents driven by dense basal layers, directly observed in deep ocean environments.

Precipitation-assisted heterostructure in a FeMnCoCrCuC high entropy alloy enables superior mechanical property

High-entropy alloys in which the face-centered cubic structure is dominant cannot meet practical engineering application requirements due to their insufficient strength. Traditional strengthening methods can improve strength of materials, but they inevitably lead to decreased ductility. In this work, mechanical properties of a face-centered cubic-structured FeMnCoCrCu high-entropy alloy were improved by doping a substantial amount of carbon and employing a processing route that combines cold rolling and annealing. A dual-heterostructure characterized by both bimodal grain-size distribution and non-uniform distribution of nanoscale precipitates was constructed. The average grain sizes were 21.6 and 5.9 μm for the coarse and fine grains, accounting for 56.6% and 43.4% of the material, respectively. On the other hand, the finer M23C6 precipitates in the grain interior had an average size of 73.1 nm, constituting 3.4% of the coarse-grained region and 10.7% of the fine-grained region. The larger M23C6 precipitates at grain boundaries had an average size of 182.4 nm, with an overall volume fraction of 1.5%. This heterogeneous microstructure endowed the alloy with superior strength and work-hardening capacity compared to the carbon-free alloy. The yield and tensile strengths reached 500 MPa and 979 MPa, respectively, while maintaining a uniform elongation of 42%. This study not only identifies the origin of strengthening and micromechanism of plastic deformation in the carbon-alloyed dual-heterostructured alloy but also elucidates the formation of the specified microstructure. The findings provide theoretical guidance for developing advanced alloys with both high strength and good ductility.

Enhancing the magnetic and dielectric properties of M type strontium hexaferrite nanoparticles via aluminum substitution: a sol-gel synthesis approach

Abstract This research evaluates the impact of aluminum (Al) substitution on the properties of strontium hexaferrite (SrFe12O19) nanoparticles synthesized via a sol-gel method. A comprehensive suite of characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Brunauer Emmett Teller (BET) surface area analysis, vibrating sample magnetometry (VSM), and dielectric measurements were employed. The Rietveld refinement confirmed the formation of a pure hexagonal phase (space group P63/mmc) devoid of any secondary phases. With increasing Al content, a reduction in X-ray density and lattice parameters was observed, which correlates with changes in the Raman spectral features, notably the pronounced A1g peak between 670–710 cm−1. SEM analysis revealed a uniform distribution of grain size. This study also found that greater Al concentrations increase coercivity while reducing both the saturation magnetization and magneton number, reflecting the substitution of nonmagnetic Al3+ ions. Additionally, the dielectric properties of both undoped and Al-doped samples demonstrated a typical exponential decline in dielectric constant with increasing frequency, showcasing their potential for various advanced magnetic and electronic applications. Graphical Abstract

Rheology of debris flows: Insights from experiments with coarse‐grained matrix

Abstract Debris flow is characterized by a heterogeneous mixture of water and sediment with varying rheology. The granular effects on rheology are usually attributed to the bulk concentration of solids without considering the variability of granular configuration, as signified in the grain size distribution (GSD). In this work, the GSD effects on debris flow rheological properties were explored using the parameters μ and Dc derived from a unified GSD function, P(D) ~ D‐μ exp(‐D/Dc), that are widely applicable for debris flow materials. Compared with other experiments using artificial fine‐grained slurry (with grain size <2 mm) at a given solid volume concentration (Cv), the realistic coarse‐grained matrix (up to 10 mm) of fresh debris flows was used for the experimentation, under shear rate up to 40 (s−1) as in natural conditions. The results show that the flow can be categorized as Herschel‐Bulkley (HB) fluid, with an average consistency index of 0.45, signifying the shear thinning effect. The yield stress and effective viscosity exhibit a power‐law with μ and an exponential relationship with Dc, revealing the interlock between fine and coarse grains. Then, a modified HB model was proposed using the GSD parameters to specify the granular effects and explain the velocity fluctuation of debris flow surges. This work represents the first attempt to express rheological properties as a function of the unified GSD parameters and is potentially instrumental in formulating debris flow dynamics incorporating granular effects.