Segregation Mechanism Research Articles

Smoothed particle hydrodynamics modelling of particle-size segregation in granular flows

In this work, smoothed particle hydrodynamics (SPH) is employed to investigate the segregation evolution in granular flows. We first provide the Lagrangian description-based governing equations, including the linear momentum conservation and the segregation–diffusion equation. Then the hybrid continuum surface reaction scheme is introduced to formulate the concentration-related inhomogeneous Neumann boundary condition on the free and wall surfaces. We follow a two-stage strategy to advance boundary particle searching and normal direction identification. Moreover, $C^1$ consistency is considered based on the Taylor series to obtain accurate segregation flux gradient along the boundary. Our SPH model is validated with a shear box experiment. The model is then applied to investigate the segregation mechanism in bidisperse-sized granular flows in a rotating drum.

Growth behavior and mechanism of atomic layer deposition of Ru for replacing Cu-interconnects

The growth behavior and nucleation mechanism of Ru films on various substrates using Ru(EtCp)2 as the precursor and O2 as the reactant were studied systematically. The results show that the Ru films grow rapidly on TiN substrates with almost no incubation time. Different of the segregation and combustion mechanism reported in the previous literature, we established the adsorption and combustion mechanism of ALD-Ru on TiN substrates. SEM and XPS confirmed that the grown Ru films were polycrystalline (average grain size of 16.53 nm, negligible impurities). The Ru films annealed at 600 °C showed significantly low resistivity of 9.73 μΩ•cm, which is one of the lowest resistivities reported in the literature so far. Suppressing electron scattering at grain boundaries is crucial factor to preparing Ru films with low resistivity. The work uses a simple plasma-free technique to construct high-quality Ru films with extremely low resistivity and low impurities, making them one of the ideal candidates for replacing Cu in future ultrafine-pitch interconnects. Furthermore, the work is significant for understanding the growth behaviors and nucleation mechanisms of Ru films on different substrates.

Hydrophobicity as the key to understanding the nanostructural behavior of eutectic mixtures upon apolar cosolvent addition

The influence of the addition of the apolar n-hexane (HEX) cosolvent on the structural arrangement of eutectic mixtures with different degrees of hydrophobicity, namely butylated hydroxytoluene (BHT), L-menthol (MEN), thymol (TYM), and choline chloride (ChCl), has been studied with a combined approach using small- and wide-angle X-ray scattering and molecular dynamics simulations. The cosolvent introduction has a similar impact on the molecular scale-length aggregation in BHT:MEN:HEX, TYM:MEN:HEX, and ChCl:TYM:HEX mixtures at different 1:3:H, 1:2:H, and 1:7:H molar ratios, specifically a dramatic perturbation of the main interactions present in the pure eutectics where hydrogen-bonds dominate. On larger scale-lengths, HEX addition results in a homogeneous electron-density distribution in the BHT:MEN:HEX and TYM:MEN:HEX mixtures due to a high affinity of the cosolvent for the BHT, MEN, and TYM components. Conversely, the presence of the more hydrophilic ChCl compound in the ChCl:TYM 1:7 system is the driving force for the segregation mechanism of this component which causes the formation of nano-scale inhomogeneities at high HEX concentrations, before macroscopic phase separation. The different degree of hydrophobicity is therefore key to understanding the nanostructural behavior of these eutectics in the presence of an apolar cosolvent. These findings have important implications for the employment of deep eutectic solvent mixtures, as the formation of pseudo-phase aggregates can help explaining the macroscopic behavior of these alternative media in applications like extraction procedures.

Mechanism of phase segregation in ilmenite oxygen carriers for chemical-looping combustion

The solid particle of oxygen carrier (OC) plays a vital role in chemical looping combustion (CLC) for fossil fuel combustion and inherent carbon capture. Phase segregation or active metal surface layer formation upon redox cycle had been recently noticed to be a predominant factor causing complete failure of OCs. To explored and identified the mechanism behind rapid phase segregation and external iron-rich shell formation of ilmenite OCs during CLC process, this study investigated into OCs’ phase and element distributions, and surface layer morphologies at various redox cycles, and the cross-sectional microstructures of oxidizing OC particles with different exposure times. The detailed information on the exterior Fe-rich shell formation and the progression of phase segregation were visualized, which provided vital information for the new mechanism of rapid Fe phase migration. The new finding ruled out Kirkendall effects or the ionic diffusion mechanism. The immediate formation of surface layer was found to initiate the segregation of Fe2O3 form TiO2 phase. The rapid Fe phase migration was attributed to the driving force arising from the increased local pressure of particles and the violent exothermic oxidation on reaction front. The strong driving force could directly eject iron-containing phases from the reaction front to surface layer. In the new mechanism, different phases separated inside the reduced OC particles provided the vital intermediates for the starting points of deep phase segregation or rapid surface layer formation; O2 dissociation of on the metallic Fe outmost layer and the oxygen ion conduction in TiO2 phase seemed to provide a short-circuit diffusion pathway for particle oxidation. Finally, this study also explored the strategies that might succeed in improving the integrity of ilmenite OC particles.

Exploring mechanisms of spatial segregation between body size groups within fish populations under environmental change

Ample evidence has indicated shifts in distribution of fish populations in response to environmental stress. However, most studies focused at the whole population scale. This neglects the spatial dynamics between groups of different body size (body size groups), that fundamentally shapes the spatial structure of a population. Here, we explored the mechanisms that modulate spatial dynamics of body size groups, and applied our analyses to three North Sea fish populations which experienced severe declines in biomass from 1977 to 2019: Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangius. All three populations exhibited strong declines in the overlapped area between body size groups in winter over 43 years, yet their mechanisms differed. These declines were either due to 1) different magnitudes of contraction of the distribution area of body size groups; and/or 2) different speeds and directions of spatial shift among various body size groups, both increasing spatial segregation within populations. These patterns were either associated with ocean warming, and/or declining population biomass, and such associations often varied according to distinct body size groups. Increasing spatial segregation between size groups of a population likely hampers life‐cycle connectivity and stability to local perturbations. Our analytical approach provides a powerful tool for identifying vulnerable populations under environmental stress and can be generalized to study a variety of size/age structured populations at various ecosystem types.

Numerical and Experimental Study on Carbon Segregation in Shaped Billet of Medium Carbon Steel with Combined Electromagnetic Stirring

Carbon segregation is the major and classical internal defect in the continuous casting process of carbon steel. Based on the combined electromagnetic stirring equipment for new billet in a steel plant, China, the influence of combined electromagnetic stirring (M-EMS + F-EMS) on the carbon segregation of 300 mm × 340 mm special-shaped billet was studied via numerical simulation and on-site industrialization tests. The Lorentz force and carbon solute distribution were simulated under different EMS parameters. The formation mechanism of the carbon segregation of medium carbon steel with different combined electromagnetic stirring processes was analyzed. The results show that: (1) with the combined action of “solute flushing” effect and gravity, the carbon concentration in the loose side of the medium carbon steel casting billet is gradually lower than the fixed side, while the carbon concentration on the fixed side gradually accumulates more; and (2) under the action of combined electromagnetic stirring, the segregation index of casting billet could be controlled to remain between 0.96–1.05 and shows an increasing change in solidification from the skin to the center. When the current and frequency of M-EMS are 250 A and 2.0 Hz and the F-EMS are 180 A and 8.0 Hz, the carbon segregation defects in the special-shaped (300 mm × 340 mm) casting billet can be significantly improved.

Phase-field study of the solutes-interstitial loops interaction in Fe–Cr alloys

Interstitial dislocation loops are typically formed in post-irradiated materials, such as Ferritic-Martensitic Fe–Cr alloys. These loops demonstrate solute segregation along their perimeters, effectively pinning the dislocation climb and resulting in high-density, small-sized loops that cause embrittlement. Phase-field simulations were conducted to investigate the behavior of Cr segregation in the stress field of a<100> type and various a/2<111> type interstitial dislocation loops in post-irradiated Fe–10Cr alloy. The study considers the long-range elastic interaction of solute Cr within the stress field of dislocation loops in a cubic elastic anisotropic material. The findings reveal a nonuniform stress distribution along the loop's perimeter depending on the included angle of habit plane normal n and Burgers vector b; the nonuniformity becomes more pronounced as the Burgers vector deviates from the normal direction. Furthermore, this nonuniform stress induces Cr segregation within regions experiencing tensile stress and Cr depletion in compression stress regions. Furthermore, a comprehensive analytical solution has been developed to characterize the diverse stress fields and solute segregation induced by interstitial dislocation loops with varying habit planes and Burgers vectors. The proposed analytical model effectively depicts the stress distribution of various dislocation loops, resulting in a Cr segregation profile that closely approximates those obtained through phase-field simulations. A thorough analysis of solute segregation mechanisms also elucidates the dispersed fine-scale nature and high density observed in experimental investigations of dislocation loops.

Impact of heat-set and cold-set gelling polysaccharides on potato protein gelation: Gellan gum, agar, and methylcellulose

The plant-based meat market is growing due to concerns about the sustainability of the modern food system. Plant-based meats are often constructed from blends of food biopolymers, such as plant proteins and polysaccharides. This study characterizes the thermal setting properties of potato protein (10%) and polysaccharide (2 wt%) mixtures containing polysaccharides with different reversible gelling behaviors: agar (cold set); gellan gum (cold set); or methyl cellulose (heat set). Each sample was heated above the thermal denaturation temperature of the potato proteins to promote protein unfolding, aggregation, and network formation. The addition of the polysaccharides tended to increase the complex shear modulus of the biopolymer blends before heating but increase or decrease it after heating depending on polysaccharide type. The shear modulus and hardness of the gels formed after heating tended to increase after addition of the cold-set polysaccharides but decrease after the addition of the heat-set polysaccharides, especially at refrigerator temperatures. Differential scanning calorimetry data showed that the potato proteins underwent irreversible denaturation after heating for all samples. Zeta-potential analysis showed that the potato proteins and all polysaccharides were negatively charged under the pH conditions used. There was greater water loss during heating for the composite gels containing methyl cellulose, which may have been due to its increase hydrophobicity at high temperatures. Appearance and microstructure analysis showed that phase-separation occurred after mixing the polysaccharides with the potato proteins, which was attributed to a segregation mechanism. The knowledge obtained from this study may help the food industry to optimize protein-polysaccharide blends to create gels with characteristics and structures that can mimic different plant-based meat products.

Mechanism of elemental segregation around extended defects in high-entropy alloys and its effect on mechanical properties

Elemental segregation around extended defects is common in high-entropy alloys (HEAs) composed of multi-principal elements, which profoundly impacts their mechanical properties. In HEAs, the driving force for segregation usually competes with chemical short-range ordering (CSRO) formation, making it challenging to elucidate the segregation mechanisms. In this study, we systematically investigate the chemical composition changes around extended defects, including dislocations, stacking faults, and grain boundaries (GBs) in CoNiCrFe HEAs, to explore the chemical-structure-mechanical relationship utilizing hybrid Monte Carlo and molecular dynamic (MC/MD) simulations and theoretical analysis. We find a pronounced Cr enrichment and Co/Ni/Fe depletion around all defects considered in this work. A correlation between the degree of structural disorder and the chemical segregation/depletion phenomenon in the proximity of extended defects has been uncovered. Our results show that due to the extreme chemical complexity in HEAs, CSRO inevitably contributes to the elemental rearrangement and affects segregation. Consequently, the segregation behavior in HEAs is mainly controlled by interactions between different atomic pairs, and the segregation entropy also plays a dominant role. By decoupling the strengthening contribution from elemental segregation and CSRO, we demonstrate and highlight that the strengthening in HEAs can be modulated by elemental segregation. The positive impact of element segregation on interfacial properties - improved ultimate tensile strength and elongation, has been evidenced through experimental comparisons of CoNiCrFe with different Fe additions. This work elucidates the mechanism of heterogenous elemental distributions in HEAs where elemental segregation and CSRO coexist, paving the way for manipulating their mechanical properties by modulating the compositional variations.

Exploring the influence of cosegregation on mechanical properties of Mg [formula omitted] twin boundaries: A first-principles investigation

This study employs first-principles calculations to investigate the impact of solute segregation on the mechanical properties of the Mg twin boundary (TB). The investigation delves into single-element segregation and multielement cosegregation at the Mg{101¯1} twin boundary. Several parameters, including segregation energy, solubility energy, and strengthening/embrittlement energy, are determined, and Voronoi volume and electronic structure evolution are analyzed. The study discloses the effects of 21 solute single-segregation, as well as the segregation mechanism of Ca, Y, and Zn solute elements in paired combinations. A comparative assessment of the optimal combination for cosegregation of Ca/Y atoms with larger atomic radii and Zn atoms with smaller atomic radii reveals that the solute elements Ca and Y induce more robust energy changes at the interface segregation than Zn. Additionally, electronic structure analysis suggests that charge transfer between solute atoms with large atomic radii and solute atoms with small atomic radii can strengthen the chemical bond at the twin boundary, thereby enhancing the maximum tensile degree, ductility, and formability of the material. The outcomes of this investigation have significant theoretical implications for composition design and the development of novel high-performance multielement magnesium alloys.

Computational modeling of grain boundary segregation: A review

Nearly all metals, alloys, ceramics, and their associated composites are polycrystalline in nature, with grain boundaries that separate well-defined crystalline regions that influence materials properties. In all but the most pure elemental systems, intentional solutes or impurities are present and can segregate to, or less commonly away from, the grain boundaries, in turn influencing boundary behavior, their stability, and associated materials properties. In some cases, grain-boundary segregation can also trigger “phase-like” structural transitions that dramatically alter the essential nature of the boundary. With the development of advanced electron microscopy techniques, researchers can directly observe grain-boundary structures and segregation with atomic precision. Despite such spatial resolution, the underlying mechanisms governing grain-boundary segregation remain difficult to characterize. As a result, computational modeling techniques such as density functional theory, molecular dynamics, mesoscale phase-field, continuum defect theory, and others are important complementary tools to experimental observations for studying grain-boundary segregation behavior. These computational methods offer the ability to explore the underlying formation mechanisms of grain-boundary segregation, elucidate complex segregation behavior, and provide insights into solutions to effectively controlling microstructure.

The morphology features, formation mechanism and elimination of channel segregation in industrial-scale Ti–Nb ingots produced by vacuum arc remelting

In this study, the morphology characteristics and formation mechanism of channel segregation in the industrial-sized Ti–Nb binary ingots produced by vacuum arc remelting (VAR) are researched based on experiments and calculations. The results show that the channel segregation is usually located at the 1/4–3/4 radius of the ingot and the morphology is closely related to the VAR process. The Ti-enriched channel segregation stripes tend to parallel to the ingot centerline and columnar dendrites in steady-state remelting region and hot-top region, respectively, while along the molten pool profile in residual molten pool region. For the first time, the Ti2O3 particles precipitated in the channel segregation were observed, following the orientation relationship of <001>β//<133>Ti2O3 and {11‾0}β//{011‾}Ti2O3 with β matrix in coherent boundary. First-principles calculations evident that the enrichment of Ti-solute tends to decrease the formation enthalpy, and hence makes for the precipitation of Ti2O3 particles. The numerical simulation and the experiment results manifest that the channel segregation originates from the convergence of interdendritic Ti-enriched liquid, resulting in the density inversion between the Ti-enriched initiation site and the surrounding liquid. The density gradient and the solidification rate dominate the growth direction and the radius distribution of the channel segregation. Based on the above, an optimized technique with helium cooling and the external stirring magnetic field was conducted and the channel segregation was eliminated successfully.

Indirect squeeze casting of ZM5 baffle with linear segregation and its formation mechanism

Macro-segregation in squeeze casting leads to inhomogeneous compositional distribution and degradation of mechanical properties. The distribution and formation mechanism of segregation in squeeze casting baffle were investigated by combining simulation software and experiments. The results showed that the segregation in the baffle was mainly distributed in the abrupt transition region of wall thickness. The evolution of segregation was simulated by the phase-field method to study the formation mechanism of segregation. During the solidification of the casting, pressure is applied to force the metal fluid to convect and complement the shrinkage, and the high solute content metal fluid meets in the wall thickness transition region. Highly brittle precipitated phases with overly dense distribution of segregation areas are easy to cracking during the load loading process, which leads to simultaneous cracking of the matrix through the extension of cracks into the matrix by means of load transfer. The T6 (410 °C × 20h + 200 °C × 8h) heat treatment process can reduce the segregation by dissolving the agglomerated island eutectic tissues into the matrix and then aging them uniformly with granular precipitation. The tensile strength of the castings after T6 treatment increased from 172 MPa (141 MPa at the segregation position) to 245 MPa, and the elongation was 3.3 %.

Study on screening process and segregation mechanism of wet sand and gravel particles based on discrete element method

Study on screening process and segregation mechanism of wet sand and gravel particles based on discrete element method

Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds.

Ecological theory predicts that closely-related species must occupy different niches to coexist. How marine top predators achieve this during breeding, when they often gather in large multi-species colonies and are constrained to central-place foraging, has been mostly studied in productive temperate and polar oceans with abundant resources, but less so in poorer, tropical waters. Here, we track the foraging movements of two closely-related sympatric seabirds-the white-tailed and red-tailed tropicbirds Phaethon lepturus and P. rubricauda-breeding on Aldabra Atoll, Seychelles, to investigate potential mechanisms of niche segregation and shed light on their contrasting population trends. Combining data from GPS, immersion, depth and accelerometry loggers, we show that the two species have similar behaviour at sea, but are completely segregated spatially, with red-tailed tropicbirds flying further to feed and using different feeding areas than white-tailed tropicbirds. Using nest-based camera traps, we show that low breeding success of both species-which likely drives observed population declines-is caused by high nest predation. However, the two species are targeted by different predators, with native avian predators mainly targeting red-tailed tropicbird nests, and invasive rats raiding white-tailed tropicbird nests when they leave their eggs unattended. Our findings provide new insight into the foraging ecology of tropicbirds and have important conservation implications. The extensive range and spatial segregation highlight the importance of considering large-scale protection of waters around tropical seabird colonies, while the high level of nest predation provides evidence in support of rat eradication and investigating potential nest protection from native avian predators.

Formation of Iodide-Rich Domains During Halide Segregation in Lead-Halide Perovskite Nanocrystals.

Mixed iodide-bromide methylammonium lead perovskite (MAPbIxBr3-x) nanocrystals (NCs) hold promise for use in light-emitting applications owing to the size- and composition-tunability of their bandgap. However, the segregation of halides during light exposure causes their band gaps to become unstable and narrow. Here, we use transient absorption spectroscopy to track excited-state dynamics during photoinduced halide segregation. The Auger recombination dynamics are observed to accelerate as the bandgap narrows, suggesting enhanced electron-hole overlap. We simulate the motion of iodide within the NC and estimate the evolving bandgap and electron-hole overlap during two possible mechanisms of halide segregation. Our results support a segregation mechanism in which iodide anions form a domain within the NC, rather than a mechanism in which iodide anions independently segregate toward the NC surface. Such mechanistic insight will contribute to future NC bandgap stabilization strategies.

The REE-Zr-U-Th Minerals of the Maronia Monzodiorite, N. Greece: Implications on the Saturation and Segregation Mechanisms of Critical Metals in Intermediate–Mafic Compositions

This work delves into the presence of REE-Ti-Zr-U-Th minerals, in the mafic–intermediate rocks of the Maronia pluton, Greece, an Oligocene intrusion formed through arc-magmatism during subduction. In Maronia monzodiorite, critical metals are contained in three principal mineral groups, namely, the REE-Ti-Zr, REE-Ca-P, and U-Th assemblages. The REE-Ti-Zr group includes REE-ilmenite, chevkinite-like phases, zirconolite, and baddeleyite. The REE-Ca-P assemblage is represented by allanite-(Ce), monazite-(Ce), and huttonitic monazite-(Ce). The U-Th assemblage comprises thorite–coffinite and uraninite–thorianite solid solutions. The paragenetic sequencing of these minerals offers insights into their formation conditions and correlation with the pluton’s magmatic evolution. In the REE-Ti-Zr group, mineral formation progresses from REE-ilmenite to baddeleyite through chevkinite-like phases and zirconolite under oxidizing conditions. The REE-Ca-P sequence involves allanite-(Ce), followed by monazite-(Ce), late allanite-(Ce), and huttonitic monazite-(Ce). In the U-Th group, earlier thorite–coffinite phases are succeeded by uraninite–thorianite solid solutions, indicating Si-undersaturation at late magmatic stages. Fluctuations in Ca-activity induce alternating formations of allanite-(Ce) and monazite-(Ce). These mineral variations are attributed to early-stage interactions between high-K calc-alkaline and shoshonitic gabbroic melts, influencing critical metal enrichment and mineral speciation. The study’s insights into paragenesis and geological processes offer implications for mineral exploration in analogous geological settings.

The good, the bad and the tenant: Rental platforms renewing racial capitalism in the post-apartheid housing market

This article examines how racial capitalism intersects with platform capitalism through the rise of rental platforms and corporate landlords in the post-apartheid housing market. Combining 18 months of fieldwork in Cape Town with the spatial analysis of sales and longitudinal census data, I demonstrate how rental platforms enabled the consolidation of the private rental sector and the emergence of corporate landlords through the classification of tenants centered upon credit scoring. To automate tenant screening solutions, rental platforms leveraged and extended the information dragnet knitted by credit bureaus. This dragnet of unprecedented depth and volume is built upon the infrastructures and devices that enabled the for-profit, racial classification of people, housing and neighborhoods during colonialism and apartheid, notably ID numbers. In the context of racialized indebtedness and housing inequalities engineered by racial property regimes, the use of platforms to sort the “good” from the “bad” tenant and manage rental portfolios shifts mechanisms of segregation and reproduces racialized patterns of capital accumulation across the post-apartheid city. The article argues that rental platforms extend the extractive logic of racial capitalism through two joint rentier mechanisms: the transformation of rental housing into a new asset class; the extraction and assetization of rental data.

Plasmodium ARK2 and EB1 drive unconventional spindle dynamics, during chromosome segregation in sexual transmission stages

The Aurora family of kinases orchestrates chromosome segregation and cytokinesis during cell division, with precise spatiotemporal regulation of its catalytic activities by distinct protein scaffolds. Plasmodium spp., the causative agents of malaria, are unicellular eukaryotes with three unique and highly divergent aurora-related kinases (ARK1-3) that are essential for asexual cellular proliferation but lack most canonical scaffolds/activators. Here we investigate the role of ARK2 during sexual proliferation of the rodent malaria Plasmodium berghei, using a combination of super-resolution microscopy, mass spectrometry, and live-cell fluorescence imaging. We find that ARK2 is primarily located at spindle microtubules in the vicinity of kinetochores during both mitosis and meiosis. Interactomic and co-localisation studies reveal several putative ARK2-associated interactors including the microtubule-interacting protein EB1, together with MISFIT and Myosin-K, but no conserved eukaryotic scaffold proteins. Gene function studies indicate that ARK2 and EB1 are complementary in driving endomitotic division and thereby parasite transmission through the mosquito. This discovery underlines the flexibility of molecular networks to rewire and drive unconventional mechanisms of chromosome segregation in the malaria parasite.

Determining the mechanism for biomass segregation between granules and flocs in anammox granular system from the prospective of EPS

Granules and flocs have been widely found co-existing in anammox granular systems, but the segregation mechanism of granules and flocs is still largely unknown. Here, the chemical composition, physical properties, spectral characteristics, and adherence properties of extracellular polymeric substances (EPS) extracted from anammox granules (Granule-EPS) and flocs (Floc-EPS), which were closely related to sludge aggregation, were tested and compared. Granule-EPS exhibited more complex texture with larger biomolecule size and higher molecular weight than Floc-EPS. Moreover, Floc-EPS showed weaker co-aggregation ability, which might be due to its lower proteins/polysaccharides ratio, more compact protein secondary structure, stronger hydrophilicity, and lower intermolecular hydrogen bond proportion, than Granule-EPS. Besides, due to the looser connection between Floc-EPS biomolecules compared to Granule-EPS biomolecules, the structure of adhered Floc-EPS layer was looser than that of the adhered Granule-EPS, which was in accordance with the lower sludge intensity of anammox flocs compared to granules (595.2 ± 36.8 Pa vs. 315.3 ± 13.8 Pa; p = 0.001). More importantly, during the process of anammox flocs aggregation, a portion of EPS formed structure EPS that was difficult to extract, to maintain a tight structure of the granules. We therefore assumed that biomass segregation between anammox granules and flocs was due to the difference in the tightness of the adhered layer structure they formed. Overall, the results improve our understanding of anammox granular system, especially for the segregation phenomenon between granules and flocs.