Aggregation Properties Research Articles

Self-Assembly of Super-Uniform Covalent Organic Framework Colloidal Particles into Multi-Dimensional Ordered Superstructures.

Precise self-assembly of colloidal particles is crucial for understanding their aggregation properties and preparing macroscopic functional devices. It is currently very challenging to synthesize and self-assemble super-uniform covalent organic framework (COF) colloidal particles into well-organized multidimensional superstructures. Here, simple and versatile strategies are proposed for synthesis of super-uniform COF colloidal particles and self-assembly of them into 1D supraparticles, 2D ordered mono/multilayers, and 3DCOF films. For this purpose, several self-assembly techniques are developed, including emulsion solvent evaporation, air-liquid interfacial self-assembly, and drop-casting. These strategies enable the superstructural self-assembly of particles of varying sizes and species without any additional surfactants or chemical modifications. The assembled superstructures maintain the porosity and high specific surface area of their building blocks. The feasibility of the strategies is examined with different types of COFs. This research provides a new approach for the controllable synthesis of super-uniform COF colloidal particles capable of self-assembling into multidimensional superstructures with long-range order. These discoveries hold great promise for the design of emerging multifunctional COF superstructures.

Tubulin-binding region alters tau-lipid interactions and changes toxicity of tau fibrils formed in the presence of phosphatidylserine lipids.

Alzheimer's disease is the fastest-growing neurodegenerative disease that affects over six million Americans. The abnormal aggregation of amyloid β peptide and Tau protein is the expected molecular cause of the loss of neurons in brains of AD patients. A growing body of evidence indicates that lipids can alter the aggregation rate of amyloid β peptide and modify the toxicity of amyloid β aggregates. However, the role of lipids in Tau aggregation remains unclear. In this study, we utilized a set of biophysical methods to determine the extent to which phospatidylserine (PS) altered the aggregation properties of Tau isoforms with one (1N4R) and two (2N4R) N terminal inserts that enhance the binding of Tau to tubulin. We found that the length and saturation of fatty acids (FAs) in PS altered the aggregation rate of 2N4R isoform, while no changes in the aggregation rate of 1N4R were observed. These results indicate that N terminal inserts play an important role in protein-lipid interactions. We also found that PS could change the toxicity of 1N4R and 2N4R Tau fibrils, as well as alter molecular mechanisms by which these aggregates exert cytotoxicity to neurons. Finally, we found that although Tau fibrils formed in the presence and absence of PS endocytosed by cells, only fibril species that were formed in the presence of PS exert strong impairment of the cell mitochondria.

DNA Framework-Guided Self-Limiting Aggregation for Highly Luminescent Metal Cluster Nanoaggregates.

The photoluminescent properties of atomically precise metal nanoclusters (MCs) have garnered significant attention in the fields of chemical sensing and biological imaging. However, the limited brightness of single-component nanoclusters hinders their practical applications, and the conventional ligand engineering approaches have proven insufficient in enhancing the emission efficiency of MCs. Here, we present a DNA framework-guided strategy to prepare highly luminescent metal cluster nanoaggregates. Our approach involves an amphiphilic DNA framework comprising a hydrophobic alkyl core and a rigid DNA framework shell, serving as a nucleation site and providing well-defined nanoconfinements for the self-limiting aggregation of MCs. Through this method, we successfully produced homogeneous MC nanoaggregates (10.1 ± 1.2 nm) with remarkable nanoscale precision. Notably, this strategy proves adaptable to various MCs, leading to a substantial enhancement in emission and quantum yield, up to 3011- and 87-fold, respectively. Furthermore, our investigation using total internal reflection fluorescence microscopy at the single-particle level uncovered a more uniform photon number distribution and higher photostability for MC nanoaggregates compared to template-free counterparts. This DNA-templating strategy introduces a conceptually innovative approach for studying the photoluminescent properties of aggregates with nanoscale precision and holds promise for constructing highly luminescent MC nanoparticles for diverse applications.

The delayed kinetics of Myddosome formation explains why amyloid-beta aggregates trigger Toll-like receptor 4 less efficiently than lipopolysaccharide

The Myddosome is a key innate immune signalling platform. It forms at the cell surface and contains MyD88 and IRAK proteins which ultimately coordinate the production of pro-inflammatory cytokines. Toll-like receptor 4 (TLR4) signals via the Myddosome when triggered by lipopolysaccharide (LPS) or amyloid-beta (Aβ) aggregates but the magnitude and time duration of the response are very different for reasons that are unclear. Here, we followed the formation of Myddosomes in live macrophages using local delivery of TLR4 agonist to the cell surface and visualisation with 3D rapid light sheet imaging. This was complemented by super-resolution imaging of Myddosomes in fixed macrophages to determine the size of the signalling complex at different times after triggering. Myddosomes formed more rapidly after LPS than in response to sonicated Aβ 1–42 fibrils (80 vs 372 s). The mean lifetimes of the Myddosomes were also shorter when triggered by LPS compared to sonicated Aβ fibrils (170 and 220 s), respectively. In both cases, a range of Myddosome of different sizes (50–500 nm) were formed. In particular, small round Myddosomes around 100 nm in size formed at early time points, then reduced in proportion over time. Collectively, our data suggest that compared to LPS the multivalency of Aβ fibrils leads to the formation of larger Myddosomes which form more slowly and, due to their size, take longer to disassemble. This explains why sonicated Aβ fibrils results in less efficient triggering of TLR4 signalling and may be a general property of protein aggregates.

The investigation on targeted micro-surface treatment methods for waste tires recycling in cementitious construction materials

Defects in the interfacial transition zone (ITZ) between recycled tire rubber and cement matrix obstacle to the large-scale application of sustainable rubberized cementitious materials. This paper proposed and evaluated different targeted treatment methods for micro-surface properties enhancement of rubber aggregate by the Polyvinyl Alcohol (PVA), Polyethylene Glycol-200 (PEG), and Hydroxypropyl methylcellulose (HY) polymer solutions through copolymerization and drafting processes. The optimum modification condition was determined through the FT-IR analysis, contact angle, and surface free energy of treated rubber aggregates and the micro-surface morphology and element distribution were analyzed by using ESEM and EDX, respectively. The flexural strength and pore size distribution of steel fiber-reinforced rubberized mortar with relatively high replacing volumes (20%, 40%, and 60%) were evaluated to validate the targeted micro-surface modification efficiency. The surface microstructure and hydrophilic properties of rubber aggregate were significantly improved and the mechanism for enhancing the interface adhesion between rubber and cement matrix was revealed.

The delayed kinetics of Myddosome formation explains why amyloid-beta aggregates trigger Toll-like receptor 4 less efficiently than lipopolysaccharide.

The Myddosome is a key innate immune signalling platform. It forms at the cell surface and contains MyD88 and IRAK proteins which ultimately coordinate the production of pro-inflammatory cytokines. Toll-like receptor 4 (TLR4) signals via the Myddosome when triggered by lipopolysaccharide (LPS) or amyloid-beta (Aβ) aggregates but the magnitude and time duration of the response are very different for reasons that are unclear. Here, we followed the formation of Myddosomes in live macrophages using local delivery of TLR4 agonist to the cell surface and visualisation with 3D rapid light sheet imaging. This was complemented by super-resolution imaging of Myddosomes in fixed macrophages to determine the size of the signalling complex at different times after triggering. Myddosomes formed more rapidly after LPS than in response to sonicated Aβ 1-42 fibrils (80 vs 372 s). The mean lifetimes of the Myddosomes were also shorter when triggered by LPS compared to sonicated Aβ fibrils (170 and 220 s), respectively. In both cases, a range of Myddosome of different sizes (50-500 nm) were formed. In particular, small round Myddosomes around 100 nm in size formed at early time points, then reduced in proportion over time. Collectively, our data suggest that compared to LPS the multivalency of Aβ fibrils leads to the formation of larger Myddosomes which form more slowly and, due to their size, take longer to disassemble. This explains why sonicated Aβ fibrils results in less efficient triggering of TLR4 signalling and may be a general property of protein aggregates.

Response surface methodology mediated optimization of phytosulfokine and plant growth regulators for enhanced protoplast division, callus induction, and somatic embryogenesis in Angelica Gigas Nakai

BackgroundAngelica Gigas (Purple parsnip) is an important medicinal plant that is cultivated and utilized in Korea, Japan, and China. It contains bioactive substances especially coumarins with anti-inflammatory, anti-platelet aggregation, anti-cancer, anti-diabetic, antimicrobial, anti-obesity, anti-oxidant, immunomodulatory, and neuroprotective properties. This medicinal crop can be genetically improved, and the metabolites can be obtained by embryonic stem cells. In this context, we established the protoplast-to-plant regeneration methodology in Angelica gigas.ResultsIn the present investigation, we isolated the protoplast from the embryogenic callus by applying methods that we have developed earlier and established protoplast cultures using Murashige and Skoog (MS) liquid medium and by embedding the protoplast in thin alginate layer (TAL) methods. We supplemented the culture medium with growth regulators namely 2,4-dichlorophenoxyaceticacid (2,4-D, 0, 0.75, 1.5 mg L− 1), kinetin (KN, 0, 0.5, and 1.0 mg L− 1) and phytosulfokine (PSK, 0, 50, 100 nM) to induce protoplast division, microcolony formation, and embryogenic callus regeneration. We applied central composite design (CCD) and response surface methodology (RSM) for the optimization of 2,4-D, KN, and PSK levels during protoplast division, micro-callus formation, and induction of embryogenic callus stages. The results revealed that 0.04 mg L− 1 2,4-D + 0.5 mg L− 1 KN + 2 nM PSK, 0.5 mg L− 1 2,4-D + 0.9 mg L− 1 KN and 90 nM PSK, and 1.5 mg L− 1 2,4-D and 1 mg L− 1 KN were optimum for protoplast division, micro-callus formation and induction embryogenic callus. MS basal semi-solid medium without growth regulators was good for the development of embryos and plant regeneration.ConclusionsThis study demonstrated successful protoplast culture, protoplast division, micro-callus formation, induction embryogenic callus, somatic embryogenesis, and plant regeneration in A. gigas. The methodologies developed here are quite useful for the genetic improvement of this important medicinal plant.

Genome wide association mapping of end-use gluten properties in bread wheat landraces (Triticum aestivum L.)

Numerous studies have aimed to dissect the genetic basis of wheat end-use quality, yet the consideration of gluten aggregation properties in this context has been limited despite its important role in determining the processing quality. This study has addressed the evaluation of the end-use quality of a collection of 189 Spanish bread wheat (Triticum aestivum L.) landraces. For phenotyping, we utilized the GlutoPeak methodology to assess gluten aggregation traits, the SDS-sedimentation test to measure gluten strength and NIR for grain protein content. In addition to previous genotyping data with numerous DArT-seq markers distributed across the entire wheat genome, we developed ten KASP-based molecular markers designed for GLU-1 loci, which encode high molecular weight glutenins (HMW-GS). The reliability of these markers was thoroughly assessed. Our genome-wide association analysis (GWAS) focused on gluten properties and protein content, revealed 89 marker-trait-associated loci (MTAs). These loci were further grouped into 50 MTA-QTLs across various chromosomes based on linkage disequilibrium. While some MTA-QTLs overlapped with regions identified in other studies, others represented novel genomic regions. Inside these regions, we identified several candidate genes with gluten quality-related annotated functions or grain-specific expression patterns, which represent potential targets for marker development and future wheat end-use quality improvement.

Synergistic effects of GGBFS addition and oven drying on the physical and mechanical properties of fly ash-based geopolymer aggregates

Synergistic effects of GGBFS addition and oven drying on the physical and mechanical properties of fly ash-based geopolymer aggregates

Role of ultrasonic freezing­treated pork dumpling filling during frozen storage: Insights from protein oxidation, aggregation, and functional properties

The effects of air freezing (AF), immersion freezing (IF), and ultrasonic freezing (UF) on the oxidation, aggregation, and functional properties of myofibrillar protein (MP) in pork dumpling filling during frozen storage were investigated. The findings demonstrated that, compared to AF and IF treatments, UF treatment had higher total and reactive sulfhydryl content, solubility, and absolute zeta potential. Conversely, it exhibited lower values in carbonyl content, dityrosine content, turbidity, and particle size within the same storage time (p < 0.05). SDS-PAGE revealed that UF treatment delayed the oxidation and excessive aggregation of MP during frozen storage. Moreover, samples treated with UF at 180 days (d) displayed similar functional and qualitative characteristics to those treated with IF at 90 d or AF at 60 d, as per the hierarchical cluster analysis findings. In conclusion, UF effectively delayed the oxidation, aggregation, and loss of functional properties of MP in pork dumpling filling during frozen storage.

Preparation and properties of mullite ceramic-based porous aggregates with high closed porosity utilizing low-voltage electroceramics waste

Mullite ceramic-based porous aggregates, known for their high strength and closed porosity, are widely utilized in engineering. This study successfully prepared mullite-ceramic-based porous aggregates from low-voltage electroceramics waste, investigating the impact of pore-forming agents, bauxite chamotte, and sintering temperature on the physical properties and cold compressive strength. Finally, a mechanism of closed and open pores formation was proposed. The results show that when 10 wt% activated carbon was added, enhanced particle dispersion and stability in apparent porosity, bulk density, and diameter shrinkage ratio were observed, with an optimal range of activated carbon addition identified at around 10.0 wt%. Furthermore, increasing bauxite chamotte addition from 5.0 wt% to 15.0 wt% at 1000°C promoted mullite nucleation, facilitating mullite crystal formation and reducing the relative content and viscosity of the liquid phase. This led to increased apparent porosity, reduced closed porosity, and a decrease in average pore size. However, stress concentration around surface pores resulted in reduced cold compressive properties. The sintering temperature was then increased from 900°C to 1200°C using 10.0 wt% activated carbon and 15 wt% bauxite chamotte, leading to changes in crystallinity and porosity. At 1100°C, isolated islands of the liquid phase between grain boundaries resulted in the highest cold compressive strength and bulk density, while further heating to 1200°C led to a reduction in these properties due to excess liquid phase filling grain boundaries. The formation of closed and open pores is primarily influenced by changes in sintering temperature, which affect the quantity, viscosity, and flowability of the aluminum-silicon liquid phase.

Ultrasonic Pulse Velocity and Mechanical and Physical Properties of Structural Geopolymer Concrete Containing Lightweight Expanded Clay Aggregates: Experimental and Computational Study

Ultrasonic Pulse Velocity and Mechanical and Physical Properties of Structural Geopolymer Concrete Containing Lightweight Expanded Clay Aggregates: Experimental and Computational Study

A study on estimating deterioration in multi recycled aggregate concrete using surface imaging techniques

The study presents a novel method for sustainable construction using multi-recycled concrete, embracing a cradle-to-cradle approach. It utilies image analysis to detect concrete deterioration due to different chemical exposures. It also demonstrates the effectiveness of the Compressible Packing Method in improving recycled aggregate properties and reducing cement content for sustainable concrete production. The image-based colour stability analysis for determining Hue (H), Saturation (S), and Intensity (I) values reveals the significant deterioration is caused by sulphuric acid and hydrochloric acid exposures relevant to field applications. A unified factor termed as Durability Loss Factor (DLF) provides a comprehensive metric for assessing deterioration, with sulphuric acid exposure resulting in the most substantial deterioration. Also, there is a strong correlation between residual strength of concrete specimen and the parameters governing image analysis in the current study. These findings offer valuable insights into mix design strategies, colour-based indicators of deterioration, and the development of a comprehensive Durability Loss Factor for multi-recycled concrete.

Porphyrin Aggregation under Homogeneous Conditions Inhibits Electrocatalysis: A Case Study on CO2 Reduction.

Metalloporphyrins are widely used as homogeneous electrocatalysts for transformations relevant to clean energy and sustainable organic synthesis. Metalloporphyrins are well-known to aggregate due to π-π stacking, but surprisingly, the influence of aggregation on homogeneous electrocatalytic performance has not been investigated previously. Herein, we present three structurally related iron meso-phenylporphyrins whose aggregation properties are different in commonly used N,N-dimethylformamide (DMF) electrolyte. Both spectroscopy and light scattering provide evidence of extensive porphyrin aggregation under conventional electrocatalytic conditions. Using the electrocatalytic reduction of CO2 to CO as a test reaction, cyclic voltammetry reveals an inverse dependence of the kinetics on the catalyst concentration. The inhibition extends to bulk performance, where up to 75% of the catalyst at 1 mM is inactive compared to at 0.25 mM. We additionally report how aggregation is perturbed by organic additives, axial ligands, and redox state. Periodic boundary calculations provide additional insights into aggregate stability as a function of metalloporphyrin structure. Finally, we generalize the aggregation phenomenon by surveying metalloporphyrins with different metals and substituents. This study demonstrates that homogeneous metalloporphyrins can aggregate severely in well-solubilizing organic electrolytes, that aggregation can be easily modulated through experimental conditions, and that the extent of aggregation must be considered for accurate catalytic benchmarking.

Long-Term Organic Cultivation in Greenhouses Enhances Vegetable Yield and Soil Carbon Accumulation through the Promotion of Soil Aggregation

The long-term use of fertilizers and pesticides in conventional cultivation has resulted in a decrease in soil productivity and vegetable yields in greenhouses. However, there is little research exploring the changes in soil organic carbon and the microbial community mediated by soil aggregates, or their impacts on soil productivity. This study investigated the properties of soil aggregates, including the levels of organic carbon fractions, microbial community, and enzyme activity with the three aggregate classes: microaggregates (&lt;0.25 mm), small macroaggregates (2–0.25 mm) and large macroaggregates (&gt;2 mm) under conventional cultivation (CC), integrated cultivation (IC), and organic cultivation (OC) in greenhouses. The results showed that (1) OC and IC promoted the formation of small macroaggregates and enhanced aggregate stability compared to CC; (2) SOC in the three size fractions of OC increased by 92.06–98.99% compared to CC; EOC increased by 98.47–117.59%; POC increased by 138.59–208.70%; MBC increased by 104.71–230.61%; and DOC increased by 21.93–40.90%, respectively; (3) organic cultivation significantly increased enzyme activity in all three particle-size aggregates and increased the relative abundance of bacteria in microaggregates as well as the relative abundance of fungi in small macroaggregates. Structural equation model (SEM) analysis revealed that organic farming practices fostered the development of smaller macroaggregates, elevated microbial and enzyme activities within soil aggregates, and facilitated the conversion of soil nutrients and carbon sequestration. Therefore, long-term organic cultivation increases soil carbon content and vegetable yield in greenhouses by increasing the proportion of small aggregates. In conclusion, long-term organic cultivation in greenhouses improves soil structure, increase soil fertility and vegetable yield, and has a positive impact on the environment. Organic cultivation increases soil fertility and contributes to maintaining ecological balance and protecting the environment in greenhouses.

Elucidating the mechanisms of α-Synuclein-lipid interactions using site-directed mutagenesis

α-Synuclein (α-syn) is a small protein that is involved in cell vesicle trafficking in neuronal synapses. A progressive aggregation of this protein is the expected molecular cause of Parkinson's disease, a disease that affects millions of people around the world. A growing body of evidence indicates that phospholipids can strongly accelerate α-syn aggregation and alter the toxicity of α-syn oligomers and fibrils formed in the presence of lipid vesicles. This effect is attributed to the presence of high copies of lysines in the N-terminus of the protein. In this study, we performed site-directed mutagenesis and replaced one out of two lysines at each of the five sites located in the α-syn N-terminus. Using several biophysical and cellular approaches, we investigated the extent to which six negatively charged fatty acids (FAs) could alter the aggregation properties of K10A, K23A, K32A, K43A, and K58A α-syn. We found that FAs uniquely modified the aggregation properties of K43A, K58A, and WT α-syn, as well as changed morphology of amyloid fibrils formed by these mutants. At the same time, FAs failed to cause substantial changes in the aggregation rates of K10A, K23A, and K32A α-syn, as well as alter the morphology and toxicity of the corresponding amyloid fibrils. Based on these results, we can conclude that K10, K23, and K32 amino acid residues play a critical role in protein-lipid interactions since their replacement on non-polar alanines strongly suppressed α-syn-lipid interactions.

Effect of Curing Time and Variations in Na2SiO3: NaOH Ratio on the Mechanical Properties of Fly Ash-based Geopolymer Artificial Aggregates using the Crushing Method

Burning coal to produce electrical energy in PLTU produces waste in the form of fly ash. This waste must be managed properly so that it does not cause detrimental environmental effects. Fly ash has potential as a building material because it contains silica, aluminum, and other oxides that can react with alkaline solutions to form geopolymer compounds. Geopolymer has good mechanical properties and is resistant to acidic and alkaline environments. The development of the crushing method for aggregate materials, artificial geopolymers, and fly ash is an interesting work direction because it can utilize fly ash waste and reduce the dependence on aggregates. Moreover, this material can be used to help reduce the effects of development construction on the environment. The crushing method is utilized to obtain geopolymer artificial aggregate with the desired size. Aggregates can be destroyed to become small particles by using destruction techniques and mechanical crushing tools, such as hammer mills, jaw crushers, and ball mills. The aggregate impact value (AIV) percentage reaches 13.20% at a Na2SiO3/NaOH ratio of 2, but it decreases to 12.64% at a Na2SiO3/NaOH ratio of 3.5. The AIV percentage reaches 12.82% without the addition of sand, but it decreases to 12.64% when the added amount of sand is 20%. The AIV percentage increases to 12.76% when the added sand is 40%. Moreover, the AIV percentage reaches 12.64% after curing for 24 hours, decreases to 12.46% after 48 hours of curing, and increases to 12.94% after 72 hours of curing.

The Effect of Refined Separation on the Properties of Reclaimed Asphalt Pavement Materials

Refined separation not only controls the variability of reclaimed asphalt pavement (RAP), but also improves the mixing ratio of RAP and the quality of recycled asphalt mixtures. This study examines RAP treated with various refined separation frequency parameters, analyzes the variation rules and the variability of RAP aggregate gradation, asphalt content, asphalt properties, and aggregate properties, and calculates the maximum mixing percentage of coarse RAP material by using the gradation variability control method and the asphalt content variability control method. The results show that the variability of gradation and asphalt content of coarsely separated RAP is considerable, and a refined separation process significantly reduces the variability of gradation and asphalt content of RAP; the agglomeration of RAP decreases with an increase in the refined separation frequency; and the RAP agglomeration of three kinds of RAPs (E1, E2, and E3) under a refined separation frequency of 55 Hz reduces by 6.40%, 4.30%, and 4.30%, respectively, as compared with that of coarsely separated RAPs. The asphalt content of the refined separation RAP gradually decreases with an increase in frequency, and the asphalt content of E1 and E2 (55 Hz) was only 0.95% and 1.10%, respectively. The maximum percentage of RAP in recycled asphalt mixtures was calculated using the gradation variability control method and the asphalt content variability control method, respectively. The maximum proportions of RAP were 45% and 33% for A1 (0 Hz), respectively, and the maximum proportions of RAP for E1 (55 Hz) were all 100%. The results of the two methods show that the process of refined separation can increase the maximum proportion of blended RAP materials. They also demonstrate that the refined separation process can increase the maximum blending ratio of coarse RAP materials, thereby improving the quality of the RAP, increasing the proportion of RAP blending, and ensuring the quality of the recycled asphalt mixture. In conclusion, the refined separation process holds promise for maximizing the potential value of RAP and optimizing its recycling, environmental, and economic benefits.

Cyanobacteria-ferrihydrite aggregates, BIF sedimentation and implications for Archaean- Palaeoproterozoic seawater geochemistry

Abstract Precambrian banded iron formations (BIFs) are iron- and silica-rich (bio)chemical sediments that are widely believed to have been precipitated by microbial oxidation of dissolved Fe(II). The by-product of these metabolisms – insoluble ferric iron – would have settled through the water column, often as aggregates with the cell biomass. While the mineralogy, composition and physical properties of cell-iron mineral aggregates formed by anaerobic Fe(II)-oxidising photoferrotrophic bacteria have been extensively studied, there are limited studies that characterise cyanobacteria-iron mineral aggregates that formed during oxygenic photosynthesis. This gap in knowledge is important because it impacts sedimentation velocities and the Fe(III) to organic carbon (Corg) ratios in the marine sediment pile. Here, we used a recently introduced approach to precisely measure the sedimentation velocity of cyanobacteria-ferrihydrite aggregates and the Fe(III):Corg ratios of the cyanobacteria-ferrihydrite aggregates over a wide range of pH and initial Fe(II) concentrations under predicted Palaeoproterozoic atmospheric conditions. Our results indicate that it was highly unlikely BIFs formed at pH &amp;lt;7 via chemical oxidation due to the insufficient sedimentation velocity, even at the maximum predicted Fe(II) concentration of 1800 μM with excess oxygen. Instead, large Banded Iron Formation (BIF) deposits, such as those associated with the ca. 2.47 Ga Kuruman Formation in South Africa, would only had been deposited at minimum Fe(II) concentrations of 500 μM at pH 7 or 250 μM at pH 8. The Fe:Corg ratios in cyanobacteria-ferrihydrite sediments formed during initially anoxic Fe(II) oxidation experiments represent the maximum values under each condition because we specifically extracted samples after all Fe(II) was oxidised. The Fe(III) to organic carbon ratio was consistently below 4, which is also the ratio required for dissimilatory Fe(III) reduction (DIR). This result indicates that biomass in this case was in excess, which contradicts the low organic carbon content seen in most BIFs. Thus, we suggest that biomass was either physically separated from ferrihydrite aggregates during sedimentation under the influence of ocean currents and waves, or it was degraded prior to DIR. The mineralogical and geochemical evidences of both oxide and carbonate facies from the Kuruman Iron Formation (IF) suggest that ferrihydrite was most likely the precursor along with a significant initial organic carbon input, supporting the proposed cyanobacterially-mediated BIF depositional model and experimental results.

Evaluating the influence of volumetric properties on back-calculated asphalt layer moduli using falling weight deflectometer data

The back-calculation process performed in pavement systems is the numerical analysis of captured deflections to estimate layer stiffness parameters. Prediction of fatigue performance in terms of back-calculated asphalt layer moduli by using a Falling Weight Deflectometer (FWD) has specific challenges in terms of testing protocol, skillset, and complex back-calculation analysis. The performance of the asphalt layer is primarily governed by extrinsic parameters such as temperature, vehicular transient loading characteristics, moisture content, and intrinsic parameters such as binder properties and aggregate mix properties. The role of volumetric properties of asphalt mixes contributes significantly to the back-calculated asphalt layer moduli in terms of the overall life of the structure. The asphalt layer moduli value is dependent on the traditional volumetric properties of asphalt mixes such as air voids in the mix, voids in mineral aggregate, and the percentage of bitumen mix. In this study, a total of 60 in-service pavement sections are identified from three different categories of roads to perform FWD tests and collection of asphalt layer core samples. A detailed laboratory investigation has been carried out to estimate the volumetric properties of different core samples. This study uses field investigations to determine the degree of interdependency between the volumetric characteristics of asphalt mixtures and temperature on the back-calculated layer moduli. Furthermore, the findings from this study are utilized to establish several correlations at the aggregate level, demonstrating strong relationships with R2 values ranging from 0.84 to 0.875. The developed model is validated and depicted in good agreement with the actual values.