Fractal Dimension Of Aggregates Research Articles

New Insights into the Formation of Aggregates of Bidisperse Nano- and Microplastics in Water Based on the Analysis of In Situ Microscopy and Molecular Simulation.

Microplastics (MPs) and nanoplastics (NPs) in water pose a global threat to human health and the environment. To develop efficient removal strategies, it is crucial to understand how these particles behave as they aggregate. However, our knowledge of the process of aggregate formation from primary particles of different sizes is limited. In this study, we analyzed the growth kinetics and structures of aggregates formed by polystyrene MPs in mono- and bidisperse systems using in situ microscopy and image analysis. Our findings show that the scaling behavior of aggregate growth remains unaffected by the primary particle size distribution, but it does delay the onset of rapid aggregation. We also performed a structural analysis that reveals the power law dependence of aggregate fractal dimension (df) in both mono- and bidisperse systems, with mean df consistent with diffusion-limited cluster aggregation (DLCA) aggregates. Our results also suggest that the df of aggregates is insensitive to the shape anisotropy. We simulated molecular forces driving aggregation of polystyrene NPs of different sizes under high ionic strength conditions. These conditions represent salt concentration in ocean water and wastewater, where the DLVO theory does not apply. Our simulation results show that the aggregation tendency of the NPs increases with the ionic strength. The increase in the aggregation is caused by the depletion of clusters of ions from the NPs surface.

Study on the influence of fractal dimension and size effect of coarse aggregate on the frost resistance of hydraulic concrete

In cold regions, hydraulic concrete structures are exposed to harsh environmental conditions that greatly impact their durability and safety. The role of aggregates in influencing concrete performance is paramount. This study aims to investigate how the fractal distribution and size of aggregates affect the frost resistance of hydraulic concrete, with air void characteristics, mass loss rate, Elastic Modulus of dynamic, and strength serving as primary references. Two experiment series, fractal distribution influence and aggregate size influence of concrete frost resistance, were conducted to analyze the frost resistance of hydraulic concrete with different aggregates. Based on the fractal theory, four grading fractal distributions were utilized to fractalize aggregate gradation, aiming to investigate the influence of aggregate fractal dimension on the frost resistance of hydraulic concrete. Simultaneously, concrete specimens of fully graded aggregate and wet-screened aggregate were also constructed to simultaneous freeze-thaw cycle tests, the impact of aggregate size on concrete's frost resistance performance was also studied by analyzing the air void structure in the frost-resistant concrete specimens. Results indicate that the specimens exhibit varying frost resistance performance under different aggregate gradation fractals, ranking from strongest to weakest as follows: D=2.5, D=2.3, D=2.1, D=2.7, which is attributed to the differences of air void spacing factors. Increasing aggregate size leads to greater internal structural heterogeneity in concrete, resulting in an increase in defects and weak points. This causes microcracks to develop more rapidly in the transition zone of fully graded concrete during freeze-thaw cycles, leading to more severe damage. The findings of this study can serve as a fundamental scientific basis for the designing and constructing of hydraulic concrete structures in cold areas.

Predictive modeling of low-temperature performance of SMA-13 cold-patching asphalt mixtures based on fractal theory

In order to study the relationship between the low-temperature performance of cold-patching asphalt mixtures and the fractal of gradation, 13 groups of SMA-13 gradations were designed, and then the low-temperature performance test of cold-patching asphalt mixtures was carried out. The overall fractal dimension D, coarse aggregate fractal dimension Dc, fine aggregate fractal dimension Df were obtained by using fractal theory, and according to the correlation analysis of low-temperature performance and fractal dimension, the low-temperature performance prediction model of cold-patching asphalt mixtures based on fractal dimension was established.

Predictive Modeling of High Temperature Performance of SMA-13 Cold Patch Asphalt Mixture Based on Fractal Theory

In order to study the relationship between the high temperature performance of cold-patched asphalt mixtures and gradation fractal, 13 groups of SMA-13 asphalt mixtures were designed, and high temperature rutting test was carried out to study the high temperature performance of cold-patched asphalt mixtures, and the fractal theory was applied to get the overall fractal dimension D, coarse aggregate fractal dimension Dc, fine aggregate fractal dimension Df, and the predictive model of high temperature performance for cold-patched asphalt mixtures was set up according to the correlation analysis of the high temperature performance and fractal dimension. The high-temperature performance prediction model of cold-patched asphalt mixtures was established based on the correlation analysis between high-temperature performance and fractal dimension. This can reduce the test workload, improve work efficiency, and provide reference for engineering design.

The Effects of Partial Substitution of Fertilizer Using Different Organic Materials on Soil Nutrient Condition, Aggregate Stability and Enzyme Activity in a Tea Plantation.

Fertilization plays a crucial role in enhancing tea production. However, it has been demonstrated that the long-term single application of chemical fertilizer will reduce soil nutrient content and the formation of soil aggregates, which is not conducive to the sustainable development of soil and agriculture. Many studies have shown that partial substitution of chemical fertilizer with organic fertilizer can improve soil physicochemical properties and soil nutrient content. This study compared the effects of different organic materials as substitutes for chemical fertilizer. We partially replaced chemical fertilizer with rabbit manure, wine lees and rapeseed cake, amounting to 30% of the total annual nitrogen application in the field experiment, and we set nine different fertilization methods to assess and analyze the soil nutrient condition, aggregate stability and enzyme activity. The results showed that the experimental soil aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) were significantly increased compared with control (p < 0.05); the aforementioned fertilization methods also decreased the soil aggregate fractal dimension (D), disruption rate (PAD), average weight-specific surface area (MWSSA) and soil erodibility factor (K). The application of the fertilizer containing organic materials and microbial agent increased soil organic carbon (SOC) by 20.7% to 22.6% and total nitrogen (TN) by 34.6% to 38.1%; it also significantly promoted sucrase, urease and protease activities in all aggregate sizes (p < 0.05) and increased the 2-5 mm aggregate content. The correlation coefficients between the SOC and the enzyme activities were 0.18-0.95, and most of them showed an extremely significant positive correlation (p < 0.01). In conclusion, the application of fertilizers containing organic materials and microbial agents can improve soil aggregate stability, aggregate enzyme activity and soil structural stability.

Responses of water‐stable aggregates, their associated organic carbon and crop yield to the application of biogas slurry in a fluvo‐aquic soil of the North China plain

AbstractCrop productivity under intensive agriculture depends on the maintenance of fertility and soil structure. Chemical fertilizers are effective in supplying nutrients for crops but eventually lead to loss of the soil organic carbon that is important in supporting soil structure. Biogas slurry is an alternative to chemical fertilizers that potentially can both provide nutrients and promote organic carbon content. A field experiment was conducted to compare the effects of applying biogas slurry (BS), chemical fertilizer (CF) or a combination of both with 50% of nitrogen derived from each (BSCF) and no fertilizer application control (CK) to a fluvo‐aquic soil of the North China Plain. All fertilizer application treatments had equal nutrient supply and were continuously applied over 4 years. Annual yields of wheat and maize were determined. Water‐stable aggregates in size classes &gt;5 mm, 2–5 mm, 0.25–2 mm, 0.053–0.25 mm and &lt;0.053 mm in the topsoil of 20 cm were separated by wet sieving; mean weight diameter (MWD), geometric mean diameter (GMD), percentage of aggregates destruction (PAD) and fractal dimension (D) were derived. The concentrations of organic carbon associated with the aggregates were measured, and the distribution of soil organic carbon (SOC) was quantified. Fertilizer application treatments enhanced total crop yield by 49.1%–75.0%. Fertilizer application also increased the mass proportions of water‐stable macro‐aggregates by 81.6%–164.4%, MWD by 100.0%–264.3%, GMD by 54.5%–227.3%, while decreasing PAD by 15.4%–47.8% and D by 1.0%–3.8% (all relative to CK). The highest proportions of macro‐aggregates, the greatest aggregate stability and the greatest crop yield all resulted from BSCF. All fertilizer application treatments substantially increased the SOC content of water‐stable aggregates, with greater relative contribution in macro‐aggregates. Increased SOC in macro‐aggregates was mainly attributable to mass proportion changes rather than changes in their SOC concentrations. However, SOC concentration tended to account for a larger proportion of the total changes in micro‐aggregates. BSCF also produced the highest total soil organic carbon stocks in aggregates (40.3% and 57.3% greater than CF and CK, respectively). Our work demonstrates that half substitution of chemical fertilizer with biogas slurry is a practical management to enhance soil aggregation and its stability that is associated with a higher crop yield than either treatment individually. It also promotes organic carbon accumulation in soil aggregates, which will support sustainable agricultural development in fluvo‐aquic soil.

The Impact of Fractal Gradation of Aggregate on the Mechanical and Durable Characteristics of Recycled Concrete

Properties of recycled aggregate concrete (RAC) are influenced by the composition and particle size distribution of recycled coarse aggregate (RCA). The study herein designed seven distinct groups of RACs with varying aggregate fractal dimensions (D) and one group of natural concrete (NAC). The impact of D on the workability, compressive strength, resistance to chloride ion penetration, and carbonation resistance of RAC was measured. It was found that an increase in the D value led to a decrease in the slump and slump flow, with the compressive strength and chloride ion penetration increasing and then decreasing, and carbonation gradually declined. The optimal fractal dimension was thereby determined to be 2.547 by a strength model accommodating two parameters of D and the curing age. Additionally, the mass percentage of each particle size for the corresponding gradation was presented. The compressive strength and chloride permeation resistance of RAC (D = 1.0) relative to RAC (D = 2.5) was increased by 16.7% and 13.3%, respectively. Furthermore, the carbonation depth of RAC (D = 2.5) was comparable to that of NAC. Additionally, the carbonation resistance of RAC was influenced by both the size distribution and the degree of natural carbonation of RCA, resulting in four distinct features relative to NAC. It is thereby feasible to enhance RAC performance through the manipulation of RCA’s fractal dimensions.

Observed Polarized Scattered Light Phase Functions of Planet-forming Disks

Abstract Dust particles are the building blocks from which planetary bodies are made. A major goal of studies of planet-forming disks is to constrain the properties of dust particles and aggregates in order to trace their origin, structure, and the associated growth and mixing processes in the disk. Observations of the scattering and/or emission of dust in a location of the disk often lead to degenerate information about the kinds of particles involved, such as the size, porosity, or fractal dimensions of aggregates. Progress can be made by deriving the full (polarizing) scattering phase function of such particles at multiple wavelengths. This has now become possible by careful extraction from scattered light images. Such an extraction requires knowledge about the shape of the scattering surface in the disk, and we discuss how to obtain such knowledge as well as the associated uncertainties. We use a sample of disk images from observations with the Very Large Telescope/SPHERE to, for the first time, extract the phase functions of a whole sample of disks with broad phase-angle coverage. We find that polarized phase functions come in two categories. Comparing the extracted functions with theoretical predictions from rigorous T-Matrix computations of aggregates, we show that one category can be linked back to fractal, porous aggregates, while the other is consistent with more compact, less porous aggregates. We speculate that the more compact particles become visible in disks where embedded planets trigger enhanced vertical mixing.

Simulation of radioactive plume transport in the atmosphere including dynamics of particle aggregation and breakup

Accurate prediction of the atmospheric transport of debris particles relies heavily on our knowledge of the size distribution of the particles within a debris cloud. Assuming a fixed particle size during simulations is not always viable since the size distribution of the debris can change during transport. Various microphysical processes, such as aggregation and breakup, influence debris particles and dictate any changes to the size distribution. To track those changes that can occur, a population balance model can be adopted and instituted within a model framework. Nonetheless, many of the models that simulate the transport of radioactive debris following a device-driven fission incident have historically neglected to consider these processes. As such, this work describes our effort to develop a modeling framework capable of simulating the transport and deposition of a radioactive plume generated from a fission incident with a dynamic population balance including particle aggregation and breakup. The impact of aggregation and breakup, individually and collectively, on the particle size distribution is explored using the developed framework. When simulating aggregation, for example, six mechanisms, including Brownian coagulation, the convective enhancement to Brownian coagulation, van der Waals-viscous force correction for Brownian coagulation, gravitational collection, turbulent inertial motion, and turbulent shear, are considered. Brownian coagulation and its corrections have, as one would expect, a large impact on relatively small aggregates. Aggregates with a diameter that is less than or equal to 1.0 μm, for instance, comprise 50.6 vol % of all aggregates in the absence of aggregation and 31.2 vol % when Brownian coagulation and its corrections are considered. Gravitational collection and, to a much lesser extent, turbulent shear and turbulent inertial motion are, conversely, of great importance to relatively large aggregates (i.e., diameter greater than 3.0 μm). Additionally, the individual effects of atmospheric and particle parameters, such as wind speed and particle density, are examined. Of the parameters examined, turbulent energy dissipation and aggregate fractal dimension (i.e., aggregate shape with lower values representing more irregular particles) were of substantial importance since both terms directly impact aggregate stability and, by extension, the breakup rate. Large-scale transport and deposition simulations in a dry atmosphere are also presented and discussed as a proof of concept.

Reconstruction of the meso-scale concrete model using a deep convolutional generative adversarial network (DCGAN)

The deep learning has been widely used in engineering mechanics, composite materials and other fields due to its powerful information analysis ability. A Deep Convolutional Generative Adversarial Network (DCGAN) is trained in this paper and used to generate a large number of meso-scale concrete models. The CT scanning technology is employed to obtain the 2D slice images of concrete, which are transformed into binary images through a series of preprocessing operations and used as the training dataset of neural network to train the DCGAN. The pre-processing of input dataset, such as the CT image preprocessing and the data enhancement, and some training strategies of the DCGAN are provided in detail. The meso-scale concrete model generated by the trained DCGAN is similar with the training samples and cannot be identified with the naked eye. The reliability of the generated concrete samples is further verified by two indexes (i.e. the aggregate area fraction and the aggregate fractal dimension), and the results show that the generated samples have high consistency with the training samples on the boxplot and box-counting D (the errors are within around 10% and 2%, respectively). In addition, the similar stress–strain curves and the damage evolution processes of the training and generated samples are obtained by the uniaxial compression tests. Compared with the traditional modeling method of meso-scale concrete, the proposed method is more convenient on generating the mass of meso-scale concrete samples and resolves the conflict between computational efficiency and sample quantity. It can be used to study the relationship between the macroscopic and mesoscopic behaviors of concrete from the statistical perspective.

Compressive Yield Stress of Flocculated Kaolin Suspensions in Seawater.

The mining industry has resorted to using seawater while trying to find a solution to the water shortage, which is severe in some regions. Today, the industry looks to tailings dams to recover more water and, thus, increase recirculation. The migration of interstitial water due to the consolidation of particle networks can give rise to large water mirrors in different dam areas. These pools can contain enough water to be recovered and recirculated if the external stress caused by the weight of the pulp exceeds the compressive yield stress. The density and rheological properties of the discarded pulps determine the feasibility of water expulsion during tailings consolidation. As these conditions are largely established in the thickening stage, it is necessary to revisit operations, looking at the dam as a water source. Thus, a thorough understanding of the compressive properties that determine the level of consolidation of typical pulps and their relationships to aggregate properties, such as size and fractal dimension, is crucial. Here, the effect of two types of water, industrial water and synthetic seawater, on kaolin flocculation, sedimentation rate, yield stress, and compressive yield stress were studied. In addition, the relationship of these properties with the flocculant dose and the resulting aggregate size and fractal dimension was examined. One promising finding to practitioners was that salt and small doses of high molecular weight flocculant improved the consolidation of kaolin slurries under compression. These conditions generated low compressive yield stress compared to fresh water and water with low salt content, favoring the consolidation of the pulps and the release of water.

Soil aggregate structure, stability, and stoichiometric characteristics in a smelter-impacted soil under phytoremediation

Smelter-impacted soils often result in soil degradation and the destruction of the soil structure. Although soil aggregate typically plays a crucial role in soil structure, the influence of phytoremediation on soil aggregate structure stability and stoichiometric characteristics remains unclear. To study the influence of phytoremediation on soil aggregate structure, stability and stoichiometric characteristics, a 3-year in situ experiment was conducted. After hydroxyapatite was applied, Elsholtzia splendens, Sedum plumbizincicola, and Pennisetum sp. were planted in a smelter-impacted soil. After 3 years, the soil aggregate structure, stability, and stoichiometric of chemical elements were analyzed. The results showed that the three phytoremediation treatments increased the content of &amp;gt;0.25 mm mechanically-stable (DR0.25) and water-stable (WR0.25) aggregates by 6.6%–10.4% and 13.3%–17.5%, respectively. Aggregate mean weight diameter (MWD), geometric mean diameter, and aggregate stability rate (AR, %) were significantly increased, and the soil mechanically stable aggregate fractal dimension (D) was significantly reduced after the 3-year remediation. Soil total nitrogen and phosphorus in aggregates with different particle sizes were significantly increased by 11.4%–46.4% and 107%–236% after different plant treatments. For the stoichiometric characteristics of the aggregates, the combined remediation only significantly reduced the value of N:P and C:P in different particle size aggregates and had no significant effect on the C:N in all particle size aggregates. Meanwhile, the combined remediation of hydroxyapatite and Elsholtzia splendens, Sedum plumbizincicola, and Pennisetum sp. in heavy metal heavily contaminated soil could reduce the availability of Cu and Cd by 54.1%–72.3% and 20.3%–47.2% during the 3 years, respectively. In summary, this combined remediation method can be used for the remediation of farmland that is contaminated by heavy metals.

Effects of the application of different improved materials on reclaimed soil structure and maize yield of Hollow Village in Loess Area.

In order to solve the soil problem of poor structure and low fertility after the abandoned homestead reclamation of Hollow Village in Loess Area and to improve the quality of the reclaimed soil in Hollow Village, a five-year field experiment was conducted here. In this experiment, the following seven treatments were applied: no modified material (CK), maturing agent (TM), fly ash (TF), organic fertilizer (TO), maturing agent + fly ash (TMF), maturing agent + organic fertilizer (TMO) and fly ash + organic fertilizer (TFO), and the effects of different improved materials on soil properties and crop yield were studied. The results showed that: soil organic matter (SOM) and total nitrogen contents increased significantly after the application of different improved materials, which promoted the cementation and aggregation of water-stable microaggregates (< 0.25 mm), and the water-stable macroaggregates showed an increasing trend. In the 0–0.15 m soil layer, the proportion of water-stable macroaggregates under TM, TF, TO, TMF, TMO, and TFO treatment increased by 328.2%, 130.0%, 87.8%, 81.1%, 36.7%, and 12.2% compared with CK, respectively. Meanwhile, TF, TO, TMF, TMO, TFO treatments significantly increased the mean weight diameter (MWD) and geometric mean diameter (GMD) values, reduced soil bulk density, the stable aggregate index (ELT) and fractal dimension (D) values (P < 0.05), and the stability of soil structure and the capacity of soil moisture retention has been significantly improved. The SOM content had a significant positive correlation with MWD, GMD, and > 2 mm water-stable aggregates and a significant negative correlation with the ELT, D, and water-stable microaggregates. In particular, the organic–inorganic coupling treatment of TFO showed the highest SOM content, soil moisture content, water-stable macroaggregates and maize yield, which was the most appropriate amendment for improving the reclaimed soil structure and fertility of Hollow Village in Loess Area.

Effects of economic fruit forest planting on the stability of red soil aggregates in the subtropical hilly area

The stability of aggregates is of great significance to evaluate water and soil environment in regions plan-ting economic fruit forest. We explored the effects of economic fruit forest types on the structure and stability of soil aggregates in the 0-50 cm soil layer from 5-year-old Amygdalus persica, Pyrus sorotina, Citrus reticulata, Camellia oleifera and Actinidia chinensis forests in the hilly area in northern Hunan. The content, distribution characteristics and stability indices of soil aggregates from each economic fruit forest were quantitatively analyzed by the Shavinov method. The results showed that most soil aggregates were mechanically stable, with a minimum content of 92.3%. After wet sieving, the size of water-stable aggregates in the soil from Camellia oleifera forest was mainly &gt;2 mm, accounting for 55.9% of the total aggregates. The 0.25-2 mm aggregates were the dominant particles in the A. persica, P. sorotina, C. reticulata and A. chinensis forest soils, with contributions higher than 43.6%. The mean weight diameter (MWD) and the geometric mean diameter (GMD) of soil aggregates for the five economic fruit forest types ranged from 1.10 to 3.19 mm and 0.61 to 2.28 mm, respectively. Furthermore, the percentages of soil aggregate destruction (PAD) and fractal dimension (D) were in the range of 2.9%-37.3% and 2.30-2.68, respectively. With the increases of soil depth, the stability of soil aggregates from A. persica, C. oleifera and A. chinensis forest soils became worse; MWD and GMD decreased by 1.7%-57.7% and 4.5%-65.8%, respectively; PAD and D increased by 0.4%-17.3% and 1.6%-11.1%, respectively. The effects of economic fruit forest types on the stability of soil aggregates decreased with increasing soil depth. Based on the stability indices, aggregate stability from five economic fruit forests followed the order of C. oleifera &gt; A. chinensis &gt; P. sorotina &gt; C. reticulata &gt; A. persica. The type of economic fruit forest improved the stability of soil structure mainly by affecting the content of large-size aggregates. In terms of improving the distribution and stability of soil aggregates, it was suggested that C. oleifera should be given the top priority as the economic fruit forest in the subtropical hilly area, followed by A. chinensis. Whereas A. persica planting might reduce the degree of soil agglomeration, thus, the protective measures of soil loss should be considered during planting. Our results could provide theoretical basis and application guidance for the development, utilization, and ecological management of economic fruit forests in subtropical hilly areas.

Rice-crayfish farming increases soil organic carbon

Soil in agriculture systems is important for carbon sequestration. To explore the influence of rice-crayfish farming on soil organic carbon (SOC) content, 0–30 cm soil samples were collected from rice monoculture and rice-crayfish systems (1, 6, 10 and 15 years) scattered in Nanxian County, Hunan Province, China. Results showed that the SOC content in rice monoculture was approximately 22 g kg−1, while enhanced SOC content was observed in 6, 10 and 15-year rice-crayfish systems, around 27–33 g kg−1. The formation of water-stable aggregates mainly depends on the cementation of SOC. Meanwhile, the decomposition of organic matter may further lower the oxygen content and lead to accumulation of reduction substances in soil. Similar increasing trends also occurred in soil water-stable macro-aggregates (WR0.25) content (78–83%), mean weight diameter (MWD) (1.1–1.2 mm) and geometric mean diameter (GMD) (0.8–1.0 mm), whereas the aggregate fractal dimension (D) (2.58–2.44) decreased. Moreover, rice-crayfish farming over 6 years enhanced the content of total reducing matter (TRM), active reducing matter (ARM), Fe2+ and Mn2+ content by 1.7–3.4 cmol kg−1, 0.6–1.3 cmol kg−1, 0.5–1.2 cmol kg−1 and 0.2–0.6 cmol kg−1, respectively. However, the 1-year rice-crayfish system did not show significant changes after the conversion from rice monoculture systems. Overall, rice-crayfish farming has the capability to increase and preserve SOC, but it aggravates soil gleization.

Strength prediction based on ultrasonic property of fractal gangue cemented rockfill reinforced by carbon nanotubes

Producing cemented rockfill for supplying building material and underground filling material is currently the most effective approach to recycle solid mineral waste. Investigating its ultrasonic property and constructing a model for predicting its strength are of great significance to its on-site assessment and engineering stability. Ultrasonic detection test was carried out on the fractal gangue cemented rockfill reinforced by carbon nanotubes (CNTs) to study the effects of the curing time, CNT dosage and aggregate size distribution on its ultrasonic property. The relation between ultrasonic pulse velocity (UPV) and uniaxial compressive strength (UCS) was established through uniaxial compression test, and the model I for predicting the strength of cemented rockfill was built based on this relationship. The coupling relationship between the curing time, CNT dosage, particle size distribution (PSD) fractal dimension of aggregates, UPV and the UCS of cemented rockfill was established by genetic algorithm (GA), and the strength prediction model II was constructed based on this coupling relationship. The difference between both prediction models and the matching degree between predictive strength and experimental data were discussed, a more accurate method for predicting the strength of cemented backfill was proposed. The results show that the relationship between CNT dosage and UPV can be described by the quadratic function, it believes that the optimal CNT dosage is between 0.05% and 0.10% for cemented rockfill. The relationship between PSD fractal dimension and UPV can be characterized by the quadratic function, it considers that the optimal PSD fractal dimension is in the range of 2.4150 and 2.6084 for the aggregates in cemented rockfill, and this optimal aggregate size distribution is easily affected by other conditions. The exponential function σ1c=ξ10eξ11v-ξ10 can be used to describe the relationship between UPV and UCS, the prediction model I based on this relationship for predicting the strength of cemented rockfill has the determination coefficient of 0.9164 matching with the experimental data. The prediction model II based on the coupling relationship combining material parameters with UPV correction by using GA performs the reliable prediction accuracy with 4.5223% of mean absolute percentage error (MAPE) and 0.9513 of determination coefficient better than model I.

Hyperspectral response and quantitative estimation on soil aggregate characters

Soil aggregate stability can be used to describe soil structure quality. In contrast, the conventional determination for soil aggregate stability, relying on dry-sieving and wet-sieving methods, is too resource consuming, especially for mass soil samples covering a large-scale field. Exploring the application of hyperspectral technology will provide a rapid, efficient and alternative method for the estimation of soil aggregate characteristics. In this study, we collected 199 soil samples (0–15 cm soil depth) from the Loess Plateau regions in the south areas of Shanxi province in China. Afterwards, we analyzed the relationship between spectra in region of 350–2500 nm and seven soil aggregate characters. The quantitative models for each soil aggregate character were built and the sensitive wavebands were determined by using the method of partial least squares. The results showed there was a negative relationship between soil spectra and soil aggregate stability, and the extreme correlation coefficient could reach −0.60 and 0.62, respectively, indicating that soil spectra could produce a significant response on soil aggregate characteristic. The significant waveband regions for soil aggregate characters were 350–870, 1250–1360, 1885–2020, and 2215–2450 nm. The important wavelengths were around 427, 599, 1326, 1890, 1926, 2208, 2311, and 2336 nm, which were also confirmed by the consistent correlation between soil spectra and each aggregate character. In addition, the reliable models (R2 = 0.612–0.714; RPD = 1.584–1.796) were produced for most of the soil aggregate indicators, while percentage of aggregate destruction (PAD) led to the worst predictive model (R2 = 0.599; RPD = 1.261). Aggregate fractal dimension (D) character was proved as the perfect indicator for spectral monitoring of soil aggregate stability, mainly due to the two-fold interpretation functions to soil structure distribution and soil adhesion with organic matter and soil moisture. It indicated that hyperspectral technology provides an alternate method for soil aggregate characters, especially for a large area.

Temporal evolution of the structure of tailings aggregates flocculated in seawater

Mineral processing produces large volumes of dilute tailings that are flocculated and thickened, returning water to the process. The drive towards more sustainable processing has seen seawater considered to replace fresh water usage and an increased focus on how flocculation conditions can influence the fractal-like aggregates formed. The fragility of such structures and the likelihood that they change with time makes their study challenging.A synthetic tailings slurry of quartz and kaolin in seawater was flocculated at different mixing times and flocculant dosages, with aggregate size monitored over time by focused beam reflectance measurement (FBRM) and hindered settling rates determined after set reaction times. A model relating hindered settling rate to size as estimated by FBRM was used to derive an aggregate fractal dimension (Df) at each time. With flocculation at typical tailings solids concentrations rapid, aggregate breakage will normally dominate after very short reaction times. Under mild mixing conditions, settling rates are higher than expected from sizes measured in real time due to aggregate growth continuing after mixing ceases, leading to inflated Df estimates. An apparent decline in Df under more intense mixing was consistent with an increased presence of high aspect ratio (low effective porosity) aggregate fragments, supported by in situ aggregate imaging at different reaction times. In contrast, the observed trends for a reduction in Df with mixing intensity and an increase with dosage are both thought to represent the expected aggregate structure changes for the synthetic tailings.While estimating aggregate structural properties by relating FBRM sizes to settling rates can offer useful insights, it is important to recognise the aggregation state observed by FBRM under mixing applied to induce flocculation may differ from that which exists during hindered settling. Values of Df derived in this manner must therefore be viewed with caution.

Soil Hydraulic Properties of Plinthosol in the Middle Yangtze River Basin, Southern China

Soil hydraulic properties are ecologically important in arranging vegetation types at various spatial and temporal scales. However, there is still a lack of detailed understanding of the basic parameters of plinthosol in the Middle Yangtze River basin. This paper focuses on the soil hydraulic properties of three plinthosol profiles at Yueyang (YE), Wuhan (WH), and Jiujiang (JU) and tries to reveal the origin of plinthosol and the relationship among the soil hydraulic parameters. Discriminant analysis indicated that the plinthosol in the JU profile was of aeolian origin, while that in the WH and YE profiles was of alluvial origin; soil hydraulic properties varied greatly among these profiles. The proportion of macro-aggregates (&gt;0.25 mm, weight%) in the JU profile (88.28%) was significantly higher than that in the WH (73.63%) and YE (57.77%) profiles; the water holding capacity and saturated hydraulic conductivity of JU plinthosol was also higher than that of WH and YE plinthosol; the fact that Dr and Di of the JU profile are lower than those of the YE and WH profiles illustrates the stability of JU plinthosol is better than that of YE and WH plinthosol, which is consistent with the fractal dimension of aggregates. The disintegration curves of white vein and red matrix demonstrated a large discrepancy in the JU profile, but these curves showed a similar trend in the WH and YE profiles. The differences in hydraulic properties might be ascribed to the origin of plinthosol, and the results of the fractal dimension also confirmed this conclusion. This study might provide a better understanding of the soil physical properties of plinthosol and shed light on the soil and water conservation measures in the Middle Yangtze River basin.

Effect of geometric form of concrete meso-structure on its mechanical behavior under axial tension

The coarse aggregate content and fractal dimension were used to describe the geometric form of concrete at the meso-level. After the simulation results were validated, several meso-models of concrete with various fractal dimensions and coarse aggregate content were simulated under tension using Random Fractal Modeling. With increasing coarse aggregate content, the elastic modulus increased, and the tensile strength and the strain corresponding to the maximum stress decreased. The fractal dimension did not obviously influence the tensile mechanical behavior. The comprehensive consideration of both fractal geometry and classical Euclidean geometry can aid in predicting the macroscopic behavior of concrete.