Mass Fractal Dimension Research Articles

Morphology analysis of soot particles from a modern diesel engine fueled with different types of oxygenated fuels

Using a transmission electron microscopy (TEM), the morphological characteristic variations of exhaust soot particles have been studied on a modern diesel engine fuelled with a commercial diesel fuel (D100, as a baseline fuel) and three different oxygenated fuel blends with the same oxygen content, including a 11.5% methanol blend (M11.5), a 8.3% dimethyl carbonate blend (DMC8.3), and a 13% dimethyl methane blend (DMM13). The results showed that oxygenated fuel blends emitted smaller soot primary particles with respect to neat diesel, with the most significant decrease in M11.5 followed by DMM13 and DMC8.3. Similar variations with primary particle diameter were found in the decrease of the mean radius of gyration, mean primary particle number and estimated mass for an agglomerate when making comparisons among diesel and the three oxygenated fuel blends. Aggregates shape analysis showed that M11.5 soot had the minimal trend to form a rather circular structure and maximal boundary irregularity among the four fuels, while all soot particles showed larger deviation to the sphere (i.e. higher elongation) regardless of fuel type used. In addition, both mass and perimeter fractal dimension showed consistent results for diesel and the three oxygenated fuel blends, with the particle aggregates being the least compacted morphology for M11.5, followed by DMM13, DMC8.3 and diesel. Therefore, compared to diesel, the exhaust soot particles from the oxygenated fuel blends (especially for M11.5) are more prone to be trapped (lowest fractal dimension) and display a higher reactivity towards oxidation (smallest primary particle size).

Effect of tillage and maize-cowpea intercrop on fractal features of particle and aggregate size distribution on a tropical sandy loam soil in southwest Nigeria

The effects of tillage and cropping pattern on soil aggregation, fractal dimensions and distribution of organic carbon fractions were studied. Treatments were notillage (NT), conventional tillage (CT), and four cropping patterns viz: sole maize, sole cowpea, maize-cowpea intercrops and control (no crop). Soil samples were analysed for particle size distribution (PSD); aggregation ratio (AR), meanweight diameter (MWD) and aggregated silt+clay (ASC). Mass fractal dimension (Dm) was obtained from PSD; while fragmentation fractal dimension (Df) was obtained from aggregate sizes. Total organic carbon (TOC), free and occluded particulate organic carbon (fPOC and oPOC), were measured. Results showed that structural stability at micro-aggregate scale measured by aggregated silt + clay (ASC) was significantly (p < 0.05) highest for NT (4.07) than CT (1.58). The CT significantly (P ≤ 0.05) reduced the larger aggregate fraction (5.66-2.00 mm). The difference in fractal dimensions was significantly higher with NT than control with CT. Lower difference between Dm and Df with CT represents higher degree of fragmentation of aggregates. Correlation showed significant positive linear relationships between Dm and sand (p < 0.05, r = 0.627) and negative relationship with silt and clay (r = -0.675). Therefore, fractal dimensions derived from aggregates sizes rather than particle size distribution reflected the impact of land management practices on fragmentation of aggregates of most tropical soils.

Effect of tillage and maize-cowpea intercrop on fractal features of particle and aggregate size distribution on a tropical sandy loam soil in southwest Nigeria

The effects of tillage and cropping pattern on soil aggregation, fractal dimensions and distribution of organic carbon fractions were studied. Treatments were no- tillage (NT), conventional tillage (CT), and four cropping patterns viz: sole maize, sole cowpea, maize-cowpea intercrops and control (no crop). Soil samples were analysed for particle size distribution (PSD); aggregation ratio (AR), mean- weight diameter (MWD) and aggregated silt+clay (ASC). Mass fractal dimension (Dm) was obtained from PSD; while fragmentation fractal dimension (Df) was obtained from aggregate sizes. Total organic carbon (TOC), free and occluded particulate organic carbon (fPOC and oPOC), were measured. Results showed that structural stability at micro-aggregate scale measured by aggregated silt + clay (ASC) was significantly (p < 0.05) highest for NT (4.07) than CT (1.58). The CT significantly (P ≤ 0.05) reduced the larger aggregate fraction (5.66-2.00 mm). The difference in fractal dimensions was significantly higher with NT than control with CT. Lower difference between Dm and Df with CT represents high- er degree of fragmentation of aggregates. Correlation showed significant positive linear relationships between Dm and sand (p < 0.05, r = 0.627) and negative rela- tionship with silt and clay (r = -0.675). Therefore, fractal dimensions derived from aggregates sizes rather than particle size distribution reflected the impact of land management practices on fragmentation of aggregates of most tropical soils.

Insights into in-situ sol-gel conversion in graphene modified polymer-based silica gels for multifunctional aerogels

Schematic representing the hydrolytic polycondensation of P-VTMS in the presence of GnP or GO. • In-dept study on the polymer orientation in the presence of graphene materials. • Engineering of bimodal mesoporous structure during sol-gel transition. • The strategy of nanoplatelets exfoliation by controlling pH during gelation. • graphene platelets contribution at the polymer/graphene interface during gelation. • Effect of GnP and GO on the surface area, insulation, and mechanical properties. Graphene-modified polymer-based silica aerogels (G-PSAs) are an emerging class of multifunctional material, receiving a lot of attention for a wide range of applications such as sensors, drug-delivery, and tissue-engineering. The bimodal mesoporous structure of G-PSAs is dictated during the gelation process, and it can be tailored by optimizing material and processing parameters. In this study, the main focus is to investigate the mechanism for the formation of the structure that furnished the aerogels with unique pore structures and superb mechanical properties. The dynamic structures along the fabrication process were assessed using advanced techniques such as rheometry, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and pore-structure-analyzer. DLS and SAXS results support the notion that the gelation of polyvinyltrimethoxysilane (P-VTMS) yields a nonparticulate structure. A chemically induced spinodal decomposition phase separation was found to explain the collected data. The mass fractal dimension was found to be 1.8, confirming that the percolation theory cannot be used to describe the gelation of both neat P-VTMS and Graphene-modified P-VTMS. The findings showed that, while adding GO to the formulation does not change the stoichiometric ratio of the gelation reaction, it creates spatial hindrance that interferes with the reaction process, delaying the gelation process. Conversely, GnP provides a platform for the reaction that promotes the gelation process. However, GO and GnP shows similar effects on bimodal mesoporous structure of aerogels although provides dramatically different surface areas. This dramatic difference roots in the open pore structure induced by GnP in P-VTMS aerogels. The strategy of nanoplatelets exfoliation during the sol–gel transition by controlling pH opens a new avenue for producing G-PSAs with an exceptionally high surface area (up to ~2100 m 2 .g −1 ).

Soil fragmentation and aggregate stability as affected by conventional tillage implements and relations with fractal dimensions

Due to a lack of accurate information regarding soil aggregate size distribution and stability, farmers in Sindh, Pakistan often apply excessive tillage, creating an overly fine seedbed that can lead to the depletion of soil organic matter (SOM) and make the soil more vulnerable to wind and water erosion. The current paper investigates the effects of conventional tillage implements on soil fragmentation and aggregate stability, along with how these factors relate to fractal dimensions. The study aims to: (i) achieve a better understanding of soil structure and establish which tillage implement provides the best soil structure and (ii) determine the function that best describes the proportion of small aggregates in the soil. Six tillage treatments were studied, including: moldboard plough + disk harrow two passes (MPDH2), disk plough + cultivator two passes (DPC2), cultivator two passes (C2), cultivator four passes (C4), cultivator six passes (C6), and minimum tillage (disk harrow one pass) (MT) for a clay loam soil. At each of two depths (0-0.15 m and 0.16-0.30 m), four soil samples from randomly selected locations in each plot were collected (3 blocks × 6 tillage × 2 depths × 4 samples, n = 144) with the help of a soil auger. Aggregate size distribution was measured by a dry sieving method, and aggregate stability was determined by a wet sieving method. The correlations between mean weight diameter (MWD), mass fractal dimension (Dm), and soil aggregation were investigated. The greatest proportions of small aggregates and the lowest proportions of intermediate aggregates were found under DPC2 followed by C6, while a greater proportion of intermediate aggregates and a lower proportion of small aggregates was observed under MT. However large aggregates (>25 mm) were negligible across all treatments. The highest values of Dm were found after DPC2, while the highest values of MWD were found after MT. The highest proportion of water stable aggregates (WSA) was found under DPC2, while the lowest proportion was found under MPDH2 followed by MT. Similarly, aggregate stability was greatest under DPC2. Across all tillage implements, the highest fuel consumption was recorded under C6 followed by MPDH2, while the lowest occurred under MT. The Dm showed a negative correlation with intermediate aggregates (5.0–25.0 mm) and a positive correlation with small aggregates (<5.0 mm), while MWD had a positive correlation with intermediate aggregates (5.0–25.0 mm) and a negative correlation with small aggregates (<5.0 mm). Similarly, Dm was negatively correlated with MWD. This suggests that farmers should adopt the technique of using a disk plough followed by two passes of the cultivator to achieve the best possible seedbed conditions in a clay loam soil. Higher values of Dm and lower values of MWD may be used to quantify fine seedbeds, with the converse being preferable for quantifying coarse seedbeds.

Interfacial Structures of Droplet-Stabilized Emulsions Formed with Whey Protein Microgel Particles as Revealed by Small- and Ultra-Small-Angle Neutron Scattering.

Droplet-stabilized emulsions (DSEs) were made from oil droplets coated with whey protein microgel (WPM) particles. The WPM particles with z-average hydrodynamic diameters of 270.9 ± 4.7 and 293.8 ± 6.7 nm were obtained by heating whey proteins with 10 mM phosphate buffer, pH 5.9 (-PB) and no buffer (-NPB), respectively. The primary emulsions coated by WPM-NPB and WPM-PB particles had mass fractal dimensions of ∼2.75, as determined by small- and ultra-small-angle neutron scattering (SANS and USANS). The size of the subsequently formed DSEs (D32 ≈ 7-23 μm), which were stabilized by the primary emulsion droplets, made with either WPM-NPB (termed DSE-NPB) or WPM-PB (termed DSE-PB) was dependent on the concentration of the primary emulsion (10-60 wt %) in the aqueous phase. At the DSE-NPB interface, the adsorbed primary emulsion droplets formed a fractal network with a surface fractal dimension of about 3, indicating a rough interfacial layer. Combined SANS and USANS allowed a comprehensive understanding of the multilength scale structures from WPM particles to DSEs.

Size-exclusion chromatography combined with solution X-ray scattering measurement of the heat-induced aggregates of water-soluble proteins at low ionic strength in a neutral solution

The heat-induced (80 ± 1 ℃, 1 h) aggregates of bovine serum albumin and ovalbumin at neutral pH and low ionic strength (10 mM sodium phosphate buffer, pH 6.9) were characterized using size-exclusion chromatography combined with small-angle X-ray scattering measurement. The values calculated for the radius of gyration and molecular weight of the eluted aggregates of the bovine serum albumin were 9–11 nm and 540,000–820,000, respectively. Those of ovalbumin were 11–16 nm and 500,000–1,820,000, respectively. The overall linear conformation of the bovine serum albumin aggregates slightly differed from that of the ovalbumin aggregates since the mass fractal dimensions were found from calculation to be 1.63–1.7 for the bovine serum albumin and 1.36–1.51 for the ovalbumin. The surface property of the aggregates of both proteins was suggested to be similar to that of their native monomer since all the surface fractal dimensions were almost equivalent. The dimensionless Kratky plots of the eluted aggregates indicated that the non-globular conformation of the bovine serum albumin aggregates differs from that of the ovalbumin aggregates. These analyses using size-exclusion chromatography combined with the solution X-ray scattering measurement will be helpful for characterization of the components of the denatured protein aggregation in solution.

Comparative Study on the Fractal Dimensions of Soil Particle Size

The application of fractal theory provides a new approach for the study of soil science. The calculation of fractal dimension is the basis. The purpose of the study is to find a suitable method for calculating the fractal dimension of the soil particle size and to analyse how the fractal dimension reflects soil properties. We mostly use comparative analysis to study. Comparing the mass fractal dimension method with volume fractal dimension method, we analyze their advantages and disadvantages, and the fractal dimension performance of the soil in different land types.

Effect of dimethyl carbonate on the micromorphology and structure of combustion particles from diesel engines

ABSTRACTParticulate matter emitted by internal combustion engines is one of the main sources of air pollution. Oxygenated fuels can partially replace diesel fuel in combustion and reduce the emission level, especially the particulate matter emitted by diesel engines. In this paper, the emitted particles from the combustion of dimethyl carbonate (DMC)/diesel blends with different blending ratios were collected, and the effects of DMC on the morphology of the diesel particles were analyzed via scanning electron microscopy and small-angle X-ray scattering (SAXS) with a synchrotron radiation source. By studying the small-angle scattering intensity, particle size distribution, fractal dimension, and interface thickness of DMC/diesel combustion particles, the effects of DMC on the degree of agglomeration of particles, particle size distribution, and surface roughness were investigated. The results showed that as the DMC blending ratio increased, the radius of gyration of the particles decreased, the particle size of the primary carbon particles formed by combustion decreased, and the particle size distribution became narrower. With increasing DMC blending ratio, the electron density differences in the particles gradually decreased, the statistical average distance between the particles decreased, the fractal dimension increased, the degree of agglomeration increased, and the structural arrangement was more compact. SAXS analysis revealed that the combustion particles exhibited surface fractal characteristics at a wide angle range and exhibited mass fractal characteristics at a small angle range. The surface fractal dimension and mass fractal dimension of the particles were both higher than those of diesel particles, indicating that the surface roughness, irregularity, and degree of agglomeration of the particles all increased.

Strength and filtration stability of cement grouts in porous media

The diffusion of cement-based grouts in porous media is an important issue in soil sealing and grouting effects. To better understand the effects of grouting parameters, including grouting temperature, water-cement ratios and mass fractal dimensions, on the retention of slurry particles, the permeability of injected media, and the strength of cementation under a constant pressure condition, several types of tests, including filtration, permeability and uniaxial compressive strength tests, were performed. The experimental results indicate the following: (1) The retention rate of cement particles decreases sharply with an increase in the distance from the grouting source in the porous media with a higher mass fractal dimension, whereas the retention rate of cement particles decreases slowly with increasing diffusion distance in the porous media with a lower mass fractal dimension. (2) Within a certain distance, the retention of cement particles at a lower temperature is slightly higher than that at a higher temperature. Beyond this critical distance, the retention of cement particles at a lower temperature is generally lower than that at a higher temperature. (3) Regardless of the cement slurry, the damage is not uniform in the injected porous media. (4) The compressive strength of the porous media with a higher fractal dimension at the test point near the grouting source is higher than that of the media with a lower fractal dimension. However, at the test point far from the grouting source, the compressive strength of the porous media with a lower fractal dimension is greater than that of the media with a higher fractal dimension.

Study on the Structure Characteristics of Diesel Engine Particulates Based on Small‐Angle X‐Ray Scattering

In this article, the particulates formed by the combustion of diesel, 20% and 50% biodiesel blended in diesel (denoted as B20 and B50, respectively), and biodiesel were collected. The micromorphologies of the particulates were observed by scanning electron microscopy. Furthermore, the small‐angle X‐ray scattering technique was used to analyze the gyration radius, size distribution, interfacial characteristics, and fractal characteristics of the particulates. The results show that the size of the particulates formed by combustion of the fuels was concentrated between 10 and 35 nm and obeyed a Gaussian distribution. Moreover, the addition of biodiesel to diesel led to smaller particulate sizes for the biodiesel/diesel blend: the mean radii of the particulates for diesel, B20, B50, and biodiesel were 11.5 nm, 10.8 nm, 10.2 nm, and 9.7 nm, respectively. In addition, an interfacial layer was observed between the particulates, and the average interfacial thickness of the particulates was between 1.54 and 1.89 nm. The mass fractal dimension of the particulates was between 0.2 and 2.5, and the surface fractal dimension of the particulates was between 2.1 and 2.9. The addition of biodiesel to diesel resulted in a more compact particulate structure and the rougher surface. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

Polyelectrolyte character of rigid rod peptide bundlemer chains constructed via hierarchical self-assembly.

Short α-helical peptides were computationally designed to self-assemble into robust coiled coils that are antiparallel, homotetrameric bundles. These peptide bundle units, or 'bundlemers', have been utilized as anisotropic building blocks to construct bundlemer-based polymers via a hierarchical, hybrid physical-covalent assembly pathway. The bundlemer chains were constructed using short linker connections via 'click' chemistry reactions between the N-termini of bundlemer constituent peptides. The resulting bundlemer chains appear as extremely rigid, cylindrical rods in transmission electron microscopy (TEM) images. Small angle neutron scattering (SANS) shows that these bundlemer chains exist as individual rods in solution with a cross-section that is equal to that of a single coiled coil bundlemer building block of ≈20 Å. SANS further confirms that the interparticle solution structure of the rigid rod bundlemer chains is heterogeneous and responsive to solution conditions, such as ionic-strength and pH. Due to their peptidic constitution, the bundlemer assemblies behave like polyelectrolytes that carry an average charge density of approximately 3 charges per bundlemer as determined from SANS structure factor data fitting, which describes the repulsion between charged rods in solution. This repulsion manifests as a correlation hole in the scattering profile that is suppressed by dilution or addition of salt. Presence of rod cluster aggregates with a mass fractal dimension of ≈2.5 is also confirmed across all samples. The formation of such dense, fractal-like cluster aggregates in a solution of net repulsive rods is a unique example of the subtle balance between short-range attraction and long-rage repulsion interactions in proteins and other biomaterials. With computational control of constituent peptide sequences, it is further possible to deconvolute the underlying sequence driven structure-property relationships in the modular bundlemer chains.

Effect of Hydrothermal Coupling on Physical and Dynamic Mechanical Properties of Sandstone

Split‐Hopkinson pressure bar (SHPB) tests were conducted for sandstone after recurrent heat‐cool (H‐C) cycles. Physical and mechanical properties, damage, and fracture characteristics of sandstone after the H‐C cycle were explored. Additionally, the damage variable and release rate of damage strain were defined to describe the damage degree of the sandstone specimen after recurrent H‐C cycles. Finally, the relationship between mass fractal dimension of fragmentation and cycling number was discussed. Results show that the P‐wave velocity and density decrease with the increase of cycling number, while the porosity increases. It was found that the dynamic compressive strength and relative elastic modulus decrease with the increase of cycling number. 20 cycles is the critical point for the low temperature (L‐T) group and moderate temperature (M‐T) group, while it is 4 cycles for the high temperature (H‐T) group. With the increase of cycling number, both the damage variable and release rate of damage strain of rock increase, while the destruction degree of sandstone becomes greater, and the corresponding fragments show more evenly.

An Analytical Flow Model for Heterogeneous Multi-Fractured Systems in Shale Gas Reservoirs

The use of multiple hydraulically fractured horizontal wells has been proven to be an efficient and effective way to enable shale gas production. Meanwhile, analytical models represent a rapid evaluation method that has been developed to investigate the pressure-transient behaviors in shale gas reservoirs. Furthermore, fractal-anomalous diffusion, which describes a sub-diffusion process by a non-linear relationship with time and cannot be represented by Darcy’s law, has been noticed in heterogeneous porous media. In order to describe the pressure-transient behaviors in shale gas reservoirs more accurately, an improved analytical model based on the fractal-anomalous diffusion is established. Various diffusions in the shale matrix, pressure-dependent permeability, fractal geometry features, and anomalous diffusion in the stimulated reservoir volume region are considered. Type curves of pressure and pressure derivatives are plotted, and the effects of anomalous diffusion and mass fractal dimension are investigated in a sensitivity analysis. The impact of anomalous diffusion is recognized as two opposite aspects in the early linear flow regime and after that period, when it changes from 1 to 0.75. The smaller mass fractal dimension, which changes from 2 to 1.8, results in more pressure and a drop in the pressure derivative.

Relating Coral Skeletal Structures at Different Length Scales to Growth, Light Availability to Symbiodinium, and Thermal Bleaching

Light scattering of coral skeletons and tissues increases light availability to photosynthetic endosymbionts to form one of the most efficient biological collectors of solar radiation. Rapid increases in light availability during thermally-induced symbiont loss (bleaching) impair photosynthetic performance of the remaining Symbiodinium and precipitate a more severe bleaching response (optical feedback-loop hypothesis). Here we focus on light scattering of the skeleton, which is determined by light interaction with skeletal components assembled in a hierarchical fractal-like structure from tens of nanometers (e.g., calcium carbonate nanograins) to micro- and milli-meters (septa, corallites, and coenosteum) to centimeters and higher (colony form). We examined the association between skeletal structures, their role in light scattering, and species-specific bleaching responses for 88 coral species using phylogenetically-corrected analysis. We also explored the effect of growth on light scattering by modeling the fractal-like accretive growth of the skeleton (assuming a diffusion limited process of biomineralization) as a function of skeletal density, size of nanograins, fractal range of biomineralized clusters, and overall mass-fractal dimension, and validated the model with experimental data. Our results show that differences in light scattering from the top ~200µm (micro-μ_s^') of the skeleton, and not from the whole skeleton (bulk-μ_s^'), are related to bleaching susceptibility. We also demonstrate how differences in micro-μ_s^' of corallites and coenosteum could explain, in part, heterogeneous light environment between polyp and coenosarc. The average effective light transport distance of coenosteum measured in 14 coral species indicates that coenosteum could transport light to the corallites, which could then function as ‘light-trapping devices’ where photons are scattered multiple times by septa and corallite walls until absorbed by Symbiodinium. Furthermore, our fractal skeletal growth model suggests that corals that grow faster typically have lower mass-fractal dimension, denser skeletons, lower skeletal micro-μ_s^', and higher bleaching susceptibility. Finally, our results demonstrate that several skeletal structures of varying length scales known to modulate the light microenvironment of Symbiodinium in coral tissue are not associated with bleaching susceptibility. This work provides evidence of the relationship between skeletal growth, light scattering, and bleaching, and further supports the optical feedback-loop hypothesis of coral bleaching.

Dispersion state of carbon black in polystyrene produced with different dispersion media and its effects on composite rheological properties

The dispersion state and aggregate structure of carbon black in polystyrene composites prepared by solvent casting suspensions in different dispersion media, i.e., chloroform, tetrahydrofuran, and toluene, with different particle contents and their effects on the bulk rheological properties of the composites were investigated by transmission electron microscopy, ultrasmall-angle and small-angle X-ray scattering, and dynamic viscoelasticity measurements. The macroscopic dispersion state of carbon black in the solvent-cast films was largely affected by the dispersion medium, reflecting the stability of the suspension in the polystyrene solution. The mass fractal dimension of carbon black in the polymeric matrix, which was evaluated by X-ray scattering techniques with a resolution of nanometers, tended to exhibit a higher value for the dispersion media with less carbon black dispersibility. The surface fractal dimension of carbon black in the polymer was independent of the dispersion medium and exhibited a lower value than carbon black powder due to physical adsorption of the polymer on the particle surface. The viscoelastic moduli for the melt polymer composites below and above the percolation limit varied according to the dispersion media, reflecting the difference in the macroscopic dispersion state and aggregate structure of carbon black in polystyrene. The dispersion state and aggregate structure of carbon black in polystyrene composites prepared by solvent casting suspensions in different dispersion media with different particle contents and their effects on the bulk rheological properties of the composites were investigated by transmission electron microscopy, ultrasmall-angle and small-angle X-ray scattering, and dynamic viscoelasticity measurements. The viscoelastic moduli of the melt polymer composites below and above the percolation limit varied with the dispersion medium, reflecting the difference in the macroscopic dispersion state and aggregate structure of carbon black in polystyrene.

On the pore structures of lightweight self-compacting concrete containing silica fume

This paper presents the results of an experimental study about the pore structure of lightweight self-compacting concrete with different amounts of silica fume and water-to-cement ratios. Mercury intrusion porosimetry was used to test the porosity and pore sizes. The fractal characteristics of the pore structures were studied, and the pore mass and solid mass fractal dimensions were calculated based on well-established methods. The optimum amount of silica fume was determined based on fractal dimension. The results have showed that compressive strength and water penetration depth increase with the increase of fractal dimension and have good correlation with fractal dimensions.

A growth model for the generation of particle aggregates with tunable fractal dimension

A new 3D off-lattice model is proposed to generate porous and controlled fractal aggregate structures. The method is a variation of the Eden Model with the additional capability of randomly inactivating particles with a given inactivation probability. As this probability increases from 0 to 1, the proposed model follows a continuous transition from an off-lattice Eden Model leading to a core-dense random structure to a self-avoiding random walk model leading to a linear chain with partially constrained growth directions. The resulting aggregates have been characterized in terms of their radius of gyration, shape factor, mass and surface fractal dimensions, pore volume fraction, specific surface area and pore size distribution. A large range of microstructural properties can be controlled by adjusting the inactivation probability and the number of particles (e.g. mass fractal dimension from 1.6 to 3). In addition the proposed approach is convenient to implement and highly computationally efficient. The morphology (radius of gyration and mass fractal dimension) of silica aggregates characterized by small angle X-ray scattering in the literature was successfully reproduced to demonstrate the capabilities of the method.

Silicon oxycarbide glasses and glass‐ceramics: “All‐Rounder” materials for advanced structural and functional applications

AbstractSilicon oxycarbides can be considered as being carbon‐containing silicates consisting of glass networks in which oxygen and carbon share bonds with silicon. The carbon‐for‐oxygen substitution in silicate glass networks has been shown to induce significant changes in the network connectivity and consequently strong improvements in the properties of the silicate glass network. For instance, SiOC glasses exhibit Young's moduli, hardness values, glass transition, and crystallization temperatures which are superior to those of vitreous silica. Moreover, the silicon oxycarbide glass network exhibits unique structural features such as reduced mass fractal dimension and nano‐heterogeneity, which significantly affect and/or dictate its properties and behavior. In the present Review, a consideration of the current state of the art concerning the synthesis, processing, and various structural and functional properties of silicon‐oxycarbide‐based glasses and glass‐ceramics is done. Thus, the synthesis of silicon oxycarbides starting from macromolecular precursors such as polysiloxanes or alkoxysilanes‐based sol‐gel systems as well as current advances related to their processing will be critically reviewed. In addition, various structural and functional properties of silicon oxycarbides are presented. Specific emphasis will be put on the intimate correlation between the molecular architecture of the precursors and the structural features and properties of the resulting silicon oxycarbides.

Micromechanism of the diffusion of cement-based grouts in porous media under two hydraulic operating conditions: constant flow rate and constant pressure

Cement-based grout has been widely used in various civil engineering applications. The diffusion of cement-based grouts in porous media is an important issue in soil sealing and the estimate of grouting. To better understand the effects of grouting parameters on the viscosity of slurry, the porosity of an injected media and the pressure variations under constant flow rate and constant pressure conditions, a series of laboratory tests were conducted on the fractal characteristics of sand in a column. Additionally, different grouting flow rates and pressures, water/cement ratios and mass fractal dimensions were studied. The experimental results show the following responses: (1) the variation in the diffusion pressure of the slurry under the condition of a constant pressure is clearly different from that under constant pressure. (2) There is a strong correlation between the porosity and water/cement ratio regardless different hydraulic operating conditions, whereby a reduction or increase in the water/cement ratio control the range of the slurry diffusion. (3) Regardless of the hydraulic operating conditions, the grouting pressure presents a nonlinear decreasing law with the increase in distance from the grouting source. (4) An excessive flow rate or pressure is not conducive to the diffusion of slurry.