Decrease In Fractal Dimension Research Articles

Optometry in adults with microdeletion 22q11.2: The eye as a window to the brain

PurposeThe 22q11.2 deletion syndrome (22q11.2DS) has an estimated prevalence of 1:2148 live births and is associated with an increased risk of schizophrenia, cognitive decline and early-onset Parkinson’s disease. Because retinal and cerebral tissue share embryological, physiological and anatomical characteristics, retinal blood vessel morphology and retinal nerve fiber layer (RNFL) thickness have been proposed as non-invasive biomarkers for psychiatric and neurodegenerative disorders. In this exploratory study, we examined these potential biomarkers in adults with 22q11.2DS relative to controls, and in relation to age. MethodsCentral retinal artery and vein equivalent, fractal dimension, and vascular tortuosity, obtained through fundoscopy, and peripapillary RNFL and macular thickness, obtained through optical coherence tomography, were compared between adults with 22q11.2DS and sex- and age-matched controls. ResultsMean retinal vascular fractal dimension and tortuosity values were significantly higher in the group of adults with 22q11.2DS than in controls (p < 0.001; p < 0.001). RNFL was thicker in the nasal segment (p = 0.002) in 22q11.2DS, and a trend for thinner RNFL in the nasal and temporal inferior segments (p = 0.05 and p = 0.06, respectively) was found. There were significant negative correlations with age for fractal dimension (p < 0.001) and RNFL thickness in the global (p = 0.007), temporal inferior (p = 0.005) and temporal superior (p = 0.04) segments in adults with 22q11.2DS, but not in controls. ConclusionsOur results indicate higher retinal vascular fractal dimension and tortuosity, and a decrease in fractal dimension and RNFL thickness in relation to age in adults with 22q11.2DS. Our findings support future studies that focus on retinal fractal dimension and RNFL thickness as potential biomarkers for age-related manifestations in 22q11.2 including psychotic and (early) neurodegenerative disorders.

A multi-scale fractal model of gas flow considering the evolution of kerogen microstructure and the multi-physical coupling

Shale is a complex porous medium. The migration mechanism within its different microstructural systems is crucial for the efficient recovery of shale gas. The kerogen microstructure influences the adsorption–desorption effect of the reservoir. This study accounts for the heterogeneity of shale and uses fractal dimension to characterize the fracture and inorganic matrix systems. It also establishes a kerogen fractal diffusion model by integrating fractal diffusion with fractal theory. Furthermore, this study analyzes the effect of evolution of micro structural parameters of kerogen on macro permeability, such as: (1) kerogen fractal dimension; (2) effective diffusion coefficient of kerogen; (3) maximum kerogen aperture. Numerical simulation shows that: The maximum pore size and porosity of kerogen in direct proportion to fractal dimension and effective diffusion coefficient. The fractal dimension and effective diffusion coefficient decrease gradually during shale gas extraction. The fractal effective diffusion has a significant impact on cumulative gas extraction.

Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching. The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 104–107 μm2, whose pore quantities accounted for 96.89%, 94.94%, 90.48%, and 89.45%, respectively, while the corresponding pore volume only accounted for 30.74%, 14.55%, 7.58%, and 2.84% of the total pore volume. With the decrease of fractal dimension, the average pore throat length increased, but pore throat quantities, the average pore throat radius and coordination number decreased. Compared with that before leaching, the change degree of pore structure during leaching increased with the fractal dimension decreasing. For example, the reduction rate of the average coordination number of ore samples was 14.36%, 21.30%, 28.00%, and 32.90%, respectively. Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing. Besides, the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.

Tectonic Control on Shale Pore Structure and Gas Content from the Longmaxi Formation Shale in Southern Sichuan Basin, China: Insights from Fractal Analysis and Low-Pressure Gas Adsorption

Tectonic deformation of different intensities significantly controls shale pore structure, seepage channels, and gas content. The Longmaxi Formation shales in the southern Sichuan Basin have experienced multi-stage tectonic movements, resulting in a diverse fracture system and tectonic deformation. This study focuses on three representative tectonic morphologies: deeply buried strongly deformed (DBSD), deeply buried weakly deformed (DBWD) and shallowly buried weakly deformed (LBWD). We investigated the pore structure characteristics and heterogeneity of these shales under various tectonic conditions using total organic carbon (TOC) content, X-ray diffraction (XRD), scanning electron microscopy (SEM), a low-pressure N2/CO2 adsorption experiment (LP-N2/CO2 GA), and multi-scale fractal theory. The results reveal that strong tectonic compression and deformation conditions lead to the compression and flattening of organic pores by brittle minerals, resulting in long, oriented OM pores. Fracturing of brittle pore creates multiple internal fracture systems linked to dissolution pores, forming a complex micro-fracture–pore network. With intense tectonic deformation, mesopores tend to be compressed, increasing micropore pore volume (PV) and surface area (SA). The DBSD shale exhibits the highest micropore heterogeneity, while the LBWD shale shows the lowest heterogeneity. Fractal analysis indicates a significant decrease in micropore fractal dimension (Df) with increasing burial depth. In contrast, the surface and matrix fractal dimensions (Ds and Dm) of low-buried shale micropores and meso-macropores align vertically. Shale reservoirs in tectonically stable regions exhibit more favourable gas-bearing characteristics than strongly tectonically deformed areas. The LBWD has stable tectonic conditions that are favourable for shale gas preservation. Conversely, slip faults under deep burial conditions lead to extrusion and deformation of shale pore space, ultimately compromising the original reservoir capacity and hindering shale gas enrichment. These findings contribute significantly to our understanding of pore structure and heterogeneity in tectonically deformed shale reservoirs, providing invaluable guidance for the exploration, development, and prediction of shale gas resources.

The impact of ocular hypertension on retinal nerve fiber layer and optic disc perfusion during treatment with brolucizumab in patients with neovascular form of age-related macular degeneration

PURPOSE. To evaluate the effect of elevated intraocular pressure (IOP) after multiple intravitreal injections (IVI) of brolucizumab on changes in the retinal nerve fiber layer (RNFL) and perfusion of the optic nerve head.METHODS. The study included 20 patients with newly diagnosed exudative form of age-related macular degeneration (AMD). All patients underwent IVI of brolucizumab. IOP measurements were taken with an ICare Pro tonometer before IVI, one minute after IVI, then after 30 minutes and 180 minutes. Thickness of the peripapillary RNFL was measured using Spectralis OCT (Heidelberg Engineering, Germany). The optic disc was examined using OCT angiography on Revo NX (Optopol Technology SA, Poland). All studies were carried out before the start of treatment, after one month, after the third injection, and one year after the start of treatment.RESULTS. Analysis of peripapillary scans in a patient with a history of multiple IVI a year after the start of treatment with brolucizumab showed a statistically significant decrease in perfusion density and fractal dimensions (skeleton) in the entire optic nerve head (ONH) (p&lt;0.001), in the inner ONH area (p&lt;0.001, p=0.01, respectively), in the nasal sector (p=0.03, p=0.04, respectively), temporal sector (p&lt;0.001) and inferotemporal sector (p=0.03) according to OCT angiography. It was determined that a greater increase of IOP one min after IVI was associated with a greater decrease in the density and fractal dimensions of the radial peripapillary capillaries of the inner ONH (p=0.005, rs=0.5; p=0.004, rs=0.6, respectively). A decrease in RNFL thickness was found one year after the start of IVI treatment with brolucizumab (p&lt;0.001).CONCLUSION. According to OCT angiography, vascular perfusion density of the ONH was decreased during IVI of brolucizumab, and RNFL thickness was also decreased one year after the start of treatment.

Relationships between quantitative retinal microvascular characteristics and cognitive function based on automated artificial intelligence measurements.

Introduction: The purpose of this study is to assess the relationship between retinal vascular characteristics and cognitive function using artificial intelligence techniques to obtain fully automated quantitative measurements of retinal vascular morphological parameters. Methods: A deep learning-based semantic segmentation network ResNet101-UNet was used to construct a vascular segmentation model for fully automated quantitative measurement of retinal vascular parameters on fundus photographs. Retinal photographs centered on the optic disc of 3107 participants (aged 50-93years) from the Beijing Eye Study 2011, a population-based cross-sectional study, were analyzed. The main parameters included the retinal vascular branching angle, vascular fractal dimension, vascular diameter, vascular tortuosity, and vascular density. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Results: The results showed that the mean MMSE score was 26.34 ± 3.64 (median: 27; range: 2-30). Among the participants, 414 (13.3%) were classified as having cognitive impairment (MMSE score < 24), 296 (9.5%) were classified as mild cognitive impairment (MMSE: 19-23), 98 (3.2%) were classified as moderate cognitive impairment (MMSE: 10-18), and 20 (0.6%) were classified as severe cognitive impairment (MMSE < 10). Compared with the normal cognitive function group, the retinal venular average diameter was significantly larger (p = 0.013), and the retinal vascular fractal dimension and vascular density were significantly smaller (both p < 0.001) in the mild cognitive impairment group. The retinal arteriole-to-venular ratio (p = 0.003) and vascular fractal dimension (p = 0.033) were significantly decreased in the severe cognitive impairment group compared to the mild cognitive impairment group. In the multivariate analysis, better cognition (i.e., higher MMSE score) was significantly associated with higher retinal vascular fractal dimension (b = 0.134, p = 0.043) and higher retinal vascular density (b = 0.152, p = 0.023) after adjustment for age, best corrected visual acuity (BCVA) (logMAR) and education level. Discussion: In conclusion, our findings derived from an artificial intelligence-based fully automated retinal vascular parameter measurement method showed that several retinal vascular morphological parameters were correlated with cognitive impairment. The decrease in retinal vascular fractal dimension and decreased vascular density may serve as candidate biomarkers for early identification of cognitive impairment. The observed reduction in the retinal arteriole-to-venular ratio occurs in the late stages of cognitive impairment.

Efficient Evaluation of Concrete Fracture Surface Roughness Using Fringe Projection Technology.

The evaluation of concrete surface roughness is crucial in the field of civil engineering. The purpose of this study is to propose a no-contact and efficient method for the measurement of the roughness of concrete fracture surfaces based on fringe-projection technology. A simple phase-correction method using one additional strip image is presented for the phase unwrapping to improve the measurement efficiency and accuracy. The experimental results indicate that the measuring error for plane height is less than 0.1mm, and the relative accuracy for measuring a cylindrical object is about 0.1%, meeting the requirements for concrete fracture-surface measurement. On this basis, three-dimensional reconstructions were carried out on various concrete fracture surfaces to evaluate the roughness. The results reveal that the surface roughness (R) and fractal dimension (D) decrease as the concrete strength increases or the water-to-cement ratio decreases, consistent with previous studies. In addition, compared with the surface roughness, the fractal dimension is more sensitive to the change in concrete surface shape. The proposed method is effective for detecting concrete fracture-surface features.

Correlation between morphological characteristics of retinal microvessels and diabetic kidney disease in patients with type 2 diabetes mellitus based on a machine learning model

Objective: To explore the correlation between the morphological characteristics of retinal microvessels and diabetic kidney disease (DKD) in patients with type 2 diabetes mellitus (T2DM). Methods: The clinical data and fundus photography of patients with T2DM treated in the First Affiliated Hospital of Zhengzhou University from January 2018 to December 2020 were retrospectively collected and analyzed. According to the presence of abnormal renal function, the patients were divided into DKD group and control group. The morphology and structure of fundus vessels were digitized by U-Net depth convolution neural network, and the correlation between fundus vascular morphology and DKD was analyzed by multivariate logistic regression. Results: A total of 648 patients with T2DM were enrolled, including 410 males and 238 females, and aged (53±10) years. There were 398 and 250 cases in control and DKD groups, respectively. Meanwhile, 1 296 fundus images were collected. Compared with control group, the male ratio (68.4% vs 60.1%, P=0.032), age [(54±9) vs (52±10) years, P=0.005], blood pressure [(136.8±17.3) vs (130.3±15.4) mmHg（1 mmHg=0.133 kPa）, P<0.001], total cholesterol [(4.5±1.4) vs (4.2±1.0) mmol/L, P=0.009], triglyceride [M (Q1, Q3)][1.7 (1.2, 3.0) vs 1.4 (1.0, 2.3) mmol/L, P<0.001] and Cystatin C [(0.9 (0.8, 1.0) vs 0.8 (0.7, 0.9) mg/L, P<0.001] were higher in the DKD group, while high-density lipoprotein [(1.0±0.3) vs (1.1±0.3) mmol/L, P=0.001] was lower in the DKD group. Multivariate logistic regression analysis showed that the risk of DKD in the third quartile (right eye: OR=1.825, 95%CI: 1.204-2.768, P=0.005) and fourth quartile (left eye: OR=1.929, 95%CI: 1.218-3.055, P=0.005) was higher than that in the lowest quartile of vascular curvature after adjusting for age and gender. The increase of average diameter of retinal vein was associated with the risk of DKD (left eye: OR=1.044, 95%CI: 1.013-1.075, P=0.005). The decrease of vascular fractal dimension (fourth quartile of left eye: OR=0.444, 95%CI: 0.199-0.987, P=0.046) and retinal vascular density (the second and fourth quartile of the right eye: OR=0.639, 95%CI: 0.409-0.998, P=0.049; OR=0.534, 95%CI: 0.331-0.864, P=0.010) were related to the risk of DKD. Conclusions: The abnormal morphological characteristics of retinal microvessels are related to the occurrence of DKD. The increase of retinal vein diameter and the decrease of retinal vessel density correlate with the occurrence of DKD.

Experimental and numerical investigations on damage evolution of concrete under sulfate attack and freeze-thaw cycles

The macro-microstructure tests of concrete under the alternating action of salt freezing (ASF) were conducted to investigate the macro-mechanical properties and microstructure pore evolution patterns of concrete. Combined with CT scanning and 3D pore model reconstructing technologies, we present the evolution equation of concrete porosity and the quantitative relation between the fractal dimension of concrete pores and the macroscopic strength under the ASF. Then, a macro-microscopic damage evolution model of concrete was proposed to study the structural performance evaluation of an aqueduct. The results show that the compressive strength (fc), splitting tensile strength (ft), and relative dynamic modulus (Erd) of concrete specimens under the ASF show a decreasing trend as a whole, and the mechanical properties of concrete gradually decrease with the increase of sulfate solution concentration. With the increase of the cycles of salt freezing alternation, the pore fractal dimension of the concrete gradually decreases and the porosity gradually increases. After the cycle of 8 times, the pore fractal dimension decreases by 6.06%, and the porosity increases by 7.30% compared with the initial state. The porosity of concrete is negatively correlated with the strength, while the fractal dimension of the pore structure is positively correlated with the strength. When the ASF reaches 8 times, the maximum compressive stress and tensile stress of the groove body are 9.48 MPa and 3.13 MPa, respectively, which appear at the ends of the lower chord. The displacements of the bottom and side wall plates are 0.384 mm and 3.289 mm, respectively. The penetrating cracks appear at the junction, and the structure severely deteriorates.

An USAXS-SAXS study of nano-TATB under uniaxial die pressures

The microstructure of a compressed explosive solid is closely related to its shock sensitivity and mechanical properties. In this study, ultra-small-angle and small-angle X-ray scattering (USAXS and SAXS) techniques were combined to explore the hierarchical microstructure of die-pressed 2,4,6-trinitro-1,3,5-benzenetriamine (TATB) discs obtained from nanostructured TATB (nano-TATB) powder as the precursor. Using the Guinier-Porod model, the pseudo-invariants, and Porod's law, this study analyzed the microstructures of the materials on a nanometer scale to track the changes in void size, porosity, and interfacial area, which reflected the response of TATB under applied pressures of 1, 2, 5, 10, 15 ​kN and 30 ​kN. Results show that there existed three populations of voids in the measured q range. The intergranular voids with sizes of tens of nanometers were sensitive to low pressures (<15 ​kN) and presented a smooth interface with the TATB matrix. The intragranular voids with sizes of 7–8 ​nm exhibited a fairly small volume-filling ratio under high pressures (>15 ​kN), as indicated by the decrease in the volume fractal dimension. Porosities of the voids with sizes of 1–900 ​nm, which were determined by the pseudo-invariants obtained from the scattering data, decreased from 6% to 1% as the pressures increased from 1 ​kN to 30 ​kN. The response of these structural parameters to external pressures implies that the main densification mechanisms under die compression include the flow, fracturing, and plastic deformation of the TATB granules. This study provides a direct insight into the structural evolution of TATB during compression.

A computational technique for the Caputo fractal-fractional diabetes mellitus model without genetic factors.

The concept of a Caputo fractal-fractional derivative is a new class of non-integer order derivative with a power-law kernel that has many applications in real-life scenarios. This new derivative is applied newly to model the dynamics of diabetes mellitus disease because the operator can be applied to formulate some models which describe the dynamics with memory effects. Diabetes mellitus as one of the leading diseases of our century is a type of disease that is widely observed worldwide and takes the first place in the evolution of many fatal diseases. Diabetes is tagged as a chronic, metabolic disease signalized by elevated levels of blood glucose (or blood sugar), which results over time in serious damage to the heart, blood vessels, eyes, kidneys, and nerves in the body. The present study is devoted to mathematical modeling and analysis of the diabetes mellitus model without genetic factors in the sense of fractional-fractal derivative. At first, the critical points of the diabetes mellitus model are investigated; then Picard's theorem idea is applied to investigate the existence and uniqueness of the solutions of the model under the fractional-fractal operator. The resulting discretized system of fractal-fractional differential equations is integrated in time with the MATLAB inbuilt Ode45 and Ode15s packages. A step-by-step and easy-to-adapt MATLAB algorithm is also provided for scholars to reproduce. Simulation experiments that revealed the dynamic behavior of the model for different instances of fractal-fractional parameters in the sense of the Caputo operator are displayed in the table and figures. It was observed in the numerical experiments that a decrease in both fractal dimensions and leads to an increase in the number of people living with diabetes mellitus.

Study on the Soil Deterioration Mechanism in the Subsidence Zone of the Wildcat Landslide in the Three Gorges Reservoir Area

The stability of soil mass near the dam bank in the Three Gorges Reservoir is closely related to the periodic variation in the reservoir water level. In order to study the influence of water level variation on soil mass, the soil mass in the water level fluctuation zone of the Wildcat landslide was taken as the research object, and the mechanism of soil mass deterioration in this area was revealed by comparing the strength and mineral structure characteristics of soil mass at different elevations by means of macro- and meso-microscopic analysis. The results show the following: (1) With the increase in sampling elevation, the natural water content of the soil decreases, and the dry density of the soil is a minimum when the elevation is 155 m and at a maximum when the elevation is 175 m. (2) The soil mass in the water dissipation zone of the Wildcat landslide can be divided into three areas: When the elevation is 145–155 m, the fractal dimension increases, the soil fragmentation increases, the cohesion decreases, and the soil deterioration increases. When the elevation is 155–175 m, the fractal dimension decreases, the soil fragmentation decreases, the cohesion increases, and the soil deterioration weakens. When the elevation is greater than 175 m, there is no soil deterioration. (3) X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) were used to test the soil’s mineral composition and pore size at different elevations. It was found that the main reason for the severe deterioration of macro-strength parameters of the soil at the elevation of 155 m was that the proportion of clay minerals and quartz was at the lowest, and the proportion of medium pores and large pores was at the highest. (4) Through the combination of macro and mesoscopic testing and analysis, it was found that the rise and fall of the reservoir water level will lead to the strong chemical action of the skeleton and cemented mineral dissolution in the soil degradation-enhanced area, as well as the physical action of soil particles, resulting in the formation of more medium pores and large pores in the soil and eventually the formation of seepage channels.

Rheological properties of cemented gangue backfill material based on fractal characteristics of waste coal gangue.

The study herein was intended to evaluate the rheological properties of cemented gangue backfill material (CGBM). For this purpose, the rheological test of CGBM with fractal aggregate particle size distribution was carried out, and variations of static yield stress, dynamic yield stress, and plastic viscosity were investigated as a function of fractal dimension and time. The results reveal that aggregate particle size distribution exerts a significant influence upon the rheological properties of CGBM, and with the escalation of the fractal dimension of the aggregate, the yield stress and plastic viscosity initially decline and then increase. In addition, with elapsing time, the correlation between the static yield stress and the fractal dimension of CGBM specimens increases, while the correlations between the dynamic yield stress and the plastic viscosity and the fractal dimension decrease. The relationships between rheological parameters and fractal dimensions at different times are established based on the experimental results. The influence mechanism of aggregate particle size distribution on CGBM is analyzed from the perspective of the aggregate packing state. This study can provide a basis for the ratio design of CGBM in backfill mining.

Age- and sex-related differences in cortical morphology and their relationships with cognitive performance in healthy middle-aged and older adults.

The impacts of age and sex on brain structures related to cognitive function may be important for understanding the role of aging in Alzheimer disease for both sexes. We intended to investigate the age and sex differences of cortical morphology in middle-aged and older adults and their relationships with the decline of cognitive function. In this cross-sectional study, we examined the cortical morphology in 204 healthy middle-aged and older adult participants aged 45 to 89 years using structural magnetic resonance imaging (sMRI) data from the Dallas Lifespan Brain Study data set. Brain cortical thickness, surface complexity, and gyrification index were analyzed through a completely automated surface-based morphometric analysis using the CAT12 toolbox. Furthermore, we explored the correlation between cortical morphology differences and test scores for processing speed and working memory. There were no significant interactions of age and sex with cortical thickness, fractal dimension, or gyrification index. Rather, we found that both males and females showed age-related decreases in cortical thickness, fractal dimension, and gyrification index. There were significant sex differences in the fractal dimension in middle-aged participants and the gyrification index in older adult participants. In addition, there were significant positive correlations between the cortical thickness of the right superior frontal gyrus and Wechsler Adult Intelligence Scale (WAIS)-III Letter-Number Sequencing test scores in males (r=0.394; P<0.001; 95% CI for r values 0.216-0.577) and females (r=0.344; P<0.001; 95% CI for r values 0.197-0.491), respectively. Furthermore, a significant relationship between the gyrification index of the right supramarginal gyrus (SupraMG) and WAIS-III Digit Symbol test scores was observed in older adult participants (r=0.375; P<0.001; 95% CI for r values 0.203-0.522). The results suggest that, compared with males, females have more extensive differences in cortical morphology. The gyrification index of the right SupraMG can be used as an imaging marker of sexual cognitive differences between males and females in older adults. This study helps to further understand sex differences in the aging of the brain and cognition.

A HYBRID NUMERICAL/ANALYTICAL MODEL OF TRANSIENT SEEPAGE FOR VERTICAL FRACTURED WELL IN TIGHT GAS RESERVOIR BY USE OF FRACTAL THEORY AND CONFORMAL MAPPING METHOD

Insufficient consideration of the complex morphology of hydraulic fractures (HF) and heterogeneous physical properties of fractured reservoirs in seepage models can result in unreliable well testing analyses. The fractal porosity and permeability (FPP) model provides an effective method for characterizing reservoir heterogeneity in the near-wellbore zone. However, its application to scenarios involving irregularly-shaped hydraulic fracture networks and multiple fracture clusters is challenging due to the lack of spatial symmetry. To address this issue, this paper proposes a combined approach of FPP and conformal mapping (FPP-CM) to transform the region of fractured formation into the exterior of the unit disk domain using numerical conformal mapping. The transient seepage flow model of the vertical fracture well (VFW) is then established by coupling it with the FPP model. The typical curve of pressure transient behavior with the division of flow stages was plotted, and the model verification and sensitivity analysis of parameters were conducted. The results indicate that the fractal dimension primarily affects the formation linear flow stage and its subsequent flow stages; with a decrease in fractal dimension resulting in an increase in the position of the typical curve. For VFW with multiple HF wings, a decrease in the included angle of fracture wings causes an increase in the heterogeneity distribution of microfracture physical properties, resulting in an increase in the position of the pseudo-pressure derivative curve during the late flow stage.

Experiment and numerical simulation study of dynamic mechanical behavior of granite specimen after high temperature treatment

The dynamic compression experiments were conducted on granite specimens after high-temperature treatments by using split Hopkinson pressure bar test system. Subsequently, we collected the granite fragments after impacting, and the fragmentation characteristics were evaluated by the fractal dimension and average fragment size. Finally, combined with the numerical simulation results, we investigate the law of crack propagation during dynamic compression. The results show that the change in physical properties such as bulk density and mass of granite are closely related to the temperature. Microcracking occurred on the surface of granite when the temperature is 900℃. Dynamic peak strain and strain rate increased with the increase of temperature, while the peak strength and elastic modulus decreased. Additionally, the fractal dimension and average fragmentation size are closely related, and the relationship is negatively linear. The fractal dimension and average fragmentation size increase and decrease with the temperature, respectively. By combining the experimental and numerical results, we observed that the crack initially appears on the surface of the rock and then gradually propagates to the interior under impact loading. The rupture surface of granite fragmentation is approximately parallel to the axial direction and the ultimate failure mode mainly comprises the axial tensile splitting failure.

Investigation of polyaluminum chloride (PACl) coagulation to remove cyanobacteria from maintenance to decay stage: Performance and mechanism

Cyanobacterial bloom is a global issue affecting drinking water supply, and coagulation process is important to remove cyanobacteria. Cyanobacteria can get into decay stage after a long-term maintenance stage during a successive bloom. Some studies compared cyanobacterial coagulation at both stages, but their removal performance is still an argument. To well address this debate, the performance and mechanism of PACl coagulation to remove cyanobacterial cells at both stages, was compared with or without extracellular organic matters (EOMs) in this study. Results showed that cyanobacterial coagulation performed better at decay stage than that at maintenance stage without EOMs, treated by equal dosages of PACl. However, an opposite result was observed with EOMs, since EOMs at maintenance stage exhibited lower inhibitory effects on the coagulation due to fewer contents and negative charge. Meanwhile, inter-particle bridging for cyanobacterial coagulation at maintenance stage became stronger via elevated high-MW EOMs than that at decay stage. Analyses of Zeta potential and flocs characteristics revealed that electrical neutralization was the main coagulation mechanism at both stages without EOMs, and electrostatic patch was responsible for cyanobacterial coagulation with EOMs. Moreover, inter-particle bridging and sweeping flocculation were involved in cyanobacterial coagulation with EOMs, leading to loosely flocs with a decrease of fractal dimension (Df, 0.6–0.7), intensity factor (If, 0.2–0.7), and recovery factor (Rf, 0.3–0.9). Overall, EOMs could differ the performance and mechanism of cyanobacterial coagulation at both stages, and thus, managing varied EOMs would be vitally necessary to optimize cyanobacterial coagulation from maintenance to decay stage of a successive bloom.

Effect of Particle Size Distribution on the Dynamic Mechanical Properties and Fractal Characteristics of Cemented Rock Strata

To investigate the dynamic mechanics and post-failure characteristics of fault-cemented rock strata, broken rock particles were reshaped to obtain cemented rock samples with various particle size distributions (PSDs). Split Hopkinson pressure bar (SHPB) dynamic impact tests were performed on the cemented rock samples under different strain rates. The test results show that plastic deformation occurs in the cemented rock sample as a result of its porous structure. Therefore, there is no linear phase in the dynamic stress–strain curves. With an increase in the Talbot index and mixture type, more large particles were contained inside the cemented rock sample, and the dynamic strength gradually increased. A power function can effectively describe the relationship between the strain rate and dynamic strength for various Talbot indices. After dynamic impact, the fragments of the cemented rock samples exhibit evident fractal laws, and the breakage of the samples includes breakage of the original rock particle itself and breakage between the rock particles and cementations. The breakage ratio and fractal dimension both decrease with the increase in the number of mixture type and Talbot index but increase with the increase in strain rate. It is worth noting that the breakage ratio and fractal dimension have a linear relationship regardless of the PSD or strain. The relationship between the dynamic strength and fractal dimension has different response laws for the PSD and strain rate effects. The dynamic strength is negatively linearly related to the fractal dimension under the PSD effect but positively linearly related to the fractal dimension under the strain rate effect. This research work can provide foundation support for investigating the instability mechanism of fault cemented rock strata under dynamic stress.

Rheo-microscopy in situ synchronous measurement of shearing thinning behaviors of waxy crude oil

Shear thinning is one of the most significant Non-Newtonian rheological behaviors of waxy crude oil, which is also the macroscopic performance attributing to the microstructural evolution. In this work, Rheo-microscopy synchronous measurement of shearing thinning behaviors is first accomplished. Direct dynamic evolution vision of wax crystals and synchronous rheological data are obtained. Overall dynamics and morphological characteristics of wax crystals show that with the shear rate increasing from 0.5 s−1 to 10 s−1, the number of wax crystals in the field of view decreases by 89%, representing a larger dispersion degree, weaker aggregation and layered arrangement. The average angle decreases by nearly 24°, and the standard deviation of the angle also decreases, implying the wax crystals have greater tendency to orient along the flow field and regular arrangement. The shear also has a slight effect on wax crystals micro-morphology, which is demonstrated by the decrease of fractal dimension. The correlation with viscosity is strongest for the motion behavior and arrangement state of wax crystals(Relational degree is 0.8741) near the abnormal temperature. During the cooling down to the gel temperature, the aggregation becomes the dominant factor influencing the viscosity(Relational degree is 0.8316). And the morphology of wax crystals is always the secondary factor. Furthermore, the individual dynamic response of wax crystals to changes in external shear strength is also quantitatively characterized. The alignment of the trajectories with the flow field, the rotation and tumbling motions, together with the dynamic changes in morphology and structure of wax crystals are also discussed.

Experimental study on pore structure evolution of high volatile bituminous coal with thermal treatment

Pores and cracks are the main flow channels of coal, which affects the fluid migration and their reactions under high temperature. In this paper, high volatile bituminous coal in Ordos Basin was used to conduct the heating treatment experiments in N 2 atmosphere. The results show that: (1) Pore evolution always occurred in the vitrinite that displays swelling, shrinkage, and rheology accompanying with pores creating, expanding, merging, collapsing and nesting. (2) The thermal evolution of pores presents three stages: in the initial stage, micropore remain occupied the main body before 300 °C; and in the middle stage, the mesopore and macropore displayed gradual increase ranging from 300 °C to 600 °C; and in the last stage, the micropores increased again and showed abundant porosity after 600 °C. Accordingly, the fractal dimension shown firstly decrease, and then increase corresponding to pores coalition and nesting. (3) The pore evolution is controlled by the thermal weight loss. The increase of weight loss rate is corresponding to the increase in mesopore and macropore and decrease in fractal dimension.