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The evolution characteristics of rock fracturing in presplit blasts are generally affected by in situ stress resulting from tectonic forces in the Earth's crust and from gravity. In this study, rock fracturing under coupled static stress and presplit blasting conditions is comprehensively investigated by combining experimental, theoretical and numerical methods. Model tests of two-borehole presplitting on 200 × 200 × 50 mm granite samples are carried out using a biaxial hydrostatic loading system, and blast-induced rock fracture is identified using high-speed digital image correlation. The postblast granite samples are further image processed using ImageJ to show the detailed rock fragmentation and fracture networks. The rock fracturing behaviours and fractal characteristics in presplitting under various biaxial and uniaxial stresses, and under constant uniaxial stress with different β values (angle between the orientation of uniaxial stress and the line connecting blastholes), are examined. Blast tests show that the number and length of blast-created fractures in presplitting decrease with increasing static stress, and thus, presplit crack formation gradually fails, producing a rock crack pattern with relatively low fractal dimension and fractal damage levels. Moreover, the formation of crack coalescence fails between presplit holes, and the damage to the remaining rock significantly increases when β is larger than 15°. Then, the variations in crack patterns in recent presplitting tests are analysed based on elastic mechanics by calculating the transmission and superimposition of detonation stress waves and the static stress distribution near presplit holes. Later, after performing numerical verification, the rock fracturing processes in presplitting are numerically modelled in LS-DYNA. The influences of boundary conditions on presplitting test results and the implications of the recent findings for practical presplitting are discussed accordingly. Highlights: Rock cracking in presplitting under static stress is experimentally tested. Rock cracking in presplitting under initial stress is numerically 3D modelled. The fractal characteristic of rock fractures in presplitting is investigated. The effects of uniaxial and biaxial stresses on presplit blasting are analysed. [ABSTRACT FROM AUTHOR]

Fish feces affect the structure and function of aquatic ecosystems, and they are affected by the functional fish organizations. In this research, Ctenopharyngodon idellus, Hypophthalmichthys molitrix, and Cyprinus carpio were selected to study the effects of different functional fish organizations on the fractal characteristics of fecal micro-structure by scanning electron microscopes (SEM), particles (pores) and cracks analysis system (PCAS). The results showed that fish feces pores mainly consisted of medium pores (cumulative pore number, 97%) classified by the International Union of Pure and Applied Chemistry (IUPAC). The grain area fractal dimension D1 and the pore-number and pore-size fractal dimension D2 were 1.94–1.96 and 2.07–2.19, respectively. The distribution of fish feces pores was very close to the Sierpinski carpet structure, which is the basic fractal construction methods widely used to describe the fractal of pore surface distribution. D1 (1.96) and D2 (2.19) of Hypophthalmichthys molitrix were the maximum values of the three functional organizations. Combining with the habit of fish, it is inferred that the feces of H. molitrix, the finer the feed and the faster the swimming of fish, the higher the content of feces clay, the larger the fractal dimension of feces, the easier it is to decompose feces, and the high the content of nutrients and organic matter to release into the water. It is demined that fish functional organizations affected the fractal characteristics and the stability of fish feces in water. This study is helpful for further research on water quality prediction and the impact of functional fish organizations on the structure and function of the ecosystem. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the process of coal mining, the residual goaf will destroy the stress balance state of the overlying strata, which will result in a large number of fractures. The development of overburden fractures not only affects the movement of strata and the subsidence of surface, but also determines the dominant channel of gas, groundwater and other fluid migration. Therefore, this paper uses 3DEC software to simulate the temporal and spatial evolution of fractures in overlying strata during the mining of coal seam #15 in Pingshu Coal Mine, Qinshui Coalfield, and studies the fractal characteristics of mining overburden fissure development, then we use the drilling hole backwater method to verify the development height of mining-induced fractures. The results show that the overlying strata bend and collapse obviously with the advance of the working face. The development of overburden fractures shows very regular fractal characteristics, and the fractal dimension can be divided into four stages in time and two stages in space. The research results have guiding significance for mastering the law of overburden movement, accurately identifying groundwater and gas enrichment areas, and strengthening the prevention and control of mine water hazards and the effect of gas drainage. [ABSTRACT FROM AUTHOR]

This study takes the landscape space of traditional Tibetan villages in western Sichuan as the research object, and three national-level traditional villages of different Tibetan clans in Gyatso, Amdo and Baima Tibet were selected as samples. Using the fractal theory, combined with counting-box dimension measurement and spatial analysis methods, it comparatively analyzes the fractal characteristics of their landscape space and their influencing factors. The study finds that the landscape space of these villages has certain fractal characteristics, which are characterized by self-similarity and irregularity. The fractal characteristics of different villages are influenced by various factors such as geographic location, natural conditions, religious beliefs, folk costumes, etc., showing differences and diversity. There is a certain correlation between the fractal dimension and the distribution of landscape elements and spatial patterns, which can be used to describe the complexity and diversity of landscape space pattern. The article believes that the fractal theory provides a new perspective and method for analyzing the landscape space of traditional Tibetan villages, which helps to reveal its intrinsic formation mechanism and cultural connotation and provides new insights for the protection of traditional village heritage and the maintenance of cultural traditions. Meanwhile, the study also points out the limitations and shortcomings of the fractal theory in the study of traditional villages and puts forward directions and suggestions for future research. [ABSTRACT FROM AUTHOR]

In this paper, we have explored the local structure and fractal characteristics of fractal functions with certain fractal dimensions. The conclusion that points with inconsistent oscillation amplitudes with the upper Box dimension of the corresponding fractal functions have been proved to be nowhere dense. This will play an important supporting role in exploring the fractal dimension estimation of the combination of fractal functions. [ABSTRACT FROM AUTHOR]

Using poly(acrylic acid) (abbreviated as PAA) as a shell, bimodal mesoporous silicas (abbreviated as BMMs) as a core, and bipyridine-proline (abbreviated as Z) as an active species, a facile approach for preparation of the P-Z@BMMs nanocomposites with core–shell structure was proposed, which was used as a suitable pH-sensitive catalyst for asymmetric aldol reaction between p-nitrobenzaldehyde and cyclohexanone. Their microstructural features and physicochemical properties were extensively characterized by various methods, such as powder X-ray diffraction patterns, N2 adsorption–desorption isotherms, the scanning (and transmission) electron microscopy images, the dynamic light scattering measurements, the thermogravimetric analysis, the elemental analysis, and the Fourier transform infrared spectroscopy spectra. Particularly, their fractal evolution, the pair distance distribution function, and the Porod plots were demonstrated via the small-angle X-ray scattering patterns. The results elucidated that the PAA was successfully incorporated onto the external amino-modified surfaces of the mesoporous BMMs, and the particles having PAA grafted thereon had a pH-responsive shell in thickness of around 0.97 nm for controlled release of Z species by adjusting pH value of the reaction medium. Besides, the synthesized P-Z@BMMs presented the satisfactory catalytic yields (around 80%) in comparison with the homo- and heterogeneous catalytic system using Z or Z@BMMs as the catalysts.

CO2 + O2in situ leaching has been extensively applied in uranium recovery in sandstone-type uranium deposits of China. The geochemical processes impact and constrain the leaching reaction and leaching solution migration; thus, it is necessary to study the CO2 + O2–water–rock geochemical reaction process and its influence on the physical properties of uranium-bearing reservoirs. In this work, a CO2 + O2–water–rock geochemical reaction simulation experiment was carried out, and the mineralogical and multiscale pore characteristics of typical samples before and after this simulation experiment were compared by X-ray diffraction and high-pressure mercury intrusion porosimetry (HPMIP). The results show that the CO2 + O2–water–rock geochemical reaction has complicated effects on the mineral compositions due to the various reaction modes and types. After the CO2 + O2–water–rock geochemical reaction, the femic minerals decrease and the clay minerals in the coarse sandstone, medium sandstone, fine sandstone, and siltstone increase, while the femic minerals and clay minerals in sandy mudstone show a contrary changing trend. The CO2 + O2–water–rock geochemical reaction decreases the total pore volume of uranium-bearing reservoirs and then promotes pore transformation from small scale to large scale. The fractal dimensions of macropores are decreased, and the fractal dimensions of mesopores, transition pores, and micropores are increased. The effects of felsic mineral and carbonate dissolution, secondary mineral precipitate, clay mineral swelling, and mineral particle migration are simultaneously present in the CO2 + O2in situ leaching process, which exhibit the positive transformation and the negative transformation for the uranium-bearing reservoirs. The mineral dissolution may improve reservoir permeability to a certain degree, while the siltation effect will gradually reveal with the extension of CO2 + O2in situ leaching. This research will provide a deep understanding of the physical property response of uranium-bearing reservoirs during CO2 + O2in situ leaching and indicate the direction for the efficient recovery of uranium resources.

Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To explore the influence of liquid nitrogen (LN 2) cooling on the structural damage and failure characteristics of coal, a series of structural experiments, uniaxial compression tests, and crack morphology characterization experiments were carried out in this study. Based on the fractal theory, the pore structure damage and failure characteristics of the coal before and after the LN2 cooling treatment were compared. After the LN2 treatment, the structural damage inside the coal increases. Compared to the untreated coal, the fractal dimensions of the total pores, seepage pores, and adsorption pores in the LN2-treated coal decrease by 0.88%, 0.24%, and 5.16%, respectively. The results indicate that the LN2 cooling treatment can increase the connectivity of pores, especially adsorption pores. The internal structure damage of the coal induced by the LN2 treatment reduces its compressive strength and elastic modulus by 27.86% and 32.62%, respectively. Simultaneously, it can be found that the fragments fractal dimension of the coal decreases by 9.53%, and the fractal dimension of the induced fracture surface increases from 2.134 to 2.151 after the LN2 treatment. By the LN2 treatment, the distribution of fragments becomes more uniform, and the complexity of the generated fracture surface increases. Therefore, the LN2 cooling treatment can increase the effective seepage path and the contact area between the crack and the coal matrix to promote the gas flow and enhance the gas desorption in the coal matrix. The experimental results also show that the damage of the single LN2 treatment on the coal is limited. LN2 cycling treatment is suggested to use to improve the efficiency of the coalbed methane extraction because that it can give full play to the multiple cracking effects of LN2 on the coal. [ABSTRACT FROM AUTHOR]

Soil particle-size distribution (PSD) is the most important physical attributes due to its influence on soil properties related to water movement and soil management, erosion. Therefore, characterizing variations in the PSDs of soil are an important issue in environmental research. Till now, the fractal model could well characterize soil particle-size distribution, and its calculation is a function of the subdivisions of soil fractions (clay, silt, and sand). But few studies are carried on to analyzed the effects of soil particlesize classification (PSC) systems on calculating single volume fractal dimensions. Therefore, top soil across different stands, which composed of Pinus sylvestris var. mongolica, Pinus tabuliformis and Populus were selected. The study was undertaken in the Magu forestry farm, China. Soil PSD was measured with a laser diffraction technique, and fractal dimensions (D) were calculated. The experimental results showed that: (1) The PSD was distributed within the sand classification followed by clay and silt particle contents. The order of D values was USDA(1993)> ISO14688 (2002)> ISSS (1929) PSC systems. (2) Fractal dimensions exhibit a significant negative linear correlation with the sand content and a significant positive correlation with the content of clay and silt. (3) The D values of three PSC systems are significantly positive correlated, which indicated that they could achieve mutual transformation. (4) According to the fractal model and descriptions of soil fractions under different soil PSC systems, refining clay and sand fractions could increase D values. From above, it was suggested that USDA (1993) soil PSC system is highly recommended. [ABSTRACT FROM AUTHOR]

• Introducing two characteristic parameters, T 0 and n , yielded a modified Arrhenius formula. • A wax deposition model was established to quantitatively calculate the wax damage. • A fractal model for pseudo threshold pressure gradient of high-pour-point oil was established. As an essential replacement for conventional crude oils, accurately grasping the flow behavior and threshold pressure characteristics of high-pour-point (high-PPT) oil is pivotal for studying the pressure field and remaining oil distribution in development, and formulating effective strategies. This paper delves into the internal factors contributing to the deterioration of the flow capacity of high-PPT oil, focusing on reservoir and crude oil characteristics, and comprehensively explores its non-Darcy percolation behavior through experiments and analytical methods. The findings highlight that complex reservoir structures, coupled with significant non-Newtonian rheological behavior and notable wax deposition damage, exacerbate the reduction in high-PPT oil flow capacity. Percolation experiments unveil a power-exponential relationship (G = 5.367 ∙ λ oil - 1.018 ) between the pseudo threshold pressure gradient (PTPG) and oil mobility, constructing a flow boundary chart. Based on this relationship, the critical oil mobility and an ultimate drainage radius formula are derived. Furthermore, leveraging the mechanical equilibrium relationship and fractal theory of porous media, a PTPG prediction model accounting for pore structure characteristics, non-Newtonian characteristics, and wax deposition damage is established. The predicted threshold pressures align well with experimental results, validating the model's efficacy. Notably, PTPG values positively correlate with pore radius fractal dimension, tortuosity fractal dimension, and yield stress of high-PPT oil, while negatively correlating with maximum pore radius and permeability retention degree after wax deposition. These research findings offer valuable insights for designing development schemes for high-PPT oil reservoirs under complex working conditions. [ABSTRACT FROM AUTHOR]

The fractal characteristics of the security market were considered in portfolio strategy optimization. First, the detrended cross-correlation analysis was adopted to measure the fractal correlation of different securities. Second, the fractal correlation was embedded into the mean-variance criterion of the modern portfolio theory. Third, the mean-detrended cross-correlation analysis portfolio strategy of multiple risk assets was constructed, and the analytic solution of the strategy was given. Finally, the evaluation results revealed that the constructed the mean-detrended cross-correlation analysis portfolio strategy clearly improved investment performance, thus achieving the goal of optimizing the multiple risk asset portfolio strategy. [ABSTRACT FROM AUTHOR]

Based on physical property, casting thin section, scanning electron microscope, high-pressure mercury injection and other test analysis data, the fractal dimension of pore structure of tight sandstone reservoir was calculated by the method of mercury saturation and water saturation in the first Member of Lower Shihezi Formation in Hangjinqi area, and the relationship between fractal dimension and the physical properties of reservoir was analyzed.The results have shown that the average porosity and permeability of the Lower Shihezi Formation reservoir were 9.83% and 1.03×10-3 μm2, respectively.The reservoir space is mainly composed of intergranular dissolved pores, intragronular dissolved pores and residual intergranular pores.The overall fractal dimension calculated by the mercury saturation method is distributed in 2.138 4-2.829 2 with an average value of 2.396 5 while calculated by the water saturation method is distributed in 2.529 4-2.879 7 with an average value of 2.679 1.Compared with the water saturation method, the fractal dimension calculated by the mercury saturation method has a better correlation with the porosity, permeability and pore structure parameters, because the water saturation method tends to produce deviation on samples with smaller pore throat.The pore structure was divided into four types based on fractal dimension: Type Ⅰ(Df≤2.31), Type Ⅱ(2.31 < Df < 2.4), Type Ⅲ(2.4≤Df < 2.52), Ⅳ(Df≥2.52).Fractal dimension(Df), averoged radius of pore throct(Rm) and porosity(φ) were selected to calculate permeability by multiple nonlinear regression.The calculated permeability by multiple nonlinear regression shows strong correlation with measured permeability, whose correlation coefficient squared is more than 0.9, which means the permeability estimation model is suitable for the study area.

This study aims to ensure the safe and efficient mining of No.69 tantalum–niobium ore bodies in an underground metal mine in Jiangxi Province. Brazilian splitting tests were conducted on disc samples of two types of surrounding rocks (sandy slate and granite) from the + 417 m middle section of the mine at different loading rates (0.002, 0.005, and 0.01 mm/s). The tensile strength, failure mode, acoustic emission (AE) characteristics, and fractal features of disc samples during splitting failure were analyzed in relation to the loading rate. The study demonstrates that with an increase in the loading rate, the duration of splitting failure of both sandy slate and granite significantly decreases, and the corresponding ultimate load at the time of failure significantly increases. The tensile strength of the sandy slate and granite increases linearly with the loading rate, and the growth rate of the tensile strength of the granite samples was slightly larger than that of the sandy slate. The loading rate has a significant effect on the failure pattern of the splitting process of rock disc samples. The AE ringing counts and energy of the sandy slate and granite both show an increasing trend with the loading rate. Under low loading rate, the AE ringing count signal is generally of "solitary vibration" type, and under high loading rate, the ringing count curve is generally of "group vibration" type. The peak mean values of ringing counts and energy of the sandy slate were larger than those of granite under different loading rates. The maximum values of the AE fractal dimension of both sandy slate and granite appeared between 60 and 80% of the peak stress. The research results can provide a reference for the analysis and prediction of rock stability during the design and construction of ore body mining. [ABSTRACT FROM AUTHOR]

Abstract Broken coal and rock masses are the major part of the goaf. The compaction characteristics of coal and rock masses and the breakage law of whose particles during compaction exert an important influence on various aspects including control of strata motion, prediction of surface subsidence, and backfill mining. In this paper, the triaxial compaction experiment on broken coal‐rock masses with different mixing ratios was carried out. The test results showed that with the increase of stresses, the strain of coal‐rock masses gradually rose while the porosity, bulking factor, and degree of compaction gradually declined. During the compaction of coal‐rock masses, the fitting curves of the strain, porosity, bulking factor, and degree of compaction with stresses of coal samples all appeared as a cubic function of stresses. The breakage behavior of coal particles underwent three stages: structure re‐arrangement and breakage of particles, particle breakage, and compression‐induced deformation of particles. With increasing stress, the crushing amount of particles gradually grew while the increase rate of the crushed particles gradually decreased and the larger the particle strength was, the lower the increase rate of the crushing amount. Additionally, in the compaction process of samples, particle breakage mainly appeared before the stress reached to 8 MPa while the coal and rock particles were hardly crushed after the stress was larger than 8 MPa. With increasing stresses, the particle size gradation of samples gradually became reasonable and the lower the particle strength of samples was, the more reasonable the particle size gradation of compacted samples. The particle size gradation of various compacted and crushed samples showed a favorable fractal characteristic. In the stage with a low stress, the value of fractal dimension D rapidly grew and the fractal dimensions D of various samples tended to be stabilized after the stress reached to a high level.

The Permian Lucaogou Formation in the Jimusar sag, Junggar Basin, northwestern China, is increasingly receiving attention for its shale oil potential, which is still in the exploration stage. In this work, core samples were obtained from two wells in the Jimusar sag, and their mineralogy, pore structure, and fractal characteristics were investigated by XRD (X-ray diffraction) analysis, LPNA (low-pressure N2 adsorption) analysis, FE-SEM (field emission scanning electron microscopy), CTS (casting thin sections), and fractal analysis. The results showed that the major mineral compositions were plagioclase (average 34.82%), quartz (average 17.07%), and dolomite (average 17.66%). Compared with well-known marine shales in China, the shales have higher feldspar (average 44.64%) and carbonate (average 26.03%), and lower quartz (average 17.07%). Based on the FE-SEM and CTS, organic matter, intergranular, interlayer, dissolved, intercrystalline pores, and microfractures were observed. The specific surface area ranged from 10.181 to 26.648 m2/g, and the total pore volume was between 0.03595 and 0.07102 cm3/g. The results of the DFT-PSD curves indicated that shales showed multi-modal distribution characteristics, whereas the results of the BJH-PSDs curves revealed that shales displayed unimodal distribution characteristics with a peak between 20 and 40 nm. Pore sizes of less than 5 nm had an important influence on the specific surface areas, whereas pore sizes ranging from 20 to 40 nm had an important influence on the total pore volume. The fractal dimension values ranged from 2.7564 to 2.8382. The fractal dimension decreased as the average pore size increased and increased as the total pore volume and specific surface area increased. [ABSTRACT FROM AUTHOR]

Pore structure parameters are significant for investigating the diffusion properties of volatile organic compounds from building materials. Traditional characterization methods could provide ether surface morphology or some pore parameters of the material, which could not comprehensively reflect the overall information. X-ray tomography, as an advanced nondestructive method, can not only characterize the three-dimensional structure characteristics but also comprehensively measure pore parameters of materials. This study applied X-ray tomography to systematically analyze the geometry and volatile organic compound emission paths of medium-density fiberboard. The three-dimensional structures of pores and materials were reconstructed respectively. The isolated pores and connective pores were extracted to indicate the pore connectivity, and skeletonization was simultaneously applied, allowing visualization of the volatile organic compound diffusion paths. The porosity was 54.67%, and 99.91% of the pores were connective pores. The tortuosity was 2.07, and the fractal dimension was 2.605, indicating the heterogeneity and self-similarity of pore structures. Scanning electron microscopy was used to characterize the two-dimensional morphology of the material, and mercury intrusion porosimetry was applied to analyze the pore parameters. The results were consistent with that of X-ray tomography, and their coupling with X-ray tomography could comprehensively characterize the structures and parameters of indoor building materials, which could contribute significantly to future research on volatile organic compound emission mechanisms and building physics. [ABSTRACT FROM AUTHOR]

Machine joint surface has an important impact on the performance of mechanical systems. Based on fractal theory, joint surface is assumed to be the contact between absolute smooth surface and rough surface. Through the analysis of the contact process, the contact mechanics model, the contact stiffness model and the three-dimensional surface micro-contact model are studied. To obtain fractal characteristic, the factors and laws affecting the contact characteristics are indicated through digital simulation. The concept of micro-convex body hierarchy is proposed. The critical values are related to the scale of micro-convex bodies and affected by the property parameters of the material. It is proved that the critical point is smooth and continuous, the parameter characteristics of the critical point are determined and the error between prediction and practice is reduced. In the integral calculation of the model, the experimental constants are also established to facilitate the calculation. The results show that the contact process of rough surface is consistent with the actual contact. It makes up the deficiency of KE model by considering the interaction between micro-convex bodies. [ABSTRACT FROM AUTHOR]

Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• SDS synergistic acidification increased the proportion of seepage pores by 5.99%. • SDS synergistic acidification promotes the pores connectivity of coal. • The average size of corrosion hole is distributed at the nanometer scale. • Coal quality characteristics have a great influence on the pore fractal dimension. In order to study the influence of surfactant on pore fractal characteristics of composite acidized coal. In this paper, the coal samples were acidified by solution constituted with the Sodium Dodecyl Sulfate (SDS), hydrochloric acid (HCL) and hydrofluoric acid (HF). And the proximate and ultimate analysis, X-ray diffraction (XRD) testing, scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS) and nuclear magnetic resonance (NMR) testing were carried out. The fractal dimension of pore in coal was evaluated by fractal theory, and the evolution relationship between coal quality, NMR fractal features and coal pore structure parameters were characterized. The results show that the addition of surfactant has a great influence on the coal characters. The mineral content in coal is exponential positively correlated with the fractal dimension (D s) of seepage pores. The relative content of ash is linear positively correlated with the fractal dimension. Conversely, the volatiles is linear negatively correlated with the fractal dimension. SDS synergistic acidification compared to without SDS, the fractal dimension (D w) of the total pore distribution and the fractal dimension (D s) of the seepage pores are both reduced, indicated that the addition of SDS promotes the improvement of coal pore connectivity by acidification treatment. The results showed that after SDS synergistic acidification, the proportion of seepage pore volume was increased by 5.99%, and the fractal dimension is linear negatively correlated with the porosity. The changes of these parameters are beneficial to the seepage, migration and extraction of coalbed methane. Therefore, SDS synergistic composite acid fracturing technology has practical guiding significance for improving acid fracturing effect and increasing coal seam permeability. The research results are of great significance for improving the efficiency of coalbed methane mining and reducing coalbed methane pollution. [ABSTRACT FROM AUTHOR]

Enhanced coalbed methane (ECBM) recovery is significantly affected by the pore structure and cleat network of coal during liquid CO 2 (LCO 2) injection into unmineable coal seams. However, the changes in the microstructure after coal samples are treated with LCO 2 freezing-thawing are poorly understood. Therefore, a combination of mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) methods was employed to investigate the evolution of the pore structure and cleat network in coal samples treated with LCO 2 under reservoir conditions (0.5 MPa, −50 °C, for 6 h). The results indicated that average increase rates of the total pore volume, total pore area, and average pore diameter are 18.60, 3.24, and 29.90%, respectively, for the treated coal specimens. The increase rates of the specific surface area and incremental pore volume were higher for seepage pores than for adsorption pores after the coal samples were treated with LCO 2. Numerous new pores are generated and the seepage capacity of the pores is increased as a result of LCO 2 injection for ECBM processes. Comparison of the fractal dimension D 1 ′ of the treated specimens (average value of 2.82) with that of raw coal samples (D 1 , average value of 2.71) revealed that the treated specimens had more evident fractal characteristics, indicating their more complex morphology and stronger seepage capacity. Micro-CT analyses indicated a significant amount of newly generated fractures and showed that many original cleats expanded after the coal samples underwent LCO 2 freezing-thawing. The connectivity of the cleat network in the coal slices was poor, resulting in slightly increased permeability of the treated specimens, which indicateds that the degree of LCO 2 -induced damage to the coal pore structure was greater than that to the cleat network under the laboratory conditions. [ABSTRACT FROM AUTHOR]

Broken coal and rock masses are the major part of the goaf. The compaction characteristics of coal and rock masses and the breakage law of whose particles during compaction exert an important influence on various aspects including control of strata motion, prediction of surface subsidence, and backfill mining. In this paper, the triaxial compaction experiment on broken coal‐rock masses with different mixing ratios was carried out. The test results showed that with the increase of stresses, the strain of coal‐rock masses gradually rose while the porosity, bulking factor, and degree of compaction gradually declined. During the compaction of coal‐rock masses, the fitting curves of the strain, porosity, bulking factor, and degree of compaction with stresses of coal samples all appeared as a cubic function of stresses. The breakage behavior of coal particles underwent three stages: structure re‐arrangement and breakage of particles, particle breakage, and compression‐induced deformation of particles. With increasing stress, the crushing amount of particles gradually grew while the increase rate of the crushed particles gradually decreased and the larger the particle strength was, the lower the increase rate of the crushing amount. Additionally, in the compaction process of samples, particle breakage mainly appeared before the stress reached to 8 MPa while the coal and rock particles were hardly crushed after the stress was larger than 8 MPa. With increasing stresses, the particle size gradation of samples gradually became reasonable and the lower the particle strength of samples was, the more reasonable the particle size gradation of compacted samples. The particle size gradation of various compacted and crushed samples showed a favorable fractal characteristic. In the stage with a low stress, the value of fractal dimension D rapidly grew and the fractal dimensions D of various samples tended to be stabilized after the stress reached to a high level. [ABSTRACT FROM AUTHOR]

Highlights • Multiscale image-based shale pore structure fractal characteristic is studied. • The real gas permeability fractal model considering second order slip is derived. • Image resolution for accurate permeability prediction should be less than 50 nm. Abstract The heterogeneities of shale are manifested in the complex pore spatial configurations and the wide distribution of pore sizes. The recent advances of high-resolution imaging techniques such as Scanning Electron Microscope (SEM) and Focussed Ion Beam Scanning Electron Microscopes (FIB-SEM) enable accurate characterization of shale pore structure in the limited imaging area. Due to the nature of multiscale pore size, image-based petrophysical properties are highly dependent on the selection of image resolution. Fractal theory proves to be an effective approach to characterize pore structure as well as calculate fluid transport properties. In this study, the image-based fractal characteristic of shale pore structure at multiscale resolutions is investigated and its impact on the accurate prediction of gas permeability is analyzed. The fractal dimensions of pore phase in 100 SEM images at resolutions ranging from 15.5 nm to 420 nm are calculated by the box counting method and Sierpinski carpets analytical solution. The real gas permeability model in consideration of second order slip is derived based on the fractal theory. Two groups of gas permeabilities at different resolutions are estimated respectively based on the fractal dimensions obtained from the box counting method and Sierpinski carpets analytical solution. The results found that fractal dimensions obtained from the box counting method at different resolutions are more close to the exact fractal dimension compared with that obtained from the Sierpinski carpets analytical solution at low resolutions and gas permeabilities calculated at different resolutions based on the box counting estimated fractal dimensions are more close to the exact gas permeability. The image resolution for accurate calculation of shale pore structure properties and gas permeability should be less than 50 nm based on our analysis results. [ABSTRACT FROM AUTHOR]

Aiming at the problem of load test data volume of transmission system of heavy tracked vehicles（HTVs） is huge and extraction rate of effective information is low,the inherent fractal hierarchical rule of this data is studied,this data have the typical fractal characteristic is verified and the fractal parameter of the tracked vehicle transmission system load data under a certain road condition.Under the premise of ensurse data accuracy and fractal character,a new fractal interpolation method（FIM） is built,the continuation to simplify data information is realized.Moreover,obvious advantages could be observed in the results of the FIM,comparing to those of the linear interpolation method and the spline interpolation method.It could be concluded that by combining a’low-frequency-and-long- time’ sampling approach and the proposed FIM,the test efficiency of load history can be improved,the complex chaotic feature of high frequency sampling data can be represented.And a analysis way for researching the dynamic chaos characteristic of the HTVs transmission system is provided.

Using poly(acrylic acid) (abbreviated as PAA) as a shell, bimodal mesoporous silicas (abbreviated as BMMs) as a core, and bipyridine-proline (abbreviated as Z) as an active species, a facile approach for preparation of the P-Z@BMMs nanocomposites with core–shell structure was proposed, which was used as a suitable pH-sensitive catalyst for asymmetric aldol reaction between p-nitrobenzaldehyde and cyclohexanone. Their microstructural features and physicochemical properties were extensively characterized by various methods, such as powder X-ray diffraction patterns, N 2 adsorption–desorption isotherms, the scanning (and transmission) electron microscopy images, the dynamic light scattering measurements, the thermogravimetric analysis, the elemental analysis, and the Fourier transform infrared spectroscopy spectra. Particularly, their fractal evolution, the pair distance distribution function, and the Porod plots were demonstrated via the small-angle X-ray scattering patterns. The results elucidated that the PAA was successfully incorporated onto the external amino-modified surfaces of the mesoporous BMMs, and the particles having PAA grafted thereon had a pH-responsive shell in thickness of around 0.97 nm for controlled release of Z species by adjusting pH value of the reaction medium. Besides, the synthesized P-Z@BMMs presented the satisfactory catalytic yields (around 80%) in comparison with the homo- and heterogeneous catalytic system using Z or Z@BMMs as the catalysts. [ABSTRACT FROM AUTHOR]

In order to study the fractal characteristics and energy dissipation of concrete suffered freeze-thaw cycle actions and impact loading, C35 concrete was taken as the research object in this paper, and freeze-thaw cycle tests were carried out with a freeze-thaw range of −20 °C~20 °C and a freeze-thaw frequency of 0~50 times. The degradation characteristics of concrete material and the variation rules of basic physical parameters under various freeze-thaw cycle conditions were obtained consequently. By using the SHPB (separated Hopkinson pressure bar) test device, impact compression tests of concrete specimens under different freeze-thaw cycle actions were developed, then the process of impact crushing and the mechanism of damage evolution were analyzed. Based on the screening statistical method and the fractal theory, the scale-mass distribution rules and fractal dimension characteristics of crushing blocks are investigated. Furthermore, the absorption energy, fracture energy and block kinetic energy of concrete under different conditions were calculated according to the energy dissipation principle of SHPB test. The relationship between the energy consumption density and the fractal dimension of fragments was established, and the coupling effect mechanism of freeze-thaw cycle action and strain rate effect on the fractal characteristics and energy consumption was revealed additionally. The research results show that the concrete under different freeze-thaw cycle conditions and impact loading speeds has fractal properties from the microscopic damage to the macroscopic fracture. The energy dissipation is intrinsically related to the fractal characteristics, and the energy consumption density increases with the increase of the fractal dimension under a certain freeze-thaw cycle condition. When at a certain loading speed, with the growth of freeze-thaw cycles, the energy consumption density reduces under the same fractal dimension, while the fractal dimension improves under the same energy consumption density.

The structure and fractal characteristic of micro- (0.32∼2 nm) and meso-pores (2–50 nm) in low, middle-rank (maximum vitrinite reflectance, R o, max = 0.65–1.34%) tectonic deformed coals (TDCs) were revealed by combining low temperature N 2 /CO 2 adsorption (LPN 2 /CO 2 GA) and fractal theory. The main conclusions are as follows: 1) The evolution of pore shapes in TDC sequence manifests as the stable existence of Type II pores (<3.3 nm) of bad connectivity, gradually increasing of the fine bottleneck pores of 3.3∼4 nm, and gradually decreasing of open plate pores of <10 nm 2) The total specific surface area (SSA, determined by Brunauer-Emmett-Teller (BET) model) and pore volume (PV, determined by Barrett-Joyner-Halenda (BJH) model) of meso-pores increase with the enhancement of tectonic deformation, especially for the ductile deformation. The meso-pores’ SSA are mainly provided by meso-pores of 2–10 nm and 10–20 nm in TDCs, however both the SSA proportion of 2–10 nm and of 10–20 nm increase with the increasing tectonic intensity, indicating that the tectonic deformation especially the ductile deformation can promote the migration of meso-pores’ SSA to small aperture directions. The micro-pore SSA and PV (determined by Density-Function-Theory (DFT) model) are mainly provided by the micro-pores of 0.4–0.7 nm and 0.8–1.0 nm, respectively. 3) The volume heterogeneity are characterized by D V1 (8–50 nm, Frenkel-Halsey-Hill (FHH) model), D V2 (2–8 nm, FHH model), and D V3 (0.32–2.0 nm, Sierpinski model). The D 2V increases both with the brittle and ductile deformation. D 1V only increase significantly with the ductile deformation. The significant increase of D V3 with the ductile deformation indicates that the ductile deformation process has a significant promoting effect for the micro-pores’ volume heterogeneity. 4) The surface heterogeneity can be characterized by D S1 (0.32–0.62 nm), D S2 (0.62–2.0 nm), D S3 (2–25 nm), and D S4 (25–50 nm), all of which increase with the enhancement of the tectonic deformation, demonstrating that the tectonic deformation has a more significant transformation effect for the surface heterogeneity than the volume heterogeneity. However, D S2 increases more sharply than D S1 and also D S4 increases more sharply than D S3 , demonstrating that the transformation effect of tectonic deformation on the surface heterogeneity gradually weakened with the decreasing of the pore scale. [ABSTRACT FROM AUTHOR]

New principal component analysis (PCA) respirator fit test panels had been developed for current American and Chinese civilian workers based on anthropometric surveys. The PCA panels used the first two principal components (PCs) obtained from a set of 10 facial dimensions. Although the PCA panels for American and Chinese subjects adopted the bivairate framework with two PCs, the number of the PCs retained in the PCA analysis was different between Chinese subjects and Americans. For the Chinese youth group, the third PC should be retained in the PCA analysis for developing new fit test panels. In this article, an additional number label (ANL) is used to explain the third PC in PCA analysis when the first two PCs are used to construct the PCA half-facepiece respirator fit test panel for Chinese group. The three-dimensional box-counting method is proposed to estimate the ANLs by calculating fractal dimensions of the facial anthropometric data of the Chinese youth. The linear regression coefficients of scale-free range R2 are all over 0.960, which demonstrates that the facial anthropometric data of the Chinese youth has fractal characteristic. The youth subjects born in Henan province has an ANL of 2.002, which is lower than the composite facial anthropometric data of Chinese subjects born in many provinces. Hence, Henan youth subjects have the self-similar facial anthropometric characteristic and should use the particular ANL (2.002) as the important tool along with using the PCA panel. The ANL method proposed in this article not only provides a new methodology in quantifying the characteristics of facial anthropometric dimensions for any ethnic/racial group, but also extends the scope of PCA panel studies to higher dimensions. [ABSTRACT FROM AUTHOR]

This study considers the fractal characteristics of differentiated xylem cells of the fast-growing Populus×euramericana cv. ‘74 /76’ during the active phase by the method of differential box-counting fractal dimension. The fractal characteristics of differentiated xylem cells as well as the relationship between fractal dimension and tissues proportion were considered. Results showed that the fractal dimensions of cross sections were larger than those of tangential sections. Fractal dimension of cross sections had a remarkable negative correlation with the ratio of vessel element, significant positive correlations with the proportion of wood fiber and the proportion of parenchyma. The correlation of fractal dimension with wood fiber proportion was more significant than that with parenchyma proportion. The results were also verified by replacement of the tissues in the cross section. It was observed that fractal characteristics of the wood microstructure were very much related to the proportions of different tissues of the xylem cells.

Pore structure has a significant influence on coal-bed methane (CBM) enhancement. Injecting liquid CO2 into coal seams is an effective way to increase CBM recovery. However, there has been insufficient research regarding the damage effects and fractal characteristics of pore structure at low temperature induced by injecting liquid CO2 into coal samples. Therefore, the methods of low-pressure nitrogen adsorption-desorption (LP-N2-Ad) and mercury intrusion porosimetry (MIP) were used to investigate the damage effects and fractal characteristics of pore structure with full aperture as the specimens were frozen by liquid CO2. The adsorption isotherms revealed that the tested coal samples belonged to type B, indicating that they contained many bottle and narrow-slit shaped pores. The average pore diameter (APD; average growth rate of 18.20%), specific surface area (SSA; average growth rate of 7.38%), and total pore volume (TPV; average growth rate of 18.26%) increased after the specimens were infiltrated by liquid CO2, which indicated the generation of new pores and the transformation of original pores. Fractal dimensions D1 (average of 2.58) and D2 (average of 2.90) of treated coal samples were both larger the raw coal (D1, average of 2.55 and D2, average of 2.87), which indicated that the treated specimens had more rough pore surfaces and complex internal pore structures than the raw coal samples. The seepage capacity was increased because D4 (average of 2.91) of the treated specimens was also higher than the raw specimens (D4, average of 2.86). The grey relational coefficient between the fractal dimension and pore structure parameters demonstrated that the SSA, APD, and porosity positively influenced the fractal features of the coal samples, whereas the TPV and permeability exerted negative influences.

Tight gas sandstone is a unique kind of unconventional hydrocarbon resource in that its intricate pore throat structure governs reservoir physical properties and gas reservoir productivity. However, the effect of differential diagenesis of various lithofacies on the heterogeneity of pore throat structure remains unclear. In this paper, a series of experiments were integrated to evaluate pore throat structures and fractal characteristics of the different lithofacies in a tight sandstone gas reservoir, and followed by a study of the impact of diagenetic alteration on them. Results demonstrate that the mineral composition, dominant pore types, pore throat structural parameters, fractal dimension, and physical properties of various lithofacies are notably different, which is mostly attributable to diagenetic alteration variability. There are more primary pores and less clay mineral content in coarser lithofacies. Pebbly coarse-grained sandstone and sandy conglomerate reservoirs that have undergone strong dissolution have more composite pores composed of residual intergranular pores and dissolution pores, which help to form a homogeneous pore throat system with good connectivity, resulting in the best reservoir quality. Due to the strong compaction and high clay mineral content filling pores and throats in medium-grained sandstone and fine-grained sandstone lithofacies, a large number of primary pores were lost, and throats were blocked, which easily formed intercrystalline pores, leading to poor reservoir quality. Coarse-grained sandstone reservoirs with moderate clay mineral content have undergone moderate compaction and dissolution and have moderate reservoir quality. Filamentous illite is the most destructive clay mineral to pore throat connectivity. Intergranular dissolution pores and moldic pores contribute significantly to the physical properties of pebbly coarse-grained sandstone and sandy conglomerate reservoirs. Pebbly coarse-grained sandstone and sandy conglomerate lithofacies are considered high-quality reservoirs with greater development potential for tight gas. This work has important guiding significance for the prediction of high-quality reservoirs in similar tight sandstone reservoirs. • Diverse techniques were combined to investigate the pore throat heterogeneity. • Pore throat fractal characteristics of various lithofacies were characterized based on NMR data. • Illite is the most damaging to pore throat connectivity among clay minerals. • Secondary dissolution pores significantly improve the reservoir's physical properties. • The variability of diagenesis in various lithofacies causes pore throat heterogeneity. [ABSTRACT FROM AUTHOR]

Acidification erosion can seriously affect the pore structure characteristics of anthracite. In this paper, the low-temperature nitrogen adsorption method, mercury intrusion method, and Micro-CT scanning are used to analyze the pore structure of coal samples. The microscopic morphology and spatial distribution of coal pores are characterized by fractal dimension calculation and three-dimensional reconstruction. The results show that HCl has the highest removal efficiency of minerals in the Yuwu coal sample, which reduces the mass of coal samples by about 4%. HNO 3 increases the proportion of micropore volume by 4.93%. HCl increases the proportion of mesoporous pore volume by 11.4%. Through the 3D reconstruction of coal, it is found that the mineral content in coal decreased by 48.14% after HCl dissolution, and the maximum diameter of mineral particles decreased from 173.588 μm to 57.449 μm. The spatial distribution of minerals is uneven, and the mineral content of coal samples decreases significantly along the direction of strong fluidity. At the same time, HCl increases the pore connectivity of coal samples, the pore roar increases by 56.72%, the isolated pores decrease, and the peak frequency of pore coordination number increases by 4 units, which greatly improves the transport capacity of fluid in coal matrix. • The pore expansion mechanism of acidified coal is being further studied. • Liquid intrusion method and Micro-CT scanning are applied to study pore structure. • The changes of pore morphology are described by fractal dimension. • Spatial law of pores and minerals are revealed by 3D reconstruction technology. [ABSTRACT FROM AUTHOR]

The heterogeneity of shale pore structure is a vital problem that cannot be ignored in the process of shale oil exploration and development. The organic-rich laminated shale (ORLS) and organic-poor layered shale (OPLS) show significantly different pore system heterogeneity. In this study area, the porosity and permeability of ORLS (2.7% and 0.00053mD) are higher than those of OPLS (2.29% and 0.00041mD). The heterogeneity of the pore system in ORLS is reflected by the wider pore size range of intercrystalline pores (pore size of 0.002–5.5 μm), the stronger holistic distribution heterogeneity of intergranular pores (average △α of 1.61) and organic pores (average △f of 2.65) at local locations. The wider range and discontinuity of the pore size distribution for intergranular pores and organic pores, and the instability of the morphological structure for intercrystalline pores and microfractures, all lead to the heterogeneity of the pore system in OPLS. The micropore (<2 nm) volume and macropore (>50 nm) volume of ORLS are higher than that of OPLS, while the surface area and volume of mesopores (2–50 nm) are lower than those of OPLS. The macropore has the most obvious fractal characteristics and three fractal dimensions. The macropore volume of ORLS is positively correlated with reservoir physical and pore multifractal properties, while the mesopore volume of OPLS is positively correlated with reservoir properties and negatively correlated with fractal properties. Pore system evolution patterns of shale reservoirs are obviously controlled by the mineral composition, laminae, TOC content, thermal evolution degree and fluid pathways. The macropore volume in ORLS shows a clear positive correlation with the pyrite content. The high TOC content and high thermal evolution degree are more likely to produce erosive fluids. Laminar interfaces, microfractures and primary pores provide channels for the fluid migration. The development degree of secondary dissolution may be an important factor leading to the difference of reservoir qualities between ORLS and OPLS. • Pore structures of multi-type pores and multi-scale pores in the ORLS and OPLS have strong heterogeneity. • The integration of CGA, NGA, HPMI and fractals can characterize shale pores more finely. • The dominant pore volume is helpful to physical properties, while pore fractal shows dual effects. • The reservoir qualities of ORLS and OPLS are the function of five main controls. • ORLS and OPLS have different pore evolution patterns. [ABSTRACT FROM AUTHOR]

CO 2 intrusion has a crucial effect on the pore structure of mineral-bearing coal. In this study, we selected long flame coal, lean coal, and anthracite after CO 2 adsorption at different pressures and tested the coal samples using X-ray diffraction, mercury intrusion porosimetry, and N 2 (77 K) adsorption methods. The tests were conducted to determine the variations in mineral content, pore structure, and fractal characteristics. The results showed that supercritical CO 2 had a greater ability to dissolve minerals in coal than that of subcritical CO 2. Although the total pore volume and BET specific surface area gradually increased with the increase in CO 2 intrusion pressure in coal, the transformation of different pores and partial new pores caused by the dissolution of minerals and the adsorption swelling of coal matrix caused the micro-macropores in the three coal samples to exhibit different trends. The pore surface roughness and pore structure complexity of seepage pore in the long-flame coal after CO 2 adsorption increased while those of the lean coal and anthracite decreased. Meanwhile, CO 2 intrusion caused the surface of the adsorption pore in coal to become smooth, and the pore structure was more regular, except for the lean coal. A conceptual model of the mineral-bearing coal was developed to describe the relationship between the mineral composition and pore structure induced by CO 2 intrusion. These findings help to understand the transformation effect of CO 2 on coal seams. Thus, a higher CO 2 injection pressure should be used to obtain a larger injection volume and shorter injection time during CO 2 storage implementation. • Supercritical CO 2 has a greater ability to dissolve minerals than subcritical CO 2. • The pore volume in coal gradually increases with increasing CO 2 intrusion pressure. • CO 2 intrusion smoothes the surface and regularizes the structure of adsorption pore. • A conceptual model of the effect of mineral on pore structure was established. [ABSTRACT FROM AUTHOR]

• The pore structure evolution of coal before and after stimulation was investigated. • Oxidation simplifies pore structure while microwave heating destroys pore space. • Microwave-assisted oxidation promotes the dilatation and connection of pores. • The pore volume of bituminous coal increases by 31.94% after stimulation. Coal reservoir stimulation is a process of enhancing coalbed methane (CBM) production by dilating, opening, and extending the width, length, and connectivity of the natural pore/fracture systems. Novel stimulation techniques including N 2 injection, ultrasonic wave, acidification, and plasma treatment have been proposed, but none is ubiquitously successful. As an alternative stimulation method, oxidation dissolves the organic molecules that plug the pores and fractures resulting in opening and interconnecting passageways to flow gas through the reservoir. However, oxidation has minimal effect on pores and microfractures. Microwave-assisted oxidation may be a potential stimulation strategy. In this study, the influence of microwave-assisted oxidation on pore structure and fractal characteristics of bituminous coal was investigated based on low-temperature nitrogen adsorption. Results show that microwave-irradiated coal has the highest fractal dimension D 2 , implying that microwave heating destroys the pore structure. The microwave-induced fractures are blocked by coal particles and mineral debris. The reduction in the micropore volume, specific surface area, and D 2 of oxidized coal confirms that oxidation simplifies the pore structure. Combined with microwave heating, the oxidizer easily penetrates into the coal matrix. As a result, the total pore volume increases by 31.94% and the isolated pores are connected. This study fills a knowledge gap on microwave-assisted oxidation stimulation and contributes to the decision of selecting appropriate method to enhance the exploitation of CBM. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature on the morphology and surface fractal dimension of titanium dioxide (TiO2) films prepared via the spray deposition process was investigated. Thin films with various morphologies were obtained at different temperatures and characterized by X-ray diffraction and atomic force microscopy (AFM). It was found that the crystalline structure of TiO2 films depends strongly on annealing temperature. At higher temperatures, the partial phase transformation of anatase-to-rutile was observed. The morphology and surface fractal dimensions were evaluated by image analysis methods based on AFM micrographs. The results indicate that the value of surface roughness (the standard deviation of the height values within the given area of AFM image) of TiO2 films increases with increasing annealing temperature. Fractal analysis revealed that the value of the fractal dimension of the samples decreases slowly from 2.23 to 2.15 following the annealing process.

In order to evaluate the cutting performance of conical picks, this paper has used fractal theory to analyze cutting resistance spectrums measured by the multi-picks parameter adjustable rotary cutting test bench, but also investigated the relationship between the fractal characteristic of cutting resistance spectrums, installation angle and cutting thickness. According to the specific energy calculated by measured axial resistance spectrums and power spectrums, the paper has established a relation model of picks on specific energy, installation angle and cutting thickness. It shows that box dimension and R (proportional coefficient) have a squared relationship with installation angle, as well as an exponential relationship with cutting thickness. The paper analyses mutual influences and restriction relation of cutting specific energy and half cone angle and installation angle. Half cone angle increase, cause the best installation angle range which can make specific energy decreases smaller When the half cone angle decreases, the conclusion is on the contrary. When half-cone angle is certain, specific energy and the tangential installation angle has a squared relationship. Decreased with the tangential installation angle increases, that increased first and then decreased. There is a best tangential installation angle to make specific energy minimum. The specific energy and the cutting thickness have an exponential relationship, and decreases with the increase of cutting thickness under the experimental conditions. This study proves the fractal characteristics and specific energy in the evaluation of cutting in performance consistency and provides a reference of Shearer efficient cutting and evaluation of the performance. [ABSTRACT FROM AUTHOR]

To quantitalively prove the effect of temperature on RPC internal pore structure changes,the characteristics of pore structure and the fractality of RPC after high temperatures were tested by mercury intrusion porosimetry ( MIP). The development of the characteristics of pore parameters, such as the pore volume, the threshold pore size, the most probable pore size,etc.,with increasing temperature was analyzed. The volume fractal dimension of RPC in the effective region of capillary pores and transition pores were calculated. The results indicate that the pore structure degrades at high temperature, which lead to the porosity and pore volume increase with the temperature rising. The damage process of RPC can be described by means of the fractal method,at the temperature 150 °C, RPC starts to show fractal effect, the volume fractal dimension of RPC in the range of capillary pores and transition pores increase with the rising temperature. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature on the morphology and surface fractal dimension of titanium dioxide (TiO2) films prepared via the spray deposition process was investigated. Thin films with various morphologies were obtained at different temperatures and characterized by X-ray diffraction and atomic force microscopy (AFM). It was found that the crystalline structure of TiO2 films depends strongly on annealing temperature. At higher temperatures, the partial phase transformation of anatase-to-rutile was observed. The morphology and surface fractal dimensions were evaluated by image analysis methods based on AFM micrographs. The results indicate that the value of surface roughness (the standard deviation of the height values within the given area of AFM image) of TiO2 films increases with increasing annealing temperature. Fractal analysis revealed that the value of the fractal dimension of the samples decreases slowly from 2.23 to 2.15 following the annealing process. [ABSTRACT FROM AUTHOR]

Considering characteristics of urban land price space system, fractal feature extraction models of urban land price space system based on Moran's I index, Getis-Ord General G index and the box counting dimension principle were proposed. The experiment was carried out with residential land market data of Beijing. The results show that there are significant positive autocorrelations for residential land price space system within 3500m. Spatial autocorrelation degree of land price decreases with the increase of spatial scale. Residential land prices are clustered in space such that higher land price tends to be surrounded by higher land price neighbors and lower land price by lower land price neighbors. Further, fractal dimension of residential land price space system is between 2 and 3. The bigger fractal dimension, the more complicated land price space system. The empirical results suggest the existence of fractal features in urban land price space system. It helps us not only for knowing the land price distribution in space better, but also for exploring fractal interpolation of land price space. [ABSTRACT FROM AUTHOR]

This study considers the fractal characteristics of differentiated xylem cells of the fast-growing Populus x euramericana cv. '74 /76' during the active phase by the method of differential box-counting fractal dimension. The fractal characteristics of differentiated xylem cells as well as the relationship between fractal dimension and tissues proportion were considered. Results showed that the fractal dimensions of cross sections were larger than those of tangential sections. Fractal dimension of cross sections had a remarkable negative correlation with the ratio of vessel element, significant positive correlations with the proportion of wood fiber and the proportion of parenchyma. The correlation of fractal dimension with wood fiber proportion was more significant than that with parenchyma proportion. The results were also verified by replacement of the tissues in the cross section. It was observed that fractal characteristics of the wood microstructure were very much related to the proportions of different tissues of the xylem cells. [ABSTRACT FROM AUTHOR]

Abstract: Direct numerical simulation of a hydrogen–air turbulent premixed flame propagating in homogeneous turbulence was conducted to investigate the local flame structure and the fractal characteristics of the flame front at different Reynolds number turbulences. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions was used to represent the hydrogen–air reaction in turbulence. At high Reynolds number turbulence, the multilayer and the multiply folded flame structures were observed. Flame peninsulas toward unburned mixture were also created and they tended to diminish due to the heat conduction to the surrounding unburned mixture at low temperature. The local extinction of hydrogen–air turbulent flames was frequently generated at the leading edge of corrugated flame fronts at high Reynolds number turbulence. Fractal features of the flame surface were also investigated by the three-dimensional box counting method. Fractal dimensions of the flame surface were 2.3–2.5 and were independent of Reynolds number and equivalence ratio. A strong correlation between the inner cutoff in Kolmogorov length units and the ratio of the diameter of the coherent fine scale eddy, which is a universal fine scale structure of turbulence, to the laminar flame thickness (D/δF ) was shown, and an inner cutoff scale expression based on D/δF was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Characterizing soil particle size distributions (PSD) and their variation is an important issue in environmental research. In this study, fractal theory was used to analyse the soil PSD and its variations in the Cele Oasis, which is located at the southern margin of the Tarim Basin. The characteristics of the soil PSD were then evaluated to identify the primary factors that influence soil PSD. The results showed that the fractal dimension () values ranged from 2.11 to 2.27, and that there were significant differences among groups. Furthermore, the values showed a significant positive correlation with fine particles (<50 μm) and soil organic matter contents. According to a comparative analysis of values, the utilization years of farmlands had a significant influence on PSD, while the difference in the spatial distribution of farmlands did not. These results indicated that long-term and effective tillage management of the farmlands will be beneficial to keeping and improving the states of the soil PSD and other soil properties. [Copyright &y& Elsevier]

By using Ripley's K(r) function and fractal dimension, this paper studied the spatial pattern and fractal characteristics of four ecotypes Haloxylon ammodendron population at different development stages in Gurbantonggut desert. Of the four ecotypes, soil ecotype clumped in 1-18 m scale, while sand, saline soil and gravel ecotypes clumped in all scales, suggesting that desert plant could adapt a habitat via clumping. The spatial pattern of H. ammodendron population differed with its development stage. Seedlings and saplings clumped, while adult trees showed random distribution. Compared with Ripley's K(r) function, correlation dimension could reflect the ability of spatial occupation, but couldn't directly reflect the clump or not clump in arid area. Moreover, the dimension was susceptible to the number and size of H. ammodendron. [ABSTRACT FROM AUTHOR]