This paper systematically investigated the effects of alkali activator modulus (AM), alkali dosage (AD), and water-fly ash ratio (W/FA) on the pore volume, pore size distribution, pore volume fractal ...dimension (Dv), and pore surface fractal dimension (Ds) of fly ash-based geopolymer (FABGs) by orthogonal test and mercury intrusion porosimetry test. Dv and Ds of FABG can be calculated by the Menger sponge model and Zhang and Li's models, respectively. The relationship between multiple synthesis parameters and pore characteristics of FABGs was detailedly studied through range analysis and correlation detection analysis, which provides a basic understanding of the influence of multiple parameters on the pore characteristics of FABG, as well as the relationship between pore characteristics and mechanical properties. The results show that AM has the greatest effect on the volume proportion of gel pores and transition pores, and AD and W/FA have the greatest effect on the volume proportion of capillary pores and large pores, respectively. W/FA has the greatest effect on the porosity, and the porosity and the most probable aperture increase with the increment of W/FA and decrease with a rise in AD. It is worth noting that AM, AD, and W/FA have little effect on the Dv of larger pores, but have a greater on the Dv of smaller pores, with the influence order of AD-W/FA-AM. Ds of the large pores and capillary pores range between 2.70–2.90, and the Ds of the transition pores and gel pores are mostly greater than 3.00, which suggests that there may be more ink-bottle pores in transition pores and gel pores. In addition, there was a strong linear relationship between the porosity and compressive strength of FABGs, and the compressive strength of FABGs showed a decreasing trend with the increase of porosity. Compared with Dv, there is a stronger correlation between Ds and compressive strength, indicating that the roughness of the pore surface and the pore size distribution have a greater influence on the compressive strength of FABGs.
•The influence order of synthesis parameters on the porosity of FABGs was W/FA-AD-AM.•AM, AD and W/FA have the greatest effect on the volume proportion of gel and transition pore, capillary pore and large pore.•The pore surface fractal dimensions of the large pores and capillary pores range between 2.70-2.90.•There was a strong linear relationship between the porosity and compressive strength of FABGs.
The complexity of the fracture network, formed by the interaction of hydraulic fractures and natural fractures during hydraulic fracturing, is one of the important criteria for guiding shale gas ...field production. In this study, we selected the deep shale of the Longmaxi formation as the object of study. Through indoor hydraulic fracturing experiments and fracture 3-D reconstruction technology, we conducted a quantitative study on the complexity of the fracture network created by the influence of hydraulic and natural fractures interacting with each other during hydraulic fracturing. The results show that the fractal dimensions, average connection numbers of topological structure branches, and relative lengths of fracture intersections for hydraulic fractures in 10 groups of specimens are 1.93-2.27, 0-1.143, and 1.02-1.98, respectively.
The pore characteristics of hybrid basalt–polypropylene fibre-reinforced concrete (HBPRC) are investigated using mercury intrusion porosimetry. The research results indicate that the cumulative pore ...volume of concrete increases with fibre addition. The pore surface fractal dimension (DS) of HBPRC in gel, capillary, and large pore regions decreases sequentially although it has no physical characteristics in a transition pore region. The incorporation of fibres has an insignificant effect on DS in gel and capillary pore regions; however, it has a reducing effect on DS in the large pore region. Furthermore, the greater the concrete strength, the larger DS becomes and the greater the reducing effect of fibres on DS in the large pore region. Through microscopic and mesoscopic analyses, it has been suggested that bubbles introduced by fibres and the weak dispersion of such fibres are the main reasons for the deterioration of the large pore structure of HBPRC.
The unsmooth boundary will greatly affect motion morphology of a shallow water wave, and a fractal space is introduced to establish a generalized KdV-Burgers equation with fractal derivatives. The ...semi-inverse method is used to establish a fractal variational formulation of the problem, which provides conservation laws in an energy form in the fractal space and possible solution structures of the equation.
•Pore evolution in coal during loading was investigated based on NMR measurement.•Characteristics of T2 distribution and pores in coals were analyzed during loading.•NMR fractal dimensions of ...stress-damaged coal were measured.
In this paper, triaxial compression tests on coals with real-time T2 and MRI (Magnetic Resonance Imaging) image measurement are performed by using a nuclear magnetic resonance (NMR) testing system equipped with a loading device. Pore and fracture development in coal under stress conditions are investigated based on NMR and fractal theory. The results show that the accumulation of NMR signal intensity as well as sample porosity decrease slightly at first, then increase slowly, and finally increase rapidly during the deformation of coal. The measured T2 distributions indicate that stress damage mainly induces the generation of mesopores and macropores (or micro-fractures). A new method for estimating crack-initiation stresses is proposed based on the evolution of T2 curve. By using this method, we estimate the crack-initiation stress of the tested coal samples, which is 34.6%, 32.2%, and 30.1% of its corresponding peak strength, respectively. Fractal dimensions of seepage pores show significant fractal characteristics, while fractal characteristics of adsorption pores are not obvious. The evolution of fractal dimension DT of the total pores with stress is similar to the changing trend of porosity. But the fractal dimension of DS shows a negative correlation with the stress.
•Stand structural complexity is quantified using single terrestrial laser scans.•The fractal dimension based index SSCI differentiates stand types.•SSCI increases with tree species diversity.•Daily ...temperature and VPD amplitude decrease from low to high SSCI within stands.
Measures to describe stand structural complexity efficiently and objectively are increasingly demanded to understand the relationship between forest management, stand structure, biodiversity and ecosystem functioning. Here, we present an approach to quantify stand structural complexity based on fractal dimension derived from single terrestrial laser scans (TLS) that were made on 126 permanent forest research plots in Germany, representing major stand and management types. The newly developed SSC-index (SSCI) was positively correlated to conventional tree-based measures of stand structural complexity, tree size differentiation, diversity of tree diameters and random tree spacing patterns. Beyond that, it successfully differentiated between stand types of different main tree species and management systems. SSCI increased from low to high tree species diversity and explained microclimatic fluctuations better than conventional, tree-based measures. Given the high efficiency during data collection, TLS can be used to assess stand structural complexity for large sample sizes to provide an explanatory variable for the effects of forest management on biodiversity, productivity and ecosystem processes.
•The optimal ratio of IDS and SDS is determined to be 1:3.•The pore characteristics of bituminous coal and anthracite are divided.•The combination of IDS and SDS has a good synergistic effect on ...expanding the pore structure of coal.•The regulation mechanism of IDS and SDS on the wettability of coal is discussed.
The pore and wetting characteristics of bituminous coal and anthracite treated with different proportions of tetrasodium iminodisuccinate (IDS) and sodium dodecyl sulfate (SDS) were measured. The pore structure characteristics of the coal were studied via low-temperature nitrogen adsorption analysis and the Frenkel-Halsey-Hill fractal theory. Zeta potential measurements were conducted to quantitatively analyze the degree of aggregation or dispersion of coal particles dissolved in solution. Changes in the coal surface morphology were observed and analyzed by scanning electron microscopy (SEM). The results show that when the ratio of IDS:SDS is 1:3, the specific surface area (SSA) values of bituminous coal and anthracite are the lowest. The composite reagent has a greater effect on improving the pore structure of anthracite than bituminous coal. Compared with bituminous coal, anthracite has better pore connectivity and a wider pore network. The absolute zeta potentials of bituminous coal and anthracite reach the maximum at an IDS:SDS ratio of 1:3, with values of 91.08 mV and 91.35 mV, respectively. The electrostatic potential distributions of the molecules show that the advantages of the electrostatic potential difference with water molecules enable IDS and SDS molecules to effectively attract water molecules and form hydrogen bonds, thus revealing the optimization mechanism of coal wettability.
•Machine learning approaches can assess the temporal complexity of spiking activities.•Higuchi fractal dimension acts as an indicator of working memory content in firing patterns.•The middle temporal ...area likely encodes spatial memory based on linear and nonlinear temporal features.
While top-down modulation can be observed by increases in neuronal firing in some brain areas, modulation in other areas demonstrates complex nonlinear dynamics. When these signal modifications cannot be identified by classical methods, fractal analysis can be used to better describe the resulting changes. It was previously shown that the Higuchi dimension could detect such modification. However, these changes likely extend to multiple fractal dimensions. In this paper, machine learning algorithms were employed to extract the fractal features of neuronal firing and detect the occurrence of top-down modulation. We assessed the performance of classifiers trained on different fractal features as well as the Fourier transform and wavelet transform-based features obtained from the firing rate signals during a spatial memory task to measure the ability of individual neurons in the middle temporal cortex to hold memory information. By comparing the results of the different classifiers, Higuchi fractal dimension was confirmed as the strongest indicator of working memory content in cortical firing patterns compared to other fractal features. We demonstrated the utility of this approach and observed that the middle temporal cortex likely encodes spatial working memory based on linear and nonlinear temporal features rather than simply increasing the average firing rate.
•A new impact resistant concrete is developed in this study.•Pottery sand is included into low water/binder cementitious composites (LWBCC).•The fractal dimension of the crack pattern for the new ...composite is detailed analyzed.•Nanoindentation is employed to clarify the ITZ between pottery sand and matrix.•Comparison between the newly developed material and others is presented.
Impact resistance is an important index of durability of concrete materials. As a kind of porous aggregate, pottery sand has the ability to absorb impact energy, which can be used to improve the impact resistance of cement-based composites. This study intends to use macro and micro method to analyze the influence of pottery sand on the impact resistance of low water/binder cementitious composites (LWBCC). Firstly, a series of mix proportions are designed according to the characteristics of each raw material and pottery sand. Then, the compressive strength and impact resistance of the test blocks are tested and the cracks of the test block are further analyzed. The results show that the incorporation of pottery sand can significantly improve the impact resistance of the test blocks. The fractal dimension of the crack pattern shows a decreasing trend after an initial increase with the increase of the pottery sand content. Finally, the micro-structures of pottery sand and river sand LWBCC samples are further analyzed by nanoindentation and SEM. The interfacial transition zone (ITZ) between the LWBCC matrix and pottery sand is proved to be better compared with that between the matrix and river sand. It is established that the incorporation of pottery sand as fine aggregates can effectively improve the impact resistance of concrete materials.
