•Temperature has obvious transformation effect on coal pore structure.•The effect of reforming macropores and micropores was more obvious.•Increasing the temperature appropriately can improve the gas ...production.
Coal has a complex pore network, which affects the reserves and production capacity of coalbed methane. To analyze the feasibility of coal seam heat injection mining and improve the theory of the influence of temperature on coal adsorption and desorption characteristics, scanning electron microscopy, mercury intrusion, and low-temperature liquid-nitrogen adsorption were used to evaluate the pore structure of coal at different temperatures. With the increase in temperature, the volume of macropores increased from 0.0249 to 0.0454 mL/g, and the specific surface area of micropores decreased from 2.6836 to 0.7250 m2/g. In addition, the pore fractal dimension of the large pore section, D1, increased gradually, while the pore fractal dimension of small pore section, D3, decreases with the increase in temperature. A higher temperature led to a larger pore fractal dimension of the large pores in coal and more developed pores, which is conducive to the migration of gas in the coal seam. The pore fractal dimension of the small pores decreased with the increase in temperature. The structure of the micropores became increasingly regular. The temperature has an obvious transformation effect on the structure of coal pores, especially on macropores and micropores.
To study the pore structure and fractal characteristics of acid-treated coal, in this paper, the low-temperature nitrogen adsorption method, scanning electron microscopy and the fractal theory were ...used to analyze the coal samples. The results show that the acid treatment enlarged the wedge-shaped hole into a cylindrical hole. Under the influence of HNO3, the ash, volatile and sulfur contents are negatively correlated with the fractal dimension of the pore surface (D1) and positively correlated with the fractal dimension of the pore structure (D2). And the specific surface area and total pore volume of the coal samples are positively correlated with D1 and negatively correlated with D2 after acid treatment. Influenced by the specific surface area and total pore volume, the relationship between the fractal dimension and adsorption is consistent with the relationship between the fractal dimension and specific surface area/total pore volume.
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•The effect of acid treatment on coal quality was evaluated quantitatively.•The effect of acid treatment on adsorption property was investigated.•The relationship between fractal dimension and pore structure parameters is established.•The relationship between fractal dimension and coal characteristics is established.
In this paper we study quantitative recurrence and the shrinking target problem for dynamical systems coming from overlapping iterated function systems. Such iterated function systems have the ...important property that a point often has several distinct choices of forward orbit. As is demonstrated in this paper, this non-uniqueness leads to different behaviour to that observed in the traditional setting where every point has a unique forward orbit.
We prove several almost sure results on the Lebesgue measure of the set of points satisfying a given recurrence rate, and on the Lebesgue measure of the set of points returning to a shrinking target infinitely often. In certain cases, when the Lebesgue measure is zero, we also obtain Hausdorff dimension bounds. One interesting aspect of our approach is that it allows us to handle targets that are not simply balls, but may have a more exotic geometry.
•3D fractal fracture existed in a geothermal doublet system.•Coupled thermo-hydro-mechanical interaction for bedrock and fracture.•Normal and shear deformations of fracture based on thin elastic ...layer assumption.•Evaluation of thermal breakthrough due to preferential fracture flow.
The existence of preferential flow paths, such as fractures and/or fault play an vital role on the thermal breakthrough of geothermal doublet system. The interaction between the preferential flow path and bedrock is often uneven and may have typical fractal characteristic. This study proposes a thermo-hydro-mechanical coupling model considering the deformation of fractal fractures. The fractal fracture is regarded as a thin elastic layer existed in the bedrock, whoes deformation depends to the bedrock and its own mechanical properties. Subsequently, the geothermal doublet system with a three-dimensional fractal fracture is modelled and the parameters affecting thermal breakthrough are investigated numerically. Research results indicate that the thin elastic layer assumption is remarkably robust for modelling fracture opening and closing under coupling conditions. Owing to complex fracture geometry, the fracture permeability evolution presents certain heterogeneity, which is related to fractal dimension, in-situ stress, and geothermal wells layout. The cool water in fracture with larger fractal dimension can interact with the bedrock more fully and further affect the thermal breakthrough. This further suggests that the site selection of geothermal wells should consider the specific geometry of preferential flow paths to avoid premature thermal breakthrough inducing low system efficiency.
A compact and low-profile wearable antenna is presented for on-body wireless body area network (WBAN) applications. The proposed triangular patch antenna is designed using low-cost widely available ...vinyl polymer-based flexible substrate. The final antenna topology is obtained by the combination of the Koch fractal geometry, meandering slits, and defected ground structure, to achieve a novel hybrid structure with compact footprint, good structural conformability, and enhanced impedance bandwidth (BW) to operate in the Industrial, Scientific, and Medical band with center frequency at 2.45 GHz. The fabricated prototype of the antenna has shown a good agreement between numerical and experimental results. In comparison to state-of-the-art prototypes, our design has more compact form factor of 0.318λ o × 0.318λ o × 0.004λ o , along with 7.75% impedance BW, a peak gain of 2.06 dBi, and overall radiated efficiency of 75%. For the assessment of a specific absorption rate (SAR) performance of our design, it is tested on realistic heterogeneous HUGO voxel model. Both numerical and experimental investigations revealed extremely good robustness to both human body loading and structural deformation, making it an ideal candidate for flexible and body-worn devices.
•Microfractures were analyzed using micro-CT scanning technique and fractal theory.•Type B microfractures are mainly developed in the experimental coal samples.•Microfracture length, width, volume, ...and aperture reduces as coal rank increases.•Quantity and fractal dimensions of microfractures increase as coal rank increases.•CT porosity changes with fractal dimensions, displaying a ‘U-shaped’ trend.
Microfracture structures of coal seams are the key parameters in the context of enhanced coalbed methane (ECBM) recovery as they determine permeability and productivity. Significant progress has been made in fracture characteristics, however, the detailed structural and fractal characteristics of microfractures of different rank coals (especially high-rank coals in China) are poorly understood. This study aims to analyze the physical characteristics of microfractures with X-ray computed tomography (X-ray CT) and fractal theory, identify the effects of coal rank on the physical properties of microfractures, and discern the relationship between fractal features and permeability. The results show that the experimental coals are dominated by type B microfractures, followed by type A microfractures. Additionally, for the coals investigated in this study, the microfracture network in low-rank coals is usually well-connective, whereas the connectivity and scale of the microfracture network reduces with increasing coal rank. The average microfracture length, width and volume reduces but quantity increases as coal rank increases, and these downward trends can be divided into three stages: rapid decline stage (0.59% < Ro, ran < 1.25%), slow decline stage (1.25% < Ro, ran < 2.25%), and stable stage (Ro, ran > 2.25%). The average aperture first decreases but then slightly increases with coalification. Furthermore, the fractal dimension (D) of these microfractures increases as coal rank increases in the range of 1.64–1.78, indicating that the microfracture structure gets more complicated with coalification. The CT porosity displays a ‘U-shaped’ trend as the fractal dimension increases: first decreases from 2.12% to 0.94% and then increases from 0.94% to 1.49% (turning point at D = 1.72). These Chinese coal samples have very low to medium permeability, with highly variable values ranging from 0.004 to 1.465 mD. Coals with higher fractal dimensions are commonly less permeable for gas, and such a relationship is especially apparent for coals with higher ranks. The negative correlation between permeability and fractal dimensions means that coals with higher fractal dimensions are not favorable for CBM exploitation. Our results show that microfracture structures contribute to the permeability of coal reservoirs, and that fractal dimensions plays a significant role in assessing the exploitation potential of a coal seam.
The utilization of phosphorus slag (PHS) to replace the fly ash in the construction of hydraulic projects has attracted a growing attention in China. In this study, the influence of PHS fineness and ...content on cement hydration, mechanical strength, permeability as well as the pore structure and fractal dimension (
D
s
)
of concrete have been discussed. The results indicate that the PHS addition retards the cement hydration and hence decreases the hydration heat within three days. The incorporation of PHS with a Blaine specific surface area of 505
m2/kg could participate in the early pozzolanic reaction and consequently offsets the retarding effect to some extent. The incorporation of 20–40
wt.% PHS declines the early strength of concrete, but this reduction effect on strength can be eliminated to some degrees by mechanically grinding the PHS. The compressive strengths of concrete added with PHS with a high fineness of 505
m2/kg (abbreviated as PHS-H) are about 16.0–20.6% higher at three days and 8.9–11.0% higher at 180 days compared that of the control concrete. The contribution of PHS-H to the pore structure refinement is more significant than that of PHS with a low fineness of 302
m2/kg (abbreviated as PHS-L) at various ages because PHS-H is of much higher reactivity and can consume more Ca(OH)2 than PHS-L which leads to a denser microstructure and a lower chloride diffusion coefficient (
D
RCM
)
. The incorporation of PHS decreases the
D
s
at three days, whereas the concrete incorporated with PHS has much higher
D
s
than that of control one at late age. The
D
RCM
value increases with increasing the porosity and the most probable aperture, while
D
s
has a more significant effect on
D
RCM
than the porosity and the most probable aperture. The concrete added with 20
wt.% PHS-H exhibits the highest
D
s
and the lowest
D
RCM
value at long-term age among the five concrete mixtures in this work.
Deposition of Bi on InSb(111)B reveals a striking Sierpiński-triangle (ST)-like structure in Bi thin films. Such a fractal geometric topology is further shown to turn off the intrinsic electronic ...topology in a thin film. Relaxation of a huge misfit strain of about 30% to 40% between Bi adlayer and substrate is revealed to drive the ST-like island formation. A Frenkel-Kontrova model is developed to illustrate the enhanced strain relief in the ST islands offsetting the additional step energy cost. Besides a sufficiently large tensile strain, forming ST-like structures also requires larger adlayer-substrate and intra-adlayer elastic stiffnesses, and weaker intra-adlayer interatomic interactions.
The article shows the presence of proportional correspondence of the parts and the whole using the principles of fractal geometry in the natural objects and phenomena beauty concept formation. The ...objects of the artificial environment are studied for the formation of images using the mathematical models' example for calculating natural objects with fractal properties.
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