المؤلفون: Qiu, Chao¹ (AUTHOR), Yang, Yugui¹ (AUTHOR) ygyang2009@126.com, Huang, Bingxiang² (AUTHOR), Gao, Feng¹ (AUTHOR), Hou, Shanshan¹ (AUTHOR), Mu, Guangyu³ (AUTHOR)

المصدر: Physics of Fluids. Jun2024, Vol. 36 Issue 6, p1-13. 13p.

مصطلحات موضوعية: *TORTUOSITY, *MULTIFRACTALS, *PERMEABILITY, *FRACTAL dimensions, *ROCK deformation, *MICROSCOPY, *SURFACE roughness, *ANALYTICAL solutions

مستخلص: The seepage of rock strata is greatly influenced by the pore network and fracture network; however, the prediction of permeability becomes challenging due to the changes in the cross section of pore channels and the morphology of fractures. In this study, a novel pore-fracture permeability model based on a fractal theory is proposed, and the analytical solutions of the model are given. In contrast to the traditional smooth parallel plate and uniform cross section straight capillary, this model not only considers the roughness of the fracture surface, but also the cross section variation and tortuosity of the pore channel. The comparisons between the calculated results and the experimental data verify the reliability of this model. The quantitative analyses of microscopic parameters indicate a positive correlation between the permeability and the fractal dimension, size, and proportion of pores and fractures. Conversely, there is a negative correlation with roughness, tortuosity, and cross-sectional changes. The range in which the seepage contribution of pores cannot be ignored is determined. Two logarithmic relationship expressions for permeability are presented. This study contributes to explore the effects of the geometry and morphology of the pore-fracture media on seepage and supplements the studies on the permeability models. [ABSTRACT FROM AUTHOR]

المؤلفون: Zong, Peng^1,2 (AUTHOR), Xu, Hao^1,2 (AUTHOR) xuhao600@163.com, Tang, Dazhen^1,2 (AUTHOR), Huo, Feiyu³ (AUTHOR)

المصدر: Physics of Fluids. Jun2024, Vol. 36 Issue 6, p1-11. 11p.

مصطلحات موضوعية: *TORTUOSITY, *MATHEMATICAL models, *FLUID flow, *FRACTAL dimensions, *SIMULATION methods & models, *WATER pressure

مستخلص: Aiming to solve the problems of unclear fluid flow laws and controlling factors in fractured reservoirs, as well as the lack of a mathematical model of threshold pressure gradient (TPG) considering fracture structural parameters, research on the structural characterization of fractured reservoirs, physical simulation of fluid flow, and TPG prediction models has been carried out. Physical simulations demonstrate that fluid flow in fractured reservoirs under stress is nonlinear and exhibits TPG. The TPG displays a significant positive exponential relationship with confining pressure and water saturation. As the confining pressure or water saturation increases, the effective opening of fractures decreases. The TPG will increase dramatically when the fracture opening decreases to the critical thickness for the rapid increase in TPG. On the basis of the fluid flow law study, the TPG fractal prediction model is further developed based on fractal dimension of fracture length distribution ( D f ), fractal dimension of tortuosity ( D T ), water saturation ( S w ), maximum fracture width ( w max ), limit shear stress ( η 0 ), and sample characteristic length ( L 0 ). The results predicted by the model show good agreement with physical simulations (with average relative error of 7.56%). Experimental simulation and mathematical modeling of TPG in fractured reservoirs can reveal the fluid flow mechanism and improve the accurate evaluation of production capacity during different development processes. [ABSTRACT FROM AUTHOR]

المؤلفون: Jizhang Chen¹ chenjizhang@njfu.edu.cn, Minfeng Chen¹, Hongli Chen², Ming Yang³, Xiang Han¹, Dingtao Ma³, Peixin Zhang³, Ching-Ping Wong⁴ cp.wong@mse.gatech.edu

المصدر: Proceedings of the National Academy of Sciences of the United States of America. 5/21/2024, Vol. 121 Issue 21, p1-11. 36p.

مصطلحات موضوعية: *HYDROGELS, *TORTUOSITY, *ELECTROLYTES, *CARBOXYMETHYLCELLULOSE, *IONIC conductivity

مستخلص: While aqueous zinc-ion batteries exhibit great potential, their performance is impeded by zinc dendrites. Existing literature has proposed the use of hydrogel electrolytes to ameliorate this issue. Nevertheless, the mechanical attributes of hydrogel electrolytes, particularly their modulus, are suboptimal, primarily ascribed to the substantial water content. This drawback would severely restrict the dendrite-inhibiting efficacy, especially under large mass loadings of active materials. Inspired by the structural characteristics of wood, this study endeavors to fabricate the anisotropic carboxymethyl cellulose hydrogel electrolyte through directional freezing, salting-out effect, and compression reinforcement, aiming to maximize the modulus along the direction perpendicular to the electrode surface. The heightened modulus concurrently serves to suppress the vertical deposition of the intermediate product at the cathode. Meanwhile, the oriented channels with low tortuosity enabled by the anisotropic structure are beneficial to the ionic transport between the anode and cathode. Comparative analysis with an isotropic hydrogel sample reveals a marked enhancement in both modulus and ionic conductivity in the anisotropic hydrogel. This enhancement contributes to significantly improved zinc stripping/plating reversibility and mitigated electrochemical polarization. Additionally, a durable quasi-solid-state Zn//MnO2 battery with noteworthy volumetric energy density is realized. This study offers unique perspectives for designing hydrogel electrolytes and augmenting battery performance. [ABSTRACT FROM AUTHOR]

المؤلفون: Eun, Mi-Yeon^1,2 (AUTHOR), Song, Ha‑Na³ (AUTHOR), Choi, Jong‑Un^3,4 (AUTHOR), Cho, Hwan‑Ho⁵ (AUTHOR), Kim, Hyung Jun³ (AUTHOR), Chung, Jong-Won³ (AUTHOR), Song, Tae-Jin⁶ (AUTHOR), Jung, Jin-Man⁷ (AUTHOR), Bang, Oh‑Young³ (AUTHOR), Kim, Gyeong‑Moon³ (AUTHOR), Park, Hyunjin^8,9 (AUTHOR), Liebeskind, David S.¹⁰ (AUTHOR), Seo, Woo-Keun^3,4 (AUTHOR) mcastenosis@gmail.com

المصدر: Scientific Reports. 5/17/2024, Vol. 14 Issue 1, p1-9. 9p.

مصطلحات موضوعية: *TORTUOSITY, *MAGNETIC resonance angiography, *STROKE patients, *ISCHEMIC stroke

مستخلص: The effect of arterial tortuosity on intracranial atherosclerosis (ICAS) is not well understood. This study aimed to evaluate the effect of global intracranial arterial tortuosity on intracranial atherosclerotic burden in patients with ischemic stroke. We included patients with acute ischemic stroke who underwent magnetic resonance angiography (MRA) and classified them into three groups according to the ICAS burden. Global tortuosity index (GTI) was defined as the standardized mean curvature of the entire intracranial arteries, measured by in-house vessel analysis software. Of the 516 patients included, 274 patients had no ICAS, 140 patients had a low ICAS burden, and 102 patients had a high ICAS burden. GTI increased with higher ICAS burden. After adjustment for age, sex, vascular risk factors, and standardized mean arterial area, GTI was independently associated with ICAS burden (adjusted odds ratio [adjusted OR] 1.33; 95% confidence interval [CI] 1.09–1.62). The degree of association increased when the arterial tortuosity was analyzed limited to the basal arteries (adjusted OR 1.48; 95% CI 1.22–1.81). We demonstrated that GTI is associated with ICAS burden in patients with ischemic stroke, suggesting a role for global arterial tortuosity in ICAS. [ABSTRACT FROM AUTHOR]

المؤلفون: MIAO, TONGJUN¹ (AUTHOR) mtong2004@163.com, CHEN, AIMIN² (AUTHOR), LIU, RICHENG³ (AUTHOR), XU, PENG⁴ (AUTHOR), YU, BOMING⁵ (AUTHOR) yubm_2012@hust.edu.cn

المصدر: Fractals. 2024, Vol. 32 Issue 3, p1-16. 16p.

مصطلحات موضوعية: *TORTUOSITY, *FRACTALS, *POROSITY, *FRACTAL dimensions, *PERMEABILITY, *THERMAL expansion, *THERMAL stresses

مستخلص: The temperature effect on the permeability of porous rocks continues to be a considerable controversy in the area of reservoirs since the thermal expansion of mineral grains exhibits complicated influence on pore geometries in them. To investigate the degree of effect of pore structures on the hydro-thermal coupling process, a study of the thermal evolution of permeability and porosity of porous rocks is performed based on fractal theory and on thermal as well as stress effects. This work can provide a general physical explanation on some arguments in this area. The proposed models for permeability and porosity can be associated with temperature and the pore-structural parameters as well as physical parameters of porous rocks, such as the initial porosity ( ϕ 0) , the initial fractal dimension ( D f , 0) , the fractal dimension for tortuosity ( D T , T) and the thermal expansion coefficient of pore volume ( α T). The validity of the proposed models for temperature-dependent permeability and temperature-dependent porosity is validated by comparing them with the available experimental results. The investigations are performed in detail considering the essential effects of pore-structural parameters and physical parameters of porous rock on the dimensionless temperature-dependent permeability and temperature-dependent porosity as well as the fractal dimensions for pore areas and tortuosity. It is found that the pore distribution scale range ratio ( λ min , T / λ max , T) , and pore thermal expansion coefficient ( α T) have significant effects on the dimensionless temperature-dependent permeability and temperature-dependent porosity of porous rock as well as the fractal dimensions for pore areas and tortuosity. The proposed models may provide a fundamental understanding of the coupled hydro-thermal process of rocks. [ABSTRACT FROM AUTHOR]

المؤلفون: Zhang, Heng¹ (AUTHOR), Hu, Hao² (AUTHOR), Sarker, Mrittunjoy³ (AUTHOR), Shao, Xuanyu⁴ (AUTHOR), Zhan, Zhigang⁴ (AUTHOR), Sui, Pang-Chieh⁵ (AUTHOR), Chuang, Po-Ya Abel^1,3 (AUTHOR) abel.chuang@ucmerced.edu

المصدر: International Journal of Hydrogen Energy. Apr2024, Vol. 62, p591-600. 10p.

مصطلحات موضوعية: *TORTUOSITY, *PROTON exchange membrane fuel cells, *FUEL cells, *STRAINS & stresses (Mechanics), *FINITE element method

مستخلص: The microporous layer (MPL) plays an important role in water and thermal management of proton exchange membrane fuel cells (PEMFCs). An in-depth investigation of the mechanical compression effect on transport properties in the MPL can help optimize cell performance. In this work, the microstructure of the MPL is numerically reconstructed and the finite element method is applied to simulate mechanical behavior. Besides, the distribution of stress-strain, porosity, and pore size in the MPL under ten different levels of mechanical compression strains are studied. Lastly, the pore-scale model is employed to investigate the effective transport properties of the MPL as a function of compression strain. The analysis reveals that as the MPL strain increases from 0% to 40%, there is a 29% decrease in porosity, a 50% reduction in average pore diameter, a 60% decrease in effective gas diffusivity, a 100% increase in tortuosity, and an 80% increase in electrical and thermal conductivity. With the escalation of mechanical compression, both the magnitude and uniformity of stress-strain-displacement concurrently rise. Mechanical compression strains below 20% exhibit a lesser impact on transport properties. Beyond this threshold, exceeding the 20% compression strain point, mechanical stress assumes a critical role in influencing MPL transport properties. • The realistic microstructure of the microporous layer is reconstructed numerically. • The properties of each component of the microporous layer are fully considered. • The finite element method is utilized to simulate mechanical stresses. • Pore-scale simulations are utilized to obtain the effective transport properties. • Critical compressive strain points are identified to guide assembly optimization. [ABSTRACT FROM AUTHOR]

المؤلفون: Yang, He^1,2 (AUTHOR), Liu, Zhen^1,2 (AUTHOR) liuzhensdust@163.com, Yu, Zehan^1,2 (AUTHOR), Zhu, Muyao^1,2 (AUTHOR), Dong, Shuai^1,2 (AUTHOR), Sun, Shuyang^1,2 (AUTHOR), Zhang, Fuchang^1,2 (AUTHOR), Wu, Fengting^1,2 (AUTHOR), Yan, Zihao^1,2 (AUTHOR)

المصدر: Physics of Fluids. Apr2024, Vol. 36 Issue 4, p1-10. 10p.

مصطلحات موضوعية: *TORTUOSITY, *COAL, *WATER seepage, *FRACTAL dimensions, *WATER-gas, *OIL field flooding, *GAS injection

مستخلص: In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient. [ABSTRACT FROM AUTHOR]

المؤلفون: Lu, Guangteng^1,2 (AUTHOR), Lai, Fengpeng^1,2 (AUTHOR) laifengpeng@cugb.edu.cn, Li, Bince^1,2 (AUTHOR)

المصدر: Ground Water. Mar2024, Vol. 62 Issue 2, p276-284. 9p.

مصطلحات موضوعية: *PERMEABILITY, *TORTUOSITY, *LOGARITHMIC functions, *FRACTAL dimensions, *AQUIFERS, *POROSITY, *WATER salinization

مستخلص: Permeability is a required parameter for studying aquifer properties. However, for sandstone aquifers with low permeability, it is difficult to measure permeability directly through experiments. Based on fractal theory and the J function, a new method to calculate the permeability of a sandstone aquifer is derived. This work first solves the J function under each water saturation according to its definition. Combined with mercury pressure data, the J function and logarithmic curve equation of water saturation are then fitted by the drawing method, and the fractal dimension and tortuosity of the aquifer are further solved. Finally, the aquifer's permeability is calculated using the new permeability calculation method. To verify the accuracy of the proposed method, 15 rock samples from the Chang 7 Group, Ordos Basin, are taken as research objects. The permeability is calculated using the new method combined with mercury injection data and aquifer characteristic parameters, and the results are compared with the real permeability. The relative error of most samples is <20%, which shows the permeability calculated by this method is accurate and reliable. The effects of fractal dimension, tortuosity, and porosity on permeability are also analyzed. [ABSTRACT FROM AUTHOR]

العنوان البديل: Efecto de la resolución de la imagen en la evaluación de la tortuosidad de los vasos retinales.

المصدر: Óptica Pura y Aplicada. Mar2024, Vol. 57 Issue 1, p1-10. 10p.

مصطلحات موضوعية: *TORTUOSITY, *RETINAL blood vessels, *FUNDUS oculi, *RETINAL imaging, *CARDIOVASCULAR diseases, *IMAGE analysis

الملخص (بالإنجليزية): Several ocular and cardiovascular disorders are characterized by an elevated tortuosity of retinal blood vessels. Objective tortuosity measurements can be obtained through the computation of a set of tortuosity indices derived from digital image analysis of an eye fundus image. These calculations require the parametrization of the vessel path traced in the image. As a vessel descriptor, tortuosity should be independent of scale, but this property demands thorough examination and assessment for each index. We investigate the impact of altering image resolution on the local tortuosity indices of retinal vessels. [ABSTRACT FROM AUTHOR]

Abstract (Spanish): Algunas enfermedades oculares y cardiovasculares presentan un aumento de la tortuosidad de los vasos sanguíneos de la retina. Se pueden obtener medidas objetivas de la tortuosidad a través del cálculo de un conjunto de índices de tortuosidad mediante análisis digital imágenes del fondo de ojo (o retinografías). Este cálculo requiere la parametrización de la curva dibujada por el vaso en la imagen. Los descriptores de los vasos deben ser independientes de la escala (resolución) de la imagen, pero esta propiedad debe ser estudiada y evaluada para cada índice de tortuosidad. Nosotros analizamos cómo un cambio en la resolución de la imagen de fondo de ojo afecta a los índices de tortuosidad locales de los vasos retinianos. [ABSTRACT FROM AUTHOR]

المؤلفون: MIAO, TONGJUN¹ (AUTHOR) mtong2004@163.com, CHEN, AIMIN² (AUTHOR), YANG, XIAOYA¹ (AUTHOR), YU, BOMING³ (AUTHOR) yubm_2012@hust.edu.cn

المصدر: Fractals. 2024, Vol. 32 Issue 1, p1-16. 16p.

مصطلحات موضوعية: *ROCK permeability, *TORTUOSITY, *POROSITY, *ROCK properties, *ELASTIC constants, *MASS transfer

مستخلص: The pore geometry of porous rocks is fundamental for accurate description of stress dependence of effective permeability, which is an important parameter of mass transfer in porous rocks. An important physical assumption that porous rocks contain numerous elliptical or spherical pores has been shown to be successfully applied to many aspects of hydromechanical coupling properties of porous rocks. To investigate the detailed description of pore structures on the degree of effect on the coupled hydromechanical process, in this work, a generalized stress-dependent model for permeability of porous rocks has been proposed based on fractal geometry theory and mechanics of porous rock. The proposed model is expressed as a nonlinear function of pore structure parameters, such as aspect ratio ( γ σ ), the fractal dimensions ( D T , σ and D T , a v ) for tortuosity, the initial fractal dimension ( D f , 0 ), and initial porosity ( ϕ 0 ) as well as matrix elastic constants (E and ν) of porous rocks without any empirical parameter. The validity of the proposed models is verified by the good agreements between available experimental data and theoretical predictions of stress-dependent permeabilities of porous rocks. Detailed discussions of the essential effects of pore structures parameters and material elastic constants of porous rocks on the dimensionless stress-dependent permeabilities are performed. It is found that the stress parameters (E and γ 0 ) have remarkable effects on the dimensionless stress-dependent permeabilities compared with other parameters ( ϕ 0 and ν). The proposed model may contribute to a better quantitative understanding of the coupled hydromechanical properties of porous rocks. [ABSTRACT FROM AUTHOR]