Search results for "TORTUOSITY"

Pore scale modelling of calcite cement dissolution in a reservoir sandstone matrix

2019

E3S Web of Conferences 98, 05010 (1-5) (2019). doi:10.1051/e3sconf/20199805010

Combined numerical and experimental study of microstructure and permeability in porous granular media

2020

<div> <div> <div> <p>Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities, representing shallow depth crustal sediments. The microstructure, namely effective porosity …

Permeability and effective porosity of porous media

1997

The concept of permeability of porous media is discussed, and a modification of Kozeny’s permeability equation to include the effect of effective porosity is introduced. An analytical expression for the specific surface area of a system constructed of randomly placed identical obstacles with unrestricted overlap is derived, and a lattice-gas cellular automaton method is then used to simulate the dependence on porosity of permeability, tortuosity, and effective porosity for a flow of Newtonian uncompressible fluid in this two-dimensional porous substance. The simulated permeabilities can well be explained by the concept of effective porosity, and the exact form of the specific surface area. …

2016

Abstract. Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier–Stokes–Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading–unloading cycle (0.7 to 22.1 MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray…

The effect of cigar smoking on the lingual microcirculation

2005

The aim of this study was to analyze the lingual microcirculation in vivo and to evaluate the effects on it of cigar smoking, using computerized videocapillaroscopy. Twenty-five healthy nonsmokers and 25 healthy smokers were examined. For each subject we evaluated the visibility, course, tortuosity, and any images characteristic of capillary loops, as well as the possible presence of microhemorrhages, the average caliber of the capillary loops, and the number of capillary loops visible per square millimeter. The investigation of the lingual mucosa revealed capillary loops with a course parallel to the surface. In smokers, capillary loops had a smaller caliber (P < 0.001) and there was a hig…

Statistical shape analysis of ascending thoracic aortic aneurysm: Correlation between shape and biomechanical descriptors

2020

An ascending thoracic aortic aneurysm (ATAA) is a heterogeneous disease showing different patterns of aortic dilatation and valve morphologies, each with distinct clinical course. This study aimed to explore the aortic morphology and the associations between shape and function in a population of ATAA, while further assessing novel risk models of aortic surgery not based on aortic size. Shape variability of n = 106 patients with ATAA and different valve morphologies (i.e., bicuspid versus tricuspid aortic valve) was estimated by statistical shape analysis (SSA) to compute a mean aortic shape and its deformation. Once the computational atlas was built, principal component analysis (PCA) allow…

Computer assisted evaluation of retinal vessels tortuosity in Fabry disease.

2012

. Purpose:  Fabry Disease (FD) is a rare X-linked metabolic disorder characterized by diffuse deposition of sphingolipids in many tissues. Retinal vessel tortuosity is a common ocular manifestation in FD and may represent a useful marker for the disease. Unfortunately its clinical evaluation is poorly reproducibile and alternative means of evaluation may be of interest. We tested a new semi-automatic software measuring retinal vessel tortuosity from eye fundus digital images in a group of FD patients. Methods:  Observational case-control study evaluating four mathematical parameters describing tortuosity (relative length, sum of angle metric [SOAM], product of angle distance [PAD], triangul…

Hierarchical imaging and computational analysis of three-dimensional vascular network architecture in the entire postnatal and adult mouse brain

2021

The formation of new blood vessels and the establishment of vascular networks are crucial during brain development, in the adult healthy brain, as well as in various diseases of the central nervous system. Here, we describe a step-by-step protocol for our recently developed method that enables hierarchical imaging and computational analysis of vascular networks in postnatal and adult mouse brains. The different stages of the procedure include resin-based vascular corrosion casting, scanning electron microscopy, synchrotron radiation and desktop microcomputed tomography imaging, and computational network analysis. Combining these methods enables detailed visualization and quantification of t…

A custom image-based analysis tool for quantifying elastin and collagen micro-architecture in the wall of the human aorta from multi-photon microscopy

2014

The aorta possesses a micro-architecture that imparts and supports a high degree of compliance and mechanical strength. Alteration of the quantity and/or arrangement of the main load-bearing components of this micro-architecture - the elastin and collagen fibers - leads to mechanical, and hence functional, changes associated with aortic disease and aging. Therefore, in the future, the ability to rigorously characterize the wall fiber micro-architecture could provide insight into the complicated mechanisms of aortic wall remodeling in aging and disease. Elastin and collagen fibers can be observed using state-of-the-art multi-photon microscopy. Image-analysis algorithms have been effective at…

Convective mass transfer to partially recessed and porous electrodes

2003

Abstract The diffusional problem of a rotating porous electrode has been analysed based on the mass transfer equations for a partially blocked electrode. It is shown that the porous geometry leads to a dependence of the current on rotation rate identical to that corresponding to a coupled diffusion-activated electron transfer mechanism. The apparent rate constant, however, is related only to the geometry of the porous surface. It is shown that the characteristic diffusional length corresponds to the pore dimension modified by a term including the transition from linear to spherical diffusional geometry at the pore entrance. The theory is compared with experimental results for the reduction …