Tortuosity Coefficient Research Articles

Electrochemically Grown Energy and Power Dense Cathodes for Li and Na Ion Batteries

Electrochemical synthesis of materials has contributed to significant breakthroughs in materials processing by replacing high temperature, cost and energy intensive pyrometallurgical processes. Although electrodeposition as a technology for reduction of elements and alloys has been practiced since at least the 1940s, a current key and exciting question is to identify and develop electrodeposition strategies for the growth of secondary battery cathodes. Specifically, we focus on anodic electrolytic deposition methods to grow alkali-ion intercalated, layered/spinel transition metal oxide intercalation cathode systems. State-of-the-art synthesis for layered oxide cathodes for Li and Na-ion battery involves prolonged high temperature (>700°C) processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we demonstrate an intermediate temperature (250-350°C) electrodeposition process to grow alkali ion (Li+, Na+) intercalated transition metal oxides across multiple transition metal chemistries of the Li system (orthorhombic LiMnO2, Li2MnO3, LiNixMn1-xO4, LiMn2O4, LiCoO2) and Na system (O3 and P2 NaxCoO2, O’3 NaxMnO2) in thick film form factors. Even though our cathodes are electrochemically grown at the lowest reported synthesis temperature and reaction times, they retain the key structural and electrochemical performance of the high temperature bulk synthesized analogues. The key features of this alternate high throughput cathode manufacturing technique include formation of binder-and-additive-free, tens of microns thick, >75% dense electrodeposits exhibiting near theoretical gravimetric capacity, low tortuosity, and chemical diffusion coefficient of Li+/Na+ ions. Our findings highlight the influence of the unique molten hydroxide-based solution chemistry platform and electrochemical processing parameters, on regulating the phase assemblage, designing the microstructure, and controlling crystallographic orientation during electrocrystallization.

Optimal electrode-scale design of Li-ion electrodes: A general correlation

Multi-scale physics-based models, which have been parameterized and validated with discharge experiments, are optimized by varying porosity and mass loading to achieve maximum energy density. Although transport losses occur on both the electrode and particle scales, the electrode-scale optimal design is independent of the smaller scale properties. Electrode-scale properties such as tortuosity, electrolyte concentration, and Li-ion diffusion coefficient all impact optimal design. However, the impact can be generalized and the optimal results follow a general design rule that is captured in convenient correlations: ϵ=0.13log10(kϵCrτFD0c0) and Qa=kQ/kϵCrτ/(FD0c0), which provide guidelines for optimization of electrode architectures. The correlations are also in agreement with prior optimization results in the literature.

Impact of corneal parameters, refractive error and age on density and morphology of the subbasal nerve plexus fibers in healthy adults

The purpose of this study was to analyze corneal sub-basal nerve plexus (SBNP) density and morphology and their relationships with corneal parameters and refractive status. In this single center study, in vivo confocal microscopy (IVCM) was performed in 76 eyes of 38 healthy subjects aged 19–87 (mean age 34.987 ± 1.148). Nerve fiber analysis was performed using Confoscan 4 microscope with semi-automated software (Nidek Technologies, Italy) The nerve fiber length (NFL) µm/mm2, nerve fiber density (NFD) no./mm2, tortuosity coefficient (TC), and nerve beadings density (NBD) no./mm were considered. Relationship between SBNP parameters and corneal curvature, thickness, diameter, and refraction were analyzed. Additionally, the association with gender, laterality and age were determined. NFL was inversely correlated with age (r = − 0.528, p < 0.001), myopic refractive error (spherical value) (r = − 0.423, p < 0.001), and cylindrical power (r = − 0.340, p = 0.003). NFD was inversely correlated with age (r = − 0.420, p < 0.001) and myopic refractive error (r = − 0.341, p = 0.003). NBD showed a low inverse correlation with cylindrical power (r = − 0.287, p = 0.012) and a slight positive correlation with K (r = 0.230, p = 0.047). TC showed a significant negative correlation between age (r = − 0.500, p < 0.001) and myopic refractive error (r = − 0.351, p = 0.002). Additionally, there were strong positive correlations between NFL and NFD (r = 0.523, p < 0.001), NFL and TI (r = 0.603, p < 0.001), and NFD and TC (r = 0.758, p < 0.001). Multiple regression analysis revealed age to be the most significant factor affecting SBNP density (B = − 0.467, p = 0.013) and length (B = − 61.446, p < 0.001); myopic refractive error reduced both SBNP density (B = − 2.119, p = 0.011) and length (B = − 158.433, p = 0.016), while gender and laterality had no significant effects (p > 0.005). SBNP fiber length decreases with age, myopic refractive error and cylindrical power. SBNP fiber density reduces with age and myopic refractive error. Corneal nerve parameters are not influenced by gender or laterality.

Early detection of neuropathy in patients with type 2 diabetes with or without microalbuminuria in the absence of peripheral neuropathy and retinopathy

Our goal is early detection of neuropathy in patients with type 2 diabetes with or without microalbuminuria in the absence of diabetic retinopathy and peripheral neuropathy by using in vivo corneal confocal microscopy (IVCCM). A total of 60 type-2 diabetic patients, assigned to either a diabetes mellitus (DM) with microalbuminuria group (DM/MA+, n=30) or a DM without microalbuminuria group (DM/MA-, n=30), and 30 age-matched control subjects were enrolled in this study. All cases underwent evaluation of blood glucose level, HbA1c, lipid fractions, body mass index (BMI), and corneal sensitivity (CS). Corneal nerve fiber length (NFL), nerve fiber density (NFD), nerve branch density (NBD), and tortuosity coefficient (TC) were quantified by IVCCM. None of the patients had peripheral neuropathy or retinopathy. Compared with the healthy subjects, NFL and NFD were reduced in both diabetic groups (P<0.0001), while NBD was significantly reduced in the DM/MA+ group. Between the diabetic groups, NFL, NFD, and NBD were significantly higher in the DM/MA- group (all P's<0.001). CS was significantly lower in DM/MA+ compared with DM/MA- and controls (both P's<0.0001). NFD and NFL were inversely correlated with age, triglyceride level, and BMI. These results indicate that significant damage to small nerves, quantified using IVCCM, can be detected in the absence of retinopathy, peripheral neuropathy or microalbuminuria in type 2 diabetic patients. The severity of corneal nerve involvement may further increase in the presence of nephropathy. This feature may also be valuable for early detection of microvascular complications of DM, allowing for the prevention of progression of life threatening microvascular complications.

Test and analysis of the porosity of cotton fiber assembly

Porosity is one of the most important properties of textile materials that ensures their comfort and usability. The internal pore structure of the cotton fiber assembly is complex and changeable, surface pore is difficult to explain its pore structure. It is intended to develop a method to predict the pore morphology of cotton fiber assembly. Pore image of the multi-layer fiber assembly is collected by a fiber photography instrument, used the Image Pro Plus 6.0 software to analyze, and obtained the white area indicators of image which can be applied to describe void space of fiber assembly. Using multiple linear regression analysis method, the regression equation of the white area index of image and porosity index of cotton fiber assembly is established. The results indicate that the white area index can largely be explained by three pore index namely the porosity ε, mean length of fiber between the adjacent contacts B and fiber tortuosity coefficient. Appropriate regression equations can be formulated for the pore of white area index which can aid in predicting the pore texture. Comparing the data indicators, it is found that mean length of fiber between the adjacent contacts B and the porosity ε, fiber tortuosity coefficient τ, and air permeability q have good linear correlation.

Evolution in sandstone pore structures with freeze-thaw cycling and interpretation of damage mechanisms in saturated porous rocks

Measuring the evolution of pore structures is the most straightforward approach to assessing frost damage in porous rocks. Systematic and fine measurement of pore structures is critical to the interpretation of frost damage mechanisms. We conducted experiments where sandstone samples were subjected to 50 freeze-thaw cycles and their T2 spectra measured after each cycle via the nuclear magnetic resonance (NMR) method. This allowed the evolution in pore size distribution, porosity (pore volume), permeability (pore connectivity), tortuosity (pore curvature), and pore size uniformity coefficient (pore non-uniformity) to be comprehensively estimated. The results show that: (1) variation in pore structures is mainly caused by the propagation and expansion of nanopores and micropores and generation of new nanopores. (2) The porosity of sandstone has a three-stage trend of increasing-stabilizing- increasing, while tortuosity exhibits an opposite trend of decreasing-stabilizing-decreasing with freeze-thaw cycling. (3) The permeability and surface roughness of sandstone increase with freeze-thaw cycling, while the pore size uniformity coefficient decreases linearly. Based on the above results and scanning electron microscopic observations of the pore structure of sandstone, we found that: (1) the pore structure of layered sandstone can be simplified as a main stem type. (2) In this pore structure, there are two main damage processes: (a) where water in secondary cracks migrates to stem cracks and freezes, causing propagation and expansion of stem cracks; and (b) where unfrozen water in secondary cracks freezes in-situ, leading to the propagation, expansion and generation of secondary cracks. The above two damage processes coexist and alternately play pivotal roles during repeated frost activity, resulting in multistage changes to the porosity, permeability, and tortuosity of sandstone.

Structural Characteristics and Electrical Conductivity of Porous Glasses with Different Compositions in Solutions of Sodium, Lanthanum and Iron(III) Chlorides

The structural characteristics (structural resistance coefficient, volume porosity, tortuosity coefficient, average pore radius, specific surface area) and specific electrical conductivity of high-silica micro- and macroporous glasses with different compositions (basic magnetite-free and magnetite-containing glasses) have been studied in solutions of sodium, lanthanum, and iron(III) chlorides at a constant ionic strength. It has been found that the differences in the morphology of the pore space and characteristics of secondary silica are the reasons for different intensities of variations in the structural parameters of microporous glasses upon their long-term contact with electrolyte solutions, with the most pronounced time variations occurring in lanthanum chloride solutions. In indifferent electrolyte solutions, glass composition has no effect on the value of the efficiency coefficient. For microporous glasses in solutions containing specifically adsorbabable ions, the value of the efficiency coefficient is mainly affected by the structure of secondary silica in pore space, other conditions being equal. It has been revealed that, in iron chloride solutions, the specificity of the counterions is more pronounced for the basic porous glasses.

Local quantification of mesoporous silica microspheres using multiscale electron tomography and lattice Boltzmann simulations

The multiscale pore structure of mesoporous silica microspheres plays an important role for tuning mass transfer kinetics in technological applications such as liquid chromatography. While local analysis of a pore network in such materials has been previously achieved, multiscale quantification of microspheres down to the nanometer scale pore level is still lacking. Here we demonstrate for the first time, by combining low convergence angle scanning transmission electron microscopy tomography (LC-STEM tomography) with image analysis and lattice Boltzmann simulations, that the multiscale pore network of commercial mesoporous silica microspheres can be quantified. This includes comparing the local tortuosity and intraparticle diffusion coefficients between different regions within the same microsphere. The results, spanning more than two orders of magnitude between nanostructures and entire object, are in good agreement with bulk characterization techniques such as nitrogen gas physisorption and add valuable local information for tuning mass transfer behavior (in liquid chromatography or catalysis) on the single microsphere level.

Enabling fast charging of lithium-ion batteries through secondary- /dual- pore network: Part I - Analytical diffusion model

Battery performance is strongly correlated with electrode microstructural properties. Enabling fast charging of lithium-ion batteries requires improved through-plane ionic diffusion that can be achieved through, among other strategies, structured electrodes with a secondary- or dual-pore network (SPN). In this work, an analytical model investigates the impact of such an SPN on ionic diffusion with a composite electrode, considering various pore-channel geometries and comparing to standard electrodes with identical gravimetric- and volumetric-specific theoretical capacities. Relevant SPN design parameters and tortuosity coefficients are identified according to three optimization objectives that aim to balance the improved overall through-plane diffusion, thanks to the coarse aligned channels, and degraded in-plane diffusion because of the porous matrix densification required to maintain gravimetric- and volumetric-specific theoretical capacities. The model indicates that a relatively low amount of SPN is required and that electrodes with high through-plane tortuosity and low in-plane tortuosity benefit most from such architecture.

Experimental and theoretical quantification of the relationship between electrical resistivity and hydrate saturation in porous media

An equivalent resistivity model is proposed and validated to determine hydrate saturation based on the experimentally measured resistivity. Experimentally, hydrate with different saturations is formed in an artificial sandpack to measure pressure, temperature, and resistivity as a function of time. The resistivity evolution includes induction of nucleation, large-scale hydrate nucleation, and hydrate rearrangement. Theoretically, a mathematical model on the basis of the parallel circuit principle is developed to quantify the relationship between resistivity and hydrate saturation by taking sand skeleton, temperature, brine salinity, and formation tortuosity into account. The formation tortuosity is expressed as a function of water relative permeability which can be determined by incorporating the existing semi-empirical models. In addition, the cementation exponent and saturation index in the Archie formula are empirically obtained by nonlinearly regressing the experimental measurements, while the sand skeleton resistivity, the correlation coefficient of formation tortuosity, and hydrate saturation index are introduced and determined in the equivalent resistivity models. It is found that the equivalent resistivity models are in a better agreement with the experimental measurements, while the Archie formula introduces an obviously larger error at higher hydrate saturation. Furthermore, it is recommended to use the dynamic porosity expressed as a function of hydrate saturation when characterizing the electrical properties and three-phase flow in porous media. Also, the equivalent resistivity models are found to have a less dependence on the accuracy of porosity compared with the Archie’s formula.

Early diagnosis of diabetic polyneuropathy based on the results of corneal nerve fibers examination

To conduct comparative analysis of the results of CNF assessment using CCM and other known neurological instrumental techniques as well as evaluate their applicability to the early diagnosis of diabetic polyneuropathy (DPN). We examined a total of 46 patients (85 eyes) with type 1 DM and either subclinical (24 patients), or clinical-stage DPN (22 patients) and 50 patients (87 eyes) with type 2 DM (subclinical DPN in 27 patients and clinical-stage DPN in 23 patients). The control group consisted of 34 healthy volunteers (68 eyes). All patients underwent standard ophthalmological examination, CCM with nerve tortuosity assessment (including calculation of coefficients of CNF orientation anisotropy, KΔL, and symmetry, Ksym) and interocular asymmetry, electroneuromyography (ENMG), and quantitative sensory testing (QST). Analysis of the CCM results revealed a reliable decrease in the average KΔL values in patients with type 1 and type 2 DM compared with the control group. In the group of patients with type 1 DM and subclinical DPN, correlations were revealed between the CNF tortuosity coefficients and a number of ENMG parameters, such as the M-response amplitude of the peroneal nerve (r=0.73, p≤0.02), M-response amplitude of the tibial nerve (r=0.58, p≤0.01), residual latency (r= -0.62, p≤0.05), and peroneal nerve conduction velocity (r=0.57, p≤0.01). Ksym values correlated with the warm sensitivity threshold (r=0.6, p≤0.008). Among patients with type 2 DM and subclinical DPN, the KΔL coefficient correlated with the peroneal nerve conduction velocity (r=0.46, p≤0.02), M-response amplitude of the tibial nerve (r=0.6, p≤0.04), and residual latency of the peroneal nerve (r=-0.56, p≤0.05). The state of thin corneal nerves correlates with functional changes in the peripheral nerves. Pathological changes in CNF in patients with DM can be detected at an early (subclinical) stage of DPN using laser CCM and a program for corneal nerve tortuosity analysis.

An experimental method to visualize shear-induced channelization of fluid flow in a rough-walled fracture

This study proposes an experimental method to visualize the channelization of fluid flow through a rough-walled fracture during the shear-flow process using a visualization technique. Transparent fracture samples that have the same surface morphology as natural fractures are prepared for testing. The coupled shear-flow test is carried out and the tracer distributions at different shear displacements and times are captured. The results show that as the shear displacement increases, the number of contacts reduces significantly due to the shear-induced dilation, yet the area of each contact increases. The tortuosity coefficient, defined as the tortuous length of the representative flow path to the straight length between the inlet and outlet boundaries, exhibits a decreasing trend with the increment of shear displacement. This indicates that the expanded aperture induced by dilation gives rise to a less tortuous streamline and weakens the effect of surface roughness on the permeability. In the initial stage of shear, the fluid flow bypasses the contacts, forming a large number of small flow channels. At the residual stage of shear, the fluid flow is concentrated in two or three major channels that have relatively large permeability. The proposed experimental method provides a platform that has a promising potential to intuitively investigate the complex rock–fluid interactions within fractures.

Using dry pyrolysis to understand crude oil production characteristics and calculate tortuosity in unconventional shales

In situ fractionation in shales means differential movement of the light versus heavy components of the crude oil in the shale formation. This can be due to multiple phenomenon like molecular sieving, varying diffusion coefficients for different hydrocarbon components and multi-component adsorption all acting simultaneously. Many companies have reported change in composition of produced fluid with time. Insitu fractionation is important because it has strong implications on EOR, both selecting the timing of EOR, and the solvent for EOR. Additionally, simulators for history matching, prediction and optimizing well spacing, must account for this effect. Earlier studies have proved the occurrence of the insitu fractionation both experimentally using GC-MS (gas chromatography and mass spectrometry) and theoretically using molecular dynamic simulations. However, cores are available in limited number of wells and, tools and measurements required to understand insitu fractionation are both time consuming and very expensive. We have found that dry pyrolysis can be used to effectively study insitu fractionation, the advantage being it is cheap and fast. The same experiment can be used to calculate effective diffusion coefficient and tortuosity. The study was done on samples from Berea sandstone, and Eagle Ford and Wolfcamp shales covering a wide range of petrophysical properties. The point source solution of the diffusivity equation was used to back out the effective diffusion coefficients. The effective diffusion coefficients determined for Berea, Wolfcamp and Eagle Ford samples were 5.38E-11 m2/s, 2.61E-11 m2/s and 5.35E-12 m2/s, respectively. These coefficients were then used to calculate the tortuosity of the samples which were validated by the resistivity measurements. The tortuosity values for the Berea, Wolfcamp and Eagle Ford samples were determined to be 3.1, 3.4 and 7.1, respectively. Tortuosity and diffusion coefficients are of paramount importance especially given the fact that permeability measurements in shales are unreliable and Knudsen diffusion and ordinary diffusion have to be integrated with Darcy flow to model production behavior in shales.

Monitoring of horizontal displacements of the Prut River bed using geoinformation technologies

River beds are one of the most dynamic geographical features on the surface of the earth, accompanied by constant movements and displacements. They respond well to the dynamics of temperature and climatic conditions, changes and variability of meteorological conditions, as well as human load. Increasing rainfall during the season, the recurrence of abnormal seasons lead not only to an increase in the water level in the channel, but also to an increase in both the number and width of the river's hoses, contributes to the change of the location of the main channel, accompanied by watering old women and floodplains, the accumulation of sediment and the increase of washouts. Horizontal displacements of the channel significantly affect the cultural and natural landscapes and human economic activity. Conversely, human activity, in particular, mining and large-scale hydrotechnical works in the valleys, also change their course. Insufficient study and research of riverbed issues can lead to the flooding of large areas, which is particularly dangerous for settlements. The current insufficient number of existing hydrological posts, the reduction of field research opportunities, the deterioration of the quality and the inaccessibility of hydrometeorological, mapping information, and for most water bodies simply the lack of data leads to the impossibility of a comprehensive hydrological and morphological study of the river basin and the assessment of intensities. For this reason, in most of the works encountered and related to similar issues, a small local body of water or a section of the main channel or its tributary is selected for research. An important problem is also the comparison of the morphometric characteristics of the river network on topographic maps and plans of different scale series. The river meandering close to reality can only be displayed on large-scale maps. The smaller the scale of the map, the more straightened or generalized the drawing of the rivers. Therefore, it is advisable to carry out such assessments and study of horizontal displacements of the channel on the cartographic material of one scale series. The horizontal displacements of the Prut River bed within the city of Chernivtsi were investigated using topographic maps and plans of different scale, for more than 160 years of observations. About 15 km of the Prut River bed has been digitized. For a better and more detailed analysis of the change in horizontal displacements of the riverbed, the study area was divided into three sections - West, Central, and East. The choice of a place of division is caused by features of the winding channel. The search of maps of different scales in previous years for this territory made it possible to compare the horizontal displacements of the Prut River bed both in time and in space. Topographic maps of 1: 100000 scale in 1982, 1:50000 - 1940 and 1977 and 1:25000 of 1947 and 1957, maps of the Austrian monarchy of 1:75000 - 1855 were found. Analysis of the spatial-temporal changes of horizontal displacements of the Prut River bed by space images and topographic maps during the 161-year observation period showed significant differences in terms of the most meandering channel and its size and shape. Using time analysis, it was found that the highest meandering of the channel was observed in the middle of the twentieth century and amounted to 1.33 and decreased to 1.12 as of 2016. Virtually unchanged, in terms of horizontal displacements, the channel remained in the central part of the study area. In the eastern and western parts, the tortuosity coefficient is increased due to the meandering of the channel and due to the presence of the sleeves, especially in the Kalichanka area. For the western part, the greatest changes are observed in the area of the Prut River near the villages of Lenkivtsi and Streletsky Kut. The highest values of deviations of the channel from the current location are in the range of 300-400 meters.

Impact of Carbon Deposition on Diffusion Parameters in Porous Anodes of Solid Oxide Fuel Cells Using the Lattice Boltzmann Method

A solid oxide fuel cell (SOFC) is an electrochemical device that converts energy of a chemical reaction into electrical and thermal energy. Besides lack of pollutants and high electrical efficiency, one of the main advantages of SOFCs is the flexibility of using a wide range of fuels, i.e., natural gas, biogas, or any reactant with hydrogen as constituent. However, the use of hydrocarbon fuels can affect the transport phenomena within the SOFC porous anode due to carbon deposition. The purpose of this work is to investigate, at pore-scale level, the impact of carbon deposition on the microstructural parameters that describes the diffusion process. The single-phase fluid flow behavior through digitally generated SOFC anodes is obtained by the Lattice Boltzmann method (LBM). Diffusion transport parameters, i.e., porosity, gas-phase tortuosity and effective diffusion coefficient are computed for different content of carbon deposition to be able to evaluate its impact.

Structural and electrosurface properties of iron-containing nanoporous glasses in KNO3 solutions

The paper is devoted to study and comparison of the structural (volume porosity W, structural resistance coefficient β, tortuosity coefficient K, average pore radius r, specific surface area S0) and electrosurface (efficiency coefficient α, counter-ion transport number n+, electrokinetic potential ζ) properties of micro - and macroporous sodium borosilicate glasses containing (Fe 4–6) and not containing (8 V-NT) magnetite phase in 10−4 – 10−1 M KNO3 solutions. It has been found that the incorporation of an iron (III) oxide into basic sodium-borosilicate glass results in changes in the structure of the pore space of both microporous and macroporous glasses. Moreover, it is shown that the presence of magnetite in the structure of porous glasses does not have a noticeable effect on the values of the efficiency coefficients and potassium counter-ion transport number in the neutral pH region. It has also been established that the absolute values of the electrokinetic potential for microporous membranes of both compositions in the neutral pH region are close to each other. For macroporous membranes obtained under the same conditions, the absolute values of the electrokinetic potential for the iron-containing membrane are higher than these for basic membrane 8 V-NT.

Investigation on the permeability of porous asphalt concrete based on microstructure analysis

ABSTRACT Drainage is an important function in porous asphalt concrete (PAC); however, permeability is decreased gradually due to pores clogging. The aim of this paper is to evaluate the influence of microstructures of pores on anti-clogging performance of PAC. To create different types of pore structures, aggregates with different sizes and shapes were used to form specimens, and a self-designed equipment was employed to measure the permeability and anti-clogging performance of PAC. X-ray CT device scanned specimens before and after clogging test, so the influence of aggregates on pores can be determined, and the relationship between pore characteristics and anti-clogging performance was investigated. The results show that aggregates with different shapes affect pore states obviously, including volume, number and effective porosity, and the permeability of PAC decreases if effective pores are clogged. Clogging happens shortly, and PAC constructed by aggregates with regular shape presents excellent anti-clogging performance. Aggregates with irregular shape cause more tortuous drainage channel compared with regular aggregates, and tortuosity coefficient is an effective indicator that quantifies the complexity of pores and evaluates the anti-clogging performance of PAC.

Microfiltration membrane characterization by gas-liquid displacement porometry: Matching experimental pore number distribution with liquid permeability and bulk porosity

The variable viscosity Poiseuille model (VVPM), developed recently to treat gas-liquid displacement (GLD) porometry data for track-etched polyethylene terephthalate (PET) membranes, is applied to polyethersulfone (PES) and polypropylene (PP) microfiltration membranes prepared by phase inversion. It is found that in general aspects the pore size distribution as estimated by the model, with the intrinsic assumption of isolated capillary pores, perfectly reproduces wet and dry fluxes during porometry measurements, but the estimated porosity appeared to be much higher than unity. To eliminate the discrepancy, two additional parameters, namely non-uniformity and tortuosity coefficient, have been introduced in the flux and porosity estimating equations. The apparent viscosity of the gas in porometry analysis is found to be several fold higher than that available in literature, and also the viscosity range appeared to be membrane type dependent. The pore size distribution curve shifts along the diameter axis depending on the gas flow direction applied in porometry data acquisition. However, because the membranes had narrow pore size disribution, the estimated parameters had been averaged within acceptable confidence range. With the inclusion of non-uniformity and tortuosity of the capillaries, the revised version of the VVPM made an advancement in porometry data analysis of membranes with both isolated and interconnected pore structure; it characterizes the assumed model capillaries in terms of Young-Laplace pore diameter, but also non-uniformity and tortuosity of pores. The procedure for data treatment has been illustrated in detail and the method could easily be adapted to gas-liquid displacement porometer software system for regular data treatment. Based on a set of readily available experimental data, including the typical output from standard GLD porometry, the here established extended version of the VVPM allows the step-by-step determination of all the parameters which characterize the pore structure of the membranes. Also the absolute pore number density distributions can be obtained, including estimates of additional pore characteristics such as non-uniformity and tortuosity.

The effect of permeability on supercritical CO2 diffusion coefficient and determination of diffusive tortuosity of porous media under reservoir conditions

A general method for determining the diffusivity coefficient of supercritical CO2 in cores saturated with oil is presented in this paper. Theoretically, a mathematical model including Fick’s diffusion equation and Peng–Robinson Equation of State (PR EOS) is proposed to evaluate the mass transfer of CO2 in the cores with different permeabilities. Experimentally, the pressure-decay method is employed by monitoring the CO2 pressure in the diffusion cell during diffusion experiments. The CO2 diffusion coefficients in the cores with different permeabilities are determined when the discrepancy of the calculated and measured pressure-decay curves has been minimized. The diffusion coefficient of supercritical CO2 increases gradually with rising permeability at the range of 0.1–10 mD, and then it reaches a plateau at the permeability range of 10–300 mD. The impact of the permeability on the CO2 diffusion coefficient is attributed to the pore radius and pore structure of the cores. The Pore radius of the core whose permeability is less than 10 mD is less than 1 μm, and pore walls restrict CO2 mass transfer under such condition, which accounts for the relative low diffusion coefficient. When the permeability exceeds 10 mD, the pore radius is larger than 1 μm, and the influence of the solid boundary is negligible. Moreover, the textural coefficients of cores decrease with the permeability, which shows that the less tortuous pore structure facilitates the mass transfer process. Diffusive tortuosities for the cores with different permeabilities are determined by using the CO2 diffusion coefficients in porous media and bulk phase, which show the same trend with the pore radius distribution.

Survival Time to Biopsy-Proven Acute Rejection and Tacrolimus Adverse Drug Reactions in Pediatric Liver Transplantation.

Despite advances in surgical procedures and the optimization of immunosuppressive therapies in pediatric liver transplantation, acute rejection (AR) and serious adverse drug reaction (ADR) to tacrolimus still contribute to morbidity and mortality. Identifying risk factors of safety and efficacy parameters may help in optimizing individual immunosuppressive therapies. This study aimed to identify peritransplant predictors of AR and factors related to the risk of ADR to tacrolimus in a large Latin American cohort of pediatric liver transplant patients. We performed a retrospective cohort study in a pediatric liver transplant population (n = 72). Peritransplant variables were collected retrospectively including demographic, clinical, laboratory parameters, genomic (CYP3A5 donor and recipients polymorphism), and tacrolimus trough concentrations (C0) over a 2-year follow-up period. Variability in tacrolimus C0 was calculated using percent coefficient of variation and tortuosity. ADR- and AR-free survival rates were calculated using the Kaplan-Meier method, and risk factors were identified by multivariate Cox regression models. Cox-proportional hazard models identified that high tortuosity in tacrolimus C0 was associated with an 80% increased risk of AR [hazard ratio (HR), 1.80; 95% confidence interval (CI), 1.01-3.22; P < 0.05], whereas steroid in maintenance doses decreased this risk (HR, 0.56; 95% CI, 0.31-0.99; P < 0.05). Forty-six patients experienced at least one ADR including hypomagnesemia, nephrotoxicity, hypertension, malignancies, and tremor as a first event. Multivariate analysis showed that C0 values 10 days before the event (HR, 1.25; 95% CI, 1.21-1.39; P < 0.0001) and CYP3A5 expresser recipients (HR, 2.05; 95% CI, 1.03-4.06; P < 0.05) were independent predictors of ADR. Tacrolimus C0 values, its variability, and CYP3A5 polymorphisms were identified as risk factors of AR and tacrolimus ADR. This knowledge may help to control and reduce their incidence in pediatric liver transplant patients. Prospective studies are important to validate these results.