Increase In Tortuosity Research Articles

Aging-associated changes in cerebral vasculature and blood flow as determined by quantitative optical coherence tomography angiography.

Normal aging is associated with significant alterations in brain's vascular structure and function, which can lead to compromised cerebral circulation and increased risk of neurodegeneration. The invivo examination of cerebral blood flow (CBF), including capillary beds, in aging brains with sufficient spatial detail remains challenging with current imaging modalities. In the present study, we use 3-dimensional (3-D) quantitative optical coherence tomography angiography (OCTA) to examine characteristic differences of the cerebral vasculatures and hemodynamics at the somatosensory cortex between old (16 months old) and young mice (2 months old) invivo. The quantitative metrics include cortical vascular morphology, CBF, and capillary flow velocity. We show that compared with young mice, the pial arterial tortuosity increases by 14%, the capillary vessel density decreases by 15%, and the CBF reduces by 33% in the old mice. Most importantly, changes in capillary velocity and heterogeneity with aging are quantified for the first time with sufficiently high statistical power between young and old populations, with a 21% (p < 0.05) increase in capillary mean velocity and 19% (p ≤ 0.05) increase in velocity heterogeneity in the latter. Our findings through noninvasive imaging are in line with previous studies of vascular structure modification with aging, with additional quantitative assessment in capillary velocity enabled by advanced OCTA algorithms on a single imaging platform. The results offer OCTA as a promising neuroimaging tool to study vascular aging, which may shed new light on the investigations of vascular factors contributing to the pathophysiology of age-related neurodegenerative disorders.

High fat diet induces pre-type 2 diabetes with regional changes in corneal sensory nerves and altered P2X7 expression and localization

Type 2 diabetes is one of the leading pathologies that increases the risk of improper wound healing. Obesity has become a major risk factor for this disease that is now considered to be the 4th highest cause of preventable blindness according to the World Health Organization. The cornea is the most densely innervated structure in the human body and senses even the slightest injury. In diabetes, decreased corneal sensitivity secondary to diabetic peripheral neuropathy can lead to increased corneal abrasion, ulceration, and even blindness. In this study, a diet induced obesity (DIO) mouse model of pre-Type 2 diabetes was used to characterize changes in sensory nerves and P2X7, a purinoreceptor, a pain receptor, and an ion channel that is expressed in a number of tissues. Since our previous studies demonstrated that P2X7 mRNA was significantly elevated in diabetic human corneas, we examined P2X7 expression and localization in the DIO murine model at various times after being fed a high fat diet. Fifteen weeks after onset of diet, we found that there was a significant decrease in the density of sub-basal nerves in the DIO mice that was associated with an increase in tortuosity and a decrease in diameter. In addition, P2X7 mRNA expression was significantly greater in the corneal epithelium of DIO mice, and the increase in transcript was enhanced in the central migrating and peripheral regions after injury. Interestingly, confocal microscopy and thresholding analysis revealed that there was a significant increase in P2X7 distal to the injury, which contrasted with a decrease in P2X7-expressing stromal sensory nerves. Therefore, we hypothesize that the P2X7 receptor acts to sense changes at the leading edge following an epithelial abrasion, and this fine-tuned regulation is lost during the onset of diabetes. Further understanding of the corneal changes that occur in diabetes can help us better monitor progression of diabetic complications, as well as develop new therapeutics for the treatment of diabetic corneal dysfunction.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (µCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from µCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.

Controllable construction of polymer/inorganic interface for poly(vinyl alcohol)/graphitic carbon nitride hybrid pervaporation membranes

Highly water-selective hybrid pervaporation membranes with excellent water/ethanol separation performance and superior water channels were fabricated by incorporating graphitic carbon nitride (g-C3N4), activated g-C3N4 (O-g-C3N4) and polydopamine modified g-C3N4 (PDA@O-g-C3N4) nanosheets into poly(vinyl alcohol) (PVA) matrix. The nonselective polymer/inorganic interface channels between PVA and g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 in hybrid membranes were controllable constructed through hydrogen bonds, rigid and flexible chemical bonds, respectively. The membrane performances were tested in the pervaporation (PV) process for the dehydration of 90 wt% ethanol/water mixtures at 75 °C. The results revealed that with the increase of binding force among polymer/inorganic interface, from hydrogen bonds (CPVA-g-C3N4), to rigid (CPVA-O-g-C3N4) and flexible chemical bonds (CPVA-PDA@O-g-C3N4), the total flux decreased from 4634 to 2328 g/(m2h) and the separation factor increased from 32.4 to 57.9. It is implied that the nonselective polymer/inorganic interface channels were controlled successfully. Meanwhile, compared with the pure cross-linked PVA (CPVA) membrane (total flux 2325 g/(m2h) and separation factor 18.7), incorporation of g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 could all lead to an increase of surface hydrophilicity of the CPVA membranes along with an increase in membrane tortuosity and membrane water-selective channels that was favorable to the selective permeation of water molecules. Namely, these new hybrid membranes can break the “trade-off effect” effectively. Moreover, due to the ordered alignment of g-C3N4, O-g-C3N4 and PDA@O-g-C3N4 nanosheets and the strong interfacial interactions among these nanosheets, succinic acid (Sa) and the PVA matrix, the hybrid composite membranes showed both high swelling resistance and mechanical stability.

Relationship between the particle size and dosage of LDHs and concrete resistance against chloride ingress

The present study investigates the transport properties of cement mortar with Ca-Al-NO3 layered double hydroxides (LDHs). A co-precipitation method is applied to synthesize the Ca-Al-NO3 LDHs and the effect of the synthesis environment on the size and particle shape is studied. The synthesized Ca-Al-NO3 LDHs are analytically characterized by XRD, SEM and FTIR analyses. The relationships between the sizes and addition amount of Ca-Al-NO3 LDHs and the mechanical and transport properties of mortars are investigated. Rapid chloride migration (RCM) tests are performed to the cement mortars with Ca-Al-NO3 LDHs. The results show that permeability of the designed concrete decreased with the addition of Ca-Al-NO3 layered double hydroxides (LDHs). The decrease of chloride migration coefficients can be attributed to the enhanced barrier effect because of the increase of tortuosity. In long-term natural diffusion tests, LDHs present significantly enhanced barrier effect due to the combined chloride binding ability and improved tortuosity.

Characterization of Vessel Deformations During EVAR: A Preliminary Retrospective Analysis to Improve Fidelity of Endovascular Simulators

During endovascular aneurysm repair (EVAR), vessel deformations occur due to the insertion of tools and deployment of stent grafts in the arteries. We present a method for the characterization of vessel deformations during EVAR, and its application on patient datasets for a preliminary retrospective analysis that may be used to improve fidelity of endovascular simulators. The method provides the extraction of vessel profiles from intraoperative fluoroscopic images and the calculation of a tortuosity index in the 2D fluoroscopy view (τ2D) used to quantify the vessel deformations (δ%) during EVAR caused by the stiff guidewire insertion (δ%Stiff) and the stent graft deployment (δ%Graft), when compared with the undeformed vessel configuration (no device inserted). We applied the method to analyze retrospectively 7 EVAR patient datasets, including vasculature anatomies with different grades of vessel tortuosity or calcification: 2 patients (Pts) with absent tortuosity and mild calcification, 2 with mild tortuosity and mild calcification, 2 with severe tortuosity and mild calcification, and 1 with severe tortuosity and severe calcification. The analysis was focused on deformations of the left common iliac artery (LCIA), which is one of the arterial segments most affected by deformations. In patients with mild LCIA calcification, the vessel straightening effect due to the stiff guidewire insertion increases as the severity of LCIA tortuosity increases (δ%Stiff = 0 ± 2%, -19 ± 2%, -45 ± 2% for absent, mild, and severe tortuosity, respectively). In patients with mild/severe LCIA tortuosity, the artery with the deployed graft seems to retain part of the straightening effect caused by the stiff guidewire (δ%Graft = -9 ± 3%, -31 ± 2%, for mild and severe tortuosity, respectively). In case of severe LCIA calcification, the stiff guidewire causes only a slight straightening effect (δ%Stiff = -12%) despite the severe vessel tortuosity. The method was effective in characterizing real vessel deformations during EVAR. Results gave evidence of a relationship between the obtained deformations and the anatomical vessel conformation. These results may be useful to drive predictive models of vessel deformations during EVAR to be implemented in endovascular patient-specific simulators for improving their fidelity.

Microcirculatory parameters in compensated and decompensated type 2 diabetes mellitus

To reveal the features of microcirculatory parameters in compensated and decompensated type 2 diabetes mellitus (T2DM). A total of 196 patients with T2DM were examined and divided into 2 groups: 1) 52 patients (40.4% of men) aged 52.8±8.7 years with compensated T2DM (glycated hemoglobin (HbA1с), 6.3±0.5%); 2) 68 patients (38.2% of men) aged 52.8±8.1 years with decompensated T2DM (HbA1с, 9.4±1.7%). Both patient groups had concomitant hypertension (its prevalence, degree, stage of hypertension were comparable). A control group consisted of 76 volunteers (40.8% of men) aged 52.2±8.7 years with normal carbohydrate metabolism and without signs of cardiovascular disease (HbA1с, 5.3±0.49%). Capillary blood flow in the finger nail-fold area was investigated in all the participants. A digital optical capillaroscope with image-processing software was used to obtain quantitative blood microcirculatory parameters. The diameters of arterial and venous capillary segments were measured, by calculating the remodeling rate. The degree of capillary tortuosity, network density, and polymorphism and the size of the perivascular zone (PZ) were estimated. Blood rheological properties and capillary blood flow velocity were also investigated. The decompensated T2DM group compared to the compensated T2DM group was found to have a narrowing of the arterial capillary segment diameter (8.4±2.0 µm; p=0.009) and an increase in remodeling rates (1.47±0.22; p=0.000). The tendency of the PZ size to be larger in patients with decompensated T2DM compared to those with compensated T2DM (p=0.080) and the increase in this indicator compared to the control group (p=0.001) reflect the presence of edema syndrome in Group 2, as laboratory confirmed by a statistically significantly elevated sodium level (p=0.000; p=0.006). The enlarged venous capillary segment demonstrates involvement of the venous component in microcirculatory disorders in T2DM. The reduction in the density of the capillary network and the increase in capillary tortuosity and polymorphism, which were also observed in the patients of both groups versus the control group, are referred to as disorders that are characteristic of T2DM. In decompensated T2DM, capillary bed structural and functional changes are found as a narrowing of the arterial capillary segment, an increase in the rate of remodeling, and enlargement of the PZ. Digital capillaroscopy opens up new possibilities for assessing the magnitude of changes in the microcirculatory system in DM and can simultaneously evaluate the efficiency of treatment, by monitoring the status of the microvasculature.

Cross-linked poly(acrylic acid)-carboxymethyl cellulose and styrene-butadiene rubber as an efficient binder system and its physicochemical effects on a high energy density graphite anode for Li-ion batteries

An increase in graphite anode thickness is an effective way to achieve a high-energy density lithium ion battery by designing a compact cell with a high mass loading and density. However, this may cause critical problems in Li+ diffusivity due to drastic increases in length and tortuosity of the ionic migration path. A mixture of cross-linked poly (acrylic acid) (PAA)–carboxymethyl cellulose hydrogels (CMC) was developed using styrene-butadiene rubber (SBR) as an efficient binder system to increase Li+ diffusivity and adhesion strength. Electrolyte permeability and adhesion strength of the electrode were enhanced by 2.5 and 2 times, respectively, compared to a conventional CMC–SBR system, which led to excellent electrochemical properties due to enhanced affinity with electrolytic and interpolymeric properties. Particularly, capacity retention was improved from 81 to 91% at a high 1C rate.

A geometric reappraisal of proximal landing zones for thoracic endovascular aortic repair according to aortic arch types

ObjectiveThis study assessed whether the additional use of the aortic arch classification in type I, II, and III may complement Ishimaru's aortic arch map and provide valuable information on the geometry and suitability of proximal landing zones for thoracic endovascular aortic repair. MethodsAnonymized thoracic computed tomography scans of healthy aortas were reviewed and stratified according to the aortic arch classification, and 20 of each type of arch were selected. Further processing allowed calculation of angulation and tortuosity of each proximal landing zone. Data were described indicating both proximal landing zone and type of arch (eg, 0/I). ResultsAngulation was severe (>60°) in 2/III and in 3/III. Comparisons among the types of arch showed an increase in proximal landing zones angulation (P < .001) and tortuosity (P = .009) depending on the type of arch. Comparisons within type of arch showed no change in angulation and tortuosity across proximal landing zones within type I arch (P = .349 and P = .409), and increases in angulation and tortuosity toward more distal proximal landing zones within type II (P = .003 and P = .043) and type III (P < .001 in both). ConclusionsThe aortic arch classification is associated with a consistent geometric pattern of the aortic arch map, which identifies specific proximal landing zones with suboptimal angulation for stent graft deployment. Arches II and III also appear to have progressively less favorable anatomy for thoracic endovascular aortic repair compared with arch I.

Increased capillary tortuosity and pericapillary basement membrane thinning in skeletal muscle of mice undergoing running wheel training.

To work out which microvascular remodeling processes occur in murine skeletal muscle during endurance exercise, we subjected C57BL/6 mice to voluntary running wheel training for 1 week (1 wk-t) or 6 weeks (6 wks-t). By means of morphometry, the capillarity as well as the compartmental and sub-compartmental structure of the capillaries were quantitatively described at the light microscopy level and at the electron microscopy level, respectively, in the plantaris (PLNT) muscle of the exercising mice in comparison to untrained littermates. In the early phase of the training (1 wk-t), angiogenesis [32% higher capillary/fiber (C/F) ratio; P<0.05] in PLNT muscle was accompanied by a tendency for capillary lumen enlargement (30%; P=0.06) and a reduction of the pericapillary basement membrane thickness [(CBMT) 12.7%; P=0.09] as well as a 21% shortening of intraluminal protrusion length (P<0.05), all compared with controls. After long-term training (6 wks-t), when the mice reached a steady state in running activity, additional angiogenesis (C/F ratio: 76%; P<0.05) and a 16.3% increase in capillary tortuosity (P<0.05) were established, accompanied by reversal of the lumen expansion (23%; P>0.05), further reduction of the CBMT (16.5%; P<0.05) and additional shortening of the intraluminal protrusion length (23%; P<0.05), all compared with controls. Other structural indicators, such as capillary profile sizes, profile area densities, perimeters of the capillary compartments and concentrations of endothelium-pericyte peg-socket junctions, were not significantly different between the mouse groups. Besides angiogenesis, increase of capillary tortuosity and reduction of CBMT represent the most striking microvascular remodeling processes in skeletal muscle of mice that undergo running wheel training.

Three Dimensional Quantification of Microarchitecture and Vessel Regeneration by Synchrotron Radiation Microcomputed Tomography in a Rat Model of Spinal Cord Injury.

A full understanding of the mechanisms behind spinal cord injury (SCI) processes requires reliable three-dimensional (3D) imaging tools for a thorough analysis of changes in angiospatial architecture. We aimed to use synchrotron radiation μCT (SRμCT) to characterize 3D temporal-spatial changes in microvasculature post-SCI. Morphometrical measurements revealed a significant decrease in vascular volume fraction, vascular bifurcation density, vascular segment density, and vascular connectivity density 1 day post-injury, followed by a gradual increase at 3, 7, and 14 days. At 1 day post-injury, SRμCT revealed an increase in vascular tortuosity (VT), which reached a plateau after 7 days and decreased slightly during the healing process. In addition, SRμCT images showed that vessels were largely concentrated in the gray matter 1 day post-injury. The maximal endothelial cell proliferation rate was detected at 7 days post-injury. The 3D morphology of the cavity appears in the spinal cord at 28 days post-injury. We describe a methodology for 3D analysis of vascular repair in SCI and reveal that endogenous revascularization occurs during the healing process. The spinal cord microvasculature configuration undergoes 3D remodeling and modification during the post-injury repair process. Examination of these processes might contribute to a full understanding of the compensatory vascular mechanisms after injury and aid in the development of novel and effective treatment for SCI.

Dark field optical imaging reveals vascular changes in an inducible hamster cheek pouch model during carcinogenesis.

In this study, we propose a low-cost cross-polarized dark field microscopy system for in vivo vascular imaging to detect head and neck cancer. A simple-to-use Gabor-filter-based image processing technique was developed to objectively and automatically quantify several important vascular features, including tortuosity, length, diameter and area fraction, from vascular images. Simulations were performed to evaluate the accuracies of vessel segmentation and feature extraction for our algorithm. Sensitivity and specificity for vessel segmentation of the Gabor masks both remained above 80% at all contrast levels when compared to gold-standard masks. Errors for vascular feature extraction were under 5%. Moreover, vascular contrast and vessel diameter were identified to be the two primary factors which affected the segmentation accuracies. After our algorithm was validated, we monitored the blood vessels in an inducible hamster cheek pouch carcinogen model over 17 weeks and quantified vascular features during carcinogenesis. A significant increase in vascular tortuosity and a significant decrease in vessel length were observed during carcinogenesis.

Effect of porous structure of catalyst layer on effective oxygen diffusion coefficient in polymer electrolyte fuel cell

Abstract It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.

The gas effective permeability of porous media with Klinkenberg effect

Gas transport properties in micro and nano-scale porous media are of significance for low-permeability reservoirs. Gas slippage and gas molecular diffusion in micro- and nano-pores take important effect on the gas permeability of porous media. Therefore, gas effective permeability of micro and nano-scale porous media over the entire Knudsen regime is presented by a fractal model. The analytical expression for gas effective permeability with Klinkenberg effect which is a function of structural parameters of porous media (porosity, fractal dimensions and pore diameter) and gas property (mean free path of gas molecule) is derived based on the microflow model and fractal capillary model. In order to further address the local flow field characteristics, numerical simulations are also performed on a fractal Sierpinski carpet. The fractal model is validated by comparison with available experimental results, and the effect of gas slippage on the gas permeability is discussed also. The present results indicate that gas effective permeability with slippage effect increases with the increase of fractal dimension for pore size distribution and decreases as the fractal dimension for tortuosity increases. And the gas slip factor increases with the decrease of pore size, it can be also increased by increased fractal dimension for pore size distribution under fixed maximum pore size and porosity. The current fractal model can characterize the multi-scale microstructures in porous media, and every parameter in the proposed gas effective permeability model has specific physical meaning.

Exploring the scale-dependent permeability of fractured andesite

Extension fractures in volcanic systems exist on all scales, from microscopic fractures to large fissures. They play a fundamental role in the movement of fluids and distribution of pore pressure, and therefore exert considerable influence over volcanic eruption recurrence. We present here laboratory permeability measurements for porous (porosity = 0.03–0.6) andesites before (i.e., intact) and after failure in tension (i.e., the samples host a throughgoing tensile fracture). The permeability of the intact andesites increases with increasing porosity, from 2×10−17 to 5×10−11 m2. Following fracture formation, the permeability of the samples (the equivalent permeability) falls within a narrow range, 2–6×10−11 m2, regardless of their initial porosity. However, laboratory measurements on fractured samples likely overestimate the equivalent permeability due to the inherent scale-dependence of permeability. To explore this scale-dependence, we first determined the permeability of the tensile fractures using a two-dimensional model that considers flow in parallel layers. Our calculations highlight that tensile fractures in low-porosity samples are more permeable (as high as 3.5×10−9 m2) than those in high-porosity samples (as low as 4.1×10−10 m2), a difference that can be explained by an increase in fracture tortuosity with porosity. We then use our fracture permeability data to model the equivalent permeability of fractured rock (with different host rock permeabilities, from 10−17 to 10−11 m2) with increasing lengthscale. We highlight that our modelling approach can be used to estimate the equivalent permeability of numerous scenarios at andesitic stratovolcanoes in which the fracture density and width and host rock porosity or permeability are known. The model shows that the equivalent permeability of fractured andesite depends heavily on the initial host rock permeability and the scale of interest. At a given lengthscale, the equivalent permeability of high-permeability rock (10−12 to 10−11 m2) is essentially unaffected by the presence of numerous tensile fractures. By contrast, a single tensile fracture increases the equivalent permeability of low-permeability rock (<10−15 m2) by many orders of magnitude. We also find that fractured, low-permeability rock (e.g., 10−17 m2) can have an equivalent permeability higher than that of similarly fractured rock with higher host rock permeability (e.g., 10−15 m2) due to the low-tortuosity of fractures in low-porosity andesite. Our modelling therefore outlines the importance of fractures in low-porosity, low-permeability volcanic systems. While our laboratory measurements show that, regardless of the initial porosity, the equivalent permeability of fractured rock on the laboratory scale is 2–6×10−11 m2, the equivalent permeability of low-permeability rock is significantly reduced as the scale of interest is increased. Therefore, due to the scale-dependence of permeability, laboratory measurements on pristine, low-permeability rocks significantly underestimate the equivalent permeability of fractured volcanic rock. Further, measurements on fractured rock samples can significantly overestimate the equivalent permeability. As a result, care must be taken when selecting samples in the field and when using laboratory data in volcano outgassing models. The data and modelling presented herein provide insight into the scale-dependence of the permeability of fractured volcanic rock, a prerequisite for understanding outgassing at active volcanoes.

Evaluation of Microstructure and Transport Properties of Deteriorated Cementitious Materials from Their X-ray Computed Tomography (CT) Images.

Pore structure, tortuosity and permeability are considered key properties of porous materials such as cement pastes to understand their long-term durability performance. Three-dimensional image analysis techniques were used in this study to quantify pore size, effective porosity, tortuosity, and permeability from the X-ray computed tomography (CT) images of deteriorated pastes that were subjected to accelerated leaching test. X-ray microtomography is a noninvasive three-dimensional (3D) imaging technique which has been recently gaining attention for material characterization. Coupled with 3D image analysis, the digitized pore can be extracted and computational simulation can be applied to the pore network to measure relevant microstructure and transport properties. At a spatial resolution of 0.50 μm, the effective porosity (φe) was found to be in the range of 0.04 to 0.33. The characteristic pore size (d) using a local thickness algorithm was found to be in the range of 3 to 7 μm. The geometric tortuosity (τg) based on a 3D random walk simulation in the percolating pore space was found to be in the range of 2.00 to 7.45. The water permeability values (K) using US NIST Permeability Stokes Solver range from an order of magnitudes of 10−14 to 10−17 m2. Indications suggest that as effective porosity increases, the geometric tortuosity increases and the permeability decreases. Correlation among these microstructure and transport parameters is also presented in this study.

The heat and mass transfer of vacuum membrane distillation: Effect of active layer morphology with and without support material

Abstract The aim of this research was the analysis of heat and mass transfer in vacuum membrane distillation (VMD), specifically for a dead-end feed set-up. The influence of support material on the supported membranes VMD performance was identified. A mathematical model was proposed to evaluate the membrane/feed interface temperature, membrane tortuosity, membrane mass transfer coefficient, and temperature polarization coefficient (TPC). The model was solved by an excel solver based on experimental results of feed temperature, system pressure and the evaporative fluxes. The SEM images showed that the thickness of unsupported membrane was reduced by 42% after the VMD test. Pore shrinkage and tortuosity increase were also expected during this pore collapsing process. On the other hand, the cross-sectional views of the supported membranes did not show significant changes. These results show that the support material can help prevent the membrane pore channel structure from collapsing during the VMD experiment. TPC is close to unity at low feed temperatures. However, it decreases with an increase in evaporation flux as the feed temperature increases, or when a high flux supported membrane is applied.

Mathematical modelling of wustite pellet reduction: grain model in comparison with USCM

A mathematical time-dependent and non-isothermal model has been carried out on the basis of the grain model to study the behaviour of a wustite pellet undergoing chemical reactions with reducing gases. The behaviour of wustite pellet reduction analysed by the grain model has been compared with unreacted shrinking core model (USCM). The results show, unlike the grain model, USCM cannot properly predict the impact of gas mixture parameters and pellet characteristics on the local reduction degree. The results also display that when the grain diameter, temperature and tortuosity increase, the diffusivity resistance in the pellet increases which causes more heterogeneous reduction. However, an increment in porosity causes gases to easily diffuse in the pellet and as a result a less heterogeneous reduction will occur.

In situ studies of materials for high temperature CO2 capture and storage.

Carbon capture and storage (CCS) offers a possible solution to curb the CO2 emissions from stationary sources in the coming decades, considering the delays in shifting energy generation to carbon neutral sources such as wind, solar and biomass. The most mature technology for post-combustion capture uses a liquid sorbent, amine scrubbing. However, with the existing technology, a large amount of heat is required for the regeneration of the liquid sorbent, which introduces a substantial energy penalty. The use of alternative sorbents for CO2 capture, such as the CaO-CaCO3 system, has been investigated extensively in recent years. However there are significant problems associated with the use of CaO based sorbents, the most challenging one being the deactivation of the sorbent material. When sorbents such as natural limestone are used, the capture capacity of the solid sorbent can fall by as much as 90 mol% after the first 20 carbonation-regeneration cycles. In this study a variety of techniques were employed to understand better the cause of this deterioration from both a structural and morphological standpoint. X-ray and neutron PDF studies were employed to understand better the local surface and interfacial structures formed upon reaction, finding that after carbonation the surface roughness is decreased for CaO. In situ synchrotron X-ray diffraction studies showed that carbonation with added steam leads to a faster and more complete conversion of CaO than under conditions without steam, as evidenced by the phases seen at different depths within the sample. Finally, in situ X-ray tomography experiments were employed to track the morphological changes in the sorbents during carbonation, observing directly the reduction in porosity and increase in tortuosity of the pore network over multiple calcination reactions.

Carotid artery stenting may be performed safely in patients with radiation therapy-associated carotid stenosis without increased restenosis or target lesion revascularization

Neck radiation therapy (XRT) can induce carotid artery stenosis and may increase the technical difficulty of endarterectomy. It is considered a relative indication for carotid angioplasty and carotid artery stenting (CAS). This study sought to evaluate differences in CAS embolic potential and restenosis performed on XRT and non-XRT patients. At three institutions, 366 CAS procedures were performed on 321 patients (XRT, n = 43; non-XRT, n = 323). Mean follow-up was 410 days (median, 282 days; range, 7-1920 days). Patients were observed with duplex ultrasound to assess for restenosis. Additional end points included target lesion revascularization (TLR), myocardial and cerebrovascular events, and perioperative complications. Captured particulate from embolic protection filters was analyzed with photomicroscopy and image analysis software for 27 XRT and 214 non-XRT filters. XRT patients were more likely to be male and had lower rates of hypertension, coronary artery disease, and diabetes mellitus, although the mean age at procedure did not differ. There was no increase in severe internal carotid tortuosity among XRT patients (XRT: 50% vs non-XRT: 34.7%; P = .06). Indication for CAS did not differ between the two groups, including the number of CAS procedures performed for symptomatic carotid stenosis (XRT: 39.7% vs non-XRT: 39.0%; P = NS). Perioperative outcomes, including the composite 30-day stroke, myocardial infarction, and mortality, were not significantly different (XRT: 2.6% vs non-XRT: 3.9%; P = NS.) There were no significant differences in restenosis rate at the 50% (XRT: 9.4% vs non-XRT: 8.6%; P = NS) or 70% (XRT: 3.5% vs non-XRT: 8.6%; P = NS) threshold. Filter particle analysis revealed that filters from XRT patients had more numerous large particles per filter (1.4 vs 0.7; P < .05) and larger mean particle size (464.1 μm vs 320.0 μm; P < .05). TLR did not differ significantly between the groups. In contrast to earlier studies, this analysis reveals that there are significant differences in XRT and non-XRT patients undergoing CAS in terms of medical comorbidities and embolic material captured in embolic protection filters. The decreased incidence of atherosclerotic risk factors was observed in XRT patients probably because XRT was the primary factor responsible for carotid stenosis. Despite increased embolic particle size, CAS can be performed safely with no increased morbidity, TLR, or restenosis in XRT patients.