High-resolution X-ray Micro-computed Tomography Research Articles

Structural stress response of segmented natural shells: a numerical case study on the clypeasteroid echinoid Echinocyamus pusillus.

The skeleton of Echinocyamus pusillus is considered as an exceptional model organism for structural strength and skeletal integrity within the echinoids as demonstrated by the absence of supportive collagenous fibres between single plates and the high preservation potential of their skeletons. The structural principles behind this remarkably stable, multi-plated, light-weight construction remain hardly explored. In this study, high-resolution X-ray micro-computed tomography, finite-element analysis and physical crushing tests are used to examine the structural mechanisms of this echinoid's skeleton. The virtual model of E. pusillus shows that the material is heterogeneously distributed with high material accumulations in the internal buttress system and at the plate boundaries. Finite-element analysis indicates that the heterogeneous material distribution has no effect on the skeleton's strength. This numerical approach also demonstrates that the internal buttress system is of high significance for the overall skeletal stability of this flattened echinoid. Results of the finite-element analyses with respect to the buttress importance were evaluated by physical crushing tests. These uniaxial compression experiments support the results of the simulation analysis. Additionally, the crushing tests demonstrate that organic tissues do not significantly contribute to the skeletal stability. The strength of the echinoid shell, hence, predominantly relies on the structural design.

Application of high-resolution X-ray microcomputed tomography for coal washability analysis

Float and sink testing is the standard laboratory method for determining the coal washability characteristics using heavy liquids. In this paper, we describe an alternative technique for determining coal washability using High-Resolution X-ray Microcomputed Tomography (HRXMT). Specifically, the application of HRXMT and specialized software have enabled us to determine the particle characteristics of coal samples with the considerable details needed for building washability analysis. Coal samples taken from the feed streams to the dense medium circuits at two plants in Australia were obtained, characterized and used in the analysis. The coal samples were fractioned into the size and density fractions using sieves and heavy liquids as per the Australian Standard AS 4156.1-1994. The fraction-averaged densities were determined using helium gas pycnometry. The float and sink results were obtained for calibration and validation of the HRXMT results. Our results show that HRXMT can be used to perform coal washability analysis. It provides a new methodology for non-destructive and non-toxic determination of coal washability data. It is safe and fast. Significantly, the successful applications of X-ray computed tomography to perform coal washability analysis would allow for developing an on-line coal washability monitoring system, which would not be achievable with the traditional float-and-sink analysis.

Novel insights into renal mineralization and stone formation through advanced imaging modalities

ABSTRACTPurpose/Aim: The most common kidney stone composed of calcium oxalate forms on interstitial calcium phosphate mineral known as a Randall’s plaque (RP). Due to limited information about events leading to the initial deposition of nanometer size interstitial calcium phosphate pre-clusters, there continues to be a debate on the initial site of calcium phosphate deposition and factors leading to stone formation. Materials and Methods: High-resolution X-ray micro-computed tomography (CT), and light and electron microscopy techniques were used to characterize human renal pyramids and five representative kidney stones with identifiable stems. Mineral densities of mineralized aggregates within these specimens were correlated with micro- and ultra-structures as seen using light and electron microscopy techniques. Results: The earliest detectable biominerals in the human renal papilla were proximal intratubular plate-like calcium phosphate deposits. Unoccluded tubules in stems connected to calcium phosphate stones were observed by electron microscope and X-ray micro-CT. These tubules were similar in diameter (30–100 μm) and shape to those observed in the distal regions of the renal papilla. Conclusions: Observations were patterned through a novel and unified theory of stepwise-architecture guided biomineralization (a combination of smaller structures leading to a larger but similar structural framework). A plausible stepwise progression in renal biomineralization is proposed; proximal intratubular calcium phosphate deposits can lead to interstitial yet calcium phosphate rich RP and mature into a stem on which a calcium oxalate stone grows within the collecting system of a kidney.

Application of Image Texture Analysis for Evaluation of X-Ray Images of Fungal-Infected Maize Kernels

The feasibility of image texture analysis to evaluate X-ray images of fungal-infected maize kernels was investigated. X-ray images of maize kernels infected with Fusarium verticillioides and control kernels were acquired using high-resolution X-ray micro-computed tomography. After image acquisition and pre-processing, several algorithms were developed to extract image textural features from selected two-dimensional (2D) images of the kernels. Four first-order statistics (mean, standard deviation, kurtosis and skewness) and four grey level co-occurrence matrix (GLCM) features (correlation, energy, homogeneity and contrast) were extracted from the side, front and top views of each kernel and used as inputs for principal component analysis (PCA). The first-order statistical image features gave a better separation of the control from infected kernels on day 8 post-inoculation. Classification models were developed using partial least squares discriminant analysis (PLS-DA), and accuracies of 67 and 73% were achieved using first-order statistical features and GLCM extracted features, respectively. This work provides information on the possible application of image texture as method for analysing X-ray images.

New Virtual Endocasts of Eocene Ischyromyidae and Their Relevance in Evaluating Neurological Changes Occurring Through Time in Rodentia

Little is known about the early evolution of the brain in rodents. We report on nine new virtual endocasts for one of the most primitive family of rodents, Ischyromyidae, based on five specimens of Pseudotomus and Notoparamys (Paramyinae) and four specimens of Reithroparamys and Rapamys (Reithroparamyinae), dating from the early Eocene to the late middle Eocene of North America (Colorado, Wyoming, Utah and Montana). The virtual endocasts were obtained from high-resolution X-ray micro-computed tomography data. Comparisons with previously described ischyromyid virtual endocasts allow us to make inferences about the ancestral condition of the brain in rodents. Since Reithroparamyinae are suggested to be more closely related to the squirrel-related clade than other Ischyromyidae, comparisons were also made with the oldest virtual endocast for a squirrel, which gave us the opportunity to look at finer neurological changes occurring in the early evolution of squirrels. These new data permit a preliminary assessment of the endocranial diversity in Ischyromyidae. The results do not show evidence for a clear increase in Encephalization Quotient through time for early rodents. Instead, variation among species could be due to ecological factors (e.g., locomotion). Significant expansion in the neocortex and increase in paraflocculi ratios may have occurred in the transition from Ischyromyidae to Sciuridae, as previously hypothesized. Large olfactory bulbs and exposed midbrain are inferred to have been features present in the common ancestor of rodents, while neocortical expansion is reconstructed as having occurred twice independently within Ischyromyidae.

Visualization and prediction of supercritical CO2 distribution in sandstones during drainage: An in situ synchrotron X-ray micro-computed tomography study

Pore-scale distribution of supercritical CO2 (scCO2) exerts significant control on a variety of key hydrologic as well as geochemical processes, including residual trapping and dissolution. Despite such importance, only a small number of experiments have directly characterized the three-dimensional distribution of scCO2 in geologic materials during the invasion (drainage) process. We present a study which couples dynamic high-resolution synchrotron X-ray micro-computed tomography imaging of a scCO2/brine system at in situ pressure/temperature conditions with quantitative pore-scale modeling to allow direct validation of a pore-scale description of scCO2 distribution. The experiment combines high-speed synchrotron radiography with tomography to characterize the brine saturated sample, the scCO2 breakthrough process, and the partially saturated state of a sandstone sample from the Domengine Formation, a regionally extensive unit within the Sacramento Basin (California, USA). The availability of a 3D dataset allowed us to examine correlations between grains and pores morphometric parameters and the actual distribution of scCO2 in the sample, including the examination of the role of small-scale sedimentary structure on CO2 distribution. The segmented scCO2/brine volume was also used to validate a simple computational model based on the local thickness concept, able to accurately simulate the distribution of scCO2 after drainage. The same method was also used to simulate Hg capillary pressure curves with satisfactory results when compared to the measured ones. This predictive approach, requiring only a tomographic scan of the dry sample, proved to be an effective route for studying processes related to CO2 invasion structure in geological samples at the pore scale.

Multiwalled carbon nanotube promotes crystallisation while preserving co-continuous phase morphology of polycarbonate/polypropylene blend

The influence of multiwalled carbon nanotubes (MWCNTs) on phase morphology, lamellar structure, thermal stability, melting behaviour and isothermal crystallisation kinetics of polycarbonate/polypropylene (PC/PP) blend nanocomposites has been investigated. Both neat blends and PC/PP (60/40)/MWCNT nanocomposites were prepared by melt mixing method. Morphological analyses were performed by high-resolution X-ray micro-computed tomography and scanning electron microscopy. The co-continuous morphology of the blend was retained irrespective of MWCNT loading. In addition, a substantial refinement in the co-continuous structure was observed. Wide angle and small angle X-ray scattering studies were used to analyse the structural properties of the blend nanocomposites. The addition of MWCNT increases the long period of polypropylene. The influence of addition of MWCNT on the crystallisation temperature and equilibrium melting temperature (Tm°) of polypropylene was followed. The MWCNTs promote crystallisation rate of polypropylene in the blend nanocomposites.

Comparative skull anatomy of terrestrial and crevice-dwelling Trachylepis skinks (Squamata: Scincidae) with a survey of resources in scincid cranial osteology.

Skinks account for more than 25% of all lizard species; however, representatives of fewer than a quarter of all species have been characterized osteologically. All but a few of the available cranial descriptions concentrate solely on characters that can be seen externally on the intact skull. Mabuyid skinks of the genus Trachylepis are the dominant, fully limbed skinks in Sub-Saharan Africa, and nearly all species have the same generalized body plan. Although a few rock crevice-dwelling species possess slight body depression, extreme dorsoventral depression is observed only in Trachylepis laevis. We investigated the detailed skull anatomy of three Trachylepis skinks (T. laevis, T. sulcata, and T. gonwouoi, a recently described species allied to T. affinis) using high-resolution X-ray micro-computed tomography. Our goals were to review the scincid cranial osteology literature in a phylogenetic context, provide a detailed anatomical atlas for the mabuyid lineage, and investigate the morphological adaptations of the highly modified T. laevis. Our results demonstrate that there is significant morphological variation between these three taxa, including the loss and fusion of structures, as well as changes in the shape, scale, and relationship between individual elements. Trachylepis laevis possesses several osteological modifications that have produced a reducton in head depth that are likely functional consequences of extreme rupicolous habits, including a flat skull roof, many strongly recumbent elements, and a depressed neurocranium.We hypothesize these modifications may correspond to descreased bite force and increased capabilities of cranial kinesis. Our study is the first element-by-element description of a skink using computed tomography technology.

First non-destructive internal imaging of Rangea, an icon of complex Ediacaran life

The origins of multicellular life have remained enigmatic due to the paucity of high-quality, three-dimensionally preserved fossils. Rangea was a centimetre- to decimetre-scale frond characterised by a repetitive pattern of self-similar branches and a sessile benthic lifestyle. Fossils are typically preserved as moulds and casts exposing only a leafy petalodium, and the rarity and incompleteness of specimens has made it difficult to reconstruct the three-dimensional (3D) morphology of the entire organism. This, in turn, has led to many differing interpretations of its morphology and phylogenetic affinities. Here we use high resolution X-ray micro-computed tomography (microCT) to investigate the 3D internal morphology of rare, exceptionally preserved ironstone fossils of Rangea from the Nama Group in southern Namibia. Our investigation reveals a series of structures that represent boundaries between individual fronds or structural elements that divide into smaller secondary and tertiary elements, leading to a repetitive pattern of branches. These elements surround an internal core of a distinctly different texture and internal appearance. There is no distortion of the walls of the primary elements, thus we conclude that Rangea likely had a rigid or semi-rigid skeleton-like structure that prevented buckling or compression and maintained integrity during life. We compare these findings with previous interpretations of Rangea morphology and present new insights on the architecture of internal structures, such as the central core, and the overall appearance of this complex Ediacaran life form. Our insights based on microCT scans of these rare, uniquely-preserved specimens provide a more accurate interpretation of the 3D morphology essential for determining the true affinities and modes of life of the Ediacaran biota during this early stage in the evolution of complex macroscopic life.

Effect of vegetation type on microstructure of soil aggregates on the Loess Plateau, China

Several types of vegetation restoration have been implemented on the Loess Plateau in China to control soil erosion and improve soil quality. Different revegetation types, however, have varying effects on soil structure; effects on the pore network of aggregates are especially not well understood. We used synchrotron-based high-resolution X-ray micro-computed tomography to quantify the microstructure of soil aggregates under four types of revegetation and an active cropland on the plateau. Five aggregates (3–5mm) collected from the topsoil at each site were scanned at a voxel resolution of 3.25μm, and the aggregate pore structure was visualized and quantified with ImageJ. Total porosities, >75μm porosities, fractions of elongated pores, 3D mass fractal dimensions, and connectivity were higher and the numbers of pores, <75μm porosities, the mean pore-shape factors, and the fractions of regular and irregular pores were lower in the revegetated sites than the control plot. Total porosities, macro-porosities, micro-porosities, fractions of regular pores, and 3D mass fractal dimensions differed significantly among the revegetated sites. We suggest that the fraction of elongated pores can be used as an important indicator for monitoring the recovery of soil structure. 3D mass fractal dimensions differed more than connectivity in the aggregates in the same samples, and thus could be a more sensitive indicator of changes in the pore network. Age and revegetation type both significantly affected the development of soil structure, but revegetation type was more important for the recovery of soil structure. We used a soil structural index (SSI) obtained by principal component analysis to assess the overall quality of soil structure. SSI values were higher in all revegetated sites than the cropland site and differed among the revegetated sites in the order: shrubland>grassland>woodland>pastureland. We recommend shrub plantation and natural grassland for the revegetation of degraded land on the Loess Plateau.

Use of High-Resolution X-Ray Micro-Computed Tomography for the Analysis of Internal Structural Changes in Maize Infected with Fusarium verticillioides

X-ray micro-computed tomography (X-ray micro-CT) is a non-destructive, three-dimensional (3D) imaging and analysis technique for the investigation of internal structure of a large variety of materials, including agricultural produce. As a relatively new method in the field of food science, X-ray micro-CT has been applied successfully to obtain micro-structural information of foods undergoing different physical and chemical changes. In this study, high-resolution X-ray micro-CT was used for non-destructive analysis of the internal structure of maize kernels infected with Fusarium verticillioides. The major anatomical features of the maize kernel were identified based on their differences in X-ray attenuation, i.e. the germ, scutellum, vitreous and floury endosperm. Fungal infection caused changes in the internal structure of the kernels over time, which included a decrease in total kernel volume and an increase in total volume of void space, with more voids observed in the germ and floury endosperm regions. No significant (P > 0.05) difference was observed between the control and the infected kernels; it was apparent that the changes observed in the infected kernels were not solely as a result of fungal growth. The grey level histograms of the control and infected kernels shifted to the lower grey value intensity range over time indicating an increase in void space within the kernels. In the 3D images, the increase in total volume of void space with fungal progression was clearer and the effect of fungal damage on the internal structure was evident.

Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange.

Extant crocodilians are a highly apomorphic archosaur clade that is ectothermic, yet often achieve large body sizes that can be subject to higher heat loads. Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. The cephalic vascular anatomy of extant crocodilians, particularly American alligator (Alligator mississippiensis) was investigated using a differential-contrast, dual-vascular injection technique and high resolution X-ray micro-computed tomography (μCT). Blood vessels were digitally isolated to create representations of vascular pathways. The specimens were then dissected to confirm CT results. Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The evolutionary history of crocodilians is complex, with large-bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building-blocks for such an extensive vascularization of sites of thermal exchange. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids.

Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels.

Extant squirrels exhibit extensive variation in brain size and shape, but published endocranial data for living squirrels are limited, and no study has ever examined brain evolution in Sciuridae from the perspective of the fossil record to understand how this diversity emerged. We describe the first virtual endocast for a fossil sciurid, Cedromus wilsoni, which is known from a complete cranium from Wyoming (Orellan, Oligocene), and make comparisons to a diverse sample of virtual endocasts for living sciurids (N = 20). The virtual endocasts were obtained from high-resolution X-ray micro-computed tomography data. Comparisons were also made with endocasts of extinct ischyromyid rodents, the most primitive rodents known from an endocranial record, which provide the opportunity to study the neuroanatomical changes occurring near the base of Sciuridae. The encephalization quotient of C. wilsoni is higher than that of Ischyromys typus from the same epoch, and falls within the range of modern terrestrial squirrel variation, but below the range of extant scansorial, arboreal and gliding sciurids when using cheek-tooth area for the estimation of body mass. In a principal components analysis, the shape of the endocast of C.wilsoni is found to be intermediate between that of primitive fossil taxa and the modern sample. Cedromus wilsoni has a more expanded neocortical surface area, especially the caudal region of the cerebrum, compared with ischyromyid rodents. Furthermore, C. wilsoni had proportionally larger paraflocculi and a more complex cerebellar morphology compared with ischyromyid rodents. These neurological differences may be associated with improvements in vision, although it is worth noting that the size of the parts of the brain most directly involved with vision [the rostral (superior) colliculi and the primary visual cortex] cannot be directly assessed on endocasts. The changes observed could also relate to balance and limb coordination. Ultimately, the available evidence suggests that early squirrels were more agile and visually oriented animals compared with more primitive rodents, which may relate to the process of becoming arboreal. Extant sciurids have an even more expanded neocortical surface area, while exhibiting proportionally smaller paraflocculi, compared with C.wilsoni. This suggests that the neocortex may continue increasing in size in more recent sciurid rodents in relation to other factors than arboreality. Despite the fact that both Primates and Rodentia exhibit neocortical expansion through time, since the adoption of arboreality preceded major increases in the neocortex in Primates, those neurological changes may be related to different ecological factors, underlining the complexity of the inter-relationship between time and ecology in shaping the brain in even closely related clades.

Structural analysis of the tongue and hyoid apparatus in a woodpecker

Woodpeckers avoid brain injury while they peck at trees up to 20Hz with speeds up to 7m/s, undergoing decelerations up to 1200g. Along with the head, beak and neck, the hyoid apparatus (tongue bone and associated soft tissues) is subjected to these high impact forces. The shape of the hyoid apparatus is unusual in woodpeckers and its structure and mechanical properties have not been reported in detail. High-resolution X-ray micro-computed tomography and scanning electron microscopy with energy dispersive X-ray spectroscopy were performed and correlated with nanoindentation mapping. The hyoid apparatus has four distinct bone sections, with three joints between these sections. Nanoindentation results on cross-sectional regions of each bone reveal a previously unreported structure consisting of a stiff core and outer, more compliant shell with moduli of up to 27.4GPa and 8.5GPa, respectively. The bending resistance is low at the posterior section of the hyoid bones, indicating that this region has a high degree of flexibility to absorb impact. These new structural findings can be applied to further studies on the energy dissipation of the woodpecker during its drumming behavior, and may have implications for the design of engineered impact-absorbing structures. Statement of SignificanceWoodpeckers avoid brain injury while they peck at trees, which results in extreme impact conditions. One common adaptation in woodpeckers is the unusual shape of the elongated tongue, also called the hyoid apparatus. The relationship between the structure and mechanical properties of the bony part of the hyoid apparatus has not been previously reported. A three dimensional model of the bony tongue was developed, and the hardness and stiffness were evaluated. A new type of bone structure, which is opposite of typical skeletal bone structure was found. The combined microstructural and mechanical property analysis indicate possible energy absorption routes for the hyoid apparatus and are applicable to the design of engineered structures.

Inside Marginal Adaptation of Crowns by X-ray MicroComputed Tomography

Prosthetics treatments with total or partial reconstruction are highly recommended in order to investigate caries, fractures and for better aesthetic. The purpose of this study was to evaluated marginal and internal fit of infrastructures (ceramic and metal) by using a high resolution X-ray micro-computed tomography. Each framework was placed on the original model and scanned. Image processing analysis and statistical approaches were combined together to evaluated directly in 3D the gap between the crown and the dental, which makes it possible to have a realistic dental arcade model.

A micro-computed tomography technique to study the quality of fibre optics embedded in composite materials.

Quality of embedment of optical fibre sensors in carbon fibre-reinforced polymers plays an important role in the resultant properties of the composite, as well as for the correct monitoring of the structure. Therefore, availability of a tool able to check the optical fibre sensor-composite interaction becomes essential. High-resolution 3D X-ray Micro-Computed Tomography, or Micro-CT, is a relatively new non-destructive inspection technique which enables investigations of the internal structure of a sample without actually compromising its integrity. In this work the feasibility of inspecting the position, the orientation and, more generally, the quality of the embedment of an optical fibre sensor in a carbon fibre reinforced laminate at unit cell level have been proven.

Partial least squares regression for linking aggregate pore characteristics to the detachment of undisturbed soil by simulating concentrated flow in Ultisols (subtropical China)

Soil pores are known as an effective medium for water, air, and chemical movement. However, quantifying pore structures and their relationship to the detachment of undisturbed soil by concentrated flow is not fully understood. The objectives of this study were to quantify 3D aggregate microstructures using synchrotron-based high-resolution X-ray micro-computed tomography (SR-μCT) under wetting and drying cycles and to investigate the effects of pore characteristics on the detachment of undisturbed soil by simulating concentrated flow. The detachment rates (Dr) of undisturbed topsoil samples, which were subjected to a pretreatment of zero to eleven wetting and drying cycles, were measured in a 3.8-m-long, 0.2-m-wide hydraulic flume under unitary flow shear stresses (τ = 14.49 Pa); 3–5 mm aggregates were collected from the pretreatment soils, which were subjected to zero, five, and eleven wetting and drying cycles and were scanned at a 3.7 μm voxel-resolution for reconstructing three-dimensional microtomography images. The relationships among pore characteristics and Dr were analyzed using partial least squares regression (PLSR). The results indicated that Dr and the aggregate microstructure changed significantly after the wetting and drying cycles. Dr was closely associated with the pore characteristics. The pore characteristics, such as a >100 μm porosity, total porosity, fraction of regular pores, 30–75 μm porosity, fraction of elongated pores, and fraction of irregular pores, were identified as the primary parameters that control the Dr. The pore characteristics and clay content could account for as much as 68.2% of the variation in Dr. Dr was significantly and positively related to a >100 μm porosity, total porosity, and fraction of elongated pores. Thus, soil fragmentation depended on microcracks that formed during the wetting and drying cycles and on the geometrical characteristics of the pores or cracks. The results from this study provide a quantitative evaluation of the relationships between pore characteristics and the detachment of undisturbed soil by simulated concentrated flow. A further understanding of the effect of topsoil microstructure on water erosion and quantitative information for assessing and modeling erosion processes was obtained.

Non-destructive high-resolution X-ray micro computed tomography for quantifying dry water particles

Dry water, a powder containing up to 98%wt. water and 2–6%wt. hydrophobic nanoparticles, is a novel material for novel applications like CO2 capture, transportation and storage in the form of clathrate hydrates. In this study, novel high-resolution X-ray micro computed tomography (HRXMT) was used as an in situ, non-destructive tool to visually and quantitatively examine the inner structure of dry water that has not been accessible previously. Specifically, the HRXMT was used to study the effect of silica/water wt. ratio on the number, surface area and volume distributions of dry water. The results showed that dry water was stable under ambient condition for long time. The technique was also successful in characterizing the structure changes in dry water after exposing to low temperature, high pressure and stirring. Low temperature did not affect the structure significantly, while high pressure and slow stirring broke the structure fairly readily with separation of dry water into the primary solid and liquid phases. These findings are useful to our understanding of the role of dry water in promoting the formation of CO2 and gas hydrates.

Pore-scale modelling of 3D moisture distribution and critical saturation in cementitious materials

The understanding and prediction of moisture distribution and critical moisture content above which fluid and ion transport can occur in porous media is of significant technological importance. A novel computational methodology for simulating moisture distribution and calculating critical content in 3D images of microstructures is presented. The method accounts for the liquid–gas interaction and liquid/gas–solid interaction at the pore scale. Microstructures of cement pastes at different curing ages, obtained by high-resolution X-ray micro-computed tomography, are analyzed. The equilibrium moisture distribution in the 3D microstructures is acquired. The degree of connectivity of the liquid and gas phases is calculated as a function of water saturation level. The critical water saturation for each phase is obtained. It is shown that the moisture distribution and connectivity of each phase depend strongly not only on the degree of water saturation but also on the structures of the pore space and the solid phase. The critical water saturation increases with the decrease of porosity. The results from the simulations are in very good agreement with the experimental data reported in the literature. The proposed methodology is applicable to image-based modelling of all porous media.

Tomography-based determination of transverse permeability in fibrous porous media

Precise characterization of nonwoven fabrics such as their transport properties are of paramount importance in development of advanced filtration processes. Currently majority of available knowledge on transport behavior of fibrous materials is based on macro-scale empirically researched phenomena. Thus, evaluation of transport behavior of nonwovens based on fundamental scientific principles at micro-scale still remains a challenge that has to be tackled by scientists. In this paper, an integrated approach employing high-resolution X-ray micro-computed tomography and finite volume method are presented to predict permeability of needled nonwoven fabrics. In order to achieve the objectives of this research, dimensionless permeability of needled nonwoven fabrics with various porosities was computed using CFD tools. Comparisons of simulated results with experimentally obtained data and the published empirical and analytical models were made. Considering solid volume fraction of the samples, acceptable agreement between the results and previously published findings was observed. It was also established that experimental samples ideally can be represented as a three-dimensional random structure.