Elliptical Pores Research Articles

Characterization of compact carbonate pore–throat network systems in the Xiagou Formation in Qingxi Sag, Jiuquan Basin, China

The Xiagou Formation is the main tight oil reservoir in the Qingxi Depression of the Jiuquan Basin; however, its poor physical properties have restricted tight oil exploration and development. Therefore, itis important to gain a better understanding of its micropore structure. The results show that the lithology of the Xiagou Formation reservoir is dominated by gray argillaceous dolomite and dolomitic mudstone. The pore types are primarily composed of elliptical and irregular intergranular pores. Intercrystalline and organic-matter-hosted pores are mostly isolated and have poor connectivity. Moreover, NMR spectroscopy results show that the T2spectra of the rock samples in the study area are predominantly unimodal or bimodal in distribution, with pore sizes principally ranging between 0.01 and 0.69 μm. Using CT scanning, we obtained a three-dimensional (3D) pore–throat stereogram. At the micrometer scale, the pore throats differed in size and exhibited shelf-like, banded, and spheroidal shapes. At the nanometer scale, we observed a greater number of nanometer-scale micropores. These pores were shelf-like and spheroidal in shape and were distributed inside or at the mineral grain (crystal) surface. The nanometer-scale spheroidal micropores showed poor connectivity and were isolated in 3D space, with most serving as reservoir spaces. However, the nanometer-scale short-shelf-like micropores showed connectivity with the micrograde shelf-like micropores, were adjacent to the isolated spheroidal nanometer-scale micropores, and acted as both pore throats and pores. The larger throat-to-pore ratio coefficient indicates a greater correlation between the pore and throat, which further results in a higher concentration of pores. The larger average pore volume leads to higher porosity and, together with the higher average coordination number, enables better pore connectivity, thereby yielding a better potential reservoir and penetration capacity.

Effect of micro-pores on cracks formation in metallurgical coke

ABSTRACTThe relationships of micro-pores and cracks in metallurgical coke have been investigated by optical microscope and field emission scanning electron microscope, using surface section samples. The pores have circular, elliptical and irregular shapes with smooth outlines, formed during the thermoplastic stage of the coking process. They often associate with connecting cracks between neighbouring pores. In case of elliptical pores, the connecting cracks are usually oriented along the longer axis of the pore. The connecting cracks can be developed between the pores, depending on their size and the distance between them. The coke with a large number of small pores rather than with a small number of larger pores will have lower strength due to the increased amount of connecting cracks. When compared with circular pores, elliptical and flattened pores have a lower ability to resist load pressure. Nano-sized pores have polygonal outlines, indicating an ‘explosion’-type formation in the solidified matrix.

Identification of the prehistoric catastrophes at the Lajia Ruins using micromorphological analysis within the Guanting Basin, Minhe County, Qinghai Province

The Lajia Ruins is a large Neolithic settlement of the Qijia Culture that is dated to 4200–3950 bp within the Guanting Basin along the upper Yellow River. Archaeological excavations have exposed extraordinary pictures of prehistoric catastrophes that ruined this settlement and caused great loss of human life. The causation of the prehistoric catastrophes is an arguable topic in the field of environmental archaeology in China and over the world. Our fieldwork investigations indicated that the palaeo-ground of the Qijia Culture at the Lajia Ruins was broken by several groups of earthquake fissures. A layer of conglomerated red clay buried the Qijia Culture at the Lajia Ruins and filled in these earthquake fissures. Determining the macro- and microscale morphological features of the conglomerated red clay provides an alternative reference for understanding the cause of the prehistoric catastrophes at the Lajia Ruins. The macrofeatures of the conglomerated red clay has a rolling surface and wavy structure, with human bodies of the Qijia Culture, stones, loess soil clods, pottery shards, burnt earth, charcoal and ash from the palaeo-ground entrapped inside. And the micromorphological features of the conglomerated red clay is characterized by rolling and wavy structure along with no directional alignment of grains within horizons and a large numbers of pores with complicated shapes, including large regular pores that can be characterized as sub-round, elliptical and cloud-like pores, as well as small irregular pores. Thus, the conglomerated red clay is classified as dense mudflow deposits. And then, we can conclude that the large Neolithic settlement of the Qijia Culture at the Lajia Ruins was buried and devastated by immense mudflows that accompanied a major earthquake.

Experimental percolation studies of random networks.

This report establishes an experimental method of studying electrically percolating networks at a higher resolution than previously implemented. This method measures the current across a conductive sheet as a function of time as elliptical pores are cut into the sheet. This is done utilizing a Universal Laser System X2-600 100 W CO2 laser system with a 76 × 46 cm2 field and 394 dpc (dots/cm) resolution. This laser can cut a random system of elliptical pores into a conductive sheet with a potential voltage applied across it and measures the current versus time. This allows for experimental verification of a percolation threshold as a function of the ellipse's aspect ratio (minor/major diameter). We show that as an ellipse's aspect ratio approaches zero, the percolation threshold approaches one. The benefit of this method is that it can experimentally measure the effect of removing small pores, as well as pores with complex geometries, such as an asterisk from a conductive sheet.

Osseous differentiation on freeze casted 10CeTZP-Al2O3 structures

Three-dimensional structures with directionally oriented pore networks were fabricated from a 10mol% ceria-stabilized zirconia and alumina composite (10CeTZP-Al2O3) via freeze casting. Ceramic suspensions of different concentrations (30, 40 and 50wt% solids) were frozen at various rates (2, 5 and 10°C/min) to obtain lamellar structures with aligned tubular pores of different characteristics: porosity (75–84%), pore dimensions (small diameter of the elliptical pores: 10–23μm; large diameter of the elliptical pores: ∼200±70μm), lamella thickness (2.7–4μm) and compression strength (1–12MPa). In vitro assays confirmed the non-cytotoxic nature of the samples. Furthermore, specific osseous differentiation genes were quantified after incubating osteoblasts on different cross sections of the samples during 7days in supplemented culture medium; results demonstrated that the freeze casted structures induce up to nine times more osseous gene expression than tissue culture polystyrene (TCPS), an advanced surface used for optimized in vitro cell growth.

The impact of defect morphology, defect size, and SDAS on the HCF response of A356-T6 alloy

This paper aims to investigate the influence of defect morphology, defect size, and SDAS on the fatigue behavior of A356-T6 aluminum alloy. A 3D finite element analysis for specimens containing different pore morphologies—(i) spherical pore, (ii) elliptical pore, and (iii) complex pore—was implemented. The Chaboche kinematic hardening model embedded in Abaqus is used to characterize the material response during cyclic loading. Kitagawa diagrams for defective A356-T6 are simulated using the defect stress gradient (DSG) approach. A good agreement is found between experimental and numerical results for predicting fatigue limit in the case of spherical defects. The impact of defect morphology on the fatigue resistance is clearly demonstrated. This paper shows that aluminum fatigue resistance is strongly dependent on the defect size, SDAS, and the defect morphology. Therefore, a mathematical model that takes into account the impact of these three parameters is developed using response surface (RS) approach to predict fatigue limit of porous aluminum alloy. Moreover, the effects of defect morphology, defect size, and SDAS on fatigue response and their interactions under fully reserved tensile loading are investigated.

The influence of pore geometry and orientation on the strength and stiffness of porous rock

The geometry of voids in porous rock falls between two end-members: very low aspect ratio (the ratio of the minor to the major axis) microcracks and perfectly spherical pores with an aspect ratio of unity. Although the effect of these end-member geometries on the mechanical behaviour of porous rock has received considerable attention, our understanding of the influence of voids with an intermediate aspect ratio is much less robust. Here we perform two-dimensional numerical simulations (Rock Failure Process Analysis, RFPA2D) to better understand the influence of pore aspect ratio (from 0.2 to 1.0) and the angle between the pore major axis and the applied stress (from 0 to 90°) on the mechanical behaviour of porous rock under uniaxial compression. Our numerical simulations show that, for a fixed aspect ratio (0.5) the uniaxial compressive strength and Young's modulus of porous rock can be reduced by a factor of ∼2.4 and ∼1.3, respectively, as the angle between the major axis of the elliptical pores and the applied stress is rotated from 0 to 90°. The influence of pore aspect ratio on strength and Young's modulus depends on the pore angle. At low angles (∼0–10°) an increase in aspect ratio reduces the strength and Young's modulus. At higher angles (∼40–90°), however, strength and Young's modulus increase as aspect ratio is increased. At intermediate angles (∼20–30°), strength and Young's modulus first increase and then decrease as pore aspect ratio approaches unity. These simulations also highlight that the influence of pore angle on compressive strength and Young's modulus decreases as the pore aspect ratio approaches unity. We find that the analytical solution for the stress concentration around a single elliptical pore, and its contribution to elasticity, are in excellent qualitative agreement with our numerical simulations. The results of our numerical modelling are also in agreement with recent experimental data for porous basalt, but fail to capture the strength anisotropy observed in experiments on sandstone. We conclude that the alignment of grains or platy minerals such as clays exerts a greater influence on strength anisotropy in porous sandstones than pore geometry. Finally, we show that the strength anisotropy that arises as a result of preferentially aligned elliptical pores is of a similar magnitude to that generated by bedding in porous sandstones and foliation in low-porosity metamorphic rocks. The modelling presented herein shows that porous rocks containing elliptical pores can display a strength and stiffness anisotropy, with implications for the preservation and destruction of porosity and permeability, as well as the distribution of stress and strain within the Earth's crust.

Microstructural Evaluation of Effective Elasticity Coefficients in Materials with Micro-voids

The paper deals with homogenization of linear elastic continuum involving empty voids. The concept of homogenization is meaningful provided that the size of voids is much smaller than the characteristic length in structural design. Assuming a uniform distribution of voids, one can utilize the concept of the representative volume element (RVE) which is a finite part of the macrostructure with involving one or more voids. In general, a numerical approach is necessary for solution of micro-structural boundary value problems in case of arbitrary shape and/or distribution of voids. Several approaches are discussed and mathematical models developed for numerical calculation of effective material coefficients for linear elastic continuum involving arbitrary empty voids. Appropriate micro-structural boundary value problems in the RVE are proposed for numerical analyses which are utilized for a posterior evaluation of effective material coefficients. Comparisons of results by various numerical approaches are discussed for the circular and elliptical pores.

Pore geometry as a control on rock strength

The strength of rocks in the subsurface is critically important across the geosciences, with implications for fluid flow, mineralisation, seismicity, and the deep biosphere. Most studies of porous rock strength consider the scalar quantity of porosity, in which strength shows a broadly inverse relationship with total porosity, but pore shape is not explicitly defined. Here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples, and numerical modelling to consider the influence of pore shape on rock strength. Micro computed tomography (CT) shows that pores range from sub-spherical to elongate and flat ellipsoids. Samples that contain flat pores are weaker if compression is applied parallel to the short axis (i.e. across the minimum curvature), compared to compression applied parallel to the long axis (i.e. across the maximum curvature). Numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress, compared to compression applied across the maximum curvature. Certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field, while others are inherently weak. Quantifying the shape, orientations, and statistical distributions of pores is therefore a critical step in strength testing of rocks.

Stretched homoporous composite membranes with elliptic nanopores for external-energy-free ultrafiltration.

Extremely permeable ultrafiltration membranes with elongated elliptical pores are fabricated by stretching composite membranes with homoporous selective layers and macroporous supports. With simultaneously increased porosities both for the selective layers and supports and the thinned selective layers, the stretched membranes exhibit multifold-enhanced permeability with little sacrifice in selectivities. Thus the produced membranes enable, for the first time, gravity-driven ultrafiltration and discrimination of similarly sized nanoparticles with diameters down to 30 nm.

New earthworms of the Amynthas morrisi-group (Oligochaeta, Megascolecidae) from Hainan Island, China.

This paper describes two new species of earthworms belonging to the Amynthas morrisi-group from Hainan Island, China: Amynthas zonarius sp. nov. and Amynthas wuzhimontis sp. nov. Both have two pairs of spermathecal pores in 5/6-6/7, and simple intestinal caeca. Amynthas zonarius sp. nov. has a pad-like male porophore, with flat-topped tubercle surrounded by 5 skin folds distal half of the spermathecal diverticulum dilated into band-shaped seminal chamber. Amynthas wuzhimontis sp. nov. has a seminal chamber constricted into moniliform subchambers and a glandular pad-like elliptical male pore porophore surrounded by the tumid area. Partial COI sequences of the holotypes of the two new species have been submitted to GenBank as DNA barcodes to enable molecular species identification.

Study of electrical current reconstruction on macropore arrays etched electrochemically on lightly-doped n-Si

Silicon macropore arrays are fabricated on lightly-doped n-Si by electrochemical etching. The opening diameter, inner diameter, and wall thickness of the macropores are observed to depend on HF concentration and current. A current reconstruction model is proposed to elucidate the formation mechanism of the macropores. Two geometric models are established for the silicon macropores according to the experimental results. The finite element method is used to simulate the electric field and current in the electrolyte-silicon system. The reconstruction of electrical current on the silicon macropore arrays is described by simulating the electric field and current. The ratio of major to minor semi-axes of the elliptical pore (b/a) decreases with increasing the ratio of diameter to wall thickness as confirmed experimentally. The results indicate that the b/a ratio is correlated with the HF concentration and applied voltage.

An elliptical pore model for the mechanical properties of paper

A simple mechanical model for paper comprising only isotropic cell-wall cellulose and a single elliptical pore is presented. Finite element method analysis applied to this model produced two stress-strain curves equivalent to the anisotropy observed in machine-made paper. Nissan’s hydrogen-bond domination theory for cellwall material with a density of 1000 kg/m3 provided the stress-strain functionality to control the displacement of the mesh nodes. Experimental data were collected from a single roll of paper produced on a pilot machine run where formation was decreased in five steps. Fiber properties, sheet grammage, and density were held constant in the final paper. Regardless of the level of formation, all breaking stress and strain data fell into one of two stress-strain curves, a machine-direction curve and a cross-direction curve. The initial modulus of each stress-strain curve was used to estimate the shape of the elliptical pore used in the finite element method model. The results for the model matched the results from the experimental data.

Elliptical pore regularisation of the inverse problem for microstructured optical fibre fabrication

A mathematical model is presented describing the deformation, under the combined effects of surface tension and draw tension, of an array of channels in the drawing of a broad class of slender viscous fibres. The process is relevant to the fabrication of microstructured optical fibres, also known as MOFs or holey fibres, where the pattern of channels in the fibre plays a crucial role in guiding light along it. Our model makes use of two asymptotic approximations, that the fibre is slender and that the cross-section of the fibre is a circular disc with well-separated elliptical channels that are not too close to the outer boundary. The latter assumption allows us to make use of a suitably generalised ‘elliptical pore model (EPM)’ introduced previously by one of the authors (Crowdy, J. Fluid Mech., vol. 501, 2004, pp. 251–277) to quantify the axial variation of the geometry during a steady-state draw. The accuracy of the elliptical pore model as an approximation is tested by comparison with full numerical simulations. Our model provides a fast and accurate reduction of the full free-boundary problem to a coupled system of nonlinear ordinary differential equations. More significantly, it also allows a regularisation of an important ill-posed inverse problem in MOF fabrication: how to find the initial preform geometry and the experimental parameters required to draw MOFs with desired cross-plane geometries.

Thermal transport properties of graphene nanomeshes

Using molecular-dynamics simulations, we study the thermal transport properties of graphene nanomeshes (GNMs) as a function of material density, pore morphology, pore edge passivation, and the lattice arrangement of the nanomesh pores. Relations for the density dependence of the GNMs' thermal conductivity are established. For GNMs with circular pores, we find that the thermal conductivity is an exponential function of the GNM's neck width with a very weak dependence on the pore lattice structure and pore edge passivation. For GNMs with elliptical pores, the thermal conductivity becomes anisotropic and this anisotropy becomes stronger with decreasing GNM density.

Macromolecular and pore structures of Chinese tectonically deformed coal studied by atomic force microscopy

In this study, the macromolecular and nanoscale pores of different types of tectonically deformed coals were characterized by AFM. The nanostructures of coal differed in terms of the metamorphism degree, deformation degree, and deformation properties. The macromolecular grid-like structure of low-rank bituminous coal was loosely reticular, and the round or elliptical pores between chains were largely isolated. The macromolecular reticular grid-like structure of high-rank bituminous coal was more compact than that of low-rank bituminous coal. The large molecules of anthracite exhibited enhanced polymerization with significant reductions in the spacing between macromolecular layers. The reticular grid-like structure of this coal was fairly compact, and the pores between the chains were squeezed flat. Flat micropores were the predominant pore morphology in this type of coal. Metamorphism generally increased the quantity of micropores in the coal. The macromolecular reticular grid-like structures and pore structures of coal varied according to their properties and deformation degree. Under brittle deformation, the ratio of the transitional pores and the interconnectivity of the pores increased with increasing deformation degree. This phenomenon was beneficial for gas diffusion. Under ductile deformation, the coal surface exhibited creep flow features, the surface pore morphology of the coal was irregularly developed, and the ratios of micropores and transitional pores in the coal increased.

Advanced micro- and nanofabrication technologies for tissue engineering

The ability of the living body to heal and regenerate itself following trauma is astonishing. Numerous events of repair and regeneration occur during our lifetime, most of which we are never aware of. Unfortunately, in some cases, the injury or defect cannot be adequately repaired solely by nature and medical intervention is required.

Controlling the structural and functional anisotropy of engineered cardiac tissues

The ability to control the degree of structural and functional anisotropy in 3D engineered cardiac tissues would have high utility for both in vitro studies of cardiac muscle physiology and pathology as well as potential tissue engineering therapies for myocardial infarction. Here, we applied a high aspect ratio soft lithography technique to generate network-like tissue patches seeded with neonatal rat cardiomyocytes. Fabricating longer elliptical pores within the patch networks increased the overall cardiomyocyte and extracellular matrix alignment within the patch. Improved uniformity of cell and matrix alignment yielded an increase in anisotropy of action potential propagation and faster longitudinal conduction velocity (LCV). Cardiac tissue patches with a higher degree of cardiomyocyte alignment and electrical anisotropy also demonstrated greater isometric twitch forces. After two weeks of culture, specific measures of electrical and contractile function (LCV = 26.8 ± 0.8 cm s−1, specific twitch force = 8.9 ± 1.1 mN mm−2 for the longest pores studied) were comparable to those of neonatal rat myocardium. We have thus described methodology for engineering of highly functional 3D engineered cardiac tissues with controllable degree of anisotropy.

Fracture analysis for ceramic disk with semi-elliptical crack and pore

Crack resistance is important to exam the structures destroyed under static and dynamic load as well as to the ceramic products under extreme mechanical and thermal load. But in addition to the metallic material, ceramic and ceramic composite materials have been pointed out as low resistance referred to a brittle materials form thermal impact. As destroyed ceramics are impossible to be restored, so the development of high toughness ceramics is required. To get high strength material design variables while keeping light weight, this study derives the modulus of elasticity for ceramic disk with elliptical crack pore and performs fracture behaviors assessment by applying the modulus of elasticity derived and MSST(Maximum Shear Stress Theory) techniques to compare with test data. As a result of assessment of fracture behavior based on the MSST, if stress is greater than fracture strength of material, it showed high probability of occurring of the shear fracture when fracture strength is 38 kgf.

The Criterion of Particle-Induced Cracking of Filled Polymers

Failure of high density polyethylene, low density polyethylene, and polypropylene filled with grinded rubber particles was studied. In tension, particles debond from the matrix and initiate appearance of pores. Small particles lead to formation of elliptical pores. In contrast, large particles initiate appearance of diamond cracks leading to fast failure of filled polymer. In the intermediate case elliptical pore gradually transforms into diamond cracks. The diamond crack appears when the elongation of an elliptical pore reaches the critical crack tip opening of the unfilled polymer. The size D of filler particles should be lower than Dc = GIc/[(ld - 1)?d)], where GIc is the fracture toughness, sd - the draw stress and ld - the natural draw ratio of the matrix in the neck. Ductile or brittle behavior of filled polymer depends on whether the polymer yields uniformly or with necking. If the neck does not appear, filler particles usually do not initiate brittle fracture. In contrast, filled polymers, yielding with necking, often are brittle.