Elliptical Grains Research Articles

Texture development of mesophase in reservoir pyrobitumen and the temperature-pressure converting of the gas reservoir in the Chuanzhong Uplift, Southwestern China

The Neoproterozoic-Lower Paleozoic dolostone gas reservoirs in the Chuanzhong Uplift in Southwestern China contain the mesophase pyrobitumen (pyrobitumen with mesophase). The mesophase in the pyrobitumen is mostly composed of a mixture of condensed macromolecule polycyclic aromatic hydrocarbons (PAH), and has been mostly converted to various grain, flow, and domain textures. The volcanic activity nearby the Chuanzhong Uplift may have generated very hot (over 300 °C) hydrothermal fluid, with migration of the fluid into the dolostone reservoir transforming the hydrocarbons in the reservoir into an anisotropic carbon by-product, which formed under high temperature and pressure conditions; over 300 °C and 200 MPa according to fluid inclusion analysis. The high temperature-pressure in reservoir was caused by sudden devolatilization of the hydrocarbons due to hydrothermal heating, which formed the unusual texture of the mesophase. The elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen deposits are all unusual textures. This study investigates the texture development of this pressure-affected pyrobitumen. Observation and study of the mesophase suggest that the class of mesophase in pyrobitumen is determined by temperature, while pressure (assessed from associated fluid inclusions) significantly affected the texture. Analysis of the texture of the pyrobitumen in conjunction with previous thermometry results from methane inclusions suggests that the high class mesophase of the pyrobitumen could be applied as a temperature indicator for geological conditions. Furthermore, the unusual textures of the pyrobitumen including elliptical mesophase grains (EG), the honeycomb structure of pyrobitumen, and the occurrence of polarized classes of mesophase in single pyrobitumen could reflect the abnormal high formation pressure.

Stick-Slip Dynamics in a Granular Material With Varying Grain Angularity

Experiments, simulations, and theoretical treatments of granular materials typically feature circular or elliptical grains. However, grains found in natural systems often have flat faces that introduce local rotational constraints; these rotational constraints have been shown to affect, for example, the jamming transition, discontinuous shear thickening, and ordered states in colloids and thermalized grains. In this work, we experimentally investigate the effects of grain angularity on stick-slip dynamics. A weighted slider is pulled by a spring over a gravity-packed granular bed composed of polygonal grains with varying angularity. We find that packings of triangular or square grains have higher shear strengths than packings of pentagons, hexagons, heptagons, or disks. Additionally, as the number of sides increases, sticking periods, during which the slider remains motionless while the spring force on it increases, become shorter on average, with the material yielding at smaller applied stresses. Lastly, we find that dilation of the medium during sticking periods tends to be larger for grains with higher angularity, in part because of the presence of stilt-like columnar structures that prop the slider up. We report on measurements of the pulling force on the slider, particle dynamics during slip events, and properties of force-bearing contact networks identified via photoelasticity. Our findings indicate that high angularity of grains (pentagons, squares, triangles) leads to differences in grain-scale flow and macroscopic stick-slip dynamics of bulk granular materials. Our experiments also indicate a continuous change in dynamics with decreasing angularity as the circular grain limit is approached.

Structure and Electrical Properties of β-Ga2O3 Films Obtained by Radio Frequency Magnetron Sputtering on Porous Silicon

A wide range of possible applications of gallium oxide requires further investigations on growth techniques of its thin films, especially deposited on non-native substrates. One of the ways to avoid imperfection of Ga2O3 film because of variations in structure and lattice parameters of substrate could be an exploitation of buffer porous layer previously synthesized on the substrate. The 170 nm films deposited on porous-Si/Si substrate by rf magnetron sputtering are found out to be composed of β-Ga2O3 elliptical grains with sizes ∼150 nm. Both EDAX and Raman spectroscopy results show formation of a thin interfacial SiO2. Impedance spectroscopy measurements reveals two charge transfer processes with activation energies of 1.33 eV and 1.79 eV.

The effect of exposure to elevated temperatures on the microstructure and hardness of Mg–Ca–Zn alloy

Abstract The die cast Mg-5 wt.% Ca-6 wt.% Zn ternary alloy was exposed to 160 °C for different times of up to 40 days. Microstructural analysis and microhardness and hardness measurements of the samples after different exposure times enabled the thermal stability of the cast alloy to be monitored. The as-cast structure is composed mainly of α-Mg solid solution, elliptical grain boundary particles of CaMg2, and an intergranular eutectics of Mg and Ca2Mg6Zn3. The grain size of α-Mg and the structure of the alloy did not change during the treatment, but the amount of the intergranular phases increased slightly. Exposure to 160 °C resulted in a decrease in micro-hardness of the α-Mg grains, but no change in the overall hardness of the samples was observed. Microstructural analyses indicated diffusion of the solute elements from the α-Mg grains to the grain boundaries, resulting in a decrease in hardness of the α-Mg which is, however, compensated by an increase in hardness related to intergranular precipitates. Using a simple diffusion model, the diffusion coefficient of Ca atoms in Mg at 160 °C was estimated to be 2.1 · 10 –17 m2 s– 1, which is greater than that of Zn by two orders of magnitude.

СІНТЕЗ І ФОТОКАТАЛІТИЧНІ ВЛАСТИВОСТІ КОМПОЗИЦІЙНИХ ПОКРИТТІВ НА ОСНОВІ КОБАЛЬТУ З ТУГОПЛАВКИМИ КОМПОНЕНТАМИ

The possibility of electrosynthesis and control of the surface composition and morphology of the electrolytic cobalt coatings with refractory metals by varying the parameters of electrolysis has been proved. It was found that oxygen and carbon are included in the composition of the coatings as well as the main components, thus such systems can be considered as composite. The coatings deposited by pulsed current can be considered as composite materials the oxide phase for which is formed directly in the electrode process as an intermediate of incomplete reduction of tungstates and hydrolysis of zirconium (IV) salts. The topography of the films is distinguished by the presence of elliptical and spherical grains with crystallite sizes of 80 - 180 nm. On the surface of the coatings, there are hills (large grains) with a diameter of 1 - 3 μm. The fractal dimension of the surface is 2.77, which indicates the 3D mechanism of crystal growth during the formation of coatings. In terms of phase composition, composites are predominantly amorphous materials that contain nanocrystalline cobalt and the intermetallic compound Co3W and Zr3Co. The study of the morphology and topography of the composite coatings surface, as well as its quantitative and phase composition, indicates the possibility of photocatalytic activity of the Co-Mo-WOх, Co-Mo-ZrO2 and Co-W-ZrO2 coatings. Investigation of the photodegradation of the azo dye methyl orange found that the efficiency of MO removal from the solution was 24%, 18%, and 10% for 30 min of ultraviolet irradiation in the presence of Co-Mo-WOх, Co-Mo-ZrO2 and Co-W-ZrO2 on composite coatings, respectively. The higher photoactivity of Co-Mo-WOx composite coatings can be explained by the presence of non-stoichiometric molybdenum and tungsten oxides.

Еволюція мезозойських перидотитів угольського офіолітового комплексу (мармароська скельна зона, внутрішні українські Карпати)

The paper presents the results of the study of peridotites of the Ugolka ophiolite complex of the Inner Ukrainian Carpathians. The work is based on the data of prior research and original materials of geological observations from the middle course of the Tereblya River, and on new laboratory analyzes of peridotites. Middle Triassic – Lower Cretaceous (?) Peridotites of the Ugolka ophiolite complex form olistolites in the Lower Cretaceous olistostrome-conglomerates of Soimul formation. Petrographic data make it possible to classify disparate olistolites of the ophiolite complex, and peridotites in particular, into two types of ophiolite associations, which were formed in different conditions according to indicator minerals (including spinelides). Results of the study of spinelites form two groups that correlate with two equilibrium mineral associations: first – olivine + spinel + orthorhombic pyroxene + monoclinic pyroxene; and second – amphibole + talc. Larger isometric or xenomorphic individuals of chromium spinels are found in harzburgites and lherzolites. Smaller chromium spinel individuals form elongated and elliptical grains, stretched along the structure of the rock, and are found in the interstices of pyroxene and olivine crystals. X-ray microprobe analysis revealed that the composition of chromium spinel grains of the first group contains more magnesium and less chromium. chromium spinels of the second group are smaller, and contain less magnesium and more chromium. On the binary diagram Cr#–Mg# chromium spinels from the peridotites of the Ugolka complex are concentrated in two areas: abyssal peridotites and suprasubduction peridotites. chromium spinel grains from the first group crystallized at a low degree of partial melting (Dmelt up to 14 %), which is typical for abyssal peridotites. chromium spinels of the second group crystallized at a higher degree of melting (Dmelt up to 30 %), which is characteristic of peridotites of suprasubduction zones. On the correlation diagram of the average chromium spinel and the total spreading speed, the chromium spinel compositions of the first group of the Ugolka complex corresponds to the peridotites of ultra-slow spreading zones. Small grains from the second group of chromium spinels of the Ugolka complex are associated with peridotites of fast spreading zones. The temperature of metamorphism of rocks of the first mineral association is estimated by spinel and olivine-spinel geothermometers, and is contained within range of 900–1 290 ºС, at pressure aprox. 15 kbar. The temperature of metamorphism of rocks forming the second mineral association, I estimated at 430–450 °C, at pressure of 4.0–4.5 kbar. The study of peridotites of the Ugolka complex is informative for reconstruction of the geological evolution of the original sediments and determining the stages of formation of thrust-nappe structures.

Effects of grains shapes of porous media on combustion onset—A numerical simulation using Lattice Boltzmann method

The Lattice Boltzmann method is used to simulate the propane–air mixture combustion in a porous media with different grain shapes of triangular, elliptical, rectangular, and star. The effects of these shapes on the flow and temperature fields and the flame characteristics were investigated. In order to simulate the flow in the porous medium, the method of creating barriers against the flow is used. The black and white photos are transformed into the matrix of 0 and 1, written in the form of the lattice Boltzmann code for solving the momentum, energy, and concentration equations. The results show that the porous media made by grains with sharp corners provide the highest reverse flow. The porous media with grain shapes of rectangular and triangular provide the highest and least pressure drop, respectively. The length of the flame decreases by using the porous media and the star shape has the largest length of the flame, while the rectangular one has the smallest flame length. The shapes of flames obtained for the elliptical and triangular grains are very similar to each other, while, the shape of flame for the star grain is close to the non-porous medium case. In general, using the porous media increases the heat transfer rate from the walls and also creates the fluctuations in the heat transfer along the wall.

Physical and photo-electrochemical properties of MgFe2O4 prepared by sol gel route: application to the photodegradation of methylene blue

The spinel MgFe2O4 synthesized by sol gel method, was characterized by physical and electrochemical methods. The thermal analysis (TG) gives an optimal synthesis temperature of 650 °C where the X-ray diffraction pattern exhibits a single phase crystallizing in a cubic symmetry (Space Group: Fd\(\stackrel{-}{3}\)m) with spherical crystallites (~ 0.45 µm). The morphology observed through the SEM image shows elliptical and spherical grains of ~ 0.8 µm. The spinel possesses a direct optical transition (2.16 eV) due to electrons transfer Fe3+: d−d transition, coming from the crystal field splitting in agreement with the red color. The low electrons mobility is assigned to a narrow conduction band of Fe3+: 3d parentage with activation energy (0.14 eV) in conformity with a conduction mechanism by small polaron hopping. The semi-logarithmic plot confirms the chemical stability of oxide. Unlike other spinels, the capacitance plot exhibits n type conduction confirmed by chrono-amperometry with a flat band potential (Efb) of 0.27 V. The electrochemical impedance spectroscopy displays a semi-circle attributed to the bulk behavior. As application, the photodegradation of methylene blue (10 mg L− 1) was successfully on the spinel suspension; 87% are eliminated after 2 h of exposure to sunlight irradiation.

Complex resistivity of mineral rocks in the context of the generalised effective‐medium theory of the induced polarisation effect

ABSTRACTThis paper develops the generalised effective‐medium theory of induced polarisation for rock models with elliptical grains and applies this theory to studying the complex resistivity of typical mineral rocks. We first demonstrate that the developed generalised effective‐medium theory of induced polarisation model can correctly represent the induced polarisation phenomenon in multiphase artificial rock samples manufactured using pyrite and magnetite particles. We have also collected representative rock samples from the Cu–Au deposit in Mongolia and subjected them to mineralogical analysis using Quantitative Evaluation of Minerals by Scanning Electron Microscopy technology. The electrical properties of the same samples were determined using laboratory complex resistivity measurements. As a result, we have established relationships between the mineral composition of the rocks, determined using Quantitative Evaluation of Minerals by Scanning Electron Microscopy analysis, and the parameters of the generalised effective‐medium theory of induced polarisation model defined from the laboratory measurements of the electrical properties of the rocks. These relationships open the possibility for remote estimation of types of mineralisation and for mineral discrimination using spectral induced polarization data.

Pore scale evaluation of thermal conduction anisotropy in granular porous media using Lattice Boltzmann method

PurposeThermal conduction anisotropy, which is defined by the dependency of thermal conductivity on direction, is an important parameter in many engineering and research studies such as the design of nuclear waste depositional sites. In this context, the authors aim to investigate the effect of grain shape in thermal conduction anisotropy using pore scale modeling that utilizes real shapes of grains, pores and throats to characterize petrophysical properties of a porous medium.Design/methodology/approachThe authors generalize the swelling circle approach to generate porous media composed of randomly arranged but regularly oriented elliptical grains at various grain ratios and porosities. Unlike previous studies that use fitting parameters to capture the effect of grain–grain thermal contact resistance, the authors apply roughness to grains’ surface. The authors utilize Lattice Boltzmann method to solve steady state heat conduction through medium.FindingsBased on the results, when the temperature field is not parallel to either major or minor axes of grains, the overall heat flux vector makes a “deviation angle” with the temperature field. Deviation angle increases by augmenting the ratio of thermal conductivities of solid to fluid and the aspect ratios of grains. In addition, the authors show that porosity and surface roughness can considerably change the anisotropic properties of a porous medium whose grains are elliptical in shape.Originality/valueThe authors developed an algorithm for generation of non-circular-based porous medium with a novel approach to include grain surface roughness. In previous studies, the effect of grain contacts has been simulated using fitting parameters, whereas in this work, the authors impose the roughness based on the its fractal geometry.

Phase characterisation and mechanical behaviour of Fe–B modified Cu–Zn–Al shape memory alloys

The microstructures, phase characteristics and mechanical behaviour of Cu–Zn–Al alloys modified with Fe, B, and Fe–B mixed micro-alloying additions has been investigated. Cu–Zn–Al alloys were produced by casting with and without the addition of the microelements (Fe, B and Fe–B). The alloys were subjected to a homogenisation – cold rolling – annealing treatment schedule, before the alloys were machined to specifications for tensile test, fracture toughness, and hardness measurement. Optical, scanning electron microscopy and X-ray diffraction analysis were utilised for microstructural and phase characterisation of the alloys. A distinct difference in grain morphology was observed in the alloys produced – the unmodified alloy had predominantly needle-like lath martensite structure with sharp grain edges while significantly larger transverse grain size and curve edged/near elliptical grain shape was observed for the modified Cu–Zn–Al alloys. Cu–Zn with fcc structure was the predominant phase identified in the alloys while Cu–Al with bcc structure was the secondary phase observed. The hardness of the unmodified Cu–Zn–Al alloy was higher than that of the modified alloys with reductions in hardness ranging between 32.4 and 51.5%. However, the tensile strength was significantly lower than that of the modified alloy grades (28.37–52.74% increase in tensile strength was achieved with the addition of micro-alloying elements). Similarly, the percent elongation and fracture toughness (10–23% increase) of the modified alloy was higher than that of the unmodified alloy grade. The modified alloy compositions mostly exhibited fracture features indicative of a fibrous micro-mechanism to crack initiation and propagation, characterised by the prevalence of dimpled rupture.

Direct relations between morphology and transport in Boolean models.

We study the relation of permeability and morphology for porous structures composed of randomly placed overlapping circular or elliptical grains, so-called Boolean models. Microfluidic experiments and lattice Boltzmann simulations allow us to evaluate a power-law relation between the Euler characteristic of the conducting phase and its permeability. Moreover, this relation is so far only directly applicable to structures composed of overlapping grains where the grain density is known a priori. We develop a generalization to arbitrary structures modeled by Boolean models and characterized by Minkowski functionals. This generalization works well for the permeability of the void phase in systems with overlapping grains, but systematic deviations are found if the grain phase is transporting the fluid. In the latter case our analysis reveals a significant dependence on the spatial discretization of the porous structure, in particular the occurrence of single isolated pixels. To link the results to percolation theory we performed Monte Carlo simulations of the Euler characteristic of the open cluster, which reveals different regimes of applicability for our permeability-morphology relations close to and far away from the percolation threshold.

Anther Wall Development, Microsporogenesis, and Microgametogenesis inAbolbodaandOrectanthe: Contributions to the Embryology of Xyridaceae (Poales)

Premise of research. Xyridaceae includes two subfamilies with a total of five genera. Xyridoideae has only the single genus Xyris, and Abolbodoideae includes the remaining genera. The inter- and intrafamilial relationships among Xyridaceae have not yet been clarified, and this study therefore aimed to investigate the anther wall and pollen grain development in Abolboda and Orectanthe species, searching for characters that can be used in taxonomic and phylogenetic analyses.Methodology. Anthers from flowers at different stages of development were examined using both LM and SEM.Pivotal results. All studied species present the following: monocotyledonous type of anther wall development, single-layered endothecium with band-like thickenings in the mature anther, single ephemeral middle layer, multilayered and plasmodial tapetum, successive microsporogenesis, and spherical inaperturate pollen grains. Characteristics such as reduced type of anther wall development, single-layered and secretory tapetum with uninucleate or binucleate cells, and elliptical sulcate pollen grains with a reticulate exine are present in Xyris and differentiate this genus from Abolboda and Orectanthe. The characteristics reported for Xyris are also present in Mayacaceae, which used to form the xyrid clade of Poales with Eriocaulaceae and Xyridaceae. Abolboda and Orectanthe share with Eriocaulaceae the monocotyledonous type of anther wall development with an ephemeral middle layer, an endothecium with band-like thickenings, and pollen grain exine with projections. The presence of a multilayered tapetum is exclusive to Abolboda and Orectanthe among the Xyridaceae and also among the Poales.Conclusions. The embryological characteristics support the division of Xyridaceae into two subfamilies. In contrast with the megasporogenesis and megagametogenesis, the microsporogenesis and microgametogenesis characteristics were quite variable within the xyrid clade, with successive microsporogenesis being the only characteristic shared by Xyridaceae, Eriocaulaceae, and Mayacaceae.

Selective Laser Melting of Ti-45Nb Alloy

Ti-45Nb is one of the potential alloys that can be applied for biomedical applications as implants due to its low Young’s modulus. Ti-45Nb (wt.%) gas atomized powders were used to produce bulk samples by selective laser melting with three different parameter sets (energy inputs). A β-phase microstructure consisting of elliptical grains with an enriched edge of titanium was observed by scanning electron microscopy and X-ray diffraction studies. The mechanical properties of these samples were evaluated using hardness and compression tests, which suggested that the strength of the samples increases with increasing energy input within the range considered.

Semianalytical and Analytical Formulas for the Classical Loss in Granular Materials With Rectangular and Elliptical Grain Shapes

Granular soft magnetic materials, such as ferrites or soft magnetic composites, are widely spread in modern electrical engineering applications. An important loss contribution is the classical one. It is known that in these materials, two kinds of classical loss must be distinguished: eddy currents flowing at the scale of the whole sample (therefore called macroscopic), and current lines inside the grains (called microscopic). For the macroscopic eddy currents computation, the sample cross sections are often square or rectangular. For eddy currents prediction inside the grains, two cases can be distinguished: 1) the case of low density materials, for which circular or elliptical grain shapes are often realistic and 2) the case of high density materials. In this last class of granular materials, it is more difficult to identify a precise grain shape, because the deformations occurring during the compaction process often give to the grains a random shape. For carrying out the eddy current computation, rectangular shapes are often considered, because they allow a complete filling of the available space. To our knowledge, analytical eddy current formulas only exist for cylindrical or spherical regions. For other shapes, such as squares, rectangles, or ellipses, the finite element method must be used to compute the eddy current distribution, which can be time consuming. This paper overcomes this difficulty by proposing respectively a semianalytical formula for classical loss in rectangular geometries, and an analytical formula for elliptical cases.

Phase field modeling of ideal grain growth in a distorted microstructure

In this work, we perform phase field simulations of ideal grain growth in a distorted polycrystalline aggregate. The distorted microstructure is assumed to be generated by homogenous deformation of an initially equiaxed polycrystalline aggregate. Phase field theory of curvature driven grain boundary migration under distortion is developed and the phase field kinetic relations are implemented in a numerical code based on an explicit time integration procedure. As a benchmark example, phase field simulations of the shrinkage of a distorted circular grain are performed and compared with that of an undistorted elliptical grain to validate the phase field theory and its numerical implementation and also to study the effect of distortion on the kinetics of grain boundary migration. The non-equiaxed distorted grain evolves towards an equiaxed geometry by curvature-driven boundary migration. The evolution rate towards equiaxity is proportional to the distortion magnitude. However, the distortion regardless of its magnitude has no effect on the decrease rate of the distorted grain surface area. We also investigate the evolution of a distorted polycrystalline microstructure by phase field simulations. The elongated distorted grains grow and evolve towards equiaxed grains by ideal grain growth. It has been observed that the distortion influences the directional measure of average grain size to a large extent, but the nondirectional average characteristics of the microstructure are not affected.

Earliest Paleoproterozoic supracrustal rocks in the North China Craton recognized from the Daqingshan area of the Khondalite Belt: Constraints on craton evolution

The Upper Wulashan “Subgroup” at Daqingshan in the Khondalite Belt of the Western Block of the North China Craton contains an Early Paleoproterozoic (2.5–2.45Ga) supracrustal sequence, incorporating banded iron formations, which we refer to as the Daqingshan Supracrustal Rocks. They contain rounded to elliptical zircon grains that commonly show core–rim or core–mantle–rim structures and precise SHRIMP U–Pb dating of these domains allows the discrimination of a series of tectono-thermal events that straddle the Archean/Proterozoic boundary. Detrital zircon cores with oscillatory zoning have formation ages ranging from 2.55 to 2.50Ga, indicating derivation from Late Neoarchean magmatic rocks. As a result of exhumation and erosion, these became incorporated in earliest Paleoproterozoic sediments that were deposited between 2.50 and 2.45Ga and then underwent high-grade metamorphism at 2.45–2.40Ga. This event variously recrystallized the cores into two main domains: a dark inner domain and a gray outer domain, as imaged in cathodoluminescence. The gray domains commonly show sector zoning and have Th/U ratios of 0.1–0.5, a feature commonly noted in zircons recrystallized under high-grade metamorphic conditions. Metamorphic mantles are generally more homogeneous in structure and have lower Th/U ratios (commonly <0.1) than the recrystallized domains, although they show similar age distributions. However, they are difficult to distinguish when only two domains are present in the zircon and they represent a continuum of recrystallization. The rocks then underwent a second episode of high-grade metamorphism in the Late Paleoproterozoic, as revealed by thin overgrowth rims that are homogeneous or show only weak zoning, have low Th/U ratios (commonly <0.1), and record ages of 1.95–1.90Ga. This is the first time that two tectono-thermal events of Early and Late Paleoproterozoic age have been identified in single rock samples from the Western Block of the North China Craton. The conclusion that unequivocal earliest Paleoproterozoic sediments are present in the North China Craton is also supported by evidence that the Daqingshan Supracrustal Rocks are cut by anatectic garnet granite, previously dated at 2.39Ga. Combined with evidence obtained here and elsewhere in the North China Craton, we conclude that the 2.45–2.40Ga metamorphism was not an extension of the well-established, craton-wide Late Neoarchean tectono-thermal event, but a previously unrecognized episode that followed a short quiescent period that allowed sedimentation of the Daqingshan Supracrustal Rocks.

Synthesis and Characterization of MgFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; /MgO Composite Films from Layered Double Hydroxides Precursors

MgFe2O4/MgO composite films have been successfully fabricated by a facile route using magnesium iron layered double hydroxide (MgFe-LDH) as a single-source precursor. This strategy mainly involves the formation of MgFe-LDH film by casting the slurry of MgFe-LDH precursor on the α-Al2O3substrate, followed by calcination at 900°C. The structure, morphology and magnetic properties of the resulting films were characterized by means of X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), laser particle size analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results show that the composite films are composed of spherical or elliptical grains with diameters of less than 150nm and their thickness range was 2~3 μm. EDX mapping analysis reveals that the composite films have uniform distribution of MgFe2O4particles in MgO matrix. Further investigation indicates that the magnetic properties of the composite films can be tailored by altering the Mg/Fe molar ratio of LDH precursors.

Permeability of Porous Materials Determined from the Euler Characteristic

We study the permeability of quasi-two-dimensional porous structures of randomly placed overlapping monodisperse circular and elliptical grains. Measurements in microfluidic devices and lattice Boltzmann simulations demonstrate that the permeability is determined by the Euler characteristic of the conducting phase. We obtain an expression for the permeability that is independent of the percolation threshold and shows agreement with experimental and simulated data over a wide range of porosities. Our approach suggests that the permeability explicitly depends on the overlapping probability of grains rather than their shape.

Formation of micro shear bands during cyclic deformation of sub-microcrystalline nickel

Cyclic deformation of sub-microcrystalline nickel at high plastic strain amplitude generated macro shear bands, causing fatal cracking. The macro shear bands consisted of several micro shear bands, each band containing a single layer of elliptical grains that appeared at less than 50° with respect to the loading axis. Micro texture investigations in micro shear bands revealed almost the same texture with similar shear values as in macro shear bands. During cyclic deformation local overlapping of evolving micro shear bands resulted in formation of fatal macro shear bands.