Random Orientation Distribution Research Articles

Texture and anisotropy analysis of Qusaiba shales

Scanning and transmission electron microscopy, synchrotron X-ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub’al-Khali basin, Saudi Arabia. Kaolinite, illite-smectite, illite-mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4–6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P-wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P-wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P-wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging.

Texture and mechanical properties of strip cast and hot rolled magnesium AZ31

Abstract Strips of AZ31 were produced by Direct Strip Casting and subsequent hot rolling at 400°C. The texture and microstructure of the strips in as cast and hot rolled condition were investigated. The cast strip exhibited a random distribution of the grain orientations while a strong basal-type texture was observed in the hot rolled sheets. The flow curves of the Direct Strip Cast material were obtained by hot compression experiments and dynamic recrystallization was found to occur at all studied temperatures and strain rates. The tensile properties of strip cast and hot rolled magnesium were examined by tests at room temperature. Grain refinement and the development of the basal texture during hot rolling resulted in high strength of the hot rolled magnesium sheet.

Comparison of local and global texture in HDDR processed Nd–Fe–B magnets

The local texture in polycrystalline Nd–Fe–B powder particles processed by hydrogenation disproportionation desorption and recombination (HDDR) has, for the first time, been observed directly by electron backscatter diffraction (EBSD). The local texture quality was found to vary strongly with the hydrogen pressure applied during HDDR processing. At 0.3 bar, a strong biaxial local texture occurs in the individual powder particles. Increasing the hydrogen pressure during HDDR results initially in a lower texture quality and finally leads to near-isotropic particles. Clusters of similarly oriented grains within near-isotropic particles were observed rather than a completely random spatial distribution of orientations. The local texture within the powder particles was shown to be critical in determining the magnetic properties of compacts produced by aligning the powder in an external magnetic field. A compact produced from the powder with the strongest local texture (processed at 0.3 bar) showed highly anisotropic magnetic properties with remanence (related to the density of Nd 2Fe 14B) parallel and perpendicular to the applied field direction of 1.24 T and 0.55 T, respectively.

Templating effects of lyotropic liquid crystals in the encapsulation of amyloid fibrils and their stimuli-responsive magnetic behavior

The relationship between the symmetry of inverted lyotropic liquid crystals (LLC), used as hosting complex fluid, and amyloid fibrils, confined within the LLC matrix, was studied with the aim of exploiting the LLC water reservoirs for encapsulation of large protein aggregates. We used β-lactoglobulin (βlg) fibrils as a model system for high aspect ratio amyloid fibrils and encapsulated them into three different types of LLC mesophases composed of glycerol monolinoleate, with or without linoleic acid and water, yielding respectively lamellar, inverse bicontinuous cubic and inverse columnar hexagonal symmetries. The impact of fibrils confinement within the LLC on their secondary structure and spatial organization was studied by combining small angle X-ray scattering (SAXS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy (AFM) techniques. FTIR indicated that the βlg fibrils were incorporated within the aqueous layers of the lamellar phase while in the cubic and hexagonal structures they were mostly located at the lipid–water interface, along the channels. Furthermore, each mesophase affected the assembly of the amyloid fibers in accordance with the nature of the space group of the LLC structure considered. The two-dimensional order parameter of the fibrils, which was calculated on the basis of AFM images, revealed mainly random orientation distribution of the fibrils when these were confined within the lamellar and cubic phases, which can be understood by the orientation degeneracy of the fibrils in a 2D confinement and by the isotropic nature of the cubic phases. On the contrary, the fibers exhibited nearly perfect orientation when confined within the columnar hexagonal phase as a consequence of the unidirectional orientation of the LLC and the high aspect ratio of the fibrils. These trends were further exploited to induce orientation of the LLC by decorating the encapsulated amyloid fibrils with magnetic nanoparticles capable to respond to an external magnetic field stimulus: a coupling of the orientation of the nanoparticle-decorated amyloid fibrils and that of the LLC mesophase was demonstrated by small angle neutron scattering under the application of a constant magnetic field.

Temperature-dependent structural properties of P3HT films

Structural investigations of spin coated and drop cast poly(3-hexylthiophene) P3HT films have been performed under x-ray grazing incidence geometry. Drop cast films revealed to be highly oriented and crystalline and only slightly modify with the temperature. In contrast, spin coated films provided random orientational distribution of nanocrystallites and undergo significant morphological and structural changes during annealing. Interestingly, spin coated films of low and high molecular weight fractions behavior differently as a function of temperature. Crystalline domains of the low molecular weight fractions have been decreased, and, in contrast, we found an improvement of crystallinity of high molecular weight fraction with increase of the temperature.

Influence of shape fabric and crystal texture on marble degradation phenomena: simulations

Microstructure-based finite element simulations were used to study the influence of grain shape fabric and crystal texture on thermoelastic responses related to marble degradation phenomena. Calcite was used as an illustrative example for studying extremes of shape preferred orientation (SPO) in shape fabric and lattice preferred orientation (LPO) in crystal texture. Three SPOs were analyzed: equiaxed grains, elongated grains, and a mixture of equiaxed and elongated grains. Three LPOs were considered: a random orientation distribution function and two degrees of strong directional crystal texture. Finally, the correlation between the direction of the LPO with respect to that of the SPO was examined. Results show that certain combinations of SPO, LPO, and their directional relationship have significant influence on the thermomechanical behavior of marble. For instance, while there is no major dependence of the elastic strain energy density and the maximum principal stress on SPO for randomly textured microstructures, there is a strong synergy between LPO and its directional relationship with respect to the SPO direction. Microcracking precursors, elastic strain energy density, and maximum principal stress, decrease when the crystalline c-axes have fiber texture perpendicular to the SPO direction, but increase significantly when the c-axes have fiber texture parallel to the SPO direction. Moreover, the microstructural variability increases dramatically for these latter configurations. In general, the influence of LPO was as expected, namely, the strain energy density and the maximum principal stress decreased with more crystal texture, apart from for the exception noted above. Spatial variations of these precursors indicated regions in the microstructure with a propensity for microcracking. Unexpectedly, important variables were the microstructural standard deviations of the spatial distributions of the microcracking indicators. These microstructural standard deviations were as large as or larger than the variables themselves. The elastic misfit-strain contributions to the coefficients of thermal expansion were also calculated, but their dependence was as expected.

Fossil evidence for spin alignment of Sloan Digital Sky Survey galaxies in filaments

We search for and find fossil evidence that the distribution of the spin axes of galaxies in cosmic web filaments relative to their host filaments are not randomly distributed. This would indicate that the action of large scale tidal torques effected the alignments of galaxies located in cosmic filaments. To this end, we constructed a catalogue of clean filaments containing edge-on galaxies. We started by applying the Multiscale Morphology Filter (MMF) technique to the galaxies in a redshift-distortion corrected version of the Sloan Digital Sky Survey DR5. From that sample we extracted those 426 filaments that contained edge-on galaxies (b/a < 0.2). These filaments were then visually classified relative to a variety of quality criteria. Statistical analysis using "feature measures" indicates that the distribution of orientations of these edge-on galaxies relative to their parent filament deviate significantly from what would be expected on the basis of a random distribution of orientations. The interpretation of this result may not be immediately apparent, but it is easy to identify a population of 14 objects whose spin axes are aligned perpendicular to the spine of the parent filament (\cos \theta < 0.2). The candidate objects are found in relatively less dense filaments. This might be expected since galaxies in such locations suffer less interaction with surrounding galaxies, and consequently better preserve their tidally induced orientations relative to the parent filament. The technique of searching for fossil evidence of alignment yields relatively few candidate objects, but it does not suffer from the dilution effects inherent in correlation analysis of large samples.

Molecular beam epitaxy growth and characterization of self-assembled MnAs wires on highly oriented pyrolytic graphite

The authors have grown MnAs on highly oriented pyrolytic graphite (HOPG), a strain-free and inert substrate, using molecular beam epitaxy. MnAs on HOPG grows in the form of particles, which self-assemble to form wirelike structures along the step edges on the HOPG surface. The MnAs particles have an average height of 42 nm and a diameter of 240 nm. Vibrating sample magnetometry studies indicate that the samples are ferromagnetic with no observable in-plane anisotropy, which is expected from a sample with a random distribution of particle orientations. Magnetic force microscopy (MFM) results indicate that the magnetic coupling between particles is less than that within each particle, and likely a dipole-dipole interaction, giving rise to magnetization patterns for the wires. Temperature dependent MFM measurements yield a Curie temperature of 330 K. Scanning tunneling microscopy and scanning tunneling spectroscopy were used to investigate the electronic density of states of MnAs, with the well-studied HOPG surface as a convenient reference.

Probabilistic framework for a microstructure-sensitive fatigue notch factor

To advance fatigue life prediction algorithms, more comprehensive knowledge of the intensity and distribution of slip within microstructure at the notch root is desired to quantify notch size effects. This study utilizes 3D computational crystal plasticity to assess the degree of heterogeneity of cyclic plastic deformation as a function of notch size and notch root acuity for notch root strain amplitudes near and below the macroscopic yield strain (high cycle fatigue) and for several realizations of aggregates of grains with random orientation distribution at the notch root for polycrystalline OFHC Cu. By using different notch root radii and microstructure realizations of aggregates of grains, statistical information regarding the distributions of stress/strain gradients and fatigue indicator parameters provides useful insight into the microstructure dependence of driving forces for fatigue crack formation at the scale of mean grain size. Results from simulations within a quantitatively defined notch root damage process zone are used along with a probabilistic mesomechanics approach to quantify notch size effects by defining a new microstructure-sensitive fatigue notch factor that considers the probability distribution of the high cycle fatigue strength.

An Official Research Policy Statement of the American Thoracic Society/European Respiratory Society: Standards for Quantitative Assessment of Lung Structure

Keywords: morphometry; stereology; unbiased sampling; reference lung volume; cell volume; surface area; cell size; cell number; in vivo imaging

Tensile Ductility of Cast TiAl Alloys

The microstructural characteristics and room temperature tensile ductility in some cast TiAl alloys were analyzed. It was found that grain refinement, either through Q&amp;A treatment in boron-free alloys or through low dose of boron addition in beta solidifying alloys with lamellar microstructures, is not sufficient for good ductility. For cast alloys with convoluted microstructures and fine lamellar microstructures the orientation distribution of gamma grains/lamellar colonies plays an important role in controlling ductility. In those fine-grained alloys a highly random orientation distribution of gamma grains/lamellar colonies is essential to improvement in ductility.

Misorientations in rolled and recrystallized zirconium compared with random distribution. A new scheme of misorientation analysis

The noncorrelated misorientation distributions found in a zirconium alloy after deformation, complete recrystallization and subsequent grain growth are first compared with those found in a quasi-isotropic hexagonal material (i.e.associated with a random orientation distribution). They are then recalculated with respect to the specific misorientation axes 〈0001〉, 〈10{\overline 1}0〉 and 〈11{\overline 2}0〉. The results are discussed with reference to the specific misorientations that are often assumed to play a role during the recrystallization process.

Influence of single-walled carbon nanotubes on the effective elastic constants of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) is one of the most extensively used thermoplastic polyesters out on the market, and it has been implemented in many forms. There has been limited work in the area of PET reinforced with single-walled carbon nanotubes (SWCNT) in mechanical properties. Nanocomposites based on PET with small contents of SWCNT were prepared by in situ polymerization. Elastic constants were determined by tensile tests performed on specimens instrumented with strain gauges. Assuming random orientation distribution of nanotubes, experimental Young’s modulus and Poisson’s ratio values were compared to some micromechanical models (Cox and Krenchel, Halpin–Tsai and Mori–Tanaka) which take into account orientation and aspect ratio of the nanotubes. However, the waviness of the nanotubes is a factor that influences the reinforcing efficiency.

Electron microscopy analysis for crack propagation behavior of alumina

In order to clarify crack propagation behavior of alumina (α-Al 2O 3), intergranular and transgranular fractures of alumina were investigated by electron microscopy techniques. For the intergranular fractures cracked grain boundaries were investigated by scanning electron microscopic electron back-scattered diffraction (SEM-EBSD) analysis. It was revealed that the intergranular fracture behavior of polycrystalline alumina with random distribution of crystallographic orientations is independent on grain boundary characters. For the transgranular fractures, fracture surfaces formed in a single-crystalline alumina were observed by electron tomography combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high resolution TEM (HR-TEM). Three kinds of fracture surfaces were observed: even fracture surfaces, even fracture surfaces with step-terraces and fracture surfaces composed of the even fracture surface and the curved one. The even fracture surfaces mostly consist of cleavage planes parallel to { 1 1 ¯ 0 2 } and { 1 1 ¯ 0 4 } . On the other hand, the even fracture surfaces with step-terraces consist of the cleavage planes and basal planes (0 0 0 1). For the fracture surfaces composed of the even fracture surface and the curved one, both the even and curved shapes the even parts were formed by the fine cleavage planes and basal planes, whose intervals were inhomogeneous. It was indicated that the fracture surfaces in alumina are composed of the cleavage planes or basal plane at an atomic scale.

Mechanical Constraints on Hin Subunit Rotation Imposed by the Fis/Enhancer System and DNA Supercoiling during Site-Specific Recombination

Hin, a member of the serine family of site-specific recombinases, regulates gene expression by inverting a DNA segment. DNA inversion requires assembly of an invertasome complex in which a recombinational enhancer DNA segment bound by the Fis protein associates with the Hin synaptic complex at the base of a supercoiled DNA branch. Each of the four Hin subunits becomes covalently joined to the cleaved DNA ends, and DNA exchange occurs by translocation of a Hin subunit pair within the tetramer. We show here that, although the Hin tetramer forms a bidirectional molecular swivel, the Fis/enhancer system determines both the direction and number of subunit rotations. The chirality of supercoiling directs rotational direction, and the short DNA loop stabilized by Fis-Hin contacts limit rotational processivity, thereby ensuring that the DNA strands religate in the recombinant configuration. We identify multiple rotational conformers that are formed under different supercoiling and solution conditions.

Microstructure and Microtexture Formation of AZ91D Magnesium Alloys Solidified in a Static Magnetic Field

In the present study, we solidified AZ91D magnesium alloys in a static magnetic field with a magnetic flux density up to 10 Tesla (T). Three different regions can be identified in a solidified alloy, according to their microtexture and microstructure; these regions are: (a) region (A), the central region with equiaxed dendrites, (b) region (B), the transitional region with directional dendrites grown from an unmelted region, and (c) region (C), the edge region with cellular dendrites grown from the substrate of the container. No detectable difference can be discerned with regard to the influence of the magnetic field on the microstructure in region (A). However, the microtexture evolution in the region shows a strong dependence on the magnetic field and the preferential orientation formation is briefly elucidated. Special attention is focused on the orientation development of the directional dendrites in region (B) as a function of the magnetic flux density B 0, when the electron backscatter diffraction (EBSD) technique is employed. It is shown that the directional dendrites exhibit a random orientation distribution at B 0 < 5 T, while they have a unique orientation at B 0 ≥ 5 T. Microstructure observation indicates that the crystallographic orientation selection completes at the interface of the melt/unmelted regions. A theoretical analysis reveals that the competition between the magnetization energy and the anisotropic interfacial energy difference of the crystals controls the crystallographic orientation selection. For the microstructure and microtexture in region (C), heterogeneous nucleation takes place from the polycrystalline Al2O3 substrate and thus enables a random crystallographic orientation distribution. The short growth interval may not be sufficient for the preferred growth direction to be selected near the chilling area; this applies to the cellular dendrites grown from the substrate at all levels of the magnetic field.

CONSTRAINING THE NFW POTENTIAL WITH OBSERVATIONS AND MODELING OF LOW SURFACE BRIGHTNESS GALAXY VELOCITY FIELDS

We model the NFW potential to determine if, and under what conditions, the NFW halo appears consistent with the observed velocity fields of low surface brightness (LSB) galaxies. We present mock DensePak IFU velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials that are well-matched to the spatial resolution and velocity range of our sample galaxies. We find that the DensePak IFU can accurately reconstruct the velocity field produced by an axisymmetric NFW potential and that a tilted-ring fitting program can successfully recover the corresponding NFW rotation curve. We also find that non-axisymmetric potentials with fixed axis ratios change only the normalization of the mock velocity fields and rotation curves and not their shape. The shape of the modeled NFW rotation curves does not reproduce the data: these potentials are unable to simultaneously bring the mock data at both small and large radii into agreement with observations. Indeed, to match the slow rise of LSB galaxy rotation curves, a specific viewing angle of the non-axisymmetric potential is required. For each of the simulated LSB galaxies, the observer's line-of-sight must be along the minor axis of the potential, an arrangement which is inconsistent with a random distribution of halo orientations on the sky.

Anisotropy of experimentally compressed kaolinite-illite-quartz mixtures

The anisotropy of physical properties is a well-known characteristic of many clay-bearing rocks. This anisotropy has important implications for elastic properties of rocks and must be considered in seismic modeling. Preferred orientation of clay minerals is an important factor causing anisotropy in clay-bearing rocks such as shales and mudstones that are the main cap rocks of oil reservoirs. The preferred orientation of clays depends mostly on the amount of clays and the degree of compaction. To study the effect of these parameters, we prepared several samples compressing (at two effective vertical stresses) a mixture of clays (illite and kaolinite) and quartz (silt) with different clay/quartz ratios. The preferred orientation of the phases was quantified with Rietveld analysis on synchrotron hard X-ray images. Pole figures for kaolinite and illite display a preferred orientationof clay platelets perpendicular to the compaction direction, increasing in strength with clay content and compaction pressure. Quartz particles have a random orientation distribution. Aggregate elastic properties can be estimated by averaging the single-crystal properties over the orientation distribution obtained from the diffraction data analysis. Calculated P-wave velocity anisotropy ranges from 0% (pure quartz sample) to 44% (pure clay sample, highly compacted), but calculated velocities are much higher than measured velocities. This is attributed to uncertainties about single-crystal elastic properties and oriented micropores and limited grain contacts that are not accounted for in the model. In this work, we present an effective method to obtain quantitative data, helping to evaluate the role of clay percentage and compaction pressure on the anisotropy of elastic properties of clay-bearing rocks.

FIRST PRINCIPLES NON-COLLINEAR TRANSPORT CALCULATION AND INTERFACIAL SPIN-FLIPPING OF Cu/Co MULTILAYERS

In this paper, the first principle non-collinear transport calculation for Cu/Co (111) including interfacial spin-flipping was performed. We modeled spin-flipping at the interface by assuming a non-collinear magnetic structure with random magnetization orientation which satisfied the Gaussian distribution along the average magnetization direction. The relationship between spin-dependent conductance including interfacial spin-flipping and random magnetization orientation distribution width was obtained. For certain distribution width, our defined spin-flipping ratio coincides with the range of experimental spin-flipping probability P = 1-e-δ, where δ = 0.25±0.1. The magnetoresistance in the Co/Cu/Co spin-valve system including interfacial spin-flipping has also been calculated.

Grain Selection and Texture Evolution in Directionally Solidified Al-Zn Alloys

In a recent contribution, we have reported that dendrites in the aluminum-zinc binary system can change their growth direction continuously from $$ {\left\langle {{\text{100}}} \right\rangle } $$ to $$ {\left\langle {{\text{110}}} \right\rangle } $$ as the concentration of zinc C Zn increases from 5 to 90 wt pct.[1] This was interpreted as an influence of the hcp Zn element on the low anisotropy of the solid-liquid interfacial energy of aluminum. Seaweed morphologies were even observed at the start and end of this so-called “dendrite orientation transition” (DOT), i.e., for C Zn ≈ 30 and 55 wt pct. In the present work, we analyze how this DOT influences the selection of grains and the evolution of the texture in directionally solidified (DS) specimens. The solidification texturing of $$ {\left\langle {hk{\text{0}}} \right\rangle } $$ dendritic specimens is shown to be similar to that occurring in normal $$ {\left\langle {{\text{100}}} \right\rangle } $$ specimens. It is analyzed on a similar basis by considering a random orientation distribution of nuclei at the surface of the chill plate and a minimum undercooling criterion. This produces $$ {\left\langle {hk{\text{0}}} \right\rangle } $$ textures with grains that look fairly “equiaxed” in transverse sections. For seaweed morphologies, which also exhibit an $$ {\left\langle {hk{\text{0}}} \right\rangle } $$ texture parallel to the thermal gradient, the grain selection is slower and the grains appear more elongated in transverse sections. Their elongation occurs along a (001) plane, i.e., along a $$ {\left\langle {1\ifmmode\expandafter\bar\else\expandafter\=\fi{2}0} \right\rangle } $$ direction for $$ {\left\langle {210} \right\rangle } $$ seaweeds (C Zn = 30 wt pct) and along a $$ {\left\langle {1\ifmmode\expandafter\bar\else\expandafter\=\fi{1}0} \right\rangle } $$ direction for $$ {\left\langle {{\text{110}}} \right\rangle } $$ seaweeds (C Zn = 55 wt pct). The scanning electron microscopy (SEM) observations reveal that this elongation is accompanied by a microsegregation pattern that is mainly parallel to (001) planes. This indicates that seaweeds at the onset and end of the DOT grow with some type of layered structures, but their detailed growth and grain selection mechanisms are still unknown.