Coincidence Orientation Research Articles

Microstructural constraints for the formation of net-textured Fe-Ti oxide ores of the Baima layered intrusion in the Emeishan large igneous province, SW China

The mafic–ultramafic layered intrusions in the Emeishan large igneous province (LIP) host significant amounts of Fe, Ti and V resources. The Fe-Ti oxide ore layers hosted in these layered intrusions are variable in thickness and it is enigmatic how the large amounts of Fe-Ti oxides are accumulated to form the Fe-Ti oxide ore layers. The Fe-Ti oxide ore layers are mainly composed of net-textured ores, however, the processes to form the net-textured ores have not yet been well constrained due to lack of diagnostic microstructural evidence of Fe-Ti oxides in the ores. Here we use the electron back-scattered diffraction (EBSD) technique to characterize the microstructures of Fe-Ti oxides in the net-textured ores of the Baima layered intrusion in the Emeishan LIP, e.g., crystallographic orientation and neighbor-/random-pair misorientation, and to assess the formation model of net-textured ores. The net-textured ores are composed of silicate crystals (olivine, and minor plagioclase and clinopyroxene) isolated by interconnected matrix composed of Fe-Ti oxides (titanomagnetite and ilmenite) and minor sulfides. It is likely that the Fe-Ti oxides simultaneously crystallized from a common Fe–Ti–(P)-rich melt, but postdated olivine and other cumulus minerals. The compaction induced by the gravity of overlying cumulus minerals only caused weak intragrain deformation of Fe-Ti oxides so that the Fe-Ti oxides did not experience intense dynamic recrystallization. Instead, the relatively high temperature and water-rich condition facilitated the operation of static recrystallization, resulting in the straight or smoothly curved grain boundaries of Fe-Ti oxides. The neighbor-pair misorientation patterns of Fe-Ti oxides show the preference for low-angle misorientation, supporting the idea that adjacent crystallized Fe-Ti oxides were rotated to coincident orientation in a melt. This study provides new microstructural evidence for the presence of immiscible Fe-rich melt from which the Fe-Ti oxides crystallized to form the net-textured ores.

Adaptive multiorientation resolution analysis of complex filamentous network images.

Microscopy images of cytoskeletal, nucleoskeletal and other structures contain complex junctions of overlapping filaments with arbitrary geometry. Yet, state-of-the-art algorithms generally perform single orientation analysis to segment these structures, resulting in gaps near junctions, or assume particular junction geometries to detect them. We developed a fully automated image analysis approach to address the challenge of determining the number of orientations and their values at each point in space to detect both lines and their junctions. Our approach does not assume any fixed number of orientations or any particular geometry in the case of multiple coincident orientations. It is based on analytically resolving coincident orientations revealed by steerable ridge filtering in an adaptive manner that balances orientation resolution and spatial localization. Combining this multiorientation resolution information with a generalization of the concept of non-maximum suppression allowed us to then identify the centers of lines and their junctions in an image. We validated our approach using a wide array of synthetic junctions and by comparison to manual segmentation. We also applied it to light microscopy images of cytoskeletal and nucleoskeletal networks. https://github.com/mkitti/AdaptiveResolutionOrientationSpace. Supplementary information is available at Bioinformatics online.

In situ investigation of the structural defect generation and evolution during the directional solidification of 〈110〉 seeded growth Si

This work is dedicated to the advanced in situ X-ray imaging and complementary ex situ investigations of the growth mechanisms when silicon solidifies on a monocrystalline seed oriented 〈110〉 in the solidification direction. It aims at deepening the fundamental understanding of the phenomena that occur throughout silicon crystal growth with a particular focus on mechanisms of formation of defects detrimental for photovoltaic applications. Namely, grain nucleation, grain boundary formation and evolution, grain competition, twining occurrence, dislocation generation and interaction with structural defects are explored and analysed. Nucleation of twin crystals preferentially occurs on {111} facets at the edge of the sample where solid – liquid – vapor triple point lines exist in interaction also with the crucible as well as, at grain boundary grooves at the solid – liquid interface (solid – solid – liquid triple lines), where two grains are in competition, either on the {111} facets of the groove or in the groove. Enhanced undercooling and/or stress accumulation levels are found to act as driving forces for grain nucleation. Additionally, it is demonstrated that twin formation has the property to relax stresses stored in the crystal during the growth process. However, grains formed initially in twin position can undergo severe distortion when they are in direct competition or when they are squeezed in – between grains. Moreover, we show by X-ray Bragg diffraction imaging that on the one hand, coherent Σ3 〈111〉 grain boundaries efficiently block the propagation of growth dislocations during the solidification process, while on the other hand, dislocations are emitted at the level of incoherent and/or asymmetric Σ27a 〈110〉 at the encounter with either Σ3 〈111〉 or Σ9 〈110〉 grain boundaries. Indeed, grain boundaries that deviate from the ideal coincidence orientation act as dislocation sources that spread inside the surrounding crystals.

Sophisticated Nanostructure in Stone Part of Sea Urchin Tooth: Enlightenment for Artificial Composites

Sea urchin teeth, which are used to scrape rocks for food, assume significant mechanical functions. Unraveling their design strategies could provide inspiration for the pursuit of high-performance artificial composites. In this work, we used scanning electron microscopy, transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy to probe the elaborate nanostructure in the stone part of Glyptocidaris crenularis tooth. Our results show that the mesocrystalline matrix, though diffracting as a single crystal, is composed of highly oriented nanocrystals and shares almost coincident crystal orientation with its central single-crystal fiber. Interestingly, the fiber and matrix are fitted together by numerous single-crystal nanostrips rather than being completely separated by an organic sheath. This sophisticated architecture may endow the tooth with sufficient structural stability to prevent catastrophic fractures.

THE LIMITED EFFECT OF COINCIDENT ORIENTATION ON THE CHOICE OF INTRINSIC AXIS (.).

The allocentric system computes and represents general object-to-object spatial relationships to provide a spatial frame of reference other than the egocentric system. The intrinsic frame-of-reference system theory, which suggests people learn the locations of objects based upon an intrinsic axis, is important in research about the allocentric system. The purpose of the current study was to determine whether the effect of coincident orientation on the choice of intrinsic axis was limited. Two groups of participants (24 men, 24 women; M age = 24 yr., SD = 2) encoded different spatial layouts in which the objects shared the coincident orientation of 315° and 225° separately at learning perspective (0°). The response pattern of partial-scene-recognition task following learning reflected different strategies for choosing the intrinsic axis under different conditions. Under the 315° object-orientation condition, the objects' coincident orientation was as important as the symmetric axis in the choice of the intrinsic axis. However, participants were more likely to choose the symmetric axis as the intrinsic axis under the 225° object-orientation condition. The results suggest the effect of coincident orientation on the choice of intrinsic axis is limited.

The development of grain boundary orientation distribution in quartz

The fabric of high-angle boundaries in recrystallized quartz aggregates deformed under distinct strain and metamorphic conditions has been investigated in samples from iron formations recrystallized under lower greenschist to lower amphibolite facies conditions. Orientation of grain boundaries was measured using U-stage, while crystallographic fabric and misorientation between grains were measured using EBSD. In domains where grains were recrystallized under lower greenschist facies conditions, grain boundaries are sutured, composed of several small straight segments, whose traces can be parallel to traces of any crystallographic plane. In contrast, in domains of upper-greenschist–lower-amphibolite facies, grain boundaries are predominantly composed of long straight segments and belong to girdle of rhombohedral planes, while segments within girdle of basal or prism planes are rare. The longest segments (larger than 270 μm) are commonly within girdle of rhombohedral planes for the two grains that share a boundary surface, possibly representing Dauphine twin boundaries. Under higher temperature condition of the lower amphibolite facies (500–550 °C), boundary segments are longer and tend to represent coincident crystallographic orientations for the two grains that share a boundary.

Coincident Orientation of Objects and Viewpoint-Dependence in Scene Recognition

Viewpoint-dependence is a well-known phenomenon in which participants' spatial memory is better for previously experienced points of view than for novel ones. In the current study, partial-scene-recognition was used to examine the effect of coincident orientation of all the objects on viewpoint-dependence in spatial memory. When objects in scenes had no clear orientations (e.g., balls), participants' recognition of experienced directions was better than that of novel ones, indicating that there was viewpoint-dependence. However, when the objects in scenes were toy bears with clear orientations, the coincident orientation of objects (315 degrees), which was not experienced, shared the advantage of the experienced direction (0 degrees), and participants were equally likely to choose either direction when reconstructing the spatial representation in memory. These findings suggest that coincident orientation of objects may affect egocentric representations in spatial memory.

The Effect of Orientation Coincidence of Objects on Intrinsic Frame of Reference System in Symmetrical Scene

Intrinsic frame of reference system theory is a newly-developed theory in spatial memory researches.It suggests that when people learn locations of objects in a new environment,they are inclined to mentally represent a layout of objects according to a frame of reference system defined by the collection of objects.Many studies have proven that the dominant axis of intrinsic frame of reference may differ from their egocentric orientation.But there was few research in intrinsic frame of reference system theory on the effect of orientation information provided by the objects themselves in the scene.This research focused on the effect of orientation coincidence of objects in environment on people's construction of intrinsic frame of reference system and hypothesized the coincident orientation of objects would be one of the choices of the dominant axis in intrinsic frame of reference system in symmetrical scene.53 undergraduates took part in three experiments.In Experiment 1,participants stood at 0 degree facing the axis of symmetry and learned a symmetrical scene that was composed by balls with no apparent headings.In Experiment 2,participants stood at 0 degree and learned a symmetrical scene composed by toy bears with their faces orienting 315 degree,which was different from the axis of symmetry.In Experiment 3,participants stood at 0 and 315 degree and learned the same scene as that in Experiment 2.After learning,the participants needed to finish triplet recognition task in each experiment.In the task,they were required to judge if the directional relationship in these triplets were the same as the learned scene.The correct response latencies to the targets were analyzed by ANOVA.In Experiment 1,when the objects in scenes had no apparent headings,the results of repeated measures showed the mean response latency to triplets including the direction of axis of symmetry was significantly shorter than that not including the direction.In Experiment 2,when the objects in scenes had apparent headings and they all oriented the direction different from the axis of symmetry,the difference between the mean response latencies to triplets including the axis of symmetry and including the coincident orientation of objects was not significant.This result was different from the significant difference found in Experiment 1.In Experiment 3,the difference between mean response latencies to triplets including the axis of symmetry and including the coincident orientation of objects was still not significant.The result was the same as that found in Experiment 2,even if the scene was learned from both the axis of symmetry and the coincident orientation of objects to eliminate the possible interference of learning viewpoint.Results indicate that orientation coincidence of objects in symmetrical scenes affects the construction of intrinsic frame of reference system.However,there is no significant difference between the symmetry axis and the coincident orientation in the chances to be the dominant axis of intrinsic frame of reference system.

Contributing vertices-based Minkowski sum of a nonconvex--convex pair of polyhedra

The exact Minkowski sum of polyhedra is of particular interest in many applications, ranging from image analysis and processing to computer-aided design and robotics. Its computation and implementation is a difficult and complicated task when nonconvex polyhedra are involved. We present the NCC-CVMS algorithm, an exact and efficient contributing vertices-based Minkowski sum algorithm for the computation of the Minkowski sum of a nonconvex--convex pair of polyhedra, which handles nonmanifold situations and extracts eventual polyhedral holes inside the Minkowski sum outer boundary. Our algorithm does not output boundaries that degenerate into a polyline or a single point. First, we generate a superset of the Minkowski sum facets through the use of the contributing vertices concept and by summing only the features (facets, edges, and vertices) of the input polyhedra which have coincident orientations. Secondly, we compute the 2D arrangements induced by the superset triangles intersections. Finally, we obtain the Minkowski sum through the use of two simple properties of the input polyhedra and the Minkowski sum polyhedron itself, that is, the closeness and the two-manifoldness properties. The NCC-CVMS algorithm is efficient because of the simplifications induced by the use of the contributing vertices concept, the use of 2D arrangements instead of 3D arrangements which are difficult to maintain, and the use of simple properties to recover the Minkowski sum mesh. We implemented our NCC-CVMS algorithm on the base of CGAL and used exact number types. More examples and results of the NCC-CVMS algorithm can be found at: http://liris.cnrs.fr/hichem.barki/mksum/NCC-CVMS

Object Properties and Frame of Reference in Spatial Memory Representations

Considerable evidence suggests that humans flexibly select reference frames for spatial memory based on qualities such as the shape of the environment, the configuration of elements, and one's own egocentric experience of the space. We propose that the elements, or objects themselves, may also convey useful information about salient reference orientations. In Experiment 1, participants viewed objects elongated along their front-back axis that were either all oriented in the same direction or oriented at 10 different randomly selected directions. Participants in the random orientation condition were most accurate at the orientation they visually experienced at learning, whereas participants in the shared orientation condition were most accurate at an orientation consistent with or orthogonal to the coincident object orientations. Experiment 2 replicated these effects using animals that were less elongated but had clear conceptual orientations. These results suggest that the principles governing spatial memory capitalize on a wide range of properties that likely interact to support an enduring representation.

Grain-boundary shear-migration coupling. II. Geometrical model for general boundaries

Grain boundary-mediated plasticity is now a well-established phenomenon, especially in fine-grained or nanocrystalline metals. It has been described in several models, but most of these apply to very exclusive configurations such as symmetrical grain boundaries, or grain boundaries that possess a specific coincidence orientation relationship. In real polycrystals, grain boundaries have random orientations, and the current models cannot account for the shear associated with their migration (see part I of this study [1]). The present work presents a model of shear-migration coupling in which grain boundaries do not have specific orientation relationships. It consists in defining couples of shear and rotation values, able to transform one lattice orientation into another, regardless of the type of boundary that separate them. This purely geometrical model can be seen as a generalized formulation of the existing shear coupling theories. No long-range diffusion is involved, but very localized atomic shuffling is generally necessary in the core of mobile interfacial dislocations.

10.1007/s11700-008-1019-8

The structure of the (001) fcc/(001) fcc interphase boundary of a system consisting of a hemispherical Ni (or Cu) crystal nanoparticle and a Pd crystal substrate was studied depending on the nanoparticle rotation angle θ = 15°, 20°, 25°, and 30°. A molecular dynamics simulation including multiparticle potentials calculated in the framework of the embedded atom method was used in this study. It was shown that, under given annealing conditions, the nanoparticle rotation depends on the size; namely, the annealing of small nanoparticles leads to their rotation to the position corresponding to the coincidence orientation at the interphase boundary, while the position of large islands remains practically unchanged. It was established that the atomic rearrangement at the interphase boundary affects only lattices with a larger parameter.

Modification of Local Structure and Its Influence on Electrical Activity of Near (310) Σ5 Grain Boundary in Bulk Silicon

We report on the modification of the local structures of (310) Σ5 grain boundary in bulk silicon as the growth of crystal and its influence on electrical activity. The grain boundary was formed via floating-zone growth method utilizing bicrystal seed. The misalignment of the seed resulted in formation of the grain boundary with small deviations of crystal orientation from the Σ5 singular coincidence orientation. The deviations consist of tilt and twist components and they were found to monotonically decrease with respect to the distance from the seed crystal accompanied by the decrease in density of dislocations on the grain boundary. The change in the grain boundary structure allows a systematic study on the correlation between the structure and the electrical activity at the GB. The density of dislocations was found to control the electrical activity and the (310) Σ5 coincidence grain boundary without any dislocations is expected to show a very low electrical activity.

Influence of Primary Recrystallization Texture through Thickness to Secondary Texture on Grain Oriented Silicon Steel.

It is well known that the sharpness of secondary recrystallized Goss texture ({110} ) is deteriorated by nitriding primary recrystallized sheet on the ordinary grain oriented silicon steel. The cause of this deterioration was investigated. It was found that secondary recrystallization of Dispersed Goss ({110} ) caused the deterioration. From the surface to the central position in the primary recrystallization texture, the intensity of Goss Texture decreased and Dispersed Goss increased. Furthermore, nitriding increased the temperature of secondary recrystallization outset. As a result, the nucleation site of secondary recrystallization might shift to the central position where the circumstance that Dispersed Goss could grow easily is satisfied by the CSL model. This can be explained by using the CSL model with consideration of the intensity, Σ5 and Σ9 coincident orientation of Goss, and Dispersed Goss and assuming that Σ9 boundary is more mobile than Σ5 boundary.

Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary misorientation-driven rotations

Two types of garnet porphyroblast occur in the Schneeberg Complex of the Italian Alps. Type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz, decussate mica and small garnet grains, and a margin containing large garnet grains. Orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains. Individual garnet grains without subdomains are small (< 50 µm), faceted and idioblastic, and have simple zoning profiles with Ca-rich cores and Ca-poor rims. Subdomains of larger garnet grains are similar in size to the individual, small garnet grains. Type 2 porphyroblasts comprise only ellipsoidal garnet, with small subdomains in the centre and larger subdomains at the margin. Each subdomain has its own Ca high, Ca dropping towards subdomain boundaries. Garnet grains, with or without subdomains, all have the same Ca-poor composition at rims in contact with other minerals. The compositional zonation patterns are best explained by simultaneous, multiple nucleation, followed by growth and amalgamation of individual garnet grains. The range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre. The difference between Type 1 and Type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast. Electron backscatter diffraction shows that small, individual garnet grains are randomly oriented. Large marginal garnet grains and subdomain-bearing garnet grains have a strong preferred orientation, clustering around a single garnet orientation. Misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations. The only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other. This process was driven by the reduction of subdomain boundary energy associated with misorientation loss. Rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals (quartz and mica) around the garnet. An analytical model, in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz, suggests that, at the conditions of metamorphism, the rotation required to give a strong preferred orientation can occur on a similar time-scale to that of porphyroblast growth.

Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary misorientation‐driven rotations

AbstractTwo types of garnet porphyroblast occur in the Schneeberg Complex of the Italian Alps. Type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz, decussate mica and small garnet grains, and a margin containing large garnet grains. Orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains. Individual garnet grains without subdomains are small (&lt; 50 µm), faceted and idioblastic, and have simple zoning profiles with Ca‐rich cores and Ca‐poor rims. Subdomains of larger garnet grains are similar in size to the individual, small garnet grains. Type 2 porphyroblasts comprise only ellipsoidal garnet, with small subdomains in the centre and larger subdomains at the margin. Each subdomain has its own Ca high, Ca dropping towards subdomain boundaries. Garnet grains, with or without subdomains, all have the same Ca‐poor composition at rims in contact with other minerals. The compositional zonation patterns are best explained by simultaneous, multiple nucleation, followed by growth and amalgamation of individual garnet grains. The range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre. The difference between Type 1 and Type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast.Electron backscatter diffraction shows that small, individual garnet grains are randomly oriented. Large marginal garnet grains and subdomain‐bearing garnet grains have a strong preferred orientation, clustering around a single garnet orientation. Misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations. The only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other. This process was driven by the reduction of subdomain boundary energy associated with misorientation loss. Rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals (quartz and mica) around the garnet. An analytical model, in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz, suggests that, at the conditions of metamorphism, the rotation required to give a strong preferred orientation can occur on a similar time‐scale to that of porphyroblast growth.

Monte Carlo simulation of grain growth with the full spectra of grain orientation and grain boundary energy

Monte Carlo simulations of grain growth were performed for two-dimensional polycrystals with crystallographic orientations being assigned to individual grains in terms of randomly generated Euler angles. Individual grain boundaries were characterized based on the orientation relationships of grains across them and grain boundary energies were given with a continuous function of deviation angle from the exact coincidence orientation relationships. The physical and technical significance of the conditions of the orientation change in the simulations is discussed in terms of the degree of the probablistic nature of the simulation. The simulations showed the following characteristic features: (1) the energy spectra make the grain size distribution more symmetric; (2) they make the average grain growth rate smaller; and (3) the fraction of low energy boundaries increases with grain growth. These results are discussed with respect to local boundary configurations and the nature of the present model.

Near Coincidence Grain Boundary in Alumina

The rhombohedral twin orientation in alumina has been obtained by diffusion bonding and studied by transmission electron microscopy. It corresponds to a Σ7 near coincidence orientation with a grain boundary plane parallel to (0112). The grain boundary contains two arrays of dislocations with the same line direction and alternately distributed Burgers vectors which are translation vectors of the DSC lattice. The associated step vectors are large, up to 1.75nm. Starting from symmetry considerations on the various dichromatic complexes, all possible unrelaxed atomic configurations are constructed. Oxygen terminated grain boundary structures as well as those passing through non occupied aluminium sites are selected on the basis of optimal compacity at the interface. Correlations between simulated and experimental high resolution images favor the structures based on empty octahedral sites at the interface. The most probable structure has a two fold screw axis at the interface and leaves Al-O bonds with very little distorsions from the perfect coordination in alumina.

The Effect of Pressure on Indium Diffusion along 〈001〉 Tilt Grain Boundaries in Copper Bicrystals

The effect of pressure on the diffusion of indium along two grain boundaries (GBs) in copper bicrystals has been investigated. The GBs studied were of symmetrical tilt type with a 〈001〉 misorientation axis. The tilt angle of one GB was 36.5°, which corresponds to the near Σ5 coincidence orientation, where Σ is the inverse density of the coincidence sites in the two misoriented crystal lattices. The other GB was a general boundary with a tilt angle of 45°. The diffusion along the 〈001〉 tilt axis has taken place at the temperature of 923 K and under argon gas pressures up to 1 GPa. The following activation volumes have been found: 0.94±0.11 ΩCu for bulk diffusion,–0.5 ±0.7 ΩCu for the diffusivity of the near Σ 5 GB and −0.6±0.3 ΩCu for the diffusivity of the 45° 〈100〉 GB, where ΩCu is the atomic volume of copper. Two interpretations of this result seem plausible. The first interpretation is that the In atoms diffuse along the 〈001〉 tilt axis by an instertitialcy mechanism. It is known that for such a diffusion mechanism the activation volume is close to zero. The alternative explanation bases on the observation that the parameter measured is the GB diffusivity, which depends on the product of the GB diffusion coefficient and the segregation factor. An enhancement of the In segregation under pressure would lead to an increase of the GB diffusivity. It seems plausible that both interpretations are true and the fact that the atomic volume of In is a factor of 2.2 larger than that of Cu plays an important role both for the increased segregation of In under pressure and the diffusion mechanism.

Low-Angle and High-Angle Grain Boundaries in AIN/GaN Layers Grown on (0001) Sapphire by MBE

AbstractAIN buffer and GaN layers grown on (0001) sapphire substrate by molecular beam epitaxy have been analysed by high resolution electron microscopy. They are found to be made of mosaic grains rotated around the c-axis by angles in the range of 0-20°. According to the value of the rotation angle, these boundaries can be classified as low-angle and high-angle grain boundaries. Some of these high-angle grain boundaries correspond to special misorientations which can be described in terms of coincidence site lattice. For one of these grains, the rotated angle is equal to 18.94° that is very close to the coincidence orientation, sigma = 31 with a rotation angle equal to 17.89°. This leads to a new epitaxial relationship (0001)sap// (0001)AIN and [1120]sap//[2130]AIN.