Coherence Of Orientation Research Articles

Anisotropic structure of the central North American Craton surrounding the Mid-Continent Rift: Evidence from Rayleigh waves

The subsurface of the central North American Craton has been imaged by body-, surface-, and full-waveform studies at varying resolutions. These studies offer tantalizing clues about the evolution of Archean and Proterozoic lithosphere. The oldest cratonic lithosphere may have been formed under a different or pre-plate-tectonic regime and, in this region, was later modified by orogenesis around the edges, hotspot passage, rifting and magmatism. We improve the resolution of seismic imaging across the Great Lakes region of North America by carrying out two-station phase velocity dispersion measurements at selected station pairs and inverting them for anisotropic phase velocity maps at periods 20–200 s. We also perform extensive resolution tests to identify robust features in the data. Isotropic features to note are the strong signatures of the Trans-Hudson Orogen, Superior Craton, and Mid-Continent Rift (MCR) at periods most sensitive to the lower crust and uppermost mantle, relatively low velocities near the Great Lakes region at periods most sensitive to the middle lithosphere, and extremely fast velocities in the western Superior at long periods, corresponding to the lowermost cratonic lithosphere. We note a strong contrast in seismic anisotropy across the MCR, with strong anisotropy to the north and weaker anisotropy to the south at shorter periods, consistent with observations from other data types and studies. Fast orientations are heterogeneous within the Superior craton at intermediate periods. At periods ⩾160 s, an increase in magnitude of the anisotropy, and coherence of the fast orientation, suggest an asthenospheric contribution to the signal.

Who’s the realest?

The revival of interest in realism in political theory is comprehensively explored in Politics Recovered, a major new volume of 14 original essays edited by Matt Sleat. Wide-ranging and engaging throughout, the book takes in both supporters and critics of the realist turn and addresses neglected questions of the political application of realism and of the connection between contemporary political realism and the classical IR tradition of realist thought. But I argue that the book also prompts some troubling questions about the ultimate coherence of the realist orientation and about the way in which realists interpret the limits of political theory and of political theorists.

Ideological Inconsistencies on the Left and Right as a Product of Coherence of Preferences for Values. The Case of Poland

Abstract The terms ‘left’ and ‘right’ cannot describe two extremes of a single ideological dimension. Instead, a bi-dimensional model including socio-cultural and socio-economic facets of leftism/rightism is postulated. Several studies conducted in the USA and Western Europe show a relative coherence of left-wing and right-wing orientation regarding both dimensions, whereas very diverse patterns can be found in the countries of Eastern Europe. In Poland cultural and economic leftism-rightism seem to be clearly negatively related. The general hypothesis in this paper claims that such ideological inconsistency is a product of coherence at the level of preferences for values, i.e. covariance within individualistic (Openness to change and Self-enhancement) as well as within collectivist values (Conservation and Self-transcendence). Based on a survey study (N = 750) conducted on a representative sample of Poles, it was shown that preferences for values made up two distinct dimensions: Openness to change vs Conservation, and Self-enhancement vs Self-transcendence. They are positively related but have fundamentally different relationships with political self-identification and ideology.

Evaluation of Coarse Aggregate in Cold Recycling Mixes Using X-Ray CT Scanner and Image Analysis

Abstract The performance of cold recycling (CR) mixtures has been widely evaluated, but these studies rarely focused on the internal structure of CR mixtures. The objective of this research is to investigate the distribution, orientation, and shape properties of coarse aggregates in CR mixtures with emulsion by processing a series of sectional images from an X-ray CT scanner. The uniformity index (UI) was derived to describe the distribution of coarse aggregates. The aggregate orientation was obtained by calculating the average angle of inclination θ and the coherence of orientation Δ. The morphological indices, such as the flat and elongated ratio (FER), angularity index (AI), and surface texture index (STI) were used to address the shape properties of CR mixtures. According to the results, the distribution uniformity of CR aggregates becomes worse with coarser gradation. Compaction methods significantly influence the aggregate orientation in CR mixtures. The superpave gyratory compaction (SGC) method makes the best coherence of aggregate orientation, but the static load compacted specimen shows the opposite result. The CR mix tends to have worse uniformity of aggregate distribution, larger angle of aggregate inclination, and more random aggregate orientation compared with the HMA mix. It is estimated that more crushed faces of aggregates are produced in the process of pavement milling and the surface texture of RAP materials decreases with the long-term effects of traffic loading and environment. Adding new coarse aggregates to CR mixtures disturbs the aggregate distribution, but it can improve the average surface texture of aggregates in CR mixtures.

Structured sparsity for spatially coherent fibre orientation estimation in diffusion MRI

We propose a novel formulation to solve the problem of intra-voxel reconstruction of the fibre orientation distribution function (FOD) in each voxel of the white matter of the brain from diffusion MRI data. The majority of the state-of-the-art methods in the field perform the reconstruction on a voxel-by-voxel level, promoting sparsity of the orientation distribution. Recent methods have proposed a global denoising of the diffusion data using spatial information prior to reconstruction, while others promote spatial regularisation through an additional empirical prior on the diffusion image at each q-space point. Our approach reconciles voxelwise sparsity and spatial regularisation and defines a spatially structured FOD sparsity prior, where the structure originates from the spatial coherence of the fibre orientation between neighbour voxels. The method is shown, through both simulated and real data, to enable accurate FOD reconstruction from a much lower number of q-space samples than the state of the art, typically 15 samples, even for quite adverse noise conditions.

Age‐related differences in multiple measures of white matter integrity: A diffusion tensor imaging study of healthy aging

Diffusion tensor imaging (DTI) measures diffusion of molecular water, which can be used to calculate indices of white matter integrity. Early DTI studies of aging primarily focused on two global measures of integrity; the average rate (mean diffusivity, MD) and orientation coherence (fractional anisotropy, FA) of diffusion. More recent studies have added measures of water movement parallel (axial diffusivity, AD) and perpendicular (radial diffusivity, RD) to the primary diffusion direction, which are thought to reflect the neural bases of age differences in diffusion (i.e., axonal shrinkage and demyelination, respectively). In this study, patterns of age differences in white matter integrity were assessed by comparing younger and healthy older adults on multiple measures of integrity (FA, AD, and RD). Results revealed two commonly reported patterns (Radial Increase Only and Radial/Axial Increase), and one relatively novel pattern (Radial Increase/Axial Decrease) that varied by brain region and may reflect differential aging of microstructural (e.g., degree of myelination) and macrostructural (e.g., coherence of fiber orientation) properties of white matter. In addition, larger age differences in FA in frontal white matter were consistent with the anterior-posterior gradient of age differences in white matter integrity. Together, these findings complement other recent studies in providing information about patterns of diffusivity that are characteristic of healthy aging.

Visualization of the coherence of the principal diffusion orientation: An eigenvector-based approach

A novel method for spatially mapping anisotropy/orientation coherence of the eigenvector is presented. By using an eigenvector-based approach, an intervoxel diffusion coherence (IVDC) index was used to quantify the coherence of the principal diffusion directions within a voxel neighborhood. This method may allow reconstruction of a whole brain map to be used for diagnostic purposes. The IVDC index is calculated by a scatter matrix-based method in a voxel-wise manner. A simulation was performed using two fiber populations crossing at various separation angles. We demonstrate that the IVDC index was more sensitive than fractional anisotropy (FA) to changes in separation between the fibers under a noise-free condition. Diffusion-tensor images of six healthy volunteers were acquired on a 3.0T MR imager. The FA, coherence index, and IVDC were then calculated. The results showed that IVDC improved the contrast in several brain areas including thalamus, middle cerebral peduncle, and pons. We therefore conclude that the IVDC index provides reliable and complementary information on water diffusion in the brain. It may be useful in white matter tractography, especially to determine the termination point of a trajectory.

Bayesian image segmentation using local iso-intensity structural orientation

Image segmentation is a fundamental problem in early computer vision. In segmentation of flat shaded, nontextured objects in real-world images, objects are usually assumed to be piecewise homogeneous. This assumption, however, is not always valid with images such as medical images. As a result, any techniques based on this assumption may produce less-than-satisfactory image segmentation. In this work, we relax the piecewise homogeneous assumption. By assuming that the intensity nonuniformity is smooth in the imaged objects, a novel algorithm that exploits the coherence in the intensity profile to segment objects is proposed. The algorithm uses a novel smoothness prior to improve the quality of image segmentation. The formulation of the prior is based on the coherence of the local structural orientation in the image. The segmentation process is performed in a Bayesian framework. Local structural orientation estimation is obtained with an orientation tensor. Comparisons between the conventional Hessian matrix and the orientation tensor have been conducted. The experimental results on the synthetic images and the real-world images have indicated that our novel segmentation algorithm produces better segmentations than both the global thresholding with the maximum likelihood estimation and the algorithm with the multilevel logistic MRF model.

Representations of PolycrystallineMicrostructure by n‐Point Correlation Tensors

An important class of representations of polycrystalline microstructure consists of the n‐point correlation tensors. In this paper the representation theory of groups is applied to a consideration of symmetries in the n‐point correlation tensors. Three sources of symmetry are included in the development: indicial symmetry in the coefficients of tensors, symmetry associated with the crystal lattice, and statistical symmetries in the microstructure induced by processing. The central problem discussed here is the “residence space”, or the space of minimum dimension occupied by correlation tensors possessing such symmetries. In addition to the general case of correlation tensors possessing such symmetries, a model microstructure is also considered which embodies an assumption of no spatial coherence of lattice orientation between neighboring grains or crystallites. It is shown that the model microstructure generally results in residence spaces of lower dimension.

A statistical theory of creep in polycrystalline materials

Estimates for the properties of creeping polycrystals, which exhibit a power-law dependence of the stress on the strain-rate, are derived in the framework of statistical continuum theory. A creep modulus is obtained which incorporates n-point statistics for the spatial coherence of lattice orientation. For uniform boundary conditions and statistically homogeneous microstructures the modulus is shown to have local character. A hierarchy of mean field approximations enables estimates for the evolution of n-point statistical measures of the microstructure. Numerical implementation of the theory for isotropic face-centered-cubic polycrystals, incorporating two-point statistics of lattice orientation, results in substantial softening of the tensile reference stress relative to the Taylor-like uniform strain-rate upper-bound and the self-consistent estimate. Comparisons of the initial flow for the tensile axis show that estimates incorporating two-point statistics reduce the rate of rotation of the tensile axis over a significant area-fraction of the stereographic projection.