Search results for "Isotropy"

On generalized harmonic fields in domains with anisotropic nonhomogeneous media

1982

Multicenter stability of diffusion tensor imaging measures: a European clinical and physical phantom study.

2011

Diffusion tensor imaging (DTI) detects white matter damage in neuro-psychiatric disorders, but data on reliability of DTI measures across more than two scanners are still missing. In this study we assessed multicenter reproducibility of DTI acquisitions based on a physical phantom as well as brain scans across 16 scanners. In addition, we performed DTI scans in a group of 26 patients with clinically probable Alzheimer's disease (AD) and 12 healthy elderly controls at one single center. We determined the variability of fractional anisotropy (FA) measures using manually placed regions of interest as well as automated tract based spatial statistics and deformation based analysis. The coefficie…

Charge-density analysis of 1-nitroindoline: refinement quality using free R factors and restraints

2011

Nitramines and related N-nitro compounds have attracted significant attention owing to their use in rocket fuel and as explosives. The charge density of 1-nitroindoline was determined experimentally and from theoretical calculations. Electron-density refinements were performed using the multipolar atom formalism. In order to design the ideal restraint strategy for the charge-density parameters, R-free analyses were performed involving a series of comprehensive refinements. Different weights were applied to the charge-density restraints, namely the similarity between chemically equivalent atoms and local symmetry. Additionally, isotropic thermal motion and an anisotropic model calculated by …

Insight into Disrupted Spatial Patterns of Human Connectome in Alzheimer’s Disease via Subgraph Mining

2012

Alzheimer’s disease (AD) is the most common cause of age-related dementia, which prominently affects the human connectome. In this paper, the authors focus on the question how they can identify disrupted spatial patterns of the human connectome in AD based on a data mining framework. Using diffusion tractography, the human connectomes for each individual subject were constructed based on two diffusion derived attributes: fiber density and fractional anisotropy, to represent the structural brain connectivity patterns. After frequent subgraph mining, the abnormal score was finally defined to identify disrupted subgraph patterns in patients. Experiments demonstrated that our data-driven approa…

Discovering Aberrant Patterns of Human Connectome in Alzheimer's Disease via Subgraph Mining

2012

Alzheimer's disease (AD) is the most common cause of age-related dementia, which prominently affects the human connectome. Diffusion weighted imaging (DWI) provides a promising way to explore the organization of white matter fiber tracts in the human brain in a non-invasive way. However, the immense amount of data from millions of voxels of a raw diffusion map prevent an easy way to utilizable knowledge. In this paper, we focus on the question how we can identify disrupted spatial patterns of the human connectome in AD based on a data mining framework. Using diffusion tractography, the human connectomes for each individual subject were constructed based on two diffusion derived attributes: …

Numerical simulation of fibre growth in antitaxial strain fringes

2000

A two-dimensional computer model (‘Fringe Growth’) is used to simulate the incremental growth of crystal fibres in undeformed antitaxial strain fringes. The user can define the shape of a core-object (e.g. a pyrite crystal), the growth velocity and anisotropy of growing crystals, the rotation of fringes and core-object with respect to a horizontal datum and with respect to each other, and the opening velocity of fringes. Growth is simulated by movement of nodes connecting line segments that define the grain boundaries. Modelling results predict that face-controlled strain fringes will grow around smooth core-objects and strain fringes with displacement-controlled and face-controlled fibres …

Fluctuating Interfaces in Liquid Crystals

2008

We review and compare recent work on the properties of fluctuating interfaces between nematic and isotropic liquid-crystalline phases. Molecular dynamics and Monte Carlo simulations have been carried out for systems of ellipsoids and hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface positions (the capillary wave spectrum) has been analyzed. In addition, the capillary wave spectrum has been calculated analytically within the Landau-de Gennes theory. The theory predicts that the interfacial fluctuations can be described in terms of a wave vector dependent interfacial tension, which is anisotropic at small wavelengths (stiff director regime) and becomes isotropic at l…

Strain-induced Shape Anisotropy in Antiferromagnetic Structures

2022

We demonstrate how shape dependent strain can be used to control antiferromagnetic order in NiO Pt thin films. For rectangular elements patterned along the easy and hard magnetocrystalline anisotropy axes of our film, we observe different domain structures and we identify magnetoelastic interactions that are distinct for different domain configurations. We reproduce the experimental observations by modeling the magnetoelastic interactions, considering spontaneous strain induced by the domain configuration, as well as elastic strain due to the substrate and the shape of the patterns. This allows us to demonstrate and explain how the variation of the aspect ratio of rectangular elements can b…

Magnetic anisotropy in Fe/U and Ni/U bilayers

2021

Magnetometry measurements of Fe/U and Ni/U bilayer systems reveal a non-monotonic dependence of the magnetic anisotropy for U thicknesses in the range 0 nm - 8 nm, with the Fe/U bilayers showing a more prominent effect as compared to Ni/U. The stronger response for Fe/U is ascribed to the stronger 3d-5f hybridization of Fe and U. This non-monotonic behaviour is thought to arise from quantum well states in the uranium overlayers. Estimating an oscillation period from the non-monotonic data, and comparing it to Density Functional Theory calculations, we find that wavevector matches to the experimental data can be made to regions of high spectral density in (010) and (100) cuts of the electron…

Enhanced perpendicular magnetocrystalline anisotropy energy in an artificial magnetic material with bulk spin-momentum coupling

2019

We systematically investigate the perpendicular magnetocrystalline anisotropy (MCA) in $\mathrm{Co}\ensuremath{-}\mathrm{Pt}/\mathrm{Pd}$-based multilayers. Our magnetic measurement data show that the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd multilayer samples. We further support this experiment by first-principles calculations on ${\mathrm{CoPt}}_{2}, {\mathrm{CoPd}}_{2}$, and CoPtPd, which are composite bulk materials that consist of three atomic layers in a unit cell, Pt/Co/Pt, Pd/Co/Pd, and Pt/Co/Pd, respectively. By estimating the contribution of bulk spin-momentum coupling to the …