Structural Isotropy Research Articles

Using structural modularity in cocrystals to engineer properties: elasticity

Cocrystal formation of heterocyclic bases with halogenated aromatic acids increases the tendency for stacking and with this, an increase in structural isotropy occurs that leads to crystal elasticity.

Evaluation of structural isotropy of Cr-V ledeburitic steel made by powder metallurgy of rapidly solidified particles

Evaluation of structural isotropy of Cr-V ledeburitic steel made by powder metallurgy of rapidly solidified particles

CytoSpectre: a tool for spectral analysis of oriented structures on cellular and subcellular levels.

BackgroundOrientation and the degree of isotropy are important in many biological systems such as the sarcomeres of cardiomyocytes and other fibrillar structures of the cytoskeleton. Image based analysis of such structures is often limited to qualitative evaluation by human experts, hampering the throughput, repeatability and reliability of the analyses. Software tools are not readily available for this purpose and the existing methods typically rely at least partly on manual operation.ResultsWe developed CytoSpectre, an automated tool based on spectral analysis, allowing the quantification of orientation and also size distributions of structures in microscopy images. CytoSpectre utilizes the Fourier transform to estimate the power spectrum of an image and based on the spectrum, computes parameter values describing, among others, the mean orientation, isotropy and size of target structures. The analysis can be further tuned to focus on targets of particular size at cellular or subcellular scales. The software can be operated via a graphical user interface without any programming expertise. We analyzed the performance of CytoSpectre by extensive simulations using artificial images, by benchmarking against FibrilTool and by comparisons with manual measurements performed for real images by a panel of human experts. The software was found to be tolerant against noise and blurring and superior to FibrilTool when analyzing realistic targets with degraded image quality. The analysis of real images indicated general good agreement between computational and manual results while also revealing notable expert-to-expert variation. Moreover, the experiment showed that CytoSpectre can handle images obtained of different cell types using different microscopy techniques. Finally, we studied the effect of mechanical stretching on cardiomyocytes to demonstrate the software in an actual experiment and observed changes in cellular orientation in response to stretching.ConclusionsCytoSpectre, a versatile, easy-to-use software tool for spectral analysis of microscopy images was developed. The tool is compatible with most 2D images and can be used to analyze targets at different scales. We expect the tool to be useful in diverse applications dealing with structures whose orientation and size distributions are of interest. While designed for the biological field, the software could also be useful in non-biological applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-015-0782-y) contains supplementary material, which is available to authorized users.

Structure and properties of low-carbon steel after twist extrusion

The new developing technologies of metal formation, based on simple shear, are known as severe plastic deformation (SPD) technologies. They are actively used for improving the mechanical properties of metals. Even complex systems such as steels have not been adequately investigated for SPD process. However, studies are in progress as is reflected from the publications in the literature. Due to insufficient knowledge of the structural changes, occurring in low-carbon steels during SPD, there is a need for a more detailed consideration by modern methods. This paper discusses the characteristics of the formation of structure and texture of low-carbon steels subjected to warm twist extrusion (TE). A relatively new method, which makes possible a detailed study of the structure of metals, is electron backscattered diffraction (EBSD). EBSD has shown that warm TE increases the structure isotropy, thus leading to significant fragmentation and activation of the mechanisms of dynamic polygonization, recrystallization and grain-boundary sliding. These structural features lead to hardening of the material by 1·5 times, while maintaining a high level of plasticity.

Isotropic Accelerometer Strapdowns and Related Algorithms for Rigid-Body Pose and Twist Estimation

A novel design of accelerometer strapdown, intended for the estimation of the rigid-body acceleration and velocity fields, is proposed here. The authors introduce the concept of isotropic-polyhedral layout of simplicial biaxial accelerometers (SBA), in which one SBA is rigidly attached at the centroid of each face of the polyhedron. By virtue of both the geometric isotropy of the layout and the structural planar isotropy of the SBA, the point tangential relative acceleration is decoupled from its centripetal counterpart, which is filtered out, along with the angular velocity. The outcome is that the rigid-body angular acceleration can be estimated independent of the angular velocity, thereby overcoming a hurdle that mars the estimation process in current accelerometer strapdowns. An estimation algorithm, based on the extended Kalman filter, is included. Simulation results show an excellent performance of the proposed strapdowns in estimating the acceleration and velocity fields of a moving object along with its pose.

Micro-Computed Tomography Derived Anisotropy Detects Tumor Provoked Deviations in Bone in an Orthotopic Osteosarcoma Murine Model

Radiographic imaging plays a crucial role in the diagnosis of osteosarcoma. Currently, computed-tomography (CT) is used to measure tumor-induced osteolysis as a marker for tumor growth by monitoring the bone fractional volume. As most tumors primarily induce osteolysis, lower bone fractional volume has been found to correlate with tumor aggressiveness. However, osteosarcoma is an exception as it induces osteolysis and produces mineralized osteoid simultaneously. Given that competent bone is highly anisotropic (systematic variance in its architectural order renders its physical properties dependent on direction of load) and that tumor induced osteolysis and osteogenesis are structurally disorganized relative to competent bone, we hypothesized that μCT-derived measures of anisotropy could be used to qualitatively and quantitatively detect osteosarcoma provoked deviations in bone, both osteolysis and osteogenesis, in vivo. We tested this hypothesis in a murine model of osteosarcoma cells orthotopically injected into the tibia. We demonstrate that, in addition to bone fractional volume, μCT-derived measure of anisotropy is a complete and accurate method to monitor osteosarcoma-induced osteolysis. Additionally, we found that unlike bone fractional volume, anisotropy could also detect tumor-induced osteogenesis. These findings suggest that monitoring tumor-induced changes in the structural property isotropy of the invaded bone may represent a novel means of diagnosing primary and metastatic bone tumors.

SU‐E‐J‐201: Correlations Between Mechanical and Structural Anisotropy: A Foundation for Non‐Invasively Assessing Radiation Injury

Purpose: Tour long‐term goal is to develop techniques for evaluating radiation injury based upon mechanical changes to tissue. Here, we study the mechanical response of white matter ex vivo using dynamic shear testing (DST) and indentation testing in an animal model, with the goals of establishing in normal (non‐radiation‐injured) tissue (1) a baseline degree of mechanical anisotropy, and (2) correlations between mechanical and structural anisotropy. Methods: Fresh whole brains were acquired from local slaughter house. White matter samples were dissected and from the central corpus callosum region, while gray matter samples were acquired from temporal region. Dynamic shear testing and indentation testing were applied to both white and gray matter samples. White matter samples were tested in shear with axonal fibers aligned or perpendicular to the shear force direction, and in indentation with the fiber axis parallel or perpendicular to the long side of the indenter head. Gray matter samples were tested in an arbitrary direction and rotated 90 degrees for the second test, for each testing procedure. Shear modulus and indentation stiffness were calculated for each sample. Results: The storage and loss moduli of the white matter samples were significantly larger when the samples were tested with primary axonal fibers aligned with the shearing direction. The indentation stiffness was also significantly higher when indented perpendicular to the fiber direction. No significant differences were observed for gray matter samples for both testing procedures. Conclusion: The results confirm that white matter exhibits larger moduli when stretched or sheared along the fiber direction; mechanical anisotropy correlates with structural anisotropy. The mechanical isotropy observed in gray matter is consistent with the structural isotropy. These results will be useful for investigations of changes in mechanical properties after radiation therapy in cerebral tumor patients, and for numerical modeling of surgery and traumatic brain injury (TBI).

A FIRST APPLICATION OF THE ALCOCK-PACZYNSKI TEST TO STACKED COSMIC VOIDS

We report on the first application of the Alcock-Paczynski test to stacked voids in spectroscopic galaxy redshift surveys.We use voids from the Sutter et al. (2012) void catalog, which was derived from the Sloan Digital Sky Survey Data Release 7 main sample and luminous red galaxy catalogs. The construction of that void catalog removes potential shape measurement bias by using a modified version of the ZOBOV algorithm and by removing voids near survey boundaries and masks. We apply the shape-fitting procedure presented in Lavaux & Wandelt (2012) to ten void stacks out to redshift z=0.36. Combining these measurements, we determine the mean cosmologically induced "stretch" of voids in three redshift bins, with 1-sigma errors of 5-15%. The mean stretch is consistent with unity, providing no indication of a distortion induced by peculiar velocities. While the statistical errors are too large to detect the Alcock-Paczynski effect over our limited redshift range, this proof-of-concept analysis defines procedures that can be applied to larger spectroscopic galaxy surveys at higher redshifts to constrain dark energy using the expected statistical isotropy of structures that are minimally affected by uncertainties in galaxy velocity bias.

Catalytic Activity of the Spinel Ferrite Nanocrystals on the Growth of Carbon Nanotubes

We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe2O4) (ii) ferrite where cobalt was substituted by nickel (NixCo1−xFe2O4, with x=0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (ZnyNi1−yFe2O4 with y=1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the size of grains by field emission scanning electron microscopy images and their magnetic properties by vibrating sample magnetometer. Next, carbon nanotubes were grown on these nanocatalysts by the catalytic chemical vapor deposition method. We show that the catalytic activity of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy, and catalytic activity due to cations. Our study may have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites.

Length-scale dependence of elastic strain from scattering measurements in metallic glasses

Several recent studies have reported that the elastic strain in metallic glasses, as measured from peak shifts in the pair-correlation functions of samples under load, increases with distance from an average atom, approaching the macroscopic strain at large distances. We have verified this behavior using high-energy x-ray scattering on metallic glasses loaded under uniaxial compression, uniaxial tension, and pure shear, and show that the apparent length-scale dependence of elastic strain is not an artifact of the assumption of structural isotropy in the data analysis. Molecular dynamics simulations of a binary Lennard-Jones glass loaded in uniaxial tension reproduce, qualitatively, the behavior observed in the experiments when the elastic strain is calculated from the shifts in the peaks of the pair-correlation function. Under hydrostatic loading, however, the length-scale dependence of elastic strain observed in the simulations is greatly reduced. This suggests that nonaffine atomic displacements, which are smaller under hydrostatic loading than under uniaxial loading, may play a key role in the length-scale dependence of elastic strain. Furthermore, no length-scale dependence is observed in simulations, for either uniaxial or hydrostatic loading, when the elastic strain is calculated from the average local deformation gradient tensor. We explain this apparent contradiction and show that the atomic displacements resulting from elastic loading are largest in the low-density regions between atomic shells around an average atom. Finally, we present an analysis of length-scale dependence of elastic strain calculated from the pair-correlation function for the case of homogeneous deformation, which is in good agreement with the simulations conducted under hydrostatic loading. For uniaxial loading, however, the analysis diverges from both the experimental and simulated results in the first two near-neighbor atomic shells. This suggests, in agreement with our observations from the molecular dynamics simulations, that the observed length-scale dependence of elastic strain from scattering measurements reflects the nature of the nonaffine atomic displacements in the glass.

Experimental study of kaolin particle orientation mechanism

The aim of the experimental study is to analyse the association between the behaviour of a clayey material at the macroscopic level and its local deformation properties. The approach is based on the study of the orientation of the clay particles by scanning electron microscopy picture analysis after different phases of triaxial loading. This leads to a better understanding and characterisation of the relation between the microfabric and the strain mechanisms (i.e. contractancy and dilatancy) observed at the macroscopic level. In the initial state (one-dimensional compression), the observations highlight the microstructural anisotropy of the slightly overconsolidated specimens with a preferential orientation of the particles normal to the loading direction. During isotropic loading, densification of the clayey matrix occurs associated with a re-orientation of the particles, leading to an increase in structural isotropy, indicated by the term ‘depolarisation'. On the triaxial path, up to 5% axial strain, depolarisation is reinforced. A rotation mechanism of the particles then seems to become activated beyond a critical threshold, directly related to the increase in the deviatoric part of the stress tensor.

Interferometry based high-precision dilatometry for dimensional characterization of highly stable materials

We present an optical dilatometer for high-accuracy and high-resolution absolute measurement of the linear coefficient of thermal expansion (CTEl). Based on a highly symmetric differential heterodyne interferometer, dimensional changes of a tubular shaped specimen under controlled thermal conditions can be characterized. Our measurement facility is located in vacuum where the test specimen can be temperature controlled in a temperature range between 20 °C and 60 °C. A thermally stable support and two identical isostatic mirror clamps were specifically designed to fix a reference and a measurement mirror inside the tube enabling a measurement, where no load in the axial direction was applied to the device under test (DUT). We measured the linear CTE of two carbon-fibre reinforced plastic (CFRP) tubes with different predicted linear CTEs at room temperature: −0.647 × 10−6 K−1 and 0 ± 2.5 × 10−9 K−1, respectively. Currently, we are investigating the manufacture limitations of the CFRP and the limitations of our apparatus in terms of measurement accuracy. In the next step, we will characterize a specifically manufactured zero-class Zerodur™ tube with a CTEl value <10 × 10−9 K−1. Due to its high thermal stability and non-directional structural isotropy this material has been chosen for macroscopic calibration of the metrology system. The results of these measurements will thus provide the resolution limitations of our facility and can be taken as an absolute accuracy reference.

Approximate ray tracing for qP-waves in inhomogeneous layered media with weak structural anisotropy

We present approximate equations for qP-wave ray tracing and paraxial ray tracing in inhomogeneous layered weakly transversely isotropic (TI) media. Inside layers, the symmetry axis direction of the TI medium is allowed to vary continuously. Approximate equations are based on perturbation theory in which deviations of anisotropy from isotropy are considered to be first-order quantities. For qP-waves propagating in a TI medium, the approximate ray-tracing and paraxial ray-tracing equations depend on three parameters and two angles defining the direction of the symmetry axis. We also present the boundary conditions at interfaces for first-order rays and paraxial rays and compute reflection/transmission coefficients to the first order. All the quantities required for evaluation of the Green’s function are calculated to the first order, except the traveltime that is calculated to the second order. The accuracy of the presented algorithm is verified on simple models with respect to exact ray-tracing results. For anisotropy of about [Formula: see text], considered in the examples presented, the relative errors in traveltime and amplitude are less than [Formula: see text] and [Formula: see text], respectively. We then consider media where the symmetry axis is conformable with the structure, named structural transverse isotropy (STI). The method is applied to simple STI models and to a realistic overthrust model, showing significant differences with vertical transverse isotropy (VTI) models not only for traveltimes, but also for amplitudes.

Thick and anisotropic D″ layer beneath Antarctic Ocean

Waveform modeling and travel times analyses of S, ScS and SKS phases recorded at the broad‐band permanent station SYO in the Antarctic are used to determine the shear wave velocity structure and transverse isotropy in the D″ layer beneath the Antarctic Ocean. The SH wave structure has a discontinuity with the velocity increase of 2.0% at 2550 km. The SV structure is similar to PREM model. The magnitude of the anisotropy is highest at the top of D″ layer and lowest at the core‐mantle boundary. The D″ layer beneath the Antarctic Ocean is significantly thicker than those beneath Alaska and the Caribbean Sea. We attribute this anisotropic D″ layer to paleo‐slab materials. The subduction in and around the Antarctic Ocean has started ∼180 Ma and is the one of the oldest in the world. It has provided a large amount of the slab materials in the lowermost mantle.

Advanced characterization of ultra-low-k periodic porous silica films – pore size distribution, pore-diameter anisotropy, and size and macroscopic isotropy of domain structure

AbstractWe have shown previously the results from out-of-plane and in-plane X-ray scattering /diffraction measurements together with transmission electron microscope and X-ray reflectance measurements and shown that they are effective in characterization of a periodic porous silica low-k film [1]. In the present work, we report the results on pore-size distribution, pore-diameter anisotropy, and size and macroscopic isotropy of domain structure.

Control of structure and optical anisotropy in porous Si by magnetic-field assisted anodization

The effects of an applied magnetic field during anodization on the structural and optical isotropy of luminescent porous silicon (PS) are investigated. The PS layers are prepared by anodizing p-type Si wafers in HF solutions with an external magnetic field of 0–1.7 T applied perpendicular to the Si surface. It is shown that the photoluminescence intensity of PS significantly increases with increasing magnetic field. This effect is accompanied by an increase in both the porosity and the optical isotropy without affecting the surface chemical composition. The structural uniformity in the PS layer and at the PS-substrate interface are also improved. These results suggest that an external magnetic field during anodization regulates the supply of holes from the substrate and produces well-controlled optical and structural properties of PS.

An Insight into the Characteristics of a Nucleation Catalyst in CFC-Free Rigid Foam Systems

The establishment of CFC-free polyurethane foam systems, aimed at total CFC elimination by the year 1995, is of paramount importance in the present day polyurethane foam technology. Especially in rigid foam systems, the attempts to apply a variety of alternative blowing agents such as HCFC-22, -141b, and -142b, HFC-134a and -356, and hydrocarbons such as n-pentane, isopentane and cyclopentane, as well as all-water blown systems, are being examined. In all cases of alternative blown systems, however, there exist differences in foaming behavior as well as inferior foam properties compared to traditional CFC-11 blown systems. Especially in HCFC-141b and cyclopentane blown systems, which have gained the greatest interest among the above-mentioned options, the following three subjects are of major concern. The requirements involved in achieving the resolution of these problems are dependent not only on the development of major raw materials but also on the selection of suitable auxiliary intermediates such as catalysts and foam stabilizers. (1) Thermal Conductivity; HCFC-141b, cyclopentane and carbon dioxide, which is generated from the reaction of water and isocyanate, have high thermal conductivity compared to CFC-11, thereby causing inferior insulation performance of the foam. Fine cell technology is now being examined in order to improve the thermal conductivity. For the achievement of the fine cell structure, the selection of suitable amine catalyst systems is important, although the effect of foaming stabilizers has an especially large contribution. (2) Dimensional Stability; not only in all-water blown systems, but also in HCFC-141b and cyclopentane blown systems which use water in high concentration, dimensional stability becomes a large problem due to the diffusion of carbon dioxide gas from the foam cell. For the improvement of dimensional stability, there exists the option to increase the foam strength; moreover, it is important to improve the isotropy of cell structure by adjusting amine catalyst systems. (3) Foam density; since 141b and cyclopentane have relatively higher boiling points and less blowing efficiency, lowering the foam density becomes rather difficult. Moreover, lower foam density normally provides poor dimensional stability. It can be said that the catalytic activity ratio in blowing/gelling of amine catalysts play an important role for the lowering of foam density with improved dimensional stability. It is very difficult to improve these three factors simultaneously. In this report, however, the improvements of these subjects are discussed from a standpoint of amine catalysts; also special newly developed nucleation catalyst systems are introduced for cyclopentane and HCFC-141b blown systems.

Fine-Scale Structure of High-Reynolds-Number Turbulence.

Fine-scale structure and local isotropy were experimentally investigated for turbulence fields of turbulence Reynolds numbers of Rλ=80∼393. Waveform analysis was performed for velocity fluctuations independently in the low wavenumber range, the inertial subrange and the viscous dissipation range and also for the time derivative of the velocity fluctuations. For Rλ>200, the turbulence fluctuations were random in the low wavenumber range but intermittent in the other two wavenumber ranges. Probability density analysis showed that the flatness factor was about 3 in the low wavenumber range and the intermittency was stronger in the viscous dissipation range that in the inertial subrange. The flatness factor of the time derivative of the velocity fluctuations monotonically increased with Rλ and reached about 7.08 at Rλ=393. We introduced the anisotropic tensor spectrum. The scale of the maximum isotropic eddy, lG, determined the upper limit of the inertial subrange where the turbulence eddies smaller than lG attained local isotropy and universal equilibrium in the energy cascade process.

The response of isotropic turbulence to isotropic and anisotropic forcing at the large scales

The nonlinear interscale couplings in a turbulent flow are studied through direct numerical simulations of the response of isotropic turbulence to isotropic and anisotropic forcing applied at the large scales. Specifically, forcing is applied to the energy-containing wave-number range for about two eddy turnover times to fully developed isotropic turbulence at Taylor-scale Reynolds number 32 on an 1283 grid. When forced isotropically, the initially isotropic turbulence remains isotropic at all wave numbers. However, anisotropic forcing applied through an array of counter-rotating rectilinear vortices induces high levels of anisotropy at the small scales. At low wave numbers the force term feeds energy directly into two velocity components in the plane of the forced vortices. In contrast, at high wave numbers the third (spanwise) component receives the most energy, producing small-scale anisotropy very different from that at the large scales. Detailed analysis shows that the development of small-scale anisotropy is caused primarily by nonlocal wave-vector triads with one leg in the forced low-wave-number range. This latter result is particularly significant because asymptotic analysis of the Fourier-transformed Navier–Stokes equations shows that distant triadic interactions coupling the energy-containing and dissipative scales persist at asymptotically high Reynolds numbers, suggesting that the structural couplings between large and small scales in these moderate Reynolds number simulations would also exist in high Reynolds number forced turbulence. The results therefore imply a departure from the classical hypothesis of statistical independence between large- and small-scale structure and local isotropy.

A quantitative method for the estimation of the degree of uniformity and isotropy of the structures of the central nervous system in cytoarchitectonic preparations

The statistical method for the estimation of the degree of uniformity and isotropy of structures in brain sections proposed in this paper allows integral estimates to be made of the character of the distribution of nerve cells during the formation of the central nervous system. The method is convenient to work with in photomicrographs. Automatic computerized counting of cell elements takes little time and involves a minimum of images.