Quantitative Analysis Of Microstructure Research Articles

Application of the radial distribution functions for quantitative analysis of neuropil microstructure in stratum radiatum of CA1 region in hippocampus

Various structures in the brain contain important clues to the brain’s development and function. Among these, the microscopic organization of neural tissue is of particular interest since such organization directly affects the formation of local synaptic connectivity between axons and dendrites, serving as a potential factor in the brain’s development. While the organization of the brain at large and intermediate lengths had been well studied, the organization of neural tissue at scales of micrometers remains largely unknown. In particular, at present it is not known what specific structures exist in neuropil at those scales, what effect such structures have on the formation of synaptic connectivity in the brain, and what processes shape the small-scale organization of neuropil. In this work, we present an analysis of recent 3D electron microscopy reconstructions of blocks of tissue of hippocampal CA1 neuropil from rat s. radiatum to offer new insights into these questions. We propose a new statistical method for systematical analysis of the small-scale organization of neuropil, based on an adaptation of the approach of radial distribution functions from statistical physics. Our results show that the micrometer-scale organization of hippocampal CA1 neuropil can be well understood as a disordered arrangement of axonal and dendritic processes without significant small-scale coordination. We observe several deviations from this picture in the distributions of glia and dendritic spines, and discuss their significance. Finally, we shed some light on the relationship between the small-scale organization of neuropil and local synaptic connectivity.

Acute stress alters autonomic modulation during sleep in women approaching menopause

Hot flashes, hormones, and psychosocial factors contribute to insomnia risk in the context of the menopausal transition. Stress is a well-recognized factor implicated in the pathophysiology of insomnia; however the impact of stress on sleep and sleep-related processes in perimenopausal women remains largely unknown. We investigated the effect of an acute experimental stress (impending Trier Social Stress Task in the morning) on pre-sleep measures of cortisol and autonomic arousal in perimenopausal women with and without insomnia that developed in the context of the menopausal transition. In addition, we assessed the macro- and micro-structure of sleep and autonomic functioning during sleep. Following adaptation to the laboratory, twenty two women with (age: 50.4±3.2 years) and eighteen women without (age: 48.5±2.3 years) insomnia had two randomized in-lab overnight recordings: baseline and stress nights. Anticipation of the task resulted in higher pre-sleep salivary cortisol levels and perceived tension, faster heart rate and lower vagal activity, based on heart rate variability measures, in both groups of women. The effect of the stress manipulation on the autonomic nervous system extended into the first 4h of the night in both groups. However, vagal tone recovered 4–6h into the stress night in controls but not in the insomnia group. Sleep macrostructure was largely unaltered by the stress, apart from a delayed latency to REM sleep in both groups. Quantitative analysis of non-rapid eye movement sleep microstructure revealed greater electroencephalographic (EEG) power in the beta1 range (15–≤23Hz), reflecting greater EEG arousal during sleep, on the stress night compared to baseline, in the insomnia group. Hot flash frequency remained similar on both nights for both groups. These results show that pre-sleep stress impacts autonomic nervous system functioning before and during sleep in perimenopausal women with and without insomnia. Findings also indicate that women with insomnia had increased EEG arousal and lacked recovery in vagal activity across the stress night suggesting a greater sensitivity to stress in this group.

Synthesis and structural study of a self-organized MnTiO3–TiO2 eutectic

A microstructured manganese titanate – titanium dioxide, MnTiO3–TiO2, hybrid eutectic has been grown by the micro-pulling-down method from a TiO2 57 mol.% – MnO 43 mol.% composition. X-ray powder diffraction verifies that two phases have been formed: rhombohedral MnTiO3 and tetragonal TiO2. The TiO2 phase forms a three-dimensional network of micron-scale oval precipitates interconnected with c.a. 0.5 μm in thickness lamellas and the MnTiO3 is the matrix phase. The two TiO2 precipitate types grow in different crystallographic orientations, which results in this complex geometry made of faceted and non-faceted inclusions. The lamellas grow in the [010] orientation in which a 2-fold axis is present, while the oval precipitates grow in the [001] orientation in which the 4-fold screw axis is present. A qualitative and quantitative analysis of the eutectic microstructure is presented. The MnTiO3–TiO2composite is interesting due to its potential application in photoelectrochemistry.

Automatic quantitative analysis of microstructure of ductile cast iron using digital image processing

Ductile cast iron is preferred as nodular iron or spheroidal graphite iron. Ductile cast iron contains graphite in form of discrete nodules and matrix of ferrite and perlite. In order to determine the mechanical properties, one needs to determine volume of phases in matrix and nodularity in the microstructure of metal sample. Manual methods available for this, are time consuming and accuracy depends on expertize. The paper proposes a novel method for automatic quantitative analysis of microstructure of Ferritic Pearlitic Ductile Iron which calculates volume of phases and nodularity of that sample. This gives results within a very short time (approximately 5 sec) with 98% accuracy for volume phases of matrices and 90% of accuracy for nodule detection and analysis which are in the range of standard specified for SG 500/7 and validated by metallurgist.

Quantitative analysis of microstructure and deformation mechanisms during isothermal compression of Ti–5Al–5Mo–5V–1Cr–1Fe alloy

The effects of the processing parameters on the grain size and volume fraction of equiaxed α for Ti–5Al–5Mo–5V–1Cr–1Fe are quantitatively investigated using isothermal compression tests. The microstructure features, such as the morphology of equiaxed and acicular α phase, the dislocation distribution, the formation of substructure are in depth discussed with the help of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) experiments so as to clarify the deformation mechanisms. The results show that few DRX α grains appear in the α+β phase region. In the β phase region, selective DRX occurs and the amount of DRX increases with increasing strain rate. DRV is main softening mechanism in the tested deformation temperature range. The elongated β grains are observed at medium deformation temperatures and lower strain rates. This phenomenon demonstrates that β phase is mainly involved in the deformation. At higher deformation temperatures and lower strain rates, acicular α is not observed for this alloy. Possible reason is that acicular α dissolves into the β matrix.

Quantitative analysis of three-dimensional fibrillar collagen microstructure within the normal, aged and glaucomatous human optic nerve head.

The aim of this study was to quantify connective tissue fibre orientation and alignment in young, old and glaucomatous human optic nerve heads (ONH) to understand ONH microstructure and predisposition to glaucomatous optic neuropathy. Transverse (seven healthy, three glaucomatous) and longitudinal (14 healthy) human ONH cryosections were imaged by both second harmonic generation microscopy and small angle light scattering (SALS) in order to quantify preferred fibre orientation (PFO) and degree of fibre alignment (DOFA). DOFA was highest within the peripapillary sclera (ppsclera), with relatively low values in the lamina cribrosa (LC). Elderly ppsclera DOFA was higher than that in young ppsclera (p < 0.00007), and generally higher than in glaucoma ppsclera. In all LCs, a majority of fibres had preferential orientation horizontally across the nasal–temporal axis. In all glaucomatous LCs, PFO was significantly different from controls in a minimum of seven out of 12 LC regions (p < 0.05). Additionally, higher fibre alignment was observed in the glaucomatous inferior–temporal LC (p < 0.017). The differences between young and elderly ONH fibre alignment within regions suggest that age-related microstructural changes occur within the structure. The additional differences in fibre alignment observed within the glaucomatous LC may reflect an inherent susceptibility to glaucomatous optic neuropathy, or may be a consequence of ONH remodelling and/or collapse.

Quantitative Analysis of Heterogeneous Microstructure and Diversified Strengthening Mechanisms in Spark Plasma Sintered Molybdenum Disilicide

Molybdenum disilicide (MoSi2) was in situ synthesized by spark plasma sintering into fully dense bulk material. Electron backscatter diffraction revealed that over the range from the center to periphery of the cylindrical sample, the microstructure is heterogeneously constituted by gradually refined MoSi2 grains and increasing amounts of Mo5Si3 impurity phase. The diversified strengthening mechanisms are primarily attributed to the Peierls–Nabarro stress in MoSi2 matrix, the Hall–Petch strengthening effect, and thermal mismatch stress between Mo5Si3 and MoSi2.

On control of flow instabilities in cutting of metals

Large strain plastic flow in cutting of metals is studied at multiple length scales using high-speed imaging and marker techniques, complemented by particle image velocimetry and electron microscopy. Quantitative analysis of streak-lines, strain fields and microstructure, shows the flow to be often unsteady. Instabilities such as segmentation driven by ductile fracture, vortex-like flow in ductile metals, and shear banding in low-thermal diffusivity systems are elucidated using direct observations. A constrained-cutting process is demonstrated for suppressing the instabilities and unsteady flow.

Influence of Mixing Parameters on Homogeneity of Al/Sic Composites/ Wpływ Parametrów Mieszania Na Jednorodność Kompozytów Al/Sic

Abstract The main aim of this work was to study the effect of time and method of Al, SiC powders mixing on the microstructure and mechanical properties of composites. Moreover, the influence of applicating direct extrusion with a reversibly rotating die on the homogeneity of the composites was examined. Microstructure observations with the use of an optical microscope and scanning electron microscope were applied. A quantitative analysis of composite microstructure was conducted. The density (helium pycnometer method), Vickers hardness and the Young’s Modulus of the composites were also determined. The results show that the homogeneity of Al/SiC composites rises with an increase of mixing time. However, better results were obtained by application of high energy ball milling process.

Laser beam welding of aluminum to Al-base coated high-strength steel 22MnB5

The microstructure of aluminum—Al-coated steel laser beam welding joints was analyzed with respect to the welding energy. Quantitative and qualitative analysis of the welding microstructure were used to measure the weld width as well as the thickness of the resulting intermetallic layer at the 22MnB5/aluminum interface in relation to the welding parameters. Weldability of Al-coated steel could be improved by removing brittle coating particles and oxides on the steel surface by sandblasting. Adhesion of aluminum filler material to the 22MnB5 steel sheet could be enhanced by inductive preheating of the steel surface during laser welding. This produced welded 22MnB5/aluminum joints that exhibited a linear mechanical resistance of 220MPa and which failed away from the brittle intermetallic layer on the aluminum side under a tensile load. The shear strength of the intermetallic layer on the 22MnB5/aluminum interface was evaluated to 74±21MPa.

Quantitative analysis of brain microstructure following mild blunt and blast trauma

We induced mild blunt and blast injuries in rats using a custom-built device and utilized in-house diffusion tensor imaging (DTI) software to reconstruct 3-D fiber tracts in brains before and after injury (1, 4, and 7 days). DTI measures such as fiber count, fiber length, and fractional anisotropy (FA) were selected to characterize axonal integrity. In-house image analysis software also showed changes in parameters including the area fraction (AF) and nearest neighbor distance (NND), which corresponded to variations in the microstructure of Hematoxylin and Eosin (H&E) brain sections. Both blunt and blast injuries produced lower fiber counts, but neither injury case significantly changed the fiber length. Compared to controls, blunt injury produced a lower FA, which may correspond to an early onset of diffuse axonal injury (DAI). However, blast injury generated a higher FA compared to controls. This increase in FA has been linked previously to various phenomena including edema, neuroplasticity, and even recovery. Subsequent image analysis revealed that both blunt and blast injuries produced a significantly higher AF and significantly lower NND, which correlated to voids formed by the reduced fluid retention within injured axons. In conclusion, DTI can detect subtle pathophysiological changes in axonal fiber structure after mild blunt and blast trauma. Our injury model and DTI method provide a practical basis for studying mild traumatic brain injury (mTBI) in a controllable manner and for tracking injury progression. Knowledge gained from our approach could lead to enhanced mTBI diagnoses, biofidelic constitutive brain models, and specialized pharmaceutical treatments.

A synchrotron-based local computed tomography combined with data-constrained modelling approach for quantitative analysis of anthracite coal microstructure.

Quantifying three-dimensional spatial distributions of pores and material compositions in samples is a key materials characterization challenge, particularly in samples where compositions are distributed across a range of length scales, and where such compositions have similar X-ray absorption properties, such as in coal. Consequently, obtaining detailed information within sub-regions of a multi-length-scale sample by conventional approaches may not provide the resolution and level of detail one might desire. Herein, an approach for quantitative high-definition determination of material compositions from X-ray local computed tomography combined with a data-constrained modelling method is proposed. The approach is capable of dramatically improving the spatial resolution and enabling finer details within a region of interest of a sample larger than the field of view to be revealed than by using conventional techniques. A coal sample containing distributions of porosity and several mineral compositions is employed to demonstrate the approach. The optimal experimental parameters are pre-analyzed. The quantitative results demonstrated that the approach can reveal significantly finer details of compositional distributions in the sample region of interest. The elevated spatial resolution is crucial for coal-bed methane reservoir evaluation and understanding the transformation of the minerals during coal processing. The method is generic and can be applied for three-dimensional compositional characterization of other materials.

Effect of Critical Void Volume Fraction f&lt;sub&gt;F&lt;/sub&gt; on Results of Ductile Fracture Simulation for S235JR Steel under Multi-Axial Stress States

The article describes an example of the GTN material model parameters determination and application. The main objective of the study was to determine experimentally the value of the critical volume fraction of voids fFfor S235JR steel and to assess the impact of this parameter on the numerical force-elongation curve under the multi-axial stress state. Value of fFwas obtained by the quantitative analysis of the material microstructure at fracture surfaces. For a sake of comparison, two other values of fF, described in the literature, were also used in numerical simulations.

The Quality of Produced Sand-Cast Engine Block Made from Elektron 21 Magnesium Alloy

The casting defects, microstructure and hardness of Elektron 21 Mg sand casting alloy was investigated. Visual and radiographic examination showed the presence of non-metallic inclusions and porosity. Quantitative analysis of microstructure was performed, no correlation between section thickness, grain size, volume fraction of eutectic areas and hardness was observed. Casting defects were responsible for cracking at magnesium casting/steel tube interface.

Quantitative Analysis of Microstructure in Low Carbon Steel after Thermomechanical Process in (α+γ) Region

Abstract This paper presents results of quantitative analysis of ferrite grains in low carbon steel C15V with microalloying addition of vanadium. Thermomechanical treatment in the intercritical (α+γ) region was performed using the dilatometer DIL805A. On the basis of dilatometric researches the critical temperatures of α ↔ γ transformation for C15V steel during heating with v5−8=0.5 K/s and cooling with v8−5=1 K/s were estimated. The steel deformation was carried out with application of two different variants: deformation in (α+γ) region after cooling from full austenitization temperature and deformation in (α+γ) region after heating from ambient temperature (ferritic-bainitic microstructure). The effects of these treatments were observed by means of a light optical microscope in bright and polarized field. The quantitative analysis of microstructure was investigated using Image Pro Plus (IPP) program. Characteristic parameters for ferrite grains such as: field area, average diameter, shape factor were estimated. For each of these parameters, histograms and maps of average grain diameter distribution were performed using STATISTICA 9 and IPP programs. It was observed that deformation in the intercritical range (α+γ) promotes the occurrence of many ferrite nucleus in the obtained structures, especially at grain boundaries. For low carbon steel this results in formation of very fine microstructure.

Quantitative Analysis of Soft Soil Microstructure in Unloading Levels

Quantitative analysis of soft soil microstructure in unloading levels are made by using scanning electron microscope (SEM) images, IPP and PS of image technology ,which includes image segmentation, pore size measuring and counting, three dimensional simulation of soft soil microstructure, etc. The results indicate that, with the increase of unloading grade, pore number and area of big aperture are in a sharp increase, the corresponding porosity also in ascension, so the deformation of the soil is mainly due to the change of pore; compared with the apparent 3d images of soil under the transverse profile in unloading levels. The results also indicate that, with the increase of unloading grade, pore area of cross section are in a increase.

Quantitative Analysis of Ductile Iron Microstructure – A Comparison of Selected Methods for Assessment

Abstract Stereological description of dispersed microstructure is not an easy task and remains the subject of continuous research. In its practical aspect, a correct stereological description of this type of structure is essential for the analysis of processes of coagulation and spheroidisation, or for studies of relationships between structure and properties. One of the most frequently used methods for an estimation of the density Nv and size distribution of particles is the Scheil - Schwartz - Saltykov method. In this article, the authors present selected methods for quantitative assessment of ductile iron microstructure, i.e. the Scheil - Schwartz - Saltykov method, which allows a quantitative description of three-dimensional sets of solids using measurements and counts performed on two-dimensional cross-sections of these sets (microsections) and quantitative description of three-dimensional sets of solids by X-ray computed microtomography, which is an interesting alternative for structural studies compared to traditional methods of microstructure imaging since, as a result, the analysis provides a three-dimensional imaging of microstructures examined.

Effect of density and pore morphology on fatigue properties of sintered Ti–6Al–4V

The fatigue properties of sintered Ti–6Al–4V were investigated as a function of sintered density and pore morphology. A quantitative analysis of microstructure was conducted to correlate with tensile and fatigue properties to understand the influence of sintered density and pore morphology. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests were conducted using two alloys with different sintered densities (95% and 99%). It was found that there was no significant difference in tensile strength but the fatigue endurance limit was increased by 20% when the sintered density was increased from 95% to 99%. Fracture surface analysis indicated that the fatigue cracks initiated from clusters of pores either at the surface or at the near sub-surface. The effect of pore morphology and porosity on mechanical behavior and fatigue fracture of P/M Ti–6Al–4V was quantified using the pore shape factor. It was found that specimens with a higher pore shape factor had a higher fatigue endurance limit.

Microstructural Aspect of Ageing Process of GP91 Cast Steel

The microstructure of 9% Cr cast steel for advanced power plants, serviced at around 580 − 600°C, after ageing has been characterized. The investigated cast steel was subject to ageing at the temperature of 600°C for 6000 and 8000 hrs. Quantitative TEM analysis of the cast steel microstructure was performed to describe the dislocation density within subgrains, the width of martensite subgrains and the M23C6 carbides parameters (shape and mean diameter). Moreover, the phase identification was carried out using electron diffraction. The results have shown that an increase in ageing time at 600°C temperature is the reason for slight increase in the subgrain size, the size of M23C6 carbides and a decrease in dislocation density within subgrains. The MX particle size was not changed. The Laves phase was identified in the cast steel microstructure after 6000 hrs of ageing.

In situ observation of syntactic foams under hydrostatic pressure using X-ray tomography

Syntactic foams (hollow glass microspheres embedded in a polymeric matrix) are being used increasingly for the purpose of thermal insulation in ultradeep water. A better understanding of the damage mechanisms of these materials at the microsphere scale under such a hydrostatic loading condition is of prior importance in determining actual material limits, improving phenomenological modelling and developing novel formulations in the future. To achieve this goal, a study based on X-ray microtomography was performed on two syntactic foam materials (polypropylene and polyurethane matrix) and a standard foamed PP. A special set up has been designed in order to allow the X-ray microtomographic observation of the material during hydrostatic pressure loading using ethanol as the pressure fluid. Spatial resolution of (3.5μm)3 and in situ non-destructive scanning allowed a unique qualitative and quantitative analysis of the composite microstructure during stepwise isotropic compression by hydrostatic pressure up to 50MPa. The collapse of weaker microspheres were observed during pressure increase and the damage parameters could be estimated. It is shown that the microspheres which are broken or the porosities which are close to the surface in the foamed PP are filled by a fluid (either the ethanol or the polymeric matrix itself). The hydrostatic pressure decreases the volume of the foam only slightly. In the PU matrix, ethanol diffusion is seen to induce swelling of the matrix, which is an unexpected phenomenon but reveals the high potential of X-ray microtomographic observation to improve diffusion analysis in complex media.