Jacek Tarasiuk

Estimation of recrystallized volume fraction from EBSD data

Abstract The recrystallized volume fraction is an important parameter in the study of recrystallization processes. This paper proposes a new method to estimate this parameter, based on quantitative EBSD data analysis. The principle of the method is first presented. The method is then tested on experimental EBSD data obtained on copper and brass. Estimated recrystallized volume fractions for different annealing temperatures are compared with values estimated from micro-hardness measurements. The presented method appears to be precise and very easy to implement, provided that some conditions are met; these are discussed in the final section.

Genetic algorithms as a useful tool for trabecular and cortical bone segmentation

The aim of this study was to find a semi-automatic method of bone segmentation on the basis of computed tomography (CT) scan series in order to recreate corresponding 3D objects. So, it was crucial for the segmentation to be smooth between adjacent scans. The concept of graphics pipeline computing was used, i.e. simple graphics filters such as threshold or gradient were processed in a manner that the output of one filter became the input of the second one resulting in so called pipeline. The input of the entire stream was the CT scan and the output corresponded to the binary mask showing where a given tissue is located in the input image. In this approach the main task consists in finding the suitable sequence, types and parameters of graphics filters building the pipeline. Because of the high number of desired parameters (in our case 96), it was decided to use a slightly modified genetic algorithm. To determine fitness value, the mask obtained from the parameters found through genetic algorithms (GA) was compared with those manually prepared. The numerical value corresponding to such a comparison has been defined by Dices coefficient. Preparation of reference masks for a few scans among the several hundreds of them was the only action done manually by a human expert. Using this method, very good results both for trabecular and cortical bones were obtained. It has to be emphasized that as no real border exists between these two bone types, the manually prepared reference masks were quite conventional and therefore charged with errors. As GA is a non-deterministic method, the present work also contains a statistical analysis of the relations existing between various GA parameters and fitness function. Finally the best sets of the GA parameters are proposed.

Metformin Decreases Reactive Oxygen Species, Enhances Osteogenic Properties of Adipose-Derived Multipotent Mesenchymal Stem Cells In Vitro, and Increases Bone Density In Vivo.

Due to its pleiotropic effects, the commonly used drug metformin has gained renewed interest among medical researchers. While metformin is mainly used for the treatment of diabetes, recent studies suggest that it may have further application in anticancer and antiaging therapies. In this study, we investigated the proliferative potential, accumulation of oxidative stress factors, and osteogenic and adipogenic differentiation potential of mouse adipose-derived stem cells (MuASCs) isolated from mice treated with metformin for 8 weeks. Moreover, we investigated the influence of metformin supplementation on mice bone density and bone element composition. The ASCs isolated from mice who were treated with metformin for 8 weeks showed highest proliferative potential, generated a robust net of cytoskeletal projections, had reduced expression of markers associated with cellular senescence, and decreased amount of reactive oxygen species in comparison to control group. Furthermore, we demonstrated that these cells possessed greatest osteogenic differentiation potential, while their adipogenic differentiation ability was reduced. We also demonstrated that metformin supplementation increases bone density in vivo. Our result stands as a valuable source of data regarding the in vivo influence of metformin on ASCs and bone density and supports a role for metformin in regenerative medicine.

High temperature thermogenerators made on DBC substrate using vapour phase soldering

Purpose – The purpose of this paper is to assess the reliability of thermoelectric generators after ageing at elevated temperature and to determine the influence of the technology used (i.e. type of thermoelectric material, type of substrate and soldering technology) for thermogenerator (TGE) assembly. Design/methodology/approach – In this paper, the Seebeck coefficient and the current voltage were measured for lead telluride doped with either manganese (PMT), germanium (PGT) or sulfur (PST) TGEs. The Seebeck coefficient measurements were taken at temperatures between 230 and 630 K. Findings – The Seebeck coefficient determined for PMT, PGT and PST TGEs increases approximately linearly with increasing temperature and is greater by about 40 per cent for PST and about 30 per cent for PMT than in commercially available PbTe TGEs. The best outcome in terms of stability after long-term ageing was that of PMT material. Originality/value – The choice of proper technology (i.e. thermoelectric materials, type of s...

Electron backscatter diffraction investigation of local misorientations and orientation gradients in connection with evolution of grain boundary structures in deformed and annealed zirconium. A new approach in grain boundary analysis

The main aim of the present work is to study the relation between microstructural features – such as local misorientations, grain orientation gradients and grain boundary structures – and thermomechanical treatment of hexagonal zirconium (Zr702α). Electron backscatter diffraction (EBSD) topological maps are used to analyze the aforementioned material parameters at the early stages of plastic deformation imposed by channel-die compression, as well as at a partial recrystallization state achieved by brief annealing. The evolution of local misorientations and orientation gradients is investigated using the so-called kernel average misorientation (KAM) and grain orientation spread (GOS) statistics implemented in the TSL OIM data analysis software [TexSEM Laboratories (2004), Draper, UT, USA]. In the case of grain boundaries (GBs) a new method of analysis is presented. As an addition to the classical line segments method, where the grain boundary is represented by line segments that separate particular pairs of neighboring points, an approach that focuses on grain boundary areas is proposed. These areas are represented by sets of EBSD points, which are specially selected from a modified calculation procedure for the KAM. Different evolution mechanisms of intragranular boundaries, low-angle grain boundaries and high-angle grain boundaries are observed depending on the compression direction. The observed differences are consistent with the results obtained from KAM and GOS analysis. It is also concluded that the proposed method of grain boundary characterization seems to be promising, as it provides new and interesting analysis tools such as textures, absolute fractions and other EBSD statistics of the GB areas. This description may be more compatible with a real deformed microstructure, especially for grain boundaries with very small misorientation, which are indeed clustered areas of lattice defect accumulation.

X-ray computed microtomography—a useful tool for petrophysical properties determination

The main goal of the research was to employ the unique data delivered by various methods to improve the determination of rock reservoir properties. Results of X-ray computed tomography (XRCMT), one of the newest techniques providing high-resolution images of rocks, were used to show that very precise information from this tool is complementary to results from other methods. Standard laboratory measurements (helium pycnometer, mercury injection porosimetry, permeameter) and sophisticated experiments (X-ray computed tomography and nuclear magnetic resonance spectroscopy) were performed to obtain and compare results. Four types of specimens: typical Miocene sandstone-mudstone-claystone rock samples, artificial corundum specimens, shale gas plugs, and limestone sample were investigated to obtain the porosity, permeability, density, and other parameters used in rock descriptions. Mutual relationships between selected groups of rock material properties were presented to provide an integral picture of rock characteristics. The XRCMT results were in general not influenced by lithology, but there were observed shaliness effects on the shape of pores, cross sections, and the tortuosity of porous channels. An analysis of the average porosity and the standard deviation of each XRCMT plot provided information about differences in the heterogeneity of a formation. Thus, the XRCMT method was recommended in pore space parameter determination for microfracture fluid propagation monitoring. There was also observed equivalence between part of the NMR signal from clay-bound water and the XRCMT volume subgroups in porosity/permeability—structural classes I and II. So, the use of the two-subsample approach in the XRCMT interpretation was promoted.

Semi-automated algorithm for cortical and trabecular bone separation from CT scans

One of the most challenging problems in modern medical imaging techniques is tissue recognition based on image segmentation procedure. The image segmentation may be described as a process of assigning a type of tissue to each pixel of the medical image. Segmentation belongs to an illposed problem class. Usually, its solution is not unique. Even results of segmentation performed manually by two specialists may slightly differ. The main difficulty in bone tissue recognition is to distinguish between cortical and trabecular parts of bone. It is relatively easy to recognise bone among other tissues, especially in computed tomography images. However, a problem arises when two types of bone have to be discriminated. The method proposed in this work combines both medical expert knowledge and skills with genetic algorithm (GA) procedure. The aim is to achieve, in a semi-automatic process saving human expert time, the best possible image segmentation. Our work follows the idea proposed by Bosco (2001) and Cagnoni et al. (1999). A two-stage procedure with learning and appropriate segmentation phases was developed. The GA approach was applied only for the first phase. In contrast to the concepts mentioned by authors, our subjects of evaluation are image-processing filters instead of segmentation curves.

Generalized Vertex Model - Study of Recrystallization in Copper

Classical vertex model till now described only the grain growth stage and not the primary recrystallization. In the present work the vertex model is first extended in order to take into account the both stages of recrystallization process. The influence of the stored energy is taken into account and some phenomenological laws describing the evolution of grain boundary energy and mobility with misorientation angle are used. Nucleation is considered to be site-saturated. The experimentally determined stored energy values, crystallographic orientations and boundary misorientation distributions are used in order to characterize the initial microstructure. The model is tested to study the recrystallization of 70% and 90% cold rolled polycrystalline copper during an annealing treatment. In order to explain the texture evolution in both cases, it is necessary to introduce an energy threshold for grain boundary movement, i.e. a minimal value of the stored energy difference between a nucleus and the deformed material necessary to provoke grain boundary motion. The developed model is shown to predict texture evolutions in good agreement with experimental data.

Study of the Texture Formation during Strain Induced Boundary Migration in Electrical Steel Sheets

Texture formation through strain induced boundary migration (SIBM) was investigated. Temper rolling reduction before final annealing for SIBM was varied between 0 and 26% and grain sizes and textures were measured using EBSD. In the specimen which was temper rolled to 5%, in which grain growth by SIBM occurred most efficiently, a strong Goss component (which was a minor component after rolling), developed during annealing. From the EBSD image quality analysis, it was found that stored energy increased significantly in the Goss component with strain (from 5 to 9 %), whereas it was always relatively small in the D-Cube component ({001}<110>), compared to Goss and g-fibre components. Based on these results, a mechanism of grain growth by SIBM was suggested. Texture evolution during annealing could thus be explained by the hypothesis, speculated from the analysis of orientation stability, that D-Cube grains are associated with more homogeneous dislocations distributions than Goss grains, in which the co-existence of high and low dislocation density zones could favour grain growth by SIBM.

Application of genetic algorithms to texture analysis

Application of genetic algorithms to texture analysis is presented in this paper. The genetic algorithm technique was applied to the calculation of the orientation distribution function from a set of pole figures. The results are very satisfying. The same algorithm may be also applied to other problems of texture analysis, e.g., to find an optimal texture for a given application.