• Microbiology and Biotechnology Letters
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• v.28 no.2
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• pp.71-79
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• 2000

Two typess of copolyesters, poly(3-hydroxybutyric acid-co-4-hydroxy-butyric acid)[P(3HB-co-4HB] and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)[P(3HB-co-3HV)], with various monomer ratios and different degree of microstructural heterogeneity were synthesized from Ralstonia eutropha H16 and Hydrogenophaga pseudoflava by using ${\gamma}$-butyrolactone and ${\gamma}$-valerolactone, respectively. The two bacteria showed a large difference in the utilization of ${\gamma}$-butyrolactone for cell growth and PHA synthesis. H. pseudoflava synthesized P(3HB-co-4HB) copolyesters with a wide range of 4HB content from 13 to 96 mol% depending on culture conditions, whiel R. eutropha H16 was able to synthesize the copolyesters containing less than 20 mol% of 4HB. An increase in the 4HB content in the P(3HB-co-4HB) copolyesters synthesized by H. pseud-oflava induced an lowering of their melting temperatures as well as their enthalpies of fusion. The increase in the 4HB content, however, increased the rate of degradation by an extracellular P(3HB) depolymerase. NMR spectros-copy and differential scanning calorimetry showed that the P(3HB-co-4HB) copolyesters from H. pseudoflava were generally microstructurally heterogeneous. The P(3HB-co-4HB) copolyesters) synthesized by R. eutropha H16 were rather random copolymers showing less microstructural heterogeneity than those synthesized by H. pseudoflava. The NMR D value analysis suggested that the monomer distribution of the P(3HB-co-3HV) copolymers from the two bacteria were relatively random.

• Journal of Korea Foundry Society
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• v.33 no.5
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• pp.193-203
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• 2013

The Ni-base superalloy CM247LC was directionally solidified (DS) using the Bridgman-type furnace to understand the effect of the chill plate on the microstructural evolution, such as dendrite arm spacing, microporosity, and MC-type carbide. The DS process was also modeled by the PROCAST to predict the solidification rate, thermal gradient, and resultant cooling rate in the entire length of the DS specimen. Due to the quenching effects of chill plate, four distinct areas were found to form in the specimen, in which the solidification rate was changed, during DS at a given withdrawal rate of 0.083 mm/s. Among the microstructural features investigated, the dendrite arm spacings and average size of the MC-type carbide near the chill plate were found to be influenced by the quenching effect of the chill plate. However, no significant influence was found on the size and volume fraction of microporosity, and the volume fraction of the MC-type carbide. The relationship between the microstructural features and the solidification variables was also analyzed and discussed on the basis of a combination of experimental and modeling results.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.65-73
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• 2002

Artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540^{\circ}C$. Microstructural analysis (mean equivalent size, number of carbides per unit area) and measurement of mechanical properties(UTS, Vickers hardness) and magnetic properties(coercivity, remanence) were performed. By comparing these results, the relationship between magnetic properties and microstructural changes with artificial aging was clarified. The carbides were classified as rod, globular and acicular type in terms of morphology. The fine acicular carbides were found to diminish drastically in the initial stage of aging. The magnetic coercivity and remanence were observed to decrease rapidly in the initial about 920 hours of aging time and then decrease slowly afterwards. Linear correlations between the mechanical properties and magnetic properties such as correlations remanence were found.

• Korean Journal of Radiology
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• v.22 no.7
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• pp.1142-1151
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• 2021

Objective: To evaluate microstructural damage in high myopia (HM) patients using 3T diffusion kurtosis imaging (DKI). Materials and Methods: This prospective study included 30 HM patients and 33 age- and sex-matched healthy controls (HCs) with DKI. Kurtosis parameters including kurtosis fractional anisotropy (FA), mean kurtosis (MK), axial kurtosis (AK), and radial kurtosis (RK) as well as diffusion metrics including FA, mean diffusivity, axial diffusivity (AD), and radial diffusivity derived from DKI were obtained. Group differences in these metrics were compared using tract-based spatial statistics. Partial correlation analysis was used to evaluate correlations between microstructural changes and disease duration. Results: Compared to HCs, HM patients showed significantly reduced AK, RK, MK, and FA and significantly increased AD, predominately in the bilateral corticospinal tract, right inferior longitudinal fasciculus, superior longitudinal fasciculus, inferior fronto-occipital fasciculus, and left thalamus (all p < 0.05, threshold-free cluster enhancement corrected). In addition, DKI-derived kurtosis parameters (AK, RK, and MK) had negative correlations (r = -0.448 to -0.376, all p < 0.05) and diffusion parameter (AD) had positive correlations (r = 0.372 to 0.409, all p < 0.05) with disease duration. Conclusion: HM patients showed microstructural alterations in the brain regions responsible for motor conduction and vision-related functions. DKI is useful for detecting white matter abnormalities in HM patients, which might be helpful for exploring and monitoring the pathogenesis of the disease.

• Nuclear Engineering and Technology
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• v.44 no.6
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• pp.673-682
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• 2012

Three dimensional atom probe tomography (3D APT) is applied to characterize the dissimilar metal joint which was welded between the Ni-based alloy, Alloy 690 and the low alloy steel, A533 Gr. B, with Alloy 152 filler metal. While there is some difficulty in preparing the specimen for the analysis, the 3D APT has a truly quantitative analytical capability to characterize nanometer scale particles in metallic materials, thus its application to the microstructural analysis in multi-component metallic materials provides critical information on the mechanism of nanoscale microstructural evolution. In this study, the procedure for 3D APT specimen preparation was established, and those for dissimilar metal weld interface were prepared near the fusion boundary by a focused ion beam. The result of the analysis in this study showed the precipitation of chromium carbides near the fusion boundary between A533 Gr. B and Alloy 152.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.410-416
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• 2015

Microstructural analysis of a (${\alpha}+{\beta}$) Ti alloy was investigated to consider phase transformation in each step of the thermo-mechanical process using by SEM and TEM EDS. The TAF (Ti-6Al-4Fe) alloy was thermo-mechanically treated with solid solution at $880^{\circ}C$, rolling at $880^{\circ}C$ and annealing at $800^{\circ}C$. In the STQ state, the TAF microstructure was composed of a normal hcp ${\alpha}$ and metastable ${\beta}$ phase. In a rolled state, it was composed of fine B2 precipitates in an ${\alpha}$ phase, which had high Fe segregation and a coherent relationship with the ${\beta}$ matrix. Finally, in the annealing state, the fine B2 precipitates had disappeared in the ${\alpha}$ phase and had gone to the boundary of the ${\alpha}$ and ${\beta}$ phase. On the other hand, in a lower rolling temperature of $704^{\circ}C$, the B2 precipitates were more coarse in both the ${\alpha}$ and the boundary of ${\alpha}$ and ${\beta}$ phase. We concluded that microstructural change affects the mechanical properties of formability including rolling defects and cracks.

• Advances in concrete construction
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• v.12 no.6
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• pp.479-490
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• 2021

Present research is mainly focused on, microstructural and durability analysis of Graphene Oxide (GO) in Wollastonite (WO) induced cement mortar with silica fume. The study was conducted by evaluating the mechanical properties (compressive and flexural strength), durability properties (water absorption, sorptivity and sulphate resistance) and microstructural analysis by SEM. Cement mortar mix prepared by replacing 10% ordinary portland cement with SF was considered as the control mix. Wollastonite replacement level varied from 0 to 20% by weight of cement. The optimum replacement of wollastonite was found to be 15% and this was followed by four sets of mortar specimens with varying substitution levels of cementitious material with GO at dosage rates of 0.1%, 0.2%, 0.3% and 0.4% by weight. The results indicated that the addition of up to 15%WO and 0.3% GO improves the hydration process and increase the compressive strength and flexural strength of the mortar due to the pore volume reduction, thereby strengthening the mortar mix. The resistance to water penetration and sulphate attack of mortar mixes were generally improved with the dosage of GO in presence of 15% Wollastonite and 10% silica fume content in the mortar mix. Furthermore, FE-SEM test results showed that the WO influences the lattice framework of the cement hydration products increasing the bonding between silica fume particles and cement. The optimum mix containing 0.3% GO with 15% WO replacement exhibited extensive C-S-H formation along with a uniform densified structure indicating that calcium meta-silicate has filled the pores.

• Journal of the Korean Society of Clothing and Textiles
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• v.11 no.3 s.25
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• pp.33-40
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• 1987

PET FDY was heat set at various temperatures and times and the microstructural changes was investigated through crystallinity, birefringence and melting behavior analyses. Crystallinity of heat set PET increased as the treatment temperature and time increased. Birefringence also increased as temperature and time increased. The melting behavior of heat set PET was as follows: In most cases, PET showed double melting peaks. As temperature and time increased, form II crystal became sharp and increased in size, and form I crystal decreased in size. The slower the heating rate, the higher the programmed heating effect during DSC analysis.

• Structural Engineering and Mechanics
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• v.38 no.4
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• pp.503-516
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• 2011

Uncertainty in concrete properties, including concrete modulus of elasticity and modulus of rupture, are predicted by developing a microstructural homogenization model. The homogenization model is developed by analyzing a concrete representative volume element (RVE) using the finite element (FE) method. The concrete RVE considers concrete as a three phase composite material including: cement paste, aggregate and interfacial transition zone (ITZ). The homogenization model allows for considering two sources of variability in concrete, randomly dispersed aggregates in the concrete matrix and uncertain mechanical properties of composite phases of concrete. Using the proposed homogenization technique, the uncertainty in concrete modulus of elasticity and modulus of rupture (described by numerical cumulative probability density function) are determined. Deflection uncertainty of reinforced concrete (RC) beams, propagated from uncertainties in concrete properties, is quantified using Monte Carlo (MC) simulation. Cracked plane frame analysis is used to account for tension stiffening in concrete. Concrete homogenization enables a unique opportunity to bridge the gap between concrete materials and structural modeling, which is necessary for realistic serviceability prediction.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.429-433
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• 2006

High Temperature deformation behavior of newly developed beta-gamma TiAl alloy was investigated in this study. The optimum processing condition was investigated with the aid of Dynamic Materials Model (DMM). Processing maps representing the efficiency of power dissipation for microstructural evolution and instability were constructed utilizing the results of hot compression test at temperatures ranging from $1000^{\circ}C$ to $1200^{\circ}C$ and strain rate ranging from $10^{-4}/s$ to $10^2/s$. The Artificial Neural Network (ANN) simulation was adopted to consider the deformation heating. With the help of processing map and microstructural analysis, the optimum processing condition was presented and the role of $\beta$ phase was also discussed in this study.