• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1939-1943
• /
• 2003

The precise structural analysis of $SnO_{2}$ thin film, which was prepared by PECVD and thickness 2400 ${\AA}$, was tried to do the structural refinement using X -ray diffraction data. The observed diffraction patterns of $SnO_{2}$ thin film had the strongly preferred orientation effect. WIMV method was used to correct the preferred orientation effect. The final weighted R-factor, $R_{WD}$ was 7.92 %. The lattice parameters, a = b == 4.7366(1) ${\AA}$ and c = 3.1937(1) ${\AA}$, were almost in accordance with ones of $SnO_{2}$ powder.

• Structural Engineering and Mechanics
• /
• v.56 no.3
• /
• pp.423-442
• /
• 2015

This study examines the wavelet transform for output-only system identification of ambient excited engineering structures with emphasis on its utilization for modal parameter estimation of high-order and closely-spaced modes. Sophisticated time-frequency resolution analysis has been carried out by employing the modified complex Morlet wavelet function for better adaption and flexibility of the time-frequency resolution to extract two closely-spaced frequencies. Furthermore, bandwidth refinement techniques such as a bandwidth resolution adaptation, a broadband filtering technique and a narrowband filtering one have been proposed in the study for the special treatments of high-order and closely-spaced modal parameter estimation. Ambient responses of a 5-story steel frame building have been used in the numerical example, using the proposed bandwidth refinement techniques, for estimating the modal parameters of the high-order and closely-spaced modes. The first five natural frequencies and damping ratios of the structure have been estimated; furthermore, the comparison among the various proposed bandwidth refinement techniques has also been examined.

• Nuclear Engineering and Technology
• /
• v.37 no.4
• /
• pp.299-308
• /
• 2005

The behavior of fission gas in all major types of nuclear fuel has been reviewed with an emphasis on more recently discovered aspects. It is proposed that the behavior of fission gas can be classified in a number of characteristic types that occur at a high or low operating temperature, and/or at high or low fissile burnup. The crystal structure and microstructure of the various fuels are the determinant factors in the proposed classification scheme. Three types of behavior, characterized by anisotropic $\alpha$-U, high temperature metallic $\gamma$-U, and cubic ceramics, are well-known and have been extensively studied in the literature. Less widely known are two equally typical low temperature kinds: one associated with fission induced grain refinement and the other with fission induced amorphization. Grain refinement is seen in crystalline fuel irradiated to high burnup at low temperatures, whereas breakaway swelling is observed in amorphous fuel containing sufficient excess free-volume. Amorphous fuel, however, shows stable swelling if insufficient excess free-volume is available during irradiation.

• Advances in materials Research
• /
• v.7 no.2
• /
• pp.105-118
• /
• 2018

Magnesium and its alloys are attracted towards all engineering applications like automotive, marine, aerospace etc. due to its inherent high strength to weight ratio. But, extensive use of Mg alloys is limited to the current scenario because of low wear and corrosion resistance behavior. However, equal channel angular press is one of the severe plastic deformation technique which has been effective method to improve the wear and corrosion resistance by achieving fine grain structure. In this study, the effect of grain refinement on wear and corrosion resistance of AZ80 Mg alloys were investigated. The wear behavior of the coarse and fine-grained Mg alloys was examined through $L_9$ orthogonal array experiments in order to comprehend the wear behavior under varies control parameters. It was shown that ECAPed alloy increased the wear and corrosion resistance of the Mg alloy through the formation of fine grain and uniform distribution of secondary ${\beta}-phase$. Also, the performance of AZ80 Mg alloy for these changeswas discussed through SEM morphology.

• Korean Journal of Materials Research
• /
• v.24 no.11
• /
• pp.591-598
• /
• 2014

In this research, magnesium powder was prepared by gas atomizing. Refinement behaviors of magnesium powder produced under different conditions were investigated using a mechanical milling (attrition milling) process. Analyses were performed to assess the characterization and comparison of milled powder with different steel ball sizes and milling times. The powders were analyzed by field emission scanning electron microscope, apparent density and powder fluidity. The particle morphology of the Mg powders changed from spherical particles of feed metals to irregular oval particles, then plate type particles, with an increasing milling time. Because of the HCP structure, deformation occurs due to the existence of the easily breakable C-axis perpendicular to the base, which results in producing plate-type powders. An increase in ball size and the impact energy of the magnesium powder maximizes the effect of refinement. Furthermore, it is possible to improve the apparent density and fluidity according to the smoothness of the surface of the initial powder.

• Journal of Korea Foundry Society
• /
• v.18 no.3
• /
• pp.283-288
• /
• 1998

Interest in rapid solidification of magnesium alloys stems from the fact that conventional ingot metallurgy alloys exhibit poor strength, ductility, and corrosion resistance. Such properties can be improved by microstructural refinement via rapid solidification processing. In this study, Mg-Zn alloys have been produced as continuous strips by melt overflow technique. In order to evaluate the influence of additional elements on the grain refinement and mechanical properties, Th and Zr were added in rapidly solidified Mg-5wt%Zn alloy. Then the microstructual observations were undertaken with the objective of evaluating the grain refinement as function of the cooling rate and the additional elements. The tremendous increase in hardness of Mg-Zn base alloys was mainly due to the refinement of the grain structure by the effect of rapid solidification and alloying elements. The formation of intermetallic phases on the grain boundaries may have a positive effect on the corroion resistance. Therefore, despite competition from many other developments, the rapid solidification processing of magnesium alloys emerges as a valuable method to develop superior and commercially acceptable magnesium alloys.

• The Korean Journal of Ceramics
• /
• v.6 no.4
• /
• pp.354-358
• /
• 2000

The SnO$_2$film was deposited on a corning glass 1737 substrate by plasma enhanced chemical vapor deposition using a gas mixture of SnCl$_4$, $O_2$, and Ar. The film thickness was measured using $\alpha$-step and was about 9400$\AA$. The conventional X-ray diffractometry and pole figure attachment were used to refine the crystal structure of SnO$_2$ thin film. Six pole figures, (200), (211), (310), (301), (321), and (411), were measured with CoK$_\alpha$ radiation in reflection geometry. The X-ray diffraction data were measured at room temperature using CuK$_\alpha$ radiation with graphite monochromator. The agreement between calculated and observed patterns for the normal direction of SnO$_2$ thin film was not satisfactory due to the severely preferred orientation effect. The Rietveld refinement of heavily textured SnO$_2$ thin film was successfully achieved by adopting the pole density distribution of each reflection obtained from the inverse pole figure as a correction factor for the preferred orientation effect. The R-weighted pattern, R$_wp$, was 15.30%.

• Journal of the Korean Magnetic Resonance Society
• /
• v.26 no.1
• /
• pp.1-9
• /
• 2022

There are two distinct approaches to improving the quality of protein NMR structures during refinement: all-atom force fields and accumulated knowledge-assisted methods that include Rosetta. Mao et al. reported that, for 40 proteins, Rosetta increased the accuracies of their NMR-determined structures with respect to the X-ray crystal structures (Mao et al., J. Am. Chem. Soc. 136, 1893 (2014)). In this study, we calculated 32 structures of those studied by Mao et al. using all-atom force field and implicit solvent model, and we compared the results with those obtained from Rosetta. For a single protein, using only the experimental NOE-derived distances and backbone torsion angle restraints, 20 of the lowest energy structures were extracted as an ensemble from 100 generated structures. Restrained simulated annealing by molecular dynamics simulation searched conformational spaces with a total time step of 1-ns. The use of GPU-accelerated AMBER code allowed the calculations to be completed in hours using a single GPU computer-even for proteins larger than 20 kDa. Remarkably, statistical analyses indicated that the structures determined in this way showed overall higher accuracies to their X-ray structures compared to those refined by Rosetta (p-value < 0.01). Our data demonstrate the capability of sophisticated atomistic force fields in refining NMR structures, particularly when they are coupled with the latest GPU-based calculations. The straightforwardness of the protocol allows its use to be extended to all NMR structures.

• Journal of the Mineralogical Society of Korea
• /
• v.12 no.2
• /
• pp.55-65
• /
• 1999

Spotted cordierite occurs as the result of intrusion of Wolaksan Granite of Cretaceous age in the northern part of the Ogcheon Metamorphic Belt, forming a contact metamorphic zoning in accordance with the distance from the granite body: a cordierite-muscovite-biotite-quartz assemblage and the higher-temperature cordierite-biotite-quartz-(cummingtonite). These quartz-ubiquitous mineral assemblages identified in the cordierite spot seem to reflect Al-deficient condition of the protolith. TEM observations of textural relations between the cordierite and mica within the cordierite spot clearly reflect that cordierite was formed at the expense of micaceous matrix. A structure refinement of the poikiloblastic cordierite was performed by the Rietveld refinement method. Unit cell of the cordierite was determined to be as follows : lower-temperature type: a=17.1480(9)${\AA}$, b=9.7743(6)${\AA}$, c=9.3184(5)${\AA}$, V=1561.9(4)${\AA}$3, higher-temperature type: a=17.136(2)${\AA}$, b=9.751(1)${\AA}$, c=9.322(1)${\AA}$, V=1557.7(4)${\AA}$3. They show a remarkable difference in the unit cell dimension. The refinement results indicate that structural sites of lower-temperature cordierite are wholly occupied by appropriating ions. Compared to this, tetrahedral sites of the higher-temperature type exhibit an order/disorder ranging about 5-8% as the result of substitution between Si4+ and Al3+, except for T26 site occupied wholly by Al3+. These structural differences seem to be related to the formation temperatures of both cordierite types.

• ETRI Journal
• /
• v.28 no.6
• /
• pp.697-708
• /
• 2006

Various adaptive mesh refinement techniques are often employed in numerical simulations for increasing spatial and temporal resolution beyond the limits imposed by available CPU time and memory space. Recently, an octree-based adaptive mesh structure was successfully used in fluid animation to place more grid cells efficiently in visually interesting regions of fluids. In an attempt to optimize the use of computational resources further in fluid animation, this paper extends this adaptive technique by modifying the mesh refinement scheme so that the camera's viewing properties are dynamically exploited during the simulation. Based on a simple adaptive mesh structure, we show that the new meshing strategy can save a substantial amount of computation time and memory space by using a view-dependent adaptive approach. The experimental results reveal that the proposed technique provides a good compromise between the computational effort and the simulation's fidelity, and may be used quite effectively in 3D animation production.