• Journal of Powder Materials
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• v.9 no.6
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.9-17
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• 2013

This paper describes an experimental program to investigate the shear behavior of insulated concrete sandwich panels (CSPs) with different types of GFRP shear connector. The study included testing of 13 insulated CSP specimens with two types of surface conditions for extruded polystyrene (XPS) insulation and various shapes of shear connectors. All specimens were loaded in direct shear by means of push-out and were consist of three concrete panels, two insulation layer and four rows of GFRP shear connectors. Load-relative slip between concrete panel and insulation response of CSP specimens has been established through push-out shear test. Test results indicate that the surface condition of insulation has a significant effect on the bond strength between concrete panel and insulation. The specimen used XPS foam with 10mm deep slot shows higher bond strength than those used XPS foam with meshed surface. Corrugated GFRP shear connectors show equivalent strength to grid GFRP shear connectors. Cross-sectional area and embedded length of shear connector have a notable effect on overall response and inplane shear strength of the CSP specimens.

• Current Research on Agriculture and Life Sciences
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• v.1
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• pp.67-83
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• 1983

The new microsporidia S80 isolated from, Bombyx mori L. in Korea showed ovoid in the morphology of the spores and the size were measured $2.9{\pm}0.28{\mu}$ in length and $1.7{\pm}0.29{\mu}$ width. No other microsporidian spore like this has not been so far isolated from Silkworm. The length of the polar filament extruded in hydrogen peroxide ($H_2O_2$) at $30^{\circ}C$ was $26{\mu}$ of a round cytoplasm on the top. The spores were partly stained with Giemsa, Safranin-O and Gram as the same staining properties as Nosema bombycis, Microsporidia K 79 and other microsporidian spores. The fine structures were observed under scanning eleceron microscope through ultrathin sectioning. The spore wall was composed of three layers ; the thin exospore of an electron dense rippled layer, the thick electron lucent endospore which was thinning considerably at the polar filament insertion point, and the inner limiting membrane. Polar cap present at the sporeapex, with a long polar filament of 12-13 coils, subtending angle of $60^{\circ}$ to spore axis, which is tubular made up of a multilayered and are a benes core, light ring structure enclosing the dance core, the dark ring structure enclosing the inner light ring structure and the other than and light ring structure bounded from cytoplasm. Lamellate polaroplast occupied the anterior part of the spore, and the two neclei with dense nucleoplasm bounded by a double nuclear envelope were cited in the slight downer middle portion of spore. From the characteristics of the shape, size and fine structures, it is certain to reason the Microsporidia S80 belong to the phylum Microspora, class Microspora, order Microsporida, order Microsporida. The shape of two nuclei cited seems to be genus Nosema, but in the classification for the suborder it should be defined wheather pansporoblasts be formed or not and for the genis especial attempts have been made to define the characters which distinguish the disporous genera in the life cycle. Survey through the infection of the bad cocoons during 1980 to 1982 in South Korea the areas contaminated with new microsporidia were revealed 5 provinces of Kyung-Gi, Kang-Won, Chung-Nam and Chun-Nam. Pathological effects inoculated per os at second instar larvae of silkworm, the LD 50 was $7.1{\times}10^7/ml$ as lower pathogenecity than that of Nosema bombycis Naegeli of $1.2{\times}10_7/ml$. While on the other hand the inoculation of the microsporidia at fourth instar larvae lowerd the whole cocoon weight and cocoon shell weight and significant at 1% level. The microsporidia S80 defined it can not be transmitted transovarially from the result of predictive and collective examination of 21 egg batches from the infected female moth.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.344-351
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• 2006

The purpose of this study was to evaluate the thermal expansion characteristics of injectable ther-moplasticized gutta-perchas and a Resilon. The materials investigated are Obtura gutta-percha, Diadent gutta-percha, E&Q Gutta-percha Bar and Epiphany (Resilon). The temperature at the heating chamber orifice of an Obtura II syringe and the extruded gutta-percha from the tip of both 23- and 20-gauge needle was determined using a Digital thermometer. A cylindrical ceramic mold was fabricated for thermal expansion test, which was 27 mm long, with an internal bore diameter of 3 mm and an outer diameter of 10 mm. The mold was filled with each experimental material and barrel ends were closed with two ceramic plunger. The samples in ceramic molds were heated in a dilatometer over the temperature range from $25^{\circ}C$ to $75^{\circ}C$. From the change of specimen length as a function of temperature, the coefficients of thermal expansion were deter-mined. There was no statistical difference between four materials in the thermal expansion in the range from $35^{\circ}C$ to $55^{\circ}C$ (p > 0.05). However, Obtura Gutta-percha showed smaller thermal expansion than Diadent and Metadent ones from $35^{\circ}C$ to $75^{\circ}C$ (p < 0.05). The thermal expansion of Epiphany was similar to those of the other gutta-percha groups.