• The Journal of the Korea Contents Association
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• v.21 no.3
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• pp.609-615
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• 2021

The aim of the present study was to investigate the mechanical properties of melt-injected poly lactic acid (PLA) composites with β-tricalcium phosphate (β-TCP). The PLA mixed with calcined PLA/β-TCP powder to be contents of 0, 10, 30, 50 wt%, respectively, was dissolved in chloroform solvent under stirring for 24 h. Then the liquid mixtures were dropped into ethanol to extract solvent. After drying, the well-dispersed PLA/β-TCP composites were granulated and melt-injected to prepare specimens for various mechanical testing. PLA/β-TCP induced the precipitation of an apatite bone-mineral phase on the surface after immersion in a human simulated body fluid (SBF) for 90 days, showing in bioactivity. Mean various mechanical properties PLA/β-TCP composite were increased up to 10-30 wt% with significantly in part and composite were decreased 50 wt% of showing in mechanical properties. In conclusion, Over 30 wt% addition of β-TCP to PLA may be not advisable to improve the mechanical properties of melt-injected polymeric composites. Results indicated that β-TCP can be used considered as potential reinforcing agent for increasing mechanical properties for PLA. Therefore, it was suggest that the additional effects of β-TCP and research on a wide range of substances.

• Journal of the Mineralogical Society of Korea
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• v.6 no.2
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• pp.57-79
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• 1993

Chuncheon nephrite, which was formed by the polymetasomatic alteration of dolomitic marble, can be classified into pale green, green, dark green, and grey types on the basis of their occurrence, mineralogical and textural characteristics. The nephrites consist obiefly of fibrous or hairlike(length/width ratio>10) cryptocrystalline(crystal width < $2{\mu}m$) tremolite, and include less amounts of micro-crystalline diopside, calcite, clinochlore, and sphene as impurities. The oriented and rather curved crystal aggregate, of nephritic tremolite are densely interwoven, resulting in a massive-fibrous texture which may explain the characteristic toughness of nephritic jade. The characteristic greenish color of the nephrite may be preferably related to Fe rather than Cr and Ni. However, the variation of color and tint in the Chuncheon nephrite also depends on the mineralogical and textural differences such as crystallinity, texture, and impurities. The chemical composition of the nephritic tremolite is not stoichiometric and rather dispersed especially in the abundances of Al, Mg, and Ca. Al content and Mg/Ca ratio for the nephritic tremolite are slightly increased with deepening in greenish color of the nephrite. Fe content in the nephritic tremolite is generally very low, but comparatively richer in the dark green nephrite. In nephritic tremolite, wide-chain pyriboles are irregularly intervened between normal double chains, forming a chain-width disorder. Most nephritic tremolites in the Chuncheon nephrite show various type of chain-width defects such as triple chain(jimthompsonite), quintuple chain (chesterite), or sometimes quadruple chain in HRTEM observations. The degree of chain-width disorder in the nephritic tremolite tends to increase with deepening in greenish color. Triple chain is the most common type, and quadruple chain is rarely observed only in the grey nephrite. The presence of pyribole structure in the nephritic tremolite is closely related to the increase of Al content and Mg/Ca ratio, a rather dispersive chemical composition, a decrease of relative intensity in (001) XRD reflection, and an increase in b axis dimension of unit cell. In addition, the degree and variation of chain-width disorder with nephrite types may support that an increase of metastability was formed by a rapid diffusion of Mg-rich fluid during the nephrite formation.

• Parasites, Hosts and Diseases
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• v.28 no.3
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• pp.183-194
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• 1990

In an attempt to develop prophylactic and therapeutic measures of the intestinal giant-cystic disease caused by Thelohanellus kitauei in the Israel carp, Cyprinus carpio nodus, pathological observations were conducted upon the carps which were hatched in May 1988 and raised in a net cage fish farm at the Soyang lake, managed by Horim Fisheries for the period of 21 months with 1~2 months interval. After a gross inspection of the carps, necropsy was carried out periodically in order to clarify the pathological changes in various internal organs and muscular tissues. Also. the prevalence of the disease was checked during the period from 1988 to 1990. Gross inspections revealed that the infected carps showed some degree of fading in body and gill color, back-emaciation symptoms, reddish anus accompanying erosion and relaxation and pot-belly, as well as discharge of yellowish white mucoid material from the anus. However, most carps died eventually of intestinal obstruction. Other significant necropsy fadings included cyst formation of various size in the intestinal mucosa, ascites, anemic condition through internal organs and muscular tissues, hyperemia and dilation of intestines with decreased tension, thinness and fragility, and full contents of semi-fluid or yellowish white mucoid material in the intestinal canals. Based on the morphological characteristics of the spores found in the cysts, parasitic location in the intestines, macro- and microscopic findings of the lesions, the parasites were identised as Thelohanellus kitauei Egusa os Nakajima, 1981. Although monthly changes of water temperature were distinct, the extrusion rates of the polar filaments of the spores stayed constant throughout the year with an exception of a lower rate in July, The lesions initiated from mucosa and submucosa in early July became large swellings and then complete mature (orms following the peracute course. From late August the upper cysts were gradually opened and most of the spores were dispersed from anus into the surrounding water through December but only a few lasted until next April. The cysts were completely recovered until next September. Comparing the incidence and prevalence of the disease by year tremendous infection and death rates were checked in the first prevalent year, 1988, but the rates were significantly decreased in the second year, and showed an almost normal status in the third year, 1990. As the above summarized results showed, the disease entity might come to an end in three years after the first prevalent year, however, the spores must be strictly prevented because they could be infective in the water for one year.

• Journal of the Korean association of regional geographers
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• v.3 no.1
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• pp.115-134
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• 1997

We now live in the new era of globalization which implies the functional integration or increase of inter-dependency between internationally dispersed economic activities. As globalization impacts our various activities and daily lives, social sciences, including, geography, attempt to approach social phenomena from a global perspective. From this point of view. new regional geography, which has been articulated in recent social theory since the 1980s, also must adjust to these new world realities. This paper aims to search for a suitable methodology or approach to area study or regional geography in the era of globalization and to suggest the field of area study that Korean geographers should be concerned with in the future. This paper has reviewed the existing various methodologies of regional geography such as the ecological approach, the landscape approach. the areal differentiation approach, the system approach, the structuration theory, the spatial division of labour, and the world-system, which have deviced in the traditional and new regional geography. Peter Taylor's regional geography of world systems among them has an appropriate rationale of area study in the globalization era, because world-systems theory explains well globalization. However the regional geography of world-systems must be revised to become more suitable to the area-study approach in the globalization era. Firstly, the regional geography of world-systems explains that regions(historical regions) are made by general mechanisms of the capitalist world-economy that operate through social, economic, and political agents within regions such as individuals, households, social classes, economic enterprises, states, political movements, and many other organizations. But these mechanisms can also act through other regional agents of geographical location, natural conditions, and cultural characteristics. Therefore, the generating process of regions needs to be explained by locational, natural, and cultural elements in addition to social, economic, and political elements within regions. Secondly, Taylor's world-systems approach does not express composite characteristics of regions, because it focuses on the economic characteristics or position of regions within the world-economy. Regions incorporated into world-economy systems are not only changed economically, but also changed spatially, socially, culturally, and politically. Hence the world-systems approach must try to analyze these composite characteristics and their change of regions. Thirdly, The world-system approach proposed that the geography of regions within world-systems could be divided and analyzed as three regional types at the geographical scale such as international regions, state regions, and intra-state regions. However such a regionalization is usually not identified distinctly, because the geographical range of regions in world-systems shaped by economic boundaries of the general mechanisms of the world-economy is fluid and also occasionally overlaps with other political regions. Hence I propose that the world-systems approach should choose political boundaries of states and local autonomies in addition to economic boundaries for objective regionalization and systematic areal study. The revised regional geography of world-systems that I have suggested in this paper can be more effectively and properly applied to regional geography or area study in the globalization era. Globalization intensifies competition between states and also between local autonomies in the world. Therefore we must make efforts to study such areas or regions through the revised regional geography of world-system.