• Economic and Environmental Geology
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• v.29 no.5
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• pp.545-559
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• 1996

Rare metal (Nb-Zr-REE) ore deposits are located in the Chungju area. Geotectonically, the rare metal ore deposits are situated in the transitional zone between Kyeonggi massif and Okcheon belt. The rare metal deposits are distributed in Kyemyeongsan Formation which consist of schist and alkaline igneous rocks. Alkali granite has suffered extensive post-magmatic metasomatism and hydrothermal processes. The ore contains mainly Ce-La, Ta-Nb, Y, Y-Nd, Nd-Th group minerals. More than 15 RE and REE minerals are found in the ore deposits. Allanite, one of the Ce-La rich REE minerals belonging to the epidote group, is the most common mineral in the studied area. The allanite- bearing rocks may be devided into seven types by features of occurrence and mineral associations; zircon type (ZT), allanite-vein type (AT), feldspar type (KT), fluorite type (FT), quartz-mica type (QT), iron-oxide type (MT), and amphibole type (HT). The allanite veins (AT) and zircon rich rocks (ZT) contain the highest total REE contents. Differences in REE abundance can be interpreted in terms of varying portions of magmatic hydrothermal fluid. Petrographical and chemical data are presented for allanites which were collected from different types. The allanites show wide variations in optical properties, due in part to differences in their chemical composition (depending on the types) and to the degree of crystallinity of the individual specimens. Allanite metamicts in biotite are generally surrounded by well developed pleochroic haloes. Usually, allanite is accompanied by zircon and other REE-bearing minerals. CaO and total REE contents $({\sum}RE_2O_3)$ range from 9.29 to 18.79% and 11.66 to 26.31%, respectively. Also, SiO, (28.87~32.61%), $Al_2O_3$ (8.30~16.88%), and $Fc_2O_3$ (16.74~24.38%) contents show varying contents from type to type. The ${\sum}RE_2O_3$ of allanite has positive relationships with $Fe_2O_3$ and negative relaton with CaO, $SiO_2$, and $Al_2O_3$ Backscattered electron microscope images (BEl) of allanite shows that the its mineral composition and texture is very complex. The allanite-bearing hosts show distinct light REE enrichment with strong negative Eu anomaly except for HI. The HT has an almost flat REE distribution pattern with a small negative Eu anomaly. The chemical variation of the allanites with occurrences and mineral association can be related to condition of temperature and oxidation states in precipitation environment.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.3
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• pp.67-71
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• 2014

An attempt to grow high quality GaN on silicon substrate using metal organic chemical vapor deposition (MOCVD), herein GaN epitaxial layers were grown on various Si(111) substrates. Thin Platinum layer was deposited on Si(111) substrate using sputtering, followed by thermal annealing to form Pt nano-clusters which act as masking layer during dry-etched with inductively coupled plasma-reactive ion etching to generate nano-patterned Si(111) substrate. In addition, micro-patterned Si(111) substrate with circle shape was also fabricated by using conventional photo-lithography technique. GaN epitaxial layers were subsequently grown on micro-, nano-patterned and conventional Si (111) substrate under identical growth conditions for comparison. The GaN layer grown on nano-patterned Si (111) substrate shows the lowest crack density with mirror-like surface morphology. The FWHM values of XRD rocking curve measured from symmetry (002) and asymmetry (102) planes are 576 arcsec and 828 arcsec, respectively. To corroborate an enhancement of the growth quality, the FWHM value achieved from the photoluminescence spectra also shows the lowest value (46.5 meV) as compare to other grown samples.

• Journal of Technologic Dentistry
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• v.33 no.4
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• pp.299-306
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• 2011

Purpose: This study aimed to investigate the shear bond strength by manufacturing the veneering porcelain on the IPS e.max $ZirCAD^{(R)}$ zirconia core, using the layering technique and heat-pressing technique, and to evaluate the clinical stability by comparing to the conventional metal ceramic system. Methods: The Schmitz-Schulmeyer test method was used to evaluate the core-veneer shear bond strength of zirconia core ceramic(IPS e.max $ZirCAD^{(R)}$) and their manufacture recommended two veneering ceramic systems(IPS e.max $ceram^{(R)}$, IPS e. max $ZirPress^{(R)}$). A metal ceramic system(Bellabond $plus^{(R)}$, VITA $VM13^{(R)}$) was used as a control group for the two all ceramic system test groups. The maximum loading and shear bond strength was measured. The average shear strength(MPa) was analyzed with the one-way ANOVA and the Tukey's test(${\alpha}$=.05). The fracture specimens were examined using Microscope to determine the failure pattern. Results: The mean shear bond strengths(SD) in MPa were MBSB control 43.62(2.13); ZBSB 18.65(1.76); ZPSB 18.89(1.54). The shear strengths of the zirconia cores were not significantly different(P>.05). Microscope examination showed that zirconia specimens presented mixed failure, and base metal alloy specimens showed adhesive failure. Conclusion: There was no siginificant different between the layering technique and the heat pressing technique in the veneering methods on the zirconia cores. None of the zirconia core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.2
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• pp.195-204
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• 2008

Orthodontic brackets often need to be bonded to porcelain such as porcelain fused to metal crowns and porcelain jacket crowns. The purpose of this study was to evaluate the clinical usability of direct bonding system on porcelain teeth by measuring shear bond strength according to various conditions and observing adhesive failure patterns. The specimens, 20 maxillary premolars and 80 porcelain teeth that were produced by duplication of the labial surface of a maxillary first premolar were used and randomly divided into four groups of twenty teeth each. The 5 different preparation procedures tested: (1) application of 37% phosphoric acid on natural teeth, (2) sandblasting on porcelain surfaces, (3) sandblasting and application of 9.6% hydrofluoric acid on porcelain surfaces, (4) sandblasting and application of silane on porcelain surface, (5) sandblasting and application of 9.6% hydrofluoric acid and silane on porcelain surfaces. The metal brackets were bonded with Transbond $XT^{(R)}$ bonding material. The shear bond strength was tested by the micro universal testing machine(Kyung-Sung, Korea) and the amount of residual adhesive on the tooth surface after debonding was examined by stereoscope and assessed with an adhesive remnant index. The results of this study suggest that the direct bonding system on porcelain teeth with sandblasting, HF and porcelain primer is clinically useful.

• Journal of Industrial Technology
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• v.9
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• pp.21-28
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• 1989

For the study of the fatigue behavior, high-strength bolted connections on a small scale were manufactured, and carried on fatigue tests. Its experimental values were analysed by stress-fatigue life (S-N) curve. Three types of specimens : the base metal, the cireular hole and the welded sperimens had same net section were made. Through the same tests those experimental values were compared with those of the high-strength bolted conneetions. The results of these studies are as followings. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted conneetions were much more about 14% and 16% than that of the base metal specimen. It was thought that this trend was due to frictional force increasing fatigue strength. It was known that fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the welded joints were less 29% and 21% than that of base metal specimen. It was thought that that trend was due to weld flaw. It was appeared that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted connections were much more about 38% and 30% than that of welded joint. It was thought that it was due to both frictional force increasing the fatigue strength in bolted connections and weld flaw decreasing the fatigue strength in welded connections. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the B3 specimens were much more 2% and -2% than that of the B4 specimen. It was thought that that trend was due to the frictional force, which concerned with shape of specimen. It was known that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the specimen with circular hole was less 61% and 65% than that of base metal. It was known that the allowable stress for bolted joint was higher than that of welded Joints. If that research is continued and more data are accumulated it can be expected that a basic pattern to provided the indicator of the fatigue design of the bolted connections of steel structures and persume the safety and lifeproof of existing structures is given.

• Korean Journal of Soil Science and Fertilizer
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• v.39 no.1
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• pp.21-28
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• 2006

We investigated the mobilization of Cd, Pb, and Cr in two different soils in response to sorption capacities and competition for available sorption site while they moved under saturated water conditions. Two soil samples that were clay and sandy clay loam were collected within 20 cm from the upland surface. To do this, we used three different systems of heavy metal combinations such as single, binary, and ternary as solution phase. And then we observed the breakthrough curve (BTC) and elution as a function of pore volume by applying heavy metal solution and displacing K solution until these curves reached to maximum and minimum. The results showed that BTC and elution curves were not symmetric and it required more pore volumes with increasing species of heavy metals in solution phase, as well as longer tailings. Compared the areas over and under BTC and elution curve, relatively small amount of heavy metal was displaced by K even though there were differences in electronegativity among heavy metals. Conclusively, we assumed that heavy metals transport in soil could be influenced by soil physical nonequilibrium and chemical equilibrium in solution as far as there were more than two species of heavy metals existed.

• Korean Journal of Ecology and Environment
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• v.52 no.3
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• pp.266-273
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• 2019

Heavy metal contamination in freshwater ecosystem has been receiving increased worldwide attention due to their direct or indirect effect on human health and aquatic organisms. In this study, we investigated biological effects such as survival rate, growth rate, emergence rate, sex ratio and mouthpart deformity of Chironomus plumosus. The survival rate of C. plumosus decreased with the increase in heavy metal concentration as well as exposure time after cadmium (Cd) or zinc (Zn) exposure. The growth rate decreased at days 4 and 7 after Cd exposure and significantly reduced at the relatively high concentration of $50mg\;L^{-1}$ Cd. The emergence rate was decreased at $50mg\;L^{-1}$ Cd and $100mg\;L^{-1}$ Zn. The sex ratio showed imbalance pattern at relatively low concentrations (0.5 and $2mg\;L^{-1}$ Cd) with high proportion of male and relatively high concentration ($100mg\;L^{-1}$ Zn) with high proportion of female (60%). In addition, mentum deformities were observed at high concentration of Cd and Zn. These results suggest that heavy metal exposure in aquatic ecosystem may affect biological and morphological responses, and aquatic midge C. plumosus is a potential indicator for assessment of environmental pollutant such as heavy metals.

• Korean Journal of Heritage: History & Science
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• v.54 no.1
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• pp.4-17
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• 2021

This study analyzed 19 samples of harness fittings and pendants, which were excavated in Tomb No. 15 in Songhyeon-dong, Changnyeong. Harness fittings and pendants are used for ostentation, rather than practicality, and were excavated from ancient tombs in Gaya culture. So, they are considered artifacts that compare the production techniques and raw materials. This study aimed to examine the production techniques and provenience studies of Bihwa Gaya, which is estimated to be from the 5th to 6th centuries. According to the research, harness fittings were made of pure copper and were gilded with Au·Ag alloys on their surfaces. Hg was detected together and plated with a mercury amalgam method. As a result of the pendant (fish scales-pattern, oval and fish-tail shape), analysis showed that Fe in the background metal, Cu in the middle layer, and Au and Ag on the surface were the main components. The method of adhesion between Cu and Au·Ag gilded layers are plated by a mercury amalgamation method. So, it was identified by the gilt-iron·gold·bronze technique. Since the pendant (heart shaped) is found to be the main component of Fe in the background metal and Ag in the surface layer, the metal was made gilt-iron·silver technique. The background metal and gilding were additionally fixed using a rivet. The raw materials of 3 harnesses excavated from Changnyeong are plotted in zone 2 in the southern Korean Peninsula. And 16 harnesses were plotted in Chinese copper ore by Mabuchi Hishao in the Chinese Peninsula.

• The korean journal of orthodontics
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• v.34 no.4 s.105
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• pp.325-332
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• 2004

A self-etching primer that combines the etchant and primer in one chemical compound saves time and should be mote cost-effective to the clinician and patient. The purpose of this study was to evaluate the clinical effectiveness of a self-etching primer by measuring shear bond strengths according to various conditions and observing adhesive failure patterns. For this Investigation, 120 upper and lower premolars extracted for orthodontic purposes were used and randomly divided into six groups of twenty teeth each. Human premolars were embedded in a metal cylinder with orthodontic resin. Metal brackets and ceramic brackets were bonded with XT primer and self-etching primer by means of XT adhesive. Upon curing, plasma arc light and visible light were used. After bonding, the shear bond strength was tested by Instron universal testing machine, and the amount of residual adhesive that remained on the tooth after debonding was measured by stereoscope and assessed with an adhesive remnant index. The results were as fellows: 1. When brackets were bonded, if other conditions remained the same, there was no significant difference in shear bond strength due to the type of primer - either self-etching primer or XT primer. 2. When metal brackets were bonded, there was no significant difference in shear bond strength according to the source of light - plasma arc light or visible light - and type of primer. 3. There was a very significant difference in shear bond strength according to the type of brackets - metal or ceramic brackets. The shear bond strength of ceramic brackets was stronger than metal brackets. 4. When the adhesive failure patterns of metal brackets bonded with self-etching primer were observed by using the adhesive remnant index, the bond failure of the metal bracket occurred more frequently at the bracket-adhesive. The failure of the ceramic bracket, however, occurred more frequently at the enamel-adhesive interface. The adhesive failure patterns of metal brackets bonded with XT primer observed the same patterns. The above results suggest that self-etching primer can be clinically useful for bonding the brackets without fear of a decrease in shear bond strength.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.5
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• pp.478-482
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• 2001

This study was conducted to get a knowledge on food components of cuttle bone (CB) as a food resource. The yields and ash contents of CB were about $7.5\%$ on whole cuttle fish and about $90\%$ on dry basis, respectively, The contents of heavy metal might not invoke health risk in using food resource, The major mineral of CB was calcium as about $22\%$ in content. The yields, proximate compositions, heavy metal and mineral contents were not significantly different between domestic and imported CB. Judging from X-ray diffraction pattern, most of calcium in CB was present as a form of calcium carbonate (CC), and scanning electron micrograph showed irregular form. Buffering capacity of CB showed strongly at pH 7, and its pattern was the same as shown in that of CC, And CB solution showed a very high degree in turbidity comparing to that of CC solution. The solubility of CB was superior to that of CC, but inferior to those of calcium powders on the market, It was concluded from above results that CB could be effectively utilized as a calcium source.