• 한국재료학회지
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• 제11권9호
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• pp.763-768
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• 2001

Molybdenum-based thermal spray powder is widely used for coating the moving parts of the internal combustion engines due to its excellent wear resistance. A composite powder of the $Mo_{40}(Al_{1-x}Si_x)_{60}$ system was synthesized using the SHS method. The synthesized bulk was pulverized and specially treated to produce thermal spray powder. It was found that the synthesis reaction consisted of two-steps: the formation of $Al_8/Mo_3$ and the formation of Mo(Al,Si)$_2$. Both the temperature and the rate of the SHS reaction linearly increased with the increase of the value of x in $Mo_{40}(Al_{1-x}Si_x)_{60}$, The temperature and the rate of the reaction were also affected by the compacting density of the specimens, exhibiting the maximum valves at 62% and 60%, respectively. Since spherical shape is advantageous to the thermal spraying process, shape-control of the powder was attempted with PVA as a binding additive, resulting in the successful production of almost perfectly spherical powder of 80 $\mu\textrm{m}$ Ø$(d_{50})$ mean particle size.

• 통합자연과학논문집
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• 제4권1호
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• pp.58-71
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• 2011

The precambrian gneisses are widely distributed in the Jangsu area. This study focuses on the metamorphic mineral assemblages and metamorphic P-T conditions of the gneiss. We have analyzed garnet, biotite and plagioclase among the gneiss through the EPMA analysis, and calculated the metamorphic temperature and pressure accordingly. The metamorphic temperature was estimated by the average of values from the garnet and biotite formulas, and the metamorphic pressure by value of the Hoisch(1990) geopressured on garnet-biotite-plagioclase. The mineral sample we examined shows garnet-biotite-plagioclase-quartz composite and garnet-plagioclase-orthoclase-quartz composite. Garnet shows almandine-pyrope solid solution in general, while porphyroblastic gneiss shows almandine-grossluar solid solution. The fact that the abundances, observed by garnet profile, are almost identical in both the central region and the outer egion indicates that the crystal was developed uniformly. There is almost negligible variance in biotite on metamorphic grade, and andesine is observed in plagioclase. The metamorphic temperature and pressure from EPMA analysis and its indications are as follows: the middle-temperature, high-pressure metamorphism ($500-650^{\circ}C$, 6.9-10 kbar) ensued in the beginning, and then was followed by the high-temperature, middle-pressure($600-740^{\circ}C$, 2.7-5.9 kbar) to ($500-540^{\circ}C$, 3.1 kbar) retrograde metamorphism.

• 대한원격탐사학회지
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• 제35권4호
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• pp.535-544
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• 2019

This study demonstrated the ability of a Landsat-8 OLI multispectral data to identify and delineate hydrothermal alteration zones around auriferous prospects within the crystalline basement, North-western Nigeria. Remote sensing techniques have been widely used in lithological, structural discrimination and alteration rock delineation, and in general geological studies. Several artisanal mining activities for gold deposit occur in the surrounding areas within the basement complex and the search for new possible mineralized zones have heightened in recent times. Systematic Landsat-8 OLI data processing methods such as colour composite, band ratio and minimum noise fraction were used in this study. Colour composite of band 4, 3 and 2 was displayed in Red-Green-Blue colour image to distinguish lithologies. Band ratio ${\frac{4}{2}}$ image displayed in red was used to highlight ferric-ion bearing minerals(hematite, goethite, jarosite) associated with hydrothermal alteration, band ratio ${\frac{5}{6}}$ image displayed in green was used to highlight ferrous-ion bearing minerals such as olivine, amphibole and pyroxenes, while ratio ${\frac{6}{7}}$ image displayed in blue was used to highlight clay minerals, micas, talc-carbonates, etc. Band rationing helped to reduce the topographic illumination effect within images. The result of this study showed the distribution of the lithological units and the hydrothermal alteration zone which can be further prospected for mineral reserves.

• Restorative Dentistry and Endodontics
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• 제45권4호
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• pp.43.1-43.9
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• 2020

A variety of therapeutic modalities can be used for the endodontic treatment of a traumatized tooth with internal root resorption (IRR). The authors present a case report of the successful restoration of a traumatized upper central incisor that was weakened due to severe IRR and subsequent periapical lesion formation. A 20-year-old female patient was referred to our clinic with severe internal resorption and subsequent periapical pathosis destroying the buccal bone wall. Root canal treatment had been initiated previously at another dental practice, but at that time, the patient's condition could not be managed even with several treatments. After cone-beam computed tomography imaging and proper chemomechanical cleaning, the tooth was managed with a mineral trioxide aggregate plug followed by root canal filling using short fiber-reinforced composite, known as the Bioblock technique. This report is the first documentation of the use of the Bioblock technique in the restoration of a traumatized tooth. The Bioblock technique appears to be ideal for restoring wide irregular root canals, as in cases of severe internal resorption, because it can uniquely fill out the hollow irregularities of the canal. However, further long-term clinical investigations are required to provide additional information about this new technique.

• Composites Research
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• 제23권4호
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• pp.1-6
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• 2010

진주조개를 모방한 생체모방 복합재료의 저속충격 하에서의 동적 거동에 대해 연구하였다. 이러한 복합재료는 단백질과 미네랄 층이 계층구조를 이루고 있다. 유한요소해석을 사용하여 복합재료의 충격거동을 해석하였다. 복합재료의 계층구조가 동적 거동에 미치는 영향을 고찰하였다. 생체모방구조물은 계층구조의 차수가 높아짐에 따라 저속충격에 대해 충격지점에서 구조물이 받는 최대 응력과 변위, 접촉하중을 감소시킨다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.313-316
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• 2005

In the recent design of high ductile fiber-reinforced cementitious composite ECC, which exhibits tensile strain-hardening behavior in the hardened state, optimizing both processing mechanical properties for specific applications is critical. This study introduced a method to develop useful ECCs in field, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing, while retaining the ductile material properties. To control the rheological properties of the composite, we first determined basic ECC compositon, which is based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of suspensions were, then, mediated by optimizing dosages of chemical and mineral admixtures. The rheological properties altered by this approach were revealed to be effective in obtaining ECC hardened properties, allowing us to readily achieve the desired function of the fresh ECC.

• Computers and Concrete
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• 제23권4호
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• pp.295-301
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• 2019

In this paper, buckling analyses of composite concrete plate reinforced by piezoelectric nanoparticles is studied. The Halphin-Tsai model is used for obtaining the effective material properties of nano composite concrete plate. The nano composite concrete plate is modeled by Third order shear deformation theory (TSDT). The elastic medium is simulated by Winkler model. Employing nonlinear strains-displacements, stress-strain, the energy equations of concrete plate are obtained and using Hamilton's principal, the governing equations are derived. The governing equations are solved based on Navier method. The effect of piezoelectric nanoparticles volume percent, geometrical parameters of concrete plate and elastic foundation on the buckling load are investigated. Results showed that with increasing Piezoelectric nanoparticles volume percent, the buckling load increases.

• KIEAE Journal
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• 제1권2호
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• pp.47-54
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• 2001

Single sound absorbers such as porous materials, panels, and Helmholts resonators have limited performance with some extents of frequency region. For example, porous materials do not attenuate low frequency sounds, while panels do not absorb high frequency sounds. Composite absorption structure with coverings, porous materials, and air gaps are an alternative for wide band sound absorption. Slits, panels, perforated panels are those materials for coverings, glass wool, mineral wool, polyester, and polyurethane are frequently used porous materials. Air gap between the porous material and background surface is one of major factors which governs the absorption characteristics of composite absorption structures, especially in the low frequency area. Calculations and measurements show that the absorption coefficients of composite absorption structure, in mid and low frequency bands, are getting higher with increased air gaps. Perforated panels rather than slits and panels are good coverings with higher number as far as absorption coefficient is concerned. Perforated panels with porous materials and 37 cm of air gaps in background have high absorption coefficients for all frequency bands, above 0.7 to 1.0. All measurements are performed in reverberation chamber, Mokpo National University, according to ISO 354 and ISO 3382.

• 한국물환경학회지
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• 제32권2호
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• pp.216-221
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• 2016

The adsorption characteristics of mixed heavy metals (Cr(III), As(VI)) in aqueous solution were investigated using a sediment amendment composite. Sediment amendment composite was composed of clean sediment (40%), zeolite (20%), recycled aggregate (10%), steel slag (10%), oyster shell (10%), and cement (10%). The experimental results showed that the adsorption equilibrium was attained after 180 mins. Heavy metal adsorption was characterized using Freundlich and Langmuir equations. The equilibrium adsorption data for the sediment amendment composite better fitted with the Langmuir model than the Freundlich model. The maximum adsorption capacity of Cr(VI) (36.07 mg/g) was higher than As(III) (25.54 mg/g); and the adsorption efficiency of the Cr(VI) and As(III) ions solution decreased with decreasing pH from 2 to 10. The collective results suggested that the sediment amendment composite is a promising material for a reactive cap that controls the release of Cr(VI) and As(III) from contaminated sediments.

• 복합신소재구조학회 논문집
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• 제6권4호
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• pp.8-15
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• 2015

The demand for environmental consideration is on the increase in civil engineering. This study focuses on the development of technology to reduce the use of carbonate cement and improve its performance by using a silicate mineral and hardening agents, and presents the test results for the demonstrative evaluation of the properties of the raw material. Highly active feldspar was used as a binder to augment the bonding of the carbonate cement, and their change in strength was observed after test piece construction with the addition of soluble hardening agent. The uniaxial compression strength of the test piece of the general Portland cement with the addition of 0.5% soluble hardening agent, showed an increase by 33% and that of the test piece of cement with the addition of 70% substituted with feldspar increased by 28%. The strength of viscous soil; classified as soft ground, showed an increase of a maximum of 1.7 times when it was mixed with cement and solidifier depending on the curing period. These tests confirmed that a soluble solidifier is effective for improving the strength of a cement binder and that the highly active feldspar can be used as a binder.