• Journal of Conservation Science
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• 제37권6호
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• pp.701-711
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• 2021

This study identifies the structure and material characteristics of the mural paintings in Daeungjeon at Ssanggyesa temple in Jindo by conducting scientific research and analysis including microscope examination, SEM-EDS, XRD, particle size analysis, and others. According to the analyses, the murals were considered to be of a typical soil mural style for Korean Buddhist murals, given that the walls were made of sand and soil and the murals had layers consisting of wall layers and a finishing layer. However, some finishing layer used calcite, while some ground layer used zinc white beneath the thick paint. In addition, there were similar features to those found on the surfaces of oil paintings such as cracks along with the paint layer, high gloss on surfaces, and thick brush strokes in many areas. It was found that the walls on which the murals were painted were made of soil but that the paint layer was created based on the oil painting technique using drying oil. It determined that the murals were painted in a unique painting style that is rarely found in other typical Buddhist murals in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제28권4A호
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• pp.537-548
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• 2008

Recently, the prestressed unbonded concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with unbonded tendon is different from that of normal bonded PSC beams in that the increment of tendon stress was derived by whole member behavior. The purpose of the present paper is therefore to evaluate the flexural behavior and to propose the equation of ultimate tendon stress by performing static flexural test according to span/depth, concrete compression strength, reinforcement ratio and the effect of existing bonded tendon. From experimental results, for cracking, yielding and ultimate load, the effect of reinforcement ratio was more effective than concrete compression strength, and the beams having high strength concrete had a good performance than having low concrete, but there was no difference between high strength and low strength. And as L/dp was larger, test beams had a long region of ductility. This means that unbonded tendon has a large contribution after reinforcement yielding. Especially, the equation of ACI-318 was not match with test results and had no correlations. After analysis of test results, the equation of ultimate unbonded tendon stress without slip was proposed, and the proposed equation was well matched with test results. So the proposed equation in this paper will be a effective basis for the evaluation of unbonded tendons without slip, analysis and design.

• Composites Research
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• 제36권6호
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• pp.441-447
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• 2023

Recently, as demand for high-strength, lightweight materials has increased, there has been great interest in joining with metals. In the case of mechanical bonding, such as bolting and riveting, chemical bonding using adhesives is attracting attention as stress concentration, cracks, and peeling occur. In this paper, surface treatment was performed to improve the adhesive strength, and the change in adhesive strength was analyzed. For the adhesive strength test were conducted with Carbon Fiber Reinforced Plastic(CFRP), CR340(Steel), and Al6061(Aluminum), and laser and plasma surface treatment were used. After plasma surface treatment, the adhesive strength improved by 7.3% and 39.2% in CFRP-CR340 and CFRP-Al6061, respectively. CR340-Al6061 was improved by 56.2% in laser surface treatment. Surface free energy(SFE) was measured by contact angle after plasma treatment, and it is thought that the adhesion strength was improved by minimizing damage through a chemical reaction mechanism. For laser surface treatment, it is thought that creates a rough bonding surface and improves adhesive strength due to the mechanical interlocking effect. Therefore, surface treatment is effect to improve adhesive strength, and based on this paper, the long-term fatigue test will be conducted to prevent fatigue failure, which is a representative cause of actual structural damage.

• The Journal of the Acoustical Society of Korea
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• 제29권5호
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• pp.314-324
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• 2010

In waveguide structures, waves may be partially reflected by local non-uniformities. The effects of local non-uniformities has been previously investigated by means of a combined spectral element and finite element (SE/FE) method at relatively low frequencies. However, since the SE is formulated based on a beam theory, the SE/FE method is not appropriated for analysis at higher frequencies where complex deformation of the waveguide occurs. So it is necessary to extend this approach for high frequencies. For the wave propagation at higher frequencies, a combined spectral super element and finite element (SSE/FE) method is introduced in this paper. As an example of the application of this method, wave reflection and transmission due to a local defect in a rail are simulated at frequencies between 20kHz and 30kHz. Also numerical errors are evaluated by means of the conservation of the incident power.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• 제13권3호
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• pp.168-177
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• 2008

Trafficablility of a miner and potential environmental impacts due to mining activities should be considered in the selection of a commercial manganese nodule mining site. These two factors can be evaluated comparatively with physical properties and shear strength of sea-bed sediments. For the qualitative comparison of potential minig sites in terms of these two factors, physical properties such as water contents, void ratios, porosities, and grain densities, and shear strengths of surface sediments were determined for the three potential manganese nodule mining sites(KR1, KR2, and KR5) in the Korean manganese nodule contract area, northeast Pacific. For the study, sediment samples were collected from 107 stations from 2004 to 2006. The physical properties of surface sediments showed more significant differences between northern(KR1, KR2) and southern(KR5) blocks than between northern blocks(KR1 vs. KR2). Water content, void ratio, and porosity of sediments from KR5 were relatively higher than those from KR1 and KR2. Grain density of sediments from KR5 was relatively lower than those from KR1 and KR2. Shear strengths of the top 10cm sediments were higher in KR1 and KR2, whereas those of the deeper part were highest in KR5 block. Generally, sediments of high water contents are less suspendible than those of the low water contents by benthic disturbances, thus less disturbance is expected in the sediments of high water content by mining activities. In terms of trafficability, the shear strength of sediment below 10 cm deep is more important than shallower part because miner will disturb at least top 10 cm interval of the surface sediments. Base on these results, we conclude that KR5 area will be the best site for commercial mining among three investigated sites in this study.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.205-208
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• 2005

최근 열선 화학 기상 증착법(HWCVD)은 낮은 온도에서 TFT용 Poly Si 중착을 할 수 있다는 점과 실리콘 박막을 빠른 속도로 증착할 수 있다는 점에서 각광을 받고 있다. 본 연구에서는 HWCVD를 이용하여 태양전지를 제조하고 그 특성을 평가하였다. 조건에 따른 실리콘 박막의 특성 변화를 알기 위해 corning glass 및 실리콘 wafer에 다양한 조건에서 단위 박막(intrinsic layer)을 증착하였고 이 결과를 바탕으로 p/i/n 구조의 태양전지를 제조하였다. Ta 열선 온도는 1700-2000도였고 가스 원료인 $SiH_4$와 수소의 비율을 조절하면서 그 영향을 관찰하였다. 태양전지의 경우 p충과 n충은 PECVD로 증착하였으며 단위박막 및 태양전지 i충 증착시 기판과 열선간의 거리는 7cm, 기판 온도는 $200^{\circ}C$와 $250^{\circ}C$로 고정하였고 작업압력은 30mTorr였다. 단위 박막 특성 평가를 위해 암/광 전도도, SEM, Raman Scattering, FT-IR등을 사용하였으며 태양전지 특성 평가를 위해 I-V 및 Spectral response를 측정하였다. 열선 온도가 증가함에 따라 증착속도 및 결정화 분율은 증가하였다. 특히 비정질에서 결정질로 전이되는 구간은 매우 좁았으며 여러 분석 방법에서 일치되는 결과를 보였다. $SiH_4$ 유량이 늘어날수록 비정질이 결정질로 바뀌는 열선 온도가 증가하였으며 기판 온도가 낮을 경우 또한 결정으로 바뀌는 열선 온도가 증가하였다. 태양전지의 경우 열선 온도가 증가함에 따라 $V_{oc}$ 및 W가 낮아졌으며 $J_{sc}$, 는 증가하는 경향을 보였으며 결정질 비율이 증가하는 것을 관찰할 수 있었다. 이러한 경향은 quantum efficiency 결과에서도 확인할 수 있었다.용을 반복하면서 석재 내부와 외부의 암석 및 결정에 균열과 미세열극 등이 생성되어 석재 자체의 구조적 안정성에 영향을 주고 있다. 따라서 감은사지 석탑은 지리적 환경 차이로 인해 일반적인 환경의 석조물들과는 다른 형태의 풍화양상을 보이고 있어서 풍화양상 및 풍화형태에 대한 정확한 연구와 이해를 바탕으로 보존대책이 마련되어야 한다.되었다. 이런 모든 시편들을 각 탈염방법에 따라 탈염처리한 후 XRD와 SEM-EDS으로 분석한 결과 인철광과 침철광은 어떠한 변화도 보이지 않았고, 다만 적금광으로 동정된 시편만이 잔존하지 않았다. 철기 제작별 $Cl^-$ 이온 추출량과 탈염효과에 대한 비교 실험은 이온 크로마토그래피 분석 결과와 마찬가지로 단조 철제유물이 주조 철제보다 $Cl^-$ 이온을 많이 가지고 있었으며, 탈염 처리 후에는 $Cl^-$ 이온은 전혀 발견되지 않았다. 이상의 결과 $K_2CO_3$와 Sodium 용액은 탈염처리에서 가장 적합한 탈염처리 용액으로 알수가 있었으며 특히 어떠한 탈염 용액으로 유물을 처리한다 해도 철제유물에 생성된 부식물은 제거되지 않는다는 것을 알게 되었다. 따라서 보존처리자는 유물 표면의 부식 상태만을 보고 처리하기 보다는 철기제작물로 고려하여 처리하는 것이 필요하다. 또한 금속에 부식을 야기시키는 $Cl^-$ 이온과 부식물을 완전하게 제거하여 탈염처리를 하는 것이 유물 부식을 최대한 지연시킬 수 있는 것이라 생각된다.TEX>$88\%$)였다.(P=0.063). 결론: 본 연구에서는 MTHFR C/T & T/T 유전자 다형성이 위암의 발생과 그 위치에 대해 관련이 있는 것으로 여겨지고, 흡연력, 음주력과는 관련이 없는 것으로 여겨진다.험이 커지는 경향을 보였으나, 나이 및 병기, 종양의 크기, MD-BED $Gy_{10}$ 등의 예후 인자를 보정한 다변

• The Journal of the Petrological Society of Korea
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• 제21권2호
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• pp.263-275
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• 2012

Jurassic Daebo biotite granites, known as one of the main stone resources in the country, are widely and away distributed in the Pocheon and Yangju areas of the mid Gyeonggi massif. The objects of the study are mainly to reveal the unique characteristics of grain size, rock color, mineral composition, physical property and fracture system from the above biotite granites. Biotite granites from the Pocheon area (PG) and Yangju area (YG) are represented by coarse-grained and light gray, and medium to coarse-grained and grayish to light gray, respectively. In modes, main minerals of Qz+Af+Pl (quartz+alkali feldspar+plagioclase) are more increased in the PG, and accessories of biotite are more increased in the YG, which differences can cause the PG more bright light gray than the YG. Specific gravity (SG) shows somewhat more increasing in the YG than the PG. These differences can be caused by more increasing in biotite contents of higher specific gravity compared to the major minerals in the former than the latter. Absorption ratio (AR) and porosity (PR) of the PG and YG show the same values of 0.33 % and 0.86 %, respectively. In the correlations, PR vs SG and AR vs PR show gradually negative and distinctly positive trends, respectively. Compressive strength (CS) and tensile strength (TS) show increasing in the PG (CS: 1,775 $kg/cm^2$, TS: 87 $kg/cm^2$) than the YG (CS: 1,647 $kg/cm^2$, TS: 79 $kg/cm^2$). These strength characteristics could be attributed to the inherent rock textures of them. Abrasive hardness (AH) also shows a little increasing in PG, which can be caused by increase in quartz contents having higher hardness than the other major minerals. Orientations of fracture sets from the PG and YG were compared with those of vertical rift and grain planes in Mesozoic granites of the country. From the overlapped diagram, the distribution pattern between fracture sets and above vertical planes suggests that microcrack systems developed in Mesozoic granites in Korea occur also in the Daebo biotite granite bodies of the mid Gyeonggi massif. From the relation diagram showing the characteristics of fracture patterns for the above two area, PG and YG may have more potentiality for dimension and non-dimension stone resources, respectively.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.165-165
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• 2017

지난 수 십 년 동안, 전 세계적으로 자원의 소비가 급격히 증가하게 되면서 최근 자원 고갈은 물론 환경오염이 커다란 이슈로 문제가 되고 있다. 이에 따라 재료 관련 분야에 있어서는 보다 효율적이고 친환경적인 방법으로 자원을 활용해야 된다는 필요성이 대두되었고 이와 같은 관점에서 목적하는 성분이 우수하고 환경 친화적인 표면처리 재료 개발연구가 활발하게 진행되고 있는 실정이다. 그 중 플라즈마 전해 산화(Plasma Electrolytic Oxidation, PEO)는 알루미늄, 마그네슘 등의 경금속의 경도를 향상시키고 높은 내마모성, 내식성을 갖게 하는 표면처리로써 그 관심이 증가하고 있다. 이 플라즈마 전해 산화는 일반적으로 공정비용 대비 효과적이고 환경 친화적이며 코팅 성능 면에서 우수하다고 알려져 있다. 이러한 고유한 특성으로 인해 플라즈마 전해 산화 코팅은 최근 몇 년 동안 기계, 자동차, 우주항공, 의학 및 전기 산업 등의 분야에서 그 적용이 점차 증가하고 있는 상황이다. 한편, 플라즈마 전해 산화 코팅을 하는 모재들의 경우 부동태 산화피막을 용이하게 형성할 수 있는 특성의 모재에 한정되고 있어서 그 응용확대에 한계가 있는 것이 사실이다. 따라서 본 연구에서는 플라즈마 전해 산화법을 사용하여 용융알루미늄도금 강판 상에 산화피막 형성을 시도하였다. 전원공급 장치의 양극은 전해질 속에 잠겨있는 작동전극에 연결하고 음극은 대전극 역할을 하는 스테인레스강 전해질 용기에 연결되었다. 전해질은 Sodium Aluminate 및 기타 첨가제를 함유한 것을 사용하였고 온도는 열교환기를 사용하여 $30^{\circ}C$ 이하로 유지되었다. 또한 여기서 전류밀도는 $5{\sim}10A/dm^2$, 실험 주파수는 700Hz, Duty cycle은 30 및 90%의 각 조건에서 공정처리 시간을 각각 30분 및 60분 동안 진행하였다. 이와 같은 조건에서 형성한 막들에 대해서는 주사형전자현미경(SEM)을 이용하여 코팅 막의 표면 및 단면의 모폴로지를 관찰하였음은 물론 EDS 및 XRD 측정을 통하여 원소조성분포 및 결정구조를 각각 분석하였다. 또한 이 코팅 막들에 대한 내식성은 5% 염수분무 환경 중 노출시험(Salt spray test), 3% NaCl 용액에서의 침지 시험 및 전기화학적 동전위 양극분극(Potentiodynamic Polarization) 시험을 진행하여 평가하였다. 이상의 실험결과에 의하면, 제작조건별 플라즈마 전해 산화 코팅 막의 모폴로지 및 결정구조가 상이하게 나타나는 것을 알 수 있었다. 코팅 막의 모폴로지 관찰 결과, 공정 시간에 비례하여 표면에 존재하는 원형 기공의 수는 감소하였으나 그 크기가 커지고 크레이터의 직경 또한 커진 것이 확인되었다. 이 기공은 마이크로 방전에 의해 형성된다고 알려져 있는데 공정 시간이 증가함에 따라 코팅 두께가 점차 증가하여 마이크로 방전의 빈도수가 줄어들고 그 강도는 증가하게 되어 기공 크기가 증가한 것으로 사료된다. 또한 공정시간이 긴 시편에서 표면에 크랙이 다수 존재하는 것으로 확인되었다. 이것은 방전에 의해 고온이 된 소재가 차가운 전해질과 만나게 되어 생긴 큰 온도구배로 인해 강한 열응력이 발생하여 균열을 초래한 것으로 보인다. 조성원소 분석 결과 원형 기공 주변의 크레이터 영역에는 알루미늄이 풍부하였으며 그 주변에 결절상을 갖는 구조에서는 전해질 성분의 원소가 포함되어 있는 것이 확인되었다. 이러한 코팅 막의 표면 특성은 내식성에 영향을 주게 된 원인으로 사료된다. 동전위 분극측정 결과에 의하면 플라즈마 전해 산화 공정 시간이 길어질수록 부식전류밀도가 증가하였다. 이것은 공정시간이 길어짐에 따라 강한 방전이 발생하여 기공의 크기가 증가하고 크랙이 발생하게 되면서 내식성이 저하된 것으로 판단된다. 종합적으로 재료특성 분석 및 내식성 평가를 분석한 결과, 플라즈마 전해 산화의 공정 시간이 너무 길게 되면 오히려 내식성은 저하되는 것이 확인되었다. 이상의 연구를 통하여 고내식 특성을 갖는 플라즈마 전해 산화 막의 유효성을 확인하였으며 용융알루미늄강판 상에 실시한 플라즈마 전해 산화 처리에 대한 기초적인 응용 지침을 제시할 수 있을 것으로 사료된다.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• 제2권2호
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• pp.125-137
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• 1997

To study the vertical variation of heavy metal and Rare Earth Element (REE) contents in deep-sea sediments, eighteen cores were sampled from the Korea Deep-sea Environmental Study (KODES)-96 area in the C-C zone (Clarion-Clipperton fracture zone), northeast equatorial Pacific. Sediment columns can be divided into three units based on sediment colors and geochemical characters; uppermost Unit I with brown color, middle Unit II with pale brown color and smaller Ni/Cu ratio than the ratio in Unit I, and lowermost Unit III with dark (brown) colors and higher contents of Mn, Ni, Cu, and REEs than those in Unit I and II. Unit II can be divided more into two layers of upper Unit IIa and lower Unit IIb. Unit IIb is characterized by high contents of Cu, 3+REEs (REEs except Ce), smectite, and severely deteriorated fossil tests. Unit III can also be divided into two units; upper Unit IIIa with dark brown color, and lower Unit IIIb with black color and enriched Mn and Fe. The KODES area was located near from the East Pacific Rise (EPR) When Unit III Sediments were deposited, considering the hiatus between Unit II and III (Quaternary-Tertiary boundary) and the spreading rate (10 cm/yr) and direction (north southern west) of the Pacific plate from the EPR. High contents of Mn and Fe in Unit IIIb may be related with hydrothermal influence from the EPR. Meanwhile, Unit IIb (about 2~3 Ma) and Unit III (11~30 Ma) layers were probably formed near (or under) the equatorial high productivity zone, and accordingly received a lot of organic materials. As a result, Cu and 3+REEs, closely associated with organic materials, are enriched in smectite and/or Ca-P composites (fish bone debrise, biogenic apatite) after decomposition and reprecipitation on the sea floor. Higher contents of Cu and 3+REEs in Unit IIb and III are suggested to be the result of abundant supply of organic substances in the equatorial high productivity zone.

• The Journal of Korean Academy of Prosthodontics
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• 제47권4호
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• pp.424-434
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• 2009

Statement of problem: Problems such as loosening and fractures of retained screws and fracture of implant fixture have been frequently reported in implant prosthesis. Purpose: Implant has weak mechanical properties against lateral loading compared to vertical occlusal loading, and therefore, stress analysis of implant fixture depending on its material and geometric features is needed. Material and methods: Total 28 of external hexed implants were divided into 7 of 4 groups; Group A (3i, FULL $OSSEOTITE^{(R)}$Implant), Group B (Nobelbiocare, $Br{\aa}nemark$ $System^{(R)}$Mk III Groovy RP), Group C (Neobiotec, $SinusQuick^{TM}$ EB), Group D (Osstem, US-II). The type III gold alloy prostheses were fabricated using adequate UCLA gold abutments. Fixture, abutment screw, and abutment were connected and cross-sectioned vertically. Hardness test was conducted using MXT-$\alpha$. For fatigue fracture test, with MTS 810, the specimens were loaded to the extent of 60-600 N until fracture occurred. The fracture pattern of abutment screw and fixture was observed under scanning electron microscope. A comparative study of stress distribution and fracture area of abutment screw and fixture was carried out through finite element analysis Results: 1. In Vicker's hardness test of abutment screw, the highest value was measured in group A and lowest value was measured in group D. 2. In all implant groups, implant fixture fractures occurred mainly at the 3-4th fixture thread valley where tensile stress was concentrated. When the fatigue life was compared, significant difference was found between the group A, B, C and D (P<.05). 3. The fracture patterns of group B and group D showed complex failure type, a fracture behavior including transverse and longitudinal failure patterns in both fixture and abutment screw. In Group A and C, however, the transverse failure of fixture was only observed. 4. The finite element analysis infers that a fatigue crack started at the fixture surface. Conclusion: The maximum tensile stress was found in the implant fixture at the level of cortical bone. The fatigue fracture occurred when the dead space of implant fixture coincides with jig surface where the maximum tensile stress was generated. To increase implant durability, prevention of surrounding bone resorption is important. However, if the bone resorption progresses to the level of dead space, the frequency of implant fracture would increase. Thus, proper management is needed.