• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
• /
• pp.415-429
• /
• 2002

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi-mode conversion of guided wave scattering problems.

• Korean Journal of Radiology
• /
• 제1권3호
• /
• pp.162-164
• /
• 2000

Malignant transformation of teratoma in the anterior mediastinum is rare; the mass usually has a long history and is seen in older patients. We report a case of teratoma with malignant transformation in the anterior mediastinum, complicated by rupture. CT revealed a lobulated, inhomogeneous cystic mass with a fat component and wall calcifications. The lateral wall was disrupted and consolidation in the adjacent left upper lobe was noted, suggesting rupture. A heterogeneously enhanced solid portion, obliterating the fat plane between the mass and the great vessels was present in the medial aspect of the mass, and pathologic examination demonstrated the presence of adenocarcinoma.

• Journal of Electrochemical Science and Technology
• /
• 제13권3호
• /
• pp.407-415
• /
• 2022

Surface coating of cathodes is an essential process for all-solid-state batteries (ASSBs) based on sulfide electrolytes as it efficiently suppresses interfacial reactions between oxide cathodes and sulfide electrolytes. Based on computational calculations, Li₃PO₄ has been suggested as a promising coating material because of its higher stability with sulfides and its optimal ionic conductivity. However, it has hardly been applied to the coating of ASSBs due to the absence of a suitable coating process, including the selection of source material that is compatible with ASSBs. In this study, polyphosphoric acid (PPA) and (NH₄)₂HPO₄ were used as source materials for preparing a Li₃PO₄ coating for ASSBs, and the properties of the coating layer and coated cathodes were compared. The Li₃PO₄ layer fabricated using the (NH₄)₂HPO₄ source was rough and inhomogeneous, which is not suitable for the protection of the cathodes. Moreover, the water-based coating solution with the (NH₄)₂HPO₄ source can deteriorate the electrochemical performance of high-Ni cathodes that are vulnerable to water. In contrast, when an alcohol-based solvent was used, the PPA source enabled the formation of a thin and homogeneous coating layer on the cathode surface. As a consequence, the ASSBs containing the Li₃PO₄-coated cathode prepared by the PPA source exhibited significantly enhanced discharge and rate capabilities compared to ASSBs containing a pristine cathode or Li₃PO₄-coated cathode prepared by the (NH₄)₂HPO₄ source.

• Journal of Radiation Protection and Research
• /
• 제33권4호
• /
• pp.151-160
• /
• 2008

국내 원전에서는 과거에 불균일 방사선장이 형성되는 고피폭 방사선작업에 2개의 복수선량계(TLD)를 머리와 기슴에 패용하였으며, 이들 선량계 판독값 중에서 최대값을 유효선량으로 평가함으로써 일정 부분이 과대평가되고 있는 것으로 나타났다. 따라서 이러한 문제점을 개선하고자 국제적인 기관에서 제시된 복수선량계 알고리즘을 대상으로 적절한 알고리즘을 선정하기 위한 현장적용 시험을 실시하였다. 여기에는 캐나다 원전사업자(OPG), 미국표준기술협회(ANSI HPS N13.41), NCRP(55/50), NCRP(70/30), EPRI (NRC), Lakshmanan, Kim(Texas A&M University) 알고리즘 등을 대상으로 하였고, 국내 원전의 계획예방정비기간동안 고피폭이 예상되는 방사선작업을 대상으로 작업종사자에게 3개의 복수선량계를 가슴, 머리, 등에 동시에 패용하였고 판독하였다. 이 시험 결과에 따르면 Lakshmanan 알고리즘을 제외하고 유효선량 평가에서 모든 복수선량계 알고리즘이 거의 유사한 경향을 보이는 것으로 나타났다. 한편 현장적용시험 결과와 이들 알고리즘의 기술적 배경과 방사선작업과정에서의 편의성 등을 종합적으로 고려하여 NCRP(55/50) 알고리즘을 최종적으로 선정하였다. 또한 복수선량계 지급조건은 INPO와 ANSI의 지침을 검토하여 빙사선량율이 1 mSv/hr 이상이면서 인체 특정부위 간의 선량율이 30% 이상차이가 나고 단일 작업에서 2mSv 이상피폭을 받을 것으로 예상될 때 지급하는 것으로 결정하였다.

• 제어로봇시스템학회논문지
• /
• 제13권11호
• /
• pp.1060-1066
• /
• 2007

When a high-energy ultrasound propagates through a solid body that contains a crack or a delamination, the two faces of the defect do not ordinarily vibrate in unison, and dissipative phenomena such as friction, rubbing and clapping between the faces will convert some of the vibrational energy to heat. By combining this heating effect with infrared imaging, one can detect a subsurface defect in material efficiently. In this paper a detection of the welding defect of thin SUS 304 plates using the UIR (ultrasonic infrared imaging) technology is described. A low frequency (20kHz) ultrasonic transducer was used to infuse the welded thin SUS 304 plates with a short pulse of sound for 280ms. The ultrasonic source has a maximum power of 2kW. The surface temperature of the area under inspection is imaged by a thermal infrared camera that is coupled to a fast frame grabber in a computer. The hot spots, which are a small area around the defect tip and heated up highly, are observed. From the sequence of the thermosonic images, the location of defective or inhomogeneous regions in the welded thin SUS 304 plates can be detected easily.

• 한국세라믹학회지
• /
• 제27권2호
• /
• pp.187-194
• /
• 1990

Effects of MnO2 addition ranged from 0.0wt% to 5.0wt% on the microstructure and dielectric and piezoelectric properties of the Pb(Zr0.52 Ti0.48)O3 Ceramics have been investigated. The solubility limit of MnO2 in Pb(Zr0.52 Ti0.48)O3 is about 0.5wt%, and MnO2 as a valence state of Mn3+ is substituted for (Zr, Ti) lattice site in PZT solid-solution. The addition of MnO2 up to 0.5wt% in Pb(Zr0.52 Ti0.48)O3 brings increase of density, but decreased of grain size and tetragonality. Dielectric constant slightly decreases, but both coupling factor(Kp) and mechanical quality factor(Qm) increase with the addition of MnO2. However, excess amount of MnO2 addition more than 0.75wt% results in rapid decrease of resistance. Dielectric constant and tan $\delta$ increase due to the second phase and inhomogeneous Mn distribution.

• Journal of Electrical Engineering and Technology
• /
• 제10권3호
• /
• pp.1181-1187
• /
• 2015

Sulfur hexafluoride (SF₆) gas is used widely in electric power equipment such as Gas Insulated Switchgear (GIS), Gas Insulation transmission Line (GIL), and Gas Circuit Breaker (GCB). But applications of SF₆ should be restricted because SF6 gas is one of the greenhouse effect gases. To reduce use of SF₆ gas, a study on eco-friendly alternative insulation medium is needed. In this paper, we investigated lightning impulse (LI) breakdown of dry-air which is attracting attention as an ecofriendly alternative gas and the LI breakdown of hybrid insulation combined with dry-air and solid insulation (Room-Temperature Vulcanizing Silicone Rubber-RTV SIR) and dry-air in inhomogeneous fields according to gap distance and pressure. The experiment results showed that the LI breakdown strength of hybrid insulation system was higher than that of dry-air insulation system. It was verified that the development of technology related to eco-friendly power apparatus compact such GIS, GCB and GIL can be used as basic research data.

• 한국재료학회지
• /
• 제27권3호
• /
• pp.155-160
• /
• 2017

Doped-$LaCrO_3$ perovskites, because of their good electrical conductivity and thermal stability in oxidizing and/or reducing environments, are used in high temperature solid oxide fuel cells as a gas-tight and electrically conductive interconnection layer. In this study, perovskite $(La_{0.8}Ca_{0.2})(Cr_{0.9}Co_{0.1})O_3$ (LCCC) coatings manufactured by atmospheric plasma spraying followed by heat treatment at $1200^{\circ}C$ have been investigated in terms of microstructural defects, gas tightness and electrical conductivity. The plasma-sprayed LCCC coating formed an inhomogeneous layered structure after the successive deposition of fully-melted liquid droplets and/or partially-melted droplets. Micro-sized defects including unfilled pores, intersplat pores and micro-cracks in the plasma-sprayed LCCC coating were connected together and allowed substantial amounts gas to pass through the coating. Subsequent heat treatment at $1200^{\circ}C$ formed a homogeneous granule microstructure with a small number of isolated pores, providing a substantial improvement in the gas-tightness of the LCCC coating. The electrical conductivity of the LCCC coating was consequently enhanced due to the complete elimination of inter-splat pores and micro-cracks, and reached 53 S/cm at $900^{\circ}C$.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제45권1호
• /
• pp.43-47
• /
• 2019

The characteristics of extra-nasopharyngeal angiofibromas tend to be different from angiofibromas of the nasopharynx according to patient gender, patient age, prevalence, affected site, pathogenesis, and clinical and epidemiological features. We report a case of an extra-nasopharyngeal angiofibroma in a 28-year-old man referred to the ENT Clinic for right-sided epistaxis, airflow impairment and nasal swelling. The right nostril was completely occluded works by a reddish-yellow mass that bled easily. The computed tomography scan revealed an "inhomogeneous solid lesion in the nasal fossa". With the patient under general anesthesia, the formation in the anterior portion of the right side of the nasal septum was removed up to its vascular base. Although electrical cauterization efficiently controlled the bleeding, we abraded the sub-perichondral area to prevent further bleeding as well as recurrence. The histological exam report confirmed the diagnosis of angiofibroma. As in our case, epistaxis is commonly the presenting sign of angiofibroma. Yet its onset was peculiar, given that the bleeding started with a low impact trauma. The nasal swelling was also a relevant feature as well as the breathing impairment. Although uncommon, nasal septal angiofibromas should considered in patients with epistaxis.

• 한국광물학회지
• /
• 제29권3호
• /
• pp.131-139
• /
• 2016

마스컬리나이트(maskelynite)는 강한 충격에 의해 운석이나 크레이터(crater)에서 형성된 장석 조성의 비정질 상으로서, 마스컬리나이트의 형성 메커니즘에 대한 이해는 운석의 충격 변성 압력에 대한 중요한 정보를 제공한다. 본 연구는 마스컬리나이트의 형성 메커니즘을 규명하기 위한 예비연구로서, 달운석 Mount DeWitt (DEW) 12007에서 관찰되는 사장석과 마스컬리나이트의 충격 압력의 불균일성을 연구하였다. 달운석 DEW 12007에서 대부분의 사장석 입자 일부가 마스컬리나이트로 전이하여, 하나의 입자 내에서 사장석과 마스컬리나이트가 방향성을 가지고 혼재하는 양상이 관찰된다. 주사 전자 현미경의 후방 산란 이미지 관찰 결과, 마스컬리나이트 내부에 평면 변형 구조가 남아 있는 것은 다이어플렉틱 글래스일 가능성을 지시하는 것으로 보이는 반면, 입자 경계를 따라 사장석이 용융 후 재결정된 흔적도 나타난다. 라만 분광분석 결과는 사장석이 약 5-32 GPa, 마스컬리나이트가 26-45 GPa의 충격 변성 압력을 받았음을 지시한다. 이와 같이 한 입자 내에서 서로 다른 충격 변성 압력은 충격파의 불균일한 분포와 같은 운석 외부에 의한 원인 또는 사장석 입자의 물리적, 화학적 특성과 같은 운석 자체의 원인에 의해 발생할 수 있다. 하지만 라만 분광분석은 비정질 상(phase)인 마스컬리나이트의 원자 구조를 규명하기에는 한계가 있으며, 고압 환경에서 형성될 것으로 예상되는 고배위수 원자 환경의 관찰이 힘들다. 따라서 장석과 마스컬리나이트의 충격 압력 및 형성 메커니즘을 이해하기 위해, 장석과 마스컬리나이트의 화학 조성 및 원자 단위 구조의 규명이 필요하다.