• 한국산학기술학회논문지
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• 제16권6호
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• pp.4131-4136
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• 2015

본 논문은 반사방지막의 성능을 더 정확히 비교 및 분석하기 위하여 기존 방법과 달리 반사방지막에 수직입사가 아닌 입사각이 $8^{\circ}$에서 $60^{\circ}$까지 변화한다고 가정하고 단층 구조와 다층 구조의 반사방지막의 평균반사율을 계산하고 비교하였다. 입사파의 파장범위를 400 nm ~ 1200 nm 라고 가정하고, 분석에 사용된 반사방지막의 구조는 두께 180 nm인 1차 및 5차 함수의 굴절률 분포를 갖는 6층 구조와 균일한 굴절률 분포를 갖는 단층구조이다. 분석 결과로써 180 nm 단층구조의 경우 평균반사율이 19.6 % 이고, 같은 두께의 6층 구조의 1차 함수 굴절률 분포에서는 14.2 % 이고, 5차 함수 경우에는 11.6 %의 결과를 얻어 균일한 굴절률 분포의 단층구조 보다 5차 함수 굴절률 분포를 갖는 6층 구조의 경우 약 8%의 반사율 감소 효과를 보았다. 이러한 결과는 향후 광소자 및 광 필터에 적용되는 반사방지막 제작에 용용 될 수 있다고 판단된다.

• 한국토양환경학회지
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• 제3권1호
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• pp.21-30
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• 1998

본 조사의 목적은 적적한 조사방법이 미흡한 주유소에서의 오염현황 조사방법 및 그에 따른 주변지역으로의 오염물질이전 및 환경적 영향을 평가하는 것이다. Site assessment 방법에는 몇가지의 접근방법이 있는데, 본 연구에서는 정덕영(1997)에 의해 제안된 임의선정법/특별조사법 중 임의 격자법을 사용하였다. 조사결과에 의하면, 주유소에서의 물질성상은 몇 가지의 형태로 분류할 수 있었다. 지층구조는 약 1.5M까지는 매립토 (잡석&모래)로 충진하였으며, 1.8-3.5M 까지는 부드러운 모래와 미사토(Silty Sand빈 자연적인 토양층을 나타내고 있었다. 또한 4.0M 가까이에는 풍화토(C층) 출현하였다. (그림3. 지층구조측면도 참조). 또한, 저장탱크지역의 지하수위는 약 2.0M이며 남쪽에 흐르고 있는 개천의 수위와 거의 일정하게 유지되고 있음을 알 수 있었다. 결론적으로, 본 주유소 현황조사에 의하면, 실제의 누출이 UST 및 배관에서 진행되었으며, 오염농도는 대책지역기준인 200PPM을 초과한 것이 확인되었고, 오염원은 면적기준 $45M^{2}$내지 $50M^{2}$에 깊이 약 4M정도로 확산되어 있으며 2.0M에 서 3.5M사이에 부분적으로 고농도로 축적되어 있는 것이 확인되었고 오염의 정도는 계절에 따른 지하수위의 차이에 의해 이동된 것을 본 연구를 통하여 알아낼 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.109-109
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• 2010

$Er^{3+}$ ion shows a stable and efficient luminescence at 1.54mm due to its $^4I_{13/2}\;{\rightarrow}\;^4I_{15/2}$ intra-4f transition. As this corresponds to the low-loss window of silica-based optical fibers, Er-based light sources have become a mainstay of the long-distance telecom. In most telecom applications, $Er^{3+}$ ions are excited via resonant optical pumping. However, if nanocluster-Si (nc-Si) are co-doped with $Er^{3+}$, $Er^{3+}$ can be excited via energy transfer from excited electrical carriers in the nc-Si as well. This combines the broad, strong absorption band of nc-Si with narrow, stable emission spectra of $Er^{3+}$ to allow top-pumping with off-resonant, low-cost broadband light sources as well as electrical pumping. A widely used method to achieve nc-Si sensitization of $Er^{3+}$ is high-temperature annealing of Er-doped, non-stoichiometric amorphous thin film with excess Si (e.g.,silicon-rich silicon oxide(SRSO)) to precipitate nc-Si and optically activate $Er^{3+}$ at the same time. Unfortunately, such precipitation and growth of nc-Si into Er-doped oxide matrix can lead to $Er^{3+}$ clustering away from nc-Si at anneal temperatures much lower than ${\sim}1000^{\circ}C$ that is necessary for full optical activation of $Er^{3+}$ in $SiO_2$. Recently, silicon-rich silicon nitride (SRSN) was reported to be a promising alternative to SRSO that can overcome this problem of Er clustering. But as nc-Si formation and optical activation $Er^{3+}$ remain linked in Er-doped SRSN, it is not clear which mechanism is responsible for the observed improvement. In this paper, we report on investigating the effect of separating the nc-Si formation and $Er^{3+}$ activation by using hetero-multilayers that consist of nm-thin SRSO or SRSN sensitizing layers with Er-doped $SiO_2$ or $Si_3N_4$ luminescing layers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.281.2-281.2
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• 2013

Since heavy metal ions included in water or food resources have critical effects on human health, highly sensitive, rapid and selective analysis for heavy metal detection has been extensively explored by means of electrochemical, optical and colorimetric methods. For example, quantum dots (QDs), such as semiconductor QDs, have received enormous attention due to extraordinary optical properties including high fluorescence intensity and its narrow emission peaks, and have been utilized for heavy metal ion detection. However, the semiconductor QDs have a drawback of serious toxicity derived from cadmium, lead and other lethal elements, thereby limiting its application in the environmental screening system. On the other hand, Graphene oxide (GO) has proven its superlative properties of biocompatibility, unique photoluminescence (PL), good quenching efficiency and facile surface modification. Recently, the size of GO was controlled to a few nanometers, enhancing its optical properties to be applied for biological or chemical sensors. Interestingly, the presence of various oxygenous functional groups of GO contributes to opening the band gap of graphene, resulting in a unique PL emission pattern, and the control of the sp2 domain in the sp3 matrix of GO can tune the PL intensity as well as the PL emission wavelength. Herein, we reported a photoluminescent GO array on which heavy metal ion-specific DNA aptamers were immobilized, and sensitive and multiplex heavy metal ion detection was performed utilizing fluorescence resonance energy transfer (FRET) between the photoluminescent monolayered GO and the captured metal ion.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.731-736
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• 2000

The recently developed BEM-based NAH(nearfield acoustical holography) is a useful technique for identifying the sound source of vibrating objects. The acoustic parameters of a sound source can be reconstructed by using the vibro-acoustic transfer matrix, which is determined by means of BEM, and the sound pressure measured in the nearfield. Theoretically, one can come up with a very nice reconstructed result as the field plane gets near to the source surface. However, when a microphone is placed in the very close nearfield of the source surface, the scattering, reflection, or resonance in the gap between the source and the microphone can distort the acoustic field, and therefore, the measured field pressure would differ from the actual one in the absence of the microphone. In order to analyze this problem, the interference effect of the microphone is numerically calculated by using the nonsingular BEM that yields very small error in the nearfield. From this analysis, it is found that the prediction error of the field pressure decreases firstly and then increases as the microphone approaches the vibrating surface from the farfield to the close nearfield. It is noted that the microphone should be separated from the source surface by at least a diameter of the microphone for an error ratio less than 2% in the low frequency range less than about 2.7kHz. This means that if one wants to put a microphone in the very close nearfield. a microphone with small diameter should be used.

• 한국산업정보학회논문지
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• 제13권1호
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• pp.37-45
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• 2008

본 논문에서는 반투영 거울을 사용하여 원하는 출력물을 허공에 디스플레이 하는 방식의 전시물 안내 시스템을 제안한다. 관람객이 전시물을 관람시 즉각적인 정보 획득이 가능하도록, 전시물에 대한 설명을 전시물 주변에 출력한다. 이를 위해 본 논문에서는 세 가지 문제를 해결한다. 첫째, 실시간 입력 카메라영상을 사용하여 위치 추적을 한다. 이를 통하여 고정된 전시물뿐만 아니라, 유동적인 전시물에도 사용이 가능하다. 둘째, 실시간으로 계산되어진 대상의 위치좌표를 이용하여 결과물을 출력할 때, 자연스러운 이동을 위하여 병렬처리를 통한 추적 알고리즘을 사용한다. 셋째, 공간 증강 현실 시스템제작을 위해 전시 공간 앞면에 반투영 거울을 설치하는데, 설치된 거울의 기울기로 인하여 생기는 왜곡은 반사 변환 행렬을 사용하여 보정한다. 본 논문의 제안 시스템은 전시물에 대하여 관람자의 호기심을 유발하며, 쉽고 즉각적인 설명을 통하여 관람자가 전시물에 대한 정보를 쉽고 빠르게 획득하도록 한다.

• 약학회지
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• 제48권3호
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• pp.189-196
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• 2004

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) playa key role in tumor invasion and metastasis. As an inhibitor of MMP-2, TIMP-2 is known to block both the invasive and metastatic behavior of cancer cells, and decrease tumor growth activity. We performed this study to investigate the effects of TIMP-2 over-expression induced by retroviral mediated gene transfer in vitro and in vivo. The human colon cancer cell line SW480 was transfected with the retroviral vector encoding TIMP-2. The effects of TIMP-2 over-expression were analyzed by invasion assay and gelatinase activity test in colon cancer cells and tumorigencity in nude mice. In evaluation of the transfection efficiency of the retroviral vector encoding TIMP-2 in colon cancer cells, we confirmed up-regulation of TIMP-2 expression dependent on the time of cell culture. In addition, inhibition of MMP-2 expression in SW480/TIMP-2 was shown by gelatin zymography. In the in vitro invasion assay SW480/TIMP-2 inhibited the invasiveness on matrigel coated with collagen. To determine whether TIMP-2 can modulate in vivo tumorigenicity and metastasis, SW480/TIMP-2 cells were injected subcutaneously in nude mice. The tumor mass formation of SW480/TIMP-2 cells in nude mice was markedly decreased compared to nontransfected cancer cells. These results showed that colon cancer cells transfected with the retroviral vector encoding TIMP-2 inhibits the invasiveness in vitro and tumorigenicity in vivo.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2256-2268
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• 2018

Hydrophilic and hydrophobic polyethersulfone (PES)-zinc oxide (ZnO) sublayers were prepared by loading of ZnO nanoparticles into PES matrix. Both porosity and hydrophilicity of the hydrophilic sublayer were increased upon addition of hydrophilic ZnO, while these were decreased for the hydrophobic sublayer. In addition, the results demonstrated that the hydrophilic membrane exhibited smaller structural parameter (S value or S parameter or S), which is beneficial for improving pure water permeability and decreasing mass transfer resistance. In contrast, a higher S parameter was obtained for the hydrophobic membrane. With a 2 M NaCl as DS and DI water as FS, the pure water flux of hydrophilic TFN0.5 membrane was increased from $21.02L/m^2h$ to $30.06L/m^2h$ and decreased for hydrophobic TFN0.5 membrane to $14.98L/m^2h$, while the salt flux of hydrophilic membrane increased from $10.12g/m^2h$ to $17.31g/m^2h$ and decreased for hydrophobic TFN0.5 membrane to $3.12g/m^2h$. The increment in pure water permeability can be ascribed to reduction in S parameter, which resulted in reduced internal concentration polarization (ICP). The current study provides a feasible and low cost procedure to decrease the ICP in FO processes.

• 한국재료학회지
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• 제32권11호
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• pp.508-514
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• 2022

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO₃ nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO₃ particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO₃ particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.961-965
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• 1998

The rapid development of small-scale (1-10 MJ) Superconducting Magnetic Energy Storage Systems (SMES) can be explained by real perspective of practical implementation of these devices in electro power nets. However the serious problem of all high mechanically stressed superconducting coils-problem of training and degradation (decreasing) of operating current still exists. Moreover for SMES systems this problems is more dangerous because of pulsed origin of mechanical stresses-one of the major sources of local heat disturbances in superconducting coils. We investigated acoustic emission (AE) phenomenon on model and 0.5 MJ SMES coils taking into account close correlation of AE and local heat disturbances. Two-coils 0.5 MJ SMES system was developed, manufactured and tested at Russian Research Center in the frames of cooperation with Korean Electrical Engineering Company (KEPCO) [1]. The two-coil SMES operates with the stored energy transmitted between coils in the course of a single cycle with 2 seconds energy transfer time. Maximum operating current 1.55 kA corresponds to 0.5 MF in each coil. The Nb-Ti-based conductor was designed and used for SMES manufacturing. It represents transposed cable made of Nb-Ti strands in copper matrix, several cooper strands and several stainless steel strands. The coils are wound onto fiberglass cylindrical bobbins. To make AE event information more useful a real time instrumentation system was used. Two main measured and computer processed AE parameters were considered: the energy of AE events (E) and the accumulated energy of AE events (E ). Influence of current value in 0.5 MJ coils on E and E was studied. The sensors were installed onto the bobbin and the external surface of magnets. Three levels of initial current were examined: 600A, 1000A, 2450 A. An extraordinary strong dependence of the current level on E and E was observed. The specific features of AE from model coils, operated in sinusoidal vibration current changing mode were investigated. Three current frequency modes were examined: 0.012 Hz, 0.03 Hz and 0.12 Hz. In all modes maximum amplitude 1200 A was realized.