• 한국세라믹학회지
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• 제44권5호
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• pp.179-183
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• 2007

BCB $Resin-BaNd_2Ti_4O_{12}$(BNT) composites with BNT contents were prepared by tape casting method and epoxy resin-BNT composites were prepared by using heating press. Their dielectric properties and microstructures were investigated. The dielectric properties such as dielectric constant and dielectric loss at 1 MHz for epoxy resin-BNT composites and BCB resin-BNT composites are improved with an increase of BNT volume fraction. The dielectric constant of the Epoxy-BNT composite increased from 5.9 to 7.8 as the volume fraction of BNT increased from 15 to 25. The dielectric constant of the BCB-BNT composite increased from 9.1 to 15.5 as the volume fraction of BNT increased from 30 to 50. The dielectric behavior of BCB-BNT system can be explained by Lichtenecker's equation. The dielectric constant of epoxy resin-BNT composite is smaller than that of BCB resin-BNT composite. These results are considered to be related with the dispersion of BNT filler in polymer matrix from the result of SEM photograph.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마
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• pp.74-77
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• 2000

The main objective of this paper is to design and test a new type of polymer ZnO surge arrester for AC power system of railroad vehicles. Metal oxide surge arrester for most electric power system applications, electric train and must not have explosive breakage of the housing to minimize damage to other equipment when subjected to internal high short circuit current. When breakdown of ZnO elements in a surge arrester occurs due to flashover, fault short current flows through the arrester and internal pressure of the arrester rises. The pressure rise can usually be limited by fitting a pressure relief diaphragm and transferring the arc from the inside to the outside of the housing. However, there is possibility of porcelain fragmentation caused by the thermal shock. pressure rise, etc. Non-fragmenting of the housing is the most desired way to prevent damage to other equipment. The pressure change which is occurred by flashover become discharge energy. This discharge energy raises to damage arrester housing and arrester housing is dispersed as small fragment. Therefore, the pressure relief design is requested to obstruct housing dispersion. The main research works are focused on the structure design by finite element method, pressure relief of module, and studies of performance of surge arrester for electric railway vehicle.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 SMICS 2004 International Symposium on Maritime and Communication Sciences
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• pp.113-116
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• 2004

The materials showing high structure dispersion with functional properties were developed on the quartz base and those were obtained by mechano-chemical reaction technology. Depending on the processing conditions and subsequent applications the materials produced by mechano-chemical reaction show concurrently magnetic, dielectric and electrical properties. The obtained magnetic-electrical powders classified by aggregate complex of their features as segnetomagnetics, containing a dielectric material as a carrying nucleus, particularly the quartz on that surface one or more layers of different compounds were synthesized having thickness up to 10~50 nm showing magnetic, electrical properties and others. The similarity of the structure of surface layers of quartz particles subjected to mechano-chemical processing and nano-structure cluspol (clusters in a polymer matrics) material was also confirmed by the fact that the characteristics of ferromagnetic quartz of insulating nano-composite powder were changed with time, after its preparing process was completed. The magnetic permeability of the sample was decreasing within first two months down by 15~20 %. Then, the magnetic characteristics were almost stabilized steadily and continuously. The observed changes were related with defective structure of the particles, elastic stress relief, and changes of electron density and magnetic moment in deformation zones. This process of stabilization of the investigated properties could be intensified by the thermal annealing heat treatment in short time period of the nano-composite quartz powders at the temperature ranges of 100~15$0^{\circ}C$.

• 한국광학회지
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• 제3권2호
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• pp.77-85
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• 1992

Varied-line spacing concave grating을 이용하여 결상면에서 거의 균일한 분해능을 갖는 평면결상 극자외선 분광기를 설계하엿다. 레이저-프라즈마에서 복사되는 발산광의 집속과 분광기의 수차보정을 위해 toroidal mirror를 사용하였고, 비축광선에 의한 수차를 줄이기 위해 toroidal mirror와 회절격자 사이에 10$\mu \textrm m \times2$mm크기의 입사슬릿을 두었다. 평면결상이 가능한 파장영역은 50~300$\AA$이고, 계산된 분해능은 4000이상이다. 회절격자의 효율과 toroidal mirror에서의 반사율을 고려하면 복사 에너지의 집속도는 toroidal mirror를 사용하지 않았을 때보다 3.5배 증가하고, fluorescence는 파장 100.angs.에서 1000배 이상 증가했다.

• 한국약용작물학회지
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• 제26권4호
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• pp.317-327
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• 2018

Background: The root of Angelica gigas Nakai is used as a traditional herbal medicine in Korea for the treatment of many diseases. However, the poor water solubility of the active components in A. gigas Nakai is a major obstacle to its bioavailability. Methods and Results: This work aimed at enhancing the solubility of the active compounds of A. gigas Nakai by a chemical (using a surfactant) and physical (hot melt extrusion, HME) crosslinking method. Fourier transform infrared spectroscopy revealed multiple peaks in the case of the extrudate solids, attributable to new functional groups including carboxylic acid, alkynes, and benzene derivatives. Differential scanning calorimetry analysis showed that the extrudate soilid had a lower glass transition temperature ($T_g$) and enthalpy (${\Delta}H$) ($T_g:43^{\circ}C$, ${\Delta}H$ : < 6 J/g) as compared to the non-extrudate ($T_g:68.5^{\circ}C$, ${\Delta}H:123.2$) formulations. X-ray powder diffraction analysis revealed the amorphization of crystalline materials in the extrudate solid. In addition, enhanced solubility (53%), nanonization (403 nm), and a higher amount of extracted phenolic compounds were achieved in the extrudate solid than in the non-extrudate (solubility : 36%, nanonization : 1,499 nm) formulation. Among the different extrudates, acetic acid and span 80 mediated formulations showed superior extractions efficiency. Conclusions: HME successfully enhanced the production of amorphous nano dispersions of phenolic compound including decursin from extrudate solid formulations.

• 한국재료학회지
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• 제22권7호
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• pp.362-367
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• 2012

Magnetite nanoparticles(NPs) have been the subject of much interest by researchers owing to their potential use as magnetic carriers in drug targeting and as a tumor treatment in cases of hyperthermia. However, magnetite nanoparticles with 10 nm in diameter easily aggregate and thus create large secondary particles. To disperse magnetite nanoparticles, this study proposes the infiltration of magnetite nanoparticles into hybrid silica aerogels. The feasible dispersion of magnetite is necessary to target tumor cells and to treat hyperthermia. Magnetite NPs have been synthesized by coprecipitation, hydrothermal and thermal decomposition methods. In particular, monodisperse magnetite NPs are known to be produced by the thermal decomposition of iron oleate. In this study, we thermally decomposed iron acetylacetonate in the presence of oleic acid, oleylamine and 1,2 hexadecanediol. We also attempted to disperse magnetite NPs within a mesoporous aerogels. Methyltriethoxysilicate(MTEOS)-based hybrid silica aerogels were synthesized by a supercritical drying method. To incorporate the magnetite nanoparticles into the hybrid aerogels, we devised two methods: adding the synthesized aerogel into a magnetite precursor solution followed by nucleation and crystal growth within the pores of the aerogels, and the infiltration of magnetite nanoparticles synthesized beforehand into aerogel matrices by immersing the aerogels in a magnetite nanoparticle colloid solution. An analysis using a vibrating sample magnetometer showed that approximately 20% of the magnetite nanoparticles were well dispersed in the aerogels. The composite samples showed that heating under an inductive magnetic field to a temperature of $45^{\circ}C$ is possible.

• 비파괴검사학회지
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• 제24권4호
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• pp.331-340
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• 2004

기기 건전성의 온라인 검사 및 감시 기술은 기존의 원전의 가동 중 검사의 효율적 수행에 필요한 정보를 제공한다. 유도 초음파는 온라인 검사와 감시에 활용 가능성이 있는 기술 중의 하나로 알려져 있다. 본 연구에서는 온라인 검사 겐 감시 기술 개발의 일환으로 유도초음파를 이용하여 파이프의 건전성을 검사/감시하는 기술을 개발하고자 한다. 이를 위해 증기 발생기 세관을 실험 대상으로 하여 분산 선도 덴 특정 모드에 대응하는 초음파 입사각을 계산하였다. Short time Fourier transform을 이용한 시긴-주파수 분석을 통하여 유도초음파 모드를 확인하였으며, 유도 초음파가 증기발생기 세관의 곡관 부분을 통과할 때 모드 변환이 발생하지 않는 것을 실험적으로 확인하였다. 유도 초음파를 이용한 증기발생기 세관의 최적 검사 모드를 제안하고 실험에 의하여 이를 확인하였다.

• 비파괴검사학회지
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• 제32권5호
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• pp.509-517
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• 2012

본 연구에서는 상용화된 monomer-cast nylon (MC nylon)계 고분자 재료로 만든 6종류의 시편에 대하여 감쇠계수 및 위상속도와 같은 초음파 특성의 온도 및 주파수 의존성을 조사하였다. 시편의 초음파 특성은 수중에서 2 MHz부터 8 MHz까지의 광대역 주파수 범위에 대하여 펄스투과법을 이용하여 측정하였다. 수온은 $10^{\circ}C$부터 $60^{\circ}C$까지 $10^{\circ}C$ 간격으로 변화시켰다. 측정에 사용된 모든 시편에서 감쇠계수는 주파수가 증가함에 따라 증가하였으며, 주파수의 지수 의존성 n이 선형 (n=1)에서 약간 벗어난 1.16부터 1.44이내의 값을 가졌다. 위상속도는 $60^{\circ}C$에서 ivory 시편을 제외한 모든 경우에 대하여 주파수가 증가함에 따라 감소하는 음의 분산 특성을 나타냈다. 주파수에 의존하는 위상속도는 모든 시편에서 온도가 증가함에 따라 감소하는 특성을 나타내었다.

• 폴리머
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• 제35권6호
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• pp.565-573
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• 2011

Poly(methyl methacrylate)/aluminum hydroxide(PMMA/AH) 컴포지트의 기계적 강도를 향상시키기 위해 그래핀 산화물(GO)을 충전제로 사용하여 나노컴포지트를 제조하였다. GO는 흑연을 Hummers법으로 산화한 후 열처리에 의해 박리시켜 제조하였다. PMMA/AH 컴포지트 매트릭스와의 계면혼화성을 향상시키기 위해 산소 플라즈마를 사용하여 노출 시간을 0분에서 70분까지 변화를 주어가며 GO 표면을 개질시켰다. 노출 시간이 50분까지 증가함에 따라 산소 플라즈마 처리한 GO를 충전제로 사용한 나노컴포지트는 PMMA/AH 컴포지트에 비해 굴곡강도, 굴곡탄성률, Rockwell 경도, Barcol 경도, Izod 충격강도 모두 현저히 증가하였다. 적절한 조건에서 산소 플라즈마 처리된 GO는 PMMA/AH 컴포지트 매트릭스와의 계면접착력이 매우 우수함을 파단면 모폴로지로부터 확인하였다. 하지만 GO의 함량이 0.07 phr 이상으로 증가하면 충전제의 분산이 균일하지 못하여 나노컴포지트의 기계적 강도는 오히려 감소하는 경향을 나타내었다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.148-148
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• 2018

Land subsidence caused by excessive groundwater pumping is a serious hydro-geological hazard. The spatial variability in land use, unbalanced groundwater extraction and aquifer characteristics are the key factors which make the problem more difficult to monitor using conventional methods. This study uses the European Space Agency (ESA) Sentinel satellites to investigate and monitor land subsidence varying with different land covers and groundwater use in the arid Quetta valley, Pakistan. The Persistent Scattering Differential Interferometry of Synthetic Aperture Radar (PS-DInSAR) method was used to develop 28 subsidence interferograms of the study area for the period between 16 Oct 2014 and 06 Oct 2016 using ESA's Sentinel-1 SAR data. The uncertainty of DInSAR result is first minimized by removing the dynamic effect caused by atmospheric factors and then filtered using the radar Amplitude Dispersion Index (ADI) to select only the stable pixels. Finally the subsidence maps were generated by spatially interpolating the land subsidence at the stable pixels, the comparison of DInSAR subsidence with GPS readings showed an R 2 of 0.94 and mean absolute error of $5.7{\pm}4.1mm$. The subsidence maps were also analysed for the effect of aquifer type and 4 land covers which were derived from Sentienl-2 multispectral images. The analysis show that during the two year period, the study area experienced highly non-linear land subsidence ranging from 10 to 280 mm. The subsidence at different land covers was significantly different from each other except between the urban and barren land. The barren land and seasonally cultivated area show minor to moderate subsidence while the orchard and urban area with high groundwater extraction rate showed excessive amount of land subsidence. Moreover, the land subsidence and groundwater drawdown was found to be linearly proportional to each other.