• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3465-3474
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• 2014

Porous silica particles are the most prevailing raw material for stationary phases of liquid chromatography. During a long period of time, various methodologies for production of porous silica particles have been proposed, such as crashing and sieving of xerogel, traditional dry or wet process preparation of conventional spherical particles, preparation of hierarchical mesoporous particles by template-mediated pore formation, repeated formation of a thin layer of porous silica upon nonporous silica core (core-shell particles), and formation of specific silica monolith followed by grinding and calcination. Recent developments and applications of useful porous silica particles will be covered in this review. Discussion on sub-$3{\mu}m$ silica particles including nonporous silica particles, carbon or metal oxide clad silica particles, and molecularly imprinted silica particles, will also be included. Next, the individual preparation methods and their feasibilities will be collectively and critically compared and evaluated, being followed by conclusive remarks and future perspectives.

• Journal of Magnetics
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• 제22권1호
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• pp.100-103
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• 2017

We studied the microstructure and magnetic properties of Fe nanosized powder synthesized by the pulsed wire evaporation method. The x-ray diffraction spectrum confirmed that this powder had a pure ${\alpha}$-Fe phase. Scanning electron microscope and transmission electron microscope measurements indicated that the prepared powder had uniform spherical shape with core-shell structure. The mean powder size was about 35 nm and the thickness of the surface passivation layer was about 5 nm. Energy dispersive X-ray spectroscopy measurement indicated that the surface passivation layer was iron oxide. Magnetic field dependent magnetization measurement at room temperature showed that the maximum magnetization of the prepared powder was 177.1 emu/g at 1 T.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.1750-1753
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• 1997

This paper describes how the directivity pattern of the back-scattered sound pressure is distributed when a plane acoustic wave is incident on a righid spherical shell underwater. A coupled Finite Element-Boundary Element mehtod is developed as numerical technique. The result of the coupled FE-BE method is agreed with theoretical solution for algorithmic confirmation.

• Journal of Astronomy and Space Sciences
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• 제11권2호
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• pp.165-174
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• 1994

We have investigated the chemical composition of dust grains in novae by computing the model spectra for the novae that showed temporary infrared developments shortly after their optical explosions. We find that a simple spherical dust shell models with hot blackbody central sources fit observations fairly well. Optical properties of dust grains deduced from modeling of AGB stars have been used for present calculations. We find that amorphous carbon grains appear to be the major infrared re-emission sources for the carbon-rich nova shells, and the silicate grains for the oxygen-rich nova shells.

• 한국재료학회지
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• 제24권9호
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• pp.502-507
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• 2014

Recently, improvement in the conversion efficiency of silicon-based solar cells has been achieved by decreasing emitter doping concentration, because the lightly doped emitter can effectively prevent the recombination of electrons and holes generated by solar light irradiation. This type of emitter is very thin due to the low doping concentration, thus conductive materials (i.e., silver) used for front electrodes can easily penetrate the emitter during a firing process because of their large diffusivity in silicon. This results in junction leakage currents which might reduce cell efficiencies. In this study, $Al_2O_3$-coated Ag powders were synthesized by an ultrasonic spray pyrolysis method and applied to the conductive materials of the front electrode to control the junction leakage current. The $Al_2O_3$ shell obstructs the Ag diffusion into the emitter during the firing process. The powder is spherical with a core-shell structure and the thickness of the $Al_2O_3$ shell is tens of nanometers. Solar cells were fabricated using pure Ag powders or the $Al_2O_3$-coated Ag powder as front electrode materials, and the conversion efficiency and junction leakage current were compared to investigate the role of the $Al_2O_3$ shell during the firing processes.

• Archives of Pharmacal Research
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• 제29권8호
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• pp.712-719
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• 2006

In this study, we prepared core-shell type nanoparticles of a poly(DL-lactide-co-glycolide) (PLGA) grafted-dextran (DexLG) copolymer with varying graft ratio of PLGA. The synthesis of the DexLG copolymer was confirmed by $^1H$ nuclear magnetic resonance (NMR) spectroscopy. The DexLG copolymer was able to form nanoparticles in water by self-aggregating process, and their particle size was around $50\;nm{\sim}300\;nm$ according to the graft ratio of PLGA. Morphological observations using a transmission electron microscope (TEM) showed that the nanoparticles of the DexLG copolymer have uniformly spherical shapes. From fluorescence probe study using pyrene as a hydrophobic probe, critical association concentration (CAC) values determined from the fluorescence excitation spectra were increased as increase of DS of PLGA. $^1H-NMR$ spectroscopy using $D_2O$ and DMSO approved that DexLG nanoparticles have core-shell structure, i.e. hydrophobic block PLGA consisted inner-core as a drug-incorporating domain and dextran consisted as a hydrated outershell. Drug release rate from DexLG nano-particles became faster in the presence of dextranase in spite of the release rate not being significantly changed at high graft ratio of PLGA. Core-shell type nanoparticles of DexLG copolymer can be used as a colonic drug carrier. In conclusion, size, morphology, and molecular structure of DexLG nanoparticles are available to consider as an oral drug targeting nanoparticles.

• 보존과학회지
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• 제32권2호
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• pp.261-271
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• 2016

굴 패각 분말의 입자분포가 채색시의 작업성과 채색도막의 내구성에 미치는 영향을 연구하기 위하여 입도분포와 입자형태(구형, 타원형, 길쭉한 막대형, 부정형)의 분포가 각각 다른 3종의 패각분말을 제조하여 연구에 이용하였다. 채색시의 작업성의 척도로서 발림성과 도막의 균일성을 평가하였으며, 도막내구성의 척도로서 도막의 밀착성과 표면경도를 평가하였다. 그 결과 작업성과 내구성은 입자크기보다는 입자형태에 의해 더 큰 영향을 받으며, 특히 길쭉한 막대형 입자의 구성비율이 높을수록 작업성은 떨어지는 반면 내구성이 향상되는 것으로 확인되었다. 이것은 단청 등 회화문화재 보존에 있어 중요한 고려사항인 내구성에 영향을 주는 중요인자를 확인한 결과로서, 단청문화재 보존 및 복원재료의 선정과 품질기준 마련뿐만 아니라 향후 이러한 특성이 제어된 고품질의 전통재료 생산에 중요한 근거자료가 될 수 있을 것으로 기대된다.

• 한국입자에어로졸학회지
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• 제14권3호
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• pp.65-72
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• 2018

Core-shell structured $Fe_3O_4/graphene$ composites were synthesized by aerosol spray drying process from a colloidal mixture of graphene oxides and $Fe_3O_4$ nanoparticles. The structural and electrochemical performance of $Fe_3O_4/graphene$ were characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, cyclic voltammetry, and galvanometric discharge-charge method. Core-shell structured $Fe_3O_4/GR$ composites were synthesized in different mass ratios of $Fe_3O_4$ and graphene oxide. The composite particles were around $3{\mu}m$ in size. $Fe_3O_4$ nanoparticles were encapsulated with a graphene. Morphology of the $Fe_3O_4/graphene$ composite particles changed from a spherical ball having a relatively smooth surface to a porous crumpled paper ball as the content of GO increased in the composites. The $Fe_3O_4/GR$ composite fabricated at the weight ratio of 1:4 ($Fe_3O_4:GO$) exhibited higher specific capacitance($203F\;g^{-1}$) and electrical conductivity than as-fabricated $Fe_3O_4/GR$ composite.

• 천문학논총
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• 제12권1호
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• pp.111-143
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• 1997

We have developed a spherical FCT code in order to simulate the interaction of supernova remnants with stellar wind bubbles. We assume that the density profile of the supernova ejecta follows the Chevalier mode1(1982) where the outer portion has a power-law density distribution($\rho{\propto}\gamma^{-n}$) and the SN ejecta has a kinetic energy of $10^{51}$ ergs. The structure of wind bubble has been calculated with the stellar mass loss rate $\dot{M}=5\times10^{-6}M_{\odot}/yr$ and the wind velocity $\upsilon=2\times10^3$ km/s We have simulated seven models with different initial conditions In the first two models we computed the evolution of SNRs with n=7 and n=14 in the uniform medium The numerical results agree with the Chevalier's similarity solution at early times. When all of the power-law portion of the ejecta is swept up by the reverse shock, the evolution slowly converges to the Sedov-Taylor stage. There is not much difference between the two cases with different n's The other five models simulate SNRs produced inside wind bubbles. In model III, we consider the SN ejecta of 1.4 $M_{\odot}$ and the radius of bubble ~2.76 pc so that ratio of the mass $\alpha(=M_{W.S}/M_{ej}$ is 2. We follow the complex hydrodynamic flows produced by the interaction of SN shocks with stellar shocks and with the contact discontinuities, In the model III, the time scale for the SN shock to cross the wind shell $\tau_{cross}$ is similar to the time scale for the reverse shock to sweep the power-law density profile $\tau_{bend}$. Hence the SN shock crosses the wind shell. At late times SN shock produces another shell in the ambient medium so that we have a SNR with double shell structure. From the numerical results of the remaining models, we have found that when $\tau_{cross}/\tau_{bend}\leq2$, or equivalently when $\alpha\leq50$, the SNRs produced inside wind bubbles have double shell structure. Otherwise, either the SN shock does not cross the wind shell or even if it crosses at one time, the reverse shock reflected at the center accelerates the wind shell to merge into the SN shock Our results confirm the conclusion of Tenorio-Tagle et a1(1990).

• 대한화학회지
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• 제53권6호
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• pp.677-682
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• 2009

본 논문에서는 ZnS:Mn/ZnS 코어-쉘 양자점을 유기금속전구체의 열분해 방법으로 합성하였다. 쉘의 형성온도를 135$^{\circ}C$로 고정한 반면 코어 나노입자의 합성 온도 조건을 다양화 하여 각 조건하에서 형성된 양자점들의 특성을 조사하였다. 실험을 통해 얻은 양자점들은 UV-Vis, 액체 photoluminescence (PL) spectroscopy 방법으로 광 특성을 조사하였으며, 또한 XRD, HR-TEM, 및 EDXS 분석으로 입자크기와 조성 등을 측정하였다. 실험 결과 가장 좋은 광 특성을 보인 나노입자의 합성조건은 코어와 쉘 모두 135$^{\circ}C$인 것으로 밝혀 졌으며, 이 조건에서 얻은 양자점은 583 nm 의 PL 발광 피이크와 42.15%의 높은 양자효율을 나타내었다. HR-TEM 으로 측정한 ZnS:Mn/ZnS 양자점의 평균 입자크기는 지름이 약 4.0 - 5.4 nm 정도였으며, 특히 150$^{\circ}C$의 온도 조건에서는 타원형의 입자가 형성되는 것이 관찰되었다.