• Advances in environmental research
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• 제2권1호
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• pp.35-49
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• 2013

Research work on removal of fluoride from water, referred to as water defluoridation, has resulted into the development of a number of technologies over the years but they suffer from either cost or efficiency drawbacks. In this work, enhancement effects of phosphate and silicate on defluoridation of water by low-cost Plaster of Paris (calcined gypsum) were studied. To our knowledge, the influence of silicate on defluoridation was not reported. It was claimed, that the presence of some ions in the treated water samples, was decreasing the fluoride removal since these ions compete the fluoride ions on occupying the available adsorption sites, however, phosphate and silicate ions, from its sodium slats, have enhanced the fluoride % removal, hence, precipitation of calcium-fluoro compounds of these ions can be suggested. Percentage removal of $F^-$ by neat Plaster is 48%, the electrical conductance (EC) curve shows the typical curve of Plaster setting which begins at 20 min and finished at 30 min. The addition of phosphate and silicate ions enhances the removal of fluoride to high extent > 90%. Thermodynamics parameters showed spontaneous fluoride removal by neat Plaster and Plaster-silicate system. The percentage removal with time showed second-order reaction kinetics.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 추계 학술논문 발표대회
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• pp.31-32
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• 2019

In this study, oxidized graphene nanoplatelet(GO) was prepared by oxidizing graphene nanoplatelet(GNP) with nitric acid in order to solve the problem of dispersion of GNP, one of nano materials. GNP/Epoxy and GO/Epoxy paint were prepared by mixing GNP, GO with 0.1, 0.3, 0.5 and 1.0 wt.% in epoxy paint and the mechanical properties were evaluated. As a result, GNP/Epoxy and GO/Epoxy paints showed better mechanical properties than Neat Epoxy which did not incorporate GNP, GO. Especially, when 0.3 wt.% of GO was incorporated into epoxy resin, it showed higher tensile strength than Neat Epoxy. It was confirmed that acid treatment of GNP was effective in improving the mechanical properties of epoxy paint. However, graphene material was found that it was not effective in improving the bond performance of the epoxy paint.

• 천문학회보
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• 제39권1호
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• pp.68.1-68.1
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• 2014

We present the results of far-ultraviolet (FUV) observations of comet C/2001 Q4 (NEAT) obtained with Far-ultraviolet Imaging Spectrograph (FIMS) on board the Korean microsatellite STSAT-1, which operated at an altitude of 700 km in a sun-synchronous orbit. FIMS is a dual channel imaging spectrograph (S-channel 900-1150 ${\AA}$, L-channel 1350-1710 ${\AA}$, and ${\lambda}/{\Delta}{\lambda}$ ~ 550 for both channels) with large image fields of view (S-channel $4.0^{\circ}{\times}4.6^{\prime}$, L-channel $7.5^{\circ}{\times}4.3^{\prime}$, and angular resolution ~ $5-10^{\prime}$) optimized for the observation of diffuse emission of astrophysical radiation. Comet C/2001 Q4 (NEAT) were made in two campaigns during its perihelion approach between May 8 and 15, 2004. Based on the scanning mode observations in the wavelength band of 1400-1700 ${\AA}$, we have constructed an image of the comet with an angular size of $5^{\circ}{\times}5^{\circ}$, which corresponds to the central coma region. Several important fluorescence emission lines were detected including S I multiplets at 1429 and 1479 ${\AA}$, C I multiplets at 1561 and 1657 ${\AA}$, and the CO $A^1{\Pi}-X^1{\Sigma}^+$ Fourth Positive system; we have estimated the production rates of the corresponding species from the fluxes of these emission lines. The estimated production rate of CO was $Q_{CO}=(2.65{\pm}0.63){\times}10^{28}s^{-1}$, which is 6.2-7.4% of the water production rate and is consistent with earlier predictions. The average carbon production rate was estimated to be $Q_C={\sim}1.59{\times}10^{28}s^{-1}$, which is ~60% of the CO production rate. However, the observed carbon profile was steeper than that predicted using the two-component Haser model in the inner coma region, while it was consistent with the model in the outer region. The average sulfur production rate was $Q_S=(4.03{\pm}1.03){\times}10^{27}s^{-1}$, which corresponds to ~1% of the water production rate.

• 대한화학회지
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• 제28권1호
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• pp.34-40
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• 1984

라만 분광법을 사용하여 순수한 액체 상태의 $C_6F_6$의 재배치 운동을 연구하였다. 라만 스펙트럼 중 ${\nu}_2$와 ${\nu}_16$ 밴드를 선정하여 그 모습을 293~333K온도 범위에서 측정하였다. 분자의 주대칭축($C_{6-}$축)의 회전 및 스핀운동에 관한 회전 확산 상수 ($D_{\bo}$, $D_{\parallel}$)가 온도의 함수로써 결정되었으며 이로부터 $C-6F_6$의 재배치운동은 명백히 비등방적임을 알게 되었다. 실험 결과를 유체역학적 모델로 분석하여 본 결과 주대칭축의 회전운동은 확산적이며 스핀운동은 관성적이라는 것이 밝혀졌다.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.140-145
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• 2013

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.

• Advances in nano research
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• 제2권2호
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• pp.121-133
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• 2014

Polymer nanocomposites are advanced nanomaterials which exhibit dramatic improvements in various mechanical, thermal and barrier properties as compared with the neat polymer. Polystyrene/ alumina nanocomposites were prepared by an ultrasound-assisted solution casting method at filler loadings ranging from 0.2 to 2% and also at different ultrasonic frequencies, viz. 58 kHz, 192/58 kHz, 430 kHz, 470 kHz and 1 MHz. The composites were subjected to mechanical property tests (tensile and impact tests) and cavitation erosion tests to study the enhancement in functional properties. Filler dispersion in the polymer matrix was observed by SEM analysis. The effect of frequency on filler dispersion in the matrix was studied by SEM analysis and functional property enhancement of the composite material. The composites prepared at dual (high/ low) frequency (192/58 kHz) were found to show better property enhancement at low filler loadings as compared with neat polymer and also with composites prepared without ultrasound, thus reinforcing the finding that ultrasound-assisted synthesis is a promising method for the synthesis of nanocomposites.

• 대한수학회지
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• 제51권6호
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• pp.1305-1319
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• 2014

A submodule N of a right R-module M is called coneat if for every simple right R-module S, any homomorphism $N{\rightarrow}S$ can be extended to a homomorphism $M{\rightarrow}S$. M is called coneat-flat if the kernel of any epimorphism $Y{\rightarrow}M{\rightarrow}0$ is coneat in Y. It is proven that (1) coneat submodules of any right R-module are coclosed if and only if R is right K-ring; (2) every right R-module is coneat-flat if and only if R is right V -ring; (3) coneat submodules of right injective modules are exactly the modules which have no maximal submodules if and only if R is right small ring. If R is commutative, then a module M is coneat-flat if and only if $M^+$ is m-injective. Every maximal left ideal of R is finitely generated if and only if every absolutely pure left R-module is m-injective. A commutative ring R is perfect if and only if every coneat-flat module is projective. We also study the rings over which coneat-flat and flat modules coincide.

• Bulletin of the Korean Chemical Society
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• 제34권5호
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• pp.1345-1348
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• 2013

We investigated the tribochemical and wear properties of Polytetrafluoroethylene (PTFE) based polymer matrix composites with nanoceramic (NC) ${\beta}$-sialon, and $Al_2O_3$ particles for the mechanical seal applications at low temperature. SEM showed that NC particles were homogeneously distributed in the polymer matrix and initiated the formation of the supramolecular spherulites around NC. From the temperature stimulated depolarization (TSD) current results, it was analyzed that the surface charge on nanoceramic affected the formation of the spherulites structure. 2 wt % $Al_2O_3$ NC did not degrade the mechanical properties of PTFE so that composites showed the similar values of tensile strength, elongation at the rupture and friction coefficient as those of neat PTFE. However, the composite with 2 wt % $Al_2O_3$ NC revealed the improved wear resistance, wear rate of 0.4-1.2 mg/h at room temperature and 0.28 mg/h at $-40^{\circ}C$, respectively, while the neat PTFE the 70-75 mg/h at room temperature and 70.3 mg/h at $-40^{\circ}C$.

• Composites Research
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• 제24권2호
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• pp.30-37
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• 2011

에폭시 수지와 유리섬유직물 간의 젖음성을 분석하였다. 에폭시 수지와 산무수물 경화제의 혼합비는 당량비 1:0.5, 1:1, 1:1.2로 하였고, 촉매는 혼합된 수지의 0.lwt%로 첨가하였다. DSC 경화거동분석 결과 이 혼합 수지는 상온에서 함침이 가능하였다. 혼합 수지에 대해 유리평판에 놓여진 유리섬유직물 위에 수지 한 액적(방울)을 투하 후 시간에 따른 접촉각 변화를 측정하였다, 또한, 일정량의 에폭시 수지 액적을 투하시켜 시간에 따른 젖음면적 변화를 측정하였다, 접촉각, 액적높이, 순수 젖음면적, 젖음계수를 측정함으로써 유리섬유직물에 대한 에폭시 수지의 젖음성을 비교 평가하였다. 그 결과 당량비 1:1.2에서 유리섬유직물에 대한 젖음성이 가장 우수하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.106-106
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• 2012

Strategies to facilitate carrier transfer/transport while preserving confined characteristics of isolated nanocrystal quantum dots (NQDs) will be discussed. Specifically, synthesis and characterizations of 1) the fabrication of neat NQD solids (assembled NQD films) with modified surfaces by attaching ligands or by applying physical processes such as heat annealing [J. Phys. Chem. C (2011), 115(3), 607] and 2) coupling NQDs to one-dimensional nanostructures such as single-walled carbon nanotubes (SWNTs) [ACS Nano, (2010) 4(1), 324] will be presented. Further, recent achievement ours of fabricating NQDs assemblies into photovoltaic devices for elucidating transfer mechanism witll be discussed.