• 한국재료학회지
• /
• 제26권5호
• /
• pp.258-265
• /
• 2016

Fluorine-doped tin oxide (FTO) nanoparticles have been successfully synthesized using ultrasonic spray pyrolysis. The morphologies, crystal structures, chemical bonding states, and electrochemical properties of the nanoparticles are investigated. The FTO nanoparticles show uniform morphology and size distribution in the range of 6-10 nm. The FTO nanoparticles exhibit excellent electrochemical performance with high discharge specific capacity and good cycling stability ($620mAhg^{-1}$ capacity retention up to 50 cycles), as well as excellent high-rate performance ($250mAhg^{-1}$ at $700mAg^{-1}$) compared to that of commercial $SnO_2$. The improved electrochemical performance can be explained by two main effects. First, the excellent cycling stability with high discharge capacity is attributed to the nano-sized FTO particles, which are related to the increased electrochemical active area between the electrode and electrolyte. Second, the superb high-rate performance and the excellent cycling stability are ascribed to the increased electrical conductivity, which results from the introduction of fluorine doping in $SnO_2$. This noble electrode structure can provide powerful potential anode materials for high-performance lithiumion batteries.

• 폴리머
• /
• 제34권6호
• /
• pp.527-533
• /
• 2010

Pioglitazone을 봉입한 poly(lactide-co-glycolide)(PLGA) 나노입자를 emulsion-evaporation 방법을 이용하여 제조하여 최적의 나노입자와 봉입률을 조절하였다. 제조된 나노입자의 크기는 125~170 nm이었으며 30% pioglitazone이 봉입된 나노입자(3% PVA)의 봉입률은 85% 이상이었다. 이러한 나노입자들은 40일 동안 일정하게 용출이 되었다. 당뇨병 모델을 이용한 동물실험에서 글루코오스 농도를 저하시켰을 뿐만 아니라, 조직검사에서는 낮은 독성을 가지고 있는 것을 확인하였다. 이러한 결과는 pioglitazone 경구투여를 위한 약물전달을 위한 운반체로 사용될 수 있음을 확인하였다.

• 대한환경공학회지
• /
• 제39권4호
• /
• pp.214-219
• /
• 2017

건물의 우수관에 연결하여 초기빗물의 부유물질을 처리할 수 있는 장치를 개발하기 위하여 건물옥상 유출 빗물의 수질특성 변화를 파악하고 다양한 여재를 활용해 초기빗물의 부유물질 제거를 연구하였다. 건물옥상 유출빗물의 입자성 물질은 대부분 $10{\sim}30{\mu}m$의 크기로, 부유물질 농도는 강우시 초기 10~20분까지 높았고 점진적으로 감소하였다. 옥상유출빗물의 용존성 유기물과 무기물의 농도도 유출 초기에 높게 나타났다. Anthracite (AC), Polyurethane (PU), Polypropylene (PP) 여재로 여과시 초기에 50%의 부유물질을 제거할 수 있었으나 20분 이상 여과시 제거율이 급격히 낮아졌다. 세척후 반복여과를 고려하면 AC 여재만 9회까지 재사용가능하였다. 여재층의 높이가 높을수록, 통과유량이 적을수록 시간에 따른 SS 제거율 감소폭은 적었고, 여재층 30 cm, 유량 12 L/min 이하로 운전할 경우 초기빗물(SS = 450 mg/L)의 SS 제거율 50%를 달성할 수 있었다.

• 한국농공학회논문집
• /
• 제60권3호
• /
• pp.135-148
• /
• 2018

Reservoir sedimentation is a major environmental issue, and various sediment load controls and plans have been proposed to secure clean and safe water resources. The objectives of this study were to estimate soil loss in the upper basins and predict sediment deposition in Ipjang reservoir using hydrologic and hydraulic model. To do so, SWAT (Soil and Water Assessment Tool) and EFDC (Environmental Fluid Dynamics Code) was used to estimate soil loss in two upper basins and to predict spatial distribution and amount of sediment deposition in the Ipjang reservoir, respectively. The hydrologic modeling results showed that annual average soil loss from the upper basins was 500 ton. The hydraulic modeling results demonstrated that sediment particles transported to the reservoir were mostly trapped in the vicinity of the reservoir inlet and then moved toward the bank over time. If long-term water quality monitoring and sediment survey are performed, this study can be used as a tool for predicting the dredging amount, dredging location and proper dredging cycle in the reservoir. The study findings are expected to be used as a basis to establish management solutions for sediment reduction.

• Clinical and Experimental Pediatrics
• /
• 제51권4호
• /
• pp.355-361
• /
• 2008

Pollen is very important causing factor for allergy such as allergic rhinitis, allergic conjunctivitis, and asthma, and pollen allergy has a remarkable clinical impact all over Korea. The main pollination period covers about half the year, from spring to autumn, and the distribution of airborne pollen taxa of allergological interest is related to pollen season dynamics. Korean academy of pediatric allergy and respiratory diseases (KAPARD) has evaluated the pollen characteristics and nationwide pollen count for over 10 years since 1997. Airborne particles carrying allergens were collected daily from nationwide 8 stations (Seoul, Guri, Cheongju, Daegu, Kwangju, Busan, Kangneung, and Jeju) by using 7 days-Burkard sampler (Burkard Manufacturing Co Ltd, Hertfordshire, UK) in South Korea (July 1, 1997-June 30, 2007). They were counted and recorded along with the meteorological factors daily. Tree pollen is a major airborne allergen in spring, grass is most common in summer, and weed pollen is major pollen in autumn in Korea. There has two peak seasons for pollen allergy, as summer and autumn. There is some evidence suggesting that the prevalence of allergic diseases in Korea has been on the increase in the past decade. However, recent findings of the phase I and II studies of the international Study of Asthma and Allergies in Childhood (ISAAC) study showed the absence of increases or little changes in prevalence of asthma symptoms and diagnosis rates in Korea, whereas the prevalence of allergic rhinitis and atopic dermatitis were increased. We reported the evidence that sensitization rate to weed pollen has been increased yearly since 1997 in childhood. Climate change and air pollution must be the major causing factors for the increase of pollen counts and sensitization rate to pollen. Climate change makes the plants earlier pollination and persisting pollination longer. In conclusion, data on pollen count and structure in the last few years, the pathogenetic role of pollen and the interaction between pollen and air pollutants with climate change gave new insights into the mechanism of respiratory allergic diseases in Korea.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2009년도 춘계학술대회 논문집
• /
• pp.350-352
• /
• 2009

The effect of porosity on the high-cycle fatigue properties of Al-Si-Mg casting aluminum alloys was investigated in this study. Microstructure examination, tensile and high-cycle fatigue test were conducted on both Al-Si-Mg casted (F) and heat-treated (T6) conditions. Porosity characteristics on the fracture surfaces of fatigue-tested samples were examined using SEM and image analysis. The microstructure observation results showed that eutectic Si particles were homogeneously dispersed in the matrix of the Al-Si-Mg casting alloys, but there were porosities formed as cast defects. The high-cycle fatigue results indicated that the fatigue strength of the 356-T6 alloy was higher than that of the 356-F alloys because of the significant reduction in volume fraction of pores by heat treatment. The SEM fractography results showed that porosity affected detrimental effect on the fatigue life: 80% of all tested samples fractured as a result of porosity which acted as the main crack initiation site. It was found that fatigue life decreased as the size of the surface pore increased. A comparison was made between surface pore and inner pore fur its effect on the fatigue behavior. The results showed that the fatigue strength with the inner pores was higher than that of the surface pore.

• 한국환경보건학회지
• /
• 제19권3호
• /
• pp.52-57
• /
• 1993

This study was carried out to investigate the air pollution in Hwasoon Nulitjae tunnel for two months, from August 1992 to September 1992. The total suspended particles were collected by high volume air sampler at inside and outside of Hwasoon Nulitjae tunnel, of which major water soluble component and heavy metalic element were analyzed. Size distribution and respirable mass fraction of aerosol at inside were measured by filters on nine stages Andersen air sampler. The average concentration of TSP at inside was 657.57 $\mu$g/m$^3$, which appeared about 9.2 times as high as that of 71.47 $\mu$g/m$^3$ at outside. The decrease effect caused by using new tunnel was 31.2%. As a result of correlation analysis between concentration of TSP at inside of Hwasoon Nulitjae tunnel and that at outside, correlation coefficient was 0.713. The average concentrations of SO$_4^{2-}$ , NO$_3^-$, CI$^-$ were 43.02 $\mu$g/m$^3$, 19.86 $\mu$g/m$^3$, 4.96 $\mu$g/m$^3$, those of NH$_4^+$, Na$^+$, K$^+$ 1.42 $\mu$g/m$^3$, 4.45 $\mu$g/m$^3$, 2.89 $\mu$g/m$^3$ and those of Ca$^{2+}$, Mg$^{2+}$, Pb$^{2+}$ 3.92 $\mu$g/m$^3$, 2.27 $\mu$g/m$^3$. 1.52 $\mu$g/m$^3$, respectively. It was estimated that mass fraction rate of respirable particle at inside was about 84.54% of aerosol. The average concentration of suspended particle to be collected by Andersen sampler was 478.90 $\mu$g/m$^3$, this was about 72.8% of that by high volume air sampler.

• 펄프종이기술
• /
• 제44권4호
• /
• pp.16-24
• /
• 2012

To characterize the coating structure, diverse methods such as mercury intrusion, nitrogen adsorption and oil absorption methods have been developed and widely employed. These indirect techniques, however, have some limitation to explain the actual coating structure. Recently microscopic observation methods have been tried for analyzing structural characteristics of coating layers. Preparation of the undamaged cross section of a coating layer is essential for obtaining high quality image for analysis. In this study, distortion-free cross-section of the coating layer was prepared using a grinding and polishing technique. The coated paper was embedded in epoxy resin and cured. After curing the resin block it was ground with abrasive papers and then polished with diamond particle suspension and nylon cloth. Polished coating layer was sufficient enough to obtain undamaged cross sectional images with scanning electron microscope under backscattered electron image mode. In addition, the SEM images allowed distinction of the coating layer components. Also S/B latex film formed between pigment particles was visualized by osmium tetroxide staining. Pore size distribution and pore orientation were evaluated by image analysis from SEM cross-sectional images.

• Ocean and Polar Research
• /
• 제41권2호
• /
• pp.63-77
• /
• 2019

In order to investigate the behavior and seasonal variability of Mn as one of the bio-essential metals in the Amundsen sea, which is known as the most biologically productive coastal area around the Antartica, seawaters were collected using a clean sampling system for 10 stations (96 ea) in 2014 (ANA04B) and for 12 stations (139 ea) in 2016 (ANA06B) surveys of RV ARAON. Dissolved and particulate Mn concentration varied in the range of 0.15-4.43 nmol/kg and <0.01 to 2.42 nM in 2014 and in the range of 0.25-4.15 nmol/kg and 0.01-2.64 nM in 2016, respectively. From the sectional distribution of dissolved and particulate Mn, it might be suggested that dissolved/particulate Mn was provided from iceberg melting and diffusion/resuspension from sediments, respectively. Although this sea is highly productive, there was little evidence regarding the biological origin of dissolved Mn, but particulate Mn only in sea ice and offshore areas could be explained as originating from organic matters, e.g. phytoplanktons. And it could be suggested that the subsurface maximum of dissolved Mn was formed by isopycnal transport of melting materials from ice wall to offshore. Compared to early (2014) summer, temperature, salinity, biomass, dissolved and particulate Mn in late (2016) summer indicated that temporal variations might be resulted from the reduction of ice melting and mCDW flow, which induced a reduction in resuspension. In addition, in the late summer, particles including biomass were reduced, which brought about a reduction in the removal rate of dissolved Mn.

• 대한금속재료학회지
• /
• 제46권3호
• /
• pp.182-188
• /
• 2008

Carbon nanotubes(CNTs) have outstanding mechanical, thermal, and electrical properties. Thus, by placing nanotubes into appropriate matrix, it is postulated that the resulting composites will have enhanced properties. Cold spray can produce thick metal-based composite coatings with very high density, low oxygen content, and phase purity, which leads to excellent physical properties. In this study, we applied cold spray coating process for the consolidation of Cu/CNT composite powder. The precursor powder mixture, in which CNTs were filled into copper particles, was prepared to improve the distribution of the CNT in copper matrix. Pure copper coating was also conducted by cold spraying as a reference. Annealing heat treatment was applied to the coating to examine its effect on the properties of the composite coating. The hardness of Cu/CNT composite coating represented similar value to that of pure copper coating. It was importantly found that the electrical conductivity of the Cu/CNT composite coating significantly increased from 53% for the standard condition to almost 55% in the optimized condition, taking annealed ($500^{\circ}C/1hr$.) copper coating as a reference (100%). The thermal conductivity of Cu/CNT composite coating layer was higher than that of pure Cu coating. It was also found that the electrical and thermal conductivities of Cu/CNT composite could be improved through annealing heat treatment. The microstructural evolution of Cu/CNT coating was also investigated and related to the macroscopic properties.