• Advances in materials Research
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• 제2권2호
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• pp.119-131
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• 2013

Impedance and electrical conduction studies of $Ba(Nd_{1/2}Nb_{1/2})O_3$ ceramic prepared using conventional high temperature solid-state reaction technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group $Pm\bar{3}m$. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of compound. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealized model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in $Ba(Nd_{1/2}Nb_{1/2})O_3$. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.

• Korean Chemical Engineering Research
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• 제54권1호
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• pp.81-88
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• 2016

리모넨은 오렌지 향이 있는 천연의 키랄 화합물로 주로 감귤껍질과 레몬껍질에 함유되어 있다. $4^{\circ}C$로 냉장 보관한 감귤 껍질을 에탄올을 용매로 속슬렛 추출기에서 2시간동안 $120^{\circ}C$에서 추출하였다. 역상 HPLC 분석을 통해 d-리모넨과 불순물의 헨리 상수를 계산하여 $H_{Lim}=8.55$, $H_{imp}=0.223$를 얻었다. Aspen chromatography 프로그램을 사용해서 $0.46{\times}25cm$ 칼럼으로 이루어진 4-bed SMB의 리모넨 전산모사를 수행하였고 삼각도내의 $m_2$, $m_3$ 값을 변경하면서 순도가 가장 높은 분리 조건을 찾았다. 그 결과 가장 높은 순도는 98.59%이고, $m_2=2.57$, $m_3=9.55$였다. 이 때의 feed 유량은 1 mL/min, desorbent 유량은 1.19 mL/min, extract 유량은 0.857 mL/min, raffinate 유량은 1.34 mL/min이었다. Scale-up 전산모사를 위해 칼럼의 직경을 1.6 cm로 늘린 4-bed SMB에서 직경이 0.46 cm인 4-bed SMB와 같은 결과를 갖는 조건을 찾기 위해 유량을 칼럼 부피 비에 정비례하여 증가시켰다. 이 때 feed, desorbent, extract, raffinate의 유량은 각각 12 mL/min, 14 mL/min, 10 mL/min, 16 mL/min이었다. 리모넨과 불순물의 등온흡착곡선을 선형으로 가정하였기에 칼럼 부피에 정비례하여 유량을 증가시키는 scale-up이 가능하였다.

• 산업기술연구
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• 제33권A호
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• pp.3-8
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• 2013

Reduction of risk plays a pivotal role in the development of medical instruments. A hyperbaric oxygen chamber, as a medical device, is known to help medical therapy for diversity of diseases through provision of high purity oxygen. The use of hyperbaric oxygen is expected to increase in the future and study to rigorously examine reliability and safety is needed. We have performed risk assessment for a newly developed hyperbaric oxygen chamber in this study. We first briefly discussed the system structure and concept of risk assessment for the study. Based on the hazards identified, we performed preliminary hazard analysis for the chamber.

• Rapid Communication in Photoscience
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• 제3권4호
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• pp.64-66
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• 2014

Synthesis of a deuterium-labeled derivative of nitrospirobenzopyran (NSP), one of representative photochromic compounds, has been described. Four deuteriums were successfully introduced on 1-methyl and ${\alpha}$-methyne relative to spiro-carbon in the title compound with more than 95atom%D purity. Main photodegraded products of NSP were two oxindoles in acetonitrile, and additional products were formed in poly(isobutyl-methacrylate) films possibly due to restricted molecular motion in polymer matrix. Quantitative HPLC analysis revealed that partial introduction of deuterium to NSP brought a noticeable isotope effect, recognizable enhancement in photo-resistivity of NSP, i.e.,8.3% in solutions and 29% in polymeric films.

• KEPCO Journal on Electric Power and Energy
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• 제5권3호
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• pp.173-179
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• 2019

심랭식 공기분리공정은 공기를 액화시켜 질소와 산소, 아르곤 등 다양한 산업가스를 생산하며, 가스생산조건(순도, 종류)에 따라 공정 또한 달라진다. 그 중 SNG 플랜트 공급용 공기분리공정은 99.5% 이상의 초고순도 산소 생산을 요구하기 때문에 공정의 효율이 타 공기분리공정에 비해 떨어지며, 공정효율을 낮추는 요인에는 공기압축에 의한 소모동력이 대표적이다. 본 연구에서는 SNG 플랜트에 적용하는 공기분리공정의 에너지 효율 향상을 위하여 소모동력과 관련된 공기 압축 설비의 민감도 분석을 수행하였다. 민감도 분석을 위해 ASPEN PLUS를 이용해 공기분리공정을 모사하였다. 모사 결과, 99.5% 이상의 산소 18.21 kg/s를 생산하였으며, 33.26 MW의 동력이 소모되었다. 모사된 공정 중 공기압축설비는 주 압축기 1대와 2대의 재 압축기가 있으며, 2대의 재압축기에서의 공기압축비 변화에 따른 고압질소, 저압산소, 저압질소의 유량과 순도에 대한 영향과 공정 내 소모동력 변화에 대해 분석하였다. 분석 결과, 99.5% 산소, 99% 질소(고압), 90% 질소(저압)를 생산하기 위한 최적의 운전조건은 재압축비가 각각 0.48, 0.50가 되었으며, 재압축비 조정 후 $0.507kWh/O_2kg$에서 $0.473kWh/O_2kg$으로 소모동력도 약 7%가량 줄었음을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제16권3호
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• pp.238-243
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• 2005

Mg and Mg-based alloys are most important hydrogen storage materials. It is a lightweight and low-cost materials with high hydrogen storage capacity. However, the formation of hydride at high temperature, the deterioration effect, the hydriding and dehydriding kinetics are bad factor for application. In this study, Mg and Ni have been produced by hydrogen induced mechanical alloying(HIMA) process. The raw materials, Mg(purity 99.9%) chip and Ni(purity 99.95%) chip was prepared by using a planetary ball mill apparatus(FRITSCH pulverisette 5). The balls to chips mass ratio(BCR) are 30:1. The hydrogen pressure induced 2.0MPa and milling times were 12, 24, 48, 72, 96 hours with a rotating speed of 200rpm. X-ray diffraction(XRD) analysis was made to characterize the crystallite size and misfit strain. The crystallite size measured by laser particle size analysis(PSA). Microstructure changes were investigated by scanning electron microscopy(SEM) and the transmission electron microscopy(TEM). The hydrogen storage properties were evaluated by using an Sivert's type automatic pressure-composition-therm(PCT) apparatus.

• 한국세라믹학회지
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• 제35권6호
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• pp.529-534
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• 1998

Agglomeration-free indium oxide particles were produced by ultrasonic pyrolysis of indium nitrate(3 hy-drate) solution. Th mean size of particles was increased from 3 $\mu\textrm{m}$ to 11$\mu\textrm{m}$ with increasing intial con-centrations of indium nitrate from 0.05mol% to 4.83 mol% When the input rate of indium nitrate solution was increased from 0.1 cm3/min to 0.8cm3/min the size of particles remained same and only the pro-duction rate of particles was increased. At 300$^{\circ}C$ the particles were white color with low crystallinity. But the color turned into yellow with increasing reaction temperature. The change of particle size was not ob-served with increasing temperatuer up to 700$^{\circ}C$ IR spectrum and TGA analysis confirmed that the purity of indium oxide was increased with temperature of reaction.

• 분석과학
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• 제33권5호
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• pp.215-223
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• 2020

The objectives of the present study were to assess the oxidative stability of South Korean n-3 (omega-3 fatty acid) supplements carried out from 2018 to 2019 and evaluate the influence of product characteristics on oxidative safety. A total of 76 n-3 supplements were analysed for oxidation safety by four markers, including acid value (AV), primary oxidation (peroxide value, PV), secondary oxidation (p-anisidine value, pAV) and total oxidation value (TOTOX). Among the supplements tested, 5.3 %, 55.3 %, 28.9 % and 46.1 % exceeded the international voluntary recommended levels for AV, PV, pAV and TOTOX, respectively. Purity (%) of products, remainder of expiration date (suggested shelf life), package in press through package (PTP) and products with additives had statistically significant differences oxidation assessment levels (p < 0.05). In addition, n-3 group found in Algae oil had significantly lower AV levels than the group that did not, and product with Alaska pollack oil, had significantly higher pAV levels than without group (p < 0.05). The high oxidation status of South Korean n-3 products in the present study could not be considered a public health problem right now. However, the levels of oxidation may affect a lot the efficacy and safety of using n-3 supplements. Thus, current oxidation safety limits should be reestablished by regulatory bodies to ensure the safety and efficacy of n-3 supplements, so that the standards could be applied to the products available to consumers.

• 한국기계가공학회지
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• 제3권3호
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• pp.52-57
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• 2004

Many kinds of gases, such as erosion gas, dilution gas, and toxic gas have been used in manufacturing process of LCD at semiconductor. In order to increase accumulation rate of manufacturing process, high degree of purity in these gases and minimized metalllic dust are required. All wetted stainless steel surface must be 316L electro-polished with $0254{\mu}m$ in average. Based on the AES analysis, Cr/Fe 11 and $Cr_2O_3$ thickness $25{\AA}$ are measured Molybdenum and silicon contaminants which is characteristic of stainless steel and oxygen were found on the surface.

• 대한지구과학교육학회지
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• 제3권3호
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• pp.248-256
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• 2010

This study analyzed National Assessment of Educational Achievement items surveying to sixth-year student in elementary school utilizing three dimentional scientific assessment framework. Study's findings are as following. Science contents territory of national level study achievements estimation were set a problem energy, substance, life, earth relatively evenly. Action territory was set a problem most 'Comprehension' territory. In the case of science situation area, 'Purity scientific situation' among 5 category appeared the most.