• 분석과학
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• 제24권4호
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• pp.249-255
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• 2011

물의 흡수에 의한 전분알갱이의 swelling은 물과 친화력이 있는 새로운 부분의 노출에 의하여 구조적인 변화로써 점진적으로, 때로는 갑작스럽게 변화를 일으킨다. 이러한 이유로 인해서, 물과의 접촉 시간에 따르는 전분 알갱이의 크기 또는 모양의 변화에 관심을 가진다. 중력 장-흐름 분획법(gravitation field-flow fractionation, GrFFF)은 마이크론 범위의 크기를 가지는 입자들을 분리하는 데에 유용한 분리기술이다. 본 연구에서는 감자와 고구마 전분알갱이들의 크기와 크기 분포도를 결정하는 데에 있어서 GrFFF의 응용가능성을 검사하고자 한다. GrFFF를 이용하여 물과의 접촉 시간에 따르는 전분 알갱이들의 크기분포도 변화를 모니터하였다. GrFFF로부터 얻어진 전분알갱이들의 크기 및 크기분포는 광학현미경(optical microscopy, OM) 결과와 비교하였다. 결과적으로 감자와 고구마 전분의 swelling은 물과의 접촉시간이 증가함에 따라 전분알갱이의 크기가 증가하며, 전분의 종류가 달라지면 swelling 속도가 달라짐을 확인하였다.

• 한국세라믹학회지
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• 제37권2호
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• pp.186-193
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• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.304-304
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• 2010

The study on the catalytic oxidation of carbon monoxide (CO) to carbon dioxide ($CO_2$) using the noble metals has long been the interest subject and the recent progress in nanoscience provides the opportunity to develop new model systems of catalysts in this field. Of the noble metal catalysts, we selected ruthenium (Ru) as metal catalyst due to its unusual catalytic behavior. The size of colloid Ru NPs was controlled by the concentration of Ru precursor and the final reduction temperatures. For catalytic activity of CO oxidation, it was found that the trend is dependent on the size of Ru NPs. In order to explain this trend, the surface oxide layer surrounding the metal core has been suggested as the catalytically active species through several studies. In this poster, we show the influence of surface oxide on Ru NPs on the catalytic activity of CO oxidation using chemical treatments including oxidation, reduction and UV-Ozone surface treatment. The changes occurring to UV-Ozone surface treatment will be characterized with XPS and SEM. The catalytic activity before and after the chemical modification were measured. We discuss the trend of catalytic activity in light of the formation of core-shell type oxide on nanoparticles surfaces.

• 한국표면공학회지
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• 제52권3호
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• pp.138-144
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• 2019

In this work, PEO (Plasma Electrolytic Oxidation) film formation behavior of Al6061 alloy was investigated as a function of applied current density of AC at 310 Hz in the range from $120mA/cm^2$ to $300mA/cm^2$ in 0.5 M $Na_2SiO_3$ solution. When applied current density is lower than a critical voltage of about $132mA/cm^2$, voltage reaches a steady-state values less than 120 V without generation of arcs and metallic color of the alloy surface remains. On the other hand, when applied current density exceeds about $132mA/cm^2$, voltage increases continuously with time and arcs are generated at more than 175 V, resulting in the formation of PEO films with grey colors. Two different types of arcs, large size and small number of arcs with orange color, and small size and large number of arcs with white color, were generated at the same time when the PEO film thickness exceeds about $50{\mu}m$, irrespective of applied current density. Formation efficiency of the PEO films was found to increase with increasing applied current density and the growth rate was obtained to be about $5{\mu}m/min$ at $300mA/cm^2$. It was also found that surface roughness of the PEO films with $70{\mu}m$ thickness is not dependent on the applied current density.

• 한국재료학회지
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• 제32권11호
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• pp.466-473
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• 2022

The effect of Cr and Mo contents on the hydrogen embrittlement of tempered martensitic steels was investigated in this study. After the steels with different Cr and Mo contents were austenitized at 820 ℃ for 90 min, they were tempered at 630 ℃ for 120 min. The steels were composed of fully tempered martensite with a lath-type microstructure, but the characteristics of the carbides were dependent on the Cr and Mo contents. As the Cr and Mo contents increased, the volume fraction of film-like cementite and prior austenite grain size decreased. After hydrogen was introduced into tensile specimens by electrochemical charging, a slow strain-rate test (SSRT) was conducted to investigate hydrogen embrittlement behavior. The SSRT results revealed that the steel with lower Cr or lower Mo content showed relatively poor hydrogen embrittlement resistance. The hydrogen embrittlement resistance of the tempered martensitic steels increased with increasing Mo content, because the reduction in the film-like cementite and prior austenite grain size plays an important role in improving hydrogen embrittlement resistance. The results indicate that controlling the Cr and Mo contents is essential to achieving a tempered martensitic steel with a combination of high strength and excellent hydrogen embrittlement resistance.

• 한국산업융합학회 논문집
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• 제26권6_3호
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• pp.1289-1295
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• 2023

Polyurethane foam insulation required for storing and transporting cryogenic liquefied gas is already widely used as a thermal insulation material for commercial LNG carriers and onshore due to its stable price and high insulation performance. These polyurethane foams are reported to have different mechanical performance depending on the density, and the density parameter is determined depending on the amount of the blowing agent. In this study, density-dependent polyurethane foam was fabricated by adjusting the amount of blowing agent. The mechanical properties of polyurethane foam were analyzed in the room temperature and cryogenic temperature range of -163℃ at 1.5 mm/min, which is a quasi-static load range, and the cells were observed through microstructure analysis. The characteristics of linear elasticity, plateau, and densification, which are quasi-static mechanical behaviors of polyurethane foam, were shown, and the correlation between density and mechanical properties in a cryogenic environment was confirmed. The correlation between mechanical behavior and cell size was also analyzed through SEM morphology analysis. Polyurethane foam with a density of 180 kg/m³ had a density about twice as high as that of a polyurethane foam with a density of 96 kg/m³, but yield strength was about 51% higher and cell size was about 9.5% smaller.

• 한국ITS학회 논문지
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• 제21권2호
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• pp.152-166
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• 2022

본 연구에서는 본 연구에서는 사고원인 및 예방이론을 적용하여 사업용 화물자동차의 운행특성과 위험운전행동 및 교통사고 위험성 간의 인과관계를 분석하였다. 사업용 화물자동차 운전자 303명을 대상으로 운전자별 근무특성, 운전경력, 운전능력, 운전심리, 차량특성(크기), 위험운전행동, 교통사고와 관련된 자료를 수집하였으며 근무특성 및 위험운전행동에 관한 자료는 운전자가 제출한 디지털운행기록을 활용하고 교통사고 자료는 실제 교통사고를 반영하기 위해 보험사고 자료를 활용하였다. 다수의 독립변수와 종속변수 간의 인과관계를 동시에 분석하기 위해 구조방정식 모형을 구축하고 모형 적합도 지수를 활용하여 모형을 검증하였다. 4가지 위험운전행동(급감속, 급가속, 급추월, 급정지)이 교통사고와 연관성이 높은 그룹으로 분석되었다. 소형 화물자동차, 운전능력이 부족한 운전자, 위험운전행동이 많은 운전자에 대한 안전관리 대책 마련 및 집중관리가 필요한 것으로 판단된다.

• Korean Chemical Engineering Research
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• 제46권2호
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• pp.330-339
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• 2008

본 연구에서는 비이온 계면활성제, 보조계면활성제 등의 첨가제가 AOT 계면활성제 시스템의 water-in-oil(W/O) 마이크로에멀젼을 이용한 AgCl 나노입자 제조에 미치는 영향에 관하여 살펴보았다. AOT 계면활성제, isooctane, 무기염 수용액으로 이루어진 삼성분 시스템에 NP 계열 비이온 계면활성제를 첨가한 결과, 단일상으로 존재하는 W/O 마이크로에멀젼 영역은 증가하였으며, 일반적으로 첨가한 비이온 계면활성제의 친수성이 증가할수록 단일상의 영역은 증가하였다. 또한 첨가한 비이온 계면활성제는 마이셀의 계면을 보다 유연하게 함으로써 생성된 입자의 크기는 증가하고 분포도는 넓어졌다. 한편 보조계면활성제로 알코올을 첨가하면서 상평형 실험을 수행한 결과, 알코올의 사슬 길이가 증가하거나 첨가량이 증가할수록 단일상으로 존재하는 W/O 마이크로에멀젼이 보다 좁은 영역에서 형성되었다. 상평형 실험결과에 의하여 결정된 단일상의 W/O 마이크로에멀젼 영역 내에 해당하는 조건에서 보조계면활성제의 사슬 길이와 첨가량을 변화시키면서 AgCl 나노입자 제조실험을 수행한 결과, 생성된 AgCl 입자의 특성은 보조계면활성제 첨가에 따른 마이크로에멀젼의 radius of spontaneous curvature와 필름 rigidity의 변화에 의하여 결정됨을 알 수 있었다.

• 콘크리트학회논문집
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• 제19권2호
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• pp.171-178
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• 2007

경사 보강근이 철근콘크리트 연속 깊은 보의 구조적 거동에 미치는 영향을 파악하기 위하여 내부 전단경간에 개구부를 갖는 연속 깊은 보 12개가 실험되었다. 주요 변수는 개구부 크기와 경사 보강근 양이다. 개구부 주위의 경사 보강근 양과 개구부 크기의 영향을 동시에 고려하기 위한 유효 경사 보강근 계수가 제시되었다. 실험 결과 개구부를 갖는 연속 깊은 보의 하중 분배, 경사균열 폭 및 치대 내력은 유효 경사 보강근 계수에 의해 결정되었다. 유효 경사 보강근 계수가 클수록 경사균열 폭 및 이들의 진전 속도는 낮았다. 특히 유효 경사 보강근 계수가 0.077 이상인 보의 최대 내력은 동일 개구부 없는 보의 것에 비해 높았다. 내부 전단경간에 개구부를 갖는 연속 깊은 보의 최대 내력을 평가하기 위하여 상계치 이론을 이용한 수치해석 모델이 제시되었다. 제시된 모델로부터 얻은 최대 내력은 실험 결과와 잘 일치하였다.

• 대한간호학회지
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• 제31권2호
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• pp.221-231
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• 2001

This study was conducted by analyzing all 33 articles based on the LISREL, published from January 1991 to March 1999 in Korea. The analyses consisted of the publication date of articles, principal dependent variables, subjects of the research, adequacy of sampling, adequacy of research purposes and results, accordance between theoretical model and hypothetical model, fit measures, theoretical base of model modification, and adequacy of conclusion. The results were as follows : . The thesis of 33 articles in total were outnumbered as 25 (75.8%) to 8 (24.2%) research articles. As for a sex classification of the subjects, 45.5% of the research were conducted around a female group of subjects, while 54.5% were done for both sex, The range of the sample size was 105 to 803, and the average was 259 subjects. . A single theoretical variable was measured for each measurement variable, any difference between variables was hardly found in 8 articles (24.2%), and 19 articles (57.6%) did not consider any measurement error. To analyze if the representative has been articles (21.2%) were seen with a sign of a representative. Questionnaires were used in a majority (31 articles) of the data collecting process. Only 2 articles (6.1%) were measured with a physiologic index simultaneously. . 14 articles (42.2%) were centered on theory development, 10 articles on theory synthesis, and 9 articles on theory test. The research purposes and results were consistent in 25 articles (75.5%) and 8 articles (24.2%) were inconsistent. The quality of life and health promotion behavior were the concepts most frequently studied as a dependent variable, and 7 articles centered on them. In applied theories a health promotion model was used on 4 articles (12.1%), while role theory and stress-coping models were in 3 articles respectively. . The articles were analyzed to see if the hypothetical model was elaborated and tested by the theoretical model. Twenty-five articles proved to be rationale for the inconsistencies. Also, 56.5% proposed hypotheses were supported among the subject articles, and 30 articles (90.0%) suggested a revised model. Path coefficient (17 articles) and theoretical adequacy (17 articles) were the standards mostly used. In conclusion, the principal factors were obtained from the research are to be considered as the principes of LISREL application. First, a model has to be established on a theoretical base rather than empirical results dependent on the data. The results are also required to be globally interpreted. Secondly, at least 200 samples are necessary to satisfy the need. Third, more than 3 measurement variables are to be adjusted to a single theoretical variable; the measurement errors must be suggested as well. Finally, normal distribution characteristics of the data and the estimation method need to be reported. Based on the research result, the follows are suggested; . Systematic criteria on the LISREL application and procedure need to be developed . Agreement form is required to report the results of research using the LISREL