• 한국대기환경학회지
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• 제19권2호
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• pp.167-177
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• 2003

The number size distribution of urban aerosols ranging from 0.02 to 20 ${\mu}{\textrm}{m}$ in diameter was measured by using a scanning mobility particle sizer (SMPS) system and an aerodynamic particle sizer spectrometer (APS) at Seoul from November 30,2001 to January 14, 2002. The gaseous species such as CO, NO, NO$_2$, and $O_3$ were also continuously monitored. The daily average concentration of urban aerosols sorted into three groups (0.02~0.1 ${\mu}{\textrm}{m}$, 0.1~1 ${\mu}{\textrm}{m}$ and 1~10 ${\mu}{\textrm}{m}$) and the typical number, surface, and volume distributions of urban aerosols were discussed in this paper. The weekly variation of aerosol concentration was compared with those of gaseous concentrations. relative humidity, and visibility. The results showed that the particle number concentration seemed to increase in the morning and the number concentration of fine particles less than 1 fm in diameter seemed to increase when the concentrations of CO, NO, and NO$_2$ were high. The number concentration of fine particles was relatively high when the relative humidity was greater than 70％ during the increasing period of relative humidity. The visibility was weakly correlated with the concentration of aerosols ranging 0.1 to 1 ${\mu}{\textrm}{m}$, and the number size distribution for high visibility episode was apparently different from that for low visibility episode.

• Macromolecular Research
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• 제16권5호
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• pp.404-410
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• 2008

In order to obtain 'value added products' from polypropylene (PP)/waste ground rubber tire powder (WGRT) composites, PP/WGRT microcellular foams were prepared via supercritical carbon dioxide. The effects of blend composition and processing condition on the cell size, cell density and relative density of PP/WGRT micro-cellular composites were studied. The results indicated that the microcellular structure was dependent on blend composition and processing condition. An increased content of waste ground rubber tire powder (WGRT) and maleic anhydride-grafted styrene-ethylene-butylene-styrene (SEBS-g-MA) reduced the cell size, and raised the cell density and relative density, whereas a higher saturation pressure increased the cell size, and reduced the cell density and relative density. With increasing saturation temperature, the cell size increased and the relative density decreased, whereas the cell density initially increased and then decreased.

• 한국전기전자재료학회논문지
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• 제24권3호
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• pp.224-228
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• 2011

This research, integratable capacitive relative humidity sensor was produced using polyimide on glass substrate. Also, at the time of upper electrode formation, upper electrode grain size was affected by giving changes to sputtering condition. Through this analyzing electrical characteristics affect from capacitive relative humidity sensor was possible. Capacitance of capacitive relative humidity sensor was 330 pF, linearity of 0.6%FS and it showed less than 3% of low hysterisis. Specially, hysterisis was affected more from interface than interstitial. Also was affected by the grain size which is one of the formation condition of upper electrode.

• 지식경영연구
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• 제7권2호
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• pp.69-96
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• 2006

The purpose of this study is to find success factors of knowledge management in Korean firms, confirm them empirically, and verify their relative importance in terms of company size and industry type. The major studies on the knowledge management were deliberately selected and interpretively analyzed to find the success factors of Korean firms. As a result of the analysis, five success factors(top management's will, evaluation reward, organizational culture, knowledge management system, organizational structure) have been found. The empirical researches to make certain whether the above five factors derived are actually true or not have been separately performed by using questionnaire method. Based on the data collected, it is found that all five factors are significant. The degree of relative importance among the success factors of knowledge management in Korean firms has been found as: (i)top management's will, (ii)organizational culture, (iii)evaluation-reward, (iv)knowledge management system, (v)organizational structure. In company size, large firm's degree of relative importance among the success factors are: (i)top management's will, (ii)organizational culture, (iii)evaluation-reward, (iv)knowledge management system, (v) organizational structure. And medium-small firm's degree of relative importance among the success factors of knowledge management in Korean firms has been found as: (i)top management's will, (ii)organizational culture, (iii) evaluation-reward, (iv)knowledge management system, (v)organizational structure. Finally, in type of industry, manufactural firm's degree of relative importance among the success factors of knowledge management in Korean firms has been found as: (i)top management's will, (ii)organizational culture, (iii)evaluation-reward, (iv)knowledge management system, (v)organizational structure. And non-manufactural firm's degree of relative importance among the success factors of knowledge management in Korean firms are: (i)top management's will, (ii)organizational culture, (iii)evaluation-reward, (iv)knowledge management system, (v)organizational structure.

• Journal of Preventive Medicine and Public Health
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• 제43권6호
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• pp.543-548
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• 2010

Objectives: The objective of this study was to calculate sample size and power in an ongoing cohort, Korea radiation effect and epidemiology cohort (KREEC). Method: Sample size calculation was performed using PASS 2002 based on Cox regression and Poisson regression models. Person-year was calculated by using data from '1993-1997 Total cancer incidence by sex and age, Seoul' and Korean statistical informative service. Results: With the assumption of relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, sample size calculation was 405 events based on a Cox regression model. When the relative risk was assumed to be 1.5 then number of events was 170. Based on a Poisson regression model, relative risk=1.3, exposure:non-exposure=1:2 and power=0.8 rendered 385 events. Relative risk of 1.5 resulted in a total of 157 events. We calculated person-years (PY) with event numbers and cancer incidence rate in the nonexposure group. Based on a Cox regression model, with relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, 136 245PY was needed to secure the power. In a Poisson regression model, with relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, person-year needed was 129517PY. A total of 1939 cases were identified in KREEC until December 2007. Conclusions: A retrospective power calculation in an ongoing study might be biased by the data. Prospective power calculation should be carried out based on various assumptions prior to the study.

• 응용통계연구
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• 제34권5호
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• pp.697-710
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• 2021

상대오차를 이용한 예측법은 상대오차(혹은 퍼센트오차)가 중요시되는 분야, 특히 계량경제학이나 소프트웨어 엔지니어링, 또는 정부기관 공식통계 부분에서 기존 예측방법 외에 선호되는 예측방법이다. 그 동안 상대오차를 이용한 예측법은 선형 혹은 비선형 회귀분석 뿐 아니라, 커널회귀를 이용한 비모수 회귀모형, 그리고 정상시계열분석에 이르기까지 그 범위가 확장되어 왔다. 그러나, 지금까지의 분석은 고정효과(fixed effect)만을 고려한 것이어서 임의효과(random effect)에 관한 상대오차 예측법에 대한 확장이 필요하였다. 본 논문의 목적은 상대오차예측법을 일반화선형혼합모형(GLMM)에 속한 감마회귀(gamma regression), 로그정규회귀(lognormal regression), 그리고 역가우스회귀(inverse gaussian regression)의 패널자료(panel data)에 적용시키는데 있다. 이를 위해 실제 자동차 보험회사의 손해액 자료를 사용하였고, 최량예측량과 최량상대오차예측량을 각각 적용-비교해 보았다.

• 한국농공학회논문집
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• 제48권6호
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• pp.59-67
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• 2006

Particles of soil are crushed when soil is compacted in the in-situ or lab. Among many factors that affect the crush of particles, compaction energy is a major factor. Because the crush of particles can change physical properties, the analysis of effect of compaction energy is very important. In this study, the fragmentation fractals were used for determining the change in grain size distribution and the effect due to change in grain size distribution was estimated. Compaction energy was increased by 50, 100, 200 and 300% based on the energy of standard A compaction test. As a result, grain size distribution curves were changed and fine particles increased as compaction energy were increased. Relative compaction were ranged between $93.38{\sim}107.67$. Fractal dimension of each site increased as compaction energy increased. Relative compaction is proportional to the fractal dimension but coefficients of permeability were in inverse proportional to the involution of fractal dimension.

• Geomechanics and Engineering
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• 제20권3호
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• pp.243-254
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• 2020

Due to the permanent damage to structures during earthquakes, soil liquefaction is an important issue in geotechnical earthquake engineering that needs to be investigated. Typical examples of soil liquefaction have been observed in many earthquakes, particularly in Alaska, Niigata (1964), San Fernando (1971), Loma Prieta (1989), Kobe (1995) and Izmit (1999) earthquakes. In this study, liquefaction behavior of uniform sands of different grain sizes was investigated by using the energy-based method. For this purpose, a total of 36 deformation-controlled tests were conducted on water-saturated samples in undrained conditions by using the cyclic simple shear test method and considering the relative density, effective stress and mean grain size parameters that affect the cumulative liquefaction energy. The results showed that as the mean grain size decreases, the liquefaction potential of the sand increases. In addition, with increasing effective stress and relative density, the resistance of sand against liquefaction decreases. Multiple regression analysis was performed on the test results and separate correlations were proposed for the samples with mean grain size of 0.11-0.26 mm and for the ones with 0.45-0.85 mm. The recommended relationships were compared to the ones existing in the literature and compatible results were obtained.

• Environmental Engineering Research
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• 제20권3호
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• pp.237-245
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• 2015

Particulate matter in indoor environments has caused public concerns in recent years. The objective of this research is to explore the influence of radiators on particle size distributions and concentrations. The particle size distributions as well as concentrations above radiators and in the adjacent indoor air are monitored in forty-two indoor environments in Xi'an, China. The temperatures, relative humidity and air velocities are also measured. The particle size distributions above radiators at ten locations are analyzed. The results show that the functional difference of indoor environments has little impact on the particle size distributions above radiators. Then the effects of the environmental parameters (particle concentrations in the adjacent indoor air, temperatures, relative humidities and air velocities) on particle concentrations above radiators are assessed by applying multiple linear regression analysis. Three multiple linear regression models are established to predict the concentrations of $PM_{10}$, $PM_{2.5}$ and $PM_1$ above radiators.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.638-643
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• 2001

Macroporous pellets were prepared from industrial waste flyash by foaming method. The surface and inside of flyash pellets, the shape was almost spherical and the average size was about 3 mm, were composed of the spherical pores interconnected through windows. The controlling of pellet size was conducted with solid loading. The flyash pellets with different relative density were characterized for porosity, average pore size, and specific surface area. As results, most physical properties had a tendency to increase as relative density decreased - extension ratio increased. The correlation between relative density and other properties was inspected through microstructural features evaluated by SEM. As a result, high porosity and high specific surface area were estimated to result from the superior connectivity between pores.