• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.143-147
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• 2002

본 연구의 목적은 부산 동남부 해안지역의 대수층에서 염수화에 미치는 조건들을 파악하고 해수침투 범위를 추정하는데 있다. 이를 위하여 Tidal damping method와 SUTRA 모델링을 실시하고 대수층의 특성 및 염수화가능성을 파악하였으며, 모델링 결과의 타당성을 판단하기 위하여 전기비저항 탐사를 실시하였다. Tidal damping method에 의한 시간지연과 조석효율효과를 계산하여 대수층의 저류계수를 산출한 결과 시간지연 현상에 의한 방법이 적합하게 나타났다. SUTRA 모델링 결과, 건기인 5월에는 종분산 지수가 2.5m 일 때 500ppm의 TDS 등치선을 기준으로 해안에서 약 510m 내륙까지 해수의 영향을 받고 있는 것으로 나타났다. 그러나 우기인 7월에는 강수로부터 다량의 지하수 함양에 의한 지하수위 상승을 고려하여, 평균수리경사를 0.008로 설정한 조건에서는 500ppm의 TDS 등치선을 기준으로 해안에서 약 410m 내륙까지 해수의 영향을 받는 것으로 나타난다. 5월과 7월의 전기비저항 탐사결과를 비교하면 7월의 전기비저항 분포가 전반적으로 높게 나타났다. 그 이유는 6, 7월의 강수에 의한 지하수의 유입이 증가하여 침투된 염수의 농도가 다소 낮아졌기 때문이다.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.12 no.19
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• pp.31-37
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• 1989

The recursive residuals are obtained by the iterative processes as descrbed in section 2. They may require more efforts and time to compute and may face difficultie in ordering of data. But we can investigate each case to be deleted and gather more informations on each case. The recursive residuals are much more effective with conjecture of cusum technique. We suggest to use the predicted residual for the construction of recursive residuals in nonlinear regression models. The assessment of influence and leverage by the connection with recursive residuals will be necessary.

• The Korean Journal of Applied Statistics
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• v.2 no.1
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• pp.18-34
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• 1989

The problem of simultaneously estimating the pairwise differences of means of four independent normal populations with equal variances is considered. A statistical computing procedure involving a trivariate t density constructs the exact confidence intervals with simultaneous co verage probability equal to $1-\alpha$. For equal sample sizes, the new procedure is the same as the Tukey studentized range procedure. With unequal sample sizes, in the sense of efficiency for confidence interval lengths and experimentwise error rates, the procedure is superior to the various generalized Tukey procedures.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.1
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• pp.14-26
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• 2011

Surface currents were observed by high-frequency (HF) radars off the Keum River estuary from December 2008 to February 2009. The dataset of observed surface currents had data gaps due to the interference of electromagnetic waves and the deteriorating weather conditions. To fill the data gaps an optimal interpolation procedure was developed. The characteristics of spatial correlation in the surface currents off the Keum River estuary were investigated and the spatial data gaps were filled using the optimal interpolation. Then, the temporal and spatial distribution of the interpolated surface currents and the patterns of interpolation error were examined. The correlation coefficients between the surface currents in the coastal region were higher than 0.7 because tidal currents dominate the surface circulation. The sample data covariance matrix (C), spatially averaged covariance matrix with localization ($C^G_{sm}$) and covariance matrix fitted by an exponential function ($C_{ft}$) were used to interpolate the original dataset. The optimal interpolation filled the data gaps and suppressed the spurious data with spikes in the time series of surface current speed so that the variance of the interpolated time series was smaller than that of the original data. When the spatial data coverage was larger (smaller) than 70% of the region, the interpolation error produced by $C^G_{sm}$ ($C_{ft}$) was smaller compared with that by C.

• Resources Recycling
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• v.23 no.5
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• pp.55-61
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• 2014

Froth flotation was performed to study the effect of phosphate addition in the experiment to remove As from tailing of Sang-dong Mine. The experiment without Trisodium phosphate (T.S.P) showed that the removal rate of As was 88.7% and weight-ratio of floating material was 2.52%. By contrast, the experiment with T.S.P showed that the removal rate of As was 92.74% and weight-ratio of floating material was 2.26%. In flotation without T.S.P, the average particle size of float material was 19.34 um and the amount less than 10um was 40.2%. On the other hand, in flotation with T.S.P the average particle size of float material was 176.8 um and the amount less than 10um was 6.5%. The result of X.R.F analysis presented that contents of $SiO_2$ was 42.74% in float material of the experiment without T.S.P. In contrast, contents of $SiO_2$ was 29.56% in float material of the experiment with T.S.P.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.143-143
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• 2015

기존의 빈도해석에서는 자료의 정상성을 가정하며, 이에 따라 적정모형 선정 시에 $x^2$ 검정이나 PPCC(Probability Plot Correlation Coefficient)검정과 같은 적합도 검정방법을 사용한다. 하지만 자료에서 경향성이 나타나거나 평균, 분산, 매개변수 등이 시간에 따라 변하는 등의 비정상성 현상들이 관측됨에 따라 비정상성 빈도해석에 관한 연구들이 활발히 진행되고 있다. 비정상성 빈도해석에서는 시간항과 같은 공변량이 포함된 매개변수를 가지는 비정상성 모형을 적용하게 되는데, 시간에 따라 매개변수가 계속 변하므로 매개변수에 따라 검정통계량이 고정되어 있는 기존의 적합도 검정방법의 적용이 어렵다. 따라서 비정상성 빈도해석의 적정 모형 선정에 적용할 수 있는 방법으로 최우도 함수에 기반한 모형 평가 방법인 AIC와 BIC가 추천되고 있으며 자료길이가 충분하지 않은 경우에는 AIC 대신하여 AICc의 사용이 추천되고 있다. 본 연구에서는 극치사상을 나타내는데 적합한 분포형인 GEV분포형의 위치, 규모 매개변수를 시간항으로 나타낸 다양한 비정상성 GEV모형에 대하여 Monte-Carlo 모의실험을 통해 AICc와 BIC의 적용성을 검토하였으며, 비정상성이 관측되는 실측 자료에 적용해보았다.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2008.11a
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• pp.306-309
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• 2008

본 연구에서는 순천만(전남 순천시 해룡면 농주리) 연안습지에서 온도(퇴적물/대기), 퇴적물 내 유기탄소 및 대기 중 이산화탄소의 관계에 대해 분석하였다. 현장관측은 2008년 3월 16일11시부터 15시 사이에 수행되었으며, 약 300 m X 100 m의 갯벌 지역 내 30개 지점에서 조사되었다. 퇴적물과 대기의 온도와 대기 중 이산화탄소량은 현장에서 측정되었으며, 각 지점에서 채취된 퇴적물 내 유기탄소량은 부경대학교 공실관에서 TOC Analyzer를 이용하여 분석되었다. 퇴적물과 대기 중의 온도는 각각 13.2$\sim$17.5$^{\circ}C$ 및 15.0$\sim$18.9$^{\circ}C$의 범위이었으며, 평균은 15.65$^{\circ}C$와 17.51$^{\circ}C$로서 대기 온도가 약 2$^{\circ}C$ 정도 높았다. 대기 중 이산화탄소량은 퇴적물 직상부, 상부 0.5 m 및 1.0 m의 3개 지점에서 측정되었다. 각 지점별 평균 이산화탄소량은 퇴적물 직상부 352 ppm, 상부 0.5 m 지점 355 ppm, 상부 1.0 m 지점 363 ppm으로서 거의 유사하였으나, 퇴적물에서 상부로 갈수록 약간 증가하는 경향을 보였다. 대기 중 이산화탄소량의 분산은 퇴적물 직상부와 상부 0.5 m 지점에 비해 상부 1.0 m 지점에서 약 3배 정도 높게 나타났으며, 이는 주변 대기의 영향에 의한 것으로 판단된다. 현장에서 채취된 퇴적물 내 유기탄소량은 0.60$\sim$1.12%의 범위이었으며, 평균은 0.72% 이었다. 유기탄소량의 분산은 0.01로서 매우 낮았으며, 또한 1개 지점(1.12%)을 제외하면 유기탄소량의 범위는 0.60$\sim$0.82% 정도로서 연구지역 내 유기탄소량의 공간적인 분포가 비교적 균질함을 알 수 있었다. 본 연구를 통해, 대기 중 이산화탄소량은 온도효과와 주변 대기와의 혼합 정도에 따라 영향을 받고 유기탄소는 이러한 영향성이 적었음을 알 수 있었다.

• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.12-15
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• 2006

The purpose of this study was to investigate the effect of reaction conditions, solvents, and surfactants on the average size and size distribution of silica particles in preparing silica fine powders by sodium silicate. Silica fine particles were synthesized by varying kinds of solvents and surfactants using the emulsion method. Span 20, Span 40, Span 60, and Span 80 were used as nonionic surfactants, Dispersing solvents were n-Hexane, n-Heptane, iso-Octane, and n-Decane of the alkane group. In these experiments, it was known that the optimum dispersion stirring time to form the emulsion of the constant size was around 6 min. The mean sizes of silica particles, at a variety of the dispersion stirring speeds, decreased as the dispersion stirring speed increased. Also, in the case of the solvents, the size of the formed silica particles decreased when the molecular weight of the solvent increased. Lastly, in the case of the surfactants, the mean size of silica particles increased as the hydrophobic lipophilic balance (HLB) value of the surfactant decreased.

• Food Engineering Progress
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• v.21 no.3
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• pp.267-272
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• 2017

To improve dispersibility of cereal powder without additives, granulation of cereal powder was conducted using fluidized-bed granulator. Operation condition was sample 300 g, internal temperature $40^{\circ}C$, ventilation speed $30-90m^3/h$, inlet temperature $90^{\circ}C$ and spray pressure 2.5 bar. The amount of distilled water (20-45%) as binder, granulation time (10-15 min) and drying time (3-10 min) were controlled. Mean diameter over volume (Brouckere mean, $D_{4,3}$) was increased from $123{\mu}m$ to $263{\mu}m$ and dispersibility was improved from 73% to 92.25% at experiment conditions. Wettability (wetting time) was drastically decreased from 5,000 second to 7 second. Granulation of cereal powder did not affect sinkability and mean diameter over volume as wet analysis was about the same between raw and granulated cereals. Such phenomenon means that granulation with only water as binder enables cereal powder to disperse in water or milk without rapid sedimentation.

• The Korean Journal of Financial Management
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• v.26 no.1
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• pp.165-188
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• 2009

This paper has suggested the methodology for the frontier portfolios and the optimal portfolio under the mean-VaR framework, not assuming the normal distribution and considering the investor's preferences for the higher moments of return distributions. It suggested the grid and rank approach which did not need an assumption about return distributions to find the frontier portfolios. And the optimal portfolio was selected using the utility function that considered the 3rd and the 4th moments. For the application of the methodology, weekly returns of the developed countries index, the emerging market index and the KOSPI index were used. After the frontier portfolios of the mean-variance framework and the mean-VaR framework were selected, the optimal portfolios of each framework were compared. This application compared not only the difference of the standard deviation but also the difference of the utility level and the certainty equivalent expressed by weekly expected returns. In order to verify statistical significances about the differences between the mean-VaR and the mean-variance, this paper presented the statistics which were obtained by the historical simulation method using the bootstrapping. The results showed that an investor under the mean-VaR framework had a tendency to select the optimal portfolio which has bigger standard deviation, comparing to an investor under the mean-variance framework. In addition, the more risk averse an investor is, the bigger utility level and certainty equivalent he achieves under the mean-VaR framework. However, the difference between the two frameworks were not significant in statistical as well as economic criterion.