• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.400-403
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• 2011

We performed Instron and Impact tests to estimate necessary explosive charge weight for cutting the cable whose diameter is 22 mm. The cutting energy measured by Instron was 21.3 J. Impact test were performed 8 times each at 5 different energies. The Impact test results were analysed by Probit methods. The cutting energy was calculated 37.7 J with 99.99% probability at 99% confidence, which is roughly equivalent to 250 mg of Zirconium potassium Perchlorate (ZPP).

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.118-126
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• 2005

Abrasive waterjet (AWJ) cutting is an emerging technology for precision cutting of difficult-to-machining materials with the distinct advantages of no thermal effect, high machinability, high flexibility and small cutting forces. This paper investigated theoretical and experimental cutting characteristics associated with abrasive waterjet cutting of quartz GE214. It is shown that the proper variations of several cutting parameters such as waterjet cutting pressure, cutting speed and cutting depth improve the roughness on workpiece surfaces produced by AWJ cutting. From the experimental results by AWJ cutting of quartz GE214, the optimal cutting conditions to improve the surface roughness and precision were proposed and discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.367-371
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• 2010

가뭄 발생원인은 기후학적인 인자(온도, 바람, 상대습도 등)들과 밀접한 관계를 갖고 있으나, 가장 큰 원인은 강수부족이라고 말할 수 있다. 따라서 가뭄은 정상수준 이하의 강수 상황이 연속적으로 발생하여 나타나며, 설정된 절단수준에 대해 가뭄의 지속기간, 심도, 발생간격 등을 정의한 후 이에 대한 시계열 분석을 수행하여 가뭄의 특성을 분석한다. 본 연구에서는 가뭄 절단수준의 변화에 따른 한반도 내 가뭄의 특성분석을 위하여 하나의 절단수준으로 고정된 경우의 가뭄특성과 각 년도 월별 특성을 고려하여 절단수준이 지속적으로 변화하는 경우로 구분하여, 가뭄특성의 변화를 분석하였다. 또한 위 두 가지 경우에 대해 각각 가뭄해소 여부를 판단하여 총 4가지 경우에 따른 가뭄 특성을 분석하였다. 가뭄 절단수준의 변화 및 가뭄 해소여부에 따른 한반도 내 가뭄 특성을 분석하기 위해, 가뭄의 지속기간, 심도의 기초통계량 등을 산정하여 비교 분석하였다. 본 연구는 한반도 내의 가뭄특성을 보다 정확하게 해석하기 위해서는 다양한 가뭄정의에 따라 가뭄 해석결과가 나타내는 상대적 차이를 비교할 필요성이 있음을 증명하였다.

• The Korean Journal of Applied Statistics
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• v.25 no.2
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• pp.311-319
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• 2012

The simplest and the most important distribution in survival analysis is exponential distribution. Koziol and Green (1976) derived Cram$\acute{e}$r-von Mises statistic's randomly censored version based on the Kaplan-Meier product limit estimate of the distribution function; however, it could not be practical for a real data set since the statistic is for testing a simple goodness of fit hypothesis. We generalized it to the composite hypothesis for exponentiality with an unknown scale parameter. We also considered the classical Kolmogorov-Smirnov statistic and generalized it by the exact same way. The two statistics are compared through a simulation study. As a result, we can see that the generalized Koziol-Green statistic has better power in most of the alternative distributions considered.

• The Korean Journal of Applied Statistics
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• v.11 no.1
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• pp.113-127
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• 1998

There have been a great deal of interests in comparing two survival distributins in clinical trials. This paper compares some well-known statistical methods for testing the equality of two survival distributions. Simulation studies also provide some insights into the properties of these test statistics across several types of survival distributions and degrees of censorship.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1998.03a
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• pp.89-92
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• 1998

압연철판의 생산라인에 있는 카메라에 입력되는 영상정보를 Image Frame Grabber를 이용하지 않고 Video Overlay Board를 사용하여 라인에 입력되는 압연철판을 분석하여 외곽선을 가로지른 선분의 길이가 기준에 준할 때 정확한 절단정보를 발생시킴으로 기존에 사용해온 작업자의 대략적인 지식을 이용한 절단에서 발생되는 압연 철판의 손실을 최소화시키며 불량률을 줄인다. 그리고 발생되는 정보를 DB화시킴으로 생산품의 정확한 재고량을 관리하는 시스템을 개발한다.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.28 no.4
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• pp.481-487
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• 1983

The need to synchronize flowering in two lines of different maturities is frequently encountered in hybrid com (Zea mays L.) seed production. To establish the methods for synchrony of flowering in parent lines of different maturities be effects of clipping at 4 and 6-leaf stages of growth and two levels, clear polyethylene mulching and five different planting dates on flowering date growth and seed yield of two dent com inbred lines of different maturities were evaluated Clipping just above the shoot-apex delayed pollen sheeding 6 to 9days and silking 5 to 13 days but reduced stand and seed yield 30 to 70% and 67 to 81%. respectively. Clipping 5cm above the shoot apex delayed flowering 1 to 4 days without stand reduction but reduced yield 3 to 29%. Laterclipping was slightly more effective for delaying flowering than earlier clipping but reduced stand more severely when clipped just above the shoot apex. Under clear polyethylene film mulching, flowering of two lines was 13 to 15 days earlier and seed yield of B68 (late line) was significantly increased. As planting was delayed from April 18 to June 13, the number of days from planting to flowering of two lines decreased due to increase in air temperature. However, growing degree days (GDD) from planting to flowering of each lines was similar regardless planting dates indicating that GDD can be satisfactoryly used for choosing the planting dates of parent lines of different maturities. Seed yields of two lines were decreased with delaying planting dates.

• Journal of the Korean Data and Information Science Society
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• v.25 no.2
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• pp.393-402
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• 2014

The simplest and the most important distribution in survival analysis is the exponential distribution. In this paper, we investigate the influence of the random censorship model on the estimation of the scale parameter of the exponential distribution. The considered random censorship models are Koziol-Green model and the generalized exponential distribution model. Two models have different meanings. Through the simulation study, the averages of the estimated values of the parameter do not show big differences, however the MSE of the estimator tends to be bigger when the supposed model is significantly different from the true model.

• The Korean Journal of Applied Statistics
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• v.22 no.1
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• pp.29-39
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• 2009

Among others, ROC and CAP curves are used to explore the discriminatory power between the defaults and non-defaults, based on the distribution of the probability of default in credit rating works. ROC and CAP curves are plotted in terms of various ratios of the probability of default. Each point on ROC and CAP curves is calculated according to cutting points (scores) for classifying between defaults and non-defaults. In this paper, adjusted ROC and CAP curves are proposed by using functions of ratios of the probability of default. It is possible to recognize the score corresponding to a point oil these adjusted curves, and we can identify the best score to show the optimal discriminatory power. Moreover, we discuss the relationships between the best score obtained from the adjusted ROC and CAP curves and the score corresponding to Kolmogorov - Smirnov statistic to test the homogeneous distribution functions of the defaults and non-defaults.

• The Korean Journal of Applied Statistics
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• v.34 no.5
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• pp.735-744
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• 2021

Maintaining the lifetime of a product is one of the objectives of quality control. In real processes, most samples are constructed with censored data because, in many situations, we cannot measure the lifetime of all samples due to time or cost problems. In this paper, we propose two cumulative sum (CUSUM) control charting procedures to monitor the mean of type I right-censored lognormal lifetime data. One of them is based on the likelihood ratio, and the other is based on the binomial distribution. Through simulations, we evaluate the performance of the two proposed procedures by comparing the average run length (ARL). The overall performance of the likelihood ratio CUSUM chart is better, especially this chart performs better when the censoring rate is low and the shape parameter value is small. Conversely, the binomial CUSUM chart is shown to perform better when the censoring rate is high, the shape parameter value is large, and the change in the mean is small.