• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.1
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• pp.3-5
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• 2023

Objective: This study introduces exposure concentrations of time-weighted average standard (TWA) evaluation and short-time exposure standard (STEL) evaluation for trichloroethylene in the cleaning process. Methods: Trichloroethylene measurement was conducted according to the KOSHA Guide (A-24-2019) method. It was carried out twice. Results: As a result of the first measurement, TWA concentration exceeded 4 times the exposure standard and STEL concentration exceeded 16 times, but the inaccuracy and breakthrough of the collection time could not be considered, so the second measurement was conducted. The second measurement result was lower than the first measurement result, but exceeded the exposure standards (TWA, STEL). Conclusions: We were able to confirm that the exposure level of workers in the cleaning process using trichloroethylene exceeded the exposure standard. And it is also considered necessary to grasp the approximate concentration using a detector tube in the preliminary survey.

• Journal of the Korean Operations Research and Management Science Society
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• v.39 no.1
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• pp.1-12
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• 2014

This article proposes a variable sampling interval (VSI) $\bar{X}$ control chart using weighted standard deviation (WSD) method for skewed populations. The WSD method decomposes the standard deviation of a quality characteristic into upper and lower deviations and adjusts control limits and warning limits of a control chart in accordance with the direction and degree of skewness. A control chart constant is derived for estimating the standard deviation of skewed distributions with the mean of sample standard deviations. The proposed chart is compared with the conventional VSI $\bar{X}$ control chart under some skewed distributions. Simulation study shows that the proposed WSD VSI chart can control the in-control average time to signal (ATS) as an adequate level better than the conventional VSI chart, and the proposed chart can detect a decrease in the process mean of a quality characteristic following a positively skewed distribution more quickly than the standard VSI chart.

• Journal of Korean Society for Quality Management
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• v.34 no.4
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• pp.125-132
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• 2006

An adjusted control limit of the $\overline{X}$ chart is proposed for monitoring the continually improving processes. The continual improvement of the process implies the decrease of the process variance, which is represented by a logistic curve. The process standard deviation is estimated by the exponentially weighted moving average of the sample standard deviations from the past to the current times. The control limits are adjusted by the estimated standard deviation at every sampling time. The performance of the adjusted control limit is compared with that of the standard control limits for various cases of the decreasing speed and size of the variance. The results show that the $\overline{X}$ chart with the adjusted control limits provides better performances for monitoring the small and moderate shifts in continually improving processes.

• Journal of Welding and Joining
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• v.8 no.1
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• pp.31-42
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• 1990

Arc must be stable during welding first of all other factors for obtaining sound weldment, especially in the automation of welding process. Arc stability is somewhat sophisticated phenomenon which is not clearly defined yet. In consumable electrode welding, the voltage and current variation due to metal transfer enables to assess arc stability. Recently, statistical analyses of the voltage and current waveform factors are performed to assess the degress of arc stability which is assessed and controlled by operator's own experience by now. But, considering the increasing need and the trend of automation of welding process, it is necessary to monitor arc stability in real-time. In this sutdy, the modified stability index composed of two voltage and current wvaeform factors (arc time and short circuit time) reduced from four factors (arc time, short circuit time, average arc current and average short circuit current) in Mita's index by the welding electrical circuit modeling is proposed and verified by experiments to be well estimating arc stability in the static sense. Also, the recursive calculation form estimating present arc stability in the dynamic sense is developed for real-time estimation. The results of applying the recursive index during welding show good estimation of arc stability in real-time. Therefore, the results of this study offers the mean for real-time control arc stability.

• The Korean Journal of Applied Statistics
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• v.31 no.2
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• pp.205-216
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• 2018

This paper is concerned with volatility computations for high frequency time series. A threshold-asymmetric realized volatility (T-RV) is suggested to capture a leverage effect. The T-RV is compared with various conventional volatility computations including standard realized volatility, GARCH-type volatilities, historical volatility and exponentially weighted moving average volatility. High frequency KOSPI data are analyzed for illustration.

• Journal of KIBIM
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• v.13 no.2
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• pp.1-15
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• 2023

Since the 1960s, the Korean Peninsula, which consists of 77.4 of the country's land and mountains, has seen a surge in demand for buildings due to population concentration due to urbanization and industrialization. Since then, the development of slopes has been inevitable due to the concentration and expansion of the city's population. When building a building on a slope, it is important to set the height of the surface. In this case, the means of regulating buildings in construction-related laws, such as the building closure ratio, floor area ratio, number of floors and total floor area of buildings, have an overall effect on buildings through the height of the surface. In the Korean Building Act, the setting of the height of the ground affects the calculation of the building height limit standard and the calculation of the underground floor, and it takes a long time to calculate. Therefore, the time required for attempts to change various design plans of buildings increases. The purpose of this study is to speed up the time required to calculate the weighted average of the surface when constructing buildings on slopes. In addition, the existing calculation process allows various design attempts compared to the same time given.

• Korean Journal of Remote Sensing
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• v.28 no.6
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• pp.635-651
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• 2012

To produce a level-3 monthly composite image from daily level-2 Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll-a concentration data set in the East Sea, we applied four average methods such as the simple average method, the geometric mean method, the maximum likelihood average method, and the weighted averaging method. Prior to performing each averaging method, we classified all pixels into normal pixels and abnormal speckles with anomalously high chlorophyll-a concentrations to eliminate speckles from the following procedure for composite methods. As a result, all composite maps did not contain the erratic effect of speckles. The geometric mean method tended to underestimate chlorophyll-a concentration values all the time as compared with other methods. The weighted averaging method was quite similar to the simple average method, however, it had a tendency to be overestimated at high-value range of chlorophyll-a concentration. Maximum likelihood method was almost similar to the simple average method by demonstrating small variance and high correlation (r=0.9962) of the differences between the two. However, it still had the disadvantage that it was very sensitive in the presence of speckles within a bin. The geometric mean was most significantly deviated from the remaining methods regardless of the magnitude of chlorophyll-a concentration values. Its bias error tended to be large when the standard deviation within a bin increased with less uniformity. It was more biased when data uniformity became small. All the methods exhibited large errors as chlorophyll-a concentration values dominantly scatter in terms of time and space. This study emphasizes the importance of the speckle removal process and proper selection of average methods to reduce composite errors for diverse scientific applications of satellite-derived chlorophyll-a concentration data.

• Atmosphere
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• v.24 no.3
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• pp.365-378
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• 2014

The limits of S-band dual-polarization radars in Korea are not reflected on the recent weather forecasts of Korea Meteorological Administration and furthermore, they are only utilized for rainfall estimations and hydrometeor classification researches. Therefore, this study applied four merging methods [SA (Simple Average), WA (Weighted Average), SSE (Sum of Squared Error), TV (Time-varying mergence)] to the QPE (Quantitative Precipitation Estimation) model [called RAR (Radar-AWS Rainfall) calculation system] using single-polarization radars and S-band dual-polarization radar in order to improve the accuracy of the rainfall estimation of the RAR calculation system. As a result, the merging results of the WA and SSE methods, which are assigned different weights due to the accuracy of the individual model, performed better than the popular merging method, the SA (Simple Average) method. In particular, the results of TVWA (Time-Varying WA) and TVSSE (Time-Varying SSE), which were weighted differently due to the time-varying model error and standard deviation, were superior to the WA and SSE. Among of all the merging methods, the accuracy of the TVWA merging results showed the best performance. Therefore, merging the rainfalls from the RAR calculation system and S-band dual-polarization radar using the merging method proposed by this study enables to improve the accuracy of the quantitative rainfall estimation of the RAR calculation system. Moreover, this study is worthy of the fundamental research on the active utilization of dual-polarization radar for weather forecasts.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.2
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• pp.209-220
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• 2021

The noise is defined as unwanted sound that causes discomfort and physical changes. This study was conducted to evaluate intensity of noise in the pediatric dental clinic and to investigate noise environment of a pediatric dentist. Human ear shaped microphone and mobile noise level meter were used for recording noise and calculating intensity of noise. By recording according to the method specified by Korea Occupational Safety and Health Agency (KOSHA) of Korea Ministry of labor and employment, the following results were obtained. For 16 experimental days, 8 hour time weighted average (8hr-TWA) was 49.33 dBA (A-weighted deci-Bell) on daily average with maximum 58.54 dBA and minimum 33.97 dBA. And Dose was 0.49% on daily average with maximum 1.28%, minimum 0.04%. These values are less than criteria of KOSHA standard (85 dBA, 100%). Comparing the highest noise level for each patient, pulp therapy group and Frankel grade I group were the highest. The intensity of dental noise of pediatric dental clinic didn't meet standard of KOSHA. It is necessary to re-evaluate noise environment by establishing new standards considering environment of pediatric dental clinic.

• Journal of Korea Water Resources Association
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• v.54 no.11
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• pp.925-932
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• 2021

A drought-flood abrupt alternation event is an overlapping extreme event that is harder to cope with than a single event of drought and flood. It is also expected to have a significant adverse impact on ecosystems as well as industries and agriculture. However, there has not yet been a comprehensive study that characterizes the drought-flood abrupt alternation events in Korea. Therefore, this study employed a standard weighted average precipitation (SWAP) index, which is efficient to analyze not only individual events of drought and flood but also the drought-flood abrupt alternation events considering various time scales. The SWAP standardized the weighted average precipitation (WAP) by adding temporal weights to the precipitation. The SWAP indices were calculated for middle-sized watersheds of the Han River basin using the area average precipitation during 1966 and 2018. The severity K was calculated to represent the relative regional severity considering normal rainfalls, and used to characterize the drought-flood abrupt alternation in the study areas. The results indicated that 20 of the 30 middle-sized watersheds in the Han River basin were confirmed to increase the severity of drought-flood abrupt alternation over time. Considering the frequency and severity of drought-flood abrupt alternation events in each watershed, vulnerable areas and dangerous areas due to drought-flood abrupt alternation were identified, for example, the Upstream Namhan River (#1001).