• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.1
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• pp.25-33
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• 2015

The Strait of Malacca is one of the most important fairways in the world and its traffic safety has direct effect on economic development of East Asian countries including China, Japan and Korea. Because of this reason, a safety analysis of the marine traffic in the strait has a great significance. In this paper, we analysed the statistic distribution of marine traffic in the Strait of Malacca based on the vessels' AIS data for 1 month by using the TOAIS and EasyFit programs. As the results of the analysis, it was found that the traffic distribution of this strait was different with normal distribution, which had been still widely used in marine traffic engineering field. Furthermore, with the traffic distribution analysis results, the traffic safety of the strait was also assessed by using the IWRAP model. The results showed that the highest level of risk were overtaking and crossing situations. Finally, we found that the highest risk of collision area in the Strait of Malacca was crossing area between the Strait of Malacca and the Port Klang fairway.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.209-213
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• 2001

The reliability data analysis for components of CNC machining center is studied in this paper. The failure data of mechanical part is analyzed by Exponential, Weibull, and Log-normal distributions. And then, the optimum failure distribution model is selected by goodness of fit test. The reliability data analysis program is developed with ASP language to use on the Internet. The failure rate, MTBF, life, and failure mode of mechanical parts are estimated and searched by this program. The failure data and analysis results are stored in the database.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.57.2-57.2
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• 2014

Protostellar jets and outflows are signatures of star formation and promising mechanisms for driving supersonic turbulence in molecular clouds. We quantify outflow-driven turbulence through three-dimensional numerical simulations using an isothermal version of the total variation diminishing code. We drive turbulence in real space using a simplified spherical outflow model, analyze the data through density probability distribution functions (PDFs), and investigate density and velocity power spectra. The real-space turbulence-driving method produces a negatively skewed density PDF possessing an enhanced tail on the low-density side. It deviates from the log-normal distributions typically obtained from Fourier-space turbulence driving at low densities, but can provide a good fit at high densities, particularly in terms of mass-weighted rather than volume-weighted density PDF. We find shallow density power-spectra of -1.2. It is attributed to spherical shocks of outflows themselves or shocks formed by the interaction of outflows. The total velocity power-spectrum is found to be -2.0, representative of the shock dominated Burger's turbulence model. Our density weighted velocity power spectrum is measured as -1.6, slightly less that the Kolmogorov scaling values found in previous works.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.26 no.4
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• pp.263-279
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• 2022

This paper presents an automatic inspection of defects in semiconductor images. We devise a statistical method to find defects on homogeneous background from the observation that it has a log-normal distribution. If computer aided design (CAD) data is available, we use it to construct a signed distance function (SDF) and change the pixel values so that the average of pixel values along the level curve of the SDF is zero, so that the image has a homogeneous background. In the absence of CAD data, we devise a hybrid method consisting of a model-based algorithm and two neural networks. The model-based algorithm uses the first right singular vector to determine whether the image has a linear or complex structure. For an image with a linear structure, we remove the structure using the rank 1 approximation so that it has a homogeneous background. An image with a complex structure is inspected by two neural networks. We provide results of numerical experiments for the proposed methods.

• Wind and Structures
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• v.37 no.3
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• pp.211-227
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• 2023

To investigate the non-Gaussian feature of fluctuating wind pressures on rectangular high-rise buildings, wind tunnel tests were conducted on scale models with side ratios ranging from 1/9~9 in an open exposure for various wind directions. The high-order statistical moments, time histories, probability density distributions, and peak factors of pressure fluctuations are analyzed. The mixed normal-Weibull distribution, Gumbel-Weibull distribution, and lognormal-Weibull distribution are adopted to fit the probability density distribution of different non-Gaussian wind pressures. Zones of Gaussian and non-Gaussian are classified for rectangular buildings with various side ratios. The results indicate that on the side wall, the non-Gaussian wind pressures are related to the distance from the leading edge. Apart from the non-Gaussianity in the separated flow regions noted by some literature, wind pressures behind the area where reattachment happens present non-Gaussian nature as well. There is a new probability density distribution type of non-Gaussian wind pressure which has both long positive and negative tail found behind the reattachment regions. The correlation coefficient of wind pressures is proved to reflect the non-Gaussianity and a new method to estimate the mean reattachment length of rectangular high-rise building side wall is proposed by evaluating the correlation coefficient. For rectangular high-rise buildings, the mean reattachment length calculated by the correlation coefficient method along the height changes in a parabolic shape. Distributions of Gaussian and non-Gaussian wind pressures vary with side ratios. It is inappropriate to estimate the extreme loads of wind pressures using a fixed peak factor. The trend of the peak factor with side ratios on different walls is given.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.119-130
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• 2008

Uncertainties in physical and engineering parameters for the design of shallow foundations arise from various aspects such as inherent variability and measurement error. This paper aims at investigating and reducing uncertainty from deterministic method by using the reliability-based design of shallow foundations accounting for the variation of various design parameters. A probability distribution type and statistics of random variables such as unit weight, cohesion, infernal friction angle and Young's modulus in geotechnical engineering are suggested to calculate the ultimate bearing capacities and immediate settlements of foundations. Reliability index and probability of failure are estimated based on the distribution types of random variables. Widths of foundation are calculated at target reliability index and probability of failure. It is found that application and analysis of the best-fit distribution type for each random variables are more effective than adoption of the normal distribution type in optimizing the reliability-based design of shallow foundations.

• Journal of Navigation and Port Research
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• v.38 no.6
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• pp.689-694
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• 2014

The Korean government has introduced and enforced maritime traffic safety assessment to secure traffic safety since 2010. The maritime traffic safety assessment is needed by law to design a new port or modify an existing one. According to Korea Maritime Safety Act, in the assessment the propriety of marine traffic system consists of the safety of channel transit and berthing/unberthing maneuver, safety of mooring, and safety of marine traffic flow. The safety of channel transit and berthing/unberthing maneuver can be evaluated only by ship-handling simulation. The ship-handling simulation is carried out by sea pilots working with the port concerned. The vessel's proximity measure is an important factor to evaluate traffic safety. The proximity measure is composed of vessel's closest distance to channel boundary and probability of grounding/collision. What is more, the probability of grounding becomes important. According to central limit theorem, a sample has a normal distribution on condition that its size is more than 30. However, more than 30 simulation runs bring about the increase of assessment period and difficulty of employing sea pilots. Therefore this paper is to find out minimum sample size for evaluating vessel's proximity. First sample sets of size of 3, 5, 7, 9 etc. are selected randomly on the basis of normal distribution. And then KS test for goodness of fit and t-test for confidence interval are applied to each sample set. Finally this paper decides the minimum sample size. As a result this paper suggests the minimum sample size of 5, that is, the simulation of more than five times.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.17-26
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• 2019

In this study, the statistical characteristics of the resistance bias factors were analyzed using a high-quality field load test database, and the total resistance bias factors were estimated considering the soil uncertainty and construction errors for the application of the limit state design of aggregate pier foundation. The MLR model by Bong and Kim (2017), which has a higher prediction performance than the previous models was used for estimating the resistance bias factors, and its suitability was evaluated. The chi-square goodness of fit test was performed to estimate the probability distribution of the resistance bias factors, and the normal distribution was found to be most suitable. The total variability in the nominal resistance was estimated including the uncertainty of undrained shear strength and construction errors that can occur during the aggregate pier construction. Finally, the probability distribution of the total resistance bias factors is shown to follow a log-normal distribution. The parameters of the probability distribution according to the coefficient of variation of total resistance bias factors were estimated by Monte Carlo simulation, and their regression equations were proposed for simple application.

• Journal of Korean society of Dental Hygiene
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• v.9 no.4
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• pp.659-669
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• 2009

Objectives : The degree of depression in dental hygienist was analyzed to reveal the various factors related to them. Methods : The self-administered questionnaires were filled out from 202 dental hygienist in Daejeon City. The survey items included subjects' socio-demographic and job-related characteristics, health-related behaviors, depression. Chi-Square analysis and Pearson's correlation coefficient was put into survey results, in which a degree of depression was dependent variable and others were independent variable. Results : 1. The distribution for depression degree has shown the rate as 80.2% in normal range group and 19.8% in depression group. 2. As for depression, long working hours(p=0.042), poor sense satisfaction in work(p=0.000), not fit to the job(p=0.003), low personal relation with peer works or supervisors(p=0.039), without alcohol drinking(p=0.048), poor subjective condition of health(p=0.000) than their respective counterparts. 3. Concerning correlation between depression and various factors, poor sense satisfaction in work(r=-0.332, p=0.000), not fit to the job(r=-0.353, p=0.000), low personal relation with peer works or supervisors(r=-0.215, p=0.002), without alcohol drinking(r=-0183, p=0.009), poor subjective condition of health(r=-0.333, p=0.000). Conclusions : These results showed that depression state could be influenced by various factors, which include socio-demographic, job-related characteristics and health-related behaviors. Therefore, in order to reduce depression state of dental hygienists, development and application of programs to manage and research for them are required to be revitalized as well as socio-demographic and job-related characteristics and health-related behaviors.

• Journal of Distribution Science
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• v.18 no.5
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• pp.89-98
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• 2020

Purpose: The growth of online commerce is now becoming a major threat and a new opportunity for retailers. Existing offline retailers struggle to cope with new online retailers' threats by utilizing offline infrastructure. Besides, online retailers expand their online strengths to offline sales by opening their offline stores. Many retailers are paying close attention to the O2O business and the resulting changes. Thus, this research focuses on the O2O business model and process that retailers can adopt. Research design, data and methodology: Considering the features of products that retailers sell, this paper divides O2O business process with the following criteria: delivery lead-time and delivery area. And This research uses the business model canvas to define the features of O2O commerce business process. This paper also uses nine key elements in the business model canvas for analyzing the structure of O2O commerce business. Results: This paper suggests the delivery model of retailers respond to offline customer orders and summarizes the following results. (1) Considering characteristics such as logistics process, delivery area, and product type, we define the features of O2O business models: wide-area (warehouse) based O2O business model, regional area (store) based O2O business model and time-separated O2O business model. (2) This study checks the availability of the business model through the business cases of O2O business models. (3) This study also analyzes the O2O business model of domestic retail companies by the factors defined in the business model canvas. Conclusions: Retailers can adopt the O2O business process to fit their business requirements and strategy. The online retailers who deal with normal consumer products mainly have the wide-area based O2O business model. The wide-area based O2O business model can be suitable for retailers who manage inventory centrally. The time-separated O2O business model can be a good solution for fresh food retailers to operate the logistics process efficiently. And to shorten the delivery lead-time of fresh foods, the regional area based O2O business model can be fit to the retailer that utilizes its offline logistics or sales infrastructure. It may be much more important for retailers to share the inventory information with other branches and to change the role of offline stores.