• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1439-1443
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• 2011

A theoretical study on the ground water flow adjacent to buried pipe was conducted. Incompressible and irrotational flow were considered in analytical study. Ground water flow were defined by complex potentials. Firstly, uniform flow without buried pipe was analysed and then the effect of buried pipe was considered by superposition via circle theorem. Although two kinds of flow can be added by linearity of complex potentials, investigation of the singularities of the complex potentials should be done in advance. Finally, ground water flow past a buried pipe was analysed via complex potentials and net force exerted on the buried pipe by the ground water flowing past with circulation was derived.

• Journal of the Korea Convergence Society
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• v.11 no.8
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• pp.1-6
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• 2020

There are various approaches to evaluate a watermelon sweetness. However, there are some limitations to evaluating cost, watermelon damage, and subjective issue. In this study, we developed a novel approach to predict a watermelon sweetness using reflected sound and the machine learning algorithm. It was observed that higher brix watermelon produced higher spectral power is reflected sound. Based on the spectral-temporal features of reflected sound, the machine learning algorithms could accurately predict the sweetness group at a rate of 83.2 and 59.6 % in 2-groups and 3-groups classification, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.2
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• pp.107-119
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• 2013

We study three axis attitude control method including two axis high agile maneuver using four reaction wheels and two control moment gyros. We investigate singularity conditions due to two control moment gyros and propose singularity escape method. Based on this, we propose actuator control algorithm for high agile maneuver. Also, we propose actuator momentum management method which preserves momentum of reaction wheels and control moment gyroscopes before and after satellite attitude control. Through numerical simulation, we show that our method achieves three axis attitude control including two axis high agile maneuver and preserves actuators' momentum.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.3
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• pp.253-261
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• 2015

A parallel mechanism with redundancy can be regarded as a means for not only maximizing the benefits of parallel mechanisms but also overcoming their drawbacks. We proposed a novel parallel mechanism by eliminating an unnecessary degree of freedom of the configuration space. Because of redundancy, however, the solution for the inverse kinematics of the developed parallel mechanism is infinite. Therefore, we defined a cost function that can minimize the movement time to the target orientation and found the solution for the inverse kinematics by using a numerical method. In addition, we proposed a method for determining the boundary of the geometric singularity in order to avoid singularities.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.19-27
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• 2002

The early damage detection of large structures is very important to prevent the disaster due to its global failure. In this paper, a crack detection method of the beam-analogy structure based on the wavelet transformation of mode shape is presented. The method can effectively detect the singularity of mode shape caused to the inconsistency of bending moment and shear force at the damaged part using the discrete wavelet of mode shape and its inverse transforms of detail components. To investigate the validity and the applicability of the presented damage detection method, numerical simulation and experiment are carried out for the idealized beam and the real ship structures.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.782-786
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• 2010

Thrust deduction related to the prediction of power performance of a ship is rather resistance increase, and as a preliminary study for it forces upon a circular cylinder in a uniform flow of ideal fluid due to singularities located behind it are investigated. The circle theorem is used to get the complex velocity potential for the flow field under consideration, and the Blasius theorem is applied to obtain forces upon the circular cylinder. As singularities sinks, point vortices and dipoles and their combinations are treated. $\varepsilon$, standing for the strength of a singularity, and $\delta$, representing the distance between the cylinder and the singularity, are important small parameters for the resistance and lateral forces. For sinks or point vortices it is shown that the dimensionless forces upon the cylinder is O($\epsilon$) if $\epsilon$= O($\delta$) is assumed, and the same holds for dipoles if $\epsilon$= O(${\delta}^3$) is supposed. Forces upon the cylinder by a symmetric pair of sinks are greater than a single sink located at the central plane since there is an additional term due to cross effects, and the same is also valid for the case of dipole. Combination of dipole and a point vortex is also considered and a few new aspects are clarified.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.131-136
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• 1985

The calculation of the resulting fluid motion is an important problem of ship hydrodynamics. For a partially immersed body the condition of constant pressure at the free surface can be linearized. The resulting linear boundary-value problem for the velocity potential is the Neumann-Kelvin problem. The two-dimensional Neumann-Kelvin problem is studied for the half-immersed circular cylinder by Ursell. Maruo introduced a slender body approach to simplify the Neumann-Kelvin problem in such a way that the integral equation which determines the singularity distribution over the hull surface can be solved by a marching procedure of step by step integration starting at bow. In the present pater for the two-dimensional Neumann-Kelvin problem, it has been suggested that any solution of the problem must have singularities in the corners between the body surface and free surface. There can be infinitely many solutions depending on the singularities in the coroners.

• The Korean Journal of Applied Statistics
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• v.33 no.5
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• pp.541-553
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• 2020

The receiver operating characteristic (ROC) curve is expressed as both sensitivity and specificity; in addition, some optimal thresholds using the ROC curve are also represented with both sensitivity and specificity. In addition to the sensitivity and specificity, the expected usefulness function is considered as disease prevalence and usefulness. In particular, partial the area under the ROC curve (AUC) on a certain range should be compared when the AUCs of the crossing ROC curves have similar values. In this study, partial AUCs representing high sensitivity and specificity are proposed by using sensitivity and specificity lines, respectively. Assume various distribution functions with ROC curves that are crossing and AUCs that have the same value. We propose a method to improve the discriminant power of the classification models while comparing the partial AUCs obtained using sensitivity and specificity lines.

• Child Health Nursing Research
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• v.20 no.3
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• pp.215-224
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• 2014

Purpose: This study was conducted to identify risk factors in hospitalized children, and to develop and validate a fall-risk assessment tool for hospitalized children. Methods: A retrospective chart review was performed at one university children's hospital, and an analysis was done of the characteristics of all patients who fell during a 44-month period (n=48). These patients were compared with another 149 hospitalized children who did not fall. Results: Significant predictors of falls as identified in a multivariate logistic regression analyses were age of less than 3 years old, neurological diagnosis including epilepsy, children's dependency of ADL, physical developmental delay, multiple usage of fall-risk-increasing drugs. The respective odds ratios ranged from 2.4 to 7.1 with 95% confidence interval (p<0.05). Accordingly, defining patients with either 5 risk factors as fall-prone hospitalized children provided a sensitivity of 93.6% and specificity of 16.2%. Conclusion: The results show that this tool has an acceptable level of sensitivity to assess the risk factors of fall in hospitalized children even though the specificity was low, suggesting that this tool may enable nurses to predict the risk level of childhood falls, and develop preventive strategies against pediatric falls in children's units.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10b
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• pp.899-902
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• 2000

지문인식 분야는 크게 분류(classification)와 정합 (matching)으로 나누어져 연구되어왔다. 분류는 일반적으로 와상문, 궁상문, 솟은궁상문, 오른쪽제상문, 왼쪽제상문 등의 5종류로 분류되며, 지문이 어떤 분류에 속하는지 구별하여 특정인의 지문 형태를 결정하여 주는 작업으로 대형 데이터베이스에서 인덱스로 사용되어 검색시간 단축과 매칭의 정확도를 높여준다. 본 논문에서는 지문 분류에서 품질이 나쁜 이미지는 분류를 위한 특이점 (핵 과 삼각점)의 검술이 어려운 점을 감안하여 방향성과 주파수 선택력이 강한 Gabor 필터의 특징을 이용한 지문 분류 방법으로 지문 분류의 정확성을 향상시킬 수 있는 방안을 제시하고 실험을 통하여 이를 증명한다.