• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.2 s.42
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• pp.71-80
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• 2005

The solution to a liquid sloshing problem is challenge to the field of engineering. This is not only because the dynamic boundary condition at the free surface is nonlinear, but also because the position of the free surface varies with time in a manner not known a priori. Therefore, this nonlinear phenomenon, which is characterized by the oscillation of the unrestrained free surface of the fluid, is a difficult mathematical problem to solve numerically and analytically. In this study, three-dimensional boundary element method(BEM), which is based on the so-called an arbitrary Lagrangian-Eulerian(ALE) approach for the fluid flow problems with a free surface, was formulated to solve the behavior of the nonlinear free surface motion. An ALE-BEM has the advantage to track the free surface along any prescribed paths by using only one displacement variable, even for a three-dimensional problem. Also, some numerical examples were presented to demonstrate the validity and the applicability of the developed procedure.

• Journal of Korea Entertainment Industry Association
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• v.13 no.3
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• pp.203-211
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• 2019

The purpose of this study was to investigate the relations between sensory processing and sleep disturbances and to investigate the effect of sensory processing on sleep disorder in preschool children with developmental disorder. This study was conducted for 110 children with developmental disorder in developmental clinic and rehabilitation hospital in Gwang Ju from June to August, 2017. The final 109 data were analyzed. Sensory processing and Sleep disturbances were measured using the Shortened sensory profile(SSP) and Korean-the Children's Sleep Habits Questionnaire(K-CSHQ). Statistical analysis was performed using descriptive analysis, Pearson correlation analysis, and multiple regression analysis were performed. Children with developmental disorder had problems with sensory processing and sleep habits. Sensory processing was related to sleep habit and most important factors of sensory processing influencing sleep was taste/olfactory sensitivity, auditory filtering. Conclusion: In order to help children with developmental disorder with sleep problem, it is necessary to consider the sensory processing especially taste/olfactory sensitivity, auditory filtering.

• The Journal of the Korea Contents Association
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• v.10 no.10
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• pp.451-455
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• 2010

Hydraulics usually deals with flows with free surface. When the surface curvature is small, the assumption of hydrostatic pressure distribution is enough. However, in the case, when the curvature is big, the non-hydrostatic pressure distribution should be taken into account and the Navier-Stokes equations should be employed instead of the depth-averaged shallow water equations. For the simulation of two immiscible fluids with different characteristics (e.g. water and air, water and oil), the level set method is selected for this purpose. The developed model is applied to classical dam break problem and the computational results are compared with the experimental data. The effectiveness of the developed model is confirmed.

• Journal of Korea Water Resources Association
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• v.45 no.12
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• pp.1227-1241
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• 2012

In this study, a novel water surface detection method was proposed. In the method water surface is detected by analysis on correlation coefficients obtained from rectangular control areas of the same vertical position in two successive images including both water surface and staff gauge. Four methods respectively based on threshold, peak, slope and variance ratio, are used to identify water surface from vertical distribution of correlation coefficient. In addition, swaying correction algorithm and statistical filtering are applied to minimize outliers caused by positional image mismatch. Images taken from 28 different sites during low flow were tested to evaluate the method. Mean relative error to eye measurement was approximately from 3.4 to 5.7 cm. As long as water surface moves, this method can be used to improve image stage gauge by supplementing the previous water surface detection method.

• Journal of Digital Convergence
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• v.17 no.9
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• pp.311-320
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• 2019

This study is a descriptive research designed to determine the effects of smartphone addiction on sleeping time and sleep deprivation among college students. For this purpose, the study made a questionnaire survey of 280 health science college students attending at C college located U Metropolitan city. Data collected from the survey were analyzed using SPSS 22.0 program. The findings of this study can be summarized as follows. there were correlations between smartphone addiction and students' sleep deprivation but weren't correlations between their smartphone addiction and sleeping time. furthermore college students' sleep deprivation was influenced by their smartphone addiction. Therefore, in order to induce sufficient sleep for physical and mental health, it is needed to reduce the smartphone addiction rate of college students. To do that, it is necessary to develop and provide interventive programs to eradicate unnecessary smartphone use.

• The Journal of the Korea Contents Association
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• v.16 no.5
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• pp.420-427
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• 2016

The purpose of this study was to identify association between total sleep time and suicidal ideation in adults with mental problems and without. The data were derived from the fifth Korea national health and nutrition examination survey and analyzed using the IBM SPSS Statistics version 21.0 software package considering complex samples analysis. The subjects were 6,199 adults. The rate of suicidal ideation was 13.7% (880 people). 13.3% (846 people) of the subjects had experienced depression and out of whom 43.1% (329 people) have had suicidal ideation. 2.7% (164 people) of the subject had received the mental health counseling, and out of whom 40.2% (63 people) have had suicidal ideation. Comparing to group having sleep over 6 hours of more, the group of short sleep had 1.33 times high risk of suicidal ideation among general adults, 1.92 times high risk of suicidal ideation among group who had experienced depression and, 7.10 times high risk of suicidal ideation among group who had received the mental health counseling. Therefore, these results indicate that general adults with short sleep time as well as adults with depression or mental health problems have to be managed to prevent suicide.

• Korean Journal of Psychosomatic Medicine
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• v.25 no.2
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• pp.166-175
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• 2017

Objectives: Shiftwork is known to be one of the common causes of sleep and health problems and finally causes the decreased quality of life. The purpose of this study was to investigate the sleep patterns of shift-working and daytime psychiatric nurses using actigraphy and compare it with subjective assessment for sleep. Methods : Twenty-three shift-working and 25 daytime nurses were enrolled. They rated their sleep quality using Pittsburgh Sleep Quality Index(PSQI) and other self-rating scales were measured for psychosocial aspects. Actigraphy was applied to the subjects for a total of 7 days to measure the sleep parameters. They also wrote sleep diaries during the period of wearing actigraphy. Sleep-related parameters of actigraphy, global score and components of PSQI, and the results of other self-rating scales were compared between shift-working and daytime nurses. Results : Although the global score of PSQI did not show significant difference, the PSQI components showed significant differences between two groups: the shift-working nurses showed lower sleep quality, more sleep disturbance and hypnotic medication use, and worsened daytime dysfunction than daytime nurses. The shift-working nurses showed significantly shorter total time in bed and total sleep time, lower sleep efficiency, and longer average awakening time than those of daytime nurses in actigraphy. Conclusions : The results showed that shift-working nurses experienced more sleep disturbances in both subjective and objective aspects of sleep than daytime nurses. This study also suggests that actigraphy may be useful to measure the objective aspects of sleep that are difficult to assess with subjective questionnaires alone.

• Sleep Medicine and Psychophysiology
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• v.26 no.2
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• pp.86-103
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• 2019

Objectives: The objective of this study was to develop evidence- and consensus-based clinical safety usage guidelines for sedative hypnotics using the Delphi technique. Methods: A group of 15 sleep experts from Korean Academy of Sleep Medicine were chosen for this study comprising a three-round web-based Delphi survey. The first round survey was composed of 39 questions to identify problems with sedative hypnotics usage in Korean clinical practice and the result roughly outlined what should be included in the guidelines. The second round survey was composed of 21 questions to collect specific opinions of experts on clinically important issues in prescribing sedative hypnotics, and its result provided the basis for the guidelines. A third round survey aimed to evaluate the reliability and validity of the established guidelines. Results: In the third round, all 17 items showed a median of 4 or more, with an average of 4.12 and a standard deviation of 0.32. Thus we present safety usage guidelines with 13 propositions for prescription, maintenance, and withdrawal of sedative hypnotics. Conclusion: The safety usage guidelines on sedative hypnotics developed from this study could lead to safe and effective prescription of hypnotics in clinical practice, especially for the non-experts in sleep medicine. Furthermore, the guidelines will help to improve the quality of insomnia treatment by contributing to the establishment of a safe regime for sedative hypnotics without excessive use of drugs.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.44-44
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• 2011

저수지와 같은 갇혀진 수체는 상류에서 유입되는 오염물질 뿐만 아니라 성층현상에 의해서도 오염될 수 있다. 안정된 성층은 혐기성 조건을 제공하여 바닥에서의 과도한 조류성장을 유발하고 연직순환흐름을 방해한다. 갇혀진 수체에서의 연직순환은 환경적인 문제를 감소시킬 수 있도록 중요한 역할을 한다. 갇혀진 수체에서의 연직순환은 이러한 오염을 줄이는데 중요한 역할을 하는데, 연직순환을 일으키는 인자로는 빛의 입사, 바람, 물의 온도 및 열의 확산 등이 있으며, 그중에서도 가장 중요한 것은 바람의 영향이다. 그러므로 성층화된 흐름에서 바람에 의해 발생하는 연직순환에 대한 수치모형을 개발하고 적용하는 것이 필요하다. 본 연구에서는 수온성층흐름에서의 순환흐름을 해석하기 위하여 유속성분을 계산하고 자유수면 변위와 온도, 염도등과 같은 스칼라양의 해석을 위해 다음과 같은 3단계의 방법을 이용하였다. 첫 번째 단계(정수압 계산단계)에서는 운동량 방정식의 경사항을 음해적으로 해석하고, 두 번째 단계(자유수면 보정단계)에서는 자유수면의 변화를 계산하고 수평방향 유속성분을 계산한다. 예측-수정자 방법(predictor-corrector step method)을 이용하여 자유수면변위와 유속을 구하였다. 마지막으로 세 번째 단계(이송-확산단계)에서는 이송-확산 방정식을 이용하여 스칼라양을 계산하였다. 본 연구에서 제시한 모형의 정확도를 검증하기 위하여 정사각형수조에서 진동하는 자유수면의 해석해와 비교하였고, 성층화된 흐름에서 발생하는 연직순환에 대하여 수치모의를 실시하였다. 그 결과, 본 연구에서 개발된 수치모형이 흐름 내부의 현상을 잘 묘사함을 알 수 있었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.483-487
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• 2010

하천에서 물이 비교적 빠른 속도로 흘러가면 압력 변동, 하상의 조도, 하천내 구조물 등의 영향에 의해 수면이 끊임없이 변형을 일으키며 수면에 작은 물결(수면 파문)이 생긴다. 이러한 수면 파문은 유수에 의해 유수의 평균 유속으로 이류되며, 이 때문에 인간이 유수의 흐름을 시각적으로 인식할 수 있다. 이러한 표면 파문은 적절한 영상 분석을 하면 표면 유속 측정의 추적자로 이용할 수 있다. 본 연구는 유수 표면을 연속된 영상을 촬영하고, 일련의 영상을 시공간 영상(space-time image)으로 만든 뒤, 휘도 경사법(graylevel gradient method)으로 유속 벡터를 추출하는 새로운 방법을 제시하였다. 이 분석 과정은 기존의 입자 영상 유속계(PIV, Particle Image Velocimetry) 기법을 이용하는 방법보다 훨씬 간단하고 분석 시간도 크게 절약할 수 있다. 또한, 수면 파문의 전파에 따른 중력파의 영향을 시공간 영상의 처리 과정에서 잡음으로 간주하여 처리할 수 있다는 장점을 가지고 있다. 개발된 루틴을 표면 영상 유속계(SIV, Surface Image Velocimtery)에 구현하여 새로운 영상 유속계를 개발하였다. 시공간 영상 분속을 이용하는 새로운 영상 유속계를 실험실 수로의 영상 자료에 적용하여 그 정확도, 적용성, 장단점 등을 분석하였다. 제안된 방법에 의한 평균류 산정 결과는 물리적으로 타당하며, 저속 또는 저휘도에서의 분석 성능이 뛰어난 것으로 밝혀졌다. 다만, 이방향 흐름의 분석에서는 문제가 있는 것이 밝혀졌다.