• 한국산학기술학회논문지
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• 제15권8호
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• pp.4749-4755
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• 2014

본 연구는 고용량 인버터 등의 열 발생 환경에서 히트싱크의 방열성능을 극대화하기 위한 파라미터 연구의 일환으로 히트싱크 베이스 두께 변화에 대한 방열성능 변화를 조사하였다. 베이스 두께가 각각 5, 9.5 및 14 mm인 히트싱크의 방열성능을 히트싱크 베이스의 윗면 중앙 온도, 히트싱크를 통한 방열량 및 열원부의 온도 등의 세 가지 지표의 비교를 통하여 고찰하였다. 실험연구와 전산유체역학 프로그램을 이용한 해석연구를 병행하여 베이스 두께 변화에 따른 각 방열 성능 지표에 변화가 있음을 확인하였다. 베이스의 윗면 중앙 온도와 방열율은 베이스의 두께가 얇을수록 향상되는 효과를 보였고, 베이스 열원부의 온도는 베이스의 두께가 두꺼울수록 낮아지는 경향을 보였다. 성능 지표의 비교 고찰을 통해 연구에 사용된 세 히트싱크 내에서는 베이스의 두께가 9.5 mm인 히트싱크에서 최적점이 나타났다. 따라서 제한적이지만 본 연구결과 내에서는 9.5 mm 두께의 베이스를 가지는 히트싱크가 최적의 방열 성능을 보이는 것으로 판단되었다.

• Physical Therapy Rehabilitation Science
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• 제7권2호
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• pp.72-77
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• 2018

Objective: This study aimed to compare the effects of core exercise methods on muscle activation and muscle thickness in healthy young adults and to propose effective core exercise methods. Design: Three-group pretest-posttest design. Methods: A total of 30 healthy young adults (14 males, 16 females) voluntarily participated in the study. Subjects were randomized to the prone plank exercise (n=10), reverse plank exercise (n=10), or bridge exercise (n=10) groups. Muscle activity and thickness of the rectus abdominis (RA), multifidus (MF), external oblique (EO), and internal oblique (IO) muscles were measured using surface electromyography and ultrasound. Subjects from each group participated in the exercises five times a week, with five 20-second sets during week 1. The set time was increased by 10 seconds per week. Results: Muscle activity and thickness in the prone plank, reverse plank, and bridge exercise group were statistically significant different for RA, MF, EO, and IO changes over time, and interaction between time and groups were also significantly different (p<0.05). We analyzed statistically significant differences between groups using a one-way analysis of variance for each period. A significant difference was observed after 4 weeks of exercise (p<0.05). Conclusions: The results suggest that the prone plank exercise is a beneficial method for enhancing muscle activation and thickness of the RA, EO, and IO compared to the reverse plank and bridge exercises. On the other hand, the reverse plank and bridge exercises are effective methods for enhancing the MF compared to the prone plank exercise.

• 한국구조물진단유지관리공학회 논문집
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• 제23권5호
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• pp.23-29
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• 2019

본 연구는 굵은골재의 완전 리사이클 기술개발을 위해서 시멘트계 재료를 이용한 개질 페이스트를 이용하여 원골재의 표면을 코팅하는 표면개질 기술을 적용하고 있다. 이 때에 원골재와 개질 페이스트의 계면은 개질 페이스트의 점착력과 점도에 의존되어 개질골재의 피막두께가 결정된다고 생각할 수 있다. 본 연구에서는 굳지 않은 상태에서의 개질 페이스트의 유동특성을 파악하고 표면 개질골재의 피막 두께에 대해 검토한 결과, 개질 페이스트를 빙엄유체로서 가정하여, 잉여 페이스트 이론과 유동학 정수 (항복치)를 고려하는 것으로 개질 페이스트의 정량적인 피막 두께의 설계가 가능하여, 표면개질 골재를 이용한 콘크리트의 정량적인 배합설계가 가능할 것으로 판단된다.

• 대한물리치료과학회지
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• 제30권1호
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• pp.72-84
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• 2023

Background: The purpose of this study was to investigate the effect of whole-body vibration stimulation training on the thickness of the transversus abdominis muscle and the balance of sitting posture in children with spastic cerebral palsy. Design: Single-subject design(A-B-A-B). Methods: The subjects of this study were 9 children with spastic cerebral palsy. The study period was 12 weeks in total, and the baseline period and the intervention period were each assigned 3 weeks. Intervention was conducted twice a week for 30 minutes. During the baseline period, trunk stabilization exercise was performed, and during the intervention period, trunk stabilization exercise and whole-body vibration stimulation training were performed. Measurements were carried out at before the experiment, baseline 1, intervention 1, baseline 2, intervention 2 and the total number of measurements was 5 times. Repeated ANOVA was performed to compare the effects of exercise according to the intervention method. Results: The thickness of the transversus abdominis muscle and the balance of the sitting posture were statistically significantly increased compared to the baseline during whole-body vibration stimulation training (p<.05). Conclusion: Therefore, it was confirmed that whole-body vibration stimulation training improved the thickness of the transversus abdominis muscle in children with spastic cerebral palsy and was an effective intervention method for improving sitting posture balance.

• 대한물리치료과학회지
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• 제30권3호
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• pp.72-83
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• 2023

Background: Normal-weight obese women have a normal weight with relatively low muscle mass resulting from high body fat. We aimed to investigate the effects of core exercise on body composition, abdominal muscle thickness, trunk muscular endurance, and psychological factors in normal-weight obese women. Design: One group pre-, mid-, and post-test design. Methods: A total of 20 normal-weight obese women were recruited voluntarily. Core exercises were performed for 30 minutes, three times a week for 4 weeks. InBody measurements, ultrasound imaging, and clinical tests were used to assess body composition, abdominal muscle thickness, trunk and core muscular endurance, and psychological condition(satisfaction with appearance and self-esteem). The dependent variables were measured three times: before the intervention (pre-test), 2 weeks after the intervention (mid-test), and 4 weeks after intervention (post-test). One-way repeated measures ANOVA and Friedman test were used for statistical analysis. Results: Although there was no change in the body composition (p>0.05), thickness of the transversus abdominis and internal and external oblique muscles, endurance of the trunk flexors and extensors and core muscles, and psychological condition showed significant differences after the intervention (p<0.05). Conclusion: Our findings will help develop exercise programs for normal-weight obese individuals that utilize the beneficial effect of core exercises.

• 한국정보전자통신기술학회논문지
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• 제16권5호
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• pp.325-330
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• 2023

본 논문은 머신러닝을 활용하여 교량 데이터 설계 시 기존 엔지니어의 구조해석결과 또는 경험 및 주관에 따라 슬래브 두께를 예측하여 왔던 프로세스를 머신러닝 기법을 적용하여 디지털 기반 의사결정이 가능하도록 제시한다. 본 연구에서는 슬래브 두께 선정을 구조해석 외에 머신러닝 기법을 활용하여 엔지니어에게 가이드 값을 제공하게 함으로써 신뢰성 있는 설계 환경을 구축하고자 한다. 교량 데이터 중 가장 많은 비중을 차지하고 있는 거더교를 기준으로 상부구조물 중 슬래브 두께를 예측하기 위한 예측모델 프로세스를 정의 하였다. 각 프로세스 별 예측 값을 산출하기 위하여 다양한 머신러닝 모델 (Linear Regress, Decision Tree, Random Forest, Muliti-layer Perceptron)을 프로세스별 경합하여 최적의 모델을 도출하였다. 본 연구를 통해 기존 구조해석을 통해서만 슬래브 두께 예측을 하였던 영역에 머신러닝 기법의 적용 가능성을 확인하였으며 정확도 또한 95.4%를 도출하였다, 향후 프로세스 확장 및 데이터를 지속 확보하여 예측모델 정확도를 향상시킨다면 공사 환경에 머신러닝 모델이 지속 활용될 수 있을 것으로 기대된다.

• Tribology and Lubricants
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• 제33권3호
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• pp.119-125
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• 2017

In this study, we perform a numerical analysis to predict the film thickness and lubrication regions for a thrust ball bearing under different operating conditions. Film thinning and replenishment affect the film thickness in starved lubrication. As the inlet meniscus position is brought to the edge of the Hertz contact, the thin film thickness is calculated as starved equation. We use a film replenishment model to determine the recovery film thickness between rolling elements. We use a hydrodynamic model to describe film recovery, that results from the effects of surface tension. In this model, we consider the surface tension gradient in fluid depression as the driving force for fluid recovery. We use Fourier transform method to determine the time-dependent depth of depressed oil. We calculate the change in the central film thickness graphically by using the recovery equation in starved elastohydrodynamic lubrication(EHL) under operating conditions that include numbers of balls, sliding velocity, applied force, and ambient film thickness. We evaluate the degree of starvation by using the distance from the center of the contact area to the meniscus position. Parched lubrication, a phenomenon where the film thickness decreases consistently, occurs at the severe condition. We determine optimal values with respect to the numbers of balls, and sliding velocity. The investigation can contribute to the design operating conditions for proper lubrication.

• Physical Therapy Rehabilitation Science
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• 제8권4호
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• pp.218-224
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• 2019

Objective: This reliability study examined the effects of applying varying induced inward pressures using a transducer placed at 0° neutral ankle position (NEU) and 15° ankle dorsiflexion (DF) on tibialis anterior (TA) muscle thickness using a custom-made device with a force indicator during rehabilitative ultrasound imaging. Design: Cross-sectional study. Methods: Twenty-four healthy subjects were recruited in this study. Two examiners measured the muscle thickness of the TA at 0° NEU and 15° DF in 3 conditions of inward pressures (1.0 N, 2.0 N, and 4.0 N) using a custom-made holder. The muscle thickness was measured three times for each of the conditions arranged in random order. For intra- and inter-rater reliability, the intraclass correlation coefficients (ICCs) with 95% confidence intervals, standard error of measurement, minimal detectable change, and coefficient of variation were analyzed. One-way repeated measures analysis of variance was conducted for investigating changes of TA muscle thickness according to the inward pressures of the transducers. Results: The intra-rater reliability of TA muscle thickness measurement was excellent (ICC_3,1: 0.92-0.96) for all conditions (at both ankle joint angles per varying inward pressure). Likewise, the inter-rater reliability of TA muscle thickness measurement was excellent (ICC_2,1: 0.89-0.97) under same conditions. The mean of TA thickness showed the trend of decreasing significantly with increased inward pressures at all ankle joint angles (p<0.05). Conclusions: Use of this custom-made device with a force indicator is useful to accomplish the high intra- and inter-rater reliability of TA muscle thickness measurement at both ankle joint angles in reducing the measurement error.

• Physical Therapy Rehabilitation Science
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• 제4권1호
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• pp.11-16
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• 2015

Objective: Prone bridge exercise is one of the core strengthening exercise for improving abdominal, lower and upper extremity muscles. In addition, coactivation of the trunk muscles and extremities is important for treatment of low back pain. This study aimed to investigate the correlation between the thickness, cross-sectional area of the target muscle, and endurance during prone bridge exercise. Our hypothesis was that an increase in muscle thickness is positively related to the hold time for the static prone bridge exercise. Design: Cross-sectional study. Methods: Fourteen healthy university students (8 men and 6 women) voluntarily participated in the study at Sahmyook University. Hold time for the prone bridge with one and both legs was measured. The resting and contracted thickness of the lateral abdominal, rectus femoris, and triceps muscles was measured using rehabilitative ultrasound imaging. The correlation between muscle thickness and endurance for maintenance time was evaluated. Results: The prone bridge with both legs and the contraction thickness of the triceps muscle showed a positive correlation (r=0.692, p<0.05); the prone bridge with one leg and the contraction thickness of the internal oblique and transversus abdominis muscles showed a positive correlation (r=0.545, 0.574, p<0.05, 0.05, respectively). Conclusions: Endurance for the prone bridge exercise with a stable support surface is correlated with the contraction thickness of arm muscles; the prone bridge exercise with an unstable support surface is correlated with the contraction thickness of the deep abdominal muscles.

• Journal of Periodontal and Implant Science
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• 제49권3호
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• pp.185-192
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• 2019

Purpose: Implant wall thickness and the height of the implant-abutment interface are known as factors that affect the distribution of stress on the marginal bone around the implant. The goal of this study was to evaluate the long-term effects of supracrestal implant placement and implant wall thickness on maintenance of the marginal bone level. Methods: In this retrospective study, 101 patients with a single implant were divided into the following 4 groups according to the thickness of the implant wall and the initial implant placement level immediately after surgery: 0.75 mm wall thickness, epicrestal position; 0.95 mm wall thickness, epicrestal position; 0.75 mm wall thickness, supracrestal position; 0.95 mm wall thickness, supracrestal position. The marginal bone level change was assessed 1 day after implant placement, immediately after functional loading, and 1 to 5 years after prosthesis delivery. To compare the marginal bone level change, repeated-measures analysis of variance was used to evaluate the statistical significance of differences within groups and between groups over time. Pearson correlation coefficients were also calculated to analyze the correlation between implant placement level and bone loss. Results: Statistically significant differences in bone loss among the 4 groups (P<0.01) and within each group over time (P<0.01) were observed. There was no significant difference between the groups with a wall thickness of 0.75 mm and 0.95 mm. In a multiple comparison, the groups with a supracrestal placement level showed greater bone loss than the epicrestal placement groups. In addition, a significant correlation between implant placement level and marginal bone loss was observed. Conclusions: The degree of bone resorption was significantly higher for implants with a supracrestal placement compared to those with an epicrestal placement.