• 소음진동
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• 제6권6호
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• pp.819-825
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• 1996

Nonlinear dynamic characteristics of rubbing phenomenon in rotor dynamics are investigated experimentally and numerically. Rubbing phenomenon occurs when rotor contacts with stator during whirling and causes the large amplitude of vibration, high whirl frequencies, and possibly catastrophic failure. Rubbing has various types of forward whirl, backward rolling, backward slipping, and partial rub depending on the system parameters of rotating machinery and running speed. Experiments are performed for forward whirl and backward whirl. And numerical analysis are conducted to explain the changes between backward rolling and backward slipping. Experimental and numerical results show that the types of whirling motion depends on the friction coefficient between rotor and stator and the eccentricity of rotor.

• 융복합기술연구소 논문집
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• 제4권1호
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• pp.33-35
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• 2014

Investigation of flow characteristics behind a edged backward facing step is important for selecting appropriate positions of building constructions in the desert area. In the present study, the effect of edge angles on the flow characteristics is investigated using a commercial software CFD-ACE+. When the edge angle is less than 30 degree, reattachment length decreases, whereas when the edge angle is larger than 30 degrees, reattachment angle increases. It can be concluded that the flow patterns behind an edged backward facing step is classified as the two, streamlined and bluffed bodies. Appropriate edge angles have an effect of increasing the momentum toward the wall, which can reduce the reattachment length. It can be said that present results can be utilized for diverse industrial applications that includes the backward facing step.

• 교육심리연구
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• 제31권4호
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• pp.819-845
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• 2017

시험은 일반적으로 학습을 평가하기 위한 목적으로 활용되지만, 약 100여 년에 걸쳐 축적된 연구결과는 시험이 학습을 증진시키기 위한 효과적인 도구가 될 수 있음을 시사한다. 시험 또는 인출연습은 앞에서 배운 내용에 대한 학습을 증진할 수도 있고, 앞으로 배울 내용에 대한 학습을 촉진시킬 수도 있는데 전자를 '시험의 후방효과'라 하고, 후자를 '시험의 전방효과'라 일컫는다. 하지만 시험효과에 관한 대부분의 선행연구들은 이 두 가지의 효과를 명확하게 구분하지 않았으며, 최근에야 이 둘을 구분하려는 시도가 이루어지고 있다. 이에 본 논문에서는 일반적 의미의 시험효과를 가리키는 시험의 후방효과와 최근에 특히 주목을 받게 된 시험의 전방효과를 구분하여 시험이 학습에 미치는 영향에 관한 선행 연구를 검토하고, 후방효과와 전방효과의 검증 절차, 경험적 연구결과, 관련 효과에 대한 이론적 설명, 시험효과를 교육 현장에서 활용하기 위해 해결해야 할 과제 및 방법을 살펴보았다. 선행연구는 시험이 기억 수정자의 역할을 함으로써 이미 배운 내용에 대한 기억을 강화하고, 학습자의 메타인지 등에 영향을 미침으로써 앞으로 새롭게 배울 내용에 대한 학습을 증진시킴을 보여주었다. 이는 시험이 학습의 평가를 넘어서 학습을 증진시키기 위한 효과적인 도구로 사용될 수 있다는 교육적 함의를 제공한다.

• 한국전문물리치료학회지
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• 제27권3호
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• pp.185-190
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• 2020

Background: Backward walking exercise may offer some unique and potentially beneficial differences compared with forward walking exercise. There is still a lack of research on backward walking exercises and forward head posture. Objects: The purpose of this study was to determine the effect of backward walking exercise on college students forward head posture in their 20s. Methods: Twenty-one subjects participated in the experiment. The subjects were those with a craniovertebral angle (CVA) of 55 degrees or less who understood the purpose and method of this study and voluntarily agreed. A camera capable of taking pictures of the lateral plane was installed at a distance of 1.5 meters before exercising. Pictures were taken before walking backward, and after walking for 15 minutes on the treadmill, the images were taken in the same way. The composition of the backward walking exercise was walking at a rate of 1.0 for 5 minutes, and the remaining 10 minutes were walking at a rate of 1.5. Wilcoxon signed rank test was used to compare CVA and craniorotational angle (CRA) before and after exercise. Results: As a result of this study, there was a significant difference in CVA before and after exercise (p < 0.05). There was a significant difference in CRA before and after exercise (p < 0.05). Conclusion: The backward walking exercise and verbal command seems to have positively influenced the changes in CVA and CRA among college students in their 20s. It seems that studies to confirm balance or muscle activity as well as changes in forward head posture through the long-term intervention of the backward walking exercise should be conducted.

• PNF and Movement
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• 제22권1호
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• pp.91-99
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• 2024

Purpose: Backward walking has shown positive effects on gait recovery in rehabilitation patients. It is increasingly used as an aerobic training method in rehabilitation populations, inducing more sensory and motor stimulation than forward walking. Therefore, the purpose of this study is to investigate the effects of visual stimulation during backward walking. Methods: Twenty-seven healthy adults with a visual acuity of 0.8 or higher participated in the study. To compare the effects of visual stimulation during various walking conditions among healthy individuals, the participants randomly selected cards numbered one to six and walked a distance of 10 meters. Walking ability was measured using Optogait. Results: Statistically significant differences were observed in speed, stride, and percentages of single support and contact phase during backward walking. Within eyes-closed conditions during backward walking, significant differences were found in percentages of single support, terminal stance, and contact phase. Moreover, the percentage of terminal swing significantly differed during backward walking with head turn conditions. Conclusion: Gait parameters such as speed, stride, and percentages of single support and contact phase were higher during backward walking than forward walking. These results indicate that backward walking involves multiple sensory systems and varying conditions.

• 비파괴검사학회지
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• 제21권6호
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• pp.658-662
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• 2001

후방산란된 초음파의 입사각 의존성을 이용한 표면 결함유형의 평가가 시도되었다. 평탄한 유리위에 순수한 홈, 구리로 채워진 홈, 표면위 붙여진 구리선등의 표면결함 시편에 대한 후방산란 프로파일은 제 1 임계각에서 종파의 산란과 관련된 새로운 프로파일을 보여주었다. 결함에 의한 산란효과가 클수록 후방프로파일들의 정점 위치는 작게 나타났으며 후방복사 프로파일과 정점 위치에서의 파열의 모양은 결함의 유형과 위치에 따라 누수파와 산란파의 복합적 요인에 의해 다른 형태를 보여주었다.

• 대한물리의학회지
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• 제11권3호
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• pp.1-9
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• 2016

PURPOSE: The purpose of this study was to identify the effects on flexibility of bridge and plank exercises using sling suspension on an unstable surface. METHODS: The subjects of this study were 20 healthy adults in their 20s (plank=10, bridge=10). Both types of exercise were performed three times per week for a period of four weeks. Each exercise was performed in the front and side direction. Exercise intensity was altered through the use of a sling, which was placed at the knee and ankle. Flexibility at trunk forward flexion and backward extension was measured. The trunk forward flexion was measured at sitting position. The trunk backward extension was measured at prone position. The data were analyzed by Two-way ANOVA. RESULTS: There were significant differences in the pre- and post-test for both the bridge and plank exercise groups. In the bridge exercise, significant differences were shown in the trunk forward flexion and the trunk backward extension (p<.05). In the plank exercise, a significant difference was shown in the trunk backward extension (p<.05). No significant differences were noted in interaction effect or the main effects in either group. CONCLUSION: Bridge and plank exercises on an unstable surface improve flexibility. The bridge exercise improves the flexibility of the forward and backward muscles of the trunk. The plank exercise improves the flexibility of the forward muscles of the trunk. This information would be useful in the development of exercise programs including bridge and plank exercises for improving flexibility and core stability.

• 대한물리의학회지
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• 제13권2호
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• pp.53-60
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• 2018

PURPOSE: This study aimed to identify the effect of a backward walking exercise using a mirror on balance and gait in patients with stroke. METHODS: Twenty subjects with post-stroke hemiparesis volunteered to participate in this study. The experimental and control groups performed backward walking exercise plus conventional therapy or conventional physical therapy, respectively, for 6 weeks. Assessment instruments included the Berg Balance Scale (BBS), timed up and go test (TUG), and 10-m walking test (10MWT). Evaluation was performed before and after the 6-week training period. We conducted a paired t-test to compare the within-group changes before and after the intervention. An independent t-test was used to compare between-group differences. The statistical significance level was set at ${\alpha}=.05$ for all variables. RESULTS: The experimental group showed a significant within-group change in the BBS, TUG, and 10MWT (p<.05). The control group also showed a significant change (p<.05). A significant difference was observed between the experimental and control groups with regard to changes in the BBS, TUG, and 10MWT results after the interventions (p<.05). CONCLUSION: This study demonstrated that backward walking exercise using a mirror may be valuable for future research. Further studies with a wider range of pathology and longer experiment duration are required to validate the results of the present study.

• 대한물리치료과학회지
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• 제16권2호
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• pp.1-9
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• 2009

Background: The ability for backward walking is considered to be necessary for the neuromuscular control and maintenance of balance in daily ambulatory activity. This study aimed to determine the effect of backward walking training on the walking speed and balance control in patients with hemiplegia. Methods: Fourteen patients with hemiplegia were randomly allocated to an experimental and control groups of seven patients each. For the experimental group, we performed both conventional training and backward walking training, and conventional training only for the control group. The conventional training programs for the 2 groups were conducted for 30 min, twice a day, 5 times a week for 4 weeks, and backward walking training for the experimental group was conducted for 30 min, 3 times a week. The outcomes were assessed using the functional reach test (FRT), timed up-and-go (TUG) Test, and the 10 meter walk time test (10mWT). Result: A comparison of the FRT, TUG test, and 10mWT scores obtained before and after the 4-week treatment revealed statistically significant differences (p<.05) for the experimental group; however, there was no such difference in the case of the control group (p>.05). On assessment after the 4-week treatment, statistically significant differences were noted in the TUG test and 10mWT scores of the experimental group (p<.05). Conclusion: Our findings suggest that backward walking training is an effective clinical strategy for improving the walking speed and functional mobility of patients with hemiplegia.

• 한국전문물리치료학회지
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• 제28권4호
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• pp.273-279
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• 2021

Background: Lunge exercises are lower extremity rehabilitation and strengthening exercises for patients and athletes. Most studies have shown the effectiveness of the forward and backward lunge exercises for treating patellofemoral pain and anterior cruciate ligament injuries (by increasing lower extremity muscle activity) and improving kinematics. Objects: However, it is not known how the two different lunge movements affect trunk muscle activities in healthy individuals. The purpose of this study was to investigate the electromyographic activity of the rectus abdominis and erector spinae muscles during forward and backward lunge exercises in healthy participants. Methods: Twelve healthy participants were recruited. Electromyographic activity of the rectus abdominis and erector spinae was recorded using surface electrodes during forward and backward lunges, and subsequently normalized to the respective reference voluntary isometric contractions of each muscle. Results: Activity of the erector spinae was significantly higher than that of the rectus abdominis during all stages of the backward lunge (p < 0.05). The activity of the erector spinae was significantly greater during the backward than forward lunge at all stages (p < 0.05). Conclusion: Backward lunging is better able to enhance trunk motor control and activate the erector spinae muscles.