• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.750-756
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• 2002

The effect of equivalence ratio and velocity on the stability of flame in dump combustor was studied in an atmospheric pressure, laboratory scathe dump combustor operating natural gas. Traditionally, peak-to-peak pressure, fluctuation of the heat release rate and Rayleigh index were used to find and control the combustion instability. Cross correlation coefficients, Ci,j which is defined as the normalized value of the integration of the product of two of the mixer pressure, dump plane pressure and heat release rate, are introduced to see whether the flame is stable or not. Ci,j shows more sensitive to combustion status than Rayleigh index in steadily burning flame. Also, the result indicates that the amplitude of Ci,j between heat release and mixer pressure goes up before the flame at the rich de-stabilizing equivalence ratio near $\psi$=0.85. t means Ci:j at this case has a potential to detect the de-stablizing moment in prior to becoming unstable in dump combustor.

• Journal of the Korea Safety Management & Science
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• v.17 no.2
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• pp.55-66
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• 2015

In the perspective of industrial health management, it is important for the employee to decrease their job stress, to improve their productivity and quality of labor. In this study, the job stress, and it's influence on PWI(Psychosocial Wellbeing Index) were investigated by the questionnaire survey of 138 industrial workers who had studied assistive technology in college. The contents of questionnaire consist of the demographic characteristics, job-related characteristics, job stress and psycho-social stress. We evaluated job stress by KOSS-SF(Korean Occupational Stress Scale-Sort Form) and psychosocial stress by PWI-SF(Psychosocial Well-being Index-Short Form). To analyze the results, we evaluated the exposure level of KOSS and PWI by demographic characteristics and job-related characteristics using significance tests. Also, we estimated the relationship among demographic characteristics, job-related characteristics, job stress and psychosocial stress, using correlation analysis. As a results, all workers were found to be in a group under the high risky stress. It showed that the scale index of female's job non-autonomy and pwi were much larger than those of male's. Therefore, to guarantee job autonomy of female workers should be more emphasized, to improve their working environment. Job type had significant relationships with many job stress category; physical environment, job demand, job instability and organization culture. Regarding pwi, the scale index of the workers who is in charge of the civil service such as contacting the disabled and the aged in person, were much larger than that of the other workers. Accordingly, the job stress management program including physical environment, job demand, job instability and organization culture, should be suggested, to decrease the stress of the workers in charge of the disabled and the elders service. The strongest predictors of pwi was organization system through maximum positive relations between organization system and pwi. Therefore, it indicates that improvement of organization system such as a fair merit rating, a manpower supply, demand plan and department cooperation is urgently needed to reduce pwi.

• Journal of Information Technology Applications and Management
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• v.23 no.4
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• pp.25-39
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• 2016

Asset prices decline sharply and stock markets collapse when financial crisis happens. Recently we have encountered more frequent financial crises than ever. 1998 currency crisis and 2008 global financial crisis triggered academic researches on early warning systems that aim to detect the symptom of financial crisis in advance. This study proposes a risk recovery index for detection of good opportunities from financial market instability. We use SVM classifier algorithms to separate recovery period from unstable financial market data. Input variables are KOSPI index and V-KOSPI200 index. Our SVM algorithms show highly accurate forecasting results on testing data as well as training data. Risk recovery index is derived from our SVM-trained outputs. We develop a trading system that utilizes the suggested risk recovery index. The trading result records very high profit, that is, its annual return runs to 121%.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.42-48
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• 2004

Lean laminar premixed propane and methane flames which were anchored by a hydrogen-pilot flame in a tube were investigated experimentally. The flame shapes were observed by varying mean velocity from 10cm/s to 140cm/s and equivalence ratio from 0.45 to 0.8. In this study, behaviors of flames are divided into five regions such as tail-out, flash-back, flickering, stable and vibrating flames with respect to the mean velocity and the equivalence ratio. Although the flames are unstable in both the flickering and the vibrating region, they have different characteristics such as the frequency, sound generation and creation process of flame curvature. The flickering region exists near the flammability limit and the flame flickers in a frequency of about 10Hz. When flame front is bended, the propane flame front is straightened and the methane flame front is bended more by thermo-diffusive instability. In the vibrating region, the flame vibrates emitting audible sound in a frequency of about 100Hz. In the boundary of vibrating region, the vibration of flame changes between two modes such as single frequency vibration and dual frequency vibration. Increase and decrease of vibration in each mode are determined by thermo-acoustic instability.

• The Journal of Korean Physical Therapy
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• v.26 no.6
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• pp.459-463
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• 2014

Purpose: The purpose of this study was to investigate the correlations between functional movement screen (FMS) and ankle dysfunctions in subjects with chronic ankle instability (CAI). Methods: This study was a cross-sectional study of 20 participants with CAI. The ankle dorsiflexion range of motion (ROM), Foot and Ankle Disability Index (FADI), center of pressure (COP) path length, and COP velocity for ankle dysfunction were measured in all the subjects. All the subjects underwent the FMS concerned with ankle functions consisted of deep squats, hurdle steps and in-line lunges. The Spearman rank-order correlation coefficient was used to determine relationship between the ankle ROM, FADI, COP and FMS. Results: The results of the deep squat and in-line lunge exercises revealed a significant correlation with the ankle dorsiflexion ROM, FADI, COP path length, and COP velocity. The hurdle step showed no correlation with the ankle dorsiflexion ROM and FADI but a significant relationship with the COP path length and COP velocity. Conclusion: The results of this study showed that relationship deep squat and in-line lunge and it is suggested that an assessment tool using ankle dorsiflexion ROM and ankle instability would be clinically effective.

• Journal of Korean Foot and Ankle Society
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• v.23 no.1
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• pp.1-5
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• 2019

Surgical treatment to restore stability in the ankle and hindfoot and prevent further degenerative changes may be necessary in cases in which conservative treatment has failed. Anatomical direct repair using native ligament remnants with or without reinforcement of the inferior retinaculum is the so-called gold standard operative strategy for the treatment of lateral ankle instability. Non-anatomical lateral ligament reconstruction typically involves the use of the adjacent peroneus brevis tendon and applies only those with poor-quality ligaments. On the other hand, anatomic reconstruction and anatomic repair provide better functional outcomes after the surgical treatment of chronic ankle instability patients compared to a non-anatomic reconstruction. Anatomical reconstruction using an autograft or allograft applies to patients with insufficient ligament remnants to fashion direct repair, failed previous lateral ankle repair, high body mass index, or generalized ligamentous laxity. These procedures can provide good-to-excellent short-term outcomes. Arthroscopic ligament repair is becoming increasingly popular because it is minimally invasive. Good-to-excellent clinical outcomes have been reported after short and long-term follow-up, despite the relatively large number of complications, including nerve damage, reported following the procedure. Therefore, further investigation will be needed before widespread adoption is advocated.

• Journal of the Economic Geographical Society of Korea
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• v.17 no.1
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• pp.129-146
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• 2014

This paper investigates how industrial diversity affects unemployment and employment instability from the perspective of the regional economy. Through this analysis, we examine how the industry-specific policy to promote some industry strategically in most of areas affects the stability of the regional economy. We measure Herfindahl indexes using the 1993-2010 data of 16 regions in Korea, and use panel regression model for empirical analysis. The main results from this empirical analysis are summarized as follows. First, we confirm that the industrial structure of most regions has been changed to the direction of specialization in 1990s and to the direction of diversification in 2000s through analyzing the changes in the values of Herfindahl indexes during the given period. Second, we find from the estimation results of panel regression model that the higher industrial diversity in most of regions is, the lower the unemployment rate is. However, a statistically significant relationship between industrial diversity and employment instability only partially confirmed. Third, there exist high unemployment rate and employment instability in most metropolitan areas, but it is hard to say that this relationship is highly statistically significant. From the results of the empirical analysis, it is likely that the industry-specific policies such as the regional strategic industry development policies unlike policy goals make the unemployment rate to rise and economic instability to increase. From the viewpoint of employment aspects, the strategies to increase industrial diversity would be desirable rather than those to specialize in the industrial structure.

• Journal of the Korean Society of Physical Medicine
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• v.11 no.4
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• pp.115-125
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• 2016

PURPOSE: This study aimed to compare the effects of lumbar stabilization exercise with those of the neurodynamic technique on low back pain in patients with lumbar instability. METHODS: The subjects included those with more than three tests with positive results for lumbar instability and those with a positive sign during the neurodynamic test, all of whom had low back pain. For the lumbar stabilization exercise group (n=15), lumbar stabilization exercise was performed using a sling system, while the neurodynamic technique group (n=15) performed the neurodynamic technique. The intervention was performed 5 days a week for 4 weeks. All measurement of each subject were measure at pre-intervention and post-intervention (after 4 weeks). SPSS/PC ver. 18.0 program was used to compile results. RESULTS: There was no significant difference in general characteristics of subjects between both groups (p>.05). Assessed items included the visual analog scale score (VAS), Korean version of the Oswestry Disability Index (KODI), lumbar instability test positive response counter (LIC) and Fear-Avoidance Beliefs Questionnaire score (FABQ), and a significant reduction was observed post-intervention compared to pre-intervention values in both groups (p<.01). Other assessed items such as trunk flexibility and lumbar extensor endurance and lumbar flexor endurance were significantly increased post-intervention in both groups compared to pre-intervention values (p<.01). There was no significant difference in all parameters between both groups (p>.05). CONCLUSION: Our results indicate that the neurodynamic technique may be useful for improving low back pain in patients with lumbar instability.

• Journal of The Korean Society of Integrative Medicine
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• v.9 no.4
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• pp.191-200
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• 2021

Purpose : Chronic ankle instability can lead to problems in balance and gait due to weakness of the ankle muscles and decreased proprioceptive sensation. Balance training that stimulates proprioceptors is necessary to improve ankle stability. We aimed to compare the effects of unstable support balance exercises using whole body sonic vibration and an aero-step (TOGU) on proprioception and balance in individuals with unilateral functional ankle instability. Methods : Thirty-six participants with unilateral functional ankle instability were randomly recruited and divided into two groups (group 1 = sonic whole body vibration, group 2= TOGU). Individuals in each group participated in training for 5 weeks, 40 minutes per session, 5 times per week, and performed weight-bearing exercises in five postures on different unstable support surfaces. Proprioception was measured by digital inclinometer (Dualer IQ), and balance was measured by force platform (Biodex balance system). Results : Significant differences were observed in proprioception before and after intervention within both group (p<.05). Significant differences were also observed in the balance index before and after intervention within both groups (p<.05). Conclusion : As a result of this study, it is suggested that for individuals with ankle instability, unstable support surface training using a whole body sonic vibrator and TOGU can have a positive effects on proprioception and balance ability.