• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.30-37
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• 1998

This paper investigates the linear stability of wakes with special emphasis on the effect of chemical reaction. Velocity and density profiles for laminar flows are obtained from analytic profiles as well as from simulation. Wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For analytical laminar profiles, sinuous modes are more unstable than varicose modes irrespective of density variation, which shows wakes will be destabilized by sinuous modes. Large velocity difference and density difference lead to more unstable wakes due to large momentum difference. For simulated laminar profiles, chemical reaction with stoichiometric chemistry increases temperature and stabilizes the flow due to increase in compressible reacting wades, flow becomes stable as velocity increases due to viscous dissipation.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.206-210
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• 2004

This paper proposes a new training system for equilibrium sense using unstable platform. This training system for equilibrium sense consists of an unstable platform, a computer interface circuit and software program. Postural instability changes the weighting of different types of sensory information and the state of the equilibrium maintenance system. In order to improve the equilibrium sense, we developed software program such as a block game, sine curve training (SCT) and pingpong game using Visual C++. Using this system and training programs, we performed an experiment to train the equilibrium sense of a subject. To evaluate the effects of balance training, the time maintained on the target and the moving time to the target are measured. As a result, the moving time to the target and time to maintain cursor on the target improved through repeating equilibrium sense training. It was concluded that this system was reliable in the evaluation of equilibrium sense. We expect that this system might be applied to clinical use as an effective balance training system.

• Journal of Korean Association for Spatial Structures
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• v.2 no.4 s.6
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• pp.61-76
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• 2002

The structure system that is discreterized by continuous shells is usually used to make a large space structures and these structures show the collapse mechanisms that are captured at over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. Moreover, resist force of structure can be reduced by initial condition and initial imperfection significantly. In order to investigate the instability of shell structures, the finite deformation theory can be applied and it becomes a nonlinear mathematics in which use equation of tangential stiffness incrementally. With an initial imperfection, using simple example and Flow Truss Dome, the buckling characteristics of space truss is main purpose of this paper, and unstable behavior is studied by proposed the numerical method. Also, by using MIDAS, this research work analyzes displacements and inner forces as the design load of model, and the ratio of buckling load of design load is investigated.

• Journal of The Korean Society of Integrative Medicine
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• v.5 no.1
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• pp.25-34
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• 2017

Purpose : The purpose of this study was to identify comparison of the abdominal muscle thickness and activity by using tool and unstable surface which is accompanied bridge exercise doing abdominal drawing-in breath. Method : This study was performed on normal 13 males and 17 females subjects doing bridge exercise accompanied abdominal drawing-in breath used tools. At this time muscle thickness and muscle activity is measured through ultrasound and EMG. Result : The results of this study, rectus abdominis, internal oblique and transverse abdominis showed a significant difference in muscle thickness when performed using pilates circle. And external oblique showed a significant difference muscle thickness when performed using gym ball. Rectus abdominis and external oblique showed a significant difference in muscle activity when performed using pilates circle. And internal oblique showed a significant difference in muscle activity when performed using sling. Conclusion : Therefore it is suggested that it would be effective to apply the gymball and pilates circle in the unstable surface for abdominal weakness.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.72-80
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• 2005

Recent studies have dealt with brake squeal in terms of the coupled vibration of brake component parts. In this paper, we assemble the mode models derived from FE analysis of the individual components of the drum brake system into the system model by considering the friction interaction of the lining and drum at the interface. The validity of the component models are backed up by the experimental confirmation work. By scrutinizing the real parts of the complex eigen-values of the system, the unstable modes, which may be strong candidate sources of squeal noise, are identified. Mode participation factors are calculated to examine the modal coupling mechanism. The model predictions for the unstable frequencies pointed well the actual squeal noise frequencies measured through field test. Sensitivity analysis is also performed to identify parametric dependency trend of the unstable modes, which would indicate the direction for the squeal noise reduction design. Finally, reduction of the squeal noise tendency through shape modification is tried.

• The Journal of Korean Physical Therapy
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• v.24 no.5
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• pp.300-305
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• 2012

Purpose: This study examined the muscle activity of the trunk muscles during weight shifting exercises on a stable and unstable surface. Methods: Ten healthy young subjects (4 males, 6 females) with no medical history of lower-extremity or lumbar spine disease were enrolled in this study. The muscle activity was recorded using surface electromyography (EMG) electrodes from the both sides of the external obliques and erector spinae muscles. Results: The EMG activities of the both rectus abdominalis, both external obliques and erector spinae muscles were significantly higher when the weight shifting exercise was performed on a firm surface than when a balance pad with a balance ball was used. In weight shifting exercises, the EMG activity of the contralateral external obliques and erector spinae muscles was significantly higher than that of the ipsilateral external obliques and erector spinae muscles under all three support surface conditions. Conclusion: Performing weight shifting exercise using an unstable surface is a useful method for facilitating the trunk-muscle strength and trunk stability.

• Journal of the Korean Society of Physical Medicine
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• v.11 no.3
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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.

• Journal of the Korean Society of Physical Medicine
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• v.3 no.1
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• pp.11-20
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• 2008

Purpose : This study was to comparison of EMG of an stable exercise group and unstable exercise group on patients who have had anterior cruciate ligament reconstruction(ACL reconstruction). Methods : The subjects of the study were patients who had no less than 4 weeks after ACL reconstruction and could stand on one leg, and they divided into a control group with 9 patients doing closed kinetic chain exercises on the stable floor and an experimental group with 10 patients doing closed kinetic chain exercises on the unstable floor and in order to compare degrees of the muscle activity of the thigh extensor and flexor was tested each before the exercise, in 3 weeks and 6 weeks after doing exercises by using surface electromyography (Surface EMG). The patients made 3 sets of exercises (10 times per set), each of which consisted of exercises using elastic bands and the squat. Results : There was statistic significance about the vastus medialis muscle. Conclusion : It is thought that the closed-chain exercise could be an exercise program through which patients could enhance the muscle activity of the vastus medialis muscle optionally among the quadriceps muscle and the hamstring muscles which should weaken after ACL reconstruction.

• The Journal of Korean Physical Therapy
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• v.17 no.4
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• pp.621-631
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• 2005

The purpose of this study was to measure magnitude of lower leg muscle activity during dynamic stability tests performed on an unstable board by subjects with sprained lateral ankles. Fifteen lateral ankle sprain subjects(8 male, 7 female) participated in this study. The muscle activity was measured at gastrocnemious, tibialis anterior, peroneus longus during dynamic stability tests performed on Biodex stability system as surface EMG. The EMG amplitude of each muscle was normalized to the amplitude in the maximal voluntary isometric contraction(MVIC) of each muscle. As results, peroneus longus evidenced significant difference at stable and unstable grade comparing injured with uninjured sides. Gastrocnemious and tibialis anterior evidenced no significant difference. Change of muscle activity with stable and unstable grade evidenced no significant difference on injured and uninjured sides. The data provided information on peroneus longus contributes to dynamic stability after lateral ankle sprains. Peroneus longus training program may have to be emphasized after an ankle sprain.

• Journal of Society of Preventive Korean Medicine
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• v.4 no.2
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• pp.214-234
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• 2000

This study was carried to identify whether acupuncture of several acupuncture points can affect the brain and to observe which aspects appear in EEG mapping, using electroencephalography. Those results are as follows ; 1. The pattern of resting computerized EEG map in intact human is appered normal 2. Each Acupuncture in Kwan Weon or Jog Sam Ri meridian points bring about the increase in $\theta,\;\alpha-wave$ activity and at various area of the cerebrium and the decrease in $\delta,\;\beta-wave$ activity. It strands to reason that brain function is elevated On the other hand , synchronous acupuncture bring about the decrease of brain function in view of the decrease of $\delta,\;\theta-wave$ activity at frontal area, and the unstable brain state in view of the increase of $\beta-wave$ activity. 3. Acupuncture in Hyeon Jong meridian point bring about the increase of $\delta,\;\theta-wave$ activity at frontal area and $\beta-wave$ activity at temporal area. From these we deduce that brain function is declined and brain is unstable. Synchronous acupuncture with other meridian points reversly showed that brain function is elevated. 4. Synchronous acupuncture in Kwan Weon , Jog Sam Ri, Hyeon Jong bring about the decrease of the brain function and the unstable brain state, showing the pattern of increased $\delta,\;\theta-wave$ activity at frontal, parietal area, and increased $\beta-wave$ activity at temporal area.