• 천문학회보
• /
• 제39권1호
• /
• pp.37.2-37.2
• /
• 2014

Gas in disk galaxies interacts nonlinearly with a underlying stellar spiral potential to form galactic spiral shocks. Numerical simulations typically show that these shocks are unstable to the wiggle instability, forming non-axisymmetric structures with high vorticity. While previous studies suggested that the wiggle instability may arise from the Kelvin-Helmholtz instability or orbit crowding of gas elements near the shock, its physical nature remains uncertain. It was even argued that the wiggle instability is of numerical origin, caused by the inability of a numerical code to resolve a shock that is inclined to numerical grids. In this work, we perform a normal-mode linear stability analysis of galactic spiral shocks as a boundary-value problem. We find that the wiggle instability originates physically from the potential vorticity generation at a distorted shock front. As the gas follows galaxy rotation, it periodically passes through multiple shocks, successively increasing its potential vorticity. This sets up a normal-mode that grows exponentially, with a growth rate comparable to the orbital angular frequency. We show that the results of our linear stability analysis are in good agreement with the those of local hydrodynamic simulations of the wiggle instability.

• 한국수소및신에너지학회논문집
• /
• 제29권5호
• /
• pp.538-548
• /
• 2018

The thermo-acoustic instability in the combustion process of a gas turbine is caused by the interaction of the heat release mechanism and the pressure perturbation. These acoustic vibrations cause fatigue failure of the combustor and decrease the combustion efficiency. This study is to develop a segmented dynamic thermo-acoustic model to understand combustion instability of gas turbine. Therefore, this study required a dynamic analysis rather than static analysis, and developed a segmented model that can analyze the performance of the system over time using the Matlab/Simulink. The developed model can confirm the thermo-acoustic combustion instability and exhaust gas concentration in the combustion chamber according to the equivalent ratio change, and confirm the thermo-acoustic combustion instability for the inlet temperature and the load changes. As a result, segmented dynamic thermo-acoustic model has been developed to analyze combustion instability under the operating condition.

• 대한기계학회논문집B
• /
• 제32권9호
• /
• pp.659-668
• /
• 2008

Combustion instability has been considered as very important issue for developing gas turbine and rocket engine. There is a need for fundamental understanding of combustion instability. In this study, combustion instability was numerically and experimentally investigated in a dump combustor with bluff body. The fuel and air mixture had overall equivalence ratio of 0.9 and was injected toward dump combustor. The pressure oscillation with approximately 256Hz was experimentally obtained. For numerical simulation, the standard k-$\varepsilon$ model was used for turbulence and the hybrid combustion model (eddy dissipation model and kinetically controlled model) was applied. After calculating steady solution, unsteady calculation was performed with forcing small perturbation on initial that solution. Pressure amplitude and frequency measured by pressure sensor is nearly the same as those predicted by numerical simulation. Furthermore, it is clear that a combustion instability involving vortex shedding is affected by acoustic-vortex-combustion interaction. The phase difference between the pressure and velocity is $\pi$/2, and that between the pressure and heat release rate is in excitation range described by Rayleigh, which is obvious that combustion instability for the bluff body combustor meets thermoacoustic instability criterion.

• 국제물리치료학회지
• /
• 제11권2호
• /
• pp.2077-2089
• /
• 2020

Background: Chronic ankle instability is a common injury that decreases balance and negatively affects functional movements, such as jumping and landing. Objectives: To analyze the effect of taping types and jump heights on balance with eyes open and closed during jump landings in chronic ankle instability. Design: Within-subject design. Methods: The study involved 22 patients with chronic ankle instability. They performed both double-leg and single-leg drop jump landings using three conditions (elastic taping, non-elastic taping, and barefoot) on three different jump platforms (30, 38, and 46 cm). Balance was measured using the Romberg's test with eyes open and closed. Results: Interaction effect was not statistically significant. Balance with eyes open and closed was significantly improved in both the elastic taping and non-elastic taping conditions compared to the barefoot condition. There was no significant difference according to the jump height. Conclusion: Individuals with chronic ankle instability demonstrated increased balance ability with eyes open and closed when jump landing. Elastic taping and non-elastic taping on the ankle joint can positively affect balance during landing in individuals with chronic ankle instability.

• 국제물리치료학회지
• /
• 제11권1호
• /
• pp.1950-1953
• /
• 2020

Background: Ankle instability usually occurs after stroke, and contributes to unsafe walking and associated risk of falling in the affected patients. Objective: To investigate the effects of kinesiology taping (KT) on gait and balance ability (center of pressure, CoP) in patients with ankle instability after stroke. Design: One group, pre-post design. Methods: A total of 11 patients with ankle instability after stroke were enrolled. In all subjects, the gait and balance ability were assessed under 2 conditions: KT and barefoot. Gait and balance ability was assessed using GAITRite system and FDM-S platform. Results: Comparison between KT and barefoot condition, KT condition was significantly higher in velocity, cadence, step length, and stride length than barefoot condition (P<.05). KT condition was significantly lower in CoP path length and sway speed than barefoot condition (P<.05). Conclusion: KT indicated potential as a helpful method for walking and balancing ability in patients with ankle instability after stroke. Therefore, this study recommends KT as an option applicable to the stroke with ankle instability.

• The Journal of Korean Physical Therapy
• /
• 제33권5호
• /
• pp.224-230
• /
• 2021

Purpose: The purpose of this study was to investigate the effects of the fascia distortion model (FDM), one of the fascia treatments, on unstable ankle subjects. This was done through the chronic ankle instability tool (CAIT) questionnaire on maximum isometric muscle strength, proprioception, dynamic balance, and maximum angle. Methods: An experiment was conducted using the chronic ankle instability tool questionnaire on males and females in their twenties who suffered from ankle instability. Before the experiment, maximum isometric strength, proprioceptive, dynamic balance, and maximum angle were measured. The fascia distortion model was applied and then measurements were taken again to compare and analyze the changes. Analysis was carried out using the paired t-test. Results: After applying the fascia distortion model, maximum isometric strength, proprioceptive, dynamic balance, and maximum angle significantly improved (p<0.05). Conclusion: This study found that the fascia distortion model method was effective in improving maximum isometric strength, proprioceptive, dynamic balance, and maximum angle. The results suggest that the fascia distortion model method is a new intervention that could be used for subjects with chronic ankle instability.

• 대한정형도수물리치료학회지
• /
• 제27권1호
• /
• pp.13-20
• /
• 2021

Background: The serratus anterior and upper trapezius muscles act synergistically to allow for an appropriate scapulothoracic rhythm. However, a decrease in serratus anterior activation causes the upper trapezius to become overactivated, resulting in dysfunction. This study compared serratus anterior and upper trapezius muscle activity according to sling angle and compared serratus anterior strength between healthy adults and patients with shoulder instability. Methods: Twenty participants (10 healthy adults and 10 patients with shoulder instability) were included in this study. The participants had their arms extended at sling angles of 30°, 60°, and 90° in reach forward with shoulder flexion using goniometer. Serratus anterior strength was measured three times while the participants were supine. The outcome measures were surface electromyography amplitude of the upper trapezius and serratus anterior and serratus anterior strength. Results: The Wilcoxon signed-rank test indicated that the upper trapezius was significantly different between healthy group and shoulder instability group at a sling angle of 60°, and both the upper trapezius and serratus anterior exhibited significant differences at 90°. Moreover, a significant difference was noted in the muscle strength of the serratus anterior. Conclusion: Our results provide novel and promising clinical evidence that patients with shoulder instability have decreased serratus anterior activation and upper trapezius overactivation, resulting in muscle imbalance. In addition, there was a significant difference between the healthy group and shoulder instability group in the serratus anterior muscle strength

• 대한물리의학회지
• /
• 제16권1호
• /
• pp.1-7
• /
• 2021

PURPOSE: The purpose of this study is to conduct inter-rater and intra-rater reliability tests in patients with low back pain (LBP) using the prone instability test (PIT) and side-lying instability test (SIT). We have analyzed the Korean version Oswestry disability index (K-ODI) correlations and radiograph finding (RF) for validity. METHODS: Individuals (n = 51) (mean age of 40.27 ± 13.28) with LBP for at least over a week were recruited, together with two participating physical therapist examiners. The measurement consisted of PIT, PST, K-ODI, and RF. Sensitivity (Sn), specificity (Sp), positive predictive value, negative predictive value, prevalence index, agreement %, Cohen's kappa, and prevalence-adjusted bias-adjusted kappa (PABAK) were calculated. The PIT and SIT were compared with RF for validity analysis, while PIT, SIT, K-ODI, and RF were calculated for the correlation analysis. RESULTS: The intra-rater reliability test measured for the PIT (kappa = .79, PABAK = .88) and SIT (kappa = .73, PABAK = .84), and inter-rater reliability test measured for the SIT (kappa = .80, PABAK = .88) showed good agreements. The PIT (Sn = .65, Sp = .63) and SIT validities (Sn = .68, Sp = .70) were compared with RF, showing a significant correlation in PIT and RF (r = .69), SIT and RF (r = .73), and PIT and K-ODI (r = .53). CONCLUSION: The SIT is a more comfortable position test than the PIT in patients. Both PIT and SIT have acceptable reliability and validity.

• The Korean Journal of Pain
• /
• 제34권1호
• /
• pp.94-105
• /
• 2021

Background: Many patients with complex regional pain syndrome (CRPS) have been known to be at risk of suicide, due to severe pain and its comorbid conditions. The risk of suicide may be associated with affective instability, which is an indicator of emotional dysregulation. Particularly, unstable shifts in negative emotions are difficult to cope with, which may result in individuals feeling uncontrollable, hopeless, and entrapped. This study aimed to examine the role of affective instability in the relationship between pain intensity and suicide risk (suicidal ideation and impulsivity) in patients with CRPS, by employing a daily diary. Methods: Twenty-three patients registered at the CRPS Association in Korea were asked to complete a day-to-day routine for 15 days, followed by a diary composed of pain intensity, suicidal ideation, impulsivity, and positive and negative affects. Results: Results showed that the interactions between negative affective instability and daily pain intensity were statistically significant on daily suicidal ideation (coefficient = 0.41, t (21) = 2.56, P < 0.050) and daily impulsiveness (coefficient = 1.20, t (19) = 3.35, P < 0.010). However, those between positive affective instability and daily pain intensity were not. Conclusions: This study is the first attempt to investigate the role of affective instability on the relationship between daily pain intensity and daily suicide risk in patients with CRPS. Our findings suggest that health professionals pay considerable attention to the instability of negative affects when assessing and managing patients with CRPS at risk of suicide.

• 가정과삶의질연구
• /
• 제16권2호
• /
• pp.41-52
• /
• 1998

The purpose of this research was to assess gender differences in the processes of intergenerational transmission of marital instability. This study revealed gender differences in the intergenerational transmission of marital instability. The fit indices suggest that the hypothesized model fit better for the female sample. Parental divorce marital quality and marital commitment were significant predictors of marital instability for both genders. Parental divorce was a strong predictor of marital quality for women only. While the path between age difference and marital quality for females was strong the same association disappeared for their male counterparts.