• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.2
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• pp.10-17
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• 1999

This paper investigates the linear stability of both uniform and non-uniform density plane mixing layers with special emphasis on the effect of the wake component in the velocity profile. Velocity and density profiles for laminar flows are obtained from analytic profiles. Mixing layers with wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For uniform density mixing layers, sinuous modes are more unstable than varicose modes, which shows wakes will be destabilized by sinuous modes. For non-uniform density mixing layers with high density in high speed flows, sinuous modes are more unstable than varicose modes. For non-uniform density mixing layers with high density in low speed flows, varicose modes can be more unstable than sinuous modes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1948-1966
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• 1991

Two-phase cross-flow exists in many shell-tube heat exchangers such as condensers, reboilers and nuclear steam generators. To avoid problems due to excessive vibration, information on vibration excitation in two-phase cross-flow is required. Fluid-elastic instability is discussed in this paper. Four tube bundle configurations were subjected to increasing flow up to the onset of fluid-elastic instability. The tests were done on bundles with one flexible tube surrounded by rigid tubes. The fluid-elastic instability behavior is different for intermittent flows than for bubbly flows. For bubbly flows, the observed instabilities satisfy the relationship V/fd=K(2.pi..zeta. m/rho. $d^{21}$)$^{0.51}$ in which the minimum instability factor K was found to be 2.3 for bundles of p/d=1.22. The lowest critical velocities for fluid-elastic instability were experienced with parallel-triangular tube bundles. For intermittent flow, the observed instabilities did not follow the forgoing relation-ship. Significantly lower flow velocities were required for instability..

• Journal of the Korean Arthroscopy Society
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• v.10 no.2
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• pp.135-140
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• 2006

Diagnosis and treatment of the unstable shoulder is one of the more difficult problems in orthopaedic surgery. There is confusion between the normal laxity with translation and subluxation of the humeral head relative to the glenoid and an abnormal amount of laxity, leading to pain and dysfunction. Unfortunately, there is no single treatment that applied to all lesions that cause the instability. It is imperative, therefore, that an accurate diagnosis be made, including the directions and degree of shoulder instability as well as any coexisting problems. Anatomical defects must be defined. Common factors that could most readily compromised instability repair are examined. These include techniques for making an accurate diagnosis with identification of the precise anatomical pathology, and the rationale for appropriate surgical treatment with the avoidance of technical complication such as unnecessary hardware or exposures that might lead to residual instability, arthritis, and nerve or vascular injuries. Additional injuries may be prevented by careful rehabilitation postoperatively to restore shoulder stability, flexibility, and endurance prior to an individual's return to stressful sports or work.

• Korean Journal of Applied Biomechanics
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• v.19 no.3
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• pp.519-528
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• 2009

The effects of taping on the use of such measures for prevention have already been comprehensively described in the literature. However, few studies have analyzed ground reaction forces and postural stability with functional ankle instability subject during dynamic activities with ankle taping The purpose of this study was to identify the effects of ankle taping on ground reaction force and postural stability during jump landing. Fourteen players who has ankle instability were participated in this study. we used vicon and force platform. The application of taping who has ankle instability decreased DF and inversion angular velocity and peak vertical ground reaction force during landing. It also improved A-P cop, M-L cop in stability. The findings of this study support the use of taping as part of injury prevention for subject with functional ankle instability in clinical setting.

• The Journal of the Korea Contents Association
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• v.22 no.4
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• pp.677-688
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• 2022

Precarious employment is negatively associated with mental health including depression. The aim of the study is to suggest the multidimensional definition of precarious employment and examine its impacts on depression. Using the fifth save of the Korean Working Condition Survey, we first measured six different dimensions of employment precariousness: temporariness, disempowerment, vulnerability, difficulty exercising rights, unpredictability of working times, and low wage. All of six precariousness indicators consisted of a scale from 0 to 100. Then, we conducted logistic regression to examine the association between employment precariousness and depression. For men, the risk of depression increased by 3.1%, 1%, and 0.5%, respectively, for each one point increase in vulnerability, difficulty in exercising rights, and unpredictability of working times. For women, the risk increased by 0.5%, 2.3%, and 0.8%, respectively, for each one point increase in temporariness, vulnerability, and difficulty in exercising rights. Our findings suggest that not only a secure employment contract, but also their substantive labor rights should be guaranteed for health for workers.

• Journal of Korean Orthopaedic Sports Medicine
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• v.3 no.1
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• pp.49-55
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• 2004

Purpose: we would like to suggest the proper surgical methods according to the severity of instability by analyzing the results. Materials and Methods: Between January 1998 and August 2002, eighty five patients have been operated on because of posterolateral rotatory instability (PLRI). The materials were included the patients who had followed-ups for over 2 years in sixty one patients and the patient's assessments were done by clinical score (OAK, IKDC) and posterolateral drawer and dial test. Results: Through our results, the fibular tunnel turned out to be superior compared to the tibia tunnel method in rotational stability. Hughston-Jacobson methods and biceps tenodesis showed poor results. Fibula head tunnel was superior to tibia tunnel in rotational stabiliaty Conclusion: The surgical technique that passes the modified posterolateral corner sling through the fibula head tunnel may provide good clinical results in grade II PLRI. It is necessary to reconstruct both tibia and fibula tunnel in grade III PLRI. When there is combined varus instability, a positive result may be obtained if an additional LCL reconstruction is performed.

• Journal of the Economic Geographical Society of Korea
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• v.12 no.4
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• pp.507-520
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• 2009

The purpose of this study is to analyze the changes in the housing instability of low-income households through their residential mobility. The concept of housing instability is measured by taking into consideration of housing types, number of moves, period of homelessness, and housing affordability index. The result of this study shows that housing instability of low-income households owned their homes is mainly caused from their old housing built in at least 1980, and that of tenant households is due to the heavy burden of rent-to-income ratio. By using multinominal logit model, the study finds that low-income tenant households are more likely to move upwards as they are man-headed, aged and relatively high-income if we categorize residential mobility into four types: upwards, equivalent, trade-off, and downwards migration. Considering that the share of homeowners moving downwards increases while the share of tenants moving upwards decreases as they reside increasingly nearby Seoul, the study finds that low-income households living in big cities are no better off to improve their residential instability for themselves than the low-incomes in local small and midium cities. Furthermore, both low-income owners and tenants are less likely to move downwards as the ratio of single-family housing in former residence increases. Such finding has a policy implication that government needs to maintain affordable single-family housing stock rather than supplying excessive unaffordable multi-family housing in order to enhance residential instability of low-incomes households.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.1
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• pp.62-71
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• 2016

Food insecurity is associated with poor health outcomes. In particular, previous studies marked the adverse outcomes on mental health. This study examined the association of food insecurity and mental health in Korean adults using the data from the 2013 Korean National Health and Nutrition Examination Survey (KNHANES). The study population was 5,685 adults in Korea. Food insecurity was examined using 18-items. A diagnosis of depression was considered to be depression. Depressive symptoms were defined as more than 2 weeks of depression feelings. Multivariate logistic regression models examined the associations between food insecurity and depression and depressive symptom. The overall prevalence of depression was 3.8% in the participants. Food insecurity was associated significantly with depression and depressive symptom in the unadjusted and age and sex adjusted model. Food insecurity was associated with depression, depressive symptoms in the multivariate logistic regression model (OR:3.49, OR:3.70). Marginal food insecurity was not associated with depression in the multivariate logistic regression model. The results showed that food insecurity is associated with depression and depressive symptoms in adults. Multi-disciplinary interventions are needed including nutrition, health, health policy, and a healthy environment for the food insecurity group to achieve a better health outcome, especially mental health.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.179-188
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• 2011

Experiments were conducted in a constant-pressure combustion chamber to investigate the effects of hydrocarbon addition on cellular instabilities of syngas-air flames. The measured laminar burning velocities were compared with the predicted results computed using reliable kinetic mechanisms with detailed transport and chemistry. The cellular instabilities that included hydrodynamic and diffusional-thermal instabilities of the hydrocarbon-added syngas-air flames were identified and evaluated. Further, experimentally measured critical Peclet numbers for fuel-lean flames were compared with the predicted results. Experimental results showed that the laminar burning velocities decreased significantly with an increase in the amount of hydrocarbon added in the reactant mixtures. With addition of propane and butane, the propensity for cell formation was significantly diminished whereas the cellular instabilities for methane-added syngas-air flames were not suppressed.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.6
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• pp.62-73
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• 2022

This research proposes a method to control combustion instability in a gas turbine combustor having an annular combustor form and compares the effect of flow symmetric braking through nozzle arrangement and the corresponding change in equivalent ratio. To this end, the symmetry breaking effect was confirmed through mode analysis of FFT, Time signal, and phase trajectory. In addition, the unstable area and the stable area were identified through mode analysis, and this was shown on the contour map. The present research shows that instability occurs when the equivalent ratio and the arrangement of the nozzles are symmetry or when the nozzles are continuously arranged, but if the arrangement and equivalent ratio are not symmetry, the combustion instability decreases dramatically even if the difference in the equivalent ratio is small.