• Nuclear Engineering and Technology
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• v.38 no.7
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• pp.619-638
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• 2006

Low temperature irradiation can significantly harden metallic materials and often lead to strain localization and ductility loss in deformation. This paper provides a review on the radiation effects on the deformation of metallic materials, focusing on microscopic and macroscopic strain localization phenomena. The types of microscopic strain localization often observed in irradiated materials are dislocation channeling and deformation twinning, in which dislocation glides are evenly distributed and well confined in the narrow bands, usually a fraction of a micron wide. Dislocation channeling is a common strain localization mechanism observed virtually in all irradiated metallic materials with ductility, while deformation twinning is an alternative localization mechanism occurring only in low stacking fault energy(SFE) materials. In some high stacking fault energy materials where cross slip is easy, curved and widening channels can be formed depending on dose and stress state. Irradiation also prompts macroscopic strain localization (or plastic instability). It is shown that the plastic instability stress and true fracture stress are nearly independent of irradiation dose if there is no radiation-induced phase change or embrittlement. A newly proposed plastic Instability criterion is that the metals after irradiation show necking at yield when the yield stress exceeds the dose-independent plastic instability stress. There is no evident relationship between the microscopic and macroscopic strain localizations; which is explained by the long-range back-stress hardening. It is proposed that the microscopic strain localization is a generalized phenomenon occurring at high stress.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.105-112
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• 2006

Liquefaction-induced lateral spreading has been the most extensive damage to pile foundations during earthquakes. However, a case of pile failure was reported despite the fact that a large margin of safety factor was employed in their design. This means that the current seismic design method of pile is not agreeable with the actual failure mechanism of pile. Newly proposed failure mechanism of pile is a pile failure based on buckling instability. In this study, failure behavior of pile embedded in liquefied soil deposits was analyzed considering lateral spreading and buckling instability performing 1g shaking table test. As a result, it can be concluded that the pile subjected to excessive axial loads ($near\;P_{cr}$) can fail by buckling instability during liquefaction. When lateral spreading took place in sloping grounds, lateral spreading increased lateral deflection of pile and reduced the buckling load, promoting more rapid collapse. In addition, buckling shape of pile was observed. In the ease of pile buckling, hinge formed at the middle of the pile, not at the bottom. And in sloping grounds, location of hinge got loiter compared with level ground because of the effects of lateral spreading.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.1
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• pp.177-187
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• 2022

Theoretical literature agrees on the interaction between financial instability and economic activity but explains it's dynamic in two points of view: one is that the transmission mechanism occurs in one unique regime and the other reckons a shift of regime leads to the alteration of the transmission mechanism. This study aims to find evidence of the multi-regime transmission for ASEAN developing countries. The author employs the technique of Threshold vector auto regression using the financial stress index standing for financial instability. Monthly data is collected, covering a period long enough with many episodes of high stress in recent decades. There are two conclusions: (1) A financial shock has a negative and stronger impact on economic activity during a high-stress period than it does during a low-stress period; (2) the response of economic activity to a negative financial shock during high-stress periods is stronger than it is during normal times. The findings point to the importance of the financial stress index as an additional early warning indicator for the real economy sector, as well as the positive effect that a reduction in financial stress may have on economic activity, implying the importance of "unconventional" monetary policy in times of high financial stress.

• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.906-913
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• 2003

Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.69-74
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• 2001

It is well known that an air bubble trapped in water emits light at its collapse robustly with a proper forcing amplitude of ultrasound. Instability mechanism which causes deviation from sphericity of bubble wall was investigated theoretically. The rapid change of the bubble wall velocity which is both dependent on the forcing amplitude, was found to be a major factor of instability of the interface. The Rayleigh-Taylor instability which occurs when rapid acceleration is directed from the lighter towards the heavier fluid is found to be not related to the instability of the sonoluminescing gas bubble. A good agreement between the calculation results and experimental data is found.

• Journal of Korean Foot and Ankle Society
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• v.25 no.1
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• pp.38-45
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• 2021

Subtalar joint instability (STI) is one of the causes of persistent hindfoot pain even after treatment for ankle instability. Diagnosis of STI is often neglected because it is a poorly understood concept. However, understanding of the anatomy and injury mechanism of the subtalar joint is a prerequisite of appropriate treatment. Patients with STI usually complain of several symptoms, such as recurrent sprains or a giving way sensation and rolling over. Recently, various diagnostic tools and treatment methods have been investigated. This study was undertaken with the aim of helping clinicians by providing a comprehensive understanding of STI.

• Journal of Chest Surgery
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• v.33 no.1
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• pp.60-67
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• 2000

Background: Microsatellites are short-tandem repeated uncleotide sequences present throughout the human genome. Alterations of microsatellites have been termed microsatellite instability(MI). It has been generally known that microsatellite instability detected in hereditary non-polyposis colorectal cancer (HNPCC) reflects genetic instability that is caused by impairments of DNA mismatch repair system regarding as a novel tumorigenic mechanism. A number of studies reported that MI occurred at varying frequencies in non-small cell lung carcinoma (NSCLC). However It has been unproven whether MI could be a useful market of genetic instability and have a clinical significance in NSCLC. Material and Method : We have examined whether MI can be observed in thirty NCSLC using polymerase chain reaction whether such alterations are associated with other molecular changes such as p53, K-ras and c-myc oncoproteins expression detected by immunohistochemical stain,. Result: MI(+) was observed in 16.6%(5/30) and MI(-) was 83.3% (25/30) Average age was 50$\pm$7.5 year-old in MI(+) group and 57$\pm$6.6 year-old in MI(-) group. Two year survival rate in MI(=) group (20% 1/5) was worse than MI(-) group (64% 16/25) with a statistic difference. (P=0.04) The positive rate of K-ras oncoprotein expression and simultaneous expression of 2 or 3 oncoproteins expression were higher in MI(+) group than MI(-) group with a statistic difference(P=0.05, P=0.01) Conclusion: From, these results the authors can conclude that MI is found in some NSCLC and it may be a novel tumorigenic mechanism in some NSCLC. We also conclude that MI could be used as another poor prognostic factor in NSCLS.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.18-25
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• 2014

In this paper, the mechanism of the combustion instability which may occur in a hybrid rocket motor with a diaphragm was studied. And the new design for a hybrid motor grain was suggested. It could increase a regression rate of solid fuel, and reduce a large pressure oscillation in a hybrid rocket motor with a diaphragm. It was confirmed that the main mechanism of a large pressure oscillation was hole-tone, and it was caused by a collision between a diaphragm and a vortex which was generated in a pre-chamber. And 'Stepped Grain' design which had the mechanism for high regression rate in a motor with a diaphragm and could reduce a combustion instability was suggested.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.83-87
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• 2009

Ramjet engine is weak for low frequency combustion instability because of their long air flow passage. A model combustor which has fuel injector and V-gutter shaped flame holder was designed and fabricated in order to simulate a combustion mechanism of ramjet engine, and it could demonstrate combustion instability which might occur in ramjet combustor. The frequency of the instability was very similar to that of acoustic resonance frequency of combustor, and it proved that a typical combustion instability by thermo-acoustic coupling occurred.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1218-1229
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• 1997

The diffusional-thermal instability of diffusion flames in the premixed-flame regime is studied in a constant-density two-dimensional counterflow diffusion-flame configuration, to investigate the instability mechanism by which periodic wrinkling, travelling or pulsating of the reaction sheet can occur. Attention is focused on flames with small departures of the Lewis number from unity and with small values of the stoichiometric mixture fraction, so that the premixed-flame regime can be employed for activation-energy asymptotics. Cellular patterns will occur near quasisteady extinction when the Lewis number of the more completely consumed reactant is less than a critical value( ~ =0.7). Parametric studies for the instability onset conditions show that flames with smaller values of the Lewis number and stoichiometric mixture fraction and with larger values of the Zel'dovich number tend to be more unstable. For Lewis number greater than unity, near-extinction flame are found to exhibit either travelling instability or pulsating instability.