• Journal of Contemporary Eastern Asia
• /
• v.19 no.1
• /
• pp.97-122
• /
• 2020

This paper examines the existence of herd behaviour in fifteen (15) global stock markets, which consist of Developed Markets (Canada, Hong Kong, Japan, Singapore and the United Kingdom), Advanced Emerging Markets (Brazil, Malaysia, Mexico, Poland and South Africa) and Secondary Emerging Markets (Chile, China, Indonesia, the Philippines and Russia) by using Cross Sectional Absolute Deviation (CSAD) method of Chiang and Zheng (2010). It also seeks to explore the impact of social factors such as prosperity, education, ageing society, industry orientation and gender on the existence of market-wide herding. The findings of this paper indicate that herd behaviour exists in Singapore (Developed Market), Mexico, Poland and South Africa (Advanced Emerging Markets) and China and the Philippines (Secondary Emerging Markets). No evidence of herding is observed for Canada, Hong Kong, Japan, United Kingdom, Brazil, Malaysia, Chile, Indonesia and Russia. Ageing society is also found to have significant impact on the existence of herd behaviour. Nonetheless, prosperity, education, industry orientation and gender are found to be insignificant to herding. This study sheds some light on whether social factors determine herding behaviour in the 15 selected stock markets.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.19 no.4
• /
• pp.107-113
• /
• 2011

Coolant rubber hoses for automotive radiators under thermal and mechanical loadings can be degraded and thus failed due to the influences of the locally formed electricity. In this study, an advanced test method was developed to simulate the failure problem of the rubber hose. For carbon black filled EPDM (ethylene-propylene dine monomer) rubber used as a radiator hose material the ageing behaviors by the electro-chemical stresses combined with a tensile strain were analyzed. As the tensile strain increased, the current of the rubber specimen reduced indicating an increase of the internal defects and electrical resistance of the rubber specimen. Elongation at break and IRHD hardness rapidly decreased with increasing the ageing time. Both electro-chemical stress and mechanical tensile stress clearly accelerated the degradation of EPDM rubber.

• Journal of the Korean Society of Safety
• /
• v.21 no.4 s.76
• /
• pp.33-41
• /
• 2006

Material degradation should be considered to assess integrity and residual life of high temperature equipments. However, the property data reflecting degradation are not sufficient for practical use. In this study measuring properties for 1Cr-1Mo-0.25V forging steel generally used for turbine rotor was carried out. Degradation was simulated by isothermal ageing. heat treatment and variation of microstructure was observed. Mechanical properties such as tensile strength, impact energy, hardness and fracture toughness were measured. Assuming a semi-elliptical surface crack at the bore hole in a turbine rotor, material risk was estimated by using the aged material property data obtained in this study. Safety margin was decreased and life of the rotor was exhausted. This procedure can be used in assessing the residual life of a turbine rotor due to material degradation.

• Journal of Korea Foundry Society
• /
• v.38 no.5
• /
• pp.95-102
• /
• 2018

The dependence of the tensile properties on variations in the porosity of A356 aluminium alloys was investigated in terms of the quality index of the tensile properties based upon the ultimate tensile strength and elongation as well as the variation of the strength coefficient and strain-hardening exponent with regard to a T6 treatment. The test specimens were prepared by low-pressure die-casting and a subsequent T6 treatment, and the experimental results of a tensile test carried out at room temperature were compared to the theoretical description using a modified constitutive model. The nominal value of the quality index of A356 alloys increases gradually with a lapse of the ageing time upon a T6 treatment, despite the fact that this value is temporarily decreased during the initial stage of ageing from a solutionised condition. Additionally, the quality index depends practically upon the porosity variation with a power law relationship without regard to whether in solutionised or artificial aged conditions. The theoretical description indicates that the strength coefficient directly determines the nominal level of the quality index. Moreover, the overall dependence of the quality index on the porosity variation is remarkably weakened with an increase in the tensile strain, whereas the quality index depends sensitively upon the porosity variation with a low value of the strain-hardening exponent.

• Journal of the Korean Society for Heat Treatment
• /
• v.9 no.3
• /
• pp.212-218
• /
• 1996

To clarify the influence of precipitation microstructure and inclusion on the monotonic tensile fracture behaviors in 2090 alloy aged at $180^{\circ}C$, the detailed measurement of hardness, tensile strength, elongation and the observation of scanning electron micrography, transmision electron micrography have been carried out. The transgranular shear ductile fracture has been observed in specimen quenched after solution treatment at $500^{\circ}C$ for 45min. While the under-aged specimen was fractured in both transgranular shear ductile and intergranular fracture mode, the fracture mode of peak-aged and over-aged alloy was predominantly intergranular fracture. The fracture behavior of each ageing condition was influenced by the change of precipitation microstructural features. In the case of peak-aged and over-aged alloys, the coarse and heterogeneous slip band caused by both shearable nature of the ${\delta}^{\prime}(Al_3Li)$ precipitates and PFZ along the high angle grain boundary aid the localization of deformation, resulting in low energy intergranular fracture. It was also estimated that the fractured T-type intermetallic phases (inclusion) and the equilibrium ${\delta}$(AlLi) phases which were formed at grain boundaries palyed an important role in promoting intergranular fracture mode.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
• /
• v.9 no.1
• /
• pp.79-85
• /
• 1998

Changes in the human voice occur between infancy and old age and reflect a myriad of biological changes that influence the size, shape, and physical properties of the larynx. The human larynx is located near the base of the neck and attached inferiorly to the trachea and opens superiorly into the pharynx. The larynx by the third month of fetal life has the same features recognizable at birth. The fundamental frequency of vocal fold vibration generally becomes higher in early age, lower in middle age, and higher in old age. These decreases in Fo undoubtedly result from a combination of factors, consisting of modest increase in length and mass of the muscle and connective tissues of the vocal fold. But the level of the larynx in the neck may be closely connected with Fo directly, high larynx in related with high pitch and low larynx with low pitch. The purpose of this study is to determine the developmental level difference from child to adult larynx using conventional radiography, and the change of speaking fundamental frequency from second decade to sixth decade.

• Journal of the Korean Society for Heat Treatment
• /
• v.8 no.2
• /
• pp.101-112
• /
• 1995

A study was made to examine the effects of heat-treatment on the microstructures of Cu-bearing HSLA steels. The details of microstructures were studied by using optical microscopy(OM), transmission electron microscopy(TEM) and hardness test. The as-rolled microstructure of HSLA-A consists of ferrite (${\alpha}$) whereas that of HSLA-B consists of needle-shaped phase. The difference in microstructure can be ascribed to the different amount of Ni, Mn, Mo, Cu which affect the hardenability. The austenite grain size is very small up to $1000^{\circ}C$ owing to the Nb-precipitates. As the austenitizing temperature increases above $1000^{\circ}C$, the austenite grain grows rapidly. There are two hardness peaks in the hardness versus temperature curve, at $500^{\circ}C$ and at $675^{\circ}C$ (HSLA-A), $725^{\circ}C$ (HSLA-B). The peak at $500^{\circ}C$ result from the formation of Cu-precipitates and second hardness peak is created due to the formation of M-A constituents. The hardriess decrease in HSLA-B steel with ageing temperature is small because of the higher amounts of Cu than HSLA-A steel. The fine, round ${\varepsilon}$-Cu precipitates grow with ageing temperature and finally transform into rod shape.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.5
• /
• pp.59-65
• /
• 2018

During natural aging, hydroxyl-terminated polybutadiene(HTPB) propellant undergoes a series of slow physico-chemical degradation reactions. By using accelerated ageing conditions it is possible to simulate the material behavior at different time-temperatures focusing on in-service conditions. Aging behaviors of HTPB propellant are investigated using HFC(heat flow calorimeter), a universal technique for measuring the rate of slow chemical and physical processes in long-term storage.

• Elastomers and Composites
• /
• v.52 no.4
• /
• pp.237-241
• /
• 2017

The tensile strength (TS) and elongation-at-break (EB) loss of a CR/CB rubber composite sample prepared for the automotive parts were measured after accelerated thermal ageing at temperatures of 100, 120, 140, and $150^{\circ}C$. The change in TS was observed to be linear from the master curve prepared using the time-temperature superposition-principle (TTSP). An Arrhenius type of shift factor, $a_T$ was used to predict the life time of the sample, and a plot of ln $a_T$ vs. 1/T was also shown to be linear. The activation energy ($E_a$) of the sample was calculated as 70.30 kJ/mole from the Arrhenius plot. The expected life time of the sample was predicted at the given operating conditions by applying Arrhenius analysis. Assuming the $E_a$ value was constant at lower operating condition, life time of the sample was calculated as 2.3 years when the life limit was set as time to reach the 20% decrease of the initial TS value at operating temperature of $40^{\circ}C$.

• Journal of Welding and Joining
• /
• v.13 no.2
• /
• pp.122-131
• /
• 1995

The effects of cooling rate on the microstructures, precipitation of Cu-cluster, .epsilon.-Cu and impact toughness of high strength low alloy(HSLA) steel were studied using hardness tester, impact tester, DSC(differential scanning calorimetry), AES(auger electron spectroscopy) and TEM(transmission electron microscopy). Not only the Cu-precipitates but also the segregation of Cu, As, Sb, P, S, N, Sn along grain boundary were not observed at the specimens heat treated from 800.deg. C to 300.deg. C with the cooling time of 12-125 sec. The Cu-cluster, .epsilon.-Cu are formed by introducing ageing after cooling and the effect of precipitates on hardening increase after cooling was the same in all cooling rate. The peak hardness was obtained at an ageing of 500.deg. C in all cooling conditions. The impact energy become higher as the cooling time increases. This fact can be explained to be due to the tempering effect applied on the cooling stage since the present alloy has a relatively high Ms temperature and the local high concentration of the retained austenite.