• Journal of the Korean Magnetics Society
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• v.19 no.5
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• pp.176-179
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• 2009

We report a direct observation of Barkhausen avalanches in 50-nm Fe film, using a magneto-optical microscope magnetometer, capable of time-resolved domain observation. The time-resolved domain-evolution patterns exhibit that the occurrence of Barkhausen jump is random with respect to interval, size, and location. From the repetitive measurements more than 1000 times, we found that the probability distribution of Barkhausen jump size follows a power-law distribution and the critical exponent reveals the value of 1.14 $\pm$ 0.03.

• The Journal of the Acoustical Society of Korea
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• v.10 no.1
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• pp.12-19
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• 1991

A numerical analysis is carried out for the nonlinear phenomena of the bubble oscillator. The model is based on the Keller's formulation for the bubble dynamics. Interpretation of the bubble interior is based on the formulation by Prosperetti. His formulation adopts the energy equation for the analysis of the bubble interior. The numerical simulation Shows typical nonlinear phenomena in its frequency response. Among such nonlinear aspects are the jump phenomenon, the shift of natural frequency of the system, and the appearance of superharmonic resonances. It is deduced that the nonlinear frequency response is dependent upon the initial condition of the bubble oscillator and some multi-valued frequency region can appear in the response curve. Nonlinear phenomena appeared in the bubble oscillator is compared with those of the Duffing equation and it may be said that the bubble dynamic equation has similar nonlinear aspects to the Duffing equation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.5
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• pp.455-461
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• 2008

In this paper, the performance of a scalar filter and a scalar adaptive filter are analyzed. In order to make indoor experimental environment similar to outdoor test, ultrasonic sensors are used instead of GPS. The scalar adaptive filter, which is continuously estimating velocity error covariance and measurement noise covariance by using adaptive method, is different from the scalar filter. Experimental results show that the scalar adaptive filter has better position estimating performance than the scalar filter by estimating above two parameters with an adaptive method.

• Journal of Life Science
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• v.23 no.11
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• pp.1388-1396
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• 2013

This study used an S-180 cell-injected mouse model to evaluate the antitumor effects of the acute and subacute toxicity of Keumsa (Phellinus linteus) extract intravenously administrated in ICR mice. When administered intravenously (31.3-250 mg/kg body weight), Keumsa (Phellinus linteus) extract significantly inhibited the growth of the solid tumor cell. The antitumor activity of Keumsa (Phellinus linteus) extract increased in a dose-dependent manner. The highest dose (250 mg/kg body weight) was highly effective, reducing tumor formation by 42.7% compared with the control group. In the acute toxicity test, $LD_{50}$ of the Keumsa (Phellinus linteus) extract showed 632.84 mg/kg (♂) and 814.48 mg/kg (♀) after intravenous administration. In addition, liver and spleen weight were increased in a dose-dependent manner. In the subacute toxicity test, the mice were intravenously administered over the course of 28 days. The $LD_{50}$ of the Keumsa (Phellinus linteus) extract showed 355.41 mg/kg (♂) and 383.53 mg/kg (♀) after intravenous administration. The liver and spleen weight also increased in a dose-dependent manner. In the case of the group that received more than 125 mg/kg of intravenous administration, exercise capacity, such as jumping ability and agility, were significantly increased. These results suggest that Keumsa (Phellinus linteus) extract can be regarded as a potent enhancer of the innate immune response, and it can be considered as a new natural product with low toxicity that may be used as a candidate for antitumor action.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.2
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• pp.119-126
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• 2014

An experimental study was conducted to study fuel injection characteristics through plain orifice injectors when the fuel was heated to the temperature higher than its boiling point. Three injectors with different orifice diameters were used to measure the flow coefficient (${\alpha}$) for the injection pressure ranges of 3, 5, and 10 bar and the fuel temperature ranges between 50 and $270^{\circ}C$. The study showed that ${\alpha}$ decreases gradually with the fuel temperature below $180^{\circ}C$ while it drops abruptly when the temperature goes beyond $187^{\circ}C$, the boiling temperature of the fuel. The slope of ${\alpha}$ bifurcated at the boiling temperature for different injection pressures, and ${\alpha}$ decreased faster for the lower injection pressure due to the more active boiling in the injector. In addition, the larger orifice diameter had the higher ${\alpha}$ value, and ${\alpha}$ jumped at moderate temperature ranges when the injection pressure was low, implying the turbulent-laminar transition phenomena. The measured ${\alpha}$ was plotted against the cavitation number($K_c$), and the characteristics were independent of the applied pressure for small injectors when the fuel was evaporated before it was injected.