• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.8
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• pp.1211-1216
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• 1989

To enhance the breakdown properties of low voltage-oriented ZnO varistor, sample were fabricated with additive oxides and sintering conditions. Addition of TiO2 lowered breakdown voltage` nonlinear resistances were lowered about 10V/mm and nonlinear exponents were not lowered with respect to it with the basic composition. To the samples added TiO2, V2ko5, and Cr2O3, microstructures were observed by SEM, moreover Ti was detected at grainboundaries and within the grain by EDS. Addition of Si-oxides and Sb2O3 increased nonlinear exponent and also increased nonlinear resistance, by addition of TiO2 to these samples at the sintering conditions of 1250\ulcorner and 1 hour we could fabricate low voltage-oriented ZnO varistors with nonlinear exponent of 30 or more and with real breakdown voltage of 30V/mm.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.318-321
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• 2003

In this paper, path loss and delay profile characteristics are measured in the subway platform. To evaluate the fading characteristics of the measured signals, the standard deviations are computed. The standard deviation is bigger for shorter distance. The shorter the distance, the bigger the phase difference between direct wave and reflected waves according the distance, which results in heavy fading. To compute the path loss according to distance, the average values of path loss exponent(n) is evaluated. The path loss exponents measured in the subway environment for Omni-VP(omni-directional vertical polarization) antenna and CP(circular polarization) antenna are 1.418 and 1.680, respectively, which are considerably less than 2.0, the free space path loss exponent.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.187-191
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• 2000

High temperature creep behaviour of Al-5 wt% Mg alloy reinforced with 7.5% BN flakes was studied. The composite specimens showed two main creep characteristics : (1) the value of the apparent stress exponent of the composite was high and varied with applied stress (2) the apparent activation energy for creep was much larger than that for self-diffusion in aluminum The true stress exponent of the composite was set equal to 5. Temperature dependence of the threshold stress of the composite was very strong. Which could not be rationalized by allowing for the temperature dependence of the elastic modulus change. AIN particles which were incorporated into the Al matrix during fabrication of the composite by the PRIMEXTM method were found to be effective barriers to dislocation motion and to give rise the threshold stress during creep of the composite

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.1
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• pp.49-55
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• 2006

Applied by periodic Stimulating Currents in Bonhoeffer -Van der Pol(BVP) model, chaotic and periodic phenomena occured at specific conditions. The conditions of the chaotic motion in BVP comprised 0.7182< $A_1$ <0.792 and 1.09< $A_1$ <1.302 proved by the analysis of phase plane, bifurcation diagram, and lyapunov exponent. To control the chaotic motion, two methods were suggested by the first used the amplitude parameter A1, $A1={\varepsilon}((x-x_s)-(y-y_s))$ and the second used the temperature parameterc, $c=c(1+{\eta}cos{\Omega}t)$ which the values of ${\eta},{\Omega}$ varied respectlvly, and $x_s$, $y_s$ are the periodic signal. As a result of simulating these methods, the chaotic phenomena was controlled with the periodic motion of periodisity. The feasibilities of the chaotic and the periodic phenomena were analysed by phase plane Poincare map and lyapunov exponent.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.175-178
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• 2004

The microstructure, electrical, and clamping voltage characteristics of ZPCCD-based varistors were investigated at sintering time of 2 and 3 h. The average grain size and density of varistor were increased from 15.2 to 19.0 and from 5.5 to 5.6 $g/cm^3$ with sintering time, respectively. The nonlinear exponent was 65.4 for 2 h and 37.4 for 3 h, and leakage current was 0.54 ${\mu}A$ for 2 h and 0.67 ${\mu}A$ for 3 h. The dissipation factor was 0.0397 for 2 h and 0.0457 for 3 h. The clamping voltage ratio at surge current($8/20{\mu}s$) of 10~300 A was increased in the range of 1.56~2.17.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.901-908
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• 2003

Numerical study on stirring characteristics in a microchannel with blocks arranged periodically has been performed. Viscous flows through the microchannel is simulated three-dimensionally using a commercial code, FLUENT 6.0. Focus is given to the effect on the stirring characteristics of the geometric factors including the pitch, height and angle of the block arrangement. The numerical results at low Reynolds numbers show that the particles' trajectories in the microchannel heavily depend on the block arrangement. A nonlinear dynamical tool, i.e. Lyapunov exponent, was used in analysing the mixing effect. It was found that the mixing is the most effective at a certain combination of parameter values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.889-895
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• 2007

Quantifying dynamic stability is important to assessment of falling risk or functional recovery for leg injured people. Human locomotion is complex and known to exhibit nonlinear dynamical behaviors. The purpose of this study is to quantify major joints of the body using chaos analysis during walking. Time series of the chaotic signals show how gait patterns change over time. The gait experiments were carried out for ten young males walking on a motorized treadmill. Joint motions were captured using eight video cameras, and then three dimensional kinematics of the neck and the upper and lower extremities were computed by KWON 3D motion analysis software. The correlation dimension and the largest Lyapunov exponent were calculated from the time series to quantify stabilities of the joints. This study presents a data set of nonlinear dynamic characteristics for eleven joints engaged in normal level walking.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.589-593
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• 2003

In this paper, we propose that the chaotic behavior analysis in the mobile robot of embedding Chua's equation with obstacle. In order to analysis of chaotic behavior in the mobile robot, we apply not only qualitative analysis such as time-series, embedding phase plane, but also quantitative analysis such as Lyapunov exponent in the mobile robot with obstacle. In the obstacle, we only assume that all obstacles in the chaos trajectory surface in which robot workspace has an unstable limit cycle with Van der Pol equation.

• 연구논문집
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• s.25
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• pp.169-173
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• 1995

The high temperature deformation of mechanically alloyed Al-Ti-Si alloy (Al-9.64wt% Ti-1.56wt% Si) was investigated by performing constant load compression creep tests over the temperature range of $673^\circC$K to $723^\circC$K. From the calculation based on the modified power law creep equation for dispersion strengthened alloy, the true creep activation energy, was 176kJ/mole, the true stress exponent was 4.9. Considering the value of activation energy, stress exponent, the shape of primary creep region, it could be concluded that creep deformation in the MA Al-Ti-Si alloy is controlled by dislocation climb.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.185-192
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• 2000

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 3%.