• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.2
• /
• pp.85-92
• /
• 1999

The fact that material degradation can be evaluated by measuring nonlinear acoustic effect has been proposed by previous studies. The most conventional method to measure nonlinear acoustic effect is to measure the absolute magnitude of fundamental and $2^{nd}$ order harmonic frequency component in the propagated ultrasonic wave. For this aim, power spectral analysis technique has been used widely. However, the power spectral analysis has fatal disadvantage that the gaussian additive noise superimposed in the wave signal remains in the power spectrum domain. Moreover, the magnitude of $2^{nd}$ order harmonic frequency component generated by nonlinear effect is so small that it may be suppressed by the noise remained in the power spectrum. In order to overcome this problem, this paper proposes an alternative method using bispectrum analysis, which can reduce the effect of addictive gaussian noise and. the nonlinear parameter can be obtained more stably. Simulations showed that the proposed method can obtain the value of nonlinear parameter near to the true value in the case of low SNR signal. Also, in order to confirm the usefulness of our method in actual case, we compared the nonlinear parameter obtained by using both of power spectral and bispectral analysis for several specimen intentionally degraded by fatigue load.

• 제어로봇시스템학회:학술대회논문집
• /
• 1998.10a
• /
• pp.271-274
• /
• 1998

This paper describes a new method for separation of the Volterra kernels which are identified by use of M-sequence. One of the authors has proposed a method for identification of Volterra kernels of nonlinear systems using M-sequence and correlation technique. When M-sequence are applied to a nonlinear systems, the cross-correlation function between the input and the output of the nonlinear systems includes cross-sections of high-order Volterra kernels. However, if various order Volterra kernels exixt on the obtained cross-correlation function, it is difficult to separate the Volterra kernels. In this paper, the authors show that the magnitude of Volterra kernels is maginified by the amplitude of M-sequence according to the order of Volterra kernels. By use of this property, each order Volterra kernels is obtained by solving linear equations. Simulations are carried out for some nonlinear systems. The results show that Volterra kernels can be separated in each order successfully by the proposed method.

• Wind and Structures
• /
• v.1 no.3
• /
• pp.255-269
• /
• 1998

Second-order moments of considerable magnitude arise in tall and slender RC chimneys and towers subject to along-wind loading, on account of eccentricities in the distributed self-weight of the tower in the deflected profile. An accurate solution to this problem of geometric nonlinearity is rendered difficult by the uncertainties in estimating the flexural rigidity of the tower, due to variable cracking of concrete and the 'tension stiffening' effect. This paper presents a rigorous procedure for estimating deflections and second-order moments in wind-loaded RC tubular towers. The procedure is essentially based on a generalised formulation of moment-curvature relationships for RC tubular towers, derived from the experimental and theoretical studies reported by Schlaich et al. 1979 and Menon 1994 respectively. The paper also demonstrates the application of the proposed procedure, and highlights those conditions wherein second-order moments become too significant to be overlooked in design.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.3
• /
• pp.628-639
• /
• 2017

The purpose of this study was to examine the effects of children's daily stress and employed mothers' nurturing attitude on children's problem behavior, as well as the mediating role of employed mothers' nurturing attitude. 160 children (aged 3-6, in city "D") and their mothers participated in this study. The SPSS 18.0 program was used to conduct a regression analysis to examine the correlation between the children's daily stress, their problem behavior and the employed mothers' nurturing attitude, depending on the gender of the children. The results were as follows : First, in the case of the boys, their aggression and attention have effects on their coercive attitude, and their anxiety and depression have effects of decreasing magnitude on their logical attitude, blaming / offensive stress and pride-hurt stress in that order. Secondly, in the case of the girls, their aggression has effects on their coercive attitude, and their attention has effects of decreasing magnitude on their anxiety / frustration stress and coercive logical attitude in that order. On the other hand, their anxiety / depression have effects of decreasing magnitude on their accused/offensive stress and coercive attitude in that order. Third, the employed mothers' nurturing attitude had mediating effects between the children's daily stress and their problem behavior. However, no such mediating effects were observed in the case of the boys. Therefore, the mothers tend to foster complementary and logical parenting, rather than coercive or negligent parenting. It is thought that children need to reduce their stress levels in everyday life (in order to?) reduce their problems.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.7 no.5
• /
• pp.19-24
• /
• 2003

We analysed seismic phases recorded by the 10 December 2002 Cheolwon, Korea, earthquake of $M_{L}$ 3.6 and obtained source parameters such as hypocenter, origin time, earthquake magnitude. Velocity and acceleration records used in this study are from the KMA and KIGAM seismic networks. Due to the location of the epicenter in the north of the DMZ(Demilitarized Zone), direct Pg phases were recorded only at five stations in the area south of DMZ. Identification of refracted Pn phase as the first arrival is difficult in most stations. Therefore, the hypocenter determined by existing routine methods could be affected by a large error. In order to avoid the possibility of the problem, we employed a method of seismic phase analysis developed by Kim et al.. The direct, refracted, and reflected P and S phases were successfully identified using the method together with the travel time curve data. In order to improve the accuracy in determination of the hypocenter and origin time, we included PmP and SmS phases in the analysis in addition to the phases such as Pg, Pn, Sg and Sn. The epicenter, depth, and origin time of the Cheolwon earthquake determined based on data of 11 stations within 200km from the epicenter are $38.81^{\circ}$N, $127.22^{\circ}$E, 12.0km, and 7:42:51.4(local time), respectively. The average value of the local magnitude based on the Richter's definition from all the stations is 3.6 in $M_{L}$. This magnitude is smaller by 0.2 and 0.5 compared with magnitudes determined by KMA and KIGAM, respectively.

• Transactions on Control, Automation and Systems Engineering
• /
• v.2 no.4
• /
• pp.262-267
• /
• 2000

In this paper, the magnitude of undershoot and overshoot in a prototype second order system with one positive real zero is computed by the analytic methods. Also, it will be shown that the peak times of the undershoot and overshoot can be calculated using the impulse and step response of the second order system. Three different cases are investigated: underdamped(p<ζ<1), critically damped(ζ=1) and overdamped(ζ>1) cases. We deal with the undamped(ζ=0) case as a special case of the underdamped. And a compensation method is proposed to reduce undershoots of the nonmininmun phase system using feedforward compensator.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2000.11a
• /
• pp.305-309
• /
• 2000

In this paper, we presents a new methodology for face recognition after analysing conventional ICA(Independent Component Analysis) based approach. In the literature we found that ICA based methods have followed the same procedure without any exception, first PCA(Principal Component Analysis) has been used for feature extraction, next ICA learning method has been applied for feature enhancement in the reduced dimension. However, it is contradiction that features are extracted using higher order moments depend on variance, the second order statistics. It is not considered that a necessary component can be located in the discarded feature space. In the new methodology, features are extracted using the magnitude of kurtosis(4-th order central moment or cumulant). This corresponds to the PCA based feature extraction using eigenvalue(2nd order central moment or variance). The synergy effect of PCA and ICA can be achieved if PCA is used for noise reduction filter. ICA methodology is analysed using SVD(Singular Value Decomposition). PCA does whitening and noise reduction. ICA performs the feature extraction. Simulation results show the effectiveness of the methodology compared to the conventional ICA approach.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.22 no.2
• /
• pp.318-323
• /
• 2013

For fast and accurate motion of 6-axis articulated robot, more noble motion control strategy is needed. In general, the movement strategy of industrial robots can be divided into two kinds, PTP (Point to Point) and CP (Continuous Path). Recently, industrial robots which should be co-worked with machine tools are increasingly needed for performing various jobs, as well as simple handling or welding. Therefore, in order to cope with high-speed handling of the cooperation of industrial robots with machine tools or other devices, CP should be implemented so as to reduce vibration and noise, as well as decreasing operation time. This paper will realize CP motion (especially joint-linear) blending in 3-dimensional space for a 6-axis articulated (lab-manufactured) robot (called as "RS2") by using LabVIEW$^{(R)}$ (6) programming, based on a parametric interpolation. Another small contribution of this paper is the proposal of motion blending simulation technique based on Recurdyn$^{(R)}$ V7 and Solidworks$^{(R)}$, in order to figure out whether the joint-linear blending motion can generate the stable motion of robot in the sense of velocity magnitude at the end-effector of robot or not. In order to evaluate the performance of joint-linear motion blending, simple PTP (i.e., linear-linear) is also physically implemented on RS2. The implementation results of joint-linear motion blending and PTP are compared in terms of vibration magnitude and travel time by using the vibration testing equipment of Medallion of Zonic$^{(R)}$. It can be confirmed verified that the vibration peak of joint-linear motion blending has been reduced to 1/10, compared to that of PTP.

• Journal of Preventive Medicine and Public Health
• /
• v.40 no.5
• /
• pp.381-387
• /
• 2007

Objectives: This study was conducted in order to determine how the association between socioeconomic position(SEP) and health status changes with age among Seoul residents aged 25 and over. Methods: We utilized the 2001 and 2005 Seoul Citizens Health Indicators Surveys. We used self-rated 'poor' health status as an outcome variable, and family income as an indicator of SEP. In order to characterize the differential effects of socioeconomic position on health by age, we conducted separate multivariate analyses by 10-year age groups, controlling for sociodemographic covariates. In order to assess the relative health inequality across socioeconomic groups, we estimated the Relative Index of Inequality (RII). Results: The risk of 'poor health' is significantly high in low family income groups, and this increased risk is seen at all ages. However, the magnitude of relative socioeconomic inequality in health, as measured by the odds ratio and RII, is not identical across age groups. The difference in health across income groups is small in early adulthood (ages 25-34), but increases with age until relatively late in life (ages 35-64). It then decreases among the elderly population (ages more than 65). When the RII reported in 2005 is compared to that reported in 2001, RII can be seen to have increased across all ages, with the exception of individuals aged 25-34. Conclusions: The magnitude of health inequality is the greatest during mid- to late adulthood (ages 45-64). In addition, health inequalities have worsened between 2001 and 2005 across all age groups after economic crisis.

• Journal of Digital Convergence
• /
• v.14 no.11
• /
• pp.249-255
• /
• 2016

Since the elderly voices include a lot of noise caused by physiological changes in respiration, phonation, and resonance, the performance of the convergence health-care equipments such as speech recognition, synthesis, analysis program done by elderly voice is deteriorated. Therefore it is necessary to develop researches to operate health-care instruments with elderly voices. In this study, a voice activity detection using a symmetric higher-order differential energy function (SHODEO) was developed and was compared with auto-correlation function(ACF) and the average magnitude difference function(AMDF). It was confirmed to have a better performance than other methods in the voice interval detection. The voice activity detection will be applied to a voice interface for the elderly to improve the accessibility of the smart devices.