Earticle

This study proposes a novel methodology for quantitatively evaluating the contribution of input signals in the time domain using Mutual Information (MI). Traditional contribution analysis methods based on Pearson correlation coefficients are limited by their assumption of linearity, making them inadequate for systems with time-varying characteristics or nonlinear transfer paths. To address this, we construct simulation data comprising transient, non-stationary input signals and nonlinear transfer functions, and compute time-local mutual information by adopting the windowing approach commonly used in Short-Time Fourier Transform (STFT). The results demonstrate that the proposed MI-based method outperforms conventional linear techniques in capturing the contributions of inputs under nonlinear and time-varying conditions. Notably, the MI approach provides accurate quantitative assessment even when the system's transfer path responds nonlinearly to input amplitude. This study shows that MI-based contribution analysis is a powerful and effective tool for evaluating input influence in nonlinear, non-stationary, and multi-input systems, and lays a foundation for future applications to experimental data and integration with alternative MI estimation methods.

소파블록으로 피복하는 항만 구조물의 고파랑에 대한 저항을 확보하기 위한 일반적인 방법에는 소파블록 사이의 전단 연결력을 향상시킨 새로운 형상의 소파블록을 개발하여 사용하는 방법, 기존 소파블록의 크기를 키워 중량을 증가시키는 방법 그리고 소파블록을 로프 등으로 서로 엮어 단일체로 거동하도록 유도하는 방법 등이 고 려될 수 있다. 본 연구의 커플록은 두 개의 대칭형 소파블록을 와이어 로프로 연결하여 인접 소파블록과의 마찰 결속력을 확보하고 파랑에 대한 중량 저항력을 증가시킬 수 있도록 개발되었다. 그러나 분절형 소파블록인 커플록 의 안정된 형상 유지는 운반 및 거치 과정에서 발생하는 로프의 인장력에 영향을 받을 수 있으며 발생 인장력의 크기는 연결 접촉면의 크기와 간격 그리고 로프 단면 등의 변수에 따라 변화될 수 있다. 본 연구에서는 운반 중 소파블록과 바닥 사이에 미끄러짐이 발생한 경우에 연결부 안정성을 검토하기 위하여 일련의 기하학적 비선형 수 치해석을 실시하였다.

General methods for securing resistance to high waves in port structures by covering them with armor units include developing and using new-shaped armor units that enhance the shear connection between armor units, increasing the size of existing armor units to increase their weight, and inducing armor units to move as a single body by linking them together with ropes or the like. The couple lock of this study was developed to connect two symmetrical armor units with wire ropes to secure friction binding with adjacent sofa blocks and increase weight resistance to waves. However, the stability of the coupling lock, a articulated armor unit, can be affected by the tensile force of the rope generated during transport and mounting, and the magnitude of the generated tensile force can vary depending on variables such as the size and spacing of the connection contact surface and the cross-sectional area of the rope. In the study, a series of geometric nonlinear numerical analysis was conducted to examine the stability of the connection when a slip occurred between the armor unit and the floor during transport.

오늘날 이상 기후변화에 의해 발생하는 높은 파도는 항만시설물의 피해를 증가시키고 있으며 항만 방재 의 중요성이 점점 더 높아지고 있다. 국내에서는 고파랑에 대한 저항성을 확보하기 위하여 규모가 큰 케이슨 구조 물을 방파제에 적용하는 사례도 있지만 경제적 측면에서 소파블록을 활용하여 해안이나 항만의 방파제를 조성하 는 경우가 많다. 대표적인 소파블록인 테트라포드 이후 국내에서도 다양한 형태의 소파블록들이 지속적으로 개발 되었지만 그 타당성을 인정받아 실제로 방파제 구조물에 적용된 경우는 극히 일부 불과하다. 본 연구에서는 대형 화가 가능하여 고파랑에 대응할 수 있고, 블록 사이의 결합력 확보가 용이하고, 다양한 현장조건에 적용할 수 있 는 새로운 분절형 소파블록인 커플록을 개발하였다. 그리고 경계용 소파블록을 적용하여 안정적인 소파블록의 거 동을 확보하였다. 개발된 소파블록의 수리학적 성능 및 안정성을 검토하기 위하여 3D 수치해석을 실시하였다.

Today, high waves caused by abnormal climate change are increasing damage to port facilities, and the importance of port disaster prevention is increasing. In Korea, large-scale caisson structures are applied to breakwaters to ensure resistance to high waves, but in economic terms, wave dissipating concrete blocks are widely used to create breakwaters on coasts or ports. Since Tetrapod, a representative armor unit, various types of armor units have been continuously developed in Korea, but only a few have actually been applied to breakwater structures in recognition of their validity. In this study, a new articulated armor unit, a couple lock, which can be enlarged in size to cope with high waves, is easy to secure binding force between units, and can be applied to various field conditions, was developed. In addition, stable behavior of the armor unit was secured by applying a boundary armor unit. In order to examine the hydraulic performance and stability of the developed armor unit, a 3D numerical analysis were conducted.

상호변조왜곡은 원신호의 S/N도 악화시키고 인접채널에도 간섭 영향을 미친다. 상호변조왜곡은 전력증폭기의 비선형 특성에 의해서 주로 발생된다. 비선형 특성을 갖는 전력증폭기가 메모리 효과를 갖는다면 전력증폭기에서 발생되는 상호변조왜곡은 다양하고복잡한 형태로 발생된다. 상호변조왜곡을 개선하는 방법으로 전치왜곡기가 주로 사용된다. 전치왜곡기의 성능을 충분하게 활용하기위해서는 전력증폭기가 갖는 메모리 효과를 줄여야 한다. 본 논문에서는 전력증폭기에서 발생하는 메모리 효과를 줄이기 위한 바이어스 회로의 설계 방법에 대해서 기술하였다. 메모리 효과를 줄이기 위해서 바이어스 회로는 신호에 대해서는 높은 임피던스를 가져야 하며, 포락선(변조신호)에 대해서는 낮은 임피던스를가져야 한다. 더불어 신호의 2차 고조파에 대해서도 낮은 임피던스를 가져야 한다. 메모리 효과를 고려해서 설계한 바이어스 회로의성능을 확인해 보기 위해서 170 ～ 220MHz에서 동작하는 전력증폭기를 설계 및 구현하였다. 전력증폭기에 적용한 바이어스 회로는동작주파수 대역에서 큰 임피던스를 가지며, 포락선 신호와 신호의 2차 고조파에서는 낮은 임피던스를 갖는다. 성능 측정결과 비대칭적으로 발생되는 상호변조왜곡 성분이 3.7dB 개선됨을 알 수 있었다.

Intermodulation distortion degrades the S/N(signal-to-noise) of the original signal and also affects the adjacent channels. Intermodulation distortion is mainly caused by the nonlinear characteristics of the power amplifier. If the power amplifier with nonlinear characteristics has a memory effect, the intermodulation distortions occurred in the power amplifier are generated in various and complex forms. The predistorter is used as a way to improve intermodulation distortions. In order to efficiently utilize the performance of the predistorter, the memory effect of the power amplifier must be reduced. In this paper, we describe the design method of bias circuit to reduce the memory effect in power amplifiers. To reduce the memory effect, the bias circuit must have a high impedance for the signal and a low impedance for the envelope(modulating signal) and the second harmonic component of the signal. To verify the performance of the bias circuit designed considering the memory effect, a power amplifier operating at 170 ~ 220MHz was designed and implemented. The designed bias circuit has a large impedance in the operating frequency band and low impedance in the envelope signal and the second harmonic of the signal. As a result of the performance measurement, it was found that the asymmetric intermodulation distortion component is improved by 3.7dB.

우리나라 전력시장 발전부문에 경쟁을 도입함으로써 각발전사들이 얼마나 발전해야 할지는 중요한 문제가 되었고, 안정적인 계통한계가격(System Marginal Price, SMP)유지는 중요한 문제다. 본 연구에서는 인공신경망 중 MLP(Multi-Layer Perceptron), NARX(Nonlinear Autoregressive exogenous)를 이용하여 서로 비교 분석했고 외부변수로 전력수요를 설정하여 SMP를 예측했으며, ARIMA(Autoregressive Integrated Moving Average)와도 비교를 실시했다. 모두 30일, 40일, 50일을 예측해 봤으며 MLP의 경우 은닉층의 개수가 90개, 85개, 80개 였을 때 최적의 결과를 보여준 반면, NARX의 경우 95개, 80개, 70개 였을 때 최적의 결과를 보여주었다. 전반적으로 모든 예측에서 ARIMA, MLP, NARX 순으로 예측 오차가 작게 나타났다.

With the introduction of competition in the power generation sector in Korea, determining how much each electricity company should develop and maintain a stable system marginal price (SMP) has become an important issue. In this study, SMP was predicted by comparing the values for each company using a multilayer perceptron (MLP) and nonlinear autoregressive exogenous (NARX) model among artificial neural networks (ANN), and setting electricity demand as an external variable. The Autoregressive Integrated Moving Average (ARIMA) was also compared. Each method predicted 30, 40, and 50 days. In the case of MLP, optimal results were obtained when the number of hidden layer units were 90, 85, and 80, whereas in the case of NARX, optimal results were obtained when the number of hidden layer units were 95, 80, and 70. Overall, the forecast errors were small in the order of ARIMA, MLP, and NARX for all predictions.

Due to large peak-to-average power ratio (PAPR) at the time domain OFDM signal, various peak signal reduction methods for OFDM systems have been proposed. However, in a transmit OFDM beamforming, multiplication of the transmit signal using the weights causes transmit power imbalance between antennas and increases peak signal. We propose two approaches to mitigate these problems. Adding the pseudo-noise to covariance matrix at the process of weight calculation can alleviate the transmit power imbalance. Furthermore, the companding transform of time domain signal can reduce the peak signals. We show details of proposed methods and evaluate PAPR and BER performance.

Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC/OQAM) is one of the best waveforms used in 5G communications. The FBMC is a multicarrier modulation system (MCM) which suffers from high peak to average power ratio (PAPR) causing a reduction in power efficiency. Nonlinear companding techniques are widely used to reduce the peak-to-average-power ratio (PAPR). In this paper, we have evaluated the performance of different non-linear companding techniques to reduce the PAPR in FBMC/OQAM system while achieving good Bit Error rate. We assessed the hyperbolic tangent, the error function, the logarithmic function, the A-law, and Mu-law companding techniques. It is found that the best companding function is the Mu-law.

This paper examined different 2-parameter and 3-parmeter nonlinear models for height-diameter prediction that incorporated different stands variable for the development of robust generalised height-diameter models. Stratified random sampling was employed in selecting 54 sample plots (20 m by 20 m) for six different age series (6, 9, 13, 15, 17 and 21 years old) plantation. Diameter at breast height (D), total height (h) and merchantable height (hm) for individual trees with D≥10 cm were measured. The Nonlinear model forms were fitted by ordinary nonlinear least square (ONLS) regression to select the base model without random parameters. Stands variables where then incorporated as random components for mixed-effects modelling using Gauss-Newton algorithm for nonlinear (weighted) least-squares. The best models were adjured using Standard error of estimate (SEE), Root means square (RMSE) and Akaike’s Information Criterion (AIC) and validated by Z-Score values and residual plot. The overall best height-diameter prediction equation for 2-parameter and 3-parameter estimate was Meyer function and Logistic models respectively. All the parameters of the models predicted at p＜0.05 are significant justifying the use of this model for future predictions in the study area expect for Prodan model. The nonlinear mixed effects yield model developed are efficient and biologically logical in predicting yield of teak in the study area, therefore enabling forest managers to optimise harvest planning, plantation regeneration and management in Area J4 of Omo Forest Reserve.

지난 수 십년 동안 정보통신 기술은 다양한 산업에서의 생산성을 제고하였다. 본 논문은 1990년부터 2017년 기간에 걸친 아시아 36개국의 패널 자료를 이용하여, 정보 통신기술을 반영한 경제성장 수렴에 대한 실증분석을 실시한다. 정보통신기술은 그 자체로써 생산성 향상의 직접적 요인으로 작용하는 동시에 기술전파 요인으로써 간접 적으로 생산성 향상에 기여한다. 특히 기술전파 요인이라는 차원에서, 정보통신기술이 기술확산의 원천으로 작용한다는 점에 대한 많은 관심이 필요하다. 그러나 기술확산에 대한 기존의 많은 연구에도 불구하고, 경제성장 수렴에 대한 논의에 있어서 정보통신 기술을 기술확산에 접목한 이론적 연구는 많지 않다. 이러한 선행연구의 미비한 부분 에 착안하여, 본 연구는 정보통신기술과 경제성장률 간의 관계를 살펴보는 데 있어서 비선형 함수 구조를 설정한다. 본 논문은 준모수적 추정 방법의 일종인 부분선형모형 을 이용하여 정보통신기술과 경제성장수렴의 관계를 살펴보고자 한다. 또한, 본 논문 은 부분선형모형의 추정결과와 고정효과모형의 추정결과를 비교한다. 본 연구의 실중 분석 결과에 따르면 정보통신기술 요인을 비선형함수에 포함시켜 이를 통제할 경우 회귀분석모형의 종속변수인 경제성장률의 관측주기가 낮아짐에 따라 1인당 GDP 설명 변수의 회귀분석계수 추정값은 그 절대값이 증가한다. 또한, 부분선형모형 추정으로부 터 도출된 1인당 GDP 설명변수의 회귀분석계수 추정값은 고정효과모형 추정 결과에 비해 그 값이 전반적으로 더 크다는 결과를 발견한다. 이러한 분석결과는 정보통신기 술 변수의 비선형 특성을 고려할 때 경제성장수렴 현상을 보다 더 잘 이해할 수 있다는 시사점을 제공한다. 또한 본 논문은 부분선형모형의 모형설정이 적합한 지 여부를 검정하며, 그 검정결과로부터 정보통신기술을 비선형모형으로 설정하는 것이, 선형모 형으로 설정하는 것에 비해 더 적합함을 발견하였다. 또한, 본 논문은 비선형모형을 곡선 형태로 추정할 경우 그 형태가 역 U자임을 발견한다. 이러한 비선형함수의 형태는 정보통신기술이 경제성장에 기여하는데 있어서, 최적값이 존재함을 암시한다. 이상 의 결과들을 종합할 때 본 연구는 비선형 모형이 정보통신기술과 경제성장의 관계를 파악하는데 있어서 유용하다는 시사점을 제공한다.

Over the past decades, many economies observed that the development of Information and Communication Technology (ICT) has increased productivity in various industries. This paper empirically examines an economic growth convergence under the presence of the ICT by using panel data for 36 Asian countries from 1990 to 2017. The ICT can directly work as a driving force for productivity and indirectly as a technology propagator. As a technology propagator, the ICT deserves more attention as a source of technology diffusion. Despite many existing studies on the diffusion, theoretical studies have not yet incorporated the ICT into the diffusion issue in discussing the growth convergence. Responding to the unfilled gap in the literature, we impose a nonlinear functional form on the relation between the ICT and economic growth rate. In this paper, we employ a semi-parametric partially linear model (PLM) to relate the ICT elements to the growth convergence. In this paper, we compare fixed-effect results to the PLM results. Our results show that, controlling the ICT nonlinearly, the absolute size of the estimates for the GDP per capita increases as the frequency of growth rates becomes lower. We also find that, for the GDP per capita, the PLM estimates’ absolute values are greater relative to the fixed-effect results for all the frequencies. Our findings imply that considering nonlinearity of the ICT variable enhances understanding of economic growth convergence. We also perform the specification-fit test for PLM estimation and find that the nonlinear specification of the ICT variable is suitable. Further, we observe that the fitted curves of nonlinear functions are hump-shaped for all the frequencies. Then, it is implied that there can exist optimal level of the ICT for its contribution to the economic growth. In sum, all the results suggest that nonlinear modeling is a suitable empirical strategy for the relationship between the ICT and economic growth.

This study was conducted to estimate the best-fit nonlinear height-DBH growth models for Larix kaempferi in Gangwon and North Gyeongsang province in South Korea. Exponential, Modified Logistic, Chapman-Richards, and Weibull function were used for estimating height-DBH models. To evaluate the selected models, R2, RMSE, MD, MAD, and residual plots were performed in each model. Also, the coefficients and patterns in models of the previous studies were compared with those in this study. The result showed that Weibull equation was found to be the best-fit model with R2=0.9837, RMSE=2.6133, MD=0.0089, and MAD=2.0896. All model parameters in our study had similar values to those in the previous models except for asymptotic parameter a. Our research result showed that Gangwon and North Gyeongsang province were superior to other provinces with regard to height growth for Larix kaempferi.

역투자전략(contrarian investment strategy)에 대한 실증분석은 이 전략이 기반하고 있는 주식가격의 평균회균성향에 대한 검증으로 통상 주식가격지수의 편차에 대한 단위근 검정을 통해 이루어진다. 최근의 많은 단위근 검증을 사용한 실증분석들이 시계열의 비선형성을 고려하여야 한다는 지적을 수용하여 본 논문은 비선형 단위근 검증방법을 사용하고 있다. Morgan Stanley Capital International의 12개 Asian 시장의 주식가격지수로 Taylor 근사치에 기반하지 않는 Park and Shinatni (2005, 2010)의 비선형 단위근 검증방법인 inf-t 테스트를 적용할 경우 주식가격지수는 평균회귀성향을 보이지 않았다. inf-t 테스트 결과는 또한 D-LSTAR 모형보다 보다 단순한 B-TAR 모형이 주식가격지수의 비선형성을 잘 잡아낼 수 있음을 보여준다. 실증분석 결과는 주식가격의 평균회귀성향에 기반하고 있는 역투자전략의 유효성을 뒷받침하지 않고 있는 것이다.

One of the major assumptions of the contrarian investment strategy is the mean reversion property of the asset prices. Despite of extensive studies, however, empirical evidence of mean reversion in the stock prices still remains elusive. I revisit this issue by applying nonlinear unit root test developed by Park and Shintani (2005, 2010). Using Morgan Stanley Capital International (MSCI) stock price indices for 12 Asian markets, I find that the stock price indices deviations from reference price for Asian markets are not mean-reverting. National stock price deviations may take infinite time to become halfway to the long-run equilibrium values which serves evidence against the usefulness of contrarian strategy.

This paper propose a new short-term interest rate model having a different nonlinear drift function and the same diffusion coefficient with Chan, Karolyi, Longstaff, and Sanders (1992) model. The fractional polynomial power of the drift function in our model is linked to the local volatility elasticity of the diffusion coefficient. While the nonlinear drift function estimated by A¨ıt-Sahalia (1996a) and others has a feature that higher interest rates tend to revert downward and low rates upward, the drift function estimated by our nonlinear model shows that higher interest rate mean-reverts strongly, but, medium rates has almost zero drift and low rates has a very small drift. This characteristic coincides the empirical result based on the nonparametric methodology by Stanton (1997) and the implication by the scatter plot of the short rate data. Furthermore, if our model is transformed to make the diffusion process have a constant term, the drift term in our model is very similar to that in A¨ıt-Sahalia model. In the viewpoint of data, while his model is applied to the original interest rate data, our model is applied to the transformed data.

This study investigates the role of powerful CEOs on future stock price crashes. Our results reveal an inverted U-shaped relationship between CEO power and stock price crash risk. Specifically, powerful CEOs tend to conceal more negative news, increasing stock price crash risk, which indicates the presence of incentives to take private benefits. However, extremely powerful CEOs decrease stock price crash risk, suggesting that sufficient entrenchment may mitigate further private benefits from concealing negative news. Additionally, the nonlinear relationship is observed only in competitive industries. This fact implies that strong external monitoring mitigates CEOs’ incentives to pursue private benefits, but raises extremely powerful CEOs’ career concerns, which encourages them to conceal more negative news.

본 연구는 고등학교 학생 중 학교 부적응자 결정요인을 개인수준의 주관적 자료가 아닌 학교 수준의객관적 자료에 근거하여 분석하는데 목적이 있다. 기존 연구들을 포괄할 수 있는 변수로서 학교, 교육, 교사, 학생, 부모 및 가정 요인들이 학교 부적응에 미치는 영향을 검증하였다. 검증결과 첫째, 지역적으로 학교가 대도시에 비해 중소 도시, 읍면지역에 위치할수록, 학교의 규모가 커질수록 부적응자수가 많아지고, 학교의 재정이 안정적일수록 부적응자는 줄어들었다. 둘째, 교육프로그램으로서 방과후 교과 프로그램 비율이 높아질 때 부적응자가 감소하였으며, 셋째, 교사에서는 성과급의차등지급이 증가할수록, 전문성 있는 교사의 비율이 높아질수록 부적응자가 감소하였다. 넷째, 학생요소에서는 기초학력 미달 학생들의 비율이 높아질수록 부적응자수가 많아지는 것으로 나타났으며, 관계적인 측면에서 동아리 활동이 많아질수록 부적적응자수가 감소하였다. 마지막으로 부모 및 가정 요소에서 경제적인 측면을 나타내는 급식학생 비율, 보호자 지원비율이 높을수록 부적응자 수가감소하고 있다.

This paper examines possible causal relationships of high school dropouts in the lights of 5 major categories: school, educational program, teachers and staff, students, parents and their families. Since the number of high school dropouts – a count variable – is a dependent variable in our model, the Poisson regression model with three-year panel data from 2011 to 2013 is used. Empirical findings are as follows; (1) high school dropouts are more likely to be from small or middle cities than big cities while a school’s size is positively associated with the number of dropouts, (2) after-school programs help students stay in school, (3) incentive for teachers seems to be working positively, (4) academic performance of each student is one of the main determinants for dropping out, and (5) family’s financial stability also plays a significant role in reducing dropouts.

The purpose of this study was to investigate the effect of combined lin-ear and nonlinear periodic training on physical fitness and competition times in finswimmers. The linear resistance training model (6 days/week) and nonlinear underwater training (4 days/week) were applied to 12 finswimmers (age, 16.08±1.44 yr; career, 3.78±1.90 yr) for 12 weeks. Body composition measures included weight, body mass index (BMI), percent fat, and fat-free mass. Physical fitness measures included trunk flexion forward, trunk extension backward, sargent jump, 1-repeti-tion-maximum (1 RM) squat, 1 RM dead lift, knee extension, knee flex-ion, trunk extension, trunk flexion, and competition times. Body compo-sition and physical fitness were improved after the 12-week periodic training program. Weight, BMI, and percent fat were significantly de-creased, and trunk flexion forward, trunk extension backward, sargent jump, 1 RM squat, 1 RM dead lift, and knee extension (right) were sig-nificantly increased. The 50- and 100-m times significantly decreased in all 12 athletes. After 12 weeks of training, all finswimmers who partici-pated in this study improved their times in a public competition. These data indicate that combined linear and nonlinear periodic training en-hanced the physical fitness and competition times in finswimmers.