• The Korean Journal of Applied Statistics
• /
• v.20 no.2
• /
• pp.357-371
• /
• 2007

For the time-to-failure data with competing risks, cumulative incidence functions (CIFs) are commonly estimated using nonparametric methods. If the cases of events due to the cause of primary interest are infrequent relative to other cause of failure, nonparametric methods may result in rather imprecise estimates for CIF. In such cases, Bryant et al. (2004) suggested to model the cause-specific hazard of primary interest parametrically, while accounting for the other modes of failure using nonparametric estimator. We represented the semiparametric cumulative incidence estimator and extended to the model of Weibull and log-normal distribution. We also conducted simulations to access the performance of the semiparametric cumulative incidence estimators and to investigate the impact of model misspecification in log-normal cause-specific hazard model.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.15 no.4
• /
• pp.823-832
• /
• 2011

In this paper, an efficient blind carrier frequency offset (CFO) estimation method in orthogonal frequency division multiplexing (OFDM) systems is proposed. In the proposed method, we obtain two time different received OFDM symbols by using both the cyclic prefix and oversampling technique, and a cost function is defined by using the two OFDM symbols. We show that the cost function can be approximately expressed as a cosine function. Using a property of the cosine function, a formular for estimating the CFO is derived. The estimator of the CFO requires three independent cost function values calculated at three different points of frequency offset. The proposed method is very efficient in computational complexity since no searching operation for the minimum cost value is required. The proposed method reduces 97% of the amount of FFT computation, compared with the ML method. Unlike the conventional methods such as the ML method and the MUSIC] method, the accuracy of the proposed method is independent of the searching resolution since the closed form solution exists. The computer simulation shows that the performance of the proposed method is superior to those of the MUSIC and the ML method.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2000.11a
• /
• pp.15-18
• /
• 2000

인터넷을 포함한 여러 가지 기술이 발전됨에 따라 인터넷 광고 시장도 두드러지게 성장하고 있다. 무한한 가상 공간과 디지털이 갖는 신속성, 편리함 등 다양한 서비스를 제공할 수 있는 인터넷 기반의 모든 서비스는 데이터베이스로 축적된다. 여기에 애매함과 불확실성을 가지는 실세계를 표현하기 위해 퍼지논리함수를 이용하여 효율적으로 방문객을 분류하는 방법을 제시한다.

• Communications of Mathematical Education
• /
• v.18 no.1 s.18
• /
• pp.99-109
• /
• 2004

이 논문에서는 연립방정식 및 연립부등식의 보다 나은 이해와 효율적인 지도를 위해 부동점 정리와 함께 부동점 정리와 동치인 몇 가지 주요 정리를 먼저 소개하고, 일가함수의 부동점 정리와 연립방정식의 관계성 및 집합가 함수의 부동점 정리와 연립부등식과의 관계성을 다룬다.

• Review of KIISC
• /
• v.5 no.3
• /
• pp.15-37
• /
• 1995

본 고에서는 CDMA 이동 통신망에 적용 가능한 인증 시스템을 제시한다. 이를 위하여 먼저 IS-95에 표준화된 인증과 관련된 파라메타와 인증 절차를 분석하고, 인증 시스템에 응용될 수 있는 해쉬 함수의 개념과 원리를 제시하며, 이를 바탕으로 이동 통신에 적용 가능한 해쉬 함수에 바탕을 둔 인증 시스템을 제시하고, 제시된 인증시스템을 시뮬레이션 한다.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.6 no.2
• /
• pp.87-90
• /
• 1977

핀(fin) 재료의 열전도계수는 온도에 따라 직선적으로 변한다고 가정하여 일차적, 정상상태의 해석을 하였다. 정밀해는 타원적분의 함수로 표시된다. 핀(fin) 효율은 핀끝의 온도의 함수로 주어졌다. 계산을 용이하게 하기 위하여 perturbation해도 구하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.5
• /
• pp.1559-1569
• /
• 2014

The purpose of this study is to estimate the degree of cost inefficiency for the urban railway lines of a metropolitan city operated by public institutions in Korea and identify the causes of this inefficiency. To this end, we assume that the urban railway lines produce the output of train-km by putting three production factors of labor, electric power and maintenance and set the variable cost function model with the translog function to make a stochastic cost frontier analysis. Based on estimated result, we conclude that the cost savings for 6 years of all lines are about 6,672 hundred million won and top five lines with high inefficiency are Busan Line1, Daegu Line1, Daejeon Line1, Gwangju Line1, and Daegu Line2. The causes of inefficiency are attributable to labor and maintenance factors. The results of this study can be useful in case of finding the priorities of measures and specific plans for reducing labor and maintenance costs in the urban railway operation.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.51 no.5
• /
• pp.29-34
• /
• 2014

We introduce a number of antenna optimization problem for the zero-forcing beamforming (ZFBF) scheme to enhance energy-efficiency (EE) of the multiple-input-multiple-output broadcast channel. For proposed optimization problem, we assume an instantaneous channel gain of the ZFBF scheme as an average channel gain, given by $N_a-K+1$, in order to reduce a computational complexity of finding the number of active antennas $N_a$. Then, we convert a fractional-form objective function into a subtractive-form, and find a solution of $N_a$ and the maximum EE by an iterative process. Simulation results show that the maximum EE value obtained by proposed algorithm is almost identical to the optimal EE value by the exhaustive search method.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.5
• /
• pp.267-275
• /
• 2022

Using a nonconforming mesh in enrichment methods results in several numerical issues induced by discontinuities and singularities found within the solution spaces, including the computational overhead during integration. In this study, we present a novel enrichment technique based on the selective expansion technique of moment fitting (Düster and Allix, 2020). In particular, two modifications are proposed to address the inefficiency during the integration process. First, a feedforward artificial neural network is introduced to correlate the implicit functions and integration moments. Through numerical examples, it is shown that the efficiency of the method is greatly improved when compared with existing expansion techniques, whereas the solution accuracy is maintained. Additionally, the finite element and domain representation grids are separated, which in turn improves the solution accuracy even for coarse mesh conditions.

• Journal of the Korean Data and Information Science Society
• /
• v.5 no.2
• /
• pp.29-44
• /
• 1994

본 연구는 누적위험률함수에 대한 베이지안 추정량을 이용하여 생존함수의 추정량을 제안하고, counting process 이론과 martingale 이론을 이용하여 대표본하에서 제안된 추정량의 일양적 일치성과 점근적 정규성을 밝힌다. 또한 모의실험을 통하여 추정량들의 효율성을 편의와 평균제곱오차의 측면에서 비교하고자 한다.