• 응용통계연구
• /
• 제34권2호
• /
• pp.239-254
• /
• 2021

이 논문에서는, 2개의 혼합된 t-분포(TP-T)의 오차과정을 따르는 이질적 자기회귀 (HAR) 모형을 이용하여, 한국 코로나 (COVID-19) 확진자 수 데이터에 대한 시계열 분석, 즉 추정과 예측에 대하여 연구한다. HAR-TP-T 시계열 모형을 고려하여 HAR 모형의 계수 뿐 아니라 TP-T 오차과정의 모수를 추정하고자 단계별 추정법을 제안한다. 본 연구에서 제안하고 있는 단계별 추정법은, HAR 계수 추정을 위해서는 통상적 최소제곱추정법을 채택하고, TP-T 모수 추정을 위해서는 최대우도추정법을 이용한다. 단계별 추정법에 대한 모의실험을 수행하여, 성능이 우수함을 입증한다. 한국 코로나 확진자 수에 대한 실증적 데이터 분석에서, HAR 모형에서의 차수 p = 2, 3, 4에 대해, 모형의 평균제곱오차가 최소가 되도록 하는 최적화 시간간격(optimal lag)을 포함하여, 여러가지 시간간격을 고려한 HAR-TP-T 모형의 모수 추정값을 계산한다. 제안된 단계별 추정방법과 기존의 MLE만의 방법을, 추정 결과를 제시함으로 함께 비교한다. 본 연구에서 제안하고 있는 추정은 두 가지의 오차 측면, 즉 HAR 모형의 평균제곱오차와 잔차분포에 대한 밀도함수 추정의 평균제곱오차, 두 측면에서 모두 우수함을 입증하였다. 나아가, 추정 결과를 활용한 코로나 확진자 수 예측을 수행하였고, 예측정확도의 한 측도로서 mean absolute percentage error (MAPE)를 계산하여 0.0953%의 매우 작은 오차값을 얻었다. 본 연구에서 선택한 최적화 시간간격을 고려한 HAR-TP-T 시계열 모형 및 단계별 추정 방법은, 정확한 한국 코로나 확진자 수 예측 성능을 제공한다고 할 수 있다.

• 한국정보처리학회논문지
• /
• 제6권3호
• /
• pp.710-721
• /
• 1999

In this paper, we have designed and implemented a parameter extraction system for analyzing Internet using SNMP. The extraction system has two modules; one is collection request module, and the other is analysis request module. The collection request module generates a polling script, which is used to collect management information from the managed system periodically. With this collected data, analysis request module extracts analysis parameters. These parameters are traffic flow analysis, interface traffic analysis, packet traffic analysis, and management traffic analysis parameter. For management activity, we have introduced two-step-analysis-view. One is Summary-View, which is used find out malfunction of a system among the entire managed systems. The Other is Specific-View. With this view we can analyze the specific system with all our analysis parameters. To show available data as indicators for line capacity planning, network redesigning decision making of performance upgrade for a network device and things like that.

• 한국운동역학회지
• /
• 제27권1호
• /
• pp.75-81
• /
• 2017

Objective: The purpose of this study was to compare and analyze the kinematic variables and electromyography (EMG) findings that change with varying characteristics of crouch start and feedback provision, and to provide the fundamental data for record improvement in 400 mH. Method: Four short-distance runners participated in the experiment. The analyzed variables were elapsed time per interval, stride length, and muscle activities in three lower limb muscles. These variables were analyzed by using Kwon3d XP and Noraxon Myoresearch. The participants were subjected to three conditions, including two conditions that relate to the thrusting foot on the rear block and another condition pertinent to feedback provision. Results: In terms of a one-step interval, the elapsed time in condition A was longer than that in condition B, and the one after the feedback was the longest. The stride length of a one-step interval was the longest in condition A. The stride length of a two-step interval was the shortest in condition A. The muscle activity during a one-step interval showed differences in vastus medialis and medial gastrocnemius, with condition A being the highest. Conclusion: When the non-dominant left foot was located at the back, negative results were observed in terms of elapsed time and stride length. Moreover, an imbalance in muscle activity was observed between the left and right feet when the left foot was placed at the back. As a result, significant differences in elapsed time, stride length, and muscle activity were observed depending on the foot placed on the rear block. In conclusion, we identified the characteristics of crouch start in 400 mH, and a specialized program must be suggested.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
• /
• pp.70-73
• /
• 2000

This paper present a new sort of multilayer piezoelectric ceramic transformer for AC-adapter. This piezoelectric transformer operates in the second longitudinal vibration mode. The output voltage of the multilayer piezoelectric transformer was simulated using ANSYS, that is one of the FEM analysis program. As results, the minimum displacement was occurred at the two paints where one is the middle of input and the other is middle of output side in second thickness extensional vibration mode. And output voltage was inversely decreased by increasing number of output layers. 缀Ѐ㘰〻ሀ䝥湥牡氠瑥捨湯汯杹

• 한국지능정보시스템학회:학술대회논문집
• /
• 한국지능정보시스템학회 2007년도 한국지능정보시스템학회
• /
• pp.329-337
• /
• 2007

Case-based reasoning (CBR) methods are applied to various target problems on the supposition that previous cases are sufficiently similar to current target problems, and the results of previous similar cases support the same result consistently. However, these assumptions are not applicable for some target cases. There are some target cases that have no sufficiently similar cases, or if they have, the results of these previous cases are inconsistent. That is, the appropriateness of CBR is different for each target case, even though they are problems in the same domain. Thus, applying CBR to whole datasets in a domain is not reasonable. This paper presents a new hybrid datamining technique called two-step filtering CBR and Rule Induction (TSFCR), which dynamically selects either CBR or RI for each target case, taking into consideration similarities and consistencies of previous cases. We apply this method to three medical diagnosis datasets and one credit analysis dataset in order to demonstrate that TSFCR outperforms the genuine CBR and RI.

• 천문학회지
• /
• 제42권3호
• /
• pp.61-69
• /
• 2009

Transverse velocity vectors can be determined from a pair of images successively taken with a time interval using an optical flow technique. We have tested the performance of the new technique called NAVE (non-linear affine velocity estimator) recently implemented by Chae & Sakurai using real image data taken by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. We have developed two methods of estimating the errors in the determination of velocity vectors, one resulting from the non-linear fitting ${\sigma}_{\upsilon}$ and the other ${\epsilon}_u$ resulting from the statistics of the determined velocity vectors. The real error is expected to be somewhere between ${\sigma}_{\upsilon}$ and ${\epsilon}_u$. We have investigated the dependence of the determined velocity vectors and their errors on the different parameters such as the critical speed for the subsonic filtering, the width of the localizing window, the time interval between two successive images, and the signal-to-noise ratio of the feature. With the choice of $v_{crit}$ = 2 pixel/step for the subsonic filtering, and the window FWHM of 16 pixels, and the time interval of one step (2 minutes), we find that the errors of velocity vectors determined using the NAVE range from around 0.04 pixel/step in high signal-to-noise ratio features (S/N $\sim$ 10), to 0.1 pixel/step in low signa-to-noise ratio features (S/N $\sim$ 3) with the mean of about 0.06 pixel/step where 1 pixel/step corresponds roughly to 1 km/s in our case.

• 대한기계학회논문집B
• /
• 제29권1호
• /
• pp.87-94
• /
• 2005

A computer code for Electrical Capacitance Tomography (ECT) is developed to sense the cross sectional phase distribution of two-phase flow in the rectangular pipe in which the tomography sensor furnished by the insulated wall, electrodes, and electric field screen. The computer code had two steps for the image reconstruction. In the forward projection step, the sensitivity matrix was constructed based on the electric field calculated by the finite difference method. In the backward projection step, the sensitivity matrix and the measured capacitances were used to reconstruct the cross sectional image. Several algorithms including LBP, TR, ITR, and PLI were employed to find the proper one for the two-phase flow analysis. Since the dielectric constant of the water in two-phase flow is sensitive to the thermal parameter such as, temperature and pressure, the developed code was evaluated to find their accuracy, speed of calculation, and sensitivity to the variation of the dielectric constant. It was found that the iterative methods are superior to the direct methods for the image reconstruction, and the PLI method was the best in the variation of the dielectric constants.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 추계학술대회논문집
• /
• pp.806-811
• /
• 2007

In this study, we propose a more systematic design process for the structure-borne noise. The proposed way consists of 4 steps: Problem definition, Cause analysis, Development of counter-measure and Validation. Especially, we improved the second step: Cause analysis. According to the PCA(Panel Contribution Analysis), a reduction in vibration of the panels of which panel contribution is positive and larger, results in a reduction in structure-borne noise. We have, however, met the case in which the concept of PCA is no valid in a few vehicle tests. In order to understand this phenomenon, we compared the major panels selected by PCA with the one chosen by DSA(Design Sensitivity Analysis). After investigating the difference between the two results, a more improved process is suggested. The proposed one for the second step in the design process consists of not only the previous way: PCA with deformation analysis results but also DSA. It is finally validated that the proposed design process decreases the sound pressure of the concerned noise transfer function more than 3.5 dB.

• Journal of the Korean Statistical Society
• /
• 제29권4호
• /
• pp.435-441
• /
• 2000

Ko(1998, 1999) proposed certain flexible two-stage plans that could be served as one-step interim analysis in on-going clinical trials. The proposed Plans are optimal simultaneously in both a Bayes and a Neyman-Pearson sense. The Neyman-Pearson interpretation is that average expected sample size is being minimized, subject just to the two overall error rates $\alpha$ and $\beta$, respectively of first and second kind. The Bayes interpretation is that Bayes risk, involving both sampling cost and wrong decision losses, is being minimized. An example of this correspondence are given by using a binomial setting.

• 대한기계학회논문집A
• /
• 제23권7호
• /
• pp.1129-1138
• /
• 1999

[$Moir\acute{e}$] technique is now being extensively investigated as a fast non-contact means of three-dimensional profile measurement especially for reverse engineering. One problem with $moir\acute{e}$ technique is so called $2\pi$-ambiguity problem that limits the maximum step height difference between two neighboring sampling points to be less than half the equivalent wavelength of $moir\acute{e}$ fringes. In this investigation, a new two-wavelength scheme of projection $moir\acute{e}$ topography is proposed and tested to cope with the $2\pi$-ambiguity problem. Experimental results are discussed to assess the new method in measuring large objects with high step discontinuities.