• Korea Trade Review
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• v.48 no.1
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• pp.83-126
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• 2023

The revenue histogram of venture businesses is shifting from bell-shaped normal distribution to power-law distribution, which implies that the fitness landscape of the venture businesses ecosystem is changing to be more rugged terrain. We argue that the firm should adopt both exploitation (fast follower) and exploration (or first mover) strategies not to get stuck in local maxima in the rugged fitness landscape from the complex system perspective. By designing and performing agent-based modeling simulation experiments which consist of three types of agents (new technologies, entrepreneurs, and consumers), we demonstrated that the ambidexterity strategy showed the highest performance score in three of four different environment except 'Fast Widening' case where the exploitation strategy showed the highest performance score under low technology appropriation and fast disruptive technology development speed. By investigating the financial and other statistics of 617 top venture businesses who have earned 100B won or higher annual revenue, we concluded that 82% and 9% of firms are bent on the exploitation and exploration strategy.

• Communications for Statistical Applications and Methods
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• v.18 no.3
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• pp.377-389
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• 2011

A higher quality level is generally perceived by customers as improved performance by assigning a correspondingly higher satisfaction score. The third generation index $C_{pmk}$ is more powerful than two useful indices $C_p$ and $C_{pk}$ that have been widely used in six sigma industries to assess process performance. In actual manufacturing industries, process capability analysis often entails characterizing or assessing processes or products based on more than one engineering specification or quality characteristic. Since these characteristics are related, it is a risky undertaking to represent the variation of even a univariate characteristic by a single index. Therefore, the desirability of using vector-valued process capability index(PCI) arises quite naturally. In this paper, we consider more powerful vector-valued process capability index $C_{pmk}$ = ($C_{pmkx}$, $C_{pmky}$)$^t$ that consider the univariate process capability index $C_{pmk}$. First, we examine the process capability index $C_{pmk}$ and plug-in estimator $\hat{C}_{pmk}$. In addition, we derive its asymptotic distribution and variance-covariance matrix $V_{pmk}$ for the vector valued process capability index $C_{pmk}$. Under the assumption of bivariate normal distribution, we study asymptotic confidence regions of our vector-valued process capability index $C_{pmk}$ = ($C_{pmkx}$, $C_{pmky}$)$^t$.

• The Korean Journal of Applied Statistics
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• v.34 no.3
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• pp.449-460
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• 2021

ASVspoof 2017 deals with detection of replay attacks and aims to classify real human voices and fake voices. The spoofed voice refers to the voice that reproduces the original voice by different types of microphones and speakers. data augmentation research on image data has been actively conducted, and several studies have been conducted to attempt data augmentation on voice. However, there are not many attempts to augment data for voice replay attacks, so this paper explores how audio modification through data augmentation techniques affects the detection of replay attacks. A total of 7 data augmentation techniques were applied, and among them, dynamic value change (DVC) and pitch techniques helped improve performance. DVC and pitch showed an improvement of about 8% of the base model EER, and DVC in particular showed noticeable improvement in accuracy in some environments among 57 replay configurations. The greatest increase was achieved in RC53, and DVC led to an approximately 45% improvement in base model accuracy. The high-end recording and playback devices that were previously difficult to detect were well identified. Based on this study, we found that the DVC and pitch data augmentation techniques are helpful in improving performance in the voice spoofing detection problem.

• The Korean Journal of Applied Statistics
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• v.34 no.2
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• pp.239-254
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• 2021

This paper studies time series analysis with estimation and forecasting for Korean COVID-19 confirmed cases, based on the approach of a heterogeneous autoregressive (HAR) model with two-piece t (TP-T) distributed errors. We consider HAR-TP-T time series models and suggest a step-by-step method to estimate HAR coefficients as well as TP-T distribution parameters. In our proposed step-by-step estimation, the ordinary least squares method is utilized to estimate the HAR coefficients while the maximum likelihood estimation (MLE) method is adopted to estimate the TP-T error parameters. A simulation study on the step-by-step method is conducted and it shows a good performance. For the empirical analysis on the Korean COVID-19 confirmed cases, estimates in the HAR-TP-T models of order p = 2, 3, 4 are computed along with a couple of selected lags, which include the optimal lags chosen by minimizing the mean squares errors of the models. The estimation results by our proposed method and the solely MLE are compared with some criteria rules. Our proposed step-by-step method outperforms the MLE in two aspects: mean squares error of the HAR model and mean squares difference between the TP-T residuals and their densities. Moreover, forecasting for the Korean COVID-19 confirmed cases is discussed with the optimally selected HAR-TP-T model. Mean absolute percentage error of one-step ahead out-of-sample forecasts is evaluated as 0.0953% in the proposed model. We conclude that our proposed HAR-TP-T time series model with optimally selected lags and its step-by-step estimation provide an accurate forecasting performance for the Korean COVID-19 confirmed cases.

• The Korean Journal of Applied Statistics
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• v.37 no.2
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• pp.209-224
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• 2024

Speaker verification is becoming popular as a method of non-face-to-face identity authentication. It involves determining whether two voice data belong to the same speaker. In cases where the criminal's voice remains at the crime scene, it is vital to establish a speaker verification system that can accurately compare the two voice evidence. In this study, to achieve this, a new speaker verification system was built using a deep learning model for Korean language. High-dimensional voice data with a high variability like background noise made it necessary to use deep learning-based methods for speaker matching. To construct the matching algorithm, the ECAPA-TDNN model, known as the most famous deep learning system for speaker verification, was selected. A large dataset of the voice data, Voxceleb, collected from people of various nationalities without Korean. To study the appropriate form of datasets necessary for learning the Korean language, experiments were carried out to find out how Korean voice data affects the matching performance. The results showed that when comparing models learned only with Voxceleb and models learned with datasets combining Voxceleb and Korean datasets to maximize language and speaker diversity, the performance of learning data, including Korean, is improved for all test sets.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5A
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• pp.397-401
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• 2005

A different alternative method for simulating bit error rate(BER) performance of Satellite Digital Multimedia Broadcasting(DMB) in tunnel environments is presented. The method based on a channel model obtained by ray-tracing is able to support BER estimation over the channel presents arbitrary statistics that are difficult to fit to an analytic expression. The BER performance for System E over the tunnel fading channel that obtained by ray-tracing is predicted by the monte-carlo method. It can be observed that the BER performance for a straight tunnel channel is better than that for a line-of-sight(LOS) area in curved tunnel. Also, the BER performance for LOS areas in a curved tunnel outperforms that for non-line-of-sight(NLOS) areas in a curved tunnel. The BER performances for straight, curved LOS and curved NLOS tunnel channels are better than that for a Rayleigh channel(K=0) and less than that for a Rician channel with K=3. Moreover, for BER=10-3, it can be seen that there is approximately a $1{\sim}1.5\;dB$ difference between those three types of tunnel channels and a Rayleigh channel.

• Ocean Systems Engineering
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• v.10 no.2
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• pp.201-226
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• 2020

A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. un the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.

• Journal of Korean Academy of Nursing Administration
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• v.7 no.3
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• pp.497-509
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• 2001

The purpose of this study was to examine frequency of job performance, level of urgency, index of importance experienced by 138 new nurses who were working at 6 hospitals that had over 400 bed in Incheon and Bucheon. The data were analyzed using a SPSS program for descriptive statistics [numbers of job performance, level of urgency, index of importance(job performance+1/4 level of urgency)]. Some of the most frequent job performance were application of aseptic technique, application of principle of infection control, and medication (IV, PO, IM, supply fluid and electrolyte). Some of the most uncommon job performance were activity as a lecturer in nursing department, activity of arrangement of community resources, and participation in multidisciplinary conference. Some of the highest level of urgency were use of aseptic technique, CPR, application of principle of infection control, defibrillation for dysrhythmia, blood transfusion, observation of patient's status in procedure (operation), v/s check, intervention for improvement of respiratory function and medication of antihypertensives. Some of the lowest level of urgency were activity as a lecturer in nursing department, preceptor's activity, supervisor and delegation of job to nurse aids, attendance at nursing conference, activity of arrangement of community resources, participation in clinical teaching practice, participation in multidisciplinary conference, and delegation of patient care. Those were indirect patient care. The order was physiologic integration(60.99%), safety and effective nursing environment, psychosocial care, and health maintenance and improvement. The most importance item in maintenance of physiologic integration was medication. Some of the highest index of importance were aseptic technique and application of principle of infection control, v/s check, observation of patient's status in operation and medication. Some of the lowest index of importance were activity as a lecturer in nursing department, preceptor's activity, activity of arrangement of community resources, participation in multidisciplinary conference, nursing conference, participation in clinical teaching, and delegation of job to nurse aids.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.15 no.2
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• pp.191-202
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• 2011

Objectives: The questionnaires of body condition were developed to increase golf performance and to find psychological factors in junior golfer. This study was how much golf performances got improved after acupuncture treatment. Methods: October $28^{th}$, $29^{th}$ 2010 and January 2011, 130 junior golfers were taken 8 questionnaires. Sixty junior golfer of them were selected, twenty of them were taken acupuncture treatment spontaneously and forty of them were not taken it. The acupoints were K10, H3, Sp3, H7. The statistics was used paired student t-test of before and after treatment and correlates analysis for analyzing relationship with questionnaires. Results: 1. The result of reliability among questionnaires was signified. 2. About questionnaires, golf score was related with satisfied shots, to endure hungry and about digestion. (p<0.5) 3. Anxiety was related with pain in ribs, about sleep, about bowl movement and about digestion. 4. It was obtained Regression equation of 41.9 % prediction between anxiety and 4 questionnaires. 5. The result of paired T-Test, the difference was $2.45{\oplus}4.69$ between $1^{st}$ score and $2^{nd}$ score in acupuncture treated group. (p<0.05) Conclusions: This study was important to improve golf performance with Asian medicine. Further clinical research is necessary to develop more delicate analyses and questionnaires. Also through the diagnosis and corresponding treatments based on the Asian Medicine, the ways of improving golf performance should be developed.

• The Journal of the Korea Contents Association
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• v.10 no.8
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• pp.392-397
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• 2010

The purpose of this study was to examine the effects of self management and mental power on athletic performance. To attain the goal of the study some athletics of D city physical education middle school, high school, University in D city. Then, using the physical education middle and high school were complete collection, and University were random sampling method, finally drew out and analyzed 353 athletics in total. Data collected through a questionnaire designed for this study consist of fixed alternative choice response to items constructed to represent the operational definition for each variable. Statistics employed for data analysis was correlation and regression. Based upon the results of the study, the following conclusions appear warranted: 1. Self management influence on athletic performance. 2. Mental power influence on athletic performance.