• The Journal of the Acoustical Society of Korea
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• v.16 no.2E
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• pp.21-26
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• 1997

We propose to use transverse waves instead of longitudinal waves in a scanning tomographic acoustic microscope (STAM) and new type of multiple-transducer with the functions of muliple-angle and multiple-frequency tomography. Proposed multiple-transducer scheme has three insonification angles and three resonance frequencies in order to operate in the transverse wave mode and multiple-angle and multiple frequency tomography for the STAM. In order to evaluate the performance of proposed transducer scheme we have simulated tomographic reconstruction with back-and-forth propagation(BFP) algorithm. Simulation results showed proposed multiple-transducer scheme is capable of obtaining good resolution with transverse wave mode and multiple-frequency tomography. It is also showed that proposed scheme is an efficient rotation scheme by proportion to the number of projections.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.7
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• pp.26-40
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• 2010

We propose a new routing protocol, MCQosR, that is based on bandwidth estimation, admission control, and a routing metric, MCCR - suitable for wireless ad-hoc networks with multiple radios and channels. To use the full capacity of a wireless link, we assume a node with multiple radios for full duplex operation, and a radio using multiple channels to exclude route-intra interference. This makes it possible to use the capacity of a wireless link. Then, to provide bandwidth and delay guarantee, we have a radio with a fixed channel for layer-3 data reception at each node, used to estimate the available bandwidth and expected delay of a wireless link. Based on the estimate of available bandwidth and delay, we apply the call admission control to a new call requiring bandwidth and delay guarantee. New calls with traffic that will overflow link or network capacity are rejected so the accepted calls can use the required bandwidth and delay. Finally, we propose a routing metric, MCCR, which considers the channel contentions and collisions of a wireless link operating in CSMA/CA. MCCR is useful for finding a route with less traffic and distributing traffic over the network to prevent network congestion as much as possible. The simulation of the MCQosR protocol and the MCCR metric shows traffic is distributed and guaranteed service is provided for accepted calls.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.8
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• pp.437-444
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• 2014

In this paper, we propose a path loss model with the multiple antennas and doppler shift for high speed railroad communication. Path loss model is very important in order to design consider diverse characteristic in high-speed train communication. Currently wireless communication systems use the multiple antennas in order to improve the channel capacity or diversity gain. However, until recently, many researches on path loss model only consider geographical environment between the transmitter and the receiver. There is no study about path loss model considering diversity effect and doppler shift. In order to make average residuals considering doppler shift we use tuned free space path loss model which is utilized for measurement results at high speed railroad. The environment of high speed rail is mostly at viaduct and flatland over than 50 percent. And in order to make average residuals considering multiple antenna we use theoretical estimation of diversity gain with MRC scheme. proposed model predict loss of received signal by estimating average residuals between diversity effect and doppler shift.

• Journal of the Korean Data and Information Science Society
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• v.13 no.2
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• pp.105-113
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• 2002

The statistical analysis of incomplete data sometimes requires handling of incomplete observations. Towards this end, each case with some missing values generally should be deleted, namely, resulting in only use of non-missing cases. EM algorithm(Dempster et al., 1977) which involves prediction and estimation steps is a general method among others. In this article, we use the free software NORM developed for multiple imputation, which uses DA(Data Augmentation) algorithm in its imputation, and evaluate its efficiency through a numerical example.

• The Korean Journal of Applied Statistics
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• v.21 no.4
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• pp.659-664
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• 2008

Missing continuous covariates are pervasive in the use of generalized linear models for medical data. Multiple imputation is the most common and easy-to-do method of dealing with missing covariate data. However, there are always serious warnings in using this method. There should be concern to make imputed values more proper. In this paper, proper imputation from posterior predictive distribution is developed for implementing with arbitrary priors. We use empirical distribution of the posterior for approximating the posterior predictive distribution, to sample from it. This method is preferable in comparison with a presented imputation method of us which uses a full model to impute missing values using available software. The proposed methods are implemented on glucocorticoid data.

• International Commerce and Information Review
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• v.12 no.4
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• pp.509-535
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• 2010

This paper examines the Spaghetti bowl effect that different tariffs and rules of origin in multiple FTAs have resulted in increasing the significantly additional burden for business when it comes to apply for the use of FTA preference. The wide spread of FTAs in the several years, from 2003 to 2010, has been the most important trade policy development in economically important Korea. Korea presently has 5 FTAs in effect, and made 3 additional agreements which will be expected to take effect in next year. With the study result and expecting a growing number of FTAs in Korea in a next decade, the international trading firms will face rise of transaction costs for enterprises, particularly small- and medium-sized enterprises(SMEs) to cope with multiple tariffs and rule of origins in FTAs. To help mitigate negative effects and facilitate a more SEMs to use the FTA preference, providing new computer programs system, increasing the awareness of FTA provisions, improving business participation in FTA consultations, and SME support in light of education, and financial support are needed.

• Communications for Statistical Applications and Methods
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• v.24 no.2
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• pp.115-127
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• 2017

This paper proposes a Bayesian test for the equivalence of survival functions in multiple groups. Proposed Bayesian test use the model of Cox's regression with time-varying coefficients. B-spline expansions are used for the time-varying coefficients, and the proposed test use only the partial likelihood, which provides easier computations. Various simulations of the proposed test and typical tests such as log-rank and Fleming and Harrington tests were conducted. This result shows that the proposed test is consistent as data size increase. Specifically, the power of the proposed test is high despite the existence of crossing hazards. The proposed test is based on a Bayesian approach, which is more flexible when used in multiple tests. The proposed test can therefore perform various tests simultaneously. Real data analysis of Larynx Cancer Data was conducted to assess applicability.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.112-121
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• 2017

Purpose: The most previous works on designing accelerated life tests (ALTs) are focused on the application of a single stress. Because of the difficulty to obtain the sufficient information in a reasonable duration using single stress only, there is needed in practice to use multiple-stress ALTs frequently. This paper presents new practical plans with two stresses for Weibull distribution. Methods: The four-level practical plans based on rectangle test region are proposed and compared with the corresponding three-level statistically optimal plans. Sensitivity analyses for assumed design parameters and life-stress relationship are conducted. Results: A procedure to choose practical ALT plans is illustrated with a numerical example and guidelines for planning two-stress ALTs are provided. Conclusion: The proposed two-stress ALT plans on practical constraints to assess a quantile of Weibull lifetime distribution at the use condition are efficient and robust.

• The Research Journal of the Costume Culture
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• v.10 no.6
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• pp.601-616
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• 2002

Qualitative research is a method widely used in marketing research. However, the method has seldom been used in fashion marketing research in Korea. The purpose of this study was to prove that using both qualitative and quantitative research methods in main stage is much useful than using qualitative research method only in exploratory stage. Qualitative data were gathered by conducting Focus Group Interview(FGI) with 48 college students. Quantitative data were gathered by surveying college students, and 487 questionnaires were used in the statistical analysis. The data were analyzed using content analysis, mean, standard deviation, and t-test. As a result, FGI, one of the tools used in qualitative research methods, was proved to be useful in revealing consumers´deep emotional needs as well as purchase motives. FGI also revealed information which quantitative research method tools such as survey could have missed. Therefore, it is best to use multiple methods-simultaneous use of quantitative and qualitative methods-to understand fast changing consumers´needs and purchase motives.

• Journal of muscle and joint health
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• v.20 no.2
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• pp.141-150
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• 2013

Purpose: This study was conducted to identify relationships among nursing activities, the use of body mechanics, and job stress in nurses with low back pain. Methods: Participants were 225 nurses with low back pain working at an university hospital. The data were collected with self-reported questionnaires at March, 2012 and analyzed by descriptive statistics, t test, ANOVA, Scheff$\acute{e}$e test and multiple regression analyses. Results: There was significantly a higher degree of pain in subjects who working at special units including intensive care units and emergency room than at general wards. Low back pain was negatively correlated with the use of body mechanical principles while it was positively associated with the degree of job stress. According to results of multiple regression analyses, low back pain was significantly associated with the use of body mechanics and job stress in nurses working at general ward and special units including intensive care units and emergency room. Conclusion: The use of the principles of body mechanics and reducing job stress are important to prevent low back pain in nurses. It is necessary to develop and apply stress management and education program about the use of the principles of body mechanics.