• 한국산업정보학회논문지
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• 제25권5호
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• pp.13-21
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• 2020

이 논문은 직교 주파수 분할 다중화 시스템에 사용하는 공간 주파수 블록 코딩에서의 부호 반전 채널 스위칭 알고리즘을 제안한다. 소스 데이터를 다른 안테나로 보내는 경우에는 수신기는 바뀐 그 채널에 적합하도록 결합 방법을 바꾸어야 한다. 만일 미리 정의된 채널 스위칭 시퀀스를 모르는 수신기라면, 수신한 데이터를 정확하게 복호할 수 없게 된다. 채널 스위칭을 위한 송신 데이터를 바꾸는 경우에는 데이터 심볼들을 공간 주파수 블록 코딩 형식에 맞추어서 바꾸어야 한다. 이 논문에서는 송신 안테나 간의 데이터 심볼들을 바꾸는 것이 아닌 단지 부호 반전 방법을 제안한다. 이 방법을 사용하면 다른 결합 방법을 발생시킴으로써 수신기에서 간단한 암호화로 동작함을 보였다.

• Journal of Power Electronics
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• 제19권1호
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• pp.307-315
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• 2019

Condition monitoring has been recognized as an effective and low-cost method to enhance the reliability and improve the maintainability of power electronic converters. In power electronic converters, high-frequency oscillation occurs during the switching transients of power transistors, which is known as ringing. The ringing frequency mainly depends on the values of the parasitic capacitance and stray inductance in the oscillation loop. Although circuit stray inductance is an important factor that leads to the ringing, it does not change with transistor aging. A shift in either the inside inductance or junction capacitance is an important failure precursor for power transistors. Therefore, ringing frequency can be used to monitor the health of power transistors. However, the switching actions of power transistors usually result in a dynamic behavior that can generate oscillation signals mixed with background noise, which makes it hard to directly extract the ringing frequency. A frequency extraction method based on empirical mode decomposition (EMD) and Fast Fourier transformation (FFT) is proposed in this paper. The proposed method is simple and has a high precision. Simulation results are given to verify the ringing analysis and experimental results are given to verify the effectiveness of the proposed method.

• 한국콘텐츠학회논문지
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• 제8권10호
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• pp.95-103
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• 2008

이 연구는 IPTV 가입자 규모가 하나 TV와 메가 TV를 합하여 140만 가구를 넘어서고 있는 시점에서 시청 방식 또한 시청자의 능동적 선택에 의한 비선형적 방식으로 변화하고 있다는 점에 착안하여 기획하게 되었다. 우선, 하나 TV의 시청 실태를 2007년 3월과 2008년 3월을 기준으로 비교해본 결과, 가입자 규모는 2배 증가한 반면, 접속 수는 15배 이상 늘어나 IP-VOD 서비스 이용 빈도가 빠르게 증가하고 있음을 알수 있었다. 이에 따라 1인당 시청 시간도 4배 이상 증가하였다. 한편, 가장 많이 이용되는 장르는 역시 지상파 방송 프로그램인 것으로 나타나, 하나 TV가 지상파 방송의 보완 매체 역할을 하고 있음을 입증해 주었 다. 그러나, MBC의 홀드백 변화에 따른 프로그램 유료화로 지상파 프로그램 시청 비중이 크게 감소하여 유료화에 대한 부정적 태도를 감지할 수 있었다. 반면 키즈 프로그램과 애니메이션은 상대적으로 크게 증가했고 영화는 제공 편수가 늘었음에도 불구하고 소비 비중이 오히려 감소하여 개선 방안이 요구된다.

• 한국실내디자인학회논문집
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• 제21권1호
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• pp.95-102
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• 2012

This study analyzed the observation characteristics with the subject of observation data through defining the change of the observation degree as attention /conscious observation /visual understanding. Furthermore, by obtaining the formular with which to estimate the subjects' observation amount, this study suggests a potential method for easier analysis of observation characteristics. The conclusions from the study are as the followings. First, the observation frequency was being generated with wide deviation among subjects while there was a flow-on characteristics depending on the degree of observation. These characteristics enabled the study to obtain the formular with which to estimate the observation amount. Second, the study could establish the area frequency by grade from the entire observation data. The area I was at most 4% for the area frequency but accounted for 18.2% of the entire effective observation time, and the area II 16% and 38.7% respectively. Accordingly, only considering the observation area distribution of the area I or the areas I and II shows which position of the space the subjects were observing. Third, with the subject of the relatively higher observation time at at the subject's observation characteristics, as the observation phase was getting higher, the observation time decreased more. Forth, by obtaining the formular to estimate the observation amount for observation data according to the change of observation degree, the study could find the estimating observation characteristics of additional subjects. The formular shortens the analysis time and facilitates the analysis process.

• 한국치위생학회지
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• 제1권1호
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• pp.19-37
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• 2001

The purpose of this study was to develop effective oral health education programs for mentally retarded children and promote their oral health, by offering oral health education for 45 mentally retarded children between age 6 to 20, tracking the change of their knowledge depending on the frequency of education, and examining the educational effect before and after oral health education. The children with mental retardation attended a special school for idiots in Gweonseon-gu, Suwon, Kyonggi Province, being able to take training(IQ 25-49). The education program was designed to be suitable for their cognitive power after consultation with a special school teacher. A teacher provided the same education seven times, once a week, and an interview was held with each of them to assess their correct answer rate. The findings of this study were as below: 1. The repeated oral health education served to have the children with mental retardation acquire better knowledge about harmful food for the teeth, what had to be done after eating cookies or candies between meals, the right time for toothbrushing, the concept of dental caries, and how to cope with dental caries(p<0.01). But after that education was offered four times, the frequency of that education made no difference. 2. The repeated oral health education increased, their knowledge on the role of the teeth and the right choice of toothbrush(p<0.01), yet there was no significant difference in their knowledge about oral health behavior, because they had already been familiar with that. 3. As a result of investigating the change of their oral health know-ledge before and after oral health education according to the type of handicap, the type of handicap made no significant difference to the change of their oral health knowledge. 4. The oral health education for the children with menial retardation had a significantly different effect on their knowledge about harmful food for the teeth, what had to be done after eating between meals, the right time for toothbrushing, the role of the teeth. the right choice and use of toothbrush, how to do toothbrushing, and fluorine(p<0.01).

• 한국식생활문화학회지
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• 제14권4호
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• pp.271-287
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• 1999

A change in distribution structure affect a consumption structure which may result in considerable changes in lifestyle including food purchase. The purpose of this study was to investigate the effect of change of distribution structure on the indigenous fermented food purchase. The informations of this study were obtained from 407 housewives residing in Seoul and the capital area by using questionnaire during May to June, 1997 Their data were statistically analyzed based on frequency, mean, and $X^2-test$. The results were as follows; 1) The percentages of subjects buying ready made fermented food were 69.8% for Jotkals(salt-fermented fish products), 22.3% for Kochujang(fermented red pepper soybean paste), 21.6% for Janachis(pickled basic side dishes), 21% for Kanjang(Korean style soybean sauce), 17.1% for Toenjang(Korean style soybean paste), and 3% for Kimchi(seasoned and fermented vegetables). 2) With decreasing age, preparation ability of Kanjang, Janachis, and Kimchi. The subjects living close to the new distribution channel were higher in ready made fermented food than the others. 3) Compared to the subject living far from the new distribution channel, the subject living close to the new distribution channel was high in frequency of new distribution channel utilization for indigenous fermented food purchase but low in frequency of conventional market utilization. The younger in age, higher in educational level, and nuclear family, the higher the utilization of new distribution channel for indigenous fermented food purchase.

• 제어로봇시스템학회논문지
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• 제8권8호
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• pp.691-697
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• 2002

Myocardial ischemia is a disorder of cardiac function caused by insuficient blood flow to the muscle tissue of the heart. We can diagnose myocardial ischemia by observing the change of ST-segment, but this change is temporary. Our primary purpose is to detect the temporary change of the 57-segment automatically In the signal processing, the wavelet transform decomposes the ECG(electrocardiogram) signal into high and low frequency components using wavelet function. Recomposing the high frequency bands including QRS complex, we can detect QRS complex more easily. Amplitude comparison method is adopted to detect QRS complex. Reducing the effect of noise to the minimum, we grouped ECG by 5 data and compared the amplitude of maximum value. To recognize the ECG .signal pattern, we adopted the polynomial approximation partially and statistical method. The polynomial approximation makes possible to compare some ECG signal with different frequency and sampling period. The ECG signal is divided into small parts based on QRS complex, and then, each part is approximated to the polynomials. After removing the distorted ECG by calculating the difference between the orignal ECG and the approximated ECG for polynomial, we compared the approximated ECG pattern with the database, and we detected and classified abnormality of ECG.

• Journal of Acupuncture Research
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• 제22권5호
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• pp.111-120
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• 2005

Objectives : The aim of this study is to investigate the effect of acupuncture stimulation on the relationship of change in magnetocardiography (MCG). Methods : For this purpose, 30 heart deficiency volunteers were acupunctured at Shinmun (HA7) and Naegwan (PC6) acupoint. Then, we measured and observed the change of frequency parameters in MCG. Results : In the mean frequency, during and after acupuncture treated groups of PC6 were decreased the activity of $f\;_{mean-max}$ compared to the control group. In the median frequency, during the acupuncture treated group of PC6 was decreased the activity of $f\;_{median-max}$ compared to the control group. Conclusion : These results suggested that acupuncture stimulation plays an important role to the activities of MCG.

• 대한원격탐사학회지
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• 제34권1호
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• pp.25-43
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• 2018

The effects of hydro-meteorological and surface variables on the frequency of Asian dust events (FAE) were investigated using ground station and satellite-based data. Present weather codes 7, 8, and 9 derived from surface synoptic observations (SYNOP)were used for counting FAE. Surface wind speed (SWS), air temperature (Ta), relative humidity (RH), and precipitation were analyzed as hydro-meteorological variables for FAE. The Normalized Difference Vegetation Index (NDVI), land surface temperature (LST), and snow cover fraction (SCF) were used to consider the effects of surface variables on FAE. The relationships between FAE and hydro-meteorological variables were analyzed using Z-score and empirical orthogonal function (EOF) analysis. Although all variables expressed the change of FAE, the degrees of expression were different. SWS, LST, and Ta (indices applicable when Z-score was < 0) explained about 63.01, 58.00, and 56.17% of the FAE,respectively. For NDVI, precipitation, and RH, Asian dust events occurred with a frequency of about 55.38, 67.37, and 62.87% when the Z-scores were > 0. EOF analysis for the FAE showed the seasonal cycle, change pattern, and surface influences related to dryness condition for the FAE. The intensity of SWS was the main cause for change of FAE, but surface variables such as LST, SCF, and NDVI also were expressed because wet surface conditions suppress FAE. These results demonstrate that not only SWS and precipitation, but also surface variables, are important and useful precursors for monitoring Asian dust events.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2010년도 학술발표회
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• pp.268-272
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• 2010

The research presented here represents a collaborative effort with the SFWMD on developing scenarios for future climate for the SFWMD area. The project focuses on developing methodology for simulating precipitation representing both natural quasi-oscillatory modes of variability in these climate variables and also the secular trends projected by the IPCC scenarios that are publicly available. This study specifically provides the results for precipitation modeling. The starting point for the modeling was the work of Tebaldi et al that is considered one of the benchmarks for bias correction and model combination in this context. This model was extended in the framework of a Hierarchical Bayesian Model (HBM) to formally and simultaneously consider biases between the models and observations over the historical period and trends in the observations and models out to the end of the 21st century in line with the different ensemble model simulations from the IPCC scenarios. The low frequency variability is modeled using the previously developed Wavelet Autoregressive Model (WARM), with a correction to preserve the variance associated with the full series from the HBM projections. The assumption here is that there is no useful information in the IPCC models as to the change in the low frequency variability of the regional, seasonal precipitation. This assumption is based on a preliminary analysis of these models historical and future output. Thus, preserving the low frequency structure from the historical series into the future emerges as a pragmatic goal. We find that there are significant biases between the observations and the base case scenarios for precipitation. The biases vary across models, and are shrunk using posterior maximum likelihood to allow some models to depart from the central tendency while allowing others to cluster and reduce biases by averaging. The projected changes in the future precipitation are small compared to the bias between model base run and observations and also relative to the inter-annual and decadal variability in the precipitation.