• 한국정보통신학회논문지
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• 제4권4호
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• pp.751-758
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• 2000

본 논문은 국내 5GHz 대역에서 초고속 무선접속 망을 도입하기 위한 주파수의 분배 및 공유조건에 관한 것이다. 본 논문에서는 초고속 무선접속 망과 기존 기상 레이더 사이의 공유 가능성을 평가 하기 위해서 최소결합손실(Minimum Coupling Loss) 방법과 Monte-Carlo 시뮬레이션을 이용하여 기상 레이더가 초고속 무선 접속용 기기에 미치는 전파간섭을 분석하였다. 그리고 시뮬레이션과 실제 측정 결과에 의하면 기상 레이더와 초고속 무선접속 망의 주파수 공유를 위해서는 DFS(Dynamic Frequency Selection)기법을 사용하는 것이 필수적이라는 결론을 얻었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 추계종합학술대회
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• pp.176-179
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• 2000

통신회로에서 많이 사용되는 PLL 방식에 의한 주파수 합성기는 여러 장점이 있지만 위상잡음 특성이 나쁘고 긴 주파수 도약 시간을 갖기 때문에, 최근의 고속(1$\mu\textrm{s}$이하)으로 주파수 호핑(Frequency Hopping)을 요구하는 디지털 통신 시스템에서는 사용이 어렵다. 본 연구는 디지털 영상 패턴 발생기에서 1600hops/s로 600개 이상의 랜덤한 주파수를 발생하는 주파수합성기를 DDS (Direct Digital Synthesis) 방식을 이용하고, CPLD에 의해 구현하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.443-447
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• 2001

통신회로에서 많이 사용되는 PLL 방식에 의한 주파수 합성기는 여러 장점이 있지만 위상잡음 특성이 나쁘고 긴 주파수 도약 시간을 갖기 때문에, 최근의 고속(l$\mu\textrm{s}$이하)으로 주파수 호핑(Frequency Hopping)을 요구하는 디지털 통신 시스템에서는 사용이 어렵다. 본 연구는 디지털 영상 패턴 발생기에서 1600hops/s 로 600개 이상의 랜덤한 주파수를 발생하는 주파수합성기를 DDS (Direct Digital Synthesis) 방식을 이용하고, CPLD에 의해 구현하였다.

• 방송공학회논문지
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• 제16권1호
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• pp.96-107
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• 2011

최근 들어 3D HDTV (3-Dimensional High Definition Television)에 대한 연구가 활발히 진행되고 있다. 국내에서도 3D HDTV 방송 서비스를 위하여 기존의 HDTV 전송 방식인 ATSC (Advanced Television Systems Committee) 8-VSB (8-Vestigial Side Band) 시스템을 수정하려는 연구가 진행되고 있다. 그 중에서도 프레임헤더에 PN (Pseudo-Noise)심볼을 삽입하여 반송파 주파수 오차와 반송파 위상 오차 복구를 이루도록 하는 프레임 구조와 VSB 변조방식을 채택하고자 한다. 본 논문에서는 이 시스템을 수정된 ATSC 전송시스템이라 부르려 한다. 수정된 ATSC 전송시스템의 수신기는 방송 신호의 원활한 수신을 위하여 반송파 주파수 오차(심볼속도 대비 최대 1%)를 정확하게 추정하고 복구하여야 한다. 기존 ATSC 시스템이 파일럿 신호를 삽입하여 반송파 주파수 오차를 복구 하였다면, 수정된 ATSC 시스템은 별도의 파일럿 신호 첨가 없이 PN심볼을 이용하게 된다. 본 논문에서는 수정된 ATSC 전송 시스템에 적용 가능한 반송파 주파수 복구 방식을 소개한다. 제안된 방식은 Fitz 알고리즘을 이용한 거친 반송파 주파수 오차 복구부과 간단한 PN심볼 상관 알고리즘을 이용한 미세 반송파 주파수 오차 복구부를 가진다. 그리고 QAM (Quadrature Amplitude Modulation) 변조된 신호는 심볼 정보가 동위상 채널과 직각위상 채널에 존재하는 반면 VSB 변조된 신호는 심볼 정보가 동위상 채널에만 존재하고 직각위상 채널은 단지 동위상 채널의 힐버트 변환된 값이다. 그러므로 VSB 변조된 신호는 QAM 변조된 신호와 같은 고정된 위상을 가지지 못하고, 반송파 주파수 옵셋에 더욱 민감하게 된다. 이 같은 문제를 해결하고 성능을 향상시키기 위하여 이상적인 송수신 시스템에서 수신된 PN 심볼을 이용한 수신된 신호의 위상보정 과정을 수행하게 된다.

• 한국소음진동공학회논문집
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• 제15권8호
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• pp.924-930
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• 2005

Sound absorptive materials have good performance in high frequency range, not at low frequencies. Therefore it has been great challenge to develop a sound absorbing structure that is good at low frequency. We propose to use a Helmholtz resonator array panel for this purpose. A Helmholtz resonator is one of noise control elements widely used in many practical applications. The resonator is a simple structure composed of a rigid-walled cavity with a neck, but it has very high performance at resonance frequency. This paper discusses the sound absorption of Helmholtz resonator array panels at normal and random incidence. First, various experimental results are introduced and studied. Secondly, we theoretically predict the absorptive characteristics of the resonator away panel. The theoretical approach is based on the Fourier analysis for a periodic absorber. We believe that this method can be used to design a panel for low frequency noise control.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.1890-1901
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• 2007

This paper explored train frequency of intercity rail station. Main factors to decide train frequency are location of station, social-economic index and land use of station area and travel demand. In this paper, we focused on travel demand which is critical factor to decide train frequency. Tests on a KTX case show that train frequency can be efficiently decreased in weekday to transport same demand. The work has shown many subjects that need further research. It is important to include various factors influencing on train frequency decision.

• Tribology and Lubricants
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• 제33권4호
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• pp.148-152
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• 2017

The feel of writing is important to customers when they buy smart devices with stylus such as smartphones and tablet computers. With an aim to reproduce the tactile sensibility of writing instruments when people write on the glass display using a stylus, this study focuses on the frequency characteristics of writing instruments that can describe the vibrations of writing instruments sliding over counter surfaces. In addition, this study includes the effect of various factors influencing the friction of writing instruments such as lubricant, nib material, and contact type. We perform sliding experiments with six types of writing instruments and a sheet of paper to understand the relation between the friction conditions of the nib and the frequency characteristics. As this research focuses on the tactile perception of human skin when people use a writing instrument, the analysis of frequency characteristics is performed in the perceptible frequency range of mechanoreceptors in the human skin. As a result, three types of frequency characteristics are identified. Low frequency peaks are observed for a metal nib with ink; high frequency peaks are observed for a nib without ink; and, middle frequency peaks with a wide range of distribution occurs for fabric nibs with ink. Therefore, to implement the proper feel of writing, at least three types of vibrations have to be made.

• 한국항공운항학회지
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• 제20권3호
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• pp.16-21
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• 2012

Global navigation satellite systems (GNSS) use dual frequency signals to remove ionosphere delay effect. GNSS receivers have their own biases, called inter-frequency bias (IFB) between dual frequencies due to differential signal delays in receiving each frequency codes. The IFB degrades pseudo-range and ionosphere delay accuracies, and they must be accurately estimated. Simultaneous estimation of ionosphere map and IFB is applied in order to analyze the IFB estimation accuracy and variability. GPS network data in Korea is used to compute each receiver's IFB. Accuracy changes due to ionosphere model changes is analyzed and the effect of external GNSS satellite IFB on the receiver IFB is analyzed.

• 한국문헌정보학회지
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• 제18권
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• pp.55-98
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• 1990

This research attempts to verify the hypothesis that the workers in the small-and medium-sized industries use more informal information channels than formal ones do to get the information necessary to industrial activities. Information sources are divided by the internal and the external ones and these are sub-divided by their acquiring channels, publishers and holding institutions. It is intended to investigate the information sources according to the use frequency, age, origin and format of documents used. The degree of benefit to the workers in their practical work through the use of information sources and the use frequency of information sources by the department and years of experience are also investigated. The data to test the hypothesis was collected through the questionnaires distributed to the workers in 300 sampled firms from June 5 to June 20, The following facts have been verified as the result : 1. Workers in industries acquire information mainly through the contacts with the colleagues or superiors in their departments, and the junior workers depend more on the colleague and superiors than senior workers are. 2. Among the documents published internally, the ones from the research and development departments are mostly used. The documents issued by the worker's own departments are also frequently used and the senior workers, the more frequently use the internal publications than the junior workers do. 3. Among the internal documents stored in various places in the industries, the documents kept in the worker's own departments are used most frequently. The senior workers the more use privately owned documents than the junior workers do. 4. As far as the external channels are concerned, information is obtained mainly through suppliers of equipment and raw materials and the use frequency of information channels varies according to department. The senior workers the more receive information through supporting institution, seminar and exhibition than the junior workers do. 5. Among the external publication, the ones published by the industrial supporting institutions are heavily used and the workers in research and developments frequently use the external publications. 6. The documents held in governmental industrial institutions and industrial supporting institutions are heavily used compared with the ones stored in other external institutions. The holding places of frequently used documents vary according to the working departments. 7. The degree of benefit to practical work performance resulted from the internal information use is less than by the use of external information. 8. The documents published more than five years ago are more used than the ones of less than five years, Korean and Japanese documents are used frequently and catalogues, patents and standards are used to a great extent. The documents are used differently in accordance with work departments.

• 대한간호학회지
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• 제2권1호
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• pp.49-61
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• 1971

The purpose of this study is to observe the administering of analgesics and sedatives to cases of surgery, the influence of the patients'situational variables on the use of these drugs, and the required number of recovery days in relation to the patients'situational variables and general conditions. Fifty patients in the age range of 15 through 65 who had undergone general surgery at Seoul national University Hospital. Woo Sok University Hospital and Koryo Hospital between May and August of 1971 were chosen for this study. They were observed with regard to the frequency of postoperative uses of analgesics and sedatives age, the required period of recovery in comparison with the situational variables of patients such as sex, age, marital status, the type and duration of anesthesia, experience of previous operation, history of other diseases, preoperative period of hospitalizations and the general conditions of patients such as sleep, stomach condition, bowel condition, urination, interest in surroundings, strength and energy, self-assistance and appetite. The study results were reviewed in a statistical method to obtain the following findings: 1. There was a significant decrease in the frequency of analgesic uses according to the number of days passed after operation. 2. The mean postoperative recovery days were 5.31 days and mote than half of the patients have never used analgesics until recovery. 3. There was a significant decrease in the frequency of sedative uses according to the number of days passed after operation. 4. The rank-order correlation between the frequency of analgesic use and that of sedative use following surgery observes in relation to the number of postoperative days was a low and negative one. 5. All of the patients except one hate used sedatives only once a day for the whole recovery period. 6. The longer they stayed in the hospital before surgery, the less have they used analgesics after surgery. 7. There were significant differences in use of analgesics after surgery by age groups; the 25-44 age group used more analgesics than the 15-24 and 45-65 age groups. 8. There were no significant differences in use of analgesics after surgery by all situational variables except the number of days of hospitalization and age. 9. The longer they stayed in the hospital before surgery, the earlier have they recovered from the surgery. 10. There were no significant differences in the number of required recovery days by all situational variables except the length of preoperative hospitalization. 11. There were no significant differences in the number of required postoperative recordedly days by the general conditions of patients.