• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1077-1080
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• 2002

In building acoustics, reverberation time is an important acoustic parameter. However, it is often difficult to measure short reverberation times at low frequencies using the traditional band pass filter bank if the product of bandwidth (B) and reverberation time (T) is small. It is well known that the minimum permissible product of bandwidth and reverberation time of the traditional band pass filter is at least 16 ［F. Jacobsen, J. Sound Vib. 115, 163-170 (1987)]. This strict requirement makes it difficult to measure short reverberation times of an acoustic room at low frequencies exactly. In order to reduce this strict requirement, recently, the wavelet filter bank is developed and the minimum permissible product of bandwidth and reverberation time is replaced with 4 [S. K. Lee, J, Sound Vib. 252, 141-153 (2002)]. In the present paper, it is demonstrated how the short reverberation times at low frequencies are successfully measured by using the wavelet filter bank. In order to present this job, two synthetic signals and one measured signal are used for impulse responses of an acoustic room.

• 로봇학회논문지
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• 제6권3호
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• pp.230-236
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• 2011

In previous researches, the self-stability was studied for the spring-mass model and the two segment leg model. In these researches, it was presented that the spring-mass model has the self-stable region at relatively high speed running and the two segment leg model has the self-stable region at relatively low speed running. If the model was run in the self-stable region, the cost of transport is zero ideally. That is, actually, only the energy loss is needed to compensate for running. This means that the energy efficiency is high, running in the self-stable region. We want to have high energy efficiency at low and high speed running. So, in this paper, we propose the design direction of the three segment leg having the self-stable region at low and high speed running. And we prove the self-stable region of the three segment leg designed by the proposed design direction.

• 음성과학
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• 제13권3호
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• pp.35-48
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• 2006

The present study examined whether words with higher frequency have more exposure to the lenition process such as intervocalic stop voicing or /h/ reduction in the production of the Korean speakers. Experiment 1 and Experiment 2 tested if word-internal intervocalic voicing and /h/ reduction occur more often in the words with higher frequency than less frequent words respectively. Results showed that the rate of voicing was not significantly different between the high frequency group and the low frequency group; rather both high and low frequency words were shown to be fully voiced in this prosodic position. However, intervocalic /h/s were deleted more in high frequency words than in low frequency words. Low frequency words showed that other phonetic variants such as [h] and [w] were found more often than in high frequency group. Thus the results of the present study are indefinitive as to the relationship between the word frequency and lenition with the data at hand.

• Nuclear Engineering and Technology
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• 제37권4호
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• pp.299-308
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• 2005

The behavior of fission gas in all major types of nuclear fuel has been reviewed with an emphasis on more recently discovered aspects. It is proposed that the behavior of fission gas can be classified in a number of characteristic types that occur at a high or low operating temperature, and/or at high or low fissile burnup. The crystal structure and microstructure of the various fuels are the determinant factors in the proposed classification scheme. Three types of behavior, characterized by anisotropic $\alpha$-U, high temperature metallic $\gamma$-U, and cubic ceramics, are well-known and have been extensively studied in the literature. Less widely known are two equally typical low temperature kinds: one associated with fission induced grain refinement and the other with fission induced amorphization. Grain refinement is seen in crystalline fuel irradiated to high burnup at low temperatures, whereas breakaway swelling is observed in amorphous fuel containing sufficient excess free-volume. Amorphous fuel, however, shows stable swelling if insufficient excess free-volume is available during irradiation.

• 한국통신학회논문지
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• 제27권5C호
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• pp.522-529
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• 2002

GaAs pHEMT 기술로 V-band 수신단 각 MMIC 회로들을 설계 제작하였다. 또한 이를 집적하여 V-band downconverter module을 제작하였다. 제작된 downconverter는 24 dBm의 출력을 내는 LO 구동 전력 증폭기, 20dB의 소신호 이득을 가지는 저잡음증폭기, -1.6dBm의 출력을 내는 active parallel type의 발진기, 6 dB 이상의 변환이득 특성을 나타내는 cascode type의 혼합기로 구성되어 있다. 이처럼 혼합기의 우수한 변환이득 특성은 밀리미터파 대역에서 변환 이득 특성을 키우기 위해 반드시 필요한 거대한 IF buffer amplifier의 필요를 없애 주었다. 완성된 downconverter module의 측정결과 별도의 IF buffer amplifier없이 57.5 GHz와 61.7 GHz 사이에서 20 dB 이상의 높은 변환이득을 얻을 수 있었다.

• 대한물리치료과학회지
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• 제3권4호
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• pp.207-214
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• 1996

Main cause of low back pain is a poor posture. Most low back pains are due to a poor posture. The poor posture induces muscle tension and finaliy low back pain. The poor posture arehabitually trained from the childhood by the environmetal factors. In general, maintaining good posture during working and sleeping hours are the first line of defence against back pam. (1) Supine posture is the easiest posture that relaxes and fixes muscles. Supine posture is thus a starting position for on exercise. Lying down releases the weight pressures of head and shoulder and thus body can be relaxed and extended which are helpful for treating back pain. However, supine posture can increase the pressure in ribcage posture aspect and disphragram due to visceral oragans. (2) Sitting in one position for a long time results in fatigue and relaxation of spinal muscies. Finally, body strength is weakened and sitting posture will become poor. If this poor posture continues for a longer time, pain will be accompanied due to overelongation of muscle ligaments. The habitual poor posture could induce intervertebral disc distortion. If the intervertebral disc is damaged, sitting in one position or movement causes pain. (3) Abnormal lumbar curve induces the tention of abdominal muscle and paravertebral muscle groups as well as tention of lower limb muscle group connected to pelvis. For a person with weak body strength, muscle relaxation increases curvature in lumbar, chest and cervical regions. This will induce a pelvic anterior tilting of the imaginary line between A. S. I. S. and P. S. I. S. Hip joint extensor muscle acts on releasing the pelvic anterior tilting. Contrections of hamstring muscle and femoral muscle recover the imaginary line between A.S.LS. and P.S.I.S. from pelvic anterior tilting. thus, contraction of rectus abdominis muscle are required to maintain the normal lumbar curve.

• 한국항행학회논문지
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• 제9권2호
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• pp.103-109
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• 2005

본 논문에서는 이중게이트 FET 구조를 이용하여 광대역 하이브리드 믹서를 RF신호와 LO신호를 출력단과 격리하는 저역통과필터와 같이 설계하였다. 저역통과필터는 1.5-5.5GHz에서 RF와 LO신호에 대하여 40dBc의 억압특성을 나타낸다. 이중게이트 FET 믹서는 두 개의 FET를 캐스코드 구조로 연결하여 설계하였으며, 첫번째 FET는 선형영역에서 동작되고 두번째 FET는 포화영역에서 동작한다. 입력매칭은 1.5-5.5GHz에서 높은 변환이득을 갖도록 설계하였다. 설계된 믹서는 IF를 21.4MHz로 고정시키고 0dBm의 국부발진기 전력에서 1.5-5.5GHz 대역에서 7dB이상의 변환이득을 가진다.

• KIEAE Journal
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• 제16권5호
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• pp.103-109
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• 2016

Purpose: In Korea, to reduce greenhouse gas emissions, energy performance standard of buildings is being reinforced with goals of Passive House until 2017 and Zero Energy House until 2025 in order to reduce emissions from buildings which constitute a quarter of greenhouse gas emissions. In order to achieve the target of Zero Energy House, it is certainly necessary to develop renewable energy that can replace cooling and heating energy occupying a significant amount of building energy consumption after increasing the energy performance firstly. Method: In this study, effects of heat in greenhouse heated by solar heating on indoor heating were analyzed by constructing a greenhouse in front of the Low Energy Building. Result: As a result, indoor temperature was increased by peak average $27.8^{\circ}C$, peak average $6.8^{\circ}C$ was increased from when heat in greenhouse has not been used for heating and indoor surface temperature was increased by average $5.1^{\circ}C$. It shows it can be possible to use heat in greenhouse for heating, if the heating effects can be same as this experimental result because Energy Saving-Type buildings such as Low Energy House or Passive House keep from 18 to $20^{\circ}C$ in winter. Therefore, even if energy supply is cut off by disasters and other reasons, cooling and heating can be possible for some time.

• 정보교육학회논문지
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• 제14권3호
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• pp.355-364
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• 2010

환경문제가 부각되고 글로벌 환경위기에 대응한 저탄소 녹색성장 정책에 따라 초·중등학교도 저탄소 녹색성장 구현을 위한 방안을 마련해야 할 것이다. 그러므로 본 논문에서는 교육정보화를 통한 초·중등 녹색학교를 만들기위해 'IT 정보자원의 그린화'와 '교육정보화를 통한 교육환경의 그린화'로 구분하여 추진과제를 제시한다. 'IT 정보자원의 그린화'는 그린 IT 제품 도입시 필요한 가이드라인과 IT 제품 재활용을 고려한 폐기 방안을 제안하고, 친환경 정보 인프라 모델을 제안한다. 교육정보화를 통한 교육환경의 그린화는 학교 구성원들인 교사.학생들이 지켜야할 그린 IT 실천방안 및 교육활동을 제안하고. IT를 활용한 저탄소 교육환경으로 전환을 추구하는 다양한 교육정보화 서비스 활용을 제시한다. 앞으로 이러한 제안이 학교현장에 실현되면 녹색학교 구현에 도움이 될 것으로 기대한다.

• 한국통신학회논문지
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• 제33권12B호
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• pp.1066-1074
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• 2008

본 논문에서는 충돌이 잦은 무선 저속 Personal Area Network에서 펄스 (pulse) 신호를 이용한 효율적인 그룹폴링 알고리즘을 제안한다. 현재 IEEE 802.15.4 (LR-WPAN) 표준은 저속, 저가, 저 전력 소모를 목표로 한다. 하지만, 최근 LR-WPAN (Low Rate Wireless PAN)의 응용범위가 확대되고 이에 따라 잦은 충돌이 발생하는 상황 또한 늘어나고 있다. 여기서 충돌의 대부분은 '히든노드 문제'로 인하여 발생되고 이는 CSMA/CA 만으로 해결하기 어렵고 연속해서 일어날 경우 네트워크 성능을 크게 저하시킨다. 또한, 현재 히든노드 충돌에 관한 대부분의 연구는 연속된 충돌이 잦은 상황에서 많은 채널 낭비를 유발한다. 본 논문에서 제안한 알고리즘은 잦은 충돌 상황이 발생하였을 때 이미 그룹핑 되어 있는 PAN을 전제로 펄스신호를 이용하여 각 그룹에게 채널 할당과 순서를 정해주고 할당 받은 그룹의 노드들만 경쟁 시킨다. 이에 따라 데이터를 보내기 위해 경쟁하는 노드의 수가 현저히 줄어 연속된 충돌을 줄이고, 충돌로 인한 채널낭비와 낮은 데이터 전송률이 보다 향상되어, 잦은 충돌로 인한 네트워크의 손상을 막는다. 이러한 성능 향상을 NS-2 시뮬레이션을 통해 확인하였다.