• 한국전자파학회논문지
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• 제20권7호
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• pp.657-663
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• 2009

본 논문에서는 IR-UWB 통신에 적합한 저전력, 저복잡도의 CMOS RF 수신기를 제작하였다. 제안된 IR-UWB 수신기는 비교적 구조가 간단한 non-coherent demodulation 방식으로 설계, 제작되었다. 설계된 IR-UWB 수신기는 single-ended 2-stage LNA, S2D, envelop detector, VGA, comparator로 구성되어 있으며, 0.18 ${\mu}m$ CMOS 공정 기술을 이용하여 단일 칩으로 설계, 제작하였다. 측정 결과 data rate이 1 Mbps 일 때 BER값이 $10^{-3}$ 조건에서 sensitivity는 -80.8 dBm이다. 제작된 단일 칩 CMOS IR-UWB 수신기의 전류 소모는 전압이 1.8 V 일 때, 13 mA이며 23.4 nJ/bit 의 성능을 갖는다.

• 소음진동
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• 제5권4호
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• pp.515-524
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• 1995

Tubes in heat exchanger of fuel rods in reactor core are supported at intemediate point by support p0lates or springs. Current practice is, in case of heat exchanger, to allow clearance between tube and support plate for design and manufacturing consideration. And in case of fuel rod the clearance in support point can be generated due to the support spring force relaxation. Flow-induced vibration of a tube can cause it to impact or rub against support plate or against adjacent tubes and can result in fretting-wear. The tube-to- support dynamic interaction is used to relate experimental wear data from single-span test rigs to real multi-span heat exchanger configurations. The dynamic interaction cna be measured during experimental wear tests. However, the dynamic interaction is difficult to measure in real heat exchangers and, therefore, analytical techniques are required to estimate this interaction. This paper describels the nonlinear impact model of DAGS(Dynamic Analysis of Gapped Structure) code which simulates the tube response to external sinusodial or step excitation and predicts tube motion and tube-to-support dynamic interaction. Three experimental measurements-two single span rods excited by sinusodial force and a two span rod impacted by a steel ball are compared from the simulation nonlinear model of DAGS code. The simulation results from DAGS code are in good agreement with measurements. Therefore, the developed model of DAGS code is good analytical tool for estimating tube-to-support dynamic interaction in real heat exchangers.

• 한국항공우주학회지
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• 제43권5호
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• pp.456-465
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• 2015

듀얼 벨 노즐은 일반적인 벨 형상 노즐의 문제점인 저고도에서의 과대팽창, 고고도에서의 과소팽창을 감소시키며, 이로 인해 손실되는 비추력을 최소화 할 수 있는 노즐이다. 미국의 Rocketdyne사에서는 확장 노즐의 형상에 따른 추력특성을 분석하였고, NASA에서는 고도에 따른 연소실험을 수행하였다. 유럽은 DLR을 중심으로 굴곡각, 노즐 길이, 팽창비 등에 따른 연구를 진행하고 있으며, 러시아의 MAI에서는 팽창부에 슬롯을 추가하여 추력손실을 줄일 수 있는 연구가 진행되고 있다. 아시아에서는 일본, 인도 등에서 연구가 진행되고 있고, 일본의 미쓰비시사에서 슬롯 노즐과 유사한 개념의 기술을 특허로 등록하였다. 본 논문에서는 고도 보정이 가능한 노즐로써 듀얼 벨 노즐의 개념 및 성능과 국외 연구 개발 현황을 정리하였다. 국내에서도 경제성 있는 우주개발을 위해 듀얼 벨 노즐에 대한 연구가 필요하다.

• 전자공학회논문지SC
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• 제46권1호
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• pp.55-62
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• 2009

본 논문에서 증폭 후 전달 전송 기법을 사용하는 중계망의 채널 추정을 하는데 있어서 일어나는 문제점을 해결할 수 있는 방법으로 학습 계열(training sequence)을 이용하는 방법을 제안하였다. 현재의 고속 페이딩 채널 환경에서 기존 파일럿의 추정이 적절하지 않아 송신국(source)과 중계국(relay) 사이의 채널과 중계국(relay)과 수신국(destination) 사이의 채널을 결합하여 추정할 경우 많은 문제점이 초래되기에$^{[1{\sim}2]}$ 전송한 신호의 주파수 영역을 선택하여 얻은 정규(Gaussian) 분포에 대하여 최대 우도 함수의 평균을 내어 채널 추정량(estimator)을 유도해 낼 수 있는, 즉, 파일럿 대신에 하나의 OFDM 신호를 사용하여 모든 채널 충격 응답(CIR)을 추정할 수 있는 새로운 방법을 살펴보았다. 컴퓨터 모의실험으로 높은 SNR 영역에서 제안한 채널 추정기(estimator)의 성능이 [1]과 비교하여 약 1dB 정도 높음을 확인할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.636-639
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• 2004

This paper presents the fabrication and performance evaluation of zinc oxide varistors for the arresters used for station system. ZnO varistors were fabricated with typical ceramic production methods and the structural and electrical characteristics were investigated. All varistors exhibited high density, which were in the range of $5.41{\sim}5.49g/cm^3$. In the electrical properties the reference voltage increased in the range of $4.410{\sim}5.250kV$ with increasing their thickness and the residual voltage exhibited the same trends as the reference voltage. In the long duration current impulse withstand test, E-2 and F-1 samples failed in the two and four shots, respectively, but E-1 and F-2 samples survived 18 shots during the test. Before and after this test, the variation ratio of residual voltage of E-1 and F-2 samples were -0.34% and 0.05%, respectively, which were in the acceptance range of 5%. According to the results of tests, it is thought that if the fabrication process such as insulating coating, sintering condition, and soldering method is improved, these ZnO varistors would be possible to apply to the station class arresters in the new future.

• Progress in Superconductivity
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• 제13권3호
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• pp.189-194
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• 2012

Studies on the development of high voltage superconducting apparatuses, such as transmission superconducting fault current limiters (SFCLs) and superconducting cables, have been performed worldwide. In this paper, a study on the electrical insulation characteristics of electro negative gas according to various pressures and utilization factors was conducted as a part of developing a high voltage superconducting coil with a sub-cooled nitrogen cooling system. Some gases such as helium (He), nitrogen ($N_2$), and sulfur hexafluoride ($SF_6$) are considered for pressurizing the sub-cooled nitrogen cooling system of high voltage SFCLs and superconducting cables. $SF_6$ is used to pressurize and enhance the dielectric performance of a superconducting system of a sub-cooled nitrogen cooling system for superconducting cables being developed in the Republic of Korea. In this paper, dielectric experiments on AC voltage, as well as lightning impulse voltage of $SF_6$, are conducted according to various utilization factors by using several kinds of sphere-to-plane electrode systems. As results, it is known that the empirical formulae of $SF_6$, known as an electro negative gas, are derived according to various pressures and utilization factors. Also, the appropriate pressure condition for designing a high voltage superconducting coil is found from the viewpoint of dielectric performance.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.93-93
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• 2017

고전력 펄스 전원공급장치를 이용한 마그네트론 스퍼터링(high-power impulse magnetron sputtering; HiPIMS)과 직류(direct current; DC) 전원공급장치를 이용한 마그네트론 스퍼터링(DC 스퍼터링)을 이용하여 제조한 티타늄 질화물(titanium nitride; TiN) 박막의 특성을 비교하였다. HiPIMS와 DC 스퍼터링 공정 중에 빗각증착을 적용하여 TiN 박막의 미세구조와 기계적 특성의 변화를 확인하였다. TiN 박막을 코팅하기 위한 기판으로 스테인리스 강판(SUS304)과 초경(cemented carbide; WC-10wt.%Co)을 사용하였다. 기판은 알코올과 아세톤으로 초음파 처리를 실시하여 기판 표면의 불순물을 제거하였다. 기판 청정 후 진공용기 내부의 기판홀더에 기판을 장착하고 $2.0{\times}10^{-5}torr$의 기본 압력까지 진공배기를 실시하였다. 진공 용기의 압력이 기본 압력에 도달하면 아르곤(Ar) 가스를 진공용기 내부로 ${\sim}10^{-2}torr$의 압력으로 주입하고 기판홀더에 라디오 주파수(radio frequency; rf) 전원공급장치를 이용하여 - 800 V의 전압을 인가하여 글로우 방전을 발생시켜 30 분간 기판 표면의 산화막을 제거하는 기판청정을 실시하였다. 기판청정이 완료되면 기본 압력까지 진공배기를 실시하고 Ar과 질소($N_2$)의 혼합 가스를 진공용기 내부로 ${\sim}10^{-3}torr$의 압력으로 주입하여 HiPIMS와 DC 스퍼터링으로 TiN 박막 제조를 실시하였다. 빗각의 크기는 $45^{\circ}$와 $-45^{\circ}$이었다. 제조된 TiN 박막은 주사전자 현미경, 비커스 경도 측정기 그리고 X-선 회절 분석기를 이용하여 특성을 분석하였다. HiPIMS로 제조한 TiN 박막은 기판 전압을 인가하지 않아도 색상이 노란색을 보이지만, DC 스퍼터링으로 제조한 TiN 박막은 기판 전압을 인가하지 않으면 노란색을 보이지 않고 어두운 갈색에 가까운 색을 보였다. TiN 박막의 경도는 HiPIMS로 제조한 TiN 박막이 DC 스퍼터링으로 제조한 TiN 박막보다 높았다. 이러한 TiN 박막의 특성 차이는 DC 스퍼터링과 비교하여 높은 HiPIMS의 이온화율에 의한 결과로 판단된다. 빗각을 적용한 TiN 박막은 미세구조 변화를 보였으며 이러한 미세구조 변화는 TiN 박막의 특성에 영향을 미치는 것을 확인하였다.

• The Korean Journal of Pain
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• 제12권1호
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• pp.64-69
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• 1999

Background: The new drug HP228 is a cytokine restraining agent with a broad spectrum of anti-inflammatory, analgesic, and antipyretic activity. Six healthy, adult, male volunteers were studied to determine the independent and interactive effects of HP228 and morphine on pain perception. Methods: Two groups of stimuli were applied to each volunteers before drug administration as control, 20 min after morphine and HP228 administration, and 20 min after combined administration of these two drugs. Two adhesive electrically-conducting pads were applied on opposite sides of the arm approximately 8 cm apart. The electrode were connected to an electrical impulse generator and 50 Hz 1 msec pulses of incrementally increasing intensity were delivered at 1 sec intervals. The analgesic endpoints were the current intensity (mA) at which the subject first detected the stimulus (THRESH), the intensity at which the stimulus was first idenfied as being painful (PAIN), and the intensity at which the subject requested that the stimulus be terminated due to discomfort (LIMIT). A second series of stimuli were applied immediately thereafter using 1-sec duration 50 Hz tetanus pulses with increasing intensities at 2~5 sec intervals. Results: There were significant differences between drug treatments (Morphine, HP228, HP228/Morphine) and control (No drugs) in any of the measurements (PAIN, LIMIT) except THRESH with the twitch and tetanus test. Conclusions: The data suggests that HP228 is an analgesic, but it does not appear to interact with morphine in an additive manner.

• 복식문화연구
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• 제24권4호
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• pp.511-529
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• 2016

The current study aims to segment Chinese female consumers using their lifestyle dimensions in the cosmetics market, and analyze their cosmetics purchasing behavior based on that segmentation. Specifically, lifestyle groups were examined to see if there is any group difference(s) in consumer behavior for Korean cosmetics. Lifestyle groups were examined based on: consumers' demographic characteristics, perceived brand attributes, loyalty toward Korean cosmetics, usage of Korean cosmetics products, preferred stores of shopping for Korean cosmetics, and use of information sources in purchase decisions. An online survey was administered to female consumers who live in Beijing and Shanghai. A total of 493 surveys were used for data analyses. The results of the study were as follows: First, factor analysis revealed 11 significant lifestyle dimensions. Second, using these 11 lifestyle dimensions, cluster analysis was conducted, which revealed four distinct groups of consumers: (1) "timid inactive group," characterized by having low scores in most lifestyle dimensions; (2) "showcase goers," who tend to be highly fashion/appearance-conscious and brand-oriented; (3) "practical buyers," who tend to be price-conscious, sensitive and timid; and (4) "sensible buyers," who enjoy finer meals and wellbeing lifestyles, as well as hardworking in everything and impulse-buy things. Third, consumer behavior of purchasing Korean cosmetics brands were examined; significant differences among the four lifestyle groups were found. The study concludes with a discussion of the results and practical implications.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.65-68
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• 2003

Interconnected power system operation has given rise to the problem of increased fault levels and leads to over stressing of all the components. Use have been made of recently developed high Tc superconductor in devising a superconducting fault current limiter (SFCL) that promises optimum performance in terms of capital cost, size, auto sensing, operational losses, response time and reliability. Recently, research about the application of the SFCL is actively progressing in Korea. To be applied for SFCL practically, the electrical insulation design of SFCL must be developed. Therefore, this paper presents the result of an investigation of the dielectric characteristics of turn-to-turn insulation for SFCL in liquid nitrogen. The dielectric characteristics of turn-to-turn insulation models of SFCL were investigated. We obtained following results. The breakdown voltages increased as the spacer thickness and length increased. And the breakdown voltages of turn-to-turn model without spacer were higher than the breakdown voltages of turn-to-turn model with spacer under impulse as well as AC voltages. The information gathered in this test series should be helpful in the design of liquid nitrogen filled SFCL.