• 한국해양공학회지
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• 제1권1호
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• pp.138-143
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• 1987

Friction welding has emerged as a reliable process for high-production commercial applications with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristcs of the pulse echo effects according to various change in welding conditions. This paper presents an attempt to determine the relationship between the varios welding conditions and the coefficients of reflection using the ultrasonic pulse echo method in dissibilar metals friction weld. The new approach of calculating the coefficients of reflection based on measured amplitudes of the echoes is applied in this paper. These coefficients provides a single quantitative measurement which involves both acoustic energy reflected at the welded interface as well as transmitted across the interface. As a result, it was known that the quantitave relationship between welding conditions and the coefficients of reflection using the ultrasonic pulse echo exists in dissimilar metals friction weld.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.153-157
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• 2003

Supersonic and hypersonic aircrafts must pass wide range of speed to reach high speed region. But for existing engines the most efficient operating speed ranges are decided according to their flying speed, so an engine which mixes several engines like TRJ (Turbo Ramjet) and ARJ (Air Turbo Ramjet) has been planed. This mixed type engine has inefficiency that more than two engines must be installed simultaneously, but the pulse detonation engine (PDE) that uses detonation wave has a strong point that it can operate in all speed range with single engine. This paper deals with the simulation of the pulse detonation engine which uses hydrogen peroxide $(H_2O_2)$ mono propellant. Hydrogen peroxide is low-cost propellant, and it is reacted without oxidizer. Comparison between $H_2-O_2$ mixture with $H_2O_2$ mono propellant about thrust, pressure, temperature and velocity shows that $H_2O_2$ is a very useful propellant.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.159-162
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• 2003

Cooling with easy, reliable cryocooler is highly desirable for the commercial and military application The pulse tube refrigerator has no moving parts at the cold end, so that the mechanical vibration and magnetic noise can be reduced to the low level with higher relaibility and longer lifetime than the Stilting cryocooler. The inertance tube improve the performance of pulse tube refrigerator by providing optimal phase shift between pressure and amss flow rate, and it is easiest to implement at large cooling capacity and high operating frequency. In this study, the performance of the inertance pulse tube refrigerator was investigated by analysis. The results show the influence of the diameter and length of the inertance tube on the performance of the refrigerator.

• 동의생리병리학회지
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• 제23권1호
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• pp.237-244
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• 2009

We investigated the effects of acupuncture stimulation on pulse wave variables and heart rate variability (HRV) in healthy adults. To evaluate twenty healthy volunteers (10 men, 10 women) had acupuncture into both Hapkok (Ll4) and Taechung (Liv3) for 15 minutes. Radial pulse, Heart Rate Variability, body temperature and blood pressure were checked before and after acupuncture to evaluate Pulse Wave Variability and Autonomous Function. The results were as follows; Heart rate was significantly increased while systolic blood pressure (mmHg) and diastolic blood pressure (mmHg) were significantly increased after acupuncture treatment. Sixteen subjects didn't change representative pulse wave variables after acupuncture treatment. Energy, height of main peak (H1), height of pre-dicrotic valley (H2) and height of descending valley (H4) were decreased while height of dicrotic peak (H5) was significantly decreased after acupuncture treatment. Time to main peak (T1), time to pre-dicrotic valley (T2), time to dicrotic peak (T5), total time (T) and T-T4 were decreased while time to descending valley (T4) was increased after acupuncture treatment. Total area (At), area of main peak (Aw) and ratio of diastolic period area (Ad) were decreased while ratio of systolic period area (As) and angle of main peak (MPA) were increased after acupuncture treatment. The standard deviation of all normal RR intervals (SDNN) was increased while the root mean square of successive differences between the normal heart beats (RMSSD) was significantly increased after acupuncture treatment by time domain analysis. Low frequency power (LF) and LF/HF ratio were decreased while high frequency power (HF) was significantly increased after acupuncture treatment by frequency domain analysis. This study suggests that acupuncture treatment changes pulse wave variability and heart rate variability. Further study on various acupuncture treatment for pulse wave variability and heart rate variability is required.

• 한국초전도ㆍ저온공학회논문지
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• 제20권3호
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• pp.21-27
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• 2018

It is difficult to fabricate and maintain moving parts of expander at cryogenic temperature. This paper describes numerical analysis and experimental investigation on a cryogenic reciprocating expander without moving piston. An intake valve which takes high-pressure gas, and an exhaust valve which discharges low-pressure gas, are connected to a tube. The inside pressure of the tube is pulsated for work production. This geometric configuration is similar to that of pulse tube refrigerator but without regenerator. An orifice valve and a reservoir are installed to control the phase of the mass flow and the pressure. At the warm end, a heat exchanger rejects the heat which is converted from the produced work of the expanded gas. For the numerical analysis, mass conservation, energy conservation, and local mass function for valves are used as the governing equations. Before performing cryogenic experiments, we carried out the expander test at room temperature and compared the performance results with the numerical results. For cryogenic experiments, the gas is pre-cooled by liquid nitrogen, and then it enters the pulse tube expander. The experiments are controlled by the opening of the orifice valve. Numerical analysis also found the expander conditions that optimize the expander performance by changing the intake pressure and valve timing as well as the opening of the orifice valve. This paper discusses the experimental data and the numerical analysis results to understand the fundamental behavior of such a newly developed non-mechanical expander and elucidate its potential feature for cryogenic application.

• 한국공작기계학회논문집
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• 제12권3호
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• pp.38-44
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• 2003

The solenoid valve in ABS hydraulic modulator is a two directional on-off valve and is controlled by around 100Hz high speed pulse width modulation. When the valve is switched from open state to closed state, noise and vibration due to pressure surge phenomena in the hydraulic line and wheel cylinder are made. In this study, we identify Pressure surge phenomenon in the braking process of a ABS, and investigate the way to reduce the phenomenon. For the purpose of theoretical analysis on the pressure surge in the closed state hydraulic line, characteristic curve method based on wave equation was utilized. To reduce the surge, high frequency control of 20kHz was attempted. The result showed that the surge pressure of 50% was reduced compared to one observed in the low frequency control. Duty variation of high frequency can control current of solenoid valve and prevent sudden change of displacement.

• 전자공학회논문지SC
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• 제45권5호
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• pp.21-27
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• 2008

최근까지 맥진기에 대한 연구 및 상용화 요구가 지속되고 있으나 재현성 확보에 어려움을 겪고 있다. 이러한 재현성을 평가하는 중요 파라미터 중 하나는 맥압의 크기이다. 그러나 맥안은 동잡음에 매우 취약한 특성을 갖고 있다. 본 논문에서는 동잡음에 강한 맥진기 개발을 위하여 동잡음을 자동으로 검출하고 맥 측정구간에서 동잡음이 있는 구간을 제외함으로써 맥진기의 신뢰도를 높일 수 있는 방법을 제안하고자 한다. 동잡음 검출 시스템은 3축 가속도 센서, 근전도, 2축 기울기 센서로 구성하였으며, 시스템의 적합성을 평가하기 위하여 신장, 굴곡, 회전의 세 가지 동작에 대한 센서별 출력 신호 특성을 살펴보았다. 또한 맥진 센서를 맥진 위치에 적용한 상태에서 고주파 동잡음 및 저주파 동잡음을 유발하여 각 센서별 출력 신호 특성을 살펴보았다. 그 결과 저주파 동잡음은 근전도, 가속도 신호, 기울기 신호 순으로 동잡음 발생을 확인할 수 있었으며, 안정된 맥파 신호는 고주파 동잡음과 비슷하게 근 수축이 중단된 뒤 약 2초가 경과한 후에 얻어지는 것을 확인할 수 있었다. 이러한 사실을 근거로 동잡음 검출 규칙을 설정하였으며, 이를 구현한 동잡음 검출 알고리즘을 제안하였다.

• 대한임상검사과학회지
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• 제52권2호
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• pp.119-127
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• 2020

선행 연구에서 동맥경화와 폐기능이상과 연관성이 있었다. 맥압은 동맥경화의중요한 예측이지만 아직까지 폐기능이상과 맥압의 연관성은 불분명하다. 따라서, 본 연구는 대한민국 비흡연 성인을 대상으로 맥압과 폐기능장애(예측 강제 폐활량, 예측 강제 날숨량 1초율)의 관련성을 알아보고자 실시하였다. 본 연구는 2013년부터 2015년까지 3년간의 대한민국 국민건강영양조사자료에서 비흡연 성인(6,857명)을 대상으로 실시하였다. 본 연구의 주요 결과는 맥압과 폐기능장애에 대한 관련 변수를 보정한 후의 결과에서, 정상 맥압(pulse pressure, PP≤60 mmHg)에 비하여 고맥압(PP>60 mmHg; 1.337 [95% confidence interval (CI), 1.049~1.703)에서 제한성 폐질환(restrictive pulmonary disease, RPD; the predicted FVC<80.0% with FEV₁/FVC≥70.0%)의 교차비(odds ratio, OR)가 유의하게 높았다. 추가적으로, 정상맥압에 비하여 고맥압(1.339 [95% CI, 1.093~1.642])에서 폐쇄성 폐질환(obstructive pulmonary disease, OPD; FEV₁/FVC<70.0%)의 교차비가 유의하게 높았다. 결론적으로, 대한민국 비흡연 성인에서 제한성 폐질환 및 폐쇄성 폐질환은 고맥압과 유의한 관계가 있었다.

• 대한기계학회논문집A
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• 제34권8호
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• pp.981-987
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• 2010

Split Hopkinson Pressure Bar(SHPB) 실험기법은 고변형률 하중 조건하에서 변형하는 여러 가지 공업 재료의 변형 거동 특성을 규명하는데 가장 널리 사용되는 실험 방법 중의 하나이다. 본 논문에서는 봉을 통하여 전파하는 응력파의 모양과 라이징 시간을 제어할 수 있는 pulse shaper를 사용하는 수정 SHPB 실험기법을 이용하였다. 수정 SHPB 실험 장치에 고온 장치를 부착하고 알루미늄 합금 7075-T6의 고변형률 하에서의 고온 변형거동에 대한 연구를 수행하였다. 고온 수정 SHPB 실험 장치를 이용하여 알루미늄 합금 7075-T6의 온도와 변형률속도에 따른 기계적 특성을 규명하고, 실험적으로 얻어진 데이터를 Johnson-Cook 구성방정식을 적용하여 알루미늄 합금 7075-T6의 동적 거동을 모델 하는 변수를 결정하였다.

• Journal of Magnetics
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• 제15권4호
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• pp.213-220
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• 2010

Since the hypothalamus immediately reacts to a nerve by processing all the information from the human body and the external stimulus being conducted, it performs a significant role in internal secretion; thus, a diverse and rapid stimulus pulse is required. By detecting Zero Detector accurately via the application of AVR on-Chip (ATMEL) using commercial electricity, chopping generates a stimulus pulse to the brain using an IGBT gate to designate a new magnetic stimulation following treatment and diagnosis. To simplify and generate a diverse range of stimuli for the brain, chopping can be used as a free magnetic stimulator. Then, commercial frequency (60Hz) is chopped precisely at the first level of the leakage transformer to deliver an appropriate stimulus pulse towards the hypothalamus when necessary. Discharge becomes stable, and the chopping frequency and duty-ratio provide variety after authorizing a high-pressure chopping voltage at the second level of the magnetic stimulator. These methods have several aims. The first is to apply a variable stimulus pulse via accurate switching frequency control by a voltaic pulse or a pulse repetition rate, according to the diagnostic purpose for a given hypothalamus. Consequently, the efficiency tends to increase. This experiment was conducted at a maximum of 210 W, a magnetic induced amplitude of 0.1~2.5 Tesla, a pulse duration of $200{\sim}350\;{\mu}s$, magnetic inducement of 5 Hz, stimulus frequency of 0.1~60 Hz, and a duration of stimulus train of 1~10 sec.