• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.426-434
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• 2006

The impact of leakage was incorporated into the transfer functions of the complex head and discharge. The impedance transfer functions for the various leaking pipeline systems were also derived. Hydraulic transients could be efficiently analyzed by the developed method. The simulation of normalized pressure variation using the method of characteristics and the impulse response method shows good agreement to the condition of turbulent flow. The leak calibration could be performed by incorporation of the impulse response method with Genetic Algorithm (GA) and Harmony Search (HS). The objective functions for the leakage detection can be made using the pressure-head response at the valve, or the pressure-head or the flow response at a certain point of the pipeline located upstream from the valve. The proposed method is not constrained by the Courant number to control the numerical dissipation of the method of characteristics. The limitations associated with the discreteness of the pipeline system in the inverse transient analysis can be neglected in the proposed method.

• 한국전자파학회논문지
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• 제19권11호
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• pp.1223-1232
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• 2008

본 논문에서는 비공진형 협벽 도파관 슬롯 배열 설계를 위해 필요한 기준이 되는 단위 슬롯 어드미턴스를 해석적으로 추출하는 방법을 제시하였다. 충분한 개수의 동일 기울임 각을 가지는 교번 슬롯 구조에 대해, 도파관 협벽의 단위 슬롯과 단위 슬롯 양쪽에 이웃한 전송선 부분을 균일한 손실 전송선으로 근사하고, 이로부터 손쉽게 전체의 ABCD 행렬을 계산하여 전체의 시뮬레이션 또는 측정값과 비교함으로써, 손실 전송선의 복소 특성 임피던스와 복소 전파 상수를 구하고 해석 적으로 정규화 된 슬롯 어드미턴스를 추출하였다. 제안한 방법의 타당성을 입증하기 위해, 대역 협벽 도파관 슬롯 배열 설계용으로 제작된 기준 슬롯 도파관 샘플의 정규화 된 슬롯 어드미턴스를 구하고 기존의 방법으로 얻은 값과 비교하여 잘 일치함을 보였다.

• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3475-3481
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• 2014

This paper describes how primary contaminants in ambient air affect the performance of the cathode in fuel cell electric vehicle applications. The effect of four atmospheric pollutants ($SO_2$, $NH_3$, $NO_2$, and CO) on cathode performance was investigated by air impurity injection and recovery test under load. Electrochemical analysis via polarization and electrochemical impedance spectroscopy was performed for various concentrations of contaminants during the impurity test in order to determine the origins of performance decay. The variation in cell voltage derived empirically in this study and data reported in the literature were normalized and juxtaposed to elucidate the relationship between impurity concentration and performance. Mechanisms of cathode degradation by air impurities were discussed in light of the findings.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.462-468
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• 2018

The piezoelectric energy harvesting characteristics of a trapezoidal cantilever generator with lead zirconate titanate (PZT) laminate were investigated with various Ag inner electrodes. The piezoelectric mode of operation was a transverse mode by using a planar electrode pattern. The piezoelectric cantilever generator was fabricated using trapezoidal cofired-PZT/Ag laminates by five specimens of 2, 3, 4, 7, and 13 layers of Ag. As the number of Ag electrodes increased, impedance and output voltage at resonant frequency significantly decreased, and capacitance and output current showed an increasing tendency. A maximum output power density of $7.60mW/cm^3$ was realized for the specimen with seven Ag layers in the optimal condition of acceleration (1.2 g) and resistive load ($600{\Omega}$), which corresponds to a normalized power factor of $5.28mW/g^2{\cdot}cm^3$.

• 한국운동역학회지
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• 제16권3호
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• pp.137-148
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• 2006

The purpose of this study was to compare muscle activity in the lower extremity during walking wearing jogging and roller shoes. Twelve male middle school students (age: 15.0 yrs, height 173.7 cm, weight 587.7 N) who have no known musculoskeletal disorders were recruited as the subjects. Seven pairs of surface electrodes (QEMG8, Laxtha Korea, gain = 1,000, input impedance >$1012{\Omega}$, CMMR >100 dB) were attached to the right-hand side of the body to monitor the rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), and medial (GM) and lateral gastrocnemius (GL) while subjects walked wearing roller and jogging shoes in random order at a speed of 1.1 m/s. An event sync unit with a bright LED light was used to synchronize the video and EMG recordings. EMG data were filtered using a 10 Hz to 350 Hz Butterworth band-passdigital filter and further normalized to the respective maximum voluntary isometric contraction EMG levels. For each trial being analyzed, five critical instants and four phases were identified from the recording. Averaged IEMG and peak IEMG were determined for each trial. For each dependent variable, paired t-test was performed to test if significant difference existed between shoe conditions (p<.05). The VM, TA, BF, and GM activities during the initial double limb stance and the initial single limb stance reduced significantly when going from jogging shoe to roller shoe condition. The decrease in EMG levels in those muscles indicated that the subjects locked the ankle and knee joints in an awkward fashion to compensate for the imbalance. Muscle activity in the GM for the roller shoe condition was significantly greater than the corresponding value for the jogging shoe condition during the terminal double limb stance and the terminal single limb stance. Because the subjects tried to keep their upper body weight in front of the hip to prevent falling backward, the GM activity for the roller shoe condition increased. It seems that there are differences in muscle activity between roller shoe and jogging shoe conditions. The differences in EMG pattern may be caused primarily by the altered position of ankle, knee, and center of mass throughout the walking cycle. Future studies should examine joint kinematics during walking with roller shoes.

• 지구물리와물리탐사
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• 제5권4호
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• pp.299-308
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• 2002

소형루프 전자탐사의 가탐심도를 추정하기 위하여 주파수영역에서 2층구조에 대한 감도를 해석적으로 유도하였다. 이를 기초로 송수신 간격 2m 내외의 다중주파수 전자탐사 기기의 감도를 분석하고, 반응의 크기를 기준으로 가탐심도를 추정하였다. 먼저 감도 계산 결과는 하부층에 대한 감도는 동상성분이 이상성분에 비해 매우 높고 상부층의 두께가 20m에 이르더라도 저주파수 대역에서는 상부층의 감도에 비해 절대적으로 크다는 것을 나타낸 반면, 이상성분은 하부층에 대한 감도가 매우 약함을 보여준다. 따라서 다중 주파수를 이용한 소형루프 전자탐사에서는 동상성분의 정확한 측정이 가탐심도의 증대에 필수적임을 입증하였다. 전기비저항이 100ohm-m인 상부층 밑에 10ohm-m의 전기비저항을 갖는 하부층이 존재할 경우에는, 동상성분의 정확한 측정을 통하여 잡음 수준을 고려하더라도 10m까지의 가탐심도를 충분히 확보할 수 있으며 따라서 매립장의 침출수 분포 범위 영상화 등을 위해서 유용할 것으로 보인다. 그러나 전기비저항이 1,000ohm-m로 높은 기반암이 존재할 경우에는 비록 하부층의 감도는 상부층에 비해 매우 높으나 반응의 절대값이 매우 미약하여 탐지가 어려우며 이상성분 자료와의 복합적인 해석을 통해서도 기기의 정확도를 고려할 때, 가탐심도가 5 m를 넘기 힘든 것으로 나타났다. 따라서 전기비저항이 높은 지역에서는, 송수신 간격이 2m 내외로 짧은 다중주파수 소형루프 전자탐사법이 금속성 매설물의 탐지를 위해서는 유용하지만 기반암의 심도 규명에는 적절치 않다.