• Smart Structures and Systems
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• 제16권2호
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• pp.281-294
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• 2015

Bolted joint connection is the most commonly used connection element in structures and devices. The loosening due to external dynamic loads cannot be observed and measured easily and may cause catastrophic loss especially in an extreme requirement and/or environment. In this paper, an innovative Real-time Cross-Correlation Method (RCCM) for monitoring of the bolted joint loosening was proposed. We apply time reversal process on stress wave propagation to obtain correlation signal. The correlation signal's peak amplitude represents the cross-correlation between the loosening state and the baseline working state; therefore, it can detect the state of loosening. Since the bolt states are uncorrelated with noise, the peak amplitude will not be affected by noise and disturbance while it increases SNR level and increases the measured signals' reliability. The correlation process is carried out online through physical wave propagation without any other post offline complicated analyses and calculations. We implemented the proposed RCCM on a single bolt/nut joint experimental device to quantitatively detect the loosening states successfully. After that we implemented the proposed method on a real large structure (reaction wall) with multiple bolted joint connections. Loosening indexes were built for both experiments to indicate the loosening states. Finally, we demonstrated the proposed method's great anti-noise and/or disturbance ability. In the instrumentation, we simply mounted Lead Zirconium Titanate (PZT) patches on the device/structure surface without any modifications of the bolted connection. The low-cost PZTs used as actuators and sensors for active sensing are easily extended to a sensing network for large scale bolted joint network monitoring.

• 자원환경지질
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• 제14권3호
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• pp.111-122
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• 1981

This study is a model analysis for an effective application of the geophysical prospecting to the investigation of geological structures or useful resources, and the purpose of it is to research a property of the electrical resistivity prospecting, especially by using a Three-Point electrode array method. In using the Three-Point electrode array method, it is theoretically assumed to choose the infinite for a distance between the two current electrodes, however it is impossible in applying to the practical field prospecting. Therefore this study was conducted for determination and presentation of a minimum appropriate distance between the two current electrodes by making a study on prospecting effect in the variation of distance between both the electrodes. In case that the ratios of the distance between the two current electrodes to that between the two potential electrodes are respectively chosen for 40, 400, 5,000, the experimental data of this study showed that the minimum appropriate distance between the two current electrodes is forty times as much as that between two potential electrodes. In order to make clear a problem about prospecting depth which is essential to the data processing, it had been chosen equally to the distance between two potential electrodes. As a result of it, it was shown that the anomaly is appeared along the position of an assumed ore body. Consequently it was found out that the prospecting depth of the Three-Point electrode array method is the same as the distance between the two potential electrodes. From the model experiment on the sheeting ore body(or linear structure) of horizontal, dipping of $30^{\circ}$, $60^{\circ}$ and vertical on the basis of above experimental condition, it was found out that the position and dip of assumed ore body could be inferred from the aspects of the equiresistivity curve. In consequence of performing out the simultaneous Normal and Reversal electrode movement, it was shown that the electrode movement of the Reversal forms the anomaly more clearly than that of Normal when the sheeting ore body is situated obliquely, therefore it could be ascertained that the electrode movement have to be performed simultaneously in the manner of Normal and Reversal. It was also exhibited that the aspect of the equiresistivity curve forms symmetrically when an assumed ore body (or linear structure) is situated horizontally or vertically, that is, symmetrically, and moreover that the aspect of the equiresistivity curve forms unsymmetrically when an assumed ore body (or linear structure) is situated obliquely. On the basis of these experimental analysis it is thought that it can be inferred from the aspect of equiresistivity curve whether an assumed ore body is obliquely situated or not.

• 한국수자원학회논문집
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• 제55권9호
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• pp.701-705
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• 2022

이상기후로 가뭄이 빈번해짐에 따라 수자원 시설의 가뭄대응력 산정에 대한 필요성이 커지고 있다. 이를 위해서는 신뢰할 수 있는 갈수빈도 유입량 추정 연구가 선행되어야 한다. 본 연구는 기존 K-water의 가뭄 빈도유입량 추정방법인 누가차분법의 세 가지 한계, 즉 음의 값과 역전현상, 그리고 평년 이상으로 과대 산정되는 문제의 발생조건에 대해 각각 2변수 log-normal 분포와 Gumbel 분포를 적용하여 이론적 고찰을 실시하였다. 그 결과, 음의 값은 누가 과정에서 scale parameter보다 location parameter의 변화가 커지는 경우 발생함을 확인하였고, 역전현상 및 평년보다 큰 가뭄유입량은 누가 과정에서 표준편차가 감소하는 경우 발생하는 것으로 분석되었다.

• Journal of Electrical Engineering and Technology
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• 제7권5호
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• pp.705-713
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• 2012

In this paper, a novel 12/14 hybrid pole type bearingless switched reluctance motor (BLSRM) with short flux path and no flux-reversal in the stator is proposed. The proposed BLSRM has separated rotating torque and suspending force poles. Because of independent characteristics between torque and suspending force poles, the torque control can be decoupled from the suspending force control. Due to the short flux path without any reversal flux, compared to the 8/10 hybrid stator pole BLSRM, the output torque is significantly improved and the air-gap is easier to control. Meanwhile, basic design principle for the proposed structure is described. To verify the proposed structure, finite element method (FEM) is employed to get characteristics of the proposed structure and 8/10 hybrid stator pole BLSRM. Based on the analysis, a prototype of the proposed BLSRM is designed and manufactured. Finally, validity of the proposed structure is verified by the experimental results.

• 한국발생생물학회지:발생과생식
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• 제14권1호
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• pp.1-5
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• 2010

We investigated the androgenic effects of 11-ketotestosterone (11-KT) on gonadal sex reversal and spermatogenesis in honeycomb grouper Epinephelus merra by method of gonadal biopsy. 11-KT was injected intramuscularly at a concentration of 1 and $10{\mu}g$ body weight. The proportion of cross sectional area of the gonad occupied by each germ cell type was measured and compared pre- and post-injection group. During the sex change phase, the distribution ratio of oocytes was decreased in all fish of 11-KT treatment group while the distribution ratio of spermatocytes was increased than pre-injection group. In male phase, all fish of 11-KT treatment group shown the increased distribution ratio of spermatocytes, but the distribution ratio of spermatozoa was decreased than pre-injection group. The present results suggest that 11-KT can stimulate degeneration of oocytes, proliferation of spermatocytes and spermiation in honeycomb grouper.

• Archives of Pharmacal Research
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• 제29권9호
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• pp.757-761
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• 2006

Six protoberberine alkaloids were isolated from the chloroform layer of the rhizome of Coptis japonica Makino (Ranunculaceae). The structures of the isolated compounds were determined to be 6-([1,3]dioxolo[4,5-g]isoquinoline-5-carbonyl)-2,3-dimethoxy-benzoic acid methyl ester (1), oxyberberine (2), 8-oxo-epiberberine (3), 8-oxocoptisine (4), berberine (5) and palmatine (6) by physicochemical and spectroscopic methods. The compound 3 (8-oxo-epiberberine) was first isolated from natural sources. The compounds were tested for cytotoxicity against five tumor cell lines in vitro by SRB method, and also tested for the MDR reversal activities. Compound 4 was of significant P-gp MDR inhibition activity with ED50 value $0.018\;{\mu}g/mL$ in MES-SA/DX5 cell and $0.0005\;{\mu}g/mL$ in HCT15 cell, respectively.

• Smart Structures and Systems
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• 제4권4호
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• pp.391-406
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• 2008

This study attempts to develop a real-time debonding monitoring system for carbon fiber-reinforced polymer (CFRP) strengthened structures by continuously inspecting the bonding condition between the CFRP layer and the host structure. The uniqueness of this study is in developing a new concept and theoretical framework of nondestructive testing (NDT), in which debonding is detected without relying on previously-obtained baseline data. The proposed reference-free damage diagnosis is achieved based on the concept of time reversal acoustics (TRA). In TRA, an input signal at an excitation point can be reconstructed if the response signal measured at another point is reemitted to the original excitation point after being reversed in the time domain. Examining the deviation of the reconstructed signal from the known initial input signal allows instantaneous identification of damage without requiring a baseline signal representing the undamaged state for comparison. The concept of TRA has been extended to guided wave propagations within the CFRP-strengthened reinforced concrete (RC) beams to improve the detectibility of local debonding. Monotonic and fatigue load tests of large-scale CFRP-strengthened RC beams are conducted to demonstrate the potential of the proposed reference-free debonding monitoring system. Comparisons with an electro-mechanical impedance method and an inferred imaging technique are provided as well.

• The Journal of Asian Finance, Economics and Business
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• 제5권4호
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• pp.21-34
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• 2018

The study tests the Fama and French three-factor model by using the newly created Islamic equity style indices. Based on a dataset from May 2006 to April 2011, the three-factor model is tested based on returns of Islamic unit trust funds using the Generalized Method of Moments (GMM) methodology. The sample period is also divided between periods before and after the Global Financial Crisis in August 2008 to test for robustness, and the Bai and Perron (2003) multiple structural break test was used to determine the structural break in the series. The analysis shows that the Fama and French model is valid for Islamic unit trust funds before and after the collapse of Lehman Brothers. The result further indicates the reversal of size effect. As for trading strategies, value funds outperform growth funds by annualized 3.13 percent for the full period. During pre-crisis period, value funds perform better than growth funds while in post-crisis, size factor yields better return than other strategies. As policy suggestion, fund managers need to be aware of the reversal of size effect, and they need to ensure a more transparent stock selection process so that investors can make an informed decision in their asset allocation.

• 한국통신학회논문지
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• 제19권9호
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• pp.1782-1792
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• 1994

$Ti:LiNbO_3$채널형 광도파로와 Asymmetric Coplanar Strip(ACPS) 전극구조를 이용해서, $1.3{\mu}m$에서 동작하는 진형파형 위상 광변조기를 설계, 제작한 다음 변조특성을 관찰하였다. 위상정합이 개선되도록 ACPS 진행파형 전극을 설계하기 위해서 전극과 완충박막의 두께를 포함하여, 전극제원의 해석적 함수로 특성저항, 변조파의 유효굴절률 및 전극손실 등을 고려하였다. Ti 확산방법으로 저손실 채널형 광도파로 제작하였으며, double-spin image reversal 공정을 이용해서 $2.5{\mu}m$ 두께의 전극을 형성하였다. 9GHz 부근에서의 전극구조 공진형상 때문에 변조특성이 제한 되었지만, 2.5GHz 까지는 큰 왜곡없이 변조특성이 관찰되었다.

• 한국전산구조공학회논문집
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• 제19권4호
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• pp.347-356
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• 2006

본 논문에서는 단면상의 화이버 요소를 사용하여 3차원 강구조물의 점진적인 소성화를 고려하는 실용적인 비선형 비탄성 해석방법을 개발하였다. 부재의 p-$\delta$, p-$\Delta$ 등의 기하비선형은 안정함수로 고려하였다. 잔류응력은 단면상에 있는 화이버 요소에 초기응력을 가하여 고려하였다. 각 하중 단계에서 탄성상태인 단면을 계산하여 축강성과 휨강성을 직접 결정함으로서 점진적인 소성화를 고려하였다. 각 화이버 요소의 응력 변화를 계산하여 변형률 반전효과를 고려하였다. 제안된 해석 방법은 3차원 강구조물의 실용적인 해석 및 설계에 유용하게 사용될 것이라 판단한다.