• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.166-173
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• 2014

A noncontact nondestructive testing (NDT) method is proposed to detect the damage of pipeline structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND: YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using three dimensional Fourier transformation (3DFT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a pipeline structures is conducted using the damage-sensitive features. Finally, the pipes with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.391-395
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• 1999

We present the measurement of the diffraction efficiency and response time of the photorefractive grating recorded in $LiNbO_3$ photorefractive crystal doped with 4%-mole MgO. Two laser sources were used in the experiments; frequency-doubled Q-switched Nd:YAG laser ($\lambda$=532 nm) and cw Ar-ion laser ($\lambda$=514.5 nm). The same optical geometry was also used in both experiments in order to maintain the experimental consistency. Using the two-wave mixing scheme in both experiments we measured the maximum diffraction efficiency in the range of beam intensity of 1.6~100 W/ $\textrm{cm}^2$, and the response times for both cases of recording and erasing. Two sets of results obtained from the experiments are compared and analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.5
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• pp.785-793
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• 2016

This paper analyzes an LCL-type isolated dc-dc converter operating for constant output voltage in the continuous conduction mode(CCM) with resistances of parasitic losses-static drain-source on resistance of power switch, ESR of resonant network(L-C-L)-using a high loaded quality factor Q assumptions and fourier series techniques. Simple analytical expressions for performance characteristics are derived under steady-state conditions for designing and understanding the behavior of the proposed converter. The voltage-driven rectifier is analyzed, taking into account the diode threshold voltage and the diode forward resistance. Experimental results measured for a proposed converter at low input voltage and various load resistances show agreement to the theoretical performance predicted by the analysis within maximum 4% error. Especially in the case of low output voltages and large loads, It is been observed that introduction of both rectifier and the parasitic components of converter had considerable effect on the performance.

• BMB Reports
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• v.38 no.3
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• pp.266-274
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• 2005

High temperature requirement A (HtrA) and its homologues constitute the HtrA familiy proteins, a group of heat shock-induced serine proteases. Bacterial HtrA proteins perform crucial functions with regard to protein quality control in the periplasmic space, functioning as both molecular chaperones and proteases. In contrast to other bacterial quality control proteins, including ClpXP, ClpAP, and HslUV, HtrA proteins contain no regulatory components or ATP binding domains. Thus, they are commonly referred to as ATP-independent chaperone proteases. Whereas the function of ATP-dependent chaperone-proteases is regulated by ATP hydrolysis, HtrA exhibits a PDZ domain and a temperature-dependent switch mechanism, which effects the change in its function from molecular chaperone to protease. This mechanism is also related to substrate recognition and the fine control of its function. Structural and biochemical analyses of the three HtrA proteins, DegP, DegQ, and DegS, have provided us with clues as to the functional regulation of HtrA proteins, as well as their roles in protein quality control at atomic scales. The objective of this brief review is to discuss some of the recent studies which have been conducted regarding the structure and function of these HtrA proteins, and to compare their roles in the context of protein quality control.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.12
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• pp.609-615
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• 2005

A 30kW electrical power conversion system is developed for a variable speed wind turbine. In the wind energy conversion system(WECS) a synchronous generator with field current excitation converts the mechanical energy into electrical energy. As the voltage and the frequency of the generator output vary according to the wind speed, a 6-bridge diode rectifier and a PWM boost chopper is utilized as an ac-dc converter maintaining the constant dc-link voltage with only single switch control. An input current control algorithm for maximum power generation during the variable speed operation is proposed without any usage of speed sensor. Grid connection type PWM inverter converts dc input power to ac output currents into the grid. The active power to the grid is controlled by q-axis current and the reactive power is controlled by d-axis current with appropriate decoupling. The phase angle of utility voltage is detected using software PLL(Phased Locked Loop) in d-q synchronous reference frame. Experimental results from the test of 30kW prototype wind turbine system show that the generator power can be controlled effectively during the variable speed operation without any speed sensor.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1347-1349
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• 1995

Insulators contaminated by salt particles may cause flashovers in humid climate or light rain. Therefore, the quantity of salt on insulators should be monitored not to exceed a critical value. We propose a new remote sensing technique to measure the quantity of salt on insulators of power systems. The amount of the salt is measured from the intensity of the spontaneous emission from the sodium atoms. In this paper, a compact remote on-line salt-meter composed of Q Switch pulsed Nd:YAG laser and emission signal detection system will be introduced. And as the first result of this study, the operating characteristics of our developing laser system is also introduced.

• Proceedings of the Korea Multimedia Society Conference
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• 2000.04a
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• pp.40-48
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• 2000

ABR 서비스에서 전송률 제어 방식은 크게 크래딧 방식과 전송률 기반 방식으로 구분되는데, 전송률 기반 방식의 대표적인 스위치 알고리즘인 EPRCA(Enhanced Properties RATE Control Algorithm)를 비롯하여 지금까지 제안된 전송률 기반 폭주제어방법은 대부분 스위치의 평균 큐 길이 Q 에 의한 폭주제어 방식을 사용한다. [2, 6, 8]. 폭주판단방법은 큐 임계치 방식, 부하 임계치 방식, 큐 증가 임계치 방식으로 나눌 수있다. 큐 임게치 만을 사용하는 방법이 가장 일반적이지만, 큐 길이와 큐 임계치의 비교에 따른 지연이 발생하게 된다. 본 논문에서는 큐 길이의 증감 상태를 큐 임계치와 동시에 사용하여 폭주제어를 신속히 할 수 있는 스위치 알고리즘을 제안한다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.623-628
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• 2007

This paper presents the new power line coupler which is applicable to spread spectrum power line communications. The proposed coupler maintains the adequate value of a capacitor between the transmitter mode and the receiver mode using a switch. In the transmit mode, the relatively high value of the capacitor is chosen to minimize the attenuation of transmitted signals. In the receiver mode, the value of the capacitor is chosen to be small enough so that the coupler attenuates power line noises. This coupler reduced the magnitude distortion due to having a high Q value and the power consumption caused by the AC current flowing into the capacitor. The simulation and measurement results show the improved performance in the transmitter and receiver mode, respectively.

• Journal of information and communication convergence engineering
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• v.7 no.3
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• pp.377-382
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• 2009

In this paper, theoretical analysis for metropolitan optical networks is performed. First, analytical optical SNR is derived assuming each node consists of an EDFA, an optical filter, an optical switch, and a VOA, and then the relationship between OSNR and BER is studied. In a metropolitan optical network, an optical signal can be dropped to deliver data, and we also studied the effect of drop loss on system performance. When the drop loss is relatively small, the receiver structure of the node can be treated as a preamplifier receiver which is widely used in long-haul systems. In that case, ASE noise from EDFAs is the dominant noise source in the receiver. However, system performance is relatively insensitive to OSNR when the drop loss is significant because of the noise sources in the receiver (thermal and shot noise).

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.197-204
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• 2014

In this paper an Improved Zero Voltage Zero Current Pulse Width Modulation Forward converter which employs a simple resonance snubber circuit is introduced. A simple snubber circuit consists of a capacitor, an inductor and two diodes. In proposed converter, switch Q1 operates at ZCS turn-on, and ZVS turn-off conditions and all-passive semiconductor devices operate at ZVZCS turn-on and turn-off state. The proposed converter is analyzed and various operating modes of the ZVZCS-PWM forward converter are discussed. Analysis and design considerations are presented and the prototype experimental results of a 100w (40 V/2.5A) proposed converter operating at 30 KHz switching frequency confirm the validity of theoretical analysis.