• Smart Structures and Systems
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• 제18권2호
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• pp.267-291
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• 2016

In this research work, an exact analytical solution for thermal buckling analysis of functionally graded material (FGM) sandwich plates with clamped boundary condition subjected to uniform, linear, and non-linear temperature rises across the thickness direction is developed. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory accounts for parabolic distribution of the transverse shear strains, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present refined theory. The non-linear governing equations are solved for plates subjected to simply supported and clamped boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The effects of aspect and thickness ratios, gradient index, on the critical buckling are all discussed.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.324-331
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• 2010

Cavitation in cryogenic fluids generates substantial thermal effects and strong variations in fluid properties, which in turn alter the cavity characteristics. In order to investigate the cavitation characteristics in cryogenic fluids, numerical simulations are conducted around an axisymmetric ogive in liquid nitrogen and hydrogen respectively. The modified Merkle cavitation model and energy equation which accounts for the influence of cavitation are used, and variable thermal properties of the fluid are updated with software. A good agreement between the numerical results and experimental data are obtained. The results show that vapor production in cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity becomes lower. The cavitation characteristics in cryogenic fluids are obtained that the cavity seems frothy and the cavitation intense is lower. It is also found that when the fluid is operating close to its critical temperature, thermal effects of cavitation are more obviously in cryogenic fluids. The thermal effect on cavitation in liquid hydrogen is more distinctively compared with that in liquid nitrogen due to the changes of density ratio, vapour pressure gradient and other variable properties of the fluid.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 춘계종합학술대회
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• pp.289-292
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• 2005

각종 산업기기에서 사용되는 PID 제어기는 단순한 구조와 모델링 오차에 대한 강인성으로 인하여 광범위하게 사용되고 있다. 그러나 외란이 인가되거나 부하 특성이 비선형적으로 변화할 때에 적절한 이득과 성능을 얻기 어려워 고성능 제어 특성을 기대하기 어렵다. 본 연구에서는 구조가 간단하고, 시스템 파라메터의 변화에 강인한 적응 PID 제어기를 제안한다. 제안된 적응 PID제어기의 성능 평가를 위하여 비선형 DC 모터의 가변 속도제어에 적용하고, 결과를 모의실험을 통하여 보이고자한다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.701-704
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• 2005

PID 제어기는 구조가 간단하고 적용이 용이하다는 장점으로 인하여 널리 사용되고 있는 제어방식이다. 이러한 선형 PID 제어기는 시스템의 파라메터가 변화가 있거나 부하 특성이 비선형적으로 변화할 때에 적절한 이득과 성능을 얻기 어려워 고성능 제어 특성을 기대하기 어렵다. 본 연구에서는 세포성 면역 반응과 경사감소학습에 기초하여 비선형 PID 제어기를 설계하고, 설계된 제어기의 이득과 비선형 함수의 파라메터들을 실시간 적응적으로 학습할 수 있는 학습 알고리즘을 개발하고, 이를 제어시스템에 적용하였다. 제안된 비선형 PID 제어기는 비선형 직류 모터 시스템의 파라메터들이 변화하거나 주파수가 다른 추종 명령에 대하여, 적응적으로 이득을 변화 시키며 추종함을 보였다.

• 대한전기학회논문지
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• 제38권11호
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• pp.861-869
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• 1989

본 논문에서는 폰트라이긴의 최대원리를 이용한 가압경수형 원자로(PWR)의 부하추종 운전시 제논진동 최적화 문제가 제시되었다. 최적화 모델은 2차 목적함수를 갖고 있는 최적 추적제어문제로 정식화 하였으며, 1군 확산방정식과 제논-아이오다인 동특성 방정식을 등호 제약조건으로 고려하였다. 최적화 모델에 최대원리를 적용하므로서, 문제는 제약조건이 없는 단일시간 문제로 분리되었으며, 분리된 부 문제는 공액 경사법을 이용하여 최적화 하였다. 계산결과는 제논진동이 최소화되어 원자로가 규정된 출력분포를 유지하면서 전력계총에서 요구하는 출력을 잘 추종 하였다.

• 한국전기전자재료학회논문지
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• 제24권6호
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• pp.504-509
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• 2011

The conducting current of non-uniform plasma immersed electrode consists of ion current and secondary electron emission current caused by the impinging ion current. The ion current is determined by the ion dose passing through the sheath in front of electrode and the ion distribution in front of the electrode plays an important role in the secondary electron emission. The investigation of the distributed plasma and secondary electron effect on electrode ion current was carried out as the stainless steel electrode plugged with quartz tube was immersed in the inductively coupled Ar plasma using the antenna powered by 1 kw and the density profile was measured. After that, the negative voltage was applied by 1 kV~6 kV to measure the conduction current for the analysis of ion current.

• 생약학회지
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• 제42권3호
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• pp.240-245
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• 2011

A high-performance liquid chromatography (HPLC) method was developed for quantitative analysis of liquiritin and glycyrrhizin in Sagunja-tang (SGT, Sijunzi-tang in Chinese), a traditional Korean medicine. HPLC analysis was performed using a Gemini C18 column operating at $40^{\circ}C$, and photodiode array (PDA) detection at 254 nm and 280 nm for quantification of the two components in SGT. The mobile phase using a gradient flow consisted of two solvent systems. Solvent A was 1.0% (v/v) aqueous acetic acid and solvent B was acetonitrile with 1.0% (v/v) acetic acid. Calibration curves were acquired with $r^2$ values > 0.9998, and the relative standard deviations (RSDs, %) for intra- and inter-day precision were not exceed 4.0%. The recovery of each component was in the range of 91.85 - 108.62%, with a RSD less than 4.0%. The contents of the two components in SGT were 7.94 - 13.83 mg/g.

• Molecular & Cellular Toxicology
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• 제2권1호
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• pp.11-14
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• 2006

In this study we attempted to develop a novel genomic method to selectively isolate target functional microbial genomes from environmental samples. For this purpose, stable isotope probing (SIP) was applied in selectively isolating organic pollutant-assimilating populations. When soil microbes were fed with $^{13}C-labeled $ biphenyl, biphenyl-utilizing cells were incorporated with the heavy carbon isotope. The heavy DNA portion was successfully separated by CsCl equilibrium density gradient. And the diversity in the heavy DNA was sufficiently reduced, being suitable for the current DNA microarray techniques to detect biphenyl-utilizing populations in the soil. In addition, we proposed a new way to get more genetic information by combining this SIP method with selective metagenomic approach. The increased selective power of these new DNA isolation methods will be expected to provide a good quality of new genetic information, which, in turn, will result in development of a variety of biomarkers that may be used in assessing ecotoxicology issues including the impacts of organic hazards, and antibiotic-resistant pathogens on human and ecological systems.

• 약학회지
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• 제58권3호
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• pp.158-164
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• 2014

Dangguisu-san is a well-known traditional Korean herbal medicine prescription and has been widely used to treat ecchymosis, blood stagnation, and pain resulting from physical shock in Korea. In this study, an ultra-performance liquid chromatography-electrospray ionization-mass spectrometer method was established for the simultaneous determination of the 17 biomarker components in Dangguisu-san. All analytes were separated on an UPLC BEH $C_{18}$ ($100{\times}2.1$ mm, $1.7{\mu}m$) column and maintained at $45^{\circ}C$. The mobile phase consisted of two solvent systems, 0.1% (v/v) formic acid in water (A) and acetonitrile (B) by gradient flow. The injection volume was $2.0{\mu}l$ and the flow rate was 0.3 ml/min with detection at mass spectrometer. Calibration curves of the 17 biomarker components were acquired with $r^2$ values ${\geq}0.9951$. The values of limit of detection and quantification of all analytes were 0.02~6.32 ng/ml and 0.05~18.95 ng/ml, respectively. The amounts of the 17 components in Dangguisu-san sample were $3.17{\sim}13,224.50{\mu}g/g$.

• Coupled systems mechanics
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• 제8권1호
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• pp.1-17
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• 2019

The present paper deals with delamination fracture analyses of the multilayered functionally graded non-linear elastic Symmetric Split Beam (SSB) configurations. The material is functionally graded in both width and height directions in each layer. It is assumed that the material properties are distributed non-symmetrically with respect to the centroidal axes of the beam cross-section. Sine laws are used to describe the continuous variation of the material properties in the cross-sections of the layers. The delamination fracture is analyzed in terms of the strain energy release rate by considering the balance of the energy. A comparison with the J-integral is performed for verification. The solution derived is used for parametric analyses of the delamination fracture behavior of the multilayered functionally graded SSB in order to evaluate the effects of the sine gradients of the three material properties in the width and height directions of the layers and the location of the crack along the beam width on the strain energy release rate. The solution obtained is valid for two-dimensional functionally graded non-linear elastic SSB configurations which are made of an arbitrary number of lengthwise vertical layers. A delamination crack is located arbitrary between layers. Thus, the two crack arms have different widths. Besides, the layers have individual widths and material properties.