• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.55 no.9
• /
• pp.365-375
• /
• 2006

This paper is presented by the application of parallel adaptive evolutionary algorithm(PAEA) to search an optimal solution of a thermal unit commitment problem. The adaptive evolutionary algorithm(AEA) takes the merits of both a genetic algorithm(GA) and an evolution strategy(ES) in an adaptive manner to use the global search capability of GA and the local search capability of ES. To reduce the execution time of AEA, the developed algorithm is implemented on an parallel computer which is composed of 16 processors. To handle the constraints efficiently and to apply to Parallel adaptive evolutionary algorithm(PAEA), the states of thermal unit are represented by means of real-valued strings that display continuous terms of on/off state of generating units and are involved in their minimum up and down time constraints. And the violation of other constraints are handled by repairing operator. The procedure is applied to the $10{\sim}100$ thermal unit systems, and the results show capabilities of the PAEA.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.49 no.2
• /
• pp.62-69
• /
• 2000

In this paper, we design a GA-fuzzy precompensated PID controller for the load frequency control of two-area interconnected power system. Here, a fuzzy precompensated PID controller is designed as a fuzzy logic-based precompensation approach for PID controller. This scheme is easily implemented simply by adding a fuzzy precompensator to an existing PID controller. And we optimize the fuzzy precompensator with a genetic algorithm for complements the demerit such as the difficulty of the component selection of fuzzy controller, namely, scaling factor, membership function and control rules. Simulation results show that the proposed control technique is superior to a conventional PID control and a fuzzy precompensated PID control in dynamic responses about the load disturbances of power system and is convinced robustness reliableness in view of structure.

• Journal of Astronomy and Space Sciences
• /
• v.36 no.3
• /
• pp.181-186
• /
• 2019

The attitude information of spacecraft can be obtained by the sensors attached to it using a star tracker, three-axis magnetometer, three-axis gyroscope, and a global positioning signal receiver. By using these sensors, the spacecraft can be maneuvered by actuators that generate torques. In particular, electromagnetic-torque bars can be used for attitude control and as a momentum-canceling instrument. The spacecraft momentum can be created by the current through the electrical circuits and coils. Thus, the current around the electromagnetic-torque bars is a critical factor for precisely controlling the spacecraft. In connection with these concerns, a solar-cell array can be considered to prevent generation of a magnetic dipole moment because the solar-cell array can introduce a large amount of current through the electrical wires. The maximum value of a magnetic dipole moment that cannot affect precise control is $0.25A{\cdot}m^2$, which takes into account the current that flows through the reaction-wheel assembly and the magnetic-torque current. In this study, we designed a 300-W solar cell array and presented an optimal wire-routing method to minimize the magnetic dipole moment for space applications. We verified our proposed method by simulation.

• Journal of Microbiology and Biotechnology
• /
• v.22 no.11
• /
• pp.1486-1493
• /
• 2012

In this study, we investigated whether galactooligosaccharide (GOS) can be stably and steadily synthesized using immobilized ${\beta}$-galactosidase (${\beta}$-gal) inclusion body (IB)-containing E. coli cells during long-term repeated-batch operation. To improve the operational stability of this enzyme reactor system, immobilized E. coli cells were crosslinked with glutaraldehyde (GA) after immobilization of the E. coli. When we treated with 2% GA for E. coli crosslinking, GOS production continued to an elapsed time of 576 h, in which seven batch runs were operated consecutively. GOS production ranged from 51.6 to 78.5 g/l ($71.2{\pm}10.5$ g/l, n = 7) during those batch operations. In contrast, when we crosslinked E. coli with 4% GA, GOS production ranged from 31.5 to 64.0 g/l ($52.3{\pm}10.8$, n = 4), and only four consecutive batch runs were operated. Although we did not use an industrial ${\beta}$-gal for GOS production, in which a thermophile is used routinely, this represents the longest operation time for GOS production using E. coli ${\beta}$-gal. Improved stability and durability of the cell immobilization system were achieved using the crosslinking protocol. This strategy could be directly applied to other microbial enzyme reactor systems using cell immobilization to extend the operation time and/or improve the reactor system stability.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.400-400
• /
• 2012

산화물 반도체는 넓은 에너지갭을 가지고 높은 이동성과 높은 투명성을 가지기 때문에 초고 속 박막 트랜지스터(Thin film transistor; TFT)에 많이 응용되고 있다. 그러나 ZnO 및 $In_2O_3$ 산화물 반도체를 박막트랜지스터에 사용할 경우 소자가 불안정하여 전기적 성질이 저하되고 문턱전압의 이동이 일어난다. TFT에 사용되는 산화물 반도체로는 GaInZnO, ZrInZnO, HfInZnO 및 GaSnZnO의 전기적 특성에 관한 연구가 많이 되었다. 그러나 titanium-indium-zinc-oxide (TIZO) TFT에 대한 연구는 비교적 적게 수행 되었다. 본 연구에서는 TFTs의 안정성을 향상하기 위하여 TFT의 채널로 사용되는 TiInZnO를 형성하는데 간단한 제조 공정과 낮은 비용의 용액 증착방법을 사용하였다. 졸-겔 전해액은 Titanium (IV) isopropoxide $[Ti(OCH(CH_3)_2)_4]$, 0.1 M Zinc acetate dihydrate $[Zn(CH_3COO)_2{\cdot}2H_2O]$ 그리고 indium nitrate hydrate $[In(NO_3)_3{\cdot}xH_2O]$을 2-methoxyethanol의 용액에 합성하였다. $70^{\circ}C$에서 한 시간 동안 혼합 하였다. Ti의 몰 비율은 10%, 20% 및 40% 로 각각 달리하여 제작하였다. $SiO_2$층 위에 2,500 rpm 속도로 25초 동안 스핀 코팅하여 TFT를 제작하였다. TIZO 박막에 대한 X-선 광전자 스펙트럼 관측 결과는 Ti 몰 비율이 증가함에 따라 Ti 2p1/2피크의 세기가 증가함을 보여주었다. TiZO 박막에 Ti 원자를 첨가하면 $O^{2-}$ 이온이 감소하기 때문에 전하의 농도가 변화하였다. 전하 농도의 변화는 TiZO 채널을 사용하여 제작한 TFT의 문턱전압을 양 방향으로 이동 하였으며 off-전류를 감소하였다. TiZO 채널을 사용하여 제작한 TFT의 드레인 전류-게이트 전압 특성은 on/off비율이 $0.21{\times}107$ 만큼 크며 이것은 TFT 소자로서 우수한 성능을 보여주고 있다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.434-436
• /
• 2013

Ga-doped ZnO (GZO) was substitutes of the SnO2:F films on soda lime glass substrate in the photovoltaic devices such as CIGS, CdTe and DSSC due to good properties and low cost. However, it was reported that the electrical resistivity of GZO is unstable above $300^{\circ}C$ in air atmosphere. To improve thermal stability of GZO thin films at high temperature above $300^{\circ}C$ an $TiO_2$ thin film was deposited on the top of GZO thin films as a barrier layer by Pulsed Laser Deposition (PLD) method. $TiO_2$ thin films were deposited at various thicknesses from 25 nm to 100 nm. Subsequently, these films were annealed at temperature of $300^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$ in air atmosphere for 20 min. The XRD measurement results showed all the films had a preferentially oriented ( 0 0 2 ) peak, and the intensity of ( 0 0 2 ) peak nearly did not change both GZO (300 nm) single layer and $TiO_2$ (50 nm)/GZO (300 nm) double layer. The resistivity of GZO (300 nm) single layer increased from $7.6{\times}10^{-4}{\Omega}m$ (RT) to $7.7{\times}10^{-2}{\Omega}m$ ($500^{\circ}C$). However, in the case of the $TiO_2$ (50 nm)/GZO (300 nm) double layer, resistivity showed small change from $7.9{\times}10^{-4}{\Omega}m$ (RT) to $5.2{\times}10^{-3}{\Omega}m$ ($500^{\circ}C$). Meanwhile, the average transmittance of all the films exceeded 80% in the visible spectrum, which suggests that these films will be suitable for photovoltaic devices.

• Korean Journal of Materials Research
• /
• v.29 no.9
• /
• pp.542-546
• /
• 2019

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : $n^+-i(QD)-n^+$ QDIP with undoped quantum dot(QD) active region and $n^+-n^-(QD)-n^+$ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the $n^+-n^-(QD)-n^+$ structure, Si dopant is directly doped in InAs QD at $2{\times}10^{17}/cm^3$. Undoped and doped QDIPs show a photoresponse peak at about $8.3{\mu}m$, ranging from $6{\sim}10{\mu}m$ at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.1
• /
• pp.152-158
• /
• 1995

Eteching characteristics of the Indium Tin Oxide (ITO), which is transparent conductor, was investigated with CH4/H2 and Ar as etching gases for the Reactive Ion Etching (RIE). With CH4/H2 for the etching gas, the highly selective etching characteristics for the ITO on GaAs was obtained. It was examined that the dominant etching parameter for the selective etchning of ITO on GaAs structure was the chamber pressure. But, the etching selectivity for ITO on InP was poor eventhough we tried systematic etching. RIE etching conditins using CH4/H2 gas was limited due to the formation of polymer on the substrates. In the case of Ar gas for the reactive gas, the selectivity of ITO on BaTiO3 was above 10. The etch rete of ITO was more sensitive to the etching parameters than that of BaTiO3, which was almost constant with different etching parameters.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.241-241
• /
• 2012

$SF_6$와 $NF_3$는 디스플레이 장치의 제조공정 중 $SiN_x$박막을 건식식각공정에서 사용되고 있다. 이 논문에서는 이 두 가스에 대한 건식식각의 특성을 관찰하기 위해서 CCP-RIE를 이용하여 가스와 산소의 유량비($SF_6$/$O_2$>, $NF_3$/$O_2$), 압력, 전력 비(13.56 MHz/2 MHz)를 변화시키는 다양한 공정조건하에서 실험을 진행하였다. 이 실험에서 $NF_3$를 이용한 $SiN_x$ 박막 건식식각률이 $SF_6$를 이용한 건식식각률보다 모든 공정 조건하에서 높게 나타났다. 불소원자의 OES 강도와 V/I probe 를 이용하여 건식식각률과 비례하는 상관관계 변수를 발견하였고 이를 플라즈마 변수와 관련하여 해석하였다.

• Journal of Korean Institute of Industrial Engineers
• /
• v.27 no.1
• /
• pp.54-60
• /
• 2001

In this paper, a shape-based block layout (SBL) approach is presented to solve the facility layout problem with unequal-area and fixed shapes. The SBL approach employs hybrid genetic algorithm (Hybrid-GA) to find a good solution and the concept of bay structure is used. In the typical facility layout problem with unequal area and fixed shapes, the given geometric constraints of unequal-area and fixed shapes are mostly approximated to original shape by aspect ratio. Thus, the layout results require extensive manual revision to create practical layouts and it produces irregular building shapes and too much unusable spaces. Experimental results show that a SBL model is able to produce better solution and to create more practical layouts than those of existing approaches.