• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.2
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• pp.109-117
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• 2017

This paper describes the design and implementation of a unit module for a 10 kVA class 13.2 kV/220 V unidirectional solid-state transformer (SST) with silicon-carbide metal-oxide-semiconductor field-effect transistors. The proposed module consists of an active-front-end (AFE) converter to interface 1320 V AC voltage source to 2500 V DC link and an isolated resonant DC-DC converter for 500 V low-voltage DC output. The design approaches of the AFE and the isolated resonant DC-DC converters are addressed. The control structures of the converters are described as well. The experiments for the converters are performed, and results verify that the proposed unit module can be successfully adopted for the entire SST operation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.224.2-224.2
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• 2013

본 연구에서는 CIGS박막 태양전지의 온도 및 시간 인가에 따른 전기적 특성 변화를 분석하였다. 실험에서는 온도 스트레스를 $25^{\circ}C$, $50^{\circ}C$, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$에서 각각 10시간씩 인가한 후에 Dark I-V와 C-V측정을 통해 전기적 특성 변화를 분석하였다. $25^{\circ}C$일 때를 초기 온도로 하여 특성을 측정한 것과 온도별로 노출시킨 후에 측정한 것을 비교했을 때 소자의 효율은 $100^{\circ}C$에서 감소하기 시작하였고, 인가한 온도가 높을수록 점점 많이 감소하는 모습이 나타났다. 이와 비슷하게 I-V그래프와 C-V그래프의 모습도 초기 값과 비교해서 변화하는 모습이 나타났고, 온도가 높아질수록 점점 변화하는 양이 증가하였다. I-V그래프에서 Diode ideality factor는 온도변화에 따라 초기 값 대비 증가하는 모습이 나타났다. 온도에 노출되기 전보다 노출된 후에 current와 capacitance가 감소하는 경향을 보이는데, 이는 온도의 영향으로 인해 소자의 결함이 증가하여 전하들의 반응에 영향을 주었기 때문으로 판단된다.

• Journal of the Korean Institute of Landscape Architecture
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• v.29 no.1
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• pp.1-10
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• 2001

The purpose of this thesis is to classify landscape-type of golf course, and t provide a better understanding of landscape of existing golf courses, seek a developed method for landscape, and other useful knowledge. In order to classify landscape type of the golf course, and analyze the preference for the determinants, we have selected 4 golf courses in Yongin, Kyonggi Province. The analysis in this study shows that a variable, 'familiarity' is the most potent influence of visual preference, (Sig 0.01), and it can be divided into five classes of landscape-type in golf course. More specifically, we conducted the analysis of the image of views and visual preference to bring out major factors which could decide visual preference in golf courses. The results between visual preference and physical variable are as follows; 1. It implies that a factor for a image of the view in golf course is analyzed by 4 districts from factor 1 to factor 4. An ability explaining those factors in the whole of variable quantity is 51.742%, implying factors for the image of the scene in golf courses are appeared as familiarity, changeableness, spaciousness, and naturalness. Among those factors, since familiarity(C.V.; 26.783%) and changeableness(C.V.; 112.200%) took high rank, this represents the fact that familiarity or changeableness highly affects the forming of image. 2. Defending on degree of image ability in golf course, we could classify as five types such as Type I, Type II, Type II, Type IV, and Type V. 3. As a result of calculating type of factor score, Type I had the lowest ranking in naturalness, and rather lower than others such as organization and spaciousness. The II is a top-ranked one in familiarity and naturalness, while it has the lowest ranking in spaciousness. Type III has the highest ranking in organization and preference. Type IV is the lowest-ranked one in familiarity and preference. Type IV is the lowest-ranked one is familiarity and preference. Type V has the highest ranking in spaciousness, but the lowest ranking in organization. 4. As a result of preference, Type III, Type II, Type V, Type I, and Type IV come out in order. That water-seen place type charges the highest rank shows the importance of changeable materials. 5. These factors-familiarity, organization, spaciousness and naturalness- are the major materials of the scene of view in golf courses. The possibility of how to use those for designing and making enhanced golf courses should be reinvestigated through these factors. Especially, it is acknowledged that the duction of changeableness, which is not mentioned in the study of informational approach, is much stimulating for the designing use. A further research on this theme should be made in the future, not limiting to the golf courses in Yongin.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.51-57
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• 2010

Thermoelectric properties of the p-type $(Bi,Sb)_2Te_3$, hot-pressed with the $(Bi,Sb)_2Te_3$ powders fabricated by melting/grinding method, were characterized with variation of the hot-pressing conditions. Thermoelectric characteristics of the hot-pressed $(Bi,Sb)_2Te_3$ were also analyzed with addition of $ZrO_2$ as nano inclusions. With increasing the hotpressing temperature from $350^{\circ}C$ to $550^{\circ}C$, Seebeck coefficient and electrical resistivity decreased from 275 ${\mu}V$/K to 230 ${\mu}V$/K and 6.68 $m{\Omega}$-cm to 1.86 $m{\Omega}$-cm, respectively. The power factor decreased with addition of $ZrO_2$ nano powders more than 1 vol%, implying that the optimum amount of $ZrO_2$ nano inclusions to get a maximum power factor would be less than 1 vol%.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.150-151
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• 2011

양자점 Laser Diode(LD)는 낮은 문턱전류, 높은 미분 이득을 갖으며 또한 온도변화에도 안정적이기 때문에 광통신분야에서 광원으로 양자점 LD를 사용하기 위한 연구가 계속되고 있다. 양자점은 fill factor가 낮기 때문에 양자점의 밀도를 높이거나 양자점을 적층 성장하여 fill factor를 높인다. 그러나 양자점을 적층 성장하면 각 층간의 응력, 수직적 결합, 전기적인 결합이 생기며 이는 양자점의 전기적, 광학적 특성에 영향을 미친다. 본 연구에서는 metal organic chemical vapor deposition (MOCVD)을 이용하여 InP기판 위에 자발성장 법으로 InAs 양자점을 다주기 성장하였으며 photoluminescence (PL)을 이용하여 광학적 특성을 분석하였다. precursor는 trimethylindium (TMI), trimethylgalium (TMGa), $PH_3$, $AsH_3$를 사용하였으며 carrier gas는 $H_2$를 사용하였다. InAs 양자점은 1100 nm의 파장을 갖는 InGaAsP barrier 위에 성장하였고, InAs와 InGaAsP의 성장온도는 $520^{\circ}C$이며 InAs 양자점 성장시 V/III 비는 3.66으로 일정하게 유지하였다. 그림 1은 양자점 성장시간을 0.11분으로 고정하여 3주기(A), 5주기(B), 8주기(C) 성장한 구조이며 그림 2는 양자점 성장시간을 3주기마다 0.01분씩 줄여가며 3주기는 0.11분${\times}$3(D), 6주기는 0.11분${\times}$3+0.10분${\times}$3(E), 9주기는 0.11분${\times}$3+0.10분${\times}$3+0.09분${\times}$3(F) 으로 성장한 성장구조이다. 각 성장한 시료는 PL을 이용하여 파장과 반치폭을 측정하였다. 그림 3은 양자점 성장시간을 고정한 시료 A, B, C의 PL파장과 PL반치폭 데이터이다. PL파장은 A, B, C 시료 각각 1504 nm, 1571 nm, 1702 nm이며 반치폭은 각각 140 meV, 140 meV, 150 meV이다. PL파장과 반치폭은 각각 3주기에서 6주기로 증가할 때 67 nm, 0 meV 6주기에서 9주기로 증가할 때는 131 nm, 10 meV 증가하였다. 다음 그림4는 양자점 성장시간을 조절하여 성장한 양자점 시료 D, E, F의 PL파장과 PL반치폭 데이터이다. PL파장은 D, E, F 시료 각각 1509 nm, 1556 nm, 1535 nm이며 반치폭은 각각 137 meV, 138 meV, 144 meV이다. PL파장과 반치폭은 각각 3주기에서 6주기로 증가할 때 47 nm, 1 meV 증가하였고, 6주기에서 9주기로 증가할 때는 21 nm 감소, 6 meV 증가하였다. 양자점 성장시간을 고정하여 다주기를 성장하였고 또 3주기마다 양자점 성장시간을 달리하여 다주기를 성장하였으며 PL을 이용해 광학적 특성을 연구하였다. 성장된 양자점의 PL 파장과 PL 반치폭 변화를 통해 적층구조에서 성장 주기가 늘어날수록 양자점의 크기가 증가하는 것을 확인하였고 또한 적층성장을 할 때 양자점 성장시간을 줄임으로써 양자점의 크기 변화를 제어 할 수 있었다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.10
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• pp.1157-1162
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• 2007

In this paper, E-TDLNN(Expanded-Tapped Delay Line Neural Network) method is suggested to make the model of power amplifier effectively. This method is the one for making the model of power amplifier through the study in neural network to the target value, the measured output spectrum of power amplifier, after adding the external value factor, gate bias, as an invariant input to the TDLNN method which suggested the memory effect of power amplifier effectively. To prove the validity of suggested method, the data at 2 points, 3.45 V and 3.50 V of gate bias range $3.4{\sim}3.6V$ with the 0.01 V step change, are studied and the predicted results at the gate bias 3.40 V, 3.48 V, 3.53 V and 3.60 V shows good coincidence with the measured values.

• Journal of Power Electronics
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• v.18 no.2
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• pp.323-331
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• 2018

Buck power factor correction (PFC) converters, compared with conventional boost PFC converters, exhibit high efficiency performance in the entire range of universal line voltage. This feature has gotten more attention for eliminating the zero crossing dead angle of buck PFC rectifiers. Furthermore, bridgeless structures for the reduction of conduction losses have been proposed. The aim of this paper is to introduce a single-phase buck rectifier that simultaneously has unity power factor (PF) and bridgeless structure while operating in the continuous conduction mode (CCM). For this purpose, two auxiliary flyback converters without any active switches are applied to a bridgeless buck rectifier to eliminate the zero crossing dead angle and achieve unity power factor, low total harmonic distortion (THD) and high efficiency. The operation and design considerations of the proposed rectifier are verified on a 150W, 48V prototype using a conventional peak-current-mode control. The measurement results show that the proposed rectifier has nearly unity power factor, THD less than 7% and high efficiency.

• Journal of Power Electronics
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• v.12 no.3
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• pp.429-438
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• 2012

This paper presents the use of a novel, single-stage high-power-factor electronic ballast with a symmetrical class-DE low-$d{\upsilon}$/$dt$ resonant rectifier as a power-factor corrector for fluorescent lamps. The power-factor correction is achieved by using a bridge rectifier to utilize the function of a symmetrical class-DE resonant rectifier. By employing this topology, the peak and ripple values of the input current are reduced, allowing for a reduced filter inductor volume of the EMI filter. Since the conduction angle of the bridge rectifier diode current was increased, a low-line current harmonic and a power factor near unity can be obtained. A prototype ballast, operating at an 84-kHz fixed frequency and a 220-$V_{rms}$, 50-Hz line input voltage, was utilized to drive a T8-36W fluorescent lamp. Experimental results are presented which verify the theoretical analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1674-1682
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• 1997

Fatigue tests were performed to investigate the effect of ceramic coatings as in TiN and TiCN on fatigue crack growth properties of ceramic coated 1Cr-1Mo-0.25V steel with different coating thickness in laboratory air conditions. The experimental results are described with respect to a Paris equation, da/dN=C(.DELTA.K)$^{m}$ , where the crack growth rate of coated specimens provided as similar growth rate as that of the uncoated specimen regardless of coating thickness. Furthermore, it was observed that the type of coating layer had virtually no effect on crack growth rate in the full region of stress intensity factor range. And it was also appeared that the final crack length of TiCN coated specimens was short compared to that of TiN coated, and the substrate specimens, in which it was inferred due to lowering the toughness of coated material from high hardness of TiCN coating layer itself.

• The Korea Journal of Herbology
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• v.25 no.1
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• pp.39-43
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• 2010

Objectives : This research was investigated the anticoagulant effect of the Gleditsiae spina extract. Methods : We researched prothrombin time (PT) assay, activated partial thromboplastin time (APTT) assay in vitro and in vivo using arteriovenous (A-V) shunt rat model and shortening Rat tail bleeding time (BT). A-V shunt and BT were treated with extract of Gleditsiae spina (GS) 400 mg/kg for a week. Results : Bleeding time of Gleditsiae spina extract in vivo had a significant increase as about 1.2 times and thrombus weight of Gleditsiae spina extract had a significant reduction of thrombus weight as 26%. Gleditsiae spina extract represented an effect of anticoagulation by operating on extrinsic pathway factor II, V, VII, X and intrinsic pathway factor VIII, IX, X, XI, XII in the coagulation system. Conclusions : Considering the above mentioned results, it is judged that a Gleditsiae Spina extract has a control effect of thrombus creation.