• Journal of Power Electronics
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• 제11권2호
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• pp.188-193
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• 2011

A highly efficient AC-DC converter for small wind power generation systems using a brushless DC generator (BLDCG) is presented in this paper. The market standard AC-DC converter for a BLDCG consists of a three-phase diode rectifier and a boost DC-DC converter, which has an IGBT and a fast recovery diode (FRD). This kind of two-stage solution basically suffers from a large amount of conduction loss and the efficiency greatly decreases under a light load, or at a low current, because of the switching devices with a P-N junction. In order to overcome this low efficiency, especially at a low current, a three-phase bridgcless converter consisting of three upper side FRDs and three lower side Super Junction FETs is presented. In the overall operating speed region, including the cut-in speed, the efficiency of the proposed converter is improved by up to 99%. Such a remarkable result is validated and compared with conventional solutions by calculating the power loss based on I-V curves and the switching loss data of the adopted commercial switches and the current waveforms obtained through PSIM simulations.

• 전기학회논문지
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• 제62권8호
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• pp.1115-1119
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• 2013

The carbon nanotube/poly-vinylidene fluoride (CNT/PVDF) composite films for the use of electronic devices were fabricated by spray coating method using the CNT/PVDF solution, which was prepared by adding PVDF pellets into the CNT dispersed N-Methyl-2-pyrroli-done (NMP) solution. The CNT/PVDF composite films were peeled off from the glass substrate and were investigated by the scanning electron microscopy, which revealed that the CNTs were uniformly dispersed in the PVDF films and thickness of the films were approximately $20{\mu}m$. The capacitance of the CNT/PVDF films increased dramatically by adding CNTs into the PVDF matrix, and finally saturated approximately 1880 pF. However, the I-V curves didn't show any saturation effect in the CNT concentration range of 0 ~ 0.04 wt%. Therefore we can control the performance of the devices from the CNT/PVDF composite film by adjusting the current level resulted from the CNT concentration with the uniform capacitance value.

• Advances in concrete construction
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• 제9권4호
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• pp.337-343
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• 2020

In the present study, by employing fragility analysis, the seismic vulnerability of a concrete girder bridge, one of the most common existing structural bridge systems, has been performed. To this end, drift demand model as a fundamental ingredient of any probabilistic decision-making analyses is initially developed in terms of the two most common intensity measures, i.e., PGA and Sa (T₁). Developing a probabilistic demand model requires a reliable database that is established in this paper by performing incremental dynamic analysis (IDA) under a set of 20 ground motion records. Next, by employing Bayesian statistical inference drift demand models are developed based on pre-collapse data obtained from IDA. Then, the accuracy and reasonability of the developed models are investigated by plotting diagnosis graphs. This graphical analysis demonstrates probabilistic demand model developed in terms of PGA is more reliable. Afterward, fragility curves according to PGA based-demand model are developed.

• 한국전기전자재료학회논문지
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• 제16권12S호
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• pp.1242-1247
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• 2003

In order to passivate the GaAs surface, silicon-nitride films were fabricated by using laser CVD method. SiH$_4$ and NH$_3$ were used to obtain SiN films in the range of 100∼300$^{\circ}C$ on p-type (100) GaAs substrate. To determine interface characteristics of the metal-insulator-GaAs structure, electrical measurements were performed such as C-V curves and deep level transient spectroscopy (DLTS). The results show that the hysteresis was reduced and interface trap density was lowered to 1,012 ∼ 1,013 at 100 ∼ 200$^{\circ}C$. According to the study of surface leakage current, the passivated CaAs has less leakage current compared to non-passivated substrate.

• 한국광학회:학술대회논문집
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• 한국광학회 2001년도 제12회 정기총회 및 01년도 동계학술발표회
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• pp.6-11
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• 2001

More than ten kinds of oxide thin films and their heterostructure have been successfully fabricated on SrTiO$_3$(001) substrates by laser molecular beam epitaxy (laser MBE). Measurements of atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) and X-ray small-angle reflectivity reveal that the surfaces and interfaces are atom-level-smooth. The unit cell layers and the lattice structure are perfect. The electrical and optical properties of BaTiO$_3$-x thin films and BaTiO$_3$/SrTiO$_3$ (BTO/STO) superlattices were examined. The all-perovskite oxide P-N junctions have been successfully fabricated and the better I-V curves were observed.

• Bulletin of the Korean Chemical Society
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• 제14권1호
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• pp.101-107
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• 1993

Ab initio calculations are carried out at the 6-311G$^{**}$ level for the $C_{2v}$ interactions of Be and Li atoms with acetylene molecule. The main contribution to the deep minima on the $^3B_2\;BeC_2H_2\;and\;^2B_2 LiC_2H_2$ potential energy curves is the b_2\;(2p(3b_2)-l{\pi}_g^*(4b_2))$ interaction, the $a_1\;(2s(6a_1)-I{\pi}_u(5a_1))$ interaction playing a relatively minor role. The exo deflection of the C-H bonds is basically favored, as in the $b_2$ interaction, due to steric crowding between the metal and H atoms, but the strong in-phase orbital interaction, or mixing, of the $a_1$ symmetry hydrogen orbital with the $5a'_1,\;6a'_1,\;and\;7a'_1$ orbitals can cause a small endo deflection in the repulsive complexes. The Be complex is more stable than the Li complex due to the double occupancy of the 2s orbital in Be. The stability and structure of the $MC_2H_2$ complexes are in general determined by the occupancy of the singly occupied frontier orbitals.

• Current Optics and Photonics
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• 제4권4호
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• pp.273-276
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• 2020

We report on the relationship between output current for quadrant photodetector (QPD) and bias voltage in silicon-based p-i-n (positive-intrinsic-negative) QPD examined using millisecond pulse laser (ms pulse laser) irradiation. The mechanism governing the relationship was further studied experimentally. The output current curves were obtained by carrying out QPD under different bias voltages (0-40 V) irradiated by ms pulse laser. Compared to other photodetectors, the relaxation was created in the output current for QPD which is never present in other photodetectors, such as PIN and avalanche photodetector (APD), and the maximum value of relaxation was from 6.8 to 38.0 ㎂, the amplitude of relaxation increases with bias value. The mechanism behind this relaxation phenomenon can be ascribed to the bias voltage induced Joule heating effect. With bias voltage increasing, the temperature in a QPD device will increase accordingly, which makes carriers in a QPD move more dramatically, and thus leads to the formation of such relaxation.

• 한국재료학회지
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• 제33권6호
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• pp.229-235
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• 2023

An all-perovskite oxide heterostructure composed of SrSnO₃/Nb-doped SrTiO₃ was fabricated using the pulsed laser deposition method. In-plane and out-of-plane structural characterization of the fabricated films were analyzed by x-ray diffraction with θ-2θ scans and φ scans. X-ray photoelectron spectroscopy measurement was performed to check the film's composition. The electrical transport characteristic of the heterostructure was determined by applying a pulsed dc bias across the interface. Unusual transport properties of the interface between the SrSnO₃ and Nb-doped SrTiO₃ were investigated at temperatures from 100 to 300 K. A diodelike rectifying behavior was observed in the temperature-dependent current-voltage (IV) measurements. The forward current showed the typical IV characteristics of p-n junctions or Schottky diodes, and were perfectly fitted using the thermionic emission model. Two regions with different transport mechanism were detected, and the boundary curve was expressed by ln I = -1.28V - 13. Under reverse bias, however, the temperature- dependent IV curves revealed an unusual increase in the reverse-bias current with decreasing temperature, indicating tunneling effects at the interface. The Poole-Frenkel emission was used to explain this electrical transport mechanism under the reverse voltages.

• 대한소아치과학회지
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• 제30권1호
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• pp.132-142
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• 2003

본 연구는 Hellman 치령 IIIA기에 해당되는 전치부 반대교합아동의 구개형태에 대한 특징을 3차원 레이저 스캐너를 이용하여 조사한 것이다. 반대교합아동과 정상교합아동 각각 20개의 상악 석고모형을 채득하였다. 각 모형은 3차원 레이저 스캐너(Intertec, Korea)로 스캔한 후 rapidform 2000 프로그램 (INUS, Korea)으로 3차원 이미지를 얻었으며, Rhino 3D 프로그램(rhinoceros, USA)으로 수치화 하였다. 측정부위는 양측 유견치 및 제1대구치를 연결한 횡단면상의 구개형태 곡선 그리고 절치유두의 최정점에서 양측 제1대구치 원심면까지의 구개봉합선을 따르는 구개형태곡선들이었다. 개체들간의 크기 차이 보정을 위해 측정부위를 각각 25mm, 35mm, 35mm로 조정하여 표준화 하였다. 표준화된 구개형태곡선들에서 직선거리 각 1mm에 해당되는 점들에서의 곡선 깊이를 소수점 3자리까지 수치화 하여 평균 구개형태곡선을 얻고, 그 좌표 차이를 95% 신뢰구간의 t-test를 통해 비교, 분석하여 다음과 같은 결론을 얻었다. 1. 양측 유견치를 연결한 횡단면상의 평균구개형태곡선은 반대교합아동이 좀더 평탄한 V자형의 곡선형태를 보였으나, 반대교합아동과 정상교합아동 사이에 통계적으로 유의할 만한 차이는 보이지 않았다(P>0.05). 2. 양측 제1대구치를 연결한 횡단면상의 평균구개형태곡선은 반대교합아동이 정상교합아동보다 더 구개의 깊이가 깊었으며, 상악 우측 제1대구치 치은 최하방점에서부터 8mm와 21mm위치 사이의 구간에서 통계적으로 유의할 만한 차이가 있었다(P<0.05). 3. 반대교합아동과 정상교합아동간의 구개봉합선의 평균구개형태곡선에서는 전구간에 걸쳐 반대교합아동이 더 깊은 곡선 형태를 보였고, 통계적으로도 유의할 만한 차이를 보였다(P<0.01).

• 한국진공학회지
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• 제20권1호
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• pp.57-62
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• 2011

열처리 방식을 통하여 형성된 FePt 나노 입자를 사용하는 자기 양자점 소자를 제작하고, 전기적 및 자기적 특성을 연구하였다. FePt 자기 양자점 터널링 소자는 p 형 Si 기판 상부에 약 20 nm의 $SiO_2$ 터널 절연막을 형성하고 FePt 박막을 3 nm 두께로 증착한 후에 열처리 방식을 이용하여 8~15 nm 크기의 양자점을 갖는 구조이다. 터널링 소자의 전류-전압 특성을 자기장과 온도 변화에 따라 관찰하였고 특히, 저온에서 비선형적인 전류-전압 곡선을 확인하였으며 이러한 단전자 수송현상을 전자의 hopping 모델과 양자점의 터널링 현상을 이용하여 설명하였다. FePt 양자점 터널링 소자는 20 K에서 터널링 현상을 보였으며, 양단에 가해준 전압과 관계없이 외부 자기장이 증가할수록 음의 자기저항이 커지는 현상을 관찰하였고, 9,000 G에서 약 26.2 %의 자기저항 비를 확인하였다.