• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1505-1506
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• 2011

염료감응형 태양전지(Dye-Sensitized Solar Cell, DSSC)의 FTO 표면에 compact layer를 형성시켜 직접적인 마찰에 의한 전자의 재결합을 줄일 수 있다. 따라서 광전극에서의 compact layer의 효과를 최대화하기 위하여 $TiCl_4$ 용액에 acetic acid를 첨가하여 특성변화를 측정하였다. UV-Vis 분광기, I-V 특성곡선, EIS 분석장비를 이용하여 검토한 결과, UV-Vis 분광분석을 통해서 acetic acid를 첨가한 compact layer의 투과도가 현저하게 높아진 것을 확인하였다. 이 결과는 $TiCl_4$ 처리에 의하여 compact layer를 구성하고 있는 $TiO_2$ 입자의 응집현상이 개선되므로 표면특성이 향상되었기 때문이다. Acetic acid를 첨가한 compact layer가 입자응집으로 인한 표면저항의 감소를 유발하여, 전자의 이동이 원활해진 것을 내부 임피던스 분석을 통하여 확인하였다. Compact layer에 의해 재결합이 감소하여 효율이 향상된 것을 I-V 특성곡선을 분석하여 확인하였다.

• Journal of Astronomy and Space Sciences
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• v.16 no.1
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• pp.21-30
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• 1999

We perform CCD observations in VRI filters for AK Her during 3 nights in Feb 1997 and Mar 1998 at Mt. Sobaek National Observatory, and obtained 236 images in V, 198 in R, and 197 in I filter. From the data, we construct light curves which contain a pair primary and secondary minima and (O-C) diagram. We analyzed the obtained light curves of AK Her using the Wilson-Devinney code. From the analyses, we find that AK Her is more likely detached or semi-detached than contact system. From the (O-C) diagram, we find that the (O-C) residuals increases out of accordance with the expectation of Borkovits & Hegedus since 1990. However, we cannot identify cause of the periodic variation of the (O-C) residuals.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.5
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• pp.368-374
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• 2016

This paper presents an experimental study on an electrical circuit model of the TiO2-based nano-wired memristor device for neuromophic applications. The electrical circuit equivalent model of the proposed memristor device consists of several electronics components and some passive devices including operational amplifiers, multipliers, resistors and capacitors. In order to verify the proposed design, both of simulation (using PSPICE) as well as hardware implementation were performed for the analysis of the memristor circuit with time waveforms, frequency spectra, I-V curves and power curves. The gained results from the measured data showed a good agreement with the simulation result that confirm the proposed idea.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.307-307
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• 2012

현재 태양전지 시장은 결정질 태양전지가 주류를 차지하고 있으며 이중 상대적으로 재료비가 저렴한 다결정 실리콘 기반의 고효율 태양전지 제작에 대한 연구가 활발히 진행되고 있다. 이에 본 실험에서는 표면 텍스처링 방법에 따른 태양전지 소자의 특성 변화에 대한 실험을 진행하였다. 일반적으로 다결정 태양전지의 경우 산성용액을 이용한 표면 텍스처링을 실시하는데 이 경우 표면에 형성된 텍스처 구조는 산성용액의 등방성 식각으로 인해 반구(Hemisphere) 형태의 구조를 띄게 된다. 이는 표면에서의 광흡수율을 떨어뜨려 태양전지 소자의 효율을 저해하는 원인이 된다. 따라서 본 연구에서는 다결정 실리콘 태양전지의 효율 향상을 위해 레이저를 이용한 차세대 텍스처링 방법에 대한 연구를 진행하였다. 우선 355 nm 파장의 Ultra-Violet (UV) 레이저를 소자 표면에 조사함으로써 $10{\mu}m$의 dot diameter와 depth를 갖는 honey comb 배열의 hole을 형성하였다. 이후 산성용액에 담가 레이저 공정 후의 slag를 제거해 최종적으로 피라미드 형태의 구조를 형성하였다. Suns_Voc 효율 측정 결과 산성용액을 이용한 텍스처링의 경우 개방 전압이 611 mV, 곡선인자가 81%, 효율이 17.32%로 각각 측정되었다. 반면, 레이저 텍스처링의 경우에서는 개방전압이 631 mV, 곡선인자가 83%, 효율이 18.33%로 용액 텍스처링 방법보다 우수한 특성을 보였다. 이는 UV 레이저 텍스처링을 통해 형성된 피라미드 형태의 표면 구조에서의 광흡수율이 산성용액을 이용한 방법보다 우수함을 말하며, 따라서 태양전지의 주요 파라미터가 향상된 결과를 보였다. 본 실험에서는 레이저 텍스처링을 통한 태양전지 제작에 대한 방법을 제시하며, 향후 고효율의 다결정 태양전지 제작에 있어 기여 할 것으로 판단된다.

• Journal of Astronomy and Space Sciences
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• v.5 no.1
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• pp.9-18
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• 1988

Gamma Cassiopeae has been observe at Yonsei University Observatory(YUO) for 31 nights in the period 1983-1987 and a total of 312 UBV observations(104 in each colour) was secured. Light curves of ${\gamma}$ Cas in V, B-V, and U-B have been constructed with the YUO data; among them we present selected light curves of 5 different long nights. Discussed are the general photometric behaviour of ${\gamma}$ Cas, especially in connection with B-V changes, V/R variations of $H\alpha$ and H$\beta$, and high velocity narrow component(hvnc) exhibited in the far UV. Six spectral image sets of $\varepsilon$Per archived on IUE satellite are reduced and their line profiles in C IV and Si IV resonance lines are analyzed to find out any change, but the evidence is unlikely.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.44-50
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• 2001

Metal oxide semiconductor (MOS) structures containing nanocrystals are fabricated by using rapid thermal oxidations of amorphous silicon films. The amorphous films are deposited either by electron beam deposition method or by electron beam deposition assisted by Ar ion beam during deposition. Post oxidation of e-beam deposited film results in relatively small hysteresis of capacitance-voltage (C-V) and the flat band voltage shift, $\DeltaV_{FB}$ is less than 1V indicative of the formation of low density nanocrystals in $SiO_2$ near $SiO_2$/Si interface. By contrast, we observe very large hysteresis in C-V characteristics for oxidized ion-beam assisted e-beam deposited sample. The flat band voltage shift is larger than 22V and the hysteresis becomes even broader as increasing injection times of holes at accumulation condition and electrons at inversion condition. The result indicates the formation of slow traps in $SiO_2$ near $SiO_2$/Si interface which might be related to large density nanocrystals. Roughly estimated trap density is $1{\times}10^{13}cm^{-2}$. Such a large hysteresis may be explained in terms of the activation of adatom migration by Ar ion during deposition. The activated migration may increase nucleation rate of Si nuclei in amorphous Si matrix. During post oxidation process, nuclei grow into nanocrystals. Therefore, ion beam assistance during deposition may be very feasible for MOS structure containing nanocrystals with large density which is a basic building block for single electron memory device.

• Journal of Astronomy and Space Sciences
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• v.24 no.2
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• pp.99-110
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• 2007

A total of 824 observations (206 in ${\Delta}B$, 206 in ${\Delta}V$, 206 in ${\Delta}R$, 206 in ${\Delta}I$ for CC Com were made on 3 nights from March 3 to April 3 in 2002 using the 61cm telescope with 2K CCD camera of the Sobaeksan Optical Astronomy Observatory of KASI. From our observations 9 times of minimum light were newly determined. Combined analysis of our new BVRI light curves with the double-lined radial velocity curves of Pribulla et al. (2007) were made with the 2004 Wilson-Devinney(WD) binary model code to yield new physical parameters of the CC Com system. Small asymmetries in light curves were explained with the adoption of two hot spots on the cool secondary.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.625-632
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• 2011

The ignition characteristics of a $CH_4$/hot air counterflow diffusion flame were investigated numerically using a flame-controlling continuation method. For the chemical reactions, the GRI-v1.2 reaction mechanism was used in the simulation. The maximum flame temperature was presented in the space of the inverse global strain rate, and showed S-curve-type behavior. The flame temperatures and velocities of the upper and middle branches were compared for different global strain rates. In addition, the global strain rate was compared with the local strain rates defined at the flame surface and the boundaries of the fuel and oxidizer sides of the fuel/air mixing layer. These local strain rates correlated well with the global strain rate.

• Journal of Korean Society of Forest Science
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• v.96 no.1
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• pp.40-47
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• 2007

The objectives of this study were to derive site index and stem volume prediction equation based on stem analysis data for Larix leptolepis in Jinan region. The function for site index was developed by algebraic difference equation method. Polymorphic site index family curves with base age of 40 were presented based on the Schumacher height equation. The best stem volume prediction equation was suggested as $V=0.00260+0.00000399D^2H$. The simultaneous F-test using this equation showed that the estimated tree stem volumes were not significantly different (${\alpha}=0.05$ level) from the observed stem volumes for model evaluation. Therefore, site index and volume prediction equations prepared in this study could provide an indication of site quality and basic information for making of yield table, and could be used for rational forest management of Larix leptolepis stands grown in Jinan region.

• Journal of the Korean Vacuum Society
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• v.7 no.2
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• pp.82-87
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• 1998

In the oxidation process of the $NH_3/O_2$ oxidation method, adding $NH_3$ gas to $O_2$ gas, the detected outlet gases in the reaction quartz chamber are N2, $O_2$ and $H_2O$ and in addition, a very small quantity of $CO_2$, NO and $NO_2$ are detected. Two kinds of species ($O_2$ and H2O) contribute to oxidation, so the growth rate is determined by oxidation temperature and by also partial pressure of the NH3 and $O_2$ gases. The slop of growth rate is identified to be medial and in parallel between that of the dry and wet oxidation. Auger electron spectroscopy (AES) indicates that $NH_3/O_2$ oxide film has a certain stoichiomerty of $SiO_2$, this oxidation method restrains the generation of defects in the $SiO_2/Si$ interface, minimizing fixed charges. The breakdown voltage of $NH_3/O_2$ oxide film (470$\AA$) is 57.5 volts, and the profile of the C-V curve including flat band voltage (0.29 volts) agree with the ideal curve.