• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
• /
• pp.257.1-257.1
• /
• 2015

Cu(In,Ga)Se2 (CIGS) 박막 태양 전지에서 buffer layer는 CIGS 흡수층과 TCO 사이의 밴드갭 차이에 대한 문제점과 lattice mismatch를 해결하기 위해 필수적이다. 흔히 buffer layer 물질로는 CdS가 가장 많이 사용되고 있으나 Cd의 독성에 관한 문제가 야기되고 있다. 따라서 ZnS(O, OH) buffer layer가 친환경 물질로 기존의 CdS 버퍼 층의 대체 물질로 각광 받고 있으며, 단파장 범위에서 높은 투과율로 인해 wide band gap의 Chalcopyrite 태양 전지에 응용되는 buffer layer로 많은 연구가 이루어지고 있다. 또한 buffer layer를 최적화 하여 carrier lifetime과 양자 효율이 증가시킬 수 있는 특성을 가지고 있다. 이 연구에서는 Cu(In,Ga)Se2 (CIGS) 박막에 화학습식공정 (CBD) 방법을 이용하여 최적화된 ZnS(O, OH)의 증착 조건을 찾고, 고품질의 buffer layer를 제조하기 위한 실험에 초점을 맞췄다. 또한, buffer layer의 막질을 개선하고 균일한 막을 제조하기 위해 processing parameters인 시약의 농도, 제조 시간 및 온도 등의 다양한 변화를 통해 실험을 진행하였다. 그 후 최적화된 ZnS(O, OH) buffer layer의 특성 분석을 위해 X-ray diffraction(XRD), photoluminescence (PL), scanning electron microscope (SEM) and GD-OES을 이용하였고, 이를 통해 제조된 CIGS 박막 태양전지는 light induced current-voltage (LIV) and external quantum efficiency (EQE)를 통해 특성 분석을 실시 하였다. 결과적으로, 제조된 ZnS(O, OH) buffer layer의 $ZnSO4{\cdot}7H2O$의 농도는 0.16 M, Thiourea는 0.5 M, NH4OH는 7.5 M, 그리고 반응 온도는 77.5 oC의 조건 하에 CIGS 기판 위에 균일하고 균열이 없는 ZnS(O, OH) 박막을 제조하였으며 이때 제조된 태양전지의 소자 특성은 Voc = 0.478 V, Jsc = 35.79 mA/cm2, FF = 47.77%, ${\eta}=8,18 %$이다.

• 대한한의진단학회지
• /
• 제11권1호
• /
• pp.48-60
• /
• 2007

Palpation of the pulse has been used in Korean traditional medicine since ancient times to assess physical health. Pulse wave contour may be obtained by measuring arterial pressure or blood volume change of skin. The latter is called as Photoplethysmography(PPG) or digital volume pulse(DVP). The PPG signal is measured by a device comprising an infrared light sourece and a photodetector. Although less widely used, this technique deserves further consideration because of its simplicity and ease of use. The contour of the PPG is formed as a result of a complex interaction between the left ventricle and the systemic circulation. It usually exhibits an early systolic peak and an early diastolic peak. the first peak is formed mainly by pressure trasmitted along a direct path from the left ventricle to the finger. The second peak is formed in part by pressure transmitted along the aorta and large arteries to sites of impedance mismatch in the lower body. The contour of the PPG is sensitive to changes in arterial tone and is influenced by ageing and large artery stiffness. Measurements taken directly from the PPG or from its second derivative can be used to assess these properties. In some mathematical approaches, the extraction of periodic components using frequency analysis was tried to analysis of the PPG. But we don't understand yet what kind of factor in the cardiovascular system or human body is related with the respective specific Fourier components of PPG. This review describes the background to measurement principles, representative contour, contour analysis and frequency domain analysis of PPG, and current and future.

• 기술혁신연구
• /
• 제15권2호
• /
• pp.25-40
• /
• 2007

It has been pointed out that the shortage of the Korean science and engineering workforce is a key issue in enterprises' competitiveness. The Korean government has conducted various surveys and research projects to determine the current situation and its causes. Nevertheless, the surveys report different results, and, to date, very few in-depth studies have been conducted on the factors that lead to such a shortage. This study aimed at investigating the factors that cause the shortage of the science and engineering workforce by looking at a recent survey on the actual employment conditions in manufacturing and major service industries. The study also estimated the determinant factors, based on the results of a survey conducted on 5,967 enterprises. Particularly, the probability of the workforce shortages are defined as a logistic probability function, which includes a diverse number of explanations that represent the characteristics of an enterprise and its internal demand conditions on workforce. The findings showed that key determinants include not only the factors that have been recognized by previous studies, but also research propensity and competitiveness aw well as the enterprises' internal demand conditions on human resources. In other words, an enterprise is more exposed to the problem of workforce shortage when it performs its R&D more proactively and its innovative activities are more organized. It has been further analyzed that the R&D and internal demand variables are more eminent to the shortage problem on skilled workers, which proves the shortage of workforce is not only caused by the quantitative aspect but also hold qualitative aspect characterized by skill obsolescence and mismatch in the labor market.

• Journal of Microbiology and Biotechnology
• /
• 제24권6호
• /
• pp.781-787
• /
• 2014

2-Ketogluconic acid production by Klebsiella pneumoniae is a pH-dependent process, strictly proceeding under acidic conditions. Unfortunately, cell growth is inhibited by acidic conditions, resulting in low productivity of 2-ketogluconic acid. To overcome this deficiency, a two-stage fermentation strategy was exploited in the current study. During the first stage, the culture was maintained at neutral pH, favoring cell growth. During the second stage, the culture pH was switched to acidic conditions favoring 2-ketogluconic acid accumulation. Culture parameters, including switching time, dissolved oxygen levels, pH, and temperature were optimized for the fed-batch fermentation. Characteristics of glucose dehydrogenase and gluconate dehydrogenase were revealed in vitro, and the optimal pHs of the two enzymes coincided with the optimum culture pH. Under optimum conditions, a total of 186 g/l 2-ketogluconic acid was produced at 26 h, and the conversion ratio was 0.98 mol/mol. This fermentation strategy has successfully overcome the mismatch between optimum parameters required for cell growth and 2-ketogluconic acid accumulation, and this result has the highest productivity and conversion ratio of 2-ketogluconic and produced by microorganism.

• 컴퓨터교육학회논문지
• /
• 제18권1호
• /
• pp.13-20
• /
• 2015

현재 컴퓨터공학 교육에 참여하고 있는 여학생들의 전공과 일에 대한 가치관을 조사하고 전공 만족도와 유지율을 증진시킬 수 있는 교육 및 평가 과정 개발을 위한 새로운 방안이 필요한 시점이다. 우리 사회에서 컴퓨터공학 기술 분야의 젠더 다양성을 높이고 여성과 컴퓨터공학 기술 분야의 새로운 관계를 모색하는 데 기여하기 위하여 컴퓨터공학 전공 학생들을 대상으로 정량적 및 정성적 조사를 실시한 결과 여학생의 경우 컴퓨터공학 교육 과정을 접하면서 흥미가 감소되고 멘토가 부족하며 자아 존중감이 저하되는 현상이 나타났고 전공과 직업 선택의 연계 과정이 불일치할 수 있어 여성의 이공계 탈출 현상을 초래할 수 있음이 드러났다. 연구 결과 컴퓨터공학 전공 여학생에게 적합한 ICT교육 방법은 지역적, 역사적, 사회적 맥락에 맞게 재설계되어야 하며 컴퓨터공학 전공 여학생들이 갖고 있는 불안감이나 약한 조직 소속감에서 드러나는 특성을 우선적으로 분석하고 이에 맞는 교수법을 제안해야 할 것으로 보인다.

• 한국병원경영학회지
• /
• 제18권1호
• /
• pp.18-41
• /
• 2013

This study was aimed to identify the current status of medical service quality of medical institutes; propose improvements; and find out the impact of medical service quality by its attribute on overall customer satisfaction. The research was conducted on the out-patients and in-patients in a high-level general hospital located in A city. To examine the research, the IPA was utilized to identify the priority requirements for improving the medical service quality. The study also applied an extended theory to the analysis on mismatch between the level of satisfaction and importance recognized by the clients, to examine the impact of the above mentioned factors on the overall satisfaction and intention to revisit and recommend the hospital. For out-patients, the result showed that "hospital hygiene" had a positive and negative impact on the clients' intention to revisit the hospital in priority improvements. In terms of the sustainable improvements, "doctor's skill" had a negative impact on the overall service satisfaction, whereas "state-of-the-art facility" and "nurse's instruction" had a positive impact on the intention to revisit the hospital. In long-term improvements,"complaint remedy" had a positive impact on the intention to recommend the hospital but there were no relevant factors in excessive investment. On the other hand, for in-patients, the result demonstrated that there were no relevant factors in priority improvements and sustainable improvements. The factor of"service procedure speed"had a positive as well as negative impact on the intention to revisit the hospital. In excessive investment,"nurse's empathy"had a positive impact on the intention to recommend the hospital.

• 대한전자공학회논문지TC
• /
• 제47권7호
• /
• pp.128-134
• /
• 2010

본 논문에서는 저부엽과 저손실 특성을 갖는 고전력 20-출력 스트립라인 전력분배기를 설계, 제작하고 측정하였다. 20-출력전력분배기는 S 대역 선형 배열 안테나의 급전회로를 위해 설계되었으며, 좁은 빔폭과 매우 낮은 저부엽 특성을 위해 Dolph-Chebyshev 전류 분포를 활용하였다. 20-출력 전력분배기는 8-출력 분배기 1개, 4-출력 분배기 3개와 링 하이브리드 전력분배기 3개로 구성되었으며, 전력분배의 기본적인 구조로는 T-접합 분배 구조를 사용하였다. 삽입손실과 반사손실을 개선하기 위해서 노치를 T-접합 분배 구조에 적용하였으며 N형 커넥터와 스트립라인 사이의 천이구조를 수정하였다. 설계, 제작된 전력분배기는 대역 내에서 약 0.3 dB의 삽입손실과 8o 보다 작은 rms 위상 부정합 특성을 보였다. 20-출력 전력분배기 2개를 대칭적으로 구성할 경우 40 dB 이상의 저부엽 특성 결과를 20-출력 전력분배기 측정 결과로부터 합성할 수 있었다.

• 제어로봇시스템학회논문지
• /
• 제21권10호
• /
• pp.910-916
• /
• 2015

A sensorless motor control scheme with conventional back-Electro Motive Force (EMF) sensing based on zero crossing point (ZCP) detection has been widely used in various applications. However, there are several problems with the conventional method for effectively driving sensorless brushless motors. For example, a phase mismatch of 30 degrees occurs between the ZCP and commutation time. Additionally, most of the motor speed/current controls are achieved based on a pulse width modulation (PWM) method, which generates significant noise that distracts the back-EMF sensing. Due to the PWM switching, the ZCP is not deterministic, and thus the efficiency of the motor is reduced because the phase transition points become uncertain. Moreover, the motor driving performance is degraded at a low speed range due to the effect of PWM noise. To solve these problems, an improved back-EMF detection method based on a differential line method is proposed in this paper. In addition, the proposed sensorless BLDC driver addresses the problems by using a variable voltage driver generated from a buck converter. The variable voltage driver does not generate the PWM switching noise. Consequently, the proposed sensorless motor driver improves 1) the signal-to-noise ratio of back-EMF, 2) the operation range of a BLDC motor, and 3) the torque characteristics. The proposed sensorless motor driver is verified through simulations and experiments.

• Animal Systematics, Evolution and Diversity
• /
• 제28권4호
• /
• pp.279-290
• /
• 2012

Plecoglossus altivelis (ayu) is an amphidromous fish widely distributed in Northeastern Asia from the East China Sea to the northern Japanese coastal waters, encompassing the Korean Peninsula within its range. The shore lines of northeastern region in Asia have severely fluctuated following glaciations in the Quaternary. In the present study, we investigate the population genetic structure and historical demographic change of P. altivelis at a population level in East Asia. Analysis of molecular variance (AMOVA) based on 244 mitochondrial control region DNA sequences clearly showed that as the sampling scope extended to a larger geographic area, genetic differentiation began to become significant, particularly among Northeastern populations. A series of hierarchical AMOVA could detect the genetic relationship of three closely located islands between Korea and Japan that might have been tightly connected by the regional Tsushima current. Neutrality and mismatch distribution analyses revealed a strong signature of a recent population expansion of P. altivelis in East Asia, estimated at 126 to 391 thousand years ago during the late Pleistocene. Therefore it suggests that the present population of P. altivelis traces back to its approximate demographic change long before the last glacial maximum. This contrasts our a priori expectation that the most recent glacial event might have the most crucial effect on the present day demography of marine organisms through bottleneck and subsequent increase of effective population size in this region.

• 마이크로전자및패키징학회지
• /
• 제21권3호
• /
• pp.7-17
• /
• 2014

Power electronics modules are semiconductor components that are widely used in airplanes, trains, automobiles, and energy generation and conversion facilities. In particular, insulated gate bipolar transistors(IGBT) have been widely utilized in high power and fast switching applications for power management including power supplies, uninterruptible power systems, and AC/DC converters. In these days, IGBT are the predominant power semiconductors for high current applications in electrical and hybrid vehicles application. In these application environments, the physical conditions are often severe with strong electric currents, high voltage, high temperature, high humidity, and vibrations. Therefore, IGBT module packages involves a number of challenges for the design engineer in terms of reliability. Thermal and thermal-mechanical management are critical for power electronics modules. The failure mechanisms that limit the number of power cycles are caused by the coefficient of thermal expansion mismatch between the materials used in the IGBT modules. All interfaces in the module could be locations for potential failures. Therefore, a proper thermal design where the temperature does not exceed an allowable limit of the devices has been a key factor in developing IGBT modules. In this paper, we discussed the effects of various package materials on heat dissipation and thermal management, as well as recent technology of the new package materials.