• 전기학회논문지
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• 제60권11호
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• pp.2064-2075
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• 2011

In this paper, robust multi-level perturbation and observation (MLPO) maximum power point tracking (MPPT) control are presented of the environmental change including the solar radiation and temperature. Because the maximum power point of the Photovoltaic (PV) is changing according to the solar radiation and temperature, the technology which traces the maximum power point in order to increase the power efficiency is recognized as the very important part. The general requirement for the MPPT is that system is simple, the cost is inexpensive, the PV tracking function and output change are small. Conventional perturbation and observation (PO) method is a simple system but there is the disadvantage that an efficiency of system becomes low. In addation, the incremental conductance (IC) control is required expensive CPU because of a large of calculations. In order to solve this problem, in this paper, the MLPO MPPT control using the method diversifying the step size according to the environment condition is presented. The validity of the MLPO method presenting from this paper is proved through analyzing the solar power generation output error at the steady state.

• 한국세라믹학회지
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• 제33권8호
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• pp.855-862
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• 1996

The nucleation and the crystal growth rates of Ge-Se-Te chalcogenide glass by two step heat-treatment and its effect on the mechanical optical properties and water-resistance were determined. The maximum nuclea-tion and crystal growth rate were 2.1$\times$103/mm3 .min at 28$0^{\circ}C$ and 0.4${\mu}{\textrm}{m}$/min at 33$0^{\circ}C$ respectively. When the crystal volume fraction with crystal size $1.5mutextrm{m}$ was about 4% the (hardness and fracture toughness were about 117kg/mm2 and 6.0 MPa.mm1/2)respectively. The weight loss of crystallized glass in water was lower than parent glass($25^{\circ}C$ for 32 hrs : 0.03% 8$0^{\circ}C$ for 16 hrs : 0.1%) as 0.01% at $25^{\circ}C$, 0.03% at 8$0^{\circ}C$ for 16 hrs : 0.1%) at $25^{\circ}C$ 0.03% at 8$0^{\circ}C$ respectively. The IR-transmittance decreased with increasing crystal size and crystal volume fraction. The IR-transmittance of crystallized glass with the crystal size of $1.5mutextrm{m}$ (crystal volume fraction : 4%) presented 56% which was about 4% lower than that of parent glass.

• 한국전기전자재료학회논문지
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• 제17권3호
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• pp.289-293
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• 2004

PNW-PMN-PZT ceramics were fabricated with the variations of Nb$_2$O$_{5}$ addition and their microstructural and piezoelectric characteristics were investigated. When the amount of Nb$_2$O$_{5}$ increased, grain size decreased gradually. At 0.3wt％ Nb$_2$O$_{5}$ which is the same weight percent with Fe$_2$O$_3$, maximum tetragonality(c/a) and density were shown due to the complexed doping effects. Also, this composition that showed Qm of 2,041, kp of 0.55, grain size of 2.5${\mu}{\textrm}{m}$ and $\varepsilon$r of 1704 were proper for high power application. Using this composition, Rosen-type piezoelectric transformer was fabricated as the size of 1 ${\times}$ 16 ${\times}$ 5㎣ and its electrical characteristics were investigated with the variations of load resistance and driving frequency. At the resistance of 200㏀, maximum step-up ratio of 13.68 was shown. After driving PDA CCFL for 25 min using the inverter circuit, at driving frequency of 214.4KHz, input voltage of 31.78 V and input current of 21.1mA were measured at the input part of piezoelectric transformer. And then, output voltage of 293.2 V and output current of 2.2mA were shown at the output part of piezoelectric transformer. At the same time, efficiency of 96.2％ and temperature rise of 3.5$^{\circ}C$ were appeared at the piezoelectric transformer.ormer.

• Composites Research
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• 제34권5호
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• pp.330-336
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• 2021

알루미나 파우더는 산업용으로 널리 사용되는 소재 중 하나이지만 파우더 패킹 상태에 따라 제품의 강도가 변하는 문제점이 있다. 위 문제해결을 위하여 입자 패킹효율을 높이려는 많은 선행연구들이 수행되었지만, 기존 연구는 밀리미터 스케일의 입자의 충진 특성을 분석한 것이 대부분이므로 마이크로미터 스케일과 물리적 특성이 달라, 그 선행연구 결과를 토대로 마이크로미터 스케일에 적용하기 어렵다. 따라서 본 논문에서는 마이크로미터 스케일의 알루미나 파우더를 이용하여 충진률을 높이기 위하여 통계적방법을 이용하여 3단계 실험을 수행하였다. 먼저, 혼합물시험계획법을 이용하여 충진율이 높은 크기 조합 및 혼합 비율을 선정하였으며, 진동 실험장치에서 가진 주파수 변경에 따른 충진 높이 변화를 분석하여 적정 가진 주파수를 선정하였다. 마지막으로 앞서 언급한 실험 결과값을 토대로 알루미나 파우더 충진율 시험을 수행하였다. 그 결과, 최대 높이 변화량은 충진 크기조합 선정을 위해 수행한 최초의 실험 결과 최댓값보다 42% 향상된 것을 확인하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.454-457
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• 2005

Mining frequent patterns in transaction databases, time-series databases, and many other kinds of databases has been studied popularly in data mining research. Most of the previous studies adopt an Apriori-like candidate set generation-and-test approach. However, candidate set generation is still costly, especially when there exist prolific patterns and/or long patterns. And calendar based on temporal association rules proposes the discovery of association rules along with their temporal patterns in terms of calendar schemas, but this approach is also adopt an Apriori-like candidate set generation. In this paper, we propose an efficient temporal frequent pattern mining using TFP-tree (Temporal Frequent Pattern tree). This approach has three advantages: (1) this method separates many partitions by according to maximum size domain and only scans the transaction once for reducing the I/O cost. (2) This method maintains all of transactions using FP-trees. (3) We only have the FP-trees of I-star pattern and other star pattern nodes only link them step by step for efficient mining and the saving memory. Our performance study shows that the TFP-tree is efficient and scalable for mining, and is about an order of magnitude faster than the Apriori algorithm and also faster than calendar based on temporal frequent pattern mining methods.

• 한국전산유체공학회지
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• 제17권4호
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• pp.24-31
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• 2012

Effects of the subgrid length-scale in the Delayed-Detached Eddy Simulation(DDES) are investigated based on the Spalart-Allmaras(S-A) and the k-$\omega$ Shear Stress Transport(SST) turbulence models. Driver & Seegmiller's experimental results are used to validate numerical results. Grid convergence with grid resolution and subgrid length-scale is investigated. The simulation results show that the volume method for the subgrid length-scale is more resistant to unfavorable effects of the grid size in the periodic direction than the maximum method. Using a sufficient grid resolution and an appropriate subgrid length-scale, both S-A based DDES and SST based DDES methods can provide a good correlation with the experimental data.

• 한국세라믹학회지
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• 제37권6호
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• pp.604-611
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• 2000

Glass-ceramics containing a cordierite (2MgO-2Al2O3-5SiO2) as a main crystal phase was prepared from MgO-Al2O3-SiO2 system glass through a controlled 2-step heat treatment for the application to magnetic memory disk substrate for higher storage capacity. Parent glasses prepared with addition of CeO2 as a fulx and TiO2 as a nucleating agent were crystallized by a 2-step heat treatment i.e. nucleation and crystal grwoth. Then the maximum nucleation and crystal growth rates were investigated and several properties such as bending strength, surface hardness and surface roughness were also studied for heat treated glass. As a result, only a $\alpha$-cordierite was precipitated as a main crystal phase for all heat treatment conditions and the maximum nucleation and crystal growth rates were 2.4$\times$109/㎣.hr at 80$0^{\circ}C$ and 0.3${\mu}{\textrm}{m}$/hr at 915$^{\circ}C$ respectively. After being nucleated at 80$0^{\circ}C$ for 5 hours and then crystallized at 915$^{\circ}C$ for 1 hour, the heat treated glass had a crystal volume fraction of 17.6% and crystal size fo 0.3${\mu}{\textrm}{m}$, and showed the optimum properties for the application to magnetic memory disk substrates as follows. ; Bending strength of 192 MPa, Vidkers hardness of 642.1kgf/$\textrm{mm}^2$, and surface roughness of 27$\AA$.

• 생명과학회지
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• 제15권4호
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• pp.584-589
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• 2005

담체인 황토볼와 Chromobacterium WS 2-14을 이용하여 F-STEP공정(혐기${\rightarrow}$ 호기${\rightarrow}$ 무산소)에서 실제폐수에 존재하는 인산을 효율적으로 제거하기 위해 최적 황토볼 크기 및 소성 온도, 폐수의 초기 pH,폐수의 초기 인산염 농도, 운전온도, 그리고 통기를 검토했다. 최적 조건은 다음과 같다. 황토볼 크기 및 소성 온도, $2\~4mm,\;960^{\circ}C$; 실페수의 초기pH, 6.0; 실페수의 초기 인산 농도, 5.0mg/1. 운전온도, $30^{\circ}C$; 그리고 통기, 5.0L/min등이 얻어졌다. 그리고 최적 운전조건을 이용해서 pilot test을 65일 동안 진행했다. 인산 평균 제거율은 $92.0\%$였고. 또한 최종 유출수에서 COD와 BOD의 평균 제거율은 각각 77.1와 $74.2\%$였으며, SS의 경우는 평균 제거율이, $86.4\%$였다. 이상의 결과로부터 황토볼을 담체로 이용한 Biofilter System은 실제폐수에 존재하는 인산 제거 가능성을 암시했다.

• 한국음향학회지
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• 제30권6호
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• pp.303-307
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• 2011

본 논문에서는 주파수 영역에서의 주요 피크를 선정하고, 주파수 크기 응답에 따라 각기 다른 스텝 사이즈를 사용하는 QIM 오디오 워터마킹을 제안한다. 오디오 신호에 대해 사각 윈도우로 오버랩 없이 L샘플을 취하고 영교차율을 통해 해당 프레임에 워터마크 삽입 가능 여부를 판단 후 푸리에 변환을 통해 주파수 영역에서의 크기 응답을 구한다. 프레임 별 주파수 크기 응답의 최대값에 따라 스텝 사이즈를 결정하고 스펙트럼에서 주요 피크 n개를 검출하여 주변 샘플 w개를 포함한 $n{\times}(w+1)$개 샘플에 대해 QIM을 이용하여 워터마크를 삽입한다. 워터마크 검출은 유클리디안 거리 (Euclidean distance)를 이용한 블라인드 검출 방식으로 수행된다. 오디오 워터마크 벤치마킹을 통한 강인성 검증에서 대부분 강인한 특성을 보였다.

• 핵의학기술
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• 제12권1호
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• pp.74-77
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• 2008

The radiopharmaceuticals are routinely injected to blood vessel for acquiring PET image. For this reason, It is imperative that they undergo strict quality control measures. Especially, Sterility test is more important than any other quality control procedures. According to the FDA guideline, It requires filter integrity test used in the processing of sterile solutions. Among several methods, we can decide to use bubble point test. We usually use vented GS-filters (Millipore co., USA) which are sterilizinggrade (0.22 um pore size) and are placed upper site on product vial. After the synthesis of $^{18}F$-FDG, solutions wet the membrane in filter and then go into the product vial. By all synthesis steps have finished, we can observe the presence of the bubbles in the product vial. Since we have started this study, we have never found any bubbles in the product vial. Because the maximum pressure intensity of the filter which has set by manufacturer is up to 5 bars, but helium gas pressure is up to 1 bar in our module system. So, we can make 5 bars pressure using helium gas bombe and increase pressure up to 5 bars step by step. However, it does not happen to anything in vial.