• 한국재료학회지
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• 제19권7호
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• pp.356-361
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• 2009

The optical characterization of self-assembled InAs/AlAs Quantum Dots(QD) grown by MBE(Molecular Beam Epitaxy) was investigated by using Photoluminescence(PL) spectroscopy. The influence of thin AlAs barrier on QDs were carried out by utilizing a pumping beam that has lower energy than that of the AlAs barrier. This provides the evidence for the tunneling of carriers from the GaAs layer, which results in a strong QD intensity compared to the GaAs at the 16 K PL spectrum. The presence of two QDs signals were found to be associated with the ground-states transitions from QDs with a bimodal size distribution made by the excitation power-dependent PL. From the temperature-dependent PL, the rapid red shift of the peak emission that was related to the QD2 from the increasing temperature was attributed to the coherence between the QDs of bimodal size distribution. A red shift of the PL peak of QDs emission and the reduction of the FWHM(Full Width at Half Maximum) were observed when the annealing temperatures ranged from 500 $^{\circ}C$ to 750 $^{\circ}C$, which indicates that the interdiffusion between the dots and the capping layer was caused by an improvement in the uniformity size of the QDs.

• 한국광학회지
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• 제29권4호
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• pp.139-148
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• 2018

본 연구에서는 250 nm와 1100 nm 사이에 있는 10개의 파장에서의 에어로졸 광학 깊이를 이용하여 에어로졸의 크기분포를 역산하는 연구를 수행하였다. 10개의 파장은 주요 대기 가스의 흡수선과 밴드를 피한 파장을 찾아서 선택하였다. 태양의 스펙트럼을 얻기 위해서 태양 추적시스템과 분광기를 구축하고 자체적으로 장치를 검정하였다. 본 장치를 이용해서 총 광학 깊이를 구하고 가스의 흡수나 공기의 산란을 제거하여 에어로졸의 광학 깊이를 구했다. 이정점 분포를 지닌 에어로졸 크기 분포를 역산하는 알고리즘을 제안하였고, 장치를 통해서 구한 에어로졸의 광학 깊이를 이용하여 다양한 임의의 대기 조건에서 그 크기분포를 역산하고 비교하였다. 이를 통하여 본 연구에서 사용한 방법론과 장치들이 미지의 입자 크기 분포를 추출하는데 매우 유용할 것으로 판단하였다.

• 자원리싸이클링
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• 제14권6호
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• pp.21-27
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• 2005

국내 은 함유 폐자원의 고부가가치 제품화를 위한 연구의 일환으로써 sodium formaldehydesulfoxy와 ascorbic acid를 각각 환원제로 사용한 Ag 나노분발의 제조실험을 수행하였다. Ag수용액은 질산은을 소정 농도로 증류수에 용해시켜 사용하였으며, Ag미립자의 응집방지를 위한 분산제로는 Tamol NN8906, PVP, SDS 및 caprylic acid를 각각 사용하었다. 환원반응을 통하여 제조한 Ag 미립자는 입도분석기 및 TEM측정을 통하여 morphology와 평균입도를 측정하였다. sodium formaldehydesulfoxylate 에 의한 은의 환원을 위해서는 이론치의 1.4배를 첨가해 주어야 하는 것으로 나타났으며, ascorbic acid와는 달리 생성된 Ag 입자가 너무 크게 성장하는 문제점이 있었다. 분산제에 따른 Ag 입자의 특성을 살펴본 결과, Tamol 및 PVP를 사용한 경우에는 bimodal distribution을 보였으나, SDS 와 caprylic acid의 경우에는 수십 nm에서 $100{\mu}m$에 이르는 매우 broad한 입도분포를 보였다.

• 자원리싸이클링
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• 제15권4호
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• pp.19-26
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• 2006

함은 폐재의 리싸이클링을 위한 연구의 일환으로써 Hydrazine Hydrate을 환원제로 사용하여 질산은 수용액으로부터 Ag 나노분말을 제조하기 위한 실험을 수행하였다. 이를 위해 질산은을 소정 농도로 증류수에 용해시킨 수용액에 Ag 미립자의 응집방지를 위한 분산제로써 Tamol NN8906 혹은 Tween 20을 미리 혼합한 다음 환원제인 Hydrazine Hydrate 용액을 첨가하는 방법으로 환원반응을 실시하였다. 환원반응을 통하여 제조한 Ag 미립자는 입도분석기 및 TEM 측정을 통하여 형상과 평균입도를 측정하였다. Hydrazine Hydrate에 의한 은의 환원을 위해서는 이론치의 약 2배를 첨가해 주어야 하는 것으로 나타났으며, Tamol NN8906을 분산제로 사용하여 제조한 Ag 나노분발은 매우 좁은 입도범위의 분포특성을 보여 주었다. Tween 20을 분산제로 사용한 경우의 입도 분포는 bimodal 혹은 multimodal distribution을 보였으며, 입자 모양에 있어서는 Tamol NN8906과 Tween 20이 모두 비슷하게 표면이 매끄러운 불규칙한 모양의 입자들로 구성되어 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.289-289
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• 2009

The series hybrid propulsion system in bimodal tram consists of CNG engine, generator, inverter, motor and battery as main components. Among them, battery is very important thing to make a hybrid bimodal tram more efficient in driving. Battery pack is composed of 168 LPB(lithium polymer battery) cells, 650Vdc-300A. LPB should be treated with a good consideration in both temperature and overvoltage. This paper had analyzed and investigated the thermal flow and distribution of LPB module(l4 LPB cells) and Pack in simulated environments by commercial thermal analysis tool.

• Nuclear Engineering and Technology
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• 제31권6호
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• pp.608-617
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• 1999

The powder mixture which has a bimodal size distribution, with a large mode corresponding to AUC-UO$_2$ powder and a small one corresponding to ADU-UO$_2$ powder, was prepared, pressed into compacts, and sintered at 1680t for 4 hours in hydrogen gas. The compact density of the powder mixture increases with increasing ADU-UO$_2$content within a content of 20 wt %, since small ADU-UO$_2$ particles can fill interstices between large AUC-UO$_2$particles. The UO$_2$ pellet made using the powder mixture has a lower open porosity than that made using AUC-UO$_2$ powder alone. The mechanism for the formation of a flake-like pore is proposed, and the decrease in open porosity may be ascribed to the decrease in the number of flake-like pores.

• 한국생산제조학회지
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• 제7권3호
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• pp.126-131
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• 1998

In computer vision system of modern industry precise measuring has lots of dfficulties because of measurement error due to distortion phenomenon. Among the difficulties, the distortion of edge is regraded as a dominent problem. which is caused by the vlurred image. The blurred image apperar when camera can not discriminate its precise focus. So. it is very important to decide focus of lens and to develop algorithm in order to correct distortion phenomenon. Thus. discrimination criteria obtained by image information of precise focus must be fixed in advance. The gray level histogram of image acquired from blurred edge tends to show a uniform distribution. Bimodal intensity histogram is related with condition of focus, and it is possible to find good condition of focus by using bimodal histogram of entropy.

• Journal of the Korean Data and Information Science Society
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• 제23권4호
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• pp.797-805
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• 2012

Many circular distributions are known to be not only asymmetric but also bimodal. Hidden truncation method of generating asymmetric distribution is applied to a bivariate circular distribution to generate an asymmetric circular distribution. While many other existing asymmetric circular distributions can only model an asymmetric data, this new circular model has great flexibility in terms of asymmetry and bi-modality. Some properties of the new model, such as the trigonometric moment generating function, and asymptotic inference about the truncation parameter are presented. Simulation and real data examples are provided at the end to demonstrate the utility of the novel distribution.

• Wind and Structures
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• 제23권4호
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• pp.351-366
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• 2016

Nowadays, wind energy is the most rapidly developing technology and energy source and it is reusable. Due to its cleanliness and reusability, there have been rapid developments made on transferring the wind energy systems to electric energy systems. Converting the wind energy to electrical energy can be done only with the wind turbines. So installing a wind turbine depends on the wind speed at that location. The expected wind power can be estimated using a perfect probability distribution. In this paper Weibull and Weibull distribution with multiple parameters has been used in deriving the mathematical expression for estimating the wind power. Statistically the parameters of Weibull and Weibull distribution are estimated using the maximum likelihood techniques. We derive a probability distribution for the power output of a wind turbine with given rated wind speeds for the regions where the wind speed histograms present a bimodal pdf and compute the first order moment of this distribution.

• 한국환경보건학회지
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• 제22권4호
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• pp.55-61
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• 1996

Measurements of the seasonal variations of concentration and size distribution of TSP, $SO_4^{2-}, NO_3^-, Cl^-, NH_4^+, Na^+, K^+, Ca^{2+}$ and $Mg^{2+}$ were made by Andersen air sampler from May 1995 to April 1996 in Seoul. The size distribution of these ions was divided into four patterns. 1) Distribution was concentrated on fine particles over a year such as $NO_3^-$ component, 2) Distribution was predominated in coarse particles fraction over a year such as $Mg^{2+}$ and $Ca^{2+}$ components, 3) Distribution was differerent from various seasons such as $NH_4^+, SO_4^{2-}, Cl^-$ and $K^+$ components, 4) Distribution was bi-modal such as $Na^+$.