Temperature dependence of the radiative recombination time in ZnO nanorods under an external magnetic field of 6 T.

Lee, W,Kiba, T,Murayama, A,Sartel, C,Sallet, V,Kim, I,Taylor, R A,Jho, Y D,Kyhm, K Optical Society of America 2014 Optics express Vol.22 No.15

<P>The Temperature dependence of the exciton radiative decay time in ZnO nanorods has been investigated, which is associated with the density of states for the intra-relaxation of thermally excited excitons. The photoluminescence decay time was calibrated by using the photoluminescence intensity in order to obtain the radiative decay time. In the absence of an external magnetic field, we have confirmed that the radiative decay time increased with temperature in a similar manner to that seen in bulk material (similar to T-1.5). Under an external magnetic field of 6T parallel to the c-axis, we found that the power coefficient of the radiative decay time with temperature decreased (similar to T-1.3) when compared to that in the absence of a magnetic field. This result can be attributed to an enhancement of the effective mass perpendicular to the magnetic field and a redshift of the center-of-mass exciton as a consequence of perturbation effects in the weak-field regime. (C) 2014 Optical Society of America</P>

Spin-Injection Dynamics and Eects of Spin Relaxation in Self-Assembled Quantum Dots of CdSe

T. Furuta,K. Hyomi,I. Souma,Y. Oka,A. Murayama,D. Dagnelund,I. A. Buyanova,W. M. Chen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We study the spin injection dynamics and the eects of spin relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons can be injected from the DMS into the QDs because of the potential dierence. The degree of circular polarization, P, of excitonic photoluminescence (PL) at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulse excitation, indicating the spin-injection dynamics. The P value tends to decay gradually because of the exciton-spin relaxation in the QDs after the spin injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from QDs with higher exciton energies to those with lower exciton energies. This inter-dot transfer of excitons also aects the P value in the lower energy region of the QD-emission band because the excitons lose their spin polarizations due to the spin relaxation in the dots during the migration. The detailed analysis for the exciton-spin transfer is presented in a coupled QD system after spin injection. We study the spin injection dynamics and the eects of spin relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons can be injected from the DMS into the QDs because of the potential dierence. The degree of circular polarization, P, of excitonic photoluminescence (PL) at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulse excitation, indicating the spin-injection dynamics. The P value tends to decay gradually because of the exciton-spin relaxation in the QDs after the spin injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from QDs with higher exciton energies to those with lower exciton energies. This inter-dot transfer of excitons also aects the P value in the lower energy region of the QD-emission band because the excitons lose their spin polarizations due to the spin relaxation in the dots during the migration. The detailed analysis for the exciton-spin transfer is presented in a coupled QD system after spin injection.

[論文] 디젤기관의 대체연료 이용에 관한 연구Ⅲ(에스테르 연료, 연소특성해석)

오영택(Y.T.Oh),정규조(K.J.Cheong),촌산 정(T.Murayama) 한국자동차공학회 1989 오토저널 Vol.11 No.1

제2보 (2)에서는 식물유를 연료로 사용할 경우 문제점인 시동성, 내구성및 카본생성을 억제하기 위하여 물리적인 방법으로 해결책을 모색하였다. <br/> 그러나, 본 연구는 기관자체는 전혀 병형시키지 않고, 점도저감을 위하여 화학적인 방법 즉, 식물유를 알콜과 반응시켜 에스테르변환을 하여 해결하려는 방법으로,ㅡ 에스테르화한 연료를 사용하였을 때의 기관성능 및 카본 퇴적문제를 비교, 시험한 것이다. 또, 기름이 식물유와 같이 지방산으로 이루어져 있다면, 언, 기름도 에스테르 변환이 가능하기 때문에, 생선기름인 정어리기름의 에스테르연료도 사용하여 그 이용 가능성을 확실히 하였다.<br/> 또한, 각종 연료의 연소상에 관하여 보다 상세한 검토를 하기 위하여, 이들의 연소를 파형을 2개의 Wiebe의 연소함수의 조합으로 표현함과 동시에 연소율 파형을 구성하는 각 변수를 해석함으로써, 기관성능치와 연소성과의 정량적인 관계에 대해서도 조사한 것이다. The paper shows a solution by giving vegetable oil a chemical treatment, i.e., transesteri fication of the rapeseed oil without any modification of the diesel engine for reducing carbon deposits, and to evaluate rate of combustion with vegetable oils, their esterified fuel and their blend fuels using a double Wiebe's function approximation in a naturally aspired D.I. diesel engine.<br/> Since any oil will be as material for ester, if it is fatty acid, the sardine oil was considered. In the experiment, engine performance, exhaust gas emissions, and combustion character­<br/> istics were measured and calculated for a number of fuels: rapeseed oil, palm oil, ester of rape­seed oil, and these fuels blended with ethanol or diesel fuel.

Polarization anisotropy of exciton in self-assembled elliptical InP/InGaP quantum dots

Kim, I.,Kiba, T.,Murayama, A.,Song, J.D.,Kyhm, K. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.6

Optical anisotropy of self-assembled elliptical InP quantum dots has been investigated in terms of the polarization dependence of excitons. Although large size inhomogeneity is present, two kinds of characteristic quantum dots, which are classified into large and small quantum dots, were found in terms of the polarization anisotropy. We have confirmed that the large quantum dots are more pronounced in the polarization anisotropy, where the degree of linear polarization for the large quantum dots is significantly larger (~60%) than that for the small ones (~36%). The effective shape of quantum dots is also estimated by using the size dependence of oscillator strength, which is in agreement with the AFM image. We also suggest that the anisotropy of exciton oscillator strength can be modified via the dipole-dipole interaction between nearest exciton dipoles.

[論文] 디젤기관의 대체연료 이용에 관한 연구Ⅱ(시동성 및 내구성 문제)

오영택(Oh Y.T.),정규조(Cheong K.J.),촌산정(Murayama Tadashi) 한국자동차공학회 1988 오토저널 Vol.10 No.6

前報에서 식물유가 디젤기관의 연료로서의 성질을 조사하였고 또 실제기관의 연료로 사용하였을 경우, 기관의 출력성능 및 배기가스농도 등이 기존연료인 경유에 비하여 우수함에도 불구하고 식물유 특유의 높은 점도때문에 생성되는 카본의 퇴적 문제때문에 장시간 운전할 수 없다는 것이 큰 단점으로 지적되었다. <br/> 따라서, 본 연구는 저온시동성, 카본의 생성조건의 파악 및 기관의 내구성 등의 문제점을 찾아내고, 해결책으로 점도를 저감시키기 위한 물리적인 처리방법을 중심으로 기술한 것이다. In a previous report, the properties of vegetable oils as diesel fuel substitutes were investi­gated and the basic load performance of a diesel engine was examined using vegetable oil. The results show that despite of the long term chain hydrocarbon structure and large droplet size due to high viscosity, vegetable oils have good basic performance and exhaust emissions, however they cause serious problems as carbon deposit buildup, they have poor durability, and also poor thermal efficiency.<br/> In this paper, the startability and engine durability with long term operation was tested by physical methods for reducing viscosity when vegetable oil was used as compared against diesel fuel.<br/> The results obtained in this investigation may be stated as follows;<br/> (1) There is no problem in startability when vegetable oil was used as diesel fuel substitutes as far as fuel temperature is higher than 30℃.<br/> (2) The carbon deposits were most extensfve at lower loads and lower engine speeds, and deposit buildup more heavily on the cooler parts of the combustion chamber wall.<br/> (3) Blends with 25% diesel fuel and 20v-% ethanol are effective in reducing the carbon deposit buildups.<br/> (4) Significant improvement in carbon deposit and piston ring stick can be obtained by heat­ing fuel ( 200℃).

[論文] 디이젤기관에 있어서 실린더 압력변동의 하모닉성분 특성

이성노(S-R Lee),궁본등(N. Miyamoto),촌산정(T. Murayama) 한국자동차공학회 1987 오토저널 Vol.9 No.6

엔진소음은 내연기관에서 중요한 관심사중의 하나이다.<br/> 본 연구는 연소소음에 주요한 영향을 미치는 실린더 압력변동에 있어서 주파수 성분의 일반적 특성을 밝혔다. <br/> 각기 다른 연소거동과 그들의 주파수성분 분석을 위한 실린더 압력변동의 계산방법을 모색하였다. <br/> 주파수 성분은 4종류의 변수, 즉 실린더 압력볒동의 4종류 특성치를 갖는 선형 연소함수에 의하여 근사적으로 기술될 수 있음을 밝혔다. <br/> 마지막으로 4 종류의 변수의 상관관계는 연소거동이나 엔진운전조건에 관계없이 단지 엔진회전수의 차수(Order)에만 의존함을 밝혔다.

Modeling the Asian Dust Aerosol Based on Ground Observations of Solar Radiation and Its Application to SeaWiFS

Sohn, B. J.,Fukushima, H.,Takahashi, W.,Nakajima, T.,Murayama, T.,Ohta, S.,Kim, D.H.,Lee, S. S. 대한원격탐사학회 1999 International Symposium on Remote Sensing Vol.15 No.1

THE HST COSMOS PROJECT: CONTRIBUTION FROM THE SUBARU TELESCOPE

TANIGUCHI YOSHIAKI,SCOVILLE N. Z.,SANDERS D. B.,MOBASHER B.,AUSSEL H.,CAPAK P.,AJIKI M.,MURAYAMA T.,MIYAZAK S.,KOMIYAMA Y.,SHIOYA Y.,NAGAO T. The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2

The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST) treasury project. The COSMOS aims to perform a 2 square degree imaging survey of an equatorial field in I(F814W) band, using the Advanced Camera for Surveys (ACS). Such a wide field survey, combined with ground-based photometric and spectroscopic data, is essential to understand the interplay between large scale structure, evolution and formation of galaxies and dark matter. In 2004, we have obtained high-quality, broad band images of the COSMOS field (B, V, r', i', and z') using Suprime-Cam on the Subaru Telescope, and we have started our new optical multi-band program, COSMOS-21 in 2005. Here, we present a brief summary of the current status of the COSMOS project together with contributions from the Subaru Telescope. Our future Subaru program, COSMOS-21, is also discussed briefly.