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Ryu, H.Y.,Ryu, G.H.,Choi, Y.H.,Ma, B. ELSEVIER 2017 Current Applied Physics Vol.17 No.10
<P>The efficiency droop of InGaN-based blue light-emitting diodes (LEDs) is analyzed using numerical simulations with a modified ABC carrier recombination model. The ABC model is modified to include the effect of reduced effective active volume of InGaN quantum wells (QWs) and incorporated into the numerical simulation program. It is found that the droop of internal quantum efficiency (IQE) can be well explained by the effect of reduced light-emitting active volume without assuming a large Auger recombination coefficient A simulated IQE curve with the modified ABC model is found to fit quite well with a measured efficiency curve of an InGaN LED sample when the effective active volume takes only 2.5% of the physical volume of QWs. The proposed numerical simulation model incorporating the reduced effective active volume can be advantageous for use in the modeling and simulation of InGaN LEDs for higher efficiency. (C) 2017 Elsevier B.V. All rights reserved.</P>
Jang, S.-B.,Ma, C.,Lee, J.-Y.,Kim, J.-H.,Park, S. J.,Kwon, A.-R.,Lee, B.-J. Oxford University Press 2009 The Journal of biochemistry Vol.146 No.5
<P>The HP0827 protein is an 82-residue protein identified as a putative ss-DNA-binding protein 12RNP2 Precursor from Helicobacter pylori. Here, we have determined 3D structure of HP0827 using Nuclear Magnetic Resonance. It has a ferredoxin-like fold, beta1-alpha1-beta2-beta3-alpha2-beta4 (alpha; alpha-helix and beta; beta-sheet) and ribonucleoprotein (RNP) motifs which are thought to be important in RNA binding. By using structural homologues search and analyzing electrostatic potential of surface, we could compared HP0827 with other RNA-binding proteins (sex-lethal, T-cell restricted intracellular antigen-1, U1A) to predict RNA-binding sites of HP0827. We could predict that beta sheets of HP0827, especially beta1 and beta3, are primary region for RNA binding. Consequently, similar to other RNA-binding proteins, RNP motifs (Y5, F45, F47), positively charged and hydrophobic regions (K32, R37, K40, K41, K43, R70, R73) are proposed as a putative RNA-binding sites. In addition, differences in amino acids composition of RNP motifs, N, C-terminal residues, loop-region fold and the orientation of alpha1-helix with other RNA recognition motif proteins could give specific biological functions to HP0827. Finally, the study on natural RNA target is also important to completely understand the biological function of HP0827.</P>
Improvement of lower hybrid current drive systems for high-power and long-pulse operation on EAST
Wang M.,Liu L.,Zhao L.M.,Li M.H.,Ma W.D.,Hu H.C.,Wu Z.G.,Feng J.Q.,Yang Y.,Zhu L.,Chen M.,Zhou T.A.,Jia H.,Zhang J.,Cao L.,Zhang L.,Liang R.R.,Ding B.J.,Zhang X.J.,Shan J.F.,Liu F.K.,Ekedahl A.,Gonich 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.11
Aiming at high-power and long-pulse operation up to 1000 s, some improvements have been made for both 2.45 GHz and 4.6 GHz lower hybrid (LH) systems during the recent 5 years. At first, the guard limiters of the LH antennas with graphite tiles were upgraded to tungsten, the most promising material for plasma facing components in nuclear fusion devices. These new guard limiters can operate at a peak power density of 12.9 MW/m2 . Strong hot spots were usually observed on the old graphite limiters when 4.6 GHz system operated with power >2.0 MW [B. N. Wan et al., Nucl. Fusion 57 (2017) 102019], leading to a reduction of the maximum power capability. With the new limiters, 4.6 GHz LH system, the main current drive (CD) and electron heating tool for EAST, can be operated with power >2.5 MW routinely. Long-pulse operation up to 100 s with 4.6 GHz LH power of 2.4 MW was achieved in 2021 and the maximal temperature on the guard limiters measured by an infrared (IR) camera was about 540 C, much below the permissible value of tungsten material (~1200 C). A discharge with a duration of 1056 s was achieved and the 4.6 GHz LH energy injected into the plasma was up to 1.05 GJ. Secondly, the fully-activemultijunction (FAM) launcher of 2.45 GHz system was upgraded to a passive-active-multijunction (PAM), for which the density of optimum coupling was relatively low (below the cut-off value). Good coupling with reflection coefficient ~3% has been achieved with plasma-antenna distance up to 11 cm for the new PAM. Finally, in order to eliminate the effect of ion cyclotron range of frequencies (ICRF) wave on 4.6 GHz LH wave coupling, the location of the ICRF launcher was changed to a port that is located 157.5 toroidally from the 4.6 GHz LH system and is not magnetically connected
Ma, J. W.,Lee, W. J.,Bae, J. M.,Jeong, K. S.,Kang, Y. S.,Cho, M. -H.,Seo, J. H.,Ahn, J. P.,Chung, K. B.,Song, J. Y. American Chemical Society 2013 Nano letters Vol.13 No.3
<P>The Young’s modulus and fracture strength of Si<SUB>1–<I>x</I></SUB>Ge<SUB><I>x</I></SUB> nanowires (NWs) as a function of Ge concentration were measured from tensile stress measurements. The Young’s modulus of the NWs decreased linearly with increasing Ge content. No evidence was found for a linear relationship between the fracture strength of the NWs and Ge content, which is closely related to the quantity of interstitial Ge atoms contained in the wire. However, by removing some of the interstitial Ge atoms through rapid thermal annealing, a linear relationship could be produced. The discrepancy in the reported strength of Si and Ge NWs between calculated and experimented results could be related to SiO<SUB>2–<I>x</I></SUB>/Si interfacial defects that are found in Si<SUB>1–<I>x</I></SUB>Ge<SUB><I>x</I></SUB> NWs. It was also possible to significantly decrease the number of interfacial defects in the NWs by incorporating a surface passivated Al<SUB>2</SUB>O<SUB>3</SUB> layer, which resulted in a substantial increase in fracture strength.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-3/nl304485d/production/images/medium/nl-2012-04485d_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl304485d'>ACS Electronic Supporting Info</A></P>
Control Effect on Root-knot Nematodes by Hot Water Dipping Treatment in Kiwifruit
Ma, K.,Cho, Y,Jeong, B.,Choi, D. 한국유기농업학회 2011 韓國有機農業學會誌 Vol.19 No.S
When kiwifruit root system infected with nematodes was treated by hot water dipping treatment, the maximum temperature for this treatment was suggested as 50℃. The lowest killing temperature of internal root-knot in the root tissue was 48℃. Consequently, root-knot nematodes could be killed without damaging root tissues by the hot water dipping treatment at 48℃ for 10 minutes. This could be useful for organic production and distribution of kiwifruit seedlings by avoiding the synthetic nematicides which are not easily decomposed in soil once applied.
AC Loss Characteristics of a Cylindrical High Temperature Superconductor
Ma, Y.H.,Li, Z.Y.,Ryu, K.,Choi, S.,Park, K.B.,Oh, I.S.,Song, H.J.,Cha, G. IEEE 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>A cylindrical high temperature superconductor (HTS) is often used in power applications such as power transmission cables and matrix fault current limiters. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density and one hollow conductor made of Bi-2212 bulk material. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analysed. The results show that the measured losses for all the conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with high critical current density is in good agreement with the numerically calculated one based on the polygon model, whereas the loss measured for the Bi-2223 conductor with low critical current density coincides with the calculated loss from the monoblock model.</P>
Effects of Reflectors and Receivers on the Thermal Performance of Dish-Type Solar Power Systems
Ma, D.S.,Kim, Y.,Seo, T.B.,Kang, Y.H.,Han, G.Y. 한국신재생에너지학회 2007 한국신재생에너지학회 학술대회논문집 Vol.2007 No.06
The thermal performance comparisons of the dish solar collector system are numerically investigated with mirror arrays and receiver shapes. In order to compare the performances of the dish solar collector systems, six different mirror arrays and four different receiver shapes are considered and the radiative heat flux distribution on the inside of the receiver is analyzed. A parabolic-shaped perfect mirror of which diameter is 1.5 m is considered as a reference of the mirror arrays. Five different mirror arrays of twelve identical parabolic -shaped mirror facets of which diameter are 0.4 m are proposed in this study. Their reflecting areas, which are 1.5 m², are the same. Four different receiver shapes are a dome, a conical, a cylindrical and a unicorn type. The solar irradiation reflected by mirrors is traced using the Monte-Carlo method. In addition, the radiative properties of the mirror surface can vary the thermal performance of the dish solar collector system so that the effects of the surface reflectivity and the surface absorptivity are considered. Based on the calculation, the design information of dish solar collector system for producing the electric power can be obtained. The results show that the dome type has the best performance in receiver shapes and the 2AND4INLINE has the best performance in mirror arrays except the perfect mirror.
마용호(Y.H. Ma),이주영(Z.Y. Li),진홍범(H.B. Jin),류경우(K. Ryu),임지현(J.H. Lim),손송호(S.H. Sohn),황시돌(S.D Hwang) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
다층구조의conductor와 shield로 구성되는 HTS-cable의 교류손실 특성 연구를 위하여 2005년부터 실증시험 중에 있는 22.9㎸, 50㎹A, 100m급 KEPCO HTS-cable system에 사용된 케이블과 동일한 두개의 short-sample에 대하여DC 및 AC 특성을 실험적으로 조사하였다. KEPCO HTS-cable system에서 처럼 shield전류를 conductor와 크기는 같게 하고 방향을 반대로하여 수주기동안 AC pulse전류를 인가했을 때, shield의 임계전류가 conductor보다 작음에도 불구하고 conductor-lead에 대하여 측정된 AC loss가 shield의 것과 비교하여 약 1.5배 큰 것을 알 수 있었다.