Synthesis and Thermoelectric Properties of Ce1−z Pr z Fe4−x Co x Sb12 Skutterudites

Song, K. M.,Shin, D. K.,Jang, K. W.,Choi, S. M.,Lee, S.,Seo, W. S.,Kim, I. H. Springer Science + Business Media 2017 Journal of electronic materials Vol.46 No.5

<P>p-Type Ce1-z Pr (z) Fe4-x Co (x) Sb-12 skutterudites were prepared by encapsulated melting, quenching, annealing, and hot pressing. While the skutterudite phase was successfully synthesized, a small amount of the secondary phase (FeSb2) was observed. According to the scanning electron microscope analysis, (Ce,Pr)Sb-2 phases were also observed for Co-substituted specimens (x = 0.5). The electrical conductivity decreased with increasing temperature, implying a degenerate semiconductor behavior, and also decreased with increasing Co contents. All specimens showed p-type characteristics having positive signs of the Hall coefficient and the Seebeck coefficient. The Seebeck coefficient increased with increasing temperature and reached a maximum value at 823 K. The power factor (PF) increased with decreasing Co content and Ce0.75Pr0.25 Fe4Sb12 showed a peak value of PF = 3.2 mW m(-1) K-2 at 823 K. The electronic thermal conductivity decreased with increasing Co contents and the lattice thermal conductivity decreased with decreasing Ce and Co contents at high temperature. The thermal conductivity increased at temperatures above 623 K due to bipolar conduction. The dimensionless figurea of pound merit (ZT) showed a maximum value of ZT = 0.84 at 823 K for Ce0.25Pr0.75Fe4Sb12.</P>

Chemical Bath Deposition 방법으로 제작한 CdSe 박막의 특성

홍광준,이상열,유상하,서상석,문종대,신영진,정태수,신현길,김택성,송정훈,유기수 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.16 No.-

Chemical bath deposition 방법으로 다결정 CdSe 박막을 세라믹 기판 위에 성장시킨 다음 온도를 변화시켜 열처리하고 X-선 회절무늬를 측정하여 결정구조를 밝혔다. 450℃로 열처리한 시료가 X-선 회절무늬로 부터 외삽법에 의해 a_o와 c_o 는 각각 4.302 Å과 7.014 Å인 육방정계임을 알았다. 이 때 낱알크기는 약 0.3㎛이었다. Van der Pauw 방법으로 Hall 효과를 측정하여 운반자 농도와 이동도의 온도의존성을 연구하였다. 이동도는 33 K 에서 200 K 까지는 압전산란에 의하여, 200 k 에서 293 K 까지는 극성광학산란에 의하여 감소하는 경향이 나타냈다. 광전도 셀의 특성으로 스텍트럼 응답, 감도(γ), 최대허용소비전력 및 응답 시간을 측정하였다. Polycrystalline CdSe thin films were grown on creamic substrate using a chemical bath deposition (CBD) method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdSe polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdSe samples annealed in N_2 gas at 450℃ it was found hexagonal structure whose lattice parameters a_o and c_o were 4.302 Å and 7.014 Å, respectively. It grain size was about 0.3 ㎛. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33 K and 200 K, and by polar optical potical scattering at temperature range of 200 K and 293 K. We measured also spectral response, sensitivily (γ), maximum allowable power dissipation and response time on these samples.

CBD 방법에 의한 CdS 박막의 성장과 광전도 특성

황광준,이상열,유상하,서상석,문종대,신영진,정태수,신현길,김택성,송정훈,유기수 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.16 No.-

Chemical bath deposition 방법으로 다결정 CdS 박막을 세라믹 기판 위에 성장시킨 다음 온도를 변화시켜 열처리하고 X-선 회절무늬를 측정하여 결정구조를 밝혔다. 550℃로 열처리한 시료의 경우 X-선 회절무늬로 부터 외삽법에 의해 a_。와 c_。는 각각 4.1364 Å과 6.7129 Å인 육방정계임을 알았다. 이 때 낱알크기는 약 0.35㎛이었다. Van der Pauw 방법으로 Hall 효과를 측정하여 운반자 농도와 이동도의 온도의존성을 연구하였다. 이동도는 33 K 에서 150 K 까지는 압전산란에 의하여, 150 K 에서 293 K 까지는 극성광학산란에 의하여 감소하는 경향이 나타냈다. 광전도 셀의 특성으로 스텍트럼 응답, 감도(γ), 최대허용소비전력 및 응답 시간을 측정하였다. Polycrystalline CdS thin films were grown on creamic substrate using a chemical bath deposition method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study CdS polycrystal structure. Using extrapolation method of X-ray diffraction patterns for the CdS samples annealed in N_2 gas at 550℃ it was found hexagonal structure whose lattice constants a_o and c_o were 4.1364 Å and 6.7120Å, respectively. Its grain size was about 0.35 ㎛. Hall effect on this sample was measured by Van der Pauw method and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by piezo electric scattering at temperature range of 33K and 150K and by polar optical scattering at temperature range of 150K and 293K. We measured also spectral response, sensitivity (γ), maximum allowable power dissipation and response time on these samples.

Development of the new KSTAR helium distribution box

Lee, Y.J.,Kwag, S.W.,Song, N.H.,Park, D.S.,Chang, Y.B.,Moon, K.M.,Kim, N.W.,Joo, J.J.,Lee, C.H.,Kim, K.P.,Song, J.I.,Park, S.H.,Kim, H.T.,Ahn, H.J.,Kim, Y.S. Elsevier 2017 Fusion engineering and design Vol.123 No.-

<P><B>Abstract</B></P> <P>KSTAR project has required the new helium distribution box named upgraded distribution box (DBU) for the operation of the cryogenic components such as in-vessel cryo-pump (CPI), super-sonic molecular beam injector (SMBI), and deuterium pellet injection system (PIS). Two CPIs are inserted into the tokamak vacuum vessel and these components shall be operated at 90K for the liquid nitrogen thermal shields and 4.5K for the hydrogen cryo-panel. One hydrogen PIS was newly mounted on the tokamak for the 2016 KSTAR campaign. Liquid nitrogen shall be supplied to the one SMBI. For the operation of above mentioned 3 kinds of cryogenic components, a helium refrigerator, which had been used for the R&D in the KSTAR facility construction phase (2002–2013), was moved and inserted into the KSTAR 9kW helium facility room. The cooling capacity of the refrigerator at 4.5K is 1kW and it was manufactured from the Linde Kryotechnik before 2002. After some maintenances in warm compressor, electrical power supply, oil-filter, and so on, commissioning of the refrigerator up to 4.5K was accomplished successfully. From the beginning of 2015, design and fabrication of the DBU was started. It shall control the liquid nitrogen for the SMBI and CPI thermal shields whereas liquid helium for the CPI cryo-panel and PIS. To minimize the temperature of the liquid nitrogen to be supplied to SMBI and CPI, a thermal damper tank was inserted into the distribution box. Nitrogen return gases are to be warmed up to room temperature at the heater in the distribution box. A 1000l of liquid helium vessel is located nearby the PIS to supply cold gas helium (∼5K). Because the CPI cryo-panel requires regeneration up to 90K, complex regeneration and re-cool down scenario was developed and applied to the DBU. Including operational results, details of the DBU progresses will be reported in this paper.</P> <P><B>Highlights</B></P> <P> <UL> <LI> There has been progresses in the construction and 1st operation of DBU in 2016 KSTAR plasma experiments. </LI> <LI> Two in-vessel cryopumps (CPIs) cool-down to 4.5K and observed pumping speed was 3.0E4l/s. </LI> <LI> Manual CPI regeneration tests were accomplished regarding future automatic control. </LI> <LI> Production of the D<SUB>2</SUB> pellets were successful and there has been lots of injection tests. </LI> </UL> </P>

A partial index for distributed broadcasting in wireless mobile networks

Song, D.,Park, K. North-Holland [etc ; Elsevier Science Ltd 2016 Information sciences Vol.348 No.-

<P>To increase the scalability of location-based services (LBSs), researchers have begun to propose methods for processing spatial queries in wireless broadcast environments. In this paper, we examine the issue of spatial query processing within wireless broadcast systems and propose a distributed broadcast system (D-Bcast) model that can be applied to spatial query processing in such environments. Instead of receiving data directly from the server, the client in our proposed system model receives, via a subserver (S-nub), only the portion of the spatial data that has been requested by the querier, which reduces the broadcasting cycle and thus the access time. This distributed data broadcast model represents an efficient method of transmitting data to an arbitrary number of clients, including those that are moving across different main server (S-main) ranges. To implement this model, a hierarchical bitmap-based spatial index (HBI) employing a tree-based indexing scheme is proposed that divides the broadcast space into grids according to the distributions of objects. The grids are constructed such that an index tree for each grid can easily be configured. A full index of the broadcast program is constructed by applying the HBI to each S-sub, with the indexes of the S(sub)s corresponding to the respective portions of the broadcast program used to broadcast data to the clients. In this manner, the total broadcasting cycle required to be read by the client is reduced and the query processing is decreased. Our proposed method is more effective than existing wireless broadcasting methods in reducing the location error that occurs when an update is induced by object movement. A cost model and experimental results are used to verify the efficacy of the proposed method. (C) 2016 Elsevier Inc. All rights reserved.</P>

AERODYNAMIC DESIGN OPTIMIZATION OF REAR BODY SHAPES OF A SEDAN FOR DRAG REDUCTION

K. S. SONG,S. O. KANG,S. O. JUN,H. I. PARK,J. D. KEE,김규홍,이동호 한국자동차공학회 2012 International journal of automotive technology Vol.13 No.6

This study proposes an aerodynamically optimized outer shape of a sedan by using an Artificial Neural Network (ANN), which focused on modifying the rear body shapes of the sedan. To determine the optimization variables, the unsteady flow field around the sedan driving at very fast speeds was analyzed by CFD simulation, and fluctuations of the drag coefficient (CD) and pressure around the car were calculated. After consideration of the baseline result of CFD, 6 local parts from the end of the sedan were chosen as the design variables for optimization. Moreover, an ANN approximation model was established with 64 experimental points generated by the D-optimal methodology. As a result, an aerodynamically optimized shape for the rear end of the sedan in which the aerodynamic performance is improved by about 5.64% when compared to the baseline vehicle is proposed. Finally, it is expected that within the accepted range of shape modifications for a rear body, the aerodynamic performance of a sedan can be enhanced so that the fuel efficiency of the sedan can be improved. The YF SONATA, a sedan manufactured by Hyundai Motors Corporate, played a major role in this research as the baseline vehicle.

Thermal and Electrical Stabilities of Solid Nitrogen (SN2) Cooled YBCO Coated Conductors for HTS Magnet Applications

Song, J B,Kim, K J,Kim, K L,Lee, J H,Kim, H M,Lee, G H,Chang, H M,Park, D K,Ko, T K,Lee, H G IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3

<P>Recently, a cooling system using a solid cryogen such as solid nitrogen (SN2), was introduced for high temperature superconducting (HTS) magnet applications. In order to apply the SN2 cooling system successfully to HTS applications, it is essential to obtain sufficient data regarding the characteristics of the SN2-cooled YBCO-coated conductor (CC), including the thermal and electrical properties. Therefore, this study examined the effect of SN2 on the thermal/electrical stability of YBCO CC tape. The SN2 was produced by conduction cooling using a GM-cryocooler and cooled to 58 K. The voltages and temperatures of the YBCO CC tapes were measured while applying an over-current. The results showed that the thermal and electrical stability of the YBCO CC tape were improved considerably in the SN2 cooling system compared to that in the conduction cooling system.</P>

Normal Zone Initiation and Propagation Characteristics of a Solid Nitrogen Cooled GdBCO Racetrack Pancake Coil

Song, J. B.,Kim, K. L.,Yang, D. G.,Jang, J. Y.,Ko, T. K.,Ahn, M. C.,Lee, H. G. IEEE 2012 IEEE transactions on applied superconductivity Vol.22 No.3

<P>This paper presents quench test results, of both experiment and simulation, of a racetrack pancake coil wound with a GdBCO-coated conductor tape in a solid nitrogen (SN2) cooling system at 58 K. The longitudinal normal zone propagation velocities in the curved section were 2 times faster than those in the straight section. Therefore, the straight section should be protected more than the curved section when using racetrack-type, GdBCO pancake coils in large-scale rotating machines. The simulated results showed good agreement with the experimentally observed normal zone initiation times.</P>

Comparison of bactericidal efficiency of 7.5MeV X-rays, gamma-rays, and 10MeV e-beams

Song, B.S.,Lee, Y.,Moon, B.G.,Go, S.M.,Park, J.H.,Kim, J.K.,Jung, K.,Kim, D.H.,Ryu, S. Pergamon 2016 Radiation physics and chemistry Vol.125 No.-

<P>This study was performed to verify the feasibility of 7.5 MeV X-rays for food pasteurization through a comparison of the bactericidal efficiency with those of other sources for selected bacterial pathogens. No significant differences were observed between the overall bactericidal efficiency for beef-inoculated pathogens based on the uncertainty of the absorbed dose and variations in bacterial counts. This result supported that all three irradiation sources were effective for inactivation of food-borne bacteria and that 7.5 MeV X-rays may be used for food pasteurization. (C) 2016 Elsevier Ltd. All rights reserved.</P>

An effect on the side chain position of D-p-A-type conjugated polymers with sp2-hybridized orbitals for organic photovoltaics

Song, K.,Song, H.,Lee, T.,Heo, S.,Moon, D. Royal Society of Chemistry 2013 Polymer chemistry Vol.4 No.11