• Korean Journal of Materials Research
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• v.12 no.9
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• pp.712-717
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• 2002

New wet chemical method so called precipitation-evaporation method was suggested for preparing spinel structure lithium manganese oxide ($LiMn_2$$O_4$) for Li ion secondary battery. Using precipitation-evaporation method, $LiMn_2$$O_4$ cathode materials suitable for Li ion secondary batteries can be synthesized. Single spinel phase $LiMn_2$$O_4$ powder was synthesized at lower temperature compared to that of prepared by solid-state method. $LiMn_2$$O_4$ powder prepared by precipitation-evaporation method showed uniform, small size and well defined crystallinity particles. Li ion secondary battery using $LiMn_2$$O_4$ as cathode materials prepared by precipitation-evaporation method and calcined at $800^{\circ}C$ showed discharge capacity of 106.03mAh/g and discharge capacity of 95.60mAh/g at 10th cycle. Although Li ion secondary battery showed somewhat smaller initial capacity but good cyclic ability. It is suggested that electro-chemical properties can be improved by controlling particle characteristics by particle morphology modification during calcination and optimizing Li ion secondary battery assembly conditions.

• Journal of The Korean Astronomical Society
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• v.50 no.1
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• pp.7-20
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• 2017

We carry out the study of $850{\mu}m$ sources in a part of the XMM-LSS field. The $850{\mu}m$ imaging data were obtained by the SCUBA-2 on the James Clerk Maxwell Telescope (JCMT) for three days in July 2015 with an integration time of 6.1 hours, covering a circular area with a radius of 15'. We choose the central area up to a radius of 9'.15 for the study, where the noise distribution is relatively uniform. The root mean square (rms) noise at the center is 2.7 mJy. We identify 17 sources with S/N > 3.5. Differential number count is estimated in flux range between 3.5 and 9.0 mJy after applying various corrections derived by imaging simulations, which is consistent with previous studies. For detailed study on the individual sources, we select three sources with more reliable measurements (S/N > 4.5), and construct their spectral energy distributions (SEDs) from optical to far-infrared band. Redshift distribution of the sources ranges from 0.36 to 3.28, and their physical parameters are extracted using MAGPHYS model, which yield infrared luminosity $L_{IR}=10^{11.3}-10^{13.4}L_{\odot}$, star formation rate $SFR=10^{1.3}-10^{3.2}M_{\odot}yr^{-1}$ and dust temperature $T_D=30-53K$. We investigate the correlation between $L_{IR}$ and $T_D$, which appears to be consistent with previous studies.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.601-608
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• 1992

We investigated the influence of several processes, including the preparation of slurry and preform and the heat-treatment of the preform, on the properties of composites to fabricate the carbon-fiber reinforced glass composites having good mechanical properties. Cerander was determined to be the best binder among Cerander, Rhoplex and Elvacite 2045 by the dipping test and the binder within a preform could be completely eliminatd by burning out the specimen under 10-6 Torr at 400$^{\circ}C$ for more than 1h. The fracture behavior of a composite was largely dependent on the uniformity of carbon-fiber distribution within the composite and the heat-treatment condition of the composite. The higher the glass content, the more difficult to obtain uniform distribution of carbon-fiber. As the hot-pressing temperature increased, the densification process of the composite and the formation of pore due to oxidation of carbon fiber occurred competitively. But, above 1000$^{\circ}C$ the latter played a predominant role. We could fabricated the densest 15 vol.% carbon-fiber-content glass composite having the highest toughness and flexural strength of 250 MPa by hot-pressing under 15 MPa at 900$^{\circ}C$ for 30 min.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.771-779
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• 1989

Numerical analysis by SIMPLE algorithm has been performed to predict the characteristics of flow and heat transfer in channels between the printed circuit boards of an electronic cabinet. It is assumed that the electronic parts release uniform heat flux per unit axial length to the cooling air. The air flow between channels is assumed fully developed laminar, incompressible, and mixed convective. In this study, the electronic parts are mounted on both sides of the prinked circuit boards by two kinds of configuration such as the zig-zag and the symmetric one. The Rayleigh numbers ranging from 0 to 10$^{6}$ are considered to predict the characteristics of the main flow and the secondary flow occurred by natural convection, the temperature distribution in channel, the heat transfer rate from heated electronic parts and the increase of friction factor by natural convection. As the results of numerical calculation, several conclusions are drawn as follows. The influence of natural convection on the flow characteristics appears strong when the Rayleigh number is above 10$^{4}$. The main axial flow rate decreases by a half or more at the Rayleigh number of 10$^{6}$ . Although the friction factor increases as Rayleigh number increases, the increasing rate of heat transfer is higher than that of the friction factor. The cooling efficiency of the zig-zig-configuration is superior to that of the symmetric configuration at same Rayleigh number.

• Transactions on Electrical and Electronic Materials
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• v.5 no.1
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• pp.1-6
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• 2004

Zinc sulfide is a semiconductor with wide band gap and high refractive index and hence promising material to be used as ARC on commercial silicon solar cells. Uniform deposition of zinc sulfide (ZnS) by using chemical bath deposition (CBD) method over a large area of silicon surface is an emerging field of research because ZnS film can be used as a low cost antireflection coating (ARC). The main problem of the CBD bath process is the huge amount of precipitation that occurs during heterogeneous reaction leading to hamper the rate of deposition as well as uniformity and chemical stoichiometry of deposited film. Molar concentration of thiorea plays an important role in varying the percentage of reflectance and refractive index of as-deposited CBD ZnS film. Desirable rate of film deposition (19.6 ${\AA}$ / min), film uniformity (Std. dev. < 1.8), high value of refractive index (2.35), low reflectance (0.655) have been achieved with proper optimization of ZnS bath. Decrease in refractive index of CBD ZnS film due to high temperature treatment in air ambiance has been pointed out in this paper. Solar cells of conversion efficiency 13.8 ％ have been successfully achieved with a large area (103 mm ${\times}$ 103 mm) mono-crystalline silicon wafers by using CBD ZnS antireflection coating in this modified approach.

• Journal of the Society of Disaster Information
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• v.8 no.2
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• pp.119-137
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• 2012

In this study, the damages and condition of road pavement were analyzed using pavement management system (PMS) for the structural improvement. Problems of road pavement management were issued by in-depth interview with workers in charge of plant, construction and supervision. By surveying advanced road pavement management, the way how to improve road pavement management in Seoul was discussed. In conclusion, it is necessary to take measures against road heavy traffic and heavy rain in summer. It was found that the problem of early damages of road pavement due to uniform layout with analyzing life cycle cost (LCC). According to the results of survey, it was suggested to strength practical training and to control precisely the temperature of pavement in the process of production and construction.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.898-901
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• 2006

In this paper, effect of ceramic processing was investigated on the magnetic properties of low loss Mn-Zn ferrite. High frequency characteristics, high saturated magnetic flux density and high magnetic permeability and low magnetism loss are required for the development of Mn-Zn ferrite, which is parts in the communication. therefore, in order to improve Mn-Zn ferrite with a high frequency , it is important to have a minimal change of particles and to control the eddy current loss caused by high resistance of the stratum of particles and to reduce the hysteresis loss by uniform change of detailed structure. In this paper, we added $V_2O_5\;and\;CaCo_3$ to Mn-Zn Ferrite to achieve a high efficiency, low loss core material. The compositions are MnO : ZnO : $Fe_2O_3$ = 21 : 10 : 69 mol%. They were sintered at $1250^{\circ}C$ for Three hours. Initial permeability was measured at 0.1MHz. At 50mT, Power loss was measured by temperature changing at 100kHz.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.11
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• pp.2085-2092
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• 2016

One of the most important properties of the IC substrate is that it should be uniform over large areas. Among the various physical approaches of wafer defect characterization, special attention is to be payed to the infrared techniques of inspection. In particular, a high spatial resolution, near infrared absorption method has been adopted to directly observe defects in semi-insulating GaAs. This technique, which relies on the mapping of infrared transmission, is both rapid and non-destructive. This method demonstrates in a direct way that the infrared images of GaAs crystals arise from defect absorption process. A new interpretation is presented for the observed reversal of contrast in the infrared absorption of nonuniformly distributed deep centers, related to EL2, in semi-insulating GaAs. The low temperature photoquenching experiment has demonstrated in a direct way that the contrast inverse images of GaAs wafers arise from both absorption and scattering mechanisms rather than charge re-distribution or local variation of bandgap.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.7
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• pp.575-580
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• 2007

A 16 Mb 1T1C FeRAM device was integrated with BLT capacitors. But a lot of cells were failed randomly during the measuring the bit-line signal distribution of each cell. The reason was revealed that the grain size and orientation of the BLT thin film were severely non-uniform. And the grain size and orientation were severely affected by the process conditions of post heat treatment, especially nucleation step. The optimized annealing temperature at the nucleation step was $560^{\circ}C$. The microstructure of the BLT thin film was also varied by the annealing time at the step. The longer process time showed the finer grain size. Therefore, the uniformity of the grain size and orientation could be improved by changing the process conditions of the nucleation step. The FeRAM device without random bit-fail cell was successfully fabricated with the optimized BLT capacitor and the sensing margin in bit-line signal distribution of it was about 340 mV.

• Journal of the Korean Institute of Gas
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• v.24 no.1
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• pp.49-55
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• 2020

Experimental investigations were conducted to understand the multi-staged combustion characteristics of a swirl-stabilized double cone premixed burner nozzle used for industrial gas turbines for power generation. Multi-staged combustion is implemented by injecting the fuel through the existing manifold of the side slots as well as through the apex of the cone with two fuel injection angles which are slanted or axial. NOx and CO emissions, and wall temperature distributions were measured for various fuel distributions and operating conditions. Results show that NOx emissions are decreased when the fuel distribution to the apex is 3% of the total amount of fuel, which is due to more uniform fuel distribution inside the nozzle, hence less hot spots at the flame. NOx emissions are rather increased when the fuel distribution to the apex is 8% of the total amount of fuel for axial fuel injection by occurrence of flash back in premixing zone of burner.