• International Journal of Aeronautical and Space Sciences
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• v.1 no.2
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• pp.1-8
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• 2000

The flow in low-density plumes expanding into a region of finite pressure shows a quite different behavior from that observed in low-density plumes expanding into a vacuum. The flow structure in the plume varies depending on applied ambient and stagnation chamber conditions. In the present study, the direct simulation Monte-Carlo (DSMC) method based on molecular gas dynamics is employed in the analysis of low-density gas flows expanding through a small converging/diverging nozzle. Special attention has been paid to the effect of non-zero ambient and stagnation pressures on the flow structure which has rarely been studied using the DSMC method.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.37-45
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• 1991

The critical current density, electrical conductivity, critical magnetic field, Meissner effect, apparent density, and microstructure of YBa2Cu3O7-x ceramic superconductor prepared by polymeric precursor, while varing calcining and sintering conditions, were investigated. The best superconducting properties could be obtained from the body sintered at 93$0^{\circ}C$ for 10h after calcining at 90$0^{\circ}C$ for 10h, which gave 383A/$\textrm{cm}^2$ of critical current density(Jc), 96K of onset temperature(Tonset), 94. 8K of zero temperature (Tzero) 225 Oe of critical magnetic field (Hc1), 72.8% of superconducting volume fraction measured by Meissner effect and 6.28g/㎤ of apparent density.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.739-745
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• 2011

This paper proposes a method for reducing the negative spatial harmonics of the radial flux density of an interior-type permanent magnet (IPM) motor. The reliability of the motor is increased by minimizing its vibrations under dynamic eccentricity (DE) state and normal state due to reduction of a negative spatial harmonics component through the influx of a zero spatial harmonics component in the radial flux density. To minimize the vibrations, optimal notches corresponding to the distribution shape of the magnetic field are designed on the rotor pole face. The variations of vibration computation by finite element method (FEM) and the validity of the analysis and rotor shape design are confirmed by vibration and performance experiments.

• KSBB Journal
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• v.7 no.4
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• pp.247-251
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• 1992

The effect of biomass concentration of Saccharomyces cerevisiae ATCC 24858 on specific growth rates, biomass yields, ethanol yields and productivity in the batch fermentation of rotary shaker was investigated. The specific growth rate decreased according to the increase in the biomass density and finally became zero at a biomass concentration, 55g/L. The ethanol yield $Y_{p/s}$ represented a constant value, 0.43, regardless of the change of biomass concentrations. However, the biomass yield $Y_{x/s}$ showed a trend to diminish in values with augmentation of biomass density and ultimately to reach zero at 55g/L of biomass concentration. The ethanol productivity increased linearly with biomass concentration so that, in case of initial sugar concentration, 170g/L, the productivity for 55g/L of biomass density rose up to 30g/L$\cdot$hr for all the batch fermentations. And also the ethanol concentration inhibiting completely the growth was verified 95g/L by applying experimental data to Luong's equation.

• The KIPS Transactions:PartA
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• v.9A no.1
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• pp.75-82
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• 2002

A robust signal transition density propagation method for a zero delay model is presented to obtain the signal transition density for estimating the power consumption. The power estimation for the zero delay model is a proper criteria for the lower boundary of power consumption. Since the input characteristics are generally unknown at design stage, robust estimation for wide range input characteristics is very important for the power consumption. In this paper, a conventional transition estimation method will be explored. And this exploration will be analyzed with the input/output signal transition behavior and used to propose the robust signal transition density propagation for the power estimation. In order to apply to practical circuits, the reconvergent path, which is crucial to affect the exactness of the power estimation, will be studied and an algorithm to take the reconvergent path into consideration will be presented. In experiment, the proposed methodology shows better robustness, comparable accuracy and elapsed time compared to the conventional methods.

• Journal of Advanced Navigation Technology
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• v.17 no.3
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• pp.298-305
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• 2013

In this paper, we propose simple combining schemes for sensing ATSC digital television signals with spectral correlation density (SCD). The detection algorithms exploiting the cyclostationarity exhibited by the pilot of ATSC digital television signals usually use the SCD value at a given particular frequency. However, we found that non-zero SCDs are found to be distributed over a certain range of frequencies in multipath fading environment. To utilize a set of non-zero SCD values computed in the vicinity of the pilot location, we formulate a class of combining methods in analogy with the maximal ratio combining, the square law combining and the equal gain combining. We show that the proposed simple combining schemes improve the detection performance by 0.5~1.0dB under multipath fading environments.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.5
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• pp.557-565
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• 2022

The effect of flow configuration in ammonia-fed solid oxide fuel cell are investigated by using a three-dimensional numerical model. Typical flow configurations including co-flow and counter-flow are considered. The ammonia is directly fed into the stack without any external reforming process, resulting in an internal decomposition of NH3 in the anode electrode of the stack. The result showed that temperature profile in the case of counter-flow is more uniform than the co-flow configuration. The counter-flow cell, the temperature is highest at the middle of the channel while in the case of co-flow, the temperature is continuously increased and reached maximum value at the outlet area. This leads to a higher averaged current density in counter-flow compared to that of co-flow, about 5%.

• Electrical & Electronic Materials
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• v.8 no.1
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• pp.6-12
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• 1995

High Tc superconducting YBa$_{2}$Cu$_{3}$$O_{7-x}$ thin films were prepared on various substrates by off-axis rf magnetron sputtering method to examine the substrate effects on the film structure and its R-T characteristics. The SEM analysis showed that the surface morphology of the grown YBa$_{2}$Cu$_{3}$O.sub 7-x/, film has different characteristic structure with different substrate used. The film on (100) SrTiO$_{3}$ substrate has critical current density of 3*10$^{5}$ A/cm$^{2}$ at 77K under zero magnetic field. The X-ray diffraction measurements revealed that the films on (100) SrTiO$_{3}$ substrate have mixed a-axis and c-axis normal to the substrate surface and the films on (100) MgO and ZrO$_{2}$/sapphire substrates have c-axis normal orientation to the substrate surface. However, YBa$_{2}$Cu$_{3}$$O_{7-x}$ films on (100) sapphire substrates showed no preferential orientation.ion.

• Progress in Superconductivity
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• v.7 no.1
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• pp.77-82
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• 2005

We report a successful fabrication of high-quality $SmBa_{2}Cu_{3}O_{7-{\delta}}$ (SmBCO) thin films on $LaAlO_3$(LAO)(100) single crystalline substrates by a modified TFA-MOD method. After the pyrolysis heat treatment of spin-coated films up to $400^{\circ}C$, SmBCO films were fired at various temperatures ranging from 810 to $850^{\circ}C$ in a reduced oxygen atmosphere (10 ppm $O_2$ in Ar). Optimally processed SmBCO films exhibited the zero-resistance temperature ($T_{c,zero}$) of 90.2 K and the critical current density ($J_c$) of $0.8\;MA/cm^2$ at 77K in self-field. Compared with the $J_c$ values (normally, > $2\;MA/cm^2$ at 77 K) of MOD-TFA processed YBCO films, rather depressed $J_c$ values in SmBCO films are most probably attributed to the existence of ${\alpha}$-axis oriented grains.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.5
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• pp.443-452
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• 2002

A new phase shift full bridge (PSFB) converter with serially connected two transformers for telecommunication equipments of several hundred watts is proposed. The main features of the proposed converter are a wide input voltage range, an easiness to meet the requirement for zero voltage switching (ZVS) condition at a light load, and a small output voltage ripple. Furthermore, the serially connected two transformers can replace both a main transformer and an output inductor since the two transformers act as not only a main transformer but an output inductor by turns. Therefore, there is no need to use an output inductor, then the proposed converter features high power density. A mode analysis, design equations through a large signal modeling, and experimental results are presented to verify the validity of the proposed converter.