• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.1
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• pp.20-23
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• 2004

BLDCMs are widely used in many industries. In certain specialized areas, they need to have high efficiency, high power rate and produce a low volume of noise, etc. In this study, a new type of slotless BLDCM is proposed that has no cogging torque, low iron loss and low volume as compared to commonly used BLDCMs. With a high performance magnet and coreless compact winding structure similar to those employed in linear synchronous motors, motor volume is reduced. The proposed motor has been put been through various experiments arid has demonstrated acceptable results for industry applications.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2007.10a
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• pp.429-430
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• 2007

• The Pure and Applied Mathematics
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• v.17 no.4
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• pp.299-306
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• 2010

In this article we consider axes of a complete embedded minimal surface in $R^3$ of finite total curvature, and then prove that there is no planar ends at which the Gauss map have the minimum branching order if the minimal surface has a single axis.

• Bulletin of the Korean Chemical Society
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• v.25 no.4
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• pp.485-490
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• 2004

Silver-needle shaped crystals of $KLa_2Sb_3S_9$ from $K_2S_x$ flux and $KSm_2Sb_3Se_8$ from NaCl/KCl flux reactions were obtained and their crystal structures were determined by the single crystal X-ray diffraction method. $KLa_2Sb_3S_9$ crystallizes in the orthorhombic noncentrosymmetric space group $P2_12_12_1$ (No.19) with a unit cell of a = 4.220(3) ${\AA}$, b = 24.145(2) ${\AA}$, c = 14.757(5) ${\AA}$ and Z = 4. $KSm_2Sb_3Se_8$ crystallizes in the orthorhombic space group Pnma (No.62) with a unit cell of a = 16.719(3) ${\AA}$, b = 4.1236(8) ${\AA}$, c = 22.151(4) ${\AA}$ and Z = 4. Both structures have three-dimensional tunnel frameworks filled with $K^+$ ions. $KSm_2Sb_3Se_8$ is an ordered version of $ALn_{1{\pm}X}B_i{4{\pm}X}S_8$, and it is made up of NaCl-type and $Gd_2S_3$-type fragments. $KLa_2Sb_3S_9$ also contains building fragments similar to those of $KSm_2Sb_3Se_8$, however, there are chalcogen-chalcogen bonds in the $Gd_2S_3$-type fragment. The formula of $KLa_2Sb_3S_9$ can be described as $(K^+ )(La^{3+})_2(Sb^{3+})^3(S^{2-})_7(S_2^{2-})$.

• Atmosphere
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• v.25 no.4
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• pp.707-718
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• 2015

This study investigates the characteristics of turbulent fluxes observed at Ieodo Ocean Research Station (IORS) in autumn 2014. The 10 Hz IORS data is quality controlled and calculated to be the 30 minutes turbulent fluxes. The quality control consists of five steps: a weather check, Vickers and Mahrt (VM) sequential check, VM parallel check, flag check, and direction check. Since the IORS is an open-sea station with no orographic influence, there are no significant diurnal variations for the turbulent fluxes and 10 m wind speed. According to stabilities, the unstable and semi-unstable states appear more than 28% and 70% in autumn, respectively and they have strong winds of over $10m\;s^{-1}$. In addition, the turbulent fluxes increase with increasing wind speed. In particular, the latent heat flux and its deviations are clearly shown because the latent heat flux is influenced by the change of both the sea surface roughness and wave height induced by the wind. To demonstrate the changes of the turbulent fluxes before and after typhoon, Vongpong (1419), which is the most intense typhoon affecting the Korean Peninsula in 2014, is considered. The turbulent flux fluctuates in accordance with the location of Vongpong. The turbulent fluxes have a large (small) variation when Vongpong approaches (retreats) at the IORS. The overall results represent that the IORS data helps us understand physical processes related to air-sea interaction by providing the valuable and reliable observed data.

• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.670-679
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• 2017

An experiment to study the effect of temperature, light, and dredging on release of nutrients downstream from Gongjicheon in the Uiam reservoir was carried out in the laboratory using sediments from different depths. At various water temperatures, dissolved total nitrogen was not released, but the average nutrient flux of dissolved total phosphorus was increased (0.034 at $15^{\circ}C$, 0.005 at $20^{\circ}C$, 0.154 at $25^{\circ}C$, $0.592mg/m^2/d$ at $30^{\circ}C$). Dissolved total phosphorous was released in controlled darkness. In contrast, in controlled light, the concentrations of dissolved total phosphorous and dissolved total nitrogen in the overlying water steadily decreased during the study period (70 d), because they were continuously consumed by the growth of photosynthetic algae. However, there was no significant relationship between water nutrient concentration, nutrient release, and the depth of the sediment. We concluded that the dredging of sediment would not affect the nutrient release rate of the sediment, because there were no significant differences in the nutrient concentrations released from the sediment. When the sediment was removed from the surface to 20 cm in depth, the nutrients were not transferred to the water body, implying that the sediment removal had little effect on secondary pollution.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.4
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• pp.486-492
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• 2004

CMP (Chemical mechanical polishing) is inevitable process to overcome $0.2{\mu}m$ wire thickness in semiconductor industry. In this study, effect of pressure to separate used CMP slurry into solid and liquid for recycle and reuse by ultrafiltration was investigated. Also, water quality after the ultrafiltration such as turbidity and TDS was evaluated. The material of membrane used in the study was PVDF. The used CMP contained 0.5% of solid content and then concentrated up to 18% by weight. The used CMP can not be concentrated higher than 18% because of viscosity and abrasion of pump. The tested feed pressures were 22.1, 29.4 and 36.8 psi. The results have shown that operating at 36.8 psi has advantages on operation time and total flux. The specific flux showed some variation at 1 to 15 of concentration factor but no difference after 15 of concentration factor. Mass balance of solid at initial stage of the operation showed some unbalance because of deposition of solid on the membrane, which was main reason to reduce flux. Turbidity was very stable at lower than 0.2NTU for 22.1 and 36.8 psi of feed pressure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.233-240
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• 2000

An experimental study of condensation heat transfer was performed for pure refrigerants HFC32, HFCI25, and HFC134a, and a ternary refrigerant mixture of HFC32/125/134a (23/25/52wt%). The heat transfer coefficients were measured inside a horizontal smooth tube 5.8 mm I.D. and 8.0 m long. The refrigerant temperature at inlet was 40 $^{\circ}C$, and the mass flux was varied from 150 to 400 $kg/m^2s$. As for the pure refrigerants, the heat transfer coefficient of HFC32/125/l34a decreased as the quality decreased. In addition, the heat transfer coefficient of HFC32/l25/134a was about 20 % lower than HFC 134a at a low mass flux but showed no reduction at a high mass flux. The heat transfer coefficient of ternary refrigerant mixtures was 30% lower on the average than that of the pure refrigerant.

• Asian Journal of Atmospheric Environment
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• v.4 no.1
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• pp.33-41
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• 2010

Because ammonia from livestock production may substantially contribute to environmental pollution, emissions from all possible sources (housing systems, manure storage, manure application, outside grazing) should be reduced. The purpose of this study was to investigate the effect of different bedding materials on ammonia emissions in a cow house. By applying a combination of four treatment types: treatment $1-T_1$ (sawdust (50%)+sawdust pellets (50%)), treatment $2-T_2$ (sawdust (50%)+corn stalk pellets (50%)), treatment $3-T_3$ (sawdust (100%)), and treatment $4-T_4$ (sawdust (50%)+palm kernel meal pellets(50%)) as bedding materials in a cow house, the effects of such treatments on ammonia flux were assessed in approximately one month. The magnitude of ammonia emissions (mg $m^{-2}\;min^{-1}$) varied in the following order: $T_1$(2.226), $T_4$(2.052), $T_2$(1.845), and $T_3$(1.712). The patterns of pH had a decreasing trend for all bedding treatments during the experiment, and there was no significant relationship with ammonia flux. The results reveal that the most important factor influencing ammonia emissions is the physical structure of the bedding types.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1048-1057
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• 2015

This paper proposes a sensorless speed control algorithm for parallel-connected dual Surface-mounted Permanent Magnet Synchronous Motors (SPMSMs) fed by a single inverter. For stable parallel operation of synchronous motors with a single inverter, each motor has to be constantly kept in the synchronization state regardless of load torque. If the master motor with the larger load is controlled, the synchronous state will be maintained. Therefore, detection of the master motor is essential. Conventionally, the master motor is determined by comparing the rotor position error from the relation between the back-EMF for torque angle and the flux position; consequently, the position sensor is deemed essential for finding the rotor position. The parallel sensorless speed control method proposed in this paper uses no position sensor, instead it compares the flux-axis current from the connection between the back-EMF for torque angle and current in unbalanced load conditions. The results of simulation and experiment conducted verify the efficacy of the proposed method.