• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.377-383
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• 2005

This paper deals with the flow characteristics of air-water two-phase flow in a vertical tube of 10mm I.D. and 600mm in length at an adiabatic condition. The obtained experimental data were covered with the liquid superficial velocity ranging from 0.095m/s to 2.56m/s. and the gas superficial velocity ranging from 0.032m/s to 21.08m/s. The effects of the gas and liquid superficial velocity on the flow pattern transitions, frictional pressure drop, and film thickness and gas-liquid interface roughness were also examined. It was found that the film thickness increased and the liquid film wave length was more longer with the liquid superficial velocity $j_L$ increasing at $j_G$ constant. It was also showed that the frictional pressure drops were experienced in three regions. namely increasing region(bubbly flow), decreasing region (Taylor bubble and slug flows) and re-increasing region (annular flow).

• Journal of electromagnetic engineering and science
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• 제17권2호
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• pp.65-70
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• 2017

The design and implementation aspects of a new single-balanced mixer for ultra-wideband (UWB) applications are presented in this study. The proposed mixer utilizes a miniaturized UWB ring coupler as a balun, consisting of a pair of in-phase and inverted-phase transitional structures. The well-balanced UWB performance of the ring coupler, aside from the optimized diode matching, results in improved conversion loss and inter-port isolations for a wide bandwidth. The size of the implemented single-balanced diode mixer is reduced to about 60% of the area of the conventional single-balanced ring diode mixer. The measured results of the proposed mixer exhibit an average conversion loss of 7.5 dB (minimum 6.7 dB) and a port-to-port isolation of greater than 18 dB over a UWB frequency range of 3.1-10.6 GHz. The measured results agree well with the simulated results.

• 한국재료학회지
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• 제22권9호
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• pp.489-493
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• 2012

Green phosphors $K_2BaW_2O_8:Tb^{3+}$(1.0 mol%) were synthesized by solid state reaction method. Differential thermal analysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and $1055^{\circ}C$ correspond to the loss of absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of the powders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310 nm were found to be due to the ${WO_4}^{2-}$ exciton transition and the 4f-5d transition of $Tb^{3+}$ in $K_2BaW_2O_8$. The excitation spectrum presents several lines in the range of 310-380 nm; these are assigned to the 4f-4f transitions of the $Tb^{3+}$ ion. The strong emission line at around 550 nm, due to the $^5D_4{\rightarrow}^7F_5$ transition, is observed together with weak lines of the $^5D_4{\rightarrow}^7F_J$(J = 3, 4, and 6) transitions. A broad emission band peaking at 530 nm is observed at 10 K, while it disappears at room temperature. The decay times of $Tb^{3+}$ $^5D_4{\rightarrow}^7F_5$ emission are estimated to be 4.8 and 1.4 ms, respectively, at 10 and 295 K; those of the ${WO_4}^{2-}$ exciton emissions are 22 and 0.92 ${\mu}s$ at 10 and 200 K, respectively.

• The Korean Journal of Ceramics
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• 제6권2호
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• pp.159-163
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• 2000

Alumina fibre has been synthesized successfully by sol-gel technique. Boehmite sol was prepared by hydrolyzing aluminium iso-propoxide and peptizing it with nitric acid. The stable sol thus obtained was used for fibre drawing when their viscosity reached the required value as a result of progress of the hydrolyzation and polycondensation reaction. The fibres dried at 11$0^{\circ}C$ for 12 hours were sintered at 1$600^{\circ}C$ for 5 hours. A reasonable sintered density with better microstructure and strength have been attained using 2 wt% of urea, magnesia and silica as sinter additives. Thermal analysis with sintering additives of 2 wt% and phase determination of the heat treated fibres using XRD and FT IR spectra confirms the phase transitions. The observation of surface and cross-section of the fibres were made using SEM. Fibres of uniform circular cross-section is obtained by fixing the shape in a setting solution.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.644-646
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• 2004

We have investigated luminescence properties of Ln-SiAlON materials doped with $Ce^{3+}$. Low-energy 4f${\leftrightarrow}$5d transitions were observed as compared to the luminescence of this ion doped in oxidic host-lattices.$^1$ Ce-doped Y-a-SiAlON show bright long wavelength luminescence with high absorption for 305 and 455nm excitation. In our experiment, the sintering temperature of this material(1400$^{\circ}C$) was lower than that of normal sintering temperature (1700$^{\circ}C$). However, Single phase of SiAlON was not composed we observed the YAG phase.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.1047-1049
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• 2001

The displacemant current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. With Maxwell-displacement-current-measuring method, the phase transitions of Poly-${\gamma}$ -benzyl D-glutamate(PBDG) on a water surface were detected. Measured surface pressure, displacement current and dipole moment of monolayers of PBDG on the water surface. We measured analyzed displacement current that occur when differed temperature. Could know that displacement current is proportional in increase of temperature and great as experiment result.

• Journal of electromagnetic engineering and science
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• 제1권1호
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• pp.18-23
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• 2001

A fast-sweep broadband FM reflectometer system has been successfully developed and operacted at the DIII-D tokamak, producing reliable density Profiles with excellent spatial (1 $\leq$ cm) and temporal resolution (~100 $\mu$ s). The system uses a solid-state microwave oscillator and an active quadrupler, covering full Q-band frequencies (33~50 GHz) and providing relatively high output power (20~60 mW). The system hardware allows fu11band frequency sweep in 10 $\mu$ s, but due to digitization rate limit on DIII-D, sweep time was limited to 75~100 $\mu$ s. Fast frequency sweep has helped to reduce density fluctuation effects on the reflectometer phase measurements, thus improving reliability for individual sweeps. The fast-sweep system with high spatial and temporal resolution has allowed to measure fast-changing edge density profiles during plasma ELMS and L-H transitions, thus enabling fast-time sca1e physics studies.

• 한국세라믹학회지
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• 제31권2호
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• pp.155-160
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• 1994

PZT ceramics substituted by La3+ and Nd3+ were fabricated according to the formula: [Pb1-x(La or Nd)x][Zr0.58Ti0.42]1-x/4$\square$x/4O3(x=0.00, 0.02, 0.05, 0.08, 0.15, 0.20). The crystal structure and microstructure were investigated by XRD and SEM. It was observed that the phase transitions among rhombohedral, tetragonal, and cubic symmetry occured as the substitutional quantity increased. Dielectric constant, dissipation factor and piezoelectric coefficient (d33), of each sample were measured. The dielectric properties were changed as the substitutional quanity of rare earth ion increased. These changes could be explained by crystal structure and compositional fluctuaction. Its d33 was higher at tetragonal region near to phase boundry between rhombohedral and tetragonal, which was explained by reorientation of domain wall.

• 한국재료학회지
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• 제24권2호
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• pp.116-122
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• 2014

$Bi_2Sr_2CaCu_2O_x$(Bi-2212) and $Bi_2Sr_2Ca_2Cu_3O_y$(Bi-2223) high-Tc superconductors(HTS) have been manufactured by plasma spraying, partial melt process(PMP) and annealing treatment(AT). A Bi-2212/2223 HTS coating layer was synthesized through the peritectic reaction between a 0212 oxide coating layer and 2001 oxide coating layer by the PMP-AT process. The 2212 HTS layer consists of whiskers grown in the diffusion direction. The Bi-2223 phase and secondary phase in the Bi-2212 layer were observed. The secondary phase was distributed uniformly over the whole layer. As annealing time goes on, the Bi-2212 phase decreases with mis-orientation and irregular shape, but the Bi-2223 phase increases because a new Bi-2223 phase is formed inside the pre-existing Bi-2212 crystals, and because of the nucleation of a Bi-2223 phase at the edge of Bi-2212 crystals by diffusion of Ca and Cu-O bilayers. In this study the spray coated layer showed superconducting transitions with an onset Tc of about both 115 K, and 50 K. There were two steps. Step 1 at 115 K is due to the diamagnetism of the Bi-2223 phase and step 2 at 50 K is due to the diamagnetism of the Bi-2212 phase.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1631-1633
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• 2000

A study was carried out on the effect of VDF mol%, on the phase transition presented by P(VDF/TrFE) copolymer cast from dimethylformamide(DMF) solution with molar ratios 70/30 and 80/20. The results from dielectric spectrum and differential scanning calorimetry(DSC) showed that the phase transitions from ferroelectric to paraelectric phase(Curie transition) were observed The Curie point slightly has shifted to high temperature with increasing in VDF mol%, however, the melting point has shifted to low temperature.