• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.326-331
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• 2006

The durability of recent motors is longer than the past one because there are the rapid technique development of the automobile industry and the vehicle maintenance of users. And then the importance of the durability test due to vibration is increased from day to day. So full vehicle and parts companies accomplish the durability test using various methods. The most public test method among them is the reliable field test but it bring on higher cost and period of the development process. The durability test using MAST(multi axis simulation table) is a solution in order to improve the development process of automobiles. Generally its excitation source uses the optimized road profiles that are obtained by the road test of belgian road, country road, cobbleston road and so on instead of a real field but the interrelations and influences accordingly vehicle damage are considered by a field test between specific roads and real fields in the first place. Therefore this study, in order to accomplish a basic research for the durability test using the MAST, performed on the real field driving test at various domestic roads and the results which are analyzed by PSD(power spectrum density) are compared with relative sensitivity among the roads. Consequently they can present a basic material for generation of road profiles which is applied to the durability test using MAST.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.183-183
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• 2011

Multiferroic materials have been widely studied in recent years, because of their abundant physics and potential applications in the sensors, data storage, and spintronics. $BiFeO_3$ is one of the well-known single-phase multiferroic materials with $ABO_3$ structure and G-type antiferromagnetic behavior below the Neel temperature $T_N$ ~ 643 K, but the ferroelectric behavior below the Curie temperature $T_c$~1,103 K. In this study, the $BiFe_{1-x}Ni_xO_3$ (x=0 and 0.05) bulk ceramics were prepared by solid-state reaction and rapid sintering with high-purity $Bi_2O_32$, $Fe_3O_4$ and NiO powders. The powders of stoichiometric proportions were mixed, as in the previous investigations, and calcined at 450$^{\circ}C$ for $BiFe_{1-x}Ni_xO_3$ for 24 h. The obtained powders were grinded, and pressed into 5-mm-thick disks of 1/2-inch diameter. The disks were directly put into the oven, which has been heated up to 800$^{\circ}C$ and sintered in air for 20 min. The sintered disks were taken out from the oven and cooled to room temperature within several min. The phase of samples was checked at room temperature by powder x-ray diffraction using a Rigaku Miniflex diffractometer with Cu K${\alpha}$ radiation. The Raman measurements were carried out by employing a hand-made Raman spectrometer with 514.5-nm-excitation $Ar^+$ laser source under air ambient condition on a focused area of 1-${\mu}m$ diameter. The field-dependent magnetization measurements were performed with a superconducting quantum-interference-device magnetometer.

• Special Issue of the Society of Naval Architects of Korea
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• 2008.09a
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• pp.16-28
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• 2008

Recent growth in LNG market has led dramatic increase in new buildings of LNG carriers and several large LNG carriers are now being constructed by shipbuilders in Korea. Large size LNG carriers has brought keen concerns on the issue regarding safety of cargo containment systems and sloshing impact load which is the critical source of loads on the membrane type containment systems. Up to the present, the best way to properly assess sloshing impact pressures on surrounding walls is a model testing for wide-ranged excitation conditions. These impact pressures obtained from model tests sometimes need to be interpreted to full-scale values and in the near future this necessity will be strengthened for more rigorous and direct safety assessment of LNG cargo containment system. In this paper, a basic experimental study is carried out with two different sized, 2D identically shaped model tanks excited in simple translational motions. Relationships between pressures of different sized model tanks are investigated Model tanks are filled with fresh water and equipped with same sized pressure sensors.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2471-2478
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• 2020

Pumps are essential machinery in the various industries. With the development of high-speed and large-scale pumps, especially high energy density, high requirements have been imposed on the vibration and noise performance of pumps, and cavitation is an important source of vibration and noise excitation in pumps, so it is necessary to improve pumps cavitation performance. The modern pump optimization design method mainly adopts parameterization and artificial intelligence coupling optimization, which requires direct correlation between geometric parameters and pump performance. The existing cavitation performance calculation method is difficult to be integrated into multi-objective automatic coupling optimization. Therefore, a fast prediction method for pump cavitation performance is urgently needed. This paper proposes a novel cavitation prediction method based on impeller pressure isosurface at single-phase media. When the cavitation occurs, the area of pressure isosurface S_iso increases linearly with the NPSH_a decrease. This demonstrates that with the development of cavitation, the variation law of the head with the NPSH_a and the variation law of the head with the area of pressure isosurface are consistent. Therefore, the area of pressure isosurface S_iso can be used to predict cavitation performance. For a certain impeller blade, since the area ratio R_s is proportional to the area of pressure isosurface S_iso, the cavitation performance can be predicted by the R_s. In this paper, a new cavitation performance prediction method is proposed, and the feasibility of this method is demonstrated in combination with experiments, which will greatly accelerate the pump hydraulic optimization design.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1047-1053
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• 2009

The future use of hydrogen as an energy source is expected to increase on account of its environmentally friendliness. In order to enhance the production of hydrogen, Pd ions (0.01, 0.05, 0.1, and 0.5 mol%) were incorporated $TiO_2$ (Pd-$TiO_2$) and used as a photocatalyst. The UV-visible absorbance decreased with increasing level of palladium incorporation without a wavelength shift. Although all the absorption plots showed excitation characteristics, there was an asymmetric tail observed towards a higher wavelength caused by scattering. However, the intensity of the photoluminescence (PL) curves of Pd-$TiO_2$ was smaller, with the smallest case being observed at 0.1 and 0.5 mol% Pd-$TiO_2$, which was attributedto recombination between the excited electrons and holes. Based on these optical characteristics, the evolution of $H_2$ from methanol/water (1:1) photo-splitting over Pd-$TiO_2$ in the liquid system was enhanced, compared with that over pure $TiO_2$. In particular, 2.4 mL of $H_2$ gas was produced after 8 h when 0.5 g of a 1.0 mol% Pd-$TiO_2$ catalyst was used. $H_2$ was stably evolved even after 28 h without catalytic deactivation, and the amount of $H_2$ produced reached 14.5 mL after 28 h. This is in contrast to the case of the Pd 0.1 mol% impregnated $TiO_2$ of $H_2$ evolution of 17.5 mL due to the more decreasedelectron-hole recombination.

• Korean Journal of Materials Research
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• v.21 no.6
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• pp.352-356
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• 2011

[ $Zn_{2(1-x)}Mn_xSiO_4$ ]$0.07{\leq}x{\leq}0.15$) green phosphor was prepared by solid state reaction. The first heating was at $900^{\circ}C-1250^{\circ}C$ in air for 3 hours and the second heating was at $900^{\circ}C$ in $N_2/H_2$(95%/5%) for 2 hours. The size effect of $SiO_2$ in forming $Zn_2SiO_4$ was investigated. The temperature for obtaining single phase $Zn_2SiO_4$ was lowered from $1100^{\circ}C$ to $1000^{\circ}C$ by decreasing the $SiO_2$ particle size from micro size to submicro size. The effect of the activators for the Photoluminescence (PL) intensity of $Zn_2SiO_4:Mn^{2+}$ was also investigated. The PL intensity properties of the phosphors were investigated under vacuum ultraviolet excitation (147 nm). The emission spectrum peak was between 520 nm and 530 nm, which was involved in green emission area. $MnCl_2{\cdot}4H_2O$, the activator source, was more effective in providing high emission intensity than $MnCO_3$. The optimum conditions for the best optical properties of $Zn_2SiO_4:Mn^{2+}$ were at x = 0.11 and $1100^{\circ}C$. In these conditions, the phosphor particle shape was well dispersed spherical and its size was 200 nm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4136-4141
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• 2013

One of the most significant requisite that should be considered for effective rapping of the electrostatic precipitator using electromagnetic vibration exciter is vibration acceleration and resonance frequency of collecting plates. This vibration acceleration shows its peak points when natural frequencies of the system are corresponded with excitation frequency from the power source, and effective rapping performance can be expected. In this research, extend view of single electrostatic precipitator using one electromagnetic vibration exciter, the system was remodeled by arrangement of the exciters in view of multiple modules of the electrostatic precipitator in fields. And vibration acceleration measurement experiment is performed and measured values are compared with these remodeled systems. By this experimental comparison in series and parallel arrangement, effectiveness of arrangement methods for the electromagnetic vibration exciter, expected rapping performance, and power consumption are verified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1180-1184
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• 2006

In a speech coding system using excitation source of voiced and unvoiced, it would be a distortion of speech quality in a voiced and an unvoiced consonants in a frame. In this paper, I propose a new multi-pulse coding method make use of V/S/TSIUVC switching and TSIUVC approximation-synthesis method in order to restrict a distortion of speech quality. The TSIUVC is extracted by using the zero crossing rate and individual pitch pulse. And the TSIUVC extraction rate was 91% for female voice and 96.2% for male voice. The important thing is that the frequency information of 0.547kHz below and 2.813kHz above can be made with high quality synthesis waveform within TSIUVC. I evaluated the MPC of V/UV and FBD-MPC of V/S/TSIUVC. As a result, the synthesis speech of FBD-MPC was better in speech quality than the MPC.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.3
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• pp.381-386
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• 2008

Virtual 3D audio methods that create 3D sound effects are researched highly for multimedia devices using 2 speakers or headphone. The most typical method to create 3D effects is a technology through use of head related transfer function (HRTF) which contains the information that sound arrives from a sound source to the ears of the listener. But it can decline some 3D effects by cone of confusion between front and back directions due to the non-individual HRTF depending on each listener. In this paper, we propose a new method to use psychoacoustic theory that creates realistic 3D audio. In order to improve 3D sound, we calculate the excitation energy of each symmetric HRTF and extract the ratio of energy of each bark range. Informal listening tests show that the proposed method improves the front-bach sound localization characteristics much better than the conventional methods.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.749-765
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• 2010

There are on-going efforts to utilize guided waves for structural damage detection. Active sensing devices such as lead zirconate titanate (PZT) have been widely used for guided wave generation and sensing. In addition, there has been increasing interest in adopting wireless sensing to structural health monitoring (SHM) applications. One of major challenges in wireless SHM is to secure power necessary to operate the wireless sensors. However, because active sensing devices demand relatively high electric power compared to conventional passive sensors such as accelerometers and strain gauges, existing battery technologies may not be suitable for long-term operation of the active sensing devices. To tackle this problem, a new wireless power transmission paradigm has been developed in this study. The proposed technique wirelessly transmits power necessary for PZT-based guided wave generation using laser and optoelectronic devices. First, a desired waveform is generated and the intensity of the laser source is modulated accordingly using an electro-optic modulator (EOM). Next, the modulated laser is wirelessly transmitted to a photodiode connected to a PZT. Then, the photodiode converts the transmitted light into an electric signal and excites the PZT to generate guided waves on the structure where the PZT is attached to. Finally, the corresponding response from the sensing PZT is measured. The feasibility of the proposed method for wireless guided wave generation has been experimentally demonstrated.