• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2512-2518
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• 2014

The praseodymium-doped $TiO_2$ photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of $TiO_2$. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was $500^{\circ}C$ for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by $Pr^{3+}$.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(1)
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• pp.450-455
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• 1995

A three-dimensional numerical tool is developed to calculate the potential distribution, electric field, and conductance for any types of conductance probes immersed in the wavy liquid film with various shapes of its free surface. The tool is validated against various analytical solutions. It is applied to find out the characteristics of the wire-wire probe, the flush-wire probe and the flush-flush probe in terms of resolution, linearity, and sensitivity. The wire-wire probe shows high resolution and excellent linearity for various film thickness, but comparably low sensitivity for low film thickness fixed. The flush-wire probe shows good linearity and high sensitivity for varying film thickness, but resolution degrading with an increase in film thickness. In order to check the applicability of the three types of probes in the real situation, the Korteweg-de Vries(KdV) two-dimensional solitary wave is simulated. The wire-wire probe is strongly affected by the installation direction of the two wires; when the wires are installed perpendicularly to the flow direction, the wire-wire probe shows large distortion of the solitary wave. In order to measure the transverse profile of waves, the wire-wire probes and the flush-wire probes are required to be separately installed 2mm and 2mm, respectively.

• 한국ITS학회 논문지
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• 제7권2호
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• pp.62-69
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• 2008

본 논문에서는 구동단의 IMD 특성과 최종단의 IMD 특성을 조절하여 선형성을 개선하는 방법에 대하여 제안을 하였다. WCDMA 4FA의 입력 신호를 사용하였을 때 평균 전력 50W에서 약 -48dBc@5MHz offset의 ACLR 특성을 얻었다. 제안된 역위상화 선형화 기법은 추가적인 선형회로 없이 구동 증폭단을 이용하여 전치왜곡 효과를 얻을 수 있었다. 이러한 점은 기존 analog predistortion 방식과 feedforward 방식의 단점을 보완하였음에 큰 의미를 가진다.

• 전기학회논문지
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• 제65권6호
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• pp.987-994
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• 2016

In this paper, we present a comparative analysis of surface-mounted permanent magnet synchronous motors (SPMSM) and interior permanent magnet synchronous motors (IPMSM). First, we use 2D finite element analysis (FEA) to analyze models satisfying the same rated conditions according to the torque-speed curve characteristics, which are determined from the operating conditions. Next, we manufacture an SPMSM and IPMSM having good performances from an electromagnetic perspective based on analysis results, namely the cogging torque, torque ripple, and efficiency. We analyze both of the manufactured machines when they are connected back-to-back and when they are used as a motor and a generator, respectively. The motor is driven by a commercial inverter and the generator is connected to a three-phase resistance load bank. Finally, based on experimental results, which include the total harmonic distortion (THD) of the back electro-motive force (EMF), cogging torque, efficiency, and mass, we determine the motor that is most suitable under requirements.

• Journal of Electrical Engineering and Technology
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• 제3권4호
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• pp.520-527
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• 2008

This work focuses on the evaluation of active power filter which is controlled by fuzzy logic and neural network based controller for harmonic mitigation and power factor enhancement. The APF consists of a variable DC voltage source and a DC/AC inverter. The task of an APF is to make the line current waveform as close as possible to a sinusoid in phase with the line voltage by injecting the compensation current. The compensation current is estimated using adaptive neural network. Using the estimated current, the proposed APF is controlled using neural network and fuzzy logic. Computer simulations of the proposed APF are performed using MATLAB. The results show that the proposed techniques for the evaluation of APF can reduce the total harmonic distortion less than 3% and improve the power factor of the system to almost unity.

• 조명전기설비학회논문지
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• 제18권3호
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• pp.120-127
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• 2004

스위칭 모드 전원 공급 장치와 같은 비선형 부하의 증가로, 3상 4선식 배전계통을 채용하는 중성선에 많은 고조파 전류가 흐른다. 중성선은 접지 시스템과 연결되어 있기 때문에 접지 임피던스는 중성선 고조파 전류에 영향을 끼친다고 알려져 있다. 현장에서 실측한 고조파 전류와 전압으로 고조파 해석용 3상 등가 회로를 구성하였다. 실측한 값과 MATLAB으로 시뮬레이션 한 값을 수치와 파형으로 비교 검토하였다. 또한 본 논문에서는 중성선 고조파 전류와 접지 임피던스와의 관계를 시뮬레이션을 통해 검증하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.860-865
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• 2000

This Paper Proposes the test pieces of X, Y and Z axes to compensate the shape distortion of Selective Laser Sintering(SLS) parts resulting from the phase change during the sintering process. In no case of the proposed compensation test pieces of X, Y axes the accurate rates of shrinkage can be measured with the reduction of curling which is obtained from adjustment of build orientation and the formula used to get scale factors are proposed with the shrinkage rates of them. The scale factors of X, Y and Z axes are generated by building up proposed compensation test pieces. The generated scale iactors are required to satisfy the dimensional accuracy even if there are changes of the build position and the size of SLS parts in the build chamber. For this reason, it is proposed that the build positions and the size be considered to be noise factors against the compensation test pieces and a method is also proposed that scale factors be selected to robustly maintain the dimensional accuracy of SLS parts under the actual operating conditions with the application of the Taguchi Method.

• 대한기계학회논문집B
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• 제27권6호
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• pp.773-780
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• 2003

The three-dimensional spatial structures of impeller flow created by a six bladed Rushton turbine have identified based on the volumetric velocity information from multi-plane stereoscopic PIV measurements. A total of 10 planes with 2 mm space and a 50 mm by 64 mm size of the field of view were targeted. To reduce the depth of focus, we adopted an angle offset configuration which satisfied the Scheimpflug condition. The distortion compensation procedure was utilized during the in situ calibration. Phase-locked instantaneous data were ensemble averaged and interpolated in order to obtain mean 3-D. volumetric velocity fields on a 60 degree sector of a cylindrical ring volume enclosing the turbine blade. Using the equi-vorticity surface rendering, the spatial structure of the trailing vortices was clearly demonstrated. Detail flow characteristics of the radial jet reported in previous studies of mixer flows were easily identified.

• 한국통신학회논문지
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• 제12권4호
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• pp.386-398
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• 1987

本 論文은 PWM(Pulse Width Modulation)인버어터의 스위칭作用에 의해서 發生하는 高周波 影響을 最小化하기 위한 Suboptimal PAWM(Pulse Amplitude Width Modulation)을 提示하였다. 本 方式은 Suboptimal PWM에서 THD(Total Harmonic Distorition)가 最小가 되는 固定點(基本波 電壓 u1=1.2)에서 하나의 스위칭패턴을 決定하였다. 그리고 電壓은 DC Link에서 DC Chopper에 의해 制御하게 하고 인버어터에서는 단지 高周波만을 制御하도록 하였다. 本 方式은 3相 誘導電動機의 VSD(Variable Speed Drive)에 適用하여 電動機의 騷音, 인버어터의 線間電壓 및 電流, 電流高周波 스펙트럼을 測定하였으며, 他 方式과 比較해 보았다. 그 結果로부터 本 方式의 妥當性을 立證할 수 있었다.

• International Journal of Contents
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• 제6권1호
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• pp.6-11
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• 2010

Recently, there has been research to use portable digital camera to recognize objects in natural scene images, including labels or marks on a cylindrical surface. In many cases, text or logo in a label can be distorted by a structural movement of the object on which the label resides. Since the distortion in the label can degrade the performance of object recognition, the label should be rectified or restored from deformations. In this paper, a new method for label detection and restoration in digital images is presented. In the detection phase, the Hough transform is employed to detect two vertical boundaries of the label, and a horizontal edge profile is analyzed to detect upper-side and lower-side boundaries of the label. Then, the biquadratic transformation is used to restore the rectangular shape of the label. The proposed algorithm performs restoration of 3D objects in a 2D space, and it requires neither an auxiliary hardware such as 3D camera to construct 3D models nor a multi-camera to capture objects in different views. Experimental results demonstrate the effectiveness of the proposed method.