• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.334.2-334.2
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• 2016

Silicon nitride (SiNx:H) films are generally used as passivation layer on solar cell and they are usually made by plasma enhanced chemical vapor deposition (PECVD). In this study, we investigated the properties of silicon nitride (SiNx:H) films made by PECVD. Effects of mixture ratio of process gases with silane (SiH4) and ammonia (NH3) on the passivation qualities of silicon nitride film are evaluated. Passivation properties of SiNx:H are focused by making antireflection properties identical with thickness and refractive index controlled. The absorption coefficient of each film was evaluated by spectrometric ellipsometery and the minority carrier lifetimes were evaluated by quasi-steady-state photo-conductance (QSSPC) measurement. The optical properties were obtained by UV-visible spectrophotometer. The interface properties were measured by capacitance-voltage (C-V) measurement and the film components were identified by Fourier transform infrared spectroscopy (FT-IR) and Rutherford backscattering spectroscopy detection (RBS) - elastic recoil detection (ERD).

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.16-20
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• 1989

In this paper, we describe the optimal driving method and magnetic flux distribution of permanent magnet which enhance torque characteristics in small-sized 3-phase brushless DC motors. The disadvantages of conventional $120^{\circ}$ constant current drive method are torque ripple, switching noise and spike voltage due to the inductance of stator coil. This shortcommings can be avoided by the switching slew-rate of driving current which is called linear voltage driving method. The aim of this study is to analyze linear voltage driving method quantatively and to determine optimal drive current waveform through computer simulation. The selection of commutation angle and slew rate of a new driving current at switching instants makes torque ripple index minimize and average torque maximize. And the validity of this new driving method was assured by Fourier analysis. Considering two dimensional nonlinear magnetic flux distribution on the permanent magnet, we suggest optimal flux distribution according to the presented driving method which improves torque characteristics.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.448-452
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• 1999

The Gaussian impulse fUllction initially assumed in the inverse problem is $e^{-\sigma^2\chi^2}$. The modified Gaussian amplitude pupil function $e^{\frac-{\omega^2}{4\sigma^2}$ is obtained by the inverse Fourier transform of $e^{-\sigma^2\chi^2}$. A Gaussian amplitude modulation plate (GAMP) is designed and fabricated by using absorption and transparence glass which are the same refractive index. It is compared the experimental transmittance with theoretical that of GAMP. It is found that the linewidth of Gaussian optical imaging system obtained by wavelength is $0.365{\mu}m$ and NA is 0.07 is decrease 2/3 than that of Rayleigh.

• Communications for Statistical Applications and Methods
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• v.20 no.4
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• pp.271-281
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• 2013

This paper considers a problem of classification of variable stars based on functional data analysis. For a better understanding of galaxy structure and stellar evolution, various approaches for classification of variable stars have been studied. Several features that explain the characteristics of variable stars (such as color index, amplitude, period, and Fourier coefficients) were usually used to classify variable stars. Excluding other factors but focusing only on the curve shapes of variable stars, Deb and Singh (2009) proposed a classification procedure using multivariate principal component analysis. However, this approach is limited to accommodate some features of the light curve data that are unequally spaced in the phase domain and have some functional properties. In this paper, we propose a light curve estimation method that is suitable for functional data analysis, and provide a classification procedure for variable stars that combined the features of a light curve with existing functional data analysis methods. To evaluate its practical applicability, we apply the proposed classification procedure to the data sets of variable stars from the project STellar Astrophysics and Research on Exoplanets (STARE).

• Steel and Composite Structures
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• v.28 no.3
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• pp.331-347
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• 2018

In this paper history of stresses, strains, radial and circumferential displacements of a functionally graded thick-walled hollow cylinder due to creep phenomenon is investigated. The cylinder is subjected to an arbitrary non-axisymmetric two dimensional thermo-mechanical loading and uniform magnetic field along axial direction. Using equilibrium, strain-displacements and stress-strain relations, the governing differential equations of the problem containing creep strains are derived in terms of radial and circumferential displacements. Since the displacements are varying with time due to creep phenomenon, an analytical solution is not available for these equations. Thus, a semi-analytical procedure based on separation of variables and Fourier series together with a numerical procedure is employed. The numerical results indicate that the non-axisymmetric loading and the material grading index have significant effect on stress redistributions. Moreover, by proper selection of material for any combination of non-axisymmetric loading, one can arrive suitable response for the cylinder to achieve optimal design. With some simplifications, the results are validated with the existing literature.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.436-450
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• 2017

Recently, the method based on fractional order partial differential equation has been used in image processing. Usually, the optional order of fractional differentiation is determined by a lot of experiments. In this paper, a denoising model is proposed based on adaptive fractional order anisotropic diffusion. In the proposed model, the complexity of the local image texture is reflected by the local variance, and the order of the fractional differentiation is determined adaptively. In the process of the adaptive fractional order model, the discrete Fourier transform is applied to compute the fractional order difference as well as the dynamic evolution process. Experimental results show that the peak signal-to-noise ratio (PSNR) and structural similarity index measurement (SSIM) of the proposed image denoising algorithm is better than that of other some algorithms. The proposed algorithm not only can keep the detailed image information and edge information, but also obtain a good visual effect.

• Textile Coloration and Finishing
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• v.25 no.4
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• pp.292-302
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• 2013

Cotton fabrics treated with hybrid materials were developed and prepared. A halogen-free flame retardant and an aromatic amide were blended and applied to cotton fabrics. Thermal and physical properties of the treated cotton fabrics were investigated. The surface of the pure and coated cotton fabrics was characterized by Fourier transform infrared spectroscopy. The elemental composition of the coated surface of the cotton fabric was measured using X-ray photoelectron spectroscopy and compared with that of pure cotton fabric. After being solved in N,N-dimethylacetamide, m-aramid and triphenylphosphine oxide (TPP) were applied to cotton fabrics through a dip-pad-coagulation process. The treated cotton fabrics with recycled m-aramid/TPP resulted in increased limited oxygen index values and thermal resistance.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1997.11a
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• pp.80-84
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• 1997

본 연구는 뇌파의 주파수 변화특성이 다양한 시각자극에 의해서 유발된 감성을 평가할 수 있는가를 알아보고자 하였다. 특히 쾌감성과 불쾌감성의 차이, 쾌감성내의 차이를 뇌파를 이용하여 객관적으로 변별할 수 있는 가를 알아보았다. 사용된 시각자극은 8개의 긍정자극과 7개의 부정자극이었다. 각각의 자극은 30초씩 무선적으로 제시되었고, 각자극의 제시사이마다 120초씩의 휴식기를 두었다. 매 자극제시 후 피험자는 제시된 자극에 대해 긍정.부정의 정도를 주관적으로 평가하였다. 실럼참가자는 20명의 대학생이었으며, 뇌파는 뇌의 21부위에서 기록되었다. 기록된 뇌파에 대해 FFT(Fast Fourier Transformation)분석을 실시한 후, normalized sensitivity를 구현하였다. 자극 중 최대긍정(the most positive stimulus), 최대부정(the most negative stimulus), 최소긍정(the least positive stimulus), 최소부정(the least negative stimulus)이라고 주관적으로 평가한 자극을 보고 있을때의 뇌파를 측정하여 비교.분석하였다. 그 결과 뇌파의 주파수 변화는 극단의 긍정감성과 부정감성의 차이를 변별할수 있고, 긍정감성내의 차이와 부전감성내의 차이를 변별할 수 있었다. 또한 부정감성을 느낄때보다는 긍정감성을 느낄수록 alpha파의 출현량은 증가하고, delta파와 beta파의 출현량은 감소하고 있음을 보여주었다. 결론적으로, 뇌파의 주파수 변화는 다양한 시각자극에 의해 유발된 감성을 측정할 수 있음을 암시한다.

• Carbon letters
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• v.27
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• pp.81-89
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• 2018

The present study aimed to prepare a novel efficient flame retardant additive for polypropylene. The new flame retardant was prepared by chemical grafting of melamine to graphene oxide with the aid of thionyl chloride. Fourier-transform infrared spectroscopy and thermogravimetric analysis proved that melamine had been successfully grafted to the graphene oxide. The modified graphene oxide was incorporated into polypropylene via solution mixing followed by anti-solvent precipitatio. Homogeneous distribution as well as exfoliation of the nanoplatelets in the polymer matrix was observed using transmission electron microscopy. Thermogravimetric analysis showed a significant improvement in the thermo-oxidative stability of the polymer after incorporating 2 wt% of the modified graphene oxide. The modified graphene oxide also enhanced the limiting oxygen index of the polymer. However, the amount of improvement was not enough for the polymer to be ranked as a self-extinguishing material. Cone calorimetry showed that incorporating 2 wt% of the modified graphene oxide lowered total heat release and the average production rate of carbon monoxide during burning of the polymer by as much as 40 and 35%, respectively. Hence, it was concluded that the new flame retardant can retard burning of the polymer efficiently and profoundly reduce suffocation risk of exposure to burning polymer byproducts.

• Macromolecular Research
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• v.17 no.8
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• pp.603-608
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• 2009

Novel ultra-high molecular weight polyethylene (UHMWPE)/zirconia composites were previously prepared by the in situ polymerization of ethylene using a Ti-based Ziegler-Natta catalyst supported on to the surface of zirconia, as a bearing material for artificial joints. Tribological tests revealed that a uniform dispersion of zirconia in UHMWPE markedly increased the wear resistance. The effects of zirconia content on the oxidation behavior of the ${\gamma}$-ray-treated UHMWPE/zirconia composite surfaces were examined. The oxidation index that estimates the oxidation degree as the content of total carbonyl compounds was monitored using Fourier transform infrared spectroscopy-attenuated total reflectance. The changes in the surface composition due to the oxidation were confirmed by electron spectroscopy for chemical analysis. The extent of oxidation decreased with increasing zirconia content, which was attributed to the increased crystallinity as well as the decreased polymer portion of the UHMWPE/zirconia composites.