• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.457-467
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• 2018

This paper presents performance comparison of several high-resolution frequency estimation algorithms for pure real tone signal. Algorithms are DFT (Discrete Fourier Transform - for reference purpose), Jacobsen, Candan, reassignment and Cedron. Each algorithm is evaluated under various experimental conditions, e.g., different SNR (Signal to Noise Ratio), window function and window length and performance is compared in the perspective of bias, MSE (Mean Square-Error) and variance. Experimental results indicate that Cedron algorithms works well in the most cases. For actual usage in the engineering problem, each algorithm needs additional analysis and modification.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.20-32
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• 2024

Metal corrosion in acidic environments is a major issue in various industrial applications. This study evaluates the 4-piperonylideneaminoantipyrine (PPDAA) corrosion inhibition efficiency for mild steel in a hydrochloric acid (HCl) solution. The weight loss method was used to determine the corrosion inhibition efficiency at different concentrations and immersion time periods. Results revealed that the highest inhibition efficiency (94.3%) was achieved at 5 mM concentration after 5 hours of immersion time. To inspect the surface morphology of the inhibitor film on the mild steel surface, scanning electron microscopy (SEM) was used before and after immersion in 1.0 M HCl. Density functional theory (DFT) calculations were performed to investigate the molecular structure and electronic properties of the inhibitor molecule to understand the corrosion inhibition mechanism. Theoretical results showed that the inhibitor molecule can adsorb onto the mild steel surface through its nitrogen and oxygen atoms, forming a protective layer that prevents HCl corrosive attack. These findings highlight the potential of PPDAA as an effective corrosion inhibitor for mild steel in HCl solution. Moreover, combining experimental and theoretical approaches provides insights into the mechanism of corrosion inhibition, which is essential for developing effective strategies to prevent metal corrosion in acidic environments.

• Journal of dental hygiene science
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• v.13 no.4
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• pp.426-433
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• 2013

The objective of this study was to examine whether there is an association of oral health conditions between mothers and their preschool children in Korea. A sample of 823 preschool children and their mothers were selected for this study from the database of the fourth Korean National Health and Nutrition examination Survey. Preschool children were defined as children aged 4, 5, and 6 years old. The subjects were clinically examined for the presence of caries lesions (dft index) and their mother was checked for the presence of dental caries (DMFT index) and periodontal status (CPI). The socio-demographic characteristics and mother's oral health behaviours were considered covariates in this study. Univariate and multivariate analysis was adapted to assess the association of oral health condition between mothers and their preschool children. In univariate analysis, there were significant differences between preschool children's dft index and their mother's age (p=0.005), dental treatment demand for the past one year (p=0.034), and DMFT index (p=0.016). In multivariate analysis, only mother's DMFT index was significantly associated with their children's dft index after adjusting for covariates. In conclusion, the mother's oral health was partly associated with their preschool children's oral health in Korea.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.409-413
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• 2013

In this paper, we device stress-diffusion full coupling multiscale analysis method for battery electrode simulation. In proposed method, the diffusive and mechanical properties of electrode material depend on Li concentration are estimated using density function theory(DFT) simulation. Then, stress-diffusion full coupling continuum formulation based on finite element method(FEM) is constructed with the diffusive and mechanical properties calculated from DFT simulation. Finally, silicon nanowire anode charge and discharge simulations are performed using the proposed method. Through numerical examples, the stress-diffusion full coupling method shows more resonable results than previous one way continuum analysis.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.1169-1172
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• 1998

We designed an ALU(Airthmetic Logic Unit) with BIST(Built-In Self Test), which is suitable for 32-bit DSP RISC processors. We minimized the area of this ALU by allowing different operations to share several hardware blocks. Moreover, we applied DFT(Design for Testability) to ALU and offered Bist(Built-In Self-Test) function. BIST is composed of pattern generation and response analysis. We used the reseeding method and testability design for the high fault coverage. These techniques reduce the test length. Chip's reliability is improved by testing and the cost of testing system can be reduced.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.430-433
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• 2014

Perovskite 구조를 가진 코발트 산화물 $SrCoO_3$와 Brownmillerite 구조인 $SrCoO_{2.5}$의 electronic structure를 제1원리 계산을 통해 분석하였다. 이들의 magnetic structure를 계산하여 실험을 통해 알려진 값과 비교하였고, 각 구조에서 코발트 이온이 갖는 spin state를 확인할 수 있었다. 코발트 이온은 $SrCoO_3$에서 intermediate spin state(IS)를, $SrCoO_{2.5}$에서는 high spin state(HS)를 갖는데 이것이 lattice constant의 차이에 의한 것인지, 아니라면 차이의 원인은 무엇인지 density of state를 분석함으로써 알아보았다.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.5
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• pp.96-103
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• 1999

본 논문에서는 sliding-DFT(SDFT)를 계수의 유한 비트 근사구현에 기초하여 실시간 구현하는 기법을 제시하고, 이의 오차영향을 해석하였다. 오차의 영향을 오차전력과 신호전력비율(noise-to-signal power ratio : NSR)로 하여 이를 해석적으로 유도하였다. 가우스 렌덤신호 및 사람의 수면 EEG 신호를 대상으로 수행한 시뮬레이션 결과가 해석식과 잘 일치하는 것을 보임으로써 본 연구에서 얻은 해석식을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.10A
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• pp.1764-1771
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• 2001

It has developed a PCM signal acquisition(PCMA) system which can analyze status of signals in order to establish rapid diagnosing in TDX-families signaling service equipment. We develop the quick Fourier transform(QFT) for length 2$\^$M/ data to analyze the power spectral of the PCMA system. This algorithm can reduces the number of floating-point operations necessary to compute the DFT by a factor of two or four over direct methods or Goertzels method for prime lengths. In the experimental results, the system classifies the type of signals and finally discriminates the digit.

• International Journal of Computer Science & Network Security
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• v.24 no.9
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• pp.1-11
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• 2024

This paper develops a generalized framework for the analysis of multicarrier communication system, using a generic pair of transmitters- and receiver side terraforms, Q_τ | Q_R, such that the DFT-transform based "conventional OFDM" is its special case. This analysis framework is then used to propose and prove theorems on various performance metrics of a multicarrier communication system, which will apply to any system that fits the architecture, which most will do. The analysis framework also derives previously unknown closed-form expressions for these metrics, such as how the performance degradation due to carrier frequency offset or timing synchronization error, amongst others, are function of generic transforms. While extensive work exists on the impact of these challenges on conventional OFDM, how are these functions of transform matrices is unknown in the literature. It will be shown, how the analysis of OFDM based system is special case of analysis in this paper. This paper is Part I of three paper series, where the other two supplements the arguments present here.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.3
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• pp.377-382
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• 2016

In 2013, a total capacity of 591.3 MW of installed wind power generation was achieved in Korea, with a total of 1,139 MWh of wind energy generated that year. More wind power plants will be installed in the coming years, and it is important to develop methods to reduce the output variability of these resources so as to provide stable power to the power grid of Korea. In this regard, this paper proposes the use of energy storage system (ESS) as a means to stabilize the output variability of wind power plants. Presented in this paper is a method that uses Discrete Fourier Transform (DFT) to determine the ESS capacity needed to provide a stable power output for ancillary services such as frequency regulation, economic dispatch, and emergency reserves. In the first step of the proposed method, four regions (namely, Samdal, Yeongdeok, Yeongyang, and Gangwon) in Korea that had the most wind power generation capacity were selected for analysis. In the second step, the individual and aggregated wind power outputs of the selected regions in 2013 were obtained This information was then used in the third step, where DFT analysis of the power outputs was used to drive the magnitudes of the output variation. And finally, the ESS capacity requirements needed to provide different ancillary services were determined based on the magnitudes of the output variation.