• Journal of the Korean Chemical Society
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• v.37 no.3
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• pp.271-278
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• 1993

The hyperfine splitting constants of phenanthrenequinone anion radical have been determined for the solution of triethylamine with 2-propanol, 2-pentanol or benzene by cwESR and time-resolved ESR methods. The radical anion was produced by photolysis using a pulsed excimer laser. The resulting hyperfine splitting constant A$_{H1}$ and A$_{H2}$ are 1.662, 0.378 in 2-propanol, 1.602, 0.361 in 2-pentanol and 1.518 in benzene respectively. The hyperfine coupling constants decrease with the decreasing of polarity of the mixed solvent. The tendency of the variation depends on the polarity of the solvents, thus, making it in impossible to observe the magnetic equivalent proton in a mixed solvent of nonpolar benzene. Particularly, time-resolved ESR spectrum of triethylamine radical (TEA${\cdot}$) has been observed in 0.15∼0.30 ${\mu}s$ from the solvent of 3 : 1 with 2-pentanol and triethylamine. Thus from the results of solvent effect, we can suggest that the identification of the unstable short-lived spin polarized phenanthrenequinone anion radical(*PQ${\cdot}^-$) proceed through photochemistry.

• Analytical Science and Technology
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• v.21 no.5
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• pp.403-411
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• 2008

Dimethyldibutyltetradecylmalonamide (DMDBTDMA) extractant was used in a solvent extraction process for a radioactive liquid waste treatment. For the study of radiolysis phenomena, DMDBTDMA was synthesized and the degradation compounds (n-methylbutylamine, tetradecane, 1-tetradecanol) in the DMDBTDMA extractant, irradiated with $^{60}Co$ gamma ray, were identified and determined as radiolysis products by a Fourier transform infrared (FT-IR), gas chromatograph/mass spectrometer (GC/MS) analysis and GC/MS with selected ion monitoring (SIM) mode. Retention behavior of n-methylbutylamine, n-dodecane, tetradecane and 1-tetradecanol in the total ion chromatogram with the standard materials and n-dodecane as the internal standard (ISTD) were 2.35 min., 8.83 min., 10.68 min. and 12.75 min., respectively. In the case of tetradecane, there was a linear relationship between the concentration of the tetradecane and the absorbed dose of the ${\gamma}$-ray irradiated DMDBTDMA.

• Korean Journal of Optics and Photonics
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• v.19 no.5
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• pp.370-375
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• 2008

High-speed high-resolution terahertz time-domain spectroscopy (THz-TDS) is demonstrated using the asynchronous-opticalsampling (AOS) method. A time-domain signal with a 10-ns time window is rapidly acquired by using two femtosecond lasers with slightly different repetition frequencies to generate and detect a terahertz pulse wave, without a mechanical delay stage. The spectrum obtained by the fast Fourier transformation (FFT) of the time-domain waveform has a frequency resolution of 100 MHz. The time resolution of our spectrometer is measured using the cross-correlation method to be 278 fs. A transmission spectrum of water vapor is measured and the absorption lines are analyzed in the frequency range from 0.1 to 1.2 THz.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.554-554
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• 2013

대기압 제트 플라즈마를 저주파(수-수십 kHz) 전압에서 구동 시, 일반적으로 '스트리머(streamer)'혹은 '플라즈마 총알(plasma bullet)'로 불리는 현상이 특정 운전조건에서 관찰된다. 본 연구에서는 동일 구조의 Ta, Ti, stainless steel, brass, Cu, Ni 전극을 이용하여 전극물질에 따른 대기압 제트 플라즈마의 특성 변화를 분석하였다. 각각의 물질은 서로 다른 이차전자방출계수, 일함수, 전기전도도 등 고유한 성질이 다르기 때문에 이들 전극을 이용하여 발생시킨 제트 플라즈마 역시 다른 특성을 갖는다. Acton SpectroPro750 분광기를 이용하여 얻은 플라즈마 방출광스펙트럼으로부터 구한 전자 여기온도(Texc=680~720 K)와 OH의 분자 회전온도(Trot=350~380K)는 물질에 따라 큰 변화를 보이지 않았으나, 발생된 스트리머 거동에서 큰 차이를 확인하였다. ICCD 카메라를 이용한 시간 분해된 이미지에서 전극물질에 따른 첫 번째 스트리머의 발생시간 및 스트리머 속력, 두 번째 스트리머의 분리시간이 모두 다른 것을 확인하였다. 제일 차이가 심하게 나타나는 Ti과 Cu의 경우 첫 스트리머의 발생시간 차이는 약 $1{\mu}s$이며, 평균속력 및 순간속력이 약 2 km/s 차이가 났다. 이 결과를 통해 물질의 이차전자방출계수 및 일함수가 대기압 제트 플라즈마에서 스트리머 발생에 영향을 주는 것을 알았고, 다른 전극물질을 사용한 제트 플라즈마의 특성이 다름에 따라 여러 응용에서의 결과에도 영향을 미칠 것이라생각한다.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.311-316
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• 2008

Since the presence of the chemical impurities and defect at surfaces and interfaces greatly influence the properties of various semiconductor devices, an unambiguous chemical characterization of the metal and semiconductor surfaces become more important in the view of the miniaturization of the devices toward nano scale. Among the various conventional surface characterization tools, Electron-induced Auger Electron Spectroscopy (EAES), X-ray Photoelectron Spectroscopy (XPS) and Secondary Electron Ion Mass Spectroscopy (SIMS) are being used for the identification of the surface chemical impurities. Recently, a novel surface characterizaion technique, Positron-annihilation induced Auger Electron Spectroscopy (PAES) is introduced to provide a unique method for the analysis of the elemental composition of the top-most atomic layer. In PAES, monoenergetic positron of a few eV are implanted to the surface under study and these positrons become thermalized near the surface. A fraction of the thermalized positron trapped at the surface state annihilate with the neighboring core-level electrons, creating core-hole excitations, which initiate the Auger process with the emission of Auger electrons almost simultaneously with the emission of annihilating gamma-rays. The energy of electrons is generally determined by employing ExB energy selector, which shows a poor resolution of $6{\sim}10eV$. In this paper, time-of-flight system is employed to measure the electrons energy with an enhanced energy resolution. The experimental result is compared with simulation results in the case of both linear (with retarding tube) and reflected TOF systems.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.33.1-33.1
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• 2010

태양전파폭발위치관측기(KSRBL)는 단일 안테나 전파분광기로써 미 뉴저지공과대학과의 협력으로 2009년 8월에 한국천문연구원에 개발 설치되었다. 1 MHz 스펙트럼 분해능과 1초의 시간 분해능을 가지고 있고 관측할 수 있는 주파수 대역은 245, 410 MHz 와 0.5-18 GHz에 이르는 광대역이다. 또한 태양 전면 $0.03^{\circ}$ 각거리 안의 오차 범위 내에 태양 폭발 위치를 감지할 수 있다. 전파 관측은 LabVIEW와 IDL 프로그램에 의해 미리 짜여진 관측 스케줄에 따라 매일 자동으로 진행된다. 하루에 생성되는 원시데이터는 90 GB 정도이며, 태양이 지고나면 원시데이터는 적분과정을 통해 용량이 6 GB 정도로 줄어들게 된다. 이렇게 처리된 파일은 바로 데이터 서버에 자동 전송된다. 또한 KSRBL 관측일지 홈페이지를 웹기반으로 개발하였으며 조만간 이를 데이터 전송과 연계하여 전파 폭발이 감지될 경우 원시데이터도 데이터 서버에 자동 전송되도록 할 예정이다. 2010년 1월에서 2월 8일 사이 5개의 전파 폭발이 관측되었고 태양활동이 점차 활발해짐에 따라 관측횟수는 더욱 늘어날 전망이다. 관측된 사례들에 대해 다른 전파 및 X선 관측과 비교분석하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.51-57
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• 2002

In this paper, a simple interpolation technique in a frequency domain is proposed for the discrete Fourier transform(DFT) algorithm. Frequency and phase resolution capabilities of the DFT algorithm can be significantly improved by the proposed interpolation technique without increase of a DFT size(the number of points for the DFT). The new technique uses a diving point in amplitude and phase spectrums. As an application, the technique can be used for joint estimation of fine frequency and phase offsets in burst mode digital transmission. Simulation results show that the joint estimator using the technique is robust to estimation errors.

• The Journal of the Acoustical Society of Korea
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• v.35 no.4
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• pp.303-309
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• 2016

This paper proposes a novel approach to the problem of audio signal clustering using a stacked autoencoder. The proposed stacked autoencoder learns an efficient representation for the input signal, enables clustering constituent signals with similar characteristics, and therefore the original sources can be separated based on the clustering results. STFT (Short-Time Fourier Transform) is performed to extract time-frequency spectrum, and rectangular windows at all the possible locations are used as input values to the autoencoder. The outputs at the middle, encoding layer, are used to cluster the rectangular windows and the original sources are separated by the Wiener filters derived from the clustering results. Source separation experiments were carried out in comparison to the conventional NMF (Non-negative Matrix Factorization), and the estimated sources by the proposed method well represent the characteristics of the orignal sources as shown in the time-frequency representation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.4
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• pp.207-217
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• 2011

In this study the complex formation reactions between uranium(VI) and 2,6-dihydroxybenzoate (DHB) as a model ligand of humic acid were investigated by using UV-Vis spectrophotometry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The analysis of the spectrophotometric data, i.e., absorbance changes at the characteristic charge-transfer bands of the U(VI)-DHB complex, indicates that both 1:1 and 1:2 (U(VI):DHB) complexes occur as a result of dual equilibria and their distribution varies in a pH-dependent manner. The stepwise stability constants determined (log $K_1$ and log $K_2$) are $12.4{\pm}0.1$ and $11.4{\pm}0.1$. Further, the TRLFS study shows that DHB plays a role as a fluorescence quencher of U(VI) species. The presence of both a dynamic and static quenching process was identified for all U(VI) species examined, i.e., ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$. The fluorescence intensity and lifetimes of each species were measured from the time-resolved spectra at various ligand concentrations, and then analyzed based on Stern-Volmer equations. The static quenching constants (log $K_s$) obtained are $4.2{\pm}0.1$, $4.3{\pm}0.1$, and $4.34{\pm}0.08$ for ${UO_2}^{2+}$, $(UO_2)_2{(OH)_2}^{2+}$, and $(UO_2)_3{(OH)_5}^+$, respectively. The results of Stern-Volmer analysis suggest that both mono- and bi-dentate U(VI)-DHB complexes serve as groundstate complexes inducing static quenching.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.427-430
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• 2006

본 논문에서는 일반적인 항법 확인 뿐만 아니라 간섭신호 제거용 필터의 성능 검증을 위한 고성능 GNSS SDR 플랫폼을 개발하였다. 개발된 수신기 플랫폼은 간섭 신호 제거 필터 응용까지 고려한 RF부와 16비트의 분해능을 갖는 고속의 USB 데이터 수집장치, PC 및 GNSS 소프트웨어 수신기 프로그램으로 구성된다. 개발된 플랫폼은 스펙트럼 분석기로 RF부를 검증하였으며, 상용의 GNSS 시뮬레이터를 사용하여 PC에서 데이터를 확인함으로써 신호 수집장치의 동작을 검증하였다. 실제 GPS 신호를 PC에 저장하고, 소프트웨어 수신기에서 항법 결과와 신호 획득시간, 신호 대 잡음 전력비를 확인하여 전체 플랫폼 기능 및 성능을 확인하였다.