• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.755-767
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• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• 한국산학기술학회논문지
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• 제19권6호
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• pp.658-663
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• 2018

현재 대기질 관측 방법은 지상관측망과 인공위성 자료를 기반으로 실시되고 있다. 그러나 현재 방법은 국소지역 및 특정 사업장에 대한 불법 대기오염 물질 배출 증거를 채집하는데 한계가 있으므로 첨단센서를 이용한 증거 채집 방법 개발이 필요한 실정이다. 이 연구에서는 이산화질소와 아황산가스 농도 측정에 있어 자외선 초분광센서의 활용 가능성을 분석하였다. 사용한 스펙트럼은 두 가지 종류로 복사전달모델을 이용하여 모의한 농도별 스펙트럼과 초분광센서를 이용하여 측정한 각 가스의 한 개 농도에 대한 스펙트럼이다. 초분광센서의 활용 가능성을 파악하기 위하여 모의한 스펙트럼과 초분광센서를 이용한 관측 스펙트럼의 차이를 분석하고, 모의 스펙트럼을 이용하여 가스의 농도에 따른 스펙트럼의 변화를 분석하였다. 그 결과 초분광센서로 관측한 스펙트럼과 복사전달모델로 모의한 스펙트럼이 매우 유사한 것으로 나타났다. 또한 모의한 스펙트럼에서 특정 파장의 흡수 깊이가 가스의 농도와 매우 높은 상관관계를 갖고 있는 것으로 나타났다. 따라서 초분광 센서를 이용하여 대기오염물질인 이산화질소와 아황산가스의 농도 추정 가능성이 높은 것으로 판단된다. 향후 연구에서는 초분광센서를 이용하여 다양한 농도에 대한 이산화질소와 아황산가스에 대한 스펙트럼을 관측하고, 농도 추정 가능성을 검증할 필요가 있다.

• 전력전자학회논문지
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• 제7권2호
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• pp.194-204
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• 2002

본 연구에서는 각 상의 PWM 펄스를 개별적으로 랜덤하게 위치시킬 수 있는 새로운 2상 공간벡터 RPWM (Random PWM) 기법을 제안하고 있다. 제안된 방식은 각 2상 펄스들을 변조 구간 내에서 임의의 위치에 랜덤하게 배치하고 이를 기준으로 한 인버터 스위칭에 의해 고조파의 스펙트럼을 광대역화 하는 RPWM 기법이다. 제안된 방법의 타당성을 검증하기 위하여, 16비트 고성능 마이크로 콘트롤러Cl67 기반의 실험을 수행하였다 제안된 2상 RPWM에 의한 인버터 출력 선간 전압과 직류 링크 전류의 고조파 스펙트럼 및 모터의 가청 스위칭 소음 저감효과를 종전의 방식과 비교 검토하였으며, 제안된 방법의 우수성을 입증할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제20권3호
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• pp.355-361
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• 1999

To improve the volatility and stability of lead complexes, the principle of stabilization by saturating the metal coordination sphere by intramolecular coordination through a β-diketonates with an ethereal group has was tested. Several new lead complexes with alkoxyalkyl-substituted β-diketonates, Pb(R1C(O)CHC(O)(CH2)3OR2)2(Rl=t-Bu, Me, OMe, i-Pr, R2=Me, Et), or carboxylate, Pb(OC(O)(CH2)3OEt)2, were prepared by the reaction between Pb(OAc)2 and corresponding alkoxyalkyl-substituted β-diketonates, and they were found to have a viscous liquid phase. The nature of the head (β-diketonate or carboxylate) or tails and substituents of β-diketonates appeared not to be important for the formation of the liquid phase. It is worth mentioning that Pb(OAc)2, which has limited use due to its low solubility, was successfully adopted as a starting material for the preparation of new lead complexes. Easy hydrolysis, reaction with HCl, and 13C NMR spectra indicated that tail portions were not coordinated to the metal as a copper derivative, Cu(t-BuC(O)CHC(O)(CH2)3OMe)2. All these complexes were not volatile enough for the MOCVD experiments, but a methyl derivative, Pb(MeC(O)CHC(O)(CH2)3OEt)2, showed some sublimation. The methoxy derivative, Pb(MeOC(O)CHC(O)(CH2)3OEt)2, was thermally unstable due to possible equilibrium between species coordinating with a keto oxygen atom and an ethereal atom of a methoxy group, which was confirmed by IR and 13C NMR spectra.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2531-2536
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• 2010

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been employed to investigate the molecular structures and absorption spectra of two dyes containing diphenylaniline and 4-diphenylamino-diphenylaniline as donor moiety (TPA1 and TPA3). The geometries indicate that the strong conjugation is formed in the dyes. The electronic structures suggest that the intramolecular charge transfer from the donor to the acceptor occurs, and the electron-donating capability of 4-diphenylamino-diphenylaniline is stronger than that of diphenylaniline. The computed highest occupied molecular orbital (HOMO) energy levels are -5.31 and -4.90 eV, while the lowest unoccupied molecular orbital (LUMO) energies are -2.29 and -2.26 eV for TPA1 and TPA3, respectively, revealing that the interfacial charge transfer between the dyes and the semiconductor electrode are electron injection processes from the photon-excited dyes to the semiconductor conduction band. Furthermore, all the experimental absorption bands of TPA1 and TPA3 have been assigned according to the TDDFT calculations.

• Near Infrared Analysis
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• 제2권1호
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• pp.43-53
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• 2001

A non-invasive spectroscopic method is presented for the measurement of pulmonary edema. Both early diagnosis and quantitative edema estimates were investigated. The spectroscopic determination of pulmonary edema involved the acquisition of diffuse reflectance spectra in the near-infrared (NIR) region with change in water concentration - water is the main constituent of edema fluid. Pulmonary edema was induced into the excised perfused lungs of seven animals by elevating the hydrostatic pressure. Estimates of edema were ascertained from a partial least squares regression of the measured spectral response. Actual edema was determined from the change (increase) in total lung weight. Estimates in relative lung weight increases due to in vitro edema were made with the near infrared spectra. The results revealed that fluid accumulation produced spectral changes in the O-H and C-H absorptions as well as scattering changes in the spectra. Histology of the lung was used to verify the presence or absence of interstitial and alveolar edema. Results demonstrated that near infrared spectroscopy might provide a new tool for clinical assessment of pulmonary edema.

• 천문학논총
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• 제27권4호
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• pp.263-264
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• 2012

We present the properties of dust and the near-infrared spectral features in nearby early-type galaxies. The properties of dust are obtained from the AKARI far-infrared all-sky survey diffuse map. The AKARI/IRC is used for the near-infrared spectra. We improve spectral data with the new dark subtraction method on the basis of the knowledge acquired in our laboratory experiments of the engineering-model detector for the IRC. We have succeeded in fitting the continuum by a power-law function and detecting CO and SiO absorption features in early-type galaxy spectra. Comparing the properties of dust and near-infrared spectral features, we find that the power-law slope depends on dust temperature, but not on the dust mass, which suggests that low-luminosity AGNs may contribute to the changes in the power-law slope and dust temperature.

• Bulletin of the Korean Chemical Society
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• 제24권8호
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• pp.1119-1125
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• 2003

Coherent multidimensional vibrational spectroscopy is a new technique for establishing correlations between features in vibrational spectra that are caused by intra- and intermolecular interactions. These interactions cause cross-peaks between vibrational transitions that reflect the coupling. In this paper, we use Doubly Vibrationally Enhanced Infrared Spectroscopy (DOVE-IR) and DOVE-Raman processes to obtain coherent two dimensional vibrational spectra. The spectra are fitted to obtain the dephasing rates and third order susceptibilities $(χ^{(3)})$ for the nonlinear processes. We show that the DOVE $χ^{(3)}$ values are directly related to the molar absorptivities and Raman $χ^{(3)}$. We then use these relationships to obtain estimates for the $χ^{(3)}$ of the stimulated photon echo and $χ^{(5)}$ of the six wave mixing spectroscopies, respectively. We also predict the ratio of the cascaded four wave mixing signal to the six wave mixing signal.

• 한국의학물리학회지:의학물리
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• 제2권1호
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• pp.29-35
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• 1991

다양한 의료용 선형가속기의 출현으로 인한 방사선 치료분야의 폭넓은 활용에 따라 정확한 선량측정이 중요한 문제중의 하나가 되어왔다. 따라서 정확한 선량계산이나 새로운 선량계산 모델을 위해서 X-선의 조사면에 따른 에너지 분포에 대한 연구가 필요하다. 본 연구에서는 의료용 선형가속기에서 발생된 X-선의 에너지 분포특성 및 기하학적 구조의 영향 요인 연구에 몬테-칼로 방법의 적용성을 자료분석에 의한 모의시험 계산값과 선량분포계산, 불에서 HVL 및 측정된 자료와 비교하여 알아 보았다. 기대한 것 처럼 X-선 빔의 축반경에 따른 평균에너지 변화로 부터 빔의 발생특성과 treatment head부분의 기하학적 구조 영향에 기인한 에너지 분포가 중심선 속으로 부터 멀어져 감에 따라 적어짐을 알 수 있었다.

• 천문학회보
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• 제41권2호
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• pp.43.3-43.3
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• 2016

We present a library of high-resolution (R~45,000) and high signal-to-noise ratio ($S/N{\geq}200$) near-infrared spectra of 147 standard stars. High quality spectra were obtained with Immersion GRating INfrared Spectrograph (IGRINS) covering the full range of H ($1.496-1.795{\mu}m$) and K ($2.080-2.460{\mu}m$) bands. The targets are mainly selected as MK standard stars which have well-defined spectral types and luminosity classes, and cover a wide range of effective temperatures and surface gravities. The spectra were corrected for telluric absorption lines and absolute flux calibrated using Two Micron All Sky Survey (2MASS) photometry. We find new spectral indices in H and K bands and provide their EWs. We describe empirical relations between the measured EWs and stellar atmosphere parameters such as effective temperature and surface gravity.