• 한국산학기술학회논문지
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• 제21권5호
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• pp.69-76
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• 2020

수중에서 방사된 음원의 신호는 해수면, 해저면 반사에 의한 다중경로 시간지연(multi-path time-delay)을 포함하여 체계(system)의 센서에 수신된다. 다중경로 환경과 복잡한 해양환경의 외란(disturbance)에 의해 수신된 신호간 상관성(coherence)이 저하된다. 따라서, 신호간 시간지연값을 이용하여 수중음원의 위치를 추정하는 체계는 추정성능의 저하가 나타난다. 이러한 환경에서도 강인한 음원 위치 추정성능을 위해 선배열(uniform line array), 평면배열(rectangular array)과 같은 다양한 형태의 센서배열과 빔형성(beamforming) 기법, 비용함수(cost-function)과 같은 신호처리를 이용하여 왔다. 본 연구에서는 선배열 형태의 doublet array와 추정된 시간지연값 보정 기법을 이용하고자 한다. 3 개의 doublet array를 동일 선에 위치하였으며 각각의 doublet array에 수신된 신호간의 시간지연값을 2 단계로 추정하였다. 수신신호에 대해 상호상관(cross-correlation) 함수를 적용하여 추정된 시간지연값을 수신신호의 중심주파수(center-frequency)와 array의 개구경(aperture) 및 수중음원과의 기하학적 관계에 따라 보정하여 최종의 시간 지연값을 얻었으며 이로부터 음원의 거리와 방위를 추정하였다. 제안한 기법의 타당성을 확인하기 위해, Monte-Carlo method를 이용하여 시뮬레이션하였다.

• 한국항공우주학회지
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• 제34권6호
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• pp.1-9
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• 2006

본 연구의 목적은 여러 가지 비행 모드 상의 로터 성능을 효율적으로 예측하는 것이다. 헬리콥터의 공력 특성을 예측하기 위한 비정상 source-doublet 패널 기법 기반의 수치 기법을 개발하였다. 후류의 형상 예측에는 시간 전진 자유후류모델이 사용되었다. 점성에 의한 확산을 고려한 후류의 roll-up 모사를 위하여 후류의 doublet 패널은 같은 강도의 와류고리로 대체하여 계산하였다. 후류와 양력면의 충돌 문제는 표면격자 내부에 들어간 와류고리의 포텐셜값을 제거하여 해결하였다. 제자리비행의 해석 시에 나타나는 와류 불안정성의 해결에는 slow starting과 vortex core growth 모델을 사용하였다. 로터 공력 해석 프로그램은 제자리비행과 전진비행에 대한 실험 결과와 비교하여 검증하였으며, 실험치와 일치하는 결과를 얻을 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.211-219
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• 1998

Propellants pressurized and fed into the combustion chamber undergoes the mechanical, chemical combustion processes. Along with their distinctive physical characteristics, propellant combustion is typically divided into the processes; injection, atomization, mixing, vaporization and chemical reaction. These processes assumed to happen in a serial manner are strongly coupled, thereby involves formidable physical complexities. In this study a numerical experiment is attempted to simulate the burning sprays due to OFO, FOF triplet / FOOF split doublet injectors. Based on Eulerian-Lagrangian frame, Navier-Stokes equation system for compressible flows is preconditioned with low Reynolds number $k-{\varepsilon}$ turbulent model and time-integrated by LU-SGS, and the sprays are described by DSF model with the characteristics initialized by experimentally determined spray characteristics. Simplified single global reaction model approximates heptane-air reaction. It was observed that FOOF split doublet injector shows better atmization with shortest residence and the FOF triplet injector produces better combustion performance.

• Tuberculosis and Respiratory Diseases
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• 제81권2호
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• pp.148-155
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• 2018

Background: Although targeted therapy and immuno-oncology have shifted the treatment paradigm for lung cancer, platinum-based combination is still the standard of care for advanced non-small cell lung cancer (NSCLC). Pemetrexed continuation maintenance therapy has been approved and increasingly used for patients with nonsquamous NSCLC. However, the efficacy of this strategy has not been proven in patients without driving mutations. The objective of this study was to compare the clinical benefit of pemetrexed continuation maintenance to conventional platinum-based doublet in epidermal growth factor receptor (EGFR)-negative lung adenocarcinoma. Methods: A total of 114 patients with EGFR-negative lung adenocarcinoma who were treated with platinum doublet were retrospectively enrolled. We compared the survival rates between patients received pemetrexed maintenance after four-cycled pemetrexed/cisplatin and those received at least four-cycled platinum doublet without maintenance chemotherapy as a first-line treatment. Results: Forty-one patients received pemetrexed maintenance and 73 received conventional platinum doublet. Median progression-free survival (PFS), which was defined as the time from the day of response evaluation after four cycles of chemotherapy to disease progression or death, was significantly higher in the pemetrexed maintenance group compared to conventional group (5.8 months vs. 2.2 months, p<0.001). Median overall survival showed an increasing trend in the pemetrexed maintenance group (22.3 months vs. 16.1 months, p=0.098). Multivariate analyses showed that pemetrexed maintenance chemotherapy was associated with better PFS (hazard ratio, 0.73; 95% confidence interval, 0.15-0.87). Conclusion: Compared to conventional platinum-based chemotherapy, premetrexed continuation maintenance treatment is associated with better clinical outcome for the patients with EGFR wild-type lung adenocarcinoma.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.126-130
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• 2000

In this study, flutter characteristics of a composite wing have been studied for the variation of laminate angles in the subsonic, transonic and supersonic flow regime. The laminate angles are selected by the aspect of engineering practice such as 0, $\pm$45 and 90 degrees. To calculate the unsteady aerodynamics for flutter analysis, the Doublet Lattice Method(DLM) in subsonic flow and the Doublet Point Method(DPM) in supersonic flow are applied in the frequency domain. In transonic flow, transonic small disturbance(TSD) code is used to calculate the nonlinear unsteady aerodynamics in the time domain. Aeroelastic governing equation has been solved by v-g method in the frequency domain and also by Coupled Time-Integration Method(CTIM) in the time domain. from the results of present study, characteristics of free vibration responses and aeroelastic instabilities of a composite wing are presented for the set of various lamination angles in the all flow range.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.1-9
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• 2007

As a first step toward a complete CFD-CSD coupling for helicopter rotor load analysis, the present study attempts to loosely couple a CFD code with a source-double panel method. The far-field wake effects were calculated by a time-marching free vortex wake method and were implemented into the CFD module via field velocity approach. Unlike the lifting line method, the air loads correction process is not trivial for the source-doublet panel method. The air loads correction process between the source-doublet method and CFD is newly suggested in this work and the computation results are validated against available data for well-known hovering flight conditions.

• 대한환경공학회지
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• 제37권4호
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• pp.218-227
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• 2015

나노기술의 이용도가 높아지면서 나노물질 유출로 인한 환경오염 문제가 제기되고 있다. 수질시료 내 나노물질의 분석을 위해서는 시료의 교란을 최소화할 수 있는 보관조건 마련이 선결 요건이지만, 아직까지 적합한 보관조건이 제시되고 있지 않다. 이에 본 연구는 citrate로 코팅된 은 나노물질(cit-AgNP)을 대상으로 금속나노물질을 함유한 수질시료의 보관조건을 제시하고자 수행되었다. 이를 위해 시간분해 동적산란법(time-resolved dynamic light scattering)을 이용하여 pH, 배경용액의 농도, 온도, 나노물질의 농도 등과 같은 환경적인 조건과 시간에 따른 cit-AgNP의 크기 변화를 관찰하였다. 실험을 통한 각 환경조건별 AgNP의 응집특성을 해석하고 이러한 결과를 바탕으로 시료의 보관조건을 제시하였다. 그리고 AgNP의 입자농도와 응집속도의 선형적 관계로부터 구한 doublet time을 이용하여 시료의 보관기간을 산정하였다. 실험결과, pH는 7 이상, 배경 용액($Ca(NO_3)_2$)의 농도는 3 mM 이하, 온도는 냉장($4^{\circ}C$) 상태, 그리고 cit-AgNP의 농도는 2 mg/L 이하에서 응집속도가 0에 가까운 값을 나타내었다. 또한 수질시료 내 존재하는 100 nm cit-AgNP의 농도를 환경에 존재할 수 있는 낮은 수준인 $1{\mu}g/L$로 가정한 후 doublet time를 구한 결과, 가능한 시료의 보관기간은 15.79~17.53일 정도인 것으로 조사되었다. 하지만 pH와 배경 용액의 농도 조절은 시료의 변질과 교란이 우려되기 때문에 보관조건으로 일반화하여 제시하는 것은 적절하지 않고, 나노물질 자체의 농도를 조절하는 것은 수질시료 내 나노물질의 농도 등의 분석을 위한 시료의 보관조건으로 바람직하지 않다. 그러므로 본 연구의 결과로부터 일반화하여 제시할 수 있는 보관조건은 냉장($4^{\circ}C$) 상태에서 2주일 정도인 것으로 판단된다.

• International Journal of Aeronautical and Space Sciences
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• 제7권2호
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• pp.110-120
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• 2006

There have been developed many structural and fluid rotorcraft analysis models in rotorcraft community, and also lots of investigations have been conducted to combine these two models. These investigations turn out to be good at predicting the airloads precisely, but they have not taken the blade nonlinear deflection into account. For this reason, the present paper adopts a sophisticated structural model which can describe three-dimensional nonlinear deflection of the blade. And it is combined with two types of aerodynamic model. First one is generalized Greenberg type of finite-time aerodynamic model, which is originally established for a fixed wing, but later modified to be suitable for coupled flap-lag-torsional aeroelastic analysis of the rotor blade. Second aerodynamic model is based on the unsteady source-doublet panel method coupled with a free wake model. The advantages of the present method are capabilities to consider thickness of the blade and more precise wake effects. Transient responses of the airloads and structural deflections in time domain are mainly analyzed in this paper.

• 대한화학회지
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• 제15권4호
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• pp.177-181
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• 1971

Free radicals of lysozyme produced by $Ti-H_2O_2$ system were studied in aqueous solution at room temperature using ESR with a continuous flow-mixing. The spectra, each consisting of a doublet with 5.5 G splitting and a broad resonance covering 80 G splitting are closely similar in shape to that for solid irradiated in vacuum at $77^{\circ}K$ and observed at room temperature immediately on warming. The result is assumed to indicate that the secondary protein radical components formed within 0.01 second, dead time of the mixing chamber, and initiated by hydrogen atom abstraction at ${\alpha}$-carbon atom of peptide chain in liquid solution at room temperature are identical to those resulting from the initial formation of a mixture of positive holes and negative ions by ionization processes as well as radical fragments by the rupture of chemical bonds in the solid during similar time at the same temperature. A broad resonance is observed with considerable amplitude on the high field side of the doublet, which is quite dissimilar to the spectra of irradiated solid lysozyme. This resonance was tentatively attributed to the polypeptide free radical in which unpaired electrons are localized on side chain.