• 천문학회지
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• 제53권2호
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• pp.35-42
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• 2020

We analyze high dispersion emission lines of the symbiotic nova AG Pegasi, observed in 1998, 2001, and 2002. The Hα and Hβ lines show three components, two narrow and one underlying broad line components, but most other lines, such as H_I, He_I, and He_II lines, show two blue- and red-shifted components only. A recent study by Lee & Hyung (2018) suggested that the double Gaussian lines emitted from a bipolar conical shell are likely to form Raman scattering lines observed in 1998. In this study, we show that the bipolar cone with an opening angle of 74°, which expands at a velocity of 70 km s^-1 along the polar axis of the white dwarf, can accommodate the observed double line profiles in 1998, 2001, and 2002. We conclude that the emission zone of the bipolar conical shell, which formed along the bipolar axis of the white dwarf due to the collimation by the accretion disk, is responsible for the double Gaussian profiles.

• 천문학회보
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• 제46권2호
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• pp.68.3-69
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• 2021

We present a novel profile stacking technique based on optimal profile decomposition of a 3D spectral line data cube, and its performance test using the HI data cubes of sample galaxies from HI galaxy surveys, THINGS and LITTLE THINGS. Compared to the previous approach which aligns all the spectra of a cube using their central velocities derived from either moment analysis, single Gaussian or hermite h3 polynomial fitting, the new method makes a profile decomposition of the profiles from which an optimal number of single Gaussian components is derived for each profile. The so-called superprofile which is derived by co-adding all the aligned profiles from which the other Gaussian models are subtracted is found to have weaker wings compared to the ones constructed in a typical manner. This could be due to the reduced number of asymmetric profiles in the new method. A practical test made on the HI data cubes of the THINGS and LITTLE THINGS galaxies shows that our new method can extract more mass of kinematically cold HI components in the galaxies than the previous results. Additionally, we fit a double Gaussian model to the superprofiles whose S/N is boosted, and quantify not only their profile shapes but derive the ratio of the Gaussian model parameters, such as the intensity ratio and velocity dispersion ratio of the narrower and broader Gaussian components. We discuss how the superprofile properties of the sample galaxies are correlated with their other physical properties, including star formation rate, stellar mass, metallicity, and gas mass.

• 한국해안해양공학회지
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• 제14권4호
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• pp.274-281
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• 2002

본 연구에서는 Boussinesq 방정식을 이용하여 유도한 한 쌍의 상미분방정식을 이용하여, 수심이 완만히 변하는 일정 경사면의 정현파형 지형 및 복합정현파형 지형에서의 Bragg반사를 해석하였다. 입사파는 크노이드파를 사용하였으며, 입사파의 분산성과 해저지형의 형태가 반사에 미치는 영향에 관하여 검토하였다. 해석결과에 의하면 정현파형 지형의 경우에는 입사파 분산성의 크기와 정현파형 지형의 진폭이 증가할수록 반사율이 증가하였으며, 복합정현파형 지형의 경우에는 지형의 진폭이 증가할수록, 해저지형을 구성하는 두 개의 정현성분 파수의 차가 감소할수록 반사율의 크기는 증가하였다.

• 한국분말재료학회지
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• 제21권4호
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• pp.271-276
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• 2014

15Cr-1Mo base oxide dispersion strengthened (ODS) steel which is considered to be as a promising candidate for high- temperature components in nuclear fusion and fission systems because of its excellent high temperature strength, corrosion and radiation resistance was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Torsion tests were performed at room temperature, leading to two different shear strain routes in the forward and reverse directions. In this study, microstructure evolution of the ODS steel during simple shearing was investigated. Fine grained microstructure and a cell structure of dislocation with low angle boundaries were characterized with shear strain in the shear deformed region by electron backscattered diffraction (EBSD). Grain refinement with shear strain resulted in an increase in hardness. After the forward-reverse torsion, the hardness value was measured to be higher than that of the forward torsion only with an identical shear strain amount, suggesting that new dislocation cell structures inside the grain were generated, thus resulting in a larger strengthening of the steel.

• International Journal of Automotive Technology
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• 제6권6호
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• pp.665-670
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• 2005

Nanocomposites of polypropylene with organically modified clays were compounded on a twin-screw extruder by two-step melt compounding of three components, i.e., polypropylene, maleic anhydride grafted polypropylene (PP-g-MA), and organically modified clay. The effect of PP-g-MA compatibilizers, including PH-200, Epolene-43, Polybond-3002, Polybond-3200, with a wide range of maleic anhydride (MA) content and molecular weight was examined. Morphologies of nanocomposites and their mechanical properties such as stiffness, strength, and impact resistance were investigated. X-ray diffraction patterns showed that the dispersion morphology of clay particles seemed to be determined in the first compounding step and the further dispersion of clays didn't occur in the second compounding step. As the ratio of PP-g-MA to clay increased, the clay particles were dispersed more uniformly in the matrix resin. As the dispersibility of clays was enhanced, the reinforcement effect of the clays increased, however impact resistance decreased.

• 폴리머
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• 제28권6호
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• pp.487-493
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• 2004

계면간 상호작용이 약한 폴리(에틸 아크릴레이트-co-t-부틸 아크릴레이트) (PEB) 에멀션 고분자를 사용한 나노복합체 혼합용액에서는 pH변화에 따라 고분자 입자들과 실리카 나노입자들의 분포 형태가 결정되었다. 이러한 나노복합체는 실리카 입자의 응집이 심하였고 불규칙적인 분산성을 나타내었다. 메타아크릴옥시프로필트리메톡시실란 (MPS)를 사용하여 개질한 용액 중합 고분자나 실리카 나노입자를 사용한 나노복합체에서는 계면간 강한 상호작용으로 인하여 실리카 나노입자가 미세하게 분산되었고 코어-쉘 형태학적 특성을 나타냈다. 계면을 MPS로 개질한 나노복합체에서는 강한 수소 결합 상호작용이 존재하는 것을 적외선 분광계로 확인하였다. 강한 계면 상호작용을 갖는 나노복합체는 고분자 사슬의 유리 전이 온도가 증가하였고 ΔC$_{p}$ 는 감소하였으며 열분해 온도는 상승되었다.며 열분해 온도는 상승되었다.

• 한국광학회지
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• 제11권5호
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• pp.353-359
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• 2000

마하젠더 광세기 변조기를 이용해 10GHz의 능동적 고조모드록킹된 어븀첨가 광섬유 레이저의 출력특성을 측정하여, 이를 모델로 레이저 공진기를 이론적으로 해석하였다. 능동형으로 모드록킹된 레이저에서의 비선형 슈뢰딩거 방정식을 통해 공진기에서 나타나는 비선형 효과인 자기위상변조(Self Phase Modulation)와 군속도 분산(Group Velocity Dispersion)을 고려하여 레이저의 각각의 구성부붐들이 레이저 펄스에 미치는 영향을 계산하여 이론적으로 해석하였다. 또한 그 해석을 바탕으로 chi게 파라메터를 줄이면서 펄스폭을 최소화하는 방향으로 펄스의 세기와 필터의 대역폭을 변화시켜가면서 기존의 것에 비해 chirp 파라메터는 2배, 펄스폭은 4배 줄일 수 있는 조건을 찾아 향상된 특성의 레이저 공진기를 설계하였다.

• 반도체공학회 논문지
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• 제2권2호
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• pp.1-9
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• 2024

반도체 소자의 집적도는 높아져 왔으며 이는 더 작고 밀도가 높은 회로 및 소자를 제조하는 것을 의미한다. 이에 따라 다양한 층간 표면을 매끄럽게 유지하여 미세한 패턴을 형성하고 고밀도 회로를 안정적으로 제작하는데 평탄화 기술이 중요한 역할을 한다. 결과적으로 반도체에서의 CMP(chemical mechanical polishing) 공정은 다층 구조 소자를 만들기 위해서 반드시 필요한 공정이 되었다. 일반적으로 CMP 공정의 슬러리 조성은 세리아(ceria), 분산제(dispersant), 물(DI water) 이렇게 3 가지 성분이 균형을 이루는 것이 중요하다. 본 연구에서는 AMP(2-Amino-2-methyle-1-propanol) 함량을 달리한 양쪽성 계면활성제를 사용한 세리아 슬러리 안정성 연구를 수행하였다. 결과적으로 AMP 함량에 따라 카복실기(-COOH) 영향으로 pH 안정화 되었으며, 세리아 슬러리 응집현상이 발생하지 않았으며 분산 안정성 문제가 없는 것으로 확인되었다.

• Smart Structures and Systems
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• 제33권1호
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• pp.41-53
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• 2024

Grouting sleeves are an essential connecting component of prefabricated components, and the quality of grouting has a significant influence on structural integrity and seismic performance. The embedded grouting sleeve (EGS)'s grouting defects are highly undetectable and random, and no effective monitoring method exists. This paper proposes an ultrasonic guided wave method and provides a set of guidelines for selecting the optimal frequency and suitable period for the EGS. The optimal frequency was determined by considering the group velocity, wave structure, and wave attenuation of the selected mode. Guided waves are prone to multi-modality, modal conversion, energy leakage, and dispersion in the EGS, which is a multi-layer structure. Therefore, a time-reversal (TR)-based multi-mode focusing and dispersion automatic compensation technology is introduced to eliminate the multi-mode phase difference in the EGS. First, the influence of defects on guided waves is analyzed according to the TR coefficient. Second, two major types of damage indicators, namely, the time domain and the wavelet packet energy, are constructed according to the influence method. The constructed wavelet packet energy indicator is more sensitive to the changes of defecting than the conventional time-domain similarity indicator. Both numerical and experimental results show that the proposed method is feasible and beneficial for the detection and quantitative estimation of the grouting defects of the EGS.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1434-1443
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• 1999

The turbulent fluctuations of temperature and two components of velocity have been measured with hot- and cold-wires in the Thermally Stratified Wind Tunnel(TSWT). Using the fin-tube heat exchanger type heaters and the neural network control algorithm, both stable ($dT/dz=109.4^{\circ}C$) and unstable ($dT/dz=-49.1^{\circ}C$) stratifications were realized. An ambient air jet was issued normally into the cross flow($U_{\infty}=1.0 m/s$) from a round nozzle(d = 6 mm) flushed at the bottom waII of the wind tunnel with the velocity ratio of $5.8(U_{jet}/U_{\infty})$. The characteristics of turbulent dispersion in the cross flow jet are found to change drastically depending on the thermal stratification. Especially, in the unstable condition, the vertical velocity fluctuation increases very rapidly at downstream of jet. The fluctuation velocity spectra and velocity-temperature cospectra along the jet centerline were obtained and compared. In the case of stable stratification, the heat flux cospectra changes Its sign from a certain point at the far field because of the restratification phenomenon. It is inferred that the main reason in the difference between the vertical heat fluxes is caused by the different length scales of the large eddy motions. The turbulent kinetic energy and scalar dissipation rates were estimated using partially non-isotropic and isotropic turbulent approximation. In the unstable case, the turbulent energy dissipation decreases more rapidly with the downstream distance than in the stable case.