• 제목/요약/키워드: Strong Edge

검색결과 296건 처리시간 0.031초

Comparison of the extraplanar Hα and UV emissions in the halos of nearby edge-on spiral galaxies

  • Jo, Young-Soo;Seon, Kwang-il;Shinn, Jong-Ho;Yang, Yujin;Lee, Dukhang;Min, Kyoung-Wook
    • 천문학회보
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    • 제43권2호
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    • pp.52.3-53
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    • 2018
  • We compare vertical profiles of the extraplanar $H{\alpha}$ emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the "diffuse" extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar $H{\alpha}$ emission. A strong correlation between the scale heights of the extraplanar $H{\alpha}$ and UV emissions is also found; the scale height at $H{\alpha}$ is found to be ~0.74 of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar $H{\alpha}$ emission is detected suggests that a larger portion of the extraplanar $H{\alpha}$ emission than that predicted in previous studies may be caused by $H{\alpha}$ photons that originate from H II regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise an advantage in studying the extraplanar diffuse ionized gas. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.

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Numerical study on Reynolds number effects on the aerodynamic characteristics of a twin-box girder

  • Laima, Shujin;Wu, Buchen;Jiang, Chao;Chen, Wenli;Li, Hui
    • Wind and Structures
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    • 제28권5호
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    • pp.285-298
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    • 2019
  • For super long-span bridges, the aerodynamic forces induced by the flow passing the box girder should be considered carefully. And the Reynolds number sensitively of aerodynamic characteristics is one of considerable issue. In the study, a numerical study on the Reynolds number sensitivity of aerodynamic characteristic (flow pattern, pressure distribution and aerodynamic forces) of a twin-box girder were carried out using large eddy simulation (LES) with the dynamic Smagorinsky-Lilly subgrid model. The results show that the aerodynamic characteristics have strong correlation with the Reynolds number. At the leading edge, the flow experiences attachment, departure, and reattachment stages accompanying by the laminar transition into turbulence, causing pressure plateaus to form on the surface, and the pressure plateaus gradually shrinks. Around the gap, attributing that the flow experiences stages of laminar cavity flow, the wake with alternate shedding vortices, and turbulent cavity flow in sequence with an increase in the Reynolds number, the pressures around the gap vary greatly with the Reynold number. At the trailing edge, the pressure gradually recovers as the flow transits to turbulence (the flow undergoes wake instability, shear layer transition-reattachment station), In addition, at relative high Reynolds numbers, the drag force almost does not change, however, the lift force coefficient gradually decreases with an increase in Reynolds number.

EFG법을 이용한 (100) β-산화갈륨 단결정 성장 및 라만 특성 연구 (Raman Characteristics of (100) β-Gallium Oxide Single Crystal Grown by EFG Method)

  • 신윤지;조성호;정운현;정성민;이원재;배시영
    • 한국전기전자재료학회논문지
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    • 제35권6호
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    • pp.626-630
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    • 2022
  • A 100 mm × 50 mm-sized (100) gallium oxide (Ga2O3) single crystal ingot was successfully grown by edge-defined film-fed growth (EFG). The preferred orientation and the quality of grown Ga2O3 ingot were compatible with a commercial Ga2O3 substrate by showing strong (100) orientation behaviors and 246 arcsec in X-ray rocking curve. Raman characterization was also performed for both samples; thereby providing various Raman-active characteristics of Ga2O3 crystals. In particular, we observed Ag(5) and Ag(10) peaks of Raman active mode, directly related to the impurity of the grown Ga2O3 crystal. Hence, the comparison of the crystal quality and Raman analysis might be useful for further enhancement of Ga2O3 single crystal quality in the future.

8 방향 색상 표현 기반 컨벌류션 정합(Convolution Matching)을 이용한 차량 검출기법 (Vehicle Detection Method Using Convolution Matching Based on 8 Oriented Color Expression)

  • 한성지;한영준;한헌수
    • 한국컴퓨터정보학회논문지
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    • 제14권12호
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    • pp.63-73
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    • 2009
  • 본 논문에서는 단순화한 색상 정보에 기반한 컨벌류션 정합(Convolution Matching)을 이용하여 차량을 검출하는 기법을 제안한다. 입력 영상을 화소 색상 벡터의 방향을 고려해 8방향 색상(Red, Green, Blue Cyan, Yellow, Magenta, White, Black)으로 표현한다. 8 방향 색상의 표현은 조명이나 환경 변화에 강인한 영상을 제공한다. 본 논문의 차량 검출 단계는 크게 후보 영역 검출 단계와 차량 검증 단계로 구성된다. 후보 영역 검출 단계에서는 수직 에지와 그림자 등을 고려하여 차량의 후보 영역을 결정한다. 차량 검증 단계에서는 차량을 판별하기 위해 컨벌류션 정합과 후보 영역내의 에지 복잡도를 사용한다. 제안하는 차량 검출 알고리즘은 조명이나 환경이 변화하는 다양한 실험들에서 빠르고 높은 검출률을 보였다.

원형 손상 구멍이 있는 날개 주위 유동장에 관한 실험적 연구 (An Experimental Investigation on the Flow Field around the Wing Having a Circular Damage Hole)

  • 이기영
    • 한국항공우주학회지
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    • 제36권10호
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    • pp.954-961
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    • 2008
  • 원형 손상구멍이 있는 날개 주위 유동장에 대한 실험연구를 수행하였다. 손상은 시위의 10% 직경의 시위에 수직인 원형 구멍으로, 구멍 중심은 1/4 시위 혹은 1/2 시위에 위치하고 있다. 입자영상유속계에 의한 유동장 측정과 날개의 아래 및 윗면에서의 정압장을 시위를 기준으로 한 레이놀즈수 Rec=2.85×105에서 측정하였다. 입자영상유속계에 의한 유동 측정 결과 손상 구멍 주위에는 두 가지 형태의 유동구조가 형성되었다. 하나는 약한 제트로 손상 구멍 하류에서 부착된 후류가 생성된다. 다른 하나는 받음각 증가에 의한 강한제트에 의한 것으로 손상구멍으로부터 자유흐름으로 관통되어 접근하는 경계층 흐름을 박리시켜 역류가 있는 박리 후류구조를 생성한다. 날개면 압력 자료는 원형 손상 구멍 근처에서 큰 압력변화를 보여주었다. 이러한 압력변화는 손상구멍이 앞전 쪽에 가까울수록 증가하였다.

Frequency Effects of Upstream Wake and Blade Interaction on the Unsteady Boundary Layer Flow

  • Kang, Dong-Jin;Bae, Sang-Su
    • Journal of Mechanical Science and Technology
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    • 제16권10호
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    • pp.1303-1313
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    • 2002
  • Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Wavier-Stokes code. The Wavier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.

2D-Video Distrometer를 이용한 강수의 물리적 특성에 관한 사례연구 (Case Study on the Physical Characteristics of Precipitation using 2D-Video Distrometer)

  • 박종길;천은지;정우식
    • 한국환경과학회지
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    • 제25권3호
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    • pp.345-359
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    • 2016
  • This study analyze the synoptic meteorological cause of rainfall, rainfall intensity, drop size distribution(DSD), fall velocity and oblateness measured by the 2D-Video distrometer(2DVD) by comparing two cases which are heavy rainfall event case and a case that is not classified as heavy rainfall but having more than $30mm\;h^{-1}$ rainrate in July, 2014 at Gimhae region. As a results; Over the high pressure edge area where strong upward motion exists, the convective rain type occurred and near the changma front, convective and frontal rainfall combined rain type occurred. Therefore, rainrate varies based on the synoptic meteorological condition. The most rain drop distribution appeared in the raindrops with diameters between 0.4 mm and 0.6 mm and large particles appeared for the convective rain type since strong upward motion provide favorable conditions for the drops to grow by colliding and merging so the drop size distribution varies based on the location or rainfall types. The rainfall phases is mainly rain and as the diameter of the raindrop increase the fall velocity increase and oblateness decrease. The equation proposed based on the 2DVD tends to underestimated both fall velocity and oblateness compared with observation. Since these varies based on the rainfall characteristics of the observation location, standard equation for fall velocity and oblateness fit for Gimhae area can be developed by continuous observation and data collection hereafter.

Sedimentary Excess Barium from a Core of the Northwest Pacific Ocean: Geochemical Proxy

  • Suk, Bong-Chool;Park, Chan-Hong;Taira, Asahiko;Hyun, Sang-Min
    • Journal of the korean society of oceanography
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    • 제35권2호
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    • pp.98-108
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    • 2000
  • A geochemical study on a hemipelagic core sediment taken from the northwest Pacific Ocean (eastern edge of the Shikoku Basin) was conducted to use of excess barium (Ba(ex)) for evaluate the paleoceano-graphic changes. Also, the excursion of sedimentary Ba(ex) was compared with those of biogenic opal, carbonate and organic carbon content in the sediment during the last glacial and interglacial periods. The calculated Ba(ex) derived from the major and minor element shows a distinctive glacial-interglacial variations, and the mass accumulation rate (MAR) of Ba(ex) shows coincident variations with the MARs of biogenic fractions. Especially, strong positive correlation (r$^2$=0.85) between the MAR of Ba(ex) and the MAR of biogenic carbonate is recognized. Based on the strong positive correlation(r$^2$=0.85) between the MAR of Ba(ex) and the MAR of carbonate content, we estimated the degree of carbonate dissolution rate during the glacial and interglacial periods. Assuming the proportional variation and the refractory nature of barium exist between two factors, the variation of index Ca/Ba ratio in sediment indicates the degree of carbonate dissolution. Sedimentary Ca/Ba ratios index clearly show a striking fluctuation between the glacial and interglacial periods with higher positive correlation during glacial and lower correlation during interglacial. This fact indicates enhanced carbonate dissolution during interglacial period. Thus, the sedimentary Ca/Ba ratio in sedimentary records can be used as one of the useful tools for estimation of the relative degree of carbonate dissolution. The excursion of Ba(ex) and the sedimentary Ca/Ba ratio follows the typical pacific carbonate dissolution type(enhanced dissolution during interglacial and reduced dissolution during glacial time) as suggested by previous work (e.g., Wu et al., 1990). Variation in sedimentary Ca/Ba ratio thus strongly supports that glacial-interglacial fluctuation in carbonate dissolution has been prevailed in the northwest Pacific Ocean.

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스핀코팅 및 저온열처리에 의한 자외선 발광특성을 갖는 산화아연 박막의 제조 (Preparation of ZnO Thin Films with UV Emission by Spin Coating and Low-temperature Heat-treatment)

  • 강보안;정주현
    • 한국안광학회지
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    • 제13권3호
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    • pp.73-77
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    • 2008
  • 목적: 본 논문은 저온열처리로 비결정 또는 결정 ZnO 박막의 UV emission 가능하다는 것이다. 방법: 화학적 용액법을 이용하여 소다-라임-실리카 유리 위에 100, 150, 200, 250 및 $300^{\circ}C$로 열처리하여 비정질 및 나노 결정질 ZnO 박막을 제조하였으며, 박막의 성장 특성 및 광학적 특성을 X-선 회절 분석법, 자외선-가시광선-근적외선 분광법 및 발광분석법을 통하여 분석하였다. 결과: $100^{\circ}C{\sim}200^{\circ}C$에서 60분간 열처리된 박막은 비정질 특성을 나타내고 있었으며, $250^{\circ}C$$300^{\circ}C$로 열처리된 박막에서는 ZnO 결정상이 나타났다. 비정질 ZnO 박막의 PL분석에 의하면 매우 강한 Near-band-edge emission이 나타났으며, Green emission은 거의 검출되지 않았다. 결론: 앞으로는 저온에서 ZnO 광전자소자를 쉽게 제조할 수 있을 것이다.

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Atomization Characteristics in Pneumatic Counterflowing Internal Mixing Nozzle

  • Lee, Sam-Goo;Rho, Byung-Joon
    • Journal of Mechanical Science and Technology
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    • 제14권10호
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    • pp.1131-1142
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    • 2000
  • In an effort to illustrate the global variation of SMD (Sauter mean diameter, or $D_{32}$) and AMD (Arithmetic mean diameter, or $D_{10}$) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA(Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterflowing internal mixing nozzles manufactured at an angle of $15^{\circ}$with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations in $D_{32}$ are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.

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