• International Journal of Railway
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• 제4권4호
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• pp.109-115
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• 2011

An analysis and design method for reducing aerodynamic noise in high-speed trains based on biomimetics of noiseless flight of owl is proposed. Five factors related to the morphology of the flight feather have been selected, and the candidate optimal shape of the flight feather is determined. The turbulent flow field analysis demonstrates that the optimal shape leads to diminished vortex formation by causing separation of the flow as well as allowing the fluid to climb up along the surface of the flight feather. To determine the effect of scaling of the owl's flight feather on the noise reduction, a two-fold and a four-fold scaled up model of the feather are constructed, and the numerical simulations are carried out to obtain the aerodynamic noise levels for each scale. Original model is found to reduce the noise level by 10 dBA, while two-fold increase in length dimensions reduces the noise by 12 dBA. Validation of numerical solution using wind tunnel experimental measurements is presented as well.

• 천문학회보
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• 제41권1호
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• pp.68.4-69
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• 2016

We report preliminary results of KaVA observations of central galaxies in cool-core and non cool-core clusters. The main goal is to study how cooling environments of galaxy clusters affect the central AGN activities especially at its innermost region. For KaVA observations, 7 radio bright AGNs have been selected from the extended Highest Flux Galaxy Cluster Sample (eHIFLUGCS; the X-ray flux limited & all sky galaxy cluster catalog) with various cooling timescales. In our previous KVN study, we have found that most AGNs in the cool-core clusters show the hint of pc-scale jet-like features while the ones in the non cool-core clusters do not. Using the KaVA 22/43 GHz data of a much higher resolution than the KVN resolution, we have investigated detailed pc-scale jet properties such as physical size, morphology, and radiative age. Based on the KaVA data, we discuss the effect of cluster cooling environment on the evolution of AGNs in the cluster center.

• 천문학회보
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• 제37권2호
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• pp.77.2-77.2
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• 2012

We have studied the physical properties of X-ray point sources in galaxy clusters for years based on the archival observations using the most sophisticated space X-ray observatory, Chandra X-ray Observatory. Because the ultimate goal of the study is comparing the physical properties of X-ray point sources found in galaxy clusters to those in X-ray blank fields; blank fields are the regions in the sky where any noticeable cosmic diffuse X-ray emission is not observed, an important key issue regarding this study is picking out the point sources related with galaxy clusters. However we do not have red-shift information of all the X-ray point sources. Therefore as a first order approximation we will consider the point sources with smaller projected cluster-centric distance than the adopted size of galaxy clusters. As a first step of this study we perform X-ray surface photometry of ~600 galaxy clusters based on ~800 Chandra ACIS observations. We carefully investigate the radial structures of diffuse X-ray emission in 3 different energy bands. Based on the highly accurate surface photometry we determine the characteristic size of diffuse X-ray emission (i.e., the boundary of X-ray emission). We also investigate the cosmological evolution of this characteristic size of galaxy clusters. General discussion regarding the two dimensional morphology of galaxy clusters will be presented.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.460-463
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• 2000

The current-voltage characteristics of the sandwich system at different annealing temperatures and different bias voltages have been studied. In order to prepare the Al/V$O_X$/Al sandwich devices structure, thin films of vanadium oxide(V$O_X$) was deposited by r.f. magnetron sputtering from $V_2$$O_5$ target in 10% gas mixture of argon and oxygen, and annealed during lhour at different temperatures in vacuum. Crystall structure, surface morphology, and thickness of films were characterized through XRD, SEM and I-V characteristics were measured by electrometer. The films prepared below 20$0^{\circ}C$ were amorphous, and those prepared above 300 $^{\circ}C$were polycrystalline. At low fields electron injected to conduction band of vanadium oxide and formed space charge, current was limited by trap. Conduction mechanism at mid fields due to Schottky emission, while at high fields it changed to Fowler-Nordheim tunneling effects.

• 천문학회보
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• 제44권1호
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• pp.69.1-69.1
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• 2019

We present the ALMA observations of the infrared dark cloud (IRDC) core MSXDC G053.11+00.05 MM1 at the distance of 1.7 kpc. While the core was first identified at 1.2 mm with a mass of 124 Msun, recent near- and mid-infrared observations have revealed a parsec-scale molecular hydrogen (H2 1-0 S(1) at 2.12 micron) outflow and two early class young stellar objects (YSOs) at the center of the core, one of which is likely massive (M > 8 Msun). From the ALMA Band 7 observations with a resolution of 0.5", we have found a dust filament of < 0.1 pc in which five dense cores are embedded in the 870 micron continuum. The brightest core is consistent with one of the two previously-detected YSOs, but the other four are newly discovered implying their very deeply embedded status. We have also detected several molecular line emission including H13CO+ and C17O as well as 13CO outflow with complicated morphology. At the brightest core, the methanol line (CH3OH) shows velocity gradients, which may support the existence of a circumstellar disk around a high-mass protostar. Based on the derived properties of the dense cores, we discuss their association with the two YSOs and H2 outflow detected in infrared and high-mass star-formation process occurring in IRDC cores.

• 천문학회보
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• 제45권1호
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• pp.59.3-60
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• 2020

We present the results of polarization observations at submillimeter wavelengths towards Monoceros R2 (Mon R2). The polarized thermal dust emission was obtained from SCUBA-2/POL-2 at 450 ㎛ and 850 ㎛, simultaneously. This observation is a part of the JCMT BISTRO survey project. The polarization angle distributions at 450 ㎛ and 850 ㎛ are similar and the mean value of angle differences at two wavelengths is 5.5 degrees. The Mon R2 is one of massive star-forming regions containing a clear hub-filamentary structure. The hub region shows star formation activities, and surrounding filaments provide channels for matters to move into the hub region. It is not well known the role of magnetic fields in a hub-filamentary structure. Some studies have shown well-ordered polarization segments along a filamentary structure and magnetic field morphology traced by polarization segments is interpreted as to help gas flow along the filamentary structrue. Our observations shows that filaments in Mon R2 have spiral structure and the magnetic field lines are parallel to the filaments. We interpret that the spiral structure can be formed by a rotation hub-filament system with gas flowing along the filaments to the hub. We found several dust clumps at the central part of the hub region of the Mon R2. They seems to be formed at locations where spiral field lines meet each other. These results show one observational example that a magnetic field play a role in gas flow.

• 천문학회보
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• 제45권1호
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• pp.30.2-31
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• 2020

We present the properties of circumnuclear gas associated with the AGN located in the center of Abell 1644-South. A1644-S is the main cluster in a merging system, which is also known for gas sloshing in its core as seen in X-ray. The X-ray emission of A1644-S shows a rapidly declining profile, indicating the presence of cooling gas flow. This flow of cool gas may fuel the supermassive black hole embedded in the brightest cluster galaxy, leading to the activation of the central AGN. Indeed, we find a parsec-scale bipolar jet feature in the center of A1644-S in our recent KaVA observation, which implies that its central AGN is likely to have been (re)powered quite recently. In order to verify the hypothesis that cooling gas flow in the cluster core can (re)activate the central AGN, we probe the cold gas properties of the central 1 kpc region of A1644-S using the archival VLA and ALMA data. Based on the spatially resolved morphology and kinematics of HI and CO gas, we challenge to identify inflow/outflow gas streams and clumps. We study the role of circumnuclear cool gas in fueling the centrally located cluster AGN in the cool-core environment. We also discuss how the feedback due to the (re)powered AGN affects the surrounding medium.

• 대한치과교정학회지
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• 제39권3호
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• pp.136-145
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• 2009

상기도 공간은 3차원 입체 구조물로서 두부규격방사선사진 등으로 분석하기에는 평가의 한계가 존재하였다. 본 연구는 최근 방사선 피폭량 등의 감소로 그 활용도가 높아진 cone beam CT (CBCT)를 이용하여 안면골격형태에 따른 상기도 공간의 면적, 전후방 폭경 및 측방 폭경을 측정하고 그 관련성을 알아보았다. 102명을 대상으로 CBCT (VCT, Vatech, Seoul, Korea)를 촬영하였으며, FH plane에 평행하면서 aa point (the most anterior point on the anterior arch of atlas), $CV_{2ia}$, $CV_{3ia}$ point (most infero-anterior point on the body of the second & third cervical vertebra)를 지나는 평면을 기준으로 설정하였다. 각 항목의 계측치는 one-way ANOVA를 이용하여 통계처리하고 Duncan test로 사후검정하였다. 연구 결과, 안면 골격형태에 따른 측방 폭경에는 유의한 차이가 없었다. Group 2 (Class II) 집단은 aa plane, $CV_2$ plane, $CV_3$ plane에 의해 형성된 상기도 공간의 단면적이 좁았으며, 전후방 폭경도 Group 3 (Class III)에 비해 유의성 있게 좁았다. 수직 안면골격형태와 정상 안면골격 형태간의 유의성 있는 차이는 없었으나, aa plane에서 형성된 상기도 공간의 전후방 폭경은 Group 1V (Class I vertical)가 Group 1N (Class I normal)에 비해 유의성 있게 좁은 것으로 나타났다 (p < 0.05).

• The Korean Journal of Pain
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• 제22권2호
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• pp.158-162
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• 2009

Background: The loss of resistance (LOR) method is most commonly used to identify the epidural space. This method is thought to rely on the penetration of the ligamentum flavum. Unfortunately the exact morphology of the ligamentum flavum is variable at different vertebral levels. Especially, it has been pointed out that the lower cervical ligamentum flavum may be discontinuous in the midline in up to 50% of patients. Thus, the LOR method may be inaccurate to confirm the cervical epidural space. The aim of this study is to determine which method is the safest and most exact for confirming the cervical epidural space. Methods: 100 adult, chronic renal failure patients who were undergoing an arteriovenous bridge graft for hemodialysis at the upper arm under cervical epidural anesthesia were recruited for this study. During the cervical epidural puncture, we identified the cervical epidural space by subjectively feeling the resistance with using a finger just through the ligamentum flavum, and we also used the drip infusion method, the loss of resistance method using air, and the hanging drop method. By using 5 grades, we classified the extent of whether or not the techniques were effective. Results: Using the drip infusion method, we identify the epidural space in all the patients as ＋/＋＋ grade. The catheter insertion method was also successful in identifying those epidural spaces over a ${\pm}$ grade. The pseudo LOR was over ${\pm}$ grade in 47 patients. Conclusions: The combined LOR/hanging drop with drip infusion method is useful for confirming the cervical epidural space.

• 천문학회지
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• 제36권spc1호
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• pp.21-27
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• 2003

In the present study, we have investigated morphology and evolution of small-scale Ha dynamic features on the quiet sun by analyzing video magnetograms and high resolution Ha images simultaneously taken for 5 hours at Big Bear Solar Observatory on April 18, 1997. From comparisons between time sequential longitudinal magnetograms and H$\alpha$ images covering $150" {\times} 150"$, several small-scale H$\alpha$ dynamic features have been observed at a site of magnetic flux cancellation. A close relationship between such features and cancelling magnetic fluxes has been revealed temporarily and spatially. Our results support that material injection by chromospheric magnetic reconnect ion may be essential in supporting numerous small-scale H$\alpha$ dynamical absorption features, being in line with recent observational studies showing that material injection by chromospheric magnetic reconnect ion is essential for the formation of solar filaments.