• 천문학회지
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• 제37권4호
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• pp.137-141
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• 2004

We have estimated the fractal dimension of the molecular clouds in the Antigalactic Center based on the $^{12}CO$ (J = 1- 0) and $^{13}CO$ (J = 1- 0) database obtained using the 14m telescope at Taeduk Radio Astronomy Observatory. Using a developed code within IRAF, we were able to identify slice-clouds, and determined the dispersions of two spatial coordinates as well as perimeters and areas. The fractal dimension of the target region was estimated to be D = 1.34 for low resolution $^{12}CO$ (J = 1 - 0) database, and D = 1.4 for higher resolution $^{12}CO$ (J = 1 - 0) and $^{13}CO$ (J = 1 - 0) database, where $P {\propto} A^{D/2}$. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Our database with higher resolution of 1 arcminute, which is corresponding to 0.2 pc at a distance of 1.1 kpc, gives us the same estimate of fractal dimension to that of local dark clouds. Fractal dimension is apparently invariant when varying the threshold temperatures applied to cloud identification. According to the dispersion pattern of longitudes and latitudes of identified slice-clouds, there is no preference of elongation direction.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.605-610
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• 2014

Clouds play an important role in climate change, in the prediction of local weather, and also in aviation safety when instrument assisted flying is unavailable. Presently, various ground-based instruments used for the measurements of the cloud base height or velocity. Lidar techniques are powerful and have many applications in climate studies, including the clouds' temperature measurement, the aerosol particle properties, etc. Otherwise, it is very circumscribed in cloud velocity measurements because there is no Doppler effect if the clouds move in the perpendicular direction to the laser beam path of Doppler lidar. In this paper, we present a method for the measurement of cloud velocity using lidar's range detection and DIC (Digital Image Correlation) system to overcome the disadvantage of Doppler lidar. The lidar system acquires the distance to the cloud, and the cloud images are tracked using the developed fast correlation algorithm of DIC. We acquired the velocities of clouds using the calculated distance and DIC algorithm. The measurement values had a linear distribution.

• Journal of Information Processing Systems
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• 제16권1호
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• pp.120-131
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• 2020

In order to solve the problem of point clouds coordinate conversion of non-directional scanners, this paper proposes a basic Rodrigues rotation method. Specifically, we convert the 6 degree-of-freedom (6-DOF) rotation and translation matrix into the uniaxial rotation matrix, and establish the equation of objective vector conversion based on the basic Rodrigues rotation scheme. We demonstrate the applicability of the new method by using a bar-shaped emboss point clouds as experimental input, the three-axis error and three-term error as validate indicators. The results suggest that the new method does not need linearization and is suitable for optional rotation angle. Meanwhile, the new method achieves the seamless splicing of point clouds. Furthermore, the coordinate conversion scheme proposed in this paper performs superiority by comparing with the iterative closest point (ICP) conversion method. Therefore, the basic Rodrigues rotation method is not only regarded as a suitable tool to achieve the conversion of point clouds, but also provides certain reference and guidance for similar projects.

• 정보처리학회논문지A
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• 제16A권5호
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• pp.307-318
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• 2009

컴퓨터 그래픽스에서 구름과 같은 대기 현상을 모델링하고 렌더링하는 것은 그 복잡성과 규모, 편재성 등으로 인해 상당히 까다로운 연구과제들 중의 하나이다. 본 논문은 컴퓨터 게임이나 항공 시뮬레이션 분야에서 요구되는, 실시간에 처리될 수 있는 구름 모델링과 렌더링 방법을 제안한다. 제안하는 방법은 사용자가 직관적이고 대화형 편집 과정을 거쳐 권운, 층운, 적운 등의 다양한 형태를 생성할 수 있다. 또한, 메타볼과 계층적 구형 파티클을 사용하여, 세부 묘사를 자동으로 추가할 수 있다. 생성된 파티클들은 다중 순방향 산란과 이방성 산란을 고려하여 빌보드 방식으로 출력함으로써 실시간 처리가 가능하다.

• 한국군사과학기술학회지
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• 제22권5호
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• pp.716-723
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• 2019

It is crucial to understand the characteristics of cloud occurrence frequency for development of high precision guided missile using infrared imaging sensor. In this paper, we investigated the vertical structure of cloud for altitude using upper-air observation data. We find that cloud occurrence frequency is high at altitudes of 1.3 km and 9.5 km. Theses features have seasonal and temporal dependency. In the summer, cloud often occur more than average regardless of altitude. In the winter, low clouds occur frequently, and high clouds do not occur well. In temporal characteristics, clouds occur more frequently in daytime than in nighttime regardless of altitude. Many of clouds exist in single layer or double layers in the air. We also find that the 40 % of cloud occurrence frequency at high altitude when low clouds under altitude of 2 km cover entire sky.

• Journal of Information Processing Systems
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• 제17권4호
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• pp.787-800
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• 2021

Three-dimensional (3D) object classification tasks using point clouds are widely used in 3D modeling, face recognition, and robotic missions. However, processing raw point clouds directly is problematic for a traditional convolutional network due to the irregular data format of point clouds. This paper proposes a pointwise convolution neural network (CNN) structure that can process point cloud data directly without preprocessing. First, a 2D convolutional layer is introduced to percept coordinate information of each point. Then, multiple 2D convolutional layers and a global max pooling layer are applied to extract global features. Finally, based on the extracted features, fully connected layers predict the class labels of objects. We evaluated the proposed pointwise CNN structure on the ModelNet10 dataset. The proposed structure obtained higher accuracy compared to the existing methods. Experiments using the ModelNet10 dataset also prove that the difference in the point number of point clouds does not significantly influence on the proposed pointwise CNN structure.

• 천문학회보
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• 제46권1호
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• pp.56.2-56.2
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• 2021

Constraining the structure and thus the fate of giant molecular clouds (GMCs), the primary sites of star formation in galaxies, is crucial to understand the evolution of galaxies themselves. Exploiting the unprecedented sensitivity and angular resolution of the Atacama Large Millimeter/sub-millimeter Array (ALMA), we have measured the spatially-resolved (~ 20 pc resolution) properties of the GMCs in two nearby late-type galaxies, NGC 5806 (SAB(s)b) and NGC 6753 ((R)SA(r)b), as part of the WISDOM project. Although these results are preliminary, we identified ~ 200 resolved GMCs in NGC 5806 within a radius of 500 pc, most within a nuclear ring structure, and ~ 400 resolved GMCs in NGC 6753 within a radius of 2 kpc, most within a flocculent spiral structure. The GMCs of NGC 5806 have similar sizes but slightly higher linewidths than clouds in the Milky Way disc. Because the GMCs also have higher surface densities, the calculated cloud Virial parameters are nevertheless about unity, suggesting that the GMCs of NGC 5806 are in gravitational equilibrium and thus long lived. This is contrary to other WISDOM results on earlier-type galaxies, where large cloud linewidths are likely due to shear associated with the local (circular) orbital motions (rather than the clouds' self-gravity), and the clouds are either marginally or not gravitationally bound. These results support the notion that spheroids alter the dynamical states of clouds (morphological quenching), that are otherwise (i.e. in galaxy discs) fairly homogenous and similar to those of the Milky Way.

• 천문학회지
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• 제37권4호
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• pp.233-235
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• 2004

High-velocity clouds are flows of neutral hydrogen, located at high galactic latitudes, with large velocities ($[VLSR]{\ge} 100 km/s$) that do not match a simple model of circular rotation for our Galaxy. Numerical simulations have been performed for the last 20 years to study the details of their evolution, and their possible interaction with the Galactic disk. Here we present a brief review of the models that have been already published, and describe newly performed three-dimensional magnetohydrodynamic simulations.

• 천문학회지
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• 제29권spc1호
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• pp.39-40
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• 1996

Using the Keck 10 m telescope data with the HIRES spectrograph, we analyzed the evolution of Lyman$\alpha$ forest clouds at z > 2 down to the HI column density $10^{12.8}cm^{-2}$. The number density per unit column density does not change with redshifts at lower HI cloumn density ($N_{HI} < 10^{14}cm^{-2}$), while the forest clouds at higher column density disappear rapidly. The cutoff b value, the thermal temperature indicator, increases as redshift decreases. The correlation strength seems to be stronger as redshift decreases.

• 천문학회지
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• 제14권1호
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• pp.37-42
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• 1981

In order to know how the magnetic field increases with density in interstellar clouds, we have analyzed observations of extinction and polarization for stars in the ${\rho}$ Oph molecular cloud complex. The size of grains in dense parts of the complex is estimated to be larger than the ones in diffuse interstellar clouds by about 15 percent in radii. Employing the Davis-Greenstein mechanism for grain alignment with this estimated grain size, we have put constraints on the exponent in the field-density relation $B{\propto}n^x:1/5{\leq}x{\leq}1/3$. It is concluded that magnetic field in gravitationally contracting clouds increases less steeply than the classical expectation based on the approximation of isotropic contraction with complete frozen-in flux.