• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.95.1-95.1
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• 2012

Halo coronal mass ejections (HCMEs) are major cause of geomagnetic storms and their three dimensional structures are important for space weather. In this study, we compare three cone models: an elliptical cone model, an ice-cream cone model, and an asymmetric cone model. These models allow us to determine the three dimensional parameters of HCMEs such as radial speed, angular width, and the angle (${\gamma}$) between sky plane and cone axis. We compare these parameters obtained from three models using 62 well-observed HCMEs from 2001 to 2002. Then we obtain the root mean square error (RMS error) between maximum measured projection speeds and their calculated projection speeds from the cone models. As a result, we find that the radial speeds obtained from the models are well correlated with one another (R > 0.84). The correlation coefficients between angular widths are less than 0.53 and those between ${\gamma}$ values are less than 0.47, which are much smaller than expected. The reason may be due to different assumptions and methods. The RMS errors of the elliptical cone model, the ice-cream cone model, and the asymmetric cone model are 213 km/s, 254 km/s, and 267 km/s, respectively. Finally, we discuss their strengths and weaknesses in terms of space weather application.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.81.2-81.2
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• 2019

We develop an image-to-image translation model, which is a popular deep learning method based on conditional Generative Adversarial Networks (cGANs), to generate solar magnetograms and EUV images from sunspot drawings. For this, we train the model using pairs of sunspot drawings from Mount Wilson Observatory (MWO) and their corresponding SDO/HMI magnetograms and SDO/AIA EUV images (512 by 512) from January 2012 to September 2014. We test the model by comparing pairs of actual SDO images (magnetogram and EUV images) and the corresponding AI-generated ones from October to December in 2014. Our results show that bipolar structures and coronal loop structures of AI-generated images are consistent with those of the original ones. We find that their unsigned magnetic fluxes well correlate with those of the original ones with a good correlation coefficient of 0.86. We also obtain pixel-to-pixel correlations EUV images and AI-generated ones. The average correlations of 92 test samples for several SDO lines are very good: 0.88 for AIA 211, 0.87 for AIA 1600 and 0.93 for AIA 1700. These facts imply that AI-generated EUV images quite similar to AIA ones. Applying this model to the Galileo sunspot drawings in 1612, we generate HMI-like magnetograms and AIA-like EUV images of the sunspots. This application will be used to generate solar images using historical sunspot drawings.

• Journal of Korean Association for Spatial Structures
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• v.4 no.1 s.11
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• pp.39-48
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• 2004

Generally, a structural system with large inextensional deformations, or in other words, non-strained deformation is called as 'Unstable Structure', Truss-linked structures, cable structures, membrane structures and movable structures as foldable space structures etc, are included in this category. In this paper, a dynamic analysis method for unstable structural systems is presented. Governing equations for dynamic analysis of unstable truss structures with inextensional displacements are derived. Because of singularity of inverse matrixin in practical analysis of unstable structure, the generalized inverse matrix is Introduced to resolve the singular problem. Also, the RREF technique is used to get the inextensional displacement mode. Two unstable truss structures are analyzed by using presented method. Damping is not considered. From the given results, it is known that proposed method is useful to figure out the dynamic behavior of unstable truss structures.

• Journal of The Korean Association For Science Education
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• v.28 no.6
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• pp.603-617
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• 2008

Inspired by the socio-cultural perspective on teaching and learning science, we have explored how the teacher and students interact with one another and develop meanings in science classrooms. Data came from four 10th grade science classrooms, and video recordings and verbatim transcripts of the lessons were analyzed. Focus of the analysis was on the participation structures as well as the possibility of developing the space for hybrid meaning making. The participation structures identified were mainly teacher-led, and students rarely took an active stance to initiate an opportunity for generating new meanings. However, some participation structures had the potential to develop a new discursive space in which hybrid meaning can be constructed through negotiation between participants. Implications for future research and more desirable educational practices were discussed based on the result.

• Journal of the Korean Mathematical Society
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• v.33 no.4
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• pp.1047-1067
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• 1996

In this paper, we are interested in left invariant flat affine structures on Lie groups. These structures has been studied by many authors in different contexts. One of the fundamental questions is the existence of complete affine structures for solvable Lie groups G, raised by Minor [15]. But recently Benoist answered negatively even for the nilpotent case [1]. Also moduli space of such structures for lower dimensional cases has been studied by several authors, sometimes with compatible metrics [5,10,4,12].

• Bulletin of the Korean Mathematical Society
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• v.38 no.3
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• pp.551-564
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• 2001

We view Weyl structures as generalizations of Riemannian metrics and study the critical points of geometric functional which involve scalar curvature, defined on the space of Weyl structures on a closed 4-manifold. The main goal here is to provide a framework to analyze critical Weyl structures by defining functionals, discussing function spaces and writing down basic formulas for the equations of critical points.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.4
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• pp.313-322
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• 2003

This research work presents 3-D behavior of adjacent structures due to tunnelling induced ground movements by means of field measuring data and nonlinear FEM tunnel analysis. The results of the analytical methods from Mohr-Coulomb model are compared with the site measurement data obtained during the twin tunnel construction. It was found that the location and stiffness of the structure influence greatly the shape and pattern of settlement trough. The settlement trough for Greenfield condition was different from the trough for existing adjacent structures. Therefore the load and stiffness of adjacent structures should be taken into account for the stability analysis of the structures.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.3
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• pp.17-21
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• 2004

Tape-wrapped structures have been generally used in nozzle parts of guided missiles. A continuous band of woven composite material is wrapped around a mandrel that is designed to produce real products. After going through a vacuum bagging process, this woven composite material is cured in a high-pressure autoclave or hydroclave. However, tape-wrapped structures are difficult to analyze because of its large thickness and inclined lay-up. The present study investigates the method of analysis and failure prediction of tape-wrapped structures. The four-point bending test and its finite element analysis were performed to study how to model tape-wrapped structures and investigate their failure characteristics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2502-2512
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• 2000

Truss structures are widely used in many space structures, such as large antenna systems, space stations, precision segmented telescopes because they are light in weight and amenable in assembly or deployment. But, due to the low damping capacity, they remain excited for a long time once disturbed. These structural vibrations can reduce life of the structures and cause unstable dynamic characteristics. In this research, vibration suppression experiment has carried out with a three-dimensional 15-member truss structure using two piezoelectric actuators. Piezoelectric actuators which consist of stacks of thin piezoelectric material disks are directly inserted to the truss structure collocated with the strain sensors. Each actuator is controlled digitally in decentralized manner, based on local integral and proportional feedback. The optimal positions of the actuators are determined by the modal damping ratio and the control force. Numerical simulation has carried out to determine optimal position of each actuator.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.57.2-57.2
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• 2019

BITSE is a balloon mission, which is a solar coronagraph to measure speed and temperature of the solar wind using 4 different wavelength filters and an pixelated polarization camera. KASI and NASA jointly designed, developed, and tested the solar coronagraph. Mainly KASI developed an imaging system and a control system, and NASA developed an optical system and mechanical structures. We mount the BITSE on Wallops Arc-Second Pointer (WASP) of Wallops Flight Facility, and launch it with a 39 mcf balloon of Columbia Scientific Ballon Facility. We will introduce the overall system of the BITSE.