• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.46.1-46.1
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• 2010

This work is a part of our project to establish a Website which provides a list of magnetic clouds (MCs) identified by WIND and ACE spacecraft. MCs are characterized by their magnetic fields that are well described by magnetic flux rope structures, whereas interplanetary coronal mass ejections (ICMEs) are interplanetary manifestations of coronal mass ejections (CMEs), usually identified by differences of plasma and magnetic field characteristics from those in the background solar wind. It is widely accepted that, while MCs are generally identified within ICMEs, the number of MCs are significantly lower than the number of ICMEs. In our effort to identify MCs, however, we have found that there was a big problem in identification method of MCs in previous works. Generally speaking, most of the previous surveys failed in identifying MCs which encounter the spacecraft at large distances from the MC axis, or near the surface of MC structures. In our survey, MCs are identified as the region of which magnetic fields are well described by appropriate flux rope models. Thus, we could selected over 45 MCs, in 1999 solar wind data for instance, while 33 ICMEs are listed in the Website of the ACE Science Center reported by Richardson and Cane.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.107-148
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• 1992

This paper presents a cosmological perturbation analysis in a Newtonian framework, using the Newtonian multi component version of the relativistic covariant equations. This work considers the fully nonlinear evolution of the perturbations, and is generalized to multicomponent systems and imperfect fluids. Known nonlinear solutions are presented in a general framework. Quasi-nonlinear analysis, considering both the compressible and rotational modes, is presented, including cases already known in the literature. The Fourier space representation of the conservation equations is also derived in a general context, with various decompositions of the velocity field. Commonly accepted cosmogonical frameworks are critically examined in the context of nonlinear evolution. This work may be regarded as the Newtonian counterpart of a recently presented general relativistic covariant formulation.

• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.1-8
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• 2009

A plane-parallel model of the diffuse Galactic light (DGL) is calculated assuming exponential disks of interstellar dust and OB stars, by solving exactly the radiative transfer equation using an iterative method. We perform a radiative transfer calculation for a model with generally accepted scale heights of stellar and dust distribution and compare the results with those of van de Hulst & de Jong for a constant slab model. We also find that the intensity extrapolated to zero dust optical depth has a negative value, against to the usual expectation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.240-246
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• 2016

The hottest news and achievements of space science and research in recent years may be NASA Curiosity rover's exploration (2013) of Mars, China Chang'e 3's exploration (2013) of Moon, ESA Rosetta's exploration (2014) of Comet 67P/Churyumov-Gerasimenko, and NASA New Horizons' exploration (2015) of Pluto, which are very astonishing achievement since such a deep space journey was possible with current technology. In contrast the wonderful cruise and navigation technologies evolution of explorer in deep space, there are no remarkable changes in deep space data communication, it is still in conservative area, of which much changes are reluctantly accepted so far. But there are some movements of deep space exploration in order to allow ground brilliant technologies to deep space. One of those experiments is internet, whose main topic of this paper. In this paper, we will present the analysis of effectiveness of solar system internet to deep space exploration.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.36.3-37
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• 2009

This is an attempt to improve a formula to predict variations of geomagnetic storm indices (Dst) from solar wind parameters. A formula which is most widely accepted was given by Burton et al. (1975) over 30 years ago. Their formula is: dDst*/dt = Q(t) - Dst*(t)/$\tau$, where Q(t) is the Dst injection rate given by the convolution of dawn-to-dusk electric field generated by southward solar wind magnetic field and some response function. However, they did not clearly specify the response function. As a result, misunderstanding seems to be prevailing that the injection rate is proportional to the dawn-to-dusk electric field. In this study we tried to determine the response function by examining 12 intense geomagnetic storms with minimum Dst < -200 nT for which solar wind data are available. The method is as follows. First we assume the form of response function that is specified by several time constants, so that we can calculate the injection rate Q1(t) from the solar wind data. On the other hand, Burton et al. expression provide the observed injection rate Q2(t) = dDst*/dt + Dst*(t)/$\tau$. Thus, it is possible to determine the time constants of response function by a least-squares method to minimize the difference between Q1(t) and Q2(t). We have found this simple method successful enough to reproduce the observed Dst variations from the corresponding solar wind data. The present result provides a scheme to predict the development of Dst 30 minutes to 1 hour in advance by using the real time solar wind data from the ACE spacecraft.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.43-50
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• 2020

We have developed an algorithm for tracking coronal mass ejection (CME) propagation that allows us to estimate CME speed and its arrival time at Earth. The algorithm may be used either to forecast the CME's arrival on the day of the forecast or to update the CME tracking information for the next day's forecast. In our case study, we successfully tracked CME propagation using the algorithm based on g-values of interplanetary scintillation (IPS) observation provided by the Institute for Space-Earth Environmental Research (ISEE). We were able to forecast the arrival time (Δt = 0.30 h) and speed (Δv = 20 km/s) of a CME event on October 2, 2000. From the CME-interplanetary CME (ICME) pairs provided by Cane & Richardson (2003), we selected 50 events to evaluate the algorithm's forecast capability. Average errors for arrival time and speed were 11.14 h and 310 km/s, respectively. Results demonstrated that g-values obtained continuously from any single station observation were able to be used as a proxy for CME speed. Therefore, our algorithm may give stable daily forecasts of CME position and speed during propagation in the region of 0.2-1 AU using the IPS g-values, even if IPS velocity observations are insufficient. We expect that this algorithm may be widely accepted for use in space weather forecasting in the near future.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.52-52
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• 2014

It is widely accepted that the evolution of galaxies is accelerated in dense environments. According to recent studies, however, the evolution by direct interactions between galaxies is known to be most active in a galaxy group rather than in a galaxy cluster. In particular, the central galaxy in a group is closely related to its satellites in the properties such as morphology, color and star formation rate, because those galaxies evolve together in a small-scale environment. Currently, however, it is not yet studied well whether such conformity between bright galaxies and their faint companions remains after a galaxy group falls into a galaxy cluster. Recently, Lee et al. (2014) have found that the colors of bright galaxies show a measurable correlation with the mean colors of faint companions around them in WHL J085910.0+294957, a galaxy cluster at z = 0.3, which may be the vestige of infallen groups in the cluster. As a follow-up study, we study Abell 2744, an ongoing cluster-cluster merger at z = 0.308, using the HST Frontier Fields Survey data. The cluster members are selected based on the distributions of color, size and concentration along magnitude. The correlation in color between bright galaxies and their companions is not found in the full area of Abell 2744. However, when the area is limited to the southeastern part of the Abell 2744 image, the mean color of faint companions shows marginal dependence (> $2{\sigma}$ to Bootstrap uncertainties) on the color of their adjacent bright galaxy. We discuss the implication of these results, focusing on their dependence on local environments.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.35.2-35.2
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• 2014

Today, it is widely accepted that dense environments tend to accelerate galaxy evolution. However, according to recent studies, the environments where galaxies evolve most considerably are galaxy groups rather than galaxy clusters. In an isolated group, the central host galaxy and its satellites co-evolve and interact with each other; as a result, they tend to have similar properties. Such conformity between host and satellite galaxies are relatively well known in galaxy groups, but it is hardly studied what happens after such galaxy groups merge into a galaxy cluster. Recently, J. H. Lee et al. (2014) have found that the colors of bright galaxies in WHL J085910.0+294957, a galaxy cluster at z = 0.3, show a measurable correlation with the mean colors of faint companions around them, which may be the vestige of infallen groups in the cluster. As a follow-up study, we explore more galaxy clusters, Abell 3659 and Abell 1146 at z ~ 0.1, using deep images obtained from the Magellan (Baade) 6.5-m telescope. Cluster members are selected based on the distributions of color, size and concentration along magnitude and spatial distribution. We investigate the dependence of the mean colors of faint companion galaxies on local environments and the properties of adjacent bright galaxies. After comparing the results with those in J. H. Lee et al. (2014), we discuss the origin of the relationships between bright galaxies and their faint companions based on their dependence on cluster properties.

• Journal of the Korean housing association
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• v.26 no.6
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• pp.61-69
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• 2015

Current criticism regarding the "uniformity" of Korean apartments has shown not only tendencies of emotional and unscholarly criticism, but also lack of academic discourse. They tend to stay at the common-sense level and be quite subjective without supporting facts. This research began with questioning the phenomenon of seeing Korean apartments as an object of negative criticism. The research questions for this study are: 1. Of the living space of so-called apartment houses, what elements should be called uniform?; 2. How should the implications of the findings be interpreted? In this context, this study aims to reinterpret criticisms on the uniformity of apartments from a new point of view. First, literature review is done to examine characteristics of Korean apartments in the social-cultural, economic, and physical contexts. Next, existing non-academic, abstract criticisms are classified into three trends, to show that the way of understanding architectural spaces by those criticisms are limited and weighted towards visual perceptions focused only on the shape of architectural structures. Finally, it is argued that the viewpoints of space and residents' experience should be treated as important for the reinterpretation of criticisms on the uniformity. This is validated through presenting relevant cases such as changes of space uses, diversified lifestyles being accepted, and the expansion of living space.

• Smart Structures and Systems
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• v.14 no.1
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• pp.17-37
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• 2014

In this study, four widely accepted and used variants of Evolution Strategies (ES) are adapted and applied to the output-error state-space identification problem. The selection of ES is justified by prior strong indication of superior performance to similar problems, over alternatives like Genetic Algorithms (GA) or Evolutionary Programming (EP). The ES variants that are being tested are (i) the (1+1)-ES, (ii) the $({\mu}/{\rho}+{\lambda})-{\sigma}$-SA-ES, (iii) the $({\mu}_I,{\lambda})-{\sigma}$-SA-ES, and (iv) the (${\mu}_w,{\lambda}$)-CMA-ES. The study is based on a six-degree-of-freedom (DOF) structural model of a shear building that is characterized by light damping (up to 5%). The envisaged analysis is taking place through Monte Carlo experiments under two different excitation types (stationary / non-stationary) and the applied ES are assessed in terms of (i) accurate modal parameters extraction, (ii) statistical consistency, (iii) performance under noise-corrupted data, and (iv) performance under non-stationary data. The results of this suggest that ES are indeed competitive alternatives in the non-linear state-space estimation problem and deserve further attention.