• Journal of the Korean Mathematical Society
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• v.56 no.6
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• pp.1689-1701
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• 2019

Let ${\star}$ be a semistar operation on the integral domain D. In this paper, we prove that D is a $G-{\tilde{\star}}-GCD$ domain if and only if D[X] is a $G-{\star}_1-GCD$ domain if and only if the Nagata ring of D with respect to the semistar operation ${\tilde{\star}}$, $Na(D,{\star}_f)$ is a G-GCD domain if and only if $Na(D,{\star}_f)$ is a GCD domain, where ${\star}_1$ is the semistar operation on D[X] introduced by G. Picozza [12].

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.75.3-75.3
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• 2019

Understanding how ram pressure stripping (RPS) affects the star formation activity of cluster galaxies is one of the important issues in astrophysics. To examine whether we can identify any discernible trend in the star formation activity of galaxies undergoing ram pressure stripping, we study the star formation properties of galaxies in the Virgo cluster for which high-resolution HI images are available. We first classify galaxies in the Extended Virgo Cluster Catalog into different stages of RPS based on their HI morphology, HI deficiency, and location in phase space. We then examine various star formation activity indicators of these galaxies, which include starburstiness, g - r color, and WISE [3.4]-[12] color. No noticeable enhancement in star formation was identified for galaxies undergoing early or active stripping. Our results suggest that star formation activity at best seems to be enhanced locally in such galaxies, making it challenging to detect with integrated photometry. With the combination of HI deficiencies and locations in phase space, we were instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, which agree with previous studies.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.49.1-49.1
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• 2018

The Xinfa Suanshu, which was an important astronomical book in East-Asia, was published in 1644. This book was including the star catalogue. We researched the data of 1365 stars recorded in this star catalogue (the equinox of the catalogue is identified to be 1628 year). According to our analysis, it can be presumed that the star catalogue's data were observed from at least two places or more. Based on historical background, we assumed that the Xinfa Sunashu's catalogue likely referenced knowledge from the Europe or Arab/Islamic culture. The researchers who have studied the Xinfa Sunashu's star catalogue have all focused on Brahe's star catalogue. But they did not provide clear evidence. Therefore, we are compared with the star data recorded in Tablae Rudolphinae. In conclusion, we confirmed that 881 stars among the 1365 stars were perfectly edited from position data of stars recorded in Brahe's star catalogue (1602).

• Bulletin of the Korean Mathematical Society
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• v.58 no.4
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• pp.837-851
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• 2021

Let R ⊆ L ⊆ S be ring extensions. Two star operations ${\ast}_1{\in}Star(R,S)$, ${\ast}_2{\in}Star(L,S)$ are said to be linked if whenever $A^{{\ast}_1}= R^{{\ast}_1}$ for some finitely generated S-regular R-submodule A of S, then $(AL)^{{\ast}_2}=L^{{\ast}_2}$. We study properties of linked star operations; especially when ${\ast}_1$ and ${\ast}_2$ are strict star operations. We introduce the notion of Prüfer star multiplication extension ($P{\ast}ME$) and we show that under appropriate conditions, if the extension R ⊆ S is $P{\ast}_1ME$ and ${\ast}_1$ is linked to ${\ast}_2$, then L ⊆ S is $P{\ast}_2ME$.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.51.1-51.1
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• 2021

Spiral arms greatly affect gas flows and star formation in disk galaxies. We use local 3D simulations of vertically-stratified, self-gravitating, gaseous disks under a stellar spiral potential to study the effects of spiral arms on galactic star formation as well as formation of gaseous spurs/feathers. We adopt the TIGRESS framework to handle radiative heating and cooling, star formation, and ensuing supernova (SN) feedback. We find that more than 90% of star formation takes place inside spiral arms. The global star formation rate (SFR) in models with spiral arms is enhanced by less than a factor of 2 compared to the no-arm counterpart. This supports the picture that spiral arms do not trigger star formation but rather redistribute star-forming regions. Correlated SN feedback produces interarm feathers in both magnetized and unmagnetized models. These feathers live short, have parallel magnetic fields along their length, and are bounded by SN feedback in the lateral direction, in contrast to instability-induced feathers formed in our previous isothermal simulations.

• Publications of The Korean Astronomical Society
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• v.25 no.4
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• pp.129-139
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• 2010

The Cowherd Star and the Weaving Maid Star have been famous stars in East Asian countries. Nowadays Altair is defined to be the Cowherd Star in public materials including science books, mass media, public outreach programs, and movies played in public planetariums and science museums. However, in astronomical books and star-charts in history, the Cowherd Big Star (牽牛大星) has been known to be Dabih or $\beta$ Cap in the constellation Capricorn, and the asterism Cowherd consists of six stars including Dabih. Since the same title is given to the different objects simultaneously, considerable misunderstanding and confusion among the public have occurred. In this paper we consider this problem in two aspects. One aspect is which star has been defined to be the Cowherd Star in ancient literatures; the other is which stars were regarded as the Cowherd or the Cowherd Star in the historical records of occultation or conjunction in History of Koryo, Annals of the Choson Dynasty, and Daily Records of Royal Secretariat of the Choson Dynasty. As a result, we see that Altair has been regarded as the Cowherd Star in folklore and literature, but Dabih has been defined to be the Cowherd Big Star in astronomical works. An explanation proposed by previous researchers on the reason why such double meanings have been appeared is introduced. In the explanation, the fact that the Altair was defined as the Cowherd Star in ancient times had not been handed over properly, and the name of Cowherd was later put to the Dabih and its surrounding five stars to form one of 28 lunar lodges. Based upon these facts, we suggest the following ideas: (1) Altair should be introduced to be the Cowherd Star in public-friendly programs, and Dabih should be noticed to be the Cowherd Big Star in the field of history of astronomy. Dabih should be added as the astronomical Cowherd Big Star in academic books such as a dictionary of astronomical terminology. (2) The Korean pronunciation for Altair should be al-tear instead of al-tairu in accordance with the definition in the astronomical terminology dictionary compiled by the Korean Astronomical Society.

• Journal of Families and Better Life
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• v.25 no.5
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• pp.15-29
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• 2007

The purposes of this study were to examine if there is a relationship between elderly people's anxiety towards death and their reactions to the Star-Wave drawing, and to verify if the Star-Wave drawing was a good enough tool to measure elderly people's degree of death anxiety. The subject for this study were 307 elderly people (male 127, female 180) over 60 years of age with no physical and cognitive damage, who were residing in Geongsan city and attending colleges or welfare centers for the aged. The collected data were analyzed with SPSS WIN(ver. 12.0) program, and factor analysis, correlation analysis, Chi-square test, t-test, one-way ANOVA, and $Scheff\acute{e}$ test were utilized. The results showed that factors showing different levels of anxiety towards death in the Star-Wave drawing were the total harmony of the drawing, drawing style, repetition of wave, size of the star, and location of the star. In particular, the group that drew the Star-Wave drawing with total harmony felt less anxiety towards death than the other group. Therefore, the results of this study suggested a possibility of the Star-Wave drawing to be used as a good tool that could diagnose the elderly's degree of anxiety towards death.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.3
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• pp.300-308
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• 2010

In order to accelerate the evolution of faster, better, cheaper spacecraft, it is evident that greatly enhanced general-purpose attitude determination methods are needed Currently, star tracker sensors based on charge coupled devices (CCD) or active pixel sensors(APS) enable one to obtain the best spacecraft attitude estimation among the existing sensors for attitude determination. In this paper, basic principles of star tracker technology are explained including major issues arising in design and development of star tracker. Also, an historical overview and worldwide survey associated with various star trackers from star scanner through microelectromechanical system(MEMS)-based star tracker is offered.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.44.2-44.2
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• 2018

G33.92+0.11, classified as a core-halo UC HII region at a distance of 7.1 kpc, contains several sub-clumps (~20-200 solar masses) as identified by dust continuum emission. This source shows very complicated features associated with vigorous massive star-forming activities with a nearly face-on projection. The ambient gas is still accreting to the massive molecular clumps dynamically, while the whole cloud is under disruption by newly formed stars. Using the recent high resolution (< 0.2") ALMA observations, we investigate the detailed structure associated with the star-forming activities by comparing different chemical tracers. The sub-clumps having extremely complex morphologies still preserve cold dense gas together with the turbulent and dense warm gas resulted by newly formed stars and interaction with accreting gas. The accretion of the ambient gas may have occurred episodically to this source. Most recent star formation, which probably the third generation of star formation in this region, is taking place in the northern part (A5 clump). The relatively small mass (~ 1/3 of A1 or A2) and the lack of turbulent gas of this star-forming core may suggest that this core was formed already during the overall collapse of the whole cloud for the first star formation. We think that gravitational collapse of these sub-clumps appears as sequential star formation of this region. The later interaction with accreting gas may have not been a direct cause of the star formation activities of this source.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.78.1-78.1
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• 2011

We report on a photometric study of star clusters in the circumnuclear star-forming region of nearby barred spiral galaxy NGC 1672. We use FUV to NIR imaging data (FUV, U, B, V, R, $H{\alpha}$, I, and H) in the Hubble Space Telescope (HST) archive. We have selected 89 star clusters with V<21.8 (MV<-9) mag in the central 600 pc region, and have derived their age & mass by comparing their colors with theoretical population synthesis models. Most of the star clusters are mildly reddened (E(B-V)~0.2 on average), but some star clusters suffer from severe reddening (E(B-V)>0.6). The mass of the star clusters are in the range from $10^4\;M_{\odot}$ to $10^7\;M_{\odot}$. About half of them are more massive than $10^5\;M_{\odot}$. Their ages range from 1 Myr to several 100 Myr, and concentrate at ~6 Myr and ~40 Myr. It indicates that the episodic starburst in the circumnuclear star-forming region lasted at least several 100 Myr. We find no obvious azimuthal age gradient, but we find a radial age gradient in some regions. We discuss these properties with theoretical expectations.