• 천문학회보
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• 제37권2호
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• pp.84.2-84.2
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• 2012

We present wide-field multiband photometry of globular cluster (GC) systems toward the central region of the Fornax cluster of galaxies, including NGC 1399, NGC 1404, and NGC 1387. Observation was carried out through four optical passbands (U, B, V, and I) with the Mosaic II CCD imager mounted on the 4-m Blanco telescope at Cerro Tololo Inter-American Observatory (CTIO). This marks one of the widest U-band photometric studies on GC systems. GC candidates are selected among point sources based on their two color diagrams together with a magnitude cut. We investigate the radial variation of color distributions for the GC systems, focusing on the fundamental parameters that characterize bimodal distributions; the number ratio between blue and red GCs, the mean colors of the groups, and their color dispersions. We discuss the implication of our result regarding the origin of GC color bimodality.

• Journal of Pharmaceutical Investigation
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• 제5권2호
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• pp.51-56
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• 1975

In the course of the investigations on drug metabolism and drug disposition in man, it has been noted that there are often rather striking individual differences in the response to drugs and in the ability to metabolize and dispose of drugs. Some of the person-to-person differences are due to environmental factors, but some have clearly demonstrated to be genetically determined. This report determined the rate of acetylation and some constants of sulfa-methizole to korean. The results are as follows: The overall removal rate of drug from the body is 0.572(k, $hr^{-1}$) the rate constant for acetylation, 0.222($k_2$, $hr^{-1}$) the rate constant for excretion of unchanged drug, 0.350($k_3$, $hr^{-1}$) and the faction of a dose ultimately excreted in the urine as unchanged drug is 0.677. And this report determined the optimal time to make a single blood level determination after an oral dose of the drug and obtain a reasonable index of the rate of sulfamethizole metabolism. The resulting data(sulfamethizole levels at 5 hours after drug administration) clearly established bimodality even though only about 106 subjects were tested.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.34.4-34.4
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• 2010

We present the properties of globular cluster systems for 10 early-type galaxies in low density environments obtained using deep images from the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). Using the ACS Virgo Cluster Survey as a counterpart in high-density environments, we investigate the role of environment in determining the properties of their globular cluster systems. We detect a strong colour bimodality of globular cluster systems in half of our galaxy sample. It is found that there is a strong correlation between the colour and richness of globular cluster populations and their host galaxy luminosities: the less bright galaxies possess bluer and fewer globular clusters as also seen in rich cluster environments. However, the mean colour of globular clusters in our field sample are slightly bluer than those in cluster environments at a given galaxy luminosity, and the colour of the red population has a steeper slope with absolute luminosity. By employing the YEPS simple stellar population model, the colour offset corresponds to metallicity difference of $\Delta$[F e/H ] ~ 0.15 - 1.20 or an age difference of $\Delta$age ~ 2 Gyr on average, implying that GCs in field galaxies appear to be either less metal-rich or younger than those in cluster galaxies. Although we have found that galaxy environment has a subtle effect on the formation and metal enrichment of GC systems, host galaxy mass is the primary factor that determines the stellar populations of GCs and the galaxy itself.

• 대한원격탐사학회지
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• 제29권6호
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• pp.645-655
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• 2013

As one of segmentation techniques for Synthetic Aperture Radar (SAR) image with oil spill, we applied a bimodal histogram method to discriminate oil pixels from non-oil pixels. The threshold of each moving window was objectively determined using the two peaks in the histogram distribution of backscattering coefficients from ENVISAT ASAR image. To reduce the effect of wind speed on oil spill detection, we selected ASAR image which satisfied a limit of wind speeds for successful detection. Overall, a commonly used adaptive threshold method has been applied with a subjectively-determined single threshold. In contrast, the bimodal histogram method utilized herein produces a variety of thresholds objectively for each moving window by considering the characteristics of statistical distribution of backscattering coefficients. Comparison between the two methods revealed that the bimodal histogram method exhibited no significant difference in terms of performance when compared to the adaptive threshold method, except for around the edges of dark oil spots. Thus, we anticipate that the objective method based on the bimodality of oil slicks may also be applicable to the detection of oil spills from other SAR imagery.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.368-371
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• 2006

A coastline is the boundary between land and ocean masses. Knowledge of coastline is essential for autonomous navigation, geographical exploration, coastal erosion monitoring and modelling, water line change, etc. Many methods have been researched to extract coastlines from the synthetic aperture radar (SAR) and optic images. Most methods were based on the intensity contrast between land and sea regions. However, in these methods, a coastline detection task was very difficult because of insufficient intensity contrast and the ambiguity in distinguishing coastline from other object line. In this paper, we propose an efficient method for the delineation of coastline using interferometric coherence values estimated from ERS tandem pair. The proposed method uses the facts that a tandem pair of ERS is acquired from a time interval of an accurate day and that the coherent and incoherent values in coherence map are land and water, respectively. The coherence map was generated from ERS tandem pair, filtered by MAP filter, and divided into land and water by the determination of threshold value that is based on the bimodality of the histogram. Finally, a coastline was detected by delineating the boundary pixels. There was a good visual match between the detected coastline and the manually contoured line. The interferometric coherence map will be helpful to identify land and water regions easily, and can be used to many applications that are related with a coastline.

• 천문학회보
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• 제37권1호
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• pp.31.2-31.2
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• 2012

We present the Yonsei Evolutionary Population Synthesis (YEPS) models for spectroscopic and photometric evolutions of simple and composite stellar populations. The models are based on the most up-to-date Yonsei-Yale stellar evolutionary tracks and BaSel 3.1 flux libraries, and provide integrated spectroscopic quantities of Lick/IDS system including high-order Balmer absorption-lines. Special care has been taken to incorporate the systematic variation of horizontal branch (HB) morphology as functions of metallicity, age, alpha-element mixture, and helium abundance of simple stellar populations. Our models for normal-helium stellar populations indicate that the realistic modeling of HB and alpha-element brings about 5 Gyr and 0.1 dex differences in age and metallicity estimations, respectively, compared to those without these effects. The HB effect does not depend on the specific choice of stellar libraries and alpha-element enhancements, and this effect is non-negligible even in the metal sensitive absorption indices, such as Mg2 and Mg b. Comparison of the models to observations reveals that the HB and alpha-element effects are critical in understanding otherwise inexplicable phenomena found in globular cluster systems in the Milky Way and nearby galaxies, including the observed bimodality of the line strengths of globular clusters in massive galaxies. In addition, we found that helium-enhanced stellar populations, which are the major sources of extreme HB stars, bring about increased FUV, NUV fluxes, and thus the model colors of those filters become extremely blue. Age dating based on the YEPS model with normal-helium stellar populations reveals that the evidence for 'downsizing' of elliptical galaxies is found not only in the local field but also in Coma cluster, and that the mean age of elliptical galaxies in Coma cluster is about 1.4 Gyr younger than the mean age of those in the local field. We also find that our models with helium-enhanced subpopulations can naturally reproduce the strong UV-upturns observed in giant elliptical galaxies assuming an age similar to that of old GCs in the Milky Way.

• 천문학회보
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• 제42권1호
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• pp.29.1-29.1
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• 2017

I present new near-infrared (NIR) photometry of globular cluster (GC) systems associated to a cD galaxy NGC 4874 in the core of the Coma cluster and 16 early-type galaxies in the Fornax and Virgo clusters of galaxies using the Infrared Channel of the Wide Field Camera 3 (WFC3/IR) on board the Hubble Space Telescope (HST). Combining these high-resolution NIR data with new HST Advanced Camera for Surveys (ACS) optical photometry for NGC 4874 and existing ACS GC catalogs from the ACS Fornax and Virgo Cluster Surveys, I have examined for the first time the GC systems in a statistically significant optical/NIR sample of galaxies spanning a wide range of luminosities and colors. A primary goal of this study is to explore empirically whether the distributions of purely optical and hybrid optical - NIR color indices for extragalactic GCs have different forms and whether the relations between these color indices are nonlinear, indicating that they behave differently with underlying metallicity. I find that some GC systems of large galaxies in our sample show color bimodalities that differ between the optical and optical - NIR colors, in the sense that they have disparate ratios of "blue" and "red" peak GCs, as well as differing ratios in their color dispersions. Consistent with these results, I find empirically that the dependence of hybrid optical-NIR color on purely optical color is nonlinear, with an inflection at intermediate metallicities. These findings underscore the importance of understanding the nature of galaxy-to-galaxy variations in the GC color distributions and color-color relations, as well as the exact forms of the color-metallicity transformations, in interpreting the observational data on GC color bimodality. Our ACS data for NGC 4874 shows that its GC system exhibits a very strong blue tilt, implying a very steep mass-metallicity scaling, and the centroid of this GC system is offset by $4{\pm}1kpc$ from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, I discuss the asymmetrical GC distribution around a dwarf elliptical galaxy in Coma that has a very high relative velocity with respect to the cluster mean at small clustercentric radius.

• Ocean and Polar Research
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• 제23권2호
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• pp.141-160
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• 2001

The challenge of predicting the Japanese coastal ocean motivated Frontier Observational Research System for Global Change (FORSGC) and the Japan Marine Science and Technology Center (JAMSTEC) to start a multiyear observational programme in the upstream Kuroshio in November 2000. This field effort, the Kuroshio Observation Program (KOP), should enable us to determine the barotropic and baroclinic components of the western boundary current system, thus, to better understand interactions of the currents with mesoscale eddies, the Kuroshio instabilities, and path bimodality. We, then, will be able to improve modeling predictability of the mesoscale, seasonal, and inter-annual processes in the midstream Kuroshio near the Japanese main islands by using this knowledge. The KOP is focused on an enhanced regional coverage of the sea surface height variability and the baroclinic structure of the mainstream Kuroshio in the East China Sea, the Ryukyu Current east of the Ryukyu's, and the Kuroshio recirculation. An attractive approach of the KOP is a development of a new data acquisition system via acoustic telemetry of the observational data. The monitoring system will provide observations for assimilation into extensive numerical models of the ocean circulation, targeting the real-time monitoring of the Japanese coastal waters.

• 천문학회보
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• 제44권1호
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• pp.37.2-37.2
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• 2019

Recent investigations of the double red clump in the color-magnitude diagram of the Milky Way bulge cast serious doubts on the structure and formation origin of the outer bulge. Unlike previous interpretation based on an X-shaped bulge, stellar evolution models and CN-band observations have suggested that this feature is another manifestation of the multiple stellar population phenomenon observed in globular clusters (GCs). This new scenario requires a significant fraction of the outer bulge stars with chemical patterns uniquely observed in GCs. Here we show from homogeneous high-quality spectroscopic data that the red giant branch stars in the outer bulge ($>5.5^{\circ}$ from the Galactic center) are clearly divided into two groups according to Na abundance in the [Na/Fe] - [Fe/H] plane. The Na-rich stars are also enhanced in Al, while the differences in O and Mg are not observed between the two Na groups. The population ratio and the Na and Al differences between the two groups are also comparable with those observed in metal-rich GCs. Since these chemical patterns and characteristics are only explained by stars originated in GCs, this is compelling evidence that the outer bulge was mostly assembled from disrupted proto-GCs in the early history of the Milky Way. We will also discuss the implications of this result on the formation of the early-type galaxies in general.

• 한국해양학회지:바다
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• 제3권2호
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• pp.94-102
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• 1998

본 조사는 인천지역 조간대 지역에 분포하는 연체동물 유해집단의 구조를 알아보기 위해 계절 분포, 밀도, 회분중량과 크기-빈도 분포, 생존곡선 등 정량적인 분석을 시도하고 또 현생 생물군집과 비교하였다. 조사 기간 중 복족류 16 종과 이매패류 12 종을 포함하여 총 28 종이 동정되었다. 유해집단을 구성하는 종들의 대부분이 조간대 지역에 서식하는 종으로 구성되었으며, 종 다양성은 이매패류보다 복족류에서 높게 나타났다. 계절별 회분중량의 변화는 동죽의 분포에 따라 좌우되었다. 천공성 복족류에 의한 천공은 주로 패각의 각정부분을 선호하고 있었다. 우점종인 접시조개류(Moerella rutila), 동죽, 왕좁쌀무늬고둥 등 3 종에 대한 크기-빈도 분포와 생존곡선에 관해 분석하였다. 접시조개류인 Moerella rutila는 각 연급군별 유사한 사망률이 나타나는 분포를 나타냈으며, 겨울철 어린 개체의 사망이 증가한 것으로 나타났고, 동죽과 왕좁쌀무늬고둥의 경우 연급군별 사망률이 다른 두 개의 굴곡을 가지는 분포를 나타냈다. 이들은 크기-빈도 분포에서도 이중모드(bimodality)를 나타냈는데, 이는 각 연급군의 가입과 계절적인 사망률의 변화에 기인한다. 유해집단을 대상으로 한 연구는 화석화 과정에서 발생하는 여러 문제들만 해결한다면 현생생물에서와 마찬가지로 개체군에 대한 유익한 정보를 제공할 수 있다.