• Geomechanics and Engineering
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• 제36권2호
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• pp.121-130
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• 2024

Many foundation projects are built on red-bed soft rocks, and the damage evolution of this kind of rocks affects the safety of these projects. At present, there is insufficient research on the damage evolution of red-bed soft rocks, especially the progressive process from mesoscopic texture change to macroscopic elastoplastic deformation. Therefore, based on the dual-porosity characteristics of pores and fissures in soft rock, we adopted a cellular automata model to simulate the propagation of these voids in soft rocks under an external load. Further, we established a macro-mesoscopic damage model of red-bed soft rocks, and its reliability was verified by tests. The results indicate that the relationship between the number and voids size conformed to a quartic polynomial, whereas the relationship between the damage variable and damage porosity conformed to a logistic curve. The damage porosity was affected by dual-porosity parameters such as the fractal dimension of pores and fissures. We verified the reliability of the model by comparing the test results with an established damage model. Our research results described the progressive process from mesoscopic texture change to macroscopic elastoplastic deformation and provided a theoretical basis for the damage evolution of these rocks.

• 한국생태학회:학술대회논문집
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• 한국생태학회 2002년도 VIII 세계생태학대회
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• pp.83-91
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• 2002

The Red Queen hypothesis for the advantage of sex predicts that pathogens will evolve by increasing fitness with frequent encounters with specific host genotypes. In this study, BMV population size, measured as an indicator of fitness, was investigated during repeated passages through the same, or different host genotypes of the crop host, Hordeum vulgare (barley). Overall, mean BMV concentration within individual hosts was significantly higher in genetically homogeneous compared to heterogeneous host passage lines. In addition, BMV populations, passaged through a specific host variety, showed higher growth in that host variety compared to BMV passaged through varying varieties. These results supports the Red Queen hypothesis. However, the decrease in viral populations during passages contradicts the Red Queen. Nevertheless, the results found here show that even under simplified conditions, pathogens do not evolve in simple, predictable ways. Constraints on pathogen evolution may lead to counterintuitive results.

• The Korean Journal of Ecology
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• 제25권4호
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• pp.217-225
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• 2002

The Red Queen hypothesis for the advantage of sex predicts that pathogens will evolve by increasing fitness with frequent encounters with specific host genotypes. In this study, BMV population size, measured as an indicator of fitness, was investigated during repeated passages through the same, or different host genotypes of the crop host, Hordeum vulgare (barley). Overall, mean BMV concentration within individual hosts was significantly higher in genetically homogeneous compared to heterogeneous host passage lines. In addition, BMV populations, passaged through a specific host variety, showed higher growth in that host variety compared to BMV passaged through varying varieties. These results supports the Red Queen hypothesis. However, the decrease in viral populations during passages contradicts the Red Queen. Nevertheless, the results found here show that even under simplified conditions, pathogens do not evolve in simple, predictable ways. Constraints on pathogen evolution may lead to counterintuitive results.

• 천문학회보
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• 제35권2호
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• pp.82.2-82.2
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• 2010

We investigate the distribution of stars along the red giant branch (RGB) in the globular clusters (GCs) NGC 288 and NGC 362 from Caby photometry using the CTIO 4m Blanco telescope. Our color-magnitude diagrams in hk index show that the RGB stars have two distinct subpopulations with different Ca abundances apparently supplied by the Type II supernovae explosions. However, the RGB splits are not shown in the b - y color, as indicated by previous observations. Our stellar population models show that the presence of two distinct RGBs in these GCs can be reproduced if metal-rich second generation stars are also enhanced in helium and younger by 1 ~ 2 Gyrs.

• 천문학회보
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• 제38권2호
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• pp.74.2-74.2
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• 2013

Recent spectroscopic observations have provided evidences for the multiple stellar populations having different abundances in some massive globular clusters (GCs). In particular, some of these GCs show clear separations of red giant-branches (RGBs) in calcium narrow band photometry. In order to confirm the differences in heavy element abundances and radial velocities among multiple RGBs, we have performed the low-resolution spectroscopy for the RGB stars in these GCs. The spectral data were taken from the multi-object spectroscopic mode with WFCCD mounted on the du Pont 2.5m telescope in Las Campanas Observatory. In this talk, we will present our progress in the spectroscopic analysis of the RGB stars in these GCs.

• 천문학회보
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• 제38권2호
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• pp.74.1-74.1
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• 2013

We have performed new narrow-band calcium photometry for Milky Way globular clusters (GCs) and detected multiple red giant branches (RGBs) in some massive GCs. Our new calcium filter was designed to avoid the CN contamination below $3883{\AA}$ and to measure only Ca II H&K lines. The fact that we are detecting multiple RGBs from the new filter is suggesting that they are indeed different in calcium abundance, which can only be produced by supernovae (SNe). Therefore, the presence of the multiple RGBs for the peculiar GCs in the calcium photometry is best understood if the later generation of stars are enhanced in some SNe products. In this talk, we will present our progress in the calcium photometry for the peculiar GCs showing the multiple RGBs.

• 천문학회보
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• 제38권1호
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• pp.30.2-30.2
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• 2013

The mean color of globular cluster (GCs) systems in early-type galaxies (ETGs) is, in general, bluer than the integrated color of field stars in their host galaxies. Recently, Goudfrooij & Kruijssen (2013) reported that even red GCs in the ETGs show bluer colors than their host field stars and suggested the different initial mass function (IMF) for red GCs and field stars to explain the observed offset in color. Here we suggest an alternative scenario that explains the observed color offsets between red GCs in ETGs and the field stars in the parent galaxies without invoking to the variation of the IMF. We find that the inclusion of second-generation (SG) helium-enhanced populations in the model fully explains the observed color offset between red GCs and field stars in the host galaxies. We have also tested the effect of the IMF slope on our models, but the effect is relatively small compared to the effect of the SG population. Our new model suggests that, in order to explain far-UV strong metal-rich GCs in M87 and the observed color offset between metal-rich GCs and the field stars in ETGs simultaneously, the inclusion of the SG populations with enhanced helium abundance is a more natural solution than the model that only adopted variations in the IMF.

• 천문학회보
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• 제43권2호
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• pp.39.3-40
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• 2018

The presence of double red clump (RC) in the Milky Way bulge is widely accepted as evidence for a giant X-shaped structure originated from the bar instability. We suggested, however, a drastically different interpretation based on the multiple stellar populations phenomenon as is observed in globular clusters. Our discovery of a significant difference in CN-band between two RCs strengthens our scenario. On the other hand, recent Gaia survey provides trigonometric parallax distances for more than one billion stars in our Galaxy. These distance measurements would provide the important test as to the origin of the double RC in the Milky Way bulge. In this talk, we will present our preliminary results from Gaia DR2.

• 천문학회지
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• 제43권4호
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• pp.105-113
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• 2010

We study the dynamical evolution of the M87 globular cluster (GC) system using the most advanced and realistic Fokker-Planck (FP) model.By comparing our FP models with both mass function (MF) and radial distribution (RD) of the observed GC system, we find the best-fit initial (at M87's age of 2-3 Gyr) MF and RD for three GC groups: all GCs, blue GCs, and red GCs. We estimate the initial total mass in GCs to be $1.8^{+0.3}_{-0.2}{\times}10^{10}M_{\bigodot}$, which is about 100 times larger than that of the Milky Way GC system. We also find that the fraction of the total mass currently in GCs is 34\%. When blue and red GCs are fitted separately, blue GCs initially have a larger total mass and a shallower radial distribution than red GCs. If one assumes that most of the significant major merger events of M87 have ended by the age of 2-3 Gyr, our finding that blue (metal-poor) GCs initially had a shallower radial distribution supports the major merger scenario for the origin of metallicity bimodality.

• 천문학논총
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• 제30권2호
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• pp.355-358
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• 2015

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group galaxy M33. The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The pulsating giant stars (AGB and red supergiants) are identified and their distributions are used to derive the star formation rate as a function of age. These stars are also important dust factories; we measure their dust production rates from a combination of our data with Spitzer Space Telescope mid-IR photometry. The mass-loss rates are seen to increase with increasing strength of pulsation and with increasing bolometric luminosity. Low-mass stars lose most of their mass through stellar winds, but even super-AGB stars and red superginats lose ~40% of their mass via a dusty stellar wind. We construct a 2-D map of the mass-return rate, showing a radial decline but also local enhancements due to agglomerations of massive stars. By comparing the current star formation rate with total mass input to the ISM, we conclude that the star formation in the central regions of M33 can only be sustained if gas is accreted from further out in the disc or from circum-galactic regions.