• Title/Summary/Keyword: NRP

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Hybrid Heuristic Using Hierarchical Decomposition and Optimization for the Nurse Rostering Problem (계층적 분할 방법과 최적화를 이용한 간호원 로스터링 해법연구)

  • Jang, Yoon Hee;Kim, Sun Hoon;Lee, Young Hoon
    • Journal of Korean Institute of Industrial Engineers
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    • v.40 no.2
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    • pp.184-194
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    • 2014

  • Numerous studies have been studied to provide an efficient solution for the Nurse Rostering Problem (NRP), most of which have suffered from its complexity arising from incorporating nurse's work shift and ability. The test-bed data for the NRP is released for the public Competition in 2010. This study suggests a new mixed integer programming for Nurse Rostering Problem and develops a hybrid approach, where a hierarchical decomposition and the corresponding optimization are combined. The computation experiment is performed to show that the suggested algorithms may give a better solution in various instances, compared to the one appeared in the literature.

  • https://doi.org/10.7232/JKIIE.2014.40.2.184 인용 PDF KSCI

Diverse Chemo-Dynamical Properties of Nitrogen-Rich Stars Identified from Low-Resolution Spectra

  • Changmin Kim;Young Sun Lee;Timothy C. Beers;Young Kwang Kim
    • Journal of The Korean Astronomical Society
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    • v.56 no.1
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    • pp.59-73
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    • 2023

  • The second generation of stars in the globular clusters (GCs) of the Milky Way (MW) exhibit unusually high N, Na, or Al, compared to typical Galactic halo stars at similar metallicities. The halo field stars enhanced with such elements are believed to have originated in disrupted GCs or escaped from existing GCs. We identify such stars in the metallicity range -3.0 < [Fe/H] < 0.0 from a sample of ~36,800 giant stars observed in the Sloan Digital Sky Survey and Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, and present their dynamical properties. The N-rich population (NRP) and N-normal population (NNP) among our giant sample do not exhibit similarities in either in their metallicity distribution function (MDF) or dynamical properties. We find that, even though the MDF of the NRP looks similar to that of the MW's GCs in the range of [Fe/H] < -1.0, our analysis of the dynamical properties does not indicate similarities between them in the same metallicity range, implying that the escaped members from existing GCs may account for a small fraction of our N-rich stars, or the orbits of the present GCs have been altered by the dynamical friction of the MW. We also find a significant increase in the fraction of N-rich stars in the halo field in the very metal-poor (VMP; [Fe/H] < -2.0) regime, comprising up to ~20% of the fraction of the N-rich stars below [Fe/H] = -2.5, hinting that partially or fully destroyed VMP GCs may have in some degree contributed to the Galactic halo. A more detailed dynamical analysis of the NRP reveals that our sample of N-rich stars do not share a single common origin. Although a substantial fraction of the N-rich stars seem to originate from the GCs formed in situ, more than 60% of them are not associated with those of typical Galactic populations, but probably have extragalactic origins associated with Gaia Sausage/Enceladus, Sequoia, and Sagittarius dwarf galaxies, as well as with presently unrecognized progenitors.

  • https://doi.org/10.5303/JKAS.2023.56.1.59 인용 PDF