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STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF THE SEXTANS DWARF SPHEROIDAL GALAXY
Lee, Myung Gyoon,Yuk, In-Soo,Park, Hong Soo,Harris, Jason,Zaritsky, Dennis IOP Publishing 2009 The Astrophysical journal Vol.703 No.1
<P>We present the star formation history (SFH) and chemical evolution of the Sextans dSph galaxy as a function of a galactocentric distance. We derive these from the VI photometry of stars in the 42' x 28' field using the SMART model developed by Yuk & Lee and adopting a closed-box model for chemical evolution. For the adopted age of Sextans 15 Gyr, we find that >84% of the stars formed prior to 11 Gyr ago, significant star formation extends from 15 to 11 Gyr ago (similar to 65% of the stars formed 13-15 Gyr ago, while similar to 25% formed 11-13 Gyr ago), detectable star formation continued to at least 8 Gyr ago, the SFH is more extended in the central regions than the outskirts, and the difference in star formation rates between the central and outer regions is most marked 11-13 Gyr ago. Whether blue straggler stars are interpreted as intermediate-age main-sequence stars affects conclusions regarding the SFH for times 4-8 Gyr ago, but this is at most only a trace population. We find that the metallicity of the stars increased rapidly up to [Fe/H] = -1.6 in the central region and to [Fe/H] = -1.8 in the outer region within the first Gyr, and has varied slowly since then. The abundance ratios of several elements derived in this study are in good agreement with the observational data based on the high-resolution spectroscopy in the literature. We conclude that the primary driver for the radial gradient of the stellar population in this galaxy is the SFH, which self-consistently drives the chemical enrichment history.</P>
Ying L. Liu,Olga T. Filippova,Qin Zhou,Alexia Iasonos,Dennis S. Chi,Oliver Zivanovic,Yukio Sonoda,Ginger J. Gardner,Vance A. Broach,Roisin E. OCearbhaill,Jason A. Konner,Carol Aghajanian,Kara Long Roc 대한부인종양학회 2020 Journal of Gynecologic Oncology Vol.31 No.1
Objective: Neoadjuvant chemotherapy (NACT) followed by interval debulking surgery (IDS)confers similar outcomes as primary debulking surgery and chemotherapy. Little is knownabout patients who receive NACT but do not undergo debulking surgery. Our aim was tocharacterize these patients. Methods: We prospectively identified patients with newly diagnosed stage III/IV ovariancancer treated with NACT from 7/1/15–12/1/17. Fisher exact and Wilcoxon rank-sum tests wereused to compare clinical characteristics by surgical status. The Kaplan-Meier method wasused to estimate survival outcomes. Log-rank test and Cox proportional hazards model wereapplied to assess the relationship of covariates to outcome, and time-dependent covariateswere applied to variables collected after diagnosis. Results: Of 224 women who received NACT, 162 (72%) underwent IDS and 62 (28%) didnot undergo surgery. The non-surgical group was older (p<0.001), had higher Charlsoncomorbidity index (CCI; p<0.001), lower albumin levels (p=0.007), lower Karnofskyperformance scores (p<0.001), and were more likely to have dose reductions in NACT(p<0.001). Reasons for no surgery included poor response to NACT (39%), death (15%),comorbidities (24%), patient preference (16%), and loss to follow-up (6%). The nosurgery group had significantly worse overall survival (OS) than the surgery group (hazardratio=3.34; 95% confidence interval=1.66–6.72; p<0.001), after adjustment for age, CCI, anddose reductions. Conclusions: A significant proportion of women treated with NACT do not undergo IDS, andthese women are older, frailer, and have worse OS. More studies are needed to find optimaltherapies to maximize outcomes in this high-risk, elderly population.