arXiv subjects

Jiwon Han

Publications and source records attributed to Jiwon Han.

2 recordsLinked to original sources

arXiv2026

Backlighting young stellar objects in the Central Molecular Zone: an ensemble-averaged abundance structure of methanol ices

The Central Molecular Zone (CMZ) contains a substantial reservoir of dense molecular gas, where numerous young stellar objects (YSOs) and dense cloud cores have been identified. However, the large distance and severe foreground extinction complicate interpretation of infrared ice absorption features tracing chemical and evolutionary properties of these embedded objects. To better characterise YSOs and dense cores in this region, we combined spectra from multiple YSOs, each likely backlit by a giant star, allowing us to probe their outer layers and derive an ensemble-averaged ice abundance profile. We obtained L-band spectra of 15 point-like sources with extremely red colours using Gemini/GNIRS, enabling measurements of the CH3OH absorption feature at 3.535 micron. To better constrain the foreground extinction and H$_2$O ice column densities, we combined these data with K-band and mid-infrared spectra using NASA/IRTF and Spitzer/IRS. We found that the CH$_3$OH abundance in the CH$_3$OH-CO$_2$ ice mixture is 2 to 5 percent, confirming that it is systematically lower than those typically observed in the Galactic disk. Furthermore, by using the local excess of foreground extinction as a proxy for the projected distance between a backlit source and the centre of a YSO, we found that the CH$_3$OH abundance relative to solid CO$_2$ remains near 10 percent in the inner regions of the envelope, but increases sharply to about 30 percent in the outer regions. The relatively low methanol ice abundance may reflect the unique chemical environment of the CMZ. However, our results offer an alternative interpretation: since our sample is biased towards massive and luminous YSOs, intense heating from the central protostar may have caused substantial sublimation of methanol ice in the inner regions of their envelopes, thereby systematically lowering the observed CH$_3$OH/H$_2$O ice ratios.

astro-ph.GA↗

arXiv2024

Exploring Factors Affecting Student Learning Satisfaction during COVID-19 in South Korea

Understanding students' preferences and learning satisfaction during COVID-19 has focused on learning attributes such as self-efficacy, performance, and engagement. Although existing efforts have constructed statistical models capable of accurately identifying significant factors impacting learning satisfaction, they do not necessarily explain the complex relationships among these factors in depth. This study aimed to understand several facets related to student learning preferences and satisfaction during the pandemic such as individual learner characteristics, instructional design elements and social and environmental factors. Responses from 302 students from Sungkyunkwan University, South Korea were collected between 2021 and 2022. Information gathered included their gender, study major, satisfaction and motivation levels when learning, perceived performance, emotional state and learning environment. Wilcoxon Rank sum test and Explainable Boosting Machine (EBM) were performed to determine significant differences in specific cohorts. The two core findings of the study are as follows:1) Using Wilcoxon Rank Sum test, we can attest with 95% confidence that students who took offline classes had significantly higher learning satisfaction, among other attributes, than those who took online classes, as with STEM versus HASS students; 2) An explainable boosting machine (EBM) model fitted to 95.08% accuracy determined the top five factors affecting students' learning satisfaction as their perceived performance, their perception on participating in class activities, their study majors, their ability to conduct discussions in class and the study space availability at home. Positive perceived performance and ability to discuss with classmates had a positive impact on learning satisfaction, while negative perception on class activities participation had a negative impact on learning satisfaction.

cs.CY↗