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  1. Free, publicly-accessible full text available December 1, 2023

    We present the first intensive study of the variability of the near-infrared coronal lines in an active galactic nucleus (AGN). We use data from a 1-yr-long spectroscopic monitoring campaign with roughly weekly cadence on NGC 5548 to study the variability in both emission line fluxes and profile shapes. We find that in common with many AGN coronal lines, those studied here are both broader than the low-ionizaton forbidden lines and blueshifted relative to them, with a stratification that implies an origin in an outflow interior to the standard narrow line region. We observe for the first time [S viii] and [Si vi] coronal line profiles that exhibit broad wings in addition to narrow cores, features not seen in either [S ix] or [Si x]. These wings are highly variable, whereas the cores show negligible changes. The differences in both the profile shapes and variability properties of the different line components indicate that there are at least two coronal line regions in AGN. We associate the variable, broad wings with the base of an X-ray heated wind evaporated from the inner edge of the dusty torus. The coronal line cores may be formed at several locations interior to the narrow line region: either along thismore »accelerating, clumpy wind or in the much more compact outflow identified with the obscurer and so emerging on scales similar to the outer accretion disc and broad-line region.

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  3. Free, publicly-accessible full text available September 1, 2023
  4. We study covariate shift in the context of nonparametric regression. We introduce a new measure of distribution mismatch between the source and target distributions using the integrated ratio of probabilities of balls at a given radius. We use the scaling of this measure with respect to the radius to characterize the minimax rate of estimation over a family of H{ö}lder continuous functions under covariate shift. In comparison to the recently proposed notion of transfer exponent, this measure leads to a sharper rate of convergence and is more fine-grained. We accompany our theory with concrete instances of covariate shift that illustrate this sharp difference.
    Free, publicly-accessible full text available July 1, 2023
  5. This research paper describes an autoethnographic study of three individuals: Julie, a tenured faculty member and experienced engineering education researcher, and two novice engineering education researchers, Paul, a more junior faculty member, and Deepthi, a graduate student. The tripartite mentoring relationship between us formed as part of a National Science Foundation Research Initiation in Engineering Formation (NSF RIEF) project. We grounded our work in the cognitive apprenticeship model of mentoring and theory of social capital, asking the question: How do mentors and mentees perceive shared experiences? Over the course of 16 months, we collected data in the form of reflective journal entries and transcripts from individual and joint interviews, combining these with other documentation such as emails and text messages. We analyzed these data by identifying three critical incidents over the course of the relationship to date and comparing each of our perceptions of these shared experiences. We found that our perceptions of the shared experiences differed greatly, providing multiple opportunities to improve our future communication. We also discovered that our initial mentoring model in which Julie mentored Paul and Paul mentored Deepthi did not withstand scrutiny. Because Paul was new to engineering education research, it was better for Juliemore »to mentor both Paul and Deepthi than to expect Paul to teach Deepthi topics and methods that were new to him. We assert that other projects would benefit by this approach as well. Our findings offer broad implications for the efficacy of reflection and communication in mentoring relationships.« less
    Free, publicly-accessible full text available June 1, 2023
  6. Recent lattice QCD results, comparing to a hadron resonance gas model, have shown the need for hundreds of particles in hadronic models. These extra particles influence both the equation of state and hadronic interactions within hadron transport models. Here, we introduce the PDG21+ particle list, which contains the most up-to-date database of particles and their properties. We then convert all particles decays into 2 body decays so that they are compatible with SMASH in order to produce a more consistent description of a heavy-ion collision.
    Free, publicly-accessible full text available July 1, 2023
  7. Transcripts of teaching episodes can be effective tools to understand discourse patterns in classroom instruction. According to most educational experts, sustained classroom discourse is a critical component of equitable, engaging, and rich learning environments for students. This paper describes the TalkMoves dataset, composed of 567 human annotated K-12 mathematics lesson transcripts (including entire lessons or portions of lessons) derived from video recordings. The set of transcripts primarily includes in-person lessons with whole-class discussions and/or small group work, as well as some online lessons. All of the transcripts are human-transcribed, segmented by the speaker (teacher or student), and annotated at the sentence level for ten discursive moves based on accountable talk theory. In addition, the transcripts include utterance-level information in the form of dialogue act labels based on the Switchboard Dialog Act Corpus. The dataset can be used by educators, policymakers, and researchers to understand the nature of teacher and student discourse in K-12 math classrooms. Portions of this dataset have been used to develop the TalkMoves application, which provides teachers with automated, immediate, and actionable feedback about their mathematics instruction.
    Free, publicly-accessible full text available July 1, 2023
  8. During the Spring 2020 semester, universities shifted into emergency remote teaching due to the COVID-19 pandemic. Globally, the pandemic disrupted students learning, their support structures, and interactions with other individuals both socially and academically. In addition, it created lasting impacts on professionals in determining strategies and altering objectives to help undergraduate engineering students achieve their learning objectives. Previous research on social support during the pandemic has focused primarily on singular cultural context, this study was conducted to understand the impact of the pandemic on students support in different cultural contexts. The purpose of this research was to explore how students experienced social capital structures at two institutions: one in the United Kingdom (U.K.) and one in the United States (U.S.) during the period of emergency remote teaching. The survey was designed around social capital theory, it provided demographic information, students agreement with their educational and social interactions, and names of individuals as well as resources they utilized during the pandemic.Results revealed similarities and differences between the two groups. Both case studies had the same top three alters: friends/roommate, professor, and family members, and reported almost the same frequency in communication with their alters. Participants in both case studies also hadhighmore »rates of support in both expressive and instrumental categories from their top two alters. Examiningthe differences, the UK case had a lower mean response for both sense of belonging and satisfaction at the university. Finally, there was a difference in the types of alters identified in each case due to different cultural contexts.« less
    Free, publicly-accessible full text available June 1, 2023
  9. We propose and analyze a reinforcement learning principle that approximates the Bellman equations by enforcing their validity only along an user-defined space of test functions. Focusing on applications to model-free offline RL with function approximation, we exploit this principle to derive confidence intervals for off-policy evaluation, as well as to optimize over policies within a prescribed policy class. We prove an oracle inequality on our policy optimization procedure in terms of a trade-off between the value and uncertainty of an arbitrary comparator policy. Different choices of test function spaces allow us to tackle different problems within a common framework. We characterize the loss of efficiency in moving from on-policy to off-policy data using our procedures, and establish connections to concentrability coefficients studied in past work. We examine in depth the implementation of our methods with linear function approximation, and provide theoretical guarantees with polynomial-time implementations even when Bellman closure does not hold.
    Free, publicly-accessible full text available April 1, 2023
  10. The Princess Elizabeth Land sector of the East Antarctic Ice Sheet is a significant reservoir of grounded ice and is adjacent to regions that experienced great change during Quaternary glacial cycles and Pliocene warm episodes. The existence of an extensive subglacial water system in Princess Elizabeth Land (to date only inferred from satellite imagery) bears the potential to significantly impact the thermal and kinematic conditions of the overlying ice sheet. We confirm the existence of a major subglacial lake, herein referred to as Lake Snow Eagle (LSE), for the first time using recently acquired aerogeophysical data. We systematically investigated LSE’s geological characteristics and bathymetry from two-dimensional geophysical inversion models. The inversion results suggest that LSE is located along a compressional geologic boundary, which provides reference for future characterization of the geologic and tectonic context of this region. We estimate LSE to be ~42 km in length and 370 km2 in area, making it one of the largest subglacial lakes in Antarctica. Additionally, the airborne ice-penetrating radar observations and geophysical inversions reveal a layer of unconsolidated water-saturated sediment around and at the bottom of LSE, which—given the ultralow rates of sedimentation expected in such environments—may archive valuable records of paleoenvironmental changesmore »and the early history of East Antarctic Ice Sheet evolution in Princess Elizabeth Land.« less
    Free, publicly-accessible full text available May 9, 2023