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  1. Free, publicly-accessible full text available February 16, 2022
  2. Free, publicly-accessible full text available April 26, 2022
  3. Free, publicly-accessible full text available February 1, 2022
  4. We performed a comprehensive demographic study of the CO extent relative to dust of the disk population in the Lupus clouds in order to find indications of dust evolution and possible correlations with other disk properties. We increased the number of disks of the region with measured R CO and R dust from observations with the Atacama Large Millimeter/submillimeter Array to 42, based on the gas emission in the 12 CO J = 2−1 rotational transition and large dust grains emission at ~0.89 mm. The CO integrated emission map is modeled with an elliptical Gaussian or Nuker function, depending onmore »the quantified residuals; the continuum is fit to a Nuker profile from interferometric modeling. The CO and dust sizes, namely the radii enclosing a certain fraction of the respective total flux (e.g., R 68% ), are inferred from the modeling. The CO emission is more extended than the dust continuum, with a R 68% CO / R 68% dust median value of 2.5, for the entire population and for a subsample with high completeness. Six disks, around 15% of the Lupus disk population, have a size ratio above 4. Based on thermo-chemical modeling, this value can only be explained if the disk has undergone grain growth and radial drift. These disks do not have unusual properties, and their properties spread across the population’s ranges of stellar mass ( M ⋆ ), disk mass ( M disk ), CO and dust sizes ( R CO , R dust ), and mass accretion of the entire population. We searched for correlations between the size ratio and M ⋆ , M disk , R CO , and R dust : only a weak monotonic anticorrelation with the R dust is found, which would imply that dust evolution is more prominent in more compact dusty disks. The lack of strong correlations is remarkable: the sample covers a wide range of stellar and disk properties, and the majority of the disks have very similar size ratios. This result suggests that the bulk of the disk population may behave alike and be in a similar evolutionary stage, independent of the stellar and disk properties. These results should be further investigated, since the optical depth difference between CO and dust continuum might play a major role in the observed size ratios of the population. Lastly, we find a monotonic correlation between the CO flux and the CO size. The results for the majority of the disks are consistent with optically thick emission and an average CO temperature of around 30 K; however, the exact value of the temperature is difficult to constrain.« less
    Free, publicly-accessible full text available May 1, 2022
  5. Abstract: Honors education values diversity, not simply to enrich our classrooms but for equity and social justice. At Columbus State University, students of color were underrepresented in honors education, and we sought to determine if institutional structures hindered them from being able to access educational programming that was commensurate with their ability. We used focus group interviews with students of color who were academically eligible to enroll in honors education yet never participated. We combined focus group interviews with an analysis of our recruiting practices. Using a theoretical framework based on intersectionality and possible selves theory, we found that ourmore »participants valued diverse learning environments, balance, and co-curricular engagement that supported their professional, hoped-for selves. However, they perceived honors students as stressed, studious, and lacking leisure time, and they perceived honors education as disconnected from their future professional selves. Since their perceptions, which were informed by participation in advanced programs in middle school and high school, as well as our recruiting practices, were in conflict with their educational aims, our participants were unwilling to invest in honors education. While not generalizable, the results provide unique insights that may implicate institutional practices as barriers to participation because they fail to address the concerns of high-achieving students of color.« less
  6. Context. Protoplanetary disks in dense, massive star-forming regions are strongly affected by their environment. How this environmental impact changes over time is an important constraint on disk evolution and external photoevaporation models. Aims. We characterize the dust emission from 179 disks in the core of the young (0.5 Myr) NGC 2024 cluster. By studying how the disk mass varies within the cluster, and comparing these disks to those in other regions, we aim to determine how external photoevaporation influences disk properties over time. Methods. Using the Atacama Large Millimeter/submillimeter Array, a 2.9′× 2.9′ mosaic centered on NGC 2024 FIR 3more »was observed at 225 GHz with a resolution of 0.25″, or ~100 AU. The imaged region contains 179 disks identified at IR wavelengths, seven new disk candidates, and several protostars. Results. The overall detection rate of disks is 32 ± 4%. Few of the disks are resolved, with the exception of a giant ( R = 300 AU) transition disk. Serendipitously, we observe a millimeter flare from an X-ray bright young stellar object (YSO), and resolve continuum emission from a Class 0 YSO in the FIR 3 core. Two distinct disk populations are present: a more massive one in the east, along the dense molecular ridge hosting the FIR 1-5 YSOs, with a detection rate of 45 ± 7%. In the western population, towards IRS 1, only 15 ± 4% of disks are detected. Conclusions. NGC 2024 hosts two distinct disk populations. Disks along the dense molecular ridge are young (0.2–0.5 Myr) and partly shielded from the far ultraviolet radiation of IRS 2b; their masses are similar to isolated 1–3 Myr old SFRs. The western population is older and at lower extinctions, and may be affected by external photoevaporation from both IRS 1 and IRS 2b. However, it is possible these disks had lower masses to begin with.« less
  7. Consider the multigraph obtained by adding a double edge to $K_4-e$. Now, let $D$ be a directed graph obtained by orientating the edges of that multigraph. We establish necessary and sufficient conditions on $n$ for the existence of a $(K^{*}_{n},D)$-design for four such orientations.
  8. From a design-based research study with 31 families, we share the design conjectures that guided the first two iterations of research. The team developed a mobile augmented reality app focused on water-rock interactions to make earth sciences appealing to rural families. We iterated on one design element, the augmented reality visualizations, to understand how these AR elements influence families’ learning behavior in a children’s garden cave as well as their resulting geosciences knowledge. This analysis is an example of how design conjecture maps can be used to support research and development of mobile computer-supported collaborative learning opportunities for families inmore »outdoor, informal learning settings.« less
  9. While planets are commonly discovered around main-sequence stars, the processes leading to their formation are still far from being understood. Current planet population synthesis models, which aim to describe the planet formation process from the protoplanetary disk phase to the time exoplanets are observed, rely on prescriptions for the underlying properties of protoplanetary disks where planets form and evolve. The recent development in measuring disk masses and disk-star interaction properties, i.e., mass accretion rates, in large samples of young stellar objects demand a more careful comparison between the models and the data. We performed an initial critical assessment of themore »assumptions made by planet synthesis population models by looking at the relation between mass accretion rates and disk masses in the models and in the currently available data. We find that the currently used disk models predict mass accretion rate in line with what is measured, but with a much lower spread of values than observed. This difference is mainly because the models have a smaller spread of viscous timescales than what is needed to reproduce the observations. We also find an overabundance of weakly accreting disks in the models where giant planets have formed with respect to observations of typical disks. We suggest that either fewer giant planets have formed in reality or that the prescription for planet accretion predicts accretion on the planets that is too high. Finally, the comparison of the properties of transition disks with large cavities confirms that in many of these objects the observed accretion rates are higher than those predicted by the models. On the other hand, PDS70, a transition disk with two detected giant planets in the cavity, shows mass accretion rates well in line with model predictions.« less
  10. Our work with teams funded through the National Science Foundation REvolutionizing Engineering and Computer Science Departments (RED) program began in 2015. Our project—funded first by a NSF EAGER grant, and then by a NSF RFE grant—focuses on understanding how the RED teams make change on their campuses and how this information about change can be captured and communicated to other STEM programs that seek to make change happen. Because our RED Participatory Action Research (REDPAR) Project is a collaboration between researchers (Center for Evaluation & Research for STEM Equity at the University of Washington) and practitioners (Making Academic Change Happenmore »Workshop at Rose-Hulman Institute of Technology), we have challenged ourselves to develop means of communication that allow for both aspects of the work—both research and practice—to be treated equitably. As a result, we have created a new dissemination channel—the RED Participatory Action Project Tipsheet. The tipsheet format accomplishes several important goals. First, the content is drawn from both the research conducted with the RED teams and the practitioners’ work with the teams. Each tipsheet takes up a single theme and grounds the theme in the research literature while offering practical tips for applying the information. Second, the format is accessible to a wide spectrum of potential users, remaining free of jargon and applicable to multiple program and departmental contexts. Third, by publishing the tipsheets ourselves, rather than submitting them to an engineering education research journal, we make the information timely and freely available. We can make a tipsheet as soon as a theme emerges from the intersection of research data and observations of practice. During the poster session at ASEE 2019, we will share the three REDPAR Tipsheets that have been produced thus far: Creating Strategic Partnerships, Communicating Change, and Shared Vision. We will also work with attendees to demonstrate how the tipsheet content is adaptable to the attendees’ specific academic context. Our goal for the poster session is to provide attendees with tipsheet resources that are useful to their specific change project.« less