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  1. Next-generation scientific applications in various fields are experiencing a rapid transition from traditional experiment-based methodologies to large-scale computation-intensive simulations featuring complex numerical modeling with a large number of tunable parameters. Such model-based simulations generate colossal amounts of data, which are then processed and analyzed against experimental or observation data for parameter calibration and model validation. The sheer volume and complexity of such data, the large model-parameter space, and the intensive computation make it practically infeasible for domain experts to manually configure and tune hyperparameters for accurate modeling in complex and distributed computing environments. This calls for an online computational steeringmore »service to enable real-time multi-user interaction and automatic parameter tuning. Towards this goal, we design and develop a generic steering framework based on Bayesian Optimization (BO) and conduct theoretical performance analysis of the steering service. We present a case study with the Weather Research and Forecast (WRF) model, which illustrates the performance superiority of the BO-based tuning over other heuristic methods and manual settings of domain experts using regret analysis.« less
    Free, publicly-accessible full text available October 1, 2022
  2. With the rapid growth of online learning at community colleges and the low course completion and performance associated with it, there has been increasing need to identify effective ways to address the challenges in online teaching and learning at this particular setting. Based on open-ended survey responses from 105 instructors and 365 students from multiple community colleges in a state, this study examined instructors’ and students’ perceptions of effective and ineffective instructional practices and changes needed in online coursework. By combining structural topic modelling techniques with human coding, we identified instructional practices that were perceived by both instructors and studentsmore »as effective in supporting online learning as well as ineffective and needing improvement. Moreover, we identified a handful of misalignments between instructors and students in their perceptions of online teaching, including course workload and effective ways to communicate.« less
    Free, publicly-accessible full text available July 1, 2022
  3. An extensive theoretical and empirical literature stresses the challenges of online learning, especially among students enrolled in open-access institutions who often struggle more due to job and family commitments and a lack of self-regulated learning skills. As online expansion continues in higher education, understanding the specific challenges students encounter in online coursework, and learning strategies that can help them cope with these challenges, can provide valuable insights to be widely shared. Using open-ended survey data collected from 365 students at a state community college system, this study examined students’ perceptions of challenges of online learning that may lead to undesirablemore »learning outcomes and specific strategies they found effective in addressing these challenges. We combined structural topic modeling and human coding in analyzing student responses. Three sets of challenges—including insufficient time management skills, greater tendencies of multitasking and being distracted in an online learning environment, and ineffective interaction and frustrations with help-seeking—emerged from student responses. In response to these challenges, students reflected on ways to improve online learning experiences and outcomes, including improving time management skills, maintaining an organized and distraction-free study environment, proactively seeking help, and using study strategies to improve learning effectiveness.« less
  4. Refractory multi-element alloys (RMEA) with body-centered cubic (bcc) structure have been the object of much research over the last decade due to their high potential as candidate materials for high- temperature applications. Most of these alloys display a remarkable strength at high temperatures, which cannot be explained by the standard model of bcc plasticity based on thermally-activated screw disloca- tion motion. Several works have pointed to chemical energy fluctuations as an essential aspect of RMEA strength that is not captured by standard models. In this work, we quantify the contribution of screw dis- locations to the strength of equiatomic Nb-Ta-Vmore »alloys using a kinetic Monte Carlo model fitted to solu- tion energetics obtained from atomistic calculations. In agreement with molecular dynamics simulations, we find that chemical energy fluctuations along the dislocation line lead to measurable concentrations of kinks in equilibrium in a wide temperature range. A fraction of these form cross-kink configurations, which are ultimately found to control screw dislocation motion and material strength. Our simulations (i) confirm that the evolution of cross kinks and self-pinning are strong contributors to the so-called ‘cocktail’ effect in this alloy at low temperature, and (ii) substantiate the notion that screw dislocation plasticity alone cannot explain the high temperature strength of bcc RMEA.« less
  5. Developmental education is the most widespread strategies used by colleges to provide academically weak students with additional training in key subject areas. To reduce costs and also to address the large volume of enrollment in these courses, many institutions have replaced traditional face-to-face instruction with online instruction in developmental coursework. This paper examines the impact of fully online instruction, compared with traditional face-to-face instruction, on both concurrent developmental course outcomes, and on downstream outcomes, using a unique administrative dataset from a state community college system that includes longitudinal student-unit record data from more than 40,000 students enrolled in developmental educationmore »courses. Results from a two-way fixed effects model that controls for selection both at the course- and student-level indicate that taking one’s first developmental course through the online format reduces developmental course completion rate by 13 percentage points and subsequent enrollment in the gatekeeper course by 7 percentage points.« less
  6. Free, publicly-accessible full text available September 1, 2022
  7. Dislocations are one-dimensional defects in crystals, enabling their deformation, mechanical response, and transport properties. Less well known is their influence on material chemistry. The severe lattice distortion at these defects drives solute segregation to them, resulting in strong, localized spatial variations in chemistry that determine microstructure and material behavior. Recent advances in atomic-scale characterization methods have made it possible to quantitatively resolve defect types and segregation chemistry. As shown here for a Pt-Au model alloy, we observe a wide range of defect-specific solute (Au) decoration patterns of much greater variety and complexity than expected from the Cottrell cloud picture. Themore »solute decoration of the dislocations can be up to half an order of magnitude higher than expected from classical theory, and the differences are determined by their structure, mutual alignment, and distortion field. This opens up pathways to use dislocations for the compositional and structural nanoscale design of advanced materials.« less