skip to main content

Search for: All records

Creators/Authors contains: "Xu, D"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. 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
  2. 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
  3. 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
  4. Little is known regarding the use of, and factors related with, interaction-oriented practices. In this study we investigate instructors’ use of interaction-oriented practices in online college courses. We begin by drawing on several strands of literature to offer a person-purpose interaction framework for categorizing interaction-oriented practices. The framework’s six sub-domains integrate for whom students are interacting (instructor, student, content) with the interaction’s pedagogical purpose (academic, social, managerial). Subsequently, we examine factors that predict instructors’ use of these six domains of practices, including instructors’ characteristics and their perceptions of online learning, using a sample of (n = 126) community college instructorsmore »teaching online courses. The results show that instructors using more interaction-oriented practices consistently have greater employment status and teaching load, greater self-efficacy for using learning management systems, and greater perceived benefits of online learning for students, with subtle distinctions found across sub-domains. The findings have several implications for future research examining pedagogical behavior, as well as the design of professional development activities aimed at enhancing the use of effective online instructional practices among college instructors.« less
  5. ABSTRACT In recent years, breakthroughs in methods and data have enabled gravitational time delays to emerge as a very powerful tool to measure the Hubble constant H0. However, published state-of-the-art analyses require of order 1 yr of expert investigator time and up to a million hours of computing time per system. Furthermore, as precision improves, it is crucial to identify and mitigate systematic uncertainties. With this time delay lens modelling challenge, we aim to assess the level of precision and accuracy of the modelling techniques that are currently fast enough to handle of order 50 lenses, via the blind analysismore »of simulated data sets. The results in Rungs 1 and 2 show that methods that use only the point source positions tend to have lower precision ($10\!-\!20{{\ \rm per\ cent}}$) while remaining accurate. In Rung 2, the methods that exploit the full information of the imaging and kinematic data sets can recover H0 within the target accuracy (|A| < 2 per cent) and precision (<6 per cent per system), even in the presence of a poorly known point spread function and complex source morphology. A post-unblinding analysis of Rung 3 showed the numerical precision of the ray-traced cosmological simulations to be insufficient to test lens modelling methodology at the percent level, making the results difficult to interpret. A new challenge with improved simulations is needed to make further progress in the investigation of systematic uncertainties. For completeness, we present the Rung 3 results in an appendix and use them to discuss various approaches to mitigating against similar subtle data generation effects in future blind challenges.« less
  6. Scientists in disciplines such as neuroscience and bioinformatics are increasingly relying on science gateways for experimentation on voluminous data, as well as analysis and visualization in multiple perspectives. Though current science gateways provide easy access to computing resources, datasets and tools specific to the disciplines, scientists often use slow and tedious manual efforts to perform knowledge discovery to accomplish their research/education tasks. Recommender systems can provide expert guidance and can help them to navigate and discover relevant publications, tools, data sets, or even automate cloud resource configurations suitable for a given scientific task. To realize the potential of integration ofmore »recommenders in science gateways in order to spur research productivity,we present a novel “OnTimeRecommend" recommender system. The OnTimeRecommend comprises of several integrated recommender modules implemented as microservices that can be augmented to a science gateway in the form of a recommender-as-a-service. The guidance for use of the recommender modules in a science gateway is aided by a chatbot plug-in viz., Vidura Advisor. To validate our OnTimeRecommend, we integrate and show benefits for both novice and expert users in domain-specific knowledge discovery within two exemplar science gateways, one in neuroscience (CyNeuro) and the other in bioinformatics (KBCommons).« less
  7. Abstract The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hardmore »scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.« less
    Free, publicly-accessible full text available December 1, 2023