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  1. Free, publicly-accessible full text available June 1, 2023
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  3. Free, publicly-accessible full text available December 1, 2022
  4. Additive Manufacturing (AM) enables the direct production of complex geometries from computer-aided designs (CAD). The AM fabrication process is often executed in a layer-by-layer manner, whereby minute printing errors in one layer can manifest significant defects in the final part. In-situ quality monitoring and control are currently limited for AM processes and cause low repeatability. Recently. advanced imaging is increasingly invested in AM and leads to the proliferation of layerwise imaging data, which provides an opportunity to transform quality control of AM from post-build inspection to in-situ quality monitoring. However, existing methodologies for in-situ inspection primarily focus on key characteristicsmore »of image profiles that tend to be limited in the ability to analyze the variance components, as well as root causes and failure patterns that are critical to process improvement. This paper presents an Additive Gaussian Process with dependent layerwise correlation (AGP-D) to model the spatio-temporal correlation of layerwise imaging data for AM quality monitoring. The AGP-D consists of three independent GP modules. The first GP approximates the base profile, whereas the second and third GP capture the correlation within the same layer and among layers, respectively. Based on posterior predictions of new layers, Hotelling 𝑻2 and generalized likelihood ratio (GLR) control tests are formulated to detect process shifts in the newly fabricated layer and analyze root causes. The proposed methodology is evaluated and validated using both simulation data and real-world case study of a cylinder build fabricated by a laser powder bed fusion (LPBF) machine. Experimental results show the proposed AGP-D is effective for real-time modeling and monitoring of layerwise-correlated imaging data.« less
    Free, publicly-accessible full text available July 1, 2022
  5. ABSTRACT Active galactic nuclei (AGNs) feedback is responsible for maintaining plasma in global thermal balance in extended haloes of elliptical galaxies and galaxy clusters. Local thermal instability in the hot gas leads to the formation of precipitating cold gas clouds that feed the central supermassive black holes, thus heating the hot gas and maintaining global thermal equilibrium. We perform 3D magnetohydrodynamical (MHD) simulations of self-regulated AGNs feedback in a Perseus-like galaxy cluster with the aim of understanding the impact of the feedback physics on the turbulence properties of the hot and cold phases of the intracluster medium (ICM). We findmore »that, in general, the cold phase velocity structure function (VSF) is steeper than the prediction from Kolmogorov’s theory. We attribute the physical origin of the steeper slope of the cold phase VSF to the driving of turbulent motions primarily by the gravitational acceleration acting on the ballistic clouds. We demonstrate that, in the pure hydrodynamical case, the precipitating cold filaments may be the dominant agent driving turbulence in the hot ICM. The arguments in favour of this hypothesis are that: (i) the cold phase mass dominates over hot gas mass in the inner cool core; (ii) hot and cold gas velocities are spatially correlated; (iii) both the cold and hot phase velocity distributions are radially biased. We show that, in the MHD case, the turbulence in the ambient hot medium (excluding the jet cone regions) can also be driven by the AGN jets. The driving is then facilitated by enhanced coupling due to magnetic fields of the ambient gas and the AGN jets. In the MHD case, turbulence may thus be driven by a combination of AGN jet stirring and filament motions. We conclude that future observations, including those from high spatial and spectral resolution X-ray missions, may help to constrain self-regulated AGN feedback by quantifying the multitemperature VSF in the ICM.« less
  6. In this work we examine youth learning in an informal computing program implemented through a library-university partnership. In particular, we introduce and illustrate a culturally responsive computing framework which served as a foundation for the design of the program. Subsequently, we examine youth collaboration as well as affective and cognitive learning outcomes. Data were collected from university program facilitators and 30 youth over one semester. Data were collected through observations, lesson plans, computational artifacts and interviews with two case study youth. Results indicated that youth formed a variety of learning communities during the collaborative development of computing artifacts. Frequent participantsmore »were found to work with a greater number of peers compared to less frequent participants. Results from case study participants also indicated improvements in their computational competencies. Findings from this work have implications for the design of informal learning environments that help broaden participation in computing.« less
  7. In this work we examine youth learning in an informal computing programimplemented through a library-university partnership. In particular, we introduce and illustrate a culturally responsive computing framework which served as a foundation for the design of the program. Subsequently, we examine youth collaboration as well as affective and cognitive learning outcomes. Data were collected from university program facilitators and 30 youth over one semester. Data were collected through observations, lesson plans, computational artifacts and interviews with two case study youth. Results indicated that youth formed a variety of learning communities during the collaborative development of computing artifacts. Frequent participants weremore »found to work with a greater number of peers compared to less frequent participants. Results from case study participants also indicated improvements in their computational competencies. Findings from this work have implications for the design of informal learning environments that help broaden participation in computing.« less
  8. Despite increased attention on promoting access to computer science among all students, female and racially minoritized youth continue to be underrepresented in STEM, often lacking opportunities for computer science due to under-resourced schools and a lack of teacher preparation. As a result, K-12 schools are unable to fulfill the goal of expanding access and broadening participation in computing alone. In this paper, we examine how our university-library partnerships can provide access to computer science instruction while attending to issues of social justice through culturally responsive informal learning design. Findings provide insights related to the design, implementation, and outcomes of informalmore »computing clubs for youth from diverse backgrounds.« less