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Revealing core-valence interactions in solution with femtosecond X-ray pump X-ray probe spectroscopy
Abstract Femtosecond pump-probe spectroscopy using ultrafast optical and infrared pulses has become an essential tool to discover and understand complex electronic and structural dynamics in solvated molecular, biological, and material systems. Here we report the experimental realization of an ultrafast two-color X-ray pump X-ray probe transient absorption experiment performed in solution. A 10 fs X-ray pump pulse creates a localized excitation by removing a 1
s electron from an Fe atom in solvated ferro- and ferricyanide complexes. Following the ensuing Auger–Meitner cascade, the second X-ray pulse probes the Fe 1s → 3p transitions in resultant novel core-excited electronic states. Careful comparison of the experimental spectra with theory, extracts +2 eV shifts in transition energies per valence hole, providing insight into correlated interactions of valence 3d with 3p and deeper-lying electrons. Such information is essential for accurate modeling and predictive synthesis of transition metal complexes relevant for applications ranging from catalysis to information storage technology. This study demonstrates the experimental realization of the scientific opportunities possible with the continued development of multicolor multi-pulse X-ray spectroscopy to study electronic correlations in complex condensed phase systems. -
null (Ed.)When designing learning environments and curricula for diverse populations, it is beneficial to connect with learners’ cultural knowledge, and the related interests, they bring to the learning context. To aid in the design and development of a computing curriculum and identify these areas of personal and cultural connection, we conducted a series of participatory design sessions. The goal of these sessions was to col- lect ideas around ways to make the instructional materials reflect the interests and voices of the learners. In this paper, we examine how the use of participatory design techniques can advance our understanding of the domains influencing today’s youth. Specifically, we examine the ideas generated by youth during these sessions as a means to understand what influences them and their ideas of cultural relevancy. In this work, we identify the resources children draw on across design activities and organize them to extend the Spheres of Influence framework (L. Archer et al., 2014). We identify seven spheres to attend to when designing for learning: Home and Family, School and Work, Hobbies and Leisure, Media, Interests, Peers, and Identity.more » « less
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With many school districts nationwide integrating Computer Science (CS) and Computational Thinking (CT) instruction at the K-8 level, it is crucial that CS instruction be eective for diverse learners. A popular pedagogical approach is Use!Modify!Create, which introduces a concept through a more scaolded, guided instruction before culminating in a more open-ended project for student engagement. Yet, little research has gone into strategies that increase learning during the Use!Modify step. This paper introduces TIPP&SEE, a learning that further scaolds student learning during this step. Results from a quasi-experimental study show statistically-signicant outperformance from students using the TIPP&SEE strategy on all assessment questions of medium and hard difficulty, suggesting its potential as an eective CS learning strategymore » « less
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Gresalfi, M. ; Horn, I. (Ed.)The design of most learning environments focuses on supporting students in making, constructing, and putting together projects on and off the screen, with much less attention paid to the many issues—problems, bugs, or traps—that students invariably encounter along the way. In this symposium, we present different theoretical and disciplinary perspectives on understanding how learners engage in debugging applications on and off screen, examine learners’ mindsets about debugging from middle school to college students and teachers, and present pedagogical approaches that promote strategies for debugging problems, even having learners themselves design problems for others. We contend that learning to identify and fix problems—debug, troubleshoot, or get unstuck—in completing projects provides a productive space in which to explore multiple theoretical perspectives that can contribute to our understanding of learning and teaching critical strategies for dealing with challenges in learning activities and environments.more » « less