Search for: All records

AI-based educational technologies may be most welcome in classrooms when they align with teachers' goals, preferences, and instructional practices. Teachers, however, have scarce time to make such customizations themselves. How might the crowd be leveraged to help time-strapped teachers? Crowdsourcing pipelines have traditionally focused on content generation. It is an open question how a pipeline might be designed so the crowd can succeed in a revision/customization task. In this paper, we explore an initial version of a teacher-guided crowdsourcing pipeline designed to improve the adaptive math hints of an AI-based tutoring system so they fit teachers' preferences, while requiring minimal expert guidance. In two experiments involving 144 math teachers and 481 crowdworkers, we found that such an expert-guided revision pipeline could save experts' time and produce better crowd-revised hints (in terms of teacher satisfaction) than two comparison conditions. The revised hints however, did not improve on the existing hints in the AI tutor, which were carefully-written but still have room for improvement and customization. Further analysis revealed that the main challenge for crowdworkers may lie in understanding teachers' brief written comments and implementing them in the form of effective edits, without introducing new problems. We also found that teachers preferred their own revisions over other sources of hints, and exhibited varying preferences for hints. Overall, the results confirm that there is a clear need for customizing hints to individual teachers' preferences. They also highlight the need for more elaborate scaffolds so the crowd can have specific knowledge of the requirements that teachers have for hints. The study represents a first exploration in the literature of how to support crowds with minimal expert guidance in revising and customizing instructional materials. 

Nonequilibrium phase transitions play a pivotal role in broad physical contexts, from condensed matter to cosmology. Tracking the formation of nonequilibrium phases in condensed matter requires a resolution of the long-range cooperativity on ultra-short timescales. Here, we study the spontaneous transformation of a charge-density wave in CeTe₃from a stripe order into a bi-directional state inaccessible thermodynamically but is induced by intense laser pulses. With ≈100 fs resolution coherent electron diffraction, we capture the entire course of this transformation and show self-organization that defines a nonthermal critical point, unveiling the nonequilibrium energy landscape. We discuss the generation of instabilities by a swift interaction quench that changes the system symmetry preference, and the phase ordering dynamics orchestrated over a nonadiabatic timescale to allow new order parameter fluctuations to gain long-range correlations. Remarkably, the subsequent thermalization locks the remnants of the transient order into longer-lived topological defects for more than 2 ns.

 

Online education is rapidly expanding in response to rising demand for higher and continuing education, but many online students struggle to achieve their educational goals. Several behavioral science interventions have shown promise in raising student persistence and completion rates in a handful of courses, but evidence of their effectiveness across diverse educational contexts is limited. In this study, we test a set of established interventions over 2.5 y, with one-quarter million students, from nearly every country, across 247 online courses offered by Harvard, the Massachusetts Institute of Technology, and Stanford. We hypothesized that the interventions would produce medium-to-large effects as in prior studies, but this is not supported by our results. Instead, using an iterative scientific process of cyclically preregistering new hypotheses in between waves of data collection, we identified individual, contextual, and temporal conditions under which the interventions benefit students. Self-regulation interventions raised student engagement in the first few weeks but not final completion rates. Value-relevance interventions raised completion rates in developing countries to close the global achievement gap, but only in courses with a global gap. We found minimal evidence that state-of-the-art machine learning methods can forecast the occurrence of a global gap or learn effective individualized intervention policies. Scaling behavioral science interventions across various online learning contexts can reduce their average effectiveness by an order-of-magnitude. However, iterative scientific investigations can uncover what works where for whom. 

Abstract Geosphere-biosphere interactions are ubiquitous features of the Earth surface, yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail. To assess the nature, rate, and magnitude of vegetation influence on parent material and sediment delivery, we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern United States. Over time, terrigenous inputs declined at both sites, with increasing amounts of organic inputs toward present. The similarities between sites were striking given that the grassland sequence began in the Early Holocene, and the forested sequence began after the last glacial maximum. Multiple mechanisms of chemical weathering, hydrologic transport, and changes in source material potentially contribute to this pattern. Although there were strong links between vegetation composition and nitrogen cycling at each site, it appears that changes in forest type, or from oak woodland to grassland, did not exert a large influence on elemental (K, Ti, Si, Ca, Fe, Mn, and S) abundance in the sedimentary sequences. Rather, other factors in the catchment-lake system determined the temporal sequence of elemental abundance. 

Male gametophytes of most seed plants deliver sperm to eggs via a pollen tube. Pollen tube growth rates (PTGRs) of angiosperms are exceptionally rapid, a pattern attributed to more effective haploid selection under stronger pollen competition. Paradoxically, whole genome duplication (WGD) has been common in angiosperms but rare in gymnosperms. Pollen tube polyploidy should initially acceleratePTGRbecause increased heterozygosity and gene dosage should increase metabolic rates. However, polyploidy should also independently increase tube cell size, causing more work which should decelerate growth. We asked how genome size changes have affected the evolution of seed plantPTGRs.

We assembled a phylogenetic tree of 451 species with knownPTGRs. We then used comparative phylogenetic methods to detect effects of neo‐polyploidy (within‐genus origins),DNAcontent, andWGDhistory onPTGR, and correlated evolution ofPTGRandDNAcontent.

Gymnosperms had significantly higherDNAcontent and slowerPTGRoptima than angiosperms, and theirPTGRandDNAcontent were negatively correlated. For angiosperms, 89% of model weight favored Ornstein‐Uhlenbeck models with a fasterPTGRoptimum for neo‐polyploids, whereasPTGRandDNAcontent were not correlated. For within‐genus and intraspecific‐cytotype pairs,PTGRs of neo‐polyploids < paleo‐polyploids.

Genome size increases should negatively affectPTGRwhen genetic consequences ofWGDs are minimized, as found in intra‐specific autopolyploids (low heterosis) and gymnosperms (fewWGDs). But in angiosperms, the higherPTGRoptimum of neo‐polyploids and non‐negativePTGR‐DNAcontent correlation suggest that recurrentWGDs have caused substantialPTGRevolution in a non‐haploid state.

 

The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune–Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft—in a class equivalent to the NASA/ESA/ASI Cassini spacecraft—would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moon's gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ∼37 minutes to the 10 bar pressure level in Neptune's atmosphere just before Odyssey's orbit-insertion engine burn. Odyssey's mission would end by conducting a Cassini-like “Grand Finale,” passing inside the rings and ultimately taking a final great plunge into Neptune's atmosphere.