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Ultra-high energy cosmic rays are the most extreme energetic particles detected on Earth, however, their acceleration sites are still mysterious. We explore the contribution of low-luminosity gamma-ray bursts to the ultra-high energy cosmic ray flux, since they form the bulk of the nearby population. We analyse a representative sample of these bursts detected by BeppoSAX, INTEGRAL, and Swift between 1998–2016, and found that in order to reconcile our theoretical flux with the observed flux, these bursts should accelerate at most 10−13 M⊙ of ultra-high energy cosmic rays.

 

Uranium (U) is an important global energy resource and a redox sensitive trace element that reflects changing environmental conditions and geochemical cycling. The redox evolution of U mineral chemistry can be interrogated to understand the formation and distribution of U deposits and the redox processes involved in U geochemistry throughout Earth history. In this study, geochemical modeling using thermodynamic data, and mineral chemistry network analysis are used to investigate U geochemistry and deposition through time. The number of U⁶⁺mineral localities surpasses the number of U⁴⁺mineral localities in the Paleoproterozoic. Moreover, the number of sedimentary U⁶⁺mineral localities increases earlier in the Phanerozoic than the number of U⁴⁺sedimentary mineral localities, likely due to the necessity of sufficient sedimentary organic matter to reduce U⁶⁺–U⁴⁺. Indeed, modeling calculations indicate that increased oxidative weathering due to surface oxygenation limited U⁴⁺uraninite (UO₂) formation from weathered granite and basalt. Louvain network community detection shows that U⁶⁺forms minerals with many more shared elements and redox states than U⁴⁺. The range of weighted Mineral Element Electronegativity Coefficient of Variation (wMEE_CV) values of U⁶⁺minerals increases through time, particularly during the Phanerozoic. Conversely, the range of wMEE_CVvalues of U⁴⁺minerals is consistent through time due to the relative abundance of uraninite, coffinite, and brannerite. The late oxidation and formation of U⁶⁺minerals compared to S⁶⁺minerals illustrates the importance of the development of land plants, organic matter deposition, and redox‐controlled U deposition from ground water in continental sediments during this time‐period.

 

Abstract We present coordinated observations of GRB 170202A carried out by the Zadko and the Virgin Island Robotic Telescopes. The observations started 59 s after the event trigger, and provided nearly continuous coverage for two days, due to the unique locations of these telescopes. We clearly detected an early rise in optical emission, followed by late optical flares. By complementing these data with archival observations, we show that GRB 170202A is well described by the standard fireball model if multiple reverse shocks are taken into account. Its fireball is evidenced as expanding within a constant-density interstellar medium, with most burst parameters being consistent with the usual ranges found in the literature. The electron and magnetic energy parameters ( ϵ e , ϵ B ) are orders of magnitude smaller than the commonly assumed values. We argue that the global fit of the fireball model achieved by our study should be possible for any burst, pending the availability of a sufficiently comprehensive data set. This conclusion emphasizes the crucial importance of coordinated observation campaigns of gamma-ray bursts, such as the one central to this work, to answer outstanding questions about the underlying physics driving these phenomena. 

Touch is often omitted or viewed as unnecessary in digital learning. Lack of touch feedback limits the accessibility and multimodal capacity of digital educational content. Touchscreens with vibratory, haptic feedback are prevalent, yet this kind of feedback is often under-utilized. This work provides initial investigations into the design, development, and use of vibratory feedback within multimodal, interactive, educational simulations on touchscreen devices by learners with and without visual impairments. The objective of this work is to design and evaluate different haptic paradigms that could support interaction and learning in educational simulations. We investigated the implementation of four haptic paradigms in two physics simulations. Interviews were conducted with eight learners (five sighted learners; three learners with visual impairments) on one simulation and initial results are shared. We discuss the learner outcomes of each paradigm and how they impact design and development moving forward. 

Presentation given at the ISC19 Workshop on Interactive High-Performance Computing 

Open OnDemand is an open source project designed to lower the barrier to HPC use across many diverse disciplines. Here we describe the main features of the platform, give several use cases of Open On-Demand and discuss how we measure success. We end the paper with a discussion of the future project roadmap. Pre-conference paper submitted to ISC19 Workshop on Interactive High-Performance Computing.