In this work we investigate the peer grading assignments which were an integral part of the astronomy Massive Open Online Course (MOOC) "Astronomy: Exploring Time and Space" provided through Coursera from March to May 2015. Our general goal is to assess the role of peer graded assignments in such courses and how they contribute to students' learning and motivation. In order to achieve this broad goal we look at the peer grading process from multiple perspectives. We present an analysis of demographics for peer grading participants and show how they are different from the general course population. We also look at different aspects of peer grading assignments such as lengths of essays, time spent grading, number of gradings performed, final grades and percentage of relevant videos watched. We compare these distributions for different assignments and also their correlations on a level of individual learners. We show that participation in the first peer graded assignment is the best predictor of completion for the course as a whole. Moreover, learners who did well on the first peer graded assignment show better engagement and do better in the course overall. Finally, we report on validity and reliability of peer graders as compared to instructor graders and trained undergraduate graders.

The covariant motion of a classical point particle with magnetic moment in the presence of (external) electromagnetic fields is revisited. We are interested in understanding extensions to the Lorentz force involving point particle magnetic moment (Stern-Gerlach force) and how the spin precession dynamics is modified for consistency. We introduce spin as a classical particle property inherent to Poincaré symmetry of space-time. We propose a covariant formulation of the magnetic force based on a 'magnetic' 4-potential and show how the point particle magnetic moment relates to the Amperian (current loop) and Gilbertian (magnetic monopole) descriptions. We show that covariant spin precession lacks a unique form and discuss the connection to g − 2 anomaly. We consider the variational action principle and find that a consistent extension of the Lorentz force to include magnetic spin force is not straightforward. We look at non-covariant particle dynamics, and present a short introduction to the dynamics of (neutral) particles hit by a laser pulse of arbitrary shape.

One side-effect of the COVID-19 pandemic has been increased enrollment in online classes. The paper explores the surge in activity from March through June 2020 in two massive open online classes (MOOCs) on Astronomy, offered by Coursera and Udemy. The increase in enrollment in both classes was an order of magnitude over the similar time span in previous years. Learners enrolling during the pandemic were more likely to be younger than thirty and less likely to have advanced degrees. A majority were full-time undergraduate students, and relatively few were professionals working in technical fields. The largest number of new students were from India and overall, the biggest surge in enrollment came from people in developing countries, particularly in Asia. Those who enrolled during the pandemic were more likely to take the course to get a certificate or to further their career goals than because they had intrinsic interest in the subject. Social motivations were important, particularly among full-time students in the course. These results, albeit limited to MOOCs in astronomy, suggest that new audiences have been turning to online classes during the pandemic for gaining credentials or advancing their professional skills.

We investigate relativistic quantum mechanics (RQM) for particles with arbitrary magnetic moment. We compare two well known RQM models: a) Dirac equation supplemented with an incremental Pauli term (DP); b) Klein-Gordon equations with full Pauli EM dipole moment term (KGP). We compare exact solutions to the external field cases in the limit of weak and strong (critical) fields for: i) homogeneous magnetic field, and ii) the Coulomb 1/r-potential. For i) we consider the Landau energies and the Landau states as a function of the gyromagnetic factor (g-factor). For ii) we investigate contribution to the Lamb shift and the fine structure splitting. For both we address the limit of strong binding and show that these two formulations grossly disagree. We discuss possible experiments capable of distinguishing between KGP and DP models in laboratory. We describe impact of our considerations in astrophysical context (magnetars). We introduce novel RQM models of magnetic moments which can be further explored. PACS. 13.40.Em Electric and magnetic moments 03.65.PmRelativistic wave equations 31.30.J-Relativistic and quantum electrodynamics (QED) 36.10.-kExotic atoms and molecules 97.60.GbPulsars, Magnetars

Interaction of magnetic moment of point particles with external electromagnetic fields experiences unresolved theoretical and experimental discrepancies. In this work we point out several issues within the relativistic quantum mechanics and the QED and we describe effects related to a new covariant classical model of magnetic moment dynamics. Using this framework we explore the invariant acceleration experienced by neutral particles coupled to an external plane wave field through the magnetic moment: we study the case of ultra relativistic Dirac neutrinos with magnetic moment in the range of 10 −11 to 10 −20 µ B ; and we address the case of slowly moving neutrons. We explore how critical accelerations for neutrinos can be experimentally achieved in laser-pulse interactions. The radiation of accelerated neutrinos can serve as an important test distinguishing between Majorana and Dirac nature of neutrinos.