Dynamics of single hydrogen bubbles at Pt microelectrodes in microgravity.

The dynamics of single hydrogen bubbles electrogenerated in acidic electrolytes at a Pt microelectrode under potentiostatic conditions is investigated in microgravity during parabolic flights. Three bubble evolution scenarios have been identified depending on the electric potential applied and the acid concentration. The dominant scenario, characterized by lateral detachment of the grown bubble, is studied in detail. For that purpose, the evolution of the bubble radius, electric current and bubble trajectories, as well as the bubble lifetime are comprehensively addressed for different potentials and electrolyte concentrations. We focus particularly on analyzing bubble-bubble coalescence events which are responsible for reversals of the direction of bubble motion. Finally, as parabolic flights also permit hypergravity conditions, a detailed comparison of the characteristic bubble phenomena at various levels of gravity is drawn.

The trainer matters: Cross-classified models of trainee reactions.

Despite the common belief that "training is only as effective as the trainer providing it" (Osborn, 2018, para. 1), training theory tends to underemphasize the trainer and instead focuses on training content and design as sources of training effectiveness. In this article, we examine whether the role of the trainer should be more central to training theory. We address this issue using a dataset of trainee reactions from more than 10,000 employees enrolled in professional development courses. We suggest that trainee reactions are more likely to be influenced by the trainer than by the content. Thus, trainee reactions should reflect more between-trainer variance than between-content variance. Across 2 studies in online and face-to-face contexts, cross-classified random-effects models provide general support for our hypotheses, with 1 notable exception: the trainer matters less for trainee reactions in online courses. Our findings suggest the trainer matters more than previously thought and, thus, training theory should incorporate the role of the trainer in training effectiveness. Based on our findings, we suggest that training researchers should (a) model the trainer as a source of variation in training evaluation metrics, (b) examine the effect of the trainer at multiple levels of analysis, and (c) explicitly model the role of the trainer in training theory and design. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Stability criterion for the magnetic separation of rare-earth ions.

The stability criterion for the magnetic separation of rare-earth ions is studied, taking dysprosium Dy(iii) ions as an example. Emphasis is placed on quantifying the factors that limit the desired high enrichment. During magnetic separation, a layer enriched in Dy(iii) ions is generated via the surface evaporation of an aqueous solution which is levitated by the Kelvin force. Later, mass transport triggers instability in the enriched layer. The onset time and position of the instability is studied using an interferometer. The onset time signals that an advective process which significantly accelerates the stratification of enrichment is taking place, although the initial phase is quasi-diffusion-like. The onset position of the flow agrees well with that predicted with a generalized Rayleigh number (Ra^{*}=0) criterion which includes the Kelvin force term acting antiparallel to gravity. Further three-dimensional analysis of the potential energy, combining magnetic and gravitational terms, shows an energy barrier that has to be overcome to initiate instability. The position of the energy barrier coincides well with the onset position of the instability.