The radiation of a uniformly accelerated charge is beyond the horizon: a simple derivation

We show, by exploring some elementary consequences of the covariance of Maxwell's equations under general coordinate transformations, that, despite inertial observers can indeed detect electromagnetic radiation emitted from a uniformly accelerated charge, comoving observers will see only a static electric field. This simple analysis can help understanding one of the most celebrated paradoxes of last century.Comment: Revtex, 6 pages, 2 figures. v2: Some small corrections. v3: Citation of a earlier paper included. v4: Some stylistic changes. v5: Final version to appear in AJ

A systematic review of the experience, occurrence, and controllability of flow states in elite sport

Objectives: This study aimed to provide an up-to-date summary of the literature on flow in elite sport, specifically relating to: (i) how flow is experienced; (ii) how these states occur; and (iii) the potential controllability of flow. Design: Systematic review. Methods: A comprehensive literature search of SPORTdiscus, PsycINFO, SAGE journals online, INGENTA connect, and Web of Knowledge was completed in August, 2011, and yielded 17 empirical studies published between 1992 and 2011. The primarily qualitative findings were analysed thematically and synthesised using a narrative approach. Results: Findings indicated that: (i) some flow dimensions appear to be experienced more consistently than others; (ii) key factors were consistently reported to induce or inhibit flow occurrence; and (iii) the perception that flow experiences could be controllable to some extent, and are not merely ‘coincidental’. Additionally, it is appears that physiology is also relevant in flow, and these experiences may be psychophysiological. Conclusions: Based on these findings, recommendations are made including the need for researchers to move from description to explanation of flow, the use of new methodologies, greater focus on the role of personality factors, and possible refinements of existing flow theory to be more specific to sport

Variational principle for the Wheeler-Feynman electrodynamics

We adapt the formally-defined Fokker action into a variational principle for the electromagnetic two-body problem. We introduce properly defined boundary conditions to construct a Poincare-invariant-action-functional of a finite orbital segment into the reals. The boundary conditions for the variational principle are an endpoint along each trajectory plus the respective segment of trajectory for the other particle inside the lightcone of each endpoint. We show that the conditions for an extremum of our functional are the mixed-type-neutral-equations with implicit state-dependent-delay of the electromagnetic-two-body problem. We put the functional on a natural Banach space and show that the functional is Frechet-differentiable. We develop a method to calculate the second variation for C2 orbital perturbations in general and in particular about circular orbits of large enough radii. We prove that our functional has a local minimum at circular orbits of large enough radii, at variance with the limiting Kepler action that has a minimum at circular orbits of arbitrary radii. Our results suggest a bifurcation at some radius below which the circular orbits become saddle-point extrema. We give a precise definition for the distributional-like integrals of the Fokker action and discuss a generalization to a Sobolev space of trajectories where the equations of motion are satisfied almost everywhere. Last, we discuss the existence of solutions for the state-dependent delay equations with slightly perturbated arcs of circle as the boundary conditions and the possibility of nontrivial solenoidal orbits

An accurate density functional theory for the vapor-liquid interface of associating chain molecules based on the statistical associating fluid theory for potentials of variable range.

Published versio

Exploring the interactions underlying flow states: A connecting analysis of flow occurrence in European Tour golfers

Objectives: Research to date has identified a range of factors suggested to facilitate flow states in sport. However, less attention has focused on how exactly those facilitating factors influence the occurrence of flow. Therefore, this study aimed to explore the specific ways in which such facilitators influenced flow occurrence in European Tour golfers. Design: Qualitative design. Method: Ten full-time golfers from the European Tour (M age=37; SD=13.08) participated in semi-structured interviews investigating the occurrence of their flow states. Data were interpreted using an iterative process of thematic and connecting analyses. Results: Ten facilitators of flow were identified, of which commitment and the caddie have not been reported previously. Twenty four connecting links were identified in the data, through which the caddie, effective preparation, and high-quality performance appeared to be most influential for flow occurrence. Confidence and concentration also emerged as key constructs underlying the flow experience in this setting. Conclusion: A central contribution of this study is the identification of ways in which facilitating factors could influence flow occurrence in elite golf. This process adds detail to understanding of flow occurrence, and moves beyond simply identifying factors which are associated with the experience. As such, connecting analysis is proposed as an additional strategy for qualitatively investigating flow occurrence in sport. Results are discussed in relation to previous literature, and recommendations are identified for researchers, athletes, coaches and practitioners