Action minimizing fronts in general FPU-type chains

We study atomic chains with nonlinear nearest neighbour interactions and prove the existence of fronts (heteroclinic travelling waves with constant asymptotic states). Generalizing recent results of Herrmann and Rademacher we allow for non-convex interaction potentials and find fronts with non-monotone profile. These fronts minimize an action integral and can only exists if the asymptotic states fulfil the macroscopic constraints and if the interaction potential satisfies a geometric graph condition. Finally, we illustrate our findings by numerical simulations.Comment: 19 pages, several figure

The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau

We have carried out an analysis of about 160 eclipse timings spanning over 30 years of the Hyades eclipsing binary V471 Tauri that shows a long-term quasi-sinusoidal modulation of its observed eclipse arrival times. The O-Cs have been analyzed for the ``light-time'' effect that arises from the gravitational influence of a tertiary companion. The presence of a third body causes the relative distance of the eclipsing pair to the Earth to change as it orbits the barycenter of the triple system. The result of the analysis of the eclipse times yields a light-time semi-amplitude of 137.2+/-12.0 s, an orbital period of P_3 = 30.5+/-1.6 yr and an eccentricity of e_3 = 0.31+/-0.04. The mass of the tertiary component is M_3 sin i_3 = 0.0393+/-0.0038 Mo when a total mass of 1.61+/-0.06 Mo for V471 Tau is adopted. For orbital inclinations i_3 > 35 deg, the mass of the third body would be below the stable hydrogen burning limit of M = 0.07 Mo and it thus would be a brown dwarf. In the next several years (near maximum elongation), it should be feasible to obtain IR images and spectra of V471 Tau C that, when combined with the known mass, age, distance, and [Fe/H], will serve as a benchmark for understanding the physical properties and evolution of brown dwarfs.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter

Contact binaries with additional components. III. The adaptive optics detections

We present results of the CFHT adaptive optics search for companions of a homogeneous group of contact binary stars, as a contribution to our attempts to prove a hypothesis that these binaries require a third star to become so close as observed. In addition to companions directly discovered at separations of >=1", we introduced a new method of AO image analysis utilizing distortions of the AO diffraction ring pattern at separations of 0.07"-1". Very close companions, with separations in the latter range were discovered in systems HV Aqr, OO Aql, CK Boo, XY Leo, BE Scl, and RZ Tau. More distant companions were detected in V402 Aur, AO Cam, V2082 Cyg. Our results provide a contribution to the mounting evidence that the presence of close companions is a very common phenomenon for very close binaries with orbital periods <1 day.Comment: Full Figs.4 and 5 are in http://www.astro.utoronto.ca/~rucinski/Triples3

Playing Ping Pong with Light: Directional Emission of White Light

Over the last decades, light-emitting diodes (LED) have replaced common light bulbs in almost every application, from flashlights in smartphones to automotive headlights. Illuminating nightly streets requires LEDs to emit a light spectrum that is perceived as pure white by the human eye. The power associated with such a white light spectrum is not only distributed over the contributing wavelengths but also over the angles of vision. For many applications, the usable light rays are required to exit the LED in forward direction, namely under small angles to the perpendicular. In this work, we demonstrate that a specifically designed multi-layer thin film on top of a white LED increases the power of pure white light emitted in forward direction. Therefore, the deduced multi-objective optimization problem is reformulated via a real-valued physics-guided objective function that represents the hierarchical structure of our engineering problem. Variants of Bayesian optimization are employed to maximize this non-deterministic objective function based on ray tracing simulations. Eventually, the investigation of optical properties of suitable multi-layer thin films allowed to identify the mechanism behind the increased directionality of white light: angle and wavelength selective filtering causes the multi-layer thin film to play ping pong with rays of light

Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus

Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P = 1.8855 and 1.3873 d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73 yr, while they undergo continuous increases at rates of dP/dt = +4.4 × 10−7 and +4.0 × 10−7 d yr−1, respectively. The periodic variations can be interpreted as light travel times effects caused by the presence of invisible tertiary components suggesting that they may be quadruple systems. It is possible that the additional bodies may play an important role in the formation and evolution of the two massive overcontact binaries by removing angular momentum from the central systems, and causing the eclipsing pairs to have lower angular momentum and shorter initial orbital periods. In this way, the original detached systems can evolve into the present overcontact configurations via a Case A mass transfer. This is in agreement with the observed long-term period increase of V382 Cyg and TU Mus, which can be explained by mass transfers from the less massive components to the more massive ones. It is found that the time-scales of the long-term period variations of both systems are much longer than the thermal time-scales of the secondary components, but are close to their nuclear time-scales. This suggests that the two massive binaries have been through the rapid mass-transfer evolutionary stage on the thermal time-scales of the secondaries, and they are now on the slow phase of Case A mass transfer. It is shown that massive overcontact binaries are going through a short-lived overcontact configuration during the evolutionary phases of Case A mass transfer, which is different from the situation of late-type overcontact binary stars where components remain in good overcontact configuration driving by a combination of thermal relaxation oscillation and variable angular momentum loss via change in overcontact depth. This conclusion is in agreement with the distribution of overcontact binary stars along with the orbital period.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus

Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P = 1.8855 and 1.3873 d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73 yr, while they undergo continuous increases at rates of dP/dt = +4.4 × 10−7 and +4.0 × 10−7 d yr−1, respectively. The periodic variations can be interpreted as light travel times effects caused by the presence of invisible tertiary components suggesting that they may be quadruple systems. It is possible that the additional bodies may play an important role in the formation and evolution of the two massive overcontact binaries by removing angular momentum from the central systems, and causing the eclipsing pairs to have lower angular momentum and shorter initial orbital periods. In this way, the original detached systems can evolve into the present overcontact configurations via a Case A mass transfer. This is in agreement with the observed long-term period increase of V382 Cyg and TU Mus, which can be explained by mass transfers from the less massive components to the more massive ones. It is found that the time-scales of the long-term period variations of both systems are much longer than the thermal time-scales of the secondary components, but are close to their nuclear time-scales. This suggests that the two massive binaries have been through the rapid mass-transfer evolutionary stage on the thermal time-scales of the secondaries, and they are now on the slow phase of Case A mass transfer. It is shown that massive overcontact binaries are going through a short-lived overcontact configuration during the evolutionary phases of Case A mass transfer, which is different from the situation of late-type overcontact binary stars where components remain in good overcontact configuration driving by a combination of thermal relaxation oscillation and variable angular momentum loss via change in overcontact depth. This conclusion is in agreement with the distribution of overcontact binary stars along with the orbital period.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

How should we measure psychological resilience in sport performers?

Psychological resilience is important in sport because athletes must constantly withstand a wide range of pressures to attain and sustain high performance. To advance psychologists’ understanding of this area, there exists an urgent need to develop a sport-specific measure of resilience. The purpose of this paper is to review psychometric issues in resilience research and to discuss the implications for sport psychology. Drawing on the wider general psychology literature to inform the discussion, the narrative is divided into three main sections relating to resilience and its assessment: adversity, positive adaptation, and protective factors. The first section reviews the different ways that adversity has been measured and considers the potential problems of using items with varying degrees of controllability and risk. The second section discusses the different approaches to assessing positive adaptation and examines the issue of circularity pervasive in resilience research. The final section explores the various issues related to the assessment of protective factors drawing directly from current measures of resilience in other psychology sub-disciplines. The commentary concludes with key recommendations for sport psychology researchers seeking to develop a measure of psychological resilience in athletes