RealTimeChess: Lessons from a Participatory Design Process for a Collaborative Multi-Touch, Multi-User Game

We report on a long-term participatory design process during which we designed and improved RealTimeChess, a collaborative but competitive game that is played using touch input by multiple people on a tabletop display. During the design process we integrated concurrent input from all players and pace control, allowing us to steer the interaction along a continuum between high-paced simultaneous and low-paced turn-based gameplay. In addition, we integrated tutorials for teaching interaction techniques, mechanisms to control territoriality, remote interaction, and alert feedback. Integrating these mechanism during the participatory design process allowed us to examine their effects in detail, revealing for instance effects of the competitive setting on the perception of awareness as well as territoriality. More generally, the resulting application provided us with a testbed to study interaction on shared tabletop surfaces and yielded insights important for other time-critical or attention-demanding applications.

A Resource Theory for Work and Heat

Several recent results on thermodynamics have been obtained using the tools of quantum information theory and resource theories. So far, the resource theories utilised to describe thermodynamics have assumed the existence of an infinite thermal reservoir, by declaring that thermal states at some background temperature come for free. Here, we propose a resource theory of quantum thermodynamics without a background temperature, so that no states at all come for free. We apply this resource theory to the case of many non-interacting systems, and show that all quantum states are classified by their entropy and average energy, even arbitrarily far away from equilibrium. This implies that thermodynamics takes place in a two-dimensional convex set that we call the energy-entropy diagram. The answers to many resource-theoretic questions about thermodynamics can be read off from this diagram, such as the efficiency of a heat engine consisting of finite reservoirs, or the rate of conversion between two states. This allows us to consider a resource theory which puts work and heat on an equal footing, and serves as a model for other resource theories.Comment: main text: 12 pages, 5 figure; appendix: 7 page

An Orbital Stability Study of the Proposed Companions of SW Lyncis

We have investigated the dynamical stability of the proposed companions orbiting the Algol type short-period eclipsing binary SW Lyncis (Kim et al. 2010). The two candidate companions are of stellar to sub-stellar nature, and were inferred from timing measurements of the system's primary and secondary eclipses. We applied well-tested numerical techniques to accurately integrate the orbits of the two companions and to test for chaotic dynamical behaviour. We carried out the stability analysis within a systematic parameter survey varying both the geometries and orientation of the orbits of the companions, as well as their masses. In all our numerical integrations we found that the proposed SW Lyn multi-body system is highly unstable on time-scales on the order of 1000 years. Our results cast doubt on the interpretation that the timing variations are caused by two companions. This work demonstrates that a straightforward dynamical analysis can help to test whether a best-fit companion-based model is a physically viable explanation for measured eclipse timing variations. We conclude that dynamical considerations reveal that the propsed SW Lyncis multi-body system most likely does not exist or the companions have significantly different orbital properties as conjectured in Kim et al. (2010).Comment: 9 pages, 6 figures, 2 tables. Submitted to and accepted by JASS -- Journal for Astronomy and Space Sciences (using JKAS LaTeX style file

Smooth invariant densities for random switching on the torus

We consider a random dynamical system obtained by switching between the flows generated by two smooth vector fields on the 2d-torus, with the random switchings happening according to a Poisson process. Assuming that the driving vector fields are transversal to each other at all points of the torus and that each of them allows for a smooth invariant density and no periodic orbits, we prove that the switched system also has a smooth invariant density, for every switching rate. Our approach is based on an integration by parts formula inspired by techniques from Malliavin calculus.Comment: 19 page

The effects of steroid hormones on osteoclast function

Although steroids are known to exert important actions on the skeleton, little is known of their effects on osteoclasts. This thesis therefore investigates the effects of hydrocortisone (HC), dexamethasone (DEX), 1715-estradiol (E2), tamoxifen (TAM), 5a-dihydotestosterone (DHT) and progesterone on the principle function of osteoclasts: bone resorption. DHT and progesterone had little influence over bone resorption by osteoclasts disaggregated from neonatal rat long bones, as assessed by scanning electron microscopy. By contrast, HC and DEX were found to reduce bone resorption, due to an inhibitory action on osteoclast survival. Since the latter was antagonised by progesterone, a receptor-mediated mechanism was thought to be responsible. The effects of E2 were more complex. Higher concentrations caused delayed stimulation of bone resorption by isolated cultures of osteoclasts, whereas lower concentrations of E2 led to moderate inhibition in mixed osteoblast- osteoclast co-cultures obtained by extended sedimentation of the rat long bone suspension, and by the addition of calvarial or osteosarcoma (UMR and HOS) cells. In the presence of TAM, which was itself without effect, neither stimulatory nor inhibitory actions of E2 were evident, again suggesting a receptor-dependent process. However, E2 did not appear to influence osteoclast differentiation in mouse bone marrow cultures, as defined by bone resorption and the development of cell surface receptors for calcitonin. Following an in vivo study, no evidence for a stimulatory effect of high concentrations of E2 on bone resorption in adult female rats was found, as assessed by histomorphometric and biochemical parameters, although an unexpected increase in bone formation was observed. Therefore, while direct actions of steroid hormones on osteoclastic bone resorption may be involved in adapting skeletal regulation to the needs of reproduction and stress, the skeletal response elicited by these hormones in the intact animal may be substantially modified, presumably due to the co-existence of significant indirect effects

Jump Rope Vortex in Liquid Metal Convection

Understanding large scale circulations (LSCs) in turbulent convective systems is important for the study of stars, planets and in many industrial applications. The canonical model of the LSC is quasi-planar with additional horizontal sloshing and torsional modes [Brown E, Ahlers G (2009) J. Fluid Mech. 638:383--400; Funfschilling D, Ahlers G (2004) Phys. Rev. Lett. 92(19):194502; Xi HD et al. (2009) Phys. Rev. Lett. 102(4):044503; Zhou Q et al. (2009) J. Fluid Mech. 630:367--390]. Using liquid gallium as the working fluid, we show via coupled laboratory-numerical experiments that the LSC in a tank with aspect ratios greater than unity takes instead the form of a "jump rope vortex", a strongly three-dimensional mode that periodically orbits around the tank following a motion much like a jump rope on a playground. Further experiments show that this jump rope flow also exists in more viscous fluids such as water, albeit with a far smaller signal. Thus, this new jump rope mode is an essential component of the turbulent convection that underlies our observations of natural systems