SATURN'S INNER SATELLITES: ORBITS, MASSES, AND THE CHAOTIC MOTION OF ATLAS FROM NEW CASSINI IMAGING OBSERVATIONS

We present numerically-derived orbits and mass estimates for the inner Saturnian satellites, Atlas, Prometheus, Pandora, Janus and Epimetheus from a fit to 2580 new Cassini ISS astrometric observations spanning February 2004 to August 2013. The observations are provided in a supplementary table. We estimate GM_ Atlas=0.384+/-0.001 x 10^(-3)km^3s^(-2), a value 13% smaller than the previously published estimate but with an order of magnitude reduction in the uncertainty. We also find GM_ Prometheus=10.677+/-0.006x10(-3)km^3s^(-2), GM_Pandora=9.133+/-0.009x10^(-3)km^3s^(-2), GM_Janus=126.51+/-0.03x10^(-3)km^3s^(-2) and GM_Epimetheus=35.110+/-0.009x10^(-3)km^3s^(-2), consistent with previously published values, but also with significant reductions in uncertainties. We show that Atlas is currently librating in both the 54:53 co-rotation-eccentricity resonance (CER) and the 54:53 inner Lindblad (ILR) resonance with Prometheus, making it the latest example of a coupled CER-ILR system, in common with the Saturnian satellites Anthe, Aegaeon and Methone, and possibly Neptune's ring arcs. We further demonstrate that Atlas's orbit is chaotic, with a Lyapunov time of ~10 years, and show that its chaotic behaviour is a direct consequence of the coupled resonant interaction with Prometheus, rather than being an indirect effect of the known chaotic interaction between Prometheus and Pandora. We provide an updated analysis of the second-order resonant perturbations involving Prometheus, Pandora and Epimetheus based on the new observations, showing that these resonant arguments are librating only when Epimetheus is the innermost of the co-orbital pair, Janus and Epimetheus. We also find evidence that the known chaotic changes in the orbits of Prometheus and Pandora are not confined to times of apse anti-alignement.Comment: 23 pages, 16 figures. Accepted for publication in The Astronomical Journal 23 September 2014 (corrected Fig. 11

Phases of driven two-level systems with nonlocal dissipation

We study an array of two-level systems arranged on a lattice and illuminated by an external plane wave which drives a dipolar transition between the two energy levels. In this set up, the two-level systems are coupled by dipolar interactions and subject to nonlocal dissipation, so behave as an open many-body quantum system. We investigate the long-time dynamics of the system at the mean-field level, and use this to determine a phase diagram as a function of external drive and detuning. We find a multitude of phases including antiferromagnetism, spin density waves, oscillations and phase bistabilities. We investigate these phases in more detail and explain how nonlocal dissipation plays a role in the long-time dynamics. Furthermore, we discuss what features would survive in the full quantum description

Decay rates and energies of free magnons and bound states in dissipative XXZ chains

Chains of coupled two-level atoms behave as 1D quantum spin systems, exhibiting free magnons and magnon bound states. While these excitations are well studied for closed systems, little consideration has been given to how they are altered by the presence of an environment. This will be especially important in systems that exhibit nonlocal dissipation, e.g. systems in which the magnons decay due to optical emission. In this work, we consider free magnon excitations and two-magnon bound states in an XXZ chain with nonlocal dissipation. We prove that whilst the energy of the bound state can lie outside the two-magnon continuum of energies, the decay rate of the bound state has to always lie within the two-magnon continuum of decay rates. We then derive analytically the bound state solutions for a system with nearest-neighbour and next-nearest-neighbour XY interaction and nonlocal dissipation, finding that the inclusion of nonlocal dissipation allows more freedom in engineering the energy and decay rate dispersions for the bound states. Finally, we numerically study a model of an experimental set-up that should allow the realisation of dissipative bound states by using Rydberg-dressed atoms coupled to a photonic crystal waveguide (PCW). We demonstrate that this model can exhibit many key features of our simpler models

Steady states of a driven dissipative dipolar XXZ chain

We study theoretically a driven dissipative one-dimensional XXZ spin$-1/2$ chain with dipole coupling and a tunable strength of the Ising and XY interaction. Within a mean-field approximation, we find a rich phase diagram with uniform, spin density wave, antiferromagnetic and oscillatory phases, as well as regions of phase bistability. We study the phase diagram of small quantum systems using exact diagonalisation, and compare the results to the mean-field theory. We find that while expectation values only capture the uniform phases of the mean-field theory, fluctuations about these expectation values give signatures of spatially non-uniform phases and bistabilities. We find these signatures for all ratios of the Ising to XY interaction, showing that they appear to be general features of spin$-1/2$ system

Stable collective dynamics of two-level systems coupled by dipole interactions

We study the dynamics of a set of two-level systems coupled by dipolar interactions under a resonant external Rabi drive. The two-level systems are prepared initially in a coherent product state, and we ask how the nonequilibrium conditions caused by the drive affect this coherence. We study the full nonlinear dynamics of the coupled two-level systems within a classical approximation by analyzing numerically the equations of motion and determining the stability of the collective coherent state within classical Floquet theory. We establish the behavior analytically in the high Rabi coupling limit by employing a Magnus expansion and spin-wave analysis. Our results show that, typically, the dipole interactions between the two-level systems lead to instabilities that cause a breakdown of the collective Rabi oscillations. However, we identify parameter regimes for which the two-level systems undergo collective coherent Rabi oscillations even in the presence of the dipole interactions.This work was supported by EPSRC Grant No. EP/K030094/1

T2{}^2K2{}^2: The Twitter Top-K Keywords Benchmark

Information retrieval from textual data focuses on the construction of vocabularies that contain weighted term tuples. Such vocabularies can then be exploited by various text analysis algorithms to extract new knowledge, e.g., top-k keywords, top-k documents, etc. Top-k keywords are casually used for various purposes, are often computed on-the-fly, and thus must be efficiently computed. To compare competing weighting schemes and database implementations, benchmarking is customary. To the best of our knowledge, no benchmark currently addresses these problems. Hence, in this paper, we present a top-k keywords benchmark, T${}^2$K${}^2$, which features a real tweet dataset and queries with various complexities and selectivities. T${}^2$K${}^2$ helps evaluate weighting schemes and database implementations in terms of computing performance. To illustrate T${}^2$K${}^2$'s relevance and genericity, we successfully performed tests on the TF-IDF and Okapi BM25 weighting schemes, on one hand, and on different relational (Oracle, PostgreSQL) and document-oriented (MongoDB) database implementations, on the other hand

Recovery of the crucian carp Carassius carassius (L.): Approach and early results of an English conservation project

Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons Ltd The crucian carp Carassius carassius, a cyprinid fish characteristic of small ponds, is in decline throughout most of its European range, including in England where it is currently thought to be non-native. The present study, undertaken by the Norfolk Crucian Project, reports on reductions in pond populations of crucian carp in Norfolk, eastern England as well as the success of recent introduction/re-introduction efforts in terms of crucian survival, recruitment and growth over the last 10 years. A 72% decline in crucian carp distribution was observed between the 1950s–1980s and the 2010s. Of 18 crucian carp introductions/re-introductions to restored and suitable existing ponds, 17 were successful in terms of survival, increasing the number of current crucian sites in Norfolk by 37%. Recruitment of young crucian carp was demonstrated for 12 of the 18 stocked ponds, with apparent elevated juvenile growth relative to other English and European populations. Delays in, or a lack of, crucian recruitment in some ponds appeared to result from the presence of other fish species (especially threespine stickleback Gasterosteus aculeatus) with predation and interspecific competition possible contributory factors. This study shows that, through combinations of pond rehabilitation and stocking, it has been possible to achieve a substantial recovery of crucian carp populations in the study region. Although the crucian carp is currently presumed to be non-native within England, given other scientific studies that show a lack of adverse impacts of this species on native biota, and because it is greatly threatened in its native range, the call is sounded for more crucian carp conservation projects in other parts of England as well as in Europe more generally

Tissue inflammation signatures point towards resolution in adhesive capsulitis

Proresolving receptors, macrophage and fibroblast activation point towards a resolving inflammatory milieu in adhesive capsulitis

Risqué Business? Interpersonal Anxiety and Humor in the #MeToo Era

This is the author accepted manuscript. the final version is available from the American Psychological Association via the DOI in this recordInterpersonal anxiety (i.e., the fear of negative consequences from interacting with someone) may be more prominent in post-#MeToo organizations when interacting with someone of a different gender. Initial exchanges may particularly trigger this anxiety, obfuscating key organizational decisions such as hiring. Given humor’s positive, intrapersonal stress-reduction effects, we propose that humor also reduces interpersonal anxiety. In three mixed methods experiments with hiring managers, we examined the effects of applicant and evaluator gender (i.e., same-/mixed-gender dyad), positive applicant humor (i.e., a pun), and context (i.e., gender salience) in job interviews. Results showed that mixed-gender (vs. same-gender) interactions elicited more interpersonal anxiety, particularly when gender was more salient; mixed-gender interactions also predicted downstream attitudinal outcomes (e.g., social attraction and willingness to hire) and hiring decisions (e.g., selection and rejection) via interpersonal anxiety. Although humor reduced interpersonal anxiety and its consequences for female applicants, the opposite was true for male applicants when gender was salient, because it signaled some of the same expectations that initially triggered the interpersonal anxiety: the potential for harmful sexual behavior. In sum, we integrated diversity and humor theories to examine interpersonal anxiety in same- and mixed-gender interactions, then tested the extent to which humor relieved it.Swiss National Science Foundatio

The Caviar software package for the astrometric reduction of Cassini ISS images: description and examples

N.J.C. is grateful to the Paris Observatory for funding as an invited researcher at the IMCCE. We thank the FP7-ESPaCE European program for funding under the agreement No. 263466. N.J.C. and C.D.M. thank the Science and Technology Facilities Council (Grant No. ST/P000622/1) for financial support. This work was also supported by the International Space Science Institute (ISSI)