Synchronisation under shocks: The Lévy Kuramoto model

We study the Kuramoto model of identical oscillators on Erdős-Rényi (ER) and Barabasi–Alberts (BA) scale free networks examining the dynamics when perturbed by a Lévy noise. Lévy noise exhibits heavier tails than Gaussian while allowing for their tempering in a controlled manner. This allows us to understand how ‘shocks’ influence individual oscillator and collective system behaviour of a paradigmatic complex system. Skewed α-stable Lévy noise, equivalent to fractional diffusion perturbations, are considered, but overlaid by exponential tempering of rate λ. In an earlier paper we found that synchrony takes a variety of forms for identical Kuramoto oscillators subject to stable Lévy noise, not seen for the Gaussian case, and changing with α: a noise-induced drift, a smooth α dependence of the point of cross-over of synchronisation point of ER and BA networks, and a severe loss of synchronisation at low values of α. In the presence of tempering we observe both analytically and numerically a dramatic change to the α1 tempered cases. Analytically we study the system close to the phase synchronised fixed point and solve the tempered fractional Fokker–Planck equation. There we observe that densities show stronger support in the basin of attraction at low α for fixed coupling, σ and tempering λ. We then perform numerical simulations for networks of size N=1000 and average degree d̄=10. There, we compute the order parameter r as a function of σ for fixed α and λ and observe values of r≈1 over larger ranges of σ for α<1 and λ≠0. In addition we observe drift of both positive and negative slopes for different α and λ when native frequencies are equal, and confirm a sustainment of synchronisation down to low values of α. We propose a mechanism for this in terms of the basic shape of the tempered stable Lévy densities for various α and how it feeds into Kuramoto oscillator dynamics and illustrate this with examples of specific paths.One of us (ACK) is supported through a Chief Defence Scientist Fellowship and expresses gratitude for the hospitality of ANU

Assessing the validity and reliability and determining cut-points of the Actiwatch 2 in measuring physical activity

Objective: The Actiwatch 2 (AW2) is a wrist-worn accelerometer typically used to measure sleep. Although it can measure physical activity, there is limited evidence supporting its validity. We assessed the validity and reliability of the AW2 to measure sedentary behavior and physical activity (light, moderate, vigorous intensities), and reported their respective count cut-points. Approach: Twenty-eight males and 22 females completed a task battery comprising three sedentary tasks and six randomized physical activity tasks at varying intensities, whilst wearing the AW2, a reference accelerometry device (Actigraph GT3X) and a cardiopulmonary gas analyzer on two separate occasions. Validity was assessed using correlations (AW2 counts versus GT3X counts and metabolic equivalent (MET) values), reliability using Bland–Altman analyses, and cut-points were determined using receiver operating characteristic (ROC) area under the curve (AUC) analyses. Main results: AW2 counts were positively correlated with GT3X counts (rho = 0.902, p < 0.001) and METs (rho = 0.900, p < 0.001). AW2-derived counts were comparable across independent assessment periods. Sedentary (AUC = 0.99, cut-point: 256 cpm) and vigorous activity (AUC = 0.95, cut-point: 720 cpm) were strongly characterized, and moderate activity (AUC = 0.66, cut-point: 418 cpm) was weakly characterized. Significance: The use of the AW2 in physical activity monitoring looks promising for sedentary behavior, moderate and vigorous activity, however, further validation is needed

Associations Between Self-Reported Sleep Duration and Mortality in Employed Individuals:Systematic Review and Meta-Analysis

Objective: Sleeping less or more than the 7-8 h has been associated with mortality in the general population, which encompasses diversity in employment status, age and community settings. Since sleep patterns of employed individuals may differ to those of their unemployed counterparts, the nature of their sleep-mortality relationship may vary. We therefore investigated the association between self-reported sleep duration and all-cause mortality (ACM) or cardiovascular disease mortality (CVDM) in employed individuals. Data sources: Based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses, searches between January 1990 and May 2020 were conducted in PubMed, Web of Science and Scopus. Inclusion/exclusion criteria: Included were prospective cohort studies of 18–64-year-old disease-free employed persons with sleep duration measured at baseline, and cause of death recorded prospectively as the outcome. Gray literature, case-control or intervention design studies were excluded. Data Extraction: Characteristics of the studies, participants, and study outcomes were extracted. The quality and risk of bias were assessed using the Newcastle-Ottawa Scale. Data synthesis: The pooled relative risks (RR) with 95% confidence intervals (CI) were obtained with a random-effects model and results presented as forest plots. Heterogeneity and sensitivity analysis were assessed. Results: Shorter sleep duration (less than or equal to 6 h) was associated with a higher risk for (ACM) (RR: 1.16, 95% CI: 1.11 -1.22) and CVDM (RR: 1.26, 95% CI: 1.12 -1.41) compared to 7-8 h of sleep, with no significant heterogeneity. The association between longer sleep (greater than or equal to 8 h) and ACM (RR: 1.18, 95% CI:1.12 -1.23, P < 0.001) needs to be interpreted cautiously owing to high heterogeneity (I2 ¼ 86.0%, P < 0.001). Conclusion: Interventions and education programs targeting sleep health in the workplace may be warranted, based on our findings that employed individuals who report shorter sleep appear to have a higher risk for ACM and CVDM

Orbital Solutions and Absolute Elements of the Massive Algol Binary ET Tauri

We acquired differential UBV photoelectric photometry and radial velocities of the relatively bright, understudied, massive Algol binary ET Tau and utilized the Wilson-Devinney (WD) analysis program to obtain a simultaneous solution of these observations. To improve the orbital ephemeris, the V measurements from the ASAS program were also analyzed. Because of the very rapid rotation of the significantly more massive and hotter component (B2/3 spectral class), only radial velocities of the secondary component, which has a ∼B7 spectral class, could be measured. We derive masses of ${M}_{1}=14.34\pm 0.28\,{M}_{\odot }$ and ${M}_{2}=6.339\pm 0.117\,{M}_{\odot }$ and equal-volume radii of ${R}_{1}=6.356\pm 0.056\,{R}_{\odot }$ and ${R}_{2}=11.84\pm 0.10\,{R}_{\odot }$ for the primary and secondary, respectively. The secondary is filling its Roche lobe, so the system is semi-detached. The effective temperature of the secondary was held fixed at 15,000 K, and the primary\u27s temperature was found to be $\mathrm{30,280}\pm 109$ K. The system, which has a period of 5.996883 ± 0.000002 days, is assumed to have a circular orbit and is seen at an inclination of 79\buildrel{\circ}\over{.} 55\pm 0\buildrel{\circ}\over{.} 05

The Moss Macromitrium Richardii (Orthotrichaceae) with Sporophyte and Calyptra Enclosed in Hymenaea Resin from the Dominican Republic

Abstract Dominican amber is an important source for Early Miocene bryophytes. We report the moss Macromitrium richardii Schwägr., an extant representative of the Orthotrichaceae, from the Dominican amber collection of the American Museum of Natural History. This species is currently a widespread Neotropical epiphyte. The specimen includes several gametophytes and sporophytes, and represents the first fossil record of Orthotrichaceae. Alongside the Macromitrium shoots we observed several fragments of the liverworts Cheilolejeunea antiqua and Frullania sp. The unusual thermal behavior of the resin sample initially led to doubts about the Miocene age of the specimen, but chemical analyses of the Hymenaea resin provides evidence that the specimen represents a highly oxidized sample of Miocene Dominican amber rather than an artificially thermally-treated subfossil resin (copal). Our inclusion demonstrates the exceptional preservation potential of tree resin, but our observations also suggest that provenance (including any possibility that a modern resin has been thermally treated to make it appear older) should be scrutinized when single pieces with atypical thermal behavior and exceptionally well-preserved extant morphotypes come to light

Multi-Objective Reinforcement Learning for Cognitive Radio-Based Satellite Communications

Previous research on cognitive radios has addressed the performance of various machine-learning and optimization techniques for decision making of terrestrial link properties. In this paper, we present our recent investigations with respect to reinforcement learning that potentially can be employed by future cognitive radios installed onboard satellite communications systems specifically tasked with radio resource management. This work analyzes the performance of learning, reasoning, and decision making while considering multiple objectives for time-varying communications channels, as well as different cross-layer requirements. Based on the urgent demand for increased bandwidth, which is being addressed by the next generation of high-throughput satellites, the performance of cognitive radio is assessed considering links between a geostationary satellite and a fixed ground station operating at Ka-band (26 GHz). Simulation results show multiple objective performance improvements of more than 3.5 times for clear sky conditions and 6.8 times for rain conditions

The S-Star Cluster at the Center of the Milky Way: On the nature of diffuse NIR emission in the inner tenth of a parsec

Sagittarius A*, the super-massive black hole at the center of the Milky Way, is surrounded by a small cluster of high velocity stars, known as the S-stars. We aim to constrain the amount and nature of stellar and dark mass associated with the cluster in the immediate vicinity of Sagittarius A*. We use near-infrared imaging to determine the $K_\mathrm{s}$-band luminosity function of the S-star cluster members, and the distribution of the diffuse background emission and the stellar number density counts around the central black hole. This allows us to determine the stellar light and mass contribution expected from the faint members of the cluster. We then use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as a means of detecting the number and masses of the perturbers. We find that the stellar mass derived from the $K_\mathrm{s}$-band luminosity extrapolation is much smaller than the amount of mass that might be present considering the uncertainties in the orbital motion of the star S2. Also the amount of light from the fainter S-cluster members is below the amount of residual light at the position of the S-star cluster after removing the bright cluster members. If the distribution of stars and stellar remnants is strongly enough peaked near Sagittarius A*, observed changes in the orbital elements of S2 can be used to constrain both their masses and numbers. Based on simulations of the cluster of high velocity stars we find that at a wavelength of 2.2 $\mu$m close to the confusion level for 8 m class telescopes blend stars will occur (preferentially near the position of Sagittarius A*) that last for typically 3 years before they dissolve due to proper motions.Comment: 14 pages, 11 figures, minor changes to match the published version in Astronomy & Astrophysic

A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation

We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The high sensitivity of these grism observations, with 1-sigma detections of emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than previously studied z~2 emission-line galaxies. Despite their lower mass, the galaxies have OIII/Hb ratios which are very similar to previously studied z~2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the OIII emission line is more spatially concentrated than the Hb emission line with 98.1 confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked OIII spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure

Space Science and Technology Partnership Forum: Integration with Commercial In-Space Assembly Activities

No abstract availabl