Fast Desynchronization For Decentralized Multichannel Medium Access Control

Distributed desynchronization algorithms are key to wireless sensor networks as they allow for medium access control in a decentralized manner. In this paper, we view desynchronization primitives as iterative methods that solve optimization problems. In particular, by formalizing a well established desynchronization algorithm as a gradient descent method, we establish novel upper bounds on the number of iterations required to reach convergence. Moreover, by using Nesterov's accelerated gradient method, we propose a novel desynchronization primitive that provides for faster convergence to the steady state. Importantly, we propose a novel algorithm that leads to decentralized time-synchronous multichannel TDMA coordination by formulating this task as an optimization problem. Our simulations and experiments on a densely-connected IEEE 802.15.4-based wireless sensor network demonstrate that our scheme provides for faster convergence to the steady state, robustness to hidden nodes, higher network throughput and comparable power dissipation with respect to the recently standardized IEEE 802.15.4e-2012 time-synchronized channel hopping (TSCH) scheme.Comment: to appear in IEEE Transactions on Communication

The use of the McIlwain L-parameter to estimate cosmic ray vertical cutoff rigidities for different epochs of the geomagnetic field

Secular changes in the geomagnetic field between 1955 and 1980 have been large enough to produce significant differences in both the verical cutoff rigidities and in the L-value for a specified position. A useful relationship employing the McIlwain L-parameter to estimate vertical cutoff rigidities has been derived for the twenty-five year period

Research study of droplet sizing technology leading to the development of an advanced droplet sizing system

An instrument to measure the size and velocity of droplets was developed. The instrument uses one of two techniques, as appropriate. In the first technique two small laser beams of one color identify the center of a larger laser beam of a different color. This defines a region of almost uniform intensity where the light scattered by the individual droplets can be related to their size. The first technique uses the visibility of a Doppler burst and validates it against the peak intensity of the signal's pedestal. Results are presented for monodisperse, bimodal, trimodal, and polydisperse sprays produced by the Berglund-Liu droplet generator and a pressure nozzle. Size distributions of a given spray obtained using three different size ranges show excellent self-consistency in the overlapping region. Measurements of sprays of known characteristics exhibit errors in the order of 10%. The principles of operation and design criteria of the instrument are discussed in great detail

Estimating the change in asymptotic direction due to secular changes in the geomagnetic field

The concept of geomagnetic optics, as described by the asymptotic directions of approach, is extremely useful in the analysis of cosmic radiation data. However, when changes in cutoff occur as a result of evolution in the geomagnetic field, there are corresponding changes in the asymptotic cones of acceptance. A method is introduced of estimating the change in the asymptotic direction of approach for vertically incident cosmic ray particles from a reference set of directions at a specific epoch by considering the change in the geomagnetic cutoff

Cosmic ray tables - Asymptotic directions, variational coefficients and cut-off rigidities IQSY instruction manual no. 10

Cosmic ray deflections in geomagnetic field, variational coefficients, and diurnal intensity variations - table

Reversible Intercalation of Fluoride-Anion Receptor Complexes in Graphite

We have demonstrated a route to reversibly intercalate fluoride-anion receptor complexes in graphite via a nonaqueous electrochemical process. This approach may find application for a rechargeable lithium–fluoride dual-ion intercalating battery with high specific energy. The cell chemistry presented here uses graphite cathodes with LiF dissolved in a nonaqueous solvent through the aid of anion receptors. Cells have been demonstrated with reversible cathode specific capacity of approximately 80 mAh/g at discharge plateaus of upward of 4.8 V, with graphite staging of the intercalant observed via in situ synchrotron X-ray diffraction during charging. Electrochemical impedance spectroscopy and 11B nuclear magnetic resonance studies suggest that co-intercalation of the anion receptor with the fluoride occurs during charging, which likely limits the cathode specific capacity. The anion receptor type dictates the extent of graphite fluorination, and must be further optimized to realize high theoretical fluorination levels. To find these optimal anion receptors, we have designed an ab initio calculations-based scheme aimed at identifying receptors with favorable fluoride binding and release properties

The Gaia Ultra-Cool Dwarf Sample -- II : Structure at the end of the main sequence

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We identify and investigate known late M, L, and T dwarfs in the Gaia second data release. This sample is being used as a training set in the Gaia data processing chain of the ultracool dwarfs work package. We find 695 objects in the optical spectral range M8–T6 with accurate Gaia coordinates, proper motions, and parallaxes which we combine with published spectral types and photometry from large area optical and infrared sky surveys. We find that 100 objects are in 47 multiple systems, of which 27 systems are published and 20 are new. These will be useful benchmark systems and we discuss the requirements to produce a complete catalogue of multiple systems with an ultracool dwarf component. We examine the magnitudes in the Gaia passbands and find that the G BP magnitudes are unreliable and should not be used for these objects. We examine progressively redder colour–magnitude diagrams and see a notable increase in the main-sequence scatter and a bivariate main sequence for old and young objects. We provide an absolute magnitude – spectral subtype calibration for G and G RP passbands along with linear fits over the range M8–L8 for other passbands.Peer reviewedFinal Published versio

Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9}

Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions, we study the effect of iron disproportionation on the magnetic ordering, and describe the first-order magnetic transition occurring in the perovskite Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of the exchange integrals for the antiferromagntic and ferromagnetic interactions, in agreement with previous works on kindered compounds. Spin-wave theory yields a magnon spectrum with a gapless antiferromagnetic mode together with two gapped ferromagnetic ones.Comment: 8 pages of RevTex, 5 figures (available upon request), submitted to J. Mag. Mag. Ma

The extremely red L dwarf ULAS J222711-004547-dominated by dust

We report the discovery of a peculiar L dwarf from the United Kingdom Infrared Deep Sky Survey Large Area Survey, ULAS J222711-004547. The very red infrared photometry (MKO J-K = 2.79 +/- 0.06, WISEW1-W2 = 0.65 +/- 0.05) of ULAS J222711-004547 makes it one of the reddest brown dwarfs discovered so far. We obtained a moderate resolution spectrum of this target using the XSHOOTER spectrograph on the Very Large Telescope, and we classify it as L7pec, confirming its very red nature. Comparison to theoretical models suggests that the object could be a low-gravity L dwarf with a solar or higher than solar metallicity. Nonetheless, the match of such fits to the spectral energy distribution is rather poor, and this and other less red peculiar L dwarfs pose new challenges for the modelling of ultracool atmospheres, especially to the understanding of the effects of condensates and their sensitivity to gravity and metallicity. We determined the proper motion of ULAS J222711-004547 using the data available in the literature, and we find that its kinematics do not suggest membership of any of the known young associations. We show that applying a simple de-reddening curve to its spectrum allows it to resemble the spectra of the L7 spectroscopic standards without any spectral features that distinguish it as a low-metallicity or low-gravity dwarf. Given the negligible interstellar reddening of the field containing our target, we conclude that the reddening of the spectrum is mostly due to an excess of dust in the photosphere of the target. De-reddening the spectrum using extinction curves for different dust species gives surprisingly good results and suggests a characteristic grain size of similar to 0.5 mu m. We show that by increasing the optical depth, the same extinction curves allow the spectrum of ULAS J222711-004547 to resemble the spectra of unusually blue L dwarfs and even slightly metal-poor L dwarfs. Grains of similar size also yield very good fits when de-reddening other unusually red L dwarfs in the L5-L7.5 range. These results suggest that the diversity in near-infrared colours and spectra seen in late L dwarfs could be due to differences in the optical thickness of the dust cloud deck.Peer reviewe

Exercise training for chronic heart failure (ExTraMATCH II): individual participant data meta-analysis of randomised controlled trials

This is the author accepted manuscript. The final version is available from NIHR Journals Library via the DOI in this record.Background: Current national and international guidelines on the management of heart failure (HF) recommend exercise-based cardiac rehabilitation (ExCR), but do not differentiate this recommendation according to patient subgroups. Objective(s): (1) to obtain definitive estimates of the impact of ExCR interventions versus control (no exercise intervention) on mortality, hospitalisation, exercise capacity, and health-related quality of life (HRQoL) in HF patients; (2) to determine the differential (subgroup) effects of ExCR in HF patients according to their age, gender, ejection fraction, aetiology, New York Heart Association (NYHA) class, and baseline exercise capacity; (3) to assess whether the change in exercise capacity mediates for the impact of the ExCR on final outcomes (mortality, hospitalisation, and HRQoL) and is an acceptable surrogate endpoint. Design: Individual participant data (IPD) meta-analysis Setting: An international literature review Participants: HF patients in randomised controlled trials (RCTs) of ExCR Interventions: ExCR for at least 3 weeks compared with no exercise control with 6 months follow-up Main outcome measures: mortality (all cause and HF-specific), hospitalisation (all-cause & HF-specific), exercise capacity, and HRQoL Data sources: Individual participant data from eligible RCTs 3 Review methods: RCTs from ExTraMATCH IPD meta-analysis and 2014 Cochrane systematic review of ExCR Results: Out of the 23 eligible RCTs (4,398 patients), 19 RCTs (3,990 patients) contributed data to this IPD meta-analysis. There was a wide variation in exercise programme prescriptions across included studies. Compared with control, there was no statistically significant difference in pooled time to event estimates in favour of ExCR although confidence intervals were wide: all-cause mortality: hazard ratio (HR) 0.83 (95% confidence interval (CI): 0.67 to 1.04), HF-related mortality: HR 0.84 (95% CI: 0.49 to 1.46), all-cause hospitalisation: HR 0.90 (95% CI: 0.76 to 1.06), and HF-related hospitalisation: HR 0.98 (95% CI: 0.72 to 1.35). There was a statistically significant difference in favour of ExCR for exercise capacity and HRQoL. Compared to control, at 12-months follow-up, improvements were seen in the six-minute walk test (6MWT) (mean: 21.0 metres, 95% CI: 1.57 to 40.4, and Minnesota Living with HF Questionnaire score (mean: -5.94, 95% CI: -1.0 to -10.9, lower scores indicate improved HRQoL). No strong evidence for differential intervention effects across patient characteristics was found for any outcomes. Moderate to good levels of correlation (R2 trial>50% & ρ>0.50) between peak oxygen uptake (VO2peak) or 6MWT with mortality and HRQoL were seen. Estimated surrogate threshold effect (STE) was an increase of 1.6 to 4.6 ml/kg/min for VO2peak. Limitations: Lack consistency in how included RCTs defined and collected the outcomes; we were unable to obtain IPD from all includable trials for all outcomes; and we did not seek patient level on exercise adherence. . Conclusions: In comparison to no exercise control, participation in ExCR improves the exercise and HRQoL in HF patients but appears to have no effect on their mortality or hospitalisation. No strong evidence was found of differential intervention effects of ExCR across patient characteristics. VO2peak and 6MWT may be suitable surrogate endpoints for the treatment effect of ExCR on mortality and HRQoL in HF.NIHR Health Technology Assessment programm