Resolving cryptic species complexes in marine protists: phylogenetic haplotype networks meet global DNA metabarcoding datasets

Marine protists have traditionally been assumed to be lowly diverse and cosmopolitan. Yet, several recent studies have shown that many protist species actually consist of cryptic complexes of species whose members are often restricted to particular biogeographic regions. Nonetheless, detection of cryptic species is usually hampered by sampling coverage and application of methods (e.g. phylogenetic trees) that are not well suited to identify relatively recent divergence and ongoing gene flow. In this paper, we show how these issues can be overcome by inferring phylogenetic haplotype networks from global metabarcoding datasets. We use the Chaetoceros curvisetus (Bacillariophyta) species complex as study case. Using two complementary metabarcoding datasets (Ocean Sampling Day and Tara Oceans), we equally resolve the cryptic complex in terms of number of inferred species. We detect new hypothetical species in both datasets. Gene flow between most of species is absent, but no barcoding gap exists. Some species have restricted distribution patterns whereas others are widely distributed. Closely related taxa occupy contrasting biogeographic regions, suggesting that geographic and ecological differentiation drive speciation. In conclusion, we show the potential of the analysis of metabarcoding data with evolutionary approaches for systematic and phylogeographic studies of marine protists

Multi-wavelength observations of 3FGL J2039.6-5618: a candidate redback millisecond pulsar

We present multi-wavelength observations of the unassociated gamma-ray source 3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source gamma-ray properties suggest that it is a pulsar, most likely a millisecond pulsar, for which neither radio nor $\gamma$-ray pulsations have been detected yet. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several candidate X-ray counterparts within/close to the gamma-ray error box. The brightest of these X-ray sources is variable with a period of 0.2245$\pm$0.0081 d. Its X-ray spectrum can be described by a power law with photon index $\Gamma_X =1.36\pm0.09$, and hydrogen column density $N_{\rm H} < 4 \times 10^{20}$ cm$^{-2}$, which gives an unabsorbed 0.3--10 keV X-ray flux of $1.02 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. Observations with the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) discovered an optical counterpart to this X-ray source, with a time-average magnitude $g'\sim 19.5$. The counterpart features a flux modulation with a period of 0.22748$\pm$0.00043 d that coincides, within the errors, with that of the X-ray source, confirming the association based on the positional coincidence. We interpret the observed X-ray/optical periodicity as the orbital period of a close binary system where one of the two members is a neutron star. The light curve profile of the companion star, with two asymmetric peaks, suggests that the optical emission comes from two regions at different temperatures on its tidally-distorted surface. Based upon its X-ray and optical properties, we consider this source as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to be a new redback system.Comment: 35 pages, 8 figures, accepted for publication on Astrophysical Journa

Long Range Magnetic Order and the Darwin Lagrangian

We simulate a finite system of $N$ confined electrons with inclusion of the Darwin magnetic interaction in two- and three-dimensions. The lowest energy states are located using the steepest descent quenching adapted for velocity dependent potentials. Below a critical density the ground state is a static Wigner lattice. For supercritical density the ground state has a non-zero kinetic energy. The critical density decreases with $N$ for exponential confinement but not for harmonic confinement. The lowest energy state also depends on the confinement and dimension: an antiferromagnetic cluster forms for harmonic confinement in two dimensions.Comment: 5 figure

Phase resolved spectroscopy of the Vela pulsar with XMM-Newton

The ~10^4 y old Vela Pulsar represents the bridge between the young Crab-like and the middle-aged rotation powered pulsars. Its multiwavelength behaviour is due to the superposition of different spectral components. We take advantage of the unprecedented harvest of photons collected by XMM-Newton to assess the Vela Pulsar spectral shape and to study the pulsar spectrum as a function of its rotational phase. As for the middle-aged pulsars Geminga, PSR B0656+14 and PSR B1055-52 (the "Three Musketeers"), the phase-integrated spectrum of Vela is well described by a three-component model, consisting of two blackbodies (T_bb1=(1.06+/-0.03)x10^6 K, R_bb1=5.1+/-0.3 km, T_bb2=(2.16+/-0.06)x10^6 K, R_bb2=0.73+/-0.08 km) plus a power-law (gamma=2.2+/-0.3). The relative contributions of the three components are seen to vary as a function of the pulsar rotational phase. The two blackbodies have a shallow 7-9% modulation. The cooler blackbody, possibly related to the bulk of the neutron star surface, has a complex modulation, with two peaks per period, separated by ~0.35 in phase, the radio pulse occurring exactly in between. The hotter blackbody, possibly originating from a hot polar region, has a nearly sinusoidal modulation, with a single, broad maximum aligned with the second peak of the cooler blackbody, trailing the radio pulse by ~0.15 in phase. The non thermal component, magnetospheric in origin, is present only during 20% of the pulsar phase and appears to be opposite to the radio pulse. XMM-Newton phase-resolved spectroscopy unveils the link between the thermally emitting surface of the neutron star and its charge-filled magnetosphere, probing emission geometry as a function of the pulsar rotation. This is a fundamental piece of information for future 3-dimensional modeling of the pulsar magnetosphere.Comment: 27 pages, 9 figures. Accepted for publication in Ap

The distance to the Vela pulsar gauged with HST parallax oservations

The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the SNR. In an effort to obtain a model free distance measurement, we have applied high resolution astrometry to the pulsar V~23.6 optical counterpart. Using a set of five HST/WFPC2 observations, we have obtained the first optical measurement of the annual parallax of the Vela pulsar. The parallax turns out to be 3.4 +/- 0.7 mas, implying a distance of 294(-50;+76) pc, i.e. a value significantly lower than previously believed. This affects the estimate of the pulsar absolute luminosity and of its emission efficiency at various wavelengths and confirms the exceptionally high value of the N_e towards the Vela pulsar. Finally, the complete parallax data base allows for a better measurement of the Vela pulsar proper motion (mu_alpha(cos(delta))=-37.2 +/- 1.2 mas/yr; mu_delta=28.2 +/- 1.3 mas/yr after correcting for the peculiar motion of the Sun) which, at the parallax distance, implies a transverse velocity of ~65 km/s. Moreover, the proper motion position angle appears specially well aligned with the axis of symmetry of the X-ray nebula as seen by Chandra. Such an alignment allows to assess the space velocity of the Vela pulsar to be ~81 km/s.Comment: LaTeX, 21 pages, 5 figures. Accepted for publication in Ap

Prevalence and profile of Australian chiropractors treating athletes or sports people: A cross-sectional study

© 2018 Objectives: A range of health-care professionals including chiropractors provide treatment for sports-related health problems. This study reports analyses from the first national workforce survey to determine practitioner and practice-related factors associated with the frequent treatment of athletes or sports people by Australian chiropractors. Design and setting: A 21-item questionnaire collecting information pertaining to practitioner and practice-related characteristics was distributed to all Australian registered chiropractors, as part of the Australian Chiropractic Research Network (ACORN) project and attracted a response rate of 43% (n = 2005). Statistical analyses compared the frequency of treating athletes or sports people against a wide range of relevant practitioner and practice characteristics. Results: Of the respondents, 49.5% (n = 936) reported frequently treating athletes or sports people, and these chiropractors were more likely to be male as well as report more patient care hours and patient visits per week than those chiropractors who did not frequently treat athletes or sports people. Chiropractors who frequently treat athletes or sports people were also more likely to perform multi-modal management, have multi-disciplinary practitioner relations, use diagnostic equipment and discuss nutrition and medication use as part of their patient care than those chiropractors who did not frequently treat athletes or sports people. Conclusions: Nearly half of participating Australian chiropractors treat athletes or sports people frequently. The current and potential role of chiropractors in sports medicine appears significant. Further research is needed to examine the role, practices and outcomes of such chiropractic care helping to, provide treatment and policy development in this area of clinical management

Fluctuation theorem for constrained equilibrium systems

We discuss the fluctuation properties of equilibrium chaotic systems with constraints such as iso-kinetic and Nos\'e-Hoover thermostats. Although the dynamics of these systems does not typically preserve phase-space volumes, the average phase-space contraction rate vanishes, so that the stationary states are smooth. Nevertheless finite-time averages of the phase-space contraction rate have non-trivial fluctuations which we show satisfy a simple version of the Gallavotti-Cohen fluctuation theorem, complementary to the usual fluctuation theorem for non-equilibrium stationary states, and appropriate to constrained equilibrium states. Moreover we show these fluctuations are distributed according to a Gaussian curve for long-enough times. Three different systems are considered here, namely (i) a fluid composed of particles interacting with Lennard-Jones potentials; (ii) a harmonic oscillator with Nos\'e-Hoover thermostatting; (iii) a simple hyperbolic two-dimensional map.Comment: To appear in Phys. Rev.

The prevalence and determinants of physical activity promotion by Australian chiropractors: A cross sectional study

© 2019 Elsevier Ltd Background: Approximately one in four adults do not meet the World Health Organisation physical activity recommendations. While health promotion (i.e., physical activity) is common within chiropractic settings, little is known about chiropractors discussing this public health issue with their patients. The aim of our study is to examine the prevalence and characteristics of Australian chiropractors who frequently discuss patient physical activity. Methods: A national cross-sectional survey of chiropractors focusing upon practitioner characteristics, practice settings and clinical management characteristics. Regression analyses were conducted on 1924 survey respondents to identify factors associated with practitioners who frequently discuss physical activity with patients. Results: Eighty-five percent of Australian chiropractors reported ‘often’ discussing physical activity as part of their patient management. The strongest factors associated with chiropractors who frequently discuss physical activity obtained from the multivariate analysis include: often discussing occupational health and safety (odds ratio [OR] = 6.10; 95%CI: 3.88, 9.59), often discussing diet/nutrition (OR = 4.56; 95%CI: 3.12, 6.66), often discussing smoking/drugs/alcohol (OR = 4.41; 95%CI: 2.06, 9.40), often use of specific exercise therapy/rehabilitation/injury taping (OR = 3.76; 95%CI: 2.62, 5.39) and often caring for athletes or sports people (OR = 2.18; 95%CI: 1.56, 3.06) within their practice setting. Conclusion: Discussing physical activity is a frequent feature of patient management among most chiropractors in Australia. The association between these practitioners and discussion of other costly public health burdens could suggest chiropractors have a valuable role to play in chronic disease prevention. Given the growing need for practitioner-led promotion of patient physical activity further research examination of the role and contribution of chiropractors in promoting this important public health topic among patients and communities is needed

Perfectly Translating Lattices on a Cylinder

We perform molecular dynamics simulations on an interacting electron gas confined to a cylindrical surface and subject to a radial magnetic field and the field of the positive background. In order to study the system at lowest energy states that still carry a current, initial configurations are obtained by a special quenching procedure. We observe the formation of a steady state in which the entire electron-lattice cycles with a common uniform velocity. Certain runs show an intermediate instability leading to lattice rearrangements. A Hall resistance can be defined and depends linearly on the magnetic field with an anomalous coefficient reflecting the manybody contributions peculiar to two dimensions.Comment: 13 pages, 5 figure

Existence of solutions to a higher dimensional mean-field equation on manifolds

For $m\geq 1$ we prove an existence result for the equation $$(-\Delta_g)^m u+\lambda=\lambda\frac{e^{2mu}}{\int_M e^{2mu}d\mu_g}$$ on a closed Riemannian manifold $(M,g)$ of dimension $2m$ for certain values of $\lambda$.Comment: 15 Page