Lagrangian measurements of turbulent dissipation over a shallow tidal flat from pulse coherent Acoustic Doppler Profilers

We present high resolution (25 mm spatial, 8 Hz temporal) profiles of velocity measured over a shallow tidal flat using pulse-coherent Acoustic Doppler Profilers mounted on surface drifters. The use of Lagrangian measurements mitigated the problem of resolving velocity ambiguities, a problem which often limits the application of high-resolution pulse-coherent profilers. Turbulent dissipation rates were estimated from second-order structure functions of measured velocity. Drifters were advected towards, and subsequently trapped on, a convergent surface front which marked the edge of a freshwater plume. Measured dissipation rates increased as a drifter deployed within the plume approached the front. A drifter then propagated with and along the front as the fresh plume spread across the tidal flats. Near-surface turbulent dissipation measured at the front roughly matched a theoretical mean-shear-cubed relationship, whereas dissipation measured in the stratified plume behind the front was suppressed. After removal of estimates affected by surface waves, near-bed dissipation matched the velocity cubed relationship, although scatter was substantial. Dissipation rates appeared to be enhanced when the drifter propagated across small subtidal channels

A novel drifter designed for use with a mounted Acoustic Doppler Current Profiler in shallow environments

We present a novel design for a surface drifter, mounted with a pulse-coherent Acoustic Doppler Current Profiler (ADCP) for measuring near-surface (depths 0.18-1 m) flows. During repeated drifter deployments over the tidal flats of Skagit Bay, the mounted ADCP recorded high quality and high resolution profiles of velocity in depths as shallow as 0.4 m. Depth-dependent velocities revealed regions of vertically sheared currents and wave motions not resolved by surface drifters alone. Although the cost of ADCPs is substantial, the drifter bodies were low cost, robust, and of simple construction

Identification of Outflows and Candidate Dual Active Galactic Nuclei in SDSS Quasars at z=0.8-1.6

We present a sample of 131 quasars from the Sloan Digital Sky Survey at redshifts 0.8<z<1.6 with double peaks in either of the high-ionization narrow emission lines [NeV]3426 or [NeIII]3869. These sources were selected with the intention of identifying high-redshift analogs of the z<0.8 active galactic nuclei (AGN) with double-peaked [OIII]5007 lines, which might represent AGN outflows or dual AGN. Lines of high-ionization potential are believed to originate in the inner, highly photoionized portion of the narrow line region (NLR), and we exploit this assumption to investigate the possible kinematic origins of the double-peaked lines. For comparison, we measure the [NeV]3426 and [NeIII]3869 double peaks in low-redshift (z<0.8) [OIII]-selected sources. We find that [NeV]3426 and [NeIII]3869 show a correlation between line-splitting and line-width similar to that of [OIII]5007 in other studies; and the velocity-splittings are correlated with the quasar Eddington ratio. These results suggest an outflow origin for at least a subset of the double-peaks, allowing us to study the high-ionization gas kinematics around quasars. However, we find that a non-neligible fraction of our sample show no evidence for an ionization stratification. For these sources, the outflow scenario is less compelling, leaving the dual AGN scenario as a viable possibility. Finally, we find that our sample shows an anti-correlation between the velocity-offset ratio and luminosity ratio of the components, which is a potential dynamical argument for the presence of dual AGN. Therefore, this study serves as a first attempt at extending the selection of candidate dual AGN to higher redshifts.Comment: 19 pages, 12 figures, accepted for publication in The Astrophysical Journa

The X-Ray Position and Infrared Counterpart of the Eclipsing X-Ray Pulsar OAO 1657-415

We have measured the precise position of the 38-s eclipsing X-ray pulsar OAO 1657-415 with the Chandra X-Ray Observatory: RA = 17h00m48.90s, Dec = -41d39m21.6s, equninox J2000, error radius = 0.5 arcsec. Based on the previously measured pulsar mass function and X-ray eclipse duration, this 10.4-d high-mass X-ray binary is believed to contain a B supergiant companion. Deep optical imaging of the field did not detect any stars at the Chandra source position, setting a limit of V>23. However, near-IR imaging revealed a relatively bright star (J=14.1, H=11.9, K_s=10.7) coincident with the Chandra position, and we identify this star as the IR counterpart of OAO 1657-415. The IR colors and magnitudes and the optical non-detections for this star are all consistent with a highly reddened B supergiant (A_V= 20.4 +/- 1.3) at a distance of 6.4 +/- 1.5 kpc. This implies an X-ray luminosity of 3e36 erg/s (2-10 keV). IR spectroscopy can verify the spectral type of the companion and measure its radial velocity curve, yielding a neutron star mass measurement.Comment: 4 pages. ApJ in press (Vol. 573, July 10 issue

Emergency medical dispatch recognition, clinical intervention and outcome of patients in traumatic cardiac arrest from major trauma : an observational study

© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.OBJECTIVES: The aim of this study is to describe the demographics of reported traumatic cardiac arrest (TCA) victims, prehospital resuscitation and survival to hospital rate. SETTING: Helicopter Emergency Medical Service (HEMS) in south-east England, covering a resident population of 4.5 million and a transient population of up to 8 million people. PARTICIPANTS: Patients reported on the initial 999 call to be in suspected traumatic cardiac arrest between 1 July 2016 and 31 December 2016 within the trust's geographical region were identified. The inclusion criteria were all cases of reported TCA on receipt of the initial emergency call. Patients were subsequently excluded if a medical cause of cardiac arrest was suspected. OUTCOME MEASURES: Patient records were analysed for actual presence of cardiac arrest, prehospital resuscitation procedures undertaken and for survival to hospital rates. RESULTS: 112 patients were reported to be in TCA on receipt of the 999/112 call. 51 (46%) were found not to be in TCA on arrival of emergency medical services. Of the 'not in TCA cohort', 34 (67%) received at least one advanced prehospital medical intervention (defined as emergency anaesthesia, thoracostomy, blood product transfusion or resuscitative thoracotomy). Of the 61 patients in actual TCA, 10 (16%) achieved return-of-spontaneous circulation. In 45 (88%) patients, the HEMS team escorted the patient to hospital. CONCLUSION: A significant proportion of patients reported to be in TCA on receipt of the emergency call are not in actual cardiac arrest but are critically unwell requiring advanced prehospital medical intervention. Early activation of an enhanced care team to a reported TCA call allows appropriate advanced resuscitation. Further research is warranted to determine which interventions contribute to improved TCA survival.Peer reviewedFinal Published versio

Currents and Superpotentials in classical gauge theories: II. Global aspects and the example of Affine gravity

The conserved charges associated to gauge symmetries are defined at a boundary component of space-time because the corresponding Noether current can be rewritten on-shell as the divergence of a superpotential. However, the latter is afflicted by ambiguities. Regge and Teitelboim found a procedure to lift the arbitrariness in the Hamiltonian framework. An alternative covariant formula was proposed by one of us for an arbitrary variation of the superpotential, it depends only on the equations of motion and on the gauge symmetry under consideration. Here we emphasize that in order to compute the charges, it is enough to stay at a boundary of spacetime, without requiring any hypothesis about the bulk or about other boundary components, so one may speak of holographic charges. It is well known that the asymptotic symmetries that lead to conserved charges are really defined at infinity, but the choice of boundary conditions and surface terms in the action and in the charges is usually determined through integration by parts whereas each component of the boundary should be considered separately. We treat the example of gravity (for any space-time dimension, with or without cosmological constant), formulated as an Affine theory which is a natural generalization of the Palatini and Cartan-Weyl (vielbein) first order formulations. We then show that the superpotential associated to a Dirichlet boundary condition on the metric (the one needed to treat asymptotically flat or AdS spacetimes) is the one proposed by Katz, Bi\u{c}{\'a}k and Lynden-Bell and not that of Komar. We finally discuss the KBL superpotential at null infinity.Comment: 16 pages, minor corrections and references added. Final version to appear in CQ