Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34

We investigate the limitations of thermonuclear X-ray bursts as a distance indicator for the weakly-magnetized accreting neutron star 4U 1728-34. We measured the unabsorbed peak flux of 81 bursts in public data from the Rossi X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66 bursts exhibited photospheric radius expansion and were distributed about a mean bolometric flux of 9.2e-8 erg/cm^2/s, while the remaining (non-radius expansion) bursts reached 4.5e-8 erg/cm^2/s, on average. The peak fluxes of the radius-expansion bursts were not constant, exhibiting a standard deviation of 9.4% and a total variation of 46%. These bursts showed significant correlations between their peak flux and the X-ray colors of the persistent emission immediately prior to the burst. We also found evidence for quasi-periodic variation of the peak fluxes of radius-expansion bursts, with a time scale of approximately 40 d. The persistent flux observed with RXTE/ASM over 5.8 yr exhibited quasi-periodic variability on a similar time scale. We suggest that these variations may have a common origin in reflection from a warped accretion disk. Once the systematic variation of the peak burst fluxes is subtracted, the residual scatter is only approximately 3%, roughly consistent with the measurement uncertainties. The narrowness of this distribution strongly suggests that i) the radiation from the neutron star atmosphere during radius-expansion episodes is nearly spherically symmetric, and ii) the radius-expansion bursts reach a common peak flux which may be interpreted as a standard candle intensity.Adopting the minimum peak flux for the radius-expansion bursts as the Eddington flux limit, we derive a distance for the source of 4.4-4.8 kpc.Comment: 9 pages, 7 figures, accepted by ApJ. Minor referee's revisions, also includes 9 newly public X-ray burst

Eddington Capture Sphere around luminous stars

Test particles infalling from infinity onto a compact spherical star with a mildly super-Eddington luminosity at its surface are typically trapped on the "Eddington Capture Sphere" and do not reach the surface of the star. The presence of a sphere on which radiation pressure balances gravity for static particles was first discovered some twenty five years ago. Subsequently, it was shown to be a capture sphere for particles in radial motion, and more recently also for particles in non-radial motion, in which the Poynting-Robertson radiation drag efficiently removes the orbital angular momentum of the particles, reducing it to zero. Here we develop this idea further, showing that "levitation" on the Eddington sphere (above the stellar surface) is a state of stable equilibrium, and discuss its implications for Hoyle-Lyttleton accretion onto a luminous star. When the Eddington sphere is present, the cross-section of a compact star for actual accretion is typically less than the geometrical cross-section (pi Rsquared), direct infall onto the stellar surface only being possible for relativistic particles, with the required minimum particle velocity at infinity typically ~1/2 the speed of light. We further show that particles on typical trajectories in the vicinity of the stellar surface will also be trapped on the Eddington Capture Sphere.Comment: 6 pages, 13 panels in 8 figure

Moving towards universal health coverage for mental disorders in Ethiopia

Background: People with mental disorders in low-income countries are at risk of being left behind during efforts to expand universal health coverage. Aims: To propose context-relevant strategies for moving towards universal health coverage for people with mental disorders in Ethiopia. Methods: We conducted a situational analysis to inform a SWOT analysis of coverage of mental health services and financial risk protection, health system characteristics and the macroeconomic and fiscal environment. In-depth interviews were conducted with five national experts on health financing and equity and analysed using a thematic approach. Findings from the situation analysis and qualitative study were used to develop recommended strategies for adequate, fair and sustainable financing of mental health care in Ethiopia. Results: Opportunities for improved financing of mental health care identified from the situation analysis included: a significant mental health burden with evidence from strong local epidemiological data; political commitment to address that burden; a health system with mechanisms for integrating mental health into primary care; and a favourable macro-fiscal environment for investment in human capabilities. Balanced against this were constraints of low current general government health expenditure, low numbers of mental health specialists, weak capacity to plan and implement mental health programmes and low population demand for mental health care. All key informants referred to the under-investment in mental health care in Ethiopia. Respondents emphasised opportunities afforded by positive rates of economic growth in the country and the expansion of community-based health insurance, as well as the need to ensure full implementation of existing task-sharing programmes for mental health care, integrate mental health into other priority programmes and strengthen advocacy to ensure mental health is given due attention. Conclusion: Expansion of public health insurance, leveraging resources from high-priority SDG-related programmes and implementing existing plans to support task-shared mental health care are key steps towards universal health coverage for mental disorders in Ethiopia. However, external donors also need to deliver on commitments to include mental health within development funding. Future researchers and planners can apply this approach to other countries of sub-Saharan Africa and identify common strategies for sustainable and equitable financing of mental health care

Toward respiratory assessment using depth measurements from a time-of-flight sensor

Introduction: There is increasing interest in technologies that may enable remote monitoring of respiratory disease. Traditional methods for assessing respiratory function such as spirometry can be expensive and require specialist training to perform and interpret. Remote, non-contact tracking of chest wall movement has been explored in the past using structured light, accelerometers and impedance pneumography, but these have often been costly and clinical utility remains to be defined. We present data from a 3-Dimensional time-of-flight camera (found in gaming consoles) used to estimate chest volume during routine spirometry maneuvres. Methods: Patients were recruited from a general respiratory physiology laboratory. Spirometry was performed according to international standards using an unmodified spirometer. A Microsoft Kinect V2 time-of-flight depth sensor was used to reconstruct 3-dimensional models of the subject's thorax to estimate volume-time and flow-time curves following the introduction of a scaling factor to transform measurements to volume estimates. The Bland-Altman method was used to assess agreement of model estimation with simultaneous recordings from the spirometer. Patient characteristics were used to assess predictors of error using regression analysis and to further explore the scaling factors. Results: The chest volume change estimated by the Kinect camera during spirometry tracked respiratory rate accurately and estimated forced vital capacity (FVC) and vital capacity to within ± <1%. Forced expiratory volume estimation did not demonstrate acceptable limits of agreement, with 61.9% of readings showing >150 ml difference. Linear regression including age, gender, height, weight, and pack years of smoking explained 37.0% of the variance in the scaling factor for volume estimation. This technique had a positive predictive value of 0.833 to detect obstructive spirometry. Conclusion: These data illustrate the potential of 3D time-of-flight cameras to remotely monitor respiratory rate. This is not a replacement for conventional spirometry and needs further refinement. Further algorithms are being developed to allow its independence from spirometry. Benefits include simplicity of set-up, no specialist training, and cost. This technique warrants further refinement and validation in larger cohorts

Structure of Protocluster Galaxies: Accelerated Structural Evolution in Overdense Environments?

We present a high spatial-resolution HST/NICMOS imaging survey in the field of a known protocluster surrounding the powerful radio galaxy MRC1138-262 at z=2.16. Previously, we have shown that this field exhibits a substantial surface overdensity of red J-H galaxies. Here we focus on the stellar masses and galaxy effective radii in an effort to compare and contrast the properties of likely protocluster galaxies with their field counterparts and to look for correlations between galaxy structure and (projected) distance relative to the radio galaxy. We find a hint that quiescent, cluster galaxies are on average less dense than quiescent field galaxies of similar stellar mass and redshift. In fact, we find only two (of nine) quiescent protocluster galaxies are of simliar density to the majority of the massive, quiescent compact galaxies (SEEDs) found in several field surveys. Furthermore, there is some indication that the structural Sersic n parameter is higher (n ~ 3-4) on average for cluster galaxies compared to the field SEEDs (n ~ 1-2) This result may imply that the accelerated galaxy evolution expected (and observed) in overdense regions also extends to structural evolution presuming that massive galaxies began as dense (low n) SEEDs and have already evolved to be more in line with local galaxies of the same stellar mass.Comment: 11 pages, 7 figures, 1 table, Accepted for publication in Ap

Epidemiology of unintentional injuries in childhood:a population-based survey in general practice

This study aimed to assess the incidence of unintentional injuries presented in general practice, and to identify children at risk from experiencing an unintentional injury. We used the data of all 0-17-year-old children from a representative survey in 96 Dutch general practices in 2001. We computed incidence rates and multilevel multivariate regression analysis in different age strata and identified patient and family characteristics associated with an elevated injury risk. Nine thousand four hundred and eighty-four new injury episodes were identified from 105 353 new health problems presented in general practice, giving an overall incidence rate of 115 per 1000 person years (95% confidence interval [CI] = 113 to 118). Sex and residence in rural areas are strong predictors of injury in all age strata. Also, in children aged 0-4 years, a higher number of siblings is associated with elevated injury risk (≥3 siblings odds ratio [OR] = 1.57, 95% CI = 1.19 to 2.08) and in the 12-17-year-olds, ethnic background and socioeconomic class are associated with experiencing an injury (non-western children OR = 0.67, 95% CI = 0.54 to 0.81; low socioeconomic class OR = 1.39, 95% CI = 1.22 to 1.58). Unintentional injury is a significant health problem in children in general practice, accounting for 9% of all new health problems in children. In all age groups, boys in rural areas are especially at risk to experience an injury.</p

Development of the Surgical Patient safety Observation Tool (SPOT)

Background: A Surgical Patient safety Observation Tool (SPOT) was developed and tested in a multicentre observational pilot study. The tool enables monitoring and benchmarking perioperative safety performance across departments and hospitals, covering international patient safety goals. Methods: Nineteen perioperative patient safety observation topics were selected from Dutch perioperative patient safety guidelines, which also cover international patient safety goals. All items that measured these selected topics were then extracted from available local observation checklists of the participating hospitals. Experts individually prioritized the best measurement items per topic in an initial written Delphi round. The second (face to face) Delphi round resulted in consensus on the content of SPOT, after which the measurable elements (MEs) per topic were defined. Finally, the tool was piloted in eight hospitals for measurability, applicability, improvement potential, discriminatory capacity and feasibility. Results: The pilot test showed good measurability for all 19 patient safety topics (range of 8-291 MEs among topics), with good applicability (median 97 (range 11.8-100) per cent). The overall improvement potential appeared to be good (median 89 (range 72.5-100) per cent), and at topic level the tool showed good discriminatory capacity (variation 27.5 per cent, range in compliance 72.5-100 per cent). Overall scores showed relatively little variation between the participating hospitals (variation 13 per cent, range in compliance 83-96 per cent). All eight auditors considered SPOT a straightforward and easy-to-use tracer tool. Conclusion: A comprehensive tool to measure safety of care was developed and validated using a systematic, stepwise method, enabling hospitals to monitor, benchmark and improve perioperative safety performance