The Most Massive Black Holes in the Universe: Effects of Mergers in Massive Galaxy Clusters

Recent observations support the idea that nuclear black holes grew by gas accretion while shining as luminous quasars at high redshift, and they establish a relation of the black hole mass with the host galaxy's spheroidal stellar system. We develop an analytic model to calculate the expected impact of mergers on the masses of black holes in massive clusters of galaxies. We use the extended Press-Schechter formalism to generate Monte Carlo merger histories of halos with a mass 10^{15} h^{-1} Msun. We assume that the black hole mass function at z=2 is similar to that inferred from observations at z=0 (since quasar activity declines markedly at z<2), and we assign black holes to the progenitor halos assuming a monotonic relation between halo mass and black hole mass. We follow the dynamical evolution of subhalos within larger halos, allowing for tidal stripping, the loss of orbital energy by dynamical friction, and random orbital perturbations in gravitational encounters with subhalos, and we assume that mergers of subhalos are followed by mergers of their central black holes. Our analytic model reproduces numerical estimates of the subhalo mass function. We find that the most massive black holes in massive clusters typically grow by a factor ~ 2 by mergers after gas accretion has stopped. In our ten realizations of 10^{15} h^{-1} Msun clusters, the highest initial (z=2) black hole masses are 5-7 x 10^9 Msun, but four of the clusters contain black holes in the range 1-1.5 x 10^{10} Msun at z=0. Satellite galaxies may host black holes whose mass is comparable to, or even greater than, that of the central galaxy. Thus, black hole mergers can significantly extend the very high end of the black hole mass function.Comment: 13 pages, 7 figures, accepted for publication in The Astrophysical Journa

Monte Carlo Simulation of Lyman Alpha Scattering and Application to Damped Lyman Alpha Systems

A Monte Carlo code to solve the transfer of Lyman alpha (Lya) photons is developed, which can predict the Lya image and two-dimensional Lya spectra of a hydrogen cloud with any given geometry, Lya emissivity, neutral hydrogen density distribution, and bulk velocity field. We apply the code to several simple cases of a uniform cloud to show how the Lya image and emitted line spectrum are affected by the column density, internal velocity gradients, and emissivity distribution. We then apply the code to two models for damped Lya absorption systems: a spherical, static, isothermal cloud, and a flattened, axially symmetric, rotating cloud. If the emission is due to fluorescence of the external background radiation, the Lya image should have a core corresponding to the region where hydrogen is self-shielded. The emission line profile has the characteristic double peak with a deep central trough. We show how rotation of the cloud causes the two peaks to shift in wavelength as the slit is perpendicular to the rotation axis, and how the relative amplitude of the two peaks is changed. In reality, damped Lya systems are likely to have a clumpy gas distribution with turbulent velocity fields, which should smooth the line emission profile, but should still leave the rotation signature of the wavelength shift across the system.Comment: 19 pages, 17 eps figures. One panel is added in Fig.1 to show the recoil effect. Revisions are made in response to the referee's comments. Accepted for publication in Ap

Assessing the efficiency of countries in making progress towards universal health coverage: a data envelopment analysis of 172 countries

Introduction: Maximising efficiency of resources is critical to progressing towards universal health coverage (UHC) and the sustainable development goal (SDG) for health. This study estimates the technical efficiency of national health spending in progressing towards UHC, and the environmental factors associated with efficient UHC service provision. Methods: A two-stage efficiency analysis using Simar and Wilson’s double bootstrap data envelopment analysis investigates how efficiently countries convert health spending into UHC outputs (measured by service coverage and financial risk protection) for 172 countries. We use World Bank and WHO data from 2015. Thereafter, the environmental factors associated with efficient progress towards UHC goals are identified. Results: The mean bias-corrected technical efficiency score across 172 countries is 85.7% (68.9% for low-income and 95.5% for high-income countries). High-achieving middleincome and low-income countries such as El Salvador, Colombia, Rwanda and Malawi demonstrate that peer-relative efficiency can be attained at all incomes. Governance capacity, income and education are significantly associated with efficiency. Sensitivity analysis suggests that results are robust to changes. Conclusion: We provide a 2015 baseline for cross-country UHC technical efficiency scores. If countries wish to improve their UHC outputs within existing budgets, they should identify their current efficiency and try to emulate more efficient peers. Policy-makers should focus on strengthening institutions and implementing known best practices to replicate efficient systems. Using resources more efficiently is likely to positively impact UHC coverage goals and health outcomes, and without addressing gaps in efficiency progress towards achieving the SDGs will be impeded

PERIOD–TIMELESS Interval Timer May Require an Additional Feedback Loop

In this study we present a detailed, mechanism-based mathematical framework of Drosophila circadian rhythms. This framework facilitates a more systematic approach to understanding circadian rhythms using a comprehensive representation of the network underlying this phenomenon. The possible mechanisms underlying the cytoplasmic “interval timer” created by PERIOD–TIMELESS association are investigated, suggesting a novel positive feedback regulatory structure. Incorporation of this additional feedback into a full circadian model produced results that are consistent with previous experimental observations of wild-type protein profiles and numerous mutant phenotypes

Older adults with weaker muscle strength stand up from a sitting position with more dynamic trunk use

The ability to stand up from a sitting position is essential for older adults to live independently. Body-fixed inertial sensors may provide an approach for quantifying the sit-to-stand (STS) in clinical settings. The aim of this study was to determine whether measurements of STS movements using body-fixed sensors yield parameters that are informative regarding changes in STS performance in older adults with reduced muscle strength. In twenty-seven healthy older adults, handgrip strength was assessed as a proxy for overall muscle strength. Subjects were asked to stand up from a chair placed at three heights. Trunk movements were measured using an inertial sensor fixed to the back. Duration, angular range, and maximum angular velocity of STS phases, as well as the vertical velocity of the extension phase, were calculated. Backwards elimination using Generalized Estimating Equations was used to determine if handgrip strength predicted the STS durations and trunk kinematics. Weaker subjects (i.e., with lower handgrip strength) were slower during the STS and showed a larger flexion angular range and a larger extension angular range. In addition, weaker subjects showed a greater maximum angular velocity, which increased with lower seat heights. Measurements with a single inertial sensor did reveal that older adults with lower handgrip strength employed a different strategy to stand up from a sitting position, involving more dynamic use of the trunk. This effect was greatest when elevating body mass. Trunk kinematic parameters were more sensitive to reduced muscle strength than durations

Evaluation of 224Ra as a tracer for submarine groundwater discharge in Long Island Sound (NY)

Altres ajuts: the government of Spain and the Fulbright Commission for a post-doctoral fellowship to J.G-O. (ref 2007-0516)The approach to quantify submarine groundwater discharge using Ra isotopes generally involves developing a Ra mass balance in an estuary, bay or lagoon. In this work we present a 224Ra mass balance used to evaluate the importance of the submarine groundwater discharge (SGD) in Long Island Sound (NY, US), the third most important estuary in US, located between Long Island and Connecticut that is usually affected by summertime hypoxia in the western basin. Three surveys were conducted between April 2009 and August 2010 where 25 water stations were sampled for Ra isotopes, oxygen and Mn. Stations were oriented along 4 transects: one axial extending from the western to the eastern Sound and three longitudinal transects in the western, central and eastern Sound. The inventory of 224Ra in the water column in summer was circa 2 times greater than in winter, suggesting an increased 224Ra flux to the Sound in summer. A mass balance for 224Ra was constructed considering tidal exchange, inputs from rivers, desorption from resuspended particles, diffusive fluxes (including bioirrigation) from bottom sediments and radioactive decay in the water column. Fluxes of 224Ra from bottom sediments were measured by incubating cores under oxic conditions in a continuous flow mode such that the overlying water was circulated through a Mn-oxide fiber to maintain a constant activity of 224Ra. Fluxes from muddy sediments (comprising ~67% of the Sound bottom) ranged from 127 to 312dpmm-2d-1 and were ~60dpmm-2d-1 in sandy sediments (33% of the Sound). Incubations under hypoxic conditions showed variable fluxes depending on reduction and mobilization of Mn. The 224Ra mass balance shows a net input of Ra to the Sound of 106±50×1012dpmy-1 in spring and 244±112×1012dpmy-1 in the summer that is attributed to SGD. Elevated 224Ra values were observed near shore and in the pore fluids of the coarse beach sands along the Long Island and Connecticut coasts, suggesting that SGD driven by tidal recirculation through the beach face is a major source of 224Ra to the Sound. Seasonal variation in this source seems unlikely, and the calculated 224Ra SGD fluxes for spring and summer overlap within the uncertainties. Nevertheless we conclude that variations in the 224Ra water column inventories could be produced by seasonal changes in bioirrigation and/or redox cycling of Mn as well as sediment resuspension and desorption of 224Ra from resuspended particles, and that our mass balance underestimates these terms, particularly in the summer. 224Ra fluxes from sediments in estuaries, especially those with significant areas of muddy sediments and seasonal hypoxia, are important and should be well constrained in future uses of this isotope as a tracer for SGD

Gaia broad band photometry

The scientific community needs to be prepared to analyse the data from Gaia, one of the most ambitious ESA space missions, to be launched in 2012. The purpose of this paper is to provide data and tools in order to predict in advance how Gaia photometry is expected to be. To do so, we provide relationships among colours involving Gaia magnitudes and colours from other commonly used photometric systems (Johnson-Cousins, SDSS, Hipparcos and Tycho). The most up-to-date information from industrial partners has been used to define the nominal passbands and based on the BaSeL3.1 stellar spectral energy distribution library, relationships were obtained for stars with different reddening values, ranges of temperatures, surface gravities and metallicities. The transformations involving Gaia and Johnson-Cousins V-I_C and Sloan DSS g-z colours have the lowest residuals. A polynomial expression for the relation between the effective temperature and the colour G_BP-G_RP was derived for stars with T > 4500 K. Transformations involving two Johnson or two Sloan DSS colours yield lower residuals than using only one colour. We also computed several ratios of total-to-selective absorption including absorption A_G in the G band and colour excess E(G_BP-G_RP) for our sample stars. A relationship, involving A_G/A_V and the intrinsic (V-I_C) colour, is provided. The derived Gaia passbands have been used to compute tracks and isochrones using the Padova and BASTI models. Finally, the performances of the predicted Gaia magnitudes have been estimated according to the magnitude and the celestial coordinates of the star. The provided dependencies among colours can be used for planning scientific exploitation of Gaia data, performing simulations of the Gaia-like sky, planning ground-based complementary observations and for building catalogues with auxiliary data for the Gaia data processing and validation.Comment: 15 pages and 19 figure (accepted in A&A

Anomalous Roughening in Experiments of Interfaces in Hele-Shaw Flows with Strong Quenched Disorder

We report experimental evidences of anomalous kinetic roughening in the stable displacement of an oil-air interface in a Hele-Shaw cell with strong quenched disorder. The disorder consists on a random modulation of the gap spacing transverse to the growth direction (tracks). We have performed experiments varying average interface velocity and gap spacing, and measured the scaling exponents. We have obtained beta=0.50, beta*=0.25, alpha=1.0, alpha_l=0.5, and z=2. When there is no fluid injection, the interface is driven solely by capillary forces, and a higher value of beta around beta=0.65 is measured. The presence of multiscaling and the particular morphology of the interfaces, characterized by high slopes that follow a L\'evy distribution, confirms the existence of anomalous scaling. From a detailed study of the motion of the oil--air interface we show that the anomaly is a consequence of different local velocities over tracks plus the coupling in the motion between neighboring tracks. The anomaly disappears at high interface velocities, weak capillary forces, or when the disorder is not sufficiently persistent in the growth direction. We have also observed the absence of scaling when the disorder is very strong or when a regular modulation of the gap spacing is introduced.Comment: 14 pages, 17 figure

The Gaia spectrophotometric standard stars survey -II. Instrumental effects of six ground-based observing campaigns

The Gaia SpectroPhotometric Standard Stars (SPSS) survey started in 2006, it was awarded almost 450 observing nights, and accumulated almost 100,000 raw data frames, with both photometric and spectroscopic observations. Such large observational effort requires careful, homogeneous, and automated data reduction and quality control procedures. In this paper, we quantitatively evaluate instrumental effects that might have a significant (i.e.,$\geq$1%) impact on the Gaia SPSS flux calibration. The measurements involve six different instruments, monitored over the eight years of observations dedicated to the Gaia flux standards campaigns: DOLORES@TNG in La Palma, EFOSC2@NTT and ROSS@REM in La Silla, [email protected] in Calar Alto, BFOSC@Cassini in Loiano, and [email protected] in San Pedro Martir. We examine and quantitatively evaluate the following effects: CCD linearity and shutter times, calibration frames stability, lamp flexures, second order contamination, light polarization, and fringing. We present methods to correct for the relevant effects, which can be applied to a wide range of observational projects at similar instruments.Comment: 16 pages, 13 figures, accepted for publication in Astron. Nach