Hubble-Lema\^itre fragmentation and the path to equilibrium of merger-driven cluster formation

This paper discusses a new method to generate self-coherent initial conditions for young substructured stellar cluster. The expansion of a uniform system allows stellar sub-structures (clumps) to grow from fragmentation modes by adiabatic cooling. We treat the system mass elements as stars, chosen according to a Salpeter mass function, and the time-evolution is performed with a collisional N-body integrator. This procedure allows to create a fully-coherent relation between the clumps' spatial distribution and the underlying velocity field. The cooling is driven by the gravitational field, as in a cosmological Hubble-Lema\^itre flow. The fragmented configuration has a `fractal'-like geometry but with a self-grown velocity field and mass profile. We compare the characteristics of the stellar population in clumps with that obtained from hydrodynamical simulations and find a remarkable correspondence between the two in terms of the stellar content and the degree of spatial mass-segregation. In the fragmented configuration, the IMF power index is ~0.3 lower in clumps in comparison to the field stellar population, in agreement with observations in the Milky Way. We follow in time the dynamical evolution of fully fragmented and sub-virial configurations, and find a soft collapse, leading rapidly to equilibrium (timescale of 1 Myr for a ~ 10^4 Msun system). The low-concentration equilibrium implies that the dynamical evolution including massive stars is less likely to induce direct collisions and the formation of exotic objects. Low-mass stars already ejected from merging clumps are depleted in the end-result stellar clusters, which harbour a top-heavy stellar mass function.Comment: 22 pages, accepted for publication in MNRA

Chemistry of Surface Waters: Distinguishing Fine-Scale Differences in Sea Grass Habitats of Chesapeake Bay

We tested the hypothesis that the physical and chemical processes acting in sea grass habitats of the lower Chesapeake Bay are spatially structured and that dissolved elemental chemistry of sea grass-habitat surface waters have their own unique identity. We sampled surface waters from July to September 2001 in five sea grass habitats of the lower bay: Potomac, Rappahannock, York, Island (Tangier-Bloodsworth), and Eastern Shore. Dissolved Mg, Mn, Sr, and Ba concentrations were measured by sector field inductively coupled plasma-mass spectrometry. As expected, Mg, Sr, and Ba exhibited conservative behavior, but Mn exhibited nonconservative behavior along the salinity gradient. Spatial differences in the chemistry of surface waters over sea grass habitats were fully resolvable independently of time. Moreover, classification accuracy of water samples was low in Rappahannock, moderate in Potomac and Eastern Shore, and high in the York and Island habitats. The chemistry of York was distinct because of the effects of physical mixing, whereas Island chemistry was unique, potentially because of the influence of Coriolis acceleration and river discharges from the Susquehanna River. The results of this study show that sites so close to one another in physical space maintain distinct chemical differences

Profiles of SUMO and ubiquitin conjugation in an Alzheimer's disease model

► Global levels of ubiquitinated proteins increased in the hippocampus of Tg2576 mice. ► No global changes in either SUMO-1 or SUMO-2/3 conjugation in any brain regions analysed. ► SUMO conjugating and deconjugating enzymes, UBC9 and SENP-1, unaltered in Tg2576 mice. ► Total levels of AMPA and kainate receptors were also unaffected in Tg2576 mice. ► Posttranslational modification by ubiquitin may play a role in Alzheimer's disease

bRing: An observatory dedicated to monitoring the β\beta Pictoris b Hill sphere transit

Aims. We describe the design and first light observations from the $\beta$ Pictoris b Ring ("bRing") project. The primary goal is to detect photometric variability from the young star $\beta$ Pictoris due to circumplanetary material surrounding the directly imaged young extrasolar gas giant planet \bpb. Methods. Over a nine month period centred on September 2017, the Hill sphere of the planet will cross in front of the star, providing a unique opportunity to directly probe the circumplanetary environment of a directly imaged planet through photometric and spectroscopic variations. We have built and installed the first of two bRing monitoring stations (one in South Africa and the other in Australia) that will measure the flux of $\beta$ Pictoris, with a photometric precision of $0.5\%$ over 5 minutes. Each station uses two wide field cameras to cover the declination of the star at all elevations. Detection of photometric fluctuations will trigger spectroscopic observations with large aperture telescopes in order to determine the gas and dust composition in a system at the end of the planet-forming era. Results. The first three months of operation demonstrate that bRing can obtain better than 0.5\% photometry on $\beta$ Pictoris in five minutes and is sensitive to nightly trends enabling the detection of any transiting material within the Hill sphere of the exoplanet

Predicting market squid (Doryteuthis opalescens) landings from pre-recruit abundance

The fishery for market squid (Doryteuthis opalescens) in California is typical of many of the world’s cephalopod fisheries, in that a very short life span and the effect of environmental forcing on recruitment result in enormous interannual variability in catches and population size. We evaluate the utility of a pre-recruit index of squid abundance that is based on midwater trawl sampling in the 3–5 months preceding the onset of the fishery as a basis for predicting landings. Catches in the survey largely represent squid in the 30–50 mm dorsal mantle length size range, representing individuals 30–90 day old. Catch-per-unit-effort statistics are derived from simple twofactor Δ-Generalized Linear Models, with year and station as main effects and numbers per tow as the dependent variable. Regional models for northern and southern squid populations are developed. Pre-recruit indices, as well as indices of squid prey (krill) abundance are compared with landings data, as well as estimates of squid spawning stock biomass derived from an egg escapement model. Our results show that the abundance of prerecruit market squid and krill sampled in the survey tracks both catches and overall population size, providing the potential to forecast landings. Our findings are consistent with a sparse but growing literature showing the potential utility of pre-recruit surveys to inform fisheries participants and managers

Variability of M giant stars based on Kepler photometry: general characteristics

M giants are among the longest-period pulsating stars which is why their studies were traditionally restricted to analyses of low-precision visual observations, and more recently, accurate ground-based data. Here we present an overview of M giant variability on a wide range of time-scales (hours to years), based on analysis of thirteen quarters of Kepler long-cadence observations (one point per every 29.4 minutes), with a total time-span of over 1000 days. About two-thirds of the sample stars have been selected from the ASAS-North survey of the Kepler field, with the rest supplemented from a randomly chosen M giant control sample. We first describe the correction of the light curves from different quarters, which was found to be essential. We use Fourier analysis to calculate multiple frequencies for all stars in the sample. Over 50 stars show a relatively strong signal with a period equal to the Kepler-year and a characteristic phase dependence across the whole field-of-view. We interpret this as a so far unidentified systematic effect in the Kepler data. We discuss the presence of regular patterns in the distribution of multiple periodicities and amplitudes. In the period-amplitude plane we find that it is possible to distinguish between solar-like oscillations and larger amplitude pulsations which are characteristic for Mira/SR stars. This may indicate the region of the transition between two types of oscillations as we move upward along the giant branch.Comment: 12 pages, 13 figures, accepted for publication in MNRAS. The normalized light curves are available upon reques

Adaptive growth factor delivery from a polyelectrolyte coating promotes synergistic bone tissue repair and reconstruction

Traumatic wounds and congenital defects that require large-scale bone tissue repair have few successful clinical therapies, particularly for craniomaxillofacial defects. Although bioactive materials have demonstrated alternative approaches to tissue repair, an optimized materials system for reproducible, safe, and targeted repair remains elusive. We hypothesized that controlled, rapid bone formation in large, critical-size defects could be induced by simultaneously delivering multiple biological growth factors to the site of the wound. Here, we report an approach for bone repair using a polyelectrolye multilayer coating carrying as little as 200 ng of bone morphogenetic protein-2 and platelet-derived growth factor-BB that were eluted over readily adapted time scales to induce rapid bone repair. Based on electrostatic interactions between the polymer multilayers and growth factors alone, we sustained mitogenic and osteogenic signals with these growth factors in an easily tunable and controlled manner to direct endogenous cell function. To prove the role of this adaptive release system, we applied the polyelectrolyte coating on a well-studied biodegradable poly(lactic-co-glycolic acid) support membrane. The released growth factors directed cellular processes to induce bone repair in a critical-size rat calvaria model. The released growth factors promoted local bone formation that bridged a critical-size defect in the calvaria as early as 2 wk after implantation. Mature, mechanically competent bone regenerated the native calvaria form. Such an approach could be clinically useful and has significant benefits as a synthetic, off-the-shelf, cell-free option for bone tissue repair and restoration.National Institutes of Health (U.S.) (Grant R01 AG029601)National Institutes of Health (U.S.) (Grant R01 EB010246)National Institutes of Health (U.S.) (Grant P30 CA014051)Natural Sciences and Engineering Research Council of Canada (Fellowship

Should Age-Dependent Absolute Risk Thresholds Be Used for Risk Stratification in Risk-Stratified Breast Cancer Screening?

In risk-stratified cancer screening, multiple risk factors are incorporated into the risk assessment. An individual’s estimated absolute cancer risk is linked to risk categories with tailored screening recommendations for each risk category. Absolute risk, expressed as either remaining lifetime risk or shorter-term (five- or ten-year) risk, is estimated from the age at assessment. These risk estimates vary by age; however, some clinical guidelines (e.g., enhanced breast cancer surveillance guidelines) and ongoing personalised breast screening trials, stratify women based on absolute risk thresholds that do not vary by age. We examine an alternative approach in which the risk thresholds used for risk stratification vary by age and consider the implications of using age-independent risk thresholds on risk stratification. We demonstrate that using an age-independent remaining lifetime risk threshold approach could identify high-risk younger women but would miss high-risk older women, whereas an age-independent 5-year or 10-year absolute risk threshold could miss high-risk younger women and classify lower-risk older women as high risk. With risk misclassification, women with an equivalent risk level would be offered a different screening plan. To mitigate these problems, age-dependent absolute risk thresholds should be used to inform risk stratification