Infrared Non-detection of Fomalhaut b -- Implications for the Planet Interpretation

The nearby A4-type star Fomalhaut hosts a debris belt in the form of an eccentric ring, which is thought to be caused by dynamical influence from a giant planet companion. In 2008, a detection of a point-source inside the inner edge of the ring was reported and was interpreted as a direct image of the planet, named Fomalhaut b. The detection was made at ~600--800 nm, but no corresponding signatures were found in the near-infrared range, where the bulk emission of such a planet should be expected. Here we present deep observations of Fomalhaut with Spitzer/IRAC at 4.5 um, using a novel PSF subtraction technique based on ADI and LOCI, in order to substantially improve the Spitzer contrast at small separations. The results provide more than an order of magnitude improvement in the upper flux limit of Fomalhaut b and exclude the possibility that any flux from a giant planet surface contributes to the observed flux at visible wavelengths. This renders any direct connection between the observed light source and the dynamically inferred giant planet highly unlikely. We discuss several possible interpretations of the total body of observations of the Fomalhaut system, and find that the interpretation that best matches the available data for the observed source is scattered light from transient or semi-transient dust cloud.Comment: 12 pages, 4 figures, ApJ 747, 166. V2: updated acknowledgments and reference

Hearing the Voice of Medical Students Worldwide

The Student Forum, a new section of PLoS Medicine, is a space where medical students from across the world can exchange ideas about the critical issues affecting health and health care from their unique perspectiv

A standardized design for quagga mussel monitoring in Lake Mead, Nevada-Arizona

The discovery of quagga mussels (Dreissena rostriformis bugensis) in Lake Mead, Nevada-Arizona, on January 6, 2007 is the first known occurrence of dreissenid species in the western United States. This study developed elements of a cost-effective and standardized quagga mussel-monitoring program for Lake Mead using preliminary data to arrive at statistically based numbers of sampling sites. To represent the abundance of adult/juvenile quagga mussels in Lake Mead’s heterogeneous floor with 95% confidence, a stratified simple random sampling design revealed a requirement of 41 samples from hard substrates (i.e., rocky areas) and 97 samples from soft substrates (i.e., sandy and muddy areas). A simple random sampling design demonstrated that 42 samples from the lake’s water column are necessary to represent veliger abundance with 95% confidence. Other important elements of the sampling program, such as standardization of protocols and processes and suggested data analyses, are discussed. The monitoring program, which is based on reconnaissance data, is intended to be optimized with data from its first year’s samples. The sample number-selection approach and the other elements of this plan can be easily implemented by lake managers and can also be adapted to other locations where dreissenid mussel monitoring is needed

We need to talk about depression and dialysis: but what questions should we ask and does anyone know the answers?

Depression is common in people with chronic kidney disease (CKD). When diagnosed via a gold standard semi-structured psychiatric interview by culturally-competent staff, depression affects one fifth to one quarter of people with CKD, whether in receipt of maintenance dialysis, with non-dialysis treated CKD, or with a functioning transplant (respective prevalence rates 22.8 (95% confidence interval (CI) 18.6 to 27.6)%, 21.4 (95%CI 11.1 to 37.2)% and 25.7 (95%CI 12.8 to 44.9)%)1. These frequencies are clearly in excess of the average population lifetime risk of ~ 9%2. Potential reasons for the high rates of depression in end stage kidney disease (ESKD) include the overlap of some risk factors for both conditions, the alteration of physiological processes associated with ESKD and the psychosocial consequences of living with ESKD3. Depression in people receiving dialysis is associated with lower quality of life, increased hospitalisations and, likely shortened survival3

Acute care for elders components of acute geriatric unit care: systematic descriptive review

OBJECTIVES: To describe the Acute Care for Elders (ACE) model components implemented as part of acute geriatric unit care and explore the association between each ACE component and outcomes of iatrogenic complications, functional decline, length of hospital stay, nursing home discharges, costs, and discharges home. DESIGN: Systematic descriptive review of 32 articles, including 14 trials reporting on the implementation of ACE components or the effectiveness of their implementation in improving outcomes. Mean effect sizes (ESs) were calculated using trial outcome data. Information describing implementation of the ACE components in the trials was analyzed using content analysis. SETTING: Acute care geriatric units. PARTICIPANTS: Acutely ill or injured adults (N = 6,839) with an average age of 81. INTERVENTIONS: Acute geriatric unit care was characterized by the implementation of one or more ACE components: medical review, early rehabilitation, early discharge planning, prepared environment, patient-centered care. MEASUREMENTS: Falls, pressure ulcers, delirium, functional decline, length of hospital stay, discharge destination (home or nursing home), and costs. RESULTS: Medical review, early rehabilitation, and patient-centered care, characterized by the implementation of standardized and individualized function-focused interventions, had larger standardized mean ESs (all ES = 0.20) averaged across all outcomes, than did early discharge planning (ES = 0.17) or prepared environment (ES = 0.11). CONCLUSION: Specific ACE component interventions of medical review, early rehabilitation, and patient-centered care appear to be optimal for overall positive outcomes. These findings can help service providers design and evaluate the most-effective ACE model within the contexts of their respective institutions to improve outcomes for acutely ill or injured older adults.Financial support provided by Canadian Institutes of Health Research (CIHR) grant #KRS-94307. Mary Fox was supported by an Ontario Ministry of Health & Long-Term Care Career Scientist Award, Kelly O’Brien by a CIHR Fellowship, Souraya Sidani and Dina Brooks by Canada Research Chairs, and Deborah Tregunno by an Ontario Ministry of Health and Long-Term Care Senior Nurse Research Award while conducting this study

Recent Star Formation in Sextans A

We investigate the relationship between the spatial distributions of stellar populations and of neutral and ionized gas in the Local Group dwarf irregular galaxy Sextans A. This galaxy is currently experiencing a burst of localized star formation, the trigger of which is unknown. We have resolved various populations of stars via deep UBV(RI)_C imaging over an area with diameter \sim 5.'3. We have compared our photometry with theoretical isochrones appropriate for Sextans A, in order to determine the ages of these populations. We have mapped out the history of star formation, most accurately for times \lesssim 100 Myr. We find that star formation in Sextans A is correlated both in time and space, especially for the most recent (\lesssim 12 Myr) times. The youngest stars in the galaxy are forming primarily along the inner edge of the large H I shell. Somewhat older populations, \lesssim 50 Myr, are found inward of the youngest stars. Progressively older star formation, from \sim 50--100 Myr, appears to have some spatially coherent structure and is more centrally concentrated. The oldest stars we can accurately sample appear to have approximately a uniform spatial distribution, which extends beyond a surface brightness of \mu_B \simeq 25.9 mag arcsec^{-2} (or, a radius r \simeq 2.'3$). Although other processes are also possible, our data provides support for a mechanism of supernova-driven expansion of the neutral gas, resulting in cold gas pileup and compression along the H I shell and sequential star formation in recent times.Comment: 64 pages, 22 figures, to appear in A

Jamming Model for the Extremal Optimization Heuristic

Extremal Optimization, a recently introduced meta-heuristic for hard optimization problems, is analyzed on a simple model of jamming. The model is motivated first by the problem of finding lowest energy configurations for a disordered spin system on a fixed-valence graph. The numerical results for the spin system exhibit the same phenomena found in all earlier studies of extremal optimization, and our analytical results for the model reproduce many of these features.Comment: 9 pages, RevTex4, 7 ps-figures included, as to appear in J. Phys. A, related papers available at http://www.physics.emory.edu/faculty/boettcher

Study protocol : the empirical investigation of methods to correct for measurement error in biobanks with dietary assessment

Peer reviewedPublisher PD