The Career and reputation of Herbert Howells

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The Outer Limits of Galaxy Clusters: Observations to the Virial Radius with Suzaku, XMM, and Chandra

The outskirts of galaxy clusters, near the virial radius, remain relatively unexplored territory and yet are vital to our understanding of cluster growth, structure, and mass. In this presentation, we show the first results from a program to constrain the state of the outer intracluster medium (ICM) in a large sample of galaxy clusters, exploiting the strengths of three complementary X-ray observatories: Suzaku (low, stable background), XMM-Newton (high sensitivity), and Chandra (good spatial resolution). By carefully combining observations from the cluster core to beyond r_200, we are able to identify and reduce systematic uncertainties that would impede our spatial and spectral analysis using a single telescope. Our sample comprises nine clusters at z ~ 0.1-0.2 fully covered in azimuth to beyond r_200, and our analysis indicates that the ICM is not in hydrostatic equilibrium in the cluster outskirts, where we see clear azimuthal variations in temperature and surface brightness. In one of the clusters, we are able to measure the diffuse X-ray emission well beyond r_200, and we find that the entropy profile and the gas fraction are consistent with expectations from theory and numerical simulations. These results stand in contrast to recent studies which point to gas clumping in the outskirts; the extent to which differences of cluster environment or instrumental effects factor in this difference remains unclear. From a broader perspective, this project will produce a sizeable fiducial data set for detailed comparison with high-resolution numerical simulations.Comment: 8 pages, 6 figures. To appear in the proceedings of the Suzaku 2011 Conference, "Exploring the X-ray Universe: Suzaku and Beyond.

A Suzaku Observation of MCG-2-58-22: Constraining the Geometry of the Circumnuclear Material

We have analyzed a Suzaku long-look of the active galactic nucleus MCG-2-58-22, a type 1.5 Seyfert with very little X-ray absorption in the line of sight and prominent features arising from reflection off circumnuclear material: the Fe line and Compton reflection hump. We place tight constraints on the power law photon index (Gamma=1.80+/-0.02), the Compton reflection strength (R=0.69+/-0.05), and the Fe K emission line energy centroid and width (E=6.40+/-0.02 keV, v_FWHM < 7100 km/s). We find no significant evidence for emission from strongly ionized Fe, nor for a strong, relativistically broadened Fe line, indicating that perhaps there is no radiatively efficient accretion disk very close in to the central black hole. In addition we test a new self-consistent physical model from Murphy & Yaqoob, the "MYTorus" model, consisting of a donut-shaped torus of material surrounding the central illuminating source and producing both the Compton hump and the Fe K line emission. From the application of this model we find that the observed spectrum is consistent with a Compton-thick torus of material (column density NH=3.6(+1.3/-0.8) x 10^24 cm^-2) lying outside of the line of sight to the nucleus, leaving it bare of X-ray absorption in excess of the Galactic column. We calculate that this material is sufficient to produce all of the Fe line flux without the need for any flux contribution from additional Compton-thin circumnuclear material.Comment: 7 pages, 4 figures, 2 table

Bostonia. Volume 4

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Facilitators and barriers to teaching undergraduate medical students in general practice

CONTEXT Globally, primary health care is facing workforce shortages. Longer and higher-quality placements in primary care increase the likelihood of medical students choosing this specialty. However, the recruitment and retention of community primary care teachers are challenging. Relevant research was predominantly carried out in the 1990s. We seek to understand contemporary facilitators and barriers to general practitioner (GP) engagement with undergraduate education. Communities of practice (CoP) theory offers a novel conceptualisation, which may be pertinent in other community-based teaching settings. METHODS Semi-structured interviews were undertaken with 24 GP teachers at four UK medical schools. We purposively sampled GPs new to teaching, established GP teachers and GPs who had recently stopped teaching. We undertook NVivo-assisted deductive and inductive thematic analysis of transcripts. We used CoP theory to interpret data. RESULTS Communities of practice theory illustrated that teachers negotiate membership of three CoPs: (i) clinical practice; (ii) the medical school, and (iii) teaching. The delivery of clinical care and teaching may be integrated or exist in tension. This can depend upon the positioning of the teaching and teacher as central or peripheral to the clinical CoP. Remuneration, workload, space and the expansion of GP trainee numbers impact on this. Teachers did not identify strongly as members of the medical school or a teaching community. Perceptions of membership were affected by medical school communication and support. The findings demonstrate gaps in medical school recruitment. CONCLUSIONS This research demonstrates the marginalisation of primary care-based teaching and proposes a novel explanation rooted in CoP theory. Concepts including identity and membership may be pertinent to other community-based teaching settings. We recommend that medical schools review and broaden recruitment methods. Teacher retention may be improved by optimising the interface between medical schools and teachers, fostering a teaching community, increasing professional rewards for teaching involvement and altering medical school expectations of learning in primary care

Neurokinin B Receptor Antagonism in Women with Polycystic Ovary Syndrome: A Randomized, Placebo-Controlled Trial

Context: Polycystic ovary syndrome (PCOS), the most common endocrinopathy in women, is characterized by high secretion levels of LH and T. Currently, there is no treatment licensed specifically for PCOS. Objective: The objective of this study was to investigate whether a targeted therapy would decrease LH pulse frequency in women with PCOS, subsequently reducing serum LH and T concentrations and thereby presenting a novel therapeutic approach to the management of PCOS. Design: This study is a double-blind, double-dummy, placebo-controlled, phase 2 trial. Settings: University hospitals and private clinical research centers were included. Participants: Women with PCOS aged 18–45 years participated. Intervention: Intervention included AZD4901 (a specific neurokinin-3 [NK3] receptor antagonist) at a dose of 20, 40, or 80 mg/day or matching placebo for 28 days. Main Outcome Measure: Change from baseline in the area under the LH serum concentration–time curve over 8 hours (area under the curve) on day 7 relative to placebo was measured. Results: Of a total 67 randomized patients, 65 were evaluable. On day 7, the following baseline-adjusted changes relative to placebo were observed in patients receiving AZD4901 80 mg/day: 1) a reduction of 52.0% (95% confidence interval [CI], 29.6–67.3%) in LH area under the curve; 2) a reduction of 28.7% (95% CI, 13.9–40.9%) in total T concentration; and 3) a reduction of 3.55 LH pulses/8 hours (95% CI, 2.0–5.1) (all nominal P &amp;lt; .05). Conclusions: The NK3 receptor antagonist AZD4901 specifically reduced LH pulse frequency and subsequently serum LH and T concentrations, thus presenting NK3 receptor antagonism as a potential approach to treating the central neuroendocrine pathophysiology of PCOS. </jats:sec

Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) for WFIRST/AFTA

Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) is a lenslet array based integral field spectrometer (IFS) designed for high contrast imaging of extrasolar planets. PISCES will be used to advance the technology readiness of the high contrast IFS baselined on the Wide-Field InfraRed Survey Telescope/Astrophysics Focused Telescope Assets (WFIRST/AFTA) coronagraph instrument. PISCES will be integrated into the high contrast imaging testbed (HCIT) at the Jet Propulsion Laboratory and will work with both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC) cofigurations. We discuss why the lenslet array based IFS is selected for PISCES. We present the PISCES optical design, including the similarities and differences of lenslet based IFSs to normal spectrometers, the trade-off between a refractive design and reflective design, as well as the specific function of our pinhole mask on the back surface of the lenslet array to further suppress star light introduced speckles. The optical analysis, alignment plan, and mechanical design of the instrument will be discussed

13 µm cutoff InAs/GaSb type-II superlattice nBn detectors with high quantum efficiency grown by MOCVD

In this work, we report the growth and fabrication optimization of a long wavelength InAs/GaSb type-II superlattice (T2SL) nBn detector grown by metal–organic chemical vapor deposition. A GaAs like interfacial scheme was employed to grow the T2SLs matched to InAs substrates. A larger bandgap InAs/GaSb T2SL was used as an electron barrier, removing the need for AlSb based materials within this detector. At 77 K and −0.1 V, the photodetector showed a dark current density of 2.2 × 10−2 A cm−2 and a 100% cutoff wavelength of 13 µm. The external quantum efficiency was found to be 54.4% at 9 µm. The peak detectivity was found to be 4.43 × 1010 cm Hz1/2/W at 9 µm, which is very comparable with similar deep etched detectors grown by molecular beam epitaxy

Sunyaev-Zel'dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager

We present observations using the Small Array of the Arcminute Microkelvin Imager (AMI; 14-18 GHz) of four Abell and three MACS clusters spanning 0.171-0.686 in redshift. We detect Sunyaev-Zel'dovich (SZ) signals in five of these without any attempt at source subtraction, although strong source contamination is present. With radio-source measurements from high-resolution observations, and under the assumptions of spherical $\beta$-model, isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in the visibility plane detects extended SZ decrements in all seven clusters over and above receiver noise, radio sources and primary CMB imprints. Bayesian evidence ratios range from 10^{11}:1 to 10^{43}:1 for six of the clusters and 3000:1 for one with substantially less data than the others. We present posterior probability distributions for, e.g., total mass and gas fraction averaged over radii internal to which the mean overdensity is 1000, 500 and 200, r_200 being the virial radius. Reaching r_200 involves some extrapolation for the nearer clusters but not for the more-distant ones. We find that our estimates of gas fraction are low (compared with most in the literature) and decrease with increasing radius. These results appear to be consistent with the notion that gas temperature in fact falls with distance (away from near the cluster centre) out to the virial radius.Comment: 18 pages, 10 figures, submitted to MNRAS (updated authors and fixed Figure 1