Environmental dependence of AGN activity in the supercluster A901/2

We present XMM data for the supercluster A901/2, at z ~ 0.17, which is combined with deep imaging and 17-band photometric redshifts (from the COMBO-17 survey), 2dF spectra and Spitzer 24um data, to identify AGN in the supercluster. The 90ksec XMM image contains 139 point sources, of which 11 are identified as supercluster AGN with L_X(0.5-7.5keV) > 1.7x10^41 erg/cm2/s. The host galaxies have M_R < -20 and only 2 of 8 sources with spectra could have been identified as AGN by the detected optical emission lines. Using a large sample of 795 supercluster galaxies we define control samples of massive galaxies with no detected AGN. The local environments of the AGN and control samples differ at >98 per cent significance. The AGN host galaxies lie predominantly in areas of moderate projected galaxy density and with more local blue galaxies than the control sample, with the exception of one very bright Type I AGN very near the centre of a cluster. These environments are similar to, but not limited to, cluster outskirts and blue groups. Despite the large number of potential host galaxies, no AGN are found in regions with the highest galaxy density (excluding some cluster cores where emission from the ICM obscures moderate luminosity AGN). AGN are also absent from the areas with lowest galaxy density. We conclude that the prevalence of cluster AGN is linked to their environment.Comment: 20 pages, 15 figures. MNRAS accepted. Version with full resolution figures, including Figure 14, is available at http://www.sc.eso.org/~rgilmour

Scaling soft matter physics to thousands of graphics processing units in parallel

We describe a multi-graphics processing unit (GPU) implementation of the Ludwig application, which specialises in simulating a variety of complex fluids via lattice Boltzmann fluid dynamics coupled to additional physics describing complex fluid constituents. We describe our methodology in augmenting the original central processing unit (CPU) version with GPU functionality in a maintainable fashion. We present several optimisations that maximise performance on the GPU architecture through tuning for the GPU memory hierarchy. We describe how we implement particles within the fluid in such a way to avoid a major diversion of the CPU and GPU codebases, whilst minimising data transfer at each time step. We detail our halo-exchange communication phase for the code, which exploits overlapping to allow efficient parallel scaling to many GPUs. We present results showing that the application demonstrates excellent scaling to at least 8192 GPUs in parallel, the largest system tested at the time of writing. The GPU version (on NVIDIA K20X GPUs) is around 3.5-5 times faster that the CPU version (on fully utilised AMD Opteron 6274 16-core CPUs), comparing equal numbers of CPUs and GPUs

Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I

We have embarked on a project, under the aegis of the Nearby Stars (NStars)/ Space Interferometry Mission Preparatory Science Program to obtain spectra, spectral types, and, where feasible, basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40 parsecs of the sun. In this paper we report on the results of this project for the first 664 stars in the northern hemisphere. These results include precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity and the overall metallicity, [M/H]) and measures of the chromospheric activity of our program stars. Observed and derived data presented in this paper are also available on the project's website at http://stellar.phys.appstate.edu/

TYC 8380-1953-1: Discovery of an RS CVn binary through the XMM-Newton slew survey

In this paper we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through the XMM-Newton slew survey and present results of our optical and X-ray follow-up. With a flux limit of $6 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the soft band ($0.2 - 2$ keV), the XMM-Newton slew has a similar sensitivity to the ROSAT All Sky Survey allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre-main and main sequence stars) and chromospherically active binaries (BY Dra and RS CVn type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary with both components having similar spectral type (likely K0/2+K3/5) and luminosity. With a typical coronal temperature for an RS CVn system ($kT \sim 1.15$ keV) and an X-ray luminosity in the $0.3-10$ keV energy band higher than $4 \times 10^{31}$ erg\,s$^{-1}$, TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.Comment: Accepted for publication in the PASP. 18 pages, 10 figure

Upstream cyclone influence on the predictability of block onsets over the Euro-Atlantic region

Atmospheric blocking has been shown to be a phenomenon that models struggle to predict accurately, particularly the onset of a blocked state following a more zonal flow. This struggle is, in part, due to the lack of a complete dynamical theory for block onset and maintenance. Here, we evaluate the impact cyclone representation had on the forecast of block onset in two case studies from the North Atlantic Waveguide and Downstream Impact Experiment field campaign and the 20 most unpredictable block onsets over the Euro-Atlantic region in medium-range forecasts from the ECMWF. The six-day forecast of block onset in the case studies is sensitive to changes in the forecast location and intensity of upstream cyclones (one cyclone for one case and two for the other case) in the days preceding the onset. Ensemble sensitivity analysis reveals that this is often the case in unpredictable block onset cases: a one-standard deviation change in 1000-hPa geopotential height near an upstream cyclone, or 320-K potential vorticity near the tropopause, two or three days prior to block onset is associated with more than a 10% change in block area on the analyzed onset day in 17 of the 20 onset cases. These results imply that improvement in the forecasts of upstream cyclone location and intensity may help improve block onset forecasts

Endovascular aneurysm repair increases aortic arterial stiffness when compared to open repair of abdominal aortic aneurysms

Objectives: The initial survival advantage seen with endovascular aneurysm repair (EVAR) over open repair does not persist in the long term. Pulse wave velocity (PWV) is a measure of arterial stiffness, and increased PWV is an independent risk factor for increased cardiovascular morbidity and mortality. This prospective comparative pilot study examined the effect of implantation of an aortic graft on PWV in patients undergoing open or endovascular aortic aneurysm repair. Patients and Methods: Thirty-four patients (15 open and 19 EVAR) were recruited. Patient demographics were similar in both the groups. Pulse wave velocity was calculated for all patients preoperatively and postoperatively using a standardized technique on a Philips IU22 Vascular Ultrasound machine and the results compared. Results: An increase in mean PWV following EVAR was demonstrated. The mean post-procedure PWV of 9.7 (+ 4.5) cm/sec detected in the open group was significantly lower than the elevated 12.2 (+ 4.5) cm/ sec detected in the EVAR group. The surgical group also demonstrated a mean decrease of 0.2 (+ 4.9) cm/sec in PWV following open repair compared to a mean increase of 3.3 (+ 3.7) cm/sec in the EVAR group. Conclusion: EVAR patients have a significantly higher postoperative PWV measurement than those undergoing open abdominal aortic aneurysm repair. Patients who have undergone EVAR may be at a higher risk of cardiovascular morbidity in the long term. A larger scale study with a longer prospective follow-up is required

Tuning hole mobility in InP nanowires

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.Comment: 4 pages, 4 figure

Developing arts-based methods for exploring virtual reality technologies: A university–industry case study

Collaborations between human–computer interaction (HCI) researchers and arts practitioners frequently centre on the development of creative content using novel – often emergent – technologies. Concurrently, many of the techniques that HCI researchers use in evaluative participant-based research have their roots in the arts – such as sketching, writing, artefact prototyping and role play. In this reflective paper, we describe a recent collaboration between a group of HCI researchers and dramatists from the immersive theatre organization Kilter, who worked together to design a series of audience-based interventions to explore the ethics of virtual reality (VR) technology. Through a process of knowledge exchange, the collaboration provided the researchers with new techniques to explore, ideate and communicate their work, and provided the dramatists with a solid academic grounding in order to produce an accurate yet provocative piece of theatrically based design fiction. We describe the formation of this partnership between academia and creative industry, document our journey together, and share the lasting impact it has had upon both parties

Use of Colour Duplex Ultrasound as a First Line Surveillance Tool Following EVAR is Associated with a Reduction in Cost Without Compromising Accuracy

CT scanning remains the postoperative surveillance imaging modality of choice following EVAR. Concerns regarding cost, exposure to ionising radiation and intravenous contrast have led to a search for a less expensive, equally efficacious and safer method of monitoring EVAR patients after endograft deployment. This study evaluated the cost saving obtained if CDUS was employed as a first line surveillance tool following EVAR, as well as comparing the two entities in terms of efficacy. Patients & methods: Postoperative surveillance CTs and CDUS scans in the 145 patients who have undergone EVAR from 1st June 2003 to 1st July 2010 were compared for the detection of endoleak and determination of residual sac size. Results: Adopting a protocol where CDUS was employed as the first line surveillance tool following EVAR would result in a reduction in the number of postoperative CTs required in 2010 from 235 to 36. Based on 2010 costings, this would equate to an estimated reduction in expenditure from V117,500 to V34,915 a saving of V82,585. CDUS had a sensitivity of 100% and a specificity of 85% in the detection of endoleaks compared to CT. The positive predictive value was 28% and negative predictive value 100%. The Pearson Coefficient correlation of 0.96 indicates a large degree of correlation between CDUS and CT when measuring residual aneurysm size following EVAR. Conclusion: CDUS can replace CT as the first line surveillance tool following EVAR. This is associated with a significant reduction in the cost of surveillance without any loss of imaging accurac

Use of Colour Duplex Ultrasound as a First Line Surveillance Tool Following EVAR is Associated with a Reduction in Cost Without Compromising Accuracy

CT scanning remains the postoperative surveillance imaging modality of choice following EVAR. Concerns regarding cost, exposure to ionising radiation and intravenous contrast have led to a search for a less expensive, equally efficacious and safer method of monitoring EVAR patients after endograft deployment. This study evaluated the cost saving obtained if CDUS was employed as a first line surveillance tool following EVAR, as well as comparing the two entities in terms of efficacy. Patients & methods: Postoperative surveillance CTs and CDUS scans in the 145 patients who have undergone EVAR from 1st June 2003 to 1st July 2010 were compared for the detection of endoleak and determination of residual sac size. Results: Adopting a protocol where CDUS was employed as the first line surveillance tool following EVAR would result in a reduction in the number of postoperative CTs required in 2010 from 235 to 36. Based on 2010 costings, this would equate to an estimated reduction in expenditure from V117,500 to V34,915 a saving of V82,585. CDUS had a sensitivity of 100% and a specificity of 85% in the detection of endoleaks compared to CT. The positive predictive value was 28% and negative predictive value 100%. The Pearson Coefficient correlation of 0.96 indicates a large degree of correlation between CDUS and CT when measuring residual aneurysm size following EVAR. Conclusion: CDUS can replace CT as the first line surveillance tool following EVAR. This is associated with a significant reduction in the cost of surveillance without any loss of imaging accurac