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Introduction: Literature suggests that up to 25% of people with HIV in North America are unaware of their status and are at risk to transmit the virus unknowingly. A high proportion of HIV patients are diagnosed when the disease is more advanced, with CD4 counts < 200. This study examined the rates of HIV testing, detection, and treatment of clients at an inner city shelter and detoxification centre after the introduction of a point of care testing (POCT) program by on-site community paramedics (CP). Methods: In 2013, in collaboration with a regional HIV program, CP received training and instituted an HIV POCT program and post-test counselling initiative. A retrospective electronic database review from October 16, 2013 to October 15, 2014 of adult patients who received testing was performed. Demographic and testing details of each patient encounter were abstracted and select variables were compared to a historic population who received POC HIV testing at an inner city emergency department (ED) in the same city. Results: 1,207 HIV POC tests were performed on 997 patients during the pilot. 57% of the patients tested were less than 40 years of age (range 18-73 years) compared to 55% in the historic ED population. A total of 9 reactive cases were identified in the study population including 3 new cases, 5 previously known cases, and 1 false reactive result. The mean age of the new cases was 47 years, vs 44 in the historical control. All 3 new cases were referred to a local HIV clinic for further care and treatment. New HIV cases represented 0.25% of total tests performed, which is less than the expected prevalence rate of 1% for this population, as well as the rate of 1.4% found in the ED population. Conclusion: Despite lower than expected reactive rates, the large scale implementation of a CP HIV POCT program in an inner city shelter and detoxification centre is feasible. All patients with new reactive tests were immediately connected to care. Future research will focus on risk factors and barriers to testing.
We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.
GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination + 25° at frequencies between 72 and 231 MHz, made with the MWA using a drift scan method that makes efficient use of the MWA’s very large field-of-view. We present the observation details, imaging strategies, and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40-kHz frequency resolution and 0.5-s time resolution; the second year using 10-kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing, and image weighting scheme. At 154 MHz, the image resolution is approximately 2.5 × 2.2/cos (δ + 26.7°) arcmin with sensitivity to structures up to ~ 10° in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA’s primary beam.
The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day−1 of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.
The science cases for incorporating high time resolution capabilities into modern radio telescopes are as numerous as they are compelling. Science targets range from exotic sources such as pulsars, to our Sun, to recently detected possible extragalactic bursts of radio emission, the so-called fast radio bursts (FRBs). Originally conceived purely as an imaging telescope, the initial design of the Murchison Widefield Array (MWA) did not include the ability to access high time and frequency resolution voltage data. However, the flexibility of the MWA’s software correlator allowed an off-the-shelf solution for adding this capability. This paper describes the system that records the 100 μs and 10 kHz resolution voltage data from the MWA. Example science applications, where this capability is critical, are presented, as well as accompanying commissioning results from this mode to demonstrate verification.
We present the results of an approximately 6 100 deg2 104–196 MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the MWACS. The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h < RA < 8.5 h, − 58° < Dec < −14°over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6–3 arcmin. The catalogue has 3 arcmin angular resolution and a typical noise level of 40 mJy beam− 1, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaicked snapshots, flux density calibration, and source-finding method. We present a catalogue of flux density and spectral index measurements for 14 110 sources, extracted from the mosaic, 1 247 of which are sub-components of complexes of sources.
The Apodizing Phase Plate (APP) coronagraph has been used to image the exoplanet β Pictoris b and the protoplanet candidate around HD 100546, and is currently in use in surveys with NaCo at the VLT. Its success is due to its tolerance to tip-tilt pointing errors in current AO systems, which degrade the performance of nearly all other coronagraphs. Currently the sensitivity of the APP is limited by non-common path errors in the science camera systems and by its chromatic behaviour. We present the achromatized Vector APP coronagraph and address how we will measure and minimise non-common path errors with Focal Plane Wavefront Sensing algorithms.
Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0″.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ≃ 1″ to 5″ (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales.
Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the southern hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21-cm emission from the EoR in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80–300 MHz, with a processed bandwidth of 30.72 MHz for both linear polarisations, and consists of 128 aperture arrays (known as tiles) distributed over a ~3-km diameter area. Novel hybrid hardware/software correlation and a real-time imaging and calibration systems comprise the MWA signal processing backend. In this paper, the as-built MWA is described both at a system and sub-system level, the expected performance of the array is presented, and the science goals of the instrument are summarised.
Early design studies for the future Exo-Planet Imaging Camera and Specrotgraph (EPICS) on the European Extremely Large Telescope (E-ELT) show the ability to probe the region of super-Earths in the habitable zone of stars within 5pc (including Gilese 581d). However, these planets will be lost to us if the correct choice of integral field spectrograph (IFS) technology is not selected for such an instrument the ability to fit and remove the speckle noise that remains is crucial to reaching these contrasts.
We conclusively demonstrate, though the use of an experimental setup producing an artificial speckle, that slicer based IFSs and post-processing using spectral deconvolution can achieve speckle rejection factors exceeding 103. Contrary to popular belief, we do not find any evidence that this choice of IFS technology limits the achievable contrast. Coupled with extreme adaptive optics and high performance coronographs, a slicer based integral field spectrograph could achieve contrasts exceeding 109, enabling these super-Earths to be detected in the habitable zone of nearby stars, making it an attractive option for the next generation of instruments being designed for the direct detection of extra solar planets.
We investigate the evolution of the Hα equivalent width, EW(Hα), with redshift and its dependence on stellar mass, using the first data from the 3D-HST survey, a large spectroscopic Treasury program with the HST-WFC3. Combining our Hα measurements of 854 galaxies at 0.8<z<1.5 with those of ground based surveys at lower and higher redshift, we can consistently determine the evolution of the EW(Hα) distribution from z=0 to z=2.2. We find that at all masses the characteristic EW(Hα) is decreasing towards the present epoch, and that at each redshift the EW(Hα) is lower for high-mass galaxies. We find EW(Hα) ~ (1+z)1.8 with little mass dependence. Qualitatively, this measurement is a model-independent confirmation of the evolution of star forming galaxies with redshift. A quantitative conversion of EW(Hα) to sSFR (specific star-formation rate) is model dependent, because of differential reddening corrections between the continuum and the Balmer lines. The observed EW(Hα) can be reproduced with the characteristic evolutionary history for galaxies, whose star formation rises with cosmic time to z ~ 2.5 and then decreases to z = 0. This implies that EW(Hα) rises to 400 Å at z = 8. The sSFR evolves faster than EW(Hα), as the mass-to-light ratio also evolves with redshift. We find that the sSFR evolves as (1+z)3.2, nearly independent of mass, consistent with previous reddening insensitive estimates. We confirm previous results that the observed slope of the sSFR-z relation is steeper than the one predicted by models, but models and observations agree in finding little mass dependence.
To assess Clostridium difficile infection (CDI)-related colectomy rates by CDI surveillance definitions and over time at multiple healthcare facilities.
Five university-affiliated acute care hospitals in the United States.
Design and Methods.
Cases of CDI and patients who underwent colectomy from July 2000 through June 2006 were identified from 5 US tertiary care centers. Monthly CDI-related colectomy rates were calculated as the number of CDI-related colectomies per 1,000 CDI cases, and cases were categorized according to recommended surveillance definitions. Logistic regression was performed to evaluate risk factors for CDI-related colectomy.
In total, 8,569 cases of CDI were identified, and 75 patients underwent CDI-related colectomy. The overall colectomy rate was 8.7 per 1,000 CDI cases. The CDI-related colectomy rate ranged from 0 to 23 per 1,000 CDI episodes across hospitals. The colectomy rate for healthcare-facility-onset CDI was 4.3 per 1,000 CDI cases, and that for community-onset CDI was 16.5 per 1,000 CDI cases (P < .05). There were significantly more CDI-related colectomies at hospitals B and C (P < .05).
The overall CDI-related colectomy rate was low, and there was no significant change in the CDI-related colectomy rate over time. Onset of disease outside the study hospital was an independent risk factor for colectomy.
Results of intrinsic As diffusion in Si as well as in strained and relaxed Si0.9Ge0.1 layers are presented. Using Molecular Beam Epitaxy in-situ As doped epitaxial Si and compressively strained and relaxed Si-Ge layers were grown on Si substrates. The samples were annealed using Rapid Thermal Annealing (RTA) at 1000 °C. Arsenic diffusion is seen to be enhanced in SiGe than in Si. The enhancement factor is calculated to be 2.3 and 1.3 for relaxed and strained Si0.9Ge0.1, respectively. Also, using RTA in oxygen atmosphere, interstitial and vacancies were selectively injected in to the sample structures. Diffusion enhancement is also recorded in Si and Si-Ge structures with interstitial as well as vacancy injections over inert anneal. The results suggest that both interstitial and vacancy defects contribute to As diffusion in Si and Si0.9Ge0.1.
A contender for future generations of CMOS technology is the strained silicon (S-Si) MOSFET. The mobility enhancement in S-Si can be exploited to maintain the performance enhancements demanded by Moore's law with reduced critical dimensions. S-Si is obtained by growth of a thin Si layer over a thick virtual substrate (VS) of relaxed silicon-germanium (SiGe). The mobility of a surface channel MOSFET is dependent on the quality of the silicon-oxide (Si/SiO2) interface. Ge may out diffuse from the virtual substrate to the oxide interface causing an increase in trapping density. As the Ge content in the virtual substrate increases surface roughness also increases. These phenomena both lead to a reduction in mobility.
The study of a matrix of devices having variable Ge composition and S-Si thickness is crucial in deconvolving the contributions of Ge diffusion and wafer cross-hatching roughness on electrical parameters. Increasing VS Ge composition increases the Ge concentration at the SSi/SiO2 interface and cross-hatching amplitude whereas reducing S-Si channel thickness only increases Ge concentration at the S-Si/SiO2 interface and does not increase cross-hatch amplitude. Interface state density, drive current, gate leakage current, transconductance and carrier mobility data are presented for this two-dimensional space of VS composition and S-Si thickness. The relative importance of Ge diffusion and cross-hatching roughness can be seen in this data. The results of this study indicate a lower limit of 7 nm for the S-Si thickness and an upper limit of approximately 20 % Ge in the virtual substrate for the current processing technology. Understanding the performance-limiting mechanisms in S-Si is crucial in the optimisation of VS Ge composition and S-Si thickness for current and future generations of S-Si CMOS.
Solid phase epitaxial regrowth (SPER) has been proven to be highly advantageous for ultra shallow junction formation in advanced technologies. Application of SPER to strained Si/SiGe structures raises the concern that the Ge may out diffuse during the implantation and/or anneal steps and thus reduce the strain in the top silicon layer.
In the present studies we expose 8-30 nm strained silicon layers grown on thin relaxed SiGe-buffers, to implant conditions and anneal cycles, characteristic for formation of the junctions by solid phase epitaxial regrowth and conventional spike activation. The resulting Geredistribution is measured using SIMS. Based on the outdiffused Ge-profiles the Ge-diffusion coefficient has been determined in the temperature range of 800-1100C from which an activation energy of ∼ 3.6 eV can be deduced. Up to 1050 C, 10 min, even a 30 nm strained film remains highly stable and shows only very moderate outdiffusion.
We also have observed a far more efficient, athermal Ge-redistribution process linked to the implantation step itself. This was studied by analysing the Ge-redistribution following an Asimplant (2-15 keV, 5 1014 – 3 1015 at/cm2). It is shown that the energy of the implant species (or more specifically the position of the damage distribution function relative to the Ge-edge) plays a determining factor with respect to the Ge-migration. For implants whereby the damage distribution overlaps with the Ge-edge, a very efficient transport of the Ge is observed, even prior to any anneal cycle. The migration is entirely correlated with the collision cascade and the resulting (forward!) Ge-recoil distribution. The scaling with dose for a given energy links the observed Ge-profile with a broadening mechanism related to the number of atom displacements induced in the sample within the vicinity of the Si-SiGe-transition.
We have studied the strain state, film and surface morphology of SiGe virtual substrates (Ge concentrations in-between 20% and 55%) grown by reduced pressure – chemical vapor deposition. The macroscopic degree of strain relaxation of those virtual substrates is equal to 97.2 ± 1.5%. The misfit dislocations generated to relax the lattice mismatch between Si and SiGe are mostly confined inside the graded layer. Indeed, the threading dislocations density obtained for Ge concentrations of 20% and 26% is indeed typically of the order of 7.5 ± 2.5 105 cm−2. Low surface root mean square roughness have been obtained, with values in-between 2 and 5 nm. In order to check the electronic quality of our layers, we have grown a MODFET-like heterostructure, with a buried tensile-strained Si channel 8 nm thick embedded inside SiGe 26%. We have obtained a well-behaved 2-dimensional electron gas in the Si channel, with electron sheet densities and mobilities at 1.45K of 5.4×1011 cm−2 and 212 000 cm2 V−1 s−1, respectively.
A unified diffusion model is developed, valid for all usual substitutional atoms in SiGe and strained SiGeC layers, in accordance with all published experimental data and predicting the enhancement of Arsenic diffusion in SiGe and SiGeC strained layers. Using a new SIMS methodology, the study of As intrinsic diffusion in SiGe and SiGeC layers is performed, at low concentration and under equilibrium annealing conditions. Arsenic diffusivity in fully-strained SiGe and SiGeC layers on Si substrates was successfully compared to the unified diffusion model.
Tensile strained Si on SiGe Strain Relaxed Buffers (SRB) is an interesting candidate to increase both electron and hole mobility which results in improved device performance. Most of this work was/is based on thick (several μm), step-graded SRBs with or without Chemical Mechanical Polishing (CMP) planarisation. This approach bears several disadvantages such as issues with STI formation in the thick SiGe structure, and considerable self-heating effects due to the lower thermal conductivity of the SiGe material. Further, pMOS improvement requires SRBs with high Ge contents (> 30 %), which complicates device fabrication even more. To overcome these issues, we developed a new and cost efficient type of thin SRB (∼200 nm). The concept is based on the introduction of a thin carbon-containing layer during growth of a constant composition SiGe layer. The process relies on standard Chemical Vapor Deposition epitaxial technology without need for CMP. It is designed to allow both non-selective growth on blanket wafers and selective growth in the active area of structured wafers with Shallow Trench Isolation (STI). The selective epitaxial process for strained Si on thin SRBs proposed here, allows relatively simple and cost-effective fabrication of strained Si layers on existing STI structures without any process modification. Further, it offers a very flexible fabrication scheme to independently improve nMOS and pMOS devices. The SRB quality is comparable to the best reported in literature so far, with 70 % and 53 % mobility enhancements for long channel nMOSFETs on 22 % Ge SRBs grown on blanket and STI patterned wafers, respectively.