A GPU based real-time software correlation system for the Murchison Widefield Array prototype

Modern graphics processing units (GPUs) are inexpensive commodity hardware that offer Tflop/s theoretical computing capacity. GPUs are well suited to many compute-intensive tasks including digital signal processing. We describe the implementation and performance of a GPU-based digital correlator for radio astronomy. The correlator is implemented using the NVIDIA CUDA development environment. We evaluate three design options on two generations of NVIDIA hardware. The different designs utilize the internal registers, shared memory and multiprocessors in different ways. We find that optimal performance is achieved with the design that minimizes global memory reads on recent generations of hardware. The GPU-based correlator outperforms a single-threaded CPU equivalent by a factor of 60 for a 32 antenna array, and runs on commodity PC hardware. The extra compute capability provided by the GPU maximises the correlation capability of a PC while retaining the fast development time associated with using standard hardware, networking and programming languages. In this way, a GPU-based correlation system represents a middle ground in design space between high performance, custom built hardware and pure CPU-based software correlation. The correlator was deployed at the Murchison Widefield Array 32 antenna prototype system where it ran in real-time for extended periods. We briefly describe the data capture, streaming and correlation system for the prototype array.Comment: 11 pages, to appear in PAS

Moanaākea

Paper submitted to The Space Between: Negotiating Culture, Place, and Identity in the Pacific; based on the indigenous Oceanic concept, va, a space marked by tension and transformation and by confluences and connection

Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging

The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors, in which direction-dependent corrections are incorporated into visibility gridding kernels, we consider the special characteristics of arrays of fixed dipole antennas operating around 100-200 MHz, looking towards instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays (HERA). We show that integrating snapshots in the image domain can help to produce compact gridding kernels, and also reduce the need to make complicated polarised leakage corrections during gridding. We also investigate an alternative form for the gridding kernel that can suppress variations in the direction-dependent weighting of gridded visibilities by 10s of dB, while maintaining compact support.Comment: 15 pages, 4 figures. Accepted for publication in JA

Editing the project of the self: Sustained Facebook use and growing up online

Now in operation for over a decade, Facebook comes to serve as a digital record of life for young people who have been using the site through key periods of transition. With significant parts of their social and cultural lives played out on the site, users are able to turn to these profiles – these texts of transition often documenting significant relationships, work lives, education, leisure, and loss – to reflect on how their use of Facebook has come to constitute a life narrative. Like reading old journals or diaries, the act of ‘scrolling back’ through a Facebook profile can be a nostalgic and challenging experience whereby users are confronted with their younger selves. In this paper, we report on findings from qualitative research into sustained use of Facebook by young people in their twenties in Australia and the UK. Here we focus on the ‘editing’ or re-ordering of narratives that our participants engage in while they scroll back through their years (5+) of disclosures – and the disclosures of others – that make up their Facebook Timelines. We present our analysis through three different arenas (employment, family life, and romantic relationships) subject to what we argue here is a reflexive re-ordering of life narratives. We argue that Facebook profiles represent visual manifestations of Giddens’ (1991) reflexive project of the self, that serve not only to communicate a sense of self to others, but that also act as texts of personal reflection and of growing up, subject to ongoing revision

Uncovering longitudinal life narratives: Scrolling back on Facebook

This article explores the potential role of sustained social media use in longitudinal qualitative research. We introduce the research design and methodology of a research project exploring sustained use (five or more years) of the social network site Facebook among young people in their twenties. By focusing on this group, we seek to uncover how ‘growing up’ stories are told and archived online, and how disclosure practices (what people say and share on social media) change over time. We question how we can understand the ‘digital trace’ inscribed through the Facebook Timeline as a longitudinal narrative text. We argue that ‘scrolling back’ through Facebook with participants as ‘co-analysts’ of their own digital traces can add to the qualitative longitudinal research (QLR) tradition. QLR and the scroll back method attend to a similar set of concerns around change over time, the depth of inquiry, and uncovering rigorous, rich life narratives. We explore limitations (especially around intentionality) and ethical challenges, while also arguing for the inclusion of these often highly personal, deep, co-constructed digital texts in qualitative longitudinal research. We also consider how the scroll back method could apply to other digital media, as the sites and applications that people user diversifies and changes over time

Being strategic and taking control: Bedrooms, social network sites and the narratives of growing up

Despite being distinct, online social spaces are governed by norms and conventions reminis-cent of those that govern offline social spaces. Our research into the ways young people’s ‘private’ or ‘quasi-private’ spaces are managed indicates that the strategies used to exert a sense of control over sites like Facebook borrow heavily from the strategies employed to manage offline private spaces like the teenage bedroom. In this article, we explore these con-tinuities and then consider the limitations of applying a bedroom metaphor to online social spaces. We then consider how these strategies of control are related to a process of ‘marking out’ the narrative of ‘growing up’ both in online and offline social spaces. Keywords Young people, social network sites, bedrooms, bedroom metaphor, strategies of control, growing up, identit

Stetson Songs

1920-1921 (36th annual) John B. Stetson University Catalogue supplement

Correlation Between Student Collaboration Network Centrality and Academic Performance

We compute nodal centrality measures on the collaboration networks of students enrolled in three upper-division physics courses, usually taken sequentially, at the Colorado School of Mines. These are complex networks in which links between students indicate assistance with homework. The courses included in the study are intermediate Classical Mechanics, introductory Quantum Mechanics, and intermediate Electromagnetism. By correlating these nodal centrality measures with students' scores on homework and exams, we find four centrality measures that correlate significantly with students' homework scores in all three courses: in-strength, out-strength, closeness centrality, and harmonic centrality. These correlations suggest that students who not only collaborate often, but also collaborate significantly with many different people tend to achieve higher grades. Centrality measures between simultaneous collaboration networks (analytical vs. numerical homework collaboration) composed of the same students also correlate with each other, suggesting that students' collaboration strategies remain relatively stable when presented with homework assignments targeting different skills. Additionally, we correlate centrality measures between collaboration networks from different courses and find that the four centrality measures with the strongest relationship to students' homework scores are also the most stable measures across networks involving different courses. Correlations of centrality measures with exam scores were generally smaller than the correlations with homework scores, though this finding varied across courses.Comment: 10 pages, 4 figures, submitted to Phys. Rev. PE

A study of the validity and the reliability of the Geriatric Anxiety Inventory in screening for anxiety after stroke in older inpatients

Objectives: To investigate the validity and reliability of the Geriatric Anxiety Inventory in screening for anxiety in older inpatients post-stroke. Design: Longitudinal. Subjects: A total of 81 inpatients with stroke aged 65 years or older were recruited at four centres in England. Main measures: At phase 1 the Geriatric Anxiety Inventory and the Hospital Anxiety and Depression Scale were administered and then the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders 4th edition (phase 2). The Geriatric Anxiety Inventory was repeated a median of seven days later (phase 3). Results: Internal reliability of the Geriatric Anxiety Inventory was high (α = 0.95) and test-retest reliability acceptable (τB = 0.53). Construct validity of the Geriatric Anxiety Inventory was evident with respect to the Hospital Anxiety and Depression Scale -Anxiety subscale (τB = 0.61). At a cut off of 6/7, the sensitivity of the Geriatric Anxiety Inventory was 0.88 and specificity 0.84, with respect to Structured Clinical Interview diagnosis of anxiety. Hospital Anxiety and Depression Scale -Anxiety subscale sensitivity was 0.88, specificity 0.54 at the optimum cut off of 5/6. A comparison the areas under the curve of the Receiver Operating Characteristics for the two instruments indicated that the area under the curve of the Geriatric Anxiety Inventory was significantly larger than that of the Hospital Anxiety and Depression Scale –Anxiety subscale, supporting its superiority. Conclusions: The Geriatric Anxiety Inventory is an internally consistent, reliable (stable) and valid instrument with acceptable sensitivity and specificity to screen for anxiety in older inpatients with stroke