1,720,960 research outputs found
Reconstruction of Diffuse Emission for Next-Generation Radio Telescopes
No full textNext-generation radio interferometers such as the Square Kilometre Array Observatory (SKAO) will produce data at petabyte scales. A central challenge is to image extremely faint, diffuse radio emission (e.g. the cosmic web, galaxy-cluster halos, or subtle solar features) amid much brighter compact sources. Traditional radio astronomy imaging (e.g. CLEAN) treats the sky as discrete sources and often requires lengthy deconvolution, which can leave residual artefacts around extended emission. In contrast, the Bluebild algorithm offers a fresh approach by treating interferometric imaging as a continuous inverse problem. Bluebild applies a functional principal-component decomposition to the measured visibilities, effectively splitting the sky into a sequence of orthogonal â energy levelsâ that are recombined into a least-squares sky map. In practice, this means bright sources are captured by the leading modes, while fainter diffuse structures appear in lower modes.
In this thesis, a high-performance implementation of Bluebildâ called Bluebild Imaging Plus Plus (BIPP)â is introduced and validated. BIPP is written in C++ with GPU acceleration and interfaces to Python, and it exploits 3-D non-uniform fast Fourier transforms (NUFFTs) to image the sky directly on the celestial sphere. The software was tested on both simulated SKA datasets and real telescope data (e.g. from LOFAR and the MWA). These tests show that BIPP produces accurate wide-field images with computational cost comparable to standard pipelines (CASA/WSClean). Importantly, BIPPâ s energy-level decomposition often exposes faint diffuse emission before any deconvolution steps. For example, after running BIPP, one
can â peelâ bright sources by removing the top principal modes, yielding residual data that cleanly reveal weak, extended structures. In effect, BIPP enables the separation of â bright foregroundâ emission from the underlying diffuse background.
One striking result obtained with BIPP is the serendipitous detection of solar limb brightening in meter-wavelength data from the MWA. The thesis shows that quiet-Sun observations imaged with BIPP display the solar disk edges as unusually bright, confirming a long-sought feature of solar radio emission. A companion simulation (with a known limb-brightening component) was processed by BIPP, which successfully split the Sunâ s central disk emission from the diffuse limb emission. This demonstrates that Bluebild/BIPP can reveal subtle astrophysical phenomena in practice. More generally, the method is well suited to science cases like quiet-Sun imaging, Epoch-of-Reionisation studies, or detection of the cosmic web, where
faint diffuse signals must be separated from strong foregrounds.
Looking ahead, the thesis argues that Bluebild/BIPP could play a key role in SKA-era data processing. By embedding the eigen-decomposition approach into the calibration and imaging pipeline, bright contaminating sources (e.g. radio galaxies, radio frequency interference, or solar emission) could be filtered out in visibility space, leaving a cleaner dataset for imaging faint features. In summary, this research provides a practical new toolkit for interferometric imaging: BIPP demonstrates that modern HPC and statistical methods can recover extended sky emission with high fidelity. As next-generation arrays come online, these tools promise to expand the scientific reach of radio astronomy by unveiling diffuse signals that are otherwise hidden.LASTR
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Separating Point Source Contaminants at the Visibility Level
No full textBright point source contaminants are an ever-present problem in astronomy. This issue is especially pronounced for radio interferometric telescopes. The calibration process for these telescopes is never perfect, and consequently even the smallest calibration errors on bright sources can cause interferometric artefacts that obscure weaker sources within the same field of view. This effect can strongly limit the dynamic range of images produced by the next generation of radio interferometric telescopes. Peeling, or subtracting modelled visibilities corresponding to the bright source in visibility space, is often employed to address this problem. However, this does not always remove all interferometric artefacts associated with the bright contaminating source.
We present a visibility‑based method, Bluebild Imaging Plus Plus (BIPP), for the removal of contaminating point sources. BIPP is an interferometric imager developed to reconstruct the sky intensity matrix directly on the celestial sphere. It uses functional principal component analysis (fPCA), based on the intensity of sources, to separate input visibilities into eigen‑visibilities. These eigen‑visibilities are then reconstructed into eigenimages, which can be optimally combined into energy levels for source separation. Since the fPCA is performed directly on the visibilities, all energy levels contain only the artefacts from the sources present within each energy level.
We use this method to separate a contaminating bright source at two different frequencies for simulated observations generated from a realistic sky model. In doing so, we demonstrate the potential of BIPP as a method for bright source separation. We also compare the BIPP output with WSClean, to analyse and contrast the results produced by the two algorithms.LASTR
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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