1,721,058 research outputs found
Galaxy And Mass Assembly (GAMA): Bulge-disk decomposition of KiDS and VIKING data in the nearby universe
No full textQuantitative measurements of the structural components of the galaxy population are crucial to constrain theory and simulations, which - in turn - constrain the formation and evolution of galaxies and the universe as a whole. This requires analysing large and diverse samples of galaxies at multiple wavelengths. Corresponding high-quality data is delivered by current and future large galaxy imaging surveys. To fully exploit these, automated analysis methods need to be developed further. In this thesis, we derive a catalogue of robust structural parameters for the components of a large sample of nearby GAMA galaxies while at the same time contributing to the advancement of image analysis, surface brightness fitting and post-processing routines for quality assurance in the context of automated large-scale bulge-disk decomposition studies. The sample consists of 13096 galaxies at redshifts z < 0.08 in the GAMA II equatorial survey regions with imaging data from the Kilo-Degree Survey (KiDS) and the VISTA Kilo-Degree INfrared Galaxy (VIKING) survey spanning the optical and near-infrared (u, g, r, i, Z, Y, J, H and Ks bands). We fit three models to the surface brightness distribution of each galaxy in each band individually: a single Sérsic model, a Sérsic plus exponential and a point source plus exponential. The fitting is performed with a fully automated Markov-chain Monte Carlo (MCMC) analysis using the Bayesian two-dimensional profile fitting code ProFit. All preparatory work, including image segmentation, background subtraction, point spread function estimation, and obtaining initial guesses, is carried out using the complementary image analysis package ProFound. After fitting the galaxies, we perform model selection and flag galaxies for which none of our models are appropriate, mainly mergers and irregular galaxies. The fit quality is assessed by visual inspections, comparison to previous works, comparison of independent fits of galaxies in the overlap regions between KiDS tiles and bespoke simulations. The latter two are also used for a detailed investigation of systematic error sources. We find that our fit results are robust across various galaxy types and image qualities with minimal biases. Errors given by the MCMC underestimate the true errors typically by factors 2-3. Automated model selection criteria are accurate to > 90 % as calibrated by visual inspection of a subsample of galaxies. We also present g − r component colours and the corresponding colour-magnitude diagram, consistent with previous works despite our increased fit flexibility. All results are integrated into the GAMA database.Quantitative Strukturanalysen von Galaxien sind unerlässlich um theoretische Modelle und Simulationen einzugrenzen, welche die Entstehung und Entwicklung von Galaxien sowie des gesamten Universums beschreiben. Entsprechende Daten werden von Himmelsdurchmusterungen in hoher Qualität geliefert. Um diese vollumfänglich nutzen zu können, sind automatisierte Methoden notwendig. Diese Promotionsarbeit präsentiert Strukturparameter für die Komponenten einer großen Anzahl von GAMA Galaxien im nahen Universum und verbessert die Bildanalyse, die Modellierung von Galaxien sowie die Nachbearbeitung solcher Modelle zur Qualitätssicherung, im Kontext von automatisierten Galaxiezerlegungsstudien. Die Probe umfasst 13096 Galaxien in den GAMA II Equatorialregionen bei Rotverschiebungen z < 0.08. Die Bilddaten stammen von den KiDS und VIKING Himmelsdurchmusterungen, welche den optischen und nah-infraroten Wellenlängenbereich abdecken (ugriZYJHKs -Filter). Wir fitten die Oberflächenhelligkeitsverteilung jeder Galaxie in jedem Filter mit drei Modellen: einer Sérsicfunktion, einer Sérsic- plus Exponentialfunktion sowie einer Punktquelle plus Exponentialfunktion. Die Modellanpassung erfolgt mit einer vollautomatisierten Markov-Chain-Monte-Carlo-Analyse mit dem bayesschen zweidimensionalen Profilanpassungs-Code ProFit. Die Vorarbeit, einschließlich der Bildsegmentierung, Hintergrundsubtraktion, Modellierung der Punktspreizfunktion und Schätzung von Anfangswerten, wird mit dem Bildanalysen-Code ProFound ausgeführt. Nach der Modellierung wird eine Modellauswahl getroffen und Galaxien für welche keines der Modelle angemessen ist - z.B. asymmetrische und verschmelzende Systeme - markiert. Die Modellierungsqualität wird durch visuelle Inspektion, Vergleiche mit bestehenden Veröffentlichungen sowie zwischen unabhängigen Ergebnissen für mehrfach-Aufnahmen derselben Galaxie und mit speziell auf diese Arbeit zugeschnittenen Simulationen überprüft. Diese werden auch für eine Untersuchung von systematischen Fehlerquellen verwendet. Die Modellierungsresultate erweisen sich als verlässlich für eine große Spannbreite an verschiedenen Galaxietypen und Bildqualitäten. Es liegen nur minimale systematische Messabweichungen vor. Die systematischen Fehler sind einen Faktor von 2-3 größer als zufällige Fehler. Die automatisierte Modellauswahl stimmt mit einer Genauigkeit von > 90 % mit der visuellen Inspektion einer Teilprobe von Galaxien überein. Eine Untersuchung der g − r-Farben von Galaxiekomponenten und des zugehörigen Farbe-Helligkeits-Diagramms ergibt, dass diese im Einklang mit bestehenden Veröffentlichungen sind, trotz der größeren Flexibilität der Modelle dieser Arbeit. Alle Resultate sind auf der GAMA-Datenbank integriert
Applications of Test Masses in Uniform Circular Motion to Detect Millihertz Gravitational Waves
No full textIn this doctoral dissertation, starting from the first principles of the general theory of relativity, the geodesic deviation of test masses in uniform circular motion is calculated, due to the passage of gravitational waves (GWs) from astrophysical sources. The results of this theoretical analysis are used to conceive of experimental setups that could utilize this principle to detect GWs. These setups are based on, but are not limited by, the current status of technology. Mainly, circular particle accelerators in the mode of storage rings are considered. The major sources of noise for a storage ring gravitational wave observatory (SRGO) are explored, and basic noise estimates are made based on the specifications of existing facilities such as the Large Hadron Collider (LHC). A major part of the dissertation consists of numerical simulations of toy models of an SRGO. The response signal of the GW detector is explored as a function of various model parameters. Errors on estimating the model parameters are found using Markov Chain Monte Carlo (MCMC) methods applied to artificially generated data with added noise. It is shown that an ideal version of such a detector would be sensitive to millihertz GWs by design, and would be able to single-handedly obtain accurate constraints on the GW source parameters. An attempt has been made to incorporate as much physics as currently possible, which covers the essential aspects of reality without over-complicating the models for a first study of this novel experiment concept. The overall focus has been to establish a strong conceptual foundation, to obtain robust qualitative conclusions, and to make order-of-magnitude estimates. Comparisons with the theory and practices of existing GW detectors have been made throughout. Wherever possible, the results are presented in the conventions followed by the GW community at the time of writing this dissertation
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
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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