1,721,017 research outputs found
Observations and modeling of the active galactic nucleus B2 1215+30 together with performance studies of the ground-based gamma-ray observatories VERITAS and CTA
Get PDFDas Gebiet der bodengebundenen Gamma-Astronomie bietet Zugang zu Photonen im TeV-Energiebereich und hat sich in den letzten Jahrzehnten vor allem durch den Erfolg der abbildenden atmosphärischen Cherenkov-Technik profiliert. In dieser Arbeit werden zwei dieser Cherenkov-Teleskop-Systeme, VERITAS und das zukünftige CTA, mit Hilfe von Monte-Carlo-Simulationen in Hinblick auf deren Sensitivität auf hochenergetische Gammastrahlung (E > 50 GeV) untersucht. Besonderes Augenmerk wird hierbei auf die Beobachtungsmöglichkeit mit CTA unter Mondlicht gelegt. Es wird gezeigt, dass dadurch eine Beobachtungszeitverlängerung um etwa 30% ohne signifikante Sensitivitätsverluste erreicht werden kann, was besonders wichtig für zeitlich variable Quellen ist. Eine dieser variablen Quellklassen sind aktive Galaxienkerne, welche zur Zeit etwa ein Drittel der bekannten hochenergetischen Gammastrahlungsquellen repräsentieren. Die meisten davon sind Blazare, deren Emission durch nicht-thermische Strahlung aus gebündelten Strömen von Materie und Energie (sogenannten Jets) dominiert wird. Diese Jets breiten sich mit annähernd Lichtgeschwindigkeit aus und sind in Sichtlinie des Betrachters ausgerichtet. Der Blazar B2 1215+30 wurde zwischen 2008 und 2012 mit VERITAS fast 100 Stunden beobachtet. Die Datenanalyse, welche in dieser Arbeit präsentiert wird, weist die Quelle mit einer Signifikanz von neun sigma nach und offenbart Langzeitvariabilität mit einem hellen Flusszustand im Jahr 2011. Multi-Wellenlängen-Daten werden verwendet um die spektrale Energieverteilung von B2 1215+30 zu konstruieren, welche gut mit einem leptonischen Ein-Zonen-Modell beschrieben werden kann. Das verwendete Modell wird im Detail vorgestellt und mögliche Einschränkungen an den Modellparameterraum untersucht. Die Ergebnisse der Modellierung von B2 1215+30 werden diskutiert und in Zusammenhang mit anderen bekannten hochenergetischen Gammastrahlen-Blazaren gesetzt.Ground-based gamma-ray astronomy, which provides access to photons in the TeV energy range, has been a rapidly developing discipline over the past decades. In this thesis, the performance of the current- and next-generation imaging atmospheric Cherenkov telescopes VERITAS and CTA is evaluated using Monte Carlo simulations. Special emphasis is given to the possible extension of the duty cycle of CTA. It is shown that an increase of about 30% in observation time can be achieved through operation under partial moonlight without significant losses in performance. The increased observation time is especially important when studying astronomical objects which are variable at very high energies (VHE; E>50 GeV), such as active galactic nuclei (AGN), as this allows the extension of monitoring or multi-wavelength campaigns on these occasionally flaring sources. AGN represent to date about one third of the population of known VHE gamma-ray sources. Most of them are blazars, whose emission is dominated by non-thermal radiation of relativistic jets closely aligned to the line of sight of the observer. The blazar B2 1215+30 has been observed by VERITAS for nearly 100 hours between 2008 and 2012. The data analysis presented in this thesis yields a detection significance of 9.0 sigma and shows long-term variability with a relatively bright flux state in 2011. Multi-wavelength data are used to construct the spectral energy distribution of B2 1215+30 which is well described by a one-zone leptonic model. The model is presented in detail and possible constraints are investigated. The results of the modeling are discussed and put in context with other VHE-detected blazars
The Science Program of the Third Generation IACTs for Exploring Cosmic Gamma Rays
No full textVery-high-energy astrophysics studies the most energetic photons in the sky allowing the exploration of the violent and extreme non-thermal phenomena in the Universe. Significant advances in knowledge have been made in this field using ground-based imaging atmospheric Cherenkov telescopes (IACTs) as detectors to study the very-high-energy physical processes in the Universe. This book reviews the progress in the field since the advent of the second generation IACTs in around 2004.Going through the scientific highlights obtained by the three current instruments of this kind, H.E.S.S., VERITAS and MAGIC, operating now for more than ten years, this book presents a state-of-the-art knowledge in four areas of modern astrophysics and cosmology, namely the origin of the cosmic rays, the physic of compact objects and their resulting relativistic outflows, gamma-ray cosmology and the search for dark matter. Along with a detailed review of the outstanding scientific outcome, a summary of the key technological developments that yielded to the recognized success of the technique is also provided.This book is written for young academics in the fields of astrophysics, high energy physics and cosmology. At the same time, it can serve as a source of reference for the expert in the field
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
"""Who speaks for me, with and to me?"" Subalternity and representation in the works of Mahasweta Devi, Bessie Head, and Assia Djebar"
Get PDF“Who Speaks for, with and to Me?” study how the gendered subaltern subjects of the global South are represented in the fictional works of three writers: Mahasweta Devi, Bessie Head, and Assia Djebar. Devi, Head, and Djebar write about disenfranchised groups of people whose ontological existences are marginalized and silenced by mainstream social and national discourses of postcolonial nation-states such as India, South Africa, and Algeria. The three chapters demonstrate the retrieval of subaltern agency by Devi, Head, and Djebar through their strategic and rhetorical shifting of attention from the spoken words of the gendered subaltern to the female subaltern’s body-in-pain, their experiences of living as social and political outcastes, and their relationships with lived spaces (home, nation, harem, prison). Devi represents female subaltern bodies as spaces exploited for the exertion of power and also as sites for resistance against gendered, class, and caste violence. I read Mahasweta’s use of pain as a narrative strategy to regard the female subject-in-pain as a dynamic being and not a passive victim. Bessie Head’s representations of subaltern agency relate subalternity to social and political conditions of living in exile. I contend that it is this lived experience that leads Head to articulate a completely new perspective for examining the elite-subaltern relationship, namely the subaltern’s inability to understand the elite. She turns the question —“can the subaltern speak?” — around to ask if the elite can speak (to the subaltern)? I explore the issue of lived experience further in Assia Djebar’s works. I focus on Djebar’s representations of subaltern agency through the marginalized space of the harem in postcolonial Algeria. Effectively, this dissertation problematizes Gayatri Spivak’s assertion that the subaltern cannot be authentically represented.Item withdrawn by Mark Zulauf ([email protected]) on 2012-12-02T19:36:28Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
No. of bitstreams: 2
Mukherjee_Reshmi.pdf.pdf: 1184546 bytes, checksum: 47290d5d8982c6c6c0da7cc5fa2b73be (MD5)
Mukherjee_Reshmi.pdf: 1184546 bytes, checksum: 47290d5d8982c6c6c0da7cc5fa2b73be (MD5)Made available in DSpace on 2013-02-03T19:46:35Z (GMT). No. of bitstreams: 2
Reshmi_Mukherjee.pdf: 1184546 bytes, checksum: 47290d5d8982c6c6c0da7cc5fa2b73be (MD5)
license.txt: 4066 bytes, checksum: cf5fc4562a63acd2a9c79b75e916555b (MD5)Item marked as restricted to the 'Administrator' Group (id=1) by Seth Robbins ([email protected]) on 2013-02-03T19:47:59Z
Item is restricted until 2015-02-03T19:47:48ZRestriction data tranferred 2014-07-01T11:36:01-05:00
Original Data
Group with Access Administrator
Release Date: 2015-02-03 13:47:48 UTC
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 42416 on 2015-02-03T11:00:33Z
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
- …
