1,720,965 research outputs found
Development of new technologies and methods for next-generation gamma-ray telescopes
No full textL’Astrofisica delle Alte Energie (AAE) è fondamentale per la comprensione di fenomeni stellari estremi ed eventi su scala cosmologica. Il campo della AAE è nato nel 1962, quando l’esperimento di Rossi e Giacconi portò alla scoperta delle prime sorgenti di raggi X extraterrestri. Nel corso degli ultimi settant’anni, sono stati fatti incredibili progressi relativamente alle tecnologie, tecniche e strumenti a disposizione per studiare il cielo X e gamma. Tuttavia, importanti questioni risultano ancora aperte, soprattutto nel regime dei raggi X duri e gamma molli, es: quale sia l’origine della linea di annichilazione e+/e- dal centro galattico, qual è la natura del motore centrale delle esplosioni dei lampi gamma (gamma-ray bursts, GRB) e molti altri.
La strumentazione attuale non dispone di sufficienti capacità di localizzazione, risoluzione spaziale, sensibilità, per affrontare questi problemi, né ha capacità di effettuare misure polarimetriche. Lo scopo di questa tesi è quindi di esplorare ed avanzare le tecnologie ed i metodi che ci permetteranno di superare queste limitazioni e, allo stesso tempo, di prepararci a sfruttare in modo ottimale le prossime missioni di AE.
Descriveremo nello specifico i recenti progressi che abbiamo ottenuto nell’aumentare il livello tecnologico delle lenti di Laue per usi astrofisici. Le lenti di Laue sono ottiche per raggi X/gamma innovative, vasato sulla legge della diffrazione di Bragg, che possono permetterci di costruire strumenti focalizzanti per AE capaci di operare oltre il limite di ∼70 keV (ottenuto dalla missione NuSTAR attraverso l’impiego di ottiche ad incidenza radente multi-layer) ed arrivare fino a∼ 700 keV. L’implementazione di ottiche focalizzanti per raggi gamma molli porterà ad un significativo aumento nella sensibilità dei nostri strumenti, fino a 3 ordini di magnitudine in più rispetto a strumenti a vista diretta.
Descriveremo il design del concetto di missione spaziale ASTENA, sottomesso alla call ESA “Voyage 2050” e basato su questo tipo di ottiche. ASTENA porterà due strumenti: il Wide Field Monitor (WFM), un rivelatore a campo ampio con capacità di imaging e spettrometria, ed il Narrow Field Telescope (NFT), un telescopio per raggi gamma molli bassato su una lente di Laue. I nostri sforzi si sono concentrati sull’ottimizzare e caratterizzare questi due strumenti. In questo lavoro, nello specifico, ci siamo concentrati sullo stimare le capacità polarimetriche di NFT e WFM, in modo da comprendere come questi strumenti potranno giocare un ruolo nel campo della polarimetria delle alte energie.
Infine, siccome progressi tecnologici devono sempre essere accompagnati da progressi metodologici, abbiamo affrontato una questione di vecchia data nel campo dei lampi gamma: trovare un metodo consistente ed affidabile per simulare curve di luce (LC) dei GRB. LC simulate sono utilizzate per ottimizzare future missioni spaziali e caratterizzare le attuali osservazioni; tuttavia, la simulazione di curve di luce è una sfida complessa, in quanto gli attuali modelli fisici basati sul paradigma degli shock interni non sono capaci di riprodurre la grande diversità morfologica delle LC osservate. D’altro canto, costruire template di LC a partire da altri strumenti/missioni richiede di disaccoppiare in maniera opportuna il segnale reale dal rumore. In questo lavoro, abbiamo investigato un nuovo approccio di simulazione basato su un modello stocastico combinato a moderni algoritmi di machine learning.
Obiettivo di questa tesi è stato lo sviluppo di tecnologie innovative per progredire la strumentazione per astrofisica delle alte energie da differenti punti di vista interconnessi. Allo stesso tempo, abbiamo iniziato ad esplorare nuove tecniche basate sull’intelligenza artificiale, che necessariamente giocheranno un ruolo fondamentale nello studio delle future missioni per AE e nel campo dei lampi gamma.High Energy Astrophysics (HEA) studies are fundamental to understanding extreme stellar and
cosmological scale phenomena. The field of HEA was born in 1962, with Rossi and Giacconi’s rocket experiment leading to the discovery of the first extraterrestrial X-ray sources. Over the last seventy years, vast improvements have been made in technologies, techniques, and instruments to study the X and gamma-ray sky. However, outstanding questions are still open, in particular in the hard X-/soft gamma-ray regime: for example, the origin of the e+/e− annihilation line coming from the galactic centre, the nature of the engine that powers gamma ray bursts’ (GRBs) explosions, the geometry and explosion mechanisms of supernova emission, and many more.
The currently available instrumentation lacks sufficient localisation capabilities, spatial and energetic resolution, sensitivity, and the ability to perform polarimetric measurements. Such limitations have thus hindered further advancements in the HEA field. In this context, this thesis aims to explore and advance the technologies and methods that will allow us to overcome such limits and prepare us for an optimal exploitation of upcoming HE missions.
We will focus specifically on the recent progress we made in advancing the technological readiness of Laue lenses for astrophysics applications. Laue lenses are innovative hard X/soft gamma-ray optics based on Bragg’s diffraction law, allowing HE focusing instruments to operate beyond the current limit of ∼70 keV, based on multi-layer grazing incident mirrors (as in the NuSTAR mission), to ∼700 keV. The implementation of soft gamma-ray focusing optics will result in a significant increase in sensitivity, up to three orders of magnitude higher than direct view instruments.
We will describe the design of a new space mission concept based on this type of optics: the Advanced Surveyor for Transient Events and Nuclear Astrophysics (ASTENA), proposed to ESA for the call "Voyage 2050". ASTENA will include two instruments: the Wide Field Monitor (WFM), a wide field detector with both imaging and spectrometric capabilities, and the Narrow Field Telescope (NFT), a soft gamma-ray telescope based on a Laue lens. We concentrated our efforts on optimising the design of those two instruments and characterising their properties to meet several scientific requirements. In this work, we specifically focused on estimating the polarimetric capabilities of both NFT and WFM to understand how those instruments can play a new competitive role in high-energy polarimetry.
Finally, technological advancements should always be accompanied by new methodological advancements. We focused on a long-standing challenge in the GRB field: finding a robust and reliable way to simulate light curves (LCs) of GRB events. GRBs are among the most fascinating sources observed in the high-energy sky, and mock GRB LCs can be used to exploit future HE missions optimally and characterise current GRB observations. However, simulating their light curves remains challenging since physical models based on the internal shock paradigm fail to reproduce the diversity of the observed LCs’ morphologies. On the other hand, by constructing LC templates from other instruments/missions, one faces the challenge of properly decoupling the real signal from the noise. This work investigates a new approach to simulate GRB LCs based on stochastic models combined with modern machine learning techniques.
This thesis work aims to develop innovative technologies to advance our instrumentation for high-energy astrophysics from different, interconnected points of view. At the same time, we start exploring new artificial intelligence-based techniques, which inevitably will play a key role in the analysis of upcoming HE missions, particularly in the ever-expanding field of GRBs
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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